Mid‐ 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 of these samples.
Infrared spectra of several 1,3-dicarbonyl compounds from different organic chemical clauses have been recorded. Assignments of characteristic enol frequencies have been made, and group frequency ranges developed. In most cases, the ranges are reasonably narrow considering the great changes in overall structure of the examples studied. The enol structure affects to a significant degree the absorption frequencies of certain modes.
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