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 ac id has been subjected to dynamic and isothermal thermogravimetries in nitro gen and air. The thermostability of the Vectra has been investigated in det ail. The thermal decomposition kinetics have been analyzed using seven calc ulating techniques. These techniques gave an average activation energy (E) of 374 kJ/mol for the nonisothermal decomposition of Vectra in nitrogen, wh ich is much higher than the E value of 255 kJ/mol determined from the isoth ermal thermogravimetric experiments. The average E value for the thermal de composition 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 calc ulating techniques used, but the nonisothermal decomposition order of 2.3 i n nitrogen shows good agreement with the order of 2.1 of nonisothermal degr adation in air and of isothermal degradation in nitrogen. The thermostabili ty of Vectra is substantially higher in nitrogen than in air, and the decom position mechanism in air is more complex because oxidation process is occu rring in air. (C) 1999 Elsevier Science Ltd. All rights reserved.