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

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 1 H 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.