RAFT Synthesis of ABA\nTriblock Copolymers as Ionic\nLiquid-Containing Electroactive Membranes

Abstract

2-(Dimethylamino)­ethyl acrylate (DMAEA) imparts versatile\nfunctionality\nto poly­[Sty-<i>b</i>-(<i>n</i>BA-<i>co</i>-DMAEA)-<i>b</i>-Sty] ABA triblock copolymers. A controlled\nsynthetic strategy minimized chain transfer reactions and enabled\nthe preparation of high-molecular-weight ABA triblock copolymers with\nrelatively narrow PDIs between 1.39 and 1.44 using reversible addition–fragmentation\nchain transfer (RAFT) polymerization. The presence of tertiary amine\nfunctionality and their zwitterionic derivatives in the central blocks\nof the triblock copolymers afforded tunable polarity toward ionic\nliquids. Gravimetric measurements determined the swelling capacity\nof the triblock copolymers for ionic liquids (IL) 1-ethyl-3-methylimidazolium\ntrifluoromethanesulfonate (EMIm TfO) and 1-ethyl-3-methylimidazolium\nethylsulfate (EMIm ES).\nA correlation of differential scanning calorimetry (DSC), dynamic\nmechanical analysis (DMA), and small-angle X-ray scattering (SAXS)\nresults revealed the impact of ionic liquid incorporation on the thermal\ntransitions, thermomechanical properties, and morphologies of the\ntriblock copolymers. IL-containing membranes of DMAEA-derived triblock\ncopolymers and EMIm TfO exhibited desirable rubbery plateau moduli\nof ∼100 MPa and electromechanical actuation to a 4 V electrical\nstimulus. Maintaining the mechanical ductility of polymer matrices\nwhile increasing their ion-conductivity is paramount for future electroactive\ndevices.