Phase transition and transition kinetics of a thermotropic poly(amide-imide) derived from 70% pyromellitic dianhydride, 30% terephthaloyl chloride, and 1,3-bis[4-(4′-aminophenoxy)cumyl]benzene

The phase transition and transition kinetics of a liquid crystalline copoly(amide-imide) (PA137), which was synthesized from 70 mol % pyromellitic dianhydride, 30 mol % terephthaloyl chloride, and 1,3-bis[4-(4′-aminophenoxy)cumyl]benzene, was characterized by differential scanning calorimetry, polarized light microscopy, X-ray diffraction, and rheology. PAI37 exhibits a glass transition temperature at 182°C followed by multiple phase transitions. The crystalline phase starts to melt at ∼220°C and forms smectic C (S_C) phase. The S_C phase transforms into smectic A (S_A) phase when the temperature is above 237°C. The S_C to S_A transition spans a broad temperature range in which the S_A phase vanishes and forms isotropic melt. The WAXD fiber pattern of PAI37 pulled from the anisotropic melt revealed an direction. The transition kinetics for the mesophase and crystalline phase formation was also studied.