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

Abstract

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

Electron Spin Resonance Spin Trapping Technique: Application to the Cleavage Process of Photoinitiators

“…For short‐lived radicals hardly accessible by CW‐ESR or TR‐ESR, this ESR‐ST technique is highly valuable since the persistent adducts are easily observed. Despite a widespread use in life sciences,9 very few studies using only phenyl N ‐ tert ‐butyl nitrone (PBN) as a spin trap (ST) have been devoted to PIs (examples concern 2,2′‐dimethoxyphenyl acetophenone, 2‐hydroxymethyl‐1‐phenylpropan‐1‐one, and benzoin ether derivatives) 11–13. In these previous works, the benzoyl radical was mainly observed.…”

A Highly Efficient Polymerizable Photoinitiator Comprising Benzophenone, Thio Moieties, and N‐Arylmaleimide

“…[17][18][19][20] Compared with MMTBP, MTPBP can initiate the polymerization of HDDA more efficiently, and the maximal polymerization rate of the former is almost 1.5 times as high as that of the later. This result may be attributed to the bis-substituted maleimides in MMTBP with respect to the mono-substituted MTPBP.…”

“…In order to further improve the photoefficiency, a thio group was also introduced into the chemically bonded photoinitiators, [9,10] because the photolysis reaction of the CÀS bond can afford active species. [17][18][19][20] A typical case is 4-[(4-maleimido)thiophenyl]benzophenone (MTPBP). Photopolymerization studies of three representative monomers with different functionality, i.e., a monofunctional monomer methyl methacrylate, a difunctional monomer 1,6-hexanediol diacrylate (HDDA), and a trifunctional monomer trimethy-A novel, highly efficient, polymerizable, thio-containing photoinitiator, 4-maleimido-4'-thiophenylbenzophenone (MTBP), was synthesized by directly introducing maleimide to benzophenone moieties.…”

Chemically Induced Dynamic Nuclear Polarization during the Thermolysis of Alkoxyamines: A New Approach to Detect the Occurrence of H-Transfer Reactions

“…The intensity of polarization is determined by CIDNP enhancement factor, nuclear relaxation time and decay rate constant. The expected time of CIDNP maximum obtained from expressions (13)(14)(15)) is equal to:…”

“…CIDNP is widely applied for the determination of the multiplicity of intermediate RPs and their precursor excited molecules, identification of radical intermediates, determination of signs of hyperfine interaction (HFI) constants, study of reversible electron transfer reactions, etc. [11][12][13][14]. Previously, Chemically Induced Dynamic Electron Polarization (CIDEP) [15,16] and CIDNP and its modification (CIDNP with fast switching of magnetic field) have been used in NMP research to measure the rate constants of coupling between acrylate-type radicals and the persistent nitroxide [17,18].…”