THE VARIATIONS OF THE CONFIGURATIONAL AND SOLVENCY PROPERTIES OF LOW-MOLECULAR-WEIGHT SODIUM POLYACRYLATE WITH IONIC-STRENGTH

The configurational and solvency properties of low molecular weight sodium polyacrylate have been determined for a wide range of ionic strength solutions, from intrinsic viscosity data in the polymer literature. The variations of the polymer properties with ionic strength (I) are described very well by simple mathematical expressions. Thus, a linear relationship was found between the solvency parameter and 1/I-(1/2), while the variations of the expansion factor and the radius of gyration with 1/I-(1/2) were described by second order polynomials. Low I solutions (i.e. < 0.01) have a high solvency for sodium polyacrylate. In such solutions the polymer is in a highly expanded configuration, Thus, the radius of gyration of a typical, low molecular weight ten, 5000 g mol(-1)) sodium polyacrylate approaches the limiting value of ca. 4.5 nm at I < 0.01. Conversely, high ionic strength solutions (i.e. > 0.10) have a low solvency for sodium polyacrylate. In such solutions the polymer is in a virtually unexpanded configuration. Thus, the radius of gyration of a typical, low molecular weight sodium polyacrylate approaches the limiting value of ca. 2.0 nm at I > 0.10.