Synthesis of formaldehyde‐dibenzo‐18‐crown‐6 condensation resins containing phosphonic acid groups and their alkali‐metal cation sorption

Ion‐exchange resins are prepared by introducing phosphonic acid monoethyl ester or phosphonic acid groups into formaldehyde condensation poly(dibenzo‐18‐crown‐6) resin. The phosphonic acid ion‐exchange groups provide accessibility for metal cations, while the ion‐selective cyclic polyether binding site influences the selectivity. The selectivities and efficiencies for competitive alkali‐metal cation sorption from aqueous solutions by these crown ether‐containing phosphonic acid resins are strongly influenced by the pH of the aqueous solution, the identity of the phosphonic acid groups, and the molar ratio of ion‐exchange groups to crown ether units.