Preparation and Properties of Blend Anion Exchange Membranes Derived from Quaternary Ammonium Poly(aryl ether sulfone)s

Two series of poly(aryl ether sulfone)s with different rigidity are synthesized by the polymerization of bis(4-fluorophenyl) sulfone (DFDPS) with 9,9'-bis(4-hydroxyphenyl) fluorine (BHPF) or 2,2'-bis(4-hydroxy phenyl) propane (BPA)/2,2-bis(4-hydroxyphenyl) hexafluoropropane (6FBPA). Two novel types of blend anion exchange membranes (AEMs) are prepared through solution casting by co-dissolving the synthesized poly(aryl ether sulfone) and its chloromethylated products with various weight ratios, while the phase-separation is avoided successfully during membrane formation. The rigidity of the polymer main chains is adjusted by introducing the monomers of BHPF (BQPAES series) and BPA (BQPES series), respectively, and their influence on membrane properties is studied in details. The ion exchange capacity (IEC), water absorbing and swelling properties, as well as ion conductivity of the obtained blend AEMs are characterized, and the hydrolytic and alkaline stability are investigated. The precursory and corresponding chloromethylated polymers show fine compatibility and their resultant blend AEMs are uniform, ductile and transparent, with moderate water uptakes and dimensional changes. Both the water uptakes and the dimensional change increase along with temperature and decrease with poly(aryl ether sulfone) content. The ion conductivity of the blend AEMs reaches the maximum of 89 mS/cm at 90 degrees C. After aging in hot water for 24 h, they still retain high mechanical strength with mass loss less than 5%; they also maintain 65% similar to 80% of the original ion conductivity after treated with 2 mol/L NaOH solutions for 168 similar to 240 h at 30 degrees C. Because of the higher rigidity of BHPF moieties, the BQPAES series blend membranes show better dimensional stability and chemical stability than those of the BQPES series at similar IEC level, while maintaining high ionic conductivity. The results imply that the blend treatment and appropriate enhancement in rigidity in the polymer main chain are helpful to improve the overall properties of the membrane.