Ring-opening polymerization of cyclic monomers by biocompatible metal complexes. Production of poly(lactide), polycarbonates, and their copolymers
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The effectiveness of calcium complexes for ring opening polymerization of L-lactide or D-lactide was examined and melt polymerizations were performed at a monomer catalyst ratio of 350:1 for 15 min under an argon atmosphere. The molecular weights of poly( L-lactide) measured by gel permeation chromatography (GPC) are found to increase with increasing M/I ratios maintaining narrow polydispersity (PDI) index. The rate of polymerization of coordinated solvent tetrahydrofuran is found to be faster in chlorinated solvent as the complexation of calcium ion by coordinating solvents enhances the nucleophilicity of the initiator. The results also show that the rate of enrichment of carbonate monomer is slower than the lactide during random copolymerization reactions. The calcium complexes containing bulky borate ligands and phenolate initiators polymerize lactide with a high degree of hetroactivity in THF.