Effect of Microstructures of Side-Chain-Type Anion Exchange Membranes on Mono-/Bivalent Anion Permselectivity in Electrodialysis

Highly monovalent/bivalent anion permselectivity of anion exchange membranes (AEMs) is of great relevance for a wide range of applications, especially in electrodialysis (ED). In this study, two series of long-side-chain-type AEMs with different microstructures were designed by a facile one-step or two-step Menshutkin reaction. It is found that varying the hydrophobicity of the side chains is a feasible method to easily regulate the permselectivity of AEMs, which was achieved by changing the length of the side chain and charge numbers in long side-chain grafting to the polymer backbone. The CMPSF-N16-1 AEM (ion exchange capacity (IEC) ≈ 1.1 mmol·g–1) exhibits the highest permselectivity (PSO42–Cl– of 60.1), low water uptake (3.5%), and high membrane surface resistance, which are attributed to its hydrophobic polymer backbone and longest alkyl chains. As the IEC of the prepared AEMs augmented or increased the charge numbers in the side chains, PSO42–Cl– obviously decreased, which can be ascribed to the enhanced electrostatic effect and hydrophobicity changes. This work demonstrates that the proposed method to regulate the membrane hydrophobicity is effective to guide the preparation of AEMs with enhanced permselectivity from the microstructure design.