Structure and thermal behaviour of a thermotropic liquid crystalline polyimide (PI-LC)

Anomalous solid structures formed by a thermotropic liquid crystalline polyimide (PI-LC) were investigated by thermal analysis, polarized light microscopy and x-ray analysis. It was revealed that PI-LC should undergo a phase transition from the crystalline to the isotropic phase through the smectic or nematic phase in the temperature range 277-300 degrees C. The PI-LC filament extruded at 280 degrees C, at which temperature the polymer was in liquid crystalline phase, was formed to have a structure similar to the smectic C phase, while that extruded and meltdrawn at 310 degrees C, at which temperature the polymer was in the isotropic phase, had a structure similar to the smectic A phase.