Abstract
The breakdown mechanism of an aromatic polyamide and four polyimides has been studied under vacuum in the temperature range of 375β620Β°C, by using techniques described earlier, involving collection and analysis of volatile products as well as analyses of residues at different temperatures. The decomposition of the polyamide up to 375Β°C yielded predominantly carbon dioxide, while between 375 and 450Β°C about equal amounts of carbon dioxide and carbon monoxide formed. Hydrogen is the major product between 450 and 550Β°C, along with hydrogen cyanide, methane, and carbon monoxide. The major reaction at the lower temperatures seems to be the cleavage of the linkage between the carbonyl group and the ring, with subsequent formation of a carbodiimide linkage via isocyanate intermediates, and liberation of carbon dioxide. Alternatively, cleavage between the carboxyl and the NHβgroup leads to the formation of carbon monoxide. Carbon dioxide and carbon monoxide are also the major volatile decomposition products of the polyimides at the lower temperatures. The primary cleavage reaction is believed to be the rupture of the imide ring between a carbonyl and nitrogen, with subsequent formation of isocyanate groups. The latter react with each other to form carbodiimide linkages and carbon dioxide, while the remaining benzoyl radical is the source for carbon monoxide.