Photoinitiators For Photopolymerization Research Articles

High Photoinitiating Efficiency of Benzothioxanthene-Based Oxime Esters in Photopolymerization via Photocleavage and/or Single Electron Transfer under Visible Light and Sunlight.

In this work, six benzothioxanthene-based oxime esters were employed as photoinitiators for photopolymerization under visible light (LED) and sunlight. Their abilities to behave as Type I photoinitiators by mean of a photocleavage mechanism of oxime esters but also in multicomponent photoinitiating systems with an iodonium salt (through an electron transfer mechanism) were both explored with the different structures. Due to their broad absorption spectra tailing up 600 nm, photoinitiating properties of the benzothioxanthene-based oxime esters were systematically tested under excitation with low-intensity LED light at wavelengths of 405 nm and 450 nm. Additionally, parallel to the polymerization tests done under artificial light, the different benzothioxanthene-based oxime esters were also investigated as solar photoinitiators and displayed a high reactivity in France (Western Europe) even in winter conditions. For the best candidates i.e. the most reactive structures, direct laser write experiments were carried out, evidencing the interest of these structures.

High Photoinitiating Efficiency of Benzothioxanthene‐Based Oxime Esters in Photopolymerization via Photocleavage and/or Single Electron Transfer under Visible Light and Sunlight

AbstractIn this work, six benzothioxanthene‐based oxime esters were employed as photoinitiators for photopolymerization under visible light (LED) and sunlight. Their abilities to behave as Type I photoinitiators by mean of a photocleavage mechanism of oxime esters but also in multicomponent photoinitiating systems with an iodonium salt (through an electron transfer mechanism) were both explored with the different structures. Due to their broad absorption spectra tailing up 600 nm, photoinitiating properties of the benzothioxanthene‐based oxime esters were systematically tested under excitation with low‐intensity LED light at wavelengths of 405 nm and 450 nm. Additionally, parallel to the polymerization tests done under artificial light, the different benzothioxanthene‐based oxime esters were also investigated as solar photoinitiators and displayed a high reactivity in France (Western Europe) even in winter conditions. For the best candidates i.e. the most reactive structures, direct laser write experiments were carried out, evidencing the interest of these structures.

Exploring the triplet state properties of thio-benzothioxanthene imides with applications in TTA-upconversion and photopolymerization.

Thio-benzothioxanthene imide (BTXI) exhibits long excited state lifetime (τT = 17.7 μs) and high ISC efficiency (ΦΔ = 97%). For the first time, BTXI derivatives were used as photosensitizers for triplet-triplet annihilation upconversion, achieving the highest efficiency of 13.8%. In addition, thio-BTXI derivatives were used as photoinitiators for photopolymerization, resulting in a series of green light-activated radical polymerization systems.

Direct and chlorine-free synthesis of phosphafluorenes or their oxides from white phosphorus

The known methods for the preparation of acylphosphine oxides and polyfluorobenzene-substituted triarylphosphines need to utilize PCl3, while the chlorine-free methods are not reported. In this work, we report a chlorine-free method by one-pot three-component reaction of white phosphorus (P4), dilithio reagents, and acyl chlorines or polyfluorobenzenes for the synthesis of biphenyl-based acylphosphine oxides and phosphines. This reaction is green and environmentally friendly compared with the traditional method, because it avoids the use of Cl2 and the discharge of a large amount of waste gas and waste acid. These two products have potential applications as photoinitiators in photopolymerization or as organophosphorus ligands in catalytic reactions.

Organic dye‐based photoinitiating systems for visible‐light‐induced photopolymerization

AbstractEven though many organic dyes have been reported as photoinitiators/photosensitizers for free radical polymerization in the literature, the design and development of novel photoinitiating systems based on organic dyes adaptable for visible light irradiation, for example, 405 nm LED and sunlight still remains challenging. Recently, major achievements in the development of high‐performance photoinitiating systems based on organic dyes as light‐harvesting compounds and their uses as photoinitiators for photopolymerization under visible‐light irradiation have clearly emerged, giving rise to abundant literature. In this review, an overview of the recently synthesized chromophores belonging to various families of organic dyes and used as photoinitiators of polymerization during the 2018–2021 period are presented and classified. Recent works have resulted in the development of new chromophores exhibiting remarkable visible light absorption properties and excellent photoinitiation abilities upon irradiation with LEDs and/or sunlight in free radical photopolymerization processes. These developments notably indicate that sunlight has the advantages of being a cheap, unlimited, broad emission spectrum, and energy‐saving light source capable to be an efficient substitute to artificial light sources. The newly developed dye‐based photoinitiating systems designed to initiate visible‐light‐induced photopolymerization processes are likely to expand the scope of application of photopolymerization in modern sciences and technologies.

Carbazolyl α-diketones as novel photoinitiators in photopolymerization under LEDs

Novel photoinitiators (α-DKs) bearing α-dicarbonyl groups as initiating group and aromatic groups as chromophore group were synthesized and developed as visible light type I photoinitiators with high performance for radical photopolymerization of acrylate. α-DKs exhibit good absorption at 405 nm and higher initiation efficiency compared with commercial initiator camphorquinone (CQ) under LED sources. Meanwhile, α-DKs were found to efficiently photosensitize bis (4-methylphenyl) hexafluorophosphate (ION) and initiate both free radical polymerization and cationic polymerization.

Photo-curing kinetics of hydroxyethyl acrylate (HEA): synergetic effect of dye/amine photoinitiator systems

The aim of this study is to examine and evaluate several dye/amine systems as photoinitiators for photopolymerization of 2-hydroxyethyl acrylate (HEA) monomer under visible light conditions. For this purpose, a series of dye/amine photoinitiators were formed using methylene blue (MB) or acridine orange (AO) as photosensitizers, and triethanolamine (TEOA), ethyl 4-(dimethylamino) benzoate (EDMAB), trioctylamine (TOA), and N,N-diméthylallylamine (DMAA) as co-initiators. The photopolymerization kinetic of the HEA monomer in the presence of proposed dye/amine systems was performed using Fourier-transform infrared spectroscopy (FTIR) analysis and the synergetic effect of the dye/amine photoinitiators systems on the photopolymerization efficiency was examined. Interestingly, (MB/EDMAB) system shows the better reactivity with a total conversion of HEA monomer.

Efficient visible photoinitiator containing linked dye-coinitiator and iodonium salt for free radical polymerization

Abstract Dye-linked initiators consisting of erythrosine B as a chromophore and ethyl 4-dimethylaminobenzoate as an electron donor linked by a different number of methylene units were prepared to achieve efficient photoinitiators of free radical polymerization in a visible-light region. The relative photoinitiating efficiencies of novel photoinitiators in photopolymerization of acrylates were evaluated. The results showed that the photoinitiating system composed of the dye-linked dyad with short methylene unit chain and diphenyliodonium salt exhibited a remarkable increase in the photoinitiation ability compared to unlinked three-component system. The enhancement mechanism aroused by the onium salt was investigated. These results showed that the excellent initiating efficiency of this system could be attributed to the favorable intramolecular photoinduced electron transfer and the close distance between reaction components caused by electrostatic interactions. This result demonstrated the importance and potential of the linked photoinitiator in the design of new efficient photoinitiators.

Novel Polymerizable Sulfur‐Containing Benzophenones as Free‐Radical Photoinitiators for Photopolymerization

AbstractSummary: Three novel polymerizable sulfur‐containing benzophenone photoinitiators, MAATPBP, CMAATPBP and BMAATPBP, were synthesized. These novel photoinitiators possess strongly red‐shifted maximum UV absorption and very weak fluorescence emission. The photopolymerization of two monomers with different functionality, bifunctional HDDA and trifunctional TMPTA, initiated by these three polymerizable photoinitiators, was studied by photo‐DSC using the unsaturated tertiary amine DMAEMA as the coinitiator. The results show that all the polymerizable photoinitiators were highly efficient and different photoinitiators exhibited different behaviors towards different monomers: BMAATPBP was the most efficient for HDDA; MAATPBP was the most efficient for TMPTA. They could also efficiently initiate the photopolymerization without the coinitiator because of photolysis at the CS bond.Structures of the polymerizable sulfur‐containing photoinitiators synthesized.magnified imageStructures of the polymerizable sulfur‐containing photoinitiators synthesized.

Polymeric amine bearing side-chain thioxanthone as a novel photoinitiator for photopolymerization

Novel polymeric photoinitator (PTX) was synthesized by introducing thioxanthone (TX) moieties to polymeric amine side-chain. Compared with low-mulecular weight model compound, PTX has similar UV–vis absorption and weaker fluorescence emission, and some radicals are trapped in the macromolecular coil cage. The kinetics for polymerization of trimethylolpropane triacrylate using PTX as photoinitiator was studied by photo-DSC. It shows that PTX is an efficient photoinitiator, and that PTX concentration and light intensity have similar effect on photopolymerization. The increase in PTX concentration and light intensity leads to the increase in the polymerization rate and the final conversion. The increase in temperature also results in the increase in the polymerization rate and final conversion, due to the enhanced molecular mobility and delay in vitrification at high temperature. At the late stage of polymerization, the reaction becomes more diffusion-controlled than that at early stage of polymerization.