Cationic Side-Chain Attachment to Poly(Phenylene Oxide) Backbones for Chemically Stable and Conductive Anion Exchange Membranes

Abstract

A series of chemically stable and ionically conductive side-chain anion exchange membranes (AEMs) based on poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) backbones and alkyltrimethylammonium cations are reported in this work. Two alkyltrimethylammonium groups with n-propyl (C3) and n-pentyl (C5) alkyl chains were tethered onto PPO backbones through secondary amine moieties, resulting in two side-chain AEMs, that is, NC3Q-PPO and NC5Q-PPO and NC5 Q-PPO. In comparison to benzylic QA groups (e.g., benzyltrimethylammonium cations in quarternized PPO (QPPO) and benzylalkyldimethylammonium cations in comb-shaped PPOs (i.e., QC3-PPO and QC6-PPO)), the alkyltrimethylammonium cations of the side-chain PPOs, which do not possess highly reactive benzylic protons adjacent to both the aromatic ring and the cation, showed superior alkaline stability. After 30 days of aging in 1 mol/L NaOH solution at 80 °C, the retention of the conductivities of NC3Q-PPO (IEC = 2.17 mmol/g), NC5Q-PPO-40 (IEC = 2.03 mmol/g), and NC5Q-PPO-...