Effects of Temperature and U.V. Light Intensity on Acrylate/Epoxide Hybrid Photopolymerization Using Raman Spectroscopy

Two typical reaction mechanisms of photopolymerization include free-radical and cationic polymerizations which are plagued by oxygen inhibition and moisture sensitivity, respectively. Hybrid free-radical/cationic photopolymerizations can potentially offer lower sensitivity to atmosphere, less shrinkage, and better adhesion and flexibility, although little is known about the interaction between the two reactions. We used real-time, in-situ Raman spectroscopy to study a hybrid monomer, 3,4-epoxy-cyclohexyl-methyl methacrylate, where the acrylate and epoxide groups undergo free-radical and cationic photopolymerization, respectively. The effects of initiation UV light intensity and temperature on the following three systems were studied: free-radical initiator, cationic initiator, and dual-initiator. As expected, we found that as the light intensity or temperature increased, the reaction rates and the ultimate conversions also increased. Furthermore, the cationic polymerization reaction in the hybrid polymer was inhibited by the fast reaction rate and cross-linking resulting from the free-radical reaction. This gives insight into what the kinetics of this complicated hybrid system could be by using Raman spectroscopy to resolve both of the reactions temporally in real-time. The reactions have also been monitored spatially by others in our lab. Further investigations include studying the effects of other hybrid acrylate/epoxide monomers, hybrid monomer mixtures, and different photoinitiators for the systems.