Linear Viscoelasticity and Cation Conduction in Polyurethane Sulfonate Ionomers with Ions in the Soft Segment-Multiphase Systems

PEO600-based polyurethane ionomers with various hard segment contents were synthesized and characterized by both linear viscoelastic (LVE) properties and dielectric relaxation spectroscopy. The ions were placed in the soft segment to achieve better ionic conductivity while the hard phase can provide mechanical strength. Microphase separation was observed in all samples with more than 23 wt % hard segment. The samples that show evidence of microphase separation share similar soft phase glass transition temperature, but the degree of microphase separation and ionic conductivity were found to be significantly affected by specimen preparation method (hot pressed or solution cast). Both ionic conductivity and polymer chain mechanical relaxation show VFT or WLF temperature dependence. At 150 °C, the microphase-separated samples were found preserving both the ionic conductivity and mechanical modulus. While most literature focuses on gel polymer electrolytes or block copolymers to obtain both high modulus and high conductivity in single-ion conductors, our polyurethane ionomers demonstrate an alternative path to simultaneously high modulus and ionic conductivity.