A novel betaine internal salt ( 3 ) has been synthesized by the reaction of pyridine with 1-methyl-2-bromo-4,5-dicyanoimidazole ( 1 ). The reaction of pyridine with 1 serves as a model for the reaction of poly(4-vinylpyridine) with 1 . The reaction of poly(4-vinylpyridine) with 1 gives betaine salt substituted polymers which were characterized by IR, NMR, UV-visible spectroscopy, and viscometry. The substituted polymers were compared to the model compound ( 3 ) and to unsubstituted poly(4-vinylpyridine) in order to determine polymer structure and the degree of substitution. One of the substituted polymers shows polyelectrolyte behavior. Thermal characterization of the substituted polymers shows two exothermic transitions at 260 and 340°C attributed to chemical reactions of the pendant groups.