Two-Step Curing Reaction of Epoxy Resin Studied by Thermal Analysis and Infrared Spectroscopy

Abstract

A curing reaction of bisphenol A diglycidyl ether epoxy resin with 4,4'-diaminodicyclohexyl methane hardener was investigated by means of modulated differential scanning calorimetry (MDSC) and infrared (IR) spectroscopy. MDSC observation revealed that the curing process of the resin occurred in two steps. Mid-infrared and near-infrared spectra of the resin were measured as a function of temperature. The obtained spectra were analyzed by perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D-COS). The first step was revealed as a polymerization reaction among the oxirane group and primary and secondary amine groups, followed by etherification; the second step of the curing process occurred in the vicinity of the gelation point and was characterized by the growth of a three-dimensional cross-linking structure with tertiary amine and etherification of the hydroxyl group.