STRUCTURES OF LIQUID-CRYSTALLINE WHOLLY AROMATIC COPOLYESTER FILMS WITH DIFFERENT COPOLYMER COMPOSITIONS

Films of wholly aromatic copolyester composed of 4-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) were prepared by a solutio n-casting method using a mixed solution of pentafluorophenol (PFP) and chloroform (weight ratio: PFP/chloroform = 3/7). Using five samples w ith different copolymer compositions (HBA/HNA [mel %] = 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. T he as-cast films obtained were shown to be transparent and highly amor phous in spite of changing the copolymer composition. When the films w ere heated above the T-g (100 degrees C), cold crystallization first o ccurred during the heating process and they had melting points. The de nsities of the films increased with increasing annealing temperature t hroughout the cold crystallization. The elongation percentages of the as-cast films reached high values of 30-74% at room temperature, indic ating their maximum of elongation at 55 mol % of HBA. (C) 1996 John Wi ley & Sons, Inc.