DEPOSITION CONDITIONS INFLUENCE THE POSTDEPOSITION OXIDATION OF METHYL-METHACRYLATE PLASMA POLYMER-FILMS

Plasma polymer films were deposited from methyl methacrylate (MMA) vap or under various plasma conditions and XPS and FTIR used to study the changes to the compositions of the films as they were stored in air fo r longer than 1 year. The plasma power input per monomer mass unit (W/ FM) markedly affected the composition of the freshly deposited MMA pla sma polymers. A low value of W/FM led to a high degree of retention of the original monomer structure, whereas a high value of W/ FM resulte d in substantial monomer fragmentation and the formation of a partiall y unsaturated material considerably different to conventional PMMA. As the MMA plasma coatings were stored in ambient air after fabrication, all showed spontaneous oxidative changes to their composition, but th e extents and reaction products differed substantially. Deposition at low W/FM led to moderate oxidative changes, whereas high power led to a pronounced increase in the oxygen content over time and resulted in a wide range of carbon-oxygen functionalities in the aged material. As the initial compositions/plasma deposition conditions thus influenced the oxidative postdeposition reactions, MMA plasma polymers deposited under different conditions not only varied in their initial compositi on but then became even more diverse as they aged. (C) 1998 John Wiley & Sons, Inc.