Improving anion exchange membranes for DMAFCs by inter-crosslinking CPPO/BPPO blends

New anion exchange membranes are prepared by heat-treating the blend base membranes of chloroacetylated poly(2,6-dimethyl-1,4-phenyleneoxide)(CPPO)/bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO). A partially inter-crosslinked structure can be formed therein via a Friedel–Crafts reaction without adding any crosslinking reagent or catalyst. FT-IR and NMR analyses are used to confirm this inter-crosslinking structure and quantify the crosslinking distribution. Physical properties, such as toughness and thermal stability, are enhanced remarkably due to this heat treatment. Furthermore, the final membranes exhibit a high hydroxyl conductivity (up to 0.032 S cm⁻¹ at 25 °C) and extremely low methanol permeability (1.26–1.04 × 10⁻⁷ cm² s⁻¹), which match the requirements for application in low temperature direct methanol alkaline fuel cells (DMAFCs).