Kinetics of mesophase transitions in thermotropic copolyesters. V: A copolyester containing TPA/PHQ/HBA

• Published in: Macromolecules Vol. 26; no. 1; pp. 94 - 101
• Main Authors: JOHNSON, R. L, CHENG, S. Z. D
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 04-01-1993
• Subjects: Applied sciences; Crystallization; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Arylate copolymer; Aryl terephthalate copolymer; Thermotropic state; Benzoate(hydroxy) copolymer; Experimental study; Lattice parameters; Liquid crystals; Phase transitions; Structure processing relationship; Ester copolymer; Melt crystallization; Aromatic copolymer; Kinetics; Crystalline structure
• ISSN: 0024-9297; 1520-5835

The copolyester consisting of 90 mol% phenylhdroquinone terephthalate (TPA/PHQ) and 10 mol% hydroxybenzoic acid (HBA) has been studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarized light microscopy (PLM). Upon cooling from the liquid crystal phase, two exothermic processes are observed. Neither of these processes can be bypassed when the sample is quenched. Results from nonisothermal DSC studies demonstrate that the exotherm occurring at higher temperatures corresponds to a nematic phase transition, and this transition is monotropic. The exotherm occurring at lower temperatures corresponds to a mesophase transition, resulting in a packing close to pseudohexagonal. Crystallization can take place using prolonged annealing times. Two kinds of crystals with different stabilities can be formed depending upon crystallization conditions. WAXD fiber patterns show that the crystals formed are monoclinic. Isothermal DSC experiments illustrate that the annealing kinetics at different temperatures is characterized by fractional Avrami exponents. Heat capacity data provide evidence that the glass transition temperature of TPA/PHQ/HBA (45/45/10) is approx 460 plus/minus 10K. The changes of the glass transition and crystal melting behavior are dependent on different thermal histories. The effect of the crystal on the interfacial structure is also discussed.