Synthesis of Highly Stretchable, Mechanically Tough, Zwitterionic Sulfobetaine Nanocomposite Gels with Controlled Thermosensitivities

Novel nanocomposite (NC) gels with zwitterionic characteristics were prepared by in situ free-radical polymerization of sulfobetaine monomers in the presence of exfoliated clay platelets in aqueous media. Two specific sulfobetaine monomers, N,N-dimethyl(acrylamidopropyl)ammonium propanesulfonate and butanesulfonate, were selected on the basis of the interactions between the monomers and clay, which result in uniform aqueous solutions of low viscosity and gel formation without using an organic cross-linker. The resulting NC gels with polymer–clay network structures were insoluble in NaCl solution or hot water, unlike conventional physically cross-linked gels. Also, NC gels with high mechanical properties and well-controlled thermosensitivities were effectively prepared by copolymerization with a small amount of N,N-dimethylacrylamide. The copolymer NC gels were uniform and simultaneously showed high stretchability, tough mechanical properties, and well-defined upper critical solution temperature (UCST) phase-transitions. Furthermore, the tensile mechanical properties and UCST were controlled over a wide range by altering the clay concentration and copolymerization ratio.