Nanocomposite Gels —Fundamental Significance and New Functions— Kazutoshi HARAGUCHI 1) 1) Material Chemistry Laboratory, Kawamura Institute of Chemical Research A novel class of nanocomposite hydrogels (NC gels) with a unique organic/inorganic network structure was synthesized by the in-situ free-radical polymerization of N- alkylacrylamides in the presence of inorganic clay (hectorite). It was revealed that an organic (polymer)/inorganic (clay) network structure, consisting of exfoliated clay platelets uniformly dispersed in an aqueous medium with a number of flexible polymer chains linking them together, was uniformly formed throughout the sample. NC gels exhibit high transparency, high degrees of swelling, and superb mechanical properties with extraordinarily large deformations. Also, NC gels formed from thermo-sensitive polymers, e.g., poly(N-isopropylacrylamide), exhibit rapid temperature-response in transparency and gel volume (de-swelling) at the transition temperature. It was also found that these optical, mechanical and swelling/de-swelling properties can be controlled over a wide range by altering the gel composition and modifying the network structure. All the properties of NC gels are very different from those of conventional, chemically crosslinked hydrogels (OR gels). Furthermore, NC gels exhibit a number of interesting new characteristics. These results indicate that NC gels are promising as soft functional materials which can be utilized in various applications, including new medical devices.