EVIDENCE FOR PREFERENTIAL SURFACE ENRICHMENT IN THE SURFACE CHEMICAL-ANALYSIS OF A SERIES OF POLY(BUTYL METHACRYLATE-CO-METHYL METHACRYLATE) LATICES USING X-RAY PHOTOELECTRON-SPECTROSCOPY AND STATIC SECONDARY-ION MASS-SPECTROMETRY

The surface chemical analysis of a series of poly(butyl methacrylate-co-methyl methacrylate) (MMA-BMA) latices, prepared by persulfate-initiated emulsion polymerization and characterized using standard colloid techniques has been undertaken using X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The surface compositions of these latices were compared with the bulk polymer compositions and the surface compositions of solvent-cast (latex) polymer films. While the average particle size of the near-monodispersed colloids was found to be independent of composition, there was a marked increase in electrophoretic mobility and zeta potential values as the proportion of the BMA in the monomer mixture was increased. The XPS and SIMS analyses both revealed a higher level of MMA component of the copolymer in the latex films than would be anticipated from the bulk composition. In contrast, a significant enrichment of the BMA component of the copolymer was observed in the surface of solvent-cast films. These findings are briefly discussed where appropriate in terms of the particle formation mechanism, but in the main, this paper highlights their relevance to the study of surface chemistry of complex polymer colloids.