Radical copolymerization of styrene (St, M1) with acrylonitrile (AN, M2) has been carried out using azobisisobutylonitrile as an initiator in benzene, dimethylsulfoxide, acetonitrile, and ethanol at 60 and 80°C. Good linear correlationships were obtained by plotting the values of log r1, log r2, Q2, and e2against those ofvC˭N andvC˭C determined in the solvents: the increase in the interaction between AN and the solvent was found to decrease the values of log r1and e2but to increase those of log r2and Q2. The results are discussed in terms of the solvation both in the ground state and in the transition state.