Phosphoric acid-doped crosslinked proton-conducting membranes with high anhydrous proton conductivity, and good chemical stability in phosphoric acid were synthesized and characterized. The synthetic procedure of the acid-doped composite membranes mainly involves the in situ crosslinking of polymerizable monomer oils (styrene and acrylonitrile) and vinylimidazole, and followed by the sulfonation of pendant imidazole groups with butanesultone, and further doped with phosphoric acid. The resultant phosphoric acid-doped composite electrolyte membranes are flexible and show high thermal stability and high-proton conductivity up to the order of 10(-2) S cm(-1) at 160 degrees C under anhydrous conditions. The phosphoric acid uptake, swelling degree, and proton conductivity of the composite membranes increase with the vinylimidazole content. The resultant composite membranes also show good oxidative stability in Fenton's reagent (at 70 degrees C), and quite good chemical stability in phosphoric acid (at 160 degrees C). The properties of the prepared electrolyte membranes indicate their promising prospects in anhydrous proton-exchange membrane applications. (C) 2013 Wiley Periodicals, Inc.