The electrolyte may be added in an amount changed appropriately in accordance with the adjustment of pH under reaction conditions. [0126] The polymerization initiator may include persulfates such as potassium persulfate and ammonium persulfate, azo compounds such as 2,2???-azobis(isobutylonitrile) and 4,4???-azobis(4-cyanovaleric acid), organic peroxides such as benzoyl peroxide and methyl ethyl k