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Novel biodegradable thermosensitive triblock copolymers of poly(D,L-3-methylglycolide)-block-poly(ethylene glycol)-block-poly(D,L-3-methylglycolide) (PMG-PEG-PMG) have been synthesized. Ring-opening polymerization of D,L-3-methyl-glycolide (MG) initiated with poly(ethylene glycol) (PEG) and CaN(SiMe3)22(THF)2 provided triblock copolymers with alternating lactyl/glycolyl sequences of controlled molecular weight, low polydispersity index and uniform chain structure. At relatively low temperatures (≈ 10 °C) these copolymers formed clear solutions in water up to high concentrations (50 wt.-%). Depending on molecular mass ratios of PMG and PEG blocks, a sol-gel transition or an increase in viscosity without gel formation was observed upon increasing the temperature of the aqueous solutions. The temperature-induced gelation was ascertained by rheology and dynamic differential scanning calorimetry (DDSC). Phase diagram of PMG-PEG-PMG 1 400-1 450-1 400 in an aqueous solution.
Zhong et al. (Thu,) studied this question.