Synthesis of thermosensitive and biodegradable methoxy poly(ethylene glycol)-polycaprolactone and methoxy poly(ethylene glycol)-poly(lactic acid) block copolymers

The sol to gel transition of aqueous solution of block copolymers consisting of methoxy poly (ethylene glycol) (MPEG) and biodegradable polyesters such as ε-caprolactone and L-lactide was investigated as a function of temperature. MPEG-PCL was prepared by ring opening polymerization of ε-caprolactone in the presence of HCl·Et₂O as monomer activator at room temperature. Also, MPEG-PLLA was prepared by ring opening polymerization of L-lactide in the presence of stannous octoate at 115°C. The properties of block copolymers were investigated by ¹H-NMR, IR, and GPC as well as the observation of thermosensitive phase transition in aqueous solution. As the hydrophobic block length increased, the sol to gel transition temperature increased and curve of that steepen to lower concentration. To confirm the gel formation at body temperature, we observed the formation of gel in the mice body after injection of 20 wt% aqueous solution of each block copolymer. After surging, we investigated the gelation in mice. The results obtained in this study confirmed the feasibility as biomaterials of injectable implantation for controlled release of drug and protein delivery.