You can manage bookmarks using lists, please log in to your user account for this.
Media type:
E-Article
Title:
On the primary processes of sensitized photopolymerization of vinylmonomers. Laser flash photolysis studies and stationary polymerization experiments
Contributor:
Kuhlmann, Ralf;
Schnabel, Wolfram
Published:
Wiley, 1977
Published in:
Die Angewandte Makromolekulare Chemie, 57 (1977) 1, Seite 195-210
Description:
<jats:title>Abstract</jats:title><jats:p>The absorption spectra of the triplets of aromatic ketones used as photosensitizers for the polymerization of unsaturated compounds — benzophenone (BP), 3,3′,4,4′‐tetramethoxycarbonylbenzophenone (TMCB) and 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) — were recorded after irradiation of benzene or acetone solutions of the ketones with 25 ns flashes from a frequency doubled ruby laser (λ = 347,1 nm) at room temperature. Furthermore, the spectra of the respective ketyl radicals were measured. Rate constants of the reaction of triplets with various monomers were measured. Very high rate constants (> 10<jats:sup>9</jats:sup> 1 · mol<jats:sup>−1</jats:sup> s<jats:sup>−1</jats:sup>) were found for styrene (St) and N‐vinylpyrrolidone (VP). The triplet energy E<jats:sub>T</jats:sub> of these monomers is smaller than E<jats:sub>T</jats:sub> of the sensitizers, except the case BP/VP. Other monomers — vinylacetate (VAc), methylmethacrylate (MMA), acrylonitrile (AN) — react relatively slowly with sensitizer triplets (5 × 10<jats:sup>6</jats:sup> to 1.4 × 10<jats:sup>8</jats:sup> l · mol<jats:sup>−1</jats:sup> s<jats:sup>−1</jats:sup>). It is assumed that these monomers have E<jats:sub>T</jats:sub> values higher than the E<jats:sub>T</jats:sub> values of the sensitizers.</jats:p><jats:p>The rate of polymerization v was determined in tetrahydrofuran solutions containing monomer (5 mol/1) and sensitizer (6–7 × 10<jats:sup>4</jats:sup> mol/1) from stationary experiments with irradiation of light with λ > 320 nm. The probabilities, α<jats:sub>R</jats:sub>, for the initiation of polymerization derived from the rate constants of triplet quenching by the monomers were correlated with the measured rates of polymerization. In accordance with expectation it was found that St and VP did not polymerize and that in the cases of VAc, MMA and AN a significant polymerization takes place (in the absence of sensitizer the rates v were negligibly small). For MMA v is proportional to α<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/tex2gif-stack-1.gif" xlink:title="urn:x-wiley:00033146:media:APMC050570116:tex2gif-stack-1" />.</jats:p>