Kinetic Studies of Cationic and Hybrid (Cationic/Radical) Photopolymerizations

     Objective: to provide a fundamental characterization of the kinetics of cationic photopolymerizations of epoxide monomers as well as hybrid cationic/radical photopolymerizations of epoxides with acrylate monomers. Research in the past year has focused on characterization of cationic photopolymerizations of epoxides. UV-initiated cationic photopolymerizations have received much less attention than free-radical photopolymerizations even through they offer several advantages since they are not inhibited by oxygen, can exhibit significant post-cure, and may be used to polymerize monomers such as epoxides and vinyl ethers.

Project Focus:

Research in this project has focused on two aspects of cationic polymerizations:

i) Characterization of the general effects of a variety of reaction variables: type and concentration of photoinitiator, type and concentration of photosensitizer, monomer functionality, temperature and initiating light intensity; on the kinetics of the cationic photopolymerizations.

ii) Dark cure studies to characterize the active center lifetime and investigate the effective propagation rate constant in cationic photopolymerizations.

     The work done so far has provided the foundation for the future research, which will focus on hybrid radical/cationic polymerizations of acrylates and epoxides using three component initiators that produce both radicals and cations. These studies will include dark cure studies that can distinguish between the radical and cationic polymerizations due to the large difference in the active center lifetime. Studies will also investigate the effect of oxygen (which will inhibit the radicals but not the cations) and the effect of moisture (which will inhibit the cations but not the radical).