Radical homopolymerizations and copolymerizations of styrene were performed in toluene and N,N-dimethylformamide (DMF) as solvents using different initiators with and without microwave irradiation. Only the homopolyrnerization of styrene under microwave irradiation in DMF with DtBP showed significantly enhanced styrene conversion whereas other initiators resulted in no or only slight increase of styrene conversion under microwave irradiation. In any case. DMF was required to gain in styrene conversion under microwave irradiation. Significantly higher monomer conversions were observed under otherwise comparable conditions in the copolymerization of styrene and methyl methacrylate (MMA) in DMF Microwave-induced selectivity of monomers was not observed in copolymerizations.