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 series of monotropic liquid crystal poly (ester imide)s (PEIMs) was synthesized from IV-[ 4-(chloroformyl)phenyl]-4-(chloroformyl)phthalimide and nine diols containing 4-12 methylene units (m).During cooling from their isotropic melts, all the polymers underwent a monotropic liquid crystal transition to form a smectic A phase, followed by a transition to a more ordered structure, which was examined with wide-angle X-ray diffraction, differential scanning calorimetry, and polarized light microscopy. The fact that the liquid crystal transition temperatures for some of the PEIMs were close to their glass transition temperatures provided an opportunity for the study of liquid crystal transition kinetics in temperature regions close to the glass transition temperature. It was found that when the temperature, and thus the molecular mobility decreased, the transition time increased despite the fact that this transition is close to equilibrium. The crystallization kinetics of PEIM(m)s from both the liquid crystal phase and the isotropic melt were also studied. In PEIM(m=even)s (except for m = 4), two different ordered structures can be formed. One is a crystalline phase formed directly from the isotropic melt, and the other is a highly ordered mesophase having a hexagonal-like packing develop from the liquid crystal state. Only one crystal structure in PEIM(m=odd)s is observed. Special attention has been paid to the effect of the presence of liquid crystal order on the crystallization kinetics. The pronounced acceleration of the crystallization was observed whenever this was preceded by liquid crystal formation, an effect pertaining within a wide temperature range from close to Tm down to Tg.

Controlled molecular weight, thermoplastic polyimides have been prepared via poly(amic acid) salt precursors. 2,2-Bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride and m-phenylenediamine (the Ultem monomers), together with calculated amounts of phthalic anhydride were reacted in N-methylpyrrolidinone as well as in tetrahydrofuran to form poly(amic acid)s with controlled molecular weights. Poly(amic acid) salts were prepared in heterogeneous reactions of the poly(amic acid)s with quaternary ammonium bases or triethylamine dissolved in methanol or water, to yield soluble salts. The poly(amic acid) salts were then melt imidized in air at 250 or 300 °C for 30 min. Results suggest that the poly(amic acid) salt counterion controls the mechanism by which the salt imidizes, which in turn controls the properties of the final polyimide. The triethylammonium poly(amic acid) salts yielded linear, thermoplastic, molecular weight controlled polyimides upon melt imidization. The polyimides prepared from the poly(amic acid) salts containing the triethylammonium, tetraethylammonium, and tetrapropylammonium counterions showed dynamic weight loss profiles comparable to the polyimide produced directly from the control poly(amic acid).

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