Light Scattering Study of Ionomers in Solution. 5. CONTIN Analysis of Dynamic Scattering Data from Sulfonated Polystyrene Ionomer in a Polar Solvent (Dimethylformamide)

Salt-free polyelectrolyte behavior of a random ionomer, partially sulfonated polystyrene (SPS) (Na salt) having an ion content of 2.7 mol %, dissolved in a polar, aprotic solvent, dimethylformamide (DMF), is studied by dynamic light scattering. CONTIN analysis of the data indicates the existence of two diffusive modes, a fast mode and a slow mode. The diffusion coefficient of the fast mode, D_f, on the order of 10^–6 (cm²/s), increases slightly with ionomer concentration, while the diffusion coefficient of the slow mode, D_s, on the order of 10^–8 (cm²/s), is independent of ionomer concentration within the concentration range studied. The D_f shows a negative angular dependence, while the D_s shows a positive angular dependence. The fast mode may be explained in terms of the diffusion process enhanced by strong intermolecular electrostatic interactions, and the slow mode may reflect the existence of large-scale “heterogeneities”. These conclusions are consistent with those drawn from static (angular) light scattering data for the same system. The results obtained for salt-free ionomers in a polar organic solvent parallel those reported for salt-free polyelectrolytes in water.