Bifunctional ion exchange resins : synthesis and characterization of ion-selective polymers

The synthesis and characterization of numerous dual mechanism bifunctional polymers (DMBPs) were accomplished. Class II (ion exchange/coordination) DMBPs based on phosphonic acid esters were synthesized and their metal ion complexation abilities evaluated in low pH environments. A bifunctional phosphonate mono/diethyl ester complexed far more silver than either monofunctional resin or a mixed bed of the monofunctional resins. A supported ligand synergistic interaction was thus displayed. Studies with a series of dialkyl phosphonate esters revealed that steric interactions between the ester alkyl groups and bulky metal salts can enhance the selectivity of the diester resins. Class II DMBPs containing either carboxylic or phosphonic acid groups in conjunction with penta(ethylene glycol) ligands were synthesized and characterized in detail. Preliminary investigations of the metal ion affinity of these networks revealed that the presence of the acidic groups modified the binding constant between the resin and sodium picrate. Direction for future research was provided. A limited amount of research aimed at the synthesis of uniform Class III (ion exchange/precipitation) DMBPs was completed. A possible side reaction which limits the utility of the partially functionalized phosphonic acid resin was identified and means of reducing its occurrence were briefly evaluated. The feasibility of producing DMBPs through the synthesis of interpenetrating polymer networks (IPNs) was investigated and found to be viable. A series of well-characterized polystyrene-based IPNs containing both pyridine and acrylic acid groups were synthesized and methods for determining their binding constants with metal ions were examined. The IPNs were selective for copper over cobalt. Scouting studies designed to produce a novel ion exchange resin containing geminal diphosphonic acid groups were completed. It was shown that the polymer could be prepared in bead form by conventional suspension polymerization techniques and that the resin displayed excellent metal ion uptake abilities. Finally, solid-state NMR spectroscopy was used to characterize the resins. The extent of reaction and possibility of network degradation during hydrolysis of the bifunctional IPNs was examined. It was found that the hydrolysis proceeded to completion without any unwanted side reactions. Phosphonic acid and phosphonate ester resins were characterized by solid-state ³¹P spectra. The interaction of ligands on the amine-containing class II and III resins was demonstrated and shown to be dependent upon the synthetic conditions.