Abstract
Abstract : The most significant accomplishments were determining the conditions for preparing microcellular structural foams from high-temperature polymers of interest to the US Air Force. The primary system was rodlike polybenzobisthiazole blended with poly(etherketoneketone) with 5% rod content. This gave microcellular foams with densities about 0.92 g/cc, and a yield strength about 9.4 ksi. A modified foaming technique gave foams with high porosity, a density of 0.65 g/cc, and pore sizes from 10 to 40 micrometers. Also, some sulfonated poly(p-phenylenebenzobismidazole)/poly(2-vinylpyidine) molecular composites gave foams of uniform microstructures and a cell size less than 10 micrometers, but with some brittleness. Molecular composites based on polysulfone (PSF) and polybenzimidazole (PBI) were also successfully prepared. PSF and PBI are immiscible, but introduction of functional groups into the PSF or PBI resulted in miscible polymer blends. Very homogeneous microcellular foams were obtained from them, and their thermal behavior and mechanical properties were encouraging.
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