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Chiral indium catalysts for the ring-opening polymerization of cyclic esters

University of British Columbia

The development of highly active and stereoselective catalysts for lactide polymerization is an area of continuing interest in asymmetric catalysis. Aluminum complexes supported by (ONNO), tetradentate, bis(iminophenolate) or salen ligands are the most isoselective catalysts for lactide polymerization reported. However, these are sluggish initiators requiring elevated temperatures and multiple days to achieve high monomer conversion. Recently, indium based catalysts have attracted considerable attention as functional group tolerant catalysts for lactide polymerization. In this thesis a family of mononuclear and dinuclear chiral indium alkoxide complexes bearing salen ligands was prepared. Solution state and solid state characterization of these complexes were carried out. These were highly active catalysts for the ring-opening polymerization of lactide, to generate the biodegradable polymer, poly(lactic acid)(PLA). Polymerization behavior and the stereoselectivity of these systems showed a well-controlled and isoselective family of catalysts. An investigation into the effects of ligand modifications revealed a profound dependence of the stereoselectivity on the ortho-aryl substituents. A detailed study was carried out to gain insights into the mechanism of polymerization. This provided evidence for a mechanism consistent with a mononuclear propagating species. Modification of the ligand backbone to a binap functionality was carried out to synthesize the first reported indium salbinap complexes. The ligand shows the ability to coordinate in both a κ² and a κ⁴ coordination mode to a metal centre. However, these complexes were sluggish initiators with modest stereoselectivity for the ring-opening polymerization of lactide. A dinuclear indium catalyst was used to generate triblock copolymers of PLA and poly(hyroxybutyrate)(PHB) via simple sequential monomer addition. After confirming the formation of these A-B-C type PLA-PHB-PLA triblocks, a series of these copolymers with varying monomer composition were prepared and their thermo-mechanical properties were studies.

Text

2015-12-31

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/51483

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/