Synthesis and characterization of sulfonated polybenzimidazoles containing 4-phenyl phthalazinone groups for proton exchange membrane

A novel series of sulfonated 4-phenyl phthalazinone-based polybenzimidazoles (SPPBIs) were synthesized by solution polycondensation of 3,3′-diaminobenzidine (DAB), 4-(4-(4-(4-carboxyphenoxy)phenyl)-1-oxophthalazin-2(1H)-yl) benzoic acid (CPPBC) and 5-sulfoisophthalic acid monosodium salt (SIPN) in polyphosphoric acid (PPA). Their chemical structures were characterized by NMR, FT-IR and wide angle X-ray diffraction (WAXD). The inherent viscosities in 98 wt.% H2SO4 were in the range of 1.49–1.78 dL/g. The SPPBIs exhibited good solubility in polar aprotic organic solvents, such as N-methyl-2-pyrolidinone (NMP), N,N-dimethylacetamide (DMAc) and dimethyl sulfoxide (DMSO). The membranes were prepared by solution casting technique using DMSO as solvent. The SPPBI polymers showed excellent thermal stability, and their membranes displayed low water uptake, low swelling ratio, good mechanical properties and excellent resistance to oxidation. The SPPBI membranes had unexpected low methanol permeability (5.46 × 10− 10– 1.27 × 10− 9 cm2/s). They exhibited high conductivities in the range of 4.8 × 10− 3 S/cm to 1.3 × 10− 2 S/cm at 80 °C and from 2.3 × 10− 3 S/cm to 8.5 × 10− 3 S/cm at 20 °C.