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

Abstract

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 · Et₂O 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. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 70A: 154–158, 2004