Synthesis of a New Stable β-Sulfinyl Nitroxide and the Corresponding Alkoxyamine for Living/Controlled Radical Polymerization of Styrene: Kinetic and ESR Studies

The syntheses of a new nitroxide bearing a sulfoxide group at the β-position (with respect to nitrogen) and the corresponding N -β-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 °C, 3.7 at 100 °C, and 3.5 at 110 °C. 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 ≈ 10 5 L mol -1 s -1 ).