The relationship of chain linearity of aromatic liquid-crystal polyesters to molecular orientation and stiffness of mouldings

Three aromatic liquid-crystal polyesters have been synthesized from monomer residues of x parts p-hydroxybenzoic acid and 1 2 (1 − x) parts each of isophthalic acid and hydroquinone, with x = 0.15, 0.27 and 0.36. Chain linearity therefore increased with x. They were injection-moulded into tensile bars which had axial moduli that were found to increase with x. The bars were sectioned to reveal the oriented layer structure formed by the injection process. The molecular orientation within the layers was characterized by X-ray diffraction and then input into the Ward aggregate model to calculate predicted moduli for comparison with experimentally measured moduli. The analysis shows that, for higher x, the increase in modulus is mainly a consequence of the increase in molecular orientation within the layers.