Multifunctional Epoxy Resin with Flame Retardancy and Thermal Stability Driven by the Rigid Multiarm Structure

Epoxy resin has excellent adhesion, mechanical strength, and chemical stability but poor high-temperature stability, which limits its application in some fields such as aerospace and electronic packaging. An epoxy monomer, 2,4,6-tri-(4-(ethylene oxide-2-methoxy)phenyl)-1,3,5-triazine (TOYPT), with a multiarm rigid structure was designed and successfully synthesized for achieving excellent thermal stability and flame-retardant performance. The weight loss of TOYPT was only 30 wt % at 450 °C, much less than 80 wt % of bisphenol A-type diglycidyl ether (DGEBA). The temperature of maximum thermal weight loss rate was as high as 500 °C due to the rigid multiaromatic rings, triazine ring, and the high cross-link density. Moreover, TOYPT/(4,4-diaminodiphenyl sulfone) DDS had low reaction energy barrier and high curing rate with the apparent activation energy of 67.54 kJ/mol and the pre-exponential factor (A) of 4.276 × 106 s–1. Importantly, the TOYPT/DDS sample had excellent flame retardancy with the UL-94 grade of V-0, the limiting oxygen index of 23.0%, and the total heat release of only 39.93 MJ/m2, because of the high carbonization performance of aromatic rings and gas-phase flame-retardancy effect of triazine rings. In addition, the TOYPT/phenol-formaldehyde resin (PF)/Filler composites exhibited a high shear strength (6.06 MPa) and an excellent flame retardancy [heat release rate of 86.8 ± 6.2 kW/m2]. As a result, this work presented a strategy to enhance the flame retardancy and thermal stability of epoxy resins.