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 (T _g) of the central block and increased overall ionic conductivity. Normalizing temperature with the central block T _g 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.