Comb-shaped polyfluorene with variable alkyl chain length for application as anion exchange membranes

To fabricate anion exchange membranes (AEMs) with high ionic conductivity and excellent chemical stability, in this study, we develop a series of comb-shaped polyfluorene copolymers with side chains of different lengths by superacid-catalyzed Friedel-Grafts polycondensation. Direct introduction of comb-shaped alkyl side chains induce obvious micro-phase separation in these AEMs, as confirmed by atomic force microscopy. PHPFP-QA with the longest side chain has the lowest IEC and the highest ionic conductivity (24.3 mS cm(-1) at 20 ?) and power density (596 mW cm-2 at 80 ?) because of its loose structure, which causes more water to be absorbed and a greater hydration number (lambda). Owing to a stable piperidinium cation and ether-free backbones, these polyfluorene-based AEMs exhibit excellent alkaline stability. The conductivities of PMPFP-QA, PBPFP-QA, and PHPFP-QA decrease by approximately 23%, 21%, and 17% after immersing them in 2 M KOH at 80 ? for 30 days, respectively. Hence, polyfluorene grafting with comb-shaped side chains can be used to design alkaline electrochemical energy conversion and storage devices.

Automated summary

In this study, a series of comb-shaped polyfluorene copolymers with different lengths of side chains were developed using superacid-catalyzed Friedel-Grafts polycondensation. The direct introduction of comb-shaped alkyl side chains caused micro-phase separation in the AEMs, and PHPFP-QA with the longest side chain exhibited the highest ionic conductivity and power density. The polyfluorene-based AEMs showed excellent alkaline stability due to stable piperidinium cations and ether-free backbones.