Quaternary Ammonium Functionalized Poly(Arylene Ether Sulfone) Copolymer Ionomers: Synthesis, Processing, and Structure-property Relationships

The synthesis of multiblock anion exchange membranes (AEMs) by chemical modification is a relatively new concept. One of the ionomer modification limits is mechanical stability since many commercial and synthesized AEM films lose their flexibility without water and become highly brittle when dry. On the other hand, once functionalized, ionomers become increasingly polar. Severe swelling of materials, when cast as thin film, causes enhanced liquid and ion transport, as well as weakening due to water plasticization, which leads to aqueous dissolution. Block ionomers typically shows higher ion conductivities relative to swelling due to phase segregated microstructure. However, evidence for this morphology in AEMs is unclear. Although, the current literature is rich with articles on improving the properties of cation exchange ionomer membranes by different processing techniques, such studies are rare for anion exchange ionomer (AEI) membranes i.e. AEMs. The current study strives to address these issues by investigating the interrelationships between structures, properties and processing methods in quaternary ammonium functionalized poly(arylene ether sulfone) ionomer AEMs. Overall, this research aim to answer some of the fundamental scientific questions pertaining to AEI morphology, composition, and transport: (1) What morphology limits are associated with block compositional differences, block length and ion exchange capacity (IEC) in polydisperse AEIs? (2) How does membrane morphology, composition, and IEC relate to toughness, strength, durability, and resistance to solvent swelling? (3) What relationships exist between transport, morphology, and AEM processing methods