H-1 nuclear magnetic resonance (NMR) studies were performed on solutions of mixtures of lightly sulfonated polystyrenes (PS-SSA), with poly(methyl methacrylate-co-4-vinylpyridine) (PMMA-4VP) copolymers. The PS-SSA (5-15 mol % sulfonation) had molecular weights (MW) ranging from 2 X 10(3) to 1 X 10(5), while the PMMA-4VP chains (5-11 mol %) had a MW of 1 x 10(5). The driving force for coil overlap was electrostatic attraction between the sulfonate anions and the pyridinium cations which were produced as a result of proton transfer from the sulfonic acid to the 4VP moieties. The coil overlap process was monitored as a function of time by the acquisition of proton spectra, which showed the gradual disappearance of the original (unshielded) methoxy signal and the appearance of a new signal originating from the shielded methoxy protons. In order to propose a complete model for the coil overlap process, it was first necessary to ascertain that the ionic species were, indeed, responsible for the interchain attraction rather than some other unsuspected mechanism. The electrostatic nature of the mechanism was confirmed by the addition of various electrolytes to the equilibrated blend solutions. The addition of electrolytes does, indeed, result in the disappearance of the shielded methoxy signal, confirming the electrostatic nature of the mechanism. In addition, the qualitative influence of other parameters on the electrostatic interaction was studied. These parameters were the water content of the solution, the ion content of the copolymers, the MW of the PS-SSA chains, and the temperature. The detailed kinetics and the mechanistic aspects of the coil overlap process are described in a subsequent paper.