A composition comprises a polymer having a first pendant group selected from at least one perfluorinated ether group or perfluoroalkanesulfonamido group, a second pendant group comprising an ammonium group, wherein the second pendant group is free of silicon, and a third pendant group comprising an ammonium group and a reactive silicon-containing group. The polymer and composition are useful for protecting a substrate, for example, to render the substrate oil repellent, water repellent, or both, or to provide stain repellency to the substrate.