Mohamad-Ali Tehfe
Centre national de la recherche scientifique
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Publication
Featured researches published by Mohamad-Ali Tehfe.
Chemistry: A European Journal | 2011
Jacques Lalevée; Mathieu Peter; Frédéric Dumur; Didier Gigmes; Nicolas Blanchard; Mohamad-Ali Tehfe; Fabrice Morlet-Savary; Jean Pierre Fouassier
Iridium(III) complexes were designed and evaluated as efficient photoinitiators of polymerization reactions in combination with iodonium salts and silanes. Mechanistically, these reactions were shown to proceed through oxidative photoredox catalysis, generating aryl and silyl radicals under very soft irradiation conditions (blue LED, xenon lamp, and even sunlight). These radicals can initiate the free radical polymerization of acrylates or can be oxidized during the catalytic cycle to promote the ring-opening polymerization of epoxy monomers. Remarkably, both the (photo)chemical reactivity and the practical efficiency are dramatically affected by the ligands. In addition, the central role played by the oxidation ability of the excited state of the photocatalyst is discussed.
Polymer Chemistry | 2011
Jacques Lalevée; Nicolas Blanchard; Mohamad-Ali Tehfe; Mathieu Peter; Fabrice Morlet-Savary; Didier Gigmes; Jean Pierre Fouassier
A new concept based on the photoredox catalysis is proposed for the design of a photoinitiating system able to efficiently generate, in a single catalytic cycle, both a radical and a cation as initiating species. This is exemplified here by the tris(1,10-phenanthroline)ruthenium(II) (Ru(phen)32+) complex in combination with a diphenyl iodonium salt and a silane. Interesting and promising photopolymerization profiles in free radical photopolymerization (FRP) and free radical promoted cationic photopolymerization (FRPCP) are obtained under air and upon xenon lamp exposure and even soft irradiation conditions (fluorescence bulb, sunlight). An acrylate/epoxide blend is also easily polymerized under air using a fluorescent bulb. The mechanisms are investigated by ESR and Laser Flash Photolysis experiments.
Macromolecular Rapid Communications | 2011
Jacques Lalevée; Nicolas Blanchard; Mohamad-Ali Tehfe; Mathieu Peter; Fabrice Morlet-Savary; Jean Pierre Fouassier
The use of a photocatalyst (tris(2-phenylpyridine)iridium [Ir(ppy)(3)]) being able to generate both radicals and cations to initiate free radical polymerization and ring opening polymerization is presented. Remarkably, under soft irradiations (fluorescence bulb, sunlight), excellent cationic polymerization profiles and final conversions are obtained. The involved mechanisms are investigated by ESR experiments.
Polymer Chemistry | 2013
Pu Xiao; Frédéric Dumur; Michel Frigoli; Mohamad-Ali Tehfe; Bernadette Graff; Jean Pierre Fouassier; Didier Gigmes; Jacques Lalevée
The abilities of two naphthalimide derivatives with a methacryloyl group to initiate, when incorporated in multi-component systems, a ring-opening polymerization of epoxides and a radical polymerization of acrylates under different irradiation sources (e.g. very soft halogen lamp irradiation, laser diode at 457 nm, laser diode at 405 nm and blue LED bulb at 462 nm) have been investigated. One of them is particularly efficient for the cationic and radical photopolymerization of an epoxide/acrylate blend in a one-step hybrid cure and leads to the formation of an interpenetrated polymer network IPN (30 s for getting tack free coatings). The migration stability of one of these naphthalimide derivatives is found to be excellent in the cured polyacrylates and IPNs. The photochemical mechanisms are studied by steady state photolysis, fluorescence, cyclic voltammetry, electron spin resonance spin trapping and laser flash photolysis techniques.
Macromolecular Rapid Communications | 2013
Jacques Lalevée; Mohamad-Ali Tehfe; Frédéric Dumur; Didier Gigmes; Bernadette Graff; Fabrice Morlet-Savary; Jean-Pierre Fouassier
Two new photoinitiators with unprecedented light absorption properties are proposed on the basis of a suitable truxene skeleton where several UV photoinitiators PI units such as benzophenone and thioxanthone are introduced at the periphery and whose molecular orbitals MO can be coupled with those of the PI units: a red-shifted absorption and a strong increase of the molecular extinction coefficients (by a ≈ 20-1000 fold factor) are found. These compounds are highly efficient light-harvesting photoinitiators. The scope and practicality of these photoinitiators of polymerization can be dramatically expanded, that is, both radical and cationic polymerization processes are accessible upon very soft irradiation conditions (halogen lamp, LED…︁) thanks to the unique light absorption properties of the new proposed structures.
Polymer Chemistry | 2011
Mohamad-Ali Tehfe; Julien Monot; Malika Makhlouf Brahmi; Hélène Bonin‐Dubarle; Dennis P. Curran; Max Malacria; Louis Fensterbank; Emmanuel Lacôte; Jacques Lalevée; Jean-Pierre Fouassier
Eight N-heterocyclic carbene-boranes (NHC-boranes) are proposed as new efficient co-initiators for acrylate photopolymerization reactions. They are particularly interesting in aerated conditions, where they help overcome the classical oxygen inhibition. The carbene boryl radicals that are the initiating species have been characterized by their transient absorption spectra obtained in laser flash photolysis (LFP) experiments. Rate constants for the generation of the carbene boryl radicals by hydrogen abstraction with t-butoxyl radical and triplet benzophenone as well as the reactions with oxygen, electron rich and electron poor alkenes, two alkyl halides (CHCl3 and iodopropane) and diphenyliodonium hexafluorophosphate have been measured. The reactivity of N-heterocyclic carbene borane radicals is clearly affected by the NHC substituent.
Chemistry: A European Journal | 2010
Jacques Lalevée; Nicolas Blanchard; Mohamad-Ali Tehfe; Anne-Caroline Chany; Jean-Pierre Fouassier
Recently, boryl radicals have been the subject of revived interest. These structures were generated by hydrogen-abstraction reactions from the corresponding boranes (i.e., from amine or phosphine boranes). However, the classical issue remains their high B--H bond-dissociation energy (BDE), thereby preventing a very efficient hydrogen-abstraction process. In the present paper, new N-heteroaryl boranes that exhibiting low B--H BDE are presented; excellent hydrogen-transfer properties have been found. Both the generation and the reactivity of the associated boryl radicals have been investigated through their direct observation in laser flash photolysis. The boryl radical interactions with double bonds, oxygen, oxidizing agent, and alkyl halides have been studied. Some selected applications of N-heteroaryl boryl radicals as new polymerization-initiating structures are proposed to evidence their high intrinsic reactivity.
Polymer Chemistry | 2014
Mohamad-Ali Tehfe; Frédéric Dumur; Pu Xiao; Marie Delgove; Bernadette Graff; Jean-Pierre Fouassier; Didier Gigmes; Jacques Lalevée
Chalcone derivatives are proposed as novel photoinitiators for polymerization upon exposure to visible light (even under soft irradiation conditions: blue LED bulb at 462 nm, halogen lamp, and sunlight). Remarkably, these structures are highly versatile allowing access to photoinitiating systems for (i) the free radical polymerization of acrylates, (ii) the cationic polymerization of epoxides and vinyl ethers, (iii) the synthesis of interpenetrated polymer networks (IPNs) and (iv) the thiol–ene processes. Excellent polymerization profiles are obtained. The initiation mechanisms are analyzed through ESR, steady state photolysis, cyclic voltammetry, laser flash photolysis and fluorescence experiments.
Polymer Chemistry | 2013
Mohamad-Ali Tehfe; Frédéric Dumur; Bernadette Graff; Fabrice Morlet-Savary; Didier Gigmes; Jean-Pierre Fouassier; Jacques Lalevée
A series of new dyes based on (thio)barbituric acid derivatives were synthesized and used as photoinitiators of polymerization upon very soft irradiation (laser diodes at 457 nm and 473 nm; blue LED bulbs or even a halogen lamp). These dyes can work according to an oxidative cycle (dye/diphenyl iodonium salt/N-vinylcarbazole system) or a reductive cycle (dye/amine/alkyl halide system) and partly behave as organic photocatalysts. Ring-opening polymerization (ROP) of epoxides and radical polymerization (RP) of acrylates are easily promoted. Excellent RP and/or ROP polymerization profiles are obtained. The contrasting behavior of the thiobarbituric vs. barbituric acid derivative is discussed. The initiation mechanisms, analyzed by Electron Spin Resonance (ESR) and steady state photolysis experiments, are detailed.
Polymer Chemistry | 2013
Mohamad-Ali Tehfe; Frédéric Dumur; Emmanuel Contal; Bernadette Graff; Fabrice Morlet-Savary; Didier Gigmes; Jean-Pierre Fouassier; Jacques Lalevée
New aromatic derivatives PyD based on a pyrene moiety are proposed here as new photoinitiators (PIs) in multi-component systems (with an iodonium salt, a sulfonium salt and optionally a silane) for the radical polymerization of acrylates and the cationic polymerization of epoxy, epoxy-silicone and vinyl ethers. These new photoinitiators allow the use of a long wavelength excitation (using visible light delivered by a halogen lamp, a laser diode at 457 nm or a Xe–Hg lamp). Excellent polymerization profiles are obtained. For polymerization processes using pyrene, very low conversions are reached in agreement with the lack of absorption of this compound for λ > 380 nm i.e.PyDs are attractive compounds for visible light. Acrylate–epoxide, acrylate–vinyl ether and vinyl ether–epoxide blends are also easily polymerized i.e. for the synthesis of interpenetrating or crosslinked polymer networks. The initiation step mechanisms analyzed by ESR, fluorescence, steady state photolysis and laser flash photolysis experiments are discussed.