Surface modification of bisphenol-A-polycarbonate by far-UV radiation. Part I: In vacuum

Abstract

Far-UV radiation (<250 nm) is totally absorbed by solid bisphenol-A-polycarbonate (PC) in the first 100 nm of the surface. Exposure, in vacuum, to radiation from a deuterium lamp with an intensity of 0·33 mW/cm 2 at <250 nm (i.e. approximately twice the solar far-UV radiation beyond the shielding effects of the atmosphere), results in rapid deoxygenation of the surface (initial quantum yield for carbonyl loss c. 0·05 mol/Einstein) and photoablation (initial quantum yield for phenylene loss c. 0·04 mol/Einstein). On increasing exposure, a cross-linked protective ‘skin’ is formed, and the quantum yields are reduced by an order of magnitude. Volatiles produced on irradiation in vacuum are largely substituted phenols and aromatic fragments of PC. While typical photo-Fries reaction products such as substituted benzophenones are detected, main-chain scission reactions appear to dominate the degradation mechanism. The relevance of these results to the long-term stability of spacecraft materials, and to photolithographic processes, is discussed.