The free radical polymerization of styrene or methyl methacrylate under semicontinuous conditions in water in the presence of randomly methylated-beta-cyclodextrin (RAMEB) is described. The polymerization reactions were carried out in water with potassium peroxodisulfate as free radical initiator at 80 degreesC in the presence of different amounts of cyclodextrins. Compared to batch polymerizations, where the water-insoluble polymer precipitates or produces high amounts of coagulum, this new method results in quantitative conversion of the monomers and leads to stable latexes with nearly monodisperse polymer particle size distributions, which are very useful in many technical applications.