Synthesis of thermoreversible and biodegradable PLGA-PEG-PLGA triblock copolymers and their molecular weight variation under irradiation

PLGA-PEG-PLGA triblock copolymer were synthesised with different compositions. Structure and molecular weight of the copolymer were characterized by FTIR, 1H-NMR and GPC. Phase diagram of the copolymer and their molecular weight variation under E-beam irradiation were studied. The results showed gelation of the co- polymer synthesized in 8h at 150℃ with 0.04g catalyst, 5.08g glycolide, and 12.61g DL-lactide (molar ratio 1:2) had sharp sol-gel phase transition. In an aqueous solution of defined concentration of the copolymer with PEG of fixed molecular weight, by increaseing the DLLA/LA ratio and molecular weight of the copolymer, the temperature of sol-gel phase transition decreased, while the temperature of gel-sol phase transition increased. Maximum polydisper- sity could be achieved by irradiating the copolymer to 20kGy.