The effects of temperature, feed ratio, and reaction time on the properties of copolymer PLA-PEG-PLA

Triblock copolymers were polymerised by the ring-opening reaction of D,L-lactide in the presence of poly(ethylene glycol) (PEG), with number-average molecular weight (Mn) of 1500 and 2050 g/mol, using Sn(Oct)2 as a catalyst. The influences of the reaction time, the ratio of PEG and Poly(D,L-lactic acid) (PLA), and PEG types on structure and sol-gel phase transition of PLA-PEG-PLA triblock copolymers were investigated. Optimal polymerisation parameters were obtained, such as reaction time of 18 hours, a catalyst amount of 1.3%, and PEG/PLA ratio of 1/1.7, PEG (Mn=1500); the efficiency of the triblock synthesis was 42.3%. The properties of PLA-PEG-PLA copolymers were evaluated by analytical methods such as proton nuclear magnetic resonance H1NMR spectroscopy, gel permeation chromatography (GPC), and the sol-gel state transition at varying temperature. The results show that the triblock was successfully synthesised and its hydrogel had capability of the sol-gel state transition when the temperature changed. The PLA-PEG-PLA copolymer in aqueous solution is a thermo-sensitive hydrogel that can be used for drug and protein delivery systems or triblock denaturation applications for commercial purposes.