Ring-Opening Polymerization Of Lactide And Its Copolymerization With Glycolide By Organic Catalysts

Biomedical polymer materials have greatly promoted the development of modern medicine and have been widely used in drug delivery,tissue engineering and biomedical devices,etc.Biodegradable polyesters are the most widely studied biomaterials,among which the most prominent materials are poly(lactide)(PLA)and poly(lactic-co-glycolic acid)(PLGA).PLA and PLGA are usually prepared by ring-opening polymerization of corresponding cyclic lactides using stannous octanoate as catalyst.However,product discoloration resulting from high reaction temperature(typically above 140�C)as well as metal residues still hamper the applications of resultant polymers in the biomedical technologies.Organocatalysts have been intensively investigated due to their easy preparation,easy manipulation,good stability and facile removal from products.In this thesis,the organocatalytic ring-opening polymerization(ROP)of lactide and its copolymerization with glycolide were investigated.This thesis mainly includes the following two sections:1?The organocatalytic ring-opening polymerization(ROP)of L-lactide(L-LA)to produce high-molar-mass poly(L-lactide)(PLLA)was successfully achieved using base/urea binary system.The L-LA purified by recrystallization from the mixture of dichloromethane and n-hexane has fewer impurities.The purified monomer can reach a high conversion producing high-molar-mass PLLA with narrow distributions.A series of PLLA with various molar masses can be prepared by changing the feeding molar ratio of monomer to initiator.The mechanical and thermal properties of the obtained PLLA were characterized by tensile test and differential scanning calorimetry(DSC)analyses.2?The first one-pot ring-opening copolymerization(ROCOP)of LA with GA to produce random PLGA copolymers with tunable monomer sequence lengths was achieved using an organophosphazene base/urea binary catalyst.Ultrafast copolymerizations with high monomer conversions(>95%)were achieved at ambient temperature within a few seconds.The well defined structures of obtained copolyesters were collaboratively characterized with 1D,2D NMR and MALDI-TOF MS techniques.A series of PLGA copolymers with molar masses ranging from 4.6 to 13.0k Da was obtained by changing monomer feeding ratios.The microstructures of obtained PLGA copolymers can be tuned by changing the feeding molar ratio of LA/GA,which were carefully characterized using ¹³C NMR spectroscopy.The thermal properties of PLGA copolymers were also explored,which exhibited composition dependent behaviors.