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1.
An amorphous, organosoluble, fluorine‐containing polybenzimidazole (PBI) was synthesized from 3,3′‐diaminobenzidine and 2,2‐bis(4‐carboxyphenyl)hexafluoropropane. The polymer was soluble in N‐methylpyrrolidinone and dimethylacetamide and had an inherent viscosity of 2.5 dL/g measured in dimethylacetamide at a concentration of 0.5 g/dL. The 5% weight loss temperature of the polymer was 520 °C. Proton‐conducting PBI membranes were prepared via solution casting and doped with different amounts of phosphoric acid. In the methanol permeability measurement, the PBI membranes showed much better methanol barrier ability than a Nafion membrane. The proton conductivity of the acid‐doped PBI membranes increased with increasing temperatures and concentrations of phosphoric acid in the polymer. The PBI membranes showed higher proton conductivity than a Nafion 117 membrane at high temperatures. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4508–4513, 2006  相似文献   

2.
A new sequence isomer of AB‐polybenzimidazole (AB‐PBI) was developed as a candidate for high‐temperature polymer electrolyte membrane fuel cells. A diacid monomer, 2,2′‐bisbenzimidazole‐5,5′‐dicarboxylic acid, was synthesized and polymerized with 3,3′,4,4′‐tetraaminobiphenyl to prepare a polymer that was composed of repeating 2,5‐benzimidazole units. In contrast to previously prepared AB‐PBI, which contains only head‐to‐tail benzimidazole sequences, the new polymer also contains head‐to‐head and tail‐to‐tail benzimidazole sequences. The polymer was prepared in polyphosphoric acid (PPA) and cast into membranes using the sol–gel PPA process. Membranes formed from the new AB‐PBI were found to be mechanically stronger, possessed higher acid doping levels, and showed improved fuel cell performance, when compared to the previously known AB‐PBI. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012  相似文献   

3.
This work investigates the effects of polymer solids content and macromolecular structure on the high temperature creep behavior of polybenzimidazole (PBI) gel membranes imbibed with phosphoric acid (PA) after preparation via a polyphosphoric acid (PPA) mediated sol‐gel process Low‐solids, highly acid‐doped PBI membranes demonstrate outstanding fuel cell performance under anhydrous, ambient pressure, and high temperature (120–200 °C) operating conditions. However, PBI membranes are susceptible to creep under compressive loads at elevated temperatures, so their long‐term mechanical durability is a major concern. Here, we report results for the creep behavior of PBI membranes subject to compression at 180 °C. For para‐ and meta‐PBI homopolymers, increasing polymer solids content results in lower creep compliance and higher extensional viscosity, which may be rationalized by increasing chain density in the sol‐gel network. Comparing various homo‐ and copolymers at similar solids loading, differences in creep behavior may be rationalized in terms of chain–chain and chain‐solvent interactions that control macromolecular solubility and stiffness in the PA solvent. The results demonstrate the feasibility of improving the mechanical properties of PA‐doped PBI membranes by control of polymer solids content and rational design of PBI macromolecular structure. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1527–1538  相似文献   

4.
《先进技术聚合物》2018,29(1):594-602
Phosphoric acid (PA)–doped polybenzimidazole (PBI) proton exchange membranes have received attention because of their good mechanical properties, moderate gas permeability, and superior proton conductivity under high temperature operation. Among PBI‐based film membranes, nanofibrous membranes withstand to higher strain because of strongly oriented polymer chains while exhibiting higher specific surface area with increased number of proton‐conducting sites. In this study, PBI electrospun nanofibers were produced and doped with PA to operate as high temperature proton exchange membrane, while changes in proton conductivity and morphologies were monitored. Proton conductive PBI nanofiber membranes by using the process parameters of 15 kV and 100 μL/h at 15 wt% PBI/dimethylacetamide polymer concentration were prepared by varying PA doping time as 24, 48, 72, and 96 hours. The morphological changes associated with PA doping addressed that acid doping significantly caused swelling and 2‐fold increase in mean fiber diameter. Tensile strength of the membranes is found to be increased by doping level, whereas the strain at break (15%) decreased because of the brittle nature of H‐bond network. 72 hour doped PBI membranes demonstrated highest proton conductivity whereas the decrease on conductivity for 96‐hour doped PBI membranes, which could be attributed to the morphological changes due to H‐bond network and acid leaking, was noted. Overall, the results suggested that of 72‐hour doped PBI membranes with proton conductivity of 123 mS/cm could be a potential candidate for proton exchange membrane fuel cell.  相似文献   

5.
Phosphoric acid‐doped crosslinked proton‐conducting membranes with high anhydrous proton conductivity, and good chemical stability in phosphoric acid were synthesized and characterized. The synthetic procedure of the acid‐doped composite membranes mainly involves the in situ crosslinking of polymerizable monomer oils (styrene and acrylonitrile) and vinylimidazole, and followed by the sulfonation of pendant imidazole groups with butanesultone, and further doped with phosphoric acid. The resultant phosphoric acid‐doped composite electrolyte membranes are flexible and show high thermal stability and high‐proton conductivity up to the order of 10?2 S cm?1 at 160 °C under anhydrous conditions. The phosphoric acid uptake, swelling degree, and proton conductivity of the composite membranes increase with the vinylimidazole content. The resultant composite membranes also show good oxidative stability in Fenton's reagent (at 70 °C), and quite good chemical stability in phosphoric acid (at 160 °C). The properties of the prepared electrolyte membranes indicate their promising prospects in anhydrous proton‐exchange membrane applications. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 , 51, 1311–1317  相似文献   

6.
In the present work, a unique series of random polybenzimidazole (PBI) copolymers consisting of the recently reported novel isomeric AB‐PBI (i‐AB‐PBI) and the well known AB‐PBI were synthesized. The i‐AB‐PBI incorporates additional linkages (2,2 and 5,5) in the benzimidazole sequence when compared with AB‐PBI. Random copolymers, varying in composition at 10 mol % increments, were synthesized to evaluate the effects of sequence isomerism in the polymer main chain without altering the fundamental chemical composition or functionality of a polymer chain consisting of 2,5‐benzimidazole units. Polymer solutions were prepared in polyphosphoric acid (PPA) and cast into membranes using the sol–gel PPA process. The resulting polymers were found to have high inherent viscosities (>2.0 dL/g) and showed elevated membrane proton conductivities (~0.2 S/cm) under anhydrous conditions at 180 °C. Fuel cell performance evaluations were conducted, and an average output voltage ranging from 0.5 to 0.60 V at 0.2 A/cm2 was observed for hydrogen/air at an operational temperature of 180 °C without applied backpressure or humidification. Herein, we report for the first time glass transition (Tg) temperatures for AB‐PBI, i‐AB‐PBI, and an anomalous Tg effect for the series of randomized PBIs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 619–628  相似文献   

7.
Phosphoric acid doped polybenzimidazole (PBI) membranes have been covalently cross‐linked with dichloromethyl phosphinic acid (DCMP). FT‐IR measurements showed new bands originating from bonds between the hydrogen bearing nitrogen in the imidazole group of PBI and the CH2 group in DCMP. The produced cross‐linked membranes show increased mechanical strength, making it possible to achieve higher phosphoric acid doping levels and therefore higher proton conductivity. Oxidative stability is significantly improved and thermal stability is sufficient in a temperature range of up to 250°C, i.e. within the temperature range of operation of PBI‐based fuel cells. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

8.
Two new kinds of fluorine‐containing polybenzimidazoles (PBI), poly(2,2′‐(tetrafluoro‐p‐phenylene)‐5,5′‐bibenzimidazole) and poly(2,2′‐tetradecafluoroheptylene‐5,5′‐bibenzimidazole), were synthesized by condensation polymerization of 3,3′‐diaminobenzidine and perfluoroterephthalic acid (or perfluoroazelaic acid), with polyphosphoric acid as solvent. Thermogravimetric analysis results show that the fluorine‐containing polymers synthesized exhibit promising thermal stability. The film‐forming properties of the fluorine‐containing polymers are improved over nonfluorinated PBI. The introduction of fluorine into the backbone of the polymers has significant positive affection on their chemical oxidation stability demonstrated by Fenton test. Compared with poly(2,2′‐(m‐phenylene)‐5,5′‐bibenzimidazole)/phosphoric acid (PA) composite membrane, the resulting fluorinated membranes with a same PA doping level exhibit better flexibility and higher proton conductivity. The maximum proton conductivity gained is 3.05 × 10?2 S/cm at 150 °C with a PA doping level of 7. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2115–2122, 2010  相似文献   

9.
Phosphoric acid (PA)‐doped m‐polybenzimidazole (PBI) membranes used in high temperature fuel cells and hydrogen pumps were prepared by a conventional imbibing process and a sol–gel fabrication process. A comparative study was conducted to investigate the critical properties of PA doping levels, ionic conductivities, mechanical properties, and molecular ordering. This systematic study found that sol–gel PA‐doped m‐PBI membranes were able to absorb higher acid doping levels and to achieve higher ionic conductivities than conventionally imbibed membranes when treated in an equivalent manner. Even at similar acid loadings, the sol–gel membranes exhibited higher ionic conductivities. Heat treatment of conventionally imbibed membranes with ≤29 wt % solids caused a significant reduction in mechanical properties; conversely, sol–gel membranes exhibited an enhancement in mechanical properties. From X‐ray structural studies and atomistic simulations, both conventionally imbibed and sol–gel membranes exhibited d‐spacings of 3.5 and 4.6 Å, which were tentatively attributed to parallel ring stacking and staggered side‐to‐side packing, respectively, of the imidazole rings in these aromatic heterocyclic polymers. An anisotropic staggered side‐to‐side chain packing present in the conventional membranes may be related to the reduction in mechanical properties. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Polym. Phys. 2014 , 52, 26–35  相似文献   

10.
A sulfonated derivative of polybenzimidazole is reported, and its properties are analyzed in comparison with related polybenzimidazole proton‐conducting materials. Poly(2,5‐benzimidazole), poly(m‐phenylenebenzobisimidazole), and poly[m‐(5‐sulfo)‐phenylenebenzobisimidazole] were prepared by condensation of the corresponding monomers in polyphosphoric acid. Several adducts of these polymers with phosphoric acid were prepared. The resulting materials were characterized by chemical analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis; also, the dc conductivity of doped and undoped derivatives was measured. Similar to what has been observed for the commercial polybenzimidazole polymer (also examined here for comparison), the title polymers exhibit high thermal stability. Furthermore, their doping with phosphoric acid leads to a significant increase in conductivity from less than 10?11 Scm?1 for the undoped polymers to 10?4 Scm?1 (both at room temperature) for their acid‐loaded derivatives. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3703–3710, 2002  相似文献   

11.
Phosphoric acid doped poly (2, 2′‐(m‐phenylene)‐5, 5′‐bibenzimidazole) (PBI) membranes were prepared by dissolving PBI powders in 85% phosphoric acid at 190–200°C and then promoting gelation of the PBI by cooling the solutions to ?18°C. The extent of acid doping of the PBI membranes was controlled by immersing the membrane in aqueous phosphoric acid solutions of different concentrations (acid de‐doping). The process of the acid de‐doping was faster than acid doping of membrane cast from N,N‐dimethylacetamide (DMAc). The de‐doping process caused shrinkage of the PBI membrane and thus an increase in the membrane strength due to the packing of PBI chains according to the X‐ray diffraction analysis. The tensile stress and proton conductivity of the obtained PBI membranes with different acid doping levels were measured. For a PBI (ηIV: 0.58 dL · g?1) membrane with an acid doping level of 7.0 (molar number of doped acid per mole repeat unit of PBI), the stress at break and proton conductivity at 120°C without humidification were 2.6 MPa and 5.1 × 10?2 S · cm?1, respectively. These results were comparable to those of the membranes cast from PBI solutions in DMAc. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

12.
Polybenzimidazole (PBI) membranes were doped in phosphoric acid solutions of different concentrations at room temperature. The doping chemistry was studied using the Scatchard method. The energy distribution of the acid complexation in polymer membranes is heterogeneous, that is, there are two different types of sites in PBI for the acid doping. The protonation constants of PBI by phosphoric acid are found to be 12.7 L mol?1 (K1) for acid complexing sites with higher affinity, and 0.19 L mol?1 (K2) for the sites with lower affinity. The dissociation constants for the complexing acid onto these two types of PBI sites are found to be 5.4 × 10?4 and 3.6 × 10?2, respectively, that is, about 10 times smaller than that of aqueous phosphoric acid in the first case but 5 times higher in the second. The proton conducting mechanism is also discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2989–2997, 2007  相似文献   

13.
Hyperbranched polybenzimidazoles (HBPBIs) were successfully synthesized by condensation polymerization of 1,3,5‐benzenetricarboxylic acid (BTA) and 3,3′‐diaminobenzidine (DAB) in polyphosphoric acid (PPA) at 190 °C. Different monomer addition manners and molar ratios resulted in different polymers, that is, simultaneous addition of BTA and DAB with the molar ratio of 1:1 (manner 1) gave carboxyl‐terminated HBPBI (HBPBI‐1), whereas the addition of BTA portion‐wise to DAB solution in PPA with the molar ratio of DAB:BTA = 2:1 (manner 2) yielded amine‐terminated HBPBI (HBPBI‐2). The free carboxyl and amino groups of HBPBI‐1 and HBPBI‐2 could further react with o‐diaminobenzene and benzoic acid, respectively, to form the chemically modified polymers. Except HBPBI‐2, all the HBPBIs showed good solubility in some organic solvents (e.g., dimethyl sulfoxide and N,N‐dimethylacetamide). Thermogravimetric analysis measurement revealed that HBPBIs except HBPBI‐1 had high thermal stability (>450 °C). HBPBI membranes with good mechanical properties were obtained by crosslinking treatment of partially chemically modified HBPBIs with terephthaldehyde (TPA) during the film cast process. The HBPBI membranes had high phosphoric acid uptake and the phosphoric acid‐doped HBPBI‐6 (40% o‐diamino groups were reacted with benzoic acid) membrane showed higher tensile strength than the acid‐doped commercial PBI despite the higher doping level of the former. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1150–1158, 2007  相似文献   

14.
A series of new polybenzimidazoles (PBIs) with pendant amino groups have been synthesized via condensation polymerization of 5‐aminoisophthalic acid (APTA), isophthalic acid (iPTA), and 3,3′diaminobenzidine (DAB) in polyphosphoric acid at 190 °C for 20 h. The molar ratios between APTA and iPTA were controlled at 1:0, 2:1, 1:1, and 1:2, respectively, and the copolymerization reactions were carried out via both random and sequenced manners. The resulting polymers showed good solubility in some organic solvents such as dimethylsulfoxide (DMSO) and N,N‐dimethylacetamide (DMAc). The pendant amino groups of the PBIs were utilized to react with two kinds of crosslinkers, 1,3‐dibromopropane and ethylene glycol diglycidyl ether, to yield various crosslinked membranes. The crosslinked membranes generally showed good mechanical properties even at high‐phosphoric acid (PA) doping levels, whereas the uncrosslinked membranes highly swelled or even dissolved in PA. Fenton's test revealed that the crosslinked PBI membranes had excellent radical oxidative stability. The proton conductivities of the PA‐doped crosslinked membranes increased with an increase in temperature and high‐proton conductivity up to 0.14 S/cm at 0% relative humidity at 170 °C was achieved. The membranes with high PA‐doping levels, good mechanical properties, and high‐proton conductivities have been successfully developed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009  相似文献   

15.
In this study, PBI‐based block copolymers were developed and their performance as membranes in high temperature polymer electrolyte membrane fuel cells was evaluated. This type of block copolymer consists of “phosphophilic” PBI and “phosphophobic” non‐PBI segments. The final properties of such block copolymers strongly depended on the length of the individual blocks and their chemical structures. In a systematic approach, a series of various block copolymers was synthesized and characterized both in terms of ex situ properties (e.g., proton conductivity, phosphoric acid uptake, swelling behavior) and in situ fuel cell tests. A very poor membrane‐electrode interface limited the performance of the membrane electrode assemblies, but was remarkably improved in power output, stability, and long‐term durability by treating the electrode interface with a fluorinated PBI derivative. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 1831–1843  相似文献   

16.
Polybenzimidazoles (PBI) are an important class of heterocyclic polymers that exhibit high thermal and oxidative stabilities. The two dominant polymerization methods used for the synthesis of PBI are the melt/solid polymerization route and solution polymerization using polyphosphoric acid as the solvent. Both methods have been widely used to produce high‐molecular weight PBI, but also highlight the obvious absence of a practical organic solution‐based method of polymerization. This current work explores the synthesis of high‐molecular weight meta‐PBI in N,N‐dimethyl acetamide (DMAc). Initially, model compound studies examined the reactivity of small molecules with various chemical functionalities that could be used to produce 2‐phenyl‐benzimidazole in high yield with minimal side reactions. 1H NMR and FTIR studies indicated that benzimidazoles could be efficiently synthesized in DMAc by reaction of an o‐diamine and the bisulfite adduct of an aromatic aldehyde. Polymerizations were conducted at various polymer concentrations (2‐26 wt % polymer) using difunctional monomers to optimize reaction conditions in DMAc which resulted in the preparation of high‐molecular weight m‐PBI (inherent viscosities up to 1.3 dL g?1). TGA and DSC confirmed that m‐PBI produced via this route has comparable properties to that of commercial m‐PBI. This method is advantageous in that it not only allows for high‐polymer concentrations of m‐PBI to be synthesized directly and efficiently, but can be applied to the synthesis of many PBI derivatives. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1795–1802  相似文献   

17.
以3,4-二氨基苯甲酸为单体合成了ab-聚苯并咪唑.研究了磷酸掺杂的该质子交换膜在80~200℃,不同湿度以及不同酸掺杂量下的质子电导率.该质子交换膜可作为燃料电池的膜电解质,在常压不增湿的条件下,可使电池运行温度达到200℃.  相似文献   

18.
Polybenzimidazole (PBI) polymers tethered with N‐phenyl 1,2,4‐triazole (NPT) groups were prepared from a newly synthesized aromatic diacid, 3′‐(4‐phenyl‐4H‐1,2,4‐triazole‐3,5‐diyl) dibenzoic acid (PTDBA). The obtained polymers show superior thermal and chemical stability and good solubility in many aprotic solvents. The inherent viscosities of all polymers were around 1 dL/g. They exhibit high thermal stability with initial decomposition temperature ranging from 515 to 530 °C, high glass transition temperature ranging from 375 to 410 °C, and good mechanical properties with tensile stress in the range of 66–98 MPa and modulus 1897–2600 MPa. XRD analysis indicates that these polymers are amorphous in nature. Physicochemical properties such as water and phosphoric acid‐uptake, oxidative stability, and proton conductivity of membranes of these polymers have also been determined. The proton conductivity ranged from 4.7 × 10?3 to 1.8 × 10?2 S cm?1 at 175 °C in dry conditions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2289–2303, 2009  相似文献   

19.
Throughout this work, the synthesis, thermal as well as proton conducting properties of acid doped heterocyclic polymer were studied under anhydrous conditions. In this context, poly(1‐vinyl‐1,2,4‐triazole), PVTri was produced by free radical polymerization of 1‐vinyl‐1,2,4‐triazole with a high yield. The structure of the homopolymer was proved by FTIR and solid state 13C CP‐MAS NMR spectroscopy. The polymer was doped with p‐toluenesulfonic acid at various molar ratios, x = 0.5, 1, 1.5, 2, with respect to polymer repeating unit. The proton transfer from p‐toluenesulfonic acid to the triazole rings was proved with FTIR spectroscopy. Thermogravimetry analysis showed that the samples are thermally stable up to ~250 °C. Differential scanning calorimetry results illustrated that the materials are homogeneous and the dopant strongly affects the glass transition temperature of the host polymer. Cyclic voltammetry results showed that the electrochemical stability domain extends over 3 V. The proton conductivity of these materials increased with dopant concentration and the temperature. Charge transport relaxation times were derived via complex electrical modulus formalism (M*). The temperature dependence of conductivity relaxation times showed that the proton conductivity occurs via structure diffusion. In the anhydrous state, the proton conductivity of PVTri1PTSA and PVTri2PTSA was measured as 8 × 10?4 S/cm at 150 °C and 0.012 S/cm at 110 °C, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1016–1021, 2010  相似文献   

20.
A concept of preparing high‐temperature proton exchange membranes with layer‐by‐layer (LBL) self‐assembly technique was proposed and the sulfonated polyetheretherketone (SPEEK) and polyurethane (PU) with 200 LBL deposition cycles denoting (SPEEK/PU)200 membrane was prepared in this research. Owing to the strong electrostatic interaction between ? group in SPEEK and ? C? N+ group in PU, (SPEEK/PU)200 membrane with LBL self‐assembly structure showed a favorable structural stability. The phosphoric acid (PA)‐doped (SPEEK/PU)200 membrane showed a higher proton conductivity relative to PA doped SPEEK/PU membrane by solution casting method (SPEEK/PU)200/40%PA membrane possessed a proton conductivity value of 2.90 × 10?2 S/cm at 150 °C under anhydrous conditions. The LBL self‐assembly structure provided a possibility to reduce the negative effect from polymer skeleton blocking charge carrier species even immobilizing protons. Moreover, the (SPEEK/PU)200 membrane presented the particularly noteworthy mechanical property even with PA doping. The tensile stress values at break were 72.8 and 24.1 MPa, respectively, for (SPEEK/PU)200 and (SPEEK/PU)200/40%PA membrane at room temperature, which were obviously higher than the reported values of 15.9 and 2.81 MPa for SPEEK/PU and SPEEK/PU/60%PA membrane. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3446–3454  相似文献   

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