Polyphosphates as Polyelectrolytes. I. Light Scattering and Viscosity of Sodium Polyphosphates in Electrolyte Solutions¹

Several samples of sodium polyphosphate, covering a molecular weight range from 7000 to 19000, were prepared by thecondensation polymerization of primary sodium phosphate. The viscosity and pH of freshly prepared solutions decreasedover the first 12-hour period, indicating the presence of a small amount of unstable branch-points in the glasses. Afterstability was obtained, light scattering and viscosity studies using sodium bromide solutions as solvents gave the followingresults: (1) The conventional Hc/ versus c plots were straight lines whose slopes decreased with increasing sodium bromideconcentration of the solvent. (2) For a given polymer sample, the Hc/ intercepts were the same in all solvents. (3) Thelight scattering molecular weights were proportional to the intrinsic viscosities obtained in 0.035 N sodium bromide. (4)The slopes of the Hc/τ versus c lines in a given solvent were independent of molecular weight. (5) Measurements of a samplein several solvents yielded a simple linear relationship between light scattering slope and intrinsic viscosity. (6) The vis-cosimetric root-mean-square end-to-end distance of a sample in the 0.35 N sodium bromide solution, in which the light scatter-ing slope is zero, supported the view of polyphosphate molecules as unbranched chains with very little steric hindrance tointernal rotation.