Mobility of Toluene in Polystyrene-Toluene Solutions: A NMR Study.

摘要

Self-diffusion coefficients, longitudinal (T1) and transverse (T2)NMR relaxation times of toluene in polystyrene-toluene solutions were determined at concentrations up to 50% polymer at room temperature to ca.-70 deg C. The self-diffusion coefficients were used to calculate the fraction of motionally-altered toluene based on deviations from the Maxwell-Fricke approximation of the obstruction effect. The fraction of motionally-altered toluene was found to be nearly constant with temperature for the lower polymer concentrations, but increased with decreasing temperature for the higher polymer concentrations. The relaxation times of the motionally-altered toluene were calculated using the two-fraction fast-exchange model and used to estimate the mean correlation times from a log-normal distribution of correlation times. The dependence of correlation times on temperature was found to be the Arrhenius type and the activation energies increased with polymer concentration. The activation energies for translational diffusion ranged from 12 to 22 kJ/mol and those of the motionally altered solvent's rotational motion from 11 to 42 kJ/mol. Polystyrene, Toluene, Solvent mobility, NMR relaxation, Dynamics, Polymer solutions.