High-resolution thermogravimetric kinetics of liquid crystalline poly(p-oxybenzoate-co-ethylene terephthalate)

Abstract

Thermotropic liquid crystalline poly(p-oxybenzoate (B)-co-ethylene terephthalate (E))s with four B/E monomer ratios were subjected to high-resolution thermogravimetry at a variable heating rate in nitrogen and air. The thermogravimetry curves, the derivative thermogravimetry curves, the second derivative thermogravimetry curves and heating rate curves are discussed. The thermal degradation temperature, the maximum weight-loss rate, char yield at elevated temperature, and kinetic parameters of the polyesters are presented with the variation of B/E monomer ratio and compared with those obtained with traditional thermogravimetry at a constant heating rate. The degradation process of the copolyesters was usually divided into three stages, i.e., the first major stage and the latter two minor stages in nitrogen or the first and third major stages and the second minor stage in air. Of four copolyesters, the B/E (70/30) copolyester exhibited the largest degradation activation energy of 276kJ/mol in nitrogen and 244kJ/mol in air, the largest decomposition order of 2.4 in air, the largest Ln (frequency factor) of 43min−1 in nitrogen and 39min−1 in air.