The formation of water-soluble coordination polymers was studied for a bifunctional monomer consisting of two terpyridin groups bridged by a poly(ethylene oxide) spacer. The complex formation between the terpyridin ligand groups and Cd2+ ions was demonstrated using UV/vis spectroscopy and potentiometric titration. Viscosimetry and voltammetry were used to study the formation of cadmium-based supramolecular coordination polymers as a function of the metal/monomer ratio and the total monomer concentration. An increase of the average degree of polymerization results in an increase of the viscosity and a decrease of the diffusion-limited voltammetric current. The results were interpreted using a theoretical model for the coordination polymerization into chains and rings. Very good, quantitative agreement was found between experiment and theory.