Cure of epoxy resins with aromatic amines: High heat‐distortion studies

Castings having unexpectedly high heat‐distortion temperatures result when certain treated resins of the EPON EPON is a registered trademark of the Shell Oil Company. 828 type and about 75% of the stoichiometric amount of m ‐phenylenediamine, are postcured for 10–20 hr. at 175–200°C. The improvement in heat‐distortion temperature is about 100°C., to values as high as 250°C. A recrystallized resin has given the highest values. Other glycidyl ethers of polyphenols have shown this phenomenon to a lesser degree, but other amine curing agents, including isomers and substitution products of m ‐phenylenediamine, have not. Some evidence of a new curing reaction has been developed, by NMR and pyrolysis studies of model compounds, which supports the postulate that the m ‐phenylenediamine is alkylated with a fifth epoxy group during the postcure, presumably at a ring carbon, resulting in greater crosslinking.