Investigation of the Microphase Separation in Blends of Polyurethane-Based Ionomers

Abstract

Blends of an anion containing polyurethane (PU1) and polyaminourethane (PU2) were investigated. Dielectric relaxation spectroscopy (DRS), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) were used in a study of the molecular mobility and microphase morphology and their dependence on the composition of these ionomers. Dielectric thermally stimulated depolarization current (TSDC) measurements of the ionomer blends showed four relaxation mechanisms. The subglass secondary γ- and β-relaxations are related to local motions; the α-relaxation is related to the glass transition of the amorphous soft phase of the ionomers, and the Maxwell-Wagner-Sillars (MWS) relaxation is related to interfacial polarization caused by the motion of ions released during the glass transition. The α- and MWS TSDC relaxations are strongly affected by the degree of microphase segregation (DMS) of the ionomer blends. Based on TSDC measurements, the parameter m TSDC, a criterion expressing a relative degree of phase mixing, is introduced. According to this parameter, the classification of the investigated ionomer blends, in order of decreasing phase mixing (PU1/PU2 in %) is 50/50 (mixed) > 0/100 > 5/95 > 10/90 > 100/0 > 30/70 (high separation). It appears that, as a result of the complexity of the systems, their structures and their properties are not simple functions of their composition. SAXS measurements show that pure PU1 ionomer has a high degree of microphase separation. The introduction of PU2 in the blend causes defects in the hard domains and leads to a structure with mixing of the soft and hard microphases. SAXS measurements concerning DMS are in good agreement with the TSDC results and support the introduced criterion of the relative degree of phase mixing.