New Sterically Hindered Nitroxides for the Living Free Radical Polymerization:  X-ray Structure of an α-H-Bearing Nitroxide

The synthesis of three new sterically hindered Hawker−Braslau type alkoxyamines for the nitroxide-mediated living radical polymerization is described. Efficient polymerizations can be performed at 105 °C. With alkoxyamine 11 controlled polymerization of n -butyl acrylate and styrene is possible even at 90 °C. AA and AB diblock copolymers can be prepared in a controlled manner using alkoxyamine 11 . Kinetic EPR experiments for the determination of the C−O bond activation energies of the new alkoxyamines are described. Furthermore, 1 H NMR alkoxyamine decomposition studies are presented. These kinetic experiments are used for the discussion of the polymerization results. Furthermore, the X-ray structure of a Hawker-Braslau type nitroxide is presented. X-ray data and ESR data are used to explain the high stability of these nitroxides.