The rate of homogeneous polymerization of N-dodecylmaleimide (DMIm) with dimethyl 2,2’-azobisisobutyrate depended significantly on the kind of solvents used. The polymerization systems involved ESR-observable propagating poly(DMIm) radical. The rate constants of propagation(k(p)) and termination(k(t)) were determined at 50 degrees C in various solvents. The k(p) value was smaller in aromatic solvents than in aliphatic ones. The Hammett’s plot of k(p) against sigma-value of the substituents on the aromatic solvents showed that k(p) took higher values in the solvents with either electron-accepting or donating substituents. The solvent effects on k(p) seemed to stem from complexion of poly(DMIm) radical with solvents.