UBC Theses and Dissertations
A study on the homogeneous and surface initiated atom transfer radical polymerization of thermoresponsive polymers from regioselectively and non-regioselectively substituted cellulose derivatives Xavier, Ana Filipa de Assunção
The demand for environmentally friendly innovative materials and chemicals is driving research focused on utilizing renewable biopolymers. Cellulose is an abundant biopolymer, and is of particular interest due to its versatility and aptitude for chemical modification. Novel cellulosic materials were prepared by grafting thermoresponsive polymers, poly(N-isopropylacrylamide) (PNIPAM) and poly(2-(2-methoxyethoxy)ethyl methacrylate-co-oligo(ethyleneglycol) methacrylate) (P(DEGMA₉₅-co-OEGMA₅), from regioselectively substituted cellulosics and corresponding cellulosic honeycomb films using homogeneous and surface initiated atom transfer radical polymerization (ATRP/SI-ATRP). First, regioselective 6-O-(2-bromoisobutyryl)-TMS-O-cellulose was synthesized and used to produce a homogeneous honeycomb film. PNIPAM was then grafted from its surface via SI-ATRP, and the successful modification was confirmed by attenuated total reflectance-Fourier transform-infra-red spectroscopy, atomic force microscopy-quantitative nanomechanical mapping and contact angle. Next, the role of regioselective substitution of cellulosics on the formation of homogeneous honeycomb films was investigated using 3-O-substituted cellulosics. 3-O-(2-bromoisobutyryl)-2,6-TDMS-O-cellulose and 2,3-O-(2-bromoisobutyryl)-2,6-TDMS-O-cellulose were synthesized and their ability to form homogeneous honeycomb films tested. Unfortunately, the poor reactivity of the 2,6-O-TDMS-cellulose resulted in very low 3-O- modification. Regardless, both 3-O-(2-bromoisobutyryl)-2,6-TDMS-O-cellulose and 2,3-O-(2-bromoisobutyryl)-2,6-O-TDMS-cellulose formed honeycomb films, however, the latter produced more homogeneous films with smaller pore diameters. NIPAM was then successfully grafted from the surface of the 2,3-O-(2-bromoisobutyryl)-2,6-O-TDMS-cellulose honeycomb films, dramatically changing their surface properties. Finally, an alternative synthetic protocol was developed to increase the initiator density of the regioselective 3-O-cellulosics. A new macroinitiator, 3-O-(3-O-(2-bromoisobutyryl)-hydroxypropyl)-2,6-O-TDMS-cellulose was synthesized and the effect of regiochemistry on the ATRP reaction, specifically termination reactions between growing chains was studied. PNIPAM and P(DEGMA₉₅-co-OEGMA₅) were grafted from 3-O-(3-O-(2-bromoisobutyryl)-hydroxypropyl)-2,6-O-TDMS-cellulose and the effects of temperature, Cu(II), ligand, dilution, monomer concentration and initiator density were assessed through kinetic plots. The grafting of PNIPAM gave promising results; linear kinetic plots and copolymers with low polydispersity index However, the linear kinetic regime was short and the conversions were low. On the other hand, the grafting of P(DEGMA₉₅-co-OEGMA₅) was very challenging mainly due to the low solubility and, in some cases, insolubility of the copolymers. Nevertheless when a macroinitiator with a lower initiator density was used, a soluble copolymer with a lower PDI was obtained.
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