Preparation of poly(ethylene glycol)-block-poly(caprolactone) copolymers and their applications as thermo-sensitive materials

The polymerization of ε-caprolactone (ε-CL) was initiated by the terminal alcohol of methoxy poly(ethylene glycol) (MPEG) as an initiator via activated ring-opening polymerization in the presence of HCl · Et ₂O as a monomer activator. The molecular weights of the poly(ε-caprolactone) (PCL) in MPEG-PCL diblock copolymers controlled with the feed ratio of ε-CL to MPEG. The polymerization was preceded by living fashion with no termination or chain transfer. This polymerization procedure offered MPEG-PCL diblock copolymers with well-defined structures. The gel-to-sol transitions of MPEG-PCL diblock copolymer solutions were also examined. The diblock copolymers synthesized with various MPEG and PCL lengths were dissolved in water at 80°C in various concentrations. The polymer solutions formed gel at room temperature. The formed gel became fluids again by increasing the temperature. The gel-to-sol transition showed strong dependence on the length of the MPEG and PCL diblock segments. When the polymer solution was injected into rat, it became a gel at body temperature. The formed gel maintained for 1 month. We confirmed that MPEG-PCL diblock copolymers with well-defined structures served as new thermo-sensitive biomaterials.