On the photoinitiation of free radical polymerization-laser flash photolysis investigations on thioxanthone derivatives

Authors

  • Gholamreza Amirzadeh,

    1. Hahn-Meitner-Institut für Kernforschung Berlin GmbH, Bereich Strahlenchemie, Glienicker Str. 100, D-1000 Berlin 39
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  • Wolfram Schnabel

    Corresponding author
    1. Hahn-Meitner-Institut für Kernforschung Berlin GmbH, Bereich Strahlenchemie, Glienicker Str. 100, D-1000 Berlin 39
    • Hahn-Meitner-Institut für Kernforschung Berlin GmbH, Bereich Strahlenchemie, Glienicker Str. 100, D-1000 Berlin 39
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  • Herrn Prof. G. Manecke zum 65. Geburtstag gewidmet

Abstract

Laser flash photolysis studies and stationary polymerizations were carried out with the aim to elucidate kinetics and mechanisms of photoinitiation processes based on thioxanthone (TX)/amine interactions. During these studies prominence was given to reactions which significantly influence the initiator efficiencies. Thus, rate constants of the reactions 3TX* + monomer (kq), 3TX* + amine (kXH), and ketyl radical + monomer (kmath image) were determined; kq decreases according to the series: styrene (St) > N-vinyl-2-pyrrolidone (VP) > methyl methacrylate (MMA) > acrylonitrile (AN) > butyl vinyl ether (BVE) > vinyl acetate (VA) from 6·109 l·mol−1·s−;1 to 2·104 l·mol−1·s−1. Substitution in the 2-position of TX by methyl (MTX), isopropyl (ITX) and Cl (CTX) generally causes a decrease of kq, except for the systems CTX/VP and CTX/BVE. The kXH values range from 6 to 8·109 l·mol−1·s−1 for typical amines, e.g. ethyl 4-((dimethylamino)benzoate). Ketyl radicals react rather slowly with monomers; for CTX kmath image in l·mol−1·s−1: 7·103 (St), 4·102 (VP), 4·101 (MMA), ⩽ 10 (BVE). O2 reacts rapidly with ketyl radicals: kmath image = 2·109 l·mol−1·s−1 (TX). Rates of polymerization ν (monomer consumption) determined at [M] = 5 mol/l and [amine] = 10−1 mol/l are equal for TX, ITX, MTX, and CTX, but increase according to the series AN < MMA < VP; ν depends on the thioxanthone and the monomer concentration according to ν ∝ [TX]1/2[M].

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