UBC Theses and Dissertations
Neutral and cationic indium complexes for the synthesis of functionalized monomers and polymers Jung, Hyuk Joon
Many efforts have been made to develop sustainable polymers that are functional as well as ultimately degradable in response to worldwide plastic pollution. Accordingly, these have prompted the development of new catalytic systems that can actively and selectively polymerize a variety of monomers. One excellent candidate is indium-based catalysts because of its low toxicity, functional group tolerance, and exceptional stability toward air and moisture. Herein, a series of neutral and cationic indium complexes were synthesized and their reactivities were explored for polymer synthesis. Monometallic cationic indium alkyl complex supported by a chiral amino-imino phenolate ligand catalyzed the highly selective coupling of epoxides and lactones to form spiroorthoesters. The quantitative conversion of both substrates allowed the synthesis of a series of functionalized spiroorthoesters by expanding the substrate scope to epoxides with various functional groups and lactones with different ring sizes. The double ring-opening polymerization of spiroorthoesters with analogous cationic indium alkyl complex resulted in the formation of the perfectly alternating copolymer of epoxide and lactone, poly(ether-alt-ester), which could be further modified via post-polymerization cross-linking and degraded in a basic medium. The reactivity of monometallic neutral and cationic indium alkyl complexes supported by a chiral diamino phenolate or a chiral amino-imino phenolate ligand was investigated for homopolymerization of methyl methacrylate and cyclic esters. The neutral complexes were active in the homopolymerizations of those monomers, whereas the cationic complexes only catalyzed one of those polymerizations depending on the counterions. In addition, block copolymers of methyl methacrylate with racemic lactide or epsilon-caprolactone were obtained via sequential copolymerizations with the neutral complex. Finally, bimetallic neutral and cationic indium complexes tethered by a binaphthol linker were investigated for homopolymerization of racemic lactide and copolymerization of CO₂ and cyclohexene oxide. A comparison of reactivity revealed that bimetallic complexes outperformed monometallic complexes, and the superior reactivity of the bimetallic system could be explained by cooperation between two indium centers, attributed to optimal In−In spacing and flexible distance by the binaphthol linker. These results are the first examples of tethered indium complexes acting cooperatively and show the potential of tethered indium complexes as promising catalysts for polymerization application.
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