Study On Preparation And Polymerization Technique For Poly{2,6-dimidazo[4,5-b:4’,5’-e]pridinylene-1,4(2,5-dihydroxy)phenylene}

Each of the general high performance fibers has its own deficiency, such as low end-use temperature, poor flame and light resistance, adhesion, storage stability, and resistance to compression, which thus limit their applications. PIPD almost overcome these deficiencies, and its performance of resistance to compression and shear resistance is superior to other high performance fibers, besides, it has excellent adhesive properties, good thermal, flame and electrical resistance. It is aimed to attain PIPD fiber with high molecular and excellent porperties.Compound salt of2,3,5,6-tereaaminopyridine-2,5-dihydroxy phthalate (TD salt) was synthesized with2,3,5,6-tetraaminopyridine (TAP) hydrochloride monomer and2,5-dihydroxy terephthalic acid (DHTA) monomer as raw materials through acid-base neutralization reaction under anaerobic condition. High molecular weight PIPD fiber was polymerized using TD salt by condensation polymerization method. Infrared spectroscopy (IR), nuclear magnetic resonance (NMR), mass spectrometer (MS), differential scanning calorimeter (DSC) and so on were used to determine the structure and purity and study porperties of TD salt. Relative viscosity of PIPD was detected to estimate molecular weight of PIPD.In this paper, optimal conditions for condensation polymerization were ascertained with univariate analysis. Relative viscosity of PIPD was used to discriminate whether the result was good or not. Optimal conditions are that rate of flow of N2to protect active groups is0.3L/min; polymer concentration is about15to17percent by weight; the polyphosphoric acid equivalent P2O5content of81percent after polymerization; the amount of tin powder is about1%by weight; final temperature in polymeraztion raction is about180℃.Model compounds were synthesized to explore mechanism of cyclization of heterocyclic ring. Model Compound Ⅰ was synthesized through condensation reaction with2,3-diaminopyridine and o-hydroxybenzoic acid. Model Compound Ⅱ was synthesized with O-hydroxybenzoic acid and2,3,5,6-tetraaminopyridine. Model Compound Ⅲ was synthesized with2,5-dihydroxy benzoic acid and2,3-diaminopyridine. NMR, IR, MS were used to determine structures of model compounds and intermediate of Model Compound Ⅰ. Mechanism of cyclization of heterocyclic ring was put forward to referred to mechanism of Poly{benzo[1,2-d:5,4-d’]bisoxazole-2,6-diyl-1,4-phenylene}(PBO) and polybenzimidazoles (PBI).