Poly(amide-imide)-Silica Gel Hybrids: Synthesis and Characterization

Several poly(amide-imide)-silica gel hybrids containing metal salts were prepared by the sol-gel reaction. Poly(amide-imide)s were prepared by low temperature polycondensation reaction of trimellitic anhydride (TMA) and diisocyanates [isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), and 4,4′-methylenebis(phenyl isocyanate) (MDI). The inherent viscosities of the poly(amide-imide)s obtained ranged from 0.39–0.69 dL/g in DMAc. The hydrolysis and condensation reaction of tetramethoxysilane (TMOS) to form a silica gel network was affected in DMAc containing 5% LiCl, CaCl₂ or ZnCl₂ during the formation of poly(amide-imide)s. Films could be cast from DMAc solution and gradual evaporation of the solvent afforded pale yellow to amber colored hybrids in which the salts were dispersed at the molecular level. About 30–60% polymer was incorporated in the hybrids. Pyrolysis of the polymer silica gel hybrid samples at 600°C resulted in the formation of porous silica. Pore size and surface area studies on representative porous silica gels, SiG–4, SiG–5, and SiG–8, obtained upon the pyrolysis of the corresponding hybrids HPAI-4, HPAI-5 and HPAI-8, indicated that the silica gels were mesoporous in nature and had narrow pore size distribution (pore radius = 1.8 nm) with a surface area of 371 m²/g, 335 m²/g and 300 m²/g, respectively. The bottle shaped pores exhibited a pore volume of 0.227 cm³/g, 0.314 cm³/g and 0.280 cm³/g, respectively. Computer simulation modeling studies indicated that the poly(amide-imide) chains were not coiled and there was no agglomeration of the chains.     

Organic–inorganic hybrid materials. I. Characterization and degradation of poly(imide–silica) hybrids

Poly(imide–silica) hybrid materials with covalent bonds were prepared by (3-aminopropyl)methyldiethoxysilane (APrMDEOS) terminated amic acid, water, and tetramethoxysilane (TMOS) via a sol–gel technique. Infrared (IR), ²⁹Si and ¹³C CP/MAS nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis (TGA) were used to study hybrids containing various proportions of TMOS and hydrolysis ratios. The microstructure and chain mobility of hybrids were investigated by proton spin–spin relaxation T₂ measurements. The apparent activation energy E_a for degradation of hybrids in air was studied by the van Krevelen method. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2275–2284, 1999     

Characterization of 6FDA‐based hyperbranched and linear polyimide–silica hybrid membranes by gas permeation and 129Xe NMR measurements

Physical and gas transport properties of novel hyperbranched polyimide–silica hybrid membranes were investigated and compared with those of linear‐type polyimide–silica hybrid membranes with similar chemical structures. Hyperbranched polyamic acid, as a precursor, was prepared by polycondensation of a triamine, 1,3,5‐tris(4‐aminophenoxy)benzene (TAPOB), and a dianhydride, 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA). 6FDA‐TAPOB hyperbranched polyimide–silica hybrids were prepared using the polyamic acid, water, and tetramethoxysilane (TMOS) by sol–gel reaction. 5% weight‐loss temperature of the 6FDA‐TAPOB hyperbranched polyimide–silica hybrids determined by TG‐DTA measurement considerably increased with increasing silica content, indicating effective crosslinking at polymer–silica interface. CO₂, O₂, N₂, and CH₄ permeability coefficients of the 6FDA‐based polyimide–silica hybrids increased with increasing silica content. In addition, CO₂/CH₄ selectivity of the 6FDA‐TAPOB–silica hybrids remarkably increased with increasing silica content. From ¹²⁹Xe NMR analysis, characteristic distribution and interconnectivity of cavities created around polymer–silica interface were suggested in the 6FDA‐TAPOB–silica hybrids. It was indicated that size‐selective separation ability is effectively brought by the incorporation of silica for the 6FDA‐TAPOB hyperbranched polyimide–silica hybrid membranes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 291–298, 2006     

Titania–Silica Materials for Enhanced Photocatalysis

Mesoporous titania–organosilica nanoparticles comprised of anatase nanocrystals crosslinked with organosilica moieties have been prepared by direct co‐condensation of a titania precursor, tetrabuthylortotitanate (TBOT), with two organosilica precursors, 1,4‐bis(triethoxysilyl) benzene (BTEB) and 1,2‐bis(triethoxysilyl) ethane (BTEE), in mild conditions and in the absence of surfactant. These hybrid materials show both high surface areas (200–360 m² g^?1) and pore volumes (0.3 cm³ g^?1) even after calcination, and excellent photoactivity in the degradation of rhodamine 6G and in the partial oxidation of propene under UV irradiation, especially after the calcination of the samples. During calcination, there is a change in the Ti^IV coordination and an increase in the content of Si?O?Ti moieties in comparison with the uncalcined materials, which seems to be responsible for the enhanced photocatalytic activity of hybrid titania–silica materials as compared to both uncalcined samples and the control TiO₂.     

A New Synthetic Route to Microporous Silica with Well‐Defined Pores by Replication of a Metal–Organic Framework

Microporous amorphous hydrophobic silica materials with well‐defined pores were synthesized by replication of the metal–organic framework (MOF) [Cu₃(1,3,5‐benzenetricarboxylate)₂] (HKUST‐1). The silica replicas were obtained by using tetramethoxysilane or tetraethoxysilane as silica precursors and have a micro–meso binary pore system. The BET surface area, the micropore volume, and the mesopore volume of the silica replica, obtained by means of hydrothermal treatment at 423 K with tetraethoxysilane, are 620 m²g^?1, 0.18 mL g^?1, and 0.55 mL g^?1, respectively. Interestingly, the silica has micropores with a pore size of 0.55 nm that corresponds to the pore‐wall thickness of the template MOF. The silica replica is hydrophobic, as confirmed by adsorption analyses, although the replica has a certain amount of silanol groups. This hydrophobicity is due to the unique condensation environment of the silica precursors in the template MOF.     

壳聚糖基多孔碳材料的制备及其超级电容性能

以胶态SiO₂纳米粒子为模板,壳聚糖为碳源,ZnCl₂为活化剂,制备了具有不同比表面积和孔体积的氮掺杂介孔碳。采用多种表征手段对碳材料的微观形貌、比表面积和孔道结构进行了表征,探究了壳聚糖与SiO₂纳米粒子的比例以及ZnCl₂活化剂对碳材料孔体积和比表面积的影响。结果表明,在未使用活化剂时碳材料(CSi-1.75)的孔体积高达4.53 cm³·g^-1,但其比表面积最小(729 m²·g^-1);使用ZnCl₂作为活化剂制备的碳材料(CSi-1.75-Zn)比表面积为1 032 m²·g^-1,但其孔体积下降到1.99 cm³·g^-1,且具有最多的吡啶氮和吡咯氮。在以6.0 mol·L^-1KOH为电解液的三电极体系中,当电流密度为0.5 A·g^-1时,CSi-1.75...     

Building Block approach to SiO2–ZrO2 porous materials†

(2‐Hydroxyethyl)trimethylammonium silicate, Si₈O₂₀[N(CH₃)₃(C₂H₄OH)]₈·nH₂O, was allowed to react with zirconium tetrakis(2,4‐pentanedionate) in methanol, resulting in gel formation. The gels were heat‐treated at 650–1000 °C in air. The product at 650 °C showed a specific surface area of 500 m² g⁻¹, and the average pore diameter was ca 4.3 nm, indicating the formation of a thermally stable mesoporous body. Gels with the same composition were also prepared by sol–gel processing using tetraethoxysilane as a silica source. The specific surface area of the product yielded by heating the gels at 650 °C was 425 m² g⁻¹ and the average pore diameter was ca 2.8 nm, which were lower than those of the product from the gels prepared with (2‐hydroxyethyl)trimethylammonium silicate. These differences have been attributed to the difference in nanostructure of the gels, caused by the structure of the silica sources and their polymerization behaviour. Copyright © 1999 John Wiley & Sons, Ltd.     

Study of carbonaceous clusters in irradiated polycarbonate with UV–vis spectroscopy

The formation of carbonaceous clusters in ion‐irradiated polymer films was investigated extensively. Information about these clusters may be obtained with ultraviolet–visible (UV–vis) spectroscopy. The optical band gap (E_g), calculated from the absorption edge of the UV spectra of these polymers, can be correlated to the number of carbon atoms (N) in a cluster with the modified Tauc equation. The structure of the cluster is also related to E_g; for example, a six‐membered‐benzene‐ring‐type structure has an E_g of ≈5.3 eV, whereas a buckminsterfullerene‐type structure has an E_g of ≈4.9 eV. These clusters are responsible for the electrical conductivity in these films. In this work, polycarbonate films (20 μm thick) were irradiated with 45‐MeV Li ions at fluences of 1 × 10¹² to 1 × 10¹³ cm⁻² and were characterized with UV–vis spectroscopy and impedance measurements. The E_g values, calculated from the absorption edge in the 280–315‐nm region with the Tauc relation, varied from 4.39 to 4.35 eV for the pristine and various irradiated samples, respectively. The cluster size showed a range of 60–62 carbon atoms per cluster. The sheet conductivity (σ_dc) and loss (tan δ) values of 10⁻¹⁶ Ω⁻¹cm⁻¹ and 10⁻³ for the pristine sample changed to 10⁻¹⁵ Ω⁻¹cm⁻¹ and 10⁻², respectively, for the irradiated samples. This increase in the values of σ_dc and tan δ may be correlated to the increase in the size of the carbonaceous clusters. This study provides insight into the mechanism of electrical conductivity in irradiated polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1589–1594, 2000     

壳聚糖基多孔碳材料的制备及其超级电容性能

以胶态SiO₂纳米粒子为模板,壳聚糖为碳源,ZnCl2为活化剂,制备了具有不同比表面积和孔体积的氮掺杂介孔碳。采用多种表征手段对碳材料的微观形貌、比表面积和孔道结构进行了表征,探究了壳聚糖与SiO₂纳米粒子的比例以及ZnCl2活化剂对碳材料孔体积和比表面积的影响。结果表明,在未使用活化剂时碳材料(CSi-1.75)的孔体积高达4.53 cm³·g^-1,但其比表面积最小(729 m²·g^-1);使用ZnCl₂作为活化剂制备的碳材料(CSi-1.75-Zn)比表面积为1032 m²·g^-1,但其孔体积下降到1.99 cm³·g^-1,且具有最多的吡啶氮和吡咯氮。在以6.0 mol·L^-1 KOH为电解液的三电极体系中,当电流密度为0.5 A·g^-1时,CSi-1.75-Zn的比电容为344 F·g^-1,而CSi-1.75的比电容仅为255 F·g^-1。这表明碳材料的比表面积对超级电容性能影响最大,而孔体积影响较小。电容贡献分析结果表明,相对于CSi-1.75,CSi-1.75-Zn的双电层电容和赝电容都得到了提高,这表明更大的比表面积和更多的吡啶氮和吡咯氮有利于提高碳材料的超级电容性能。     

Poly(silarylene–siloxane)polyimides from allyl‐terminated oligoimides and hydride‐functional silarylene–siloxanes via hydrosilylation polymerization

This research was focused on the design and execution of new synthetic routes to low‐temperature‐curable poly(silarylene–siloxane)polyimides. The synthesis of individual oligoimide and silarylene–siloxane blocks was followed by hydrosilylation polymerization to produce crosslinked copolymers. The silarylene–siloxane and polyimide blocks were structurally characterized by IR and ¹H NMR spectroscopy and size exclusion chromatography. The high‐temperature resistance of the copolymers was evaluated through the measurement of heat distortion temperatures (T_HD's) via thermomechanical analysis and by the determination of the weight loss at elevated temperatures via thermogravimetric analysis. Glass‐transition temperatures (T_g's) of the silarylene–siloxane segments were measured by differential scanning calorimetry. Hydrosilylation curing was conducted at 60 °C in the presence of chloroplatinic acid (H₂PtCl₆). The copolymers displayed both high‐temperature resistance and low‐temperature flexibility. We observed T_g of the silarylene–siloxane segment as low as ?77 °C and T_HD of the polyimide segment as high as 323 °C. The influence of various oligoimide molecular weights on the properties of copolymers containing the same silarylene–siloxane was examined. The effect of various silarylene–siloxane molecular weights on the properties of copolymers containing the same oligoimide was also examined. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4922–4932, 2005     

Polyimide–silica hybrid coatings: morphological,mechanical, and thermal investigations

In this study, polyimide–silica (PI–silica) based hybrid coating compositions were prepared from tetraethoxysilane (TEOS), γ‐glycidyloxypropyl trimethoxy silane (GOTMS), and polyamic acid (PAA) via a combination of sol–gel and thermal imidization techniques. PAA was synthesized from 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) and 3,3'‐Diaminodiphenyl sulfone (DDS) in N‐Methyl‐2‐pyrrolidone (NMP). The silica content in the hybrid coatings was varied from 0 to 20 wt%. The structural characterization of the hybrid coatings was performed using FTIR and ²⁹Si‐NMR spectroscopies. Results from both pendulum hardness and micro indentation test show that the hardness of hybrid coatings improves with the increase in silica content. The tensile tests also demonstrated that the mechanical properties at low silica content are rather striking. Their surface morphologies were characterized by scanning electron microscopy (SEM). SEM studies revealed that inorganic particles were distributed homogenously through the PI matrix. It was also found that, incorporation of the silica domains increased the thermal stability of the hybrid coatings. Copyright © 2007 John Wiley & Sons, Ltd.     

Structural characterization of silica modified polyimide membranes

Polyimide and hybrid polyimide‐siloxane were synthesized by polycondensation, imidization, and sol‐gel reaction. The polyimides were prepared from pyromellitic dianhydride (PMDA) and 4,4‐oxydianiline (ODA) in N‐methyl‐2‐pyrollidone (NMP). Trimethoxyvinyl silane (TMVS) was used as a source of silica. Their surface morphologies, structures and thermal performances were determined using scanning electron microscopy (SEM), infrared spectroscopy (IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that the silica particles were finely and rather homogeneously dispersed in polymers. The glass transition temperature (T_g) of hybrid membrane materials increased with the increasing silica content. TGA analysis showed that polyimides were thermally stable with silica. Modified polyimide‐siloxane films, thermal characteristics were found to be better than the polyimide films without silica. Copyright © 2006 John Wiley & Sons, Ltd.     

Magnetic Properties of a Single‐Molecule Lanthanide–Transition‐Metal Compound Containing 52 Gadolinium and 56 Nickel Atoms

Monodisperse metal clusters provide a unique platform for investigating magnetic exchange within molecular magnets. Herein, the core–shell structure of the monodisperse molecule magnet of [Gd₅₂Ni₅₆(IDA)₄₈(OH)₁₅₄(H₂O)₃₈]@SiO₂ ( 1 a @SiO₂) was prepared by encapsulating one high‐nuclearity lanthanide–transition‐metal compound of [Gd₅₂Ni₅₆(IDA)₄₈(OH)₁₅₄(H₂O)₃₈]?(NO₃)₁₈?164 H₂O ( 1 ) (IDA=iminodiacetate) into one silica nanosphere through a facile one‐pot microemulsion method. 1 a @SiO₂ was characterized using transmission electron microscopy, N₂ adsorption–desorption isotherms, and inductively coupled plasma‐atomic emission spectrometry. Magnetic investigation of 1 and 1 a revealed J₁=0.25 cm^?1, J₂=?0.060 cm^?1, J₃=?0.22 cm^?1, J₄=?8.63 cm^?1, g=1.95, and z J=?2.0×10^?3 cm^?1 for 1 , and J₁=0.26 cm^?1, J₂=?0.065 cm^?1, J₃=?0.23 cm^?1, J₄=?8.40 cm^?1 g=1.99, and z J=0.000 cm^?1 for 1 a @SiO₂. The z J=0 in 1 a @SiO₂ suggests that weak antiferromagnetic coupling between the compounds is shielded by silica nanospheres.     

Organic/Inorganic NLO materials based on reactive polyimides and a bulky alkoxysilane dye via sol/Gel process

A series of the organic–inorganic materials based on reactive polyimides and a bulky alkoxysilane dye (ASD) for second‐order nonlinear optics have been developed. Sol‐gel reaction of ASDs is utilized to grow a network in polymer matrices (composite) or to create inter‐polymer network among polyimide chains (hybrid). Moreover, a full interpenetrating polymer network (IPN) was formed through simultaneous free radical polymerization of a methacryloyl group containing polyimide, and sol‐gel process of ASDs. Scanning electron microscopy (SEM) results indicate that the inorganic networks are distributed uniformly throughout the polymer matrices on the molecular scale. The silica particle sizes are well under 1 µm based on AFM study. Second harmonic coefficients, d₃₃ of 4.5 to 48.5 pm/V have been obtained for the optically clear poled/cured polyimide/ASD samples. Excellent temporal stability was obtained for these NLO materials at 100 °C. The dynamic thermal and temporal stabilities of the IPN system were much better than those of composite and hybrid systems. Copyright ­© 2003 John Wiley & Sons, Ltd.     

Facile Preparation of Core–Shell Magnetic Metal–Organic Framework Nanospheres for the Selective Enrichment of Endogenous Peptides

Facile preparation of core–shell magnetic metal–organic framework nanospheres by a layer‐by‐layer approach is presented. The nanospheres have high surface area (285.89 cm² g^?1), large pore volume (0.18 cm³ g^?1), two kinds of mesopores (2.50 and 4.72 nm), excellent magnetic responsivity (55.65 emu g^?1), structural stability, and good dispersibility. The combination of porosity, hydrophobicity, and uniform magnetism was exploited for effective enrichment of peptides with simultaneous exclusion of high molecular weight proteins. The nanospheres were successfully applied in the selective enrichment of endogenous peptides in human serum.     

Quartz Rod Coated with Modified Silica Gel as a Source of CO and CO2 for Standard Gaseous Mixtures

Quartz rods coated with a thin layer of chemically modified silica gel have been used for the generation of a two-component gaseous standard mixture containing carbon monoxide and carbon dioxide. A new method based on thermal decomposition of immobilized compounds chemically bonded to the surface of silica gel has been used in the generation process. The oxalic acid moiety bonded to the glycydoxypropylsilylated surface of silica gel underwent decarbonylation and decarboxylation at 300°C, yielding carbon monoxide and carbon dioxide. On-line connection of a thermal desorber with the GC/FID enabled calibration of the detector following the process of methanization of CO and CO₂. The following amounts of CO and CO₂ were generated per unit length of the rod: 15.1 × 10⁻⁸ Mol cm⁻¹ (RSD = 5.71%) for CO and 34.2 × 10⁻⁸ Mol cm⁻¹(RSD = 5.16%) for CO₂.     

Hierarchically Porous Carbons Derived from Metal–Organic Framework/Chitosan Composites for High‐Performance Supercapacitors

Hierarchically porous carbon materials with high surface areas are promising candidates for energy storage and conversion. Herein, the facile synthesis of hierarchically porous carbons through the calcination of metal–organic framework (MOF)/chitosan composites is reported. The effects of the chitosan (CS) additive on the pore structure of the resultant carbons are discussed. The corresponding MOF/chitosan precursors could be readily converted into hierarchically porous carbons (NPC‐V, V=1, 2, 4, and 6) with much higher ratios of meso‐/macropore volume to micropore volume (V_meso‐macro/V_micro). The derived carbon NPC‐2 with the high ratio of V_meso‐macro/V_micro=1.47 demonstrates a high specific surface area of 2375 m² g^?1, and a high pore volume of 2.49 cm³ g^?1, as well as a high graphitization degree, in comparison to its counterpart (NPC) without chitosan addition. These excellent features are favorable for rapid ion diffusion/transport, endowing NPC‐2 with enhanced electrochemical behavior as supercapacitor electrodes in a symmetric electrode system, corresponding to a high specific capacitance of 199.9 F g^?1 in the aqueous electrolyte and good rate capability. Good cycling stability is also observed after 10 000 cycles.     

Modular Thiol–Ene Chemistry Approach towards Mesoporous Silica Monoliths with Organically Modified Pore Walls

The surface modification of mesoporous silica monoliths through thiol–ene chemistry is reported. First, mesoporous silica monoliths with vinyl, allyl, and thiol groups were synthesized through a sol–gel hydrolysis–polycondensation reaction from tetramethyl orthosilicate (TMOS) and vinyltriethoxysilane, allyltriethoxysilane, and (3‐mercaptopropyl)trimethoxysilane, respectively. By variation of the molar ratio of the comonomers TMOS and functional silane, mesoporous silica objects containing different amounts of vinyl, allyl, and thiol groups were obtained. These intermediates can subsequently be derivatized through radical photoaddition reactions either with a thiol or an olefin, depending on the initial pore wall functionality, to yield silica monoliths with different pore‐wall chemistries. Nitrogen sorption, small‐angle X‐ray scattering, solid‐state NMR spectroscopy, elemental analysis, thermogravimetric analysis, and redox titration demonstrate that the synthetic pathway influences the morphology and pore characteristics of the resulting monoliths and also plays a significant role in the efficiency of functionalization. Moreover, the different reactivity of the vinyl and allyl groups on the pore wall affects the addition reaction, and hence, the degree of the pore‐wall functionalization. This report demonstrates that thiol–ene photoaddition reactions are a versatile platform for the generation of a large variety of organically modified silica monoliths with different pore surfaces.     

Hierarchically Organized Silica–Titania Monoliths Prepared under Purely Aqueous Conditions

Hierarchically organized silica–titania monoliths were synthesized under purely aqueous conditions by applying a new ethylene glycol‐modified single‐source precursor, such as 3‐[3‐{tris(2‐hydroxyethoxy)silyl}propyl]acetylacetone coordinated to a titanium center. The influence of the silicon‐ and titanium‐containing single‐source precursor, the novel glycolated organofunctional silane, and the addition of tetrakis(2‐hydroxyethyl)orthosilicate on the formation of the final porous network was investigated by SEM, TEM, nitrogen sorption, and SAXS/WAXS. In situ SAXS measurements were performed to obtain insight into the development of the mesoporous network during sol–gel transition. IR‐ATR, UV/Vis, XPS, and XAFS measurements showed that up to a Si/Ti ratio of 35:1, well‐dispersed titanium centers in a macro‐/mesoporous SiO₂ network with a specific surface area of up to 582 m² g^?1 were obtained. An increase in Ti content resulted in a decrease in specific surface area and a loss of the cellular character of the macroporous network. With a 1:1 Si/Ti ratio, silica–titania powders with circa 100 m² g^?1 and anatase domains within the SiO₂ matrix were obtained.     

The preparation of novel silica modified polyimide membranes: synthesis,characterization, and gas separation properties

In this study, new monomers having siloxane groups were synthesized as an intermediate for preparation of siloxane modified polyimide polymers. Then with these monomers, the synthesis of uncrosslinked and crosslinked polyimide–siloxane hybrid polymer membranes were achieved. The purposes of the preparation of modified polyimides were to modify the thermal and chemical stability, and mechanical strength of polyimides, and to improve the gas separation properties of polymers. The new diamine monomer having siloxane groups was prepared from 3,5‐diaminobenzoic acid (3,5‐DABA) and 3‐aminopropyltrimethoxysilane (3‐APTMS) in N‐methyl‐2‐pyrollidone (NMP) at 180°C. The modified polyimide membranes having different amount of siloxane groups were synthesized from pyromellitic dianhydride (PMDA), 4,4‐oxydianiline (ODA), and 3,5‐diaminobenzamido‐N‐propyltrimethoxy silane (DABA/PTMS) in NMP using a two‐step thermal imidization process. The synthesis of modified polyimide membranes were characterized by Fourier transform infrared spectroscopy (FTIR). The thermal analysis of the polyimides were carried out by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Water absorption and swelling experiments were also carried out for the investigation of structural properties of polymers. FTIR observations confirmed that the polyimide membranes with new diamine intermediate were successfully obtained. Thermal analysis showed that the uncrosslinked copolyimides exhibited two glass transition temperatures, indicating that they were separated microphases and it was found that all the modified copolyimides had showed higher glass transition temperature (T_g) than unmodified polyimides. The separation properties of the prepared polyimide membranes were also characterized by permeability for O₂ and N₂ gases and ideal selectivity values were calculated. Copyright © 2009 John Wiley & Sons, Ltd.