Polyphosphazene-based copolymers containing pendant alkylsulfonic acid groups as proton exchange membranes

•A series of polyphosphazene-based copolymers were prepared.•They were made into the corresponding membranes by the assist of the cross-linking reagent.•The membranes showed lower water uptake and dimensional swelling.•They displayed significant methanol resistance.•The proton conductivities up to 0.14 S/cm at 80 °C under fully hydrated conditions.

A series of polyphosphazene-based copolymers containing alkylsulfonated side chains were prepared and made into the corresponding membranes by the reaction with 2,6-bis(hydroxymethyl)-4-methylphenol (BHMP) as the cross-linking reagent. All the cross-linked membranes showed lower water uptake and dimensional swelling. They displayed significant methanol resistance ranging from 1.35 to 7.18 × 10− 7 cm2/s and high oxidative stabilities. The individual membrane PFMPP1-r-PFSPP9 showed good proton conductivity (0.14 S/cm) under fully hydrated conditions at 80 °C.