Hydrophobic Aggregation in Polyurethane Ionomer Solutions.

Model polyurethane ionomers were synthesized with regularly spaced ionic groups along the polymeric backbone. Viscometry and static and dynamic light scattering applied to these ionomer solutions in a polar solvent, N-methylformamide, revealed hydrophobic interactions and aggregated ionomer chains in solution. A new regime in the solution behavior of ionomers characterized by low reduced viscosity at all dilute concentrations has been identified. Spherical particles of radius 30 nm with a polymer core and an outer ionic shell are formed. The solutions have very low viscosity because of the formation of compact structures. The electrostatic interactions in these solutions are effectively screened, resulting in the absence of polyelectrolyte behavior. Polymer-solvent interactions are found to be very important in determining the ionomer solution behavior in polar solvents. Copyright 1998 Academic Press.