Cross-linked quaternised Poly(2,6-dimethyl-1,4-Phenylene Oxide) (QPPO)-based membranes were prepared via Friedel-Crafts reactions using SnCl4 catalyst, 1,3,5-trioxane and chlorotrimethylsilane as environmentally-friendly chloromethylating reagents. New equations to calculate the degree of chloromethylation (DC) cross-linking (CLD) proposed. Ionic conductivity 133 mS cm?1 at 80 °C was obtained, ...