Synthesis of a Novel Schiff Base‐Phosphazene Flame Retardant and Application in a Dicyclopentadiene‐Phenol Epoxy Resin

ABSTRACT A novel high‐melting‐point (212.15°C) Schiff base phosphazene flame retardant, hexa(p‐methylphenyl Schiff base phenoxy)cyclotriphosphazene (HASCP), was successfully synthesized through a two‐step process with a 91% yield. HASCP exhibited excellent thermal stability with a 60.5% char yield at 800°C. Incorporation of HASCP significantly enhanced the flame retardancy of epoxy resin (EP), increasing the limiting oxygen index from 21.19% to 28.13% and achieving a UL‐94 V‐0 rating at loadings of 5–6.25 wt%. The peak heat release rate and total smoke production decreased by 21.2% and 30.5%, respectively. HASCP dispersed uniformly in the EP matrix, improving mechanical strength and preventing additive migration. The EP/HASCP‐5 composite exhibited a 28.9% increase in tensile strength. Furthermore, HASCP reduces the dielectric constant and dielectric loss factor (D _k = 3.06, D _f = 0.0202 at 10 GHz). This study provides an effective strategy for developing high‐performance flame‐retardant epoxy resins that integrate good flame retardancy, excellent mechanical properties, and low dielectric characteristics.