Efficient Photoinitiators Research Articles

Disubstituted Aminoanthraquinone-Based Multicolor Photoinitiators: Photoinitiation Mechanism and Ability of Cationic Polymerization under Blue, Green, Yellow, and Red LEDs

The investigation and clarification of the photoinitiation mechanism of novel systems are of importance for the design and development of compounds with high photoinitiation efficiency of photopolymerization. Some disubstituted aminoanthraquinone derivatives have been reported to exhibit interesting photochemical/photophysical properties and have the potential to act as high performance multicolor photoinitiators under the irradiation of various wavelengths of visible light from light-emitting diodes (LEDs). Herein, three disubstituted aminoanthraquinone derivatives, i.e., 1-amino-4-hydroxyanthraquinone, 1,4-diaminoanthraquinone, and 1,5-diaminoanthraquinone, with iodonium salt and N-vinylcarbazole as additives, have been investigated. Their photoinitiation mechanism was studied using fluorescence spectroscopy, laser flash photolysis, steady state photolysis, computational quantum chemistry, and electron spin resonance spin trapping techniques. Then, their photoinitiation ability for the cationic photopol...

Tetraacylstannanes as Long‐Wavelength Visible‐Light Photoinitiators with Intriguing Low Toxicity

The first tetraacylstannanes Sn[(CO)R]4 (R=2,4,6‐trimethylphenyl (1 a) and 2,6‐dimethylphenyl (1 b)), a class of highly efficient Sn‐based photoinitiators, were synthesized. The formation of these derivatives was confirmed by NMR spectroscopy, mass spectrometry, and X‐ray crystallography. The UV/Vis absorption spectra of 1 a, b reveal a significant redshift of the longest wavelength absorption compared to the corresponding germanium compounds. In contrast to the known toxicity of organotin derivatives, the AMES test and cytotoxicity studies reveal intriguing low toxicity. The excellent performance of 1 as photoinitiators is demonstrated by photobleaching (UV/Vis) and NMR/CIDNP investigations, as well as photo‐DSC studies.

Bismesitoylphosphinic Acid (BAPO‐OH): A Ligand for Copper Complexes and Four‐Electron Photoreductant for the Preparation of Copper Nanomaterials

AbstractBismesitoylphosphinic acid, (HO)PO(COMes)2 (BAPO‐OH), is an efficient photoinitiator for free‐radical polymerizations of olefins in aqueous phase. Described here are the structures of various copper(II) and copper(I) complexes with BAPO‐OH as the ligand. The complex CuII(BAPO‐O)2(H2O)2 is photoactive, and under irradiation with UV light in aqueous phase, it serves as a source of metallic copper in high purity and yield (>80 %). Simultaneously, the radical polymerization of acrylates can be initiated and allows the preparation of nanoparticle/polymer nanocomposites in which the metallic Cu nanoparticles are protected against oxidation. The determination of the stoichiometry of the photoreductions suggests an almost quantitative conversion from CuII into Cu0 with half an equivalent of BAPO‐OH, which serves as a four‐electron photoreductant.

Bismesitoylphosphinic Acid (BAPO-OH): A Ligand for Copper Complexes and Four-Electron Photoreductant for the Preparation of Copper Nanomaterials.

Bismesitoylphosphinic acid, (HO)PO(COMes)2 (BAPO-OH), is an efficient photoinitiator for free-radical polymerizations of olefins in aqueous phase. Described here are the structures of various copper(II) and copper(I) complexes with BAPO-OH as the ligand. The complex CuII (BAPO-O)2 (H2 O)2 is photoactive, and under irradiation with UV light in aqueous phase, it serves as a source of metallic copper in high purity and yield (>80 %). Simultaneously, the radical polymerization of acrylates can be initiated and allows the preparation of nanoparticle/polymer nanocomposites in which the metallic Cu nanoparticles are protected against oxidation. The determination of the stoichiometry of the photoreductions suggests an almost quantitative conversion from CuII into Cu0 with half an equivalent of BAPO-OH, which serves as a four-electron photoreductant.

Self-photoinitiated oligomers of water-diluted polyurethane acrylate grafted with zinc oxide of low concentrations

In order to eliminate some problems of organic photoinitiators, self-photoinitiated oligomers of water-diluted polyurethane acrylate grafted with 0.1–0.3 wt.% zinc oxide (ZnO) were prepared. ZnO was first facilely treated by vacuum dehydration and sonication, and then reacted into the oligomers by NCO and OH groups. The oligomers were synthesized using toluene diisocyanate, polyether diols, 2, 2-dimethylol propionic acid, hydroxyl propyl acrylate, pentaerythritol triacrylate, ZnO, and triethylamine. The prepared oligomers were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, particle size analyzer, and UV–vis spectroscopy. The kinetics of the UV-curing process was investigated. We observed a maximum kinetic rate constant with ZnO content of 0.2%, and the best film performance with ZnO content around 0.25%. The photoinitiation efficiency of the oligomers was similar to the value of 2-hydroxyl-2-methyl-1-phenyl-1-propanone. In general, the physical properties of the films with physically mixed ZnO were worse than those of the films with chemically grafted ZnO. This investigation demonstrated novel oligomers grafted with a few ZnO can be self-photoinitiated and facilely prepared.

Photopolymerization of hybrid monomers, Part II: Determination of relative quantum efficiency of selected photoinitiators in cationic and free-radical polymerization of hybrid monomers

A method for determination of relative initiation efficiency of free-radical photoinitiators directly in monomers by Fluorescence Probe Technique (FPT) has been expanded into cationic photoinitiators and the use of LEDs instead of monochromatic light sources. The relative initiation efficiency of a series of cationic photoinitiators relative to diphenyliodonium hexafluorophosphate, and a series of free-radical photoinitiators relative to 2,2-dimethoxy-2-phenylacetophenone (Irgacure 651), in cationic and free-radical photopolymerization of 2-(2-vinyloxyethoxy)ethyl acrylate (VEEA) and 3,4-epoxycyclohexylmethyl methacrylate (Cyclomer M100) hybrid monomers has been determined. It was found that the initiation efficiency of cationic photoinitiators does not depend on the type of monomer, while the type of monomer affects initiation efficiency of free-radical photoinitiators.

A highly efficient waterborne photoinitiator for visible-light-induced three-dimensional printing of hydrogels.

A bis(acyl)phosphane oxide (BAPO) photoinitiator was conveniently synthesized in an efficient one-pot process. It shows excellent dispersibility in water, good storage stability, and high photo-reactivity in 3D printing of hydrogels under visible-light irradiation (460 nm).

UV-curable photosensitive silicone resins based on a novel polymerizable photoinitiator and GO-modified TiO2 nanoparticles

Abstract A novel polymerizable benzophenone photoinitiator containing acryloxy (BPA) was synthesized. The photopolymerization of photosensitive methacrylic-silicone resins (MASR) initiated by BPA was studied. Results show that BPA is an efficient photoinitiator, which could generate radicals from the photolysis reaction and be consumed via copolymerizing with MASR. The designed UV-curing silicone resins system initiated by BPA showed a high carbon-carbon double bonds conversion above 80% after 20 s UV radiation. In addition, reduced graphene oxide (rGO)-TiO2 composites were elaborated by hydrothermal reaction. The synergistic effects from graphene and TiO2 further enhanced the carbon-carbon double bonds conversion of MASR to 86% with 15 s UV irradiation, demonstrating that the incorporated rGO-TiO2 significantly improve the formulation UV-curing reactivity. Additionally, UV-cured MASR with rGO-TiO2 showed an excellent thermal stability. This work proposes an efficient strategy to improve the polymerization degree of UV-curable photosensitive silicone resins.

Tetraacylgermanes as highly efficient photoinitiators for visible light cured dimethacrylate resins and dental composites

ABSTRACTTetrabenzoylgermane 1 and various substituted tetrabenzoylgermanes 2–7 were investigated as visible light (VL) photoinitiators (PIs) for dental dimethacrylate resins and dimethacrylate‐based composites. The tetrabenzoylgermanes 1–7 show a very strong VL absorption between 400 and 450 nm. Substituents on the benzoyl chromophore strongly influence their properties such as melting point, solubility, absorption behavior, or PI reactivity. A good photobleaching behavior and a very high reactivity as VL PI was found in photo‐differential scanning calorimeter experiments for selected tetrabenzoylgermanes. Composite pastes containing only ∼0.1 wt % of Ge‐PI exhibited a sufficient photocuring due to the high PI‐reactivity of the tetraacylgermanes. Among the investigated germane PIs, tetrakis(2‐methylbenzoyl)germane 2 shows the best performance as VL PI for restorative composites and enables the composites to be photocured using an LED with an emission maximum of 500 nm. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46115.

Difluoroboranyl derivatives as efficient panchromatic photoinitiators in radical polymerization reactions

Photoinitiating systems based on BF2 derivatives and tetramethylammonium phenyltriethylborate salt were tested in photopolymerization reactions through the photo-DSC method. The good rates of TMPTA polymerization and final monomer conversion were obtained for tested system. The effect of the type of heterocycle on their properties was revealed. The excited state processes, investigated by nanosecond flash photolysis, lie on a fast excited state photoinitiated cleavage leading to reactive species. A triplet state is observed for investigated derivatives.

Hyperbranched poly(ether amine) (hPEA) as novel backbone for amphiphilic one-component type-II polymeric photoinitiators

To make photoinitiators (PI) to be polymeric and water-soluble is an effective approach to develop the high efficient photoinitiator systems with low-migration, low-toxic and environment-friend. We developed a series of novel amphiphilic hyperbranched polymeric photoinitiators (hPEA-TXs, and hPEA-BPs) by introducing thioxanthone (TX) or benzophenone (BP) moieties into the periphery of the hyperbranched poly(ether amine) (hPEA) comprised of the hydrophilic poly(ethylene oxide) (PEO) short chain and coinitiator amine moieties in the backbone. Compared with their water-soluble low-molecular weight analogues, the resulting hyperbranched polymeric photoinitiators hPEA101-TX, hPEA211-TX, hPEA101-BP and hPEA211-BP could be dissolved very well not only in many organic systems including acrylate monomers, but also in water with high solubility of 10wt%. The photopolymerization kinetics of water-soluble monomer acrylamide (AM) and three hydrophobic multifunctional acrylate monomers initiated by these hyperbranched photoinitiators were investigated in detail by photo-differential scanning calorimetric (photo-DSC). Both hPEA-TXs and hPEA-BPs can initiate photopolymerization of AM as efficiently as their low-molecular weight analogues MGA-TX and MGA-BP, respectively. The final double bond conversion (DBC) of oil-soluble monomer hexanediol diacrylate (HDDA) photoinitiated by these hyperbranched photoinitiators can reach as high as 99%. Especially for photopolymerization of multifunctional monomers initiated by these hyperbranched polymeric photoinitiators, the final DBC of trimethylolpropane triacrylate (TMPTA) and pentaerythritol tetraacrylate (PETTA) can reach 80% and 60%, respectively, which is much higher than that of low-molecular weight photoinitiators.

Theoretical study on photochemistry of Irgacure 907

Abstract Irgacure 907 (2-Methyl-4′-(methylthio)-2-morpholinopropiophenone) is a highly efficient photoinitiator which undergoes standard Norrish Type I photocleavage. It is widely used to initiate the photopolymerization of chemically unsaturated prepolymers. In this work, the photocleavage reaction mechanisms, as well as excited state properties and the underlying relaxation mechanisms upon photoexcitation of Irgacure 907, are studied using DFT calculations. To investigate the mechanisms, the excited singlet and triplet states have considered in detail. Our calculations indicate that the radical formation for Irgacure 907 originates from the triplet states, which is typical Type-I photoinitiators. Upon irradiation, it will undergo a α-cleavage process to form two radical species. In line with the Jablonski-Type diagram, the ground state of Irgacure 907 excites to a higher state, which is characterized by ππ* singlet state (S 2 ), followed by an internal conversion (IC) to the first excited state (S 1 ). The subsequent intersystem crossing (ISC) can occur between S 1 and triplet state that has nπ* character. As expected, after excitation, the photoinitiator undergoes rapid intersystem crossing (ISC) which is an important step in the photochemical process.

Spectroscopic Studies of the Interactions between a Cationic Cyanine Dye and a Synthetic Phyllosilicate: From Photophysics to Hybrid Materials.

The interaction of the cationic organic dye Astrazon orange R (AO-R) with the synthetic phyllosilicate Laponite leads to very interesting hybrid materials. Indeed, the Laponite nanoparticles modify the photophysical properties of AO-R, inducing a stabilization of its excited emissive state by preventing ultrafast isomerization. The long-lived emissive clay-dye hybrid complex can be used to develop efficient photoinitiating systems, leading to organic-inorganic hybrid crosslinked polymer materials.

New near UV photoinitiators containing benzophenone part for photoinitiating polymerization of methyl methacrylate

Abstract In this study, a variety of new trans -diphenylethylene derivatives containing phenylketone segment was synthesized, which were used as hydrogen abstracting type photoinitiators to compose two-component photoinitiating systems for free radical photopolymerization of methyl methacrylate under near UV light irradiation. The corresponding photosensitizers free of phenylketone group were synthesized to compose three-component photoinitiating systems. The large molar extinction coefficients of the target molecules in near UV light region (350–400 nm) were observed. Near UV photoinitiating polymerization kinetics of methyl methacrylate by the target molecules was studied by photo-differential scanning calorimetry. The results suggested that the two-component photoinitiating systems produced more efficient photoinitiating polymerization of methyl methacrylate than the three-component ones. The photoinitiating mechanism of the studied photoinitiators was studied by the electron spin resonance as well as the cyclic voltammograms. The thermal stabilities of the studied photoinitators were further evaluated.

Wavelength-Dependent Photochemistry of Oxime Ester Photoinitiators

The design of efficient radical photoinitiating systems requires a systematic and detailed evaluation of their photochemical characteristics. Correlating absorbance and the corresponding electronic transitions of a photoinitiator is critical for understanding its photoinduced reaction pathways. In the current contribution, we provide an in-depth investigation into the photochemistry and photophysics of two oxime ester derivatives (O-benzoyl-α-oxooxime, OXE01, and O-acetyloxime, OXE02), known for their excellent performance in pigmented formulations. In particular, we shed light on their wavelength-dependent photopolymerization properties. We utilized a combination of UV–vis spectroscopy, density functional theory (DFT) calculations, photochemically induced dynamic nuclear polarization spectroscopy (photo-CIDNP), and pulsed-laser polymerization with a wavelength-tunable laser with subsequent size exclusion chromatography coupled to high-resolution electrospray ionization mass spectrometry (PLP-SEC-ESI-MS) ...

Tetraacylgermanes: Highly Efficient Photoinitiators for Visible‐Light‐Induced Free‐Radical Polymerization

In this contribution a convenient synthetic method to obtain tetraacylgermanes Ge[C(O)R]4 (R=mesityl (1 a), phenyl (1 b)), a previously unknown class of highly efficient Ge-based photoinitiators, is described. Tetraacylgermanes are easily accessible via a one-pot synthetic protocol in >85 % yield, as confirmed by NMR spectroscopy, mass spectrometry, and X-ray crystallography. The efficiency of 1 a,b as photoinitiators is demonstrated in photobleaching (UV/Vis), time-resolved EPR (CIDEP), and NMR/CIDNP investigations as well as by photo-DSC studies. Remarkably, the tetraacylgermanes exceed the performance of currently known long-wavelength visible-light photoinitiators for free-radical polymerization.

Efficient unimolecular photoinitiators for simultaneous hybrid thiol–yne–epoxy photopolymerization under visible LED light irradiation

Several unimolecular photoinitiators, which generate free radicals and super bases in one step under visible LED light irradiation, can efficiently induce simultaneous hybrid thiol–yne–epoxy photopolymerization.

Estimating the photodissociation quantum yield from PLP-SEC peak heights

A fast method for the reliable estimation of the photodissociation quantum yield Φdiss is presented. Pulsed laser polymerization (PLP) experiments are performed at various pulse energies (1.5–6 mJ) and regression analysis is performed to the ratio of the peak heights identified in the size exclusion chromatography (SEC) trace. The high accuracy of the method is demonstrated for PLP initiated by 2,2-dimethoxy-2-phenylacetophenone (DMPA), considering in silico generated data including large theoretical errors (up to 20%). The method has also been successfully applied to experimental data of DMPA based isothermal PLP of n-butyl acrylate at 306 K, with an estimated Φdiss of 0.42 ± 0.04. In the long term, the method will facilitate the evaluation of current and the design of new highly efficient photoinitiators.

Conjugated dyes carrying N, N-dialkylamino and ketone groups: One-component visible light Norrish type II photoinitiators

This work presents new conjugated dyes carrying N, N-dialkylamino and ketone groups for using as one-component Norrish type II visible light photoinitiators. The novel dyes without ketone group were also synthesized to compose two-component visible light photoinitiators for comparisons. The target dyes show the remarkable absorption in visible light region. Photo-differential scanning calorimetry was employed to study visible light photoinitiating polymerization kinetics of methyl methacrylate by new one-component photoinitiators and two-component photoinitiators respectively. The results suggest that the one-component photoinitiators showed much more efficient photoinitiating polymerization of methyl methacrylate than the two-component photoinitiating systems under visible light irradiation. The molecular weight of visible light photopolymer produced by the new photoinitiators was determined. The visible light photoinitiating mechanism of the one-component photoinitiators was studied by absorption and emission spectra, electron spin resonance spectra and cyclic voltammograms analysis.

Isomerization controlled photopolymerization: effect of dye photophysics on photoinitiation efficiency.

The efficiency of free radical polymerization by photoinitiating systems based on two Astrazon orange cyanine dyes was shown to be directly related to the isomerization process of the dye in the excited states. The impact of resin viscosity on photopolymerization reactions was measured and related to the overall radical quantum yields. The quantum yields were calculated according to the photocyclic behaviour of the initiating systems based on the Astrazon orange dyes. These dyes are characterized by a viscosity dependent photophysics, which leads to an isomerization-diffusion-controlled photopolymerization. Besides this demonstration, Astrazon orange dyes appeared to be very good candidates for free radical photopolymerization in the visible, presenting high absorption coefficient, low cost and good sensitivity.