Methylenebis(p-phenyl isocyanate)-Based Polyurethane Ionomers. 1. New Small-Angle X-ray Scattering Model

Small-angle X-ray scattering (SAXS) data have been obtained on a series of elastomeric MDI-based polyurethane model ionomers. Unlike random copolymer ionomers, the ionizable groups of the polyurethane ionomers are regularly spaced. The SAXS data for these ionomers show both the usual ionomer peak and a prominent shoulder at higher angle, suggesting an ordering of the ionic microdomains. The data are fit to a scattering model based on ionic microdomains organized as micronetworks of beads and springs, dispersed in the polymer matrix with a liquidlike order. The model parameters include the ionic aggregate (bead) radius, the distance between aggregates, the average cross-link functionality of the aggregates, the effective radius of the micronetwork, and the volume fraction of micronetworks in the material.