Peculiar behavior of β-phosphonylated nitroxides bearing a tert-octyl group during living/controlled radical polymerization of styrene:: Kinetics and ESR studies

Bulk radical polymerization of styrene, in the presence of new nitroxides bearing a tert-octyl group and various bulky phosphonate groups in beta-position to the nitrogen, is reported. From kinetics studies performed at 90 degrees 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 beta-position to the nitrogen. This behavior is related to the steric hindrance of the tert-octyl 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.