A predictable and reproducible number of sulfuric acid sites have been achieved for cation exchange resins by employing a mild SuFEx-based reagent system to effect the hydrolysis of fluorosulfonated polymer beads. The resultant poly(hydrogen sulfate) beads effectively demonstrate their utility as cation exchange resins in ion-capture experiments. Furthermore, their polyfluorosulfonated precursors have also proven to be suitable substrates for traditional SuFEx-type click reactions in both small molecule and protein immobilization applications.