The　cationic　group　distribution　along　the　polymeric　backbones　of　anion　exchange　membranes　(AEMs)　has　significant　influence　on　their　microscopic　morphology　and　anion　conductivity.　To　develop　high-performance　AEMs　for　vanadium　redox　flow　batteries　(VRFBs),　a　series　of　poly　(fluorenyl　ether)　samples　bearing　di-　and　tri-quaternary　ammonium　side　chains　with　similar　ion　exchange　capacities　(IECs)　were　synthesized　by　grafting　cationic　alkyl　chains　with　tertiary　amine-containing　poly(fluorenyl　ether)　precursors.　The　experimental　results　indicate　that　the　introduction　of　the　multi-cationic　side　chains　facilitates　the　formation　of　micro-phase-separated　morphologies　and　enhances　anion　conductivity.　Moreover,　the　number　of　spacer　atoms　between　the　quaternary　ammonium　groups　on　the　side　chains　affects　the　water　uptake　of　the　membranes,　thus　complicating　the　relationship　between　the　density　of　cationic　group　distribution　and　anion　conductivity.　The　poly(fluorenyl　ether)s　with　dicationic　side　chains　and　six　spacing　atoms　(DQA-PFE-C6)　showed　the　highest　anion　conductivity.　A　VRFB　assembled　with　DQA-PFE-C6　exhibited　a　maximum　power　density　of　239.80　mW　cm−2　at　250　mA　cm−2,　which　is　significantly　higher　than　a　VRFB　assembled　with　Nafion　212.　Therefore,　side　chain　engineering　is　an　effective　chemical　approach　to　enhance　the　properties　of　AEMs　for　VRFB　applications.　©　2020,　Science　China　Press　and　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.