Heats of dilution of aqueous solutions of polyethylenimine hydrochloride and sodium polyphosphate and their low molecular weight analogues

Abstract

The heats of dilution (ΔH) of the hydrochlorides of polyethylenimine (PEI) and sodium polyphosphate (NaPP) and their low molecular weight analogues have been measured. Under the conditions employed, the ΔH values of the hydrochlorides of PEI and ethylenediamine (ED) are negative whereas those of hydrochlorides of diethylenetriamine (DT), triethylenetetramine (TT) and tetraethylenepentamine (TP) are positive. The positive ΔH values are largely due to the hydrolysis of the salts. Taking into account the degree of hydrolysis, the ΔH values for PEI·HCl, ED(HCl)₂, DT(HCl)₃, TT(HCl)₄ and TP(HCl)₅ can be explained by the Debye–Hückel theory and Manning's limiting law. On the other hand, the observed ΔH values of NaPP and its low molecular weight analogues were negative. Excellent agreement was observed for NaPP with Manning's theory and Lifson–Katchalsky's theory. For low molecular weight phosphates a discrepancy occurs between the Debye–Hückel theory and experiment.