Synthesis of polymer latex containing SH groups on the surface, 2. Emulsion polymerization of styrene in the presence of a polymerizable isothiuronium salt as a comonomer and the subsequent hydrolysis†

Emulsion polymerization of styrene using various isothiuronium salts as comonomers and the subsequent alkaline hydrolysis of the product gave latices containing mercapto (SH) groups. Four styrene derivatives of isothiuronium salts and a methacrylate counterpart were employed as comonomers. The yield, size distribution, and sulfur content of the latices are affected by initiators and isothiuronium salts employed. With a cationic initiator (2,2′-azobis[(2-imidazolin-2-yl)propane] dihydrochloride) and any isothiuronium salt, latices of narrow size distributions were obtained in high yield. The sulfur content of the latices is comparable to that calculated from the feed ratio of the salt to styrene monomer. In case of an anionic initiator (K2S2O8), only 2-[4-vinylphenylmethyl]-and 2-[3-(methacryloyloxy)propyl]-isothiuronium chloride gave latices with narrow size distribution in high yield, whereas the sulfur content was lower than the calculated one. The isothiuronium salts on the latices were converted into mercapto groups by hydrolysis in aqueous alkaline solution. Thus, we obtained latices containing mercapto groups on the surface with narrow size distributions.