(343k) Effect of Composition on the Transport Properties of Sulfonated Polymeric Ionic Liquid Block Copolymers Membranes

Polymeric ionic liquids (PIL's) block-copolymers are compounds that have at least one PIL block in their structure. PIL's are a type of polyelectrolytes which have ionic moieties as the repeating unit, and exhibit exceptional properties such as high ionic conductivity, a wide range of glass transition temperatures, and moderate chemical and thermal stability. These copolymers are commonly synthesized using controlled radical polymerization techniques or by post-polymerization modification of uncharged polymers. They are potentially suitable in separation processes and fuel cell applications to name a few. Fuel cells are ubiquitous in the rapidly growing market of portable devices and automobile industry. One of the key components of fuel cells is the proton exchange membrane (PEM), whose ionic conductivity is integral to the performance of the fuel.

In this study, a series of sulfonated PILs block-copolymersbased on poly(styrene–isobutylene–styrene) (SIBS) were synthesized for direct methanol fuel cell applications (DMFC). The synthesis consisted of the chloromethylation of SIBS via a Friedel–Crafts reaction, followed by the incorporation of n-alkylimidazole (i.e., butylimidazole, hexylimidadole) through chemical grafting where the PIL block copolymer was obtained. Ananion exchange reaction was carried out, after which sulfonation of the resulting polymers was completed.Properties of the membranes were assessed as a function of PIL block composition due to the presence of different N-alkylimidazoles and anions. A series of materials characterization techniques (e.g.,FT-IR, HNMR AFM, SAXS) was performed to provide a fundamental understanding of the synergism between different ionic domains at different concentrations and their effect on the morphology and transport properties of the polymeric membranes.

Keywords: Polymeric ionic liquid block-copolymer, Sulfonation, Polyelectrolyte, Chemical grafting, Transport properties, Direct methanol fuel cell.