High Toughness, High Conductivity Ion Gels by Sequential Triblock Copolymer Self-Assembly and Chemical Cross-Linking

Abstract

Self-assembly of ABA triblocks in ionic liquids provides a versatile route to highly functional physical ion gels, with promise in applications ranging from plastic electronics to gas separation. However, the reversibility of network formation, so favorable for processing, restricts the ultimate mechanical strength of the material. Here, we describe a novel ABA system that can be chemically cross-linked in a second annealing step, thereby providing greatly enhanced toughness. The ABA triblock is a poly(styrene-b-ethylene oxide-b-styrene) polymer in which about 25 mol % of the styrene units have a pendant azide functionality. After self-assembly of 10 wt % triblock in the ionic liquid [EMI][TFSA], the styrene domains are cross-linked by annealing at elevated temperature for ca. 20 min. The high ionic conductivity (ca. 10 mS/cm) of the physical ion gels is preserved in the final product, while the tensile strength is increased by a factor of 5.