Mono vs. Difunctional Coumarin as Photoinitiators in Photocomposite Synthesis and 3D Printing

Abstract

This work is devoted to investigate three coumarin derivatives (Coum1, Coum2, and Coum3), proposed as new photoinitiators of polymerization when combined with an additive, i.e., an iodonium salt, and used for the free radical polymerization (FRP) of acrylate monomers under mild irradiation conditions. The different coumarin derivatives can also be employed in three component photoinitiating systems with a Iod/amine (ethyl 4-dimethylaminobenzoate (EDB) or N-phenylglycine (NPG)) couple for FRP upon irradiation with an LED @ 405 nm. These compounds showed excellent photoinitiating abilities, and high polymerization rates and final conversions (FC) were obtained. The originality of this work relies on the comparison of the photoinitiating abilities of monofunctional (Coum1 and Coum2) vs. difunctional (Coum3) compounds. Coum3 is a combined structure of Coum1 and Coum2, leading to a sterically hindered chemical structure with a relatively high molecular weight. As a general rule, a high molecular weight should reduce the migration of initiating molecules and favor photochemical properties such as photobleaching of the final polymer. As attempted, from the efficiency point of view, Coum3 can initiate the FRP, but a low reactivity was observed compared to the monofunctional compound (Coum1 and Coum2). Indeed, to study the photochemical and photophysical properties of these compounds, different parameters were taken into account, e.g., the light absorption and emission properties, steady state photolysis, and fluorescence quenching. To examine these different points, several techniques were used including UV-visible spectroscopy, real-time Fourier Transform Infrared Spectroscopy (RT-FTIR), fluorescence spectroscopy, and cyclic voltammetry. The photochemical mechanism involved in the polymerization process is also detailed. The best coumarins investigated in this work were used for laser writing (3D printing) experiments and also for photocomposite synthesis containing glass fibers.

Recent advances on ferrocene-based photoinitiating systems

“…Over the years, a wide range of families have been designed and synthesized as efficient photoinitiators of polymerization, activable under visible light and even under low light intensity. Among these structures, naphthalimides, [40,[52][53][54][55][56][57][58][59][60][61][62] copper complexes, [63][64][65][66][67][68][69][70][71][72][73] flavones, [20,74] iron complexes, [75][76][77][78][79] iodonium salts, [80][81][82] coumarins, [83][84][85][86][87][88][89], acridine-1,8dione, [90][91] iridium complexes, [92][93][94][95][96][97]…”

3-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

“…In this paper, nine coumarin derivatives (noted Coum in Scheme 1 ) varying by the substitution pattern at the 3- and 7-positions of the coumarin core were synthesized and evaluated as photoinitiators for the FRP of acrylate and methacrylate monomers. In fact, coumarin derivatives have already been tested as photoinitiators of FRP and they have shown good polymerization profile (Rp and FC) as well as good photochemical and photophysical properties [ 15 , 16 , 17 , 18 , 19 ].…”

“…In fact, coumarin derivatives are usually characterized by very high fluorescence emission and can be used as fluorescent chromophores for several applications [ 20 ]. They are also characterized by high molar extinction coefficients in the near-UV and the visible range [ 19 ]. These novel coumarin-based photoinitiators were tested in photopolymerization of acrylate functions (TMPTA or TA) in both Thick (1.4 mm) and Thin sample (25 µm) using two and three-component photoinitiating systems PISs based on Coum/Iodonium salt (0.1%/1% w / w ) and Coum/Iodonium salt/amine (NPG) (0.1%/1%/1% w / w / w ).…”

Efficacy Modeling of New Multi-Functional Benzophenone-Based System for Free-Radical/Cationic Hybrid Photopolymerization Using 405 nm LED

“…As shown by Eqs. (17) to (20), the following significant features of the A/B/E, or BT/Iod/EDB, system are summarized as follows (referred also to Scheme 4 of Liu et al [23]). Our modeling has explored the follow general features, in which some new findings are not yet explored in our previous experiment of Liu et al {23], but might be justified in our future works.…”

“…Organic dyes used as visible light photosensitizers of polymerization have been extensively studied [12,13], in which high extinction coefficients and their long-living excited states, enabling the photosensitizers to react efficiently with various additives in the photocurable resins. For cost effective with long-living excited states, copper complexes have been used as a new polymerization approach enabling the formation of acetylacetonate radicals by redox reaction with a phosphine and to initiate the free radical polymerization (FRP) of acrylates or the free radical promoted cationic polymerization (CP) of epoxides [14][15][16][17]. Recently, Coumarin as dual function of photoinitiators in photo-oxidation or photo-reduction in visible light were reported [18][19][20].…”