AbstractMid‐ and near‐infrared (IR) spectroscopy has been used to study the curing of a bisphenol‐A based epoxy resin (EPON‐828) with a tetrafunctional curing agent, viz., meta‐phenylenediamine (MPDA). Three different cure cycles were used in the study. Primary amine functionality was observed to react relatively rapidly; none remained after curing for 2 h at 75°C. Secondary amine functionality was exhausted in epoxy rich samples subjected to the standard cure cycle (2 h at 75°C followed by 2 h at 125°C). In samples with stoichiometric amount or higher MPDA, complete reaction of secondary amine or epoxy groups was not observed. In amine‐rich samples subjected to post curing (6 h at 175°C), evidence was seen for the reaction of hydroxyl and epoxy groups, resulting in a considerable increase in the crosslink density o
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