In order to clarify the effects of the sulfur atom and the alkyl groups in alkyl vinyl sulfides (RVS) on their reactivities, the radical copolymerizations of eight RVS (M2) with styrene, methyl methacrylate, and acrylonitrile (Mi) were investigated at 60°C, and the copolymerization parameters were determined. It was found that the Q and e values for RVS were estimated as 0.3 ∼ 0.5 and -1.1 ∼ -1.7, respectively, from the copolymerizations with styrene, and these values were almost unchanged, regardless of the type of alkyl group in RVS. These results indicated that the electron-sharing, 3d orbital resonance between the growing radical derived from electron-donating RVS monomer and the adjacent sulfur atom was important in the transition state of copolymerizations.