Glassy network epoxies have widespread applications as matrices for advanced composites As an alternative to thermal curing, electron beam (ebeam) processing has been demonstrated as a very powerful tool for achieving fast and efficient curing [1,2]. E-beam curing of epoxy based resins using suitable onium salts as initiators proceeds via a cationic mechanism. The final polymer network properties are highly dependent on processing conditions and curing kinetics. It was demonstrated that under certain processing conditions, heterogeneities can appear in the material, due to the agglomeration of initiator residue. Initially the initiator is miscible with the resin; however, reaction-induced phase separation occurs as the increasing molecular weight of the polymer reduces the solubility of the initiator.