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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. [ABSTRACT FROM AUTHOR]

With the rapid development of new irradiation setups as well as the ongoing interest in 3D printing, photopolymerization is extensively studied during the last decades. In photopolymerization, a photoinitiator and/or photosensitizer play(s) a crucial role in the photoinitiation step as this component absorbs light, thus creating the initiating species. In this study, a series of 17 chalcone‐based oxime esters (OXEs) featuring the pyrene chromophore are designed, synthesized, and studied for their photoinitiation properties upon irradiation with visible light. Precisely, their photoinitiation abilities are examined during the free radical photopolymerization of acrylates under the irradiation of light‐emitting diode (LED) at 405 nm. In the series of oxime esters, five of them demonstrate excellent photoinitiation abilities. Their thermal initiation abilities are also examined. To improve their photoinitiation abilities, these type I photoinitiators are also tested as type II photoinitiators in two‐component photoinitiating systems using bis‐(4‐tert‐butylphenyl)iodonium or ethyl 4‐(dimethylamino)benzoate as additives. In this process, the OXE‐B/iodonium system shows the best photopolymerization. To develop the use of these chalcone‐based oxime esters, the best OXE is used as a monocomponent photoinitiating system in 2D laser writing at 405 nm. The design of composites using glass fibers or carbon fiber as fillers is also examined. [ABSTRACT FROM AUTHOR]

In this work, three new photoinitiators, based on the phenothiazine scaffold as a chromophore and potentially bearing the oxime ester functionality as an initiating group are designed and synthesized for the free radical polymerization of acrylates, the cationic polymerization of epoxides, and the formation of interpenetrated polymer networks upon irradiation with a light emitting diode emitting at 405 nm. These phenothiazine‐based oxime and oxime esters revealed impressive photoinitiation ability manifested by excellent polymerization rates and high final reactive function conversions. Significantly, they can be used as both; one‐component (Type I) and two‐component photoinitiating systems. Photoinitiation mechanisms through which reactive species are produced are investigated by means of different complementary techniques including real‐time Fourier transform infrared spectroscopy, UV–visible absorption spectroscopy, electron spin resonance spectroscopy, fluorescence (steady state and time resolved), cyclic voltammetry, and molecular modeling calculations. Thermal initiation behavior of the different oxime esters is also studied by using differential scanning calorimetry, highlighting their dual thermal/photochemical initiation ability. Finally, 3D printed objects are successfully fabricated by conducting both direct laser writing and 3D printing experiments. [ABSTRACT FROM AUTHOR]

In order to expand the application of oxime‐esters (OXEs) and to introduce a one‐component photoinitiating system of high performance in visible light photopolymerization, a series of 5,12‐dialkyl‐5,12‐dihydroindolo[3,2‐a]carbazole‐based oxime‐esters with visible light absorption abilities is designed and synthesized. Notably, when irradiated with light‐emitting diodes at 405 nm, the proposed structures can undergo a direct cleavage of the NO bond followed by decarboxylation, generating free radicals capable to efficiently initiate free radical photopolymerizations (FRP). Furthermore, the new OXEs showed good thermal initiation abilities and can be used as dual photo and thermal initiators. An interesting structure/reactivity/efficiency relationship can be obtained by comparing the reactivity of the different radicals generated upon photoexcitation at identical chromophore but also by comparing the photoinitiating ability of the hexyl derivatives (1)–(10) with that of methyl derivatives (1′)–(10′) characterized by a lower solubility than the previous series in resins. Chemical mechanisms are studied through different techniques including real‐time Fourier transform infrared spectroscopy, UVvisible absorption spectroscopy, fluorescence (time‐resolved or steady‐state) as well as molecular modeling calculations. To finish, OXEs are incorporated in new photosensitive 3D printing resins, furnishing 3D objects with a remarkable spatial resolution. [ABSTRACT FROM AUTHOR]

A novel photoinitiator (PI) is described here for low ecological impact, p(PEGDA575‐TX): It is water soluble, polymerizable, thioxanthone (TX) functional, and is a one‐component poly(ethylene glycol)‐based poly(β‐amino ester). The PI is synthesized in one step via classical aza‐Michael addition reaction between poly(ethylene glycol) diacrylate (Mn = 575 D) and amine functionalized TX (2‐(2‐aminoethoxy)‐9H‐thioxanthen‐9‐one). It absorbs at ≈ 404 nm (ε = 14 000–44 309) in water and can photodecompose with or without additives such as ethyl 4‐(dimethylamino)benzoate (EDB) and bis‐(4‐tert‐butylphenyl)‐iodonium hexafluorophosphate (Iod). Although it is an effective one‐component visible light PI for free radical polymerization of di‐ and tri(meth)acrylates, EDB or Iod will be favorable for synergistic effect. p(PEGDA575‐TX) has higher initiating reactivity, reducing ability of oxygen inhibition and migration stability compared to TX, which make it environmental friendly. [ABSTRACT FROM AUTHOR]

This work is devoted to the study of two copper complexes (Cu) bearing pyridine ligands, which were synthesized, evaluated and tested as new visible light photoinitiators for the free radical photopolymerization (FRP) of acrylates functional groups in thick and thin samples upon light-emitting diodes (LED) at 405 and 455 nm irradiation. These latter wavelengths are considered to be safe to produce polymer materials. The photoinitiation abilities of these organometallic compounds were evaluated in combination with an iodonium (Iod) salt and/or amine (e.g., N-phenylglycine—NPG). Interestingly, high final conversions and high polymerization rates were obtained for both compounds using two and three-component photoinitiating systems (Cu1 (or Cu2)/Iodonium salt (Iod) (0.1%/1% w/w) and Cu1 (or Cu2)/Iod/amine (0.1%/1%/1% w/w/w)). The new proposed copper complexes were also used for direct laser write experiments involving a laser diode at 405 nm, and for the photocomposite synthesis with glass fibers using a UV-conveyor at 395 nm. To explain the obtained polymerization results, different methods and characterization techniques were used: steady-state photolysis, real-time Fourier transform infrared spectroscopy (RT-FTIR), emission spectroscopy and cyclic voltammetry. [ABSTRACT FROM AUTHOR]

Many academic and industrial works are carried out for the search of new classes of visible light photoinitiators. In the last decade, new Type I photoinitiator generating silyl, germyl, or stannyl radicals is elegantly reported; the chemical mechanisms being often associated with the cleavage of the C(═O)Si, C(═O)Ge, or C(═O)Sn bonds. In this context, silyl glyoxylates are also reported as dual Type I and Type II photoinitiators. Silyl glyoximides are proposed here as new near‐UV and blue light sensitive photoinitiators. The synthesis of such compounds as well as their light absorption properties is discussed. Their photochemical properties are studied through steady state photolysis experiments and molecular modeling data (i.e., through the calculations of the frontier orbitals, CC bond dissociation energies and triplet state energy levels). To finish, their photoinitiating ability upon near‐UV or blue light emitting diode light is examined in a benchmark methacrylate monomer blend (BisGMA/TEGDMA). Markedly, a Type I photoinitiator behavior is highlighted but better initiating properties are found in multicomponent systems in combination with iodonium salt and amine. [ABSTRACT FROM AUTHOR]

In recent years, hydrogels have been widely applied in daily life and industry. More and more fillers have been combined with hydrogel to broaden their fields of application and improve their mechanical properties. However, there are few works about zeolite‐based hydrogel composites via photopolymerization. Hence, in this work, it is reported that the fabrication of hydrogel composites containing zeolite (FAU‐13X ≈ 40 wt%) under mild photopolymerization conditions (visible LED light irradiation, at room temperature, under air, and without any monomer purification). Markedly, compared to pure hydrogel, the elastic modulus (G′) of hydrogel composite contains 10% FAU‐13X increased by more than 100%. When the zeolite content reached 40%, the water swelling ratio in mass reached 120%, and that in volume remained at 150%. In addition, 3D patterns with flat surface are obtained through direct laser write as a lithography technique. This means these hydrogel composites can be applied in the field of water absorption materials and 3D printing. [ABSTRACT FROM AUTHOR]

Two water soluble oligomeric photoinitiators (OAA‐B and OAA‐BP) were synthesized by first preparing an oligo(amido amine) (OAA) via aza‐Michael addition reaction of N,N'‐methylene bisacrylamide and 1,4‐diaminobutane, then carrying out another aza‐Michael addition reaction between OAA and 4‐benzoylphenyl acrylate for OAA‐B and also diethyl vinylphosphonate for OAA‐BP. Photopolymerization kinetics of 2‐hydroxyethyl methacrylate (HEMA) and HEMA: poly(ethylene glycol) diacrylate (PEGDA, Mn = 575) mixture initiated by these photoinitiators were monitored by real‐time FTIR spectrophotometer and photo‐DSC. These photoinitiators together with bis‐(4‐tert‐butylphenyl)‐iodonium hexafluorophosphate (Iod) have high polymerization efficiencies under UV and unexpectedly visible light exposure. The efficiency of the photoinitiators is based on two separate mechanisms, oxidative interaction between benzophenone group and Iod and charge transfer complex (CTC) formation between Iod and amines in OAA; verified by absorption, steady state photolysis, electron spin resonance and laser flash photolysis. The CTC formation mechanism was also studied by molecular modeling studies; and both mechanisms generating aryl radicals. [ABSTRACT FROM AUTHOR]

In this work, six new fluorescent dyes derived from the naphthalimide scaffold (Napht1–Napht6) were synthesized and used as high‐performance photoinitiating systems (PISs) in two and three‐component systems (combined with iodonium salt (Iod) and/or an electron donor amine (such as N‐phenylglycine[NPG])) for the radical photopolymerization of acrylate and methacrylate monomers under visible light using a light‐emitting diode at 405 nm. Markedly, these dyes were never synthesized before. In fact, these PISs showed high initiation efficiency with both demonstrating high final reactive function conversions and high polymerization rates. A further interest of our study is to determine the effect of the different substituents (chromophoric group) on the naphthalimide function, concerning the efficiency of initiation of the free radical polymerization. In order to improve the mechanical properties of the obtained polymers, these derivatives were also tested for the photopolymerization of a blend of acrylate/epoxy monomers (TA/EPOX); these latter properties were characterized by traction tests. To demonstrate the initiation efficiency of these dyes, several methods and characterization techniques were used, including steady state photolysis, real‐time Fourier transform infrared spectroscopy, emission spectroscopy as well as cyclic voltammetry. In our study, these naphthalimides were used for the synthesis of photocomposites (one and multiple layers of glass fibres) using a UV@395 nm (4 W/cm2) conveyor, as well as in the preparation of 3D printed polymers. Markedly, one of the naphthalimide derivatives (Napht‐4) can be used as a new high‐performance water soluble photoinitiator for photopolymerization in water and hydrogel synthesis. [ABSTRACT FROM AUTHOR]

2‐Oxo‐2‐(tert‐butyldimethylsilyl)acetic acid (DKSi‐COOH), is proposed here as a new high‐performance photoinitiator (PI) for the free radical polymerization of methacrylates under blue light irradiation. In the presence of DKSi‐COOH, very good polymerization performances are reached and outstanding bleaching properties are obtained compared to traditionally used camphorquinone‐based photoinitiating systems. Remarkably, this new developed PI exhibits good water solubility and excellent stability in acidic conditions and represents therefore a promising candidate for water‐based formulations. [ABSTRACT FROM AUTHOR]

Diethoxyacetate salts are investigated as new co‐initiators for the free radical polymerization (FRP) of (meth)acrylates upon visible light exposure, with light emitting diodes (LEDs; 405 nm, 477 nm) being employed for this purpose. Interestingly, the impact of the counter cation on their initiating ability is clearly highlighted. When these co‐initiators are combined with commercial photoinitiators such as 2‐isopropylthioxanthone (ITX) or camphorquinone (CQ), good to excellent free radical polymerization initiating performances are found and high final reactive function conversions are achieved. In the absence of these co‐initiators, no or poor polymerization occurs, clearly highlighting the importance of these co‐initiators for an efficient process. These systems can be interesting for the replacement of aromatic amines opening the way for amine‐free Type II photoinitiating systems. [ABSTRACT FROM AUTHOR]

In this article, new compounds based on the carbazole scaffold (DMs = DM1 and DM2, constituted by a carbazole unit connected on positions 3 and 6 to a two 4,4′‐dimethoxydiphenylamine groups and differing by the substituent present on the nitrogen heteroatom of the carbazole core) were synthesized and proposed as high‐performance visible light photoinitiators/photosensitizers for both the free‐radical polymerization of methacrylates and the cationic polymerization of epoxides upon visible light exposure using LED@405 nm. Remarkably, DM2 leads to higher final conversions than DM1. In order to study the photophysical and photochemical properties of the carbazole derivatives, different parameters were taken into account such as the light absorption, the steady‐state photolysis, and the fluorescence spectroscopy. Using different techniques such as fluorescence quenching, redox behavior, and cyclic voltammetry, we are able to discuss the photosensitization/photoinitiation reactions providing a full coherent picture of the involved chemical mechanisms. The photosensitization of the carbazole derivatives occurred predominantly via singlet excited states at the rate of the diffusion limit. Upon exposure to laser diode at 405 nm, DMs show high performance in initiating systems for 3D resins. Remarkably, DM2 can also be used in photocomposite synthesis using light‐emitting diode conveyor. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2081–2092 [ABSTRACT FROM AUTHOR]

New polyoxometalate (POM)/polymer hybrid composites were prepared by photopolymerization under mild conditions for suitable photocatalytic processes. Polyoxometalates were incorporated in special photosensitive resins, which were photopolymerized under visible light to obtain new materials with photocatalytic activity for dye removal. The synthesized composites were characterized by real‐time FT‐IR, and the photocatalytic ability was investigated on Eosin‐Y removal using photolysis under near UV irradiation. Interestingly, the polyoxometalates keep their photocatalytic properties, while incorporated into the polymeric matrix since very high conversion rates of Eosin‐Y were achieved. Indeed, degradation efficiencies of about 98% and 93% were registered when using H3PMo12O40/polymer and 94% for SiMo12O40(IPh2)4/polymer composites, respectively. These first results reported in this article show that the new synthesized POM/polymer composites could be considered as promising materials for green and more suitable organic dye removal from aqueous solutions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1538–1549 [ABSTRACT FROM AUTHOR]

Nowadays photo semiconductors such as ZnO are one of the driving forces of humanity towards economically and ecological safe life. Such semiconductors are used in solar applications and for light emission but also multiple investigations using the material as photocatalysts (water‐splitting), or as photo initiators were published. The combination of the inorganic material with an organic matrix leads to possible interesting hybrid materials. One drawback for ZnO and other photo semiconductors is the short UV wavelength (in the UV−range) which is necessary to photoactivation. We will present the possibility of modified ZnS‐ZnO nanocomposites being reactive towards visible light for example 406 nm LED illumination. Therefore, the particles are used as initiators for free radical polymerization. The simply to handle experimental preparation procedure of the sulphur containing ≈10 nm particles is described in this work for the first time. [ABSTRACT FROM AUTHOR]

Six new carbazole based compounds (Ca1–Ca6) are synthesized and proposed as high performance photoinitiators with iodonium salt (iod) and/or an amine (EDB) for both the free radical polymerization (FRP) of acrylates and the cationic polymerization (CP) of epoxides upon near UV and visible light exposure using light emitting diodes (LEDs) @385 nm and @405 nm. Excellent polymerization initiating abilities are found and high final reactive function conversions are acquired. A full picture of the involved photochemical mechanisms is given. [ABSTRACT FROM AUTHOR]

Abstract: The photopolymerization of styrene in emulsion is achieved in a conventional double‐wall reactor equipped with a LED ribbon coiled around the external glass wall. Styrene mixed to acridine orange is added to the water phase containing sodium dodecyl sulfate, a water‐soluble N‐heterocyclic carbene–borane and disulfide, and irradiated. Highly stable latexes are obtained, with particles up to a diameter of 300 nm. The ability to reach such large particle sizes via a photochemical process in a dispersed medium is due to the use of visible light: the photons in the visible range are less scattered by larger objects and thus penetrate and initiate better the polymerizations. They are also greener and cheaper to produce via LEDs, and much safer than UVs. The method presented does not require any specific glassware; it works at lower temperature and delivers larger particles compared to thermal processes at similar solids contents and surfactant concentrations. [ABSTRACT FROM AUTHOR]

In the present paper, new photoinitiators based on the meta-terphenyl scaffold in combination with an iodonium salt and 9H-carbazole-9-ethanol (CARET) are proposed for the free radical promoted cationic polymerization of epoxides upon visible light exposure using light emitting diodes at 405, 455, and 470 nm. Remarkably, a new high performance additive (i.e., CARET) is proposed here for cationic polymerizations. CARET shows some important advantages compared to other reported additives such as N-vinylcarbazole or benzyl alcohol used as references. Excellent polymerization initiating abilities are found and a full picture of the involved chemical mechanisms is provided. [ABSTRACT FROM AUTHOR]

ABSTRACT The development of iron complexes for the photoredox catalysis is a huge challenge. Indeed, Iron complexes can be ideal candidates due to their potential visible light absorption and redox properties but also because they are less toxic, inexpensive and environmentally friendly compared to other catalysts. In the present paper, a series of novel iron complexes have been synthesized and utilized to initiate the free radical promoted cationic polymerization of epoxides or the free radical polymerization of acrylates through photoredox catalysis processes upon exposure to near UV (385 nm) or visible violet (405 nm) light emitting diodes (LEDs). When combined with an iodonium salt and N-vinylcarbazole, the iron complex-based photoinitiating systems are able to generate radicals, cations, and radical cations. The initiation efficiency is investigated through real-time Fourier transform infrared spectroscopy and a satisfactory initiating ability is found. The mechanisms for the generation of the reactive initiating species through photoredox catalysis are studied by different methods (steady state photolysis, cyclic voltammetry and electron spin resonance spin trapping techniques) and discussed in detail. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2247-2253 [ABSTRACT FROM AUTHOR]

The observed development of one-component photoinitiators of cationic polymerization reactions in the last forty years is briefly described. Cationic photoinitiators can usually be activated by short wavelengths (<300 nm) and relatively hard conditions (high intensity). The search for cheaper and safer light sources has led to the use of Light Emitting Diodes (LEDs). In this review, a special emphasis is provided on the most recent and promising cationic initiators operating under near UV and visible LEDs. Ferrocenium salts exhibit the broadest visible light absorption and are probably, from this point of view, the most versatile near UV and visible light cationic initiators. Excellent photoinitiation performance has been found with the ferrocenium salts as one-component initiators, and the effect of ferrocenium salts based multi-component photoinitiating systems on the relevant photoinitiation performance has also been investigated. [ABSTRACT FROM AUTHOR]

ABSTRACT The utilization of visible lights for the fabrication of polymeric materials is recognized as a promising and environmentally friendly approach. This process relies on the photochemical generation of reactive species (e.g., radicals, radical cations, or cations) from well-designed photoinitiators (PIs) or photoinitiating systems (PISs) to initiate the polymerization reactions of different monomers (acrylates, methacrylates, epoxides, and vinyl ethers). In spite of the fact that metal complexes such as ruthenium- or iridium-based complexes have found applications in organic and polymer synthesis, the search of other low-cost metal-based complexes as PISs is emerging and attracting increasing attentions. Particularly, the concept of the photoredox catalysis has appeared recently as a unique tool for polymer synthesis upon soft conditions (use of light emitting diodes and household lamp). This highlight focuses on recently designed copper and iron complexes as PI catalysts in the application of photoinduced polymerizations (radical, cationic, interpenetrated polymer networks, and thiol-ene) or controlled radical polymerization under visible light irradiation. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2673-2684 [ABSTRACT FROM AUTHOR]

For polymer synthesis upon visible light, actual photoinitiator operates in a restricted part of the spectrum. As a consequence, several photoinitiators are necessary to harvest all of the emitted visible photons. Herein, 2,7-di- tert-butyldimethyldihydropyrene is used for the first time as a multicolor photoinitiator for the cationic polymerization of epoxides. Upon addition of diphenyliodonium hexafluorophosphate and optionally N-vinylcarbazole, the originality of this approach is to allow efficient monomer conversions under various excitation light sources in the 360-650 nm wavelength range: halogen lamps, and light-emitting and laser diodes. The synthesis of an interpenetrated polymer network from an epoxide/acrylate blend using a red light at 635 nm is also feasible. The formed polymer material exhibits a photochromic character. [ABSTRACT FROM AUTHOR]

In this article, five new organic dyes based on the naphthalimide scaffold (Napht-1–Napht-5) were synthesized and tested as high-performance photoinitiators for both the Free Radical Photopolymerization (FRP) of acrylates and the Cationic Polymerization (CP) of epoxides using blue Light-Emitting Diodes (LEDs) as a safe irradiation source (LED @405 nm and 455). In fact, very good photopolymerization profiles (high final conversions and high polymerization rates) were obtained once these photoinitiators were combined with an Iodonium salt (Iod) or Iod/amine NPG and NVK). Remarkably, these dyes were able to generate interpenetrating polymer networks (IPN) by polymerization of a blend of monomers. These experiments were carried out to improve the polymerization profiles as well as the mechanical properties of the obtained materials. Due to their high photoinitiation abilities, these compounds were used in some applications such as photocomposite synthesis, direct laser write, and 3D printing experiments. To determine the chemical mechanisms, the photochemical/photophysical properties of these compounds were studied using different characterization techniques such as UV–visible absorption spectroscopy, steady-state photolysis, Fluorescence quenching, time-resolved fluorescence spectroscopy, FTIR spectroscopy, and cyclic voltammetry [ABSTRACT FROM AUTHOR]

Cerium dioxide (CeO2) has huge potential in many applications ranging from biochemical engineering to the coating industry. Here, the first example of visible light photo‐mediated Pickering emulsion polymerization of (meth)acrylate monomers is reported using CeO2 nanoparticles (NPs) as solid stabilizer. A ω,ω′−dicarboxylic acid diphenyl disulfide photoinitiator is anchored on the surface of the CeO2 NPs and used to initiate the emulsion polymerization of methyl methacrylate (MMA) and of MMA/n‐butyl acrylate (MMA/BA) under visible light leading to CeO2‐armored latexes. Radicals generated upon light irradiation trigger the formation of polymer chains chemically attached to the CeO2 NPs, promoting their subsequent adsorption on the latex surface. The composite films obtained from the CeO2‐armored P(MMA‐co‐BA) latexes exhibit a unique honeycomb nanostructure with the nanoceria located in the walls giving the materials excellent mechanical, anti‐UV, and photocatalytic properties. [ABSTRACT FROM AUTHOR]

The development of visible-light 3D printing technology by using water-soluble initiating systems has attracted widespread attention due to their potential applications in the manufacture of hydrogels. Besides, at present, the preparation of water-soluble photoinitiators suitable for visible light irradiation (such as LEDs) still remains a challenge. Therefore, this work is devoted to developing water-soluble photoinitiators (PI)/photoinitiating systems (PIS) upon irradiation with a LED @ 405 nm. In detail, a new water-slightly-soluble chalcone derivative dye [(E)-3-(4-(dimethylamino) phenyl)-1-(4-(2-(2-(2-methoxyethoxy) ethoxy) ethoxy) phenyl) prop-2-en-1-one] was synthesized here and used as a PI with a water-soluble coinitiator, i.e., triethanolamine (TEA) which was also used as an electron donor. When combined together, a charge transfer complex (CTC) formed immediately which exhibited excellent initiating ability for the free radical photopolymerization of poly(ethyleneglycol)diacrylate (PEG-DA). In light of the powerful CTC effect, the [dye-TEA] CTC could not only exhibit enhanced water solubility and mechanical properties but could also be effectively applied for 3D printing. This CTC system is environmentally friendly and cost-saving which demonstrates a great potential to prepare hydrogels via photopolymerization. [ABSTRACT FROM AUTHOR]

In this paper, nine organic compounds based on the coumarin scaffold and different substituents were synthesized and used as high-performance photoinitiators for free radical photopolymerization (FRP) of meth(acrylate) functions under visible light irradiation using LED at 405 nm. In fact, these compounds showed a very high initiation capacity and very good polymerization profiles (both high rate of polymerization (Rp) and final conversion (FC)) using two and three-component photoinitiating systems based on coum/iodonium salt (0.1%/1% w/w) and coum/iodonium salt/amine (0.1%/1%/1% w/w/w), respectively. To demonstrate the efficiency of the initiation of photopolymerization, several techniques were used to study the photophysical and photochemical properties of coumarins, such as: UV-visible absorption spectroscopy, steady-state photolysis, real-time FTIR, and cyclic voltammetry. On the other hand, these compounds were also tested in direct laser write experiments (3D printing). The synthesis of photocomposites based on glass fiber or carbon fiber using an LED conveyor at 385 nm (0.7 W/cm2) was also examined. [ABSTRACT FROM AUTHOR]

In this study, eight coumarins (coumarins 1–8) are proposed as near-UV and blue light sensitive photoinitiators/photosensitizers for the cationic polymerization (CP) of epoxysilicones when combined with 4-isopropyl-4'-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate (IOD). Among these coumarins, four of them (coumarins 1, 2, 6 and 8) have never been reported in the literature, i.e., these structures have been specifically designed to act as photoinitiators for silicones upon near UV and visible irradiation. Good final reactive epoxy function conversions (FCs) and also high rates of polymerization (Rp) were achieved in the presence of the newly proposed coumarin-based systems. The polymers generated from the photopolymerization of epoxysilicones can be considered as attractive candidates for several applications such as: elastomers, coatings, adhesives, and so on. The goal of this study focuses also on the comparison of the new proposed coumarins with well-established photosensitizers i.e., 1-chloro-4-propoxythioxanthone (CPTX), 9,10-dibutoxyanthracene (DBA) or some commercial coumarins (Com. Coum). As example of their high performance, the new proposed coumarins were also used for laser write experiments upon irradiation with a laser diode at 405 nm in order to develop new cationic 3D printing systems. [ABSTRACT FROM AUTHOR]

Photo‐induced thermal polymerization upon near‐infrared (NIR) light irradiation has been reported in the literature. In this approach, a component able to convert the NIR light into heat must be used in combination with a thermal initiator to initiate the free‐radical polymerization of (meth)acrylates. In recent studies, some absorbers have been presented as very efficient heat generators (called heaters). In the present work, different fillers are investigated as heaters and compared to organic NIR absorbers. An alkoxyamine (e.g., BlocBuilder‐MA) is used as thermal initiator and is dissociated by the heat generated by the NIR photoexcitation of the fillers. In the present work, several fillers are examined: graphene oxide, graphene nanoplatelets, multi‐walled carbon nanotubes, and silicon carbide. Due to the energy of the photon delivered, NIR light curing is challenging but offers several advantages compared to visible light. The most interesting feature is the deeper penetration of the light inside the photocurable resin, enabling the polymerization of thick samples. Parallel to this, incorporation of fillers in resins allows unique access to composites through photothermal polymerization of (meth)acrylates. Three different wavelengths of irradiation have been studied: 785, 940, and 1064 nm. [ABSTRACT FROM AUTHOR]

Photopolymerization processes, and especially those carried out under visible light, are more and more widespread for their multiple advantages compared to thermal processes. In the present paper, new 1,8-naphthalimide derivatives are proposed as photoinitiators for free-radical polymerization upon visible light exposure using light-emitting diodes (LEDs) at 395, 405, and 470 nm. These photoinitiators are used in combination with both iodonium salts and phosphine. The synthesis of these compounds as well as their excellent polymerization initiation ability for methacrylate monomers are presented in this article. A full picture of the involved chemical mechanisms is also provided thanks to photolysis, radical characterization, and redox measurements. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxime esters have been examined as photoinitiators of polymerization. • Polymerization processes in the visible range have been initiated. • Carbazole and phenothiazine exhibit interesting photophysical properties. • Polymerization of a difunctional monomer was possible under low light intensity. In this study, a series of seven PCBOEs was innovatively designed and successfully synthesized for the first time by bridging a phenothiazine and a carbazole unit by mean of an acetylene spacer and bearing oxime ester groups as end groups on both sides. Structures of the different difunctional oxime esters were confirmed through NMR and HRMS. All PCBOEs exhibited excellent light absorption properties in the visible range. Upon excitation with a 405 nm LED for 60 s, a complete photolysis of the oxime esters could be achieved. Parameters such as the singlet state energy and the triplet state energy demonstrated the facile generation of the corresponding radicals upon light absorption by PCBOEs. Photopolymerization kinetics in TMPTA confirmed the homolytic cleavage of oxime esters and the generation of radicals. CO 2 absorption peaks were detected when the PCBOEs/TMPTA systems were excited with a 405 nm LED. Based on the positive results, the photochemical mechanisms of polymerization with PCBOEs was proposed. PCBOE3 was identified as the best candidate of the series and this bifunctional oxime ester was successfully used for the 3D-printing of the "IS2M" logo via DLW. Experimental results from DSC also confirmed that PCBOEs not only serve as photoinitiators but also possess high reactivity as thermal initiators. [ABSTRACT FROM AUTHOR]

Two new near-UV and visible-light-sensitive photobase generators (PBGs) are synthesized and investigated. They are built on a near-UV and visible light sensitive ( E )-3-(2,2′-bithiophen-5-yl)-2-cyanoacrylic acid chromophore and a latent strong base such as 1,8-diazabicyclo [5.4.0] undec-7-ene (DBU) and 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD). Upon irradiation, decarboxylation occurs and the base is released. The anionic curing of epoxy/thiol as well as thiol/divinylsulfone formulations in the presence of these PBGs under LEDs at 385 and 405 nm is studied. More than 60% of conversion of the thiol and epoxy functions is achieved upon LED@385 nm without any post baking. [ABSTRACT FROM AUTHOR]

Zinc tetraphenylporphyrin (ZnTPP) is proposed as a high performance visible light photoinitiator for both the free radical polymerization (FRP) of methacrylates (thick films) and the cationic polymerization (CP) of epoxides (thin films) upon visible light exposure using light emitting diodes (LEDs) at 405, 455, 477, and 530 nm. ZnTPP combined with an iodonium salt shows excellent polymerization initiating abilities and high final conversions were obtained. Remarkably, for the ligand alone (tetraphenylporphyrin derivative, H2TPMP) used as photoinitiator, no polymerization occurs, indicating the importance of the metal in the initiating complex for an efficient process. A full picture of the involved chemical mechanisms is given. The high performance of ZnTPP as cationic initiating system is also well shown for new cationic 3D printing resins upon exposure to LED projector at 405 nm. [ABSTRACT FROM AUTHOR]

Highly functionalized benzo[b]phosphole oxides were synthesized from reactions of arylphosphine oxides with alkynes under photocatalytic conditions by using eosin Y as the catalyst and N-ethoxy-2-methylpyridinium tetrafluoroborate as the oxidant. The reaction works under mild conditions and has a broad substrate scope. Mechanistic investigations have been undertaken and revealed the formation of a ground state electron donor-acceptor complex (EDA) between eosin (the photocatalyst) and the pyridinium salt (the oxidation agent). This complex, which has been fully characterized both in the solid state and in solution, turned out to exhibit a dual role, i.e., the oxidation of the photocatalyst and the formation of the initiating radicals, which undergoes an intramolecular reaction avoiding the classical diffusion between the two reactants. The involvement of ethoxy and phosphinoyl radicals in the photoreaction has unequivocally been evidenced by EPR spectroscopy. [ABSTRACT FROM AUTHOR]

[Display omitted] • New photocatalyst/polymer composites are proposed. • The obtained shaped photocomposites are obtained by photopolymerization. • A comparison of photocatalyst/polymer composites efficiency is provided. • The MIL-100(Fe)/polymer composite was selected as the most efficient system. Polyoxometalates (POMs), Metals Organic-Frameworks (MOFs), Perovskites and Metal Oxides are promising crystalline materials that have received increasing attention due to their impressive photocatalytic performances. However, these catalysts are generally produced in powdered form limiting their reuse and recyclability. A recent solution consisted of associating them with an acrylate polymer via a simple, green and rapid photopolymerization process under visible light irradiation. The obtained shaped photocomposites exhibited at the same time an excellent polymer robustness, stability and malleability while maintaining remarkable photocatalytic properties. The fruitful incorporation of the different crystallites into polymer matrixes are already reported in the literature in our previous works and the chemical mechanisms were also given. However, in order to select the most performant photocatalytic system, which could be probably applied in future technological environmental applications, it is important to compare the photocatalytic efficiency of the different and recently developed photocomposites. Moreover, a comparison with the benchmark catalyst TiO 2 is also provided for a better evaluation of their performance. Markedly, some of the reported catalysts were significantly better than TiO 2. The absorption properties, the reusability and the thermal properties as well as the mechanical stabilities were taken into account during the in-depth comparison. The MIL-100(Fe)/polymer composite was selected as the most efficient photocatalytic system, which is also reusable during 10 successive catalytic cycles with an observed little decrease in the pollutants final degradation percentages starting from the 8th cycle. Moreover, this Fe-based MOF immobilized photocatalyst is characterized by interesting mechanical and thermal stabilities as well as a good absorption property allowing its application under visible light irradiation. [ABSTRACT FROM AUTHOR]

Although there have been many reports on photoinitiating systems adapted to visible lights for radical photopolymerization, the challenge for the design and development of photoinitiating systems for cationic photopolymerization or concomitant radical/cationic photopolymerization (for interpenetrating polymer network IPN synthesis) with visible lights still remains open. Particularly, the recent development of cheap and easily accessible LEDs operating upon soft visible light irradiations has opened new fields for polymer synthesis. Since 2011, many novel photoinitiating systems based on organic and organometallic compounds with excellent visible light absorption have emerged and exhibited outstanding photoinitiating abilities especially for cationic photopolymerization. In this review, recent progress (mainly from 2011 to early 2014) in applications of photoinitiators and sensitive photoinitiating systems under visible lights are reported. In addition, their relative efficiencies in the photopolymerization of different monomers are exemplified and discussed. [ABSTRACT FROM AUTHOR]

Abstract: Nine new photoinitiating systems based on a combination of new and established dyes (having an end capped polyenic structure) with an iodonium salt have been synthesized and tested for the polymerization of divinylether and epoxy monomers upon a visible light exposure. They exhibit a strong absorption in the 350–650 nm range which well matches the visible light emission of different convenient visible light sources. Interestingly, very soft irradiation conditions can be employed. Excellent polymerization profiles have been obtained from selected dye iodonium salt combinations using a halogen amp or a laser diode à 457 nm. The chemical mechanisms associated with these novel photoinitiating systems are investigated by steady-state photolysis and ESR experiments. [Copyright &y& Elsevier]

Abstract: Several diketopyrrolopyrrole derivative based dyes (DPP), combined with an iodonium salt or an amine (and optionally an additive), are studied as photoinitiating systems for the cationic polymerization CP of epoxides or the free radical polymerization FRP of acrylates under different irradiation sources i.e. a very soft halogen lamp as well as laser diodes at 473 nm (blue light) and 532 nm (green light). The diketopyrrolopyrrole-furan derivative (FuDPP) is very efficient in CP. The structure/reactivity/efficiency relationships in this series of DPP derivatives are investigated. A comparison with a well known reference for visible light photoinitiating system (i.e. camphorquinone based photoinitiating system) is also provided showing the better efficiency of the new proposed structures. The photochemical mechanisms are studied by steady state photolysis, fluorescence, cyclic voltammetry, laser flash photolysis and electron spin resonance spin-trapping techniques. [Copyright &y& Elsevier]

[Display omitted] • Carbazole derivatives have been examined as photoinitiators of polymerization. • Polymerization processes in the visible range have been initiated. • Carbazoles exhibit interesting photophysical properties. • Polymerization of various monomers was possible under low light intensity. 5,12-Dihydroindolo[3,2- a ]carbazole is a promising scaffold for the design of visible light photoinitiators of polymerization due to the simultaneous presence of two carbazole moieties that can be differently functionalized. Notably, redshift of the absorption spectra can be facilely obtained by nitration of one of the two carbazoles, the second carbazole group being functionalized with various groups. Dinitration of 5,12-dihydroindolo[3,2- a ]carbazole is another efficient approach for designing dyes with strong absorptions extending over the visible range. In this work, a series of 36 compounds never reported in the literature and differing by the substitution pattern have been designed and synthesized. Notably, the possibility to design push–pull dyes by Knoevenagel and Claisen Schmidt reactions, to introduce electroactive groups such as thiophene by Suzuki cross-coupling reactions or to design water soluble chromophore has been explored. To evidence the interest of these structures, photopolymerization experiments have been carried out at 405 nm and the polymerization of acrylates has been examined in thick and thin films. To support the polymerization efficiency, mechanisms involved in the free radical polymerization of acrylates have been established by the combination of various techniques including UV–visible absorption and fluorescence spectroscopy, cyclic voltammetry and photolysis experiments. [ABSTRACT FROM AUTHOR]

Thiophene and polythiophene derivativeshave been prepared andused as photoinitiators upon visible light exposure. Their abilitiesto initiate, when combined with an iodonium salt (and optionally N-vinylcarbazole), a ring-opening cationic photopolymerizationof epoxides and radical photopolymerization of acrylates under variousdifferent irradiation sources (i.e., very soft halogen lamp irradiation,laser diode at 405, 457, 473, 532, and 635 nm and blue LED bulb at462 nm) have been investigated. These systems are characterized bya remarkable performance for purple to red light exposure. They arealso particularly efficient for the cationic and radical photopolymerizationof an epoxide/acrylate blend in a one-step hybrid cure and lead tothe formation of an interpenetrated polymer network IPN (30 s forgetting tack-free coatings). Their migration stability is excellentin the cured IPNs. The photochemical mechanisms are studied by steadystate photolysis, fluorescence, cyclic voltammetry, electron spinresonance spin trapping, and laser flash photolysis techniques. [ABSTRACT FROM AUTHOR]

[Display omitted] • An efficient photoactivated epoxy/anhydride reaction is proposed. • This reaction can be driven by both UV/visible and even near infrared light (NIR). • The polymerization kinetics were followed by both real-time FTIR and photorheology experiments. • The mechanical properties of this photoactivated epoxy/anhydride system are detailed. The epoxy/anhydride reaction is usually quite slow at room temperature RT (over an hour to achieve full conversion) and therefore requires heat treatment at a fairly high temperature. A new route is proposed in this work using an epoxy/anhydride photoactivated reaction. This reaction can be driven by both UV/visible and even near infrared light (NIR). To cause the polymerization of the epoxides with the anhydrides, a photoinitiating system is needed to ensure an efficient light activation. This means no external heat is required during reaction. Different epoxy/anhydride ratios are tested to optimize the system. Based on the different trials, a complete conversion of the epoxy function can be reached at 405 nm (visible light) or 785 nm (NIR light). Polymerization kinetics were followed by both real-time FTIR and photorheology experiments. The mechanical properties of this photoactivated epoxy/anhydride system are detailed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Carbazole derivatives have been examined as photoinitiators of polymerization. • Polymerization processes in the visible range have been initiated. • Carbazoles exhibit interesting photophysical properties. • Polymerization of various monomers was possible under low light intensity. 5,12-Dihydroindolo[3,2- a ]carbazole is a polycyclic structure combining in its scaffold two carbazole moieties sharing a fused aromatic ring. Since the pioneering works reported in 2019 on this structure concerning the substitution of the two carbazoles by similar functional groups, no recent investigation has been devoted to asymmetrize the substitution of the two carbazoles. In this work, a series of 13 compounds based on the 5,12-dihydroindolo[3,2- a ]carbazole scaffold is presented. By carefully controlling the reaction conditions, functional groups such as a formyl, a nitro or an acetyl group could be selectively introduced on one of the two carbazoles. By combining X-ray diffraction and 2D NMR experiments, the higher reactivity of one of the two carbazoles could be clearly evidenced, enabling to generate asymmetrically substituted structures. Thanks to this unprecedented approach on the 5,12-dihydroindolo[3,2- a ]carbazole scaffold, the absorption of the resulting dyes could be shifted towards the visible range whereas the parent structure (5,12-dihexyl-6,7-diphenyl-5,12-dihydroindolo[3,2- a ]carbazole) exhibits a strongly UV-centered absorption. In light of their visible light absorption properties, several dyes have been examined as photoinitiators of polymerization activable at 405 nm and under low light intensity in two-component photoinitiating systems for the free radical polymerization of acrylates or the cationic polymerization of epoxides. Chemical mechanisms supporting the different polymerization processes have been fully elucidated by combining several techniques including cyclic voltammetry, UV–visible absorption and photoluminescence spectroscopy as well as photolysis experiments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two new copper complexes were investigated for both radical and cationic polymerisation under air. • The formations of acrylate/epoxy interpenetrated polymer networks were successfully performed. • Several characterisations of the interpenetrated polymer networks were done. • The advantages of IPNs are highlighted. Two new copper complexes were investigated in three-component visible light photoinitiating system for both radical and cationic polymerisation under air. Their reactivity and efficiency have been compared with that of a highly efficient photoredox catalyst. The formation of acrylate/epoxy interpenetrated polymer networks were successfully performed through concomitant initiation of radical and cationic polymerisation with low copper complex content upon either LED@405 nm or LED@455 nm irradiations. Several characterisations of the acrylate/epoxy IPNs final properties, such as the mechanical properties, adhesion properties, shrinkage and swelling, indicated the possibilities to adapt or tune their properties compared to radical polymerisation of TMPTA. [ABSTRACT FROM AUTHOR]

• Porphyrins have been used as photoinitiators of polymerization. • Polymerization in the visible and near-infrared range was initiated. • Porphyrins were used as heaters. • Polymerization of acrylate was possible under low light intensity. A series of metalated porphyrins has been prepared and used as visible light photoinitiators of polymerization activable under low light intensity. Among the six metalated porphyrins examined in this work, five of them have never been reported in the literature and specifically designed to exhibit a good solubility in monomers. Three of the proposed structures were efficient @405 nm but remarkably, despites their weak absorptions at 785 nm, efficient Near Infrared (NIR) polymerization profiles could also be obtained during the free radical polymerization of a methacrylate resin. To support the experimental observation of a polymerization process, a mechanism has been proposed based on combined photochemical and photothermal pathways. [ABSTRACT FROM AUTHOR]

Visible light induced synthesis generally involves i) dyes or chromophores with potential photocleavable bonds (Type I photoinitiator), ii) hydrogen abstractions (Type II photoinitiator) by dyes/chromphores and iii) photoredox catalysis using metal-based or metal-free dyes. Beyond these strategies, charge transfer complexes (CTCs), also referred to as electron donor acceptor (EDA) complexes, were also reported to be the visible light initiating species. In these cases, the ground state intimate association of a donor and acceptor creates a new structure that can result in (bathochromic) visible light absorption compared to the separated compounds. In the present review, an update on CTCs as photoinitiating systems for photopolymerization applications will be provided with examples of CTC-specific structure/reactivity/efficiency relationships. Interestingly, CTC can act as dual photo/thermal photoinitiators both in cationic and free radical photopolymerizations. Also, low optical density of the CTC in resins allowed to access extremely thick samples and composites. The possibility of extending wavelength sensitivity of photopolymerizations by excited state complexes (exciplexes) is also discussed. [ABSTRACT FROM AUTHOR]