Thioxanthone–anthracene‐9‐carboxylic acid as radical photoinitiator in the presence of atmospheric air

Abstract

Thioxanthone–anthracene‐9‐carboxylic acid (TX‐ANCA) namely 14‐oxo‐14H‐naphthol [2,3‐b]thioxanten‐12‐carboxylic acid, is synthesized and characterized as part of our continuing interest for syntheses of polyaromatic initiators. Photoinitiator, TX‐ANCA have good absorption properties in the UV and visible region of the electromagnetic spectrum (ɛ370: 9080 M−1cm−1, ɛ430: 6151 M−1 cm−1). The fluorescence quantum yield is calculated as 0.1 which is slightly higher than of the parent thioxanthone compound (φf: 0.07). The phosphorescence lifetime is found to be 39 ms. The possible initiating mechanism of TX‐ANCA is based on photoexcitation of TX‐ANCA and quenching of triplet excited states of TX‐ANCA by molecular oxygen generates singlet oxygen. Singlet oxygen reacts with the anthracene moiety of TX‐ANCA possibly forms an endoperoxide. The endoperoxides undergoes photochemical or thermal decomposition to form radicals which are able to initiate free radical polymerization. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1878–1883

1-(2-Naphthyl)-2-(1-pyrrolidinyl)ethanone as a Photoinitiator for Methyl Methacrylate Polymerization

“…Selection of a photoinitiator with high initiation efficiency and fast bleaching under UV light is very important. Rapid photolysis of MPY is advantageous for decreasing the residual photoinitiator content and increasing cure speed [27]. The exposure of solution to the UV light generated by a spot-light curing system at intervals of 10 sec.…”

Synthesis and characterization of multiarm (Benzoin‐PS)m‐polyDVB star polymer as a polymeric photoinitiator for polymerization of acrylates and methacrylates

“…A photoinitiator (PI) is a compound that absorbs ultraviolet (UV) or visible light and is added to a formulation containing oligomers, monomers, and/or additives to convert light energy into chemical energy in the form of initiating species such as free radicals or cations. Classification of photoinitiators can be as Type I and Type II and One‐component Type II 1–20 …”

“…For Type II PIs, two main reaction pathways can be mentioned, hydrogen abstraction by the excited initiator or light‐induced electron transfer followed by fragmentation 1,2,14–19 . One component Type II photoinitiators offer a great opportunity because of their structural advantages, which are light‐absorbing and proton‐donating groups in one structure there are several examples that is, Thioxanthone and benzophenone derivatives 1–9 …”

“…Classification of photoinitiators can be as Type I and Type II and One-component Type II. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Type I photoinitiators proceed through the scission process in α-position of the carbonyl group at the triplet state and generate initiating radicals. Produced benzoyl radicals are reactive species towards vinylic and acrylic monomers.…”

Thioxanthone Derivatives as a New Class of Organic Photocatalysts for Photopolymerisation Processes and the 3D Printing of Photocurable Resins under Visible Light

“…Therefore, for example, 2-methylol-thioxanthone [31] and thioxanthone based 9-[2-(methyl-phenyl-amino)-acetyl]-thia-naphthacene-12-one [32] were used as photoinitiators in combination with N-methyldiethanolamine (MDEA) for the free radical polymerisation of methyl methacrylate (MMA) in the presence of air. Derivatives of thioxanthone were also subjected to various condensation reactions to obtain conjugated systems, for example thioxanthone-anthracene compounds were applied to initiate the polymerisation of methyl methacrylate [33][34][35]. Heterocyclic extended thioxanthones-thioxanthone linked with benzothiophene, dibenzothiophene or benzotriazole moiety-were also studied as photoinitiators for the polymerisation of methyl methacrylate in the presence of amine [36,37].…”