Improving the Heat Resistance and Flame Retardancy of Epoxy Resin Composites by Novel Multifunctional Cyclophosphazene Derivatives

A novel multiple-ring molecule containing P and N, called HCCP-SA, was successfully prepared by the nucleophilic substitution reaction of salicylamide (SA) and hexachlorocyclotriphosphazene (HCCP). Particularly, HCCP-SA possessed the dual functions of heat resistance and flame retardancy. The molecular structure of HCCP-SA was identified by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. HCCP-SA was bonded into the molecular chain of epoxy resin by the ring-opening curing reaction of epoxy resin, aiming to form a heat-resistant and flame-retardant composite (E-HS-x). In particular, the best-prepared E-HS-x composite with a 20 phr content of HCCP-SA (E-HS-20) presented excellent thermal stability, with an initial decomposition temperature of 267.94 °C and a max weight loss speed of only 0.95 mg·min−1. Moreover, E-HS-20 exhibited remarkable flame retardancy with a limiting oxygen index value of 27.1% and a V-2 rating in the UL94 flame retardancy test. The best-prepared E-HS-20 composite would be a suitable and potential candidate for heat-resistant and flame-retardant polymer materials.