Block poly(arylene ether sulfone) copolymers tethering aromatic side-chain quaternary ammonium as anion exchange membranes

Abstract

A series of poly(arylene ether sulfone) block copolymer ionomers have been synthesized through pre-polycondensation, block copolycondensation, bromomethylation and the Menshutkin reaction, where benzyl-quaternary ammonium groups are tethered to the side chains of hydrophilic blocks. Atomic force microscopy (AFM) results indicate the formation of a well-defined microphase-separated morphology in ionomer-based membranes, which is attributed to its well-controlled block copolymer as well as aromatic side-chain structures. The prepared side-chain block anion exchange membranes (bQPAES) with IECs of 0.79–1.15 mequiv g⁻¹ have isotropic membrane swelling and high hydroxide conductivity (54.8–86.3 mS cm⁻¹). Compared to random copolymer ionomer membranes, the present block anion exchange membranes exhibit acceptable high hydroxide conductivity, which is ascribed to well-connected ionic nano-channels resulting from the better microphase separation induced by block copolymer structures. Besides this, the side-chain block bQPAES membranes display reasonably high alkaline stability with good chemical stability of both quaternary ammonium ionic groups and block copolymer backbones considering the harsh aging conditions (4 M NaOH at 80 °C).