Real time in-situ spectroscopic characterization of radiation induced cationic polymerization of glycidyl ethers

Radiation curable polymeric materials for composites offer a wide range of advantages over traditional thermally cured systems, including, low energy consumption and reduced manufacturing costs. However, such materials suffer from relatively poor mechanical properties. Moreover, the curing behavior of such systems (i.e. the exact relationship between chemical kinetics and key processing variables) is not fully understood. In order to design improved epoxy based electron beam (EB) curable systems, and in order to develop appropriate process models, a detailed knowledge of the kinetics of epoxy cationic polymerization induced by UV or EB irradiation is required. In this work, we present our development of a technique based on near infrared (NIR) spectroscopy for performing real-time in-situ kinetic analysis of radiation induced cationic polymerization of epoxy systems including phenyl glycidyl ether (PGE) and diglycidyl ether of bisphenol A (DGEBA). To our knowledge this is the first time such data have been collected for EB induced polymerization. A model was developed to describe the intrinsic chemical kinetics and the diffusion limitations for crosslinkable systems and to relate the cure behavior to processing variables. The model is based on intrinsic rate expressions and free volume theory. The modeling results show very good agreement with experimental data. Thus the model provides predictive capability for the dependence of chemical conversion on time, temperature, composition and radiation intensity.