At 70degreesC, [bis(triphenylphosphino)(3,6-di-tert-butylbenzosemiquinone-1,2)copper(I)] efficiently inhibits AIBN-initiated polymerizations of styrene and butyl methacrylate. After the end of the induction period, thermal (95, 125degreesC) and photoinduced (25degreesC) polymerization of styrene exhibit features typical of pseudoliving radical polymerization, namely, a linear relation between the polymer molecular mass and conversion in the first case and M-w/M-n = 1.32 in the second. Schemes of controlled chain propagation are suggested.