Synthesis of glycolide/trimethylene carbonate copolymers: Influence of microstructure on properties

Copolymers of glycolide and trimethylene carbonate with different compositions and microstructures (i.e. random, blocky and segmented) were synthesized by two-step ring opening polymerization. NMR analyses revealed that transesterification reactions took place during the first step, which corresponded to the synthesis of soft segments, and mainly when the trimethylene carbonate content of the reaction medium was high. The transesterification percentage did not significantly change with the addition of hard blocks in the second reaction step. Infrared spectroscopy was a complementary, highly effective tool to evaluate the hard segment length, crystallinity and glycolide percentage incorporated into the crystalline phase for all studied samples. Calorimetric analyses showed dependency of properties on the length of the polyglycolide hard segment and also good miscibility between glycolide and trimethylene carbonate rich phases. Crystalline morphologies attained with segmented and random copolymers were significantly different, although in all cases a positive birefringence was detected. Thermogravimetric analyses indicated that all studied copolymers had a similar degradation behavior, which was intermediate between those observed in the corresponding homopolymers. Samples with a significant glycolide unit content showed a stabilizing effect for the degradation of poly(trimethylene carbonate) blocks.