Thermal decomposition kinetics of thermotropic poly(oxybenzoate-co-oxynaphthoate) Vectra copolyester

An advanced heat-resistant thermotropic liquid crystalline Vectra aromatic copolyester prepared from p-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid has been subjected to dynamic and isothermal thermogravimetries in nitrogen and air. The thermostability of the Vectra has been investigated in detail. The thermal decomposition kinetics have been analyzed using seven calculating techniques. These techniques gave an average activation energy (E) of 374 kJ/mol for the nonisothermal decomposition of Vectra in nitrogen, which is much higher than the E value of 255 kJ/mol determined from the isothermal thermogravimetric experiments. The average E value for the thermal decomposition in air was 288 kJ/mol from dynamic heating data. The E and Ln Z (frequency factor) are higher in nitrogen than in air from any of the calculating techniques used, but the nonisothermal decomposition order of 2.3 in nitrogen shows good agreement with the order of 2.1 of nonisothermal degradation in air and of isothermal degradation in nitrogen. The thermostability of Vectra is substantially higher in nitrogen than in air, and the decomposition mechanism in air is more complex because oxidation process is occurring in air. (C) 1999 Elsevier Science Ltd. All rights reserved.