Self-diffusion of Toluene in Polystyrene Solutions


The pulsed-gradient spin-echo (PGSE) NMR technique was used to acquire a broad range of solvent self-diffusion coefficients for the toluene/polystyrene (MW 270 000) system. Self-diffusion coefficients were determined for samples having polymer weight-fractions ranging from 0.04 to 0.90 over a temperature range of 25-115°C. Several different approaches to interpretation of the diffusion data have been considered. The temperature dependence of the data exhibits Arrhenius behavior with energies of activation that increase with concentration from 2.6 to 16.2 kcal/mol. Several theories based on the assumption that the solvent diffusion is slowed by the polymer obstructing its diffusion path are also used to interpret these data. Our results support the hypothesis that the normalized diffusion coefficient is relatively independent of thermodynamic parameters. The data are in qualitative agreement with a “standard curve” for normalized diffusion coefficients. This approach shows potential as a tool for predicting diffusion rates over a wide concentration range for a variety of polymer solvent systems. The final approach used to interpret these data is that of the free volume theory proposed by Vrentas and Duda. The agreement between the free volume theory and experimental data is improved considerably if two of the needed parameters are adjusted to give optimum fits to the experimental diffusion data. This approach yielded a root mean squared of the fractional difference between experiment and theory of 14%. © 1989 American Chemical Society.



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© 1989 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Jan 1989