Dynamics of Ionomer Networks Studies by Pulse Field Gradient (PFG) NMR*

Ionomer networks are formed in solutions at extremely low concentrations. Tuning these networks offers a means to control the structures that remain trapped as the solvents evaporate to form membranes. Here, we probe the diffusion of the polymers and the solvents in networks formed by polystyrene sulfonate (PSS) by pulse field gradient NMR. The diffusion of the polymer reflects the properties of the network and that of the solvent. Specifically, PSS networks with sulfonation levels of 0, 3 and 9 mole % were studied in toluene and cyclohexane neat and mixed with ethanol. Toluene is a good solvent for polystyrene and cyclohexane is a theta solvent at room temperature. We find that with increasing sulfonation levels, both the polymer and the solvent motions decrease in both solvents. Regardless of sulfonation level, the diffusion of PSS is almost same in cyclohexane and toluene at room temperature. With increasing temperature, the diffusion of all components increases in both solvents however it is more pronounced in cyclohexane. The solvents diffuse faster than the polymers but follow similar trends. While perturbing the ionic clusters affect the overall network dynamics, the polar solvent also affects the hydrophobic network rigidity.