A vinylpyridine/acrylic acid bifunctional interpenetrating polymer network (IPN) has been synthesized and evaluated for application in metal ion separations. Monofunctional vinylpyridine and acrylic acid IPNs were also synthesized and differences between the distribution coefficients of the three systems were used as an indication of whether an enhanced (i.e., synergistic) complexation of metal ions was occurring in the bifunctional polymer. Important effects atrtributable to the combined action of the two functionalities in the same polymer are observed. Complexation of Eu(III), a hard Lewis acidm by the bifunctional polymer is inhibited by hydrogen bonding between the two ligands. Borderline Lewis acids are complexed with high efficiency and evidence for a synergistic effect is presented.