A method for preparation of poly(N-sulfoethylaminomethylstyrene) with a degree of functionalization up to 0.54 has been developed. The composition and structure of the products of polymer analogous transformations were characterized by elemental analysis, FTIR spectroscopy, and thermogravimetric analysis. It has been established that materials with a degree of functionalization of 0.35 and 0.5 are capable of selective sorption of noble metal ions in the presence of transition metals. An increase in the sulfoethyl group content increases the degree of extraction of PdII and reduces the degree of extraction of PtIV. It was also found that the studied sorbent with a degree of functionalization of 0.35 selectively extracts AgI ions from multicomponent systems at pH 5.5–6.0 in an ammonium acetate buffer solution.