Selected Paper : Molecular Structure of Poly(vinyl alcohol)-Derived Carbon-Centered Radicals Studied by Rapid-Flow and Spin-Trapping ESR Measurements : A Short-Lived Intermediate Radical in the Initial Stage of the Graft Polymerization Reaction

  • Nishihara Yuko
    Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology Central Research Laboratory, The Nippon Synthetic Chemical Industry Co. Ltd.
  • Matsui Kazuma
    Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
  • Kuwabara Keiko
    Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
  • Murata Naoya
    Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
  • Yamaguchi Tomoko
    Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
  • Miyake Yusuke
    Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
  • Ikegami Tohru
    Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
  • Kanaori Kenji
    Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology
  • Tajima Kunihiko
    Department of Molecular Chemistry, Graduate School of Kyoto Institute of Technology

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  • Molecular Structure of Poly(vinyl alcohol)-Derived Carbon-Centered Radicals Studied by Rapid-Flow and Spin-Trapping ESR Measurements: A Short-Lived Intermediate Radical in the Initial Stage of the Graft Polymerization Reaction

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<p>Continuous rapid-flow electron spin resonance (ESR) was used to detect poly(vinyl alcohol) (PVA)-derived carbon-centered radicals, in order to characterize the short-lived intermediate radicals in the initial stage of the graft polymerization of PVA. ESR spectra were recorded by mixing PVA, hydrogen peroxide, and Ti2(SO4)3 at pH 2.0. The observed spectrum indicated three paramagnetic species: a minor species A, and two major species B1, and B2. Based on the observed proton hyperfine coupling constant (hfcc) values, species A was assigned to the carbon-centered radical of PVA produced by hydrogen atom abstraction from the methine carbon bearing a hydroxyl group. Species B1 and B2 were ascribed to two structural isomers of the PVA-derived, carbonyl-conjugated radical produced by acid-catalyzed radical reaction at the vicinal diol moiety (i.e., head-to-head structure) of PVA. Spin-trapping ESR measurements were performed at 80 °C using a water-soluble spin-trapping reagent 3,5-dibromo-4-nitroso-benzenesulfonate sodium salt (DBNBS). Based on the hfcc values observed for the spin-adducts, species B1 and B2 were confirmed to be the major PVA main-chain-derived radicals produced under the graft reaction conditions. These findings demonstrated that the PVA-derived, carbonyl-conjugated radicals are one of the intermediate radicals in the initial stage of the graft polymerization reaction under acidic conditions.</p>

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