Fast Crystallization and Toughening of Poly(L-lactic acid) by Incorporating with Poly(ethylene glycol) as a Middle Block Chain

High molecular weight poly(L-lactic acid)-poly(ethylene glycol)-poly(L-lactic acid) (PLLA–PEG–PLLA; PLGL) triblock copolymers with various lengths of the PLLA blocks were synthesized by ringopening polymerization of L-lactide. The amorphous and crystalline PLLA and PLGL films were prepared by hot pressing with different temperature treatments. PLLA and PEG blocks exhibited good miscibility in the amorphous PLGL samples, while phase separation occurred in the crystalline ones. The flexible PEG blocks not only accelerated the crystallization rate of PLLA but also greatly improve its flexibility. The crystallization time of PLGL copolymers shorten to less than 5 min and copolymers showed much better flexibility than neat PLLA, the maximum fracture strain reached about 600% for amorphous sample. The processing time of PLLA was greatly shortened and the brittleness of material was improved.