XPS analysis (ESCA) of the surface composition of poly(styrene/2-hydroxyethyl methacrylate) microspheres produced by emulsifier-free emulsion polymerization

Polymer microspheres composed of various compositions of styrene and 2-hydroxyethyl methacrylate (HEMA) were produced by batch emulsifier-free emulsion polymerization. The HEMA content at the surface, [HEMA]_s, of the microspheres powdered by freeze-drying was determined by both quantitativeC^1s/O^1s analysis andC^1s peak shape analysis of the x-ray photoelectron spectroscopic spectra. When the HEMA content in the microsphere, [HEMA]_p, was less than about 5 mole%, the [HEMA]_s values determined by the two different methods showed good agreement. At [HEMA]_p above 5 mole %, [HEMA]_s values determined by the first method were about 15 mole % greater than those determined by the second. They both showed a similar tendency with the [HEMA]_s being higher than the [HEMA]_p, e.g., when [HEMA]_p was 1 mole %, [HEMA]_s was 11 mole %. The intensity of the satellite peak due to the^* transition of the benzene ring of the styrene component decreased with an increase in [HEMA]_p, to zero at 5 mole % of [HEMA]_p. These results indicate that the HEMA component is localized at the surface.Part CVIII of the series Studies on Suspension and Emulsion.