Abstract Polystyrene latex particles with controlled size were prepared by polymerization of oil-in-water (O/W) emulsion styrene droplets obtained through the phase inversion temperature (PIT) emulsification using amphiphilic comb-like block polymers, polystyrene- b -poly[oligo(ethylene glycol) methyl ether methacrylate] (PSt n - b -POEGMA m -Cl). PSt n - b -POEGMA m -Cl block polymers were synthesized by sequential atom transfer radical polymerization (ATRP) of St and OEGMA. The interfacial properties of PSt n - b -POEGMA m -Cl in aqueous media were investigated by means of surface tension measurement, fluorescence probe technique, and transmittance measurement. The length of hydrophobic PSt block chain was found to affect the critical micelle concentration, the micelle aggregation number, and the cloud point. O/W emulsions were obtained through the PIT process using PSt n - b -POEGMA m -Cl as a surfactant by lowering the temperature of emulsions below the PIT in an ice bath. PSt particles with precisely controlled size in a range between 30 and 120 nm were successfully prepared by a free radical polymerization of St droplets initiated by the water- or oil-soluble initiators. FE-SEM observation revealed that the morphology of polystyrene particles was found to depend on the relative PSt chain length of PSt n - b -POEGMA m -Cl.