Ultrasonic study of molecular association of aqueous solutions of poly(vinyl alcohol). A method to determine molecular weight

Abstract

Ultrasonic velocity and iso-entropic compressibility measurements are reported for aqueous solutions of poly(vinyl alcohol) (PVA) of various molecular weights and various concentrations using a pulsed ultrasonic apparatus operating at 2 MHz and 303 K. The data obtained as a function of concentration indicate the magnitude of the contributions due to relaxation of the backbone and of the side-chain acetyl group. The results show a linear increase of velocity, density and viscosity with increasing molecular weight and concentration of PVA. In contrast, the iso-entropic compressibility decreases with increasing molecular weight and concentration of PVA. This suggests interaction between PVA and water molecules. A mathematical equation correlating iso-entropic compressibility and molecular weight of the polymer is suggested. It was applied to calculate the molecular weight of four unknown samples of PVA from their measured iso-entropic compressibility. The results agree well with those obtained from osmometry.