Quantifying Photoinitiation Efficiencies in a Multiphotoinitiated Free-Radical Polymerization

Authors

  • Dominik Voll,

    1. Preparative Macromolecular Chemistry, Institut für Technische, Chemie und Polymerchemie, Karlsruhe Institute of Technology, KIT, Engesserstr. 18, 76128 Karlsruhe, Germany
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  • Andrea Hufendiek,

    1. Preparative Macromolecular Chemistry, Institut für Technische, Chemie und Polymerchemie, Karlsruhe Institute of Technology, KIT, Engesserstr. 18, 76128 Karlsruhe, Germany
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  • Thomas Junkers,

    1. Institute for Materials Research, Polymer Reaction Design, Group, Universiteit Hasselt, Agoralaan, Gebouw D, BE-3590, Diepenbeek, Belgium
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  • Christopher Barner-Kowollik

    Corresponding author
    1. Preparative Macromolecular Chemistry, Institut für Technische, Chemie und Polymerchemie, Karlsruhe Institute of Technology, KIT, Engesserstr. 18, 76128 Karlsruhe, Germany
    • Preparative Macromolecular Chemistry, Institut für Technische, Chemie und Polymerchemie, Karlsruhe Institute of Technology, KIT, Engesserstr. 18, 76128 Karlsruhe, Germany.
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Abstract

Online size exclusion chromatography–electrospray ionization–mass spectrometry (SEC/ESI–MS) is employed for quantifying the overall initiation efficiencies of photolytically generated radical fragments. In a unique experiment, we present the first quantitative and systematic study of methyl-substituted acetophenone-type photoinitiators being employed in a single cocktail to initiate the free-radical polymerization of methyl methacrylate (MMA) in bulk. The photoinitiators are constituted of a set of two known and four new molecules, which represent an increasing number of methyl substituents on their benzoyl fragment, that is, benzoin, 4-methylbenzoin, 2,4-dimethylbenzoin, 2,4,6-trimethylbenzoin, 2,3,5,6-tetramethylbenzoin, and 2,3,4,5,6-pentamethylbenzoin. The absolute quantitative evaluation of the mass spectra shows a clear difference in the initiation ability of the differently substituted benzoyl-type radical fragments: Increasing the number of methyl substituents leads to a decrease in incorporation of the radical fragments.

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