Electrolytic conductivity of branched polyelectrolytes

Abstract

The conductivity behaviour of branched polyelectrolytes, obtained by substituting dextran with carboxymethyl groups to varying degrees of substitution, has been investigated. Measurements were carried out with the polyelectrolytes in the form of Na, K and Ca salts and in the form of the acid. The concentration dependence of the equivalent conductivity was studied in detail and the limiting equivalent conductivity ∧^° was determined. Compared with linear polyelectrolytes the phoreograms of branched polyelectrolytes showed some characteristic deviations, especially at high charge densities. The counterion binding was found to be stronger than in corresponding linear polyelectrolytes and the comparatively low polyion equivalent conductivities indicate a more extensive screening of the polyion charges by the counterions. For the polyacids the acid strength apparently decreased with increasing charge density. This was found to be due to local concentration effects, the dissociation constant of the carboxylic groups remaining essentially unchanged.