Article
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-Carboxylic Acid and Formyl-Derived Coumarins as
Photoinitiators in Photo-Oxidation or Photo-Reduction
Processes for Photopolymerization upon Visible Light:
Photocomposite Synthesis and 3D Printing Applications
Mahmoud Rahal 1 , Bernadette Graff 1,2, Joumana Toufaily 3 , Tayssir Hamieh 3,4 , Guillaume Noirbent 5
,2,3
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5,
1,2,
Didier Gigmes , Frédéric Dumur * and Jacques Lalevée
*
1
Université de Haute-Alsace, CNRS, IS2M UMR 7361, F-68100 Mulhouse, France;
mahmoud-rahal@outlook.com (M.R.); bernadette.graff@uha.fr (B.G.)
Université de Strasbourg, 67081 Strasbourg, France
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3
Laboratory of Materials, Catalysis, Environment and Analytical Methods (MCEMA) and LEADDER
Laboratory, Faculty of Sciences, Doctoral School of Sciences and Technology (EDST), Lebanese University,
Beirut 6573-14, Lebanon; joumana.toufaily@ul.edu.lb (J.T.); tayssir.hamieh@ul.edu.lb (T.H.)
SATIE-IFSTTAR, Université Gustave Eiffel, Campus de Marne-La-Vallée, 25, allée des Marronniers,
F-78000 Versailles, France
Aix Marseille Univ, CNRS, ICR UMR 7273, F-13397 Marseille, France; guillaume.noirbent@outlook.fr (G.N.);
didier.gigmes@univ-amu.fr (D.G.)
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5
*
Correspondence: frederic.dumur@univ-amu.fr (F.D.); jacques.lalevee@uha.fr (J.L.)
Citation: Rahal, M.; Graff, B.;
Toufaily, J.; Hamieh, T.; Noirbent, G.;
Gigmes, D.; Dumur, F.; Lalevée, J.
Abstract: 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 pho-
topolymerization (FRP) of meth(acrylate) functions under visible light irradiation using LED at
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-Carboxylic Acid and
Formyl-Derived Coumarins as
405 nm. In fact, these compounds showed a very high initiation capacity and very good poly-
Photoinitiators in Photo-Oxidation or
Photo-Reduction Processes for
merization 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
Photopolymerization upon Visible
Light: Photocomposite Synthesis and
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Academic Editor: Maria João Matos
2
glass fiber or carbon fiber using an LED conveyor at 385 nm (0.7 W/cm ) was also examined.
Received: 22 February 2021
Accepted: 18 March 2021
Published: 21 March 2021
Keywords: coumarin; free radical polymerization; LED; photocomposites; direct laser write
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. Introduction
The development of new low-cost, environmentally friendly, and energy-efficient
polymer synthesis remains more than ever at the heart of academic and industrial concerns
and the subject of many new research strategies. In fact, thanks to technological develop-
ment, light sources which are at the same time inexpensive, efficient, and with low energy
consumption have been developed recently to induce photopolymerization reactions [
Nowadays, photopolymers are present in several fields such as coatings [ ], dentistry [
automotive [ ], cosmetics [ ], 3D printing, and holography [
industrial fields, photochemical polymerization uses ultraviolet radiation, a technique
widely known as UV curing. However, this pathway based on UV lamps (Hg lamps)
remains energy-consuming. Moreover, the ultraviolet light is harmful to human health
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Licensee MDPI, Basel, Switzerland.
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conditions of the Creative Commons
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], etc. For most of these
(carcinogenic) and characterized by particularly low light penetration, which is a challenge
for the photopolymerization of thick and filled samples [10]. Therefore, alternatives to
UV lamps and the use of longer wavelengths (near UV or visible) can be advantageous.
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