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A novel type of cross-linked proton exchange membrane of lower methanol permeation and high proton conductivity is prepared, based on a newly synthesized sulfonated cross-linker: carboxyl terminated benzimidazole trimer bearing sulfonic acid groups (s-BI). Compared to membranes cross-linked with non-sulfonated cross-linker (BI), SPEEK/s-BI-n membranes show higher IEC values and proton conductivities. Meanwhile, oxidative stability and mechanical property of SPEEK/s-BI-n membranes are obviously improved. Among SPEEK/s-BI-n membranes, SPEEK/s-BI-2 exhibits high proton conductivity, low swelling ratio (0.122 S cm −1 and 15.2% at 60 °C, respectively) and low methanol permeability coefficient. These results imply that the cross-linked membranes prepared with the newly sulfonated cross-linker are promising for the direct methanol fuel cells (DMFCs) application.

A series of macromolecular cross-linked polybenzimidazole (PBI) membranes have been successfully prepared for the high temperature proton exchange membrane fuel cell (HT-PEMFC) applications. Bromomethylated poly (aryl ether ketone) (BrPAEK) is synthesized and used as a macromolecular cross-linker, the cross-linking reaction can be accomplished at 160 °C using an easy facial heating treatment. The resulting cross-linked membranes CBrPBI-X (X is the weight fraction of the cross-linker) display excellent mechanical strength. After phosphoric acid (PA) doping, the mechanical strength and proton conductivity of the PA/CBrPBI-X membranes are both enhanced comparing with the pristine PA/PBI. Considering the tradeoff of the mechanical strength and proton conductivity, 10 wt% BrPAEK is demonstrated to be an optimum content in the matrix. For instance, the proton conductivity of PA/CBrPBI-10 is 0.038 S cm−1 at 200 °C, which is higher than that of pristine PA/PBI with the proton conductivity of 0.029 S cm−1 at the same temperature. Other properties of the cross-linked membranes are also investigated in detail, including the oxidative stability, solubility and thermal stability. All the results indicate that the PA/CBrPBI-10 membrane has the potential application in HT-PEMFCs.

A novel side-chain poly(arylene ether ketone) functionalized with 1,4-butane-sultone (SQNPAEK-x, "x" refers to the number of the attaching sulfobutyl groups in one unit) were synthesized for proton exchange membrane fuel cell. SQNPAEK-x showed high proton conductivity up to 0.317 S cm(-1) at 80 degrees C and excellent dimensional stability due to the remaining hydroxyl groups. Morphological investigations revealed that SQNPAEK-x contained more uniform ionic clusters than the main-chain sulfonated poly(arylene ether ketone), which increased the proton conductivity. Other properties such as water uptake, mechanical properties were also investigated. It should be noted that SQNPAEK-x possesses the best overall performance with proton conductivity (0.204 S cm(-1) at 80 degrees C) higher that Nafion 117, while the swelling ratio was equivalent (13.2% at 80 degrees C). All the results indicate that the SQNPAEK-x membranes are promising candidates for proton exchange membrane fuel cells. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Silane-cross-linked polybenzimidazole (PBI) membranes with high proton conductivity and excellent mechanical properties were successfully prepared by using a silane monomer, γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH560), as a cross-linker. Fourier transform infrared spectroscopy and solubility tests were used to characterize and confirm the cross-linked structure in the membranes. The silane-cross-linked membranes displayed excellent chemical stability and improved mechanical strength. Especially at high temperature (130 °C), where the tensile strength value was in the range of 68.6 to 99.3 MPa, while that of the pristine PBI was 61.7 MPa. Moreover, the proton conductivity was significantly enhanced because the silane-cross-linked structure in the membranes could absorb more phosphoric acid. Considering the tradeoff of mechanical properties and proton conductivity, 3% KH560 in weight was demonstrated to be the optimum content in the membranes, for instance, the SCPBI-3/7.95 PA (the cross-linker content was 3 wt% and the PA doping level was 7.95) had a proton conductivity of 0.081 S cm−1 and that of the SCPBI-3/9.07 PA was 0.114 S cm−1 at 200 °C, while that of pristine PBI was 0.015 S cm−1 at 200 °C.

A cross-linked network is obtained by an end-group cross-linkable PBI (E-PBI) and 4,4′-diglycidyl (3,3′,5,5′-tetramethylbiphenyl) epoxy resin (TMBP). The formation of the network is proved by FT-IR and gel fraction test. Then, high temperature proton exchange membranes are constructed by incorporating the cross-linked network into poly(2,2′-(1,3-phenylene)-5,5′-bibenzimidazole) (m-PBI). The influences of the end-group cross-linked network on the properties of membranes are studied, such as, phosphonate acid doping ability, thermal stability, mechanical property, oxidative stability and proton conductivity. The E-PBI/TMBP in the membranes contributes to the improvement of acid doping ability, proton conductivity, mechanical properties and oxidative stabilities. The blend membranes with 20–90 wt% E-PBI/TMBP show higher proton conductivity than pristine PBI at 120 °C–180 °C. These results indicate that the end-group cross-linked blend membranes are promising materials as high temperature proton exchange membranes.

A series of novel block sulfonated poly(arylene ether ketone)s containing side-chain groups were synthesized by condensation polymerization and grafting reactions. The structures of the oligomer and the polymers were investigated by 1H NMR after each step. The synthetic process was simple and efficient, and the phase separation of the block polymers between the hydrophobic and the hydrophilic components became more apparent. The thermal stability of the membranes was studied by TGA. The proton conductivity of the Block-15 membrane reached up to 0.246 S cm−1 at 80 °C, which was high enough for practical use. Furthermore, the block membranes showed very strong mechanical properties, water uptake, and resistance to methanol permeability. This study shows that a combination of side chain and block structures are a simple and effective approach to increase the nanophase separation and improve the performance of the proton exchange membranes in fuel cells.

A novel series of naphthalene-based poly(arylene ether ketone) copolymers containing methoxy groups and hexafluoroisopropylidene diphenyl moieties (6F-MNPAEKs) were successfully synthesized by aromatic nucleophilic polycondensation. Chain-type fluorinated and sulfonated naphthalene-based poly(arylene ether ketone) copolymers (6F-SNPAEKs) were subsequently synthesized by demethylation and sulfobutylation. The chemical structures of 6F-SNPAEKs were confirmed by 1 H NMR. The 6F-SNPAEKs in acid form showed excellent thermal stability at elevated temperatures. The 6F-SNPAEK membranes were easily obtained by solution casting and properties for fuel cells were investigated in detail. The water uptake, swelling ratio and proton conductivity increased with degree of sulfonation (DS) and temperature. 6F-SNPAEK-90 showed the highest conductivity of 0.181 S cm −1 at 80 °C. The methanol permeability of the membranes was in the range of 0.238–6.49 × 10 −7 cm 2 s −1 , compared to 1.55 × 10 −6 cm 2 s −1 for Nafion 117. The membranes also showed excellent mechanical properties: the elongation at break was greater than 15%. These results indicate that the 6F-SNPAEK membranes are a promising candidate for use in direct methanol fuel cell (DMFC) applications.

A highly sulfonated poly (ether ether ketone) with pendant amino groups (Am-SPEEK) has been synthesized. The resulting copolymer showed good solubility in common organic solvents. Then the pendant amino groups of the Am-SPEEK were utilized to react with two kinds of cross-linker, epoxy resin and dibromide, to yield various cross-linked membranes. After cross-linking, the membranes could not dissolve in common solvents, just became swollen. In generally, all the cross-linked membranes showed improved mechanical properties and high dimensional stabilities, whereas the uncross-linked membranes highly swollen or even dissolved in water at high temperature. The proton conductivity of the membranes increased with an increase in temperature. At 80 °C, all the cross-linked membranes showed high proton conductivity, in the range of 0.111–0.140 S cm−1. Especially, the TMBP cross-linked membrane showed a proton conductivity of 0.140 S cm−1, which was higher than that of Nafion 117 (0.125 S cm−1). The membranes with high proton conductivity, good oxidative stability, and improved methanol residence have been successfully developed. Furthermore, the influence of different main chain of the cross-linker on the performance of the cross-linked membranes was also investigated.

The epoxy resin with a trifluoromethyl side chain, (3-trifluoromethyl) phenylhydroquinone epoxy resin (3F-PQE), was synthesized via a three-step procedure. The chemical structures were confirmed by FT-IR, 1 H NMR, 13 C NMR and elemental analysis. A series of trifluoromethyl epoxy networks has been prepared with four curing agents: poly (propylene glycol) bis (2-aminopropy) ether (D230), 2-methylimidazole (2MI), 4, 4-methylene-dianiline (DDM) and phthalicacidanhydride (PA). All samples exhibited excellent thermal stabilities (the decomposition temperature of 5% weight loss (Td)) ranged from 335 to 362 °C in N 2 and 291–355 °C in air). The 3F-PQE-DDM sample showed the highest T g of all the samples. Moisture absorption of 3F-PQE-DDM and 3F-PQE-PA at 80 °C for 24 h was no more than 1 wt %. The cured fluorinated epoxy resins exhibited that the contact angles were more than 90°, which is the hydrophobic properties.

In order to enhance the ion exchange capacity (IEC) in the proton exchange membrane materials, a novel sulfonated poly(arylene ether ketone) (SQNPAEK) containing tri-side chains in one unit is synthesized by direct polymerization. The SQNPAEK membrane shows excellent proton conductivity up to 0.102S cm(-1) at 80 degrees C, which are superior to previous side-chain-type and main-chain-type sulfonated polymer membranes at similar IEC. Cross-linked membranes are then obtained by a heating reaction at 190 degrees C, using 4,4'-diglycidyl (3,3',5,5'-tetramethylbiphenyl) epoxy resin (TMBP) as the cross-linker. As expected, the water uptake and the methanol permeability of the cross-linked membranes decrease with increasing the content of TMBP. Compared to Nation 117, the cross-linked membranes show comparable proton conductivities and much higher selectivities, which are in the range of 5.18 x 10(5)-1.46 x 10(6) S s(-1) cm(3). Other properties of the cross-linked membranes, such as mechanical properties, thermal properties, are also investigated. All the results indicated that the cross-linked membranes based on SQNPAEKs and TMBP are promising candidate for direct methanol fuel cells. (C) 2011 Elsevier B.V. All rights reserved.

A diamine-terminated polybenzimidazole oligomer (o-PBI) has been synthesized for introducing the benzimidazole groups (BI) into sulfonated poly(ether ether ketone) (SPEEK) membranes. SPEEK/o-PBI/4,4′-diglycidyl(3,3′,5,5′-tetramethylbiphenyl) epoxy resin (TMBP) composite membranes in situ polymerization has been prepared for the purpose of improving the performance of SPEEK with high ion-exchange capacities (IEC) for the usage in the direct methanol fuel cells (DMFCs). The composite membranes with three-dimensional network structure are obtained through a cross-linking reaction between PBI oligomer and TMBP and the acid–base interaction between sulfonic acid groups and benzimidazole groups. Resulting membranes show a significantly increasing of all of the properties, such as high proton conductivity (0.14 S cm−1 at 80 °C), low methanol permeability (2.38 × 10−8 cm2 s−1), low water uptake (25.66% at 80 °C) and swelling ratio (4.11% at 80 °C), strong thermal and oxidative stability, and mechanical properties. Higher selectivity has been found for the composite membranes in comparison with SPEEK. Therefore, the SPEEK/o-PBI/TMBP composite membranes show a good potential in DMFCs usages.

A series of novel composites based on different ratios of epoxidised cresol novolac (ECN) and 4,4′-diglycidyl(3,3′,5,5′-tetramethylbiphenyl) epoxy resin (TMBP) have been prepared with the curing agent 4,4′-methylenediamine (DDM) and 4,4′-diaminodiphenylsulfone (DDS), respectively. The investigation of cure kinetics was performed by differential scanning calorimetry using an isoconversional method. The high thermal stabilities of the cured samples were also studied by thermogravimetric analysis. In addition, no phase separation was observed for cured ECN/DDM and ECN/DDS blending with different amounts of TMBP by dynamic mechanical analysis and scanning electron microscopy. Moreover, the cured systems also exhibited excellent impact properties and low moisture absorption. All the results indicate that the ECN/TMBP/DDM and ECN/TMBP/DDS systems are promising materials in electronic packaging. Copyright © 2011 Society of Chemical Industry

A bisphenol monomer (2,5-dimethoxy)phenylhydroquinone was prepared and further polymerized to obtain poly(arylene ether ketone) copolymers containing methoxy groups. After demethylation and sulfobutylation, a series of novel poly(arylene ether ketone)s bearing pendant sulfonic acid group (SPAEKs) with different sulfonation content were obtained. The chemical structures of all the copolymers were analyzed by 1H NMR and 13C NMR spectra. Flexible and tough membranes with reasonably good mechanical properties were prepared. The resulting side-chain-type SPAEK membranes showed good dimensional stability, and their water uptake and swelling ratio were lower than those of conventional main-chain-type SPAEK membranes with similar ion exchange capacity. Proton conductivities of these side-chain-type sulfonated copolymers were higher than 0.01 S/cm and increased gradually with increasing temperature. Their methanol permeability values were in the range of 1.97 × 10−7–5.81 × 10−7 cm2/s, which were much lower than that of Nafion 117. A combination of suitable proton conductivities, low water uptake, low swelling ratio, and high methanol resistance for these side-chain-type SPAEK films indicated that they may be good candidate material for proton exchange membrane in fuel cell applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Poly(ether ether ketone) (PEEK) and sulfonated poly(ether ether ketone) (SPEEK, IEC = 2.07 mequiv.g −1 ) have been synthesized via nucleophilic aromatic substitution reaction. Bromomethylated poly(ether ether ketone) (PEEK-Br) is then prepared and reacted with 2-benzimidazolethiol to obtain the benzimidazole grafted poly(ether ether ketone) (PEEK-BI). The structures of PEEK-Br and PEEK-BI are characterized by 1 H NMR spectra. Composite membranes based on SPEEK and PEEK-BI are prepared and their properties used for fuel cells are studied in detail. The results show that the composite membranes exhibit greatly improved mechanical properties as well as reduced water uptake and methanol permeability compared with the pristine SPEEK membrane. The increased oxidative stability and selectivity indicate that the composite membranes are promising to be used as proton exchange membranes.

Sulfonated poly(arylene ether ketone) bearing pendant carboxylic acid group (C-SPAEK) had been prepared for direct methanol fuel cell applications, and subsequently cross-linked by a thermal curing reaction using hexafluoro-bisphenol-A novolac epoxy resin (HFANER) as a cross-linker. The cross-linked network structure caused significant enhancement in the mechanical properties and oxidative stability. Meanwhile, water uptake, swelling ratio and methanol permeability substantially decreased with increasing the content of cross-linker. Notably, the water uptake of C-SPAEK was 506.9% at 80 °C, but after cross-linking, Cr-SPAEK-17 exhibited a water uptake of 32.3%. Meanwhile, a 12.1% of swelling ratio was obtained which was lower than that of Nafion 117 (17.2%). Although the proton conductivities of the cross-linked membranes were lower than that of the pristine membrane, the higher selectivity defined as the proton conductivity to methanol permeability was obtained for the cross-linked membranes.

Novel self-crosslinked alkaline anion exchange membranes with high alkaline stability, excellent dimensional stability and extraordinary methanol resistance were synthesized successfully without using any catalyst or a separate crosslinker.