Barrios-Tarazona, Karen A.

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    Synthesis and characterization of sulfonated amine block copolymer membranes for fuel cells and specialty separations applications
    (2021-07-09) Barrios-Tarazona, Karen A.; Suleiman-Rosado, David; College of Engineering; Padovani, Agnes M.; Saliceti, Lorenzo; Hernández, Arturo J.; Department of Chemical Engineering; Ponce de León, Leyda
    This work focuses on the synthesis and characterization of block copolymers membranes with multi-ionic domains to analyze the effect of the morphological and chemical changes on the transport properties for their use in direct methanol fuel cells (DMFC) and chemical protective clothing (CPC) applications. To achieve that, the interaction of amine groups with additional ionic domains in the polymeric matrix was evaluated using different methodologies. First, sulfonated poly(styrene–isobutylene–styrene) (SIBS) with isopentylamine (IPA) were blended and the properties of the membranes were assessed as a function of sulfonation level (57-93%) and IPA composition (1-5 wt.%) for DMFC applications. Results showed that the interaction between sulfonic and amine groups generated significant morphological changes in the nanostructure through a well-defined phase segregation that allowed the formation of nanochannels, which facilitated the transport properties in the membranes and enhanced the proton conductivity. In the second method, sulfonated poly(ionic liquid) block copolymers membranes based on SIBS were prepared for CPC applications. The synthesis involved the chloromethylation of SIBS, followed by the incorporation of N-alkylimidazole (N-butylimidazole and N-hexylimidazole) groups via chemical grafting and concluded with the addition of sulfonic groups to available aromatic domains. The interaction between the imidazole ionic moieties and sulfonic groups increased the thermal stability of the structure. This interaction also caused differences in the morphology with moderate phase segregation which improved the water vapor permeability through the membranes while blocked the transport of dimethyl methyl phosphonate. The last method consisted of the synthesis of amine block copolymers with multiple ionic domains (i.e., ether, ester, sulfonic groups) using atom transfer radical polymerization. Different amine block compositions (15-35 wt.%) were evaluated in the properties of the membranes. The interaction between these ionic groups also showed an improvement in thermal stability and water absorption. However, the transport properties were limited due to the lack of phase segregation and poor connectivity between the hydrophilic domains in the nanostructure. The results obtained through the different interactions between amine groups with other ionic domains suggest that both chemical and morphology changes play a fundamental role in the transport properties and selectivity for DMFC and CPC applications.