The Thermal Stability of Aromatic Polyimides. Part 1. Factors Affecting the Stability of Poly N, N' (4,4 '-Diphenylether) Pyromellitimide

摘要

Polyimide samples in the form of powders, films and sintered mouldings were prepared from pyromellitic dianhydride and 4,4'-diaminodiphenylether. The effect of environmental variables on the oxidative stability at 400C of the high molecular weight films was studied and it was found that hydrolytic processes could greatly accelerate the degradation. The higher stability of the powders was attributed to the presence of low molecular weight fractions, which inhibited these hydrolytic processes. Support for this postulate was the fact that it was possible to improve the stability of the films by adding low molecular weight materials during the casting process and it was possible to destabilise the powders by prolonged solvent extraction. Comparison of weight loss results on polypyromellitimides is therefore only meaningful when these were determined on high molecular weight films under controlled humidity conditions. (Author)