Single and multi-component diffusion at infinite dilution in polyisobutylene

In this study, diffusion coefficients of acetone, benzene, chloroform, cyclohexane and methyl ethyl ketone (MEK) in polyisobutylene (PIB) have been measured at temperatures in the range 40-70 degrees C using capillary column inverse gas chromatography (CCIGC). The measured diffusion coefficients for the PIB/MEK system, considered to be at infinite dilution of the solvent, agree very well with those determined previously from gravimetric and spectroscopic techniques when extrapolated to the limit of zero MEK concentration. The Vrentas-Duda free-volume theory for diffusion is used to correlate the diffusivity data at infinite dilution as a function of temperature, and the effect of solvent size on the diffusion process in PIE is studied. In addition, diffusion coefficients of MEK/toluene and MEK/ethanol mixtures in PIE have been measured at 50 degrees C. The CCIGC model for binary systems is used to determine diffusion coefficients for each solvent individually over a wide range of mixture compositions. The resulting values are identical to those determined from pure component data, confirming the hypothesis that the diffusion coefficient at infinite dilution is independent of a second infinitely-dilute component, with or without solvation between mixture components. (C)) 1999 Society of Chemical Industry.