Relationship between gas transport properties and fractional free volume determined from dielectric constant in polyimide films containing the hexafluoroisopropylidene group

The dielectric constant and gas transport properties (i.e., permeability, diffusivity, and solubility) in 2,2′‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride (6FDA)‐based polyimides were systematically investigated in terms of their polymer fractional free volumes (FFVs) at 30°C. The permeability and diffusion coefficients of the 6FDA‐based polyimide films to hydrogen, oxygen, nitrogen, methane, and carbon dioxide were correlated with their FFVs estimated using van Krevelen's group contribution method. There appeared, however, small linear correlation coefficients. Linear correlations were also observed between the gas transport properties and dielectric constant of these polyimides. This study described FFVas a function of the dielectric constant based on the Clausius‐Mossotti equation. It was found that the gas permeability and diffusion coefficients of these 6FDA‐based polyimide films increased as their dielectric constant‐based FFV increased. A better linear relationship was observed between the gas transport properties and the FFV determined from the polymer dielectric constant in comparison to that estimated using the group contribution method. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Low‐loss passive polymer waveguides by using chlorofluorinated polyimides

Chlorofluorinated polyimides were prepared from 2,2‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 2,2′‐bis(trifluoromethyl)‐4,4′‐diaminobiphenyl (PFMB), and 2,2′‐dichloro‐4,4′‐diaminobiphenyl (DCB) for optical waveguide applications. The resulting optical polymers exhibited good thermal stability, controllable refractive index, and low optical loss in the optical communication wavelengths of 1.3 and 1.55 µm. The control of refractive indices of the polymers was achieved by copolymerization of 6FDA/PFMB and 6FDA/DCB. As the amount of DCB was increased, the refractive indices of polymer were increased. The effect of addition of chlorine on optical properties of polymers such as absorption loss in the near‐IR region were also investigated. Rib‐type optical waveguides were fabricated using these chlorofluorinated polyimides. These waveguides exhibited low loss of less than 0.4 dB/cm for both TE and TM polarizations. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 107–112, 1999     

Membrane color and gas permeability of 6FDA‐TeMPD polyimide membranes prepared with various membrane preparation protocols

The relations among polyimide membrane colors, their gas transport and separation properties, and their fluorescence spectra were systematically investigated using fluorine‐containing aromatic polyimide, 6FDA‐TeMPD {[4,4‐(hexafluoroisopropylidene) diphthalic anhydride] [(6FDA)‐2,3,5,6‐tetramethyl‐1,4‐phenylene‐diamine (TeMPD)]}, which was used in electronic device and gas separation materials. Different molecular ordering structures of 6FDA‐TeMPD polyimides were prepared by controlling kinds of casting solvents and dry conditions. This difference was based on the effect of charge transfer (CT) interaction formed by π electrons of ring structures in polyimide. Membrane color measured using spectrophotometer determined colors as intrinsic parameters without sample collection. The permeability coefficients of oxygen and nitrogen of the 6FDA‐TeMPD polyimide membranes were correlated with membrane color index parameters such as L*, a*, b*, and ΔE*, and fluorescence properties such as maximum peak emission wavelength λ_max and intensity I_max, which reflect molecular ordering affected by CT interaction in polyimide membranes. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Gas transport and optical properties of ABA‐type triblock copolymers designed using fluorine‐containing polyimide macroinitiators with methyl methacrylate

4,4'‐(Hexafluoroisopropylidene) diphthalic anhydride 2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (6FDA‐TeMPD) polyimide macroinitiator was synthesized and reacted with poly(methyl methacrylate) (PMMA) to form an ABA‐type triblock copolymer by atom transfer radical polymerization. The effect of the ABA‐type triblock copolymer structure on solid, thermal, optical and gas transport properties was systematically investigated and compared with the physical blend polymer. The blend polymer was cloudy, whereas the triblock copolymer was colorless and transparent. The PMMA component decomposition temperature for the triblock copolymer slightly shifted to higher temperature, while its gas barrier property was higher than the blend polymer. The refractive index and the gas permeability decreased while maintaining the heat resistance by a high nanoscale distribution of both polymer components. The 6FDA‐TeMPD/PMMA ABA‐type triblock copolymer can be described as a polymer material with high heat resistance, high gas barrier property and low refractive index amongst existing polymers. © 2013 Society of Chemical Industry     

Effect of thermal hysteresis on the gas permeation properties of 6FDA‐based polyimides

The effect of thermal hysteresis on the polymer chain packing and permeation properties of two 6FDA‐based polyimide isomers was investigated. Thermal quenching resulted in a small increase in the fractional free volume of the polyimides with respect to the samples that had been annealed. Quenching from above the glass‐transition temperature also resulted in larger increases in the permeabilities for both 6FDA–6FmDA and 6FDA–6FpDA with respect to annealed samples. Meta‐connected 6FDA–6FmDA exhibited a larger increase in the permeability after quenching than the para‐connected isomer, 6FDA–6FpDA. This larger increase in the permeability for 6FDA–6FmDA may have been due to differences in the effects of the increases in the free volume on the intersegmental resistance to chain motions. Although physical aging over a 3‐month period resulted in a reduction in the permeability of quenched samples of 6FDA–6FpDA, the quenched samples maintained higher permeabilities than the annealed samples. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1174–1182, 2004     

Gas transport properties of 6FDA-TAPOB hyperbranched polyimide membrane

Physical and gas transport properties of the hyperbranched polyimide prepared from a triamine, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), and a dianhydride, 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), were investigated and compared with those of linear-type polyimides with similar chemical structures prepared from diamines, 1,4-bis(4-aminophenoxy)benzene (TPEQ) or 1,3-bis(4-aminophenoxy)benzene (TPER), and 6FDA. 6FDA-TAPOB hyperbranched polyimide exhibited a good thermal stability as well as linear-type analogues. Fractional free volume (FFV) value of 6FDA-TAPOB was higher than those of the linear-type analogues, indicating looser packing of molecular chains attributed to the characteristic hyperbranched structure. It was found that increased resistance to the segmental mobility decreases the gas diffusivity of 6FDA-TAPOB, in spite of the higher FFV value. However, 6FDA-TAPOB exhibited considerably high gas solubility, resulting in high gas permeability. It was suggested that low segmental mobility and unique size and distribution of free volume holes arising from the characteristic hyperbranched structure of 6FDA-TAPOB provide effective O₂/N₂ selectivity. It is concluded that the 6FDA-TAPOB hyperbranched polyimide has relatively high permeability and O₂/N₂ selectivity, and is expected to apply to a high-performance gas separation membrane.     

Incorporation effects of fluorinated side groups into polyimide membranes on their physical and gas permeation properties

The effects of incorporation of fluorinated alkyl side groups into polyimide membranes were investigated in terms of their physical and gas permeation properties. Four polyimides with fluorinated side groups and four polyimides without the side groups were prepared by polycondensation of 2‐(perfluorohexyl)ethyl‐3, 5‐diamino benzoate (PFDAB) and m‐PDA with four aromatic dianhydrides (6FDA, ODPA, BTDA, and PMDA), respectively. It was found that the incorporation of fluorinated side groups into the polyimide membranes decreased their surface free energies (T_gs), solubility parameters, and fractional free volume (FFV)s and therefore, enhanced the permeabilities for CO₂, O₂, N₂, and CH₄ gases but reduced the selectivities for CO₂/ CH₄, O₂ /N₂, CO₂/N₂ gas pairs depending upon the structure of dianhydride monomers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2756–2767, 2000     

Monomer atomic configuration as key feature in governing the gas transport behaviors of polyimide membrane

Although the molecular design of polyimide has been extensively investigated, the role of monomer's atomic configuration in controlling the structure of polyimide membrane hence its gas transport behaviors remains relatively uncertain. Therefore, a series of polyimides with different monomer combinations were synthesized to determine the crucial features of monomer that can impose great influence on membrane properties such as the fractional free volume (FFV). The results showed that the polyimide chain length (M_w) depended strongly on the monomer reactivity, which was primarily controlled by the steric hindrance of monomers' substituent instead of their electronic nature. In addition, the polarity and atomic configuration of monomer were found to be the two dominant factors in governing the membrane FFV. A polyimide model was also constructed and validated by molecular dynamics simulation to predict the gas transport behaviors (solubility and diffusivity) of copolyimide membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46073.     

New fluorene‐based thermally stable five‐ and six‐membered rings polyimides with enhanced solubility

A novel ester diamine, 9‐(3,5‐diaminobenzoyloxy) fluorene, as a new monomer for preparation of polyimides was synthesized via two successive reactions. In the first step, reaction of 3,5‐dinitrobenzoylchloride with 9‐hydroxy fluorene in the presence of sodium hydroxide led to preparation of 9‐(3,5‐dinitrobenzoyloxy) fluorene. Second reaction was reduction of the nitro groups by tin (II) chloride and fuming hydrochloric acid to produce 9‐(3,5‐diaminobenzoyloxy) fluorene. The new diamine containing bulky fluorene group was characterized and polycondensed with different dianhydrides via two methods to produce polyimides. The new five‐membered and six‐membered ring polyimides were characterized and their properties including solubility behavior, inherent viscosity, thermal behavior and stability, and crystallinity were studied. They exhibited favorable balance of physical and thermal properties and their solubility were improved without sacrificing their thermal stability. Six‐membered rings polyimides showed higher thermal stability and lower solubility in comparison to related five‐membered ring polyimides. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal analysis and its application in evaluation of fluorinated polyimide membranes for gas separation

Seven polyimides based on (4,4′-hexafluoroisopropylidene) diphthalic anhydride, 6FDA, with different chemical structures were synthesized in a single pot two-step procedure by first producing a high molecular weight polyamic acid (PAA), followed by reaction with acetic anhydride to produce polyimide (PI). The resulting polymers were characterized using thermal analysis techniques including TGA, derivative weight analysis, TGA–MS, and DSC. The decarboxylation-induced thermal cross-linking, ester cross-linking through a diol, and ion-exchange reactions of selected polyimide membranes were investigated. Cross-linking of polymer membranes was confirmed by solubility tests and CO₂ permeability measurements. The thermal analysis provides simple and timesaving opportunities to characterize the polymer properties, the ability to optimize polymer cross-linking conditions, and to monitor polymer functionalization to develop high performance polymeric membranes for gas separations.     

Influence of carbon black on decompression failure and hydrogen permeation properties of filled ethylene‐propylene–diene–methylene rubbers exposed to high‐pressure hydrogen gas

Eight carbon black (CB)‐filled ethylene–propylene–diene–methylene linkage (EPDM) rubbers were manufactured by varying the content and type of CB. Then, the relationship among crack damage caused by high‐pressure hydrogen decompression, the hydrogen permeation properties, and the mechanical properties of the rubbers was investigated. The hydrogen gas permeability of the rubbers decreased with an increase in the CB content and depended little on primary particle size. In contrast, the hydrogen gas diffusivity and solubility depended on both the CB content and primary particle size, that is, the hydrogen gas diffusivity decreased with an increase in the CB content and a decrease in the primary particle size, and the hydrogen gas solubility increased with an increase in the CB content and a decrease in the primary particle size. As for the mechanical properties, the CB‐filled rubbers were more strongly reinforced by an increase in the CB content and a decrease in the primary particle size. The crack damage by high‐pressure hydrogen decompression became larger as the ratio of the hydrogen gas solubility to estimated internal pressure at crack initiation relating to the mechanical properties became larger. As a smaller CB particle increases the hydrogen gas solubility of EPDM rubbers, while at the same time it reinforces the rubbers, the crack damage in the CB‐filled rubbers was not influenced by the primary particle size. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Microwave assisted polycondensation of polyimides by [4,4′‐(hexafluoroisopropylidene)diphthalic anhydride,pyromellitic dianhydride] and [2,4,6‐trimethyl‐m‐phenylenediamine]. Power,time, and solvent effect

The microwave assisted polycondensation of two polyimides were studied using pyromellitic dianhydride (PMDA), and 4,4′‐(hexafluoroisopropyliden)diphthalic anhydride (6FDA) as dianhydride monomers and 2,4,6‐trimethyl‐m‐phenylenediamine (TrmPD), as diamine monomer, under microwave irradiation in DMF and DMSO solvents. The structure and performance of polymers were characterized by Fourier Transform Infrared Spectroscopy (FTIR), viscosity, density, and Thermogravimetric Analysis (TGA). The results show that the polyimides can be obtained in a short reaction time with high intrinsic viscosity and high yield. The effect of the presence of a bridging group, ? C(CF₃)₂? , in the monomer structure is apparent in the permeability parameters of the macromolecules as polymer (6FDA‐TrmPD) always presents better results than polymer (PMDA‐TrmPD). Properties as density and T_g increases with the time exposition to the microwave irradiation. Polyimides obtained present good thermal properties because they began to lose weight in a range of 8–16% at high temperature as 450°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and properties of melt‐processable polyimides based on fluorinated aromatic diamines and aromatic dianhydrides

Two series of melt‐processable polyimides were prepared from 4,4′‐bis(3‐amino‐5‐trifluoromethylphenoxy)biphenyl (m‐6FBAB) and 4,4′‐bis(4‐amino‐5‐trifluoromethylphenoxy) biphenyl (p‐6FBAB) with various aromatic dianhydrides. The effects of the chemical structures of the polyimides on their properties, especially the melt processability and organic solubility, were investigated. The experimental results demonstrate that some of the fluorinated aromatic polyimides showed good melt processability at elevated temperatures (250–360°C) with relatively low melt viscosities and could be melt‐molded to produce strong and tough polyimide sheets. Meanwhile, the polyimides showed excellent organic solubility in both polar aprotic solvents and common solvents to give stable polyimide solutions with high polymer concentrations and relatively low viscosities. Thus, we prepared high‐quality polyimide films by casting the polyimide solutions on glass plates followed by baking at relatively low temperatures. The polyimides derived from m‐6FBAB showed better melt processability and solubility than the p‐6FBAB based polymers. The melt‐processable polyimides showed a good combination of thermal stability and mechanical properties, with decomposition temperatures of 547–597°C, glass‐transition temperatures in the range 205–264°C, tensile strengths of 81.3–104.9 MPa, and elongations at break as high as 19.6%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of fractional free volume and Tg on gas separation through membranes made with different glassy polymers

The aim of this work is to study how the characteristics of the polymer used to manufacture gas separation membranes influence its permeability and selectivity. It has been shown that the gas diffusivity decreases with the kinetic diameter of the gas except for CO₂, probably due to its high condensability. While solubility increases with the gas condensation temperature and clearly with the glass transition temperature of the polymer for each gas. The permeabilities of CO₂, CH₄, O₂, N₂ increase for increasing glass transition temperatures. Nevertheless only the selectivity of CO₂ versus the other gases increases significantly when polymers with high glass transition are used. The Robeson limit in a selectivity‐versus‐permeability plot is approached for CO₂/CH₄ when T_g increases. This distance to the Robeson limit, for this pair of gases, results to decrease for increasing T_g. For the case of the O₂/N₂ selectivity remains approximately constant with an appreciable increase in permeability for polymers with increasing T_g. Permeability increases due to the corresponding increase in fractional free volume, FFV, that appears for increasing glass transition temperatures, T_g. This correlation of FFV with T_g has been confirmed by obtaining FFV by different methods. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Experimental estimation of gas‐transport properties of linear low‐density polyethylene membranes by an integral permeation method

In recent years, we have investigated gas‐transport phenomena in coextruded linear low‐density polyethylene (LLDPE) membranes. For the most part, coextruded LLDPE membranes were investigated because of their excellent mechanical properties, which explain their extensive use in the packaging industry. Because of the small thickness of coextruded LLDPE membranes, significant errors can be involved in the determination of the diffusion coefficient of gases in the membranes by the time‐lag method. To obtain more precise transport parameters for LLDPE membranes, we determined the permeability and diffusion coefficients for O₂, CO₂, He, and N₂ from 298 to 348 K by employing an alternative method recently developed. The results indicate that the procedure used in this study for determining the diffusivity of gases in membranes was precise and more efficient than a method based on the evaluation of the time‐lag parameter. With respect to permeability, the coefficients obtained in this work agree satisfactorily with those obtained by the time‐lag method. In general, the permeability and diffusivity results are in satisfactory agreement with the literature values reported for semicrystalline polyethylene membranes. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3013–3021, 2001     

Preparation of novel ZSM‐5 zeolite‐filled chitosan membranes for pervaporation separation of dimethyl carbonate/methanol mixtures

Novel mixed matrix membranes were prepared by incorporating ZSM‐5 zeolite into chitosan polymer for the pervaporative separation of dimethyl carbonate (DMC) from methanol. These membranes were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X‐ray diffraction (XRD) to assess their morphology, intermolecular interactions, and crystallinity. Sorption studies indicated that the degree of swelling for zeolite‐filled membranes increased with zeolite content in the membrane increasing and the separation selectivity of DMC/methanol was dominated by solubility selectivity rather than diffusivity selectivity. The characteristics of these membranes for separating DMC/methanol mixtures were investigated by varying zeolite content, feed composition, and operating temperature. The pervaporation separation index (PSI) showed that 5 wt % of ZSM‐5 zeolite‐filled membrane gave the optimum performance in the PV process. From the temperature‐dependent permeation values, the Arrhenius activation parameters were estimated. The resulting lower activation energy values obtained for zeolite‐filled membranes contribute to the framework of the zeolite. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis,characterization, and structure-property relationships of aromatic polyimides containing 4,4′-diaminotriphenylmethane

This work reports two series of structurally different aromatic polyimides based on 4,4´-diaminodiphenylmethane (DPM) and 4,4´-diaminotriphenylmethane (TPM) and three commercial dianhydrides. All TPM-based polyimides formed membranes due to their high molecular weight (inherent viscosities ~0.93–1.14 dl/g), they exhibited high thermal stability (5 %: 490–544 °C), glass transition temperatures between 269 and 293 °C, and reasonable mechanical properties. The incorporation of pendant phenyl moieties in the TPM-based polyimides has a strong effect producing an improvement in solubility, thermal stability, density and gas permeability coefficient in comparison with DPM-based polyimides. The most interesting polyimide TPM-6FDA, containing phenyl and trifluoromethyl as bulky pendant groups, showed higher gas permeability coefficient for CO₂ (23.73 Barrer) and the best ideal selectivity to the gas pair CO₂/CH₄ (α = 28.93).     

Studies of dielectric characteristics and surface energies of spin‐coated polyimide films

A two‐step method, that is, polyamic acid formation with subsequent curing, was used to synthesize six kinds of polyimides. Dielectric constants and surface energies were investigated to determine the nature of the fluorinated and nonfluorinated polyimides. The dielectric constant decreased from 3.3 (at 100 kHz) for PMDA/ODA to 2.6 (at 100 kHz) for 6FDA/4,4′‐6F when the fluorine content increased from 0 to 30.7 wt %. Simultaneously, the water contact angle increased from 65° for PMDA/ODA to 78° for 6FDA/4,4′‐6F. Experimental results indicated that fluorinated polyimides contained a lower dielectric constant with improved water resistance. The surface energy values obtained from experiments agreed well with Holmes' correlation between surface energy and dielectric constant. The surface energies and dielectric constants were significantly affected by the polymer backbone structures, especially by the fluorination effect. Therefore, by choosing the appropriate monomers, polyimides of low dielectric constants with hydrophobic surfaces could be obtained. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1642–1652, 2001     

Sorption and desorption of tetrachloroethylene in fluoropolymers: Effects of the chemical structure and crystallinity

In 18 fluoropolymers with different repeating‐unit structures and crystallinities, the solubility, diffusivity, and permeability at 70°C of a polarizable nonpolar solute (tetrachloroethylene) were studied. The transport properties were mostly controlled by the polarity of the polymer and to a lesser degree by the polymer crystallinity. The highest permeability was observed in the dipole‐containing ethylene–chlorotrifluoroethylenes because of their high tetrachloroethylene solubility. The lowest permeability was observed in the hydrogen‐bonding poly(vinylidene fluoride) polymers because of the combination of low solute solubility and solute diffusivity. The tetrachloroethylene diffusivity was solute‐concentration‐dependent, and sorption curves were S‐shaped, indicating that the solute surface concentration was time‐dependent. The rate at which the surface concentration approached the saturation level was proportional to the product of Young's modulus, the square of the thickness of the dry polymer, and the logarithm of the solute diffusivity. Data for the water‐hyperbranched polymer and limonene–polyethylene conformed to the same relationship. Therefore, this provides a new tool for predicting the solute‐surface‐concentration time dependence from data obtained by independent measurements. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1474–1483, 2003     

Water‐sorption behavior of P‐phenylene diamine–based polyimide thin films

Four different p‐PDA–based polyimide thin films were prepared from their respective poly(amic acid)s through thermal imidization at 400°C: poly(p‐phenylene pyromellitimide) (PMDA‐PDA); poly(p‐phenylene biphenyltetra carboximide) (BPDA‐PDA); poly(p‐phenylene 3,3′,4,4′‐oxydiphthalimide) (ODPA‐PDA); and poly(p‐phenylene 4,4′‐hexafluoroisopropylidene diphthalimide) (6FDA‐PDA). Water‐sorption behaviors of polyimide films were gravimetrically investigated at 25°C and 22–100% relative humidity by using the modified electromicrobalance (Thin Film Diffusion Analyzer). The diffusion coefficients of water for the polyimides varies in the range of 1.6 to 10.5 × 10⁻¹⁰ cm²/s, and are in the increasing order: BPDA‐PDA < PMDA‐PDA ∼ ODPA‐PDA < 6FDA‐PDA. The water uptakes of polyimides vary from 1.46 to 5.80 wt %, and are in the increasing order: BPDA‐PDA < ODPA‐PDA < 6FDA‐PDA < PMDA‐PDA. The water‐sorption behaviors for the p‐PDA–based polyimides are closely related to the morphological structure; specifically, the diffusion coefficients in p‐PDA–based polyimide thin films are closely related to the in‐plane orientation and mean intermolecular distance, whereas the water uptakes are affected by the packing order. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1315–1323, 2000