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.     

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...     

Gas transport properties of polymers based on spirobiindane bisphenol

Transport properties of pure gases in polycarbonates, polyesters, and polyetherimides based on 6,6′-dihydroxy-3,3,3′,3′-tetramethyl-1,1′-spiro biindane (SBI) and bisphenol-A (BPA) are compared at 35°C. The SBI monomer contains two spiro-linked five-membered rings which are fused to the phenyl rings at the meta and para positions to the hydroxyl groups. This molecular structure gives SBI-based polymers with higher fractional free volume (FFV) and lower intramolecular motions as compared to the BPA-based analogs. The inhibition of chain packing due to the SBI moiety yields polymers with much higher permeabilities for all the gases studied, despite the hinderance of mobility associated with the SBI structure. Simultaneous increase in selectivity was also observed for some gas pairs. Oxygen permeabilities up to 5.9-fold higher with increases of up to 13% in O₂/N₂ selectivities were observed for a polyester based on SBI as compared to its analog based on BPA. Higher permeabilities of up to 4.3-fold for He and up to 4.8-fold for CO₂ were observed due to the substitution of SBI for BPA. Not surprisingly, lower values of He/CH₄ and CO₂/CH₄ selectivities were obtained for the more open SBI-containing polymers. The changes in fractional free volume and inhibition of small-scale mobility for some materials caused by the SBI moiety were measured and used in the interpretation of the gas transport properties. The individual contributions of diffusivity and solubility to the overall transport behavior of the polymers are discussed and correlated to the structural alterations caused by the SBI substitution for BPA monomer. © 1995 John Wiley & Sons, Inc.     

Transport properties of polyimides derived from benzophenonetetracarboxylic dianhydride and other diamines

Gas-separating membrane characteristics of polyimide films composed of the common fragment of benzophenone-3,3′,4,4′-tetracarboxylic dianhydride and diamines of varying structure were studied. Permeability coefficient P, diffusion coefficient D, and solubility coefficient S for H₂, CO, CO₂, and CH₄ were determined. The polyimide derived from m-phenylenediamine exhibited the best gas-separating properties. A relationship between the chain rigidity, free volume, and transport parameters (P, D, S, and selectivity) of polyimide was established on the basis of the data. It was shown that there is an optimal chain rigidity for the studied polyimides that results in polymer structurization during film preparation and corresponds to high separation selectivity.     

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     

Transport properties of polyimides containing phenylquinoxaline moieties

The gas permeabilities of a number of new structurally related polyimides containing phenylquinoxaline moieties were studied for the first time. The test polymers had different dianhydride units, whereas their diamine components differed in the presence of flexible ether bonds-O-in the main chain, a structure that is reflected in the effective packing of chains and, as a result, in transport parameters. The permeability, diffusion, and solubility coefficients for the gases H₂, He, O₂, N₂, CO, CO₂, and CH₄, as well as the ideal separation factors for gas pairs, were determined. The transport characteristics of polymers were compared within the given polymer series and with published data for other polymer series.     

异构化对二苯醚二酐/二苯醚二胺聚酰亚胺结晶行为的影响

合成了一系列基于4,4-′ODPA,3,4-′ODPA以及3,3-′ODPA 3种异构二苯醚二酐单体的异构聚酰亚胺,以苯酐(PA)作为封端剂来控制分子量.用DSC和WAXD为主要手段研究了这几种异构聚酰亚胺的结晶行为.研究发现聚酰亚胺4,4-′ODPA/ODA(二苯醚二胺)在分子量较低的情况下能够在热处理,退火或剪切作用下结晶.并且升高热处理温度和延长热处理时间有利于结晶的完善,在玻璃化温度以上施加剪切能够加速聚酰亚胺的结晶.而对于其他的两种异构体3,4-′ODPA/ODA以及3,3-′ODPA/ODA无论是经过热处理还是施加外力剪切都未能使其结晶.     

Pretilt angle for BTDA,PMDA and CPDA series polyimides with various side chain lengths

Polyamic acid precursors were prepared by mixing dianhydride of 3,3',4,4'-benzophenone-tetracarboxylic dianhydride (BTDA), 1,2,3,4-benzene-tetracarboxylic dianhydride (pyrromellitic dianhydride PMDA), cis-1,2,3,4-cyclopentane-tetracarboxylic dianhydride (CPDA), the diamine (alkyl 3,5-diaminobenzoate) with side chain, and 4,4'-oxydianiline (ODA) without side chain. Copolyimide films with various side chain lengths were prepared by thermal imidization of polyamic acid precursors. The roughness of rubbed polyimide surface increased with increase in the side chain length. The pretilt angle for the BTDA and PMDA series polyimide (PI) increased exponentially with increase in side chain length. Various pretilt angles were obtained on the synthesized polyimides. In the case of CPDA series PI, the pretilt angle was nearly constant at 0 until the alkyl side chain length reached 12 (C12) and then increased markedly at C18. Models of pretilt angle generation were tested.     

Synthesis and properties of novel photosensitive polyimides containing chalcone moiety in the main chain

Two chalcone-derivative isomers, 4,4′-diaminochalcone ( 4DAC ) and 3,3′-diaminochalcone ( 3DAC ), were synthesized and used as monomers together with tetracarboxylic dianhydrides to prepare novel photosensitive polyimides that contain a chalcone moiety in the main chain. The polyimides were characterized and their photochemical behavior was investigated as thin films and in solutions with the aid of ultraviolet and infrared spectroscopy. Compared with 4DAC -based polyimides, the 3DAC -based polyimides exhibited lower glass transition temperatures and higher photocrosslinking rates of the carbon–carbon double bond as well as higher photosensitivities obtained from the exposure characteristic curves, suggesting that an increase in the photoreactivity of the 3DAC -based polyimides might arise from the improved flexibility of their backbones. The polyimide from 3DAC and 6FDA (2,2-bis[3,4-dicarboxypheny]hexa-fluoropropane dianhydride) showed a photosensitivity of 33 mJ/cm² with a contrast of 1.5 upon light irradiation using a Xenon lamp. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 685–693, 1998     

Correlation between the transport behavior of polyimides and the conformational rigidity of their chains

For a number of polyimides, Kuhn segment lengths have been calculated by the Monte Carlo method under the free-rotation approximation and the energies of cohesion have been estimated by the group-contribution method. It has been shown that, in the case of isomeric polyimides characterized by close energies of interchain interactions, a decrease in the rigidity of chains always leads to reductions in the free volume and gas permeability. For polyimides of allied structures, the simultaneous (and frequently oppositely directed) effects of chain rigidity and the energy of interchain interactions ambiguously influence gas permeability. Both factors should be taken into account during estimation of the influence of chain rigidity on the transport characteristics of polymers. Small-scale effects of packing and mobility of chain fragments exert the decisive effect on the transport characteristics of polyimides possessing a decreased mobility of chains.     

Thermal properties and solubility of poly-1,4,5,8-naphthalenetetracarboxydiimides containing 1,3,5-triazine rings

Aromatic polyimides were synthesized by polymerization of 1,4,5,8-naphthalenetetracarboxylic dianhydride and 2-dialkylamino-4,6-dihydrazino-1,3,5-triazines by a solution polymerization method followed by cyclodehydration. The polyimides had number-average molecular weights over 13,000–16,000 or viscosity values of 0.23–0.65 dl/g. The x-ray diffraction diagram of polyimide I showed a crystal pattern, but the pattern became less pronounced with increasing length of the polymer side chain, and thus polyimide V showed a typical amorphous pattern. Study of the thermal stability of the polyimides by thermogravimetric analysis showed that a steep weight loss occurred in the range 380–410°C. Among the polyimides, I had only poor solubility in organic solvent, while IV and V were soluble even in general organic solvents such as tetrahydrofuran and dioxane.     

Synthesis and characterization of polyimides derived from (3‐amino‐2,4,6‐trimethylphenyl)‐(3′‐aminophenyl)methanone and aromatic dianhydrides

A series of new polyimides were prepared via the polycondensation of (3‐amino‐2,4,6‐trimethylphenyl)‐(3′‐aminophenyl)methanone and aromatic dianhydrides, that is, 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), 4,4′‐oxydiphthalic anhydride, 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride, and 2,2′‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride. The structures of the polyimides were characterized by Fourier transform infrared and NMR measurements. The properties were evaluated by solubility tests, ultraviolet–visible analysis, differential scanning calorimetry, and thermogravimetric analysis. The two different meta‐position‐located amino groups with respect to the carbonyl bridge in the diamine monomer provided it with an unsymmetrical structure. This led to a restriction on the close packing of the resulting polymer chains and reduced interchain interactions, which contributed to the solubility increase. All the polyimides except that derived from BPDA had good solubility in strong aprotic solvents, such as N‐methyl‐2‐pyrrolidinone, N,N′‐dimethylacetamide, N,N‐dimethylformamide, and dimethyl sulfone, and in common organic solvents, such as cyclohexanone and chloroform. In addition, these polyimides exhibited high glass‐transition values and excellent thermal properties, with an initial thermal decomposition temperature above 470 °C and glass‐transition temperatures in the range of 280–320 °C. The polyimide films also exhibited good transparency in the visible‐light region, with transmittance higher than 80% at 450 nm and a cutoff wavelength lower than 370 nm. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1291–1298, 2006     

Packing density and gas permeability of copolyimides containing bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride constituent

Packing density and gas permeability of two copolyimide series containing an alicyclic monomer, bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA), and a fluorinated monomer, hexafluoroisopropylidene,2,2-bis(phthalic acid anhydride) (6FDA), were measured. Incorporation of a rigid BCDA segment in 6FDA polyimides either increases gas permeability or improves gas selectivity, depending on the base 6FDA polyimide. In the case of the highly gas permeable 6FDA polyimide, introduction of BCDA further increases gas permeability despite a loss in the amount of free volume. In the moderately gas permeable 6FDA polyimide, on the other hand, the introduction improves gas selectivity. © 1995 John Wiley & Sons, Inc.     

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     

Preparation of ultrathin films of aromatic polymides by vapor deposition polymerization from N-silylated aromatic diamines or aromatic tetracarboxylic dithioanhydride

A novel method for the preparation of ultrathin films of aromatic polyimides was developed through vapor deposition polymerization from combinations of monomer pairs of either N,N′-bis (trimethylsilyl)-substituted aromatic diamines and pyromellitic dianhydride or aromatic diamines and pyromellitic dithioanhydride. Both diamine component and tetracarboxylic dianhydride component were evaporated simultaneously at a stoichiometric molar ratio under vacuum, giving a deposited film on a substrate, which consisted of a polyamic acid derivative formed by the ring-opening polyaddition. The deposit was then converted to polyimide by thermal imidization at a relatively lower temperature, compared with a conventional method using the parent diamine and tetracarboxylic dianhydride. The properties of polyimide ultrathin films such as thermal stability, chemical resistance, and dielectric behavior were almost the same as those of the polyimide films prepared by a conventional method.     

In‐plane birefringence and elongation behavior of uniaxially drawn aromatic polyimide films

Six kinds of aromatic poly(amic acid) films, the precursor of polyimides, were uniaxially drawn by constant loads during thermal curing with varying the final curing temperature and the load. The in‐plane birefringence (Δn) generated by uniaxial orientation of polyimide molecules in the film plane was investigated in relation with their molecular structures and the elongation behavior of polyimide films. The polyimides derived from pyromellitic dianhydride (PMDA) showed much larger values of Δn than the polyimides derived from dianhydrides having rotatable diphenyl linkages. The Δn of the former polyimides increases with increasing the final curing temperature and the elongation between the most shrunken and the most elongated states during curing. In particular, the polyimides having rod‐like structures show the largest value of Δn. In contrast, the latter polyimides take maximal values of Δn at much lower temperatures. The introduction of hexafluroisopropiridene (? C(CF₃)₂? ) group into the main chain effectively lowers the values of Δn. This result can be related to the inherent low polarizability anisotropy and the decreased molecular packing constant that are characteristic of highly fluorinated groups. These experimental results are qualitatively explained by the calculations of polarizability anisotropies of model compounds using FPT‐MNDO‐PM3 theory. Copyright © 2001 John Wiley & Sons, Ltd.     

Structure and properties relationships for aromatic polyimides and their derived carbon membranes: experimental and simulation approaches

The main objective of this study is to investigate the factors of the chemical structure and physical properties of rigid polyimides in determining the performance of derived carbon membranes through both the experimental and simulation methods. Four polyimides made of different dianhydrides were pyrolyzed at 550 and 800 degrees C under vacuum conditions. The resultant carbon membranes exhibit excellent gas separation performances beyond the traditional upper limit line for polymer membranes. The thermal stability and the fractional free volume (FFV) of polyimides were examined by a thermogravimetric analyzer and a density meter. The chain properties of polyimide, such as flatness, chain linearity, and mobility, were simulated using the Cerius(2) software. All above characterizations of polyimides were related to the microstructure and gas transport properties of the resultant carbon membranes. It was observed that the high FFV values and low thermal stability of polyimide produce carbon membranes with bigger pore and higher gas permeability at low pyrolysis temperatures. Therefore, polyimides with big thermally labile side groups should be preferred to prepare carbon membranes at low pyrolysis temperatures for high permeability applications. On the other side, since the flatness and in-plane orientation of precursors may lead carbon membranes to ordered structure, thus obtaining high gas selectivity, linear polyimides with more coplanar aromatic rings should be first choice to prepare carbon membranes at high pyrolysis temperatures for high selectivity applications. The location of the indan group also affects chain flatness and in-plane orientation. As a result, carbon membranes derived from the BTDA-DAI precursor have superior separation performance to those derived from Matrimid.     

Thermal behavior of copolyimides containing bisbenzoylamine groups

In an effort to improve the processibility of full aromatic polyimides, copolybisbenzoylamine imides were synthesized. As this study is a continuation of our work on flexibilization of the polyimide main chain, the bisbenzoylamine group was introduced stepwise into the polyimide main chain. Mixtures of pyromellitic anhydride, the rigid component, and a bisbenzoylamine-3,3′, 4,4′-tetracarboxylic acid dianhydride, the flexible component, were polymerized with aromatic diamines in a two-step procedure. The thermal stability of the four series of resulting copolyimides shows parallel changes that depend on the dianhydride ratio. The functional dependence of glass transition temperature (T_g) on copolymer composition differs for hydrogen or alkyl group substitution on the nitrogen in the bisbenzoylamine group. The solubility of the copolyimides in dimethylformamide changes from 0 to 33 wt %; there is a nonlinear dependence between solubility and the dianhydride ratio.     

Crosslinked sulfonated polyimide networks as polymer electrolyte membranes in fuel cells

Sulfonated polyimides with tertiary nitrogen in the polymer backbone were synthesized with 1,4,5,8‐naphthalenetetracarboxylic dianhydride, 4,4′‐diaminobiphenyl 2,2′‐disulfonic acid, 2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane, and diaminoacrydine hemisulfate. They were crosslinked with a series of dibromo alkanes to improve the hydrolytic stability. The crosslinked sulfonated polyimide films were characterized for their thermal stability, ion‐exchange capacity (IEC), water uptake, hydrolytic stability, and proton conductivity. All the sulfonated polyimides had good thermal stability and exhibited a three‐step degradation pattern. With an increase in the alkyl chain length of the crosslinker, IEC decreased as 1.23 > 1.16 > 1.06 > 1.01, and the water uptake decreased as 7.29 > 6.70 > 6.55 > 5.63. The order of the proton conductivity of the crosslinked sulfonated polyimides at 90 °C was as follows: polyimide crosslinked with dibromo butane (0.070) > polyimide crosslinked with dibromo hexane (0.055) > polyimide crosslinked with dibromo decane (0.054). The crosslinked polyimides showed higher hydrolytic stability than the uncrosslinked polyimides. Between the crosslinked polyimides, the hydrolytic stability decreased with an increase in the alkyl chain length of the crosslinker. The crosslinked and uncrosslinked sulfonated polyimides exhibited almost the same proton conductivities. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2370–2379, 2005     

CO_2捕集炭膜的前驱体结构设计及性能

从分子结构设计出发,合成了一系列新型刚性、高自由体积的聚酰亚胺炭膜前驱体,并制备了炭膜.采用热重分析(TGA)、傅里叶变换红外光谱(FTIR)、X射线衍射(XRD)和高分辨透射电子显微镜(HRTEM)研究了不同聚酰亚胺前驱体的热分解特性及在热解炭化过程中化学结构、微结构的变化规律;测试了所制备炭膜的气体分离性能.结果表明,前驱体的自由体积分数显著影响炭膜的气体分离性能;聚合物结构越具刚性,自由体积越大,所得炭膜结构越疏松,极微孔道尺寸越大,越有利于气体分子在炭膜极微孔道中的渗透、扩散与传输.其中,刚性大体积基团芴基、酚酞cardo基团和六氟异丙基的引入能有效破坏分子链间的堆积,提高聚合物的自由体积,所形成炭膜的结构较疏松,均表现出优异的气体渗透性和分离选择性,超越了Robeson上限,解决了传统炭膜气体渗透性能低的问题.特别是采用羟基官能化聚酰亚胺前驱体制备的炭膜在保持较高气体分离选择性的同时,CO_2气体的渗透性高达24770 Barrer(1 Barrer≈7.5×10-18m2·s-1·Pa-1),可实现对CO_2的有效分离和捕集,展现出良好的商业化应用前景.