Cure and reaction kinetics of an anhydride-cured epoxy resin catalyzed by N-benzylpyrazinium salts using near-infrared spectroscopy

The cure behavior and the reaction kinetics of an anhydride-cured epoxy resin catalyzed by cationic thermal latent initiator, N-benzylpyrazinium salts, have been investigated by a near-infrared (NIR) spectroscopy. The spectral changes are interpreted in terms of the mechanism of cure. NIR absorption bands are due to protons connected to carbon, nitrogen, and oxygen. In this work, the homogeneous model system involves a simple addition reaction mechanism leading to an exothermic reaction between epoxide and anhydride activated groups. A comprehensive account of the origin, location, and shifts during reaction of all major NIR absorption peaks in the spectral range from 4000 to 7100 cm(-1) is provided. The extent of reaction is calculated from NIR absorption band at 4530 cm(-1), which depends on epoxide concentration. The utility of NIR spectroscopy to study the kinetics of epoxy cure reaction has been established. Consequently, absorbencies iri the NIR spectra suitable for quantitative studies of epoxy resin reaction kinetics have been identified.