EXCLUDED-VOLUME EFFECTS ON THE HYDRODYNAMIC RADIUS OF OLIGOSTYRENES AND POLYSTYRENES IN DILUTE-SOLUTION

The translational diffusion coefficient D was determined from dynamic light scattering measurements for atactic polystyrene in toluene at 15.0 degrees C and in 4-tert-butyltoluene at 50.0 degrees C in the range of weight-average molecular weight M(W) from 9.20 x 10(2) to 3.84 x 10(6). The hydrodynamic-radius expansion factor alpha(H) was then determined from the values of the hydrodynamic radius R(H) defined from D and those of R(H,Theta) previously obtained in cyclohexane at Theta. The results show that the effect of chain stiffness on alpha(H) is significant as in the case of the gyration- and viscosity-radius expansion factors alpha(s) and alpha(eta). It is also shown that alpha(H) becomes a function only of the scaled excluded-volume parameter ($) over bar z, which is defined in the Yamakawa-Stockmayer-Shimada theory for the helical wormlike chain with excluded volume, irrespective of the solvent condition, indicating that the quasi-two-parameter scheme is valid for alpha H as well as for alpha(s) and alpha(eta). The Barrett equation for alpha(H) with ($) over bar z in place of the conventional excluded volume parameter z gives values appreciably larger than the observed results for alpha(H)(($) over bar z). This disagreement between theory and experiment may be semiquantitatively explained by the new Yamakawa-Yoshizaki theory which takes account of the possible effect of fluctuating hydrodynamic interaction on alpha(H). It is interesting to find that the present data for alpha(H) happen to follow almost quantitatively the Barrett equation for alpha(eta) with ($) over bar z in place oft in the range of M(W) studied.