Microstructural analysis and structure-property relationship of poly(glycolide-co-1,3-trimethylene carbonate)

A series of linear copolymers of glycolide and 1,3-trimethylene carbonate were synthesized by bulk ring-opening polymerization. The copolymers were characterized by ¹H NMR, ¹³C 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 ¹³C NMR analysis. The microstructural analysis using ¹³C 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 °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 °C, but it was observed at a polymerization temperature range of 130-200 °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.