Synthesis and characterization of poly(ether sulfone) block copolymers containing pendent quaternary ammonium- and imidazolium groups as anion exchange membranes

A class of poly(ether sulfone) (FPES) block copolymers containing pendent quaternary ammonium (QA) and imidazolium (IM) groups were prepared as anion exchange membranes by reaction involving nucleophilic substitution, benzylic bromination, quaternization and anion exchange with hydroxide ions. Highly reactive hexafluorobenzene (HFB) was utilized as a linkage group for relatively low temperature (e.g., 105 degrees C) coupling between hydrophobic and precursor hydrophilic oligomer blocks. The phase separated morphology, water uptake, swelling ratio, conductivity, and chemical stability of the resultant copolymer membranes were also investigated. The hydroxide conductivity of the ionomer membranes (IEC similar to 2.0 mequiv./g) was 21-22 mS/cm and 56-63 mS/cm at 30 degrees C and 80 degrees C respectively. The FPES-IM membrane showed relatively very good dimensional integrity in high pH solution, whereas under the similar condition the FPES-QA membrane broke into pieces. However, the degradation of the imidazolium cations in FPES-IM was relatively faster in comparison to the ammonium cations in FPES-QA.