Characterization of the Electron Beam Curing of Cationic Polymerization of Diglycidylether of Bisphenol A Epoxy Resin

Abstract

The characterization of electron beam (E-beam) curing of diglycidyl-ether of bisphenol A-diaryliodonium hexafluoroantimonate epoxy resin-initiator system is reported as a function of (i) diaryliodonium hexafluoroantimonate catalyst (initiator) concentrations of 0.1-10 parts per hundred (phr) and (ii) total electron beam doses of 5-150 kilogray (kGy). The in situ E-beam temperature of the resin is monitored as a function of dose-time characteristics. The degree of cure is monitored after radiation exposure by Fourier transform infrared spectrometry (FTIR) and the glass transition temperatures (Tg) by differential scanning calorimetry (DSC). The degree of cure and cure rate increased with total dose exposure and initiator concentration. The maximum cure rate occurred at 5 kGy exposure and, thereafter, decreased as reactive species concentration decreased. The maximum in situ E-beam temperature of 76°C was recorded for the resin containing 10 phr of initiator, with a maximum degree of cure of 94% and a glass transition temperature of 86 C, indicating that the cure reactions under E-beam are glassy state diffusion controlled. The resin glass transition temperatures are considerably lower than the thermally cured glass transition temperatures of 170 C because of H2O termination reactions at the lower E-beam cure temperatures that result in a poor cross-linked network. In addition, the diaryliodonium hexafluoroantimonate catalytic activity for epoxide cationic polymerization is retarded by H2O. E-beam exposure causes the diaryliodonium hexafluoroantimonate to dissociate into active catalytic species, such as HSbF6, well below 100°C compared to catalytic thermal induced dissociation near 200°C. The E-beam cure reaction rate is modeled as a function of degree of cure and dose exposure by a standard autocatalytic kinetic model.