Relationships between chemical structures and solubility,diffusivity, and permselectivity of 1,3-butadiene and n-butane in 6FDA-based polyimides

The solubility, diffusivity, and permselectivity of 1,3-butadiene and n-butane in seven different polyimides synthesized from 2,2-bis (3,4-carboxyphenyl) hexafluoropropane dianhydride (6FDA) were determined at 298 K. The influence of chemical structures on physical and gas permeation properties of 6FDA-based polyimides was studied. Solubility of 1,3-butadiene in 6FDA-based polyimides can be described by a dual-mode sorption model. 1,3-Butadiene-induced plasticization is considered to be associated with the increasing permeabilities of 1,3-butadiene and n-butane and the decreasing permselectivity of 1,3-butadiene vs. n-butane in the mixed gas system containing a high concentration of 1,3-butadiene. It was found that controlling the solubility of 1,3-butadiene in an unrelaxed volume in 6FDA-based polyimides is very important to maintain the high permselectivity of 1,3-butadiene vs. n-butane in the mixed gas system. Changing the  C(CF₃)₂ linkage to a  CH₂ ,  O linkage, removing methyl substituents at the ortho position of the imide linkage, and changing the p-phenylene linkage to an m-phenylene linkage in the main chains in some 6FDA-based polyimides are effective to decrease fractional free volume and restrict the solubility of 1,3-butadiene in the unrelaxed volume of a polymer matrix. The 6FDA-based polyimides restricting the solubility of 1,3-butadiene in an unrelaxed volume exhibit high separation performance in the 1,3-butadiene/n-butane mixed gas system compared with conventional glassy polymers and, therefore, are potentially useful membrane materials for the separation of 1,3-butadiene and n-butane in the petrochemical industry. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2941–2949, 1999     

Gas transport properties of soluble poly(phenylene sulfone imide)s

Gas transport of helium, hydrogen, carbon dioxide, oxygen, argon, nitrogen, and methane in three soluble poly(phenylene sulfone imide)s based on 2,2-bis(3,4-decarboxyphenyl) hexafluoropropane dianhydride (6FDA) has been investigated. The effects of increasing length of well-defined oligo(phenylene sulfone) units on the gas permeabilities and diffusivities were determined and correlated with chain packing of the polymers. Activation energies of diffusion and permeation were calculated from temperature-dependent time-lag measurements. The influences of the central group in the diamine moiety of 6FDA-based polyimides on physical and gas transport properties are discussed. The incorporation of a long oligo(phenylene sulfone) segment in the polymer backbone decreases gas permeability and permselectivity simultaneously. The decreases in permeability coefficients can be mainly related to decreases in diffusion coefficients. Changing the central group of diamine moiety from  S to  SO₂ leads to a 45–50% decrease in CO₂ and O₂ permeabilities without appreciable increase in the selectivities. This is considered to be due to the formation of charge transfer complexes. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1855–1868, 1997     

Olefin/paraffin gas separations with 6FDA-based polyimide membranes

Pure gas permeation and sorption experiments were carried out for the gases ethylene, ethane, propylene and propane using polyimides based on 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA). Composite membranes and free films were used. Experiments were performed at 308 K and feed pressures up to 17 atm for ethylene and ethane and 9 atm for propylene and propane. Mixed gas permeation experiments were carried out with 50 : 50 olefin/paraffin feed mixtures. For all investigated polyimides, the ideal ethylene/ethane separation factor ranged between 3.3 and 4.4 and the ideal propylene/propane separation factor ranged between 10 and 16 at a feed pressure of 3.8 atm and 308 K. In mixed gas permeation experiments, up to 20% lower selectivity was found for the ethylene/ethane separation and up to 50% reduced selectivity for the propylene/propane separation compared to the ideal selectivity. The influence of feed temperature on separation and permeation properties will be discussed based on pure gas permeability data at 298 and 308 K.     

Permeability,permselectivity, and penetrant‐induced plasticization in fluorinated polyimides studied by positron lifetime measurements

The ortho‐positronium (o‐Ps) lifetime τ₃ and its intensity I₃ in various fluorinated polyimides were determined by the positron annihilation technique and were studied with the spin–lattice relaxation time T₁ and the propylene permeability, solubility, diffusivity, and permselectivity for propylene/propane in them. τ₃, I₃, and the distribution of τ₃ changed when the bulky moieties in the polyimides were changed. The polyimides, having both large τ₃ and I₃ values, exhibited a short T₁ and a high permeability with a low permselectivity. The propylene permeability and diffusivity were exponentially correlated with the product of I₃ and the average free‐volume hole size estimated from τ₃. In highly plasticized states induced by the sorption of propylene, the permeability increased with the propylene pressure in excellent agreement with the change in the free‐volume hole properties probed by o‐Ps. The large and broad distribution of the free‐volume holes and increased local chain mobility for the 2,2‐bis(3,4‐decarboxyphenyl) hexafluoropropane dianhydride‐based polyimides are thought to be important physical properties for promoting penetrant‐induced plasticization. These results suggest that o‐Ps is a powerful probe of not only the free‐volume holes but also the corresponding permeation mechanism and penetrant‐induced plasticization phenomenon. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 308–318, 2003     

Gas‐transport properties of indan‐containing polyimides

A series of indan‐containing polyimides were synthesized, and their gas‐permeation behavior was characterized. The four polyimides used in this study were synthesized from an indan‐containing diamine [5,7‐diamino‐1,1,4,6‐tetramethylindan (DAI)] with four dianhydrides [3,3′4,4′‐benzophenone tetracarboxylic dianhydride (BTDA), 3,3′4,4′‐oxydiphthalic dianhydride (ODPA), (3,3′4,4′‐biphenyl tetracarboxylic dianhydride (BPDA), and 2,2′‐bis(3,4′‐dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)]. The gas‐permeability coefficients of these four polyimides changed in the following order: DAI–BTDA < DAI–ODPA < DAI–BPDA < DAI–6FDA. This was consistent with the increasing order of the fraction of free volume (FFV). Moreover, the gas‐permeability coefficients were almost doubled from DAI–ODPA to DAI–BPDA and from DAI–BPDA to DAI–6FDA, although the FFV differences between the two polyimides were very small. The gas permeability and diffusivity of these indan‐containing polyimides increased with temperature, whereas the permselectivity and diffusion selectivity decreased. The activation energies for the permeation and diffusion of O₂, N₂, CH₄, and CO₂ were estimated. In comparison with the gas‐permeation behavior of other indan‐containing polymers, for these polyimides, very good gas‐permeation performance was found, that is, high gas‐permeability coefficients and reasonably high permselectivity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2769–2779, 2004     

Polyimides from isomeric diphenylthioether dianhydrides

3,3′,4,4′‐Diphenylthioether dianhydride (4,4′‐TDPA), 2,3,3′,4′‐diphenylthioether dianhydride (3,4′‐TDPA), and 2,2′,3,3′‐diphenylthioether dianhydride (3,3′‐TDPA) were synthesized from 3‐chlorophthalic anhydride and 4‐chlorophthalic anhydride. A series of polyimides derived from the isomeric diphenylthioether dianhydrides with several diamines were prepared. The properties, such as the solubility, thermal and mechanical behavior, dynamic mechanical behavior, wide‐angle X‐ray diffraction, and permeability to some gases, were compared among the isomeric polyimides. Both 3,3′‐TDPA‐ and 3,4′‐TDPA‐based polyimides had good solubility in polar aprotic solvents and phenols. The 5% weight loss temperatures of all the obtained polyimides was near 500 °C in nitrogen. The glass‐transition temperatures decreased according to the order of the polyimides based on 3,3′‐TDPA, 3,4′‐TDPA, and 4,4′‐TDPA. The 3,4′‐TDPA‐based polyimides had the best permeability and lowest permselectivity, whereas the 4,4′‐TDPA‐based polyimides had the highest permselectivity and the lowest permeability of the three isomers. Furthermore, the rheological properties of thermoplastic polyimide resins based on the isomeric diphenylthioether dianhydrides were investigated, and they showed that polyimide 3,4′‐TDPA/4,4‐oxydianiline had the lowest melt viscosity among the isomers; this indicated that the melt processibility had been greatly improved. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 959–967, 2006     

Atomistic models of three fluorinated polyimides in the amorphous state

Molecular models of three fluorinated polyimides based on the 4,4′‐(hexafluoroisopropylidene)diphthalic dianhydride (6FDA) have been studied using molecular dynamics (MD) simulations. The respective diamines were 4,4′‐hexafluoroisopropylidene dianiline (6FpDA), 3,3′‐hexafluoroisopropylidene dianiline (6FmDA), and 2,4,6‐trimethyl‐1,3phenylenediamine (DAM). Thirty independent samples were prepared using a hybrid pivot Monte Carlo‐MD generation technique and average densities were found to be in very good agreement with experiment. Model structures also agreed with available wide‐angle X‐ray scattering data. Cohesive energies, Hildebrand solubility parameters, fractional free volumes (FFV), void space distributions and intermolecular as well as intramolecular interactions were analyzed. The differences in bulk properties between both 6FDA‐6FpDA and 6FDA‐6FmDA isomers remain fairly small, although the configurations of the former are more extended. 6FDA‐DAM has a lower density, larger intermolecular distances, and higher free volume than the other two polyimides. Results are discussed with respect to their use as matrices for gas separation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1166–1180, 2009     

Effect of methyl substituents on permeability and permselectivity of gases in polyimides prepared from methyl-substituted phenylenediamines

Permeability and solubility coefficients for H₂, CO₂, O₂, CO, N₂, and CH₄ in polyimides prepared from 6FDA and methyl-substituted phenylenediamines were measured to investigate effects of the substituents on gas permeability and permselectivity. The methyl substituents restrict internal rotation around the bonds between the phenyl rings and the imide rings. The rigidity and nonplanar structure of the polymer chain, and the bulkiness of methyl groups make chain packing inefficient, resulting in increases in both diffusion and solubility coefficients of the gases. Polyimides from tetramethyl-p-phenylenediamine and trimethyl-m-phenylenediamine display very high permeability coefficients and very low permselectivity due to very high diffusion coefficients and very low diffusivity selectivity, as compared with the other polyimides having a similar fraction of free space. This suggests that these polyimides have high fractions of large-size free spaces.     

含叔丁基聚酰亚胺均质膜的气体分离性能

采用高温“一步法”缩聚合成了一系列含叔丁基的可溶性芳香聚酰亚胺树脂, 然后通过溶液浇注法制得相应均质薄膜, 并对其气体分离性能进行了测试, 同时研究了二酐结构和温度对聚酰亚胺均质膜气体分离性能的影响. 结果表明, 对于H₂, N₂, O₂, CO₂和CH₄ 等5种气体, 含叔丁基聚酰亚胺均质膜不仅表现出良好的透气性, 而且具有较高的气体透过选择性, 4,4'-(六氟异丙烯)二酞酸酐(6FDA)和均苯四甲酸二酐(PMDA)两类聚酰亚胺均质膜的气体分离性能最佳. 除CO₂外, 这两类聚酰亚胺均质膜的气体渗透系数随温度升高而升高, 而所有测试气体在这两种均质膜中的扩散系数和溶解度系数均随温度升高而增大.     

Gas transport properties of 6FDA‐durene/1,4‐phenylenediamine (pPDA) copolyimides

We have determined the gas transport properties of He, H₂, O₂, N₂, and CO₂ for 6FDA‐durene homopolymer and 6FDA‐durene/pPDA copolyimides. The 6FDA‐durene exhibits the highest permeability with the lowest selectivity. Permeability of copolymers decreases with increasing 6FDA–pPDA content, while permselectivity increases with an increase in 6FDA–pPDA content. 6FDA‐durene/pPDA (50/50) and 6FDA‐durene/pPDA (20/80) materials have O₂ and CO₂ permeabilities greater than those calculated from the addition rule of the semilogarithmic equation. These higher deviations from the additional rule of the semilogarithmic equation are mainly attributed to the fact that these copolyimides have higher solubility coefficients than those calculated from the additive rule. The T_g s of 6FDA‐durene/pPDA copolyimides decrease with an increase in 6FDA–pPDA content. T_g s predicted from the Fox equation are lower than the experimental data, and the their difference increases with an increase in pPDA content, implying the copolyimides of 6FDA‐durene/pPDA may have greater interstitial space among chains because of the conformation difference, and thus create more fraction free volume compared with the ideal case of simple volume addition. Density measurements also suggest these two copolymers have greater free volumes and the fractions of free volume, which supporting the gas transport results. The thermal stability and β‐relaxation temperature have also been studied for these copolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2703–2713, 2000     

Synthesis of Polyimides Containing Fluorine and Their Pervaporation Performances to Aromatic/Aliphatic Hydrocarbon Mixtures

Two kinds of polyimides containing fluorine were synthesized based on dianhydride of 2,2‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and diamines including 2,2‐bis[4‐(4‐aminophenoxy)phenyl] hexafluoropropane (BDAF) and 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane (BAPP) using solution condensation and following chemical imidization. The structures of 6FDA‐BDAF and 6FDA‐BAPP were characterized by FT‐IR, NMR, and XRD. Their glass transition temperatures characterized by DSC were in the range of 235–251°C, and the initial decomposition temperatures determined by TGA were over 540°C. The membranes of polyimide thus obtained were employed in pervaporation separation of aromatic/aliphatic mixtures. 6FDA‐BDAF membranes obtained better separation performances than 6FDA‐BAPP and had a flux of 0.66 kg · µm/m² · h and separation factor of 6.49 for toluene/n‐heptane (20/80 wt.%) at 80°C. The effects of the fluorine group on polyimides properties and separation performances were investigated.     

Design,synthesis, and gas permeation properties of polyimides containing pendent imidazolium groups

Film‐forming polymers containing ionic groups have attracted considerable attention as emerging materials for gas separation applications. The aim of this article was to synthesize new film‐forming polyimides containing imidazolium groups (PI‐IMs) and establish their structure–performance relationship. In this context, a new aromatic diamine, namely, N¹‐(4‐aminophenyl)‐N¹‐(4‐(2‐phenyl‐1H‐imidazol‐1‐yl)phenyl)benzene‐1,4‐diamine (ImTPADA), was synthesized and polycondensed with three aromatic dianhydrides, namely, 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride, 4,4‐(4,4‐isopropylidenediphenoxy) bis(phthalic anhydride), and 4,4′‐oxydiphthalic anhydride to form the corresponding polyimides containing pendent 2‐phenylimidazole groups (PI‐IEs). Next, PI‐IMs were prepared by N‐quaternization of pendent 2‐phenylimidazole groups present in PI‐6FDA using methyl iodide followed by anion exchange with bis(trifluoromethane)sulfonimide lithium salt (LiTf₂N). PI‐IEs and PI‐IMs exhibited reasonably high molecular weights, amorphous nature, good solubility, and could be cast into self‐standing films from their DMAc solutions. Thermogravimetric analysis showed that 10% weight loss temperature of PI‐IEs and PI‐IMs were in the range 545–475 °C and 303–306 °C, respectively. Gas permeability analysis of films of PI‐IEs and PI‐IMs was investigated by variable‐volume method and it was observed that incorporation of ionic groups into PI‐6FDA resulted in increased permeability while maintaining selectivity. In particular, polymer bearing Tf₂N⁻ anion exhibited high CO₂ permeability (33.3 Barr) and high selectivity for CO₂/CH₄ (41.1) and CO₂/N₂ (35.4). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1721–1729     

Preparation and properties of novel polyimides derived from 4‐aryl‐2,6 bis(4‐amino phenyl)pyridine

To prepare novel polyimides with enhanced thermal stability and high solubility in common organic solvents, diamine monomers, 4‐aryl‐2,6 bis‐(4‐amino phenyl)pyridine, were introduced. The diamines were reacted with three different conventional aromatic dianhydrides including pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, and hexafluoroisopropylidene‐2,2‐bis(phthalic‐dianhydride) (6FDA) in dimethylacetamide solvent to obtain the corresponding polyimides via the polyamic acid precursors and chemical imidization. The monomers and polymers were characterized by Fourier transform infrared spectroscopy, ¹H NMR, mass spectroscopy, and elemental analysis; and the best condition of polymerization and imidization were obtained via the study of model compound. The polyimides showed little or no weight loss by thermogravimetric analysis up to 500 °C, and those derived from 6FDA exhibited good solubility in various polar solvents. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3826–3831, 2001     

Isomeric polyimides based on fluorinated dianhydrides and diamines for gas separation applications

The gas sorption and transport properties of two isomeric polyimides with hexafluoroisopropylidene moieties in the diamine and dianhydride monomers were characterized for a variety of gases at 35°C at pressures up to 60 atm. These materials have structural properties which inhibit intrasegmental rotational mobility and intersegmental chain packing. The effect of isomerism on the physical and gas separation properties of these rigid materials was investigated. The effect of isomerism on the hindrance to packing is reflected in the wide angle X-ray diffraction (WAXD) measurements of the average spacing between adjacent polymer chains. The para connected polyimide showed significant increases in permeability relative to a series of polyimides studied earlier with less packing-disruptive substituents on the polymer backbone. The permeability of the higher flux material was 64 barrers for CO₂ and 16 barters for O₂. The meta connected polyimide showed large decreases in permeability with corresponding increases in permselectivity when compared to its para counterpart. For example, the permselectivity of the meta material for O₂ relative to N₂ is 6.9 which is 50% greater than that of the para connected material. The differences in permeability and permselectivity are due to both penetrant solubility and diffusivity effects.     

Structure/permeability relationships of polyimides with branched or extended diamine moieties

Mean permeability coefficients for CO₂, O₂, N₂, and CH₄ in seven types of 6FDA polyimides with branched or extended diamine moieties were determined at 35.0°C (95.0°F) and at pressures up to 10.5 atm (155 psia). In addition, solubility coefficients for CO₂, O₂, N₂, and CH₄ in six of these polyimides were determined at 35.0°C and at 6.8 atm (100 psia). Mean diffusion coefficients for the six gas/polyimide systems were calculated from the permeability and solubility data. The relationships between the chemical structure of the polyimides, some of their physical properties (glass transition temperature, mean interchain spacing, specific free volume), and their gas permeability, diffusivity, and solubility behavior are discussed. The 6FDA polyimides studied here exhibit a considerably lower selectivity for the CO₂/CH₄ and O₂/N₂ gas pairs than 6FDA polyimides with short and stiff aromatic diamines with comparable CO₂ and O₂ permeabilities. © 1993 John Wiley & Sons, Inc.     

Propylene sorption and coordinative interactions for poly(N‐vinyl pyrrolidone‐co‐vinyl acetate)/silver salt complex membranes

When poly(N‐vinyl pyrrolidone‐co‐vinyl acetate) (PVP‐co‐PVAc) containing amide and ester groups were complexed with silver salts to form silver polymer electrolyte membranes, their separation performance of propylene/propane mixtures showed the high selectivity of propylene over propane of 55 and the high mixed gas permeance of 12 GPU (1 GPU = 1.0 × 10^?6 cm³(STP) cm^?2 s^?1 cmHg^?1). The separation performance strongly depends on the composition of the copolymer: the higher concentration of PVP in the copolymer, the better separation performance was achieved. These results suggest that the amide group is more effective in facilitated propylene transport than the ester group, primarily due to the stronger interaction of the silver ions with the amide than the ester oxygens, as demonstrated by FT‐IR and FT‐Raman spectroscopies. In‐situ FT‐IR spectra upon propylene sorption also demonstrate that the interaction strength of the silver ions with the ligands is arranged: amide > C?C > ester. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2263–2269, 2007     

Cross‐linked Copolyimide Membranes for the Separation of Gaseous and Liquid Mixtures

Cross‐linked polymer structures gain increasing attention as membrane materials because they can fullfill the demands for industrial applications. Thereby, not only good separation characteristics but also high temperature stability and chemical resistancy are required. Furthermore, it is important that the membrane materials be plasticization resistant, because it is found that this causes strong increasing permeability with a drastic loss in selectivity. Plasticization effects occur with polyimide membranes in the presence of high CO₂concentrations, hydrocarbons as propylene, propane, or aromatics. Unfortunately, these components are present in mixtures with high relevance being separated economically by membrane units or hybrid processes. In this article, the advantages of cross‐linked 6FDA (4,4′hexafluoro isopropylidene diphthalic acid anhydride)‐copolyimides are discussed based on experimental results for the separation of propylene/propane, benzene/cyclohexane, and high‐pressure CO₂/CH₄mixtures. Additionally, opportunities for implementing the membrane units in conventional separation processes are discussed.     

Synthesis and properties of ortho‐linked aromatic polyimides based on 1,2‐bis(4‐aminophenoxy)‐4‐tert‐butylbenzene

A bis(ether amine) containing the ortho‐substituted phenylene unit and pendant tert‐butyl group, 1,2‐bis(4‐aminophenoxy)‐4‐tert‐butylbenzene, was synthesized and used as a monomer to prepare polyimides with six commercial dianhydrides via a conventional two‐stage procedure. The intermediate poly(amic acid)s had inherent viscosities of 0.78–1.44 dL/g, and most of them could be thermally converted into transparent, flexible, and tough polyimide films. The inherent viscosities of the resulting polyimides were in the range of 0.46–0.87 dL/g. All polyimides were noncrystalline, and most of them showed excellent solubility in polar organic solvents. The glass‐transition temperatures of these polyimides were in the range of 222–259 °C in differential scanning calorimetry and 212–282 °C in thermomechanicl analysis. These polyimides showed no appreciable decomposition up to 500 °C in thermogravimetric analysis in air or nitrogen. A comparative study of the properties with the corresponding polyimides without pendant tert‐butyl groups derived from 1,2‐bis(4‐aminophenoxy)benzene is also presented. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1551–1559, 2000     

四羧酸环戊烷型聚酰亚胺膜对CO_2和CH_4的透过性

四羧酸环戊烷型聚酰亚胺膜对ＣＯ２和ＣＨ４的透过性张俊彦潘光明（中国科学院兰州化学物理研究所兰州７３００００）关键词环戊烷四羧酸，聚酰亚胺，气体分离，膜理想的气体分离膜材料应具有高的透气性和良好的透气选择性，耐高低温，耐化学介质和良好的机械强度及膜加...     

Copolyimides containing alicyclic and fluorinated groups: Solubility and gas separation properties

A series of polyimides with alicyclic and fluorinated moieties previously synthesized were studied for gas separation applications. The solubility behavior of polyimides in various solvents was analyzed through the solubility parameter approach. Permeability coefficients and ideal selectivities were determined for common gases, that is, He, H₂, O₂, and N₂. Polyimide permeabilities were correlated to an improvement of the soluble character and were increased by the introduction of both alicyclic and fluorinated structures. The effect of the casting solvent on gas separation properties was also pointed out. It was found that it is enhanced with increasing diameters for the gas molecules. Finally, some correlations between permeability coefficients and microstructural parameters were discussed. The probability of correlation appears to be also dependent on the diameter and on the polarizability of the gas molecule. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2413–2426, 2005.