Huggins' k' as a Measure of Non-Linearity in Normal and Cross-Linked Polystyrene

Abstract

Polystyrene samples prepared in emulsion at 55 C were carefully fractionated. The resulting fractions were in turn fractio­nated, combined in groups having similar intrinsic viscosities, and re-­fractionated. As the intrinsic viscosity of these fractions increased, the value of Huggins' k' in methyl ethyl ketone was found to increase a slightly ( from 0.39 to 0.41). Polystyrene samples prepared in exactly the same way except for the addition of small amounts of divinylbensene, a cross-linking agent, were similarly fractionated. The value of k' in methyl ethyl ketone for these fractions increased considerably (from 0.41 to 0.68) as the intrinsic viscosity increased, even though the amount of divinylbensene added was very small (from 0.003to 0.05%). Relations were then established for these cross-linked fractions between k' and the proportion of divinylbensene present, and between k' and the intrinsic viscosity of the fractions. It was concluded that polystyrene prepared in emulsion at 55 C. is essentially linear in structure, and that the value of Huggins' k* seems to provide a convenient and sensitive test for the presence of any appreciable branching that might occur in polystyrene.