Liquid-crystalline polyesters with y-shaped mesogens: Phase structure pecularities

Liquid crystalline (LC) main-chain polyesters with y-shaped mesogenic elements have been investigated by X-ray diffraction. The X-ray pattern of the glassy nematic polyester with the largest branching shows besides the reflections in the wide angle range corresponding to the average distance between the molecules also equatorial reflections in the small angle range. This is suggesting a spontaneous formation of microfibrils. X-ray pattern of the polymer above 150 °C points to the existence of a “normal” nematic phase. The proposed order-disorder model is supported by results of calorimetric measurements and mixing experiments with a low-molecularweight LC-compound.