The stability of plasma polymers: Part I, A preliminary XPS study of the photostability of plasma polymerised styrene and methyl methacrylate

Abstract

This paper describes the first results from a study into the stability of plasma polymers (PPs). PPs prepared from styrene and methyl methacrylate were exposed to UV radiation from a ‘black lamp’ and changes in their surface chemistry were monitored by X-ray photoelectron spectroscopy. The photo-oxidation of the plasma polymerised styrene (ppS) was compared with that of conventional polystyrene (PS). The data reported show that ppS undergoes photo-oxidation almost immediately on irradiation, unlike PS, for which an induction period of several weeks is required before any degradation products are seen. A plasma polymerised methyl methacrylate was prepared under conditions that ensured considerable fragmentation of the monomer in the plasma gas. This PP, which had retained little of the monomer's original structure or functionality, also underwent rapid surface photo-oxidation. The observed behaviour of the PPs is explained by the presence of trapped residual free-radical centres in these materials. The results reported have important implications for the use of PPs as coating materials, particularly in applications where these materials may be subjected to natural sunlight.