Novel sulfonated styrenic pentablock copolymer/silicate nanocomposite membranes with controlled ion channels and their IPMC transducers

A novel ionic thermoplastic elastomer, poly((t-butyl-styrene)-b-(ethylene- r-propylene)-b-(styrene-r-styrene sulfonate)-b-(ethylene-r-propylene)-b-(t- butyl-styrene)) (tBS-EP-SS-EP-tBS; SSPB) pentablock copolymer, and its nanocomposites with sulfonated montmorillonite (s-MMT) have been investigated as polymer electrolytes for ionic polymer-metal composite (IPMC) actuators. The SSPB pentablock copolymer formed a well-defined microphase-separated nanodomain morphology on the several tens nanometer scale. Selectively sulfonated styrene (SS) middle blocks formed ionic conduction channels through which mobile ions are transported. The glassy hard tBS end blocks and the rubbery aliphatic EP inner blocks impart mechanical strength and mechanical toughness in the thermoplastic elastomer, respectively. The functionalized MMTs were homogeneously distributed in the SSPB/s-MMT nanocomposites and had the intercalated morphology. The resulting SSPB and SSPB/s-MMT nanocomposite IPMCs revealed not only higher tensile moduli but also higher ionic conductivities than conventional Nafion polymer electrolyte IPMCs. Among the IPMCs, the SSPB/s-MMT nanocomposite-based IPMCs with the developed morphology registered the best actuation performance in terms of bending displacement and blocking force, comparable to a typical Nafion-IPMC. Consequently, the SSPB/s-MMT-IPMCs are expected as a solution not only on the price concern but also on the physical drawback of conventional IPMCs such as fast back relaxation.