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 aind 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 phtwe are also discussed.

Mesophase behavior of two poly(ester imides) synthesized from N-[4-(chloroformyl)phenyl]-4-(chloroformyl)phthalimide and 1,4-butanediol or 1,9-nonanediol has been extensively studied. One of the polymers has four methylene units (even) and the other nine methylene units (odd) in its respective flexible spacers. Both polymers show monotropic liquid crystal behavior which has been identified by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarized light microscopy (PLM) experiments. The liquid crystal phase seems to be more ordered than the nematic phase. Further crystallization from this liquid crystal phase can be achieved during cooling and/or isothermal experiments below the isotropic melt to liquid crystal transition temperature. This indicates that the molecules in the liquid crystal phase possess high mobility. Isothermal experiments on these polymers at temperatures above the monotropic liquid crystal transition lead to direct crystallization from the isotropic melt with large axilitic or spherulitic texture.

A new semicrystalline polyimide has been synthesized from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride and 2,2‐dimethyl‐1,3‐(4‐aminophenoxy)propane. The polymer has a high glass transition temperature of 230°C and a melting temperature of 325°C. Its overall crystallization rate between 240 and 325°C is quite fast (t1/2<10min) and relatively insensitive to the crystallization temperature. Although the degree of crystallinity obtained is dependent on the crystallization conditions, it can be as high as 50%. The polymer's morphology, which was examined with transmission electron microscopy (TEM), has a randomly stacked, ribbon‐like, lamellar texture. Both TEM and polarized light microscopy show that mature spherulites do not develop. The crystal unit cell, which was determined from wide‐angle X‐ray diffraction measurements on highly oriented films, is monoclinic with a = 0.960nm, b = 0.582nm, c = 2.46nm and γ = 81.1°.

Thermal properties of a new semicrystalline polyimide synthesized from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) and 2,2‐dimethyl‐1,3‐(4‐aminophenoxy)propane (DMDA) have been studied. Heat capacities in the solid and liquid states of BTDA‐DMDA have been measured. The heat capacity increase at the glass transition temperature (Tg = 230°C) is 145 J/°Cmol for amorphous BTDA‐DMDA. The equilibrium heat of fusion of the BTDA‐DMDA crystals has been obtained using wide‐angle X‐ray diffraction and differential scanning calorimetry measurements, and is 75.8 kj/mol. Based on the information on crystallinity and the heat capacity increase at Tg, a rigid amorphous fraction is identified in semicrystalline BTDA‐DMDA samples, which represents an interfacial region between the crystalline and amorphous states. In particular, this fraction increases with the crystallinity of the sample, which should be associated with crystal sizes, and therefore with crystal morphology. It has also been found that this polymer has a high‐temperature crystal phase upon annealing above its original melting temperature. The thermal degradation activation energies of BTDA‐DMDA in nitrogen and air are determined to be 154 and 150kJ/mol, respectively.

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