Synthesis of imidazolium ABA triblock copolymers for electromechanical transducers

Nitroxide-mediated polymerization enabled the synthesis of cationic, imidazolium-containing triblock copolymers as a membrane for an electromechanical transducer. Nitroxide-mediated polymerization afforded poly(styrene-b-[1-ethyl-3-(4-vinylbenzyl)imidazolium bis(trifluoromethane sulfonyl)imide)]-b-styrene) in a controlled fashion as confirmed using aqueous size exclusion chromatography and 1H NMR spectroscopy. Dynamic mechanical analysis revealed a modulus of approximately 100 MPa for the triblock copolymer at 23 °C, which was suitable for fabrication of an electromechanical actuator. Evaluation of electromechanical actuators revealed device curvatures over twice the curvatures for Nafion® in both the presence and absence of a conductive network composite. Addition of the ionic liquid (IL) 1-ethyl-3-methylimidazolium trifluoromethane sulfonate selectively reduced the glass transition temperature (Tg) of the central block and increased overall ionic conductivity. Normalizing temperature with the central block Tg caused the ionic conductivity for the IL-incorporated polymers to collapse onto a single curve, which was an order of magnitude higher than the block copolymer in the absence of added IL.