Polypyromellitimides: Details of pyrolysis

Polyimide films from 4,4′-diaminodiphenyl ether and pyromellitic dianhydride were pyrolyzed at 400–600°C. in non-oxidative systems. Major gaseous products were carbon monoxide and carbon dioxide; hydrogen evolution occurred above 525°C. A mobile n-imide-isoimide equilibrium is in accord with the gas evolution data. Carbon dioxide arises from isoimide decomposition and carbon monoxide arises from the normal imide.