Influence of Ionic Content 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 characteristic polyelectrolyte behavior. An upturn is seen in reduced viscosity measurements, an abnormal Zimm plot is obtained from static light scattering (SLS) measurements, and two diffusive modes are seen in dynamic light scattering (DLS) measurements. A combined analysis of SLS and DLS data indicated the presence of single polyions, as well as loose aggregates in solution. Loose aggregates are domains consisting of polyions held together by electrostatic interactions. The results show that, even when the solvent is a poor solvent for the ionomer backbone, sufficiently high ionic content can cause dissolution of the ionomer without any backbone aggregation. The ionic content of an ionomer is identified as a critical parameter in determining ionomer solution behavior.