Effects of Epoxy Resin/Curing Agent System on Thermal Stability and Electrical Properties of Insulating Materials

The development of epoxy resins with excellent heat resistance and high insulation properties is crucial for applications in extreme environments such as high-end electrical equipment, new energy vehicles, and aerospace. This study selected bisphenol A-type epoxy resin E51 and phenolic epoxy resin F51, and tetrafunctional epoxy resin AG80 as the matrix, and combined them with aromatic amine curing agent diaminodiphenyl sulphone (DDS) and acid anhydride curing agent methyl hexahydrophthalic anhydride (MHHPA). Six crosslinked epoxy copolymers were prepared through pairwise matching to investigate the influence of molecular chain structure on thermal stability and insulation properties. The results showed that the AG80/DDS system formed a high-density rigid crosslinked network due to its tetrafunctional crosslinking sites and the high bond energy of the DDS sulfonyl group. The copolymer exhibits excellent thermal stability, with a glass transition temperature (Tg) of 215 °C, 85 °C higher than that of commercial E51/MHHPA. Additionally, the AG80/DDS copolymer combines excellent volume resistivity (2.56 × 1014 Ω·m) with high-temperature dielectric strength (breakdown field strength of 69.52MV/m at 200 °C).