MECHANISM OF X-RAY-INDUCED DEGRADATION OF PYROMELLITIC DIANHYDRIDE

The degradation of pyromellitic dianhydride (PMDA) under X-ray exposure has been studied by a combination of X-ray photoelectron spectroscopy and Fourier transform IR reflection absorption spectroscopy. Vapor deposited PMDA films show significant degradation under prolonged X-ray exposure. The data indicate that the initial degradation reaction follows a unimolecular mechanism and includes cleavage of the anhydride rings with the release of CO2 molecules, which are either trapped in the film or released into the vacuum.