EFFECTS OF ANNEALING ON THE STRUCTURE FORMATION IN A THERMOTROPIC LIQUID-CRYSTALLINE COPOLYESTER

Structure formation in a thermotropic liquid crystalline copolyester was studied by wideangle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The lateral packing of molecular chains in a copolymer of p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) was shown to be transformed from hexagonal packing to an orthorhombic one in the course of annealing above 230 °C. The lattice constants of the orthorhombic lattice of the copolymer are slightly higher than the lattice constants reported for the HBA homopolymer, suggesting that the orthorhombic lattice in the copolymer is not only formed by the sequence of the HBA homopolymer block. The WAXD intensity of the equatorial reflections was calculated at various angles of rotation of the aromatic plane in the orthorhombic lattice. From a comparison of experimental and theoretical intensities of the equatorial reflections, the aromatic plane was shown to be inclined by 6-16° and 140-156° from the 100 plane. Although the sequence distribution of the copolymer was not influenced by annealing, the repeating unit length along the fiber direction slightly increased on annealing. The experimental results are discussed in terms of interchain and intrachain correlations of molecular planes that are related to the conformational order of molecular chains. © 1990, American Chemical Society. All rights reserved.