1-tert-Butyl-3,3,5,5-tetraalkyl-2-piperazinon-4-oxyls: Highly Efficient Nitroxides for Controlled Radical Polymerization

Abstract

The paper describes nitroxide-mediated radical polymerization of styrene and n-butyl acrylate by using four sterically highly hindered 6-membered cyclic nitroxides. The syntheses of the corresponding alkoxyamine initiators are described, and also rate constants for C−O bond homolysis of these systems are discussed. It is shown that rate constants of alkoxyamines can readily be determined by 1H NMR experiments. Polymerization results obtained are compared with data previously achieved with highly efficient nitroxides. Since this class of nitroxides is readily accessible, the 1-tert-butyl-3,3,5,5-tetraalkyl-2-piperazinon-4-oxyl radicals bearing alkyl groups that are ethyl or larger n-alkyl groups are probably the most efficient cyclic 6-membered nitroxides known to date for mediating NMP.