Synthesis and characterization of polymer-supported bifunctional reagents with enhanced ionic recognition

lon-exchange/redox and ion-exchange/coordination resins have been developed as highly selective metal ion complexing agents. The resins belong to a new category of polymers termed dual mechanism bifunctional polymers (DMBP's) which contain two groups on the same support network each of which operates by a different mechanism. lon-exchange/redox resins, which form the first class of DMBP's, were prepared containing phosphinic acid ligands covalently boiind to a polystyrene matrix. The phosphinic acid moiety is capable of ion exchange with a metal ion allowing for its entry into the polymer network and of reduction of metal ions with reduction potentials greater than approximately 0.3V thus providing specificity in metal ion complexation. The second class of DMBP's, ion-exchange/coordination resins, combine an ion-exchange reaction to allow for metal ion accessibility with a coordinative component to give enhanced selectivity through metal ion complexation. These polymers were synthesized to contain a phosphonic acid group for ion exchange and either phosphonate ester or tertiary amine ligands for coordination.

The complexing ability of the ion-exchange/redox and ion-exchange/coordination resins was determined with selected lanthanide and actinide series ions (Am³⁺, Eu³⁺, Th⁴⁺, UO₂²⁺and Pu⁴⁺) and transition metal ions (Fe³⁺, Hg²⁺, Mn²⁺, Co²⁺, Cu²⁺, Zn²⁺ and Ag⁺). The performance of the bifunctional resins was compared to that of the purely ion exchanging sulfonic acid resin both in the presence and absence of excess sodium ions. The affinities of the DMBP's for the target metal ions were determined over a wide variety of conditions in order to elucidate their mechanisms of complexation. Extractions were performed both in the presence and absence of excess sodium ions under a variety of pH conditions (-0.6 to 2.5). Metal complexation was also investigated for a broad range of metal ion concentrations. The results for the polymer-supported extractants were compared to some liquid extractant analogues.