AbstractNMR was used to provide evidence of site—site interactions in bifunctional polymers. A series of polymer‐supported phosphonic acid and phosphonate ester ligands was examined by solid‐state31P NMR spectroscopy. Interaction between phosphonate monoethyl ester sites was demonstrated and disruption of this interaction by the addition of diethyl ester groups was shown. The effect of the synthesis conditions on the bifunctionality of resins containing both phosphonic acid and quaternary amine groups was examined. The spectra indicated that the phosphonic acid groups exists as phosphonate ions in the bifunctional amine/acid polymers and are capable of displacing chloride as the counterion on the amine