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

Self-diffusion coefficients of several different solvents in polystyre ne as well as methyl methacrylate in poly(methyl methacrylate) have be en determined at polymer concentrations from 0 to 50 wt % at 25-degree s-C. The solvents used for the polystyrene solutions were toluene, eth ylbenzene, cumene, tert-butyl acetate, chloroform, and methyl ethyl ke tone. The diffusion data were used to evaluate several theories for th e concentration dependence of the solvent diffusion coefficients, and in most cases the reduced diffusion coefficients, of solvents in polym er-solvent systems. In addition to the experimental data presented her e, literature data for several systems were also used to test the mode ls. The theories evaluated were based on widely different concepts inc luding electrical conductivity, tortuosity, kinetic theory, and free v olume. The results indicate that the kinetic theory and free-volume ap proaches fit the data most consistently, with the kinetic theory appro ach preferred at lower polymer concentrations and the free-volume appr oach favored at higher polymer concentrations.