ROW: Ionic Interactions and Morphology in Ionomers by Electron Magnetic Resonance Methods

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The objective of this research is to study the molecular and structural aspects of phase separation in ionomers (ionic polymers) by continuous wave (cw) and pulsed Electron Spin Resonance (ESR) methods. This approach is well suited for studying the complex heterogeneous structure of ionomers, because it is non-invasive and allows selective study of the portion of the sample where the paramagnetic probe is located. In the hydrophilic phase, attempts will be made to define the local environment of the cations, the intercation distance and the size of ionic aggregates. The mobility and degree of crystallinity of the polymer chains in the hydrophobic phase will be studied using peroxy radical probes. The interface, and the penetration of the polar regions into the organic network, will be studied by following the partition and dynamics of nitroxide probes whose hyperfine splittings are sensitive to the polarity of the medium. Weak interactions of the paramagnetic centers with neighboring protons and deuterons, which cannot be detected by cw ESR, will be studied by Electron Spin Echo (ESE) spectroscopy. DSC studies will be used to detect heterogeneity in the phase structure and to deduce the relative amounts of bound and mobile water in the system. Perfluorinated ionomers containing sulfonic and carboxylic groups and polyurethane ionomers containing carboxylic groups will be investigated. These studies are important for an understanding of ionic transport and selectivity in synthetic and biological membranes, of photo-induced charge separation processes in ionomers, and also for polymer blends in which phase separation is prevented by crosslinking ionic groups.