Gegenion binding in aqueous solutions of tetra-alkylammonium polyacrylates and poly(styrene-sulphonate)s

Abstract

Transference and conductance experiments have been carried out with aqueous solutions of tetra-alkylammonium polyacrylates [R₄NPAA, R = methyl (Me), ethyl (Et), n-propyl (Pr) and n-butyl (Bu)] in the concentration range 0.005–0.1 mol dm^–3 at 25 °C. The fraction of free gegenions (ƒ) was calculated, and it was found that (i)ƒ-values are between 0.4 and 1 and increase with increasing size of gegenion, (ii) the concentration dependence of the ƒ-values becomes great with increasing size of the gegenions, and (iii) the ƒ-concentration curves for Bu₄NPAA and Pr₄ NPAA have maxima. The ƒ-values of tetra-alkylammonium poly(styrene-sulphonate)(R₄NPSt, R = Me and Bu) have also been measured for the concentration range 0.003–0.03 mol dm^–3 at 25°C. The ƒ-values of Me₄NPSt are larger than those of Bu₄NPSt, in contrast with the R₄NPAA case. For R₄NPSt, non-electrostatic interactions between gegenions evidently become significant and lower the ƒ-values.