The invention relates to a method for manufacturing a cross-linked polymer comprising reacting at least one polymer having at least one —SO2X group, with X being F or Cl, a basic compound, and certain salts including a ring-quaternized pyridinium-type nitrogen, and possessing at least two groups in ortho or para position thereto comprising reactive hydrogen atoms; cross-linking has been proven to proceed effectively, delivering cross-linked polymers possessing improved chemical resistance and mechanical performances.