The Nature of the Thermal Transitions in Poly(p-oxybenzoate)

The high-temperature transition at 340 °C for the homopolymer of p-hydroxybenzoic acid (PHBA) has been shown to display characteristics typical of a plastic crystal or a highly ordered smectic phase transition. For low molecular weight samples of the homopolymer a nematic texture can be induced above this phase transition by modest external shear. However, for high molecular weight samples the material is intractable in this temperature regime. A much higher transition at 445 °C has been identified and characterized by DSC, TMA, and polarized light microscopy, indicating the presence of a nematic mesophase. Processing of the homopolymer above this transition results in fusion of the material. © 1988, American Chemical Society. All rights reserved.