Sulfonated Polyimide Research Articles

Novel acid–base polyimides synthesized from binaphthalene dianhydrie and triphenylamine-containing diamine as proton exchange membranes

The synthesis and characterization of novel acid–base polyimide membranes for the use in polymer electrolyte membrane fuel cell is presented in this paper. The sulfonated polyimides (SPIs) bearing basic triphenylamine groups were easily synthesized using 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride (BTDA), sulfonated diamine of 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODADS), and nonsulfonated diamines of 4,4′-diaminotriphenylamine (DATPA). The effects of the structure of the dianhydride and diamines on the properties of SPI membranes were evaluated through the study of membrane parameters including water sorption, proton conductivity, water stability, dimensional changes, and methanol permeability. It was found that the BTDA-based sulfonated polyimides displayed much better hydrolytic stability than 1,4,5,8-naphthalenecarboxylic dianhydride (NTDA)-based polyimides. This is because the former has a decreased positive charge density in the imido rings compared to the latter ones. Furthermore, the present SPI membranes also displayed much better resistance to swelling than these without DATPA due to the strong interchain interaction through basic triphenylamine functions and sulfonic acid groups. The SPI membrane with IEC value of 2.21 mequiv./g shows the proton conductivity of 0.11 S/cm at 20 °C which is higher than Nafion 117 (0.09 S/cm at 20 °C). Moreover, the SPI membranes exhibited excellent mechanical properties and decreased methanol permeability.

Sulfonated polyimide membranes grafted with sulfoalkylated side chains for proton exchange membrane fuel cell (PEMFC) applications

Grafted sulfonated polyimide (SPI) membranes for use as proton-conducting polymer electrolytes for fuel cells were obtained using a fabrication method comprised of thermal-solution imidization and subsequent incorporation of sulfoalkylated grafting agents with different alkyl chain lengths. The additional sulfonic acid (–SO 3H) groups in the sulfoalkylated side chains of the grafted SPI membranes significantly contributed to enhancing ion exchange capacity (IEC) and proton conductivity, leading to excellent electrochemical single-cell performance. Simultaneously, the alkyl groups in the side chain functioned as an internal plasticizer, resulting in an approximate sevenfold improvement in ductility of the grafted SPI as compared to pristine SPI. Interestingly, grafted SPI with long side chains exhibited lower IEC than that with short side chains. However, a relatively high number of water molecules per –SO 3H group and a large amount of bound water caused the SPI membrane grafted with long side chains to have high proton conductivity. Also, the low acidity of the SPI grafted with long side chains leads to improved membrane durability to chemical attacks, such as hydrolysis and radical-induced decomposition. Initially, the electrochemical performance of the grafted SPI membranes was superior to that of Nafion 117, whereas after a long duration for 1100 h in hot water, the single-cell performance of the grafted SPI membranes diminished below that of Nafion 117, indicating a strong dependency of electrochemical performance with membrane stability.

Synthesis and properties of novel sulfonated polyimides derived from naphthalenic dianhydride for fuel cell application

A series of sulfonated polyimides (SPI) ionomers were synthesized from a new flexible dianhydride of 4,4′-ketone dinaphthalene 1,1′,8,8′-tetracarboxylic dianhydride (KDNTDA), a sulfonated diamine of 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid and nonsulfonated diamines including dimethylsiloxane oligomer-based diamine. KDNTDA-based SPIs displayed good solubility in common aprotic solvents, which would provide an advantage of easy processing, being different from SPIs derived from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA). They showed reasonably high proton conductivities and anisotropic membrane swelling with 2–3 times larger swelling in thickness than in plane. KDNTDA-based SPIs displayed slightly lower water stability than that of NTDA-based ones. On the other hand, the branched/crosslinked KDNTDA-based SPI membrane displayed higher water stability and kept high mechanical property and proton conductivity even after the aging in water at 130 °C for 300 h.

New poly(ethylene oxide) soft segment-containing sulfonated polyimide copolymers for high temperature proton-exchange membrane fuel cells

The synthesis and characterization of a series of new poly(ethylene oxide) (PEO) soft segment-containing six-member ring sulfonated polyimide (SPI) copolymers are described in this paper. One-step high temperature polymerization method was used to prepare the SPI copolymers from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), 4,4′-diaminostilbene-2,2′-disulfonic acid (DSDSA), and diamine-terminated poly(ethylene oxide) (PEO-diamine, MW = 1000). The relative ratio of the sulfonic acid-containing hard segments to the PEO-containing soft segments was controlled through varying the molar ratio of DSDSA to PEO-diamine. Flexible, transparent, and mechanically strong free-standing membranes were successfully obtained. The membranes were characterized with ion-exchange capacity, Fourier transform infrared spectra, thermogravimetric analysis, water sorption, proton conductivity, and fuel cell performance measurements. The results showed that the new SPI membranes exhibited desirable mechanical properties and thermal stability as well as better proton conductivities than Nafion ® 115 at high relative humidity (RH) levels (>50%) at both 70 and 120 °C. The results from the fuel cell performance measurements indicated that the SPI membrane containing 5 mol% (12.4 wt.%) PEO soft segments had similar fuel cell performance as Nafion ® 112 at 70 °C and 80% RH, but better fuel cell performance than Nafion ® 112 when the current density was higher than 0.32 A/cm 2 at 120 °C and 50% RH.

Sulfonated polyimides bearing benzimidazole groups for proton exchange membranes

A series of sulfonated polyimides containing benzimidazole groups were synthesized using 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride (BTDA), 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODADS) as the sulfonated diamine, and 2-(3′,5′-diaminophenyl)benzimidazole (a) or 6,4′-diamino-2-phenylbenzimidazole (b) as the nonsulfonated diamine. The electrolyte properties of the synthesized polyimides (Ia−x, Ib−x, x refers to molar percentage of the sulfonated diamine) were investigated and compared with those of polyimides (Ic−x) from BTDA, ODADS, and m-phenylenediamine (c). All synthesized polyimides possessed high molecular weights revealed by their high viscosity, and formation of tough and flexible membranes. Polyimides with benzimidazole groups exhibited much better swelling capacity than those without benzimidazole groups. This was attributed to the strong interchain interaction through basic benzimidazole functions and sulfonic acid groups. The sulfonated polyimides that are incorporated with 1,1′,8,8′-binaphthalimide exhibited better hydrolytic stability than that with 1,4,5,8-naphthalimide. Polyimide membranes with good water stability as well as high proton conductivity were developed. Polyimide membrane (Ia−90), for example, did not lose mechanical properties after being soaked in boiling water for 1000h, while its proton conductivity was still at a high level (compared to that of Nafion 117).

Synthesis and characterization of novel sulfonated polyimide containing phthalazinone moieties as PEM for PEMFC

A novel sulfonated diamine monomer, 1,2-dihydro-2-(3-sulfonic-4-aminophenyl)-4-[4-(4-aminophenoxy)-phenyl]phthalazin-1-one (S-DHPZDA), was successfully synthesized by direct sulfonation of diamine 1,2-dihydro-2-(4-aminophenyl)-4-[4-(4-aminophenoxy)-phenyl]-phthalazin-1-one (DHPZDA). A series of sulfonated polyimides (SPIs), which can be used as the material of the proton exchange membrane (PEM) for the proton exchange membrane fuel cell (PEMFC), were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), S-DHPZDA, and nonsulfonated diamines DHPZDA. The structure of the monomer and polymers were characterized by FT-IR and 1H NMR. The solubility of the S-DHPZDA-based SPIs has been improved due to the induction of the phthalazione moiety. The SPIs membranes have high thermo-stability, predominant swelling resistance with high ion exchange capacity.

Preparation and evaluation of a proton exchange membrane based on oxidation and water stable sulfonated polyimides

A series of novel oxidation and water stable sulfonated polyimides (SPIs) were synthesized from 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride (BTDA), and wholly aromatic diamine 2,2′-bis(3-sulfobenzoyl) benzidine (2,2′-BSBB) for proton exchange membrane fuel cells. These polyimides could be cast into flexible and tough membranes from m-cresol solutions. The copolymer membranes exhibited excellent oxidative stability and mechanical properties due to their fully aromatic structure extending through the backbone and pendant groups. Moreover, all BTDA-based SPI membranes exhibited much better water stability than those based on the conventional 1,4,5,8-naphthalenecarboxylic dianhydride. The improved water stability of BTDA-based polyimides was attributed to its unique binaphthalimide structure. The SPI membranes with ion exchange capacity (IEC) of 1.36–1.90 mequiv g −1 had proton conductivity in the range of 0.41 × 10 −1 to 1.12 × 10 −1 S cm −1 at 20 °C. The membrane with IEC value of 1.90 mequiv g −1 displayed reasonably higher proton conductivity than Nafion ® 117 (0.9 × 10 −1 S cm −1) under the same test condition and the high conductivity of 0.184 S cm −1 was obtained at 80 °C. Microscopic analyses revealed that well-dispersed hydrophilic domains contribute to better proton conducting properties. These results showed that the synthesized materials might have the potential to be applied as the proton exchange membranes for PEMFCs.

Water resistant sulfonated polyimides based on 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride (BNTDA) for proton exchange membranes

A series of sulfonated polyimides (SPIs) were synthesized in m-cresol from 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride (BNTDA), 4,4′-diaminodiphenylether-2,2-disulfonicacid (ODADS), and 4,4′-diamino-diphenyl ether (ODA) in the presence of triethylamine and benzoic acid. The resulted polyimides showed much better water resistance than the corresponding sulfonated polyimides from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) and ODADS, which is contributed to the higher electron density in the carbonyl carbon atoms of BNTDA. Copolyimides S-75 and S-50 maintained their mechanical properties and proton conductivities after aging in water at 100°C for 800h. The proton conductivity of these SPIs was 0.0250–0.3565S/cm at 20°C and 100% relative humidity (RH), and increased to 0.1149–0.9470S/cm at 80°C and 100% RH. The methanol permeability values of these SPIs were in the range of 0.99–2.36×10−7cm2/s, which are much lower than that of Nafion 117 (2×10−6cm2/s).

Synthesis and properties of sulfonated polyimides from homologous sulfonated diamines bearing bis(aminophenoxyphenyl)sulfone

AbstractThree homologous sulfonated diamines bearing a bis(aminophenoxyphenyl)sulfone structure, namely, bis[4‐(4‐aminophenoxy)phenyl]sulfone‐3,3′‐disulfonic acid (pBAPPS‐3DS), bis[4‐(4‐aminophenoxy)phenyl]sulfone‐2,2′‐disulfonic acid (pBAPPS‐2DS), and bis[4‐(4‐aminophenoxy)‐2‐(3‐sulfobenzoyl)phenyl]sulfone (pBAPPS‐2DSB), were synthesized. A series of sulfonated polyimides (SPIs) were synthesized from 1,4,5,8‐naphthalene tetracarboxylic dianhydride, these sulfonated diamines, and nonsulfonated diamines, and their properties were investigated in comparison with those reported for the SPIs from another homologous diamine or bis[4‐(3‐aminophenoxy)phenyl]sulfone‐3,3′‐disulfonic acid (mBAPPS‐3DS). These SPIs were soluble in common aprotic solvents and showed reasonably high proton conductivity, except for pBAPPS‐2DS‐based SPIs, the conductivity of which was slightly lower because of the lower water uptake. The water stability of these SPIs considerably depended on the structure of the sulfonated diamines and was in the order of pBAPPS‐2DSB ≈ pBAPPS‐2DS > pBAPPS‐3DS ≫ mBAPPS‐3DS. Their water stability was much lower than that of the SPIs from 4,4′‐bis(4‐aminophenoxy)biphenyl‐3,3′‐disulfonic acid. The reason was discussed on the basis of the basicity of the sulfonated diamine and the solubility property of the SPIs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2797–2811, 2007

Water-resistant humidity sensors based on sulfonated polyimides

Abstract Sulfonated polyimides (SPIs) derived from 1,4,5,8-naphthalenetetracarboxiylic dianhydride (NTDA) and different sulfonated diamines were tested as humidity-sensing membranes. Surface-resistance-type humidity sensors were prepared by dip-coating a SPI solution onto comb-shaped electrodes on ceramic substrates, and their sensor properties were investigated. The SPI in triethylammonium form derived from NTDA and 4,4′-bis(4-aminophenoxy)-biphenyl-3,3′-disulfonic acid was the most suitable for the humidity sensor from the view points of easy fabrication, higher conductivity and better adhesion property between membrane and substrate. The pretreatment of the substrates with an amine-type silane-coupling reagent significantly improved the water stability of the sensors. They displayed excellent durability against water, heat, high temperature and high humidity, heat-shock and dewy atmosphere. The relationship of the resistance ( R ) versus relative humidity ( RH ) was stably reproduced after the severe durability tests, which the conventional polymer sensors could not stand for. The SPI sensors showed a fast 90% response time of about 1 min for the humidification from 30%RH to 90%RH but a fairly slow one of about 4 min for the dehumidification from 90%RH to 30%RH at 25 °C. They showed fairly large hysterisis of 5–6%RH in the R versus RH relationship between humidification and dehumidification runs. The 90% response time was fast at 75 °C, but the hysterisis improved only slightly. They have high potential of the applications for bathroom fans and laundry driers, where the high durability against dewy atmosphere or high temperature and high humidity is essentially required rather than the quick response.

Characterizations and stability of polyimide–phosphotungstic acid composite electrolyte membranes for fuel cell

Organic–inorganic composite membranes from partially aliphatic sulfonated polyimides and heteropolyacids (HPAs) were synthesized. A series of composite membranes with varying amounts of heteropolyacid were prepared by altering the weight ratio of polyimide and HPA. The partially aliphatic sulfonated polyimides are synthesized from 1,4,5,8-naphthalenetetracarboxylic dianhydride, 4,4′-diaminobiphenyl 2,2′-disulfonic acid as the sulfonated diamine, and decamethylenediamine as the aliphatic diamine. The incorporation of HPA is confirmed by FT-IR analyses. When appropriately embedded in a hydrophilic polymer matrix, the hydrated HPAs are expected to endow the composite membrane with their high proton conductivity, while retaining the desirable mechanical properties of the polymer film. These composite membranes were evaluated for thermal stability, ion exchange capacity, water uptake and proton conductivity. Also the extraction of HPA from the polyimide membranes and their stability in water were determined. Though water uptake and IEC decreased with increase in HPA content, the proton conductivity of the composite membranes increased with increase in HPA weight content. This study shows that partially aliphatic sulfonated polyimide composite membranes with HPA can be a viable substitute for Nafion ® for fuel cells which show good conductivity comparable to Nafion ®117 at temperatures nearing 100 °C, keeping in mind that polyimides have good thermal stability and low cost.

Synthesis and properties of novel sulfonated polyimide membranes for direct methanol fuel cell application

Two sulfonated diamine monomers, 4,4′-bis(4-aminophenoxy)benzophenone-3,3′-disulfonic acid (BAPBPDS) and 4,4′-bis(4-aminophenylthio)benzophenone-3,3′-disulfonic acid (BAPTBPDS), were synthesized via two-step reactions and a series of sulfonated polyimides (SPIs) were prepared from these sulfonated diamines, 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) and common non-sulfonated diamines via conventional one-step polymerization approach. The resulting SPIs showed good solubility, high thermal stability, high proton conductivity (comparable to that of Nafion 112) and rather low methanol permeability (one-fifth to one-tenth of that of Nafion 112). BAPTBPDS-based SPI membranes displayed better water stability than BAPBPDS-based ones because of the higher basicity of BAPTBPDS moiety.

Synthesis and characterization of rigid-rod sulfonated polyimides bearing sulfobenzoyl side groups as proton exchange membranes

A novel wholly aromatic diamine, 2,2′-bis(3-sulfobenzoyl)benzidine (2,2′-BSBB), was successfully prepared by the reaction of 2,2′-dibenzoyl-benzidine (2,2′-DBB) with fuming sulfuric acid. Copolymerization of 1,4,5,8-naphathlenetetracarboxylic dianhydride with 2,2′-BSBB and 2,2′-DBB generated a series of rigid-rod sulfonated polyimides. The synthesized copolymers with the –SO 3H group on the side chain of polymers possessed high molecular weights revealed by their high viscosity and the formation of tough and flexible membranes. The copolymer membranes exhibited excellent oxidative stability and mechanical properties due to their fully aromatic structure extending through the backbone and pendent groups. They displayed clear anisotropic membrane swelling in water with negligibly small dimensional changes in the plane direction of the membrane. The proton conductivities of copolymer membranes increased with increasing IEC and temperature, reaching value above 1.25 × 10 −1 S/cm at 20 °C, which is higher than that of Nafion ® 117 at the same measurement condition. They displayed reasonably high proton conductivity due to the higher acidity of benzoyl sulfonic acid group, the larger interchain spacing, which is available for water to occupy, taking their lower water uptake (WU) into account. Consequently, these materials proved to be promising as proton exchange membrane.

Sulfonated polyimide and poly (ethylene glycol) diacrylate based semi‐interpenetrating polymer network membranes for fuel cells

AbstractSemi‐interpenetrating polymer network (semi‐IPN) membranes based on novel sulfonated polyimide (SPI) and poly (ethylene glycol) diacrylate (PEGDA) have been prepared for the fuel cell applications. SPI was synthesized from 1,4,5,8‐naphthalenetetracarboxylic dianhydride, 4,4′‐diaminobiphenyl 2,2′‐disulfonic acid, and 2‐bis [4‐(4‐aminophenoxy) phenyl] hexafluoropropane. PEGDA was polymerized in the presence of SPI to synthesize semi‐IPN membranes of different ionic contents. These membranes were characterized by determining, ion exchange capacity, water uptake, water stability, proton conductivity, and thermal stability. The proton conductivity of the membranes increased with increasing PEGDA content in the order of 10−1 S cm−1 at 90°C. These interpenetrating network membranes showed higher water stability than the pure acid polyimide membrane. This study shows that semi‐IPN SPI membranes based on PEGDA which gives hydrophilic group and structural stability can be available candidates comparable to Nafion® 117 over 70°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Distribution profile of water and suppression of methanol crossover in sulfonated polyimide electrolyte membrane for direct methanol fuel cells

We have developed novel cross-linked sulfonated polyimide (c-SPI) membrane as an electrolyte for direct methanol fuel cells (DMFCs). When the DMFC using the c-SPI membrane (thickness = 155 μm), Pt–Ru dispersed on carbon black (Pt–Ru/CB) anode and Pt/CB cathode with a Nafion ® ionomer was operated at 80 °C and 0.1 A cm −2 with 1 M CH 3OH and oxygen (oxidant), the methanol crossover rate, j(CH 3OH), was suppressed to about 1/2 compared with that of the Nafion ® 117 membrane (thickness = 180 μm) with the same electrodes. It was found for both cells that the j(CH 3OH) was not so small as expected from the membrane thickness. In order to obtain a clue for the suppression of j(CH 3OH), the distribution profiles of water (containing CH 3OH) in thickness direction were investigated by measuring the specific resistances ( ρ) between Pt probes inserted into the electrolyte membrane. Values of ρ at the anode side were low irrespective of the discharge current density, because such a part of the membrane was humidified thoroughly by liquid water (1 M CH 3OH) allowing free penetration of CH 3OH into the swollen polymer. In contrast, the values of ρ at the cathode side were high at the low current density due to drying of the membrane contacting with oxidant gas (O 2 or air) in low humidity. We have succeeded to suppress the j(CH 3OH) further (about 1/2 at 0.2 A cm −2) by using bilayer c-SPI, having a low ion exchanging (low swelling) barrier layer at the anode side without increasing the ohmic resistance, compared with that of the single c-SPI.

Sulfonated polyimide/PTFE reinforced membrane for PEMFCs

A sulfonated polyimide (SPI)/PTFE reinforced membrane was synthesized by impregnating PTFE (porous polytetrafluoroethylene) membrane with a SPI/DMSO solution. The resulting composite membrane was mechanically durable and quite thin relative to traditional perfluorosulfonated ionomer membranes (PFSI). We expect the PTFE to restrict the swelling and dimensional change of the SPI when it is immersed into water. And the reinforcement with PTFE can increase the hydrolysis stability of the SPI due to the low swelling and low dimensional change. From ex-situ testing and a short term fuel cell “life” test, we conclude that the PTFE reinforced sulfonated polyimide had a higher hydrolytic stability than pure sulfonated polyimide. The thin SPI/PTFE membrane showed comparable fuel cell performance with the commercial NRE-212 membrane with H 2/O 2 at 80 °C under fully humidified conditions. The chemically modified membrane with Nafion layer showed good stability in a 120 h fuel cell test.

Synthesis and properties of novel sulfonated polyimides bearing sulfophenyl pendant groups for polymer electrolyte fuel cell application

A novel sulfonated diamine bearing sulfophenyl pendant groups of 2,2′-(4-sulfophenyl) benzidine (BSPhB) was synthesized. Sulfonated polyimides (SPIs) derived from 1,4,5,8-naphthalene tetracarboxylic dianhydride, BSPhB and other non-sulfonated diamines were successfully synthesized. The SPIs with ion exchange capacity (IEC) of 1.5–2.8meqg−1 showed high reduced viscosity of 3–10dLg−1 and high desulfonation temperature of 320°C. The SPI membranes were tough and flexible, having high stress at break of more than 80MPa and elongation of 80–100%. They showed highly anisotropic membrane swelling in water with larger swelling in thickness direction than in plane direction. They showed fairly high proton conductivity (σ). For example, the membrane with IEC of 1.77meqg−1 exhibited σ values of 120 and 260mScm−1 at 60 and 120°C, respectively, in water. They also showed fairly high water stability.

Novel Preparation Method of Cross-linked Sulfonated Polyimide Membranes for Fuel Cell Application

Abstract A facile cross-linking method has been successfully developed for sulfonated polyimide (SPI) membranes. The SPIs with electron-rich phenyl rings in the non-sulfonated diamine moiety were readily cross-linked by immersing the membranes into a solution of phosphorous pentoxide and methanesulfonic acid at 30–80 °C. The resulting SPI membranes cross-linked via sulfonyl groups showed greatly improved water stability compared with the uncross-linked ones, while high proton conductivity was maintained. They have potential for fuel cells at high temperatures above 80 °C.

A facile approach for the preparation of cross-linked sulfonated polyimide membranes for fuel cell application

A facile approach has been successfully developed for the preparation of a series of cross-linked sulfonated polyimide (SPI) membranes via the condensation reaction between the sulfonic acid groups and the activated hydrogen atoms of SPIs in the presence of phosphorous pentoxide : methanesulfonic acid in the ratio of 1 : 10 by weight (PPMA, method 1) or phosphorous pentoxide only (method 2). The resulting sulfonyl linkages are very stable and the cross-linked SPI membranes showed greatly improved water stability in comparison with the uncross-linked ones while high proton conductivity was maintained.

Novel multilayer Nafion/SPI/Nafion composite membrane for PEMFCs

A novel multilayer membrane for the proton exchange membrane fuel cell (PEMFC) was developed. Nafion was dispersed uniformly onto both sides of the sulfonated polyimide (SPI) membrane. The Nafion/SPI/Nafion composite membrane was prepared by immersing the SPI into the Nafion-containing casting solution. Through immersing both membranes into the Fenton solution at 80 °C for 0.5 h for an accelerated ex situ test, chromatographic analysis of the water evacuated from the cathode and the anode of the cells and a durability test of a single proton exchange membrane fuel cells, it was proved that the stability of the composite membrane has been greatly improved by adding the Nafion layer compared with the SPI membrane. The fuel cell performance with the SPI and Nafion/SPI/Nafion membranes was similar to the performance with the commercial product Nafion ® NRE-212 membrane at 80 °C.