Abstract  Poly (phthalazinone ether sulfone ketone) (PPESK) copolymer is a relatively newly developed material, which contains different component ratios of diphenyl ketone and diphenyl sulfone with respect to a certain amount of 4-(4-hydroxyphenyl)-2,3-phthalazin-1-one. In this study, the physico-chemical characteristics of this copolymer, including the glass transition temperature, the intrinsic viscosity, the DSC (differential scanning calorimeter) and FT-IR spectra have been investigated. The chemical stability of this copolymer has been tested with several commonly used acids, bases and oxidants. The apparent viscosity of this copolymer dissolved in N-methyl pyrrolidone (NMP) solvent at different concentrations and temperatures has been measured. The effect of two additives, polyethylene glycol (1000 g mol(-1)) and Tween80, on the apparent viscosity of the PPESK/NMP solution, has been investigated. Further, the PPESK/NMP solution has been used to prepare asymmetric ultra filtration membranes, and the influence of the solution viscosity on the gelation rate, the membrane structure and the ultrafiltration performance has been studied. The results present here provide fundamental data on this promising copolymer material, and will be beneficial for its future application, especially in the membrane formation area.

Abstract  Research on graphene-monolayers of carbon atoms arranged in a honeycomb lattice-is proceeding at a relentless pace as scientists of both experimental and theoretical bents seek to explore and exploit its superlative attributes, including giant intrinsic charge mobility, record-setting thermal conductivity, and high fracture strength and Young's modulus. Of course, fully exploiting the remarkable properties of graphene requires reliable, large-scale production methods which are non-oxidative and introduce minimal defects, criteria not fully satisfied by current approaches. A major advance in this direction is ionic liquid-assisted exfoliation and dispersion of graphite, leading to the isolation of few- and single-layered graphene sheets with yields two orders of magnitude higher than the earlier liquid-assisted exfoliation approaches using surface energy-matched solvents such as N-methyl-2-pyrrolidone (NMP). In this Minireview, we discuss the emerging use of ionic liquids for the practical exfoliation, dispersion, and modification of graphene nanosheets. These developments lay the foundation for strategies seeking to overcome the many challenges faced by current liquid-phase exfoliation approaches. Early computational and experimental results clearly indicate that these same approaches can readily be extended to inorganic graphene analogues (e.g., BN, MoX2 (X = S, Se, Te), WS2, TaSe2, NbSe2, NiTe2, and Bi2Te3) as well.

Abstract  Isobaric vapor-liquid equilibrium (VLE) data is determined for the binary mixtures of N-methyl-2-pyrrolidone + aminoethanol, N-methyl-2-pyrrolidone + chloroethanol, and N-methyl-2-pyrrolidone + phenyletbanol at 95.3 kPa over the entire composition range using a Swietoslawski type ebulliometer. All three systems investigated show negative deviations from Raoult's law, and none of the binary systems formed azeotropic mixtures. The experimental VLE data of the three binary mixtures are correlated using the Wilson model. The computed vapor phase mole fractions, activity coefficients, and Gibbs energy along with optimum Wilson parameters are presented. The studies indicate that all three binary systems are nonideal liquid mixtures deviating from Raoult's law exhibiting negative values of excess Gibbs energies due to strong intermolecular hydrogen bonding between unlike molecules.

Abstract  A novel solvent system consisting of CuCl/aniline/n-methyl pyrrolidone was evaluated for the reactive absorption of ethylene. Equilibrium olefin loadings significantly exceeded physical solubility values. The equilibrium ethylene-ethane selectivity was a strong function of the gas phase total pressure. Kinetic behavior was accurately described by an instantaneous reversible mechanism. The solvent exhibited acceptable chemical stability during the experimental tests.

Abstract  In this paper, the effects of gamma-butyrolactone (GBL) weight ratio (w(GBL)) and membrane thickness on the formation of asymmetric flat sheet membranes prepared with P84 (BTDA-TDI/MDI co-polyimide)/N-methyl-2-pyrrolidone (NMP)/GBL casting solutions are investigated. With the increase of membrane thickness, the transition of membrane morphology from sponge-like to finger-like structure occurs at critical structure-transition thickness L-c. L-c and the general sponge-like structure thickness (L-gs) increase with w(GBL). For 20 wt.% P84/NMP/GBL casting solution, the membrane morphology changes from finger-like to sponge-like structure at the critical weight ratio of GBL (w* = 0.69). The membrane morphology and performance of hollow fibers spun with various w(GBL) are observed. Compared with the hollow fiber membranes made of 18 wt.% P84/NMP/GBL dope solution with w(GBL) = 0.75, the hollow fiber membranes spun with w(GBL) = 0.25 present a higher permeation flux and a larger MWCO. As w(GBL) increases from 0.25 to 0.75, the membrane morphology transfers from finger-like to sponge-like structure. An increase in shear rate shifts the rejection curves towards left, and lowers the MWCO of hollow fiber membranes. For hollow fiber membranes spun with w(GBL) = 0.75, a relatively high permeation flux and a large MWCO are obtained by the wet spinning process. (C) 2011 Elsevier BM. All rights reserved.

Abstract  In this paper. asymmetric membranes are prepared with P84 (BTDA-TDI/MDI co-polyimide)/N-methyl-2-pyrrolidone (NMP)/-gamma-butyrolactone (GBL) and polyetherimide (PEI)/NMP/GBL. casting solutions by wet phase-inversion process And the transition of membrane morphology is investigated with different flat sheet and thickness-gradient membranes. For the thickness-gradient membranes, with the increase of membrane thickness, the membrane morphology changes from sponge-like to finger-like structure at the critical structure-transition thickness L(c). Meanwhile, the general sponge-like structure thickness L(gs) underneath the membrane surface is almost a constant. And the morphology of thickness-gradient membranes IS Illustrated with three different thickness regions. For the flat sheet membranes prepared with PEI/NMP/GBL casting Solutions. with the increase of GBL. weight ratio w(GBL), the transition of membrane morphology from finger-like to sponge-like structure occurs it the critical weight ratio of GBL (w* = 0.588) The presence of GBL increases the viscosity of the casting solutions and suppresses the tendency of macrovoid formation. For the thickness-gradient membranes prepared with PEI/NMI/GBL casting solutions, the presence of GBL retards the transition of membrane morphology The increase of w(GBL), results in the increase of L(c) and L(gs). When WGBL is greater than w*, the transition of membrane morphology is not investigated and a fully sponge-like structure is formed (C) 2009 Elsevier B V All rights reserved.

Abstract  The supercritical antisolvent precipitation (SAS) process has been frequently applied to pharmaceutical compounds, due to its potential capacity to control particle size (PS) and distribution and the simple separation and recovery of the solvent and of the antisolvent. However until now, the SAS process has been performed prevalently in laboratory scale apparatus; therefore, process limitations that are significant on the large scale, have not been studied yet. These limitations may even lead to the failure of translating the process to commercial dimensions. Herein we report the results of SAS precipitation of Amoxicillin from N-methylpyrrolidone performed in a semi-continuous pilot plant equipped with a 5 dm(3) precipitator, operated at 40 degreesC and 150 bar. Non coalescing spherical microparticles were obtained with mode diameters ranging from 0.3 to 1.2 mum depending on the concentration of Amoxicillin in the liquid solution. The effect of the scale enlargement and of the kind of injection device on the powder size and morphology has been investigated and a comparison with laboratory scale results is also presented. The change of nozzle arrangement and diameter from the laboratory to the pilot scale does not affect significantly the PS and distribution of Amoxicillin. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract  Extraction of phenolic antioxidants from aqueous media by hydrophilic solvents in the presence of ammonium sulfate is studied. Conditions for potentiometric titration of phenols by an acid-base mechanism are optimized. Interference of accompanying elements is studied. An extraction-potentiometric method for determination of phenolic antioxidants in extracts based on N-methylpyrrolidone is developed. Results of determination by the method suggested and by the familiar method are compared.

Abstract  High refractive index, colorless polymers with high temperature resistancy are of great industrial interest. In this study, new sulfur-containing copolyimides with high refractive indices have been synthesized via polycondensation reaction using 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA) as dianhydride monomers, and 4,4'-diaminodiphenyl sulfide (4,4'-SDA) and 2,3,5,6-tetramethyl-1,4-phenylene diamine (4MPD) as well as 3,3'-diaminodiphenyl sulfone (3,3'-DDS) as diamino monomers. The resulting copolyimides are amorphous and soluble in common organic solvents such as dimethylacetamide and N-methylpyrrolidone. They also exhibit very good optical properties such as high transparency (> 88% at 589.6 nm) for samples with a thickness of 120-150 mu m. Furthermore, higher refractive indices ranging from 1.64 to 1.72 at visible wavelengths compared to currently applied polymer materials, which show refractive indices between 1.5 and 1.6, are found. In addition, the copolyimides synthesized in this study show high thermal stability with glass transition temperatures between 273 and 306 A degrees C.

Abstract  Polyethersulfone (PES) nanofibers are produced by electrospinning solutions of PES/dimethylforamide (DMF), PES/N-methylpyrrolidone (NMP) and PES/(NMP:DMF) (of different NMP:DMF ratios) at temperature of 40 degrees C and various levels of relative humidity (RH). The influence of environmental conditions on bead formation as well as surface and interior morphologies of electrospun fibers is discussed through the phase diagram of H2O/DMF/PES and H2O/NMP/PES systems. The former case has small miscibility area while the latter one has large of which. The results demonstrate the contribution of RH of operating environment to morphology evolution of nanofibers. If the size of miscibility area increases e.g. H2O/NMP/PES system, a higher values of RE is needed to stabilize the formation of fibers. For this system, low level of humidity leads to develop beads as well as bead-on-string morphology. Adding the second solvent i.e. DMF into the PES/NMP solution shifts the binodal boundary toward the polymer-solvent side meaning a smaller miscibility area. In consequence, formation of fiber can be stabilized under broad range of humidity levels i.e. from low to high level of humidity. Implications regarding formation of surface pores by manipulating phase behavior of ternary system as well as RH of ambient conditions are discussed related to physico-chemical nature of solvent.

Abstract  We demonstrate an erbium-doped fiber laser passively Q-switched by a black-phosphorus polyimide film. The multi-layer black-phosphorus (BP) nanosheets were prepared via a liquid exfoliation approach exploiting N-methylpyrrolidone as the dispersion liquid. By mixing the BP nanosheets with polyimide (PI), a piece of BP-PI film was obtained after evaporating the mixture in a petri dish. The BP-PI saturable absorber had a modulation depth of 0.47% and was inserted into an erbium-doped fiber laser to realize passive Q-switched operations. The repetition rate of the Q-switched laser increased from 5.73 kHz to 31.07 kHz when the laser pump was enhanced from 31.78 mW to 231.46 mW. Our results show that PI is an excellent host material to protect BP from oxidation, and the BP PI film can act as a promising nonlinear optical device for laser applications.

Abstract  Five series of polyheteroarylenes have been investigated with regard to their physical properties before and after swelling with supercritical carbon dioxide. The study of the dependence of glass transition temperature and free volume of polymers on their conformational rigidity showed that the process of swelling in supercritical carbon dioxide is influenced by the voluminous side groups and by the high boiling solvent N-methylpyrrolidone used for the preparation of the polymers which facilitates the formation of crosslinks or complexes with the macromolecular chains.

Abstract  A series of organ-soluble copolyimides (co-PIs) were synthesized from 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 2,2'-bis(trifluoromethyl)-4, 4'-diaminobiphenyl (TFMB), and 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) via a one-step polymerization in N-methyl-2-pyrrolidone (NMP). The polyimide solutions were used to fabricate as-spun polyimide fiber by a wet-spinning process. SEM images of the round cross-section of the fibers indicated that a homogeneous and dense fibrous structure was produced in the coagulation bath of H2O/NMP = 90/10 (v/v) and many microfibrils appeared on the surface. The drawn fibers exhibit excellent mechanical properties, and the strength and modulus of BTDA/TFMB/BIA co-PI fibers (TFMB/BIA = 50/50) reached 2.25 and 102 GPa with a draw ratio of 3.0. The 5 % weight loss temperature of the co-PI fibers in thermogravimetric analysis spectra achieved 548-563 A degrees C in an air atmosphere. The glass transition temperatures were found to be between 340 and 366 A degrees C according to the DMA results. Annealed BTDA/TFMB/BIA co-PI fibers displayed distinct wide-angle X-ray patterns, and crystallinity and crystal orientation with various draw ratios were observed.

Abstract  The fate of injectant coal in blast furnaces has been investigated through characterizing samples collected from commercial-scale blast furnaces and laboratory-scale tests. Representative samples, including an injectant coal and the corresponding carryover dusts from a full-sized blast furnace, and a set of tuyere level core-drilled samples from another full-sized blast furnace, have been examined. The samples were extracted using 1-methyl-2-pyrrolidinone (NMP) as the solvent, and the extracts were then studied using size-exclusion chromatography (SEC). The carryover dust extracts were found to contain heavy carbonaceous materials of apparent mass similar to 10(7)-10(8) units, on the basis of polystyrene calibration. Similar materials were also found to be present in the NMP extracts of the core-drilled samples taken from the bosh, rear of bird's nest, and deadman regions of the furnace, at the tuyere level. In contrast, the feed coke did not give any extractable material. Controlled pyrolysis and combustion experiments, in an electrically heated wire-mesh reactor, suggest that the extent of injectant coal combustion in the raceway is limited by a very short exposure time to high temperatures and poor oxygen availability. These observations suggest that some coal char particles might escape from the raceway incompletely pyrolyzed. Unburned volatiles, particularly tars, may be further thermally altered, giving rise to the formation of high-molecular-weight (soot-like) materials.

Abstract  Thermally stable polyimide/titania (PI/TiO2) hybrid nano-composite films have been successfully synthesized through the in situ formation of TiO2 within a PI matrix via sol-gel process. Poly(amic acid) (PAA) solution is prepared from 3,5-diamino benzoyl amino phenyl-14H-dibenzo[a, j]xanthene and 4,4'-(hexaflouroisopropylidene)diphthalic anhydride in N-methyl-2-pyrrolidinone solvent. The different amounts of tetraethyl orthotitanate and actylacetone are incorporated into PAA matrix, and then thermally imidized to form PI/TiO2. The chelating agent, acetylacetone, was applied to reduce the gelation rate of titanium alkoxide. Thermal decomposition temperatures of nanocomposites with a 10% weight loss were in excess of 500 degrees C, and char yields higher than 63% at 800 degrees C in nitrogen. The chemical and morphological structures of the hybrid nanocomposites were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and transmission electron microscopy. The results show that the TiO2 particles are well dispersed in the PI matrix with particle size between 10 and 30 nm in diameter. (C) 2013 Society of Plastics Engineers

Abstract  Porous asymmetric polyetherimide (PEI) hollow fiber membranes were fabricated via a phase-inversion method using ethanol, glycerol and acetone as the additives in the spinning dope. Also, hollow fiber PEI membrane without additives was fabricated. An aqueous solution of 1-methyl-2-pyrrolidone (80 wt.%) was used as bore fluid to prevent forming of an inner dense skin layer. The precipitation rate of the polymer dopes with the different additives was studied using cloud point measurement. The effect of the additives on the resulting membrane structure, surface porosity, pore size, critical water entry pressure, collapsing pressure and physical and chemical CO2 absorption performance by distilled water and NaOH (1 M) solution in a gas liquid membrane contactor system were investigated and compared. Cloud point diagrams indicated that the precipitation rate of the polymer dopes increased following the trend of ethanol > acetone > glycerol. Results of gas permeation tests showed that ethanol and glycerol as additives provided the membranes with the largest and smallest pore size, respectively. Moreover, all the additives resulted in an increase in the effective surface porosity. The cross-section of the membranes was examined via a scanning electron microscopy. Ethanol in the spinning dope provided the membrane structure with a sublayer with finger-like macrovoids, originating from the inner and outer surfaces of the hollow fiber and extending to the middle section of the hollow fiber wall, which resulted in a larger pore size and higher CO2 absorption rate than the other PEI hollow fiber membranes. (C) 2012 Elsevier B.V. All rights reserved.

Abstract  Experimental data on the solubility Of CO2 in dimethylsulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP) are reported at temperatures of 298, 308 and 318 K and pressures approaching the mixture critical point for each binary system. The corresponding volumetric expansions of DMSO and NMP with CO2 are also presented. The solubility data are correlated with the Peng-Robinson equation of state (PR-EOS). At a given temperature and pressure, higher solubilities of CO2 are obtained in NMP compared with DMSO and this trend is consistent with the volumetric expansions of the solvents. A plot of the volumetric expansion data as a function of the solubility of CO2 in the liquid phase suggests that it is unlikely, as a general rule, that the expansion isotherms for the various systems collapse onto a single expansion curve. The existence of a single expansion curve appears to hold only for a given binary system over a limited range of temperature. The use of two adjustable binary interaction parameters with the PR-EOS provides a superior con-elation of the liquid phase composition in comparison with the standard PR-EOS, particularly in the vicinity of the mixture critical point. (C) 2003 Elsevier B.V. All rights reserved.

Abstract  A one step electrospinning approach was utilized for the preparation of polyaniline (PANI) modified titanium dioxide/polyacrylonitrile (PAN) composite nanofiber using a mixture of dimethylformamde (DMF) and N-methyl-2-pyrrolidone (NMP) as solvents. Several techniques were carried out to characterize the resulting electrospun fibers including SEM, FTIR, XRD, TGA and DRUV-Vis absorption spectroscopy. The later method showed an optical band gap shifting for polyaniline modified titanium dioxide/polyacrylonitrile composites in comparison to unmodified one. Due to these optical absorptions, the fibers can be considered promising candidates as visible light photocatalysts to generate more electron-hole pairs. Photodegradation was accomplished using methyl orange (MO) as a model organic pollutant. The degradation of MO, extremely increased using photocatalysts which contained PANI and decolorization in the presence of visible light achieved up to 90% in less than 60 min in comparison with the neat nanofibers (about 10%). This advantage promises a bright future for these fibers as useful photocatalysts. The effect of reaction parameters such as photocatalyst dose, concentration of the starting substrate solution and pH were studied and photocatalytic kinetics was investigated. The stability of photocatalyst was also investigated. The photocatalyst retained 87% of its initial activity after 10 replicate uses. (C) 2016 Elsevier B.V. All rights reserved.

Abstract  Polyaniline (PANI) was synthesized by oxidative polymerization of aniline using ammonium persulfate in an acid medium. The polyaniline salt was converted to base form by treatment with ammonium hydroxide. The polyaniline base was dissolved in N-methyl pyrrolidone (NMP) for film casting. The cast film was doped with HCl for obtaining higher conductivity. Both doped and undoped PANI films were characterized by UV-visible, FTIR, and XRD analyses. The electrical conductivity of the PANI film was studied by a four-point probe method at room temperature. Finally, ammonia gas-sensing characteristics of the prepared polyaniline film were studied by measuring the change in electrical conductivity on exposure to ammonia gas at different concentrations. The influence of concentration of acid during polymerization of aniline and dopant concentration on the gas sensing characteristics of PANI film are reported in this paper.

Abstract  Recommended vapor pressure data for important industrial solvents, aniline (CAS RN: 62-53-3), nitromethane (CAS RN: 75-52-5), 1-methyl-2-pyrrolidone (CAS RN: 872-50-4), and 2-aminoethanol (CAS RN: 141-43-5), were developed by the simultaneous correlation of vapor pressure and related thermal data (heat capacities of condensed phases, ideal-gas heat capacities and calorimetrically determined enthalpies of vaporization). For 1-methyl-2-pyrrolidone and 2-aminoethanol, new vapor pressure data were obtained using the static method and new liquid phase heat capacities were determined by Tian-Calvet calorimetry while for remaining compounds relevant thermodynamic data were taken from the literature. The thermodynamic properties in the ideal gaseous state were calculated using the methods of statistical thermodynamics based on experimental as well as calculated fundamental vibrational frequencies and molecular structure data. Comparisons with literature values are shown for all measured and derived properties. (C) 2015 Elsevier B.V. All rights reserved.

Abstract  This study focuses on the surface modification of polyethersulfone (PES) ultrafiltration (UF) membranes using corona air plasma in order to reduce membrane fouling during separation of oil/water emulsions. The PES membranes were fabricated using polyvinylpyrrolidone (PVP) as a pore forming agent with various solvents including N,N-dimethylacetamide (DMAc), N,N-dimethyl-formamide (DMF), 1-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO) by the phase inversion method. The effects of solvent in casting solution and corona treatment conditions on the surface properties, membrane morphology and separation performance of the membranes were investigated. The ATR-FTIR, SEM and AFM analyses were used to characterize the untreated and corona treated membranes. The results showed that viscosity of the casting solution and difference in solubility parameter between the solvent and non-solvent play an important role in the membrane structure and performance, however, the effect of viscosity is more pronounced. The corona treatment led to significant enhancement of the surface hydrophilicity, improvement of anti-fouling properties and oil/water flux in all membranes without significant changes in oil rejection. The effect of corona parameters on DMSO-solvent membrane indicated that the corona needs more time or higher power to ablate the surface, widening the pore distribution and enhancing permeation in case of membranes with a thicker dense layer. (C) 2012 Elsevier B.V. All rights reserved.

Abstract  Aniline has been copolymerized in the presence of substituted anilines as comonomers to prepare conducting copolymers of poly(aniline-co-alkylaniline) type, via the chemical oxidative polymerization route. Their thermal stabilities and conductivities are slightly less than pure polyaniline but processabilities have been improved significantly. These copolymers exhibit improved solubility in organic solvents like 1-methyl-2-pyrrolidone (NMP) dimethyl sulphoxide (DMSO), and dimethyl formamide (DMF). Conduction mechanism has been found to be 3-D VRH in case of pure HCl-doped polyaniline and 1-1D VRH for copolymers. Coating of these polymers on insulating surfaces can be used for ESD protection and corrosion prevention of iron and mild Steel under hostile conditions.

Abstract  Mineral components bonded to organic parts in some Indonesian and Chinese coals were characterized by solid-state Si-29 and Al-27 NMR, inductively coupled plasma emission spectroscopy, and X-ray fluorescence before and after high temperature solvent extraction and acid treatments. In lower ranking coals such as South Banko and Berau coals, it was found that organically bonded Si species existed as siloxane-type from the solid-state Si-29 NMR analyses. It was also found that some of aluminosilicates species were extracted by mild acid treatments with 2 M CH3COOH or HCl solution even at room temperature. Solvent extraction using N-methylpyrrolidinone (NMP) at 350degreesC or with 1-methylnaphthalene(1-MN) at 360degreesC was very effective for the production of coal extract (so-called hyper-coal: HPC) with high yields of ca. 60% and extremely low ash contents of ca. 200 ppm. It is noted that some organically associated Si, Al, Ca and Fe species still remained in the coal extract, especially siloxane-type Si species were concentrated in the extracts obtained from the lower rank coals. The same tendency was also observed for the higher rank coals such as Enshu and Nantun coals, although the contents of such organically associated minerals were lower than those of the lower rank coals. (C) 2002 Published by Elsevier Science Ltd.

Abstract  In this work composite hollow-fibers were prepared by dip-coating of commercial polypropylene (PP) with a thin layer of ethylene-chlorotrifluoroethylene copolymer (ECTFE). The employment of N-methyl pyrrolidone (NMP) as solvent improved the polymer processability favoring dip-coating at lower temperature (135 degrees C). Scanning electron microscopy (SEM) analyses showed that after dip-coating the PP support maintained its microstructure, whereas a thin coated layer of ECTFE on the external surface of the PP hollow-fiber was clearly distinguishable. Membrane characterization evidenced the effects of the concentration of ECTFE in the dope-solution and the time of dip-coating on the thickness of ECTFE layer and membrane properties (i.e., contact angle and pore size). ECTFE coating decreased the surface roughness reducing, as a consequence, the hydrophobicity of the membrane. Moreover, increasing the ECTFE concentration and dip-coating time enabled the preparation of a thicker layer of ECTFE with low and narrow pore size that negatively affected the water transport. On the basis of the superior chemical resistance of ECTFE, ECTFE/PP composite hollow fibers could be considered as very promising candidates to be employed in membrane processes involving harsh conditions.

Abstract  In preparation of polymeric gas separation membranes by phase inversion method, polymer concentration is one of the most important variables which can change membrane morphology and behavior. In this research, critical concentration of the polyetherimide (PEI) solutions in N-methyl-2-pyrrolidone (NMP) as a solvent was determined by viscometric method. The influence of temperature on critical concentration was studied. Three asymmetric PDMS/PEI membranes with different concentrations of PEI were prepared and characterized for H-2/CH4 separation. The results showed that the membranes with higher concentrations than critical concentration were more suitable for gas separation. In addition, the viscosity data were fitted by appropriate equations and the densities were satisfactorily correlated by a simple first-order polynomial with respect to temperature and the PEI mass fraction. The prepared membrane showed the selectivity of 26 for H-2/CH4 separation at 1 bar and 25 degrees C for pure gas and 24.8 for mixed gas. The influence of the pressure on the H-2 and CH4 permeance and the selectivity for a mixed binary gas showed that the permeance of both gases declined by pressure enhancement and the selectivity increased. (c) 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.