Science, Faculty of
Chemistry, Department of
DSpace
UBCV
Wright, Taylor Douglas
Doctor of Philosophy - PhD
University of British Columbia
Investigations of a number of photochemical cross-linking reactions are reported for the preparation of functional polymeric materials. Reactions that require constant inputs of light and do not proceed through radical or ionic mechanisms are studied, and the final properties of these materials are characterized. This work aims to expand the scope of available photo-cross-linking reactions for the preparation of functional materials. The incorporation of photodimerizable anthracene into a thermally healable vinylogous urethane copolymer enables light-induced post-polymerization UV cross-linking. This allows for tuning of the glass transition temperature over a 20 °C range, control over the rheological properties, and tuning the scratch healing temperature. Pendant attachment of anthracene moieties onto a flexible siloxane polymer (PDMS) results in macroscopic polymer crystallization upon photo-cross-linking, giving a heterogeneous material with up to 1 mm diameter crystallites embedded inside a flexible matrix. A thorough investigation of the growth of the polymer crystallites through microscopic and diffusion techniques revealed unique crystallite growth initiating from the bottom of the film and progressing upwards towards the irradiation source. The application of photogenerated singlet oxygen is applied to the cross-linking of amine siloxanes. Oxidative coupling of amine groups to imine groups results in facile cross-linking at room temperature in oxygen rich environments using visible light with no measurable side reactions. Solvent free precursors were prepared by covalent attachment of the sensitizer to the PDMS backbone. As coatings, these materials demonstrate contact antimicrobial activity against bacterial cells, being more effective against E. Coli than methicillin-resistant Staphylococcus aureus (MRSA), as well as inducing cell lysis in mammalian cells. This system was further developed as a dual-functional textile coating, utilizing both contact antimicrobial activity as well as photodynamic disinfection using singlet oxygen, which results in >99% bacterial disinfection in 90 minutes and a 10× decrease in SARS-CoV-2 viral infectivity in two hours. Singlet oxygen was also used to photo-cross-link thiol containing siloxanes through the oxidative preparation of a diaryl-telluroxide catalyst, effectively linking low thiol-content PDMS through disulfide formation. These polymers exhibit up to 400% elongation, and can be reductively cleaved back into liquids using NaBH4 with >90% mass recovery.
INVESTIGATION OF NOVEL PHOTO-CROSS-LINKING REACTIONS FOR THE PREPARATION OF FUNCTIONAL POLYMERIC MATERIALS by Taylor Douglas Wright B.Sc., The University of British Columbia, 2017 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Chemistry) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) February 2022 © Taylor Douglas Wright, 2022 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, the dissertation entitled: INVESTIGATION OF NOVEL PHOTO-CROSS-LINKING REACTIONS FOR THE PREPARATION OF FUNCTIONAL POLYMERIC MATERIALS submitted by Taylor Douglas Wright in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry Examining Committee: Dr. Michael Wolf, Professor, Chemistry, UBC Supervisor Dr. Carl Michal, Associate Professor, Physics & Astronomy, UBC Supervisory Committee Member Dr. Parisa Mehrkhodavandi, Professor, Chemistry, UBC University Examiner Dr. Orlando Rojas, Professor, Chemical and Biological Engineering, UBC University Examiner Additional Supervisory Committee Members: Dr. Jennifer Love, Professor, Chemistry, University of Calgary Supervisory Committee Member Dr. Mark MacLachlan, Professor, Chemistry, UBC Supervisory Committee Member iii Abstract Investigations of a number of photochemical cross-linking reactions are reported for the preparation of functional polymeric materials. Reactions that require constant inputs of light and do not proceed through radical or ionic mechanisms are studied, and the final properties of these materials are characterized. This work aims to expand the scope of available photo-cross-linking reactions for the preparation of functional materials. The incorporation of photodimerizable anthracene into a thermally healable vinylogous urethane copolymer enables light-induced post-polymerization UV cross-linking. This allows for tuning of the glass transition temperature over a 20 °C range, control over the rheological properties, and tuning the scratch healing temperature. Pendant attachment of anthracene moieties onto a flexible siloxane polymer (PDMS) results in macroscopic polymer crystallization upon photo-cross-linking, giving a heterogeneous material with up to 1 mm diameter crystallites embedded inside a flexible matrix. A thorough investigation of the growth of the polymer crystallites through microscopic and diffusion techniques revealed unique crystallite growth initiating from the bottom of the film and progressing upwards towards the irradiation source. The application of photogenerated singlet oxygen is applied to the cross-linking of amine siloxanes. Oxidative coupling of amine groups to imine groups results in facile cross-linking at room temperature in oxygen rich environments using visible light with no measurable side reactions. Solvent free precursors were prepared by covalent attachment of the sensitizer to the PDMS backbone. As coatings, these materials demonstrate contact antimicrobial activity against iv bacterial cells, being more effective against E. Coli than methicillin-resistant Staphylococcus aureus (MRSA), as well as inducing cell lysis in mammalian cells. This system was further developed as a dual-functional textile coating, utilizing both contact antimicrobial activity as well as photodynamic disinfection using singlet oxygen, which results in >99% bacterial disinfection in 90 minutes and a 10× decrease in SARS-CoV-2 viral infectivity in two hours. Singlet oxygen was also used to photo-cross-link thiol containing siloxanes through the oxidative preparation of a diaryl-telluroxide catalyst, effectively linking low thiol-content PDMS through disulfide formation. These polymers exhibit up to 400% elongation, and can be reductively cleaved back into liquids using NaBH4 with >90% mass recovery. v Lay Summary New chemical reactions to create and modify plastics are necessary to develop functional materials to address the increasing demands of modern life. This work presents studies on the use of light to drive chemical reactions that link together polymer chains to create durable materials with novel properties such as self-healing, recyclability, and antimicrobial activity. These reactions can be performed with ultraviolet to visible light, open to the air, and without the need for specialized equipment or setups. This thesis explores the fundamentals of each photoreaction as well as demonstrating the properties and application of the resulting materials. vi Preface Chapter 2 has been published.1 Wright, T.; Tomkovic, T.; Hatzikiriakos, S. G.; Wolf, M. O. Macromolecules 2019, 52, 36–42. I conducted the project design, the majority of the research, data analysis, and writing. Rheology measurements and analysis were performed by Dr. Tanja Tomkovic and Dr. Savvas Hatzikiriakos. Chapter 3 has been published.2 Wright, T.; Petel, Y.; Zellman, C. O.; Sauvé, E. R.; Hudson, Z. M.; Michal, C. A.; Wolf, M. O. Chem. Sci. 2020, 11, 3081–3088. I conducted the project design, the majority of the research, data analysis, and writing. WAXS and SAXS measurements were performed by Carson Zellman. Diffusion NMR measurements and analysis were done by Dr. Yael Petel and Dr. Carl Michal. AFM measurements and data analysis were performed by Dr. Ethan Sauve and Dr. Zachary Hudson. Chapter 4 has been published.3 Wright, T.; Tomkovic, T.; Hatzikiriakos, S. G.; Wolf, M. O. ACS Appl. Polym. Mater. 2020, 2, 4802–4808. vii I conducted the project design, the majority of the research, data analysis, and writing. Rheology and mechanical measurements and analysis were performed by Dr. Tanja Tomkovic and Dr. Savvas Hatzikiriakos. Chapter 5 has been published.4 Wright, T.; Karis, D.; Millik, S. C.; Tomkovic, T.; Hatzikiriakos, S. G.; Nelson, A.; Wolf, M. O. ACS Appl. Mater. Interfaces 2021, 13, 22195–22203. I conducted the project design, the majority of the research, data analysis, and writing. Rheology and tensile strength measurements and analysis were performed by Dr. Tanja Tomkovic and Dr. Savvas Hatzikiriakos. Polymer photo-rheology and 3D printing was done with assistance from Dr. Dylan Karis, Cem Milik, and Dr. Alshakim Nelson. Chapter 6 has been published.5 Wright, T.; Vlok, M.; Shapira, T.; Olmstead, A. D.; Jean, F.; Wolf, M. O. ACS Appl. Mater. Interfaces 2022, 14, 49–56. I conducted the project design, the majority of the research, data analysis, and writing. Viral measurements, analysis, and discussion were performed by Dr. Tirosh Shapria, Dr. Marli Vlok, Dr. Andrea Olmstead, and Dr. François Jean. Chapter 7 has been published.6 Wright, T.; Zhang, Z.; Michal, C. A.; Hatzikiriakos, S. G.; Wolf, M. O. Polym. Chem. 2022, 13, viii 395–401. I conducted the project design, the majority of the research, data analysis, and writing. Rheology, tensile measurements, and data analysis were conducted by Ziyue Zhang and Dr. Savvas Hatzikiriakos. Diffusion NMR measurements were collected by Dr. Carl Michal. Dr. Michael Wolf provided guidance on research, data analysis, project design and writing throughout. Other contributors not listed as authors on published works have been acknowledged in the respective published manuscripts. Chapters 2-7 have been adapted from the published manuscripts without significant alterations to the scientific content or additions of data. The numbering of compounds has been altered to reflect the continuity of this document, and follows the scheme below: [Chapter Letter][Compound # / ID] Chapter 2 is denoted as A, 3 as B etc, which corresponds to the appendix at the end of this document. The letter P in the compound ID denotes the material is a polymer. ix The Appendix contains the supplementary information that was provided along with the accepted manuscripts without significant alterations to the scientific content or additions of data. Figure and tables denoted with a letter ID can be found in the appendix. x Table of Contents Abstract ......................................................................................................................................... iii Lay Summary .................................................................................................................................v Preface ........................................................................................................................................... vi Table of Contents ...........................................................................................................................x List of Tables .............................................................................................................................. xiv List of Figures ............................................................................................................................. xvi List of Symbols ....................................................................................................................... xxxvi List of Abbreviations ............................................................................................................ xxxvii Acknowledgements ..................................................................................................................... xli Dedication .................................................................................................................................. xliii Chapter 1: Introduction ................................................................................................................1 1.1 Overview ......................................................................................................................... 1 1.2 Heat and Light................................................................................................................. 1 1.2.1 Early Photochemical Reactions .................................................................................. 2 1.2.2 Early Thermally Responsive Polymers ....................................................................... 4 1.3 Polymer Cross-linking .................................................................................................... 6 1.3.1 Radical Polymerizations ............................................................................................. 6 1.3.2 Photodimer Polymers .................................................................................................. 8 1.3.3 Vinylogous Urethane Vitrimers ................................................................................ 11 1.3.4 Polymer Crystals ....................................................................................................... 13 1.3.5 Photocatalytic Cross-linking ..................................................................................... 15 xi 1.3.6 Singlet Oxygen and Protein Cross-linking ............................................................... 16 1.3.7 Antimicrobial Polymers ............................................................................................ 19 1.3.8 Antimicrobial Textiles .............................................................................................. 21 1.3.9 Disulfide Polymers.................................................................................................... 23 1.4 Thesis Scope ................................................................................................................. 24 Chapter 2: Photoactivated Healable Vitrimeric Copolymers ..................................................27 2.1 Overview ....................................................................................................................... 27 2.2 Research ........................................................................................................................ 28 2.2.1 Results and Discussion ............................................................................................. 28 2.2.2 Experimental ............................................................................................................. 41 2.2.3 Synthesis and Preparation ......................................................................................... 43 2.3 Conclusions ................................................................................................................... 46 Chapter 3: Room Temperature Crystallization of Amorphous Polysiloxane using Photodimerization ........................................................................................................................47 3.1 Overview ....................................................................................................................... 47 3.2 Research ........................................................................................................................ 48 3.2.1 Results and Discussions ............................................................................................ 48 3.2.2 Experimental ............................................................................................................. 60 3.2.3 Synthesis and Preparation ......................................................................................... 62 3.3 Conclusions ................................................................................................................... 64 Chapter 4: Visible Light Sensitized Photooxidative Cross-linking of Polysiloxanes using Singlet Oxygen ..............................................................................................................................66 4.1 Overview ....................................................................................................................... 66 xii 4.2 Research ........................................................................................................................ 67 4.2.1 Results and Discussions ............................................................................................ 67 4.2.2 Experimental ............................................................................................................. 77 4.2.3 Synthesis and Preparation ......................................................................................... 78 4.3 Conclusions ................................................................................................................... 80 Chapter 5: Photo-cross-linked Antimicrobial Amino-Siloxane Elastomers...........................81 5.1 Overview ....................................................................................................................... 81 5.2 Research ........................................................................................................................ 82 5.2.1 Results and Discussions ............................................................................................ 82 5.2.2 Experimental ............................................................................................................. 94 5.2.3 Synthesis and Preparation ......................................................................................... 97 5.3 Conclusions ................................................................................................................. 100 Chapter 6: Photodynamic and Contact Killing Polymeric Fabric Coating for Bacteria and SARS-CoV-2 ...............................................................................................................................101 6.1 Overview ..................................................................................................................... 101 6.2 Research ...................................................................................................................... 102 6.2.1 Results and Discussions .......................................................................................... 102 6.2.2 Experimental ........................................................................................................... 113 6.2.3 Synthesis and Preparation ....................................................................................... 118 6.3 Conclusions ................................................................................................................. 120 Chapter 7: Photo-Oxidative Cross-Linking of Thiol Copolymers Via Disulfide Formation......................................................................................................................................................122 7.1 Overview ..................................................................................................................... 122 xiii 7.2 Research ...................................................................................................................... 123 7.2.1 Results and Discussion ........................................................................................... 123 7.2.2 Experimental ........................................................................................................... 133 7.2.3 Synthesis and Preparation ....................................................................................... 136 7.3 Conclusions ................................................................................................................. 137 Chapter 8: Conclusions and Future Work ..............................................................................138 8.1 Conclusions ................................................................................................................. 138 8.2 Future Work ................................................................................................................ 140 References ...................................................................................................................................144 Appendices ..................................................................................................................................163 Appendix A : Supplementary Information for Chapter 2 ....................................................... 163 Appendix B : Supplementary Information for Chapter 3 ....................................................... 168 Appendix C : Supplementary Information for Chapter 4 ....................................................... 185 Appendix D : Supplementary Information for Chapter 5 ....................................................... 193 Appendix E : Supplementary Information for Chapter 6 ........................................................ 213 Appendix F : Supplementary Information for Chapter 7 ........................................................ 223 xiv List of Tables Table 2.1. Relative molar ratios of monomers for polymers P1a and P2a. .................................. 32 Table 2.2. Composition and scratch healing temperature of anthracene containing copolymers before and after UV cross-linking................................................................................................. 39 Table 4.1. Effect of reaction condition, additives, and blend composition on the photooxidative cross-linking of PNH2-7 after 4 hours of 530 nm irradiation. ...................................................... 71 Table 4.2. Mechanical properties of samples measured using DMA tension experiments. ........ 73 Table 5.1. Mechanical properties of samples prepared with different amounts of RB attached to PNH2-7 and a sample (DP1-soln) prepared using a RB containing solution. The properties were measured using DMA tensile experiments. .................................................................................. 89 Table 7.1. Mechanical properties of cross-linked FP100, FP75, and FP50, determined from tensile measurements. ................................................................................................................. 130 Table B.1. Calculated translational diffusion coefficients for 1H NMR peaks corresponding to the anthracene portion, vinylogous urethane, and PNH2-7 chain, demonstrating that all components diffuse at similar speeds. Dt determined from 2D DOSY measurements, 400 MHz, RT, CD2Cl2. ................................................................................................................................ 170 Table B.2. Translational diffusion speeds, T1, and T2 values for liquid polymer samples and crystallized BP7, measured using PFG 1H NMR........................................................................ 183 Table C.1. Mass ratios and PtOEP wt% for samples with different amounts of PtOEP. .......... 187 Table C.2. Mass balance of samples before and after irradiation for CP100 and CP25 small scale tests, as well as soluble % and mass swelling % determined using DCM. ................................. 188 xv Table D.1. Photo-rheological kinetic data for the cross-linking of PNH2-7 and OEP at different [OEP]. The %T365nm was calculated using a sample thickness of 500 um, ε365nm = 82000 cm-1 M-1 and the equation242 ...................................................................................................................... 194 Table D.2. Composition and optical penetration of samples with different amounts of molar equivalents of RB reacted with PNH2-7. Thickness was calculated for 530 nm light. ............... 202 Table D.3. Soluble fraction and swelling ratio for samples cross-linked using different molar equivalents of RB. ....................................................................................................................... 206 Table E.1. Mechanical characterization data for samples of cotton and polyester coated with different polymer wt% solutions. ................................................................................................ 218 Table E.2. Comparison of cotton fabric coated with polymers of 7 and 23 wt% amine groups. RBL molar equivalencies and coating procedure were the same for all samples. ...................... 221 Table E.3. Passive antimicrobial activity of fabric treated with two different amine wt % polymers, measured against E. coli and MRSA at different fabric size amounts. ...................... 222 Table F.1. Translational diffusion coefficient measured for sample FP100 as a function of irradiation time, determined using PFG-NMR. .......................................................................... 226 Table F.2. Composition and Tg of cross-linked polymer samples, measured at 10 °C / min under. All cross-linked samples had the same melting/crystallization peaks associated with DPT...................................................................................................................................................... 228 xvi List of Figures Figure 1.1. The photoreaction cascade of santonin crystals discovered by Hermarin Trommsdorff. The final photocyclization results in cracking of the crystal. .................................. 3 Figure 1.2. First reported [4+4] and [2+2] photodimers of (a) anthracene (b) 2-phenylnaphthoquinone and (c) p-coumaric acid. ............................................................................ 4 Figure 1.3. Vulcanization reaction of polyisoprene rubber using elemental sulfur to give a network cross-linked by a mixture of different length sulfur chains. ............................................. 5 Figure 1.4. Phenolic resin network formation through the reaction of formaldehyde at the ortho and para positions of phenol. .......................................................................................................... 5 Figure 1.5. (Left) The steps of radical polymerization and (right) common radical polymerization photoinitiators. ....................................................................................................... 7 Figure 1.6. Photodimerization reactions employed in photodimer polymers including (a) anthracene (b) stilbene and (c) coumarin. ....................................................................................... 8 Figure 1.7. Three network motifs possible using polymer photodimerization reactions including chain growth, single-chain particle formation, and network cross-linking. ................................... 9 Figure 1.8. Example of how photomasks of different opacities can be used to control the light exposure and therefore cross-linking density of a polymer film containing photodimerizable subunits. ........................................................................................................................................ 10 Figure 1.9. Preparation of photo-patterned films with varying topologies. Patterned cross-linking to give incompletely cross-linked network leads to diffusion (red arrows) into the irradiated regions, followed by further irradiation to fully cross-link and lock-in the pattern. Adapted from Jérôme et al.31 ............................................................................................................................... 11 xvii Figure 1.10. Thermal vitrimeric exchange of vinylogous urethane vitrimers ............................. 12 Figure 1.11. A tricyclic anthracene monomer is dimerized in the crystalline state to prepare covalent organic framework crystalline sheets, adapted from King et al.59 ................................. 14 Figure 1.12. Proposed mechanism for metal-free photoredox mediated ROMP. The vinyl-ether initiator is photo-oxidized by the photocatalyst (PC) to give a radical species that undergoes ROMP, terminating though electron transfer from the photocatalyst. The resulting vinyl-ether can then undergo the same mechanism to chain-extend.72 ........................................................... 15 Figure 1.13. Simplified Jablonski diagram showing the production of singlet oxygen involving (1) excitation of the photosensitizer with light (2) intersystem crossing to the triplet state (3) energy transfer to oxygen. The electronic configuration of ground state oxygen and excited state singlet oxygen are shown. ............................................................................................................. 16 Figure 1.14. Proposed mechanism for the cross-linking of proteins by 1O2 involving oxidation of histidine residues. Adapted from Kopeček et al.78 ...................................................................... 17 Figure 1.15. 1O2 cross-linking of furan-modified DNA with a cytosine DNA subunit. Adapted from Madder et al.79 ...................................................................................................................... 18 Figure 1.16. Singlet oxygen oxidative coupling of two alkyl amines into an imine. .................. 19 Figure 1.17. Chemical structure of chitosan and poly(L-lysine), two antimicrobial biomaterials........................................................................................................................................................ 20 Figure 1.18. Illustration of the four steps of the antimicrobial contact killing mechanism: approach, electrostatic attraction, interdigitation, and cell lysis. .................................................. 21 Figure 1.19. Two stage photo-cross-linking of thiol groups using 1O2. Initially, a diaryltelluride precatalyst is oxidized to the active telluroxide/tellurone species. Next, this catalyzes the formation of a disulfide from two thiols. Adapted from Ando et al.138 ........................................ 24 xviii Figure 2.1. Irradiation of compound A1a (enamine) to give A1b (imine) ................................... 28 Figure 2.2. Comparison of the FT-IR spectra of A1a, A1b and ethyl acetoacetate. .................... 29 Figure 2.3. Kinetic exchange experiment for aromatic vinylogous urethanes. ............................ 30 Figure 2.4. IR spectra of AP1a after different irradiation times at 365 nm, and sample AP1c containing fully dimerized anthracene units. ................................................................................ 33 Figure 2.5. DSC traces of polymer samples before and after irradiation, measured on the second heating cycle at 10 °C/min. Solid circles indicate Tg. .................................................................. 34 Figure 2.6. G′, G″, and η for AP2a (left, 60 °C) and AP2b (right, 85 °C), measured at 0.1% strain. ............................................................................................................................................. 36 Figure 2.7. Stress relaxation curves for AP2a and AP2b under a 0.5% initial strain. ................. 37 Figure 2.8. Stress relaxation curves and Arrhenius plot for AP3 containing no anthracene units........................................................................................................................................................ 38 Figure 2.9. Optical microscope image of a) Sample AP2a initial scratch, b) AP2a after 60 °C 10 min, c) Sample AP2b initial scratch, d) AP2b after 60 °C 10 min, e) AP2b after 80 °C 10 min. Black scale bar is 300 μm. Value in parentheses indicates approximate scratch width. Images were assembled from individual photos focused at each position. ............................................... 40 Figure 3.1. Polymer structure and crystallization after UV irradiation. (a) Structure of the anthracene-containing PDMS random copolymer with varying amounts of anthracene. (b) [4+4] photocycloaddition of anthracene and photo/thermal cycloreversion reaction, showing one of two possible dimer isomers. (c) Image of a thin film of P7 after irradiation. (d) Optical microscope image of P7 after irradiation. (e) Photograph of the leaves of a sequoia redwood tree. (f) Polarized optical microscope image of P7 under a cross-polarizer and 530 nm retardation plate showing a birefringent pattern. ..................................................................................................... 50 xix Figure 3.2. Compositional effect on crystalline growth. Optical microscope image of (left) BP3 crystals after one hour of 365 nm irradiation and (right) BP25 crystals after ten minutes of 365 nm irradiation focused on the outer edges. ................................................................................... 53 Figure 3.3. Confocal microscopy of seeds and leaves. (a) Images of crystallized BP7 at different depths, showing three distinct focal planes, collected at 10× magnification. Inset numbers are distance from the lowest focal plane. (b) Schematic representation for the proposed stages of photo-induced crystallization proceeding through seed growth, crystal growth from an uppermost seed, and constriction of the bulk. ................................................................................................ 55 Figure 3.4. PFG 1H NMR diffusion measurements. Gaussian fits to the Stejskal – Tanner diffusion equation167 with an additive constant to account for slowly diffusing species are shown for liquid BP7 (left) and irradiated solid BP7 (right). ................................................................... 58 Figure 3.5. Calculated displacement for liquid polymer chains. (a) Translational diffusion coefficient (Dt) and relative rotational time (T1/T2) as functions of molar equivalents of anthracene, measured using PFG 1H NMR spectroscopy. (b) Maximum linear displacement distances for PNH2-7 and BP7 as a function of time, as calculated from Dt. .............................. 59 Figure 3.6. Atomic force microscopy imaging of crystalline leaves. (a) Non-contact mode showing feature height and (b) fast-force mapping contact mode showing Young’s modulus of crystallized BP7. Scale bar = 8 μm. .............................................................................................. 60 Figure 4.1. (Top) Chemical structures of 6-7 wt% (aminopropylmethylsiloxane)-dimethylsiloxane copolymer (PNH2-7) and platinum octaethylporphyrin (PtOEP). (Bottom) Schematic representation of the photooxidative cross-linking of pendant amine groups using oxygen and a photosensitizer (PS). ............................................................................................... 68 xx Figure 4.2. (a) FT-IR spectra of PNH2-7, the CP100 mixture irradiated for four hours using 530 nm light, and the irradiated CP100 after soaking in DCM to remove the soluble components. Inset shows the imine peak region. Spectra are offset vertically by one transmittance unit for display purposes. (b) Solid state 13C CP-MAS NMR spectrum of irradiated CP100 showing a peak characteristic of imine carbons, 400 MHz, RT. ................................................................... 70 Figure 4.3. (a) Stress-strain curves for CP100, CP25, CPA, and CPB from uniaxial tensile experiments, RT. (b) Photograph shows CP100 (top) and CP25 (bottom) used for mechanical testing. Disks are 3 cm in diameter, 1 mm thick. .......................................................................... 72 Figure 4.4. (a) Photolithographic setup prepared using two stacked glass microscope slides, a printed overhead transparency sheet, and a glass slide coated in CP25. (b) A photopatterned slide after one hour of 530 nm bulb irradiation followed by rinsing with ethyl acetate, features are 2 mm wide........................................................................................................................................ 76 Figure 5.1. Singlet oxygen cross-linking of amine-containing polymers resulting in imine cross-links (blue) and free amines (red). 1O2 is generated from atmospheric oxygen quenching the excited triplet state of a photosensitizer. ....................................................................................... 82 Figure 5.2. Photo-rheological results for the cross-linking of PNH2-7 and OEP using 365 nm light. (a) Scheme showing the structures of PNH2-7 and OEP used in these experiments, resulting in imine cross-links after irradiation in the presence of O2. (b) Onset time and initial cross-linking rate measured using different intensities of irradiation. (c) Effect of cycling irradiation on (yellow areas, 30 mW/cm2) and off (white areas) on G´ and Gʺ during a single experiment. Cross-linking kinetics measured using (d) different concentrations of the porphyrin OEP at 52.5 mW/cm2 light intensity and (e) higher amine wt% polymer and deuterated toluene-d8 at 30 mW/cm2 light intensity. ................................................................................................................ 83 xxi Figure 5.3. Condensation reaction between PNH2-7 and different molar equivalents of RB resulting in solvent-free liquid polymers after drying under vacuum. .......................................... 85 Figure 5.4. The normalized absorbance spectrum, visible region and IR region emission of a thin film of non-cross-linked DP1. IR emission at 1270 nm is a result of 1O2 phosphorescence. ....... 86 Figure 5.5. The vibrational spectra of a piece of DP1 after soaking in THF, soaking in 25 wt % ethyl acetoacetate in THF, and the spectrum of pure ethyl acetoacetate. ..................................... 87 Figure 5.6. (a) Representative stress-strain curves obtained from tensile experiments for materials cross-linked using RB dissolved in solution and solvent-free RB attached to the polymer. (b) Image of a disk of sample DP3, 1 mm thick and 30 mm diameter. ......................... 89 Figure 5.7. Normalized CFUs for E. coli and MRSA incubated with cross-linked DP3 powder for 24 h under constant shaking, compared with controls with no polymer. Determined from colony counts grown on agar plates in triplicate. ......................................................................... 92 Figure 5.8. Microscope images of CHO-K1 cells incubated for 72 hours with cell medium and (a) no additive (b) PDMS 50,000 g/mol (c) 6 μm α-Amanitin (d) cross-linked DP3. α-Amanitin results in cell death without lysis while P3 lyses all cells............................................................. 93 Figure 6.1. (a) Scheme of textile treatment using a solution soak followed by UV irradiation resulting in imine cross-links from TPP derived 1O2. (b) Polymer mass loading and unloading for cotton treated with different wt% polymer solutions. (c) Representative stress-strain curves determined from Instron mechanical testing of cotton and polyester strips treated using EP1, EP5, and EP13 solutions. (d) Cotton fabric before (top) and after (bottom) treatment with EP13 to give EC/P13. ........................................................................................................................... 103 xxii Figure 6.2. (a) Reflectance and emission spectra of EC/P13. (b) Near-IR emission and excitation spectra of a thin film of cross-linked DP3 and treated EC/P13. 1O2 phosphorescence at 1270 nm is observed for both materials as a result of RBL excitation at 525 nm. .................................... 106 Figure 6.3. (a) Passive reduction in E. coli and MRSA CFUs after 24 hours of 37 °C incubation in the dark with different size samples of EC/P13, prepared using PNH2-7 or PNH2-23 under identical conditions (relative to no fabric control). (b) aPDI activity of EC/P13 prepared using PNH2-7 (9 cm2) measured in the dark and under constant 530 nm irradiation at room temperature, assessed using the relative number of E. coli and MRSA CFUs after aliquots were drawn at set time intervals. CFUs were measured using colony counts on agar after 24 hours growth time, experiments performed in triplicate. ........................................................................................... 109 Figure 6.4. (a) Schematic of experimental design to evaluate antiviral properties of EC/P13 against SARS-CoV-2. SARS-CoV-2 stock diluted in media was incubated with fabric samples in dark or light (530 nm irradiation) conditions for two hours at room temperature. The treated virus dilutions were used to (i) infect Huh-7.5.1 cells and the resulting infectivity was measured by staining for intracellular virus nucleocapsid levels after 48 hours of infection; (ii) the treated virus was also added to Vero E6 cells for measuring plaque forming units (PFU) using plaque assay. Experiments were performed in triplicate. (b) Relative intracellular viral nucleocapsid levels of SARS-CoV-2 dilutions following incubation with fabric and infection of Huh-7.5.1 cells. (c) SARS-CoV-2 viral load following incubation of 1.5×104 PFU/mL with fabric under light and dark conditions. Circles represent individual replicates, bars are 95% CI. One way ANOVA with Tukey multiple comparisons correction presented; * p=0.0137, **** p<0.0001. Representative viral plaques of (d) dark sample and (e) 530 nm irradiated sample. .................. 110 xxiii Figure 7.1. Photo-oxidative cross-linking of statistical thiol copolymers into disulfide networks using a DPT pre-catalyst and TPP as a singlet oxygen photo-sensitizer. ................................... 123 Figure 7.2. (a) Raman spectra of a sample of FPA before and after photo-oxidative cross-linking, showing a diagnostic disulfide peak at 552 cm-1. (b) A sample of cross-linked FP50 polymer, 1.5 mm thick and 20 mm in diameter. ......................................................................... 124 Figure 7.3. (a) Proposed scheme for the photo-cross-linking in this system, proceeding through three discrete steps. (b) Photo-rheological experiment measuring P100 with the UV light toggled on (yellow) and off (white) during the measurement. Onset time and initial cure rate determined using photo-rheology of FP100 with differing concentrations of (c) DPT (d) TPP and (e) light intensity. Measurements performed in triplicate, conditions were the concentrations described for sample FP100 and a UV intensity of 23 mW/cm2 unless otherwise indicated. .......................... 126 Figure 7.4. Translational diffusion coefficient (Dt) for for toluene (1H, DPT stand-in), CF3Py (19F, TPP stand-in), and the FPB polymer backbone (1H) as a function of irradiation time, measured using PFG-NMR. Sample is P100 with CF3Py added at 1 wt% relative to the polymer...................................................................................................................................................... 127 Figure 7.5. Tensile measurement results of cross-linked FP100, FP75, and FP50 plotted according to the mass ratio of PB in the sample. ........................................................................ 130 Figure 7.6. Photo-rheological experiment measuring a FP100 mixture prepared using pristine and degraded FPB with the UV light toggled on at 120 s. UV intensity at 23 mW/cm2 ............ 132 Figure 8.1. Synthetic scheme for the preparation of hydrophilic diaryltellurides. .................... 141 Figure 8.2. Proposed modifications to the alkyl-amine groups of PNH2-23 that may result in greater antimicrobial activity. ..................................................................................................... 142 xxiv Figure 8.3. Spectral output of common light sources and indicators for the wavelength of maximum absorption for some of the molecules used throughout this document. .................... 143 Figure A.1. UV-Vis spectra of A1a after different amounts of time of irradiation at 365 nm. Arrows indicate direction of change. .......................................................................................... 163 Figure A.2. Images of solid (a) and solution (CH2Cl2, b) emission of A1a (left) and A1b (right) under 365 nm irradiation. ............................................................................................................ 163 Figure A.3. 1H NMR spectra of A1a (bottom) and the photoproduct A1b (top). 400 MHz, CD2Cl2, RT. ESI-MS inset in MeOH.......................................................................................... 164 Figure A.4. 1H NMR spectra of thermal exchange reaction between A1a and para-toluidine initially (bottom) and after 120 °C for 5 minutes (top). Red circles are assigned to A1a, green circles para-toluidine, and blue circles the new product formed. 400 MHz, (CD3)2SO, RT. ..... 165 Figure A.5. Photograph of sample AP2a in a plastic petri dish. ................................................ 165 Figure A.6. Comparison of the IR spectra of P1a with model compound 1a before and after irradiation. ................................................................................................................................... 166 Figure A.7. G′, G″, and η for AP1a (left, 70 °C) and AP1b (right, 75 °C), measured at 0.1% strain. ........................................................................................................................................... 166 Figure A.8. Strain sweep rheology experiment for AP2a at 0.1 Hz from 0.01-10% strain, 60 °C...................................................................................................................................................... 167 Figure A.9. Stress relaxation curve for AP1a under a 0.5% initial strain. ................................. 167 Figure B.1. 1H NMR spectrum of B1. 400 MHz, RT, (CD3)2SO. Other peaks are residual solvent peaks. .......................................................................................................................................... 168 Figure B.2. 1H NMR spectra of (bottom) PNH2-7 and (top) BP7 showing the new peaks due to B1 condensation. 400 MHz, RT, CD2Cl2 ................................................................................... 169 xxv Figure B.3. UV-VIS spectra of a dropcast sample of polymer BP7 as a function of irradiation time using 365 nm irradiation. .................................................................................................... 170 Figure B.4. Optical microscope image of a side-on view of a free-standing piece of irradiated BP7, showing the approximate film thickness of 115 μm. ......................................................... 171 Figure B.5. Average approximate distance (d) travelled by a sample of polymer BP25 two minutes after inversion as a function of irradiation time (t). ...................................................... 171 Figure B.6. FT-IR spectrum of the amine-containing PDMS PNH2-7, anthracene acetoacetate B1, and the polymer BP7 (condensed from B1 and PNH2-7). Arrows indicate the C=O stretch before (blue) and after condensation (red), showing a shift to lower wavenumbers resulting from increased conjugation. No changes were observed in BP7 after irradiation. .............................. 172 Figure B.7. Optical microscope image of a thin film of BP7 after 15 minutes of 365 nm irradiation showing only spherical crystalline seeds. ................................................................. 172 Figure B.8. Optical microscope image of BP7 leaves under a cross-polarizer (left) and cross-polarizer + 530 nm retardation plate (right) showing crystal structures having grown into each other without merging. ................................................................................................................ 173 Figure B.9. Optical microscope image of bulk BP7 in a vial after one hour of 365 nm irradiation from all directions, imaged through the sides of the glass vial. .................................................. 173 Figure B.10. Differential scanning calorimetry of BP7 after 60 minutes of irradiation, showing a full heating and cooling cycle with a temperature ramp speed of 10 °C/min. ............................ 174 Figure B.11. Optical microscope image of a thin film of BP7 after 60 minutes of 365 nm followed by 60 minutes at 100 °C. ............................................................................................. 174 Figure B.12. Optical microscope image of BP7 leaves after 60 minutes at 100 °C under a cross-polarizer (left) and cross-polarizer + 530 nm retardation plate (right). ...................................... 175 xxvi Figure B.13. PXRD measurements of crystallized P7 and crystallized BP7 after 1 hour at 100 °C. Cu radiation, RT. .................................................................................................................. 175 Figure B.14. Optical microscope image of the center of BP25 after ten minutes of irradiation showing buckling of the surface. ................................................................................................ 176 Figure B.15. Magnified POM image from Figure 3.3.1 with arrows showing 45° branching of the blue region from the radial orange branch. ........................................................................... 176 Figure B.16. Optical microscope image of BP7 seeds under a cross-polarizer (left) and cross-polarizer + 530 nm retardation plate (right). ............................................................................... 177 Figure B.17. Wide-angle X-ray scattering and small-angle X-ray scattering of a free-standing BP7 film after irradiation, showing only two diffuse peaks attributed to the PDMS backbone. Measurements were focused on areas containing crystalline leaves. ......................................... 177 Figure B.18. WAXS and SAXS of BP7 in a glass capillary, before irradiation and after 120 minutes of 365 nm irradiation. .................................................................................................... 178 Figure B.19. Guinier plots of the low q region of the SAXS spectrum of crystallized BP7, focused on the crystalline regions. .............................................................................................. 178 Figure B.20. Ornstein-Zernike plot of crystallized BP7 giving a correlation distance of 61 Å. 179 Figure B.21. PXRD measurements of BP7 before irradiation, after 60 minutes of 365 nm irradiation, and of PNH2-7. Cu radiation, RT. ............................................................................ 179 Figure B.22. Schematic representation of (top) cross-linking via anthracene dimerization resulting in oriented cross-linked areas surrounded by amorphous polymer chains and (bottom) cross-linking via a flexible, non-rigid moiety resulting in no ordering. ..................................... 180 xxvii Figure B.23. Confocal microscopy images of P7 leaf edges at different depths and inverted 3D reconstructed data. Inset numbers are the vertical distance from the surface. Reconstruction boxes are 60 μm × 60 μm. .......................................................................................................... 181 Figure B.24. Excitation and emission spectra of a thin film of BP7 after one hour of 365 nm irradiation. ................................................................................................................................... 182 Figure B.25. (Left) Bright field and (right) fluorescence imaging of BP7 crystals at 10× magnification, using 350 nm excitation light. ............................................................................ 182 Figure B.26. Schematic representation for confinement of anthracene molecules in the crystalline seeds and leaves giving rise to the fluorescence images from Figure B.24, proceeding from linear polymer to seed to leaf growth. ................................................................................ 183 Figure B.27. PFG 1H NMR diffusion measurement. The same data as in Figure 3.3.4, plotted as the natural logarithm of the signal intensity vs. the gradient strength squared to linearize the Gaussian behaviour of the Stejskal – Tanner diffusion equation. Liquid BP7 (left) and irradiated BP7 (right). In the liquid sample there appears to be an abrupt transition between single-component diffusion and a small (~10%), much slower diffusing component. The irradiated sample appears to make a more gradual transition, suggesting a distribution of slower diffusion coefficients. Larger error bars for the irradiated sample reflect the lower signal to noise ratio due to the slower diffusion rates and faster T2 decay. ....................................................................... 184 Figure B.28. (a) AFM height image of crystallized BP7, scale bar = 8 μm. (b) Representative force indentation curve taken at point 1. (c) Representative force indentation curve taken at point 2................................................................................................................................................... 184 xxviii Figure C.1. UV-VIS absorbance spectra of PtOEP, Rose Bengal (RB), and the spectral output of green LEDs used for irradiation. Spectra were collected in DCM (2.47 × 10-6 M) and MeOH (1.17 × 10-6 M), respectively....................................................................................................... 185 Figure C.2. 1H NMR spectra of a sample containing n-butylamine and PtOEP before irradiation (bottom) and after one hour of 530 nm irradiation (top). Integrated peaks are assigned to the formed imine product. CD2Cl2, RT, 400 MHz. .......................................................................... 186 Figure C.3. Photograph of a freestanding piece of CP100 irradiated for one hour 530 nm light. Sample is 20 mm in diameter, 0.5 mm thick. ............................................................................. 186 Figure C.4. Calculated optical transmittance of 530 nm light as a function of initial sample thickness through different initial polymer mixtures. ................................................................. 187 Figure C.5. Solid-state 13C CP-MAS NMR spectrum of a sample of CP100 after drying under vacuum for one week. 9.4 Tesla, RT. ......................................................................................... 189 Figure C.6. Proposed reaction pathway for the photooxidative cross-linking of alkyl-amine containing PDMS in the presence of oxygen. ............................................................................. 189 Figure C.7. Photograph of cross-linked CP100 (left) and CP25 (right) prepared for mechanical testing. Solutions were irradiated for 18 hours using a 530 nm lamp. Sample disks are 30 mm diameter, 1 mm thick. ................................................................................................................. 190 Figure C.8. FT-IR spectra of cross-linked P100, PA containing 30 wt% amine end-terminated PDMS, PB cross-linked using Rose Bengal, P2nd prepared using (18-24% aminoethylaminopropylmethylsiloxane, polyethyleneimine branched, and polyethyleneimine branched after attempting cross-linking. ..................................................................................... 190 Figure C.9. Thermogravimetric analysis of samples cross-linked with different amounts of PtOEP as well as the non-cross-linked PDMS-NH2 starting polymer. 10 °C / minute, N2. ....... 191 xxix Figure C.10. Differential scanning calorimetry (DSC) heating traces of P25 and P100, collected at 10 °C / minute. ........................................................................................................................ 191 Figure C.11. Photograph of the initial solutions used to cast the sample of CP100 (left) and CP25 (right) in Figure C.7. ......................................................................................................... 192 Figure C.12. Photograph of 2 mm lines photopatterned in CP25 using a mask printed on plastic transparencies. ............................................................................................................................. 192 Figure D.1. Parallel plate photo-rheological setup using a top (grey) 8 mm plate and a bottom (blue) transparent acetate plate. 365 nm light irradiates the sample from below, and atmospheric O2 diffuses into the sample through the exposed edge. The sample is initially a liquid (shown as green) and becomes solid (red) after irradiation only near the polymer-air interface due to limited O2 diffusion. Samples irradiated without the top geometry cross-link evenly. .......................... 193 Figure D.2. Representative photo-rheological results of PNH2-7 and OEP plotted in logarithmically (left) and linearly (right). Before cross-linking the material lacks any internal microstructure and as such the values of G´ and Gʺ are below the sensitivity of the instrumentation used. Upon irradiation with 365 nm light (dotted line, 60 s, 150 mW/cm2) G´ rapidly increases above Gʺ (onset time). The onset time is determined from the logarithmic plot, and the initial cure rate is determined from the slope of G´ in the first 100 s of irradiation. ..... 194 Figure D.3. The three major tautomers for neutral xanthene dyes bearing carboxylic acid and amide functionalities. A closed lactone (left), free acid (middle) and zwitterionic (right) are possible, with only the free acid isomer having absorbance in the visible region. ..................... 195 Figure D.4. Reaction scheme for PNH2-7 and fluorescein resulting in fluorescein-labelled PDMS (CPF) used for model studies. ......................................................................................... 195 xxx Figure D.5. Vibrational spectra of PNH2-7, the fluorescein labelled polymer DPF, and fluorescein. The shift in carbonyl peak is attributed to conversion from ester to amide. ........... 196 Figure D.6. 1H NMR spectrum of fluorescein labelled PDMS (DPF), CD2Cl2, RT, 400 MHz. 197 Figure D.7. 1H NMR spectrum of PDMS-NH2, CD2Cl2, RT, 400 MHz. .................................. 198 Figure D.8. UV-VIS spectra of Rose Bengal and the spectral output of the green LED used for irradiation. MeOH, 1.17×10-6 M. ................................................................................................ 199 Figure D.9. Photograph of DP1 in a glass vial. No change in appearance or precipitation was observed after four weeks in the dark. ........................................................................................ 199 Figure D.10. UV-VIS spectra of Rose Bengal and P1. Collected at 1.17×10-6 M and 5.8×10-7 M (calculated based on RB wt % in polymer) in MeOH and DCM respectively. .......................... 200 Figure D.11. Normalized absorbance spectra of DP1 measured in solution (DCM) and as a neat oil on a glass slide. ...................................................................................................................... 200 Figure D.12. Calculated initial optical transmittance for DP1 as a function of sample thickness at three different wavelengths. ........................................................................................................ 201 Figure D.13. Calculated initial optical transmittance for polymers with different amounts of Rose Bengal, calculated at 530 nm. ............................................................................................ 201 Figure D.14. (Left) 150 μL of non cross-linked DP1 and 5 mL H2O in a vial after one week of storing in the dark. (Right) UV-VIS absorbance spectrum of the neat supernatant from the vial, compared against a calculated theoretical spectrum assuming complete solubility/miscibility of the polymer and dye with water. No miscibility between the polymer and water is observed, and no Rose Bengal is leached into solution. .................................................................................... 202 Figure D.15. (Left) A focused view and (right) the full view of the vibrational spectra of PDMS-NH2, a sample cross-linked using a PtOEP solution, and a sample cross-linked using RB attached xxxi to the polymer (P1). The same imine peak at 1671 cm-1 is observed for both cross-linked samples. ....................................................................................................................................... 203 Figure D.16. Solid-state 13C CP-MAS NMR spectrum of a cross-linked sample of DP1 after drying under vacuum for one week. 9.4 T, RT. .......................................................................... 204 Figure D.17. Water contact angles of a cross-linked sample of DP1 and 10 μL droplets of deionized water, 1M NaOH, and 1 M HCl. Contact angles were measured in quadruplicate from photographs. ................................................................................................................................ 205 Figure D.18. Photograph of the sample DP1 (left) and DP2 (right) used for mechanical testing. The samples are 1 mm thick, 30 mm diameter. .......................................................................... 205 Figure D.19. Thermogravimetric analysis of the PNH2-7 starting material, DP1 liquid, and DP1 cross-linked using 530 nm light. 10 °C / min, N2. ...................................................................... 206 Figure D.20. Differential scanning calorimetry (DSC) heating traces of P1, P2, and P3, collected at 10 °C / min, N2. All samples exhibit an approximate Tg of -115 °C. ..................................... 207 Figure D.21. Cartoon demonstrating the difference in deposition shape when performed at room temperature (top) and -78 °C (bottom). ...................................................................................... 207 Figure D.22. Labelled photograph of the experimental setup used to cryo-deposit non-equilibrium 3D structures of DP1 at -78 °C. Vessel was immersed in a dry ice acetone bath before deposition. Setup is designed to exclude water while still providing oxygen. ................ 208 Figure D.23. Photograph of the hashtag shape with a quarter for reference. When observed at a low angle the overlap of the arms can be clearly seen. ............................................................... 208 Figure D.24. Photolithography of DP1 to give the letters UBC after one hour of 530 nm irradiation. (Top Left) Printed photomask used to pattern the polymer. (Top Right) P1 on a glass slide after one hour of 530 nm irradiation through the photomask. Colorless areas are regions that xxxii were exposed to light. (Bottom Left) Slide after rinsing with ethyl acetate. The pink color diffused into the printed structure during rinsing. (Bottom Right) Slide after photobleaching overnight using 530 nm light to give a clear, colorless pattern. ................................................. 209 Figure D.25. Side-on and top view of a non-equilibrium hashtag structure prepared using -78 °C deposition alongside the letters “UBC” stereolithographically printed using a 2 mm resolution photomask. .................................................................................................................................. 210 Figure D.26. Direct-write 3D printing setup used to simultaneously write and irradiate the polymer onto glass. ..................................................................................................................... 210 Figure D.27. Direct-write 3D printing of DP3 at two different print speeds, 2mm/s (left) and 8 mm/s (right) onto glass slides. .................................................................................................... 211 Figure D.28. Diagram showing the simplified steps leading to cell lysis for primary amine containing surfaces, proceeding through electrostatic attraction, interdigitation of the amine groups into the cell membrane, and disruption of membrane integrity. ..................................... 211 Figure D.29. Normalized CFUs for E. incubated with cross-linked DP3 powder and a continuous sample at the same polymer mass. Samples were incubated for 24 h under constant shaking and compared with controls with no polymer. Determined from colony counts grown on agar plates in triplicate. ................................................................................................................................. 212 Figure E.1. Structure of the Rose Bengal containing polymer (prepared from PNH2-7 and 0.048 molar equivalents of RB) and TPP used in these experiments. .................................................. 213 Figure E.2. Absorbance spectra of Rose Bengal lactone (RB) and tetraphenylporphyrin (TPP) in methanol, and the measured spectral output of the green and UV LEDs used in this work. Only TPP absorbs light in the UV region, while both TPP and RB absorb green light. ..................... 213 xxxiii Figure E.3. Absorbance spectra of a thin film of DP3 containing TPP before irradiation, and subsequently after UV then green light irradiation. UV irradiation excites and photodegrades TPP without fully degrading RBL. ............................................................................................. 214 Figure E.4. SEM images of untreated cotton (a,c) and EC/P13 (b,d) at 500× (top) and 2000× (bottom) magnification. .............................................................................................................. 215 Figure E.5. Water contact angles of cotton fabric prepared using different polymer wt% solutions, measured using 10 μL droplets. .................................................................................. 216 Figure E.6. Materials soaked in EP13 solution for 10 minutes followed by 30 minutes of 395 irradiation per side. ..................................................................................................................... 216 Figure E.7. The mass loading of EP13 onto different materials and the resulting water contact angles measured using 10 μL droplets. ....................................................................................... 217 Figure E.8. The elongation at break and break stress determined from Instron mechanical testing of cotton and polyester strips treated using EP1, EP5, and EP13 solutions, measured in triplicate at 20 cm/min. .............................................................................................................................. 217 Figure E.9. TGA traces of cotton and polyester treated using EP13, measured at 10 °C/minute under N2. ..................................................................................................................................... 218 Figure E.10. FT-IR vibrational spectra of the non-cross-linked PNH2-7, treated fabric samples EC/P5, EC/P13, and untreated cotton. Peaks at 1258 cm-1 and 793 cm-1 are assigned to the Si-CH3 and PDMS CH3 vibrational modes respectively. ................................................................ 219 Figure E.11. FT-IR vibrational spectra of the non-cross-linked PNH2-7 and materials treated with EP13. All treated materials show peaks assigned to PDMS stretching frequencies........... 219 xxxiv Figure E.12. Black colored cotton untreated (left) and treated with EP13 (right) showing no change in color. A 10 μL drop of water shows a high contact angle on the treated fabric, while the untreated fabric wets fully..................................................................................................... 220 Figure E.13. Absorbance spectra collected during the photooxidative degradation of uric acid using EC/P13 cotton samples at 0.048 molar equivalents of RB. The initial uric acid concentration was 2 × 10-4 M in 0.02 M phosphate buffer. Fabric mass was 20 mg for a 3mL solution. The sample was irradiated using 15W 530 nm LED from a distance of 4 cm. ........... 220 Figure E.14. Absorbance at 292 nm of a 3 mL 2 × 10-4 M solution of uric acid in a 0.02 M phosphate buffer containing 20 mg EC/P13 fabric samples of varying RBL molar equivalents. Samples were irradiated using 15W 530 nm LED from a distance of 4 cm and the absorbance at 292 nm used to monitor uric acid oxidation. .............................................................................. 221 Figure F.1. UV-Vis absorption of DTP and TPP in DCM. εDPT has been multiplied by 50 for display purposes. ......................................................................................................................... 223 Figure F.2. Change in UV-Vis absorption of a thin film of FPA with DPT and TPP irradiated using 430 nm light for 95 minutes. ............................................................................................. 223 Figure F.3. FT-IR spectra of polymer sample FPA before and after cross-linking. No change in the vibrational spectrum is observed........................................................................................... 224 Figure F.4. Cross-linked sample of FPA used for Raman measurements, showing surface wrinkling not observed for samples with a high content of FPB. ............................................... 224 Figure F.5. Photo-rheology experiments of samples of FP100 measured with and without DPT catalyst, measured at 23 mW/cm2 light intensity. The absence of change in G' for the sample without DPT demonstrates that 1O2 by itself does not result in cross-linking in this system. .... 225 xxxv Figure F.6. Relative amount of the three translational diffusion coefficients measured for the polymer backbone in sample FP100 as a function of irradiation time, determined using 1H PFG-NMR. .......................................................................................................................................... 226 Figure F.7. TGA curves of FPB and cross-linked polymer samples, measured at 10 °C / min under N2. ..................................................................................................................................... 227 Figure F.8. DSC curves of P100 and DPT, measured at 10 °C / min under N2. A strong crystallization and melting point can be observed for DPT, while P100 has a Tg transition and shifted Tc and Tm. ........................................................................................................................ 227 Figure F.9. % Soluble and Swell for samples FP100, FP75, and FP50. Samples were pre-weighed and then soaked with excess THF overnight. The samples were weighed to determine the % Swell, and then rinsed thoroughly with clean THF and driver overnight under vacuum. The resulting mass was used to determine the % Soluble, using the equations below. .............. 228 Figure F.10. Example stress-strain curves for samples FP100, FP75, and FP50, measured from tensile test experiments. .............................................................................................................. 229 Figure F.11. 1H NMR spectra of pristine FPB and degraded FPB recovered after reductive cleavage of the disulfide linkages using ZrCl4/NaBH4. 400 MHz, CD2Cl2, RT. ....................... 230 Figure F.12. Intrinsic viscosity plot for samples of pristine and degraded FPB at different concentrations in toluene. ........................................................................................................... 231 Figure F.13. FT-IR spectra of pristine FPB, cross-linked FP100, and degraded FPB. ............. 231 xxxvi List of Symbols 1O2 – singlet oxygen Å – angstrom Dt – translational diffusion coefficient G″ - loss modulus G′ - storage modulus Mn – number averaged molecular weight Mw – molecular weight Rg – radius of gyration Tg – glass transition temperature δ – delta ε – molar extinction coefficient η – complex viscosity ξ – correlation distance σ – tensile stress xxxvii List of Abbreviations µL - microliter µm – micrometer AFM – atomic force microscopy APCI – atmospheric pressure chemical ionization aPDI – antimicrobial photodynamic activity ATR – attenuated total reflectance ATRP - atom transfer radical polymerization BHT – butylated hydroxytoluene BPO – benzoyl peroxide CCD – charge coupled device CFL – compact fluorescent lamp CFU – colony forming unit cm – centimeter CP-MAS - cross polarization magic-angle spinning DABCO - (1,4-diazabicyclo[2.2.2]octane) DCM – dichloromethane DMA – dynamic mechanical analysis DMSO – dimethylsulfoxide DSC – differential scanning calorimetry DTT - dithiothreitol E. coli - escherichia coli xxxviii ESCI – electro spray chemical ionization EtOH – ethanol FT-IR – fourier transform infrared GPa- gigapascal MPa – megapascal HAI – hospital acquired infections HCl – hydrochloric acid Hz - hertz IR – infrared LCD – liquid crystal display LED – light emitting diode MeOH – methanol MHz – mega hertz Min – minute mm – millimeter mM – millimolar mmol – millimole mol - mole MRSA - methicillin-resistant Staphylococcus aureus MS – mass spectrometry ms – millisecond NaOH – sodium hydroxide NIR- near infrared xxxix nm - nanometer NMR – nuclear magnetic resonance OEP – octaethylporphyrin PDI – polydispersity index PDMS – polydimethyl siloxane PDMS-NH2 – (aminopropylmethylsiloxane) – dimethylsiloxane copolymer PEI – polyethyleneimine PEO – polyethylene glycol PFG - pulsed-field gradient PLLA – polylactic acid PNH2-7 – (aminopropylmethylsiloxane) – dimethylsiloxane copolymer 7 wt% NH2 PNH2-23 – (aminopropylmethylsiloxane) – dimethylsiloxane copolymer 23 wt% NH2 POM – polarized optical microscopy ppm – parts per million PtOEP – platinum octaethylporphyrin PVP – polyvinyl pyrrolidone PXRD – powder X-ray diffraction QAC – quaternary ammonium compound rad – radian RAFT - reversible addition−fragmentation chain-transfer polymerization RB – rose bengal RBL – rose bengal lactone Rf – retention factor xl ROS – reactive oxygen species RT – room temperature SARS-CoV-2 - severe acute respiratory syndrome coronavirus 2 SAXS – small angle X-ray scattering T – tesla t – time TGA – thermogravimetric analysis THF – tetrahydrofuran TPO – diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide TPP – tetraphenyl porphyrin UV – ultra violet Vis - visible W – watt WAXS – wide angle X-ray scattering xli Acknowledgements The faculty, staff, and administration at UBC and UBC Chemistry have my enduring thanks for all of their endless work that enabled my own. Particularly, Elena Polishchuk and Jessie Chen at UBC Bioservices have my thanks for their constant generosity. Marzieh Ebrahimi, Tanja Tomkovic, and Dylan Karis have my thanks for teaching me what polymer rheology is, and more importantly teaching me to surround myself with brilliant and patient experts like themselves. I thank Trevor Cross for his mentorship and guidance throughout, for his help with science, and his help with things far more important. Olga Yunyaeva, and a cup of coffee, have been a constant sounding board during my degree, and both have my gratitude for their immense support. Jackie Stewart and Jeanette Leeuwner taught me that there is so much more to a PhD than the research contained within this document, and for that they will always have my gratitude. My thanks to my committee, for pushing me to graduate when I was hesitant to take this last step. xlii Special thanks are owed to Dr. Michael Wolf and all Wolf group members past and present for their patience and careful prodding as I ventured down this unusual and path. This journey has been full of twists and turns, but I never walked it alone. This work was supported by funding from the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canada Foundation for Innovation. xliii Dedication This thesis is dedicated first and foremost to my many collaborators. I am forever thankful for their patience and expertise, without which none of this research would have been possible. Second, this thesis is dedicated to UBC Graduate and Postdoctoral Studies, for giving me the opportunity to write my manuscripts a second time. Third, this thesis is dedicated to Christina Wong, whose patience and compassion was boundless throughout this rewriting. 1 Chapter 1: Introduction 1.1 Overview Plastics are an integral part of our daily lives, involved in everything from healthcare to food packaging to clothing. Polymeric materials can be cross-linked to impart increased strength, durability, and chemical resistance to the final product. This has been historically performed using heat (thermoset plastics), but advances in photochemical reactions have enabled new ways to use light to cross-link polymers. As a stimulus, light is more easily controlled and patterned compared with heat, and can be used to target specific components within complex mixture of reactive chemicals. While radical-based photo-cross-linking methods have been extensively explored, more diverse photo-cross-linking reactions are needed to broaden the scope of functional materials that can be prepared with light. 7 This thesis aims to investigate non-conventional photo-cross-linking reactions for the preparation of functional materials, focusing on chemical reactions that require the constant input of light to drive the desired chemical reaction. These cross-linking reactions have been used to prepare healable surfaces, crystalline reinforced composites, and antimicrobial materials, studying both the fundamental processes involved and the properties of the resulting materials. 1.2 Heat and Light It is estimated that humans first began harnessing fire in approximately 2 million BCE.8 For the next millennia, fire, and the resulting heat, was integral in countless technological 2 advancements across metallurgy, agriculture, and medicine. Fire also represented the major man-made source of light up until the invention of the arc lamp in the early 19th century. The arc lamp was quickly surpassed by Edison’s incandescent lightbulb in 1879, followed by fluorescent lighting in the mid 20th century, to LED lighting in the 1990s.9,10 Modern advances in lighting technology now allow for light to be generated with minimal heat output and narrow spectral widths, largely decoupling these two stimuli. The low cost, high availability, and safety of LEDs has greatly impacted the study of photochemistry and development of photochemical reactors. However, investigations into organic photochemical reactions were performed as early as 1790, studying the effect of focused sunlight on chemical mixtures.11 1.2.1 Early Photochemical Reactions A major challenge in early photochemical research was the absence of modern characterization techniques available to probe the relatively small chemical modifications resulting from irradiation. One of the earliest studied photochemical reactions was the decomposition of gaseous nitric acid to dinitrogen tetroxide by Joseph Priestley, observed as a color change upon irradiation.12 In 1834 Hermarin Trommsdorff used a prism to investigate the wavelength dependent color change in crystals of the plant extract santonin. Crystals of santonin turned yellow and then subsequently cracked when continually irradiated.13 This reaction was later determined to be a photo-rearrangement followed by Diels-Alder dimerization and then [2+2] photocyclization (Fig 1.1).14 3 Figure 1.1. The photoreaction cascade of santonin crystals discovered by Hermarin Trommsdorff. The final photocyclization results in cracking of the crystal. The beginnings of modern photochemical reactions may best be described by the work of researchers in the late 19th century, where the changes in color, solubility, and melting point in polyaromatic compounds as a result of irradiation were first studied. Among these are the [4+4] photocycloaddition of anthracene by Fritzsche in 1867, the [2+2] photocycloaddition of thymoquinone by Liebermann in 1877 and of 2-phenylnaphthoquinone by Breuer and Zincke in 1888, and the first styrene [2+2] photodimerization performed by Bertram and Kürsten in 1895 of p-coumaric acid.15–17 Photochemical reactions involving halogenation and carbonyl chemistry would be discovered in the following decades. These styles of dimerization reactions are still in use today for the preparation of stimuli responsive polymeric materials. 4 Figure 1.2. First reported [4+4] and [2+2] photodimers of (a) anthracene (b) 2-phenylnaphthoquinone and (c) p-coumaric acid. 1.2.2 Early Thermally Responsive Polymers The word “plastic” is a non-specific term encompassing all synthetic or semi-synthetic polymeric materials. On May 21st, 1845 Thomas Hancock in Britain and on June 15th, 1845 Charles Goodyear in the USA were each granted a patent for the vulcanization of natural rubbers using sulfur.18 This process would go on to be used for the manufacturing of rubber tires, and is considered the first commercially manufactured plastic. The thermal reaction between elemental sulfur and poly-unsaturated natural rubbers such as polyisoprene results in cross-linking through the formation of various length sulfur-sulfur linkages (Figure 1.3). The cross-linking density is controlled by varying the amount of sulfur added. 5 Figure 1.3. Vulcanization reaction of polyisoprene rubber using elemental sulfur to give a network cross-linked by a mixture of different length sulfur chains. The first fully synthetic polymers were phenolic resins, a broad class of materials prepared by heating mixtures of formaldehyde and phenols until they cure into cross-linked networks (Figure 1.4).19 Catalyzed by either acid or base, this reaction involved the condensation of formaldehyde with the ortho and para positions of phenols to give highly cross-linked networks. This hard material was marketed under the name Bakelite and used for molded objects such as billiard balls and early electronics. Figure 1.4. Phenolic resin network formation through the reaction of formaldehyde at the ortho and para positions of phenol. 6 Both rubber and Bakelite are thermoset polymers, i.e. polymers that are cross-linked using heat. Similarly, both produce poorly defined networks with a variety of different cross-linking and branching motifs. The cross-links in these thermoset networks gives the materials increased thermal stability, durability, strength, and chemical resistance, as well as in the case of Bakelite converting the material from a liquid to solid.20 However, thermoset networks cannot be melted or injection molded after being cured, and are therefore more difficult to recycle or reprocess. In contrast, thermoplastics such as polyethylene (discovered 1898) are linear or branched polymers that can be fully melted and processed above their glass transition temperature (Tg).21 1.3 Polymer Cross-linking 1.3.1 Radical Polymerizations While polyethylene is prepared using coordination catalysts such as titanium (III) chloride, radical polymerization of alkene-containing monomers such as methacrylates and acrylates is widely exploited to prepare a variety of commercial, specialty, and research polymeric materials. This mechanism proceeds through initiation, propagation, and either termination or chain transfer steps (Figure 1.5).7 Initiation is most commonly carried out through the thermal decomposition or photolytic cleavage of a peroxide-like species (I2) such as benzoyl peroxide (BPO) or diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO). The resulting initiator radical (I·) can then react with a monomer (M) to form the propagating species (IM·). 7 Figure 1.5. (Left) The steps of radical polymerization and (right) common radical polymerization photoinitiators. This technique can be used to prepare homopolymers, copolymers, and cross-linked networks depending on the monomers used.22 When using photoinitiators, photomasks can be used to selectively irradiate one region of the material over another to prepare patterned surfaces. Digital Light Projection (DLP) and Stereolithography (SLA) 3D printers utilize either a liquid crystal display (LCD) photomask or laser to selectively irradiate a mixture of monomer and photoinitiator layer by layer to build cross-linked three-dimensional objects. The use of 3D printers in chemical research has greatly accelerated in the past decade as low-cost consumer grade printers have become more available.23 Radical polymerization typically produces materials with a high polydispersity index (PDI). Advances in radical polymerization techniques such as atom transfer radical polymerization (ATRP) and reversible addition−fragmentation chain-transfer polymerization (RAFT) limit chain termination and transfer, narrowing the PDI of the resulting polymer.22,24 The living nature of the polymerization also enables facile formation of polymers such as multi-8 block copolymers. While radical polymerization reactions proceed relatively quickly, one limitation is the inability to control reaction extent or to leave unreacted monomers in the system for use in post-preparation functionalization or modification. 1.3.2 Photodimer Polymers Radical polymerization and cross-linking is well explored and utilized heavily in the preparation of functional materials, but has a number of potential drawbacks. Stability of the alkene functional groups, toxicity of the initiators and byproducts, selectivity, irreversibility, and difficulty in controlling reaction extent are all potential hurdles when modifying materials through the use of radical cross-linking. One alternative method for polymer photo-cross-linking is photodimerization and photocycloaddition reactions as described in Section 1.2.1, primarily the [4+4] anthracene dimerization and [2+2] coumarin or stilbene type reactions. Figure 1.6. Photodimerization reactions employed in photodimer polymers including (a) anthracene (b) stilbene and (c) coumarin. 9 Both types of dimerization reaction are thermally forbidden but proceed in the excited state either by excimer formation or a concerted excited-state cyclization respectively. These dimer systems may undergo thermal or photo reversion back into their monomeric forms. Telechelic monomers allow for chain extension using light, while pendant monomers can result in cross-linking (Figure 1.7). Intra-chain dimerization has been demonstrated by Berda and coworkers for use in forming single-chain nanoparticles from dilute polymer solutions with pendant anthracene units.25 Figure 1.7. Three network motifs possible using polymer photodimerization reactions including chain growth, single-chain particle formation, and network cross-linking. Photodimer cross-linking has been explored as a mechanism to produce highly tunable and reversible cross-linked networks.26 Saito and coworkers demonstrated an anthracene-containing polymer film that undergoes scratch healing as a result of cycling 254 nm and 365 nm light to cleave and form anthracene dimers. As well, the large molecular deformation resulting from dimerization can cause mechanical motion in polymeric materials as a result of photodimerization in both polymer films and single crystals.27,28 As dimerization reactions only 10 produce radical or charged intermediates, they are highly tolerant of other functional groups. The stability of the monomers is often exploited to allow for the post-preparation modification of materials, for example the cross-linking of stimuli responsive hydrogels into chemically cross-linked networks using anthracene dimerization demonstrate by Hoogenboom and coworkers29 The gradual and photo-controlled nature of dimerization reactions has also been used to create functionally graded systems with differing degrees of cross-linking as a function of position or depth. The intensity of light can be controlled using a non-opaque photomask, and the resulting cross-linking density is directly proportional to the amount of light exposure at each position (Figure 1.8).30 Figure 1.8. Example of how photomasks of different opacities can be used to control the light exposure and therefore cross-linking density of a polymer film containing photodimerizable subunits. Jérôme and Shea have both demonstrated the ability to form photopatterned films with differences in surface height using coumarin-containing polymer films.31,32 Irradiation through a photomask results in selective cross-linking. Diffusion of non-cross-linked polymer chains into the cross-linked regions results in localized swelling, which can be fixed into place through further irradiation (Figure 1.9). Jérôme et al. have also demonstrated the use of this photodimer 11 system for the preparation of ocular lenses where the refractive properties can be tuned in-situ through the same cross-linking and diffusion strategy.33 Figure 1.9. Preparation of photo-patterned films with varying topologies. Patterned cross-linking to give incompletely cross-linked network leads to diffusion (red arrows) into the irradiated regions, followed by further irradiation to fully cross-link and lock-in the pattern. Adapted from Jérôme et al.31 Chapters 2 and 3 of this work explore the incorporation of anthracene into polymeric materials for use in thermally healable vitrimeric composites and polymer crystal formation, respectively. In this manner, anthracene enables the materials to be gradually tuned post-polymerization by irradiation with UV light. 1.3.3 Vinylogous Urethane Vitrimers Vitrimers are an emerging class of polymers characterized by the presence of thermally exchangeable bonds.34,35,36 Amine condensation networks are prepared with off-stoichiometric ratios to leave unreacted amines that can undergo thermal exchange (Figure 1.10). This network 12 rearrangement imparts high mechanical recyclability, an ability to undergo thermal healing, and rapid stress relaxation not found in conventional cross-linked systems.35,37,38 Figure 1.10. Thermal vitrimeric exchange of vinylogous urethane vitrimers These systems can also exhibit shape memory effects allowing for the autonomous arrangement into complex shapes.39,40 Vitrimeric systems have been modified using additives that respond to a variety of stimuli including IR light, pH, redox conditions, electrical current, and solvent.41 The kinetics of the exchange reaction have also been shown to be controllable using low amounts of a variety of small molecule additives.42 The incorporation of functional molecular groups integrated directly into the polymeric backbone of these systems may allow for the development of multifunctional and responsive materials. The relatively high temperature (> 100 °C) at which these systems are cured in the presence of the amine, ester, and ketone functional groups that comprise vinylogous urethane vitrimers, means careful consideration for functional group tolerance is required to incorporate new responsive molecules into the polymeric chain. Chapter 2 of this thesis incorporates vinylogous urethane moieties with photo-cross-linkable anthracene units to prepare vitrimeric copolymers with tunable cross-linking density through UV irradiation. 13 1.3.4 Polymer Crystals Polymer crystallinity plays a major role in the optical, physical, and conductive properties of polymeric materials.43–45 In order to optimize polymers for modern applications such as flexible batteries and solar panels, crystallinity must be considered and controlled.46–48 Crystallization of linear polymers has been widely studied both experimentally and via computer simulations, but remains difficult to predict and control due to random entanglement of the chains.49–51 Highly crystalline polymers have been prepared through the use of rigid backbones and directing linkers,52 monomers featuring a high crystallization enthalpy,53 or the topological photopolymerization and modification of crystallized monomers to yield polymeric crystals,54,55 where pre-existing crystallinity is preserved after polymerization. Macroscopic crystallization of cross-linked polymers is much less common, owing partially to the low solubility of cross-linked materials making polymer crystals growth from dissolved solutions difficult. One method for the preparation of cross-linked polymer crystals is the concurrent polymerization, cross-linking, and crystallization of small-molecules into covalent-organic frameworks.56–58 This technique requires rigid linkers that promote regioregularity between cross-linking nodes. Others have explored the photochemical polymerization of anthracene-containing molecules to produce 2D polymer crystals, beginning with monomer single crystals or interfacial thin films that can be cross-linked into crystalline sheets (Figure 1.11).59–61 14 Figure 1.11. A tricyclic anthracene monomer is dimerized in the crystalline state to prepare covalent organic framework crystalline sheets, adapted from King et al.59 While crystallization in many commercial polymers has been extensively probed, poly(dimethylsiloxane) (PDMS) crystallization is much less reported. PDMS has been widely explored for use in microfluidics, flexible conductors, and biocompatible materials.62–64 Low cost, low toxicity, and elastomeric behaviour make PDMS an attractive material for soft-polymer applications. However, the high degree of flexibility and resulting low glass transition temperature (Tg) of linear PDMS requires temperatures below -70 °C for crystallization to occur.65,66 This temperature limitation severely limits the study of the properties of crystalline siloxanes. Cross-linking can raise the crystallization temperature, but gives materials with only semi-crystalline regions without discrete crystal formation.67,68 No room temperature stable polymer crystals of PDMS have been reported, likely owing to the highly flexible nature of the backbone. In Chapter 3 of this work, anthracene units are incorporated into a PDMS copolymer 15 to provide rigid cross-linking sites with which to drive polymer crystallization upon irradiation, providing a means to prepare macroscopic siloxane polymer crystallites. 1.3.5 Photocatalytic Cross-linking First generation ATRP systems progress thermally, but more recently reported systems can be driven with light to regenerate the active radical species from the dormant metal complex.69,70 Boydston et al. have demonstrated metal-free ring opening metathesis polymerization of strained alkenes that can be controlled using photoredox chemistry, requiring light to activate the alkene bond before reaction with another monomer (Figure 1.12).71,72 Figure 1.12. Proposed mechanism for metal-free photoredox mediated ROMP. The vinyl-ether initiator is photo-oxidized by the photocatalyst (PC) to give a radical species that undergoes ROMP, terminating though electron transfer from the photocatalyst. The resulting vinyl-ether can then undergo the same mechanism to chain-extend.72 Unlike photodimers in which the monomer is directly excited with light, both of these systems are photocatalytic and excite an intermediate species that then undergoes a reaction with the monomer or growing chain. Another type of photocatalytic cross-linking is the generation of photogeneration of small molecules that can carry out reactions leading to cross-linking. The 16 photo-generation of singlet oxygen is one such strategy that has been employed to cross-link a variety of biological materials such as DNA and proteins. 1.3.6 Singlet Oxygen and Protein Cross-linking Singlet oxygen is a type of reactive oxygen species (ROS) that can be produced by aerobic excitation of a photosensitizer. The photosensitizer is promoted to the singlet excited state using light, followed by intersystem crossing to the triplet state. The energy is then transferred to ground state triplet oxygen to relax the photosensitizer back to its ground state and excite oxygen to form singlet oxygen (Figure 1.13). Figure 1.13. Simplified Jablonski diagram showing the production of singlet oxygen involving (1) excitation of the photosensitizer with light (2) intersystem crossing to the triplet state (3) energy transfer to oxygen. The electronic configuration of ground state oxygen and excited state singlet oxygen are shown. This excited species has a lifetime of approximately 1-100 s in the gas phase and 10-1000 µs in solution, being highly dependent on pressure, temperature, and solvent.73,74 1O2 has been primarily explored for use in the degradation of organic contaminants and in photodynamic cancer therapy, owing to its highly oxidative nature.75 Materials that can produce 1O2 have also 17 been demonstrated as potent antimicrobial materials that possess broad-spectrum sterilization against bacteria, viruses, and fungi when irradiated. Within biological systems, 1O2 can produce undesired cross-linking between DNA or proteins that is proposed as one chemical method that can lead to the formation of cancers.76 It has been demonstrated that essential vitamins and nutrients such as riboflavin and vitamin B1 can produce singlet oxygen when irradiated.77 Kopeček et al. have proposed a reaction mechanism for the direct cross-linking of DNA through oxidation of histidine with singlet oxygen (Figure 1.14).78 Figure 1.14. Proposed mechanism for the cross-linking of proteins by 1O2 involving oxidation of histidine residues. Adapted from Kopeček et al.78 Madder et al. have demonstrated the photo-cross-linking of furan-modified DNA through oxidation of the furan followed by reaction with either an adenosine or cytosine base pair (Figure 1.15).79 Ito et al. have used a similar mechanism for the cross-linking of furan-modified gelatin using photogenerated singlet oxygen.80 These biological examples serve as the inspiration for the 1O2 mediated cross-linking discussed in Chapters 4-7. 18 Figure 1.15. 1O2 cross-linking of furan-modified DNA with a cytosine DNA subunit. Adapted from Madder et al.79 Singlet oxygen can react with primary amine groups to give an imine coupled product, and has been reported as a source of permanent organic damage in biological systems (Figure 1.16).81–83 A re-examination of this reaction has found it to be a simple and high yielding green reaction for the coupling of small organic molecules using visible light.84 A variety of organometallic and heterogeneous inorganic sensitizers have been demonstrated for this transformation.85–87 Imine cross-linked polymers prepared from amine and aldehyde condensation have been demonstrated by Zhang et. al as a type of thermally exchangeable vitrimeric polymer, allowing for the solvent-assisted recycling of thermoset materials.88,89 The use of singlet oxygen to photo-cross-link amine containing polymers is explored in Chapter 4, 5, and 6 as a means to prepare antimicrobial materials. 19 Figure 1.16. Singlet oxygen oxidative coupling of two alkyl amines into an imine. 1.3.7 Antimicrobial Polymers Contamination of solid surfaces by microbial organisms can lead to the formation of biofilms that enhance the transmission of drug-resistant bacterial infections.90,91 Fomites (contaminated inanimate objects) are proposed to be a major vector in Hospital Acquired Infections (HAIs) that are estimated to cause almost 100,000 deaths each year in the US.92,93 The development of surfaces and materials that can inhibit/kill microbial species is an approach to help address the global issue of disease transmission. Antimicrobial surfaces include those based on metal nanoparticles, nanoscale patterning, hydrophobic coatings, and amino- or phosphino- polymers or molecular surface functionalization.94–96 Antimicrobial polymers and biomaterials can possess high antibacterial activity and may not be limited to surface coatings that can be lost due to abrasion. Primary amines are a simple and naturally occurring antimicrobial functionality found in materials such as chitosan and lysine-containing peptides, as well as in synthetic polymers including polyethyleneimine and polyallylamine (Figure 1.17).97–101 20 Figure 1.17. Chemical structure of chitosan and poly(L-lysine), two antimicrobial biomaterials. The contact antimicrobial mechanism for solid polymers is proposed to proceed through four steps (Figure 1.18).100,102 Initially, the microbe needs to approach the surface through space. Next, electrostatic attraction brings the microbe into contact with the polymer surface. The polymer then undergoes interdigitation to insert into the cell membrane, followed by leakage of the intracellular fluid leading to cell lysis. 21 Figure 1.18. Illustration of the four steps of the antimicrobial contact killing mechanism: approach, electrostatic attraction, interdigitation, and cell lysis. Materials of these types have been widely explored as antibacterial surface coatings, but suffer from water solubility, prohibitive cost, or poor mechanical properties resulting from a lack of chemical cross-linking.96 Imparting hydrophobicity to antimicrobial polymers can enhance their activity while preventing bacterial adhesion and leaching into aqueous environments.103,104 Conversion of primary amines to quaternary ammonium compounds (QACs), Schiff-bases, n-halamines, or guanidinium groups also results in enhanced bioactivity.105–108 Ren et al. used alkylated amine monomers for the 3D printing of mechanically robust antibacterial cross-linked composites. However, residual toxic monomers and photoinitiators must be removed through extensive washing for these photopolymerizable systems. Chapter 5 of this thesis explores the amine photo-cross-linking system described in Chapter 4 for the preparation of antimicrobial amine copolymers, and their antimicrobial efficacy against HAI-causing bacteria is investigated. 1.3.8 Antimicrobial Textiles While Escherichia coli (E. coli) and methicillin resistant Staphylococcus aureus (MRSA) infections are major sources of HAIs, the recently emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), responsible for over 5 million deaths worldwide (as of Nov 1, 2021), continues to spread in health care settings such as hospitals and long-term care facilities.109–113 As a precautionary measure to limit aerosol droplet transmission of SARS-CoV-2, widespread adoption of non-medical cloth facemasks has been recommended by world health authorities and 22 has immensely reduced spread in indoor settings.114,115 While SARS-CoV-2 is primarily spread through aerosolized droplets, the virus can remain infective after one week on contaminated face masks and 2-3 days on steel surfaces.116–118 Exposed personal protective equipment (PPE) remains a possible vector of disease transmission for many pathogens and necessitates the proper use of PPE to prevent contamination.114 Functionalized textiles with self-disinfecting or self-cleaning properties may play a key role in limiting the spread of these diseases.94,96,119 Antimicrobial photodynamic inactivation (aPDI) is an alternative strategy to the passive contact-killing polymeric materials described in Section 1.3.7. In aPDI capable textiles, light stimulates a photosensitizer to generate reactive oxygen species (ROS) from atmospheric O2. The generated species can be either free radicals/radical ions (Type I) or singlet oxygen (1O2, Type II) and cause non-specific and irreversible damage to microbial membranes and intracellular components.81,120 aPDI materials are effective against multiple types of pathogens including bacteria, virus, and fungi, and remain effective against antibiotic resistant bacteria.121–124 These sensitizers have been previously incorporated onto textiles through electrostatic interactions, covalent tethering, or encapsulation in a cross-linked polymer matrix.122,125 However, many of these procedures require high temperatures, generate large amounts of chemical waste, or damage the integrity of the fabric. Chapter 6 of this thesis incorporates the amine photo-cross-linking procedure demonstrated in Chapters 4 and 5 to quickly and easily prepare coated textiles capable of both contact antimicrobial inactivation and aPDI. 23 1.3.9 Disulfide Polymers Disulfide (S-S bond) bonds between macromolecules are a common motif found in nature, most prominently in protein cross-links between cysteine residues such as in keratin.126 One of the earliest synthetic uses of disulfide chemistry was for the vulcanization of natural rubber described previously (Figure 1.3).18 Disulfide bonds can be cleaved under reductive conditions to afford the corresponding thiol.127,128 Incorporation of disulfide cross-links into polymeric materials allows for reductive degradation and de-cross-linking under specific conditions. This approach has been used for drug delivery, controlled polymer swelling, and chemical recycling.126,129 Aromatic disulfides can also undergo thermal exchange, acting as reconfigurable vitrimeric bonds and enabling recycling and remolding of thermoset networks.130,131 Generally, the disulfide bond is present in the monomer before polymerization rather than being synthesized in situ within a network.130 For alkene radical polymerizations, thiol-ene reactions are competitive with alkene-alkene reactions and necessitates formation of the disulfide prior to polymerization.132 Methods to directly synthesize disulfide bonds include heat, aerobic oxidation, and inorganic photocatalysis.133–136 Recently, small molecule catalytic methods to directly photo-synthesize disulfide bonds have been reported. Noël et al. demonstrated the aerobic oxidation of thiols to disulfides using Eosin Y for a flow-through reactor with high yields using visible light but with long reaction times (hours).137 Ando et al. demonstrated a unique rapid (minutes) two-stage aerobic oxidative synthesis of disulfides using a diaryltelluride catalyst.138 First, singlet oxygen (1O2) was photogenerated from atmospheric oxygen using a porphyrin photo-sensitizer. Next, the diaryltelluride was oxidized to the 24 corresponding telluroxide/tellurone. Finally, this oxidizes two thiols to one disulfide, returning the telluride (Figure 1.19). Figure 1.19. Two stage photo-cross-linking of thiol groups using 1O2. Initially, a diaryltelluride precatalyst is oxidized to the active telluroxide/tellurone species. Next, this catalyzes the formation of a disulfide from two thiols. Adapted from Ando et al.138 Chapter 7 of this work investigates the use of diphenyltelluride and 1O2 for the direct photo-cross-linking of thiol-containing polymers into disulfide networks using visible light under atmospheric conditions, expanding the scope of singlet oxygen polymer cross-linking. 1.4 Thesis Scope This thesis aims to investigate two photo-controlled polymer cross-linking methods as a means to prepare functional polymeric materials, examining both anthracene and singlet oxygen driven cross-linking procedures. The mechanical, chemical, and biological properties of these materials are explored both as functions of polymeric composition and irradiation time. 25 Chapter 2 investigates the incorporation of photo-dimerizable anthracene units into a polymer system based on vinylogous urethane vitrimers, enabling photo-tuning of a thermally healable system. This approach opens alternative routes to control the properties of vitrimeric materials. Irradiation of the polymer permits tuning of the glass transition temperature, rheological behavior, and scratch-healing dynamics without the need for compositional modification. Chapter 3 utilizes anthracene photodimerization to cross-link a linear PDMS polymer liquid, investigating the crystallization of approximately 1 mm diameter polycrystalline structures. The use of photo-driven cross-linking allows for the growth of structures to be controlled by varying the duration or intensity of irradiation. The impact of the amount of anthracene on the polymer backbone on crystal size and morphology is studied using diffusion NMR, AFM, and confocal microscopy, and used to describe a mechanism for photo-driven crystal growth. Chapter 4 demonstrates amine oxidative coupling to imine cross-links using a metallo-porphyrin and amine-containing PDMS upon green light irradiation. The mechanism is investigated using control experiments to elucidate the use of singlet oxygen for polymer cross-linking. This procedure is further explored using side chain and end terminated amine copolymers, as well as organic 1O2 sensitizers. Chapter 5 describes the thermal preparation of a solvent-free PDMS with photosensitizer covalently tethered to the polymer. The singlet oxygen imine cross-linking described in Chapter 4 is explored in greater detail, examining the photo-cross-linking kinetics using photo-rheology 26 to probe the dependency on light intensity and reaction conditions. Antimicrobial properties of the imine cross-linked material is investigated using bacteria and mammalian cells. Chapter 6 investigates the polymeric system from the previous chapter for use as a textile coating, incorporating a second photosensitizer such that microbes can be inactivated both upon contact with the polymer and through photo-generated singlet oxygen. The mechanical properties of these fabrics are explored to determine the impact of the coating on the fabric structure, and biological activity against bacteria and the SARS-CoV-2 virus is investigated. Chapter 7 describes the singlet-oxygen cross-linking of thiol-containing PDMS through inclusion of a diaryltelluride pre-catalyst. The kinetics are explored using photo-rheology and diffusion NMR to probe the interaction between pre-catalyst, sensitizer, and polymer. The reductive cleavage of the disulfide cross-links is explored as a means of chemical degradation. 27 Chapter 2: Photoactivated Healable Vitrimeric Copolymers 2.1 Overview Vitrimers are a broad class of polymeric materials that undergo thermal exchange reactions, giving them enhanced recyclability, moldability, and a more thermoplastic behavior at elevated temperatures. A composite polymer based on vinylogous urethane vitrimer bonding with both photodimerizable and thermally exchangeable functionalities is described. Polymers containing various ratios of photodimerizable diamino-anthracene monomers and thermally exchangeable diamino-alkyl monomers linked by a common bisacetoacetate group are studied. It is demonstrated that alkyl amines undergo the necessary thermal exchange reactions for vinylogous urethane vitrimers, while aromatic amines do not. UV induced dimerization of the anthracene units results in changes due to polymer cross-linking in the rheological properties and the glass transition temperature. Rapid and near-complete scratch healing upon heating is demonstrated, with a tunable onset temperature for healing controlled by UV irradiation. The viability of a composite vitrimeric system, wherein vitrimeric monomers are combined with non-vitrimeric, stimuli-responsive monomers to generate random copolymers with new properties, is demonstrated. 28 2.2 Research 2.2.1 Results and Discussion In order to examine the effects of anthracene photodimerization on the beta-keto enamine systems that comprise vinylogous urethane vitrimers, a model compound (A1a) was synthesized via the condensation of 2-aminoanthracene with ethyl acetoacetate (Figure 2.1). Figure 2.1. Irradiation of compound A1a (enamine) to give A1b (imine) Irradiation of A1a in 1:1 ethanol:ethyl acetate to form A1b (Figure 2.1) was followed using UV-Vis spectroscopy (Figure A.1). A decrease in the absorbance in the 300-450 nm region was observed with an isosbestic point at 290 nm when the sample was irradiated with 365 nm light. Compound A1a in solution and solid state strongly emitted blue light under 365 nm irradiation while A1b was non-emissive (Figure A.2). These observations are consistent with 4+4 photocycloaddition of the anthracene units resulting in a break in the π-conjugation.139 29 Figure 2.2. Comparison of the FT-IR spectra of A1a, A1b and ethyl acetoacetate. FT-IR analysis of solid A1a and A1b showed a shift to higher wavenumber of the ester C=O stretch after irradiation (1649 to 1725 cm-1) (Figure 2.2). This indicates a decrease in conjugation with the ester, bringing it closer to the C=O stretching frequency in ethyl acetoacetate (1739 cm-1). These spectral changes are in good agreement with literature values for enamine-imine tautomerization observed in quinoxalinone and pyridopyrazinone systems.140 It is proposed that the photodimerization of A1a results in a change from the enamine to imine tautomer. The 1H NMR spectrum of A1a in CD2Cl2 contains peaks due to the alkene proton (δ 4.77 ppm) and N-H proton (δ 10.66 ppm) that are consistent with only the enamine tautomer being present at room temperature. The spectrum of A1b under the same conditions did not show any 30 peaks in these two regions, and two singlets near δ 2.6 ppm are assigned to the methylene protons of the imine tautomer (Figure A.3). Further analysis of the spectrum of A1b was not performed due to the complexity resulting from the high number of possible stereoisomers. Liebler et al. have previously examined the kinetics of the exchange reaction between aliphatic amines and beta-keto enamines.35 The exchange reaction between aromatic amines and beta-keto enamines was examined here, using a similar approach (Figure 2.3). Figure 2.3. Kinetic exchange experiment for aromatic vinylogous urethanes. Compound A1a was heated at 120 °C in DMSO in the presence of five equivalents of p-toluidine and the exchange reaction followed by 1H NMR spectroscopy (Figure A.4). Peaks matching the expected exchange product were observed, but no 2-aminoanthracene was present. In addition, the reaction stopped after only approximately 25% of the A1a present had reacted. Heating the sample at higher temperatures did not result in further A1a reacting. This result demonstrates that aromatic amines of this type do not undergo the thermal exchange reaction 31 necessary for vitrimeric behavior and that inclusion of anthracenes in vitrimers may result in the introduction of non-exchangeable cross-links into the system after dimerization. Composite systems containing vitrimeric and non-vitrimeric portions have been reported and exhibit similar properties to systems composed entirely of exchangeable monomers.141 Composite vinylogous urethane systems containing both exchangeable alkyl diamines and non-exchangeable, photoactive anthracene diamines linked by a common bis-acetoacetate monomer were subsequently prepared. Exchangeable cross-linking monomers were omitted in order to ensure only cross-links resulting from anthracene dimerization were present. The synthesis of solid polymer sheets was carried out via the thermal condensation of acetoacetate and amine monomers in different ratios, and the effects of UV irradiation on the polymer samples was studied using FT-IR spectroscopy, thermal and rheological measurements. 1,12-Dodecanebisacetoacetate (A2) was synthesized from 1,12-dodecanediol and 2,2,6-trimethyl-1,3-dioxin-4-one,142 and 1,5-diaminoanthracene (A3) was synthesized by reducing 1,5-diaminoanthraquinone using Zn/Cu.143 Polymers containing differing amounts of anthracene were prepared by using a fixed amount of A2 and altering the ratio of A3 to A4 while maintaining a 5% molar excess of amine functional groups shown to be beneficial for vitrimeric exchange (Table 2.1).35 32 Table 2.1. Relative molar ratios of monomers for polymers P1a and P2a. Polymers were synthesized by heating the monomer mixtures to reflux in 1:1 ethanol:ethyl acetate followed by transferring the solutions to a silicone mold. After evaporation of the solvent, the molds were heated at 90 °C overnight and then cured at 130 °C for one hour, resulting in nearly black polymer sheets largely free of surface defects (Figure A.5). Thinner samples from compression molding appeared red in color, consistent with the deep red color of monomer A3 in solution. 33 Figure 2.4. IR spectra of AP1a after different irradiation times at 365 nm, and sample AP1c containing fully dimerized anthracene units. AP1a was irradiated and the IR spectrum monitored as a function of irradiation time (Figure 2.4). After 5.5 hours of irradiation no further changes were observed and this remained the case upon continued UV irradiation, up to 18 hours. An isosbestic point was observed at 1665 cm-1 and the peak assigned to the ester C=O stretch shifted to higher energy after irradiation (1648 to 1725 cm-1). The peak at 1602 cm-1 was assigned as the enamine C=C stretch and decreased in intensity with irradiation. A sample with the same monomer ratios as in AP1a was prepared by fully dimerizing A3 prior to polymerization, and the IR spectrum of the resulting sample AP1c was collected. When compared against AP1c, in which all anthracene units are dimerized, the FT-IR spectrum of AP1b shows non-dimerized anthracene units that are attributed to poor spatial overlap of some of the anthracene units preventing dimerization. The 34 spectral changes between AP1a and AP1b closely match those seen in the model compounds A1a and A1b (Figure A.6), and consequently enol to keto tautomerization is also proposed for the polymeric systems upon irradiation. Similar changes were observed for irradiation of AP2a to AP2b, with no further changes after 12.5 hours of UV irradiation. The higher concentration of anthracene units in AP2a requires longer UV irradiation. Samples of AP1a and AP2a were compression molded to a thickness of 200 μm to ensure full UV light penetration and then irradiated overnight. The resulting samples were characterized using differential scanning calorimetry (DSC) (Figure 2.5). Figure 2.5. DSC traces of polymer samples before and after irradiation, measured on the second heating cycle at 10 °C/min. Solid circles indicate Tg. The glass transition temperature (Tg) increases from 30 °C for AP1a to 35 °C for AP1b consistent with the UV irradiation resulting in cross-linking of the polymer chains. A 25 °C increase in Tg was observed between AP2a and AP2b, consistent with a higher concentration of anthracene units in AP2b, and therefore a greater concentration of cross-links after irradiation 35 than in AP1a. No decrease in Tg was observed for AP1b and AP2b when heated to higher temperatures, suggesting that the photodimerization is irreversible. Samples containing less than 0.5 relative molar ratio of anthracene were not tested as the change in Tg was expected to be negligible in these cases, given there is only a 5 °C increase in Tg from AP1a to AP1b. Parallel plate rheological studies were carried out on samples before and after irradiation to probe the effect of anthracene dimerization on the flow characteristics. Experimental temperatures were adjusted between samples in accordance with the increase in Tg associated with irradiation. As discussed above, frequency sweep experiments were conducted using a constant strain of 0.1% over a frequency range from 0.01 to 100 rad/s (Figure 2.6). From the low frequency region, AP2a was observed to behave as a typical viscoelastic polymer (G″ > G′), consistent with its linear nature and exchangeable bonds. Although the terminal zone has not been attained, the tendency of reaching its Newtonian plateau is evident. After irradiation the storage modulus, G′, increased to above the loss modulus, G″, (G″ < G′) indicating a transition from a viscoelastic fluid to solid-like behavior, consistent with the formation of anthracene-based cross-links. Similar results were observed for AP1a and AP2a (Figure A.7). In all cases, a decrease in the complex viscosity (η) with increasing frequency is consistent with normal viscoelastic behavior above the Tg. 36 Figure 2.6. G′, G″, and η for AP2a (left, 60 °C) and AP2b (right, 85 °C), measured at 0.1% strain. Previously reported vitrimeric systems exhibited rapid stress relaxation attributed to the thermal exchange of urethane bonds.35,42 A sudden deformation of 0.5% was applied to AP2a and AP2b and their relaxation moduli monitored as a function of time (Figure 2.7). Two stages in their stress relaxation were observed for both AP1 (Figure A.9) and AP2. Rapid relaxation occurred for the initial 300 s, during which approximately 50% (AP2a) and 60% (AP2b) of the applied stress was relaxed nearly reaching a plateau that represents an initial elastomeric plateau modulus of the anthracene portion that initially showed solid-like behavior. After this, a slower relaxation period was observed, however the remaining stress did not fully relax during the duration of the experimental period. The two stage relaxation is attributed to mixed polymerization of the flexible, thermally exchangeable diamino-alkyl along with the rigid, non-exchangeable diamino-anthracene monomer. The alkyl portion of the polymer initially relaxed, followed by the slow stress relaxation of the anthracene component. This two stage relaxation process is also evident from Figure 2.7 (right) where G′ tends to attain a plateau before the 37 second mode of relaxation begins. Stress relaxation at higher temperatures (>150 °C) was not pursued as the polymers became too fluid to load properly into the parallel-plate rheometer. Figure 2.7. Stress relaxation curves for AP2a and AP2b under a 0.5% initial strain. To test the proposal that the two stage relaxation arises from the mixed polymerization of two different amine monomers, a polymer (AP3) composed only of monomers A4 and A2 was prepared (Tg = -15 °C). This sample exhibited rapid stress relaxation between 120 and 150 °C, relaxing fully after 36.5 mins at 120 °C and 10 mins at 150 °C (Figure 2.8). The 120 °C stress relaxation for AP3 at 100 s is comparable to the amount AP2b relaxes over the same time interval. The stress relaxation of vitrimers can be described by the Maxwell law. G(t)/G0=exp (-t/τ). Equation 2.1. Maxwell law equation for the stress-relaxation of polymeric samples. 38 Relaxation times at 37% (1/e) relaxation were fit to an Arrhenius plot for AP3 and the activation energy was found to be 47 kJ/mol. The reported activation energy for cross-linked vitrimers is typically approximately 60 kJ/mol.35 The lower value for AP3 is attributed to the linear nature of the polymer in conjunction with thermal bond exchange. The rapid relaxation of AP3 in comparison with AP1 and AP2 demonstrates that the anthracene units are responsible for deviations from expected vitrimeric stress relaxation profiles. Figure 2.8. Stress relaxation curves and Arrhenius plot for AP3 containing no anthracene units. UV penetration depth is a limiting factor for potential applications of the polymers studied here. Modification of surface properties was examined wherein the degree of anthracene dimerization can be considered consistent as a function of depth. Scratch healing experiments were conducted in order to demonstrate the photo-control of vitrimeric properties. Polymer samples before and after irradiation were scratched (approximately 25% of the total thickness) with a razor blade and mounted on glass slides. Samples were observed using an optical 39 microscope and heated in 5 °C increments using a heating stage until the scratch (≈ 100 μm wide initially) was observed to begin healing (Table 2.2). Using optical microscopy, scratches were initially observed as dark lines crossing the sample, which were seen to decrease in width during healing through a series of expansions and contractions of the material. This behavior is consistent with previously reported examples of visually observed scratch healing.36,144,145 Table 2.2. Composition and scratch healing temperature of anthracene containing copolymers before and after UV cross-linking The onset of scratch healing was observed to be a slow expansion and contraction of the polymer sample gradually resulting in closing of the scratch. Below the healing onset temperature (Table 2.2), no significant changes in scratch width or sample volume were observed. At higher temperatures (approximately 70 °C above Tg) scratches in all tested polymers healed to a width of less than 5 μm in under 5 minutes with no changes in width observed on cooling. An increase in healing onset temperature is consistent with the increase in Tg caused by UV irradiation. Despite the low Tg for AP3, the onset of healing did not begin until approximately 35 °C, close to the healing onset of polymers with a much higher Tg. The topological freezing point transition (Tv) for vitrimers is the temperature at which network 40 rearrangement begins to occur, and is commonly in the range of 30-70 °C for rigid vitrimers.35,146,147 Scratch healing necessitates heating to both above the Tg, to enable mobility of the polymer chains, and above the Tv, to allow for network rearrangement to heal the scratch. In the case of AP3, Tg is below room temperature, and the healing onset above room temperature, thus Tv can be estimated at between 25 and 35 °C. In order to demonstrate the overall effect of UV irradiation on scratch healing, samples of AP2a and AP2b were scratched and heated on a hot plate at 60 °C (the healing onset for P2a but below that for AP2b) for 10 minutes followed by heating at 80 °C (the healing onset for P2b) for 10 minutes (Figure 2.9). Figure 2.9. Optical microscope image of a) Sample AP2a initial scratch, b) AP2a after 60 °C 10 min, c) Sample AP2b initial scratch, d) AP2b after 60 °C 10 min, e) AP2b after 80 °C 10 min. Black scale bar is 300 μm. Value in parentheses indicates approximate scratch width. Images were assembled from individual photos focused at each position. 41 The scratch in polymer AP2a had an initial width of 135 μm and healed 93% to a width of 9 μm after treatment at 60 °C. Polymer AP2b had an initial scratch width of 118 μm and healed 10% to a width of 106 μm after treatment at 60 °C and healed 98% (2 μm) after treatment at 80 °C. A decrease in the darkened area of the scratch for AP2b after treatment at 60 °C was observed (Figure 7d), but the width of the scratch measured from the onset of deformation does not decrease significantly. This suggests that closing of the scratch is likely occurring slowly at this temperature for the irradiated sample and from the bottom of the scratch. Depending on the depth of the scratch, this may be consistent with a reduced amount of anthracene photodimer present at the bottom of the scratch resulting in a lower scratch healing temperature compared to the photodimerized surface. Near complete rapid healing of the scratch in AP2b at elevated temperatures (Figure 2.9) is consistent with the thermal healing of the non-irradiated sample AP2a, and demonstrated that the introduction of non-exchangeable cross-links does not disable the thermal healing of these vitrimer copolymers. 2.2.2 Experimental All chemical reagents were purchased from commercial sources and used without further purification. 1,12-Dodecanediol (99%), 1,12-dodecanediamine (98+%), 2,2,6-trimethyl-1,3-dioxin-4-one (94% containing up to 6% acetone), ethylacetoacetate (99+%) and 1,5-diaminoanthraquinone (90+%) were all purchased from Alfa Aesar. 2-Aminoanthracene (96%) and ammonium cerium nitrate (≥98.5%) were purchased from Sigma Aldrich. 42 1H NMR spectroscopic data were collected on a 400 MHz Bruker Avance 400dir spectrometer at 25 °C. Residual protonated solvent peaks were used to reference the 1H NMR spectra. Absorption spectra were collected on a Varian Cary 5000 UV-Vis-NIR spectrophotometer. FT-IR measurements were conducted on a PerkinElmer Frontier FT-IR instrument equipped with an attenuated total reflectance (ATR) crystal. UV irradiation of samples was carried out using either a Rayonet Photochemical Reactor equipped with four 365 nm light sources (35 W each) or an Entela 365 nm hand lamp (6 W). Visible light irradiation of samples was performed using a commercial CFL bulb (13 W) in tandem with a Xe arc lamp (150 W). Mass spectrometry measurements were conducted on a Waters-ZQ instrument equipped with an ESCI source. Differential scanning calorimetry (DSC) experiments were performed using a TA Instruments DSC Q2000 instrument equipped with a TA Instruments Refrigerated Cooling System 90 at a ramp rate of 10 °C/min. Compression molding of samples was performed using a Carver Laboratory Press, pressing the samples at 9 psi between two stainless steel plates at 130 °C for 15 minutes. Parallel plate rheology was carried out on an Anton-Parr MCR 501 instrument under open-air conditions. An 8 mm top plate was used, and the gap was set at approximately 1 mm for all measurements. Temperatures ranged from 70 to 150 °C. Frequency sweep experiments were conducted at 0.1% strain, measuring from 0.1-100 Hz. Strain sweep experiments were conducted at 0.1 Hz, measuring from 0.001-10% strain. Stress relaxation experiments were conducted at an instantaneous initial strain of 0.5%. 43 Optical microscope images were collected on either an Olympus BX41 microscope with a CCD camera using a ×10 objective lens equipped with an INSTEC heating stage, or on a Senterra Raman Microscope and CCD camera capable of stitching multiple images together using a ×10 objective lens. Scratches for scratch healing experiments were made with samples were mounted on glass slides and scratched on the top surface using a razor blade. 2.2.3 Synthesis and Preparation 1,12-dodecanebisacetoacetate (A2). 1,12-dodecanediol (1.7 g, 8.4 mmol) and m-xylene (4.7 mL) were combined in an open vial and brought to reflux while stirring. 2,2,6-Trimethyl-1,3-dioxin-4-one (2.6 mL, 18.5 mmol) was added dropwise and the solution stirred at 130 °C for 35 minutes. The mixture was cooled to room temperature and then dried under vacuum to afford a crude oil. The oil was purified using column chromatography on silica gel with 7:3 ethyl acetate to hexanes as the mobile phase. Rf = 0.72. Yield: 2.40 g (77%) of a pale yellow solid. ESCI MS: 371.3 (M-H)+, 393.2 (M-Na)+ 1H NMR (400 MHz, (CD3)2SO, RT): δ 4.03 (t, J = 6.6 Hz, 4H), δ 3.58 (s, 4H), δ 2.17 (s, 6H), δ 1.54 (p, J = 6.7 Hz, 4H), δ 1.27 (m, 16H). Compound A1a. 2-Aminoanthracene (0.24 g, 1.2 mmol), ethyl acetoacetate (0.8 g, 6.1 mmol), and ammonium cerium nitrate (0.034 g, 0.06 mmol) were dissolved in CH2Cl2 (2.4 mL) and DMSO (0.8 mL). The mixture was stirred at room temperature for 2.5 hours and the CH2Cl2 was then removed under vacuum. Deionized water (50 mL) was added and the mixture sonicated for 10 minutes. The crude solid was vacuum filtered and rinsed with deionized water. The 44 product was purified using flash column chromatography on silica gel with hexanes as the mobile phase. Yield: 0.128 g (34%) of a bright yellow solid. APCI MS: 306.2 (M-H)+, 328.1 (M-Na)+ 1H NMR (400 MHz, CD2Cl2, RT): δ 10.66 (s, 1H), δ 8.40 (s, 1H), δ 8.34 (s, 1H), δ 7.99 (m, 3H), δ 7.64 (m, 1H), δ 7.47 (m, 2H), δ 7.25 (dd, J = 9.2, 2.1 Hz, 1H), δ 4.77 (d, J = 0.6, 1H), δ 4.16 (q, J = 7.0 Hz, 2H), δ 2.18 (s, 3H), δ 1.29 (t, J = 7.0 Hz, 3H). Compound A1b. Compound 1a (0.056 g) was dissolved in 250 mL of 1:1 ethanol and ethyl acetate. The solution was degassed using three freeze-pump-thaw cycles and then stirred at room temperature under nitrogen for 24 hours while irradiating with a 365 nm hand lamp. The solvent was then removed under vacuum to afford a dark brown solid. AP1a and AP2a. 1,12-Dodecanediamine, 1,12-dodecanebisacetoacetate, and 1,5-diaminoanthracene were combined in the indicated molar ratios (Table 1) and dissolved in a minimum amount of hot ethyl acetate and ethanol (1:1). The solution was heated at reflux for one hour and then reduced to a minimum volume under vacuum. The solution was transferred to a silicone mold in a beaker, and heated to 70 °C in an oil bath until the solvent had evaporated. The temperature was then raised to 90 °C for 18 hours, and then to 130 °C for 60 minutes. The resulting black polymer sheets were removed intact as one piece from the warm molds. AP1c. 1,5-Diaminoanthracene (0.1 g) was dissolved in 300 mL of ethanol and ethyl acetate (1:1), degassed using three freeze-pump-thaw cycles, followed by irradiation in the same manner as for A1b over 3 days using a Xe arc lamp in conjunction with a CFL bulb. 1,12-dodecanediamine (0.097 g) and 1,12-dodecanebisacetoacetate (0.34 g) were then added, and the 45 solution volume reduced to a minimum under vacuum. The solution was polymerized in the same manner as for P1a and P2a. AP1b and AP2b. Samples of AP1a and AP2a were suspended in the middle of a Rayonet photochemical reactor using clips and irradiated on all sides for 18 hours. 46 2.3 Conclusions Composite materials based on vitrimeric bonds containing photo-responsive aromatic diamines and thermally exchangeable aliphatic diamines have been prepared. UV irradiation causes dimerization of the anthracene units resulting in cross-linking of the material and an increase in glass transition temperature. Thermal scratch healing was observed, and the healing onset temperature was tunable using both UV irradiation and changes in composition. It was seen that aromatic amines do not undergo vinylogous urethane exchange reactions, and as such alkyl amines must be present to retain the desired vitrimeric properties. This work may lead to further integration of functional and responsive molecules into the polymeric backbone of vitrimeric materials. 47 Chapter 3: Room Temperature Crystallization of Amorphous Polysiloxane using Photodimerization 3.1 Overview Building upon the UV-stimulated anthracene polymer cross-linking research in Chapter 2, a flexible silicone copolymer with pendant anthracene moieties was prepared. The effect of photo-dimerization cross-linking under UV irradiation was examined and found to result in crystallization of the material. Bulk crystallization in flexible polymeric systems is difficult to control due to the random orientation of the chains. Here, a photo cross-linking strategy that results in simultaneous cross-linking and crystallization of polysiloxane chains into millimeter sized leaf-like polycrystalline structures is reported. Polymers containing pendant anthracene groups are prepared and undergo [4+4] photocycloaddition under 365 nm irradiation at room temperature. The growth and morphology of the crystalline structures is studied using polarized optical microscopy (POM) and atomic force microscopy, and is found to progress through three unique stages of nucleation, growth, and constriction. The mobility of the individual chains is probed using pulsed-field gradient (PFG) NMR to provide insights into the diffusion processes that may govern chain transport to the growing crystal fronts. The room temperature crystallization of this conventionally amorphous polymer system may allow for a new level of morphological control for silicone materials. 48 3.2 Research 3.2.1 Results and Discussions The condensation of alkyl amines with acetoacetates is an efficient synthetic route for the preparation of dynamic polymer networks, requiring minimal solvent, purification, or reaction optimization.1,35,42 The same strategy to covalently attach a photoactive moiety onto a linear silicone backbone is employed here.141 9-Anthracenemethanol was esterified to give 9-anthracene-methylacetoacetate (B1) in high yield (96%) in a single step. B1 was condensed with 6-7 wt% (aminopropylmethylsiloxane) - dimethylsiloxane copolymer (PNH2-7) to yield the anthracene-containing random copolymers as viscous oils without the need for further purification (Figure 3.1a). Polymers were prepared with 3, 7, and 25 molar equivalents of B1 relative to the polymer backbone, named BP3, BP7, and BP25, respectively. Photo-induced dimerization was carried out on drop-cast thin films on glass substrates, irradiating from 3 cm above for one hour using a 4W handheld UV lamp at 365 nm, without any co-crystallizing agent or solvent added to the system. The absorption spectrum of BP7 was collected as a function of irradiation time (Figure B.3). A decrease in the absorbance between 300 and 400 nm is consistent with [4+4] photocycloaddition of anthracene.148 No further changes in the absorption spectra were observed after 30 minutes of irradiation, with the percent of anthracene remaining after irradiation estimated at 25% from the residual peak intensity at 365 nm. Free-standing solid pieces of polymer (approximately 115 μm thick, Figure B.4) could be removed from the substrate after irradiation using a blade and did not dissolve fully in dichloromethane (48% percent soluble fraction after 24 hours), supporting the photo cross-49 linking of the material from an oil to elastic solid. While anthracene dimerization at air interfaces can form anthracene endoperoxides, this process is non-competitive with dimerization for systems where the anthracene concentration is greater than 1 mM (B1 concentration in BP7 = 132 mM).149,150 Endoperoxide formation has been shown to inhibit the assembly and crystallization of anthracene molecules due to disruption of the planarity preventing close packing of the rings, and does not lead to cross-linking.151 A simple viscosity experiment was performed on a bulk sample, inverting a sealed vial of the polymer before and after irradiation. A decrease in creep distance was observed as a function of irradiation time, resulting in a solid sample (no observable movement after inversion) after 120 minutes of irradiation (Figure B.5). No changes were observed in the FT-IR spectrum of bulk samples or thin films after irradiation, indicating that the vinylogous urethane bonds were not disrupted (Figure B.6). Vibrational changes in the anthracene moiety are masked by the position and intensity of the stretching frequencies of the PDMS backbone. 50 Figure 3.1. Polymer structure and crystallization after UV irradiation. (a) Structure of the anthracene-containing PDMS random copolymer with varying amounts of anthracene. (b) [4+4] photocycloaddition of anthracene and photo/thermal cycloreversion reaction, showing one of two possible dimer isomers. (c) Image of a thin film of P7 after irradiation. (d) Optical microscope image of P7 after irradiation. (e) Photograph of the leaves of a sequoia redwood tree. (f) Polarized optical microscope image of P7 under a cross-polarizer and 530 nm retardation plate showing a birefringent pattern. 51 Optical microscopy imaging of BP7 after 15 minutes of irradiation shows dispersed polycrystalline spherical structures between 5-25 μm in diameter (Figure B.7). Further irradiation of the same sample for up to 60 minutes of total irradiation time resulted in the outward growth of polycrystalline sheaf-like lamellar structures of a maximum diameter of approximately 1 mm (Figure 3.1d). Image analysis of Figure 3.1c shows approximately 23% of the film surface consists of crystalline structures, but this does not account for crystallinity below the surface. These structures closely resemble the lamellar growth of PLLA/PVP and PEO/PVP composites, which are formed from controlled cooling of linear polymer melts.152,153 Each spherulitic structure is observed to nucleate from an individual spherical structure, with clearly delineated arms from which a fine structure grows. Images resemble the leaves of a redwood tree, and as such a seed and leaf model analogy is applied (Figure 3.1e). Leaves are observed to grow into contact with neighboring leaves but joining or overlap of two structures was not observed (Figure B.8). Isotropic irradiation of bulk samples in a vial produced crystal structures of a similar maximum diameter but lacking the branching and leaf structure, indicating different crystal growth dynamics (Figure B.9). Differential scanning calorimetry of BP7 films after irradiation did not show any significant thermal transitions from -80 to 150 °C, with no changes to endotherms on repeated runs (Figure B.10). The Tg is expected to be < -120 °C, and Tm values for semi-crystalline cross-linked PDMS have been reported in the region of 25-100 °C.67,68 Crystalline spherulite formation of linear PDMS has been reported at temperatures below -90 °C but not for samples at room 52 temperature.65,66 Heating samples to higher temperatures was not explored as the amine functionalities of PNH2-7 are not thermally stable above 150 °C. No visual change was observed for crystallized samples after four weeks at room temperature under ambient laboratory conditions. A crystallized film of BP7 was brought to 100 °C for one hour, resulting in a change from the observed leaf structures to long needle-shaped crystals (Figure B.11, B.12). PXRD measurements of the needle-containing film showed a new sharp peak at 11.7° 2ϴ (Figure B.13). Polymers were prepared with three different molar ratios of B1 to PNH2-7 (Figure 3.1a) and the compositional effect on crystal growth studied. BP3 produced seed structures within 15 minutes of irradiation, and upon further irradiation stunted leaf structures were observed with a maximum cross-sectional size of approximately 110 μm (Figure 3.2). BP25 showed macroscopic buckling of the thin-film surface after ten minutes of irradiation, with no crystallization seen in the deformed regions (Figure B.14). At the film edges where buckling was less pronounced, crystals of a maximum cross-sectional size of approximately 210 μm were observed (Figure 3.2). These crystals exhibit a less spherical growth and lessened fine structure near the leaf tips compared with BP7. Irradiation of BP25 beyond ten minutes did not result in further crystallization. The small growth of BP3 is attributed to insufficient anthracene units per polymer, resulting in crystal surfaces not capable of nucleating further growth. Buckling in BP25 suggests that cross-linking is too rapid for the growth of well-defined leaf structures to occur, attributed to the higher concentration of anthracene groups. Despite the large dependence of crystallization on anthracene content, for the three tested samples anthracene-containing subunits on the polymer represented only between 0.5 – 4% of the total number of repeat units per polymer chain. 53 Polarized optical microscopy (POM) of BP7 shows a distinct birefringence pattern that persists across the non-contiguous branches of the same leaf (Figure 3.1f). These POM results are consistent with birefringence in PLLA/PVP composites that is proposed to arise from sudden discontinuous branching and not from a helical twist of the growing crystal.152 Growth in these cases proceeds until a defect or breakage in the crystalline structure results in new branches extending from the original portion. Analysis of the POM images of BP7 shows a branching angle of 45° between the orange and blue regions along a single leaf direction (Figure B.15). The seed structures do not exhibit the same crystallization pattern under the same imaging conditions (Figure B.16). No polarization effects were observed in the BP7 oil before irradiation. Figure 3.2. Compositional effect on crystalline growth. Optical microscope image of (left) BP3 crystals after one hour of 365 nm irradiation and (right) BP25 crystals after ten minutes of 365 nm irradiation focused on the outer edges. Crystallinity in BP7 was probed using X-ray diffraction. The WAXS spectrum shows a similar profile before and after irradiation (Figure B.18), with only two diffuse peaks at q = 0.85 54 and 1.5 Å-1, attributed to the Si-O-Si and Si-CH3 components of the PDMS backbone, respectively.154 The SAXS spectrum of irradiated BP7 shows a broad peak at q = 0.15 Å-1 not present in the non-irradiated sample. A Guinier plot of the low q region of the SAXS spectrum of crystallized BP7 films gives a calculated radius of gyration (Rg) of 9.4 Å after irradiation (Figure B.19).155 This value is lower than Rg values for linear PDMS and globular proteins, indicating highly packed chains.156–158 Tight packing is further supported by the non-linearity of the Guinier plot at lower q values. The correlation distance, , was calculated to be 61 Å from the Ornstein-Zernike plot of crystallized P7 and is interpreted as the distance between the cross-linking nodes (Figure B.20).159,160 PXRD measurements of BP7 were performed before and after crystallization, as well as on PNH2-7. All samples show the same two broad diffraction peaks centered at 12° and 22° that align with the features in the WAXS spectrum (Figure B.21). Liquid crystal mesogens containing PDMS portions have been reported, demonstrating the ability of PDMS chains to participate in self-assembly when guided by rigid, aromatic moieties.154,161 In our system, it is proposed that interactions between anthracene dimer cross-linking nodes produce ordering that is not present when cross-linking is done using flexible moieties, however the high weight percent of amorphous PDMS prevents complete ordering here (Figure B.22). For similar sheaf-like lamellar structures prepared using two-component polymer blends, X-ray diffraction peaks are more prominent for blends featuring a higher proportion of the crystallizing polymer versus the amorphous polymer.162–164 Blends featuring a high proportion of amorphous component have been reported that exhibit only diffuse diffraction while still assembling into macroscopic structures.165 Combined with the X-ray scattering measurements, this demonstrates that the 55 birefringent structures are only weakly crystalline, exhibiting long-range ordering necessary for the observed POM results, but lacking extensive short-range crystalline order (Figure B.22). This is attributed to the high proportion of amorphous component (PDMS moieties far from an anthracene cross-linking point) that inhibits short-range ordering as well as dominating the PXRD patterns with the two diffuse peaks. Figure 3.3. Confocal microscopy of seeds and leaves. (a) Images of crystallized BP7 at different depths, showing three distinct focal planes, collected at 10× magnification. Inset numbers are distance from the lowest focal plane. (b) Schematic representation for the proposed stages of photo-induced crystallization proceeding through seed growth, crystal growth from an uppermost seed, and constriction of the bulk. Laser scanning confocal microscopy was used to map the morphology of the leaves and their spatial relation to the seeds. Three distinct focal planes were observed, each spaced approximately 40 μm apart (Figure 3.3a). The lowest plane contains seed structures from which a b 56 no leaves grew, while the middle plane has a second layer of seeds. The third plane contains the leaf structures that are observed to grow from a seed structure in the middle focal plane. Imaging only the edges of a leaf structure shows that the leaves grow up and out from the center, with a height difference of 11 μm for the observed region (Figure B.23). This demonstrates that the leaves grow upwards towards the source of illumination from an embedded seed and suggests that only seeds near the middle of the film are capable of nucleating to produce the large leaf structures. Anthracene dimerization is expected to stop once cross-linking sufficiently inhibits polymer motion, preventing anthracene molecules from adopting the correct orientation for photocycloaddition. Samples remain emissive after irradiation as approximately 25% of the anthracene is not dimerized (Figure B.24). Fluorescence microscopy imaging to examine the distribution of non-dimerized anthracene in the samples (Figure B.25) demonstrates that both seeds and leaves are clearly distinguishable from the background. This demonstrates the presence of non-dimerized anthracene molecules in the crystalline structures, possibly due to anthracene molecules becoming confined in the growing structure, preventing their photoreaction (Figure B.26). A direct comparison between emission intensities in the bulk and crystalline regions is not possible due to the changes in absorbance and quantum yield between single crystal, powder, and dissolved anthracene samples.166 Confocal imaging suggests that the leaf structures grow upwards from seed structures embedded in the interior of the film. However, photoreaction is expected to occur first near the 57 surface of the film where the light intensity is the greatest. Diffusion of polymer chains against a photo-induced cross-linking gradient has been previously reported for the preparation of heterogeneously swollen films.31,33 Diffusion in our samples was studied using pulsed field gradient (PFG) 1H NMR spectroscopy.167,168 The translational diffusion coefficient (Dt) and rotational time play important roles in crystallization events, governing the rates of mass transport and reorientation to the growing crystal facets respectively.169,170 Measurements were performed on liquid samples before irradiation and solid samples after irradiation as a function of anthracene content, probing the methyl protons on the PDMS backbone (Figure 3.4, 3.5a, Table B.2). The relative rotational times were estimated from the T1/T2 ratio.171,172 A decrease in Dt of nearly two orders of magnitude accompanied the addition of 3 equivalents of B1 to the liquid polymer, with insignificant decreases upon addition of further molar equivalents (Figure 3.5a). This suggests an aggregated state arising from the pendant anthracenes that is not impacted by further anthracene addition. The relative rotational times increase linearly with increasing B1 equivalents. However, the increase in rotational times was less than an order of magnitude between BP3 and BP25. As such, diffusional limitations are not expected to play a major role in the larger degree of crystallization of BP7 relative to BP3 and BP25. Given the morphology of the irradiated samples observed optically these findings are not surprising, as the mobility of the polymer likely depends on the proximity to crystallized structures. These measurements represent only the mobile components of the samples because the short T2 values of the crystalline components result in their suppression due to the filtering effects of the PFG pulse sequence. 58 The maximum translational diffusion lengths (assuming linear displacement) were plotted from Dt for PNH2-7 and BP7 (before irradiation) as a function of time (Figure 3.5b). BP3 and BP25 were omitted from this plot as the similar diffusion speeds to P7 results in a nearly identical profile. Crystallization of seeds in BP7 is observed to begin within approximately 15 minutes of irradiation, while leaf growth began within 30 minutes. Figure 3.4. PFG 1H NMR diffusion measurements. Gaussian fits to the Stejskal – Tanner diffusion equation167 with an additive constant to account for slowly diffusing species are shown for liquid BP7 (left) and irradiated solid BP7 (right). From the data in Figure 3.5b, it may be seen that an individual polymer chain is predicted to diffuse a maximum of 39 μm (15 minutes) and 55 μm (30 minutes). Confocal microscopy showed focal planes separated by approximately 40 μm between the layers of seeds and growing crystal leaf. As samples are irradiated from above, cross-linking and a reduction in motion should begin at the surface and propagate downward as irradiation continues. However, the leaves are observed to nucleate from seeds in the interior of the film and grow into a region that should already be cross-linked and thus unable to undergo reorientation for growth of the leaf 59 structures. Based on the data in Figure 3.5, it is reasonable to propose that diffusion from lower, non-cross-linked regions up to the growing crystalline front may be ongoing during irradiation, driven by the cross-linking gradient. Figure 3.5. Calculated displacement for liquid polymer chains. (a) Translational diffusion coefficient (Dt) and relative rotational time (T1/T2) as functions of molar equivalents of anthracene, measured using PFG 1H NMR spectroscopy. (b) Maximum linear displacement distances for PNH2-7 and BP7 as a function of time, as calculated from Dt. Atomic force microscopy (AFM) of crystallized BP7 was performed in both non-contact mode and fast-force mapping contact mode to probe the surface topology and Young’s modulus of the resulting films (Figure 3.6a, 3.6b). The leaf structures are observable using AFM with feature heights of up to 1.3 μm relative to the surrounding flat film. Similarly shaped polymer lamellae typically exhibit a sheaf thickness on the order of tens of nanometers.173 Crystallization of the leaves must proceed prior to a bulk reduction in volume causing the film to constrict, forcing the tips of the crystal leaves to protrude from the film (Figure 3.3b). 60 Force mapping of the same exposed leaf structure shows a uniform Young’s modulus of approximately 100 MPa across the crystals, an increase of nearly 10 times over the bulk material (Figure B.28). This value is comparable to the reported modulus determined using AFM for ozone cross-linked PDMS, and shows a nearly 100 times increase over the modulus for bulk measurements of PNH2-7 cross-linked with flexible linkers.141,174 The modulus for organic crystals determined by AFM is typically between 5-10 GPa, orders of magnitude higher than those found for the leaf structures, supporting the incorporation of the PDMS units into the observed structures.28,175,176 The large contrast in bulk and crystal modulus may allow the leaves to act as structural reinforcement amongst the elastomeric bulk if this chemistry can be expanded to thicker, more mechanically robust samples. Figure 3.6. Atomic force microscopy imaging of crystalline leaves. (a) Non-contact mode showing feature height and (b) fast-force mapping contact mode showing Young’s modulus of crystallized BP7. Scale bar = 8 μm. 3.2.2 Experimental a b b 61 (6-7% Aminopropylmethylsiloxane) – dimethylsiloxane copolymer (AMS-163), Mn = 50,000 g/mol, was purchased from Gelest. All other reagents were purchased from Sigma Aldrich and used without further purification. 1H NMR spectroscopic data were collected on a 400 MHz Bruker Avance 400dir spectrometer at 25 °C. 13C NMR spectroscopic data were collected on a 600 MHz Bruker Avance 600cp spectrometer at 25 °C. Residual solvent peaks were used to reference the spectra. NMR spectra are reported in parts per million (ppm). Mass spectrometry measurements were conducted on a Waters-ZQ instrument equipped with an ESCI/APCI ionization source. Elemental analysis measurements were performed on a Thermo Flash 2000 Elemental Analyzer. Infrared spectra were collected on a PerkinElmer Frontier FT-IR with a diamond ATR plate. Absorption spectra were collected on a Varian Cary 5000 UV-Vis-NIR spectrophotometer. Optical microscope images were collected on a Bruker Senterra II Compact Raman Microscope using a 10× magnification. Polarized optical microscopy images were collected on an Olympus BX53M using a linear polarizer and 530 nm retardation plate. Fluorescence microscope images were collected on an Olympus IX83 Inverted Fluorescence Microscope equipped with a metal-halide lamp. An excitation wavelength of 350 nm was used with no filters applied to the emitted light. Differential scanning calorimetry (DSC) measurements were performed using a TA Instruments DSC Q2000 instrument with a TA Instruments Refrigerated Cooling System 90 at a ramp rate of 10 °C/min. PXRD measurements were collected on a D8-Advance instrument with a Cu source and LynxEye detector at room temperature. Atomic force microscopy images were 62 collected using an Asylum Instruments Cypher S AFM system operating in tapping mode or fast force mapping mode. Mikromasch HQ:NSC14/No Al or HQ:NSC19/No Al probes, with typical resonance frequencies f and spring constants k of (f = 160 kHz, k = 5 N/m) and (f = 65 kHz, k = 0.5 N/m) were used. Confocal microscopy was performed on an Olympus FV1000 Laser Scanning Microscope using simultaneous reflectance, transmittance, and fluorescence (λex = 360 nm) modes. Data were treated using the Volocity software package. X-ray scattering measurements were performed on a Ganesha 300XL+ instrument in transmission mode. Solid-state PFG NMR experiments were performed on a home-built NMR spectrometer based on an Oxford Instruments 8.4 T wide bore magnet.177 Liquid samples were transferred to an NMR tube and measured neat. Solid samples were irradiated as described below and then removed from the glass slide and packed into an NMR tube for measurement. 3.2.3 Synthesis and Preparation 9-Anthracene-methylacetoacetate (AnAc). 9-Anthracenemethanol (1.5 g, 7.2 mmol), tert-butyl acetoacetate (2.51 mL, 14.4 mmol), and m-xylenes (3 mL) were combined in an open vial along with a magnetic stir bar. The mixture was stirred at 130 °C for 30 minutes. After cooling to room temperature, the crude oil was transferred to a round bottom flask and reduced under vacuum to minimum volume. The product was purified using flash chromatography on silica gel with 2:8 ethyl acetate:hexanes as the mobile phase. Rf = 0.22. Yield: 2.01 g (96%) of a 63 yellow solid. ESCI MS 315.1000 (M-Na)+. Elemental analysis calculated for C19H16O3: C, 78.06%; H, 5.52%. Found: C, 78.35%; H, 5.52% 1H NMR (400 MHz, (CD3)2SO, RT): δ 8.70 (s, 1H), 8.35 (d, J = 8.9 Hz, 2H), 8.14 (d, J = 8.2 Hz, 2H), 7.62 (m, 2H), 7.56, (m, 2H), 6.16 (s, 2H), 3.63 (s, 2H), 2.10 (s, 3H). 13C {1H} NMR (140 MHz, (CD3)2SO): δ 201.5, 167.4, 130.9, 130.5, 129.0, 129.0, 126.8, 126.0, 125.3, 124.0, 59.9, 49.6, 30.0. Polymer sample BP7. PNH2-7 (1 g) and 9-anthracene-methylacetoacetate (0.146 g, 25 equivalents) were combined in a vial with 2 mL of THF. The system was sonicated until homogeneous, and then heated in an oil bath at 70 °C until the THF had been removed (approximately 1 hour). The vial was stoppered and an N2 inlet was added. The system was heated at 100 °C for 18 hours under a constant flow of N2 to afford the product as a yellow oil without further purification. The resulting oil was fully miscible with CH2Cl2 and THF. Samples BP3 and BP25 were prepared using the same procedure, changing only the moles of AnAc added. 1H NMR (peaks resulting from polymer backbone have been omitted for clarity) (400 MHz, CD2Cl2, RT): δ 8.72 (s, 1H), 8.49 (s, 1H), 8.38 (m, 2H), 8.03 (m, 2H), 7.51 (m, 4H), 6.06 (s, 2H), 4.38 (s, 1H), 3.22 (m, 2H), 1.88 s, 3H), 1.65 (m, 2H), 0.60 (m, 2H) Polymer PNH2-7. 1H NMR (400 MHz, CD2Cl2, RT): δ 2.62 (m, 2H), 1.46 (m, 2H), 0.51 (m, 2H), 0.09 (s, 97H) 64 Thin Films. 20 wt % Solutions of polymer were prepared using CH2Cl2, and were dropcast (≈ 70 μL) directly onto glass slides and allowed to air dry. Irradiation on thin films was carried out using a UVGL-58 6W handheld UV lamp at a distance of 3 cm, irradiating through a Pyrex watch glass to cut-off any light below 300 nm. The soluble fraction of thin films was determined by immersing a pre-weighed sample in 100 mL of CH2Cl2 for 24 hours. Then, the sample was removed, rinsed thoroughly with clean CH2Cl2, and dried under vacuum for 24 hours. The weight of the dried mass was used to calculate the percent of mass that was soluble. Bulk samples were irradiated using a Rayonet photoreactor equipped with ten 365 nm 35W bulbs. 3.3 Conclusions 65 In this Chapter, PDMS random copolymers containing pendant anthracene groups suitable for [4+4] photocycloaddition are reported. UV irradiation of thin films of these materials resulted in cross-linking accompanied by macroscopic organization into millimeter scale lamellar crystalline structures that are stable at room temperature. The final crystalline structure size and morphology was found to depend on the anthracene content in the system, with both high and low molar equivalents producing smaller structures than an intermediate amount. The crystallinity of these structures was studied using polarized optical microscopy and diffraction techniques and was found to be similar to lamellar crystalline phases prepared using more rigid polymer structures. However, the flexibility of the siloxane chain in our system represents a departure for lamellar crystalline formation as the rigid anthracene moieties represent less than four percent of the repeat units in the polymer chain. Diffusion NMR results coupled with insights from AFM imaging and confocal microscopy allowed for a growth model to be proposed that involves diffusion against a photo-induced cross-linking gradient resulting in the crystalline phases protruding up to a micron in height from the bulk film surface. The rigidity of the lamellar structures was probed using AFM indentation and found to be much greater than the surrounding bulk material, which is envisaged to allow for a new type of crystalline-reinforced silicone material. 66 Chapter 4: Visible Light Sensitized Photooxidative Cross-linking of Polysiloxanes using Singlet Oxygen 4.1 Overview Continuing with the amine-containing PDMS from Chapter 3, I next explored alternative photo-cross-linking reactions for siloxane copolymers. Photo-cross-linking of polymeric materials generally requires an inert atmosphere due to oxygen-based inhibition and quenching of the reactive species. Here the photo-oxidative cross-linking of amine functionalized poly(dimethylsiloxane) using atmospheric oxygen as the chemical oxidant is demonstrated. Visible light irradiation of a metalloporphyrin or organic sensitizer generates reactive singlet oxygen that oxidatively couples amines into imine cross-links. This facile benchtop cross-linking reaction proceeds at room temperature and results in solvent-free elastic materials after one hour. Solid state 13C NMR and FT-IR spectroscopies show that the reaction produces only imine functionalities with no side products observed. The mechanical properties of these polymers were tested using tensile experiments and were found to depend on the initial loading of sensitizer, with a maximum elongation strain of 157% and a Young’s modulus of 2.15 MPa for the highest tested amount. Photolithography is demonstrated with this cross-linking system using visible light irradiation. 67 4.2 Research 4.2.1 Results and Discussions The targeted photo-cross-linkable system is comprised of three components: a polymer containing alkyl-amine functional groups, a 1O2 sensitizing dye, and a solvent for the sensitizer (Figure 4.1). Platinum octaethylporphyrin (PtOEP) is a metalloporphyrin species that can generate 1O2 from the photoaccessible triplet state.178,179 The absorbance spectrum overlaps well with the spectral output of commercially available 530 nm green LEDs (Figure C.1). An experiment was performed to demonstrate the use of PtOEP for the photooxidative coupling of amines. n-Butylamine was dissolved in CD2Cl2 in an NMR tube and PtOEP was added. After one hour of 530 nm irradiation open to the atmosphere, a new set of downfield peaks was observed in the 1H NMR spectrum that match literature values for aliphatic alkyl imines (Figure C.2).180 68 Figure 4.1. (Top) Chemical structures of 6-7 wt% (aminopropylmethylsiloxane)-dimethylsiloxane copolymer (PNH2-7) and platinum octaethylporphyrin (PtOEP). (Bottom) Schematic representation of the photooxidative cross-linking of pendant amine groups using oxygen and a photosensitizer (PS). Commercially available 6-7 wt% (aminopropylmethylsiloxane) - dimethylsiloxane copolymer (PNH2-7) was used as the amine containing polymer. This polymer is a colorless viscous oil at room temperature. m-Xylenes was chosen as the solvent for PtOEP due to its high boiling point that minimizes evaporation when handling and transferring the mixture. A near-saturated PtOEP solution was used for all experiments (4.12 × 10-4 M). PNH2-7 was combined with the PtOEP solution to give an approximate amine : porphyrin molar ratio of 1200 : 1 with a PtOEP content of 200 ppm (0.02% weight percent) (designated CP100, the maximum [PtOEP] tested). Irradiation of this mixture with 530 nm LED light resulted in solidification of the liquid after one hour to give a pale pink free-standing film (Figure C.3). The optical transmittance of the CP100 mixture before solvent evaporation, as well as samples with 50% and 25% of the amount of PtOEP solution relative to CP100 (named CP50 and CP25 respectively, Table C.1), 69 were calculated as a function of initial solution thickness (Figure C.4). 5% Transmittance at 530 nm for CP100 was calculated at an initial thickness of 1.3 mm allowing for the preparation of samples for mechanical testing, with optical penetration expected to increase during irradiation as the dye undergoes photobleaching. Substantially thicker samples were not prepared due to the possibility of inhomogeneous cross-linking as a result of poor light penetration throughout the sample. IR spectroscopy was used to characterize CP100 before and after irradiation (Figure 4.2). m-Xylenes is not detectable in the IR spectrum after irradiation, and a mass balance analysis of samples shows that less than 5% of the initial mass of m-xylene remains after four hours of irradiation (Table C.2). The irradiated sample shows a new peak at 1670 cm-1 that is attributed to the C=N imine stretch.181 No other changes in the IR spectrum were observed, indicating no significant side reactions are occurring. The cross-linked sample was soaked in DCM overnight to remove the soluble components, rinsed with DCM, and then dried in vacuo. The intensity of the imine peak is increased relative to other peaks in the spectrum after this procedure, demonstrating that the imine peak may be attributed to the insoluble polymer components. The presence of an imine functionality was also probed using solid state 13C CP-MAS NMR spectroscopy Figure C.5). Measurements of a cross-linked sample of CP100 showed the presence of a downfield peak centered at 165 ppm that is characteristic of imine C=N sp2 carbon centers.182 70 Figure 4.2. (a) FT-IR spectra of PNH2-7, the CP100 mixture irradiated for four hours using 530 nm light, and the irradiated CP100 after soaking in DCM to remove the soluble components. Inset shows the imine peak region. Spectra are offset vertically by one transmittance unit for display purposes. (b) Solid state 13C CP-MAS NMR spectrum of irradiated CP100 showing a peak characteristic of imine carbons, 400 MHz, RT. Sample CP100 solidified (giving a free-standing film) after one hour of irradiation and was used to compare the effect of different cross-linking conditions and additives on the photooxidation reaction (Table 4.1).A degassed sample with the same composition as CP100 was irradiated under N2 gas but did not result in a solid film or color change in the sample, indicating that the cross-linking reaction as well as the bleaching of PtOEP requires the presence of atmospheric O2 (Table 4.1, B). To further investigate the reaction, BHT (radical scavenger) and DABCO (singlet O2 quencher) were added to the system separately in equimolar amounts relative to the amine groups (Table 4.1, C and D).183,184 Both additives delayed the onset of solidification (4 hours (BHT) and 3 hours (DABCO), respectively), indicating inhibition of the b a 71 reaction leading to cross-linking. The sample containing DABCO remained the same bright red color as the initial reaction mixture, indicating that bleaching of PtOEP was also inhibited. Both samples were found to fully dissolve in DCM while cross-linked CP100 has a soluble fraction of 6.5% (Table C.2). Samples containing as low as 10% of the initial PtOEP loading (BP10) resulted in solid films after one hour of irradiation. The oxygen dependency and inhibition by DABCO supports the conclusion that the cross-linking mechanism is occurring through the photocatalytic generation of 1O2 (Figure C.6).84 Inhibition by BHT could indicate a radical intermediate in the reaction pathway, or the simultaneous occurence of a Type II photooxidation reaction that also leads to the formation of imine cross-links.120 Entry Variable Result Color wt% PtOEP A CP100 Solid, 1 hr Pink 0.020 B N2 Liquid Red 0.020 C BHT Solid, 4 hrsa) Yellow 0.014 D DABCO Solid, 3 hrsa) Red 0.014b) E Triethylamine Solid, 1 hr Pink 0.020 F CP50 Solid, 1 hrs Pink 0.014 G CP25 Solid, 1 hr Pink 0.009 H CP10 Solid, 1 hr Pink 0.004 a) Resulting solid rapidly dissolves in DCM; b)DMSO required to dissolve DABCO Table 4.1. Effect of reaction condition, additives, and blend composition on the photooxidative cross-linking of PNH2-7 after 4 hours of 530 nm irradiation. Larger samples (30 mm diameter, 1 mm thick) were prepared for mechanical testing, irradiating samples for 18 hours to ensure a maximum extent of photochemical cross-linking 72 occurs. Despite cross-linking occuring within one hour to give freestanding films, a long irradiation time was used for these samples to prevent inhomogeneous cross-linking arising from the photoreaction occuring most rapidly at the surface where the 530 light is most intense and the most O2 is present. Samples of CP100 were pale yellow while CP25 samples were pale pink (Figure 4.3). The color in CP100 is attributed to the presence of platinum photodegradation products which are present in a lower concentration in CP25. Strips were cut from these samples and the mechanical properties characterized using a RSA G2 DMA instrument, performing tensile stretching experiments in an axial mode. Figure 4.3. (a) Stress-strain curves for CP100, CP25, CPA, and CPB from uniaxial tensile experiments, RT. (b) Photograph shows CP100 (top) and CP25 (bottom) used for mechanical testing. Disks are 3 cm in diameter, 1 mm thick. a b 73 Table 4.2. Mechanical properties of samples measured using DMA tension experiments. CP100 and CP25 were found to have similar Young’s modulus of approximately 2 MPa while the ultimate elongation values of the two samples were 157% and 37% respectively, demonstrating that mechanical properties depend strongly on the initial amount of PtOEP solution (Table 4.2). Mechanical properties for CP100 are comparable to photocurable acrylate PDMS systems as well as commercially available thermally-cured Sylgard 184 (140% max elongation).185 CP100 and CP25 were found to have similar soluble fractions of 6.6 and 4.6%, respectively, in DCM and can be swollen to uptake approximately 250% of their own mass in solvent (Table C.2). The same polymer cross-linked using a stoichiometric condensation reaction had a soluble fraction of 19% at 5 equivalents of cross-linker, suggesting a greater density of cross-links in the photo-cross-linked system.141 To probe the scope of this photo-cross-linking reaction, different polymers bearing primary, secondary, and tertiary amines were used to prepare additional samples. Aminoethylaminopropyl methylsiloxane) dimethylsiloxane copolymer (18-24 wt%) has a secondary amine in the alkyl chain of the primary amine functionality. Under the same Sample Y ’ M d (MPa) Tensile Strength (MPa) Ultimate Elongation (%) CP100 2.15 ± 0.04 0.89 ± 0.06 157 ± 2 CP25 1.93 ± 0.03 0.35 ± 0.02 37 ± 1 CPA 0.96 ± 0.07 0.17 ± 0.03 22 ± 1 CPB 1.13 ± 0.01 0.17 ± 0.05 18 ± 1 74 conditions as CP100, this polymer (CP2nd) cross-linked in four hours to give a tacky solid unsuitable for mechanical testing. FT-IR analysis showed a larger imine peak than in the spectrum of CP100, supporting the oxidation of the secondary amines to imines as well as primary amines (Figure C.8). Branched polyethyleneimine has both secondary and tertiary amines present. Attempts to photo-cross-link this polymer resulted in a non-cross-linked colorless oil, which is also attributed to secondary imine formation and not quenching of 1O2 by the tertiary amines. The addition of one molar equivalent of trieththylamine, which cannot form imines, to CP100 did not inhibit the cross-linking reaction (Table 4.1, E). A sample with 30% by mass of the PNH2-7 substituted with aminopropyl end terminated PDMS (875 g/mol) at the same PtOEP concentration as CP100 was prepared using the same procedure (denoted CPA). Xylenes can cause acute health issues when ingested or inhaled and is present in the polymer system in significant quantities.186,187 As such, Rose Bengal dissolved in 1,2 propanediol and ethanol as an alternative singlet oxygen generation system (designated as CPB) was used, in which all components are relatively non-toxic.188 Rose Bengal was added at half the photocatalyst concentration in CP100 due to an increased molar extinction coefficient compared with PtOEP. Both CPA and CPB resulted in solid, pale-to-colorless, samples after irradiation with the same characteristic imine peaks in their IR spectra as in CP100 (Figure C.7). Mechanical testing of CPA and CPB demonstrated Young’s modulus of 1.6 and 1.2 Mpa, respectively, with ultimate elongation values of 22 and 18% (Figure 4.3). These values are lower than for CP100, suggesting that both samples have fewer imine cross-links than in CP100. In CPA the end-terminated chains cannot cross-link each other and for CPB the differences may be due to differences in photocatalyst concentration or photophysical properties. 75 Cross-linked samples, as well as PNH2-7, were analyzed for their thermal stability using TGA (Figure C.9). CP100 was thermally stable up to 400 °C under N2, with only a 5% mass loss. Heating further to 500 °C resulted in a total mass loss of 16%, with CP25 exhibiting very similar behaviour. The non-cross-linked PNH2-7 showed much lower thermal stability, with a mass loss of 10% between 100 °C and 200 °C, followed by a large mass loss beginning at 400 °C. The stability of the cross-linked samples is consistent with TGA results for linear, non-functionalized PDMS under N2 and O2, as well as thiol-ene photo-cross-linked PDMS.189,190 The lower stability of PNH2-7 is attributed to thermal decomposition of the free amine groups, with all samples undergoing thermal decomposition above 400 °C.191 Differential scanning calorimetry was performed on CP100 and CP25 and showed a similar Tg for both samples of -114 °C, comparable to the value for other cross-linked PDMS samples (Figure C.10).141 The thermal hydrolytic stability of these materials was tested by exposing CP100 to steam for one hour, after which no changes to the shape, visible color, or vibrational spectrum were observed, indicating good resistance to hydrolysis of the imine bonds. Cross-linking in these samples is controlled using visible light irradiation, and as such photolithography can be demonstrated using a simple patterned sheet of cellulose acetate mounted on glass slides as the photomask (Figure 4.4). CP25 was chosen for this demonstration due to the greater viscosity of this sample compared to CP100. The material was pipetted onto a glass slide and irradiated through the mask using a 530 nm LED bulb array for one hour, followed by rinsing with ethyl acetate. After drying in air for 5 minutes, the resulting photopattern could be easily resolved (Figure 4.4). Attempts to pattern features below 2 mm resulted in indistinct resolution after rinsing, which is attributde to the spacing between mask and 76 film. These results are similar to other benchtop photolithographic systems using acrylate monomers and printed photomasks, and may be applicable for the rapid fabrication of PDMS microchannels using inexpensive equipment.192,193 Figure 4.4. (a) Photolithographic setup prepared using two stacked glass microscope slides, a printed overhead transparency sheet, and a glass slide coated in CP25. (b) A photopatterned slide after one hour of 530 nm bulb irradiation followed by rinsing with ethyl acetate, features are 2 mm wide. a b 77 4.2.2 Experimental (6-7% Aminopropylmethylsiloxane) – dimethylsiloxane copolymer (AMS-163), aminopropyl-terminated polydimethylsiloxane (DMS-A11), and (18-24% aminoethylaminopropylmethylsiloxane) – dimethylsiloxane copolymer (AMS-2202) were purchased from Gelest. Platinum (II) octaethylporphyrin was purchased from Frontier Scientific. All other reagents were purchased from Sigma Aldrich and used without further purification. Absorption spectra were collected on a Varian Cary 5000 UV-Vis-NIR spectrophotometer. PtOEP was dissolved in DCM and the spectrum measured at 2.47 × 10-6 M. Rose Bengal was dissolved in MeOH and the spectrum measured at 1.17 × 10-6 M. 1H NMR spectroscopic data were collected on a 400 MHz Bruker Avance 400dir spectrometer at 25 °C. Residual proto-solvent peaks were used to reference the 1H NMR spectra. 13C CP-MAS NMR spectra with high power proton decoupling were collected on a 400 MHz Bruker solid state DRX spectrometer using a sample of CP100 dried under vacuum for one week. Samples were spun at 4 kHz at the magic angle. Ramped pulses at 50% on the 13C frequency were used for cross polarization with a contact time of 5 ms for all experiments. The relaxation delay was set to be 5 seconds, and acquisition time 50 ms. Data were processed with a 20 Hz line broadening exponential decay function. Chemical shift values (ppm) were referenced with adamantane 13CH2 signal at 29.5 ppm. All experiments were done at room temperature. Infrared spectra were collected on a PerkinElmer Frontier FT-IR with a diamond ATR plate. Thermogravimetric analysis was performed on Netzch TG209 Libra using an Al2O3 crucible at a 78 temperature ramp of 10 °C / min under a N2 purge flor of 30 mL / min. Differential scanning calorimetry (DSC) measurements were performed using a Netzch DSC 214 Polyma at a ramp rate of 10 °C / min. Mechanical testing was carried out in triplicate on a Dynamic Mechanical Analyser (DMA, RSA G2 TA Instruments) in axial mode equipped with tension fixture. Samples were cut into strips with dimensions 4 mm x 3 mm x 1 mm. Sample strips were extended until breakage at room temperature by applying constant linear rate of 0.1 mm/min. The elongational strain was calculated by: 𝜖 =𝐿 − 𝐿0𝐿0× 100 Where Lo is the initial length of the sample. The Young’s modulus was determined from the equation 𝜎 = 𝐸𝜀 ( is the tensile stress), which is valid only for the initial elastic response of the material. The tensile strength represents the maximum stress in the stress-strain curve and ultimate elongation, u shows how much the material can elongate before fracture/failure. The latter was calculated by using the following equation: 𝜀𝑢 =𝐿𝑓 − 𝐿0𝐿0× 100 Where Lf is the final length of the sample before failure. 4.2.3 Synthesis and Preparation CP100. A fresh PtOEP stock solution was prepared by dissolving the porphyrin in m-xylenes to give a concentration of 4.12 × 10-4 M. For 1.0 g of PNH2-7, 1.58 mL of PtOEP solution was added to the polymer in a vial and mixed using a vortex mixer. The resulting 79 solution was transferred to a commercially available 3 cm diameter circular silicone mold. The mold was irradiated using a Westinghouse 15 W green LED flood lamp (100 W equivalent) at a distance of 10 cm on the benchtop open to the air. Samples prepared for mechanical testing were irradiated continuously for 18 hours. During irradiation samples were not noticeably warm to the touch at any point. Other samples were prepared in the same fashion. CP50, CP25, and CP10 were prepared by combining 50%, 25%, and 10% respectively of the PtOEP stock solution used for CP100. CPA was prepared by substituting 30% of the PNH2-7 mass with the amine terminated PDMS. CPB. Rose Bengal was dissolved in an equal mass solution of ethanol and 1,2 propanediol to give a concentration of 2.08×10-3 M. For 1.0 g of PNH2-7, 157 μL of RB solution was added to the polymer in a vial and irradiation carried out using the same procedure as for CP100. These volumes were chosen to deliver half the molar amount of RB as PtOEP owing to the approximately doubled absorption at 530 nm of RB compared with PtOEP. For photolithography, 100-200 uL of CP25 solution was pipetted onto a glass slide and allowed to spread into a thin layer. Two glass slides on either side were used to support a transparency sheet that was patterned with the desired mask using a common office printer. Irradiation was carried out using the same setup as for thick samples. After one hour of irradiation the sample was rinsed by gentle irrigation with ethyl acetate using a pipette and then allowed to air dry. 80 4.3 Conclusions In this Chapter the cross-linking of functionalized PDMS using visible light and atmospheric oxygen was demonstrated. This procedure allows for the simple, visible light cross-linking of commercially available polymers using a platinum porphyrin sensitizer to generate single oxygen which mediates the formation of imine cross-links. The coupling mechanism was investigated and found to involve both a radical intermediate and 1O2, and requires the presence of atmospheric O2. The material was characterized using FT-IR and 13C CP-MAS NMR spectroscopy which demonstrated the formation of imine functional groups without significant side-reactions. Samples were found to be mechanically robust, with Young’s modulus and ultimate elongation comparable to commercially available UV-curable siloxanes. It was also shown that this photooxidative cross-linking can be performed using metal-free Rose Bengal along with a benign solvent pair targeted at using green, low toxicity components. Photo-cross-linking of siloxanes is more commonly performed using thiol-ene or vinyl chemistries using UV cleavage of a radical initiator.185,194 Cross-linking using 1O2 is an orthogonal approach that is neither photo or radical initiaited, but photocatalytically driven. Mechanistically distinct polymerization techniques have been employed in the preparation of multi-material polymer constructs by wavelength-selective polymerization.195 The rapid curing of our system also enables benchtop photolithography, which may be applicable for the preparation of photopatterned silicone microfluidic devices. The low cost, simplicity, and ease of implementation may make this photooxidative cross-linking applicable to a wide variety of polymeric fields and applications and may be a useful alternative for non-radically initiated cross-linking. 81 Chapter 5: Photo-cross-linked Antimicrobial Amino-Siloxane Elastomers 5.1 Overview Mechanically robust bulk antimicrobial polymers are one way to address disease transmission via contaminated surfaces. In this Chapter the polymeric system from Chapter 4 is further explored, developing a system without any toxic components that can be assessed for its antimicrobial properties. Here I demonstrate the visible light photooxidative cross-linking of amine-containing PDMS using a single-component, solvent-free system where amines have a dual role as antimicrobial functionalities and cross-linking sites. Rose Bengal is thermally reacted with the polymer to give a solvent-free liquid siloxane that can generate reactive singlet oxygen upon aerobic green light irradiation, coupling the amine functionalities into imine cross-links. Photo-rheological experiments demonstrate that light intensity is the largest kinetic factor in the photooxidative curing of these polymers. Room temperature irradiation under ambient atmosphere results in free-standing elastic materials with mechanical properties that depend on the amount of Rose Bengal present. An ultimate elongation strain of 117% and Young’s Modulus of 2.15 MPa were observed for the highest dye loading, with both mechanical properties found to be higher than for the same solution-based dye amounts. The antimicrobial activity was investigated, with the cross-linked material demonstrating greater efficacy against E. coli (Gram negative) compared with MRSA (Gram positive) bacterial strains and inducing complete cell lysis of incubated CHO-K1 mammalian cells, demonstrating applicability as a mechanically robust single-component antimicrobial elastomer. 82 5.2 Research 5.2.1 Results and Discussions Figure 5.1. Singlet oxygen cross-linking of amine-containing polymers resulting in imine cross-links (blue) and free amines (red). 1O2 is generated from atmospheric oxygen quenching the excited triplet state of a photosensitizer. Photo-rheology was used to study the cross-linking kinetics of this system under different compositional conditions. 6-7 wt% (Aminopropylmethylsiloxane) - dimethylsiloxane copolymer (PNH2-7) was combined with octaethylporphyrin (OEP), a porphyrin that can generate 1O2 under irradiation wavelengths compatible with our instrumentation (Figure 5.2a). A limitation of the parallel-plate geometry for studying dynamic cross-linking in this system is the small surface area over which O2 can diffuse into the material (Figure D.1). As such the polymer does not cure fully when inside the rheometer geometry and only the initial linear rate of change in moduli and onset time (G´>>Gʺ) can be determined (Figure D.2). The initial cure rate and onset time were found to depend on light intensity, with a minimum gelation time of 7 s at 150 mW/cm2 (Figure 5.2b). This relationship has been observed with thiol-ene photo-rheology kinetics.196 83 Figure 5.2. Photo-rheological results for the cross-linking of PNH2-7 and OEP using 365 nm light. (a) Scheme showing the structures of PNH2-7 and OEP used in these experiments, resulting in imine cross-links after irradiation in the presence of O2. (b) Onset time and initial cross-linking rate measured using different intensities of irradiation. (c) Effect of cycling irradiation on (yellow areas, 30 mW/cm2) and off (white areas) on G´ and Gʺ during a single experiment. Cross-linking kinetics measured using (d) different concentrations of the porphyrin OEP at 52.5 mW/cm2 light intensity and (e) higher amine wt% polymer and deuterated toluene-d8 at 30 mW/cm2 light intensity. Cycling the UV irradiation on and off during the cure resulted in no increase in G´ during dark periods, consistent with the reaction not being photoinitiated but requiring constant irradiation (Figure 5.2c). The concentration of OEP resulted in only minor changes to the cure kinetics, with slower curing at the high and low concentrations tested (Figure 5.2d). The % 84 transmittance (%T) at 365 nm was calculated for these samples (Table D.1). The %T at 1.0 μM and 0.05 μM is 0.009 and 62.7%, respectively suggesting that at high [OEP] the cure rate is decelerated due to poor light penetration while at low concentrations there is excess light and insufficient 1O2 generation. Substituting a polymer with a higher amine wt% resulted in only small increases to cure rates (Figure 5.2e). 1O2 lifetimes in deuterated solvents are more than ten-fold greater than in their non-deuterated counterparts.197 The use of toluene-d8 did not significantly affect the curing kinetics in this system, suggesting that the diffusion of 1O2 is not a rate-limiting step. These results demonstrate that excitation of the dye is the major limiting kinetic factor under these conditions. To maximize cure rates, a material was developed that could cure using safer green light as opposed to high intensity benchtop UV irradiation, and that is free of soluble initiators or monomers. Xanthene dyes have been extensively studied for use in photodynamic therapy due to their high molar absorptivity and singlet oxygen quantum yields.198,199 The non-cyclized free acid tautomer is primarily responsible for the strong absorbance in the visible region (Scheme D.3).200–202 Condensation reactions between primary amines and the 2' position on xanthene-based dyes resulting in an amide functionality are a simple method for fluorescent labelling of amine substrates.203–207 In our experiments, PNH2-7 was reacted with xanthene dyes to prepare solvent-free liquid silicones capable of generating 1O2 on irradiation (Scheme D.4). Fluorescein was used to examine the covalent attachment of the dye to the polymer, reacting 10 molar equivalents with PNH2-7 to produce a clear red oil, free from precipitate, after drying under vacuum (DPF). The solubility of this material in organic solvents was greatly reduced compared to PNH2-7, consistent with self-association of pendant aromatic groups.208 The FT-IR spectrum 85 of DPF shows a decrease in carbonyl stretching frequency from 1589 cm-1 to 1580 cm-1, consistent with the change from carboxylic acid to amide functionality in xanthene molecules (Figure D.5).209 1H NMR spectroscopy shows a new quartet at 3.72 ppm that is attributed to the CH2 directly attached to the amide functionality (Figure D.6). This reaction performed using 10 molar equivalents of Rose Bengal (RB) produced a completely insoluble material after removal of the solvent, attributed to either rapid photo-oxidative cross-linking under ambient light conditions or strong halide-halide interactions. Figure 5.3. Condensation reaction between PNH2-7 and different molar equivalents of RB resulting in solvent-free liquid polymers after drying under vacuum. RB has a 1O2 quantum yield of approximately 0.5 - 0.7, and the absorbance spectrum overlaps well with commercially available green LEDs (Figure D.8).75 RB at three different molar equivalents was reacted with PNH2-7 to produce solvent-free purple oils, denoted DP1, DP2, and DP3 (Figure 5.3). The low concentration of dye in these samples makes quantification of the extent of RB amide formation unfeasible, necessitating a reliance on the model systems with over 500 times the concentration of fluorescein present. However, no precipitation or phase separation was observed when DP1 was stored in the dark for over five weeks (Figure D.9). The 86 UV-Vis spectrum of DP1 in solution shows a similar molar extinction coefficient compared with free RB (Figure D.10), and DP1 in solution and as a neat film shows no major changes in spectral shape (Figure D.11). The transmittance at 530 nm for these samples was calculated and determined to be suitable for samples of 1 mm thickness (Figure D.12, D13). The emission spectrum of non-cross-linked DP1 shows visible region emission (575 nm) characteristic of Rose Bengal as well as IR emission centered at 1270 nm attributed to singlet oxygen phosphorescence (Figure 5.4). A sample of DP1 in water after one week showed no leaching of the dye into solution, supporting the attachment of the dye to the polymer and resulting hydrophobicity (Figure D.14). Figure 5.4. The normalized absorbance spectrum, visible region and IR region emission of a thin film of non-cross-linked DP1. IR emission at 1270 nm is a result of 1O2 phosphorescence. 87 Irradiation of a neat film of DP1 exposed to air at 530 nm resulted in a solid material after 10 minutes. Irradiation of a degassed sample in a N2 environment does not result in cross-linking, confirming the oxygen requirement. The FT-IR spectrum of cross-linked DP1 shows only a single new peak at 1671 cm-1 compared with the starting polymer, attributed to the C=N imine peak (Figure D.15).210,181 This result is consistent with our previous findings using a solution of platinum octaethylporphyrin as a photocatalyst.3 13C CP-MAS NMR of cross-linked DP1 shows a peak centered at 165 ppm consistent with the presence of imine sp2 carbons (Figure D.16).182 Figure 5.5. The vibrational spectra of a piece of DP1 after soaking in THF, soaking in 25 wt % ethyl acetoacetate in THF, and the spectrum of pure ethyl acetoacetate. The water contact angle of a cross-linked sample of DP1 was found to be 85° ± 2° and 94° ± 2° for deionized water and 1M NaOH, respectively, decreasing to 74° ± 3° for 1M HCl due to enhanced wetting of the surface as a result of amine/imine protonation (Figure D.17). A 88 sample of DP1 soaked in ethyl acetoacetate overnight followed by extensive rinsing has new vibrational peaks at 1609 cm-1 and 1659 cm-1 attributed to formation of the enamine condensation product, demonstrating that NH2 functionalities in the polymer are present and remain reactive (Figure 5.5).141 Materials for mechanical testing were prepared by irradiation for 18 h in molds using 530 nm LED lights to ensure complete photo-oxidative cross-linking. Samples thicker than 1 mm were not explored due to low optical transmittance possibly leading to heterogenous samples (Table D.2). The resulting samples were transparent off-white to pale yellow in color, measuring 1 mm thick and 30 mm in diameter (Figure D.18). Strips of these samples were cut and their mechanical properties were evaluated using a dynamic mechanical analyser (DMA, RSA G2 TA Instruments) in axial mode, averaging the results from three measurements (Figure 5.6, Table 5.1). DP1 was compared with a sample prepared at the same molar equivalency of RB but with the dye added as a solution of 1,2-propanediol and EtOH (DP1-soln). Both samples exhibited similar Young’s modulus of elasticity (initial slope of the stress-strain curve) but the ultimate elongational strain of DP1 was approximately three times greater than that observed for DP1-soln (58% versus 18%). Similarly, the tensile strength (maximum stress before failure) of DP1 was approximately 30% greater than that for DP1-soln (0.22 MPa versus 0.17 MPa). This is attributed to the evaporation of the solvent in DP1-soln during cross-linking causing precipitation of the dye, preventing further 1O2 generation. Owing to the low Tg of cross-linked PDMS, the amorphous liquid-like state of individual DP1 chains after cross-linking is proposed to allow for 1O2 generation after solidification, leading to a greater extent of cross-linking. 89 Figure 5.6. (a) Representative stress-strain curves obtained from tensile experiments for materials cross-linked using RB dissolved in solution and solvent-free RB attached to the polymer. (b) Image of a disk of sample DP3, 1 mm thick and 30 mm diameter. Sample Molar Equiv RB Young’s Modulus (MPa) Tensile Strength (MPa) Ultimate Elongation (%) DP1-soln 0.016 1.13 ± 0.01 0.17 ± 0.05 18 ± 1 DP1 0.016 1.11 ± 0.01 0.22 ± 0.01 58 ± 3 DP2 0.032 2.00 ± 0.09 0.39 ± 0.02 81 ± 4 DP3 0.048 2.15 ± 0.08 0.55 ± 0.04 117 ± 8 Table 5.1. Mechanical properties of samples prepared with different amounts of RB attached to PNH2-7 and a sample (DP1-soln) prepared using a RB containing solution. The properties were measured using DMA tensile experiments. 90 The mechanical properties of DP2 and DP3 were also measured and compared with DP1 (Figure 5.6, Table 5.1). DP2 and DP3 have similar Young’s moduli of 2 and 2.15 MPa, respectively, significantly greater (nearly double) than the value of 1.1 MPa for DP1. The ultimate elongation of the samples increases along with increasing RB content from 58% to 117% for DP1 to DP3. These mechanical properties are comparable with our previous results as well as with those for PDMS samples cross-linked using photo-acrylate UV chemistry.185,211 The soluble fraction was found to be 22% for DP1, decreasing to 4% for DP2 and DP3 consistent with a greater cross-linking extent (Table D.3). All samples were found to be completely insoluble in water. TGA analysis of DP1 shows less than 5% mass loss below 400 °C, a large improvement over PNH2-7 which is thermally unstable above 120 °C (Figure D.19). The lack of mass loss below 200 °C supports the absence of solvent in the cross-linked material. All samples showed a similar glass transition temperature of -115 °C as measured using differential scanning calorimetry, consistent with other cross-linked siloxanes (Figure D.20).141 The solvent-free single component nature of our material allows it to be worked with in ways not possible with a solvated siloxane. Samples cooled to -78 °C using a dry ice/acetone bath resulted in a low viscosity that prevents macroscopic flow, while solvated samples did not gel. This allows for the formation of non-equilibrium shapes by depositing DP1 into a vessel cooled to -78 °C, where the oil rapidly solidifies in place and can then be photo-cross-linked into non-equilibrium shapes while warming to room temperature (Figure D.21-D.23). Photolithography using masks printed onto plastic transparencies was also performed, demonstrating the efficacy of this cross-linking procedure for photo-patterning (Figure D.24). I also explored the direct-write printing of DP3 onto glass to create sub-millimeter features with more precision than 91 benchtop photomasks allow for (Figure D.27). Exposure of the printed material to 530 nm light immediately after printing fixed the shape and prevented pooling, but the lack of inherent microstructure or shear-thinning behaviour makes it unsuitable for the printing of larger free-standing objects. Despite the relatively fast gelation (G´>Gʺ) for PNH2-7 and OEP attempts to print the material using a DLP 3D printer resulted in no cross-linking, proposed to be a result of poor O2 diffusion analogous to the results seen in parallel plate rheology. In our system, the PNH2-7 and RB starting reagents are non-toxic chemicals approved for consumer and medical use, respectively.188,212–214 As a cross-linked material, the amine/imine functionalities can be protonated in aqueous environments and induce contact killing of microbial species. The antimicrobial mechanism of solubilized and immobilized quaternary-ammonium species is proposed to proceed through electrostatic attraction, interdigitation or stripping of the cell membrane, and then leakage of the intracellular fluid leading to cell lysis (Figure D.28).100,102 The antimicrobial activity of cross-linked DP3, the sample with the most robust mechanical properties, was probed using the CHO-K1 mammalian cell line as well as E. coli (Gram negative) and methicillin-resistant Staphylococcus aureus (MRSA) to investigate its activity as a broad-spectrum antimicrobial material. Cross-linked DP3 was ground to a uniform powder and incubated with the two bacterial strains for 24 h under constant shaking to dynamically reintroduce fresh bacteria to the material surface. Aliquots were taken and diluted, and the resulting colony forming units (CFUs) measured after 24 h of growth on sterile agar plates. The results were compared against controls with no polymer. An 85% reduction in CFUs of E. coli was observed at the concentrations 92 tested, with a 29% reduction in CFUs for MRSA under the same conditions (Figure 5.7). Previously reported QAC materials such as polyallylamine exhibit greater antimicrobial activity against Gram positive bacteria than Gram negative, opposite to what is observed in our system.101,215 A 61% reduction in CFU’s for E. coli was determined for a continuous piece of cross-linked DP3 at the same mass loading as in Figure 6, demonstrating that the antimicrobial activity is inherent to the material and depends on exposed surface area (Figure D.29). Solutions challenged with twice the mass of DP3 powder resulted in a > 99% reduction in CFUs for E. coli. Figure 5.7. Normalized CFUs for E. coli and MRSA incubated with cross-linked DP3 powder for 24 h under constant shaking, compared with controls with no polymer. Determined from colony counts grown on agar plates in triplicate. 93 Figure 5.8. Microscope images of CHO-K1 cells incubated for 72 hours with cell medium and (a) no additive (b) PDMS 50,000 g/mol (c) 6 μm α-Amanitin (d) cross-linked DP3. α-Amanitin results in cell death without lysis while P3 lyses all cells. CHO-K1 cells were incubated at room temperature for 72 h in a 96 well plate coated with cross-linked DP3 along with non-functionalized PDMS (50,000 g/mol) and α-amanitin, a naturally occurring toxin that results in cell death, as controls.216,217 The temperature requirement for autoclaving prevented the use of PNH2-7 as a control. The samples were then imaged using a microscope (Figure 5.8). DP3 was observed to result in complete cell lysis, with no visible intact cells in any well containing the material. Non-functionalized PDMS, the blank, and α-amanitin did not result in complete cell lysis. This shows that the amine and imine cross-links in our material possess broad-spectrum antimicrobial activity, acting on both primarily anionic bacterial membranes and zwitterionic mammalian membranes, with only weak activity against Gram positive bacteria.218 This may be a result of the high contrast in polarity between the hydrophobic polymer backbone and polar amine/ammonium functionalities, in comparison with QACs such as alkylated PEI that is uniformly hydrophilic. 94 5.2.2 Experimental (6-7% Aminopropylmethylsiloxane) – dimethylsiloxane copolymer (AMS-163), (20-25% aminopropylmethylsiloxane) – dimethylsiloxane copolymer (AMS-1203) were purchased from Gelest. Rose Bengal lactone (95%) and fluorescein (95%) were purchased from Sigma Aldrich. Porphyrins were purchased from Frontier Scientific. All other reagents were purchased from Sigma Aldrich and used without further purification. Absorption spectra were collected on a Varian Cary 5000 UV-Vis-NIR spectrophotometer. 1H NMR spectroscopic data were collected on a 400 MHz Bruker Avance 400dir spectrometer at 25 °C. Residual proto-solvent peaks were used to reference the 1H NMR spectra. 13C CP-MAS NMR spectra with high power proton decoupling were collected on a 400 MHz Bruker solid state DRX spectrometer using a sample of DP1 dried under vacuum for one week. Samples were spun at 4 kHz at the magic angle. Ramped pulses at 50% on the 13C frequency were used for cross polarization with a contact time of 5 ms for all experiments. The relaxation delay was set to be 5 s, and acquisition time 50 ms. Data were processed with a 20 Hz line broadening exponential decay function. Chemical shift values (ppm) were referenced with the adamantane 13CH2 signal at 29.5 ppm. All experiments were done at room temperature. Infrared spectra were collected on a PerkinElmer Frontier FT-IR with a diamond ATR plate. Thermogravimetric analysis was performed on Netzch TG209 Libra using an Al2O3 crucible at a temperature ramp of 10 °C / min under a N2 purge flow of 30 mL / min. Differential 95 scanning calorimetry (DSC) measurements were performed using a Netzsch Polyma 214 instrument with LN2 attachment at a ramp rate of 10 °C / min. Direct write printing was performed on a printer assembled from a Fab@Home V1 from Cornell University, translating in the x, y, and z directions at 25 μm resolution. Material was loaded into a syringe barrel and extruded through a metal nozzle using 35 psi nitrogen pressure.219 Mechanical testing was carried out on a Dynamic Mechanical Analyser (DMA, RSA G2 TA Instruments) in axial mode. Samples were cut into strips with dimensions 4 mm × 3 mm × 1 mm (length-width-thickness). Sample strips were extended/elongated until breakage at room temperature by applying constant linear strain rate of 0.1 mm/min. The linear elongational strain was calculated by: 𝜖 =𝐿 − 𝐿0𝐿0× 100 Where L0 is the initial length of the sample (t=0) and L is the length of the sample at time t. The Young’s modulus of elasticity was determined from the equation 𝜎 = 𝐸𝜀 ( is the tensile stress), which is valid only for the initial elastic response of the material. The tensile strength represents the maximum stress in the stress-strain curve and the ultimate elongation, u shows how much the material can elongate before fracture/failure. The latter was calculated by using the following equation: 𝜀𝑢 =𝐿𝑓 − 𝐿0𝐿0× 100 Where Lf is the final length of the sample before failure. 96 Photo-rheological experiments were performed on a TA Instruments Discovery HR-2 using an 8 mm plate and UV curing stage equipped with 365 nm LEDs. All samples were measured at 2% strain, 10 rad/s, using a 500 μm gap, and irradiating after a 60 s dwell time. A standard sample (Figure 2b, 2c) was prepared by first dissolving OEP in toluene at a concentration of 1 mg/mL, and then combining this in a 1:1 mass ratio with PNH2-7 using a vortexer to give a final [OEP] of 1.0 mM. Cells were purchased from ATCC and incubated in Eagle Minimum Essential Medium in Falcon BD T-25 vented flasks. Cell viability experiments were performed using 96-well flat bottom plates (Becton Dickinson). Cell monolayers were re-suspended in a fresh culture medium at an approximate density of 1 × 105 cells / mL. 100 μL was added to each well plate. All polymer samples were autoclaved before use and prepared in triplicate. P1 was added to three wells and irradiated overnight for 18 h using 530 nm LEDs. Poly(dimethylsiloxane) (50,000 g/mol) and 6 μm α-Amanitin (100 μL) were added to separate wells and then cells were loaded. The well plate was allowed to incubate for 72 h. Wells were then imaged using an Olympus IX70 microscope with an Olympus DP80 Camera. Methicillin resistant Staphylococcus aureus strain (UBC Chemistry Department Collection #1057) and Escherichia coli (UBC Chemistry Department Collection #1105) were grown overnight at 37 °C, 225 rpm in sterile Mueller-Hinton broth. The bacterial concentration in the broth was determined by absorbance at 600 nm by Cary100 spectrophotometer. The cultures were diluted in sterile distilled water to obtain a concentration of 105 bacteria/mL and 97 aliquots of bacterial suspension (10 mL) were transferred to sterile 50 mL Falcon tubes each containing 168 mg of tested material. After overnight incubation at 37 °C, 225 rpm, the suspensions were diluted 10-fold and (20 μL per plate for E. coli and 10 μL per plate for MRSA) plated onto Mueller-Hinton agar plates. The plates were incubated at 37 °C overnight. The number of visible colonies on each plate was calculated to obtain the corresponding concentration of living bacteria. Each experiment was performed in triplicate, and the reported results are averaged values. 5.2.3 Synthesis and Preparation DPF. Fluorescein (0.02 g, 0.06 mmol), PNH2-7 (0.3 g, 0.006 mmol) and 1.5 mL ethanol were added to a round bottom flask equipped with a condenser and magnetic stir bar. The system was stirred at 80 °C for four hours and then allowed to cool to room temperature. Ethanol was distilled using a rotary evaporator, and then the product dried under high vacuum overnight. Sample DP1. A stock solution of Rose Bengal in EtOH was prepared by dissolving 2.0 mg RB in 6.3 mL EtOH (3.2 × 10-4 M). 1.0 g of PNH2-7 was combined with 1.0 mL of stock solution in a round bottom flask and equipped with a condenser and magnetic stir bar. The system was stirred at 80 °C for 18 h under N2 and then allowed to cool to room temperature. EtOH was distilled using a rotovap, and then the product dried under high vacuum overnight. Sample DP2, DP3. Samples were prepared in the same manner as DP1 but altering the concentration of the RB stock solution (6.5×10-4 M and 9.8×10-4 M for DP2 and DP3 98 respectively). 1.0 g of PNH2-7 was combined with 1.0 mL of the stock solutions and the reaction carried out as described above. Cross-linking. The polymer oils (DP1, DP2, and DP3) were pipetted into commercially available 3 cm diameter circular silicone molds. The molds were irradiated using a Westinghouse 15 W green LED flood lamp (100 W equivalent) at a distance of 10 cm on the benchtop open to the air. Samples prepared for mechanical testing were irradiated continuously for 18 h. During irradiation samples were not noticeably warm to the touch at any point. DP1-Soln. Rose Bengal was dissolved in an equal mass solution of ethanol and 1,2-propanediol to give a final concentration of 2.08×10-3 M. For 1.0 g of PNH2-7, 157 μL of RB solution was added to the polymer in a vial, mixed using a vortex mixer, and irradiation carried out using the same procedure as for other samples. Sample cross-linked using PtOEP. A fresh PtOEP stock solution was prepared by dissolving platinum(II) octaethylporphyrin in m-xylenes to give a concentration of 4.12×10-4 M. For 1.0 g of PNH2-7, 1.58 mL of PtOEP solution was added to the polymer in a vial and mixed using a vortex mixer. The resulting solution was transferred to a mold and irradiation carried out using the same procedure as for other samples. Photolithography. For photolithography, 100-200 μL of DP1 solution was pipetted onto a glass slide and allowed to spread into a thin layer. Two glass slides on either side were used to support a printed transparency sheet that was patterned with the desired mask. Irradiation was 99 carried out using the same setup as for thick samples. After one hour of irradiation the sample was rinsed by gentle irrigation with ethyl acetate using a pipette and then allowed to air dry. Photobleaching was performed by irradiating the sample using 530 nm light overnight in the same setup as for bulk cross-linking. -78 °C deposition. For depositing then subsequent cross-linking of the material at low temperatures (to retain deposited shape), a setup was utilized to expose the material to -78 °C while limiting atmospheric condensation. A Schlenk drying tube was equipped with a compressed air line, passing the air intake through a drying tube packed with Drierite, and the air outtake through a silicone oil bubbler (Figure D.22). This setup excludes moisture while providing a constant supply of O2. The assembled apparatus was lowered into a bath of dry ice and acetone until the bottom was covered and then allowed to cool for 10 min. The top was removed and non-cross-linked P1 pipetted into the desired shape. The system was closed and a 530 nm lamp bulb was used to illuminate the sample. The system was allowed to warm to room temperature over 18 h under constant irradiation. The drying tube was then opened and the resulting shape removed using tweezers as a single, free-standing object. 100 5.3 Conclusions The preparation of a solvent-free liquid material capable of undergoing self-catalyzed photo-cross-linking by combining Rose Bengal with primary amine containing PDMS is demonstrated. Irradiation of this material under ambient conditions at 530 nm results in cross-linking via photooxidative 1O2 imine coupling without the need for solvent. I investigated the cross-linking kinetics of a model system using photo-rheological experiments and determined that light intensity is the largest contributor to cure speeds. The mechanical properties of this material significantly improved over those of samples prepared using the same concentration of dye in solution. Furthermore, the ultimate elongation can be increased two-fold by increasing the amount of dye attached to the polymer. The antimicrobial activity of this material is greater against E. coli compared with MRSA, and exhibits complete cell lysis of model mammalian cells. The simplicity and low cost of our single component system make it an attractive method for the preparation of self-sterilizing silicone devices. 101 Chapter 6: Photodynamic and Contact Killing Polymeric Fabric Coating for Bacteria and SARS-CoV-2 6.1 Overview Continuing with the antimicrobial system explored in Chapter 5, the application of this material towards the preparation of antimicrobial textiles was explored, as well as investigating methods to broaden the scope of the antimicrobial activity of the material. The development of low cost, non-toxic, scalable antimicrobial textiles are needed to address the spread of deadly pathogens. Here, I report a polysiloxane textile coating that possesses two modes of antimicrobial inactivation, passive contact inactivation through amine/imine functionalities and active photodynamic inactivation through the generation of reactive oxygen species (ROS). This material can be coated and cross-linked onto natural and synthetic textiles through a simple soak procedure followed by UV cure to give materials exhibiting no aqueous leaching and only minimal leaching in organic solvents. This coating minimally impacts the fabric’s mechanical properties while also imparting hydrophobicity. Passive inactivation of Escherichia coli (E. coli) and methicillin resistant Staphylococcus aureus (MRSA) is achieved with >98% inactivation after 24 hours, with a 23× and 3× inactivation rate increase against E. coli and MRSA respectively when green light is used to generate ROS. Up to a 10× decrease in infectivity of SARS-CoV-2 after two hours of irradiated incubation with the material is demonstrated. These results show that modifying textiles with dual functional polymers results in robust and highly antimicrobial materials, which are expected to find widespread use in combating the spread of deadly pathogens. 102 6.2 Research 6.2.1 Results and Discussions To modify textile samples, fabrics were treated by a room temperature soak in a solution containing the dissolved polymer and cross-linking photosensitizer, followed by 405 nm irradiation to fix the polymer onto the fabric through 1O2 cross-linking. This procedure omits any harsh chemical reagents or high temperatures that might damage the textile integrity. The antimicrobial polymer (DP3) is the same polymer used in Chapter 5, and was prepared by condensing (7 wt% aminopropylmethylsiloxane)-dimethylsiloxane copolymer (PNH2-7) with 0.048 molar equivalents of Rose Bengal lactone (RB) (Figure E.1). Both components used in this work have been assessed as non-toxic and safe for human-use.188,212 It was previously demonstrated that this system can be photo-cross-linked from a liquid to an elastomeric solid via 1O2 oxidation of the primary amine functionalities into imine cross-links.3 However, this process photo-bleaches the RB leaving it unavailable for further 1O2 production. To overcome this limitation, tetraphenylporphyrin (TPP) is used as a sacrificial 1O2 source (Figure E.2). In a thin film experiment TPP was selectively photo-bleached over RB using 405 nm irradiation followed by bleaching of RB using 530 nm light (39 and 8 mW/cm2 at 4 cm, respectively), demonstrating orthogonal excitation of one dye molecule over the other using narrow light sources (Figure E.3). 103 Figure 6.1. (a) Scheme of textile treatment using a solution soak followed by UV irradiation resulting in imine cross-links from TPP derived 1O2. (b) Polymer mass loading and unloading for cotton treated with different wt% polymer solutions. (c) Representative stress-strain curves determined from Instron mechanical testing of cotton and polyester strips treated using EP1, EP5, and EP13 solutions. (d) Cotton fabric before (top) and after (bottom) treatment with EP13 to give EC/P13. DP3 and TPP were combined using toluene and diluted with tetrahydrofuran (THF) to afford solutions of 1%, 5%, and 13% polymer weight %, denoted EP1, EP5, and EP13, respectively. Cotton fabric was soaked in these solutions for ten minutes followed by 30 minutes of 405 nm irradiation per side open to air to afford samples EC/P1, EC/P5, and EC/P13 (Figure 104 6.1a). A sample of C/P13 soaked in THF prior to irradiation gave a relative molar ratio of RBL : TPP of 3.3 : 1, closely matching the initial solution composition. The mass of polymer on the fabric increased linearly with the polymer solution wt %, to a maximum of 0.24 grams DP3 per gram of fabric for EP13 (Figure 6.1b). The change in mass of the treated fabric after soaking in THF was used to determine the extent of polymer cross-linking and attachment to the fibers. At low mass loadings (EP1), and for samples that were not exposed to 405 nm light, > 99% of the loaded polymer was soluble in THF, indicating an unsuitable degree of cross-linking (Figure 6.1b). The percentage of soluble material decreased to 13% and 7% respectively for EC/P5 and EC/P13, demonstrating a greater cross-linking extent. EC/P13 soaked in water or an aqueous solution of laundry detergent overnight showed no mass change after drying and no coloration of the supernatant. Scanning electron microscopy (SEM) images of EC/P13 show a reduction in surface roughness while still retaining distinct fibers (Figure E.4). All coated samples became hydrophobic after treatment with the maximum contact angle of EC/P13 being 147 ± 1° (Figure E.5). The same procedure for EP13 was used to treat other natural and synthetic fibers including linen, polyester, denim, silk, and paper, highlighting that only covalent bonds between the polymer chains are formed and that the chemical composition of the textile is not altered or relevant for the coating procedure (Figure E.6). Mass loadings varied from 0.12 (denim) to 0.23 (paper) grams of polymer per gram of material, attributed to differences in material morphology and porosity (Figure E.7). All coated materials were hydrophobic after treatment, with water contact angles ranging from 131 ± 2° (silk) to 142 ± 3° (polyester) (Figure E.7). The impact of polymer coating on the mechanical properties of the fabrics was tested for cotton and polyester, the most elastic textiles used in our work. Strips were cut to a uniform size 105 and coated using EP1, EP5, or EP13. Their elongation at break and break stress were determined using an Instron system in tensile mode (Figure 6.1c). An 18% decrease in elongation at break (128 ± 3% to 105 ± 7%) and a 13% decrease in break stress (102 ± 2 kPa to 87 ± 5 kPa) were observed for the highest polymer loading on cotton (EP13), with only 1% decreases in both values for polyester treated with the same solution (Figure E.8, Table E.1). Cross-linked DP3 by itself has an elongation at break of 117 ± 8% and a break stress of 550 kPa. The retention of mechanical properties is attributed to the mild nature of the treatment process and inherent flexibility of the siloxane polymer. Thermogravimetric analysis of EC/P13 compared with untreated cotton showed an increase in the onset temperature (To) of 14 °C from 304 °C to 320 °C, respectively (Figure E.9). The thermal degradation of polyester before and after treatment showed little difference, with a To of 397 °C for both samples. To of photo-cross-linked DP3 is 423 °C. FT-IR spectroscopy was used to characterize the treated samples. EP13 shows new vibrational peaks at 1258 cm-1 and 793 cm-1 that correspond with the PNH2-7 siloxane backbone, confirming the presence of the polymer (Figure E.10).220 All other tested materials coated with EP13 show the same vibrational peaks, with no samples showing vibrations unattributable to PNH2-7 or the textile itself (Figure E.11). White cotton becomes pink after treatment owing to the RB present in the system (Figure 6.1d). The appearance of black colored cotton treated with the sample procedure does not change to the eye (Figure E.12). 106 Figure 6.2. (a) Reflectance and emission spectra of EC/P13. (b) Near-IR emission and excitation spectra of a thin film of cross-linked DP3 and treated EC/P13. 1O2 phosphorescence at 1270 nm is observed for both materials as a result of RBL excitation at 525 nm. The transmittance spectrum of EC/P13 shows two peaks at 525 and 415 nm attributed to the absorbance of RB and TPP, respectively (Figure 6.2a, E.2). Excitation at these wavelengths results in emission spectra characteristic of RB and TPP, revealing that TPP is not fully photo-bleached during the UV cross-linking procedure and that both chromophores remain emissive in the treated textiles (Figure 6.2a). 1O2 exhibits diagnostic phosphorescence centered at 1270 nm.221 The near-IR emission spectra of a thin film of cross-linked DP3 and treated EC/P13 were collected and both exhibit emission at 1270 nm when excited at 525 nm, demonstrating the capability of 1O2 generation from the treated textiles (Figure 6.2b) 107 To further assess the 1O2 generating capabilities of our treated textiles, I monitored the oxidative degradation of uric acid using UV-VIS spectroscopy.122 1O2 decomposes uric acid beginning with a conversion to parabanic acid, resulting in a decrease in the absorbance at 292 nm.222 A static cuvette containing EC/P13 and the aqueous uric acid solution was irradiated using 530 nm light and the change in absorbance measured as a function of irradiation time (Figure E.13). A 55% decreases in the absorbance at 292 nm was observed after 130 minutes of irradiation (Figure E.14). A control sample of EC/P13 prepared without RB showed no decrease in absorbance on irradiation while a sample with twice the RB molar equivalence had an 81% decrease in absorbance after 130 minutes. No absorbance above 375 nm was observed during these experiments, indicating that RB was not released into solution and remained attached to the fabric. These results confirm that 1O2 can be generated from our treated fabric in sufficient quantities to oxidize dissolved or suspended molecules. While RB has high selectivity for producing 1O2 over other reactive oxygen species (Type II), diffusion distances of 1O2 are on the order of tens of nanometers.223,224 The efficacy of substrate oxidation for the bound RB may indicate the formation of subsequent reactive species such as peroxides or hydroxyl radicals resulting from quenching of 1O2 that possess greater diffusion distances. We have previously demonstrated that 1O2 cross-linked PNH2-7 induces cell lysis in mammalian cells as well as increased antimicrobial efficacy versus E. coli compared to MRSA.4 Initially for the study of our treated textiles, the antimicrobial activity versus E. coli and MRSA bacterial strains in the dark was investigated, examining only the passive contact antimicrobial activity. Coated fabric samples of EC/P13 were cut to different sizes and challenged with 10 mL of a fixed concentration (105 bacteria/mL) suspension of bacteria under dynamic shaking 108 conditions overnight at 37 °C, followed by dilution and plating onto agar to compare the number of colony forming units (CFUs) against a control with no added fabric (Figure 6.3a). Incubation using a large bacterial volume (10 mL) was chosen over droplet-based measurements (µL) to allow for comparison of different sample masses as well as consistency across the passive and active antibacterial and antiviral testing. However, this experimental setup is expected to reduce microbial contact time and therefore reported efficacy relative to droplet-based techniques which encourage microbe-surface interactions and more closely mimic real-world conditions. A 31 ± 8% decrease in E. coli CFUs was observed for a 4 cm2 sample, increasing to 99 ± 2% decrease for 18 cm2. Owing to the heterogeneous nature of our samples and dynamic agitation during incubation, a larger surface area is expected to increase the frequency of polymer-bacteria contact and result in the greater decrease in CFUs. To confirm that this antibacterial activity is a result of the primary amine groups, (23 wt% aminopropylmethylsiloxane)-dimethylsiloxane copolymer (PNH2-23) was prepared in an identical fashion to PNH2-7 and coated onto cotton (Table E.2). A 4 cm2 sample of this material resulted in a 98 ± 3% reduction in CFUs, a 3 times greater activity than for PNH2-7. No inhibition was observed for a 1 cm2 sample of this material. Samples challenged with MRSA under the same conditions resulted in >99 ± 1% reduction in CFUs for 18 cm2 samples for PNH2-7. At lower fabric loadings there was decreased effectiveness against MRSA compared with E. coli for both polymer types, with the higher amine content polymer resulting in greater inactivation compared with the lower amine content polymer (Table E.3). These experiments demonstrate the passive antimicrobial activity of our treated textiles, and suggest that the antimicrobial activity is directly related to the weight % of amine functionality in the polymer. 109 Figure 6.3. (a) Passive reduction in E. coli and MRSA CFUs after 24 hours of 37 °C incubation in the dark with different size samples of EC/P13, prepared using PNH2-7 or PNH2-23 under identical conditions (relative to no fabric control). (b) aPDI activity of EC/P13 prepared using PNH2-7 (9 cm2) measured in the dark and under constant 530 nm irradiation at room temperature, assessed using the relative number of E. coli and MRSA CFUs after aliquots were drawn at set time intervals. CFUs were measured using colony counts on agar after 24 hours growth time, experiments performed in triplicate. Antimicrobial experiments performed in the dark can interrogate selectively the passive contact killing effect of the amine groups, but aPDI from the photo-generated 1O2 cannot be isolated from the passive effect. Time-dependant experiments were run in tandem for EC/P13, irradiating one set of samples with 530 nm light (passive and active affects) while others remained in the dark (passive only). Incubation was carried out at room temperature, with other conditions the same as for the dark-only experiments. Aliquots were drawn and diluted, and the relative number of CFUs at a given time were compared between the light and dark samples (Figure 6.3b). No difference in CFUs was observed between dark and light samples in the 110 absence of EC/P13. After 30 minutes there were 85 ± 9% (dark) and 3.0 ± 0.6% (light) CFUs remaining relative to t = 0 for E. coli and 95 ± 3% (dark) and 35 ± 3% (light) for MRSA. This 28× and 3× increase in disinfection rate for E. coli and MRSA, respectively, demonstrates EC/P13 has strong aPDI activity with a greater rate than the passive amine contact killing. No CFUs were observed for either of the irradiated samples at t = 240 min A faster rate of 1O2 inactivation of E. coli over MRSA is consistent with reported sensitivities arising from differences in cell wall composition and antioxidant content.225 Figure 6.4. (a) Schematic of experimental design to evaluate antiviral properties of EC/P13 against SARS-CoV-2. SARS-CoV-2 stock diluted in media was incubated with fabric samples in dark or light (530 nm irradiation) conditions for two hours at room temperature. The treated virus dilutions were used to (i) infect Huh-7.5.1 cells and the resulting infectivity was measured by staining for intracellular virus nucleocapsid levels after 48 hours of infection; (ii) the treated virus was also added to Vero E6 cells for measuring plaque forming units (PFU) using plaque assay. Experiments were performed in triplicate. (b) Relative intracellular 111 viral nucleocapsid levels of SARS-CoV-2 dilutions following incubation with fabric and infection of Huh-7.5.1 cells. (c) SARS-CoV-2 viral load following incubation of 1.5×104 PFU/mL with fabric under light and dark conditions. Circles represent individual replicates, bars are 95% CI. One way ANOVA with Tukey multiple comparisons correction presented; * p=0.0137, **** p<0.0001. Representative viral plaques of (d) dark sample and (e) 530 nm irradiated sample. aPDI materials which are effective against bacteria have also been demonstrated to be effective at inactivating enveloped and non-enveloped viruses.124 Recently, Ghiladi and coworkers demonstrated the use of metalloporhyrins and Rose Bengal encapsulated in photo-cross-linked polymers for the inactivation of human coronaviruses on textiles.226 To investigate the antiviral properties of our treated material, activity of EC/P13 was tested against SARS-CoV-2 in a manner analogous to the aPDI bacterial experiments. Dilutions of SARS-CoV-2 were incubated with treated fabric samples or without fabric in the dark or under constant 530 nm light for 2 hours (Figure 6.4a). To assess viral infectivity, a susceptible liver cell line (Huh-7.5.1) was infected with fabric-treated SARS-CoV-2 dilutions and then the intracellular viral nucleocapsid levels (a marker of viral infection) were quantified as previously described.227 No inactivation was observed for SARS-CoV-2 samples treated in the dark compared with controls bearing no fabric, demonstrating that the passive surface effect of our material is not effective against SARS-CoV-2. In contrast, ~20%, ~80% and complete reduction in SARS-CoV-2 nucleocapsid was observed following infection with 105, 104 and 103 PFU/mL (plaque forming units), respectively, in light versus dark treated conditions (Figure 6.4b). Infectivity was also assessed using standard plaque assay by quantification of PFUs in infected Vero E6 cells (Figure 6.4). Again, under dark conditions, there was no impact of the fabric on viral plaques compared to untreated virus. Following incubation of 1.5×104 PFU/mL SARS-CoV-2 with fabric under 530 112 nM light for 2 hours, a 10× reduction in mean viral load was observed compared to treatment in the dark (3.45 × 102 PFU/mL versus 3.94 × 103 PFU/mL, respectively) and a ~ 65% reduction in viral load was compared to virus incubated in the light without fabric (3.45 × 102 PFU/mL versus 9.8 × 102 PFU/mL). An apparent reduction in plaque size under these conditions was also observed (Figure 6.4d vs. Figure 6.4e). These results confirm the antiviral properties of 1O2 generated by our aPDI material. Previous studies have reported the effect of 1O2 on enveloped virus particles, which likely impedes viral entry and fusion through modification of the viral membrane lipid and glycoprotein components.228–231 The predicted effect is consistent with our observed reduction in SARS-CoV-2 infectivity of Huh-7.5.1 cells, reduction in viral plaque counts on Vero E6 cells and reduced plaque size following incubation of the virus with aPDI. 113 6.2.2 Experimental (6-7% Aminopropylmethylsiloxane) – dimethylsiloxane copolymer (AMS-163) and (20-25% aminopropylmethylsiloxane) – dimethylsiloxane copolymer (AMS-1203) were purchased from Gelest. Rose Bengal lactone (95%) was purchased from Sigma Aldrich. Tetraphenylporphyrin was purchased from Frontier Scientific. A 36 W UV-LED Blacklight and 15 W green LED bulb were measured to have light intensities of 39 and 8 mW/cm2 from a distance of 4 cm. Absorption spectra were collected on a Varian Cary 5000 UV-Vis-NIR spectrophotometer using a quartz cuvette (solution) or glass slide (solid state). Steady-state photoluminescence measurements were collected using a Photon Technology International (PTI) QuantaMaster 50 fluorimeter utilizing a 75 W Xe arc lamp as the source. Infrared spectra were collected on a PerkinElmer Frontier FT-IR with a diamond ATR plate. Thermogravimetric analysis was performed using a Netzsch TG209 Libra with Al2O3 crucibles at a temperature ramp of 10 °C / min under a N2 purge flow of 30 mL / min. Water contact angles were determined from analysis of digital photographs of 10 μL droplets on treated fabric samples, taken in quadruplicate. SEM images were collected on a FEI Quanta 650 instrument with a tungsten hairpin filament. Human hepatoma, Huh-7.5.1 cells were obtained from Dr. Francis Chisari (Scripps Research Institute, La Jolla, CA, USA)232 and cultivated in Dulbecco's modified Eagle's medium 114 (DMEM) supplemented with 10% fetal bovine serum, 0.1 mM nonessential amino acids, 1 mM sodium pyruvate, and 10 mM HEPES. Vero E6 cells (ATCC® CRL-1586™) were cultivated in accordance with ATCC recommendations. All experiments were performed in cells below passage 30. All cells were expanded in T75 flasks with 5% carbon dioxide at 37 °C. Cell density was kept between 0.25 and 2 million cells/mL The SARS-CoV-2 nucleocapsid antibody [HL344] (GTX635679) was kindly provided by Genetex.227 Hoechst 33258 and goat anti-rabbit IgG Alexa Fluor 555 (A21428) were obtained from Invitrogen. RB (0.048 molar equivalents) was condensed with PNH2-7 to afford DP3 as previously reported.4 TPP was dissolved in toluene at a concentration of 1 mg/mL and combined with DP3 (0.2 mL per gram of DP3) to give a relative molar ratio of 0.016 moles TPP per mole of polymer. This mixture was diluted with THF to afford solutions of 1, 5, and 15 wt% DP3 and then used directly. Thin polymer films were prepared by depositing 200 µL of the DP3 and TPP polymer solution (without the addition of THF) onto glass followed by one hour of 405 nm irradiation. Fabric was cut and then soaked in the polymer solution for 10 minutes in the dark. The fabric was removed, allowed to air dry, and then air dried on foil for 10 minutes. Samples were irradiated using a 36 W 405 nm LED bulb from a distance of 4 cm for 30 minutes per side, flipping once. Samples were stored in the dark until use. The mass of fabric before and after treatment was used to determine the mass loading of polymer. Samples were soaked in THF for one hour followed by rinsing and drying overnight under vacuum, and the change in mass used to determine the polymer solubility. The same procedure (24 hour soak) was used for water, and a detergent solution made using 0.23 g / L household detergent. 115 Fabric for tensile measurements was cut to a size of 10 mm (course direction) by 70 cm (wale direction) using a Cricut cutting plotter. Strips were treated as previously described and measured until break using an Instron 5980 under a 2 kN load at 20 cm/min with a clamp distance of 40 mm. Uric acid was dissolved in a 0.02 M phosphate buffer to afford a concentration of 2 × 10-4 M. 3 mL of this was added to a quartz cuvette and 20 mg of EC/P13 added. The system was irradiated using a 15W 530 nm LED from a distance of 4 cm and the absorbance at 292 nm was monitored using UV-VIS spectroscopy. Methicillin resistant Staphylococcus aureus (MRSA) strain (UBC Chemistry Department Collection #1057) and Escherichia coli (UBC Chemistry Department Collection #1105) were grown overnight at 37 °C, 225 rpm in sterile Mueller-Hinton broth. The bacterial concentration in the broth was determined by absorbance at 600 nm by Cary100 spectrophotometer. The cultures were diluted in sterile distilled water to obtain a concentration of 105 bacteria/mL and aliquots of bacterial suspension (10 ml) were transferred to sterile 50 mL Falcon tubes each containing the specified size of treated fabric. After overnight incubation at 37 °C, 225 rpm, the suspensions were diluted 10-fold and (20 μL per plate for E. coli and 10 μL per plate for MRSA) plated onto Mueller-Hinton agar plates. The plates were incubated at 37 °C overnight. The number of visible colonies on each plate was calculated to obtain the corresponding concentration of living bacteria. Each 116 experiment was performed in triplicate, and the reported results were averaged values. Values were compared against a control containing only the bacterial broth and no sample added. For aPDI experiments, incubation with the material was carried out at room temperature either covered in foil to exclude light or irradiated using 530 nm light from a distance of 2 cm. Aliquots were drawn, diluted, and plated onto agar using the same procedure. All infections were carried out in a Biosafety Level 3 (BSL3) facility (UBC FINDER) in accordance with the Public Health Agency of Canada and UBC FINDER regulations (UBC BSL3 Permit # B20-0105). SARS-CoV-2 (SARS-COV-2/Canada/VIDO-01/2020) was kindly provided by Dr. Samira Mubareka (Sunnybrook, ONT, Canada) and passaged in Vero E6 cells. For experiments, passage three of the virus was used with a determined viral titer of 1.5 x 107 plaque forming units (PFU)/mL as described previously.227 Huh-7.5.1 cells were seeded at a concentration of 10,000 cells/well in 96-well plates the day before infection. SARS-CoV-2 stocks were diluted in Huh-7.5.1 complete media at various titers (105, 104, 103 PFU/mL). Virus dilutions were incubated with treated fabric (0.75 cm ×0.4 cm) in eppendorf tubes with or without light for two hours at room temperature and then 100 µL of the treated virus dilution was added to each well of Huh-7.5.1 cells for 48 hours, followed by fixation of the cells with 3.7% formalin for 30 min to inactivate the virus. Each treatment was done in 5 treatment replicates, with 2 quantification replicates each. The fixative was removed, cells were washed with PBS, and permeabilized with 0.1% Triton X-100 for 5 min, followed by immunostaining with rabbit primary antibody HL344 (SARS-CoV-2 nucleocapsid) at working dilutions of 1:1000 for 1 hour at room temperature. The secondary antibody, goat anti-rabbit IgG Alexa Fluor 555, was used at a 1:2000 dilution and the nuclear stain Hoechst 33342 was used at 1 µg/mL for 1 hour at room temperature in the dark. After 117 washing with PBS, plates were kept covered in aluminum foil at 4 °C until imaging on a High Content Screening (HCS) platform (CellInsight CX7 HCS, Thermo Fisher Scientific) with a 10X objective. Monitoring of the total number of cells (based on nuclei staining) and number of virus-infected cells (based on dsRNA and nucleocapsid staining) was performed using the CellInsight CX7 HCS platform (Thermo Fisher), as previously described.227 Briefly, nuclei are identified and counted using the 350⁄461 nm wavelength (Hoechst 33342); cell debris and other particles are removed based on a size filter tool. A region of interest (ROI, or “circle”) is then drawn around each host cell and validated against the bright field image to correspond with host cell membranes. The ROI encompasses the “spots” where SARS-CoV-2 nucleocapsid (549/600 nm wavelength) is localized. Finally, the software (HCS Studio Cell Analysis Software, version 4.0) identifies, counts, and measures the pixel area and intensity of the “spots” within the “circle.” The fluorescence measured within each cell (circle) is then added and quantified for each well. The total circle spot intensity of each well corresponds to intracellular virus levels (Z’ > 0.7) and is normalized to non-infected cells and to infected cells with 0.1% DMSO. Nine fields were sampled from each well. Nuclei stain (Hoechst 33342) was also used to quantify cell loss (due to cytotoxicity or loss of adherence) and to verify the changes in viral infection did not result from a decrease in cell numbers. GraphPad Prism 9™ (GraphPad Software, Inc.) was used to quantify and visualize data. A total of 250,000 Vero E6 cells were seeded in complete MEM medium in 6-well plates and incubated for 24 hours at 37 °C prior to infection. The wells were washed once with PBS 118 before 200 μL virus samples from fabric treatments (1.5 × 104 PFU/mL incubated with fabric in dark or light for 2 hours) was directly added to the wells. A 1/10 dilution of fabric-treated virus was also added to separate wells. Infected cells were incubated at 37 °C for 1 hr, mixing gently every 15 min, then covered with 2 mL overlay medium of 2% Avicel CL-611 (DuPont Pharma Solutions) diluted 1:1 with 2x minimum essential media (Gibco). The cells were then incubated for three days. To fix the cells, 2 mL 8% formalin was added to each well for 30 min, following removal of the Avicel/formalin solution. Cells were gently washed with 1 mL tap water/well, followed by staining with 200 μL 1% crystal violet for 5 min. Crystal violet was removed, and washed three times with 1 mL tap water/well, then dried before the viral plaques were manually counted. GraphPad Prism 9™ (GraphPad Software, Inc.) was used to quantify and visualize data. 6.2.3 Synthesis and Preparation Polymer Preparation. RB (0.048 molar equivalents) was condensed with PNH2-7 to afford DP3 as previously reported. TPP was dissolved in toluene at a concentration of 1 mg/mL and combined with DP3 (0.2 mL per gram of PRB) to give a relative molar ratio of 0.016 moles TPP per mole of polymer. This mixture was diluted with THF to afford solutions of 1, 5, and 15 wt % DP3 and then used directly. Thin polymer films were prepared by depositing 200 µL of the DP3 and TPP polymer solution (without the addition of THF) onto glass followed by one hour of 405 nm irradiation. Fabric Treatment. Fabric was cut and then soaked in the polymer solution for 10 minutes in the dark. The fabric was removed and then air dried on foil for 10 minutes. Samples 119 were irradiated using a 36 W 405 nm LED bulb from a distance of 4 cm for 30 minutes per side, flipping once. Samples were stored in the dark until use. The mass of fabric before and after treatment was used to determine the mass loading of polymer. Samples were soaked in THF for one hour followed by rinsing and drying overnight under vacuum, and the change in mass was used to determine the polymer solubility. The same procedure (24 hour soak) was used for water, and a simulated detergent solution made using 0.23 g / L household detergent. To determine the TPP loading relative to RBL, a sample of C/P13 was prepared without UV irradiation. After soaking on THF for two hours, a UV-VIS measurement was taken and relative concentration of TPP and RBL calculated using the molar extinction coefficients at 416 and 565 nm respectively. 120 6.3 Conclusions The coating and subsequent photo-cross-linking of a siloxane copolymer onto textiles using a room temperature procedure in approximately one hour was successfully demonstrated. Excitation of a sacrificial porphyrin molecule results in 1O2 oxidative cross-linking of the amine-containing polysiloxane to give hydrophobic fabrics with low leaching in organic solvents and only minor decreases in tensile strength and elongation at break. This procedure is amenable to synthetic fabrics (polyester) as well as natural fabrics (cotton, linen, silk) and paper. Antimicrobial inactivation from the surface amine functionalities was demonstrated to depend on weight % of amine groups on the polymer, with inactivation of >98% observed for E. coli and MRSA. Rose Bengal lactone attached to the polymer enables antimicrobial photodynamic inactivation through irradiation with green light, resulting in a 28× and 3× increase in E. coli and MRSA inactivation rates respectively compared with samples left in the dark. I anticipate that the simplicity of this treatment procedure and compatibility with wide array of textiles may broaden the applicability of polymer-base antimicrobial coatings in the healthcare setting. We also demonstrated the antiviral activity of photo-activated polymer against SARS-CoV-2, resulting in up to 10× decrease in infectious virus compared to untreated and dark-treated fabric. Although vaccines and universal masking in health care settings has greatly reduced SARS-CoV-2 transmission, the emergence of variants with increased transmissibility and higher patient viral loads warrants development and testing of additional measures for preventing transmission in high-risk settings.233,234 The use of treated masks that provide a barrier as well as an active means of viral inactivation may further prevent the spread of highly transmissible 121 SARS-CoV-2 variants to susceptible individuals. Importantly, due to the non-specific antiviral mechanism of 1O2, I predict these treated fabrics will have broad-antiviral activity and far reaching applications against many important human enveloped viruses transmitted in health care settings such as influenza A virus and other coronaviruses. 122 Chapter 7: Photo-Oxidative Cross-Linking of Thiol Copolymers Via Disulfide Formation 7.1 Overview The reduction of disulfide linkages to thiol functionalities in polymeric materials is a common strategy for the preparation of degradable materials. Here I expand upon the use of singlet oxygen for polymer cross-linking described in Chapters 4, 5, and 6, and demonstrate the photo-oxidation of thiol functionalities into disulfide cross-links using a telluride catalyst and photo-generated singlet oxygen. This procedure uses blue light to produce reactive singlet oxygen from a solubilized porphyrin sensitizer to oxidize the telluride pre-catalyst into an active state. The catalyst prepared in-situ can then catalyze the oxidation of thiol functionalities into disulfide groups. The kinetics of this process were studied using photo-rheology, with the rate of cross-linking dependant on the telluride concentration while the cross-linking onset depended on the rate of telluride oxidation. This procedure was used to photo-cross-link thiol-containing siloxane copolymers into elastic materials with mechanical elongations of between 70-420% depending on polymer composition. The disulfide cross-links can be degraded using organic reductants to revert the materials from an elastomeric solid back to a liquid. 123 7.2 Research 7.2.1 Results and Discussion Two (mercaptopropyl)methylsiloxane)-dimethylsiloxane copolymers were used in this study, either a 7000 g/mol (FPA) copolymer or a 70,000 g/mol (FPB) copolymer with 5 wt % and 1 wt % thiol component respectively. Diphenyltelluride (DPT) was prepared from diphenylditelluride using Cu powder according to literature procedures.138 The 1O2 photo-sensitizer tetraphenylporphyrin was chosen owing to its moderate 1O2 quantum yield and absorbance in the wavelength region delivered by commercial blue LEDs (Figure F.1).235 FPA was used primarily for spectroscopic characterization owing to the higher thiol content than FPB. Polymeric samples were prepared by combining the polysiloxane, photosensitizer, and telluride pre-catalyst followed by irradiation with light to give elastic materials. Figure 7.1. Photo-oxidative cross-linking of statistical thiol copolymers into disulfide networks using a DPT pre-catalyst and TPP as a singlet oxygen photo-sensitizer. FPA was mechanically mixed with DPT and a solution of TPP in toluene and allowed to stand for 30 minutes to remove bubbles (Figure 7.1). The polymer solutions are initially transparent green in color. Irradiation with a blue LED (430 nm, 0.008 W/cm2) resulted in solid (no flow) samples after 15 minutes. The photo-cross-linking reaction was monitored with UV-124 VIS spectroscopy, with bleaching of the TPP observed throughout the reaction (Figure F.2). No changes in the FT-IR spectrum were observed between the initial polymer and cross-linked samples, as expected for the formation of symmetrical disulfide bonds with no dipole moment (Figure F.3). Raman spectroscopy is commonly employed to measure symmetrical disulfide bonds.236 Cross-linked FPA showed a new peak at 550 cm-1 in the Raman spectrum consistent with alkyl disulfide moieties (Figure 7.2). These results demonstrate cross-linking of the thiol groups to disulfide groups with no evidence of significant side reactions or decomposition. No cross-linking was observed when any of DPT, TPP, or atmospheric oxygen were removed from the system, and samples stored in the dark for 24 hours did not result in cross-linking. Figure 7.2. (a) Raman spectra of a sample of FPA before and after photo-oxidative cross-linking, showing a diagnostic disulfide peak at 552 cm-1. (b) A sample of cross-linked FP50 polymer, 1.5 mm thick and 20 mm in diameter. Cross-linked samples of FPA resulted in wrinkled films that were unsuitable for mechanical testing (Figure F.4). Blends of FPA and FPB containing 100, 75, and 50% polymer a b 125 mass fraction of FPB were used for further characterization, denoted as FP100, FP75, and FP50. Blends at these ratios produced uniform, cross-linked samples after four hours that were green in color (Figure 7.2). The cross-linking reaction in this system is proposed to progress through three distinct steps (Figure 7.3a). (1) Generation of 1O2 through irradiation of the TPP photosensitizer (2) Oxidation of the telluride pre-catalyst to the telluroxide/tellurone active species (referred to collectively as DPTO) (3) Catalytic coupling of thiols to disulfide cross-links. Photo-rheology was used to examine these three steps by controlling the composition and reaction conditions. The cross-linking in FP100 could be observed by a sharp increase in G′ over G″ upon irradiation (Figure F.5). Removal of DPT resulted in no change to the storage or loss moduli upon irradiation. An experiment in which the irradiation was toggled on and off resulted in no change in G′ or G″ during the dark periods (Figure 7.3b). These results demonstrate that DPTO is converted to a non-active state after reaction with thiols, and that light is required to (re)generate the active catalytic species. The absence of a gradual increase in moduli in the dark periods suggests that DPTO reacts rapidly upon formation. The onset time (delay between beginning irradiation and G′ increase) and the initial cross-linking rate (change in G′ as a function of time) were found to both accelerate with increasing DPT concentration from 7 mM to 29 mM, with a maximum of 33 ± 5 s and 17 ± 3 Pa/s (Figure 7.3c). However, increasing the concentration of TPP by a factor of four or increasing the light intensity by a factor of 30 decreased the onset time but did not significantly affect the initial rate (Figure 7.3d,e). 126 Figure 7.3. (a) Proposed scheme for the photo-cross-linking in this system, proceeding through three discrete steps. (b) Photo-rheological experiment measuring P100 with the UV light toggled on (yellow) and off (white) during the measurement. Onset time and initial cure rate determined using photo-rheology of FP100 with differing concentrations of (c) DPT (d) TPP and (e) light intensity. Measurements performed in triplicate, conditions were the concentrations described for sample FP100 and a UV intensity of 23 mW/cm2 unless otherwise indicated. An increase in TPP or light intensity will only affect the generation and steady-state concentration of 1O2 (Steps 1 and 2). The concentration of DPT is proposed to affect the rate of Steps 2 and 3, with only Step 3 resulting in cross-linking. It follows then that the initial cure rate 127 is dependant only on the steady-state concentration of DPTO. The onset time is then governed by Step 2, which can be described as the time to produce DPTO. To further assess the dynamics in our systems, the translational diffusion speeds of the different components were explored using pulsed-field gradient NMR (PFG-NMR). Samples of FP100 were irradiated for fixed lengths of time and the diffusion coefficients measured (Figure 7.4). The 1H signal of toluene was used as a stand-in for DPT (both liquids at ambient conditions), while the 19F signal of 2-chloro-5-(trifluoromethyl)pyridine (CF3Py) was used as a stand-in for TPP (N-containing heterocyclic solids at ambient conditions). Figure 7.4. Translational diffusion coefficient (Dt) for for toluene (1H, DPT stand-in), CF3Py (19F, TPP stand-in), and the FPB polymer backbone (1H) as a function of irradiation time, measured using PFG-NMR. Sample is P100 with CF3Py added at 1 wt% relative to the polymer. 128 Both toluene and CF3Py exhibited similar diffusion coefficients (Dt) of 5 × 10-6 and 4 × 10-6 cm2/s respectively. After three days of cross-linking under constant irradiation these diffusion coefficients had decreased by less than 40%. Dt for 1O2 has been estimated as being of the same order of magnitude as these values.237 As the overall reaction is not concerted, these diffusion speeds remaining high suggests that formation and co-localization of DPTO with the thiol functionalities is not arrested as the sample transitions from liquid to solid. Three distinct diffusion coefficients were determined for the polymer, 1.5 × 10-7, 3.4 × 10-8, and 1.0 × 10-9 cm2/s. I attribute the presence of three coefficients to different modes of entanglement, and not a wide molecule weight dispersity, as the relative ratio of the three changes during cross-linking (Figure F.6).238 However, after three days of irradiation these values had decreased by up to 70% (Table F.1). The low and decreasing diffusion coefficients for the polymer may be inhibiting complete cross-linking when the amount of remaining thiol is low. Larger samples of FP100, FP75, and FP50 were prepared by irradiating samples overnight to ensure complete photo-reaction (Figure 7.2b). Thermogravimetric analysis demonstrated < 2% mass loss below 300 °C for all samples, with cross-linked samples having a greater To than the non-cross-linked FPB (Figure F.7). Little mass loss before 200 °C, along with FTIR measurements showing no peaks attributed to toluene, confirms evaporation of the solvent from the material during cross-linking. DSC measurements showed a Tg of -122 to -125 °C for all samples, with large crystallization and melting peaks attributed to the presence of liquid DPT /DPTO (Figure F.8, Table F.2). The percentage of the cross-linked polymer soluble in THF was found to increase from 29 ± 1% (FP50) to 47 ± 6% (FP100), with the swelling percentage 129 increasing from 506 ± 3% to 1390 ± 40% for the same samples (Figure F.9). These results are consistent with a decreased cross-linking density in samples with greater proportion of the higher Mw (and lower thiol wt %) copolymer. The high soluble fraction also supports incomplete network formation resulting from low thiol mobility and concentration after the initial stages of cross-linking. Mechanical measurements of cross-linked samples were performed on a DMA instrument in tensile mode (Figure F.10, Table 7.1). The Young’s modulus decreased from 178 ± 18 kPa to 19 ± 3 kPA from FP50 to FP100, decreasing linearly when the results are plotted according to the mass ratio of the higher Mw component FPB (Figure 7.5). Similarly, the maximum elongation increased from 72 ± 23% to 424 ± 12% in a near-linear fashion between FP50 to FP100 while the tensile strength did not change significantly between FP50 and FP75 but decreased from 66 ± 1 to 15 ± 4 kPa for FP100. These results are consistent with the swelling results that demonstrate a lower cross-linking density for samples with a higher mass fraction of higher molecular weight polymer, and demonstrate a high degree of tunability in mechanical properties achievable using polymer blends for this system. The trend in maximum elongation may also explain the wrinkling in blends with over 50% of PA where a predicted elongation approaching zero may cause uneven evaporation of toluene and photo-cross-linking during curing of the inelastic material. 130 Figure 7.5. Tensile measurement results of cross-linked FP100, FP75, and FP50 plotted according to the mass ratio of PB in the sample. Sample ID Young’s Modulus (kPa) Tensile Strength (kPa) Ultimate Elongation (%) FP100 19 ± 3 15 ± 4 424 ± 12 FP75 86 ± 6 66 ± 1 171 ± 3 FP50 178 ± 18 67 ± 1 72 ± 23 Table 7.1. Mechanical properties of cross-linked FP100, FP75, and FP50, determined from tensile measurements. Finally, cross-linked samples were examined for their ability to be de-cross-linked using an excess of reducing agent, cleaving the disulfide cross-link back into two thiol moieties. Dithiothreitol (DTT) is commonly used to reduce disulfide bonds in proteins as well as disulfide-containing hydrogels.127 Attempts to reduce the disulfide cross-links in FP100 using DTT or β-mercaptoethanol were unsuccessful and did not result in a greater % soluble material than soaking in neat THF. Iyengar and coworkers have previously demonstrated the reduction of 131 disulfide bonds in solution using excess NaBH4 and ZrCl4 as catalysts at elevated temperatures.239 I employed this reaction in hot THF over 18 hours to effectively reduce the disulfide cross-links in FP100 and render the solid material back into a viscous oil, with 92% mass recovery after aqueous-organic extraction and drying under high-vacuum. The presence of the alkyl-mercapto functionalities was confirmed using 1H NMR spectroscopy comparing against virgin FPB (Figure F.11). However, integration of the alkyl peaks against the PDMS CH3 peak resulted in an approximately 4× decrease in the relative amount of SH alkyl functionalities for the degraded FPB, revealing the undesirable degradation into non-mercapto functionalities. Viscosity measurements of the degraded and pristine FPB at different concentrations in toluene were used to estimate the polymer Mw (Figure F.12).240 No significant change (46.1k vs 45.8k g/mol for pristine and degraded) in Mw was observed, demonstrating only cleavage of the disulfide groups and not the polymer backbone. Photo-rheology of the degraded FPB formulated as FP100 did not result in a cross-over of Gʹ and Gʺ (Figure 7.6). The material can therefore be regarded as degradable but not recyclable under these conditions. Further optimization of the reductive disulfide cleavage that prevents by-product formation may therefore allow for recyclable photo-cross-linkable PDMS. 132 Figure 7.6. Photo-rheological experiment measuring a FP100 mixture prepared using pristine and degraded FPB with the UV light toggled on at 120 s. UV intensity at 23 mW/cm2 133 7.2.2 Experimental (Mercaptopropyl)methylsiloxane-dimethylsiloxane copolymers of 7,000 g/mol (FPA) and 70,000 g/mol (FPB) were obtained from Gelest (SMS-042) and Genesee Polymers (GP-701), respectively. Tetraphenylporphyrin (TPP) was purchased from Frontier Scientific. Diphenyl ditelluride and all other reagents were purchased from Sigma Aldrich and used without further purification. Diphenyl telluride was prepared from diphenyl ditelluride according to literature procedures.138 Absorption spectra were collected on a Varian Cary 5000 UV-Vis-NIR spectrophotometer. 1H NMR spectroscopic data were collected on a 400 MHz Bruker Avance 400dir spectrometer at 25 °C. Residual proto-solvent peaks were used to reference the 1H NMR spectra. Raman spectra were collected on a Bruker Senterra II microscope. Infrared spectra were collected on a PerkinElmer Frontier FT-IR with a diamond ATR plate. Thermogravimetric analysis was performed on Netzsch TG209 Libra using an Al2O3 crucible at a temperature ramp of 10 °C / min under a N2 purge flow of 30 mL / min. Differential scanning calorimetry (DSC) measurements were performed using a Netzsch Polyma 214 instrument with LN2 attachment at a ramp rate of 10 °C / min. Mechanical testing was carried out on a Dynamic Mechanical Analyser (DMA, RSA G2 TA Instruments) in axial mode. Samples were cut into strips with dimensions 4 mm × 3 mm × 1 mm (length-width-thickness). Sample strips were extended/elongated until breakage at room 134 temperature by applying constant linear strain rate of 0.1 mm/min. The linear elongational strain was calculated by: 𝜀𝑢 =𝐿𝑓 − 𝐿0𝐿0× 100 Where L0 is the initial length of the sample (t = 0) and L is the length of the sample at time t. The Young’s modulus of elasticity was determined from the equation 𝜎 = 𝐸𝜀 (σ is the tensile stress) which is valid only for the initial elastic response of the material. The tensile strength represents the maximum stress in the stress-strain curve and the ultimate elongation, u shows how much the material can elongate before fracture/failure. The latter was calculated by using the following equation: 𝜀𝑢 =𝐿𝑓 − 𝐿0𝐿0× 100 Where Lf is the final length of the sample before failure. Photo-rheology testing was carried out on a modular compact rheometer (MCR 502 Anton Paar) equipped with OmniCure 1500 spot curing system. A 10-20 μL sample was placed on the glass Peltier system where light with wavelength 320 nm to 500 nm was transmitted from a fiber light guide. A disposable 8 mm metal parallel plate was used as the upper measuring system to allow enough oxygen penetration. An oscillatory shear with constant angular frequency (𝜔) 10 rad/s and strain (𝛾) 2% was applied to the sample through the whole test. Light was automatically toggled on by the software 120 s after the test started and the viscoelastic moduli (storage, G' and loss modulus, G") were monitored during the tests. All tests were performed at room temperature. 135 The intrinsic viscosity was used to determine the Mw of dissolved polymer samples before and after treatment. Intrinsic viscosity [𝜂] was determined using the Huggins equation:   ( ) 00 0/ 1lim limredc c c  → →− = =    Where 𝜂𝑟𝑒𝑑 is the reduced viscosity, 𝜂 and 𝜂0 are the zero-shear viscosity of the polymer solution and the solvent respectively, c is the concentration of polymer solution in unit g/dL. PDMS was dissolved in toluene and 2 g/dL, 4 g/dL, 6 g/dL and 8 g/dL solutions were prepared. The zero-shear viscosity of the solution and solvent were measured using a modular compact rheometer (MCR 501 Anton Paar) equipped with a concentric cylinder of gap size 0.418 mm and external radius of 5.418 mm. A shear rate sweep test was carried out from 10 s-1 to 500 s-1 at 25 °C. The zero-shear viscosity was taken as the average value for the steady-state shear viscosity over the whole shear rate range. Pulsed-field gradient stimulated echo NMR (PFG-NMR) diffusion measurements were made using a home-built horizontal coil PFG probe in a home-built NMR spectrometer operating at 8.4 T.177 Samples were cross-linked inside 4-cm long sections of 5-mm diameter NMR tubes. Half-sinusoidal gradient pulses of 270 µs duration were varied in strength up to a peak amplitude of 3200 G/cm. RF field strengths were typically ~ 60 kHz and diffusion times were 4 s for polymer measurements, 2 s otherwise. A longitudinal delay of 10 ms was inserted to allow eddy currents to decay before signal acquisition. 136 7.2.3 Synthesis and Preparation For FP100, 1 gram of thiol-containing polymer FPB (1 molar equivalent) was combined with 7 mg DPT (25 molar equivalents relative to polymer) and 0.23 mL of a 1 mg / mL TPP solution in toluene (0.26 molar equivalents TPP relative to polymer). The mixture was stirred mechanically using a glass rod, and then allowed to sit for 15 minutes to remove bubbles. The sample was transferred to a silicone mold and irradiated using a 430 nm 15 W LED bulb (0.008 W/cm2). For mixtures containing FPA, the indicated mass of FPB was substituted for FPA without altering the other mass amounts in the system. For the reduction of cross-linked FP100, 1.8 g NaBH4 and 2.8 g ZrCl4 were added to 150 mL dry THF and stirred under N2 for five minutes. A single contiguous piece of FP100 (4.5 grams) was added and condenser was added. The system was heated to reflux and stirred under N2 for 18 hours, after which the clear heterogeneous mixture had turned an opaque homogeneous brown. The mixture was cooled to room temperature and then transferred to a 1 L beaker and the remaining NaBH4 quenched by dropwise addition of deionized water under vigorous stirring. The orange solution was extracted with DCM, the organic layer dried over MgSO4, and filtered. The clear colorless solution was reduced to an oil under reduced pressure and dried overnight under high vacuum. The same procedure was attempted using 100 mM DTT in THF instead of NaBH4/ZrCl4 but only resulted in swelling of the polymer sample without degradation, as determined by mass differences relative to swelling in THF alone. 137 7.3 Conclusions Here, the photo-cross-linking of PDMS through the direct formation of degradable disulfide linkages from thiol precursors was demonstrated. Photo-excitation of a porphyrin under atmospheric conditions produces singlet oxygen that oxidizes a telluride precatalyst to its active state, which then converts thiols to disulfides. Photo-rheological studies confirm that the reaction necessitates the photo-oxidation of the pre-catalyst to an active catalytic state, with the net concentration of pre-catalyst controlling the overall cross-linking rate while the rate of catalyst active state formation governs the reaction onset time. This procedure results in solidified materials within minutes, and can be performed at room temperature open to the air. These elastomeric materials had mechanical elongations ranging from 70-420% depending on the relative thiol content. Reductive degradation using sodium borohydride effectively degrades the cross-linked network back into a soluble oil. The direct photo-formation of degradable cross-links may be one way to address the issue of non-degradable cross-linked polymeric materials. 138 Chapter 8: Conclusions and Future Work 8.1 Conclusions The exploration of new polymer cross-linking reactions is necessary to broaden the types of novel materials that can be prepared in order to address global issues such as plastic recycling and disease transmission. The use of light to cross-link polymer systems enables a greater degree of tunability, both in terms of cross-linking extent and spatial-temporal control. This thesis explored three distinct photo-cross-linking mechanisms: anthracene dimerization, amine oxidative coupling, and thiol photocatalysis. The underlying reaction mechanisms and kinetics were investigated along with demonstrations of novel properties such as scratch healing and antimicrobial activity. In Chapters 2 and 3 anthracene was incorporated into polymeric systems as a UV dimerizable cross-linking moiety. In linear vitrimeric systems, it was demonstrated that UV cross-linking can increase the glass transition temperature and thereby alter the temperature at which the solid material can be thermally healed, while still maintaining the ability for scratch healing after cross-linking. In siloxane systems, anthracene dimerization resulted in macroscopic crystallization of mm sized crystallites, a potential method for the preparation of crystalline reinforced elastomers. The unique step-wise growth demonstrated in these films suggests a high degree of chain mobility is required for crystallization, possibly necessitating a liquid starting material. These two chapters demonstrate the versatility of anthracene dimerization through its inclusion and photo-reaction in both solid films and liquid coatings. 139 Chapters 4-6 explored a novel photo-cross-linking reaction involving generation of singlet oxygen from a sensitizer and subsequent oxidative coupling of the amine groups into imine groups. It was shown that this reaction can be performed using organic and inorganic sensitizers, and is sensitive to the presence of other nitrogen functional groups. The resulting siloxane materials exhibit robust mechanical properties that depend on the sensitizer content, as well as contact antimicrobial activity against bacterial and mammalian cells that is dependent on the amine content of the polymer and exposed surface area. The bio-activity was expanded by coating the polymer onto fabric in a simple photo-cross-linking procedure that did not compromise the fabric structure. Incorporation of a second photo-sensitizer enables photodynamic inactivation, allowing for two modes of antimicrobial activity that was demonstrated against bacteria and viruses. Finally, Chapter 7 expanded the scope of singlet oxygen cross-linking reactions. Photo-generated singlet oxygen was used to activate a telluride catalyst that cross-links thiol copolymers through disulfide formation. The mechanical properties of these elastomers could be tuned over a wide range by altering the ratio of the polymer blend. These disulfide linkages could be reductively cleaved to revert the elastic solid back into an oil. In conclusion, I have successfully demonstrated the applicability of photo-controlled cross-linking mechanisms for the preparation of functional materials. The anthracene and singlet oxygen cross-linking mechanisms described herein were applied to prepare materials possessing thermal healing, crystalline regions, antimicrobial activity, and degradability. This work is successful in expanding the scope of functional materials that can be cross-linked through the 140 controlled application of light. However, all of the 1O2 research was performed on siloxane-based materials, which presents opportunities for future research to expand the types of polymers capable of being cross-linked by this novel procedure. 8.2 Future Work The polymers used in Chapters 2-6 were purchased commercially and few other affordable amine or thiol containing polymers are available that are expected to be compatible with the 1O2 cross-linking procedure. One large focus of future work building upon these reports would be to explore the synthesis of novel alkyl-amine and alkyl-thiol containing polymers towards specific applications that may benefit from being cross-linked. For example, hydrophilic alkyl-amine dendrimers may be able to be photo-cross-linked into imine hydrogels that would possess antimicrobial activity. As well, a number of applications such as every-day clothing may not benefit from high degrees of hydrophobicity (can limit breathability and moisture wicking) and as such advancing this chemistry towards hydrophilic analogs may be relevant for future applications. For the design of new amine-containing polymers, careful consideration into the inclusion of either functional groups that react with 1O2 or quench 1O2 would be required. Similarly, alkyl-thiol groups are common in biological materials such as proteins (cysteine residues) and the mechanism described in Chapter 7 may be amenable to cross-linking biomaterials if they have similar thiol content as the polymers utilized in that chapter. For this application the preparation of hydrophilic aryl-tellurides would need to be investigated (Figure 8.1). 138 141 Figure 8.1. Synthetic scheme for the preparation of hydrophilic diaryltellurides. The antimicrobial activity of the polymers in Chapter 6 was demonstrated to increase with increasing amine content (Figure 6.3). Chemical modification of the alkyl-amine moieties is an additional method that may be employed to improve the antimicrobial activity of the resulting cross-linked material, and therefore the utility of these materials as antimicrobial coatings. Pyridinium, phosphonium, and guanidinium functional groups have all been demonstrated to possess greater activity than alkyl-amines and could be installed through organic reactions at the amine site without the need for synthesis of the polymer from the ground up (Figure 8.2).102,108,241 A thorough study of how small amounts of these functional groups affect the photo-oxidative coupling of amine molecules is warranted to expand the scope of this reaction, as well as exploring the effect of the different linker groups used to attach the antimicrobial functionality to the amine site. However, the existing amine-siloxane material is already regulated as safe according to the US FDA, so further modifications should be envisioned through a lens of future human safety and biocompatibility.212 As seen from Table 4.1 some functional groups can rapidly quench 1O2 and limit cross-linking or may lead to degradation of the desired antimicrobial functionality. Functionalization of the polymer (5-40 molar equivalents per polymer chain) and testing of the antimicrobial properties relative to the native PNH2-23 may reveal an optimal ratio or functionalization resulting in maximum bio-activity as well as 142 cross-linking. Optimization and maximization of the contact antimicrobial activity is a necessity before larger scale testing of these textiles as the results in this thesis were performed on non-optimized polymers and polymer loadings. As well, direct comparisons against more widely studied antimicrobial textile coatings such as silver and copper nanoparticles may provide a useful benchmark when validating future iterations of this work. Figure 8.2. Proposed modifications to the alkyl-amine groups of PNH2-23 that may result in greater antimicrobial activity. An existing limitation of the materials presented in Chapter 6 is the predominantly red-pink color of the textiles which may not be desirable for all end-user applications. Additionally, these materials only generate 1O2 over the green portion of the visible spectrum. One large area of future work would be to expand the spectral range over which 1O2 generation can occur in the materials described in Chapter 6. This would both enable the color of the textile to be easily tuned and increase the overall 1O2 generation under real-world sunlight or artificial overhead lighting. Currently, Rose Bengal and tetraphenylporphyrin do not fully exploit the blue-green (450-500 nm) and red (>600 nm) regions (Figure 8.3). By selecting additional hydrophobic dyes 143 that could be incorporated into the existing system (such as methylene blue, phthalocyanine, crystal violet etc), visible light could be fully harnessed to generate 1O2 from sunlight. Figure 8.3. Spectral output of common light sources and indicators for the wavelength of maximum absorption for some of the molecules used throughout this document. 144 References (1) Wright, T.; Tomkovic, T.; Hatzikiriakos, S. G.; Wolf, M. O. Macromolecules 2019, 52, 36–42. (2) Wright, T.; Petel, Y.; Zellman, C. O.; Sauvé, E. R.; Hudson, Z. M.; Michal, C. A.; Wolf, M. O. Chem. Sci. 2020, 11, 3081–3088. (3) Wright, T.; Tomkovic, T.; Hatzikiriakos, S. G.; Wolf, M. O. ACS Appl. Polym. Mater. 2020, 2, 4802–4808. (4) Wright, T.; Karis, D.; Millik, S. C.; Tomkovic, T.; Hatzikiriakos, S. G.; Nelson, A.; Wolf, M. O. ACS Appl. Mater. Interfaces 2021, 13, 22195–22203. (5) Wright, T.; Vlok, M.; Shapira, T.; Olmstead, A. D.; Jean, F.; Wolf, M. O. ACS Appl. Mater. Interfaces 2022, 14, 49–56. (6) Wright, T.; Zhang, Z.; Michal, C. A.; Hatzikiriakos, S. G.; Wolf, M. O. Polym. Chem. 2022, 13, 395–401. (7) Matyjaszewski, K.; Davis, T. P. In Handbook of Radical Polymerization; John Wiley & Sons, Inc.: Hoboken, 2002; pp 117–186. (8) James, S. R. Curr. Anthropol. 1989, 30, 1–26. (9) DiLaura, D. Opt. Photonics News 2008, 19. (10) Cho, J.; Park, J. H.; Kim, J. K.; Schubert, E. F. Laser Photonics Rev. 2017, 11, 1600147. (11) Roth, H. D. Angew. Chemie Int. Ed. English 1989, 28, 1193–1207. (12) Priestley, J. In Experiments and observations on different kinds of air, and other branches of natural philosophy, being the former six volumes abridged and methodized, with many additions; Thomas Pearson: London, 1790; Vol. 3, pp 1–45. 145 (13) Trommsdorff, H. Ann. Chem. Pharm 1834, 11, 190–208. (14) Matsuura, T.; Sata, Y.; Ogura, K.; Mori, M. Tetrahedron Lett. 1968, 9, 4627–4630. (15) Fritzsche, C. J. J. Prakt. Chemie 101 1887, 333–343. (16) Liebermann, C. Ber. Dtsch. Chem. Ges. 1877, 10, 2177–2179. (17) Breuer, A.; Zincke, T. Ber. Dtsch. Chem. Ges. 1878, 11, 1403–1407. (18) Guise-Richardson, C. Technol. Cult. 2010, 51, 357–387. (19) Crespy, D.; Bozonnet, M.; Meier, M. Angew. Chem. Int. Ed. 2008, 47, 3322–3328. (20) Seymour, R. B. J. Macromol. Sci. Part A - Chem. 1981, 15, 1165–1171. (21) Nowlin, T. E. In Business and Technology of the Global Polyethylene Industry: An In-depth Look at the History, Technology, Catalysts, and Modern Commercial Manufacture of Polyethylene and Its Products; John Wiley & Sons.: Hoboken, 2014; Vol. 1, pp 1–44. (22) Bisht, H. S.; Chatterjee, A. K. J. Macromol. Sci. - Rev. Macromol. Chem. Phys. 2001, 41, 139173. (23) Hartings, M. R.; Ahmed, Z. Nat. Rev. Chem. 2019, 3, 305–314. (24) Dadashi-Silab, S.; Atilla Tasdelen, M.; Yagci, Y. J. Polym. Sci. Part A Polym. Chem. 2014, 52, 2878–2888. (25) Frank, P. G.; Tuten, B. T.; Prasher, A.; Chao, D.; Berda, E. B. Macromol. Rapid Commun. 2014, 35, 249–253. (26) Trenor, S. R.; Shultz, A. R.; Love, B. J.; Long, T. E. Chem. Rev. 2004, 104, 3059–3078. (27) Kondo, M. Polym. J. 2020, 52, 1027–1034. (28) Sun, J. K.; Li, W.; Chen, C.; Ren, C. X.; Pan, D. M.; Zhang, J. Angew. Chem. Int. Ed. 2013, 52, 6653–6657. (29) Hou, Z.; Nau, W. M.; Hoogenboom, R. Polym. Chem. 2021, 12, 307–315. 146 (30) Lowen, J. M.; Leach, J. K. Adv. Funct. Mater. 2020, 30, 1909089. (31) Jellali, R.; Alexandre, M.; Jérôme, C. Polym. Chem. 2017, 8, 2499–2508. (32) Zhao, L.; Vaupel, M.; Loy, D. A.; Shea, K. J. Chem. Mater. 2008, 20, 1870–1876. (33) Jellali, R.; Bertrand, V.; Alexandre, M.; Rosière, N.; Grauwels, M.; De Pauw-Gillet, M. C.; Jérôme, C. Macromol. Biosci. 2017, 17, 1600495. (34) Montarnal, D.; Capelot, M.; Tournilhac, F.; Leibler, L. Science 2011, 334, 965–968. (35) Denissen, W.; Rivero, G.; Nicolaÿ, R.; Leibler, L.; Winne, J. M.; Du Prez, F. E. Adv. Funct. Mater. 2015, 25, 2451–2457. (36) Cho, S. H.; White, S. R.; Braun, P. V. Adv. Mater. 2009, 21, 645–649. (37) Azcune, I.; Odriozola, I. Eur. Polym. J. 2016, 84, 147–160. (38) Denissen, W.; De Baere, I.; Van Paepegem, W.; Leibler, L.; Winne, J.; Du Prez, F. E. Macromolecules 2018, 51, 2054–2064. (39) Pei, Z.; Yang, Y.; Chen, Q.; Wei, Y.; Ji, Y. Adv. Mater. 2016, 28, 156–160. (40) Zheng, N.; Fang, Z.; Zou, W.; Zhao, Q.; Xie, T. Angew. Chem. Int. Ed. 2016, 55, 11421–11425. (41) Chen, Q.; Yu, X.; Pei, Z.; Yang, Y.; Wei, Y.; Ji, Y. Chem. Sci. 2017, 8, 724–733. (42) Denissen, W.; Droesbeke, M.; Nicolaÿ, R.; Leibler, L.; Winne, J. M.; Du Prez, F. E. Nat. Commun. 2017, 8, 14857. (43) Okano, K.; Shishido, A.; Ikeda, T. Adv. Mater. 2006, 18, 523–527. (44) Perego, G.; Cella, G. D.; Bastioli, C. J. Appl. Polym. Sci. 2004, 59, 37–43. (45) Gadjourova, Z.; Andreev, Y. G.; Tunstall, D. P.; Bruce, P. G. Nature 2001, 412, 520–523. (46) He, Z.; Xiao, B.; Liu, F.; Wu, H.; Yang, Y.; Xiao, S.; Wang, C.; Russell, T. P.; Cao, Y. Nat. Photonics 2015, 9, 174–179. 147 (47) Kwon, S.; Yu, K.; Kweon, K.; Kim, G.; Kim, J.; Kim, H.; Jo, Y. R.; Kim, B. J.; Kim, J.; Lee, S. H.; Lee, K. Nat. Commun. 2014, 6, 4183. (48) Vonlanthen, D.; Lazarev, P.; See, K. A.; Wudl, F.; Heeger, A. J. Adv. Mater. 2014, 26, 5095–5100. (49) Welch, P.; Muthukumar, M. Phys. Rev. Lett. 2001, 87, 218302. (50) Anwar, M.; Schilling, T. Polymer 2015, 76, 307–312. (51) Noriega, R.; Rivnay, J.; Vandewal, K.; Koch, F. P. V.; Stingelin, N.; Smith, P.; Toney, M. F.; Salleo, A. Nat. Mater. 2013, 12, 1038–1044. (52) Lee, H. J.; Jo, Y. R.; Kumar, S.; Yoo, S. J.; Kim, J. G.; Kim, Y. J.; Kim, B. J.; Lee, J. S. Nat. Commun. 2016, 7, 12803. (53) Wang, X.; Guerin, G.; Wang, H.; Wang, Y.; Manners, I.; Winnik, M. A. Science 2007, 317, 644–647. (54) Matsumoto, A.; Yokoi, K.; Aoki, S.; Tashiro, K.; Kamae, T.; Kobayashi, M. Macromolecules 2002, 31, 2129–2136. (55) Matsumoto, A.; Odani, T.; Sada, K.; Miyata, M.; Tashiro, K. Nature 2000, 405, 328–330. (56) Beaudoin, D.; Maris, T.; Wuest, J. D. Nat. Chem. 2013, 5, 830–834. (57) Zhang, Y. B.; Su, J.; Furukawa, H.; Yun, Y.; Gándara, F.; Duong, A.; Zou, X.; Yaghi, O. M. J. Am. Chem. Soc. 2013, 135, 16336–16339. (58) Uribe-Romo, F. J.; Hunt, J. R.; Furukawa, H.; Klöck, C.; O’Keeffe, M.; Yaghi, O. M. J. Am. Chem. Soc. 2009, 131, 4570–4571. (59) Kissel, P.; Murray, D. J.; Wulftange, W. J.; Catalano, V. J.; King, B. T. Nat. Chem. 2014, 6, 774–778. (60) Kory, M. J.; Wörle, M.; Weber, T.; Payamyar, P.; Van De Poll, S. W.; Dshemuchadse, J.; 148 Trapp, N.; Schlüter, A. D. Nat. Chem. 2014, 6, 779–784. (61) Müller, V.; Hinaut, A.; Moradi, M.; Baljozovic, M.; Jung, T. A.; Shahgaldian, P.; Möhwald, H.; Hofer, G.; Kröger, M.; King, B. T.; Meyer, E.; Glatzel, T.; Schlüter, A. D. Angew. Chem. Int. Ed. 2018, 57, 10584–10588. (62) De Jong, J.; Lammertink, R. G. H.; Wessling, M. Lab Chip 2006, 6, 1125–1139. (63) Niu, X.; Peng, S.; Liu, L.; Wen, W.; Sheng, P. Adv. Mater. 2007, 19, 2682–2686. (64) Moon, J. H.; Baek, D. H.; Choi, Y. Y.; Lee, K. H.; Kim, H. C.; Lee, S. H. J. Micromech. Microeng. 2010, 20, 025032. (65) Sundararajan, P. R.; Hamer, G. K.; Croucher, M. D. Macromolecules 1980, 13, 971–973. (66) Sundararajan, P. R. Polymer 2002, 43, 1691–1693. (67) Dollase, T.; Spiess, H. W.; Gottlieb, M.; Yerushalmi-Rozen, R. Europhys. Lett. 2002, 60, 390–396. (68) Van Damme, J.; Van Den Berg, O.; Brancart, J.; Vlaminck, L.; Huyck, C.; Van Assche, G.; Van Mele, B.; Du Prez, F. Macromolecules 2017, 50, 1930–1938. (69) Dolinski, N. D.; Page, Z. A.; Discekici, E. H.; Meis, D.; Lee, I. H.; Jones, G. R.; Whitfield, R.; Pan, X.; McCarthy, B. G.; Shanmugam, S.; Kottisch, V.; Fors, B. P.; Boyer, C.; Miyake, G. M.; Matyjaszewski, K.; Haddleton, D. M.; de Alaniz, J. R.; Anastasaki, A.; Hawker, C. J. J. Polym. Sci. Part A Polym. Chem. 2019, 57, 268–273. (70) Rolland, M.; Whitfield, R.; Messmer, D.; Parkatzidis, K.; Truong, N. P.; Anastasaki, A. ACS Macro Lett. 2019, 8, 1546–1551. (71) Kensy, V. K.; Tritt, R. L.; Haque, F. M.; Murphy, L. M.; Knorr, D. B.; Grayson, S. M.; Boydston, A. J. Angew. Chem. Int. Ed. 2020, 59, 9074–9079. (72) Ogawa, K. A.; Goetz, A. E.; Boydston, A. J. J. Am. Chem. Soc. 2015, 137, 1400–1403. 149 (73) Hasegawa, K.; Yamada, K.; Sasase, R.; Miyazaki, R.; Kikuchi, A.; Yagi, M. Chem. Phys. Lett. 2008, 457, 312–314. (74) Hurst, J. R.; McDonald, J. D.; Schuster, G. B. J. Am. Chem. Soc. 1982, 104, 2065–2067. (75) DeRosa, M. C.; Crutchley, R. J. Coord. Chem. Rev. 2002, 233–234, 351–371. (76) Epe, B. Chem. Biol. Interact. 1991, 80, 239–260. (77) Dzhagarov, B. M.; Kruk, N. N.; Konovalova, N. V.; Solodunov, A. A.; Stepuro, I. I. J. Appl. Spectrosc. 1995, 62, 285–289. (78) Shen, H. R.; Spikes, J. D.; Smith, C. J.; Kopeček, J. J. Photochem. Photobiol. A 2000, 130, 1–6. (79) Op De Beeck, M.; Madder, A. J. Am. Chem. Soc. 2012, 134, 10737–10740. (80) Son, T. Il; Sakuragi, M.; Takahashi, S.; Obuse, S.; Kang, J.; Fujishiro, M.; Matsushita, H.; Gong, J.; Shimizu, S.; Tajima, Y.; Yoshida, Y.; Suzuki, K.; Yamamoto, T.; Nakamura, M.; Ito, Y. Acta Biomater. 2010, 6, 4005–4010. (81) Davies, M. J. Biochem. Biophys. Res. Commun. 2003, 305, 761–770. (82) Gracanin, M.; Hawkins, C. L.; Pattison, D. I.; Davies, M. J. Free Radic. Biol. Med. 2009, 47, 92–102. (83) Khan, A. U.; Mei, Y. H.; Wilson, T. Proc. Natl. Acad. Sci. U. S. A. 1992, 89, 11426–11427. (84) Chen, B.; Wang, L.; Gao, S. ACS Catal. 2015, 5, 5851–5876. (85) Aguirre-Díaz, L. M.; Snejko, N.; Iglesias, M.; Sánchez, F.; Gutiérrez-Puebla, E.; Monge, M. Á. Inorg. Chem. 2018, 57, 6883–6892. (86) Berlicka, A.; König, B. Photochem. Photobiol. Sci. 2010, 9, 1359–1366. (87) Jin, J.; Yang, C.; Zhang, B.; Deng, K. J. Catal. 2018, 361, 33–39. 150 (88) Taynton, P.; Yu, K.; Shoemaker, R. K.; Jin, Y.; Qi, H. J.; Zhang, W. Adv. Mater. 2014, 26, 3938–3942. (89) Zhu, C.; Xi, C.; Doro, W.; Wang, T.; Zhang, X.; Jin, Y.; Zhang, W. RSC Adv. 2017, 7, 48303–48307. (90) Marks, L. R.; Reddinger, R. M.; Hakansson, A. P. Infect. Immun. 2014, 82, 1141–1146. (91) Bryant, J. M.; Grogono, D. M.; Rodriguez-Rincon, D.; Everall, I.; Brown, K. P.; Moreno, P.; Verma, D.; Hill, E.; Drijkoningen, J.; Gilligan, P.; Esther, C. R.; Noone, P. G.; Giddings, O.; Bell, S. C.; Thomson, R.; Wainwright, C. E.; Coulter, C.; Pandey, S.; Wood, M. E.; Stockwell, R. E.; Ramsay, K. A.; Sherrard, L. J.; Kidd, T. J.; Jabbour, N.; Johnson, G. R.; Knibbs, L. D.; Morawska, L.; Sly, P. D.; Jones, A. M.; Bilton, D.; Laurenson, I.; Ruddy, M.; Bourke, S.; Bowler, I. C. J. W.; Chapman, S. J.; Clayton, A.; Cullen, M.; Dempsey, O.; Denton, M.; Desai, M.; Drew, R. J.; Edenborough, F.; Evans, J.; Folb, J.; Daniels, T.; Humphrey, H.; Isalska, B.; Jensen-Fangel, S.; Jönsson, B.; Jones, A. M.; Katzenstein, T. L.; Lillebaek, T.; MacGregor, G.; Mayell, S.; Millar, M.; Modha, D.; Nash, E. F.; O’Brien, C.; O’Brien, D.; Ohri, C.; Pao, C. S.; Peckham, D.; Perrin, F.; Perry, A.; Pressler, T.; Prtak, L.; Qvist, T.; Robb, A.; Rodgers, H.; Schaffer, K.; Shafi, N.; Van Ingen, J.; Walshaw, M.; Watson, D.; West, N.; Whitehouse, J.; Haworth, C. S.; Harris, S. R.; Ordway, D.; Parkhill, J.; Andres Floto, R. Science 2016, 354, 751–757. (92) Weber, D. J.; Rutala, W. A.; Miller, M. B.; Huslage, K.; Sickbert-Bennett, E. Am. J. Infect. Control 2010, 38, 25–33. (93) Klevens, R. M.; Edwards, J. R.; Richards, C. L.; Horan, T. C.; Gaynes, R. P.; Pollock, D. A.; Cardo, D. M. Public Health Rep. 2007, 122, 160–166. (94) Xu, C.; Akakuru, O. U.; Ma, X.; Zheng, J.; Zheng, J.; Wu, A. Bioconjug. Chem. 2020, 31, 151 1708–1723. (95) Ghilini, F.; Pissinis, D. E.; Miñán, A.; Schilardi, P. L.; Diaz, C. ACS Biomater. Sci. Eng. 2019, 5, 4920–4936. (96) Jain, A.; Duvvuri, L. S.; Farah, S.; Beyth, N.; Domb, A. J.; Khan, W. Adv. Healthc. Mater. 2014, 3, 1969–1985. (97) Froidevaux, V.; Negrell, C.; Caillol, S.; Pascault, J. P.; Boutevin, B. Chem. Rev. 2016, 116, 14181–14224. (98) Sahariah, P.; Másson, M. Biomacromolecules 2017, 18, 3846–3868. (99) Radzishevsky, I. S.; Rotem, S.; Bourdetsky, D.; Navon-Venezia, S.; Carmeli, Y.; Mor, A. Nat. Biotechnol. 2007, 25, 657–659. (100) Asri, L. A. T. W.; Crismaru, M.; Roest, S.; Chen, Y.; Ivashenko, O.; Rudolf, P.; Tiller, J. C.; Van Der Mei, H. C.; Loontjens, T. J. A.; Busscher, H. J. Adv. Funct. Mater. 2014, 24, 346–355. (101) Iarikov, D. D.; Kargar, M.; Sahari, A.; Russel, L.; Gause, K. T.; Behkam, B.; Ducker, W. A. Biomacromolecules 2014, 15, 169–176. (102) Timofeeva, L.; Kleshcheva, N. Appl. Microbiol. Biotechnol. 2011, 89, 475–492. (103) Guyomard, A.; Dé, E.; Jouenne, T.; Malandain, J. J.; Muller, G.; Glinel, K. Adv. Funct. Mater. 2008, 18, 758–765. (104) Lin, J.; Chen, X.; Chen, C.; Hu, J.; Zhou, C.; Cai, X.; Wang, W.; Zheng, C.; Zhang, P.; Cheng, J.; Guo, Z.; Liu, H. ACS Appl. Mater. Interfaces 2018, 10, 6124–6136. (105) Yue, J.; Zhao, P.; Gerasimov, J. Y.; Van De Lagemaat, M.; Grotenhuis, A.; Rustema-Abbing, M.; Van Der Mei, H. C.; Busscher, H. J.; Herrmann, A.; Ren, Y. Adv. Funct. Mater. 2015, 25, 6756–6767. 152 (106) Jin, X.; Wang, J.; Bai, J. Carbohydr. Res. 2009, 123, 3242–3247. (107) Dong, A.; Wang, Y. J.; Gao, Y.; Gao, T.; Gao, G. Chem. Rev. 2017, 117, 4806–4862. (108) Locock, K. E. S.; Michl, T. D.; Valentin, J. D. P.; Vasilev, K.; Hayball, J. D.; Qu, Y.; Traven, A.; Griesser, H. J.; Meagher, L.; Haeussler, M. Biomacromolecules 2013, 14, 4021–4031. (109) Haque, M.; Sartelli, M.; McKimm, J.; Bakar, M. A. Infect. Drug Resist. 2018, 11, 2321–2333. (110) Nguyen, L. H.; Drew, D. A.; Graham, M. S.; Joshi, A. D.; Guo, C. G.; Ma, W.; Mehta, R. S.; Warner, E. T.; Sikavi, D. R.; Lo, C. H.; Kwon, S.; Song, M.; Mucci, L. A.; Stampfer, M. J.; Willett, W. C.; Eliassen, A. H.; Hart, J. E.; Chavarro, J. E.; Rich-Edwards, J. W.; Davies, R.; Capdevila, J.; Lee, K. A.; Lochlainn, M. N.; Varsavsky, T.; Sudre, C. H.; Cardoso, M. J.; Wolf, J.; Spector, T. D.; Ourselin, S.; Steves, C. J.; Chan, A. T.; Albert, C. M.; Andreotti, G.; Bala, B.; Balasubramanian, B. A.; Beane-Freeman, L. E.; Brownstein, J. S.; Bruinsma, F. J.; Coresh, J.; Costa, R.; Cowan, A. N.; Deka, A.; Deming-Halverson, S. L.; Elena Martinez, M.; Ernst, M. E.; Figueiredo, J. C.; Fortuna, P.; Franks, P. W.; Freeman, L. B.; Gardner, C. D.; Ghobrial, I. M.; Haiman, C. A.; Hall, J. E.; Kang, J. H.; Kirpach, B.; Koenen, K. C.; Kubzansky, L. D.; Lacey, J. V.; Le Marchand, L.; Lin, X.; Lutsey, P.; Marinac, C. R.; Martinez, M. E.; Milne, R. L.; Murray, A. M.; Nash, D.; Palmer, J. R.; Patel, A. V.; Pierce, E.; Robertson, M. M.; Rosenberg, L.; Sandler, D. P.; Schurman, S. H.; Sewalk, K.; Sharma, S. V.; Sidey-Gibbons, C. J.; Slevin, L.; Smoller, J. W.; Tiirikainen, M. I.; Weiss, S. T.; Wilkens, L. R.; Zhang, F. Lancet Public Health 2020, 5, 475–483. (111) Richterman, A.; Meyerowitz, E. A.; Cevik, M. JAMA 2020, 324, 2155–2156. 153 (112) Abbas, M.; Robalo Nunes, T.; Martischang, R.; Zingg, W.; Iten, A.; Pittet, D.; Harbarth, S. Antimicrob. Resist. Infect. Control 2021, 10, 7. (113) JHU Center for Systems Science and Engineering. COVID-19 Dashboard by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University (JHU) https://coronavirus.jhu.edu/map.html (accessed Apr 13, 2021). (114) World Health Organization. Mask use in the context of COVID-19; Geneva, 2020. (115) Seidelman, J. L.; Lewis, S. S.; Advani, S. D.; Akinboyo, I. C.; Epling, C.; Case, M.; Said, K.; Yancey, W.; Stiegel, M.; Schwartz, A.; Stout, J.; Sexton, D. J.; Smith, B. A. Infect. Control Hosp. Epidemiol. 2020, 41, 1466–1467. (116) Shereen, M. A.; Khan, S.; Kazmi, A.; Bashir, N.; Siddique, R. J. Adv. Res. 2020, 24, 91–98. (117) Chin, A. W. H.; Chu, J. T. S.; Perera, M. R. A.; Hui, K. P. Y.; Yen, H.-L.; Chan, M. C. W.; Peiris, M.; Poon, L. L. M. The Lancet Microbe 2020, 1, 10. (118) van Doremalen, N.; Bushmaker, T.; Morris, D. H.; Holbrook, M. G.; Gamble, A.; Williamson, B. N.; Tamin, A.; Harcourt, J. L.; Thornburg, N. J.; Gerber, S. I.; Lloyd-Smith, J. O.; de Wit, E.; Munster, V. J. N. Engl. J. Med. 2020, 382, 1564–1567. (119) Morais, D. S.; Guedes, R. M.; Lopes, M. A. Materials 2016, 9, 498. (120) Baptista, M. S.; Cadet, J.; Di Mascio, P.; Ghogare, A. A.; Greer, A.; Hamblin, M. R.; Lorente, C.; Nunez, S. C.; Ribeiro, M. S.; Thomas, A. H.; Vignoni, M.; Yoshimura, T. M. Photochem. Photobiol. 2017, 93, 912–919. (121) Chen, W.; Chen, J.; Li, L.; Wang, X.; Wei, Q.; Ghiladi, R. A.; Wang, Q. ACS Appl. Mater. Interfaces 2019, 11, 29557−29568. (122) Henke, P.; Kirakci, K.; Kubát, P.; Fraiberk, M.; Forstová, J.; Mosinger, J. ACS Appl. 154 Mater. Interfaces 2016, 8, 25127–25136. (123) Donnelly, R. F.; McCarron, P. A.; Tunney, M. M. Microbiol. Res. 2008, 163, 1–12. (124) Peddinti, B. S. T.; Scholle, F.; Ghiladi, R. A.; Spontak, R. J. ACS Appl. Mater. Interfaces 2018, 10, 25955–25959. (125) Peddinti, B. S. T.; Morales-Gagnon, N.; Pourdeyhimi, B.; Scholle, F.; Spontak, R. J.; Ghiladi, R. A. ACS Appl. Mater. Interfaces 2021, 13, 155–163. (126) Bang, E. K.; Lista, M.; Sforazzini, G.; Sakai, N.; Matile, S. Chem. Sci. 2012, 3, 1752–1763. (127) Tsarevsky, N. V.; Matyjaszewski, K. Macromolecules 2002, 35, 9009–9014. (128) Zheng, S.; Brook, M. A. Macromol. Rapid Commun. 2021, 42, 2000375. (129) Le Neindre, M.; Nicolaÿ, R. Polym. Chem. 2014, 5, 4601–4611. (130) Lei, Z. Q.; Xiang, H. P.; Yuan, Y. J.; Rong, M. Z.; Zhang, M. Q. Chem. Mater. 2014, 26, 2038–2046. (131) Chen, M.; Zhou, L.; Wu, Y.; Zhao, X.; Zhang, Y. ACS Macro Lett. 2019, 8, 255–260. (132) Karis, D.; Nelson, A. Polym. Chem. 2020, 11, 6910–6918. (133) Naga, N.; Moriyama, K.; Furukawa, H. J. Polym. Sci. Part A Polym. Chem. 2017, 55, 3749–3756. (134) Wolfrum, M.; Schwarz, R. J.; Schwarz, M.; Kramer, M.; Richert, C. Nanoscale 2019, 11, 14921–14928. (135) Kumar, P.; Singh, G.; Tripathi, D.; Jain, S. L. RSC Adv. 2014, 4, 50331–50337. (136) Wu, W. Bin; Wong, Y. C.; Tan, Z. K.; Wu, J. Catal. Sci. Technol. 2018, 8, 4257–4263. (137) Talla, A.; Driessen, B.; Straathof, N. J. W.; Milroy, L. G.; Brunsveld, L.; Hessel, V.; Noël, T. Adv. Synth. Catal. 2015, 357, 2180–2186. 155 (138) Oba, M.; Okada, Y.; Endo, M.; Tanaka, K.; Nishiyama, K.; Shimada, S.; Ando, W. Inorg. Chem. 2010, 49, 10680–10686. (139) Chandross, E. A.; Ferguson, J.; McRae, E. G. J. Chem. Phys. 1966, 45, 3546–3553. (140) Seki, T.; Iwanami, Y.; Kuwatani, Y.; Iyoda, M. J. Heterocycl. Chem. 1997, 34, 773–780. (141) Stukenbroeker, T.; Wang, W.; Winne, J. M.; Du Prez, F. E.; Nicolaÿ, R.; Leibler, L. Polym. Chem. 2017, 8, 6590–6593. (142) Clemens, R. J.; Hyatt, J. A. J. Org. Chem. 1985, 50, 2431–2435. (143) Kuster, S.; Geiger, T. Dye. Pigment. 2015, 113, 110–116. (144) Wu, D. Y.; Meure, S.; Solomon, D. Prog. Polym. Sci. 2008, 33, 479–522. (145) Chen, X.; Dam, M. A.; Ono, K.; Mal, A.; Shen, H.; Nutt, S. R.; Sheran, K.; Wudl, F. Science 2002, 296, 1698–1702. (146) Capelot, M.; Unterlass, M. M.; Tournilhac, F.; Leibler, L. ACS Macro Lett. 2012, 1, 780–792. (147) Brutman, J. P.; Delgado, P. A.; Hillmyer, M. A. ACS Macro Lett. 2014, 3, 607–610. (148) Islangulov, R. R.; Castellano, F. N. Angew. Chem. Int. Ed. 2006, 45, 5957–5959. (149) Bouas-Laurent, H.; Castellan, A.; Desvergne, J. P.; Lapouyade, R. Chem. Soc. Rev. 2001, 30, 248–263. (150) Payamyar, P.; Kaja, K.; Ruiz-Vargas, C.; Stemmer, A.; Murray, D. J.; Johnson, C. J.; King, B. T.; Schiffmann, F.; Vandevondele, J.; Renn, A.; Götzinger, S.; Ceroni, P.; Schütz, A.; Lee, L. T.; Zheng, Z.; Sakamoto, J.; Schlüter, A. D. Adv. Mater. 2014, 26, 2052–2058. (151) Fudickar, W.; Linker, T. Langmuir 2010, 26, 4421–4428. (152) Nurkhamidah, S.; Woo, E. M.; Yeh, Y. T.; Luo, F.; Katiyar, V. Polymers 2018, 10, 545. 156 (153) Lugito, G.; Su, C. C.; Wang, Y. H.; Woo, E. M. J. Polym. Res. 2017, 24, 1–7. (154) Nickmans, K.; Murphy, J. N.; de Waal, B.; Leclère, P.; Doise, J.; Gronheid, R.; Broer, D. J.; Schenning, A. P. H. J. Adv. Mater. 2016, 28, 10068–10072. (155) Konarev, P. V.; Volkov, V. V.; Sokolova, A. V.; Koch, M. H. J.; Svergun, D. I. J. Appl. Crystallogr. 2003, 36, 1277–1282. (156) Higgins, J. S.; Dodgson, K.; Semlyen, J. A. Polymer 1979, 20, 553–558. (157) Jadav, G. L.; Aswal, V. K.; Bhatt, H.; Chaudhari, J. C.; Singh, P. S. J. Memb. Sci. 2012, 415–416, 624–634. (158) Smilgies, D. M.; Folta-Stogniew, E. J. Appl. Crystallogr. 2015, 48, 1604–1606. (159) Ornstein, L. S.; Zernike, F. Phys. Zeit 1918, 19, 134–137. (160) Matsui, S.; Kureha, T.; Nagase, Y.; Okeyoshi, K.; Yoshida, R.; Sato, T.; Suzuki, D. Langmuir 2015, 31, 7228–7237. (161) Ibarboure, E.; Rodriguez-Hernández, J.; Papon, E. J. Polym. Sci. Part A Polym. Chem. 2006, 44, 4668–4679. (162) Russell, T. P.; Ito, H.; Wignall, G. D. Macromolecules 1988, 21, 1703–1709. (163) Crevecoeur, G.; Groeninckx, G. Macromolecules 1991, 24, 1190–1195. (164) Talibuddin, S.; Wu, L.; Runt, J.; Lin, J. S. Macromolecules 1996, 29, 7527–7535. (165) Silva, V. P. R.; Silva, G. G.; Caliman, V.; Rieumont, J.; de Miranda-Pinto, C. O. B.; Archanjo, B. S.; Neves, B. R. A. Eur. Polym. J. 2007, 43, 3283–3291. (166) Katoh, R.; Suzuki, K.; Furube, A.; Kotani, M.; Tokumaru, K. J. Phys. Chem. C 2009, 113, 2961–2965. (167) Stejskal, E. O.; Tanner, J. E. J. Chem. Phys. 1965, 42, 288. (168) Saarinen, T. R.; Johnson, C. S. J. Magn. Reson. 1988, 78, 257–270. 157 (169) Gránásy, L.; Pusztai, T.; Tegze, G.; Warren, J. A.; Douglas, J. F. Phys. Rev. E - Stat. Nonlinear, Soft Matter Phys. 2005, 72, 011605. (170) Crist, B.; Schultz, J. M. Prog. Polym. Sci. 2016, 56, 1–63. (171) Korchuganov, D. S.; Gagnidze, I. E.; Tkach, E. N.; Schulga, A. A.; Kirpichnikov, M. P.; Arseniev, A. S. J. Biomol. NMR 2004, 30, 431–442. (172) Li, C.; Wang, Y.; Pielak, G. J. J. Phys. Chem. B 2009, 113, 13390–13392. (173) Wang, W.; Zhai, X.-M.; He, B.-L.; Wen, X.-J.; Ma, Z.-P.; Yuan, F.; Tang, X.-F. Macromolecules 2005, 38, 1717–1722. (174) Song, J.; Tranchida, D.; Vancso, G. J. Macromolecules 2008, 41, 6757–6762. (175) Capaldi, F. M.; Boyce, M. C.; Rutledge, G. C. J. Chem. Phys. 2006, 124, 214709. (176) Kiran, M. S. R. N.; Varughese, S.; Reddy, C. M.; Ramamurty, U.; Desiraju, G. R. Cryst. Growth Des. 2010, 10, 4650–4655. (177) Michal, C. A.; Broughton, K.; Hansen, E. Rev. Sci. Instrum. 2002, 73, 453–458. (178) Bansal, A. K.; Holzer, W.; Penzkofer, A.; Tsuboi, T. Chem. Phys. 2006, 330, 118–129. (179) Amao, Y. Microchim. Acta 2003, 143, 1–12. (180) Tan, H.; Liu, X. C.; Su, J. H.; Wang, Y. X.; Gu, X. M.; Yang, D. J.; Waclawik, E. R.; Zhu, H. Y.; Zheng, Z. F. Sci. Rep. 2019, 9, 1280. (181) Ondrus, D. J.; Boerio, F. J. J. Colloid Interface Sci. 1988, 124, 349–357. (182) Pandey, P.; Katsoulidis, A. P.; Eryazici, I.; Wu, Y.; Kanatzidis, M. G.; Nguyen, S. T. Chem. Mater. 2010, 22, 4974–4979. (183) Fujisawa, S.; Kadoma, Y.; Yokoe, I. Chem. Phys. Lipids 2004, 130, 189–195. (184) Ouannes, C.; Wilson, T. J. Am. Chem. Soc. 1968, 90, 6527–6528. (185) Bhattacharjee, N.; Parra-Cabrera, C.; Kim, Y. T.; Kuo, A. P.; Folch, A. Adv. Mater. 2018, 158 30, 1800001. (186) Revilla, A. S.; Pestana, C. R.; Pardo-Andreu, G. L.; Santos, A. C.; Uyemura, S. A.; Gonzales, M. E.; Curti, C. Toxicol. Vitr. 2007, 21, 782–788. (187) Kandyala, R.; Raghavendra, S. P.; Rajasekharan, S. J. Oral Maxillofac. Pathol. 2010, 14, 1–5. (188) Wachter, E.; Dees, C.; Harkins, J.; Scott, T.; Petersen, M.; Rush, R. E.; Cada, A. Lasers Surg. Med. 2003, 32, 101–110. (189) Camino, C.; Lomakin, S. M.; Lazzari, M. Polymer 2001, 42, 2395–2402. (190) Xue, L.; Zhang, Y.; Zuo, Y.; Diao, S.; Zhang, J.; Feng, S. Mater. Lett. 2013, 106, 425–427. (191) Camino, G.; Lomakin, S. M.; Lageard, M. Polymer 2002, 43, 2011–2015. (192) Berkowski, K. L.; Plunkett, K. N.; Yu, Q.; Moore, J. S. J. Chem. Educ. 2005, 82, 1365–1369. (193) Thompson, B. L.; Ouyang, Y.; Duarte, G. R. M.; Carrilho, E.; Krauss, S. T.; Landers, J. P. Nat. Protoc. 2015, 10, 875–886. (194) Lowe, A. B. Polym. Chem. 2014, 5, 4820. (195) Schwartz, J. J.; Boydston, A. J. Nat. Commun. 2019, 10, 791. (196) Nguyen, K. D. Q.; Megone, W. V.; Kong, D.; Gautrot, J. E. Polym. Chem. 2016, 7, 5281–5293. (197) Ogilby, P. R.; Foote, C. S. J. Am. Chem. Soc. 1983, 105, 3423–3430. (198) Dolmans, D. E. J. G. J.; Fukumura, D.; Jain, R. K. Nat. Rev. Cancer 2003, 3, 380–387. (199) Pellosi, D. S.; Estevão, B. M.; Semensato, J.; Severino, D.; Baptista, M. S.; Politi, M. J.; Hioka, N.; Caetano, W. J. Photochem. Photobiol. A 2012, 247, 8–15. 159 (200) Hasegawa, T.; Kondo, Y.; Koizumi, Y.; Sugiyama, T.; Takeda, A.; Ito, S.; Hamada, F. Bioorganic Med. Chem. 2009, 17, 6015–6019. (201) Lebed, A. V.; Biryukov, A. V.; McHedlov-Petrossyan, N. O. Chem. Heterocycl. Compd. 2014, 50, 336–348. (202) Vodolazkaya, N. A.; Gurina, Y. A.; Salamanova, N. V.; Mchedlov-Petrossyan, N. O. J. Mol. Liq. 2009, 145, 1888–1896. (203) Massif, C.; Dautrey, S.; Haefele, A.; Ziessel, R.; Renard, P. Y.; Romieu, A. Org. Biomol. Chem. 2012, 10, 4330–4336. (204) Bojinov, V. B.; Panova, I. P.; Grabchev, I. K. Dye. Pigment. 2007, 74, 187–194. (205) Popov, K.; Oshchepkov, M.; Kamagurov, S.; Tkachenko, S.; Dikareva, J.; Rudakova, G. J. Appl. Polym. Sci. 2017, 134, 1–11. (206) Carvell, M.; Robb, I. D.; Small, P. W. Polymer 1998, 39, 393–398. (207) Adamczyk, M.; Grote, J. Bioorganic Med. Chem. Lett. 2000, 10, 1539–1541. (208) Fawcett, A. S.; Brook, M. A. Macromolecules 2014, 47, 1656–1663. (209) Malanga, M.; Darcsi, A.; Balint, M.; Benkovics, G.; Sohajda, T.; Beni, S. Beilstein J. Org. Chem. 2016, 12, 537–548. (210) Sammon, C.; Li, C.; Armes, S. P.; Lewis, A. L. Polymer 2006, 47, 6123–6130. (211) Wright, T.; Tomkovic, T.; Hatzikiriakos, S. G.; Wolf, M. O. Submitted to Polym. Chem. (212) Nair, B. Int. J. Toxicol. 2003, 22, 11–35. (213) Argüeso, P.; Tisdale, A.; Spurr-Michaud, S.; Sumiyoshi, M.; Gipson, I. K. Investig. Ophthalmol. Vis. Sci. 2006, 47, 113–119. (214) Theodossiou, T.; Hothersall, J. S.; Woods, E. A.; Okkenhaug, K.; Jacobson, J.; MacRobert, A. J. Cancer Res. 2003, 63, 1818–1821. 160 (215) G., M.; D., R. Clin. Microbiol. Rev. 1999, 12, 147–179. (216) Zhao, L.; May, J. P.; Blanc, A.; Dietrich, D. J.; Loonchanta, A.; Matinkhoo, K.; Pryyma, A.; Perrin, D. M. ChemBioChem 2015, 16, 1420–1425. (217) Matinkhoo, K.; Pryyma, A.; Todorovic, M.; Patrick, B. O.; Perrin, D. M. J. Am. Chem. Soc. 2018, 140, 6513–6517. (218) Verkleij, A. J.; Zwaal, R. F. A.; Roelofsen, B.; Comfurius, P.; Kastelijn, D.; van Deenen, L. L. M. BBA - Biomembr. 1973, 323, 178–193. (219) Karis, D. G.; Ono, R. J.; Zhang, M.; Vora, A.; Storti, D.; Ganter, M. A.; Nelson, A. Polym. Chem. 2017, 8, 4199–4206. (220) Hoek, I.; Tho, F.; Arnold, W. M. Lab Chip 2010, 10, 2283–2285. (221) Schweitzer, C.; Schmidt, R. Chem. Rev. 2003, 103, 1685–1757. (222) Iida, S.; Ohkubo, Y.; Yamamoto, Y.; Fujisawa, A. J. Clin. Biochem. Nutr. 2017, 61, 169–175. (223) Lambert, C. R.; Kochevar, I. E. J. Am. Chem. Soc. 1996, 118, 3297–3298. (224) Klaper, M.; Fudickar, W.; Linker, T. J. Am. Chem. Soc. 2016, 138, 7024–7029. (225) Dahl, T. A.; Midden, W. R.; Hartman, P. E. J. Bacteriol. 1989, 171, 2188–2194. (226) Ghareeb, C. R.; Peddinti, B. S. T.; Kisthardt, S. C.; Scholle, F.; Spontak, R. J.; Ghiladi, R. A. Front. Med. 2021, 8, 657837. (227) Shapira, T.; Monreal, I. A.; Dion, S. P.; Jager, M.; Désilets, A.; Olmstead, A. D.; Vandal, T.; Buchholz, D. W.; Imbiakha, B.; Gao, G.; Chin, A.; Rees, W. D.; Steiner, T.; Nabi, I. R.; Marsault, E.; Sahler, J.; August, A.; Van de Walle, G.; Whittaker, G. R.; Boudreault, P.-L.; Aguilar, H. C.; Leduc, R.; Jean, F. bioRxiv 2021, 2021.05.03.442520. (228) Hollmann, A.; Castanho, M. A. R. B.; Lee, B.; Santos, N. C. Biochem. J. 2014, 459, 161–161 170. (229) Lenard, J.; Rabson, A.; Vanderoef, R. Proc. Natl. Acad. Sci. U. S. A. 1993, 90, 158–162. (230) Lenard, J.; Vanderoef, R. Photochem. Photobiol. 1993, 58, 527–531. (231) Zeng, L.; Wang, M. Di; Ming, S. L.; Li, G. L.; Yu, P. W.; Qi, Y. L.; Jiang, D. W.; Yang, G. Y.; Wang, J.; Chu, B. B. Redox Biol. 2020, 36, 101601. (232) Olmstead, A. D.; Knecht, W.; Lazarov, I.; Dixit, S. B.; Jean, F. PLoS Pathog. 2012, 8, e1002468. (233) Leung, K.; Shum, M. H. H.; Leung, G. M.; Lam, T. T. Y.; Wu, J. T. Eurosurveillance 2020, 26, 2002106. (234) Jones, T. C.; Biele, G.; Mühlemann, B.; Veith, T.; Schneider, J.; Beheim-Schwarzbach, J.; Bleicker, T.; Tesch, J.; Schmidt, M. L.; Sander, L. E.; Kurth, F.; Menzel, P.; Schwarzer, R.; Zuchowski, M.; Hofmann, J.; Krumbholz, A.; Stein, A.; Edelmann, A.; Corman, V. M.; Drosten, C. Science 2021, 373, 5273. (235) Rubio, N.; Prat, F.; Bon, N.; Borrell, J. I.; Teixidó, J.; Villanneva, Á.; Juarranz, Á.; Cañete, M.; Stockert, J. C.; Nonell, S. New J. Chem. 2005, 29, 378–384. (236) Van Wart, H. E.; Lewis, A.; Scheraga, H. A.; Saeva, F. D. Proc. Natl. Acad. Sci. U. S. A. 1973, 70, 2619–2623. (237) Ogilby, P. R. Chem. Soc. Rev. 2010, 39, 3181–3209. (238) Pearson, D. S.; Fetters, L. J.; Graessley, W. W.; Strate, G. Ver; Von Meerwall, E. Macromolecules 1994, 27, 711–719. (239) Purushothama Chayr, K.; Rajaram, S.; Iyengar, D. S. Synth. Commun. 2000, 30, 3905–3911. (240) Büyüktanir, E. A.; Küçükyavuz, Z. J. Polym. Sci. Part B Polym. Phys. 2000, 38, 2678–162 2686. (241) Süer, N. C.; Demir, C.; Ünübol, N. A.; Yalçin, Ö.; Kocagöz, T.; Eren, T. RSC Adv. 2016, 6, 86151–86157. (242) Taniguchi, M.; Lindsey, J. S. Photochem. Photobiol. 2018, 94, 290–327. 163 Appendices Appendix A : Supplementary Information for Chapter 2 Figure A.1. UV-Vis spectra of A1a after different amounts of time of irradiation at 365 nm. Arrows indicate direction of change. Figure A.2. Images of solid (a) and solution (CH2Cl2, b) emission of A1a (left) and A1b (right) under 365 nm irradiation. 164 Figure A.3. 1H NMR spectra of A1a (bottom) and the photoproduct A1b (top). 400 MHz, CD2Cl2, RT. ESI-MS inset in MeOH. 165 Figure A.4. 1H NMR spectra of thermal exchange reaction between A1a and para-toluidine initially (bottom) and after 120 °C for 5 minutes (top). Red circles are assigned to A1a, green circles para-toluidine, and blue circles the new product formed. 400 MHz, (CD3)2SO, RT. Figure A.5. Photograph of sample AP2a in a plastic petri dish. 166 Figure A.6. Comparison of the IR spectra of P1a with model compound 1a before and after irradiation. Figure A.7. G′, G″, and η for AP1a (left, 70 °C) and AP1b (right, 75 °C), measured at 0.1% strain. UV light167 Figure A.8. Strain sweep rheology experiment for AP2a at 0.1 Hz from 0.01-10% strain, 60 °C. Figure A.9. Stress relaxation curve for AP1a under a 0.5% initial strain. 168 Appendix B : Supplementary Information for Chapter 3 Figure B.1. 1H NMR spectrum of B1. 400 MHz, RT, (CD3)2SO. Other peaks are residual solvent peaks. 169 Figure B.2. 1H NMR spectra of (bottom) PNH2-7 and (top) BP7 showing the new peaks due to B1 condensation. 400 MHz, RT, CD2Cl2 170 ppm Dt x10-11 (m2/s) ID 8.542 1.182 Anthracene C-H 8.447 1.152 Anthracene C-H 8.075 1.152 Anthracene C-H 7542 1.158 Anthracene C-H 4.447 1.190 RC=CH-CO2R 2.69 1.199 Non-condensed propylamine 0.167 1.099 Si-CH3 Table B.1. Calculated translational diffusion coefficients for 1H NMR peaks corresponding to the anthracene portion, vinylogous urethane, and PNH2-7 chain, demonstrating that all components diffuse at similar speeds. Dt determined from 2D DOSY measurements, 400 MHz, RT, CD2Cl2. Figure B.3. UV-VIS spectra of a dropcast sample of polymer BP7 as a function of irradiation time using 365 nm irradiation. 171 Figure B.4. Optical microscope image of a side-on view of a free-standing piece of irradiated BP7, showing the approximate film thickness of 115 μm. Figure B.5. Average approximate distance (d) travelled by a sample of polymer BP25 two minutes after inversion as a function of irradiation time (t). 172 Figure B.6. FT-IR spectrum of the amine-containing PDMS PNH2-7, anthracene acetoacetate B1, and the polymer BP7 (condensed from B1 and PNH2-7). Arrows indicate the C=O stretch before (blue) and after condensation (red), showing a shift to lower wavenumbers resulting from increased conjugation. No changes were observed in BP7 after irradiation. Figure B.7. Optical microscope image of a thin film of BP7 after 15 minutes of 365 nm irradiation showing only spherical crystalline seeds. 173 Figure B.8. Optical microscope image of BP7 leaves under a cross-polarizer (left) and cross-polarizer + 530 nm retardation plate (right) showing crystal structures having grown into each other without merging. Figure B.9. Optical microscope image of bulk BP7 in a vial after one hour of 365 nm irradiation from all directions, imaged through the sides of the glass vial. 174 Figure B.10. Differential scanning calorimetry of BP7 after 60 minutes of irradiation, showing a full heating and cooling cycle with a temperature ramp speed of 10 °C/min. Figure B.11. Optical microscope image of a thin film of BP7 after 60 minutes of 365 nm followed by 60 minutes at 100 °C. 175 Figure B.12. Optical microscope image of BP7 leaves after 60 minutes at 100 °C under a cross-polarizer (left) and cross-polarizer + 530 nm retardation plate (right). Figure B.13. PXRD measurements of crystallized P7 and crystallized BP7 after 1 hour at 100 °C. Cu radiation, RT. 176 Figure B.14. Optical microscope image of the center of BP25 after ten minutes of irradiation showing buckling of the surface. Figure B.15. Magnified POM image from Figure 3.3.1 with arrows showing 45° branching of the blue region from the radial orange branch. 177 Figure B.16. Optical microscope image of BP7 seeds under a cross-polarizer (left) and cross-polarizer + 530 nm retardation plate (right). Figure B.17. Wide-angle X-ray scattering and small-angle X-ray scattering of a free-standing BP7 film after irradiation, showing only two diffuse peaks attributed to the PDMS backbone. Measurements were focused on areas containing crystalline leaves. 178 Figure B.18. WAXS and SAXS of BP7 in a glass capillary, before irradiation and after 120 minutes of 365 nm irradiation. Figure B.19. Guinier plots of the low q region of the SAXS spectrum of crystallized BP7, focused on the crystalline regions. 179 Figure B.20. Ornstein-Zernike plot of crystallized BP7 giving a correlation distance of 61 Å. Figure B.21. PXRD measurements of BP7 before irradiation, after 60 minutes of 365 nm irradiation, and of PNH2-7. Cu radiation, RT. 180 Figure B.22. Schematic representation of (top) cross-linking via anthracene dimerization resulting in oriented cross-linked areas surrounded by amorphous polymer chains and (bottom) cross-linking via a flexible, non-rigid moiety resulting in no ordering. 181 Figure B.23. Confocal microscopy images of P7 leaf edges at different depths and inverted 3D reconstructed data. Inset numbers are the vertical distance from the surface. Reconstruction boxes are 60 μm × 60 μm. 182 Figure B.24. Excitation and emission spectra of a thin film of BP7 after one hour of 365 nm irradiation. Figure B.25. (Left) Bright field and (right) fluorescence imaging of BP7 crystals at 10× magnification, using 350 nm excitation light. 183 Figure B.26. Schematic representation for confinement of anthracene molecules in the crystalline seeds and leaves giving rise to the fluorescence images from Figure B.24, proceeding from linear polymer to seed to leaf growth. Sample ID Dt (cm2/sec) T1 (ms) T2 (ms) T1/T2 PNH2-7 4.85×10-7 0.815 421 1.94 BP3 8.56×10-9 1.067 161 6.61 BP7 7.60×10-9 0.9599 74 12.92 BP25 9.30×10-9 1.1537 41 27.85 BP7 crystalline 6.20×10-10 Table B.2. Translational diffusion speeds, T1, and T2 values for liquid polymer samples and crystallized BP7, measured using PFG 1H NMR. 184 Figure B.27. PFG 1H NMR diffusion measurement. The same data as in Figure 3.3.4, plotted as the natural logarithm of the signal intensity vs. the gradient strength squared to linearize the Gaussian behaviour of the Stejskal – Tanner diffusion equation. Liquid BP7 (left) and irradiated BP7 (right). In the liquid sample there appears to be an abrupt transition between single-component diffusion and a small (~10%), much slower diffusing component. The irradiated sample appears to make a more gradual transition, suggesting a distribution of slower diffusion coefficients. Larger error bars for the irradiated sample reflect the lower signal to noise ratio due to the slower diffusion rates and faster T2 decay. Figure B.28. (a) AFM height image of crystallized BP7, scale bar = 8 μm. (b) Representative force indentation curve taken at point 1. (c) Representative force indentation curve taken at point 2. 185 Appendix C : Supplementary Information for Chapter 4 Figure C.1. UV-VIS absorbance spectra of PtOEP, Rose Bengal (RB), and the spectral output of green LEDs used for irradiation. Spectra were collected in DCM (2.47 × 10-6 M) and MeOH (1.17 × 10-6 M), respectively. 186 Figure C.2. 1H NMR spectra of a sample containing n-butylamine and PtOEP before irradiation (bottom) and after one hour of 530 nm irradiation (top). Integrated peaks are assigned to the formed imine product. CD2Cl2, RT, 400 MHz. Figure C.3. Photograph of a freestanding piece of CP100 irradiated for one hour 530 nm light. Sample is 20 mm in diameter, 0.5 mm thick. 187 Figure C.4. Calculated optical transmittance of 530 nm light as a function of initial sample thickness through different initial polymer mixtures. Optical transmittance was calculated using the rearranged Beer-Lambert equation: 𝑇 = 10−𝜀𝑏𝑐 The molar extinction coefficient was determined from the data in Figure C.1, and the concentration was calculated using the masses of PtOEP, m-xylenes, and PNH2-7 for each mixture. Table C.1. Mass ratios and PtOEP wt% for samples with different amounts of PtOEP. 188 Table C.2. Mass balance of samples before and after irradiation for CP100 and CP25 small scale tests, as well as soluble % and mass swelling % determined using DCM. For mass balance experiments, PNH2-7 and the PtOEP solution were mixed in the previously described ratios and a set amount pipetted into a silicone mold. The mold was weighed before and after four hours of irradiation. The masses after irradiation indicate that insignificant amounts of m-xylenes remain in the system after cross-linking. The soluble fraction was determined by adding a contiguous piece of polymer (From Figure C.7), approximately 0.2 g, to 10 mL of DCM in a sealed vial and allowing to stand overnight. The DCM was decanted off, the system rinsed with additional DCM, and then the sample removed and patted dry with tissue. After being weighed, the sample was then dried for three days under vacuum and reweighed. The initial and final masses were used to determine the soluble fraction, and the swollen mass and final mass was used to determine the mass percent of DCM uptaken in the swollen gels. 189 Figure C.5. Solid-state 13C CP-MAS NMR spectrum of a sample of CP100 after drying under vacuum for one week. 9.4 Tesla, RT. Figure C.6. Proposed reaction pathway for the photooxidative cross-linking of alkyl-amine containing PDMS in the presence of oxygen. 190 Figure C.7. Photograph of cross-linked CP100 (left) and CP25 (right) prepared for mechanical testing. Solutions were irradiated for 18 hours using a 530 nm lamp. Sample disks are 30 mm diameter, 1 mm thick. Figure C.8. FT-IR spectra of cross-linked P100, PA containing 30 wt% amine end-terminated PDMS, PB cross-linked using Rose Bengal, P2nd prepared using (18-24% aminoethylaminopropylmethylsiloxane, polyethyleneimine branched, and polyethyleneimine branched after attempting cross-linking. 191 Figure C.9. Thermogravimetric analysis of samples cross-linked with different amounts of PtOEP as well as the non-cross-linked PDMS-NH2 starting polymer. 10 °C / minute, N2. Figure C.10. Differential scanning calorimetry (DSC) heating traces of P25 and P100, collected at 10 °C / minute. 192 Figure C.11. Photograph of the initial solutions used to cast the sample of CP100 (left) and CP25 (right) in Figure C.7. Figure C.12. Photograph of 2 mm lines photopatterned in CP25 using a mask printed on plastic transparencies. 193 Appendix D : Supplementary Information for Chapter 5 Figure D.1. Parallel plate photo-rheological setup using a top (grey) 8 mm plate and a bottom (blue) transparent acetate plate. 365 nm light irradiates the sample from below, and atmospheric O2 diffuses into the sample through the exposed edge. The sample is initially a liquid (shown as green) and becomes solid (red) after irradiation only near the polymer-air interface due to limited O2 diffusion. Samples irradiated without the top geometry cross-link evenly. 194 Figure D.2. Representative photo-rheological results of PNH2-7 and OEP plotted in logarithmically (left) and linearly (right). Before cross-linking the material lacks any internal microstructure and as such the values of G´ and Gʺ are below the sensitivity of the instrumentation used. Upon irradiation with 365 nm light (dotted line, 60 s, 150 mW/cm2) G´ rapidly increases above Gʺ (onset time). The onset time is determined from the logarithmic plot, and the initial cure rate is determined from the slope of G´ in the first 100 s of irradiation. [OEP] (mM) Onset Time (s) Initial Rate (G´/s) %T365nm 1.0 17 ± 4 106 ± 11 0.009 0.5 12 ± 2 121 ± 5 0.94 0.25 13 ± 1 114 ± 4 9.7 0.1 26 ± 1 76 ± 2 39.4 0.05 20 ± 2 78 ± 3 62.7 Table D.1. Photo-rheological kinetic data for the cross-linking of PNH2-7 and OEP at different [OEP]. The %T365nm was calculated using a sample thickness of 500 um, ε365nm = 82000 cm-1 M-1 and the equation242 𝐴 = 𝜀 𝑏 𝑐 𝐴 = − log(𝑇) 𝑇 = 10−(𝜀 𝑏 𝑐) 195 Figure D.3. The three major tautomers for neutral xanthene dyes bearing carboxylic acid and amide functionalities. A closed lactone (left), free acid (middle) and zwitterionic (right) are possible, with only the free acid isomer having absorbance in the visible region. Figure D.4. Reaction scheme for PNH2-7 and fluorescein resulting in fluorescein-labelled PDMS (CPF) used for model studies. 196 Figure D.5. Vibrational spectra of PNH2-7, the fluorescein labelled polymer DPF, and fluorescein. The shift in carbonyl peak is attributed to conversion from ester to amide. 197 Figure D.6. 1H NMR spectrum of fluorescein labelled PDMS (DPF), CD2Cl2, RT, 400 MHz. Integration values suggest that the remaining amide-alkyl peaks overlap with the unreacted alkyl-amine signals. Broadness is attributed to the poor solubility of the polymer in CD2Cl2, which was determined to be the best NMR solvent for this sample. The low concentration of dye relative to polymer and poor solubility hinders further NMR analysis, with adding additional fluorescein to the polymer resulting in a completely insoluble material. 1H NMR (peaks also present in PNH2-7 have been omitted for clarity) (400 MHz, CD2Cl2, RT): δ 7.0 (m, 10H), 3.73 (q, 6.8 Hz, 2H). 198 Figure D.7. 1H NMR spectrum of PDMS-NH2, CD2Cl2, RT, 400 MHz. 1H NMR (400 MHz, CD2Cl2, RT): δ 2.62 (m, 2H), 1.46 (m, 2H), 0.51 (m, 2H), 0.09 (s, 97H) 199 Figure D.8. UV-VIS spectra of Rose Bengal and the spectral output of the green LED used for irradiation. MeOH, 1.17×10-6 M. Figure D.9. Photograph of DP1 in a glass vial. No change in appearance or precipitation was observed after four weeks in the dark. 200 Figure D.10. UV-VIS spectra of Rose Bengal and P1. Collected at 1.17×10-6 M and 5.8×10-7 M (calculated based on RB wt % in polymer) in MeOH and DCM respectively. Figure D.11. Normalized absorbance spectra of DP1 measured in solution (DCM) and as a neat oil on a glass slide. 201 Figure D.12. Calculated initial optical transmittance for DP1 as a function of sample thickness at three different wavelengths. Figure D.13. Calculated initial optical transmittance for polymers with different amounts of Rose Bengal, calculated at 530 nm. 202 Table D.2. Composition and optical penetration of samples with different amounts of molar equivalents of RB reacted with PNH2-7. Thickness was calculated for 530 nm light. Figure D.14. (Left) 150 μL of non cross-linked DP1 and 5 mL H2O in a vial after one week of storing in the dark. (Right) UV-VIS absorbance spectrum of the neat supernatant from the vial, compared against a calculated theoretical spectrum assuming complete solubility/miscibility of the polymer and dye with water. No miscibility between the polymer and water is observed, and no Rose Bengal is leached into solution. 203 Figure D.15. (Left) A focused view and (right) the full view of the vibrational spectra of PDMS-NH2, a sample cross-linked using a PtOEP solution, and a sample cross-linked using RB attached to the polymer (P1). The same imine peak at 1671 cm-1 is observed for both cross-linked samples. 204 Figure D.16. Solid-state 13C CP-MAS NMR spectrum of a cross-linked sample of DP1 after drying under vacuum for one week. 9.4 T, RT. 205 Figure D.17. Water contact angles of a cross-linked sample of DP1 and 10 μL droplets of deionized water, 1M NaOH, and 1 M HCl. Contact angles were measured in quadruplicate from photographs. Figure D.18. Photograph of the sample DP1 (left) and DP2 (right) used for mechanical testing. The samples are 1 mm thick, 30 mm diameter. 206 Table D.3. Soluble fraction and swelling ratio for samples cross-linked using different molar equivalents of RB. The soluble fraction was determined by adding a contiguous piece of polymer, approximately 0.3 g, to 10 mL of DCM in a sealed vial and allowing to stand overnight. The DCM was decanted off, the system rinsed with additional DCM, and then the sample removed and patted dry with tissue. After being weighed, the sample was then dried for three days under vacuum and reweighed. The initial and final masses were used to determine the soluble fraction, and the swollen mass and final mass was used to determine the mass ratio of DCM uptaken in the swollen gels. Figure D.19. Thermogravimetric analysis of the PNH2-7 starting material, DP1 liquid, and DP1 cross-linked using 530 nm light. 10 °C / min, N2. 207 Figure D.20. Differential scanning calorimetry (DSC) heating traces of P1, P2, and P3, collected at 10 °C / min, N2. All samples exhibit an approximate Tg of -115 °C. Figure D.21. Cartoon demonstrating the difference in deposition shape when performed at room temperature (top) and -78 °C (bottom). 208 Figure D.22. Labelled photograph of the experimental setup used to cryo-deposit non-equilibrium 3D structures of DP1 at -78 °C. Vessel was immersed in a dry ice acetone bath before deposition. Setup is designed to exclude water while still providing oxygen. Figure D.23. Photograph of the hashtag shape with a quarter for reference. When observed at a low angle the overlap of the arms can be clearly seen. 209 Figure D.24. Photolithography of DP1 to give the letters UBC after one hour of 530 nm irradiation. (Top Left) Printed photomask used to pattern the polymer. (Top Right) P1 on a glass slide after one hour of 530 nm irradiation through the photomask. Colorless areas are regions that were exposed to light. (Bottom Left) Slide after rinsing with ethyl acetate. The pink color diffused into the printed structure during rinsing. (Bottom Right) Slide after photobleaching overnight using 530 nm light to give a clear, colorless pattern. 210 Figure D.25. Side-on and top view of a non-equilibrium hashtag structure prepared using -78 °C deposition alongside the letters “UBC” stereolithographically printed using a 2 mm resolution photomask. Figure D.26. Direct-write 3D printing setup used to simultaneously write and irradiate the polymer onto glass. 211 Figure D.27. Direct-write 3D printing of DP3 at two different print speeds, 2mm/s (left) and 8 mm/s (right) onto glass slides. Figure D.28. Diagram showing the simplified steps leading to cell lysis for primary amine containing surfaces, proceeding through electrostatic attraction, interdigitation of the amine groups into the cell membrane, and disruption of membrane integrity. 212 Figure D.29. Normalized CFUs for E. incubated with cross-linked DP3 powder and a continuous sample at the same polymer mass. Samples were incubated for 24 h under constant shaking and compared with controls with no polymer. Determined from colony counts grown on agar plates in triplicate. 213 Appendix E : Supplementary Information for Chapter 6 Figure E.1. Structure of the Rose Bengal containing polymer (prepared from PNH2-7 and 0.048 molar equivalents of RB) and TPP used in these experiments. Figure E.2. Absorbance spectra of Rose Bengal lactone (RB) and tetraphenylporphyrin (TPP) in methanol, and the measured spectral output of the green and UV LEDs used in this work. Only TPP absorbs light in the UV region, while both TPP and RB absorb green light. 214 Figure E.3. Absorbance spectra of a thin film of DP3 containing TPP before irradiation, and subsequently after UV then green light irradiation. UV irradiation excites and photodegrades TPP without fully degrading RBL. 215 Figure E.4. SEM images of untreated cotton (a,c) and EC/P13 (b,d) at 500× (top) and 2000× (bottom) magnification. a b c d 216 Figure E.5. Water contact angles of cotton fabric prepared using different polymer wt% solutions, measured using 10 μL droplets. Figure E.6. Materials soaked in EP13 solution for 10 minutes followed by 30 minutes of 395 irradiation per side. 217 Figure E.7. The mass loading of EP13 onto different materials and the resulting water contact angles measured using 10 μL droplets. Figure E.8. The elongation at break and break stress determined from Instron mechanical testing of cotton and polyester strips treated using EP1, EP5, and EP13 solutions, measured in triplicate at 20 cm/min. 218 Fabric Type Wt % Coating Solution Elongation at break (%) Break Stress (kPa) Cotton 0 128 ± 4 102 ± 14 1 128 ± 2 97 ± 2 5 120 ± 2 86 ± 3 13 104 ± 8 86 ± 5 Polyester 0 358 ± 10 270 ± 19 1 377 ± 4 267 ± 5 5 363 ± 11 252 ± 18 13 358 ± 7 242 ± 13 Table E.1. Mechanical characterization data for samples of cotton and polyester coated with different polymer wt% solutions. Figure E.9. TGA traces of cotton and polyester treated using EP13, measured at 10 °C/minute under N2. 219 Figure E.10. FT-IR vibrational spectra of the non-cross-linked PNH2-7, treated fabric samples EC/P5, EC/P13, and untreated cotton. Peaks at 1258 cm-1 and 793 cm-1 are assigned to the Si-CH3 and PDMS CH3 vibrational modes respectively. Figure E.11. FT-IR vibrational spectra of the non-cross-linked PNH2-7 and materials treated with EP13. All treated materials show peaks assigned to PDMS stretching frequencies. 220 Figure E.12. Black colored cotton untreated (left) and treated with EP13 (right) showing no change in color. A 10 μL drop of water shows a high contact angle on the treated fabric, while the untreated fabric wets fully. Figure E.13. Absorbance spectra collected during the photooxidative degradation of uric acid using EC/P13 cotton samples at 0.048 molar equivalents of RB. The initial uric acid concentration was 2 × 10-4 M in 0.02 M phosphate buffer. Fabric mass was 20 mg for a 3mL solution. The sample was irradiated using 15W 530 nm LED from a distance of 4 cm. 221 Figure E.14. Absorbance at 292 nm of a 3 mL 2 × 10-4 M solution of uric acid in a 0.02 M phosphate buffer containing 20 mg EC/P13 fabric samples of varying RBL molar equivalents. Samples were irradiated using 15W 530 nm LED from a distance of 4 cm and the absorbance at 292 nm used to monitor uric acid oxidation. Sample ID g Polymer / g Fabric % Soluble Water Contact Angle EC/P13 PNH2-7 0.24 ± 0.02 6.7 ± 0.5 147 ± 1 EC/P13 PNH2-23 0.35 ± 0.01 14 ± 0.2 138 ± 3 Table E.2. Comparison of cotton fabric coated with polymers of 7 and 23 wt% amine groups. RBL molar equivalencies and coating procedure were the same for all samples. 222 Polymer Type Fabric Size (cm2) Bacterial Strain % Reduction in CFUs PNH2-7 4 E. coli 31 ± 9 MRSA 15 ± 1 9 E. coli 70 ± 4 MRSA 35 ± 2 18 E. coli 99.7 ± 3 MRSA 99.9 ± 0.2 PNH2-23 1 E. coli 0 MRSA 38 ± 2 2.25 E. coli 96 ± 4 MRSA 41 ± 4 4 E. coli 98 ± 4 MRSA 57 ± 6 Table E.3. Passive antimicrobial activity of fabric treated with two different amine wt % polymers, measured against E. coli and MRSA at different fabric size amounts. 223 Appendix F : Supplementary Information for Chapter 7 Figure F.1. UV-Vis absorption of DTP and TPP in DCM. εDPT has been multiplied by 50 for display purposes. Figure F.2. Change in UV-Vis absorption of a thin film of FPA with DPT and TPP irradiated using 430 nm light for 95 minutes. 224 Figure F.3. FT-IR spectra of polymer sample FPA before and after cross-linking. No change in the vibrational spectrum is observed. Figure F.4. Cross-linked sample of FPA used for Raman measurements, showing surface wrinkling not observed for samples with a high content of FPB. 225 Figure F.5. Photo-rheology experiments of samples of FP100 measured with and without DPT catalyst, measured at 23 mW/cm2 light intensity. The absence of change in G' for the sample without DPT demonstrates that 1O2 by itself does not result in cross-linking in this system. 226 Figure F.6. Relative amount of the three translational diffusion coefficients measured for the polymer backbone in sample FP100 as a function of irradiation time, determined using 1H PFG-NMR. Irradiation Time (hours) Toluene Dt (cm2/s) CF3Py Dt (cm2/s) PDMS-1 Dt (cm2/s) PDMS-2 Dt (cm2/s) PDMS-3 Dt (cm2/s) 0 5.4 ± 2 × 10-6 4.1 ± 2 × 10-6 2.0 ± 3 × 10-7 1.3 ± 1 × 10-8 1.0 ± 4 × 10-9 2 4.4 ± 2 × 10-6 3.8 ± 4 × 10-6 1.9 ± 4 × 10-7 1.4 ± 2 × 10-8 9.8 ± 6 × 10-10 4 4.7 ± 2 × 10-6 3.8 ± 1 × 10-6 1.2 ± 2 × 10-7 1.3 ± 2 × 10-8 9.3 ± 4 × 10-10 72 3.7 ± 2 × 10-6 3.0 ± 4 × 10-6 5.5 ± 9 × 10-8 5.5 ± 1 × 10-9 6.1 ± 2 × 10-10 Table F.1. Translational diffusion coefficient measured for sample FP100 as a function of irradiation time, determined using PFG-NMR. 227 Figure F.7. TGA curves of FPB and cross-linked polymer samples, measured at 10 °C / min under N2. Figure F.8. DSC curves of P100 and DPT, measured at 10 °C / min under N2. A strong crystallization and melting point can be observed for DPT, while P100 has a Tg transition and shifted Tc and Tm. 228 Sample ID Mass % FPA Mass % FPB Tg (°C) FP100 0 100 -123.5 FP75 25 75 -124.0 FP50 50 50 -122.6 Table F.2. Composition and Tg of cross-linked polymer samples, measured at 10 °C / min under. All cross-linked samples had the same melting/crystallization peaks associated with DPT. Figure F.9. % Soluble and Swell for samples FP100, FP75, and FP50. Samples were pre-weighed and then soaked with excess THF overnight. The samples were weighed to determine the % Swell, and then rinsed thoroughly with clean THF and driver overnight under vacuum. The resulting mass was used to determine the % Soluble, using the equations below. % 𝑆𝑤𝑒𝑙𝑙 = 𝑆𝑤𝑜𝑙𝑙𝑒𝑛 𝑀𝑎𝑠𝑠𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝑀𝑎𝑠𝑠× 100 % 𝑆𝑜𝑙𝑢𝑏𝑙𝑒 = 100 − (𝐷𝑟𝑖𝑒𝑑 𝑀𝑎𝑠𝑠 𝐴𝑓𝑡𝑒𝑟 𝑆𝑜𝑎𝑘𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝑀𝑎𝑠𝑠× 100) 229 Figure F.10. Example stress-strain curves for samples FP100, FP75, and FP50, measured from tensile test experiments. 230 Figure F.11. 1H NMR spectra of pristine FPB and degraded FPB recovered after reductive cleavage of the disulfide linkages using ZrCl4/NaBH4. 400 MHz, CD2Cl2, RT. 231 Figure F.12. Intrinsic viscosity plot for samples of pristine and degraded FPB at different concentrations in toluene. Figure F.13. FT-IR spectra of pristine FPB, cross-linked FP100, and degraded FPB.
Thesis/Dissertation
eng
Chemistry
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Wolf, Michael O.
Investigation of novel photo-cross-linking reactions for the preparation of functional polymeric materials
Text