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Polybenzimidazole (PBI) is a resistance to acid, alkali and high temperature resistant aromatic heterocyclic polymer, is widely used in flame retardant materials, high-temperature resins, adhesives, foams, etc.. In recent years, the acid doped PBI membrane can be used as a low-cost, high-performance fuel cell proton exchange membrane, this fuel cell can be stable under the conditions of 120 ° C, greatly improving battery performance. However, the intrinsic viscosity of the commercialization of PBI is only 0.9 dL / g, the lower the tensile strength and modulus, limiting its application in the fuel cell. PBI has low solubility in conventional organic solvents, resulting in the PBI molding processing is very difficult, especially high molecular weight PBI. In view of the above problems, we prepared solution polycondensation method of poly [2,2 '- (m-butylphenyl) -5,5' - biphenyl-imidazole] (mPBI) and its derivatives, poly (2,5 - benzo imidazole) (ABPBI), reaction temperature, monomer purity and reaction time on the polymer molecular weight, viscosity measurement and FT-IR, 1 H-NMR and TGA its structure and properties were characterized. The mPBI dissolution behavior in different ionic liquids based on research to explore the mechanism of mPBI dissolved in the ionic liquid, and prepared the alkaline ionic liquids (BMIMOH) doped mPBI film, and AC impedance test its conductive properties. Through the above research work, we get the following conclusions: (1) through the optimization of reaction conditions, can be obtained the higher the molecular weight mPBI and ABPBI. Isophthalic acid (IPA) and 3,3 ', 4,4' - diaminobenzidine (TAB) monomer polycondensation system of polyphosphoric acid (PPA) was passed through the solution, 140 ° C pre-reaction of the 3 hours, 200 ℃ for 20 hours, to prepared an intrinsic viscosity of 1.12 dL / g mPBI; while using purified monomers 3,4 - diaminobenzoic acid (DABA) in the the PPA system since polycondensation at 210 ° C for reaction for 10 hours, to give ABPBI were intrinsic viscosity of 2.3dL / g. (2) by electrophilic substitution reaction, a quaternary ammonium group introduced into the molecular chain of ABPBI, and provides an experimental basis for subsequent graft type OH - Preparation of the conductive film. (3) mPBI may be dissolved in the ionic liquid anion having a hydrogen bond acceptor, such as 1 - butyl - 3 - methyl-imidazolium chloride (BMIMCl) and 1 - butyl - 3 - methyl-imidazol hydroxides (BMIMOH, ), at 140 ℃, its solubility, respectively, 12%, 8%, 4 times higher than the system, DMAc. Without hydrogen bond acceptor anions such as - butyl - 3 - methylimidazolium tetrafluoroborate (BMIMBF 4 ) is not dissolved mPBI. The microwave heating can not only accelerate the dissolution rate, can also increase the solubility of the polymer, mPBI BMIMCl in microwave heating, 1 to 2 minutes to obtain 15% of the maximum solubility of mPBI / BMIMCl solution. (4) using 12% mPBI / BMIMCl solution was extruded through the solution, the coagulation bath for regeneration, drafting and cleaning, to obtain a smooth surface of the PBI filaments, by viscosity tests, FT-IR, TGA Characterization found the the stability of the regenerated silk and no significant change in the chemical structure. (5) doped by BMIMOH mPBI film, at room temperature, the doping amount was 4.75 × 10 -3 S / cm 5 BMIMOH / mPBI, the ionic conductivity of the electrolyte membrane. May be used as the alkaline fuel cell electrolyte membrane, the conductive mechanism needs to be studied further.
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