Dark and light reactions in EB cationic polymerization of epoxies

Process variables, such as dose, dose rate, initiator concentration, temperature, time, and impurities, influence the generation of active centers and subsequent polymerization of epoxies induced by electron beam (EB) radiation by cationic mechanisms. Longer exposure to radiation produces higher concentration of active centers that has previously been modeled by a simple first order kinetic model that assumes infinite life for the generated centers. However, it appears that such a model is not suitable for predicting the behavior of interrupted EB exposure experiments. NIR spectroscopy was used to monitor the epoxy concentration throughout the polymerization of glycidyl ethers for experiments in which the EB is turned off before complete conversion is achieved and dark reactions are monitored thereafter. This investigation is based on our continued development of a near infrared (NIR) spectroscopic technique for performing real-time in-situ kinetic measurements of EB induced cationic polymerization of epoxy systems. The results of these experiments indicate that although a portion of active centers possesses long half life, a significant fraction of the active centers is deactivated within a few seconds of interrupting EB exposure.