The free radical polymerization of styrene "initiated" by a 2,2,6,6-tetramethyl-1-poly-(styroxypiperidine) (PS-TEMPO : M-n 1700 and M-w/M-n = 1.11) was studied to examine the effect of tert-butyl hydroperoxide (BHP), a radical initiator, on the polymerization rate and molecular weights. It was demonstrated that, by the addition of BHP, the rate can be increased by a factor of up to about 3 without causing any appreciable increases of the number of chains and the polydispersity index M-w/M-n (at 114 degrees C). These results are consistent with the kinetic schemes proposed previously (Fukuda, T.; et al. Macromolecules 1996, 29, 6393) and suggest a general method to manipulate the polymerization rate of such systems. A simple analytical equation was presented showing how the polydispersity is narrowed by alternating activation-deactivation processes, and it-allowed us to evaluate the frequency of activation independently of other reactions. This equation consistently interpreted the experimental results.