UPTAKE OF METAL-IONS BY A NEW CHELATING ION-EXCHANGE RESIN .3. PROTONATION CONSTANTS VIA POTENTIOMETRIC TITRATION AND SOLID-STATE 31P NMR-SPECTROSCOPY

A new chelating ion exchange resin which incorporates methylenediphosp honate, carboxylate, and sulfonate functional groups in a polystyrene- divinylbenzene matrix has been prepared. This resin exhibits exception ally high affinity for polyvalent cations even from moderately acidic aqueous media. Metal ion coordination occurs primarily at the diphosph onate group with the secondary binding sites contributing to charge ne utralization when necessary and possible, and to increasing hydrophili city of the resin pores. In the present investigation, the protonation equilibria of the phosphonate groups in the resin are investigated vi a potentiometric titration and solid-state P-31 NMR spectroscopy of th e resin. Intrinsic equilibrium constants for the first two diphosphona te protonation reactions are pK(4) = 10.47 and pK(3) = 7.24. The last two protons added to the diphosphonate group are acidic having pK(a) v alues less than 2.5. These protonation constants are consistent with t hose reported previously for monomer analog 1,1-diphosphonic acids. Th is result implies that thermodynamic data available in the literature can be used to predict the relative affinity of the resin for polyvale nt cations.