SHEAR RATE EFFECTS IN DETERMINATION OF VISCOSITY AVERAGE MOLECULAR WEIGHT OF POLY (BUT-1-ENE SULPHONE)

Viscosity measurements on solutions of polydisperse poly(but-1-ene sulphone) with Ubbelohde-type suspended level viscometers over the range of shear rates and stresses showed that marked shear dependence occurred at shear rates below 400 sec-1 (shear stresses below 2 dyne cm-2) for polymers with M ̄v ≈ 700 000. Polymers with M̄v below about 250 000 did not show any shear dependence and identical viscosities were obtained with a variety of straight and spiral capillary viscometers. The shear dependence showed a parabolic variation with concentration with a maximum at 5 g 1-1. Plots of ηsp c against concentration for different shear stresses were curved in the shear dependent region and linear at higher shear stresses, but they could all be extrapolated to approximately the same intrinsic viscosity at zero concentration, provided that measurements at sufficiently low concentrations were included. However, linear extrapolations of viscosity measurements made at moderate concentrations in the shear dependent region could result in large errors in M̄v. © 1968.