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EPR Study into Cross-Termination and Fragmentation with the Phenylethyl–Phenylethyl Dithiobenzoate RAFT Model System

Authors

  • Wibke Meiser,

    1. Institut für Physikalische Chemie, Georg-August-Universität Göttingen, Tammannstr. 6, D-37077 Göttingen, Germany
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  • Michael Buback,

    Corresponding author
    1. Institut für Physikalische Chemie, Georg-August-Universität Göttingen, Tammannstr. 6, D-37077 Göttingen, Germany
    • Institut für Physikalische Chemie, Georg-August-Universität Göttingen, Tammannstr. 6, D-37077 Göttingen, Germany.
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  • Oliver Ries,

    1. Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstr. 2, D-37077 Göttingen, Germany
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  • Christian Ducho,

    1. Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstr. 2, D-37077 Göttingen, Germany
    2. Department Chemie, Universität Paderborn, Warburger Str. 100, D-33098 Paderborn, Germany
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  • Alana Sidoruk

    1. Institut für Physikalische Chemie, Georg-August-Universität Göttingen, Tammannstr. 6, D-37077 Göttingen, Germany
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Abstract

The reversible addition–fragmentation chain transfer (RAFT) equilibrium constant of the phenylethyl–1-phenylethyl dithiobenzoate model system is deduced via EPR spectroscopy to be 31 ± 4 L mol−1 at 110 °C. The difference in activation energies of addition and fragmentation, Ea(kad) – Ea(kβ) ≈ −45.6 kJ mol−1, is close to that of the polystyryl–polystyryl dithiobenzoate system. Significant amounts of products from cross-termination and from “missing step” reaction of the cross-termination product with the phenylethyl radical demonstrate that intermediate radical termination, rather than slow fragmentation of the RAFT intermediate radical, is responsible for the rate retardation in the dithiobenzoate-mediated styrene polymerization.

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