Concentration dependence of equivalent conductivity of polyelectrolyte

Equivalent conductivity of aqueous solutions of alternating copolymer of iso-butyl vinyl ether and maleic acid, [poly(iso BVE-co-MA)] was studied, especially its polymer-concentration dependence. Various species of counterions such as quaternary ammoniumions (NMe4+, NEt4+, NPr4+, NBu4+) and divalent ions (Ca2+, Sr2+, Ba2+) were employed besides alkali metal ions. The applicability of Manning's conductivity theory was examined for the case of univalent counterions at various degrees of neutralization (beta). A major discrepancy against the theory was observed at beta = 1.0, while a comparatively good agreement was found at beta around 0.5. This suggests that the rod-like polyion model, which is the basis of the theory, is applicable near beta = 0.5, where polyions are most expanded. The low conductivities in the case of quaternary ammonium counterions suggested the ion-binding due to hydrophobic interaction with alkyl side chains. Molecular weight dependence was not appreciably observed near beta = 0.5 similarly to usual polyelectrolytes, but it appeared slightly at beta = 1.0.