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Your search keyword '"Graff, Bernadette"' showing total 356 results
Start Over Author "Graff, Bernadette" Publication Type Academic Journals
356 results on '"Graff, Bernadette"'

19. Low‐Migration Compounds with Amine Functionality as Coinitiators of Radical Polymerization.

Author

Chen, Hong, Schmitt, Michael, Graff, Bernadette, Morlet‐Savary, Fabrice, Hahn, Christoph, Kelch, Hauke, Maletz, Reinhard, Willner, Alexander, and Lalevée, Jacques

Subjects
ELECTRON paramagnetic resonance, AROMATIC amines, MOLECULAR orbitals, DENTAL materials, FREE radicals
Abstract

The utilization of two‐component systems comprising camphorquinone (CQ) and aromatic amines has become prevalent in the photopolymerization. However, there are still concerns about the safety of this CQ/amine system, mainly because of the toxicity associated with the leaching of aromatic amines. In light of these concerns, this study aims to develop novel coinitiator combinations featuring CQ and amines which cannot be leached out of materials, enabling free radical polymerization of representative dentalmethacrylate resins under blue light irradiation. This approach involves the initial design and analysis of hydrogen donors with low C─H bond dissociation energy through molecular modeling. Subsequently, copolymerizable methacrylate functional groups are incorporated via chemical modification, allowing it to act as both coinitiator and copolymerization monomer to achieve low migrationand leachability properties. This work presents, for the first time, the synthesis of the innovative coinitiator and compares its performance with the benchmark CQ/ethyl‐4‐dimethylaminobenzoate (EDB)‐based photoinitiation system (PIS). The results demonstrate the effectiveness of the newly proposed PIS. Finally, an in‐depth investigation is conducted into the reaction mechanism associated with this PIS through molecular orbital calculations and electron spin resonance studies. [ABSTRACT FROM AUTHOR]

Published
2024
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29. Bio-based captodative ligands for redox polymerization of Elium® thermoplastic composites under mild conditions.

Author

Giacoletto, Nicolas, Le Dot, Marie, Cherif, Hizia, Morlet-Savary, Fabrice, Graff, Bernadette, Monnier, Valérie, Gigmes, Didier, Dumur, Frédéric, Olleik, Hamza, Maresca, Marc, Gerard, Pierre, Nechab, Malek, and Lalevée, Jacques

Subjects
THERMOPLASTIC composites, LIGAND exchange reactions, REDOX polymers, POLYMERIZATION, LIGANDS (Chemistry), OXIDATION-reduction reaction, REDUCTION potential
Abstract

Thermoplastic polymers obtained from resins such as Elium® combine desirable properties, including recyclability/reusability and excellent thermomechanical performances, at a relatively affordable cost. Nevertheless, their polymerization often requires a high amount of energy and/or involves hazardous chemical compounds. To address this last point, a series of bio-based captodative ligands was designed and synthesized in order to replace controversial phosphine oxides commonly used in low-energy initiating systems but suffering from toxicity issues. By using these captodative ligands, the curing time required for the polymerization of Elium® could be reduced from more than one hour to a mere 10 minutes. To gain a deeper insight into the redox mechanism involved during the polymerization process, the redox properties of a series of manganese(III) complexes containing different captodative ligands have been investigated employing cyclic voltammetry. It has been demonstrated that ligand exchange reactions induced by using the captodative (or push–pull) ligands possessing both electron-donating and electron-withdrawing groups had a significant impact on the reduction potential of the manganese(III) complexes. The reduction potential significantly changed depending on the type of heteroatom atom (X = O, S) and substituent included in the scaffold of the captodative ligands. [ABSTRACT FROM AUTHOR]

Published
2023
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40. Carbazole-fused coumarin based oxime esters (OXEs): efficient photoinitiators for sunlight driven free radical photopolymerization.

Author

Zhang, Yijun, Liu, Zheng, Borjigin, Timur, Graff, Bernadette, Morlet-Savary, Fabrice, Schmitt, Michael, Gigmes, Didier, Dumur, Frédéric, and Lalevée, Jacques

Subjects
COUMARINS, CARBAZOLE, FREE radicals, PHOTOPOLYMERIZATION, ELECTRON paramagnetic resonance, FOURIER transform infrared spectroscopy, SUNSHINE
Abstract

The use of sunlight to initiate free radical polymerization under air is a key challenge. Due to the associated low light intensity, usual or commercial photoinitiators are characterized by a low efficiency. In this work, seventeen carbazole-fused coumarin-based oxime esters were developed as monocomponent and photocleavable (Type I) initiators of polymerization displaying excellent light absorption properties in the visible range. Compared to the benchmark photoinitiator (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide), some of them (namely OXE-1 and OXE-5) could show photoinitiation performance similar to or better than the reference compound upon irradiation with a LED at 405 nm. The photoinitiation mechanism of these photoinitiators is proposed, supported by theoretical calculations; the detection of CO2 during photopolymerization was performed by means of Fourier transform infrared spectroscopy and the detection of radical species was performed by electron spin resonance analysis. Through direct laser writing, different objects exhibiting an excellent spatial resolution could be obtained. Parallel to the photoinitiating ability, the different photoinitiators also showed a thermal initiation behavior, meaning that these structures can serve both as thermal and photo-initiators on demand. Due to the high sensitivity of these structures to sunlight, OXE-1 and OXE-5 were also investigated as solar photoinitiators (reactive also in Central Europe during winter) and excellent monomer conversions could be obtained within one hour using a multifunctional acrylate monomer (Ebecryl 605). To the best of our knowledge, these two oxime esters constitute the first examples of sunlight activable oxime esters ever reported in the literature. [ABSTRACT FROM AUTHOR]

Published
2023
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41. Photoinitiation Mechanisms of Novel Phenothiazine‐Based Oxime and Oxime Esters Acting as Visible Light Sensitive Type I and Multicomponent Photoinitiators.

Author

Noon, Adel, Hammoud, Fatima, Graff, Bernadette, Hamieh, Tayssir, Toufaily, Joumana, Morlet‐Savary, Fabrice, Schmitt, Michael, Bui, Thanh‐Tuan, Rico, Alexandre, Goubard, Fabrice, Péralta, Sébastien, Dumur, Frédéric, and Lalevée, Jacques

Subjects
POLYMER networks, ELECTRON paramagnetic resonance spectroscopy, VISIBLE spectra, LIGHT emitting diodes, FOURIER transform infrared spectroscopy, ADDITION polymerization, ESTERS
Abstract

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]

Published
2023
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47. Dual photo/thermal initiation with charge transfer complexes based on bromide‐based electron acceptors.

Author

Ma, Qiang, Zhang, Xiaoxiang, Liu, Yiwu, Graff, Bernadette, and Lalevee, Jacques

Subjects
ELECTRON donor-acceptor complexes, ELECTROPHILES, POLYMERIZATION, VISIBLE spectra, THREE-dimensional printing, ACRYLATES
Abstract

Different combinations of donors and acceptors of charge transfer complexes (CTCs) can realize visible light catalysis in multiple wavelength bands. Here, we successfully demonstrated that 2‐bromoacetophenone as an electron acceptor, combined with amines (for formation of CTC), can achieve photopolymerization under LED@405 nm visible light irradiation, initiating the polymerization of (meth)acrylates, and the induction time can be completely eliminated by condition optimization. The CTC was also shown to have dual photo/thermal initiation capability and was eventually applied to 3D printing as well. [ABSTRACT FROM AUTHOR]

Published
2023
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