N-bromo poly(styrene-co-divinylbenzene) sulphonamide acid with macroporous structure has been obtained from its sodium salt using weak acid solution (0.02 mol L-1 CH3COOH) to transform the functional groups from the Na+ form to the H+ form. This transformation, carried out in a column method, allowed to obtain a new reactive polymer which exists in an aqueous medium only in a narrow pH range and does not have low-molecular weight analogue (N-bromo-p-toluenesulphonic acid is not separable from the aqueous solution and does not occur as a pure chemical compound). It has been demonstrated that the -SO2NBrH groups, stable under certain conditions (in water and in weak acid solutions), showed cation exchange and oxidizing properties. Their main properties, such as the acidity, the formal redox potential, and the stability in aqueous media of different acidities, were determined. It has been explained the difference in behavior of copolymeric Na+ and H+ form sulphonamides. FTIR spectra and TG/DTG charts of the copolymers with -SO2NBrH and -SO2NBrNa groups have been compared.