Poly(vinyl alcohol)-initiated microwave-assisted ring opening polymerization of epsilon-caprolactone in bulk was investigated, and a series of poly(vinyl alcohol)graft-poly(epsilon-caprolactone) (PVA-g-PCL) copolymers were prepared, with the degree of polymerization (DP) of PCL side chains and the degree of substitution (DS) of PVA by PCL being in the range of 3-24 and 0.35-0.89, respectively. The resultant comb-like PVA-g-PCL copolymers were confirmed by means of FTIR, H-1 NMR, and viscometry measurement. The introduction of hydrophilic backbone resulted in the decrease in both melting point and crystallization property of the PVA-g-PCL copolymers comparing with linear PCL. With higher microwave power, the DP of PCL side chains and DS of PVA backbone were higher, and the polymerization reaction proceeded more rapidly. Both the DP and monomer conversion increased with irradiation time, while the DS increased first and then remained constant. With initiator in low concentration, the DP and DS were higher, while the monomer was converted more slowly. Microwaves dramatically improved the polymerization reaction in comparison of conventional heating method. (C) 2007 Wiley Periodicals, Inc.