Synthesis of a tris(DOPO-grafted piperazine)-triazine phosphoramide and its application as a highly efficient flame retardant for epoxy resins

A tris(DOPO-grafted piperazine)-triazine phosphoramide (DOPO-TPT) was synthesized, and its structure was well characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. DOPO-TPT was used as a flame retardant additive to modify the epoxy resin to obtain a series of flame retardant epoxy thermosets. The effects of DOPO-TPT on the thermomechanical properties, thermal stability and flame retardancy of the resulting epoxy thermosets were investigated. The results showed that when the addition of DOPO-TPT was 5 mass% (phosphorus content was 0.47 mass%), the limiting oxygen index of the epoxy thermoset reached 30.0%, and it passed the UL-94 V-0 classification. Compared with unmodified epoxy resin, the maximum heat release rate and total heat release of EP/DOPO-TPT-5.0 decreased by 28% and 20%, respectively. Additionally, the presence of DOPO-TPT did not deteriorate the thermomechanical properties of the resulting epoxy thermosets. TG-FTIR test confirmed that the incorporation of DOPO-TPT could significantly inhibit the release of gaseous products. The char layer analysis results showed that DOPO-TPT had good catalytic charring performance, which was conducive to decreasing the escape of combustible gas during combustion, thus improving the flame retardancy.