One-Component Cationic Photoinitiators from Tunable Benzylidene Scaffolds for 3D Printing Applications

Abstract

This paper describes a series of novel benzylidene scaffold-based iodonium salt one-component photoinitiators containing double bonds and dialkylamino groups synthesized in one step via classical aldol condensation reactions. Systematic investigations of structure–activity relationships were performed via quantum-chemical calculations and experimental tests. New salts can efficiently decompose under irradiation from UV to visible regions of the spectrum. The design of new iodonium salts is described, followed by a description of properties of photoinitiators prepared in this way. All presented salts were characterized in terms of their spectral properties (UV–vis spectroscopy), ability to photodecompose (steady-state photolysis), cationic polymerization of the vinyl monomer, and epoxide monomer photoinitiation (quantum efficiency of acid generation and real-time Fourier-transform infrared measurements) as well as their proposed application in 3D printing. New benzylidene iodonium salts can photoinitiate the polymerization of vinyl ethers and epoxy monomers under LED@365 and LED@405 irradiation. Investigated compounds can simultaneously initiate and monitor the polymerization process according to the change of fluorescence during the photocuring process. Formulations before photopolymerization do not exhibit fluorescence, during the photopolymerization process fluorescence is “turning on”. This phenomenon might be used to monitor photopolymerization in an “online” manner.

Symmetric Iodonium Salts Based on Benzylidene as One-Component Photoinitiators for Applications in 3D Printing

“…Asymmetrical iodonium salts based on the benyzlidene scaffold have been described in detail previously. 44 Synthetic pathways that lead to the presented chromophores and iodonium salts as well as NMR and liquid chromatography−mass spectrometry (LC−MS) structural analyses results are presented in the Supporting Information. All reagents and solvents used during synthesis were purchased from Sigma-Aldrich, Alfa Aesar, Acros Organics, and Fluorochem and used without further purification.…”

“…The quantum efficiency of acid generation measurements were conducted as reported previously. 44 Polychromatic UV-LED M340L4 (intensity I 0 = 53 mW•cm −2 ; Thorlabs Inc.) was used as the light source. The LED was powered by a DC2200 regulated power supply (Thorlabs Inc.).…”

“…These values are similar to those obtained for asymmetrical salts. 44 In the case of α-modified derivatives, ϕ acid decreases as the BDE and strength of electron-accepting properties of the substituents decrease. This effect is observed for α-CN-PI-s and α-COOMe-PI-s (1.34 and 1.07%, respectively).…”

“…In a recent study, we proposed new chromospheres based on the benzylidene scaffold . This type of compound has a simple structure that is easy to modify also due to the simplicity of the synthesis .…”

Recent progress in the development of highly active dyeing photoinitiators based on 1,3-bis(p-substituted phenylamino)squaraines for radical polymerization of acrylates

“…1 There are many benefits of this technique, called briefly the "5E" principles and including the features: economy, efficiency, enabling, energy saving and being environmentally friendly. 2,3 The light-mediated polymerization reactions are commonly used in the production of protective and decorative coatings, such as lacquers and paints, 4,5 inks, 6 adhesives, [7][8][9] hydrogels, [10][11][12] and dental composites, 13,14 as well as in 3D printing, [15][16][17][18][19] and many others. However, it should be mentioned that the scope of application of photopolymerization is constantly expanding and continues to surprise.…”