(193k) Toughening of Triblock Copolymer Anion Exchange Membranes

Anionic exchange membranes (AEMs) have recently been demonstrated to function in fuel cells with non-precious electrocatalysts, offering a viable path to commercialize fuel cells. To advance solid-state ion-transport materials, three major obstacles must be confronted: (i) the stability of AEM cationic head groups is notoriously poor, especially in basic environments with nucleophilic hydroxy anions; (ii) the hydroxyl anion conductivity is too low—significantly lower than proton conductivity through PEMs, mostly due to poor anion mobility; and (iii) membranes must be mechanically tough—able to with stand repetitive swelling stresses and mechanical stresses from the cell. Our lab has successfully synthesized highly stable ABA and BAB triblock copolymers that are designed to nanophase-segregate into glassy and ion-conductive domains, addressing the stability and conductivity issues. The synthesis involves reversible addition fragmentation chain transfer (RAFT) as a controlled polymerization technique. A versatile, difunctional RAFT agent is utilized that enables triblocks to be grown from the inside-out, leaving reactive groups only on chain ends. While the polymerization is successful, resulting membranes are too brittle. With the objective of understanding and improving mechanical properties, here we report on different strategies including reaction with hydrophilic crosslinkers and copolymerization with monomers bearing H-bonding end-groups. The toughened membranes’ mechanical properties, swelling behavior, and conductivity will be discussed for different model formulations.