EXCLUDED-VOLUME EFFECTS IN DILUTE POLYMER SOLUTIONS .2. LIMITING VISCOSITY NUMBER

Measurements of [η] were made for seven fractions of polychloroprene (PCP) in methyl ethyl ketone, n-butyl acetate, and carbon tetrachloride at 25°C and for three fractions of PCP in /rajw-decalin at a number of temperatures ranging from 0.05° to 65°C. On a log-log graph paper, the values of aη3( = [η]/[η]θ) calculated from these data formed a composite curve when plotted against αs3,(= 〈S2〉3/2/ 〈S2〉0 8/2) obtained from light-scattering experiments under the same conditions. This curve is characterized by a relatively marked upward curvature in the vicinity of the origin, followed by a linear portion of unit slope. Its initial tangent has a slope of 0.65, which is much smaller than 0.81 predicted theoretically by Kurata and Yamakawa. Plots of αη3 vs the interaction parameter a were prepared by evaluating z for each as, by use of the Yamakawa equation. They were fitted by a single curve having a slight downward curvature, suggesting that no drainage effect manifests itself in the viscosity behavior of the systems studied. This curve explains why the familiar Stockmayer-Fixman method to treat [η] in non-θ solvent systems works, despite the fact that, as shown previously, data for αs as a function of molecular weight, solvent species, and temperature can be reasonably well described by the modified Flory or by the Yamakawa equation. Recent viscosity data of Berry on polystyrene were re-examined in terms of the present method, and it was found that his demonstration of the drainage effect on [η] is not yet conclusive.