Exploring the effects of flexibility of monomers on poly (isatin monomer-co-biphenyl) anion exchange membranes

To investigate the effect of the monomer with different flexibility and rigidity on the random copolymer, we prepare anion exchange membranes (AEMs) with a similar copolymerization ratio containing different monomers. The results show that the introduction of rigid dibenzofuran, moderately flexible diphenyl ether and flexible bibenzyl affects the conformation and morphology of the polymers, further tuning the overall performance of the AEMs. The three random copolymers exhibit better microphase-separated morphology and conductivity than the homopolymer owing to their more twisted conformation. It is found that the incorporation of flexible monomers has an advantage in holding size consistence and flexibility. Overall, the integration of bibenzyl monomer has the most positive impact on the membrane characteristics, the QPIBBP-40 AEM with flexible units possesses the highest OH- conductivity (80 °C, 159.6 mS cm-1) and an excellent mechanical stability (elongation at break: 48.2%, tensile strength: 15.6 MPa). The wet-stated QPIBBP-40 AEM maintains an inferior swelling ratio (80 °C, 10.8%), indicating that it possesses good size consistence and ionic conductivity simultaneously. The highest output power density of the QPIBBP-40 AEM based fuel cell is 655 mW cm-2.