Acyclic β-phosphonylated nitroxides:: A new series of counter-radicals for living/controlled free radical polymerization

Oxidation of alpha-(N-alkylamino) phosphonic acid esters, carrying one or two alkyl groups as substituents on their alpha-carbon, by m-chloroperbenzoic acid afforded the corresponding stable beta-phosphonylated nitroxides. The nitroxides derived from alpha-mono-tert-butyl alpha-alkylaminophosphonic acid esters are stable compounds despite the presence of a hydrogen atom on the alpha-carbon bound to the nitroxyl group. The ESR study of these nitroxides in solution showed that this beta-hydrogen atom lies in the nodal plane to the nitroxyl function. These beta-phosphonylated nitroxides were found to efficiently control the free radical polymerization reaction of styrene, with a much faster rate of propagation than that observed in TEMPO-mediated systems.