The present invention relates to a polymerization process for polymerizing olefinically unsaturated monomer or monomers, wherein inorganic salts are employed to substitute for the traditional emulsifiers employed in the polymerization recipe. The polymerization of olefinically unsaturated monomer or monomers is conducted in the presence of a water soluble initiator. An electrolytic solution of inorganic salt and a buffer solution are introduced into the polymerization mixture at a particular time during reaction period to adequately adjust pH value of the reaction mixture. Further, it is essential to alter the speed of agitation during polymerization by a two-stage operation. The polymer resins so produced have no emulsifier residue contained within the polymer particles, whereby the properties of plastisols from these resins such as viscosity stability, heat stability and clarity are superior to those of the polymer resins produced by conventional emulsion polymerization process or microsuspension polymerization process. The monomer/water ratio of the polymerization recipe thereof is also improved, whereby productivity per batch or run of polymerization is increased.