A new chelating resin with diphosphonate groups has been synthesized from the tetraethyl ester of 1,1-vinylidenediphosphonic acid. Comonomers such as acrylonitrile allow the sterically hindered monomer to be incorporated into the polymer network. A copolymer was prepared by suspension polymerization in high yield with diphosphonate, acrylonitrile, and styrene in the monomer solution at a 4.5:1:3.1 weight ratio and 5 wt % divinylbenzene as the cross-link agent. Bifunctionality enhances metal ion complexation kinetics. The diphosphonate ligands are selective chelators, while sulfonic acid ligands covalently bound to the phenyl groups enhance the accessibility of metal ions in the polymer matrix. The complexing ability of the polymer is studied with Eu(III) as the target ion in 0.04-4.0 N HNO3 solutions in both the presence and absence of 0.40 N NaNO3. A sulfonic acid ion exchange resin complexes 14.3% Eu(III) while the diphosphonate-based polymer complexes 96.5% from a 1 N HNO3/0.4 N NaNO3 solution.