A TIME-OF-FLIGHT SECONDARY-ION MASS-SPECTROMETRY AND X-RAY PHOTOELECTRON-SPECTROSCOPY INVESTIGATION OF THE STRUCTURE OF PLASMA POLYMERS PREPARED FROM THE METHACRYLATE SERIES OF MONOMERS

Plasma polymers (PPs) have been prepared from methacrylate precursors and analysed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (X.p.s.). The negative SIMS data for plasma polymerized methyl methacrylate (ppMMA) were compared with that of a low molecular weight oligomer and a high molecular weight conventional poly(methyl methacrylate). This facilitated the interpretation of the SIMS data and has enabled a qualitative structure for ppMMA to be proposed. The secondary ion mass spectra from PPs of ethyl methacrylate and butyl methacrylate are shown to be very similar to ppMMA, where the methyl group is replaced by an ethyl and a butyl group, respectively. The X.p.s. data for ppMMA showed that the PP had retained approximately 80% of the oxygen from the monomer. Much of this was present as the ester group which indicates that extensive fragmentation of the monomer had not occurred during plasma polymerization. Evidence that the monomer structure had been retained in the PP was also provided by the SIMS data; a number of negative ions (e.g. at m/z = 85, 87, 101 and 187) have structures which contain a complete monomer unit.