In-silico based development of photoinitiators for 3D printing and composites: Search on the coumarin scaffold

Abstract

In this work, the in-silico rational design of new photoinitiators by molecular modeling for specific wavelength (here 405 nm) and specific applications (3D printing, composites) is reported. A large number of (keto)coumarin derivatives were investigated by molecular modeling and their synthesis and more detailed photochemical investigations are based on obtaining structures having both excellent predicted light absorption properties @405 nm and high excited state energy levels (to ensure high photochemical reactivity). More particularly, four new families of coumarins were designed (4 of the 19 proposed coumarins were never synthesized (N2,M6,T1,T6)): the first family is based on Nitrocoumarins (N1-N6), the second one on Methoxybenzene-based coumarins and Ethoxycoumarins (M1-M6), the third one on Thiophene-based coumarins (T1-T6) and the last family studied concerns Alkyne-based coumarin (A1). The purpose of this work concerns the study of the photoinitiating ability of these compounds in different monomers for different polymerization processes (free radical, cationic) using FTIR technique. The different compounds reported in this work are very efficient to initiate the free radical polymerization of (meth)acrylates but also the cationic polymerization of epoxides upon mild irradiation conditions using a Light Emitting Diode (LED) at 405 nm as visible light source. Nitrocoumarins were identified as the best candidates for photoinitiation among the different families of coumarins investigated in this work. More precisely, nitrocoumarins are characterized by very good polymerization profiles, great final reactive function conversions (FC) and also high rates of polymerization (Rp). The electrochemical and photochemical properties of the different compounds were also studied to get a deeper insight into the photochemical mechanisms supporting the initiation process. A full picture of the involved photochemical mechanisms is provided. Thanks to the astounding polymerization initiating ability of these coumarins, their use in 3D printing applications can be worthwhile. Remarkably, using these compounds, the preparation of photocomposites was possible even in difficult light penetration conditions resulting from the presence of fibers inside the resins.