Studies on the State of PVA Solution

VII. Association and Precipitation of Polyvinylalcohol in Solution

Abstract

Precipitation points were measured at constant polymer concentration for the dilute polyvinylalcohol solutions, where water and dimethylsulfoxide were used as solvents and acetone, methylalcohol, ethylalcohol and n-propylalcohol were used as precipitants. A plot of the precipitation point γ′(volume fraction of precipitant added, that produces the first haze) vs. 1/[η] showed deviations at high molecular weight region from a linear relationship in all systems measured. These anomalies make the fractionation of polyvinylalcohol impossible at high molecular weight region. Then, the intrinsic viscosity, [η], of polyvinylalcohol in water-ethylalcohol mixed solvent, where the polyvinylalcohol molecules associate stably, was measured and compared with the intrinsic viscosity, [η]₀ in water at 30°[η]/[η]₀, which seems to be the measure of the degree of association, increased with the molecular weight at low molecular weight region but decreased on the contrary at high molecular weight region. Namely, there existed the molecular weight in which the degree of association became maximum. Accordingly, it was concluded that the anomalies of the precipitation point were caused by the effect of the association of polyvinylalcohol.