Di-imidazole cored epoxy thermosets: effect of amine curatives on curing behaviour, cure kinetics, thermal stability and intrinsic flame retardancy

In this work, a novel di-imidazole cored epoxy resin (DIBP-EP) was synthesized and cured with structurally diverse amine curatives,in order to study their influence on curing behavior, thermal stability, and flame retardancy. The curing behavior of DIBP-EP studied using differential scanning calorimetry (DSC), inferred that the curing temperature strongly depends on the nucleophilicity and electronic nature of the amine curatives. The peak curing temperatures were observed in the range of 110-175 °C, with 4,4’-diamino diphenylmethane(DDM)showing the lowest curing temperature of 110 °C.Cure kinetics were analyzed using non-isothermal DSC at different heating rates, and activation energy values of 50–54 kJ mol−1 and 74–77 kJ mol−1 were obtained using Kissinger and Ozawa methods for the systems DIBP-EP/DDM and DIBP-EP/DICY respectively, indicating favorable curing reactivity.Thermogravimetric analysis (TGA) demonstrated enhanced thermal stability, with the values of residual char yields ranging from 30.5% to 47.5%. Flame retardancy evaluation using UL-94 vertical burning tests showed that all the DIBP-EP thermosets achieved V-0 rating with limiting oxygen index (LOI) values in the range of 29–35. These results demonstrate that the presence of a di-imidazole core structure in the DIBP-EP facilitates improved thermal stability and intrinsic flame-retardant behavior suitable for advanced engineering applications.