A liquid pigment dispersion is disclosed. Specifically, in one embodiment, there is provided a process for preparing a polymer, wherein the process comprises: providing a reaction mixture comprising a portion of at least one polar monomer and at least one multivalent cation; adding the remaining portion of the polar monomer to the reaction mixture; and polymerizing the monomer to form the polymer. By adopting the preparation method, a desirable initial nucleus can be obtained for a polycrystalline silicon ingot, so as to reduce dislocation multiplication during the growth of the polycrystalline silicon ingot. The additive composition may also contain a dispersing agent, such as a fatty acid. Thereby, downsizing of the package and stable manufacturing are realized.