Gelation of DGEBA epoxy in the presence of a tertiary amine for temperatures above and below the ceiling temperature

The di-epoxy diglycidyl ether of bisphenol A (DGEBA) is reacted with the curative diethanolamine (DEA, HN(CH₂CH₂OH)₂). DEA has a single secondary amine that reacts rapidly with epoxide forming a non-crosslinked adduct in about 30 minutes under normal, 70°C, cure conditions. The subsequent crosslinking (or gelation) reaction is much slower, taking 24 hrs. at 70°C to near completion for the standard DGEBA/DEA mix. Cures at elevated temperature (above ~80°C) display a slowing of the overall rate of reaction in a "ceiling temperature" effect. This results from the complex series of reactions associated with the zwitterion driven addition reaction characteristic of many epoxy/tertiary amine systems. Here we measure the gel point across a wide range of temperature. For the extended tests necessary at low temperatures, a simple bubble viscometer is used, while traditional rheology is employed for high temperature tests.