Abstract: By means of soapless emulsion polymerization, graft polymerization of styrene(St) onto the surface ofalkyl nanoTiO₂ was carried out, resulting in composite particles with TiO₂, core and a polymer shell.Polystyrene(PS)ischemically attached onto the nanoparticles by a double bond introduced during the pretreatment with a coupling agent. Through analyzing the reaction mechanism, the emulsion poly- merization site was found to besituatedatthe  TiO₂ surface. The factors affecting the grafting yielding o PS on the particles were also investigated, including monomer concentration, emulsion agent content, and reaction time, an optimum grafting reaction condition was determined. The structural characteris-tics of the grafting polymers can betailored by changing the reaction conditions. This provided possibili-ties for optimizing the structure-property relationships of polymer composites filled with the modifiec nano-TiO₂ particles in the future works.

Key words: nano-TiO2；soapless emulsion polymerization;polystyrene, surface modification, nanocomposite