Fire- and heat-resistant matrix resins based on ethynyl-substituted aromatic cyclotriphosphazenes

A novel class of fire- and heat-resistant matrix resins has been synthesized by thermal polymerization of ethynyl-substituted aromatic cyclotriphosphazenes. Thermal polymerization of new tris[4-(4′-ethynylbenzanilido)phenoxy]tris(phenoxy) cyclotriphosphazene ( III ) and tris[4-(4′-ethynylphthalimido)phenoxy]tris(phenoxy)cyclotriphosphazene ( VII ) at 250°C for 1–1.5 h gave tough polymers. The thermal stabilities of the polymers were evaluated in nitrogen and in air by thermogravimetric analysis (TGA). The synthesised polymers were stable to 400–410°C and showed char yield of 78–65% at 800°C in nitrogen and of 78–69% at 700°C in air. The ethynyl-substituted polymer precursor ( III ) was synthesised by the reaction of tris(4-aminophenoxy)tris(phenoxy)cyclotriphosphazene ( I ) with 4-ethynylbenzoyl chloride. The polymer precursor ( VII ) was synthesised by a solution condensation of I with 4-ethynylphthalic anhydride followed by in situ thermal cyclodehydration at 150°C. The structure of polymer precursors was characterized using proton nuclear magnetic resonance (¹H-NMR), infrared (IR) spectroscopy, and elemental analysis. The curing of polymer precursors was monitored by differential scanning calorimetery (DSC) and IR spectroscopy. The synthesised matrix resins are potential candidates for the development of heat- and fire-resistant fiber-reinforced composites. © 1993 John Wiley & Sons, Inc.