Anion Exchange Membranes derived from Phosphonium and Ammonium-Functionalized Polynorbornenes

Efforts to develop stable, high-performance anion exchange membranes (AEMs) for alkaline electrochemical conversion devices have increased significantly over the past decade. An AEM is comprised of a polymer backbone that provides structural reinforcement and cationic moieties tethered to/within the main-chain to facilitate ion conductivity. Judicious selection of the cation and polymer is critical toward developing membranes with good hydroxide transport, long-term chemical stability, and mechanical durability. Several classes of organic and main-group cations have been evaluated with the goal of understanding how the positively charged atom and its substituents influence alkaline stability and contribute to the balance of ionic conductivity, water flux, and swelling in the AEM. The polymer backbone is also inherently related to these properties, and precise tailoring of macromolecular composition and segmental mobility are identified as some of the key rational design principles for iterative improvement. Systematic control over cation/polymer combinations would help determine how each component impacts the overall characteristics of the membrane and enable the development of the next generation of improved materials. This dissertation discloses our effort to understand how AEM performance and physical properties are governed by structural features of polyolefin backbones bearing quaternary ammonium or tetraaminophosphonium cations.