Molecular weight dependence of intrinsic viscosity, diffusion constant, and second viral coefficient of polyacrylonitrile

Careful intrinsic viscosity and diffusion constant measurements are reported for nine fractions of polyacrylonitrile prepared by repeated refractionation. For a molecular weight range of from 28,000 to 575,000, relationships are obtained between second virial coefficient, diffusion constant, or intrinsic viscosity in dimethylformamide at 35°C., and absolute molecular weight. These relationships are represented by the equations: and where the units of intrinsic viscosity are 100 ml./g. An explanation is offered for the difference between the viscosity equation and other similar equations in the literature, as well as for the discrepancies among the various equations in the literature. Empirical plots of k D vs. [η] are presented, giving lines which are straight within the limits of accuracy of the data. From these results, the following relation was obtained: c = 1 − α, where α is the exponent in [η] = K I M α , and c is the exponent in A 2 = K III M − c .