The syntheses of a new nitroxide bearing a sulfoxide group at the P-position (with respect to nitrogen) and the corresponding N-beta-sulfinyl alkoxyamine are reported. Styrene was polymerized in bulk in the presence of this new alkoxyamine. The polymerization satisfies the usual criteria of a living/ controlled radical polymerization, with a linear increase of molecular weight vs yield and a constant transient radical concentration with time. However, the polymerization rates were independent of alkoxyamine concentration but much higher than the thermal polymerization ones: R-p/R-th = 2.6 at 90 degreesC, 3.7 at 100 degreesC, and 3.5 at 110 degreesC. Kinetic and ESR studies showed that both transient and persistent radical concentrations do not follow the corresponding theoretical evolutions with time but reach stationary states. The different rate constants (k(d) and k(c)) and corresponding activation energies were estimated, showing that the sulfoxide group has a large effect mainly on the combination reaction, the value of which is unusually low for such system (k(c) approximate to 10(5) L mol(-1) s(-1)).