Application of Bio-Based Epoxy Monomers in Both Cationic and Thiol-Epoxy Photopolymerization Processes

In this work, bisphenol A diglycidyl ether (BADGE) and four bio-based epoxy monomers were used to investigate the kinetics of cationic photopolymerization of epoxy monomers and anionic photopolymerization of thiol-epoxy reaction. The real-time Fourier transform infrared spectroscopy results showed that the cationic photopolymerization process was more efficient for the two bio-based epoxy monomers derived from sorbitol and glycerol compared to BADGE, which is considered a petro-based epoxy monomer. Considering the anionic photopolymerization process, in 25 µm thin samples this process was more efficient in the presence of BADGE, whereas in 1.8 mm thick samples, the formulations accomplished complete epoxy function conversions and tack-free surface. On the other hand, the two bio-based epoxy monomers derived from vegetable oils exhibited very low reactivity in acid-catalyzed homopolymerization and using thiols as hardeners. The high efficiency of the photobase-generating system, capable of releasing strong base active species under the irradiation conditions used in this study was demonstrated using phenol red and UV–vis absorption spectra. Furthermore, the polymerization mechanism governing the thiol-epoxy reactions was outlined thoroughly. Finally, the thermo-mechanical properties of the polymers obtained from the thiol-epoxy reactions were analyzed using differential scanning calorimetry, dynamic mechanical analysis, and surface hardness tests, which revealed interesting properties for the polymers containing bio-based epoxy monomers derived from polyols.