Abstract: Cation exchange membranes are prepared via facile methods to control sulfonation of polystyrene repeat units. An amount of sulfuric acid is reacted with an acetic anhydride to form an amount of acetyl sulfate. The acetyl sulfate is then added to a known concentration of polystyrene units in boiling dichloromethane (DCM) to form sulfonated polystyrene random copolymers, including a random distribution of sulfonated polystyrene repeats and unsulfonated polystyrene repeats, with sulfonation levels between about 0.07 and about 0.225. The sulfonation level can be controlled by adjusting reaction times, reaction temperatures, and sulfuric acid loading in the reaction mediums. These membranes, neutralized via alkali metals, exhibit high charge densities and low hydration degrees, and maintain high permselectivity under various high solution concentrations.