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Our research interest is exploitation of strong ionic bonds in polymers to develop new materials and to understand such bonding in polymers. Ionic bonds are responsible for various properties of many ceramic materials, while covalent bonds are responsible for conventional polymers. We are combining these strong bonds in materials by adding ionic bonds to polymers. This can be achieved in two ways both of which involve enhancing intermolecular interactions through strong ionic bonds: (1) in the same polymer molecules (producing ionic polymers); and (2) in different polymer molecules (producing polymer blends and composites).
Our research efforts are focused on the structure-property characterization of ionic polymers in solution and solid state, and on the development of novel materials by utilizing ionic bonds in polymeric systems. Specific projects that have been investigated are as follows
First, we are investigating solution behavior of ionomers (ionic polymers with low charge density). Ionomers dissolved in organic solvent show two types of behavior: one is aggregation behavior arising from association of ion pairs in a nonpolar solvent, and another is polyelectrolyte behavior due to ionic interactions among ions in a polar solvent. Our research is focused on the elucidation of molecular (or supermolecular) structures of these solutions by using scattering techniques, such as static and dynamic light scattering.
Second, we have been developing ionic molecular composites, in which defect-free, rigid-rod molecules are used as a reinforcer. Ionic bonds are used to enhance miscibility (and dispersity) of rod molecules with the matrix polymers. Unlike many molecular composites developed elsewhere, our materials are melt-processable. It is demonstrated that the small addition of ionic rod molecules into the polar polymer matrix leads to a significant change in the deformation modes and to the effective enhancement in bulk mechanical properties. These are considered to be a new type of composite.
Third, we have been investigating ionic liquid crystalline polymers (LCP), such as ionic KevlarŽ and ionic VectraŽ. Although very high longitudinal strength and stiffness are achieved in an LCP due to alignment of polymer molecules, transverse strength and compressive strength are much smaller; this has prevented them from wider applications. We have demonstrated that the introduction of ionic groups leads to enhanced compressive strength without sacrificing excellent tensile properties. Furthermore, an ionic LCP can be more miscible with many polar polymers than unmodified LCP, again due to strong ionic interactions between them. An example is ionic Vectra/poly(ethylene terephthalate)(PET) system.
Fourth, we have been investigating nano-composites in which inorganic and metallic elements are dispersed in polymer matrix. Here, ionomers are used as a matrix polymer. Due to favorable interactions between functional groups of polymers and nano-particles, the stability of nano-sized dispersed phase is maintained and further aggregation can be prevented.
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Recent Publications
Hara, M., (2001) Polyelectrolytes in Nonaqueous Solution, in Physical Chemistry of Polyelectrolytes, Ts. Radeva ed., Marcel Dekker, New York, Chap. 9, 245-279.
Xue, Y., Yoon, H., Hara, M. (2001) Ionic Naphthalene Thermotropic Copolyesters: Enhanced Compressive Properties of Fibers, Macromolecules, 34, 844-851.
Chen, W.C., Sauer, J.A., Hara, M. (2001). Ionic Poly(p-phenylene terephthalamides): Preparation and Characterization, J. Polym. Sci., Polym. Phys. Ed., 39, 2653-2663.
Chen, W.C., Sauer, J.A., Hara, M. (2002). Molecular Composites Made of Ionic Poly(p-phenylene terephthalamide) and Poly(4-vinylpryidine): Relaxation Behavior, J. Polym. Sci., Polym. Phys. Ed., 40, 1110-1117.
Chen, W.C., Sauer, J.A., Hara, M. (2003). Molecular Composites Made of Ionic Poly(p-phenylene terephthal-amide) and Poly(4-vinylpryidine): Deformation Modes, J. Polym. Sci., Polym. Phys. Ed., 41, 429-436.
Chen, W.C., Sauer, J.A., Hara, M. (2003). Melt-processable Blends of an Ionic Poly(p-phenylene terephthalamide) and Poly(4-vinylpryidine): Relaxation Behavior, J. Polym. Sci., Polym. Phys. Ed., 41, 1468-1475.
Chen, W., Sauer, J.A., Hara, M. (2003). Synergistic Enhance-ment of Mechanical Properties and Microstructure of Homoblends made of Poly(styrene-co-styrenesulfonic acid) and Poly(styrene-co-4-vinylpyridine), Polymer, 44, 7485-7493.
Chen, W., Sauer, J.A., Hara, M. (2003). The Effect of Ionic Cross-links on the Deformation Behavior of Homoblends made of Poly(styrene-co-styrene-sulfonic acid) and Poly (styrene-co-4-vinylpyridine), Polymer, 44, 7729-7738.
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