Non-fluorinated proton-exchange membranes based on melt extruded SEBS/HDPE blends

This paper reports on functional polymer blends prepared by melt-processing technologies for proton-exchange membrane applications. Styrene–ethylene/butylene–styrene (SEBS) and high-density polyethylene (HDPE) were melt blended using twin-screw compounding, extruded into thin films by extrusion–calendering. The films were then grafted with sulfonic acid moieties to obtain ionic conductivity leading to proton-exchange membranes. The effect of blend composition and sulfonation time was investigated. The samples were characterized in terms of morphology, microstructure, thermo-mechanical properties and in terms of their conductivity, ion exchange capacity (IEC) and water uptake in an effort to relate the blend microstructure to the membrane properties. The HDPE was found to be present in the form of elongated structures which created an anisotropic structure especially at lower concentrations. The HDPE increased the membrane mechanical properties and restricted swelling, water uptake and methanol crossover. Room temperature through-plane conductivities of the investigated membranes were up to 4.5E−02 S cm⁻¹ at 100% relative humidity, with an ionic exchange capacity of 1.63 meq g⁻¹.     

Sulfonated and crosslinked polyphosphazene-based proton-exchange membranes

Proton-exchange membranes, for possible use in H₂/O₂ and direct methanol fuel cells have been fabricated from poly[bis(3-methylphenoxy)phosphazene] by first sulfonating the base polymer with SO₃ and then solution-casting thin films. The ion-exchange capacity of the membrane was 1.4 mmol/g. Polymer crosslinking was carried out by dissolving benzophenone photoinitiator in the membrane casting solution and then exposing the resulting films after solvent evaporation to UV light. The crosslinked membranes look particularly promising for possible proton exchange membrane (PEM) fuel cell applications. A sulfonated and crosslinked polyphosphazene membrane swelled less than Nafion 117 in both water and methanol. Proton conductivities in crosslinked and non-crosslinked 200 μm thick water-equilibrated polyphosphazene films at temperatures between 25°C and 65°C were essentially the same and only 30% lower than those for Nafion 117. Additionally, water and methanol diffusivities in the crosslinked polyphosphazene membrane were very low (≤1.2×10⁻⁷ cm²/s). Sulfonated/crosslinked polyphosphazene films showed no signs of mechanical failure (softening) up to 173°C and a pressure of 800 kPa and did not degrade chemically when soaked in a hot hydrogen peroxide/ferrous ion solution.     

Biomimetic molecular anode catalysts based on nickel bis(diphosphine) coordination complexes for proton-exchange membrane fuel cells

Russian Chemical Bulletin - Transition-metal complexes are candidates for replacing platinum and its combinations with other metals as catalysts for the hydrogen oxidation reaction (HOR) in...     

Gas-separation membranes based on interpolymer complexes of sulfonate-containing aromatic polyamides

The gas-separation properties of membranes prepared from sulfonate-containing aromatic polyamide and aliphatic polyamines are studied. With the use of potentiometry, IR spectroscopy, and elemental analysis, it is shown that interpolymer complexes arising in these systems are primarily stabilized by electrostatic forces, while the degree of transformation in them is dependent on the basicity of polyamine and the conditions of the interpolymer reaction. The relationship between the nature of polyamine, the composition of the interpolymer complex, and the degree of transformation in it and the gas-separation characteristics of the membranes is established.     

Ultrafiltration membranes based on interpolyelectrolyte complexes: Adsorption and mass-exchange properties

Ultrafiltration membranes based on interpolyelectrolyte complexes of a sulfonated aromatic copolyamide, an acrylonitrile–N,N-dimethyl-N,N-diallylammonium chloride copolymer, and poly-N,N-dimethyl-N,N-diallylammonium chloride were prepared. The adsorption (in batch experiments and under conditions of ultrafiltration of myoglobin, lysozyme, and bovine serum albumin solutions) and mass-exchange properties of the membranes were studied. Correlation between the procedure for performing the interpolymer reaction, the composition of the complexes formed, and the characteristics of the membranes prepared was found. The protein/membrane interaction in the system studied is mainly due to Coulomb forces. The effect of the protein adsorption on the separation and transport properties of the membranes was considered. The general level of the mass-exchange properties of the membranes based on the interpolyelectrolyte complexes is higher compared to the samples containing ionic groups of like charge.     

Using ESR spectroscopy to study radical intermediates in proton-exchange membranes exposed to oxygen radicals

Direct ESR and spin-trapping experiments were used to study the behavior of Nafion, a perfluorinated ionomer membrane used in fuel cells, when exposed in the laboratory to oxygen radicals produced by Fenton and photo-Fenton reactions. DMPO (5,5-dimethyl-1-pyroline) was used as the spin trap. The results suggest that the two ESR methods provide complementary information on Nafion fragmentation. The presence of membrane-derived fragments was suggested indirectly by the presence of a broad signal (line width ≈ 84 G) after prolonged exposure of the membrane to the Fenton reagent based on Ti(III), and by the DMPO adduct of a carbon-centered radical in the spin-trapping experiments. The most convincing proof for the presence of perfluorinated radicals was obtained in Nafion membranes partially neutralized by Cu(II), Fe(II) and Fe(III) upon exposure to UV-irradiation in the presence or absence of H₂O₂ (photo-Fenton treatment). Identification of the chain-end radical RCF₂CF ₂ ^• with magnetic parameters different to those determined for the chain-end detected in γ-irradiated Teflon, was taken as evidence for the attack of reactive oxygen radicals on the side-chain of the membrane. Additional support for this suggestion was the detection of the “quartet” ESR signal assigned to the CF₃C^•O radical, and of the “quintet” ESR signal assigned to the radical centered at the intersection of the main and side chains. The limitations and advantages of each approach are discussed.     

High-temperature resins based on aromatic amine-terminated bisaspartimides

Various 4,4′-bis{N²-[4-(4-aminophenoxy)phenyl]aspartimido}diphenylmethane (APADM)-type precursors were synthesized by Michael-type reaction of an aromatic bismaleimide (1mol) with an aromatic diamine (2 mol) in an aprotic solvent. The structures of these materials were characterized by using Fourier-transform infrared (FT-IR), ¹H nuclear magnetic resonance (NMR) and ¹³C-NMR; their curing behaviors and thermal stabilities were evaluated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The thermal polymerization of APADM by heating it above its melting temperature produced a tough polymer. From these preimidized precursors, graphite-fiber laminates were prepared and their mechanical properties evaluated. To elucidate the thermal curing mechanism and the structure of the polymer, a model compound, N-[4-(4′-aminobenzyl) phenyl] aspartimidobenzene was synthesized. The gas-chromatographic mass spectra of these compounds has suggested a mechanism for their decomposition. The structure of the polymer also was studied by using FT-IR and ¹H-NMR.     

Enhanced conductivity in polyanion-containing polybenzimidazoles. Improved materials for proton-exchange membranes and PEM fuel cells

In an effort to develop improved Proton Exchange Membranes for Polymeric Fuel cells two different forms of polyanion inclusion in poly(2,5-benzimidazole) (ABPBI) have been carried out. Namely by (i) sulfonation of pre-formed polymer membranes and (ii) by addition of inorganic phosphomolybdic acid to form hybrid ABPBI–PMo₁₂ membranes. In both cases we have detected an increased proton conductivity of the resulting membranes, associated to an enhanced capacity of the polyanion-modified materials to uptake phosphoric acid (in comparison with previously known ABPBI or even commercial PBI membranes). These new membranes are stable up to 200 °C and feature high conductivities at these temperatures, which makes them promising candidates for higher-temperature PEM Fuel Cells.     

Monitoring the dynamics of ligand-receptor complexes on model membranes

Ligand-induced cross-linking of cell surface receptors is a basic paradigm of signal activation by many transmembrane receptors. After ligand binding, the receptor complexes formed on the membrane are dynamically maintained by two-dimensional protein-protein interactions on the membrane. The biophysical principles governing the dynamics of such interactions have not been understood, mainly because the measurement of lateral interactions on membranes so far has not been experimentally addressed. Here, we describe a generic approach for measuring two-dimensional dissociation rate constants in vitro using a novel high-affinity chelator lipid for reconstituting a ternary cytokine-receptor complex on solid-supported membranes. While monitoring the interaction between the ligand and one of the receptor subunits on the membrane by fluorescence resonance energy transfer, the equilibrium on the surface was perturbed by rapidly tethering a large excess of the unlabeled receptor subunit. Displacement of labeled by unlabeled protein in the ternary complex was detected as a recovery of the donor quenching. Since the dissociation of the ligand-receptor complex in plane of the membrane was the rate-limiting step under these conditions, the two-dimensional rate constant of this process was determined. Strikingly, the two-dimensional dissociation was much slower than ligand dissociation into solution, suggesting that membrane tethering significantly affects the dissociation process. This result highlights the importance of studying ligand-receptor complexes tethered to membranes for understanding the principles governing signal activation by ligand-induced receptor assembling.     

Supramolecular complexes based on cyclodextrins

A summary of the application of cyclodextrins (CDs) in the field of supramolecular chemistry has been given. Unique structural features of CDs, namely the separation of hydrophilic and hydrophobic groups, cause unusual physical and chemical properties of these molecules. The most important property of natural or chemically modified CDs is the ability to reversibly and selectively bind organic, inorganic, and biological molecules, forming inclusion complexes (ICs) of the “guest-host” type or nanostructured supramolecular assemblies. The most interesting examples of the application of ICs with CDs in pharmaceutical, food, and chemical industry, spectrometric analysis, separation technologies, of the use of CDs as models for molecular recognition in biology, as well as the cyclical component in the construction of supramolecular architectures (rotaxanes, pseudorotaxanes) are given in the review. The mechanism and methods of the formation of ICs, their properties and the methods of analysis have been described. Particular attention has been paid to molecular necklaces. One of the new promising directions of the application of CDs, namely, the preparation of nanosized materials, has been considered.     

Proton-conducting membranes based on multicomponent copolymers

Preparation of proton-conducting polymeric composites via copolymerization of multicomponent monomeric systems using the interpenetrating polymer network preparation procedure is studied. The products are characterized by the protonic conductivity, water-retaining capacity, and mechanical properties. The approach used allows fabrication of membranes with a reasonable protonic conductivity over the temperature range 20–90°C. A possibility of modification of the proton-conducting materials with small additions of hydrolyzable organosilicon comonomers is analyzed. The structure of the resulting systems is examined by small-angle neutron scattering.     

环糊精在金属酶模拟中的应用

非共价作用（如氢键、静电和疏水作用）普遍存在于天然金属酶中,对酶活化或底物催化过程有重要的协同作用.近年来基于超分子化学理论的金属酶模拟研究不断向酶的活性中心亚稳态和次层结构的生物功能模拟方向发展.本文将根据报道的文献并结合本课题组的研究工作,对环糊精（一种重要的超分子主体）构建金属酶模型的研究进行综述.     

Hydrogels based on polycarboxylic acid-agar-agar complexes

IR spectroscopy and viscometry data have shown that poly(acrylic acid) and poly(methacrylic acid) form complexes with agar-agar in aqueous solutions as they do with other polysaccharides. The polyacid-agar-agar complexes are typical hydrogels. The swelling index of hydrogels based on the poly(methacrylic acid)-agar-agar complex has been found to be markedly lower than that of poly(acrylic acid)-agaragar complex. The hydrogels based on the complex of cross-linked poly(acrylic acid) with agar-agar can be of practical interest as polymeric carriers for drugs.     

Cyclopalladized complexes based on 2-phenylbenzothiazole

Russian Journal of General Chemistry -     

Novel polyelectrolyte complexes based on diazo-resins

Polyelectrolyte complexes containing diazonium groups (PEC-N₂) with a high ionic crosslinking rate were prepared as a precipitate by mixing the diazo-resin with polyanion solutions. The photochemical decomposition of the complexes from different polyanions was studied. It was shown that PEC-N₂ exhibit high photosensitive properties. Under irradiation of UV light, the complexes which can be dissolved in ternary mixtures such as H₂O-DMF-LiCl,H₂O-DMF-NaSCN or H₂O-DMF-ZnCl₂ (DMF: N,N-dimethylformamide) become indissoluble since the crosslinking structure of the complexes changes from ionic to covalent.     

Chitosan-sodium alginate polyion complexes as fuel cell membranes

The viability of using polyion complex (PIC) membranes made by blending 84% deacetylated chitosan and sodium alginate biopolymers for direct methanol fuel cell (DMFC) was investigated. The membranes were characterized by FTIR to verify the polyion complex formation, XRD to observe the effects of blending on crystallinity, DSC and TGA to assess the thermal stability, and tensile testing for mechanical stability. Absorption studies were carried out to evaluate the interaction with water and methanol. The blend was found to be suitable for DMFC applications because of the low methanol permeability (4.6 × 10⁻⁸ cm²/s at 50 vol.% methanol concentration), excellent physico-mechanical properties and relatively high proton conductivity (0.042 S cm⁻¹). Above all, the cost effectiveness and simple fabrication technique involved in the synthesis of such PICs make their applicability in DMFC quite attractive and cost-effective.     

Electrostatics of DNA complexes with cationic lipid membranes

We present the exact solutions of the linear Poisson-Boltzmann equation for several problems relevant to electrostatics of DNA complexes with cationic lipids. We calculate the electrostatic potential and electrostatic energy for lamellar and inverted hexagonal phases, concentrating on the effects of dielectric boundaries. We compare our results for the complex energy with the known results of numerical solution of the nonlinear Poisson-Boltzmann equation. Using the solution for the lamellar phase, we calculate the compressibility modulus and compare our findings with the experimental data available. Also, we treat charge-charge interactions across, along, and between two low-dielectric membranes. We obtain an estimate for the strength of electrostatic interactions of one-dimensional DNA smectic layers across the lipid membrane. We discuss in the end some aspects of two-dimensional DNA condensation and DNA-DNA attraction in the DNA-lipid lamellar phase in the presence of di- and trivalent cations. We analyze the equilibrium DNA-DNA separations in lamellar complexes using the recently developed theory of electrostatic interactions of DNA helical charge motifs.     

Ion transport membranes based on conducting polymers

Polypyrrole membranes containing four different dopant ions were prepared galvanostatically from aqueous solutions of pyrrole (0.1 M) and the appropriate counter ion salt (0.1 M). The transport of mono-valent cations through each membrane was achieved by applying a potential gradient across the membranes. The influence of a number of set up parameters on the flux of K⁺ ions across a PPy/pTS membrane was assessed, as well as the relative selectivities of the four membrane types for the mono-valent cations; Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺.     

Synthesis and characterization of sulfonated poly(benzoxazole ether ketone)s by direct copolymerization as novel polymers for proton-exchange membranes

A new series of sulfonated poly(benzoxazole ether ketone)s (SPAEKBO-X) were prepared by the aromatic nucleophilic polycondensation of 4,4′-(hexafluoroisopropylidene)-diphenol with 2,2′-bis[2-(4-fluorophenyl)benzoxazol-6-yl]hexafluoropropane and sodium 5,5′-carbonylbis-2-fluorobenzenesulfonate in various ratios. Fourier transform infrared and ¹H NMR were used to characterize the structures and sulfonic acid contents of the copolymers. The copolymers were soluble in N-methyl-2-pyrrolidinone, N,N-dimethylacetamide, and N,N-dimethylformamide and could form tough and flexible membranes. The protonated membranes were thermally stable up to 320 °C in air. The water uptake, hydrolytic and oxidative stability, and mechanical properties were evaluated. At 30–90 °C and 95% relative humidity, the proton conductivities of the membranes increased with the sulfonic acid content and temperature and almost reached that of Nafion 112. At 90–130 °C, without external humidification, the conductivities increased with the temperature and benzoxazole content and reached above 10⁻² S/cm. The SPAEKBO-X membranes, especially those with high benzoxazole compositions, possessed a large amount of strongly bound water (>50%). The experimental results indicate that SPAEKBO-X copolymers are promising for proton-exchange membranes in fuel cells, and their properties might be tailored by the adjustment of the copolymer composition for low temperatures and high humidity or for high temperatures and low humidity; they are especially promising for high-temperature applications. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2273–2286, 2007