Comments on Paper by Nemoto et al. Concerning Self Diffusion Coefficient, Ds, and Zero Shear Viscosity, η0 of Polystyrene in Dibutylphthalate

Abstract

KEY WORDSSelf Diffusion/ Steady Viscosity/ Dibutylphthalate / Atactic Polystyrene / Solutions / Regression Analysis / Liquid-Liquid Transition / Arrhenius Plots / T11 / Nemoto et al. 1 obtained data on two narrow distribution at-polystyrenes, M. = 43300 and M.=335000 at concentration of 40 and 50% by weight in dibutylphthalate at temperatures from O to 120°C. Data were presented in both tabular and graphical form. They concluded correctly that these data did not follow a simple Arrhenius plot for either log D, -T-1 or log Y/o -T-1 • Then they fitted these data by the WLF procedure. 2 They concluded that this free volume approach yielded a correct description of their results.Visual inspection of their plotted data, their Figures 3a and 3b specificalJy, with assistance from a straight edge, suggested to us an opposite conclusion, namely, that all experimental data for D, and Y/o followed a double or possibly a triple Arrhenius plot whose intersections implied liquid state transitions, one of which is Tu lowered from its bulk state value by diluent. T 11 is the intramolecular liquidliquid transition normalJy found in atactic polymers and copolymers at (1.20 ± 0.05) Tg(K); the other is an intramolecular event designated T14>. 6 As we have noted on several occasions, 3 • 5 -7 Frenkel and his colleagues postulate that Tu arises from intermolecular segment-segment associations which are thermalJy reversible and shear reversible. The source of these associations is the same intermolecular attraction that holds simple liquids together. These associations lead to a three dimensional physical network which inhibits but does not prevent flow. We suggest 6 that the sharp decrease in enthalpy of activation for Y/o across Tu

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