THE STABILITY OF PLASMA POLYMERS .1. A PRELIMINARY XPS STUDY OF THE PHOTOSTABILITY OF PLASMA-POLYMERIZED STYRENE AND METHYL-METHACRYLATE

This paper describes the first results from a study into the stability of plasma polymers (PPs). PPs prepared from styrene and methyl methac rylate were exposed to UV radiation from a 'black lamp' and changes in their surface chemistry were monitored by X-ray photoelectron spectro scopy. The photooxidation 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 irradia tion, unlike PS, for which an induction period of several weeks is req uired before any degradation products are seen. A plasma polymerised m ethyl methacrylate was prepared under conditions that ensured consider able fragmentation of the monomer in the plasma gas. This PP, which ha d 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-radi cal centres in these materials. The results reported have important im plications for the use of PPs as coating materials, particularly in ap plications where these materials may be subjected to natural sunlight.