Molecular Weight and Intrinsic Viscosity of Potassium Polyphosphate

Abstract

In order to study the solution behavior of polyphosphate compounds, light scattering and viscosity measurements were made on the aqueous solutions, with added sodium chloride, of potassium polyphosphate prepared under the various polymerization conditions. Under the control of heating time, potassium polyphosphate samples with a -wide variety of molecular weight were synthesized. The relationship between the weight-average molecular weight, Mw, and intrinsic viscosity, [η], of potassium polyphosphate in a saline solution (0.1mol/l) was represented by equation [η] = 1.80×10^-5 M^0.87at 25°C for the molecular weight ranging from 72000 to 1340000. On the other hand, the relationship between the z-average radius of gyration, (RG)z, and the weight-average molecular weight, Mw, could not be represented by one equation, showing different slopes in the low and high molecular weight regions. In view of the discrepancy between the viscosity and the gyration radius behavior, the polydispersity in molecular weight was examined on the several potassium polyphosphate samples by gel filtration and light scattering methods. The molecular weight distribution was found to be narrow for high molecular weight samples, but considerably broad for low molecular weight samples. After making correction of the effect of molecular weight distribution, two equations, [η]= =3.04×10^-5 M^0.83 and, [RG]w=0.48 M^0.52, were obtained for the molecular weight range from 93000 to 1340000.