Synthesis And Shape Memory Properties Of Biodegradable PLLG/PCG Multi-block Copolymers

Biodegradable shape memory polymers(BSMPs)are new stimuli-responsive materials emerged in the last decade.Due to their excellent shape-memory function and biodegradability/bioresorbility,they have found many applications in biomedical materials such as sutures,scaffolds and bone-fixing materials to facilitate knotting and fixing in surgical operations and to avoid second operation to take them out of the body.In this study,we aim to design and synthesize BSMPs with multi-block structure,adjustable transition temperature(above body temperature),biodegradation rate and satisfactory mechanical properties.First,low molecular weight macrodiols,OH-terminated poly(L-lactide-co-glycolide)(PLLG-diol)and poly(ε-caprolactone-co-glycolide) (PCG-diol)with narrow molecular weight distribution were synthesized via living/controlled ring-opening polymerization of L,L-lactide/glycolide andε-caprolactone/glycolide using stannous octoate as catalyst and 1,4-butylenediol as initiator.The molecular weight ranged from 2000 to 14000 and the copolymer composition from 100/0 to 80/20,which were controlled by the monomer ratio (LLA/GA and CL/GA)and monomer/initiator ratio,respectively.The copolymers were characterized with GPC,IR,NMR and DSC,etc.The glass transition temperature(T_g)and melt point(T_m)of PLLG and T_m of PeG decreased with increasing the GA content and/or decreasing the molecular weight.Experiential quantitative relationships among the T_ms of PLLG and PCG and the molecular weight and copolymer composition was established.Then,multi-block PLLG/PCG copolymers were synthesized via one-pot chain-extension reaction using PLLG-diols as hard segments,PCG-diols as soft segments and 2,4-toluene diisocyanate(TDI)as chain extender and characterized with GPC and DSC.The shape-memory behaviors were recorded with thermomechanical cycle experiments.The multi-block copolymers exhibited good shape-memory properties,with strain fixity rate 98.7-99.5%,strain recovery rate 93.1-98.5%.The temperature for shape-memory or switch temperature ranges from 40 to 60℃.The speed of strain recovery is affected by the environment temperature or heating rate.