A NUCLEAR-MAGNETIC-RESONANCE STUDY OF TOLUENE-POLYISOBUTYLENE SOLUTIONS .2. VRENTAS-DUDA THEORY

The self-diffusion coefficients of toluene in polyisobutylene have bee n analyzed using the Vrentas-Duda free volume diffusion model. The dif fusion coefficients were determined at different temperatures and conc entrations, using the pulsed field gradient nuclear magnetic resonance technique. The data were satisfactorily described by the model and th e size of the polymer jumping unit was extracted. Comparisons were mad e With the Fujita free volume theory and the Fujita free volume parame ters were extracted from the Vrentas-Duda free Volume parameters. From the diffusion data that now available, it can be concluded that for m ost polymers the jumping unit is about 1.5 times the polymer monomer m olecular weight. The activation energy of the toluene diffusion in pol yisobutylene is compared with the activation energies of other penetra nts in the same polymer. The diffusion data presented in this work sho w that the energy per mole required to overcome the attractive forces which constrain a diffusing species to its neighbors should be conside red to be zero, in order to be able to extract the free volume paramet ers (from viscosity and diffusion data) with an acceptable uncertainty . (C) 1995 John Wiley & Sons, Inc.