THE MICROENVIRONMENTAL EFFECT IN ION-COMPLEXING INTERPENETRATING POLYMER NETWORKS

The effect of the microenvironment surrounding a ligand within a polymer is probed with metal ions and quantified by the corresponding binding constants. Interpenetrating polymer networks (IPNs) allow for the synthesis of well-defined substrate-complexing reagents. Poly(N-vinylimidazole) has been prepared within a polystyrene network and the ability of the imidazole ligand to complex Cu(II) and Co(II) ions determined. The microenvironment surrounding the imidazole ligand is varied by synthesizing polystyrene/poly(N-vinylimidazole-co-ethyl acrylate) IPNs where imidazole is replaced by increasing levels of weakly coordinating carboxylate ester groups. The strength of the imidazole-ion interaction is sensitive to the polymer microenvironment: as the imidazole/ester ratio decreases along the series 1/0, 0.77/0.23, 0.53/0.47, 0.27/0.73, and 0/1, the Cu(II) binding constants are 3130, 4134, 8203, 3108, and 0 N-1, respectively, and the Co(II) binding constants are 294, 270, 86, 129, and 0 N-1.