New route to poly (2,6-diimidaazo(4,5-b: 4',5'-e) pyridinelene-1,4(2,5-dihydroxy)-phenylene) (PIPD) and high modulus fiber on it basis

A novel entry toward poly(2,6-diimidazo(4,5-b: 4',5'-e) pyridinylene-1,4(2,5-dihydroxy)-phenylene) (PIPD) has been elaborated. A strategy based on a new route to monomers: a sequential nitration of 2,6-diaminopyridine with KNO$_{3}$/H$_{2}$SO$_{4}$ gives 2,6-diamino-3,5-dinitro pyridine (DNDAP) in moderate yield and its hydrogenation with Raney nickel as catalyst leads to 2,3,5,6-tetraaminopyridine (TAP) in high yield. The second monomer 2,5-dihydroxyterephthalate (DHTA) was synthesized in high yield as product of sulfurmediated aromatization of dimethyl succinoyl succinate with subsequent base hydrolysis. PIPD was synthesized by step-by-step heating in polyphosphoric acid with molecular weights of 19 – 25 kilodaltons. The macromolecule of PIPD can be seen as lap-join chain form nanosized rigid fragment. The as-polymerized liquid crystalline PIPD solution was used for fiber spinning. The tensile strength of PIPD fibers were 1.28 – 1.99 GPa and depended on the molecular weight of the polymer used for spinning.