Designing Highly Conductive Anion Exchange Membranes: Tuning Domain Continuity with ABC Block Copolymer Self-Assembly
Alexandra J. Macbeth, Danielle Markovich, A. Taylor, Ethan B. Flanagan, Julia E. Borowski, Jesse H. Hsu, Cheyenne R. Peltier, David A. Muller, Brett P. Fors, Kevin J. T. Noonan, Geoffrey W. Coates
Abstract
Anion exchange membranes (AEMs) play a critical role in clean energy devices, and optimizing their performance requires a deeper understanding of morphology–performance relationships. This study investigates ABC triblock terpolymer AEMs to explore how domain continuity influences hydroxide conductivity, water uptake, and dimensional stability. High molecular weight ABC triblock terpolymers were synthesized through the controlled vinyl-addition polymerization of norbornene monomers functionalized with alkyl, benzyl, or bromobutyl substituents. Morphology was systematically varied across the series without significantly changing the molecular weight or ion exchange capacity (IEC) of the polymer by adjusting the alkyl/benzyl block length ratio. Solution-cast films exhibited either 2D-continuous lamellar or 3D- co -continuous network phase morphologies, with domain continuity largely retained after cationic functionalization. AEMs with 3D- co -continuous domains demonstrated superior performance, including enhanced dimensional stability and competitive hydroxide conductivities of up to 84 mS/cm at 25 °C and 131 mS/cm at 80 °C. This work highlights how the self-assembly of ABC triblock terpolymers can be leveraged to investigate morphology–performance relationships and achieve highly conductive, durable AEMs.