A series of linear copolymers of glycolide and 1,3-trimethylene carbonate were synthesized by bulk ring-opening polymerization. The copolymers were characterized by H-1 NMR, C-13 NMR, viscometry, and differential scanning calorimetry (DSC). The dependency of reaction temperature, reaction time, and the feed composition on the microstructure of the copolymers was examined by C-13 NMR analysis. The microstructural analysis using C-13 NMR was useful to calculate the average block length of the glycolyl (L-G) and trimethylene carbonyl (L-T) sequence. The structural change such as transesterification, which was assigned by TGT sequence, was reflected in the average block length and the sequence of each monomeric unit in the copolymer. The average length of glycolyl sequence (L-G) was much longer than that of trimethylene carbonyl sequence (L-T) in. polymerization temperature of 100-150 degrees C. Upon further increasing the polymerization temperature, the L-G decreased, but the change of L-T was insignificant. During the polymerization, transesterification did not occur at 100 degrees C, but it was observed at a polymerization temperature range of 130-200 degrees C resulting in the decrease in L-G. As the composition of trimethylene carbonate increased, L-G decreased, but L-T do not show remarkable change. DSC results showed a close relationship between crystallinity and nature of microstructural sequence. The crystallinity of block copolymers was mainly decided by the average length of the glycolyl block. (c) 2005 Elsevier Ltd. All rights reserved.