Synthesis of thermotropic polyurethanes containing imide units and their mesophase behavior

Abstract

Thermotropic polyurethanes were synthesized from 1,6-hexane diisocyanate (HDI) as a diisocyanate, 1,6-hexane diol (HD), and rigid diols containing imide unit such as N,N′-bis(4-hydroxyphenyl)-3,4,3′,4′-biphenyl-dicarboxyimide (BPDI) or bis-N-(4-hydroxyphenyl)-4,4′-oxydiphthalimide (ODPI). The effects of structure difference between BPDI and ODPI and composition of HD/BPDI (ODPI) on the thermal and liquid crystalline behavior were studied. Thermotropic polyurethanes with an inherent viscosity of 0.59–0.70 were obtained. The melting temperature of BPDI-based polyurethanes were in the range of 150–290°C, however, those of ODPI-based polyurethanes were in the range of 150–190°C. All the polyurethanes based on ODPI (25–100 mole %) clearly exhibited a stable liquid crystalline phase, and BPDI-based polyurethane having 5–25% of BPDI showed a mesophase. The melting and isotropization temperatures (T _m , T _i ) andΔT(T _i −T _m ) increased with increasing BPDI and ODPI content. The polyurethanes based on BPDI has higher melting points and thermal stability compared to ODPI-based polyurethanes.