High-temperature polymers are being used for a broad range of applications, such as composite matrices for structural applications (e.g., high speed aircraft). Polyimides are a special class of polymers that meet the thermal and oxidative stability requirements for high temperature composite aerospace applications. A weight loss study was performed on a fluorinated polyimide resin and its carbon fiber composite in an effort to determine its thermal stability and degradation mechanisms. Experiments were conducted using a preheated oven and thermogravimetric analysis to obtain the weight loss. Regardless of the method used, the resin and composite exhibited excellent thermal stability (less than 1% weight loss) below 430 C, regardless of 2-20 min of exposure. After 20 min of exposure at 510 C, the composite remained relatively stable with only 5.3% weight loss using the oven technique, whereas the neat polyimide sustained 12.6%. When degradation occurred, it was found to be the result of thermolysis and oxidation (to a lesser extent).

Refractory transition metal carbides were produced via carbothermal reduction of transition metal halides in a polymer precursor at low temperatures (<1200°C). This approach was used to generate TaC (Tm=3883°C), NbC (Tm=3610°C), and WC (Tm=2870°C) from TaBr5, NbBr5, and WCl4/WCl6, respectively. Solubility of transition metal halides and polymers in the same organic solvents allows for intimate mixing on the molecular level, which reduces the synthesis temperature. Greater than 90% TaC conversion was achieved by exposing a 50:50 weight ratio mixture of TaBr5 and polyimide (or polystyrene) to 1200°C for 1 h. Even at temperatures as low as 1000°C, the major product remains TaC. The ability to process these high‐temperature materials so simply, and at relatively low temperatures, makes them accessible for different applications requiring thermal protection such as coatings for metallic components of hypersonic aircraft, rocket engine components, fibers, or refractory containers.

A blistering study was performed on a fluorinated polyimide resin and its carbon-fiber composite in an effort to determine the blister-formation temperature and the influence of blisters on composite performance. The fluorinated resin and carbon-fiber composite exhibit higher glass-transition (435-4558C) and decomposition temperatures (above 5208C) than similar polyimide resins and their carbon-fiber composites currently used. Two techniques were used to determine moisture-induced blister formation. A transverse extensometer with quartz lamps as a heating source measured thickness expansion, as did a thermomechanical analyzer as a function of temperature. Both methods successfully measured the onset of blister formation with varying amounts of absorbed moisture (up to 3 wt%) in the samples. The polyimide resin exhibited blister temperatures ranging from 225 to 3628C, with 1.7-3.0 wt% absorbed moisture, and the polyimide composite had blister temperatures from 246 to 2948C with 0.5-1.5 wt% moisture. The blistering effects of the polyimide composites were found to have little correlation with modulus. POLYM. COMPOS., 32:185-192, 2011. ª