Oscillations of the lophyl radical concentration during the photo-decomposition of o-Cl-hexaarylbisimidazole

Schrödner, M.; Schache, Hannes; Lindauer, Heike; Schrödner, Roland; Konkin, A. A.

doi:10.1016/j.jphotochem.2012.02.013

Cited by 1 publication

(1 citation statement)

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“…This can occur through a radical triplet-pair. [19][20][21][22][23][24][25] Furthermore, the efficient initiation of initiator systems containing HABI derivatives directed the use of such materials in holographic applications based on photopolymers. [26][27][28] Thus, hexaarylbisimidazoles have been widely applied in photoinitiating systems in radical polymerization, in which they either function as a radical initiator in combination with a H-donating compound [1][2][3]29 or in combination with a sensitizer, which donates an electron from its excited state to L-L resulting in formation of the lophyl radical (L • ), lophin (L-H) and the oxidized form of the sensitizer.…”

Section: Introductionmentioning

confidence: 99%

Extended mechanistic aspects on photoinitiated polymerization of 1,6-hexanediol diacrylate by hexaarylbisimidazoles and heterocyclic mercapto compounds

Berdzinski

Strehmel

Lindauer

et al. 2014

Photochem Photobiol Sci

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Chlorine substituted hexaarylbisimidazole (o-Cl-HABI) efficiently initiates radical polymerization of multifunctional acrylic esters in the presence of a heterocyclic mercapto compound if the latter can form its tautomeric thione. Exposure of o-Cl-HABI results in lophyl radicals, which efficiently add to the thione in the first step while the second step releases a highly reactive thiyl radical from this intermediate. LC-MS and CID-MS measurements support this reaction scheme. Furthermore, photo-DSC experiments applying UV light between 320 and 380 nm showed that mercaptotriazole and phenylmercaptotriazole exhibited the best reactivity in the monomer 1,6-hexanediol diacrylate (HDDA) while alkyl substituted mercaptotriazoles showed less reactivity. Change of the triazole heterocycle by mercaptoimidazole resulted in a significant decrease of photoinitiation efficiency. This heterocycle does not form the corresponding thione in HDDA as shown by NMR measurements. Replacement of mercaptotriazole by an alkylthiol leads to a system showing the lowest photoinitiation efficiency in this series. Formation of thione structure in the case of heterocyclic mercapto compounds may cause higher reactivity of the heterocyclic mercapto compounds with the lophyl radical in the monomer chosen.

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