Density measurements of poly(acrylic acid) sodium salts

Summary Density measurements of poly(acrylic acid) sodium salts (PANa) with different degrees of neutralization and water contents are presented. The apparent partial molar volumes of polymer, V₂^*, and the partial molar volumes of water, V₁, were calculated from the densities. The values of V₂^*decreased with increasing water content and eventually leveled off. The values of Vj, which at low water contents were much smaller than that of free water increased with increasing water content and reached that of free water, showing consequently the appearance of free water. Before reaching the final value of free water, the data indicated the formation of primary and secondary hydration shells. The structure of primary hydration was suggested to be of octet coordination in which carboxyl oxygen atoms participate.