Star-Shaped Block Copolymers: Effective Polymer Gelators of High-Performance Gel Electrolytes for Electrochemical Devices

Abstract

Ion gels composed of copolymers and ionic liquids (ILs) have attracted great interest as polymer gel electrolytes for various electrochemical applications. Here, we present highly robust ion gels based on a six-arm star-shaped block copolymer of (poly(methyl methacrylate)- b-polystyrene)(6) ((MS)(6)) and an ionic liquid of 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide ([EMI][TFSI]). Compared to typical ion gels based on linear polystyrene-b-poly(methyl methacrylate)-b-polystyrene (SMS), the (MS)(6-) based gels show mechanical moduli of more than twice under various strains (e.g., stretching, compression, and shear). In addition, the outstanding mechanical property is maintained even up to 180 degrees C without a gel-sol transition. To demonstrate that (MS)6-based ion gels can serve as effective gel electrolytes for electrochemical applications, tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)), a representative electrochemiluminescent (ECL) luminophore, is incorporated into the gels. In particular, flexible ECL devices based on (MS)(6) gels exhibit high durability against bending deformation compared to devices with gels based on linear SMS having a similar molecular weight and a composition. This result implies that star-shaped block copolymers are effective gelators for achieving flexible/wearable electrochemical electronics.