The surface potential of polymeric particles obtained through soap-free emulsion polymerization using an oil-soluble initiator, 2,2'-azobis(2-methylpropionitrile) (AIBN), depended on the monomer used in the polymerization. Changing the amount of it electrons in the aromatic monomer enabled control of the surface potential of the synthesized particles. It was found that the negative charges of the synthesized particles were strengthened for their sizes to be reduced gradually as the amount of it electrons in the monomer was increased.