Random and block copolymerizations of 1,5-dioxepan-2-one (DXO) with L-, D-, or D,L-lactide (LA) were performed with Sn(oct)(2) as an initiator in order to prepare novel type of biodegradable copolymers. The degradation of random copolymers, poly(DXO-ran-D,L-LA) with a compost were slightly higher than that of the corresponding poly(DXO-ran-L-LA). When the degradation of block copolymers, poly(DXO)-block-poly(D,L-LA or L-LA), were compared with those of poly(DXO-ran-D,L-LA or L-LA), the former copolymer showed less degradability. The enzymatic degradability using proteinase K is much higher than the degradation with a compost. Poly(DXO-ran-D,L-LA) showed large degradability compared with poly(DXO-ran-L-LA), while poly(DXO)-block-poly(D,L-LA or L-LA) indicates less degradability with proteinase K. In sharp contrast to L-LA or D,L-LA copolymers, poly(DXO-CO-DLA)s are inert toward the decomposition with proteinase K, while these polymers show better degradability using a compost. Triblock copolymers, poly(DXO/L-LA/DXO)s showed extremely high enzymatic degradation compared with poly(L-LA/DXO/L-LA)s because of the large hydrophilicity of the former copolymers. Random copolymerization of DXO/L-LA/3-allyl-delta-valerolactone (3-AV) gave a interesting biodegradable copolymer, which can be modified into biodegradable graft polymer by further copolymerization with styrene. (C) 2004 Elsevier B.V. All rights reserved.