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Nanocrystalline niobium carbide (NbC) ceramics and niobium carbide-niobium nitride (NbC/NbN) composites were synthesized at low temperatures without high-pressure sintering using a single-step polymer-derived approach from a meltable pre-ceramic blend. Niobium hydride (NbH5) and 1,2,4,5-tetrakis(phenylethynyl)benzene (TPEB) reacted at 1500 °C under argon or nitrogen in a tube furnace to form NbC or NbC/NbN with high purities and nanosized grains. Superconductivity measurements indicated that NbC/NbN ceramics exhibited a mixed phase system with two distinct Tc values, and higher elemental niobium content within solids yielded lower Tc. The resulting ceramic monoliths exhibited homogeneous morphologies and controllable amounts of free carbon in the composite matrix. Niobium carbide and nitride composites demonstrated good air oxidation stability up to 450 °C.

A versatile scheme to produce a multiple aromatic ether-linked phthalonitrile has been developed and applied to the preparation of two unique resin systems. The oligomeric phthalonitrile monomer was prepared from the reaction of an excess amount of bisphenol A or bisphenol A6F with 1,3-dibromobenzene in the presence of K 2 CO 3 as the base in a N,N-dimethylformamide/toluene solvent mixture, followed by end-capping with 4-nitrophthalonitrile in a two-step, one-pot reaction. Both phthalonitrile resin systems exhibited excellent viscosities for molding various shaped articles and were thermally cured to yield crosslinked polymers. Each bisphenol-based polymer also demonstrated superb mechanical properties and thermo-oxidative stability while absorbing less than 1% percent water by weight. The two systems differed greatly in their relative reactivity toward the curing additive bis(4-[3-aminophenoxy]phenyl)-sulfone ( m -BAPS). The presence of the electron withdrawing CF 3 groups on the bisphenol A6F resulted in a faster curing reaction to the thermoset polymer but weaker mechanical properties and less overall thermal stability relative to the bisphenol A-containing resin. The bisphenol A6F polymer showed a lower overall water absorption but exhibited a comparable dielectric constant relative to the bisphenol A polymer.

A method to improve the mechanical properties of phthalonitrile (PN) resins at lower postcure temperatures is achieved by blending a second-generation oligomeric aromatic ether ketone-based PN resin with 1,1,1-tris-[4-(3,4-dicyanophenoxy)phenyl]ethane in varying concentrations. Most of the mixtures exhibit a single softening temperature indicating that the two resins are miscibile in one another at the respective concentrations. After various blends are thermally cured to several postcure temperatures yielding crosslinked polymers, the polymers demonstrate superb mechanical properties and thermooxidative stability at lower overall postcure temperatures.