Wide-angle X-ray diffraction (WAXD), polarized optical microscopy, and differential scanning calorimetry (DSC) have been employed to elucidate the mesophase transitions in a thermotropic liquid crystalline polymer (LCP) prepared by copolymerization of Bisphenol E diacetate, isophthalic acid, and 2,6-naphthalenedicarboxylic acid. A single glass transition temperature (T,) and double endotherms were discerned in the DSC scans of the neat LCP. The dual melting peaks, commonly attributed to the fast and slow melting transitions, manifest strong dependence on thermal history. Annealing slightly above the Tg transition temperature has shown the occurrence of a solid-solid crystal transformation. However, annealing in the vicinity of melting temperatures exhibits a loss of positional ordering of solid crystals, then reorganization occurs due to the large anisotropy of rod-like macromolecules. Finally, the terminal melting transition takes place. This kind of order-disorder transition of mesophase structures is similar to the phenomenon of meltingrecrystallization in some flexible chain crystals and will be discussed based on new evidence from isothermal WAXD studies.

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Poly(p‐phenylene terephthalamide) (PPTA)/amorphous nylon (AN) molecular composites were prepared from sulfuric acid solution by rapidly coagulating in distilled water. The regenerated films appear homogeneous and transparent. However, the rod‐like and flexible macromolecules are probably entrapped in a single phase during rapid coagulation, thus thermodynamically unstable and undergoing phase segregation upon thermal treatment. The miscibility between PPTA/AN was identified by a dielectric relaxation method. Phase behavior and kinetics of phase separation in PPTA/AN mixtures were thoroughly investigated by time‐resolved light scattering as well as optical microscope. A pseudo phase diagram reminiscent of a lower critical solution temperature (LCST) was established by a cloud point measurement. Several temperature‐jump experiments were undertaken from ambient to a two‐phase temperature region. The low PPTA content molecular composites were prepared by coagulating in a non‐solvent, then by compression molding below the phase separation temperatures. The 30 wt% PPTA molecular composite exhibits over three‐fold increase in tensile modulus relative to that of the neat AN, however, there is little or no improvement in the tensile strength. On the other hand, by a slight addition of AN into PPTA, the tensile and compressive failures of spun fibers may be improved.

A thermotropic liquid crystalline copolymer consisting of bisphenol E diacetate, isophthalic acid and 2,6-naphthalene dicarboxylic acid was blended with polyether imide by dissolving in a mixed solvent of phenol/1,1,2,2-tetrachloroethane in a ratio of 60/40 w/w and co-precipitating the ternary solution in non-solvent (methanol). Wide-angle x-ray diffraction and differential scanning calorimetry studies revealed that the blends were completely amorphous with a single glass transition temperature. The single phase was probably entrapped during solvent removal, but these mixes were unstable and phase separated upon heating. Mesophase structure developed in the LCP rich region with continued annealing. The evolution of crystalline texture was monitored by time-resolved wide-angle x-ray diffraction following a temperature jump from ambient to 265 °C. The recrystallization process of LCP was found to slow down in the blend state relative to that of the neat LCP.

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