Peculiar Behavior of β-Phosphonylated Nitroxides Bearing a tert-octyl Group during Living/Controlled Radical Polymerization of Styrène: Kinetics and ESR Studies
Résumé
Bulk radical polymerization of styrène, in the presence of new nitroxides bearing a tertoctyl group and various bulky phosphonate groups in /J-position to the nitrogen, is reported. From kinetics studies performed at 90 °C, with or without a radical initiator, it was shown that the polymerization presents the criteria of a living/controlled polymerization. From ESR experiments carried out in the same reaction medium, it was established that the counter radical involved in the process is a new nitroxide presenting a proton in /3-position to the nitrogen. This behavior is related to the steric hindrance of the tert-octy group that leads to the formation of the corresponding nitroso, able to react with the styryl radicals. From kinetics and ESR studies, the equilibrium constant for this nitroxide was estimated to be 6 x 10-11 mol L-1. © 2000 American Chemical Society.