Gas transport properties of polyarylates part I: Connector and pendant group effects

Gas transport of helium, hydrogen, oxygen, nitrogen, methane, and carbon dioxide gases in a series of polyarylates based on isophthalic acid has been examined. These polyarylates were prepared from bisphenol A, hexafluorobisphenol A, phenolphthalein, and fluorene bisphenol monomers to study the effects of varying the bisphenol connector group size and shape. Substitution of a tertiary butyl group at position five on the isophthalate ring increases polymer permeability. The incorporation of a large, bulky connector group increases gas permeability and maintains permselectivity while the substitution of t-butyl groups increases gas permeability by two- to fourfold but lowers permselectivity. Most of the increases in permeability can be related to increases in the diffusion coefficients of all the gases. All the polyarylates have high glass transition temperatures and may be suitable for high temperature gas separation applications. ©1995 John Wiley & Sons, Inc.     

Effect of isopropylidene replacement on gas transport properties of polycarbonates

The gas sorption and transport properties of a series of polycarbonates in which the isopropylidene unit of bisphenol A polycarbonate has been replaced with another molecular group are presented. Two new materials, bisphenol of norbornane polycarbonate (NBPC) and bisphenol Z polycarbonate (PCZ), are compared with several polymers which have been studied previously in this laboratory, including bisphenol A polycarbonate (PC), hexafluorobisphenol A polycarbonate (HFPC), and bisphenol of chloral polycarbonate (BCPC). The effect of molecular structure on chain mobility and chain packing is related to the gas transport properties. Dynamic mechanical thermal analysis and differential scanning calorimetry are used to judge chain mobility, while x-ray diffraction and free volume calculations give information about chain packing. Permeability measurements were made for He, H₂, O₂, N₂, CH₄, and CO₂ at 35°C over a range of pressures up to 20 atm. Sorption experiments were also done for N₂, CH₄, and CO₂ under the same conditions. The permeability coefficients of these polymers rank in the order HFPC ? NBPC>PC>BCPC ? PCZ for all of the gases. With the exception of BCPC, this order correlates well with fractional free volume. The low gas permeability of BCPC is attributed to a polarity effect. In general, bulky and relatively immobile substituents, as in HFPC and NBPC, can yield improved separation characteristics. The polar group of BCPC and the flexible cyclohexyl substituent of PCZ result in relatively low gas permeability.     

Effect of Molecular Structure on the GasPermeability of Cellulose Aliphatate Esters简

In this work, four kinds of cellulose aliphatate esters, cellulose acetate （CA）, cellulose propionate （CP）, cellulose butyrate （CB） and cellulose acetate butyrate （CAB） are synthesized by the homogeneous acylation reactions in cellulose/AmimC1 solutions. These cellulose aliphatate esters are used to prepare gas separation membranes and the effects of molecular structure, such as substituent type, degree of substitution （DS） and distribution of substituents, on the gas permeability are studied. For CAs, as the DS increases, their gas permeabilities for all five gases （02, N2, CH4, CO and CO2） increase, and the ideal permselectivity significantly increases first and then slightly decreases. At similar DS value, the homogenously synthesized CA （distribution order of acetate substituent： C6 〉 C3 〉 C2） is superior to the heterogeneously synthesized CA （distribution order of acetate substituent： C3 〉 C2 〉 C6） in gas separation. With the increase of chain length of aliphatate substituents from acetate to propionate, and to butyrate, the gas permeability of cellulose aliphatate esters gradually increases. The cellulose mixed ester CAB with short acetate groups and relatively long butyrate groups exhibits higher gas permeability or better permselectivity than individual CA or CB via the alteration of the DS of two substituents.     

Polypyrrolones for membrane gas separations. I. Structural comparison of gas transport and sorption properties

Despite efforts by the membrane community to develop polymeric materials with improved O₂/N₂ separation performance, limited progress has occurred for almost a decade. Molecular sieving media, which can exhibit gas separation properties superior to polymers, tend to be brittle and uneconomical to produce for large‐scale membrane separation processes. Considering this, the polymer structures investigated in this work were designed to mimic aspects of the structure of molecular sieving media such as zeolites and carbon molecular sieves while maintaining the processability associated with polymers. Significantly attractive gas separation material properties were obtained using hyper rigid polypyrrolone copolymers with controlled packing disruptions between flat, packable segments. The gas transport properties in the materials changed dramatically as a result of different average interchain spacing. Moreover, all of the polypyrrolones studied in this work exhibited performance lying on or above the existing O₂/N₂ upper bound trade‐off line between permselectivity and permeability. These results, therefore, may point the way to a new cycle of membrane materials improvements for gas separations. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1235–1249, 1999     

The effect of aryl nitration on gas sorption and permeation in polysulfone

CO_2, CH_4, O_2, and N₂ permeability and solubility of unmodified and aryl-nitrated polysulfone were determined at 35°C and pressures up to 20 atm. The degree of nitration was varied from 0 to 2 nitro groups per repeat unit. The permeability and diffusion coefficients for all gases decreased with increasing degree of nitro substitution. The decrease in gas diffusivity is attributed to a combination of decreased fractional free volume and decreased torsional mobility with increasing degree of substitution. The solubilities of N_2, O_2, and CH₄ do not show a systematic dependence on degree of substitution. However, CO₂ solubility apparently goes through a minimum as the degree of substitution is increased. CO₂ solubility may be influenced by a competition between increases in polymer polarity (favoring higher solubility) and lower free volume (favoring lower solubility) that accompanies increases in the polar nitro substituent concentration. CO₂/CH₄ solubility selectivity increases monotonically as the degree of substitution increases. CO₂/CH₄ permselectivity and diffusivity selectivity increased with increasing degree of substitution. © 1995 John Wiley & Sons, Inc.     

Gas permeability and selectivity of hexafluoroisopropylidene aromatic isophthalic copolyamides

The synthesis, thermal, and gas transport properties of poly(hexafluoroisopropylidene isophthalamide), HFA/ISO homopolymer, and HFA/TERT‐co‐HFA/ISO copolyamides with different poly(hexafluoroisopropilydene‐5‐t‐butylisophthalamide), HFA/TERT, ratios are reported. The results indicate that the glass transition temperatures of the copolyamides increase as the concentration of HFA/TERT in the polyamide increases. The gas permeability coefficients in the polyamides and copolyamides are independent of pressure or decrease slightly particularly with CO₂, N₂, and CH₄. It was seen that HFA/TERT is 2–6 times more permeable than HFA/ISO, depending on the gas being considered. This was assigned to the presence of the bulky lateral substituent, t‐butyl group in HFA/TERT and HFA/TERT‐co‐HFA/ISO copolyamides. This substituent increases fractional free‐volume, as expected. Therefore, the gas permeability and diffusion coefficients generally increase with increasing fractional free‐volume. The experimental results for the gas permeability and permselectivity for the copolyamides was well represented by a logarithmic mixing rule of the homopolyamides permeability coefficients and their volume fraction. The selectivity of gas pairs, such as O₂/N₂, CO₂/CH₄, and N₂/CH₄ decreased slightly with the addition of HFA/TERT. The temperature dependence of permeability for homopolyamides and copolyamides can be described by an Arrhenius type equation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2625–2638, 2005     

Gas permeability and selectivity of benzophenone aromatic isophthalic copolyamides

The synthesis, thermal, and gas transport properties of poly(benzophenone isophthalamide), DBF/ISO, poly(benzophenone‐5‐tert‐butylisophthalamide), DBF/TERT, homopolymers, and their copolyamides with different DBF/TERT ratios are reported. The results indicate that the glass transition temperatures of the copolyamides increase as the concentration of DBF/TERT in the polyamide increases. The gas permeability coefficients for DBF/ISO are around 10^?2 Barrers for O₂ which situates this polymer as a barrier polymer. It was also found that permeability coefficients in all polyamides and copolyamides are independent of pressure for He or decrease slightly particularly with O₂, CO₂, and N₂. It was seen that DBF/TERT is up to 15 times more permeable than DBF/ISO, depending on the gas being considered. This behavior was assigned to the presence of the bulky lateral substituent, the tert‐butyl group, in DBF/TERT and DBF/TERT‐co‐DBF/ISO copolyamides. This bulky substituent increases fractional free volume and interchain spacing; as a consequence, the gas permeability and diffusion coefficients generally increase. The experimental results for the gas permeability coefficients and permselectivity for the copolyamides was well represented by a semilogarithmic mixing rule of the homopolyamides permeability coefficients as a function of their volume fraction. The selectivity of gas pairs, such as He/O₂ and He/CO₂, decreased slightly with the addition of DBF/TERT. The temperature dependence of permeability for homopolyamides and copolyamides can be described by an Arrhenius type equation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2083–2096, 2007     

Investigation of gas transport and other physical properties in relation to the bromination degree of polymers of intrinsic microporosity

In this work, the synthesis of novel polymers of intrinsic microporosity (PIMs) with different degrees of bromine substitution by a free-radical substitution reaction was performed. The synthesized polymers were thoroughly characterized and their bromination degree was verified via nuclear magnetic resonance. The brominated PIMs were investigated by infrared spectroscopy, X-ray diffraction, and density measurements and correlated with their gas transport properties. It was found that with an increase in the bromination degree, the synthesized PIMs exhibited a significant increase in polymer chain packing density which led to reduced fractional free volume and consequent decrease in gas diffusion and permeability coefficients. The change in permeability coefficients caused an improvement in the CO₂/N₂, CO₂/CH₄, and O₂/N₂ ideal permeability selectivities. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2752–2761     

Gas‐transport properties in crosslinked polymers. I. Aliphatic polyurethane–acrylate‐based adhesives

The gas‐transport properties of one of a family of well‐known adhesives, Loctite 350^®, were studied. Permeability, solubility, and diffusivity coefficients, together with the activation energies of diffusion and permeation and the solution enthalpy, were determined from 20 to 40 °C for oxygen, nitrogen, carbon dioxide, and methane. Loctite 350^® showed relatively high permselectivity and permeability for the gas pairs O₂/N₂ and CO₂/CH₄, especially for the former. The possibility of preparing very thin layers on various kinds of supports from these photocurable polymers makes them promising materials for gas‐separation devices. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 786–795, 2001     

Synthesis, characterization, and gas permeation properties of 6FDA-2,6-DAT/mPDA copolyimides

The goal of this work is to explore new polyimide materials that exhibit both high permeability and high selectivity for specific gases. Copolyimides offer the possibility of preparing membranes with gas permeabilities and selectivities not obtainable with homopolyimides. A series of novel fluorinated copolyimides were synthesized with various diamine compositions by chemical imidization in a two-pot procedure. Polyamic acids were prepared by stoichiometric addition of solid dianhydride in portions to the diamine(s). The gas permeation behavior of 2,2′-bis(3,4′-dicarboxyphenyl) hexafluoropropane dianhydride(6FDA)-2,6-diamine toluene (2,6-DAT)/1,3-phenylenediamine (mPDA) polyimides was investigated. The physical properties of the copolyimides were characterized by IR, DSC and TGA. The glass transition temperature increased with increase in 2,6-DAT content. All the copolyimides were soluble in most of the common solvents. The gas permeability coefficients decreased with increasing mPDA content. However, the permselectivity of gas pairs such as H₂/N₂, O₂/N₂, and CO₂/CH₄ was enhanced with the incorporation of mPDA moiety. The permeability coefficients of H₂, O₂, N₂, CO₂ and CH₄ were found to decrease with the increasing order of kinetic diameters of the penetrant gases. 6FDA-2,6-DAT/mPDA (3:1) copolyimide and 6FDA-2,6-DAT polyimide had high separation properties for H₂/N₂, O₂/N₂, CO₂/CH₄. Their H₂, O₂ and CO₂ permeability coefficients were 64.99 Barrer, 5.22 Barrer, 23.87 Barrer and 81.96 Barrer, 8.83 Barrer, 39.59 Barrer, respectively, at 35°C and 0.2 MPa (1 Barrer = 10⁻¹⁰ cm³ (STP)·cm·cm⁻²·s⁻¹·cmHg⁻¹) and their ideal permselectivities of H₂/N₂, O₂/N₂ and CO₂/CH₄ were 69.61, 6.09, 63.92 and 53.45, 5.76, 57.41, respectively. Moreover, all of the copolyimides studied in this work exhibited similar performance, lying on or above the existing upper bound trade-off lines between permselectivity and permeability. They may be utilized for commercial gas separation membrane materials. __________ Translated from Acta Polymerica Sinica, 2008, 8 (in Chinese)     

Transport properties of polyphenylquinoxalines

The correlation between chemical structure and gas transport properties is considered for a new class of membrane materials based on structurally similar polyphenylquinoxalines that are characterized by different numbers of flexible-O-ether bonds in the repeating unit and different chain rigidities. Permeability, diffusion, and solubility coefficients have been estimated for the gases H₂, He, O₂, N₂, CO, CO₂, and CH₄; separation factors for various gas pairs have been determined. For the materials with a similar level of cohesive energy density, which characterizes interchain interactions, permeability decreases with a decrease in chain rigidity, whereas selectivity of gas separation increases.     

Gas permeation properties of copolyetherimide based on 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride

A series of aromatic homo- and copolyetherimides was prepared from 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride with 2,4,6-trimethyl phenylenediamine, 3,3^′-dimethyl-4,4^′-methylene dianiline, and 3,5-diaminobenzoic acid. The gas permeability coefficients of the copolyetherimides to H₂, CO₂, O₂, N₂ and CH₄ were measured under 10 atm and at 30°C. A significant change in the permeability and permselectivity resulting from the systematic variation in chemical composition was found. The experimental values of the gas permeability coefficients and permselectivity coefficients of the copolyetherimides are in satisfactory agreement with the values estimated from the gas permeability coefficients of the constituent homopolyimides and their weight fractions.     

Isomer effects on transport properties of polyesters based on bisphenol-A

Pure gas sorption and transport properties of polyesters based on bisphenol-A and both pure isophthalic and pure terephthalic acid chloride were obtained for He, N₂, O₂, CH₄, and CO₂ at 35°C. The polymers were synthesized in our laboratory and amorphous films were prepared with a specialized solvent casting procedure. The polymer containing m-phenylene groups shows higher permselectivity for most of the gas pairs. The ideal selectivity of O₂/N₂ was increased by 33% when p-phenylene units were replaced by m-phenylene ones. On the other hand, the polyester containing only p-phenylene groups, shows higher permeability to all the gases studied. The polymer based on pure terephthalic acid chloride has a 75% higher oxygen permeability and a 1.1-fold higher carbon dioxide permeability than the isophthalic acid derivative. The polyester containing meta-phenylene units has lower T_g, higher permselectivity, lower permeability, lower fractional free volume (FFV), and lower d-spacing. The values of FFV, and lower d-spacing. The values of FFV and d-spacing were only slightly different between the two isomers. Moreover, for the sub-T_gγ transition the maximum in tan δ occured at essentially the same temperature (?55°C). The polymer with a higher concentration of p-phenylene units shows somewhat larger area under the γ-peak, indicating slightly more sub-T_g motion. The Distribution of FFV is considered to be the determining factor for the differences in transport properties observed. © 1993 John Wiley & Sons, Inc.     

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     

Gas sorption and transport in UV-irradiated polyarylate copolymers based on tetramethyl bisphenol-A and dihydroxybenzophenone

Gas sorption and transport properties at 35°C are reported for a series of ultraviolet irradiated polyarylates prepared from tetramethyl bisphenol-A (TMBPA), 4,4′-dihydroxybenzophenone (DHB), and 5-tertiary-butyl isophthalic acid dichloride (tBIA). UV irradiation induces crosslinking and photo-Fries rearrangements in these polymers. The gas permeability of the polyarylates decreases with UV irradiation due to reductions in the diffusion coefficient; however, the ideal selectivity for all gas pairs increases with UV irradiation. The effect of UV irradiation on the gas transport properties of the polyarylates is compared with that reported in the literature for similar polyimide materials. The polyimides show much greater improvement in selectivity than do the current polyarylate materials. The photo-Fries rearrangements limit the amount of crosslinking achievable in these polyarylate materials in spite of the fact that additional benzophenone units are formed.     

Effect of substituent polarity,bulk, and substitution site toward enhancing gas permeation in dibromohexafluorobisphenol‐a based polyarylates

The gas permeation properties of polyarylates were tuned by varying nature and site of substituents present on both of its monomers, viz., bisphenol and dicarboxylic acid. The phenyl rings of hexafluorobisphenol‐A were substituted in asymmetric manner by polar bromine to obtain dibromohexafluorobisphenol‐A. This bisphenol was polymerized with equimolar mixture of iso‐ and terephthalic acid (base case), bromo‐ and nitroterephthalic acid (polar group substituted acids), 4,4′‐hexafluoroisopropylidene bis(benzoic acid), and t‐butyl isophthalic acid (bulky group containing acids). Physical properties and gas permeation properties of these polyarylates were investigated to assess combined effects of asymmetric nature of bisphenol substitution, polar nature of substituent bromine, hexafluoroisopropylidene group present at the bridge position of bisphenol, and substituent present on the acid moiety. The combination of these substituent types led these polyarylates to lie near Robeson upper bound. The gas sorption analysis and estimation of diffusivity in these polyarylates shed a light on observed variations in gas permeation properties by attempted structural variations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3156–3168, 2007     

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.     

Development and characterization of homogeneous membranes de from high molecular weight sulfonated polyphenylene oxide

The high molecular weight polyphenylene oxide (PPO) was sulfonated to different ion exchange capacity (IEC) values using chlorosulfonic acid. The physico-chemical properties along with the gas transport properties of the membranes prepared from sulfonated PPO (SPPO) were evaluated. Sulfonation of PPO results in a linear increase of density with the IEC value while the average d-spacing in polymer remains constant. Sulfonic groups attached to the aromatic ring in the PPO backbone are not thermally stable. On the other hand, when tested with CO₂ at room temperature, the SPPO membranes maintained a constant permeability over the period of 60 days. An increase in IEC value of SPPO results in an increase in O₂/N₂ and CO₂/CH₄ ideal selectivities and a decrease in O₂ and CO₂ permeabilities. The combination of permeability and ideal selectivity for both gas pairs places the SPPO membranes below the respective upper-bound lines for polymeric membranes. However, an increase in the IEC value brings the permeability versus ideal selectivity relationship closer to the upper-bound line, especially for the O₂/N₂ gas pair.     

Gas transport properties of 6FDA-TMPDA/MOCA copolyimides

The gas permeation behavior of 2,2′-bis(3,4′dicarboxyphenyl) hexafluoropropane dianhydride(6FDA)-2,4,6-trimethyl-1,3-phenylenediamine (TMPDA)/4,4′-methylene bis(2-chloroaniline) (MOCA) copolyimides was investigated by systematically varying the diamine ratios. All the copolyimides were soluble in most of the common solvents. The gas permeabilities and diffusion coefficients decreased with increasing MOCA content; however, the permselectivity of gas pairs such as H₂/N₂, O₂/N₂, CO₂/CH₄ was enhanced with the incorporation of MOCA moiety. Moreover, all of the copolyimides studied in this work exhibited performance near, lying on or above the existing upper bound trade-off line between permselectivity and permeability.     

Gas transport properties of thin polymeric membranes in the presence of silicon dioxide particles

The fundamental gas transport properties of thin films of six high performance polymers were evaluated in the presence of silicon dioxide particles. The silica particles were brought in close contact with the polymer inside the 200 Å. (DIA) pores of Anopore™ aluminum oxide membranes. This unique environment allows intimate contact between the polymer and the silica particles. The presence of silica improves the gas separation properties of the permselective layer, particularly for oxygen and nitrogen. The increase in O₂/N₂ selectivity for some membranes is accompanied by an increase in oxygen permeability. The oxygen/nitrogen separation properties of the polymers in the presence of silica falls above the so-called “upper limit” of performance reported for polymeric materials. The observed significant increases in the glass transition temperature suggest restriction of chain segmental mobility possibly due to adsorption of polymer to silica surface. The increase in the activation energy of permeation points to increases in energetics of diffusion as the reason for the improved selective permeation. The observed behavior was not limited to oxygen and nitrogen as demonstrated by the results for other gas pairs tested.