Hyperbranched Polystyrene Copolymer Makes Superior Anion Exchange Membrane

To meet the ever-increasing demand of energy conversion/storage devices on anion exchange membrane (AEM) conductivity, it is urgent to explore alternate polymers in terms of the backbone architecture. In contrast to linear polymers, hyperbranched polymers exhibit unexpected properties because of the unique backbone architecture. Unfortunately, reports on hyperbranched-polymer-based AEM are rare because weaker chain entanglement makes it hard to cast free-standing membranes. We proposed here two strategies, i.e., cross-linking and implementing flexible segments to strengthen chain entanglement, to fabricate free-standing hyperbranched AEMs. Our results confirm that implementing flexible segments imparts hyperbranched AEMs with superior properties compared with the ones fabricated via cross-linking and AEMs made from linear polymers. By exploiting reversible addition–fragmentation transfer polymerization, we synthesized a hyperbranched poly(vinyl benzyl chloride) core and implemented a polyisoprene shell (the flexible segment to strengthen chain entanglement). After quaternization, a free-standing highly conductive AEM was acquired, with a conductivity of 85.1 mS cm–1 at 80 °C and limited water swelling. Such gratifying properties originate from the unique membrane morphology, and by proper control, the self-assembled pattern could be directed in the hyperbranched membranes. The obtained results prove the effectiveness of our strategy, resulting in superior AEMs for energy conversion or energy storage.