Polyelectrolytes. II. Poly‐4‐vinylpyridonium chloride and poly‐4‐vinyl‐N‐n‐butylpyridonium bromide

Abstract

Poly‐4‐vinylpyridine was precipitated from a toluene solution of the monomer after addition of benzoyl Peroxide. The sample used in these experiments had a molecular weight of 77,000, (DP 730) as determined by osmotic pressure in alcohol solution, and an intrinsic viscosity of 0.36 in this solvent. The hydrochloride is water soluble and behaves like the salt of an extremely weak base with an over‐all average base dissociation constant of 0.011 × 10−9, about one thousandth that of 4‐ethylpyridine. The decrease in apparent base strength is ascribed to the chain structure which produces high local concentrations of pyridine groups, independent of the total concentration. By addition of butyl bromide to the polymer in nitromethane, a long chain quaternary ammonium salt is formed which is also water soluble. Its conductance is not sensitive to concentration down to about 0.003 N, after which the conductance rises sharply with further dilution. Dissociation, calculated by the classical Arrhenius method, indicates that a minimum of about 20% of the bromide ions are free, the remainder being associated by Coulomb attraction to the chainlike positive ion. As the dielectric constant of the solvent is decreased by addition of ethanol, the relative amount of free bromide ions decreases. The viscosity of the polyelectrolyte in aqueous or alcoholic solution, when plotted in the conventional way (ηsp/c versus c), approaches infinity at zero concentration instead of approaching a limiting constant linearly. A plot of $ {{\eta _{sp} } \mathord{\left/ {\vphantom {{\eta _{sp} } {\sqrt c }}} \right. \kern‐\nulldelimiterspace} {\sqrt c }} $ versus $ \sqrt c $ is, however, linear; this behavior is characteristic of strong electrolytes. The coefficient of the square root term in concentration for the polymer is larger, by orders of magnitude, than that for ordinary electrolytes. The coefficient of the linear term in the square root function is about equal to the intrinsic viscosity of the parent polymer.