ORDERED STRUCTURES IN A SERIES OF LIQUID-CRYSTALLINE POLY(ESTER IMIDE)S

A series of poly(ester imide)s (PEIMs) has been synthesized from N-[4-(chloroformyl)phenyl]-4-(chloroformyl)phthalimide and different diols with methylene units of 4 to 12 (n). PEIMs with both even and odd methylene units exhibit a monotropic mesophase behavior during cooling due to the supercooling necessary for crystallization. Identification of this mesophase as a monotropic liquid crystal with smectic A order has been carried out via differential scanning calorimetry, wide angle X-ray diffraction (WAXD), small angle X-ray scattering, polarized light microscopy, and transmission electron microscopy. It is found that the methylene units in these chain molecules are also largely responsible for the formation of this liquid crystal phase. After investigating different types of main chain mesogen-nonmesogen liquid crystal polymers, a general concept considering the contributions to enthalpy and entropy changes during the liquid crystal transitions may be associated with the relative rigidity, linearity, and regularity of the mesogenic groups compared to the methylene units. Detailed WAXD study of fiber and powder patterns indicates that the degree of orientation and the order correlation lengths along and perpendicular to the direction of chain molecules (chain lateral packing and layer structure) not only increase with the number of methylene units but also show an even-odd alternation. A possible chain packing model is suggested. The morphology and defects of this smectic A liquid crystal phase are also discussed.