Stepwise thermal degradation of a polybenzimidazole foam

Abstract

AbstractThe stepwise thermal degradation of a polybenzimidazole (PBI) foam, prepared from 3,3′‐diaminobenzidine and isophthaldiamide, has been studied under conditions of pyrolysis and nonflaming oxidative degradation in a thermal analyzer using gas and liquid chromatographic separation and mass spectrometric and infrared detection techniques. The recoveries of sample weight, as degradation products, were quantitative over the entire temperature ranges studied (100–300, 300–570, 570–700, and 700–1000°C for pyrolysis; and 100–570 and 570–900°C for nonflaming oxidation). In pyrolysis, 17 volatile compounds were identified with NH3 and CH4 accounting for 94 and 57 mole % of the total mass loss between 300–570 and 570–700°C, respectively. Above 700°C, HCN and H2 were formed from degradation of arylnitrile‐containing oligomers. The thermal and oxidative degradation of three substituted benzimidazole monomers was also studied, and the relative ratios of N2, NH3, and HCN that were produced from each, when compared with PBI, support a mechanism for degradation that favors cleavages that least alter the conjugation of the polymer backbone. In the presence of air, PBI formed stable oxygen‐containing residues that decomposed at high temperatures to N2, CO2, and H2O almost exclusively. Large quantities of H2 and N2 from model compounds support results from PBI that suggest that degradation begins with total erosion of the imide ring at 570°C and the formation of more condensed heterocyclic species. These quantitative techniques are generally applicable to the study of all polymeric materials.