IntroductionMany polymer latices bearing reactive groups such as amino, hydroxy, and carboxy moieties on the surface were synthesized and utilized for immobilization of biologically active compounds ' 1. Thiol is another reactive group forming symmetrical or unsymmetrical disulfides, mercaptides, and sulfides. Polymer latices containing thiol groups on the surface may be applied to immobilization of biological compounds such as enzymes, because of the unique reactivity. However, there are few reports on the synthesis of such polymer latices by reaction of glycidyl groups on latex surface with hydrogen sulfide').Isothiuronium salts are extensively used as intermediates for the synthesis of thiol compounds 3), Soluble and cross-linked polymers bearing thiol as a pendant group were also synthesized by use of isothiuronium salts4). As a hydrophilic precursor for thiol, isothiuronium salt is anticipated to be a candidate of emulsifier for polymer latex synthesis, but there is no report so far. We report here on the synthesis of latex containing thiol groups on the surface by emulsion polymerization of styrene with the polymerizable isothiuronium salt 1 as an emulsifier and the subsequent hydrolysis of the salt chemically bound to the latex.
Experimental partMeasurement: 'H NMR spectra were recorded with a JEOL FX-90Q instrument. Absorption spectra were measured with a JASCO 660 UV/VIS spectrophotometer. Transmission electron micrographs were taken with JEOL JEM-100CX and Hitachi H-500 electron microscopes.Inductively coupled radio frequency plasma spectra (ICPS) were measured with a Shimadzu ICPS-1OOoII.Materials: Unless stated otherwise, reagents and solvents were used as received. Styrene was washed with 10% NaOH and distilled under reduced pressure before use. 2,2'-Azobis[(2-imidazolin-2-yl)propane] dihydrochloride (VA-44) was recrystallized from water and acetone. Potassium persulfate (K,S,O,) was recrystallized from water. 4-Ethenylphenylmethylisothiuro-0173-2803/89/$01.00 398 K. Yamaguchi, S. Watanabe, S. Nakahama nium chloride (1) was synthesized according to the reported method '), followed by recrystallization from distilled water twice.Emulsion polymerization: Before addition of styrene, pH of the aqueous solution of a radical initiator (VA-44 or K,S,O,) and emulsifier 1 was adjusted to 1,4. The emulsion polymerization and the following treatment were carried out in the same manner as reported previously ').SuCfur content of latex ICPS measurement on a dispersed latex, diluted with deionized water (ca. 1,5 . g/ml), was performed by calibration with standard aqueous ammonium sulfate solution.Alkaline hydrolysis of latex After an emulsion (10 ml) (containing ca. 0,8 -0,9 g of polymer) and 2 M KOH (5 ml) were degassed separately by nitrogen bubbling for 10 min, the alkaline solution was poured into the emulsion. Nitrogen gas was again bubbled through the mixture for 10 min at room temperature. Occasionally, the hydrolytic treatment resulted in a coagulated latex, which was filtered, washed with water, and dried...
