Preparation of site-selective ion exchange resins

A method of preparation was sought by which ion exchange resins could be prepared which would be selective for a metal ion of choice. The approach taken concerned the copolymerization of metal ion complex compounds bearing polymerizable ligands with styrenic monomers, followed by the removal of the metal ion by washing the product with aqueous acid solutions. It was intended that the sites thus prepared in the resin would contain ligands configured to match the bonding characteristics of the ion used in their construction. Such a resin should preferentially reabsorb the metal ions by which the configurations of its exchange sites were templated.

Polymerizable metal ion complex compounds were prepared by placing the metal ion to be used as a template into solution in contact with ligands such as acrylic acid or p-vinylbenzoic acid. Upon coordination of the ligands to the metal ion in proper stoichiometry to produce a neutral compound, precipitation occurred allowing separation of the compound by filtration. The isolated product bore vinyl groups which made polymerization or copolymerization possible.

Placing the polymerizable metal compounds in solution with inert matrix monomer and crosslinking agent, and polymerizing by a free radical mechanism produced a number of copolymers with a range of ion exchange characteristics. Comparisons were made of the exchange capacity and the equilibrium constants observed for exchange of Ni2+ and Cu^^ for resins templated with each of these metal ions as well as for resins that were not templated with a divalent cation. Resins which were templated with a metal ion consistently demonstrated higher exchange capacities for that ion than the other. Order of magnitude capacity preferences were observed. The trend observed with equilibrium constants was that for templated resins the ion absorbed with the smaller capacity exhibited the higher constant. Untemplated resins showed larger capacities and equilibrium constants for Cu²⁺ than for Ni²⁺ where there was a clear distinction.