| Hybrid photopolymerization systems, which show less shrinkage, lower atmospheric sensitivity, and improved adhesion and flexibility than traditional systems, combine more than one curing mechanism and functional group. Fundamental research on their reaction mechanisms, resulting polymer properties, and applications is needed. This project focused on the hybrid monomer 3,4-epoxy-cyclohexyl-methyl methacrylate (METHB) bearing epoxide and methacrylate functionalties that undergo cationic and free-radical photopolymerization, respectively. The research aimed to characterize reaction mechanism and to correlate processing variables, chemical formulation, and chemical composition and physical properties of the resulting photopolymer using real-time Raman spectroscopy, Raman confocal microscopy, and physical property tests. The effects of temperature, light intensity, photoinitiator system, oxygen inhibition, and water concentration were studied.; By choosing among free-radical only, cationic only, and dual-initiator systems, homopolymer chains or cross-linked networks can be produced. In general, the methacrylate polymerization rate and conversion are higher than for the epoxide. Compared to the conversion in single-initiator systems, dual-initiator systems resulted in lower conversions of both functionalities.{09}Increasing temperature and light intensity increased reaction rate and ultimate conversion of all systems.{09}The synergistic effect between the two photoinitiators may accelerate acrylate and epoxide reactions.; The conversion depth profile and physical properties of the resulting coatings both depend on the initiation systems when oxygen inhibition and high water concentrations are present. Dual-initiator system resulted in narrower oxygen-diffusion affected regions, lower oxygen sensitivity, and better surface properties. Water concentration greatly impacted the epoxide ring-opening polymerization. Compared to the cationic-initiator only system, the dual-initiator system showed less sensitivity to water by diminishing the induction period for the epoxide reaction and by improving the surface hardness. The epoxide reactions continued in the dark and resulted in an increased and more homogeneous final conversion.; Finally, 3.4-epoxy-cyclohexyl-methyl acrylate and glycidyl methacrylate were also studied. The conversion profiles were obtained using different initiation systems, and their reactivities were compared with METHB.; The ultimate goal of this project is to better understand hybrid monomer photopolymerization systems and facilitate their applications. Future studies of kinetic modeling, monomer mixture hybrid system, and Raman confocal microscopic applications are suggested. |
