Bis‐, tris‐, and tetrakis‐maleimidophenoxy‐triphenoxycyclotriphosphazene resins for fire‐ and heat‐resistant applications

Novel fire‐ and heat‐resistant polymers was obtained by the thermal polymerization of various maleimidophenoxy‐triphenoxycyclotriphosphazenes. These polymers, in which the cyclic triphosphazene structure is preserved, have thermal stability to 350°C and char yields of 82–78% at 800°C in nitrogen and 78–71% at 700°C in air. Two groups of monomers were synthesized by reacting tris(4‐aminophenoxy)‐tris(phenoxy)cyclotriphosphazene with maleic anhydride alone or in combination with benzophenonetetracarboxylic or pyromellitic dianhydride. The structures of cyclic phosphazene‐trimeric precursors and the polymers were characterized by Fourier‐transform infrared, proton nuclear magnetic resonance, and elemental analysis. The thermal stabilities of the polymers were evaluated by thermogravimetric analysis.