Novel biodegradable copolymers, poly(1,4-dioxan-2-one-co-glycolide) [P(DON-co-GA)] containing a high proportion of 1,4-dioxan-2-one (DON), were synthesized by copolymerizations of DON and glycolide (GA) at 120 degreesC for 16 h using stannous octoate as catalyst. Chemical composition and microstructural. variation of the resulting copolymer were investigated by H-1- and C-13 NMR and thermal properties by differential scanning calorimetry (DSC). From the C-13 NMR spectra, it was observed that, apart from the expected preponderance of DON sequences, the minor component, GA, was indeed distributed at various points along the copolymer chain rather than incorporated as distinct blocks, which is consistent with a random sequence distribution. This view also was supported by the DSC results, which showed that most copolymers were amorphous except for one with a relatively high fraction of DON. The conclusion that it was a random structure rather than a statistical copolymer is discussed, using the theories about the mechanism of this type of polymerization in current as a reference. P(DON-co-GA) films were prepared by casting the copolymer solution in hexafluoroisopropanol (HFIP) with two concentrations of the polymeric solution (10 and 25 wt %). The in vitro hydrolytic degradation behaviors of these films were studied in phosphate buffer solution (pH = 7.4) at 37 degreesC and characterized by DSC, scanning electron microscopy, weight loss, and change in inherent viscosity. (C) 2004 Wiley Periodicals, Inc.