Mechanistic studies of the metal catalyzed formation of polycarbonates and their thermoplastic elastomers

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Title: Mechanistic studies of the metal catalyzed formation of polycarbonates and their thermoplastic elastomers
Author: Choi, Wonsook
Abstract: Studies concerning the formation of industrially useful polycarbonates are the focus of this dissertation . Of particular importance is the biodegradable polymer , poly (trimethylene carbonate ) which has a wide range of medical applications . The production of polycarbonates can be achieved by the ring -opening polymerization of cyclic carbonate , or the copolymerization of carbon dioxide and oxiranes or oxetanes . For the production of polycarbonates from these monomers , Schiff base metal complexes have been designed , synthesized , and optimized as catalysts . Detailed kinetic and mechanistic studies have been performed for the ring -opening polymerization of cyclic carbonates , as well as the copolymerization of carbon dioxide and oxiranes or oxetane . In addition , the copolymerization of cyclic carbonates and cyclic esters to modify the mechanical and biodegradable properties of materials used for medical devices has been studied using biocompatible metal complexes . In the process for ring -opening polymerizations of trimethylene carbonate or lactides , Schiff base metal complexes (metal = Ca (II ) , Mg (II ) and Zn (II ) ) have been shown to be very effective catalysts to produce high molecular weight polymers with narrow polydispersities . Kinetic studies demonstrated the polymerization reactions to proceed via a mechanism first order in [monomer] , [catalyst] , and [cocatalyst] if an external cocatalyst is applied , and to involve ring -opening by way of acyl -oxygen bond cleavage . The activation parameters ( ?H ? , ?S ? and ?G ? ) were determined for ringopening polymerization of trimethylene carbonate , ring -opening polymerization of lactides , and copolymerization of trimethylene carbonate and lactide . In the process for copolymerization of carbon dioxide and oxetane , metal salen derivatives of Cr (III ) and Al (III ) along with cocatalyst such as n -Bu4NX or PPNX (PPN = bis (triphenylphosphine )iminium , and X = Br , Cl and N3 ) have been shown to be effective catalysts to provide poly (trimethylene carbonate ) with only trace amount of ether linkages . The formation of copolymer is proposed not to proceed via the intermediacy of trimethylene carbonate , which was observed as a minor product of the coupling reaction . To support this conclusion , ring -opening polymerization of trimethylene carbonate has been performed and kinetic parameters have been compared with those from the copolymerization of carbon dioxide and oxetane .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1433
Date: 2009-05-15

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Mechanistic studies of the metal catalyzed formation of polycarbonates and their thermoplastic elastomers. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1433 .

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