Structural studies of polyurethane ionomer solutions .1. Dynamic light scattering

Viscometry and dynamic light scattering experiments have been used to characterize model polyurethane ionomers in dimethylacetamide (DMAc). The structures in solution are studied as a function of concentration and ionic content. These ionomers have regularly spaced ionic groups and form good model. systems to study the effect of ionic interactions on the properties of polymers. These ionomers in DMAc are found to exhibit characteristic behavior of salt-free polyelectrolyte solutions. Viscometric measurements show an upturn in reduced viscosity at very low concentrations. Analysis of dynamic light scattering data by CONTIN indicates the existence of two diffusive modes, a fast mode and a slow mode, differing by 2 orders of magnitude. The diffusion coefficient of the fast mode increases slightly viith concentration, whereas the diffusion coefficient corresponding to the slow mode is independent of concentration within the concentration range studied. The rate of increase of the diffusion coefficient of the fast mode with concentration increases with increasing ionic content. The fast mode arises from intermolecular electrostatic interactions while the slow mode is due to motions associated with the formation of domains of associated polymer chains. Both modes do not show any time dependence, suggesting that the solution structures are at equilibrium. The slow mode persists even after filtration through filters with pore sizes that are small compared to the size of domains and therefore the formation of domains is due to reversible interactions in solution. These results indicate that free polyions and associated species coexist in dilute solutions of polyurethane ionomers in polar solvents.