Primary aliphatic amines react with the epoxide ring at room temperature. For aromatic amines, however, a far higher temperature is needed, in some cases up to 200 ‘C. Secondary amine structures will normally be formed which can agian be reacted with the epoxide ring, thereby producing a tertiary amine compound between two epoxy resin molecules.
Here, the reactivity of the resultant hydroxyl groups with epoxide rings is limited in the presence of the secondary amine. The tertiary amines, incidentally, are too much sterically hindered to act as catalyst for this type of reaction. Since all primary amines can be regarded as bifunctional with respect to epoxy resins, relatively highly crosslinked resins will be produced with primary diamines.
One can assume that this tendency would be much more pronounced with relatively low molecular weight epoxy resins. In order to climinate toxicity risks it is advisable to either use, instead of amines, adducts with low-molecular weight epoxy resins whilst maintaining full amino-functionality, or reactive polymers formed from dimerised fatty acids and diamines.