Mechanical denaturation of high polymers in solutions

Abstract

In order to clarify the mechanism of crystallization under molecular orientation, the rates of precipitation of poly(vinyl alcohol) (PVA) from aqueous solutions under shearing force were measured under various conditions. The fractionation was carried out by separating the precipitates at time intervals. The shearing force was brought about in the solutions by stirring. The rate of precipitation was found to depend not only on the thermal motion of molecules, but also on the fluidity of the solution. In other words, at temperatures above 45°C, the initial rate of precipitation became smaller with increasing temperature, but at 45 °C it was higher than that at the lower temperature than 40°C. The rate of precipitation at 35°C decreased with the increase of the polymer concentration. At the constant polymer concentration, the maximum of the rate of precipitation was recognized at a certain chain length. The molecular weight of fractions decreased in the order of fractionation. As compared with the non-solvent addition method, the difference in the s-(diad) % of the initial fraction and the last fraction was large in the case of stirring fractionation. Therefore, the stirring fractionation of PVA depends not only on the molecular weight, but also on the tacticity.