Ion-exchange resins comprise one of the most important scientific developments of the 20th century. Their applicability to water softening, environmental remediation, wastewater treatment, hydrometallurgy, chromatography, biomolecular separations, and catalysis was recognized in numerous publications. The principle of covalently bonding ligands to cross-linked polymer networks became the basis for the area of polymer-supported reagents. The journal Industrial & Engineering Chemistry Research and its predecessors have published some of the most important papers in this field. In celebration of its 100th anniversary, this review provides a retrospective of ion-exchange resins through publications appearing in this journal.

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Calix[4]arene and its diphosphorylated derivative have been immobilized onto cross-linked polystyrene beads through an etherification reaction. The supported calixarene complexes 96.7% Cs(I) from a 10-4 N solution in 1 M NaOH. Poly(hydroxystyrene) complexes 35.6% Cs(I) from the same solution. Immobilization of the calixarene onto a polymer support thus does not affect its inherently high affinity for cesium ions. Substituting two of the three remaining hydroxyl groups on the calixarene with diethoxyphosphoryl moieties allows for quantitative complexation of Fe(III) and Pb(II) from 0.01 M nitric acid solutions. The unsubstituted calixarene complexes 6.00% Fe(III) and 7.36% Pb(II) while diethoxyphosphoryl-substituted poly(hydroxystyrene) complexes 10.0% Fe(III) and 3.76% Pb(II). The calixarene therefore acts as a platform on which ligands can be immobilized in close enough proximity to permit cooperative binding of metal ions.

A novel class of strong-base anion-exchange resins, bearing two different types of exchange sites, is described. These bifunctional resins have anion-exchange sites composed of two separate and differently sized trialkylammonium groups. In pertechnetate (TcO 4 -) uptake experiments from a solution matrix containing anions commonly encountered in groundwater, bifunctional resins containing exchange sites derived from tri-n-hexylamine in combination with either triethylamine, tri-n-propylamine, or tri-n-butylamine were shown to possess superior 24-h distribution ratios (K d ) for pertechnetate over all monofunctional anion-exchange resins (derived from a single trialkylamine) examined. For example, although monofunctional resins containing a tri-n-hexylammonium exchange site possessed excellent selectivity for pertechnetate over other anions, the exchange kinetics were poor. The superior performance of these resins can be attributed to the combination of a large trialkylammonium site for enhanced selectivity for large anions and a smaller trialkylammonium site for the retention of good exchange kinetics.