Simultaneous initiation of radical and cationic polymerization reactions using the "G1" copper complex as photoredox catalyst: Applications of free radical/cationic hybrid photopolymerization in the composites and

WOS:000469902800007This investigation presents the use of a photoredox catalyst "G1" as a photoinitiating system for free radical/cationic hybrid polymerization under mild irradiation conditions. The G1 system (G1/iodonium salt/N-vinylcarbazole), can simultaneously initiate the free radical and cationic polymerization reactions upon exposure to a visible (405 nm) light from a Light Emitting Diode (LED) source. The multicomponent G1 system is able to simultaneously generate radical and cationic species through a catalytic photoredox process. The curing of thin samples (25 mu m), thick samples (1.4 mm) as well as the manufacture of hybrid system/glass fibers composites ( 2 to 4 mm thickness) was realized and the influence of the ratio of cationic/radical monomer blends on the polymerization kinetics was studied. The use of G1 in visible light photoinitiating system for the access to composites and 3D printing experiments was particularly outlined. G1 was also shown to have low levels of migration from the cured materials. When compared to reference materials ("F1", a similar copper complex and an anthracene derivative, dibutoxy anthracene), G1 showed better polymerization efficiency. The initiation efficiency was investigated through the real-time Fourier transform infrared (RT-FTIR) spectroscopy and optical pyrometry. Dynamical Mechanical Analysis has been used to determine the glass temperature transition of the cured hybrid system as a complementary technique

Photochemistry and Radical Chemistry under Low Intensity Visible Light Sources: Application to Photopolymerization Reactions:

The search for radical initiators able to work under soft conditions is a great challenge, driven by the fact that the use of safe and cheap light sources is very attractive. In the present paper, a review of some recently reported photoinitiating systems for polymerization under soft conditions is provided. Different approaches based on multi-component systems (e.g., photoredox catalysis) or light harvesting photoinitiators are described and discussed. The chemical mechanisms associated with the production of free radicals usable as initiating species or mediators of cations are reported

Attitude of young generation to family and consequences for Czech family policy

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Mechanosynthesis of a Copper Complex for Redox Initiating Systems with a Unique Near Infrared Light Activation

International audienceThe first use of a new mechanosynthesized copper complex (Cu(acac)(2dppba)) as a initiator for the redox and redox photoactivated polymerization of methacrylates under air is proposed. This paper (i) describes the mechanosynthesis of this complex, (ii) outlines the relative efficiency of the complex for redox polymerization (mechanosynthesized product vs. solvent synthesized product), (iii) follows the polymerization enhancement under a 405 nm light, and (iv) demonstrates the high performance of this complex in near infrared photoactivated redox polymerization where a completely colorless polymer is obtained (unprecedented under NIR irradiations, 785 nm, here). The light activated polymerization exhibit higher conversions, better time controls (activation control) and higher surface conversions than redox polymerization. The mechanosynthesis is well characterized by two solvent-free methods (visual color change and Electron Spin Resonance) and two solvent-based methods (high resolution-electrospray ionization-mass spectrometry (HR-ESI-MS) and UV-vis spectrometry). The involved mechanisms are discussed. Mechanosynthesis of copper complexes opens new perspectives for copper (photo)redox polymerization catalysts as the environmental impact and economical costs of the complex synthesis are significantly reduced. (c) 2017 Wiley Periodicals, Inc

N-naphthalimide ester derivatives as Type Ⅰ photoinitiators for LED photopolymerization

International audienceIn this study, a series of N-naphthalimide ester derivatives (noted NPIE1-NPIE9) with different substituents were designed as visible light photoinitiators (PIs). These structures exhibited good light absorption properties in the visible range. Photoinitiation abilities of NPIEs were evaluated upon exposure to a light-emitting diode (LED) at 405 nm. All the structures demonstrated good performance during the free radical polymerization of acrylate monomers. Markedly, the function conversion for acrylate monomers in the presence of NPIE1 was higher than that of the benchmark PI diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO). Upon exposure to a LED@455 nm, NPIE1 could also initiate the polymerization of acrylate monomers effectively i.e. the benchmark photoinitiator (TPO) was not efficient for these longer irradiation wavelengths. Through the calculations of the N−O bond dissociation energy and the excited state energy, the cleavage of N−O bond from the singlet state proved to be favorable. Interestingly, CO2 was detected during the polymerization experiments, which indicates that there is a decarboxylation reaction during the photoinitiation process. Based on the obtained results, a mechanism of Type Ⅰ PI behavior can be proposed. Due to the good performance, NPIE1 was successfully used in 3D printing 2 experiments. In addition, high thermal stability of NPIEs in monomers was also found. This can be a great improvement for elaborating stable formulations

Copper photoredox catalyst “G1”: a new high performance photoinitiator for near-UV and visible LEDs

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Metal Acetylacetonate-Bidentate Ligand Interaction (MABLI) as highly efficient free radical generating systems for polymer synthesis

WOS:000428091400002Metal Acetylacetonate-Bidentate Ligand Interaction (MABLI) is presented here as a new chemical mechanism for the highly efficient generation of free radicals for polymer synthesis. This MABLI process involves simultaneous ligand exchange and a change of the metal oxidation degree and is associated with the efficient release of free radicals. In conventional redox two-component radical generating systems, two criteria are required to be efficient: (1) oxidizing agents must exhibit a low bond dissociation energy (BDE) i.e. they are usually unstable (e.g. peroxides) and (2) a small difference must exist between the oxidation potential of the reducing agent and the reduction potential of the oxidation agent. In contrast, here, the criteria for efficient MABLI radical generation were energetic and geometric for both bidentate ligands and metal acetylacetonates. The strength of this approach is to use stable compounds in 2-components free radical initiating systems and to generate carbon centered radicals. Mechanistic investigations demonstrated the formation of new metal adducts by means of high-resolution mass spectroscopy (HR-ESI-MS) as well as UV-vis spectrometry. As a result of its high radical generating rate, the potential of MABLI was illustrated on the methacrylate free radical polymerization under mild conditions (room temperature, in air) and initiated with a small amount of metal acetylacetonate though it opens new perspectives for acac-like additions in organic chemistry

Metal-free generation of phosphorus-centered radicals for the synthesis of phosphorus-based heterocycles: a personal account

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