Electron-beam (e-beam) and ultraviolet (UV)-induced cationic polymerization of diglycidyl ether of bisphenol A (DGEBA) using the photo-initiator diaryliodonium hexafluoroantimonate was investigated using in situ NIR spectroscopy. The effect of processing parameters, such as temperature, radiation intensity, and photo-initiator concentration, on kinetics of the reaction were determined quantitatively. In contrast to the behavior of monofunctional epoxy systems reported previously, the difunctional epoxy forms a high T-g crosslinked network, so a kinetic model that takes into account diffusion limitations associated with vitrification was developed. The combined benefits of the real-time in situ NIR spectroscopy study and the well-defined diffusion model resulted in very accurate predictions for cure of epoxy networks by e-beam-induced polymerization. The results support the view that e-beam processing of epoxies is constrained by vitrification in the same way that UV and thermally cured epoxies are. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013