NMR IMAGING OF DIFFUSION-PROCESSES IN POLYMERS - MEASUREMENT OF THE SPATIAL DEPENDENCE OF SOLVENT MOBILITY IN PARTIALLY SWOLLEN PMMA RODS

NMR imaging is used to study the spatial distribution of NMR relaxation times and self-diffusion coefficients of organic solvents in partially swollen PMMA. The solvents diffuse with Case II characteristics. T1s, T2s, and self-diffusion coefficients are measured as a function of distance from the glassy core of the polymer. The results show decreases in all three parameters toward the glassy core despite the fact that the concentration of solvent is constant throughout the swollen region. This indicates that the solvent motions are decreasing in that direction. A conceptual model is proposed which attributes the decrease in solvent relaxation times to the decrease in mobility of the polymer chains toward the core. This decrease is a result of the polymer chains being effectively fixed at the interface between the swollen and glassy regions of the sample. Several methods for acquiring images for determining T1s, T2s, and self-diffusion coefficients are demonstrated and compared. © 1990, American Chemical Society. All rights reserved.