Synthesis of a novel bis(diphenylphosphinyl)-containing pyromellitimide and its application in epoxy resins

Epoxy resin (EP) is one of the most widely used thermosetting resins. Developing EP with high-comprehensive properties still holds great significance. Thus, a novel bis(diphenylphosphinyl)-containing pyromellitimide (abbreviated as DTPMI) was synthesized as a multi-functional additive for EP. Compared with pure EP, 6 wt.% of DTPMI could increase the limited oxygen index (LOI) value of the EP/6DTPMI from 23.0 % to 28.5 %, with a 30.5 % reduction in the peak heat release rate. The satisfactory flame retardancy for the EP/6DTPMI was attributed to the formation of a thermal oxidation-resistant char layer during the combustion, effectively reducing the material's burning intensity and fire hazard. Surprisingly, the dielectric constant and loss of the EP/6DTPMI could be significantly reduced to 2.69 and 0.0527 at 10 MHz, respectively. Also, its contact angle to water was raised from 63.1° (pure EP) to 92.4°, decreasing the surface moisture absorption of the EP/DTPMI thermosets. Besides, the incorporation of DTPMI hardly deteriorated the thermal and mechanical properties of the EP/DTPMI thermosets. This work provided a feasible approach for fabricating the EP thermosets with high-comprehensive performance, especially for flame retardancy and dielectric performance, and proposed potential application prospects of the EP/DTPMI thermosets.