| Abstract: | Films of wholly aromatic copolyester composed of 4-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) were prepared by a solution-casting method using a mixed solution of pentafluorophenol (PFP) and chloroform (weight ratio: PFP/chloroform = 3/7). Using five samples with different copolymer compositions (HBA/HNA [mol%] = 25/75, 40/60, 55/45, 62/38, 73/27), the effects of the copolymer composition on the fine structures of the films were investigated using thermal analyses, density measurements, X-ray diffraction methods, and tensile tests. The as-cast films obtained were shown to be trans-parent and highly amorphous in spite of changing the copolymer composition. When the films were heated above the Tg (100°C), cold crystallization first occurred during the heating process and they had melting points. The densities of the films increased with increasing annealing temperature throughout the cold crystallization. The elongation percentages of the as-cast films reached high values of 30–74% at room temperature, indicating their maximum of elongation at 55 mol% of HBA. © 1996 John Wiley & Sons, Inc. |
