Dispersion polymerization has been widely applied to the synthesis of monodisperse micron-sized polymer colloidal spheres. Many efforts have been devoted to studying the influence of initial conditions on the size and uniformity of the resultant microspheres, aiming to synthesize micron-size monodisperse colloidal spheres. However, the inner contradiction between the size and the size distribution of colloidal spheres hinders the realization of this goal. In this work, we drew our attention from the initial conditions to the growth stage of dispersion polymerization. We tracked the size evolution of colloidal sphere during the dispersion polymerization, through which we established a kinetic model that described the relationship between the monomer concentration and the reaction time. The model may provide a guideline to prepare large polymer colloidal spheres with good monodispersity by continuous monomer feeding during the growth stage to maintain the concentration of monomer at a constant value in a dispersion polymerization process. 1. Introduction As a new functional macromolecule material, monodisperse polymer microspheres have many applications in environmental conservation, biomedicine, colloid science, electronic information material, and many other areas [1–3] due to their superiority of good sphericity, size tunability, large specific surface area, and excellent absorbability [4–6]. Particularly, monodisperse micron-sized spheres are ideal materials as advanced coatings [7], fillers of chromatographic column [8, 9], standard particles of electron microscope and Coulter particle size testers, and spacers in LCD [10], which has drawn increasing interest to synthesize monodisperse micron-sized spheres [11, 12]. The first report on monodisperse polymer colloidal spheres was the polystyrene spheres prepared by Vanderhoff and Brandford [13]. So far, many synthesis strategies have been developed such as emulsion polymerization, suspension polymerization, dispersion polymerization, and seed swelling polymerization. In view of the demand of micron size and monodispersity, the former two methods are excluded because they cannot meet the two requirements at the same time. Emulsion polymerization can only gain monodisperse colloidal spheres with the size below 1？μm. Suspension polymerization may achieve large microspheres with size ranging from 10？μm to 100？μm while the microspheres possess a bad monodispersity [14]. The latter two methods are suitable for the synthesis of uniform colloidal spheres with micron size. Seed swelling polymerization,
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