Direct Insertion Polymerization of Ionic Monomers: Rapid Production of Anion Exchange Membranes.

The limited number of methods to directly polymerize ionic monomers currently hinders rapid diversification and production of ionic polymeric materials, namely anion exchange membranes (AEMs) which are essential components in emerging alkaline fuel cell and electrolyzer technologies. Herein, we report a direct coordination-insertion polymerization of cationic monomers, providing the first direct synthesis of aliphatic polymers with high ion incorporations and allowing facile access to a broad range of materials. We demonstrate the utility of this method by rapidly generating a library of solution processable ionic polymers for use as AEMs. We investigate these materials to study the influence of cation identity on hydroxide conductivity and stability. We found that AEMs with piperidinium cations exhibited the highest performance, with high alkaline stability, hydroxide conductivity of 87 mS cm-1 at 80 °C, and a peak power density of 730 mW cm-2 when integrated into a fuel cell device.

Examining the Alkaline Stability of Tris(dialkylamino)sulfoniums and Sulfoxoniums.

Herein, a synthetic method was developed to prepare a series of tris(dialkylamino)sulfonium and sulfoxonium cations from sulfur monochloride. Alkaline stability studies of these two cation families in 2 M KOH/CD3OH solution at 80 °C revealed how degradation pathways change as a function of the oxidation state of the S center, as determined by 1H NMR spectroscopy. The sulfonium cations (+S(NR2)3) typically degrade by nucleophilic attack at the sulfur atom with loss of an amino group and a proton transfer reaction to produce sulfoxides, while the sulfoxoniums (+O═S(NR2)3) tend to degrade by loss of an R group to form sulfoximines. From the group of sulfoniums and sulfoxoniums explored in this work, the tris(piperidino)sulfoxonium cation was noted to have excellent alkaline stability. This sulfoxonium should be suitable for future examination as a tethered cation in anion-exchange membranes (AEMs), or as a phase-transfer catalyst in biphasic reactions.

Comparing Ammonium and Tetraaminophosphonium Anion-Exchange Membranes Derived from Vinyl-Addition Polynorbornene Copolymers.

Herein, we systematically examined how composition influenced the properties of vinyl addition polynorbornene anion exchange membranes (AEMs) prepared from 5-n-hexyl-2-norbornene and 5-(4-bromobutyl)-2-norbornene. Copolymerization kinetics revealed that 5-n-hexyl-2-norbornene is consumed faster than 5-(4-bromobutyl)-2-norbornene, leading to a portion of the chain being richer in bromoalkyl groups. The alkyl halide pendants can then be converted to either trimethylammonium or tetrakis(dialkylamino)phosphonium cations through straightforward substitution with trimethylamine or a tris(dialkylamino)phosphazene. A series of cationic ammonium polymers were synthesized first, where conductivity and water uptake increased as a function of increasing ionic content in the polymer. The optimized copolymer had a hydroxide conductivity of 95 ± 6 mS/cm at 80 °C. The living polymerization of the two monomers catalyzed by a cationic tert-butylphosphine palladium catalyst also enabled precise changes in the molecular weight while keeping the functional group concentration constant. Molecular weight did not have a significant impact on hydroxide conductivity over the range of ∼60-190 kg/mol (Mn). The optimized tetraaminophosphonium AEM had the highest conductivity for any tetraaminophosphonium polymer to date (70 ± 3 mS/cm at 80 °C). Clear phase separation and larger domains were observed for the phosphonium-based AEM compared to the ammonium at an identical composition, which is attributed to the larger occupied volume of the phosphorus cation. Fuel cell studies with the two membranes resulted in peak power densities of 1.59 and 0.79 W/cm2 for the ammonium and tetraaminophosphonium membrane electrode assemblies, respectively. The ammonium-based membrane was more water permeable as evidenced by water limiting current studies, which likely contributed to the improved performance.

Ionic liquids with thioether motifs as synthetic cationic lipids for gene delivery.

This study introduces a novel class of imidazolium- and ammonium-based ionic liquids possessing two C12 and C14 tails and thioether linkers designed for lipoplex-mediated DNA delivery. Imidazolium-based ionic liquids displayed efficient gene delivery properties with low toxicity. Thiol-yne click chemistry was employed for the facile and robust synthesis of these thioether-based cationic lipioids with enhanced lipophilicity and low fluidity.

Crystal structure of a methimazole-based ionic liquid.

The structure of 1-methyl-2-(prop-2-en-1-ylsulfan-yl)-1H-imidazol-3-ium bromide, C7H11N2S(+)·Br(-), has monoclinic (P21/c) symmetry. In the crystal, the components are linked by N-H⋯Br and C-H⋯Br hydrogen bonds. The crystal structure of the title compound undeniably proves that methimazole reacts through the thione tautomer, rather than the thiol tautomer in this system.