Preparation Of Collagenase Sensitive Polylactic Acid Block Copolyesters By Chain Extension

Polylactic acid(PLA) has attracted considerable attention of biomedical materials researchers due to its full degradability,renewability,good biocompatibilty.It has been used as drug delivery carriers,tissue engineering scaffolds and so on.Polylactic acid block copolymers were synthesized via lactide ring-opening polymerization with stannous octoate as catalyst,butanediol,lysine and collagenase sensitive peptide as initiators,1,6-diisocyanatohexane as chain extender.The related oligomers and chain extension products were characterized with 1H-NMR,contact angle testing,FTIR,UV,viscosity-average molecular weight and alkaline degradation molecular weight.The main conclusions were included as follows:1:Oligomers of dihydroxyl-terminated molecule (HO-PLA-BDO-PLA-OH) were synthesized via lactide ring-opening polymerization with butanediol as initiator and stannous octoate as catalyst.The chain extension products of the oligomers were synthesized with HDI in dioxane, and the viscosity average molecular weight of chain extension products was 3 times larger than those of oligomers.2:Oligomers of dihydroxyl-terminated molecule (HO-PLA-Lys-PLA-OH) were synthesized via lactide ring-opening polymerization with lysine as intiator which has diamino-terminated active hydrogen.Then polymers were synthesized through chain extension oligomers HO-PLA-Lys-PLA-OH with HDI in dioxane.The experimental conditions, such as, chain extension temperature and molar ratio between HDI and oligomer were studied.The results indicated that chain extension products viscosity average molecular weight increased with the increasing molar ratio.The optimized synthesis conditions were reaction 3h at 70℃with stannous octoate 0.3wt% of oligomer and molar ratio 2:1 between HDI and HO-PLA-Lys-PLA-OH,and the viscosity average molecular weight of chain extension products was 3.6 times larger than those of oligomers.3:The optimized conditions of HO-PLA-Lys-PLA-OH was used in the synthesis of collagenase sensitive lactic acid oligomer owing to the similar structure between lysine and collagenase sensitive peptide which they both have diamino-terminated.Then collagenase sensitive polylactic acid block copolymers was synthesized through chain extension oligomer with HDI.Viscosity average molecular weight of block copolymers were 3 times larger than those of oligomers. 4 : The hydrophilicity of HO-PLA-Lys-PLA-OH and collagenase sensitive polylactic acid oligomer were better than that of HO-PLA-BDO-PLA-OH oligomer based on contact angle testing results . The contact angle test indicated that hydrophilicity of chain extension products decreased with the inceasing molecular weight of chain extension products.