Stable dispersions of silica were coated with polystyrene by emulsifier-free polymerization

and the monodisperse composite spheres were obtained

whose thickness is about 100 nm．Silica ranging from 150 to 250 nm was core particles．To achieve a high coating efficiency

silica was first modified with 3-(trimethoxysilyl)propylmeth-acrylate (MPS) coupling agent at three different degrees of coupling．The presence of the bound MPS agent and of the polymer at the silica surface was determined by the infrared spectroscopy

and the bound amount of MPS was calculated from mass losses of thermogravimetric analysis (TGA)．Coating efficiency and the monodispersion of the composite particles were enhanced by the degree of MPS coupling and by initial concentration of the monomer．The morphology of the composite particles were determined by transmission electron microscopy (TEM)

and their monodispersities was measured by dynamic light scattering (DLS)．