The Mannich reaction is applied to the phosphorylation of amine resins with monoamine, ethylenediamine, diethylenetriamine, and tetraethylenepentamine ligands to give a series of bifunctional aminomethylphosphonic acid resins. The microenvironment around each ligand was varied by preparing fully functionalized resins, a second set of resins with 82 mol% phenyl groups in the polymer, and a third set with 82 mol% carbomethoxy groups. The affinity of the resins for Cu(II), Cd(II), Pb(II), and Eu(III) was evaluated from solutions buffered at pH 5. Synergism is observed under certain conditions where both groups operating together complex more metal ions than either one alone. Ion exchange by the phosphonate portion of the ligand and coordination by the amine portion cooperate as a dual mechanism for metal ion complexation. Synergistic complexation of Cd(II) by all bifunctional aminomethylphosphonate resins (regardless of microenvironment) and of all metal ions by all bifunctional resins within the carbomethoxy microenvironment is quantified. For example, 26% Cd(II) is complexed by the ethylenediamine resin (distribution coefficient of 26), and 49% Cd(II) is complexed by the phosphonic acid resin (distribution coefficient of 48), but the bifunctional aminomethylphosphonic acid resin complexes 98% Cd(II) (distribution coefficient of 2300), which far exceeds the combined distribution coefficients of the monofunctional resins.