Functionalized Imidazolium Ether-Free Polymer Backbones with Ion Transport Channels and Catalytic Activity.

Abstract

Novel ether-free bond polymer backbones were synthesized through polycondensation in a superacid medium by using p-terphenyl and 4-(1H-imidazol-1-yl)benzaldehyde. The presence of imidazolium groups enabled further modifications through a highly efficient nucleophilic substitution reaction introducing cationic sites essential for anionic transport. Characterization by NMR and FTIR analyses confirmed the structures and the complete functionalization of the base polymer. Critical properties for potential anion exchange membrane applications, including water uptake, ion exchange capacity, ion conductivity, morphology, and thermal and mechanical stabilities were investigated. Results indicated that these polymers form stable ion transport channels, with the formation of distinctive hydrophilic/hydrophobic microphase separation in the membranes observed through AFM, HR-TEM, and SAXS analyses. This structural configuration of the membranes exhibited high hydroxide conductivities of 61.33 and 80.33 mS/cm at 80 °C for 1AIM (quaternization with iodomethane) and 1ABPTA (quaternization with (3-bromopropyl)trimethylammonium bromide), respectively, with a thermal stability up to 240 °C, underscoring their suitability for electrochemical applications. Additionally, an organometallic polymer was successfully synthesized from the 1ABPTA polymer due to the presence of an imidazolium salt, N-heterocyclic carbene (NHC) ligand precursor. SEM images displayed the homogeneous distribution of metal atoms, and XPS spectra confirmed the formation of the C-M bond. The material obtained was utilized as a heterogeneous catalyst in a C-C Suzuki-Miyaura coupling reaction, achieving catalytic conversion percentages of 70% and 60% for the first and second cycles, respectively.