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Different fluorinated copolyimides have been synthesized using 6FDA (4,4′-(hexafluoroisopropylidene)diphthalic anhydride), DABA (3,5-diaminobenzoic acid), 4MPD (2,3,5,6-tetramethyl-1,4-phenylenediamine) and 3MPD (2,4,6-trimethyl-1,3-phenylenediamine). The copolyimides with different compositions of monomers were used as membrane materials in order to remove benzothiophene from benzothiophene/n-dodecane mixtures by pervaporation. This is especially of interest in fuel cell applications where sulphur components are poisoning the catalyst and therefore reducing the life time of the system. In order to figure out which operation parameters, e.g. temperature, pressure and membrane material are necessary for the enrichment of the sulphur-aromatic component and sufficient transmembrane fluxes, different pervaporation experiments have been performed. Feed temperatures have been varied between 353 and 413 K and permeate pressures between 19 and 45 mbar, average fluxes and enrichment factors β were determined. Activation energies for permeation were calculated for benzothiophene and n-dodecane in order to understand the temperature-dependent separation characteristics. The influence of the different diamine structures on the separation characteristics was investigated. It was found out that slight differences in structure, e.g. an additional methyl group on the polymer backbone does not have a significant effect on the pervaporation properties. Total fluxes for 6FDA–4MPD/DABA 9:1 and 6FDA–3MPD/DABA 9:1 membranes were 15.2 and 10.3 kg μm/(m2 h) at 393 K, with the corresponding enrichment factor of benzothiophene of 3.6 and 3.3, respectively. With increasing temperature, enhanced fluxes as well as enhanced enrichment factors were observed. Furthermore it was found that higher permeate pressures led to a decrease of the enrichment factor with no significant change in flux. 相似文献
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A series of copolyimides with high molecular weights, excellent mechanical properties, heat-resistant properties, and good
solubilities in organic solvents were synthesized from six kinds of commercial dianhydrides and 1,2-bis(4-aminophenoxy)-4-tert-butylbenzene. Monomers for synthesizing insoluble polyimides and monomers for synthesizing soluble polyimides were used to
synthesize semialternating copolyimides with arbitrary solubilities. Fifteen kinds of soluble copolyimides were synthesized
through chemical or thermal cyclodehydration. These copolyimides were found to be easily soluble as well as able to be processed
by casting from solutions such as N-methyl-2- pyrrolidone, N,N-dimethylacetamide, dimethylformamide, dimethyl sulfoxide, m-cresol, and tetrahydrofuran. The easily dissolved characteristics of this series of copolyimides stemmed from the tert-butyl group, the ortho-linked aromatic unit, and the ether group within 4-tert-butylbenzene. Besides, when the dianhydride molecules used contained organosoluble groups and were mixed at varying molar
ratios, the solubilities in organic solvents could be greatly enhanced. The copolyimides could improve the processability
of polymers, while maintaining or increasing their excellent mechanical properties and heat-resistant properties.
Received: 21 July 2000 Accepted: 13 December 2000 相似文献
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以丙酮为溶剂,将9,9-双(4-羟基苯基)芴(BHF)于室温下进行硝化反应得到二硝基化合物9,9-双(3-硝基-4-羟基苯基)芴,再经Pd/C-水合肼还原得到9,9-双(3-氨基-4-羟基苯基)芴(BAHF).采用上述二胺单体BAHF、与9,9-双(4-氨基苯基)芴(BAF)和六氟二酐(6FDA)通过低温溶液缩聚反应制备出一种含酚羟基的共聚聚酰胺酸溶液,经热酰亚胺化和热致重排反应得到共聚聚酰亚胺(CPI)和聚(酰亚胺-苯并恶唑)(PIPBO)热致刚性膜材料.采用核磁(NMR)、红外光谱(FTIR)、X-射线衍射仪(XRD)、热重分析仪(TGA)、差示扫描量热仪(DSC)和气体渗透性能测试等手段对所制得膜材料的结构、热性能和气体分离性能进行表征.研究结果表明,所制得的热致刚性膜主要表现出非晶结构,为无规共聚物,其Tg为340℃.随热处理温度升高,热致刚性膜的气体渗透性逐渐增加,450℃制得的热致刚性膜对O_2、N_2、H_2、CH_4和CO_2的渗透通量分别达到229.03、53.26、1497.35、33.52和818.76 Barrer. 相似文献
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《Soft Materials》2013,11(3):277-293
Cross‐linked polymer structures gain increasing attention as membrane materials because they can fullfill the demands for industrial applications. Thereby, not only good separation characteristics but also high temperature stability and chemical resistancy are required. Furthermore, it is important that the membrane materials be plasticization resistant, because it is found that this causes strong increasing permeability with a drastic loss in selectivity. Plasticization effects occur with polyimide membranes in the presence of high CO2concentrations, hydrocarbons as propylene, propane, or aromatics. Unfortunately, these components are present in mixtures with high relevance being separated economically by membrane units or hybrid processes. In this article, the advantages of cross‐linked 6FDA (4,4′hexafluoro isopropylidene diphthalic acid anhydride)‐copolyimides are discussed based on experimental results for the separation of propylene/propane, benzene/cyclohexane, and high‐pressure CO2/CH4mixtures. Additionally, opportunities for implementing the membrane units in conventional separation processes are discussed. 相似文献
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《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):1407-1435
Various new fluorinated heterocyclic copolyimides have been synthesized by a polycondensation reaction of a diacid chloride containing imide, hexafluoroisopropylidene and methylene groups with aromatic or heteroaromatic diamines containing preformed phenylquinoxaline or 1,3,4-oxadiazole rings. Other fluorinated heterocyclic copolyimides have been prepared by a polycondensation reaction of the same diacid chloride with aromatic dihydrazides, bis(o-hydroxy-amine)s or a bis(o-carboxy-amine), resulting in intermediate polyhydrazides, poly(o-hydroxy-amide)s or poly(o-carboxy-amide), respectively, which were futher cyclodehydrated to the corresponding polyoxadia zole-imide, polybenzoxazole-imide or polybenzoxazinone-imide structure. These polymers showed good solubility in polar amidic solvents, such as N-methylpyrrolidinone (NMP) and dimethylformamide (DMF), and even in less polar liquids, like tetrahydrofurane or pyridine, except for those compounds containing benzoxazole rings which were less soluble, only on heating in NMP or DMF. The weight average molecular weight measured for tetrahydrofurane-fully-soluble polymers are in the range of 12800–26700 and the polydispersity is in the range of 2–5. All these polymers exhibited good thermal stability, with decomposition temperature being above 350°C, although somewhat lower than that of related polymers prepared by using fully aromatic diacid chlorides instead of the present ones containing methylene units. The glass transition temperature is in the range of 200–300°C. The dielectric constant measured for polymer films is in the range of 3.3–3.7. Tensile strength is in the range of 35–70 MPa, elongation to break between 30–40% and tensile modulus in the range of 170–330 MPa. A study of the relation between conformational parameters and properties of some of these polymers has been carried out by using the Monte Carlo method with an allowance for hindered rotation, and the values were compared with the experimental data and discussed in relation with the rigidity of the chains. The present polymers are potential candidates for use as high performance materials. 相似文献
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