Non-destructive visual inspection of photocurable coatings based on fluorescent response of naked-eye visible colorimetric and fluorescent sensors

Abstract

• Terphenyl-based fluorescent sensors for monitoring photopolymerization processes are reported. • Colourimetric sensors for the investigation of cationic photopolymerization of epoxy monomer and vinyl monomer are developed. • Bimolecular photoinitiating systems have been successfully applied to 3D printing. • The changes in fluorescence colour before and after photopolymerization are possible using only the human naked-eye. Five novel 4,6-diphenyl-2-pyrrol-1-yl-benzene-1,3-dicarbonitrile derivatives bearing the following substituents: -H, -SCH3, –OCH3, –CN, -NPh2 were synthesized and investigated as fluorescent sensors for photopolymerization processes. It was turned out, that using these compounds provide a visible and direct strategy to monitor the photopolymerization process due to the change in fluorescence color during the photo-crosslinking process. Studied colorimetric sensors were investigated during free-radical and cationic photopolymerization as well as for the production of photocurable coatings. Furthermore, 4,6-diphenyl-2-pyrrol-1-yl-benzene-1,3-dicarbonitrile derivatives are also excellent candidates for photosensitizers of iodonium salt for photopolymerization processes, and thus they can play a double role, as a component of the photoinitiating system and sensor. Free radical of an acrylate monomer and cationic photopolymerization of vinyl and epoxy monomers was performed in the presence of two-component photoinitiating systems. Fluorescence spectroscopy was used to monitor fluorescence spectra changes during photopolymerization, what is more, it was also possible to direct observation fluorescence color changes by the naked human eye. Fourier transform infrared spectroscopy was applied for the determination of final conversion values after photopolymerization processes.