High-Resolution Thermogravimetry of Liquid Crystalline Copoly(p-oxybenzoate-ethylene terephthalate-m-oxybenzoate)

摘要

Thermotropic liquid crystalline terpolymers consisting of three units of p-oxybenzoate (B), ethylene terephthalate (E), and m-oxybenzoate (M), were investigated through high-resolution thermogravimetry to evaluate their stability and kinetic parameters of thermal degradation in nitrogen and air. Overall activation energy dataof the first major decomposition was calculated through three alculating methods. Thermal degradation occurs in three major steps in both nitrogne and air. Three kinds of degradation temperatures (T_d,T_(m1),T_(m2)) are slightly higher and the first maximum weight-loss rates are slightly lower in nitrogen than in air, suggesting a higher thermostabiltiy in nitrogen. The thermal degradation temperatures range from 450 to 457deg C in nitrogen and 441 to 447deg C in air and increase with increasing B-unit content at a fixed M-unit content of 5 mol %. The temperatures at the first maximum weight loss rate range from 452 to 466deg C in nitrogen and 444 to 449deg C in air and increase slightly with an increase in B-unit content. The first and second maximum weight-loss rates are maintained at almost 9.2-10.8 and 4.0-6.1%/min in nitrogen (11.2-12.0 and 3.9-4.2%/min in air) and vary slightly with copolymer composition. The residues after the first major step of degradation are predicted on the basis of the complete exclusion of ester and ethylene groups and hydrogne atoms and compared with those observed exprimentally. Teh char yields at 500deg C in both nitrogen and air are larger than 42.6 wt% and increase with increasing B-unit content. However, the char yields at 800deg C in nitrogen and air are different. The activation energy and In(pre-exponential factor) for the first major decomposition are slightly higher in nitrogen than in air and increase with an increase in B-unit content at a given M-unit content of 5 mol %. There is no regul variation in the decomposition order with the variation of copolymer composition and testing atmosphere. The activation energy, decomposition order, and In(preexponental factor) of the thermal degradation for the terpolymers are located in the ranges of 212-263 kJ mol~(-1), 2.4-3.5,33-41 min~(-1), respectively.