Imidazole substituted benzothiadiazole derivatives as latent curing agent for epoxy thermosetting resin

Abstract As an important thermosetting resin, epoxy resin (EP) is widely used in the field of composite materials. Long storage time, rapid curing and low viscosity of one‐component EP is ideal for preparing composite materials by vacuum assisted resin transfer molding (VARTM). For this sake, we developed and synthesized a new imidazole thermal latent curing agent, 4,7‐diimidazol‐2,1,3‐benzothiadiazole (BTD‐MZ 2 ) with a yield of about 75%. The curing behavior, thermal stability and storage time of the prepared EP system was studied by differential scanning calorimeter (DSC), thermal gravimetric analyzer (TGA), modular compact rheometer (MCR), respectively. DSC results showed that EP/17.5 wt% BTD‐MZ 2 had a good latent period at low temperature, and can rapidly cure EP when heated to 150°C. TGA results show that BTD‐MZ 2 promoted the formation of carbon residue and the residual carbon rate of EP/17.5 wt% BTD‐MZ 2 is as high as 37.9%. MCR results show that the storage time of EP/17.5 wt% BTD‐MZ 2 at 60°C can reach 850 min. In addition, it could play a role of catalyst used as co‐curing agents with aromatic amines for EP. DSC test showed that the addition of 5 wt% BTD‐MZ 2 reduced the activation energy of EP/4,4′‐diaminodiphenylmethane (DDM) and promoted the curing reaction.