RAFT Synthesis of ABA Triblock Copolymers as Ionic Liquid-Containing Electroactive Membranes

Abstract

2-(Dimethylamino)ethyl acrylate (DMAEA) imparts versatile functionality to poly[Sty-b-(nBA-co-DMAEA)-b-Sty] ABA triblock copolymers. A controlled synthetic strategy minimized chain transfer reactions and enabled the preparation of high-molecular-weight ABA triblock copolymers with relatively narrow PDIs between 1.39 and 1.44 using reversible addition−fragmentation chain transfer (RAFT) polymerization. The presence of tertiary amine functionality and their zwitterionic derivatives in the central blocks of the triblock copolymers afforded tunable polarity toward ionic liquids. Gravimetric measurements determined the swelling capacity of the triblock copolymers for ionic liquids (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIm TfO) and 1-ethyl-3-methylimidazolium ethylsulfate (EMIm ES). A correlation of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and small-angle X-ray scattering (SAXS) results revealed the impact of ionic liquid incorporation on the thermal transitions, thermomechanical properties, and morphologies of the triblock copolymers. ILcontaining membranes of DMAEA-derived triblock copolymers and EMIm TfO exhibited desirable rubbery plateau moduli of ∼100 MPa and electromechanical actuation to a 4 V electrical stimulus. Maintaining the mechanical ductility of polymer matrices while increasing their ion-conductivity is paramount for future electroactive devices.

Sulfonimide-Containing Triblock Copolymers for Improved Conductivity and Mechanical Performance

“…30 RAFT polymerization also facilitated the synthesis of high molecular weight poly[Sty-b-(nBA-co-DMAEMA)-b-Sty] triblock copolymers with tunable properties, which demonstrated actuation behavior with applied low voltage (2−4 V). 31 This article describes the synthesis and subsequent neutralization of novel, well-defined A−BC−A triblock copolymers containing a soft central "BC" block, which consists of Sty-Tf 2 N and DEGMEMA with polystyrene external blocks. These ionomeric A−BC−A triblock copolymers allow one to combine and independently tune two opposing properties in a single material, i.e., mechanical stability and ion transport.…”

Modeling the response of polymer–ionic liquid electromechanical actuators

“…Ionic polymer metal composites (IPMCs) are introduced as an important class of functional composite materials whose mechanical response (bending) is driven by transport of ions through a polymer electrolyte membrane sandwiched between two nanoscale-thin electrodes [1][2][3][4][5]. The basic element of IPMCs is a porous membrane manufactured of a polymer containing functional groups attached to main or side chains (Nafion provides the classical example of perfluorosulfonic acid ionomers, but several block polymers with a higher electroactuation ability and tailored microstructure were recently invented [6][7][8][9][10]). Before actuation, the membrane is soaked in an aqueous solution of an electrolyte, which leads to ionization of functional groups that dissociate into mobile cations and fixed anions.…”

“…Ionic liquids (ILs) are fluid semi-organic salts composed of organic cations and organic or inorganic anions with melting points below 100 • C [13]. Due to their chemical and thermal stabilities, low vapor pressure, and high ionic conductivity, replacement of water with ILs induces a strong enhancement of electromechanical performance [7][8][9][10][14][15][16].…”

Well‐Defined Imidazolium ABA Triblock Copolymers as Ionic‐Liquid‐Containing Electroactive Membranes

“…For example, an electromechanical actuator typically consists of an ionic polymeric membrane with conductive network composite (CNC) layers and external electrodes coated on both sides. The CNC is often fabricated through layer‐by‐layer (LbL) self‐assembly using positively charged poly(allylamine) hydrochloride and anionic gold nanoparticles . The CNC layers serve to increase the interfacial surface area and porosity of the electrode, which improves ion‐transport and ion accumulation, leading to improved performance of actuation …”