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

Thermotropic liquid crystalline poly(p-oxybenzoate (B)-co-ethylene terephth alate (E))s with four B/E monomer ratios were subjected to high-resolution thermogravimetry at a variable heating rate in nitrogen and air. The thermo gravimetry curves, the derivative thermogravimetry curves, the second deriv ative thermogravimetry curves and heating rate curves are discussed. The th ermal degradation temperature, the maximum weight-loss rate, char yield at elevated temperature, and kinetic parameters of the polyesters are presente d with the variation of B/E monomer ratio and compared with those obtained with traditional thermogravimetry at a constant heating rate. The degradati on 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 f irst and third major stages and the second minor stage in air. Of four copo lyesters, the B/E (70/30) copolyester exhibited the largest degradation act ivation energy of 276 kJ/mol in nitrogen and 244 kJ/mol in air, the largest decomposition order of 2.4 in air, the largest Ln (frequency factor) of 43 min(-1) in nitrogen and 39 min(-1) in air. (C) 2000 Elsevier Science Ltd. All rights reserved.