Hydrodynamic-Radius Expansion Factor of Polystyrene in Cyclohexane near the .THETA. Temperature

Abstract

The translational diffusion coefficient D was determined from dynamic light scattering measurements for atactic polystyrene (a-PS) in cyclohexane at various temperatures ranging from 30.0 to 45.0 °C, above and below Θ, in the range of weight-average molecular weight M w from 1.27 x 10 6 to 6.40 x 10 6 . The hydrodynamic-radius expansion factor α H determined from D is found to deviate from the first-order perturbation theory values even for small |z, indicating that its (first) coefficient of z may be too large, where z is the scaled excluded-volume parameter defined in the Yamakawa-Stockmayer-Shimada theory for the perturbed helical wormlike chain. The present data for α H plotted against z give a single-composite curve together with the previous ones for a-PS in toluene and in 4-tert-butyltoluene, confirming that the quasi-two-parameter scheme may be valid for α H as well as for the gyration- and viscosity-radius expansion factors as and α η irrespective of the solvent condition. It is also found that α H coincides with α η within experimental error over the whole range of z studied.