Real‐time monitoring of the cure reaction of a TGDDM/DDS epoxy resin using fiber optic FT‐IR

The feasibility of using remote FT‐IR spectroscopy to monitor the gelation reaction of an epoxy resin used in advanced composite materials has been studied. The commercial epoxy resins MY720 and MY721, consisting mostly of tetraglycidyl 4,4′‐diaminodiphenyl methane (TGDDM) were cured with diaminodiphenylsulfone (DDS) in a microcapillary cell connected to an FT‐IR spectrometer by single silica fiber optics. By operating in the near‐IR, direct measurement of the consumption of epoxide and primary amine and growth in hydroxyl groups was possible. It was found that the primary amine band at 5067 cm−1 was the most sensitive for rapid and accurate real‐time monitoring of the cure reaction up to gelation. The temperature dependence of amine consumption from 135 to 180°C gave an activation energy of 70 kJ mol−1 for the cure reaction in agreement with DSC. Several artefacts involved in using fiber optic FT‐IR in this way have been identified.