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Neutral and cationic indium complexes for the synthesis of oxygenated copolymers

University of British Columbia

The development of synthetic polymers that include more sustainable building blocks is an active area of research. Controlled synthesis of copolymers including biobased segments has shown promising results, as the great diversity of functionalities from renewable resources can be used to tune the properties of macromolecules and often allow for post-functionalization. Herein, a series of discrete cationic indium complexes were synthesized and characterized. The role of counteranions was explored and (±)-[(ONNO)In(THF)2][SbF6] proved a highly active catalyst for the polymerization of epoxides and their co-polymerization with other cyclic ethers such as THF, oxetane and oxepane. This catalyst was also active in the one-pot copolymerization of epichlorohydrin with rac-lactide with good control. Investigation of the role of counteranions and solvent donors on the kinetics of polymerization of epoxides revealed a subtle effect of solvents on initiation rates. The activity of this cationic system was improved by changing the counterion from [SbF6] to a less coordinating tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (BArF4). In this way, copolymerization of different epoxides and rac-lactide was achieved either through a mixture of monomers or via sequential addition to high molecular weight block copolymers. Mechanistic studies and control experiments indicate that the epoxide is polymerized by a cationic mechanism to yield a neutral alkoxide indium species that subsequently polymerizes the lactide by a coordination-insertion mechanism with no significant interference of the two mechanisms under polymerization conditions. The thermal and tensile properties of different block copolymers were studied, revealing mostly amorphous materials. It was possible to control the ductility and stiffness of the copolymers by tuning the nature and chain length of the blocks. Finally, a series of neutral indium complexes with different ligand frameworks containing hemi-labile donors were synthesized and characterized. Alkoxide complexes with iminophenolate ligands bearing morpholine, thiomorpholine and methylpiperazine side donors were active in the polymerization of rac-lactide with very good control over molecular weights. The role of hemi-labile side donors was explored in the synthesis of block copolymers by sequential and simultaneous addition of rac-lactide and ε-caprolactone.

Text

2022-09-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/77703

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/