Comb-like polymers with flexible side chains chemically pended onto a polymeric backbone afford some unusual properties due to their hierarchical structures, such as nanoscale confined crystallisation, phase transition and conformational variations, length scale effects, etc. Considerable attention has been paid to these featured polymers, regarding their importance in understanding the correlation between hierarchical structure and the assembled morphologies. In this review, we reviewed the recent research progress on the structure–property correlations of comb-like polymers. This article brings together and highlights the fabrication, structure determination and morphology characterization for comb-like polymers, especially for nanostructured packing patterns and frustrated mobility of chain segments from the selected examples.

An ultra-high ion-selective hybrid membrane (SPEEK/ZC-GO) composed of sulfonated poly(ether ether ketone) (SPEEK) and zwitterion-decorated graphene oxide (ZC-GO) containing ammonium and sulfonic acid groups is designed and prepared for all vanadium redox flow batteries (VRFBs). SPEEK/ZC-GO hybrid membranes exhibit higher proton conductivity and lower vanadium ion permeability than pristine SPEEK and Nafion 117 membranes. The good trade-off effect between proton conductivity and vanadium ion permeability offers ultra-high ion selectivity to SPEEK/ZC-GO hybrid membranes, and the SPEEK/ZC-GO-2 hybrid membrane gives the highest ion selectivity, 26.0 × 10³ S min cm⁻³, which is about 6.5 and 6.0-fold higher than Nafion 117 (4.0 × 10³ S min cm⁻³) and pristine SPEEK membranes (4.3 × 10³ S min cm⁻³), respectively. The VRFB with the SPEEK/ZC-GO-2 hybrid membrane exhibits a significantly slower self-discharge rate, retaining an open circuit voltage of 1.3 V for 132 h, than Nafion 117 (23.5 h) and pristine SPEEK membranes (38 h). The SPEEK/ZC-GO-2 hybrid membrane demonstrates higher coulombic efficiencies (CE: 98.5–99.2%) and energy efficiencies (EE: 91.4–83.9%) at 50–100 mA cm⁻², as compared with Nafion 117 (CE: 94.0–97.1%, EE: 83.5–74.7%) and pristine SPEEK membranes (CE: 94.5–97.6%, EE: 82.1–74.4%). Stable cycling performance over more than 200 cycles proves the high chemical stability of the SPEEK/ZC-GO-2 hybrid membrane during long-term operation. This investigation indicates that the SPEEK/ZC-GO hybrid membrane is a promising proton exchange membrane for VRFB systems through controlling the desirable ultra-high ion selectivity.