ABSTRACT:A number of samples of sodium potassium (Na: K = 9: I to 3 : 7) and lithium potassium (Li: K = 9: I to 5 : 5) copolyphosphates were prepared and characterized. Their numberaverage molecular weights were determined by end-group titration and intrinsic viscosities \Yere 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.KEY The long chain polyphosphates have been prepared and characterized by a number of workers over the last several decades. 1 -3 The techniques generally employed for determining their molecular weights include light scattering, 4 · 5 end-group titration, 6 • 7 and viscosity.4·7. Bhargava et a/. 5 • 7 · 8 have used all these techniques in a number of cases involving simple polyphosphates and Mehrotra et a/. 9 used the technique of end-group titration and viscosity in the case of compounds which could be termed 'copolyphosphates.' These are counter cation copolymers containing two kinds of cations attached to a polyphosphate chain -P-0-P-0-P-0, etc. Mehrotra et a/., 9 however, simply used the intrinsic viscosity [IJ]-weight-average molecular weight (Mw) relationship given by Strauss et a/. 4 for sodium polyphosphates without realizing that it could not hold good in the case of other poly-and copolyphosphates. In the present work [1]]-Mn relationships were obtained for a number of copolyphosphates having two cations. One series of compounds had sodium and potassium in molar ratios varying from 9 : 1 to 3 : 7 and another series had lithium and potassium in molar ratios 9: 1 to 5 : 5. While NaP0 3 and KP0 3 units made up the former copolyphosphates, LiP0 3 and KP0 3 units were interlinked in the latter ones.
