DEPENDENCE OF THE SOLVENT DIFFUSION-COEFFICIENT ON CONCENTRATION IN POLYMER-SOLUTIONS

Self-diffusion coefficients of several different solvents in polystyrene as well as methyl methacrylate in poly(methyl methacrylate) have been determined at polymer concentrations from 0 to 50 wt % at 25-degrees-C. The solvents used for the polystyrene solutions were toluene, ethylbenzene, cumene, tert-butyl acetate, chloroform, and methyl ethyl ketone. The diffusion data were used to evaluate several theories for the concentration dependence of the solvent diffusion coefficients, and in most cases the reduced diffusion coefficients, of solvents in polymer-solvent systems. In addition to the experimental data presented here, literature data for several systems were also used to test the models. The theories evaluated were based on widely different concepts including electrical conductivity, tortuosity, kinetic theory, and free volume. The results indicate that the kinetic theory and free-volume approaches fit the data most consistently, with the kinetic theory approach preferred at lower polymer concentrations and the free-volume approach favored at higher polymer concentrations.