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     

Photoelectric properties of ABA‐type triblock copolymers designed using fluorine‐containing polyimide macroinitiators with polyhedral oligomeric silsesquioxane

4,4′‐(Hexafluoro‐isopropylidene) diphthalic anhydride‐2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (6FDA‐TeMPD) was synthesized and reacted with polyhedral oligomeric silsesquioxane (POSS) to form an ABA‐type triblock copolymer by atom transfer radical polymerization. The solid‐state and optical properties of the resulting copolymers were systematically investigated, and their electronic states were analyzed. As the POSS concentration increased, the transparency across the entire wavelength range increased. In the ABA‐type triblock copolymers, a new transition was observed between the highest occupied molecular orbital in POSS and the lowest unoccupied molecular orbital in 6FDA‐TeMPD because of their high molecular size dispersion. Since the refractive index of 6FDA‐TeMPD decreased linearly as the POSS concentration increased, the refractive index of the ABA‐type triblock copolymers of 6FDA‐TeMPD with POSS could be easily controlled. POLYM. ENG. SCI., 57:1207–1213, 2017. © 2017 Society of Plastics Engineers     

Permeability of dried gases and gases dissolved in water through polyimide membranes modified by immersing in amino compound solutions

Membranes of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA)?2,3,5,6‐tetramethyl‐1,4‐phenylene diamine (TeMPD) polyimide, a fluorine‐containing polyimide synthesized using 6FDA and TeMPD, were modified by immersing them in various amino compound solutions for application in artificial lungs. Permeabilities of dried gases (P_G) and gases dissolved in water (P_L) through the membranes were investigated. The surface reaction ratios of all the modified membranes were higher than the total reaction ratio, indicating that the modified membranes exhibited graded structures that were reacted with amino compounds from both surfaces toward the interior. Both P_L (O₂) and P_L (CO₂) of the base membrane and amine‐modified membranes, except the membrane where d ‐glucamine was used, were lower than or equal to P_G (O₂) and P_G (CO₂), respectively. Both P_L (O₂) and P_L (CO₂) of the amine‐modified membranes decreased with increasing water content, which suggests that water content strongly affected permeability in liquid phase. Results indicate that water molecules interrupted gas permeation. Moreover, CO₂/O₂ permselectivity in liquid phase increases with high‐polarity amino compounds compared with the base membrane. POLYM. ENG. SCI. 56:178–186, 2016. © 2015 Society of Plastics Engineers     

Mixed gas and pure gas transport properties of copolyimide membranes

Copolyimides were synthesized from dianhydride of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with various diamine contents of 4,4′‐oxydianiline (ODA) and 2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (TeMPD) by chemical imidization in a two‐step procedure. Polyimides (PIs) were characterized using thermogravimetric analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry, as well as specific volume and free volume. The gas transport properties for pure gas and blends of CO₂ and CH₄ for the homopolymers and 6FDA‐ODA/TeMPD copolymers were investigated at 35°C and 150 psi pressure. In pure gas permeation, permeability of CO₂ and CH₄ increased with increasing TeMPD content in the diamine moiety, whereas the ideal selectivity decreased with increasing TeMPD content. In the mixed gas permeation, permeabilities and separation factor were measured as a function of CO₂ feed molar fraction for five PI membranes. The behavior of pure gas and mixed gas permeabilities and separation factor of CO₂/CH₄ mixtures as the chemical nature of the diamine and the CO₂ molar fraction in the feed gas were varied and are discussed in detail. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013     

Synthesis and gas permeability of ABA‐type triblock copolymers derived from fluorine‐containing polyimide with polyhedral oligomeric silsesquioxane

ABA‐type triblock copolymers derived from 4,4'‐(hexafluoroisopropylidene)diphthalicanhydride‐2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (6FDA‐TeMPD) and methacryl phenyl polyhedral oligomeric silsesquioxane (MPPOSS) were synthesized by atom transfer radical polymerization. The chemical structure of the synthesized ABA‐type triblock copolymer was confirmed by ¹H NMR, ¹³C NMR, ²⁹Si NMR and Fourier transform infrared analyses. The ratios of 6FDA‐TeMPD and MPPOSS determined by TGA were 94/6, 85/15, 77/23, 68/32, 57/43 and 31/69. The film density of the ABA‐type triblock copolymer films did not conform to the mixing rule because of polyimide (PI) chain aggregation. Based on contact angle and water uptake analyses, the hydrophobicity of the ABA‐type triblock copolymer film was determined to be higher than the theoretical value because of POSS cage effects and PI chain aggregation. The gas permeability coefficient of the ABA‐type triblock copolymer decreased compared with that of PI because of aggregation of PI chains and inhibition of solubility decreases by substitutes with high affinity. ABA‐type triblock copolymer CO₂/H₂ separation performance increased compared with that of PI. The ABA‐type triblock copolymer derived from PI and MPPOSS can be described as a polymer material with higher hydrophobicity and higher CO₂/H₂ selectivity than PI. © 2015 Society of Chemical Industry     

Thermal and gas permeation properties of copolymers derived from 3‐methacryloxypropyltris(trimethylsiloxy)silane and adamantyl group‐containing methacrylate derivatives

Novel copolymer membranes derived from three types of adamantyl group‐containing methacrylate derivatives and 3‐methacryloxypropyltris(trimethylsiloxy)silane (SiMA) were synthesized via free radical polymerization. The thermal and permeation properties of these copolymer membranes were investigated. Copolymer membranes with less than 11.9 mol % adamantane content exhibited good membrane forming abilities that are suitable for permeation measurement. The decomposition temperature of all copolymers increased up to approximately 40–80°C with increasing adamantane content compared with poly(SiMA). Moreover, the glass transition temperature (T_g) of all copolymers increased up to approximately 46–60°C with increasing adamantane content compared with the theoretical value, which was estimated from Fox equation. 1‐Adamantyl methacrylate copolymer had the highest fractional free volume among the three types of adamantly group‐containing methacrylate derivatives. The gas permeability coefficient of this copolymer increased by 22–45% with increasing adamantane content compared with that of poly(SiMA). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43129.     

Investigation of the thermal properties of novel adamantane‐modified polybenzoxazine

Two novel structures of adamantane‐modified benzoxazines were synthesized from 4‐(1‐adamantyl)‐phenol through the incorporation of adamantane as a pendant group into the polybenzoxazine backbone. Both ¹H‐NMR and Fourier transform infrared spectra were used to characterize these structures. The rigid structure of the adamantane tended to hinder the chain mobility (boat anchor effect) and substantially enhanced the thermal properties, including the glass‐transition temperature and decomposition temperature, especially for poly(6‐adamantyl‐3‐methyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine). In the poly(6‐adamantyl‐3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine) system, however, the opposite result for the glass‐transition temperature was observed and it was interpreted as lower crosslinking density. The phenyl group was bulkier than the methyl group, and the movement of the molecular chain was hindered between bridging points during the curing process; this resulted in a lower crosslinking density and a lower glass‐transition temperature than those of poly(6‐adamantyl‐3‐methyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 932–940, 2004     

Phototransparency and water vapor sorption properties of ABA‐type triblock copolymers derived from 6FDA‐TeMPD and poly(2‐methyl‐2‐adamantylmethacrylate)

The phototransparency and water vapor sorption properties of ABA‐type triblock copolymer membranes derived from 4,4‐(hexafluoroisopropylidene) diphthalic anhydride‐2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (PI) and poly(2‐methyl‐2‐adamantylmethacrylate) (PMAdMA) were investigated, with focus on the effect of the adamantane component. The phototransparency of PMAdMA‐block‐PI‐block‐PMAdMA [Block(PI/PMAdMA)] was about 10–20% higher than that of poly(methyl methacrylate)‐block‐PI‐block‐Poly(methylmethacrylate) [Block(PI/PMMA)] because the high symmetric structure of adamantane inhibited photoabsorbance. The water vapor solubility of Block(PI/PMAdMA) decreased with increased PMAdMA because the PMAdMA had a hydrophobic property. Interestingly, in all relative‐pressure regions, Block(PI/PMAdMA) with the least PMAdMA content showed a higher solubility coefficient than PI because the high mobility of PMAdMA in Block(PI/PMAdMA) resulted in additional sorption sites in the PI segment. A comparison of Block(PI/PMAdMA) with Block(PI/PMMA) in terms of relative pressure at the beginning of clustering further revealed that cluster formation in Block(PI/PMAdMA) was inhibited compared with Block(PI/PMMA) because bulky structure of adamantane restricted the mobility of the polymer main chain. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43795.     

Polyimide asymmetric membranes: Elaboration,morphology, and gas permeation performance

Asymmetric 2,2‐bis‐(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)‐2‐methyl‐1,3‐phenylenediamine (mPDA) polyimide membranes were prepared according to a phase‐inversion mechanism by using different solvent/nonsolvent blends. The membrane formation mechanism and the final performances of the asymmetric membranes have been found both nonsolvent and solvent nature dependent. From the visualization of cross sections of asymmetric membranes by scanning electron microscopy and the study of the permeation of two gases (N₂, CO₂) through asymmetric membranes, a relationship between elaboration conditions and asymmetric membranes characteristics could be drawn. The organization of polymer chains in solution strongly affects the final polymer arrangement and thus the final performances of the membrane. The influence of preliminary solvent evaporation before immersion has been shown to be dependent on the structure of the asymmetric membrane: finger‐like or sponge‐like structures. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1838–1848, 2003     

Effects of thermal treatment on the CO2 sorption of triblockcopolymers derived from polyimide and poly(methylmethacrylate)

ABA‐type triblock copolymers were synthesized using 4,4‐(hexafluoroisopropylidene) diphthalic anhydride‐2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (6FDA‐TeMPD) and poly(methyl methacrylate) (PMMA). The films were characterized by determining the effects of different content ratios and thermal decomposition of PMMA block on CO₂ sorption properties. TGA results showed that a thermal labile block can be completely decomposed under a previously reported thermal condition. SEM results presented that the asperity was micro‐phase separation caused by the PMMA block content rate. Numerous pores with sizes of approximately 10 to 50 nm were detected on Block(28/72) and Block(10/90). The isotherms of all films fitted the dual‐mode sorption model, and CO₂ sorption decreased with increased PMMA content rate. Infinite‐dilution CO₂ solubility depended on the Langmuir's site of each polymer because S_H0/S₀ of PI and Block(PI/PMMA) varied from 0.84 to 0.92 CO₂ affinity was increased by thermal treatment as indicated by the higher b and S₀ values of thermally treated films than those of nontreated films. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42208.     

Effect of polymer density on polyethylene hollow fiber membrane formation via thermally induced phase separation

Microporous high‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) hollow fiber membranes were prepared from polyethylene–diisodecyl phthalate solution via thermally induced phase separation. Effect of the polyethylene density on the membrane structure and performance was investigated. The HDPE membrane showed about five times higher water permeability than the LDPE membrane because it had the larger pore and the higher porosity at the outer membrane surface. The formation of the larger pore was owing to both the initial larger structure formed by spinodal decomposition and the suppression of the diluent evaporation from the outer membrane surface due to the higher solution viscosity. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 471–474, 2004     

Characterization of the polymer of a dipyrrolyl monomer by pyrolysis mass spectrometry

In this work, characterization of a homopolymer of succinic acid bis(4‐pyrrol‐1‐ylphenyl) ester prepared by galvonastatic polymerization was carried out by direct pyrolysis mass spectrometry. Although decomposition of the monomer yielding mainly butadionic acid and pyrrole occurred under the galvonastatic polymerization conditions, growth of the polymer through the pyrrole moieties was also achieved, yielding a ladder‐type polymer film. The polypyrrole chains contained both quinoid and aromatic units as in the case of polypyrrole, yet the extent of network structure was significantly diminished. A three‐step mechanism is proposed for the thermal decomposition process. The first step involves the cleavage of C₄H₄NC₆H₄O end groups. In the second step, decomposition of phenyl ester units and polypyrrole chains having quinoid structure takes place. The final stage of thermal degradation was attributed to decomposition of polypyrrole chains having aromatic structure. Copyright © 2004 Society of Chemical Industry     

Gas transport properties in (6FDA‐RTIL)‐(6FDA‐MDA) block copolyimides

This article reports synthesis and structure property studies of block copolyimides synthesized using diamino room temperature ionic liquids (RTIL) as diamine monomers. Specifically, polyimide oligomers of different lengths were synthesized using 2,2‐bis (3,4‐carboxylphenyl) hexafluoropropane dianhydride (6FDA) and diamino RTIL (1,3‐di(3‐aminopropyl) imidazolium bis[(trifluoromethyl) sulfonyl] imide). These oligomers were copolymerized with 6FDA and m‐phenylenediamine (MDA) using in situ polymerization to form (6FDA‐RTIL)‐(6FDA‐MDA) block copolyimides. The impact of the length and relative concentration of 6FDA‐RTIL oligomer in the copolymer on the resulting thermal, physical, and gas transport properties was monitored. As the concentration of the 6FDA‐RTIL segments increased, the backbone of the block copolyimides became more flexible resulting in a decrease in the glass transition temperature (T_g) and an increase in the density. The permeabilities of the RTIL containing copolyimides were consistently lower than those of the base polyimide, 6FDA‐MDA, with some increase in selectivities. Interestingly, the permeabilities of films produced with the low molecular weight oligomers were very different than those produced with same composition of the high molecular weight oligomers. This may be indicative of very different morphologies within these copolyimides. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43077.     

Light‐scattering study on porous membrane formation by dry‐cast process

The phase‐separation mechanism during porous membrane formation by the dry‐cast process was investigated by the light‐scattering method in poly(methyl methacrylate)/ethyl acetate (EA)/2‐methyl‐2,4‐pentanediol system. The evaporation of EA from the cast solution induced the phase separation and thus the porous membrane was obtained. By the light‐scattering measurement on the phase‐separation kinetics, the phase separation was found to occur by a spinodal decomposition mechanism. As the amount of nonsolvent in the cast solution decreased, the structure growth rate decreased and the growth stopped soon. The obtained porous structure was isotropic rather than asymmetric. The average interpore distances obtained from the SEM observation roughly agreed with the final constant interphase periodic distances measured by the light‐scattering method. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 10: 3205–3209, 2002     

Synthesis,characterization, and CO2 permeation properties of acetylene‐terminated polyimide membranes

A novel fluorine‐containing telechelic polyimide end‐capped with acetylene group which derived from 4,4‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 3,4‐diaminodiphenyl ether (DADE), and 4‐(2‐phenylethynyl) phthalic anhydride (PEPA) was synthesized using polycondensation. The physical and CO₂ permeation properties of its crosslinked membranes prepared by the cyclotrimerization reaction of the acetylene groups at the polymer chain end using tantalum (V) chloride (TaCl₅) as a catalyst under thermal treatment was investigated in terms of CO₂‐induced membrane plasticization. The crosslinked membranes showed a gel content in organic solvent, which was good solvent of noncrosslinked membranes, and improved their thermal stability. Based on the measurement of the high‐pressure time dependence on CO₂ permeation, the crosslinked 6FDA–DADE–PEPA membranes exhibited more resistance to CO₂‐induced plasticization than noncrosslinked 6FDA–DADE and thermal treated 6FDA–DADE–PEPA. Furthermore, the increase in TaCl₅ content resulted in more resistance to plasticization. The cyclotrimerization reaction of the acetylene groups at the polymer chain ends using a transition metal catalyst under thermal treatment was found to be more effective than conventional thermal treatments for suppressing membrane plasticization without the membrane densification. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Investigating the membrane morphology of water/solvent/nylon 6 systems

In this study, nylon 6 membranes were prepared in a water coagulation bath with two types of solvents, CaCl₂–methanol (CaClMe) and formic acid (FA). The morphology of the membranes, which was controlled by the phase behavior of their solutions, were connected to the mechanism of demixing, including liquid–liquid and liquid‐crystallization. Ternary phase diagrams showed that the CaClMe system coagulated significantly faster than the FA system. As observed by scanning electron microscopy, the CaClMe membrane had a porous, interconnected pore structure with macrovoids, whereas the FA membrane had a dense, spherulitic surface with a closed cell morphology. The high reaction surface of the CaClMe membrane with dye molecules provided outstanding dye rejection. Also, thermal analysis by differential scanning calorimetry showed that the slow coagulation of the FA system facilitated the formation of stable α‐form crystals rather than a metastable γ‐form structure. The results show that the phase‐separation mechanism was switched from liquid–liquid to liquid‐crystallization through a change in the solvent type from CaClMe to FA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of hydrophobic units on the pH‐responsive release property of polyelectrolyte complex capsules

Copolymers of acrylic acid and styrene with styrene unit contents of 2.7, 5.7, and 9.5% were synthesized by free radical copolymerization. Poly(ethylenimine)s with benzylated unit contents of 2.4, 6.0, 10.6, and 16.7% were obtained by the reaction of poly(ethylenimine) with benzyl bromide. Polyelectrolyte complex capsules consisting of these polymers were prepared. Influence of the hydrophobic units on pH‐responsive release property of the capsules was studied using phenylethylene glycol as a permeant. When the copolymer with styrene unit content of 5.7% or the poly(ethylenimine) with the benzylated unit content of 2.4–10.6% was used as the membrane components, the permeability of the capsule membrane became minimum and was 10–20 fold lower than that of the poly(acrylic acid)–poly(ethylenimine) complex capsule membrane in the pH region between 3 and 7. In contrast, the hydrophobic units did not lower the permeability of the capsule membranes significantly below pH 3 and above pH 7. Thus, the capsule membranes containing hydrophobic units exhibited remarkable permeability changes in the narrow pH regions of 2–3 and 7–9. Also, the capsule containing the benzylated PEI in the membrane changed the release rate of the contents very quickly, in response to the ambient pH alteration. Therefore, polyelectrolyte complex capsules, which are highly sensitive to pH change, were obtained by using the polyelectrolytes with the hydrophobic units as membrane components. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1763–1773, 1999     

Structure control of asymmetric poly(vinyl butyral)‐TiO2 composite membrane prepared by nonsolvent induced phase separation

Poly(vinyl butyral) (PVB)‐TiO₂ composite hollow fiber membranes were prepared via nonsolvent induced phase separation (NIPS). The membrane had a skin layer on both the outer and inner surface at the initial stage after membrane preparation. However, the outer surface became porous with the passage of time, as the polymer in the membrane's outer surface was decomposed by the photocatalysis of TiO₂. The initial water permeability increased with the increase of TiO₂ content. Furthermore, for all the membranes, as time elapsed the water permeabilities increased and became constant after about 15 days, which was in accordance with the alteration on the membrane's outer surface. Despite decomposition of the polymer on the outer surface, particle rejection hardly changed because the inner surface kept the original structure. Thus, addition of TiO₂ to the membrane is a useful way to improve water permeability while maintaining particle rejection. The clear asymmetric structure with both porous structure at the outer surface and skin layer at the inner surface was achieved by the addition of TiO₂. Therefore, the addition of TiO₂ is a new method for achieving the high porosity at the outer surface of the hollow fiber membrane. In addition, tensile strength and elasticity kept constant over time and were higher than those of original PVB membranes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Phase separation mechanism during membrane formation by dry‐cast process

Phase separation mechanisms during the membrane formation by dry‐cast process were investigated by light scattering in the cellulose acetate/dimethylformamide (DMF)/2‐methyl‐2,4‐pentanediol system. Phase separation occurred by spinodal decomposition (SD) when paths of the composition changes due to the evaporation of DMF were close to the critical point in the phase diagram. Characteristic properties of the early stage of SD such as an apparent diffusion coefficient and an interface periodic distance were obtained from the Cahn theory. Phase separation occurred by nucleation and growth (NG) when paths of the composition changes were far from the critical point. SEM observation confirmed that the membrane formed by the SD mechanism had interconnected structure, whereas that by the NG mechanism had the closed cell porous structure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 776–782, 2000