Polyvinylpyrrolidone (PVP) displays strong binding affinities toward various organic anions such as the azo dyes orange II (O-II) and benzopurpurin 4B (BP). The binding equilibria were studied by a conductance method and by a dialysis technique. It was found that one dyestuff ion is bound by chain segments of 7 or 10 monomer units for O-II and BP, respectively. It is believed that the dye ions align themselves with their long axis alongside the polymer chain and are held in place by van der Waals forces. The effect of added potassium chloride on the binding equilibria was studied. The polyelectrolyte character of the PVP-dye complex was demonstrated by its electroviscous effect. A viscosity reduction in the presence of salt was explained as a cross-linking effect due to aggregation of dye ions.(1) This work was supported by the office of the Surgeon General, Dept, of the Army.
Additional polyvinylpyrrolidone samples of great homogeneity have been prepared, and their intrinsic viscosity and molecular weight (by light scattering) have been determined in water and chloroform. In view of the new results the previous data were reinterpreted particularly with respect to the shift in K (in [η] = KMα) with homogeneity. All data were evaluated by objective statistical techniques and revised intrinsicviscosity molecular weight equations are proposed.
The lactam‐amino acid equilibria of N‐ethylpyrrolidone and poly‐N‐vinylpyrrolidone were studied in dilute aqueous solutions and in n‐butanol at 100°C. and compared with earlier investigations of similar systems. It was found that with in the intermediate pH range the lactam is the predominant form. Below and above certain critical acid and alkaline pH values increasing amounts of amino acid will be formed. It has been shown that these critical pH values are closely related to pK1 and pK2 of the corresponding amino acid. The polymeric lactam PVP is more resistant against hydrolysis than the low molecular lactams. This effect is due to the polyampholyte character of the polymeric amino acid formed in the course of the hydrolysis reaction.
The molecular weight of selected polyvinylpyrrolidone samples was determined by light scattering and by osmotic pressure in methanol. The corresponding limiting viscosity numbers were also determined, as well as the limiting viscosity number of the same samples in water. The data relating to the methanolic system conform with theory and the values for K and α in [η] = KMα were determined. The data relating to aqueous solutions do not show such conformity but an unexplained dependence on the degree of homogeneity of the samples. Nevertheless some empirical constants were deduced which may aid in industrial practice in which aqueous viscosity measurements are usual.
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