STRUCTURES OF LIQUID-CRYSTALLINE WHOLLY A ROMATIC COPOLYESTER FILMS

Films of wholly aromatic copolyesters composed of 4-hydorxybenzoic aci d (HBA), terephthalic acid (TPA), biphenol (BP), and isophthalic acid (IPA) (HBA/TPA/BP/IPA copolymer) with two different copolymer composit ions were prepared by the solution casting method using a mixed solven t of pentafluorophenol and chloroform. The structures and phase transi tions of the films were investigated by thermal analysis, density, X-r ay diffraction, and tensile test. The as-cast films exhibited low crys tallinity and isotropic structures. The crystal to hexagonal phase tra nsitions occurred at 200 similar to 230 degrees C, which were higher t han those of melt-pressed samples. In each film, cold crystallization was occurred during heating process above T-g (100 degrees C). The den sities increased with increasing annealing temperature throughout the cold crystallization. The elongation percentages of the as-cast films were high, and that of the film containing 12 mol% of IPA was 180%.