Polystyrene-grafted titanium oxide nanoparticles prepared through surface-initiated nitroxide-mediated radical polymerization and their application to polymer hybrid thin films

Polystyrene (PS)-grafted-titanium oxide (TiO₂) nanoparticles with a diameter of 15 nm were prepared by the 'grafting-from' method using the surface initiator for nitroxide-mediated radical polymerization (NMRP). The graft densities were estimated to be 0.04-0.28 chains nm^-2. Under this graft dense region it is assumed that surface polymer chains form a polymer brush structure in good solvents. Wide-angle X-ray diffraction suggested that the tacticity of the PS chains on the nanoparticle surface is mainly atactic. PS-grafted-TiO₂ nanoparticles were stably dispersed in good solvents for PS chains due to the steric repulsion between the grafted chains derived from the osmotic pressure effect and their affinity for the solvents. When the PS-grafted-TiO₂ particles were finely dispersed, the ultraviolet absorption due to TiO₂ was strong and the difference in absorbance between the visible and ultraviolet regions was ten or more times greater than that for non-grafted TiO₂. By adding PS-grafted-TiO₂ particles with PS matrix powder in CHCl₃, hybrid films were prepared by solvent casting. The PS-grafted-TiO₂-PS hybrid films showed high transmittance in the visible light region accompanied by ultraviolet absorption characteristic of TiO₂ due to the fine dispersion of nanoparticles in the PS matrix. Furthermore, friction tests revealed that the wear resistance of PS thin films with PS-grafted-TiO₂ was improved compared with PS film.