Design and Development of Polymer-Based Separations: Dual Mechanism Bifunctional Polymers as a New Category of Metal Ion Complexing Agents with Enhanced Ionic Recognition

A new series of ionic polymers has been synthesized with unique applications to separations science, in general, and metal ion separations, in particular. The unifying concept underlying these polymers is that specificity in molecular or ionic separations is most readily brought about by multifunctional substrates which can participate in multipoint interactions. The dual mechanism bifunctional polymers form a new category of synthetic multifunctional substrates with enhanced molecular/ionic recognition. These polymers are synthesized with two groups on a given support network each of which operates by a different mechanism. One mechanism is relatively aspecific and its primary purpose is to allow the solution species access to the highly specific recognition mechanism. The principal application has been to selective metal ion separations from aqueous solutions. The dual mechanism bifunctional polymers (DMBP's) are divided into three classes. In each case, ion exchange is the access mechanism while the recognition mechanism defines the class of resins. The Class I DMBP's are the ion exchange/redox resins: they superimpose a redox component on top of the ion exchange reaction and so allow for the recovery of pure metal from a solution of its ions. The Class II DMBP's are the ion exchange/coordination resins: they superimpose a purely coordinative component on top of the ion exchange reaction and so allow for tight binding of targeted ions onto the polymer support according to the principles of hard-soft acid-base theory. The Class III DMBP's are the ion exchange/precipitation resins: they superimpose a precipitation reaction on top of the ion exchange reaction and so allow for the recovery of insoluble metal salts from multi-ion solutions. Bifunctional group cooperativity is most clearly quantified with the Class III resins. The resin characteristics which allow for the observation of polymer-supported synergistic extraction and a concomitant enhanced ionic recognition are detailed.