Reactions at the interphase between an isocyanate and epoxy resins — infrared spectroscopic investigations

The formation of an interphase between an epoxy resin and an urethane is shown. The interphase is formed by the reaction of isocyanate groups with the hydroxyl groups of the already cured epoxy resin. The network density of the epoxy resin was controlled by the functionality of the curing agent. The examination of the interphase is carried out by photoacoustic IR-spectroscopy and the analysis of cross sections by IR-microscopy. It is shown, that the depth of interpenetration is controlled by the crosslinking density of the epoxy resin. Furthermore the depth of interpenetration is reduced, if additional hydroxyl groups are present in the epoxy resin.