Intrinsic Viscosity–Molecular Weight Relationships in Copolyphosphates

Abstract

A number of samples of sodium potassium (Na:K=9:1 to 3:7) and lithium potassium (Li:K=9:1 to 5:5) copolyphosphates were prepared and characterized. Their number-average molecular weights were determined by end-group titration and intrinsic viscosities were determined in 0.035 N NaBr solution. Intrinsic viscosity–molecular weight relationships according to the Mark–Houwink equation were established for each series of compounds. A highly interesting feature of the results obtained was a decrease in the value of the constant a with an increase in the mole fraction of potassium in the copolyphosphates. This is a remarkable demonstration of the dependence of a on the degree of solvation; the solubilities of both kinds of copolyphosphates were found to decrease with an increase in the proportion of potassium.