Time-temperature-transformation (TTT) diagram of dual-curable epoxy thermosets obtained via two sequential epoxy-amine condensations

A simple and robust strategy to generate time-temperature-transformation (TTT) diagrams for dual-curable thermosets is presented. TTT diagram is built for a dual-curable amine-epoxy formulation. Both curing stages are epoxy-amine polycondensations. Whereas the first stage is carried out at relatively low temperature using a strongly nucleophilic aliphatic amine, the second is carried out at high temperature with a weakly nucleophilic aromatic amine. The good separation between curing stages enabled the individual kinetics analysis of each stage by integral isoconversional procedures. Gelation was determined by thermomechanical analysis; the glass transition temperature - conversion relationship was determined by calorimetry and was used to draw the vitrification line. Gelation and vitrification lines were checked by means of solubility tests and temperature modulated calorimetry. The results presented in the form of a TTT diagram showed the disparate reactivity of both curing stages and a substantial storage stability at the intermediate curing stage. These materials show great potential in applications where processing flexibility and intermediate stability are crucial.