Anion exchange membranes with a semi-interpenetrating polymer network using 1,6-dibromohexane as bifunctional crosslinker

An anion exchange membrane (AEM) is generally expected to possess high ion exchange capacity (IEC), low water uptake (WU), and high mechanical strength when applied to electrodialysis desalination. Among different types of AEMs, semi-interpenetrating polymer networks (SIPNs) have been suggested for their structural superiorities, i.e., the tunable local density of ion exchange groups for IEC and the restrained leaching of hygroscopic groups by insolubility for WU. Unfortunately, the conventional SIPN AEMs still struggle to balances IEC, WU, and mechanical strength simultaneously, due to the lack of the compact crosslinking region. In this work, we proposed a novel SIPN structure of polyvinylidene difluoride/polyvinylimidazole/1,6-dibromohexane (PVDF/PVIm/DBH). On the one hand, DBH with two cationic groups of imidazole groups are introduced to enhance the ion conductivity, which is different from the conventional monofunctional modifier with only one cationic group. On the other hand, DBH has the ability to bridge with PVIm, where the mechanical strength of the resulting AEM is increased by the increase of crosslinking degree. Results show that a low WU of 38.1% to 62.6%, high IEC of 2.12–2.22 mmol·g⁻¹, and excellent tensile strength of 3.54–12.35 MPa for PVDF/PVIm/DBH membrane are achieved. This work opens a new avenue for achieving the high-quality AEMs.