Synthesis of a silicon‐containing cyclotriphosphazene derivative for flame‐retardant modification of epoxy resin

Although epoxy resin (EP) has been widely used in many fields, it is still urgent to effectively improve its flame retardancy by halogen‐free strategies. Herein, a silicon‐containing cyclotriphosphazene derivative (HEP‐Si) was synthesized by nucleophilic substitution and silicon–hydrogen addition reaction using eugenol, hexachlorophosphazene and triethylsilane as raw materials. Then it served as a halogen‐free flame retardant for an EP/4,4′‐diaminodiphenylmethane system, and its performance was compared with that of commercial flame retardant hexaphenoxycyclotriphosphazene (HPP). The results showed that although the initial thermal decomposition temperature (T5%) of the cured products of EP/HEP‐Si was slightly lower than that of pure EP, T5% did not decrease further as the amount of HEP‐Si increased, indicating that good thermal stability was maintained. In addition, the char yield of the cured products of EP/HEP‐Si was significantly increased (more than 20 wt%) compared to that of pure EP. The cured EP with the addition of HPP and HEP‐Si both achieved a V‐0 rating in UL‐94 vertical burning test at 0.5 wt% phosphorus content, while the limiting oxygen index of the EP/HEP‐Si system was higher, reaching 33.2%. From cone calorimetric test results, the peak heat release rate, total heat release and total smoke production of the cured products of EP/HEP‐Si decreased by 61.5%, 37.1% and 26.2%, respectively, compared with that of pure EP. The cured EP/HEP‐Si materials also exhibited good thermomechanical and mechanical properties. Therefore, HEP‐Si is suggested to be a promising P/N/Si‐containing halogen‐free flame retardant for EP. © 2024 Society of Industrial Chemistry. This paper describes a novel silicon‐containing cyclotriphosphonitrile derivative for enhancing the flame retardancy of epoxy resins. The results show that the silicon‐containing cyclotriphosphonitrile derivative enhances the flame retardancy of epoxy resin and can be used in the field of electronic packaging materials.