Poly(ethylene oxide-b-styrene oxide) macromonomers carrying p-vinylbenzyl ether end group were prepared by sequential anionic polymerization of ethylene oxide and styrene oxide with potassium 2-methoxyethoxide, followed by reaction with p-vinylbenzyl bromide to the end-group functionality up to 85%. The macromonomers have been successfully applied to emulsion and dispersion copolymerizations with styrene to afford monodisperse polymeric microsheres in water and in methanol-water (9/1 v/v) mixture, respectively.. Incorporation of the macromonomer into the particle is more effective, so resulting in smaller particle size, in. the emulsion than in the dispersion system. The particle size in the latter system decreased with the macromonomer concentration in accord with a previously proposed power-law theory and with the chain length of the styrene oxide block.