The application of precipitation-turbidity analysis to polyvinyl acetates

Abstract

The continuous precipitation method of analyzing molecular-weight distribution has been applied to polyvinyl acetate, using acetone as solvent and water as precipitant. Quite low values of concentration are found necessary to achieve reliable results. All materials studied were found to have a wide range of chain lengths extending to quite small ones, difficult to precipitate from dilute solution. This difficulty of precipitation is related to deviations from the linear P γ vs. log C γ law at low values of concentration. The effect of a small amount of hydrolysis on the precipitation point, P γ , is found to be considerable, and the degree of hydrolysis must be held closely constant in order to associate P γ values with chain length. Widely different chain lengths behave independently in their precipitation behavior. The percentage of water required to precipitate, from an acetone solution, polyvinyl acetate made using potassium persulfate in the presence of water has been shown to be greater than the percentage required for the precipitation of bead material or material made by anhydrous dope polymerization. This is due to the slight hydrolysis which occurs in the preparation of the former.