The paper describes a simple and an effective method for preparation of sulfoethylated polyaminostyrene-based sorbents with different fixed degrees of substitution of hydrogen atoms of amino groups. The chemical structure of the obtained polymers was characterized by Fourier transform infrared (FT-IR) spectroscopy. Thermogravimetric study of the sulfoethylated polyaminostyrene coupled with FT-IR analysis has shown stability of the polymer up to 250 °C, which almost does not change with the increase in the degree of substitution (DS). The study reports the influence of different factors on the selectivity of sorption of sulfoethylated polyaminostyrene-based sorbents towards alkaline earth and transition metal ions from their solutions of complex composition. The analyzed materials have shown selectivity towards copper(II) and silver(I). The selectivity towards the stipulated ions is higher when using an ammonium acetate buffer solution vs. an ammonium buffer solution. Wherein the selectivity of sorption towards silver(I) over copper(II) of sulfoethylated polyaminostyrene increases significantly with the increase in the DS of the sorbent. It was shown, that the equilibrium in the “solution of metal salts-sorbent” system was achieved within 30 min.