Highly heat-resistant silicon-containing polyurethane-imide copolymers: Synthesis and thermal mechanical stability

In order to improve the heat-resistant property of polyurethane (PU), both imide and siloxane groups were introduced into PU backbones, and silicon-containing PU-imide copolymers (PUIS) were synthesized with high reaction efficiency. The structure of PUIS copolymers was confirmed through FTIR, H-1 NMR and GPC analysis. A single glass transition temperature (T-g) was observed, which shifted slightly to higher temperature by incorporation of imide and siloxane groups. Meanwhile the trend of micro-phase separation of PUIS was reduced due to the weakening of intermolecular hydrogen bond in hard-segments. With increasing content of imide and siloxane groups, the thermal degradation characteristic temperatures and the char yield increased, while the degradation rate decreased remarkably. Moreover, the difference of the thermal degradation temperature significantly increased with increasing weight loss, indicating that the thermal stability of imide group was more pronounced at high temperature. Compared with pure PU, the thermal degradation characteristic temperatures of PUIS increased by 100-200 degrees C, and the high mechanical properties could be kept at high temperature, indicating the remarkable improvement of thermal mechanical stability. The degradation kinetics analysis further indicated that the degradation activation energy (Ea) had a large increase by incorporation of imide and siloxane groups. Such highly heat-resistant PUIS showed a considerable potential for being used in high temperature environments.