The effect of several parameters on the incorporation yield of poly(ethylene oxide) macromonomers at the surface of the particles, for the dispersion polymerization of styrene in ethanol-water mixtures, has been studied. The reactivity of the macromonomer is a key parameter in the mechanism of stabilization of the micrometer-size polymer particles, because it partly determines the amount and the composition of the copolymer stabilizer available at any moment during the process. The polarity of the reaction medium also strongly influences the polymerization process: higher incorporation yield and grafting density were obtained in medium of lower polarity. Besides, a chain length of around 50 ethylene oxide units for the macromonomer were needed to produce stable monodisperse particles with a significant incorporation yield. Thus, an incorporation yield as high as 53% and a grafting density corresponding to a surface area of 232 Å 2 / molecule have been obtained in a one-step process by using a methacrylate macromonomer. In an optimized two-step process resulting in monodisperse polymer particles, 80% incorporation yield with a very high grafting density (175 Å 2 /molecule) were reached. The particles with high grafting density (surface area lower than 600 Å 2 /molecule) could be transferred in water and exposed to a freeze-thaw cycle without massive flocculation, illustrating the efficiency of the steric stabilization.