Synthesis of monodisperse zinc sulfide particles grafted with concentrated polystyrene brush by surface-initiated nitroxide-mediated polymerization

Monodisperse zinc sulfide (ZnS) particles of diameters ranging from 120 to 400 nm were prepared and then coated with a thin layer of silica (SiO₂). After the surface modification with an alkoxyamine derivative, polystyrene (PS) brushes of chain lengths ranging from 30,000 to 114,000 in M_n with relatively low polydispersities less than 1.5 in M_w/M_n were successfully grafted by surface-initiated nitroxide-mediated polymerization, where the M_n and M_w are the number- and weight-averaged molecular weights, respectively. The graft density reached a value as high as 0.9 chains nm⁻². These core-shell hybrid particles (ZnS@SiO₂-PS) were highly dispersible, without any aggregation, in various solvents good for PS, also forming a monolayer at the air-water interface by spreading its solution. The transmission electron microscopic observation of the monolayers deposited on a solid support revealed two-dimensionally close-packed arrays of particles. These monolayers exhibited a beautiful structural color dependent on the angle of incident light because of such an ordered array of the ZnS cores with a high refractive index. Hollow spheres constituted of a SiO₂ shell with well-defined, high-density PS brushes were first synthesized by selective dissolution of the ZnS core from the ZnS@SiO₂-PS hybrid particle.