High-temperature polymers are useful for a broad range of applications, especially as composite matrices for high speed aircraft. The aerospace industry requires materials to be lightweight, high glass transition temperatures, high-temperature stability, and good mechanical properties over a wide range of temperatures. A crosslinked fluorinated polyimide and carbon-fiber composite are being investigated for future hypersonic vehicle applications. A weight-loss study was performed on a both materials in an effort to determine the thermal stability properties. The resin and carbon-fiber composite exhibits higher glass transition temperatures (435-455°C) and decomposition temperatures (above 520°C) than current high-temperature polyimide resins and their carbon-fiber composites. Experiments were conducted using a preheated oven and thermogravimetric analysis (TGA) to obtain the weight-loss of each material type. Regardless of method, the resin and composite exhibited excellent thermal stability, less than 1% weight-loss, under 430°C, regardless of exposure time. After 20 minutes of exposure at 510°C, the composite remained relatively stable with only 5.3% weight-loss using the oven technique, while the resin sustained more significant weight-loss of 12.6% using the oven. Another area of interest is synthesizing a high temperature polyimide matrix using tantalum salts and the fluorinated polyimide to form an extremely high melting protective tantalum carbide layer.