Isothermal cure kinetics of DGEBA epoxy resins initiated by thermal latent cationic curing agents containing hexafluorophosphate

The effect of different cationic curing agents as thermal latent initiators containing hexafluorophosphate (PF₆^-), Le., N-benzylpyrazinium hexafluorophosphate (BPHP) and benzyl 3-cyanopyrazinium hexafluorophosphate (BCHP) on the isothermal cure kinetics of the diglycidylether of bisphenol A (DGEBA) epoxy resin were investigated. Latent properties were investigated by measuring the conversion as a function of cure temperature using dynamic DSC. It was found that the epoxy resin initiated with BCHP results in better latent properties in relatively low temperature ranges. In this work, the isothermal DSC thermograms indicated that the cure reaction rate strongly depended on the cure temperature, and the autocatalytic reaction accelerated by the hydroxyl group produced through the reaction between DGEBA and BPHP (or BCHP). Therefore, the cure reaction rates of DGEBA/BCHP system derived from Kamal-Sourour equation were faster than those of DGEBA/BPHP, and the cure activation energies characterized by Arrhenius reaction equation were relatively lower in the case of DGEBA/BCHP containing CN electron acceptor group. This seems to be a consequence of the enhancing of leaving activity of CN-added pyrazine from benzyl-pyrarazinium salts.