Hydrolytically stable phosphorus-containing monomers, such as 4,4'-bis(fluoro-pheny1)methylphosphine oxide (BFPMPO), 4,4'-bis(hydroxyphe1nyl)methylphosphine oxide (BOHPMPO), and 4,4-bis(hydroxyphenyl)phenylpliosphine oxide (BOHPPO), were synthesized and used in nucleophilic aromatic Substitution polycondensation to prepare poly(ary1ene ether phosphine oxide) engineering thermoplastics. The synthesis and characterization of these novel polymers are described. It was determined that by incorporating the phosphine oxide moiety into the polymer backbone, certain properties of the resulting poly(ary1ene ether) were substantially improved, such as an increase in Tg, thermal stability in air, modulus, and char yield compared with control poly(ary1ene ether su1fone)s. The :high char yields obtained for these polymers in air along with observed intumescence indicates that these materials have improved fire resistance. Preliminary cone calorimetry measurements support this conclusion.

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This investigation explored the feasibility of recently developed toughened cyanate ester networks as candidate materials for high performance composite matrix applications. The resin investigated was a bisphenol‐A cyanate ester toughened with hydroxy functionalized phenolphthalein based amorphous poly(arylene ether sulfone). A series of four toughened cyanate ester resins were generated by varying the concentration and the molecular weight of the toughener. The thermoplastic modified toughened networks exhibited improvement in the fracture toughness over the base cyanate ester networks without significant reductions in mechanical properties or glass transition temperature. Carbon fabric composite panels were manufactured by liquid molding processes (resin transfer molding and resin film infusion) with the untoughened and toughened cyanate ester resin systems. The panels were subjected to physical, impact damage, and fracture toughness tests. The results of physical testing indicate consistently uniform quality, and the maximum void content was found to be less than 2%. The toughened cyanate ester composites exhibited significantly improved impact damage resistance and tolerance compared with hot‐melt epoxy systems. A marked increase in the mode II composite fracture toughness was observed with an increase in the concentration and the molecular weight of the toughener.