Abstract
Highly crystalline polyimide powders were prepared from diluted solutions of polyamic acid in N-methyl-2-pyrrolidone (NMP) which were cured at 200°C for 4 hr with a high heating rate. The chemical structures of the repetitive units were chosen to obtain rigid polymeric backbones precluding any solubility in polar aprotic solvents. Therefore the starting polyamic acids were produced by polycondensation from an equimolar ratio of the following pairs of monomers: pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA); 3,3′,4,4′-biphenyl tetracarboxylic dianhydride and ODA; PMDA and p-phenylenediamine. After optimizing the reaction conditions, the resulting powders were first characterized by scanning electronic microscopy and granulometric analysis. Well-divided particles with a spherulitic shape and average particle size of 5 μm were observed. The X-ray diffraction patterns and the solid-state 13C nuclear magnetic resonance spectra together revealed a highly organized structure. The degree of imidization of the powder is nearly complete as demonstrated by Fourier transform infrared analysis and the inherent viscosity after dissolution in concentrated sulfuric acid is about 0.8 dl/g. © 1998 John Wiley & Sons, Ltd.
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