| In this research, the differences in thermal, mechanical, surface, flammability, and degradation properties of three different, closely related, polyimide foams (namely TEEK-H, TEEK-L and TEEK-C) were comparatively studied. Foams have much higher surface areas than solid polymers and are a greater challenge to fire retard. Because of the intrinsic flame retardancy of aromatic polyimides, one has the ability to investigate the effects of changes in density, surface area, and chemical structure on flame retardancy properties, physical and mechanical properties, and foam degradation that have not been previously reported. Understanding degradation and properties as a function of whether the polymer is porous or nonporous is of significant interest. Data indicate that subtle differences in chemical structure result in large differences in surface area, which further result in large differences in heat release and other flammability properties as observed in radiant panel and cone calorimetry data.; Thermal stability and degradation studies indicate that the diamine rather than the dianhydride is the greater contributing factor to the thermal stability of polyimide foams. The degradation mechanisms follow that reported previously in the literature for polyimide films. X-ray photoelectron spectroscopy (XPS) analyses of oxygen-plasma-exposed samples indicate an overall oxidation of the foams and that the degradation mechanism follows that of thermal degradation. The mass loss data after oxygen plasma exposure indicate that chemical structure followed by density play the greatest role in atomic oxygen resistance. A unique weathering study of the polyimide foams gave further insight into the relationship of chemistry, density, and surface area effects. XPS, Infrared and Raman spectroscopies, plus thermogravimetric and thermomechanical analyses, confirm that unlike the thermal and oxygen plasma exposures, the carbonyl linkage in the dianhydride of the TEEK-L series has a greater effect than density during weathering on the stability of the polymer.; The TEEK-H series has better tensile and weathering performance. The TEEK-L series has better compression and Oxygen Index and Glow Wire performance. The TEEK-C series, because of the stabilizing SO2 of the diamine linkage, has better thermal and oxygen plasma performance; however, fire performance is overridden to a large extent by the effect of surface area. |
