Photochemistry and photocuring properties of thiol-substituted α-aminoalkylphenone as radical photoinitiator

Thiol‐substituted α‐aminoalkylphenone was newly developed as a radical photoinitiator. Introduction of the thiol group drastically improved photosensitivity in an alkaline developable resist formulation composed of a prepolymer and a multifunctional acrylate monomer. The improvement in the photocuri...

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Bibliographic Details
Published in:Journal of polymer science. Part B, Polymer physics Polymer physics, 2005-07, Vol.43 (13), p.1684-1695
Main Authors: Kura, Hisatoshi, Oka, Hidetaka, Ohwa, Masaki, Matsumura, Tadayoshi, Kimura, Akira, Iwasaki, Yohei, Ohno, Teruhisa, Matsumura, Michio, Murai, Hisao
Format: Article
Language:English
Subjects:
Applied sciences
chain transfer
ESR
Exact sciences and technology
initiators
photopolymerization
Physicochemistry of polymers
Polymerization
Polymers and radiations
sensitization
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Summary:Thiol‐substituted α‐aminoalkylphenone was newly developed as a radical photoinitiator. Introduction of the thiol group drastically improved photosensitivity in an alkaline developable resist formulation composed of a prepolymer and a multifunctional acrylate monomer. The improvement in the photocuring speed was explained by a mechanism based on chain transfer reaction of the thiol group. Time‐resolved electron spin resonance (ESR) spectroscopy indicated that the thiol group attached to the chromophore does not influence the photochemical process to generate primary radicals. The photoinitiation of α‐aminoalkylphenone can be spectrally sensitized by 2,4‐diethylthioxanthone (DETX). However, thiol‐substituted α‐aminoalkylphenone showed smaller spectral sensitization than the corresponding compound without a thiol group. Time resolved laser flash photolysis indicated that the rate constant of the quenching of the triplet state of DETX by thiol‐substituted α‐aminoalkylphenone is twice as large as that by the corresponding one without a thiol group. This suggests that, besides energy transfer from DETX in the excited triplet state to the α‐aminoalkylphenone, the thiol group quenches the excited triplet state of DETX via charge transfer and/or hydrogen transfer, as supported by the ESR analysis using a spin trapping technique, and lowers the efficiency of the spectral sensitization effect. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1684–1695, 2005
ISSN:0887-6266
1099-0488
DOI:10.1002/polb.20458