Controlled radical polymerization of styrene mediated by the <i>C</i>‐phenyl‐<i>N</i>‐<i>tert</i>‐butylnitrone/AIBN pair: Kinetics and electron spin resonance analysis

Abstract

Abstract Kinetics of the free radical polymerization of styrene at 110 °C has been investigated in the presence of C ‐phenyl‐ N ‐ tert ‐butylnitrone (PBN) and 2,2′‐azobis(isobutyronitrile) (AIBN) after prereaction in toluene at 85 °C. The effect of the prereaction time and the PBN/AIBN molar ratio on the in situ formation of nitroxides and alkoxyamines (at 85 °C), and ultimately on the control of the styrene polymerization at 110 °C, has been investigated. As a rule, the styrene radical polymerization is controlled, and the mechanism is one of the classical nitroxide‐mediated polymerization. Only one type of nitroxide (low‐molecular‐mass nitroxide) is formed whatever the prereaction conditions at 85 °C, and the equilibrium constant ( K ) between active and dormant species is 8.7 × 10 −10 mol L −1 at 110 °C. At this temperature, the dissociation rate constant ( k d ) is 3.7 × 10 −3 s −1 , the recombination rate constant ( k c ) is 4.3 × 10 6 L mol −1 s −1 , whereas the activation energy ( E a,diss. ), for the dissociation of the alkoxyamine at the chain‐end is ∼125 kJ mol −1 . Importantly, the propagation rate at 110 °C, which does not change significantly with the prereaction time and the PBN/AIBN molar ratio at 85 °C, is higher than that for the thermal polymerization at 110 °C. This propagation rate directly depends on the equilibrium constant K and on the alkoxyamine and nitroxide concentrations, as well. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1219–1235, 2007