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Description:
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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 (ΔH≠ , ΔS≠ and ΔG≠ ) 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 . |