X-RAY PHOTOELECTRON-SPECTROSCOPY AND STATIC TIME-OF-FLIGHT SECONDARY-ION MASS-SPECTROMETRY STUDY OF DISPERSION POLYMERIZED POLYSTYRENE LATEXES

Dispersion polymerized polystyrene particles were prepared using poly(N-vinylpyrrolidone) (PVP) as a steric stabilizer. The top surface composition of a series of latex particles was analyzed using a combination of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). XPS of 6.5-mum micron particles revealed a top surface composition of 30% steric stabilizer, corresponding to either two monolayers (0.5-0.6 nm) of highly ordered PVP uniformly coating the particles or a patchy surface with islands of PVP on the polystyrene surface. The SIMS experiments showed a mixture of polystyrene and PVP in the very top layer, supporting the patchy model. Similar results were obtained for several 2.5-mum particles synthesized using PVP in combination with Triton and Aerosol AOT ''costabilizers''. The additional surfactants were not found on the surface. One sample with a much higher polystyrene molecular weight had only 15 % PVP on the surface, suggesting that the majority of the surface polystyrene is simply the anchoring block of the grafted PVP-PS. The results are quantitatively consistent with the grafting mechanism of stabilization in dispersion polymerization.