Effect of salts on the electrical conductance of a fluorine-containing poly(carboxylic acid), PPFNA

Abstract Electrical conductance and other solution properties of aqueous solutions of a fluorine-containing poly(carboxylic acid), (poly(9H,9H-perfluoro-2,5-dimethyl-3,6-dioxa-8-nonenoic acid), PPFNA) were studied with special attention to the salt effect. This polymer dissociated strongly resulting in a low pH value in unneutralized state ( β  = 0, β : degree of neutralization). The specific conductance was the highest at β  = 0 and decreased as β increased. A considerable increase in conductance was observed by titrating NaCl at low β , because large amounts of bound protons were released by addition of NaCl. The amounts of released protons exceeded those originally dissociated at β  = 0. Such an anomalous proton liberation suggests that this polymer is a fairly strong polyacid but not a typical one such as poly(styrene sulfonic acid). Under fully neutralized state ( β  = 1), however, the solution conductance was lower than the sum of the polymer and NaCl added, due to polyion–salt ion interaction.