PEO-based polyurethane sulfonate ionomers with various PEO chain lengths and sodium counterions were synthesized and characterized by both linear viscoelasticity (LVE) and dielectric relaxation spectroscopy (DRS). Since p-phenylene diisocyanate is a small hard segment, the ionomers were found to be single phase with only one DSC Tg which increases with both ion content and hard segment content. An electrode polarization model was used to simultaneously determine the temperature dependence of conducting ion concentration and their mobility, which show Arrhenius and Vogel-Fulcher-Tammann (VFT) temperature dependences, respectively. The polymer dipole relaxation probed by DRS was found to be between 103 and 106 times faster than the mechanical segmental relaxation observed in LVE data near Tg, suggesting that most polymer modes need to wait for the ions to rearrange. The dielectric relaxation, mechanical relaxation, and ionic conductivity all show good correlation with DSC Tg and are related to ion rearrangement. Lower ion content creates lower Tg, lower activation energy for conducting ions, and higher ion mobility, as sodium cations interact strongly with both PEO and the urethane linkage.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry