Preparation And Properties Of PIPD

Poly{2,6-dimidazo[4,5-b:4’,5’-e]pyridinylene-1,4(2,5-dihydroxy)Phenylene}(PIPD) fiber, as a new aromatic heterocyclic polymer, contains polar groups, as well as a three-dimensional network hydrogen bond structure between intermolecular. Thus it shows excellent anti-compression and adhesive properties, making it an a new generation of fiber with excellent combined performances.In this paper, we successfully synthesized two necessary PIPD monomers 2,5-Dihydroxyterephthalic acid and 2,3,5,6-tetraaminopyridine hydrochloride salt combined with the following purification and characterization. Then we prepared PIPD fibers by simple dry jet wet spinning and systematic studied properties of the fibers, which lay the foundation for industrial production as well as its’ wide applications.(1) Based on a route that is easily been industrialized, concentrated sulfuric acid and fuming nitric acid were used to nitrify 2,6-diaminopyridine. 1H NMR and FTIR spectra of the resulting 2,6-diamino-3,5-dinitropyridine(DADNP) proved successful synthesis of final product with high purity. DADNP was reduced to get 2,3,5,6-aminopyridine hydrochloride by metal reduction method, and then recrystallized. Test results of 1H NMR and IR spectroscopy were in good agreement with the desired product. For succinylsuccinate dimethyl, aromatization approach was used to synthesize 2,5-Dihydroxyterephthalic acid(DHTA), then purified and characterized by 1H NMR and Fourier transform infrared spectroscopy. The results of DHTA proved desired product was successful synthesized with high purity.(2) Two-step polymerization, that is TD salt method, was used and made the polymerization time reduced to 4h. PIPD polymer was got with intrinsic viscosity at 19.87 dl / g, then using a liquid crystal spinning called dry-jet wet spinning to spin it, eventually PIPD fibers with metallic luster was got. IR, Raman characterization was used to verify the product structure. Surface morphology was conducted by scanning electron microscopy. PIPD fiber diameter is about 20μm and the surface is rather smooth. In addition, two-dimensional wide-angle X-ray diffraction were tested to see orientation of crystalline region of PIPD fiber and test showed its’ orientation was up to 95.8%. Mechanical test of PIPD fibers shows the average tensile strength can be achieved 4GPa with elongation at break at 2.4%, meaning a more excellent performance. TG test was carried on under a nitrogen atmosphere and the results proved that obtained PIPD exhibited better thermal stability. After dynamic thermogravimetric test, the thermal decomposition activation energy of PIPD fiber was calculated about 109.5 KJ / mol.(3) By direct spreading method, the phosphoric acid doped PIPD proton exchange membrane was prepared, and then we characterized and discussed its’ proton conductivity, oxidation resistance and mechanical properties. Besides, its application as a high temperature proton exchange membrane was also explored.