Preparation and characterization of nanofiltration membranes by coating polyethersulfone hollow fibers with sulfonated poly(ether ether ketone) (SPEEK)

A new type of nanofiltration membrane is reported based on coating a sulfonated poly(ether ether ketone) (SPEEK) layer on top of a polyethersulfone support. The membranes were characterized by dextran mixtures, salt solutions as well as negatively charged dyes. The SPEEK coated nanofiltration membranes showed molecular weight cutoff for dextran in the range of ultrafiltration, however, rather high rejection for sodium sulfate; retention for salts in the order of RNa₂SO₄>RNaCl>RMgCl₂$R_{\text{N}{\text{a}}_2\text{S}{\text{O}}_4}>R_{\text{NaCl}}>R_{\text{MgC}{\text{l}}_2}$; in addition, the membranes showed a 97–100% retention to the organic dyes. The rejection rates were improved by an increase in the coating thickness and the polymer concentration in the coating solution at the penalty of permeability decrease. Furthermore, it was found that pore penetration of SPEEK into the support membrane effectively constrained the swelling rate of SPEEK and increased the retention. The Donnan–Steric Pore Model was used to describe the transport properties of the membrane. Modeling identified a very tortuous passage within the active separation layer.     

Proton conductive membranes of sulfonated poly(ether ketone ketone)

Poly(ether ketone ketone) was sulfonated using fumic sulfuric acid and used for preparation of proton conductive membranes. The sulfonation degree was evaluated by elemental and thermal analysis and the IEC values were determined by titration. The proton conductivity of membranes with sulfonation degrees up to 70% was determined as a function of temperature by impedance spectroscopy. Membranes with sulfonation degree 38–70% were tested in DMFC experiments. Their performance was comparable to Nafion^® with the same pretreatment and clearly better than sulfonated poly(ether ether ketone) membranes with similar functionalization. The methanol crossover was lower than that of Nafion^® in the same conditions.     

Swelling behavior and solubility parameter of sulfonated poly(ether ether ketone)

The solubility parameter of sulfonated poly(ether ether ketone) (SPEEK) was investigated. SPEEK exhibited two solubility parameters, 26.4 and 35.7 J^1/2 cm^?3/2, and was similar in that respect to Nafion, which has two cohesive energy densities. The theoretical solubility parameter of SPEEK, 26.1 J^1/2 cm^?3/2, was determined with van Krevelen's method and corresponded to the experimental value. The theoretical volume fraction of SPEEK in the solvent was determined with Flory's equation. The trend of the theoretical volume fraction of SPEEK fit quite well with the experimental results when the solubility parameter of the solvent was lower than 35 J^1/2 cm^?3/2. A significant deviation of the experimental volume fraction of SPEEK with the high solubility parameter resulted from the presence of sulfonic acid groups. SPEEK in the sodium form exhibited similar solvent absorption in comparison with SPEEK in the acid form. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3128–3134, 2006     

Reduced viscosity, rheology and morphological properties of sulfonated poly (ether ether ketone): Polyetherimide blends

Blends of poly (ether ether ketone) (SPEEK) and polyetherimide (PEI) were prepared in five different weight ratios, using N,N-dimethylacetamide (DMAc) as solvent. Reduced viscosity and rheological parameters of these blends were investigated. Cannon–Fenske viscometer was used to study the viscoelastic parameters of the salt-free polyelectrolyte blends and the data obtained was fitted in Fuoss–Strauss equation. Effects of temperature and concentration have been investigated. It was observed that the storage modulus (G′) and dynamic viscosity (η′) of the blends varies significantly as compare to pure SPEEK and PEI. Surface morphology and thermal behavior of the membranes were studied using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Form SEM results it was observed that the phase separation occurs at 25% PEI contents in blends.     

Preparation and properties of UV irradiation-induced crosslinked sulfonated poly(ether ether ketone) proton exchange membranes

The crosslinkable sulfonated poly(ether ether ketone)s (SPEEKs) were synthesized by nucleophilic substitution reaction of diallyl bisphenol A, tert-butylhydroquinone, 4,4′-difluorobenzophenone and sodium 5,5′-carbonylbis(2-fluorobenzene-sulfonate). The SPEEKs with high intrinsic viscosity showed good solubility and could be cast into flexible and transparent membranes. The SPEEK membranes containing benzophenone (BP) and triethylamine (TEA) photo-initiator system were treated by UV light to promote crosslinking. The experimental results revealed that the crosslinked membrane with 10 min irradiation time showed the most potential as proton exchange membrane for direct methanol fuel cell applications. When the irradiation time increased from 0 to 10 min, the water uptake decreased from 29.1 to 26.1%, and the tensile modulus and the tensile strength enhanced sharply from 0.80 to 1.44 GPa and from 40.3 to 63.4 MPa, respectively. In addition, the methanol diffusion coefficient reduced sharply from 1.70 × 10⁻⁶ to 7.42 × 10⁻⁷ cm²/s with only slight sacrifice in the proton conductivity, which made the crosslinked membrane with 10 min irradiation time possess the highest selectivity.     

Semi-interpenetrating polymer networks toward sulfonated poly(ether ether ketone) membranes for high concentration direct methanol fuel cell

Semi-IPNs were constructed by forming the crosslinking networks via the reaction between BPPO and diamine cross-linkers to overcome the dimensional swelling and methanol-permeation issues of SPEEK.     

Polymer blend membranes of sulfonated poly(arylene ether ketone) for direct methanol fuel cell

The blend membranes of sulfonated poly(arylene ether ketone) (sPAEK) (IEC = 1.0 mequiv./g)/Nafion^® and the blend membranes of sPAEK (IEC = 1.0 mequiv./g)/sPAEK (IEC = 1.7 mequiv./g) were prepared. sPAEK with low IEC was introduced to reduce the methanol permeability through the membrane. Morphology, water uptake, proton conductivity and methanol permeability of the blend membranes were investigated by SEM, AFM, AC impedance spectroscopy and permeability measuring instrument. The cross-sections of blend membranes showed phase-separated morphologies. The effect of phase-separated morphology on the properties of blend membranes was investigated. The properties like water uptake, proton conductivity, and methanol permeability of sPAEK/Nafion^® blend membranes showed similar values with sPAEK and properties of sPAEK/sPAEK blend membranes showed intermediate values of two polymers due to the difference in morphology of the blend membranes. sPAEK/sPAEK blend membranes showed relatively high proton conductivity and lowered methanol permeability compared to Nafion^®. sPAEK/sPAEK blend membranes could be a competent substitution for Nafion^®.     

Morphology control of sulfonated poly(ether ketone ketone) poly(ether imide) blends and their use in proton-exchange membranes

Polymer blends based on sulfonated poly(ether ketone ketone) (SPEKK) as the proton-conducting component and poly(ether imide) (PEI) as the second component were considered for proton-exchange membranes (PEMs). The PEI was added to improve the mechanical stability and lower the water swelling in the fuel cell environment. Membranes were cast from solution using N-methyl-2-pyrrolidone (NMP) and dimethylacetamide (DMAc). The ternary, polymer/polymer/solvent, phase diagram was determined to provide guidance on how to control the morphology during solvent casting of blend membranes.

For blends of SPEKK (ion-exchange capacity = 2 mequiv/g) with PEI as the minority component, the morphology consisted of dispersed particles of 0.5–6 μm. Larger particles were achieved by increasing the PEI content and/or lowering the casting temperature. High-temperature annealing after solution casting did not affect the morphology of blend membranes, due to the low mobility and compatibility of the two polymers.

The possible use of SPEKK/PEI blends in PEMs is discussed in terms of existing theories of ion transport in polymers.     

Modification of sulfonated poly(ether ether ketone) with phenolic resin

Soluble phenol formaldehyde resin containing hydroxymethyl groups has been used to modify sulfonated poly(ether ether ketone) (SPEEK). Modification has been carried out with films containing both the polymers and using dimethyl formamide (DMF) as casting solvent at various temperatures under reduced pressure. Associated solvent and the hydrogen‐bonded by‐product dimethyl amine (DMA) were removed through mild alkali–acid–water treatment. Cured and treated films show good and consistent mechanical properties, water uptake (22–25%), ion‐exchange capacity (1.1–1.5 meq/g) and proton conductivity (125–150 mS/cm) at 30°C and hold promise for application in fuel cells, as indicated by a polarization study in a fuel cell test station. Copyright © 2007 John Wiley & Sons, Ltd.     

Crosslinking of sulphonated poly (ether ether ketone) using aromatic bis(hydroxymethyl) compound

2,6-Bis(hydroxymethyl)-4-methyl phenol and 1,4-bis(hydroxymethyl) benzene have been used as crosslinkers in sulphonated poly (ether ether ketone) (SPEEK DS 65%, IEC 1.84 mequiv./g) for the preparation of proton exchange membranes (PEMs). Crosslinking of SPEEK has been achieved by thermally activated bridging of the polymer chain with the hydroxymethyl group of crosslinker through condensation reaction with sulphonic acid group. The physico-chemical properties of uncrosslinked and crosslinked membrane were evaluated in terms of ion exchange capacity (IEC), water uptake, ionic conductivity and mechanical properties. The crosslinked membrane showed controlled swelling, ionic conductivity of 25–50 mS/cm at 80 °C and good mechanical properties. The chemical stability of the crosslinked membranes was studied by Fenton's test. The % loss in weight and changes in physico-chemical properties of the treated membranes were determined.     

Blend membranes of Nafion/sulfonated poly(aryl ether ketone) for direct methanol fuel cell

Sulfonated poly(aryl ether ketone) (sPAEK) synthesized by LG Chem. was confirmed by FT-IR. To estimate the thermal stability, glass transition temperature and decomposition temperature were investigated. They showed that sPAEK had good thermal properties. The proton conductivity, methanol permeability and water uptake of sPAEK were also measured. Nafion/sulfonated poly(aryl ether ketone) composite membranes were prepared by blending two materials. The blend ratios of sPAEK and Nafion were 2:1, 3:1, 5:1, and 7:1. The blend membranes showed phase separated morphology since they became immiscible during the solvent evaporation process. Due to the differences in specific gravity and solvent concentration profile during the solvent evaporation process, the upper region had lower Nafion volume fraction with smaller domains and the lower region had higher Nafion volume fraction with larger domains. Mechanical properties such as the stress at break, yield stress, Young's modulus, and elongation at break were measured. The sPAEK had better mechanical properties than Nafion. The mechanical properties increased with increasing sPAEK content. Proton conductivity and methanol permeability of the blend membranes were lower than those of Nafion. Both decreased with decreasing Nafion content. Since the methanol permeability of sPAEK was lower than that of Nafion, sPAEK acted as the methanol barrier. Water uptake of sPAEK was higher than that of Nafion.     

Isothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone)

The isothermal melt and cold crystallization kinetics of poly(aryl ether ketone ether ketone ketone) are investigated by differential scanning calorimetry over two temperature regions. The Avrami equation describes the primary stage of isothermal crystallization kinetics with the exponent n ≈ 2 for both melt and cold crystallization. With the Hoffman–Weeks method, the equilibrium melting point is estimated to be 406 °C. From the spherulitic growth equation proposed by Hoffman and Lauritzen, the nucleation parameter (K_g) of the isothermal melt and cold crystallization is estimated. In addition, the K_g value of the isothermal melt crystallization is compared to those of the other poly(aryl ether ketone)s. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1992–1997, 2000     

Glass transition and miscibility in blends of two semicrystalline polymers: Poly(aryl ether ketone) and poly(ether ether ketone)

Binary melt‐blended mixtures of two aryl ether ketone polymers (i.e., a new poly(aryl ether ketone) (code name PK99) and poly(ether ether ketone) (PEEK), have been studied. Polymer miscibility in glassy amorphous (or melt) domains has been demonstrated for the binary blend comprising of two aryl‐ether‐ketone‐type semicrystalline polymers. Composition‐dependent, single T_g was observed within full composition range in the PK99/PEEK blends, and the narrow T_g breadth also suggests that the scale of mixing was fine and uniform. To better resolve any possible overlapping T_g's, physical aging was imposed on a comparison set of blend samples for the purpose of improving detectability of overlapped multiple transitions if existing. The result still showed one single T_g. The relative sharp T_g and lack of cloud point transition suggest that the scale of molecular intermixing is good. Phase homogeneity was further confirmed using optical and scanning electron microscopy. The X‐ray diffractograms suggest that isomorphism does not exist in the PK99/PEEK blends and that the crystal forms of the respective polymers remain distinct and unchanged by the miscibility in the amorphous region. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1485–1494, 1999     

Sulfonated poly(ether ether ketone)-based silica nanocomposite membranes for direct ethanol fuel cells

This paper reports on the preparation and characterization of sulfonated poly(ether ether ketone) (sPEEK)-based mixed matrix membranes. The inorganic matrix consisted of silica: Aerosil^®380, tetraethoxysilane (TEOS) or a combination of both to obtain an interconnected silica network. The behavior of these membranes in ethanol–water systems was studied for application in a direct ethanol fuel cell (DEFC). Uptake measurements showed that the converted TEOS content had a strong influence on the hydrophilicity of the membranes. Proton conductivity was strongly related to the water content in the membrane, but the proton diffusion coefficients of membranes with various Aerosil^®380–TEOS combinations were similar. Dynamic measurements in liquid–liquid (L–L) and liquid–gas (L–G) systems were performed to study the ethanol transport through the membrane. No reduction in ethanol permeability was obtained in the L–L system, but a remarkable reduction was obtained in the L–G system when 2 M ethanol was applied. The reinforcing characteristic of the combined Aerosil^®380–TEOS-system were best observed at 40 °C with 4 M ethanol. The fuel cell performance prediction based on the selectivity of proton diffusion coefficient to ethanol permeability coefficient showed for nearly all composite membranes an improvement with respect to the polymeric reference. The presence of an inorganic phase led to relatively constant proton diffusion coefficients and lower ethanol permeability coefficients in comparison with the polymeric reference.     

Studies on cellulose acetate and sulfonated poly(ether ether ketone) blend ultrafiltration membranes

New ultrafiltration membranes based on chemically and thermally stable arylene main-chain polymers have been prepared by blending the sulfonated poly(ether ether ketone) with cellulose acetate in various compositions in N,N^′-dimethylformamide as solvent by phase inversion technique. Prepared membranes have been subjected to ultrafiltration characterizations such as compaction, pure water flux, water content, and membrane hydraulic resistance. The pore statistics and molecular weight cut-off (MWCO) of the membranes have been estimated using proteins such as trypsin, pepsin, egg albumin and bovine serum albumin. The pore size increased with increasing concentrations of sulfonated poly(ether ether ketone) in the casting solution. Similarly, the MWCOs of the membranes ranged from 20 to 69 kDa, depending on the various polymer compositions. Surface and cross-sectional morphologies of membranes were analyzed using scanning electron microscopy. The effects of polymer compositions on the above parameters were analyzed and the results are compared and discussed with those of pure cellulose acetate membranes.     

Characterization and performance of proton exchange membranes for direct methanol fuel cell: Blending of sulfonated poly(ether ether ketone) with charged surface modifying macromolecule

Modification of sulfonated poly(ether ether ketone) (SPEEK) membrane was attempted by blending charged surface modifying macromolecule (cSMM). The modified membrane was tested for direct methanol fuel cell (DMFC) application; i.e. a SPEEK/cSMM blend membrane was compared to a SPEEK membrane and a Nafion 112 membrane for the thermal and mechanical stability, methanol permeability, and proton conductivity. Thermal and mechanical stability of the blended membrane were slightly reduced from the SPEEK membrane but still higher than the Nafion 112 membrane. The blend membrane was found to be promising for DMFC applications because of its lower methanol diffusivity (2.75 × 10⁻⁷ cm² s⁻¹) and higher proton conductivity (6.4 × 10⁻³ S cm⁻¹), than the SPEEK membrane. A plausible explanation was given for the favorable effect of cSMM blending.     

Morphological investigations of block sulfonated poly(arylene ether ketone) copolymers as potential proton exchange membranes

A series of block sulfonated poly(arylene ether ketone) (SPAEK) copolymers with different block lengths and ionic contents were synthesized by a two‐stage process. The morphology of these block SPAEK copolymers was investigated by various methods, such as differential scanning calorimetry (DSC), transmission electron microscope (TEM), and small angle X‐ray scattering (SAXS). Dark colored ionic domains of hundreds of nanometers spreading as a cloud‐like belt were observed in TEM images. The sizes of the ionic domains as a function of block copolymer composition were determined from SAXS curves. The results for the evolution of ionic domains revealed that the block copolymers exhibited more clearly phase‐separated microstructure with increasing ionic contents and hydrophobic sequence lengths. Proton conductivity is closely related to the microstructure, especially the presence of large interconnected ionic domains or ionic channels. Block SPAEK membranes have interconnected ionic clusters to provide continuous hydrophilic channels, resulting in higher proton conductivity. Copyright © 2010 John Wiley & Sons, Ltd.     

聚醚醚酮醚酮的合成与表征

聚醚醚酮（ＰＥＥＫ）自工业化以来［１］，由于其优异的性能已在机械、航天等领域得到广泛应用．各种聚芳醚酮类聚合物相继被开发出来．但以亲电缩聚路线制备聚醚醚酮醚酮（ＰＥＥＫＥＫ）的报道较少［２］．本文以二苯醚和４－氟苯甲酰氯为主要反应试剂，采取付氏酰基化...     

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.     

Thermal behavior and phase behavior in blends of liquid crystalline poly(aryl ether ketone) and poly(aryl ether ether ketone) containing thioether units

Thermal behavior and phase behavior in blends of liquid crystalline poly(aryl ether ketone) with lateral methoxy groups (M-PAEK) and poly(aryl ether ether ketone) containing thioether units (S-PEEK) have been investigated by differential scanning calorimetry (DSC) and polarized light microscopy (PLM) techniques. The results indicate that the composition of the blends has great effect on the phase behavior and morphology. Thin films of pure M-PAEK and S-PEEK crystallized from the melts exhibit typical mosaic and spherulitic structures, respectively. For the blends with higher M-PAEK contents (> 50%), an unusual ring-banded spherulite with structural discontinuity is formed. The bright core and rings of the ring-banded spherulites under PLM are composed of M-PAEK phase, while the dark rings consist mainly of S-PEEK phase. For the 50:50 M-PAEK/S-PEEK blend, the ring-banded spherulites and S-PEEK spherulites coexist, which implies that a partial phase separation between the two components takes place in the melting state. In S-PEEK-rich blends, a volume-filled spherulite is produced. In addition, the effect of isothermal crystallization temperature on the phase behavior, especially the ring-banded spherulite formation in the blends, is discussed.