Synthesis and properties of novel sulfonated (co)polyimides bearing sulfonated aromatic pendant groups for PEFC applications

Novel sulfonated diamines bearing aromatic pendant groups, namely, 3,5‐diamino‐3′‐sulfo‐4′‐(4‐sulfophenoxy) benzophenone (DASSPB) and 3,5‐diamino‐3′‐sulfo‐4′‐(2,4‐disulfophenoxy) benzophenone (DASDSPB), were successfully synthesized. Novel side‐chain‐type sulfonated (co)polyimides (SPIs) were synthesized from these two diamines, 1,4,5,8‐naphthalene tetracarboxylic dianhydride (NTDA) and nonsulfonated diamines such as 4,4′‐bis(3‐aminophenoxy) phenyl sulfone (BAPPS). Tough and transparent membranes of SPIs with ion exchange capacity of 1.5–2.9 meq g^?1 were prepared. They showed good solubility and high thermal stability up to 300 °C. They showed isotropic membrane swelling in water, which was different from the main‐chain‐type and sulfoalkoxy‐based side‐chain‐type SPIs. The relative humidity (RH) and temperature dependence of proton conductivity were examined. At low RH, the novel SPI membranes showed much higher conductivity than the sulfoalkoxy‐based SPIs. They showed comparable or even higher proton conductivity than Nafion 112 in water at 60 °C (>0.10 S cm^?1). The membrane of NTDA‐DASDSPB/BAPPS (1/1)‐s displayed reasonably high proton conductivities of 0.05 and 0.30 S cm^?1 at 50 and 100% RH, respectively, at 120 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2862–2872, 2006     

Preparation of new membranes based on sulfonated aromatic copolyimides

New sulfonated aromatic copolyimides with controlled degree of sulfonation were prepared via polycondensation reactions of a sulfonated diamine and two unsulfonated diamines with 1,4,5,8‐naphthalene tetracarboxylic dianhydride (NDA). The sulfonated diamine 3,3′‐disulfonic acid‐ bis[4‐(5‐amino‐1‐naphthoxy)phenyl]sulfone (DANPS) was synthesized through nucleophilic substitution reaction of 5‐amino‐1‐naphthol with disodium‐3,3′‐disulfonate‐4,4′‐dichlorodiphenysulfone (SDCDPS) and subsequent acidification. Two unsulfonated diamines 4,4′‐(5‐amino‐1‐naphthoxy)diphenylsulfone (ANDS) and 4,4′‐(4‐aminophenoxy)diphenylsulfone (APDS) were prepared by nucleophilic reaction of 5‐amino‐1‐naphthol and 4‐aminophenol with 4,4′‐dichlorodiphenylsulfone in the presence of potassium carbonate, respectively. After characterization of the monomers and polymers with common methods, the physical properties of the polymers including thermal behavior and stability, viscosity, molecular weight, and ion exchange capacity (IEC) were studied. The polymers showed high thermal stability and ion exchange capacity which were the basic requirements for application as fuel cell membranes. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and properties of novel sulfonated polyimides from 2,2′‐bis(4‐aminophenoxy)biphenyl‐5,5′‐disulfonic acid

Novel sulfonated polyimides (SPIs) were prepared from 1,4,5,8‐naphthalenetetracarboxylic dianhydride (NTDA), 2,2′‐bis(4‐aminophenoxy)biphenyl‐5,5′‐disulfonic acid (oBAPBDS) with nonlinear configuration, and common nonsulfonated diamines. Water uptake (WU) in liquid and vapor, water stability, and proton conductivity σ of the resulting SPI membranes were investigated. They were soluble in m‐cresol and dimethylsulfoxide, and their WUs in liquid were much larger than those of the SPIs from other sulfonated diamines with linear configuration such as 4,4′‐bis(4‐aminophenoxy)biphenyl‐3,3′‐disulfonic acid (BAPBDS). NTDA‐oBAPBDS membrane was soluble in water at room temperature, whereas all the oBAPBDS‐based copolyimide membranes were insoluble in water and maintained mechanical strength after being soaked in distilled water at 80 °C for 40–1000 h. This much improved water stability was due to the enhanced solubility stability of membrane toward water. The water vapor sorption isotherms were rather similar between the SPIs with the nonlinear and linear configurations of sulfonated diamine moieties. The present SPIs with IECs of 1.8–2.6 meq/g, including NTDA‐BAPBDS, showed reasonably high proton conductivities under the highly humid conditions and roughly fell on the same σ–WU relation line. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1432–1440, 2004     

Sulfonated naphthalene dianhydride based polyimide copolymers for proton‐exchange‐membrane fuel cells. I. Monomer and copolymer synthesis

A novel sulfonated diamine, 3,3′‐disulfonic acid‐bis[4‐(3‐aminophenoxy)phenyl]sulfone (SA‐DADPS), was prepared from m‐aminophenol and disodium‐3,3′‐disulfonate‐4,4′‐dichlorodiphenylsulfone. The conditions necessary to synthesize and purify SA‐DADPS in high yields were investigated in some detail. This disulfonated aromatic diamine, containing ether and sulfone linkages, was used to prepare N‐methyl‐2‐pyrrolidinone‐soluble, six‐membered ring polyimide copolymers containing pendent sulfonic acid groups by a catalyzed one‐step high‐temperature polycondensation in m‐cresol. These materials showed much improved hydrolytic stability with respect to phthalimides. High‐molecular‐weight film‐forming statistical copolymers with controlled degrees of disulfonation were prepared through variations in the stoichiometric ratio of disulfonated diamine (SA‐DADPS) in its soluble triethylamine salt form to several unsulfonated diamines. Three unsulfonated diamines, bis[4‐(3‐aminophenoxy)phenyl] sulfone, 4,4′‐oxydianiline, and 1,3‐phenylenediamine, were used to prepare the copolymers. The characterization of the copolymers by ¹H NMR, Fourier transform infrared, ion‐exchange capacity, and thermogravimetric analysis demonstrated that SA‐DADPS was quantitatively incorporated into the copolymers. Solution‐cast films of the sulfonated copolymers were prepared and afforded tough, ductile membranes with high glass‐transition temperatures. Methods were developed to acidify the triethylammonium salt membranes into their disulfonic acid form, this being necessary for proton conduction in a fuel cell. The synthesis and characterization of these materials are described in this article. Future articles will describe the performance of these copolymers as proton‐exchange membranes in hydrogen/air and direct methanol fuel cells. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 862–874, 2004     

Structure–property correlations of sulfonated polyimides. I. Effect of bridging groups on membrane properties

A series of six‐membered sulfonated polyimides were synthesized using 1,4,5,8‐naphthalenetetracarboxylic dianhydride, 4,4′‐diaminobiphenyl 2,2′‐disulfonic acid as the sulfonated diamine, and various nonsulfonated diamine monomers having different bridging groups. These bulky bridging groups have the capacity to increase hydrolytic stability and proton conductivity. Polyimides with bulky bridging groups showed increased solubility but exhibited lower thermal stability. The ion exchange capacity and water uptake reduced with increase in the bulkiness of the bridging group. This was attributed to the increase in the molecular weight of the repeating unit and hence effectively reduced the sulfonic acid content. In low temperatures, the conductivity was lower than Nafion®115 and, with increase in temperature, the conductivity rapidly increased and exhibited better conductivity than Nafion®115. Polyimides with bulky bridging groups 4‐amino phenyl sulfone, and 2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane showed higher conductivity than other polyimides and Nafion®115 despite low ion exchange capacity. The hydrolytic stability of the polyimides with bulky bridging groups was higher than the polyimides with less bulky atoms because of the imparted flexibility. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3612–3620, 2004     

Effects of tetracarboxylic dianhydrides on the properties of sulfonated polyimides

A series of sulfonated polyimides (SPIs) were synthesized from a sulfonated diamine of 4,4′‐bis(4‐aminophenoxy) biphenyl‐3,3′‐disulfonic acid (BAPBDS), common nonsulfonated diamines, and various tetracarboxylic dianhydrides including 1,4,5,8‐naphthalene tetracarboxylic dianhydride (NTDA), 3,4,9,10‐perylene tetracarboxylic dianhydride (PTDA), 4,4′‐binaphthyl‐1,1′,8,8′‐tetracarboxylic dianhydride (BTDA), 4,4′‐ketone dinaphthalene 1,1′,8,8′‐tetracarboxylic dianhydride (KDNTDA), and isophthatic dinaphthalene 1,1′,8,8′‐tetracarboxylic dianhydride (IPNTDA). Their membrane properties were investigated to clarify the effects of the dianhydrides. They displayed reasonably high mechanical properties, thermal stability, and proton conductivity. The dianhydrides with flexible and non‐coplanar structure (IPNTDA > KDNTDA > BTDA) led to the better solubility of the SPIs than those with rigid and coplanar one (NTDA, PTDA). The dianhydride with the smaller molecular weight led to the larger value of the number of sorbed water molecules per sulfonic acid group (λ) in membrane, that is, NTDA (λ: 17) > PTDA (15) > BTDA (14) > KDNTDA (12) > IPNTDA (10), and as a result let to the larger proton conductivity in water. All of the BAPBDS‐based SPIs showed the anisotropy in membrane swelling and in proton conductivity, of which the degree hardly depended on the dianhydride moieties. The water stability of SPI membranes against the aging in water at 130 °C for 192 h was in the order, PTDA = NTDA ≧ BTDA > KDNTDA > IPNTDA. The hydrolysis stability of polymer chain was similar between the BTDA‐ and KDNTDA‐based SPIs. These results are discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 905–915, 2010     

Synthesis and properties of highly refractive polyimides derived from fluorene‐bridged sulfur‐containing dianhydrides and diamines

Highly refractive and transparent polyimides (PIs) based on fluorene‐bridged and sulfur‐containing monomers have been developed. An aromatic dianhydride, 4,4′‐[p‐thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA), was polymerized with several fluorene‐containing diamines, including commercially available 9,9′‐bis(p‐aminophenyl)fluorene (APF), 9,9′‐bis[4‐(p‐aminophenoxy)phenyl]fluorene (OAPF), and newly synthesized 9,9′‐bis[4‐(p‐aminophenyl)sulfanylphenyl]fluorene (ASPF) to afford series A PIs. Meanwhile, series B PIs were obtained from a new dianhydride, 4,4′‐[(9H‐fluorene‐9‐ylidene)bis(p‐phenylsulfanyl)]diphthalic anhydride (FPSP) and two aromatic diamines, ASPF and 4,4′‐thiobis[(p‐phenylenesulfanyl)aniline] (3SDA) via a two‐step polycondensation procedure. The PIs exhibit good thermal stabilities, such as relatively high glass transition temperatures in the range of 220–270 °C and high initial thermal decomposition temperatures (T_10%) exceeding 490 °C. The 9,9′‐disubstituted fluorene moieties endow the PI films with good optical transparency. The optical transmittances of the PI films at 450 nm are all higher than 80% for the thickness of about 10 μm. Furthermore, the highly aromatic fluorene moiety and flexible thioether linkages in the molecular chains of the PIs provide them with high refractive indices of 1.6951–1.7258 and small birefringence of 0.0056–0.0070. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1510–1520, 2008     

Structure–property correlations of sulfonated polyimides. II. Effect of substituent groups on membrane properties

A series of sulfonated polyimides with increasing alkyl substituents in the o‐position to diamine were synthesized from 4,4′‐methylene dianiline, 4,4′‐diamine‐3,3′‐dimethyl‐diphenylmethane, and 4,4′‐diamine‐3,5,3′,5′‐tetraethyl‐diphenylmethane using 1,4,5,8‐naphthalenetetracarboxylic dianhydride and perylenetetracarboxylic dianhydride by chemical imidization method. 4,4′‐Diaminobiphenyl 2,2′‐disulfonic acid was used as sulfonated diamine. The variation in the membrane properties with increase in substitution was analyzed. Solubility increased with substitution whereas the thermal stability decreased with increase in substitution. Ion exchange capacity and water uptake reduced with increase in substitution because of the low sulfonic acid content at a particular weight due to the increased molecular weight of the repeating unit. The conductivity of the substituted diamines was higher than the unsubstituted diamines at higher temperature regardless of low ion exchange capacity and water uptake. The increase in conductivity with increase in temperature was more rapid in polyimides than in Nafion®115. Hydrolytic stability of the polyimides with substitution is more than the unsubstituted diamines. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3621–3630, 2004     

Proton conductive polyimide ionomer membranes: Effect of NH,OH, and COOH groups

A new series of sulfonated polyimide (SPI) copolymers containing NH, OH, or COOH groups were synthesized by the polycondensation of 1,4,5,8‐naphthalnetetracarboxylic dianhydride, 3,3′‐bis(sulfopropoxy)‐4,4′‐diaminobiphenyl, and 3‐(4‐aminophenyl)‐5‐(3‐aminophenyl)‐1H‐1,2,4‐triazole (SPI‐8‐m), 3,5‐bis(4‐aminophenyl)‐1H‐1,2,4‐triazole (SPI‐8‐p), 3,6‐diaminocarbazole (SPI‐9), 3,5‐diamino‐1H‐1,2,4‐triazole (SPI‐10), bis(3‐aminopropyl)‐amine (SPI‐11), 2,6‐diaminopurine (SPI‐12), 2,4‐diamino‐6‐hydroxyprymidine (SPI‐13), or 3,5‐bis(4‐aminophenoxy)benzoic acid (SPI‐14). The obtained SPIs were soluble in polar organic solvents and gave tough and flexible membranes by solution casting. The SPI membranes having NH and COOH groups showed high thermal (decomposition temperature ≈200 °C) and mechanical (maximum stress >22 MPa) stability. Introducing NH groups, especially triazole and carbazole groups, was effective in improving proton conductive properties of SPI membranes at low humidity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2846–2854, 2010     

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     

Synthesis and characterization of novel fluorinated polyimides derived from 4,4′‐[2,2,2‐trifluoro‐1‐(3‐trifluoromethylphenyl)ethylidene]diphthalic anhydride and aromatic diamines

A novel fluorinated aromatic dianhydride, 4,4′‐[2,2,2‐trifluoro‐1‐(3‐trifluoromethyl‐phenyl)ethylidene]diphthalic anhydride (TFDA) was synthesized by coupling of 3′‐trifluoromethyl‐2,2,2‐trifluoroacetophenone with o‐xylene under the catalysis of trifluoromethanesulfonic acid, followed by oxidation of KMnO₄ and dehydration. A series of fluorinated aromatic polyimides derived from the novel fluorinated aromatic dianhydride TFDA with various aromatic diamines, such as p‐phenylenediamine (p‐PDA), 4,4′‐oxydianiline (ODA), 1,4‐bis(4‐aminophenoxy)benzene (p‐APB), 1,3‐bis(4‐amino‐phenoxy)benzene (m‐APB), 4‐(4‐aminophenoxy)‐3‐trifluoromethylphenylamine (3FODA) and 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzene (6FAPB), were prepared by polycondensation procedure. All the fluorinated polyimides were soluble in many polar organic solvents such as NMP, DMAc, DMF, and m‐cresol, as well as some of low boiling point organic solvents such as CHCl₃, THF, and acetone. Homogeneous and stable polyimide solutions with solid content as high as 35–40 wt % could be achieved, which were prepared by strong and flexible polyimide films or coatings. The polymer films have good thermal stability with the glass transition temperature of 232–322 °C, the temperature at 5% weight loss of 500–530 °C in nitrogen, and have outstanding mechanical properties with the tensile strengths of 80.5–133.2 MPa as well as elongations at breakage of 7.1–12.6%. It was also found that the polyimide films derived from TFDA and fluorinated aromatic diamines possess low dielectric constants of 2.75–3.02, a low dissipation factor in the range of 1.27–4.50 × 10^?3, and low moisture absorptions <1.3%. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4143–4152, 2004     

Synthesis and characterization of organosoluble ditrifluoromethylated aromatic polyimides

Two novel diamine monomers, 1,4‐bis (4‐aminophenoxy)‐2‐[(3′,5′‐ditrifluoromethyl)phenyl]benzene and 1,4‐bis [2′‐cyano‐3′(4″‐amino phenoxy)phenoxy]‐2‐[(3′,5′‐ditrifluoromethyl)phenyl] benzene, were synthesized from (3,5‐ditrifluoromethyl)phenylhydroquinone. A series of ditrifluoromethylated aromatic polyimides derived from the diamines were prepared through a typical two‐step polymerization method. These polyimides had a high thermal stability, and the temperatures at 10% weight loss were above 507 °C in nitrogen. Most of the polymers showed good solubility in anhydrated 1‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide, N,N‐dimethylformamide, chloroform, and tetrahydrofuran at room temperature. All the polymers formed transparent, strong, and flexible films with tensile strengths of 63.6–95.8 MPa, elongations at break of 5–10%, and Young's moduli of 2.38–2.96 GPa. The dielectric constants estimated from the average refractive indices are 2.69–2.89. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3018–3029, 2005     

New liquid‐crystal alignment agents based on fluorinated polyimides with trifluoromethyl‐substituted benzene or diphenylether in the side chain

Fluorinated copolyimides derived from 4,4′‐oxydiphthalic anhydride (ODPA) with 4,4′‐oxydianline (ODA) and trifluoromethyl‐containing aromatic diamines have been synthesized and characterized. The trifluoromethyl‐containing diamines include 2,4‐diamino‐3′‐trifluoromethylazobenzene, 2,4‐diamino‐1‐[(4′‐trifluoromethylphenoxy) phenyl] aniline, 3,5‐diamino‐1‐[(4′‐trifluoromethylphenoxy) phenyl] benzamide, 3,5‐diamino‐1‐[(3′‐trifluoromethyl) phenyl] benzamide, 1,4‐bis(4′‐aminophenoxy)‐2‐(3′‐trifluoromethylphenyl) benzene, 3,5‐diaminobenzenetrifluoride, 4,4′‐diamino‐4″‐(p‐trifluoromethyl phenoxy) triphenylamine, and 4‐[(4′‐trifluoromethylphenoxy) phenyl]‐2,6‐bis(4″‐aminophenyl)pyridine. Strong and flexible copolyimide films, produced by casting the polyamic acid solution followed by thermal imidization, exhibited great thermal stability and high mechanical properties. The polyimides had an ultraviolet–visible absorption cutoff at 330–340 nm and pretilt angles as high as 20° for nematic liquid crystals, making them great potential candidates for advanced liquid‐crystal display applications. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1583–1593, 2002     

Synthesis and properties of novel sulfonated polyimides containing binaphthyl groups as proton‐exchange membranes for fuel cells

A novel sulfonated diamine monomer, 2,2′‐bis(p‐aminophenoxy)‐1,1′‐binaphthyl‐6,6′‐disulfonic acid (BNDADS), was synthesized. A series of sulfonated polyimide copolymers containing 30–80 mol % BNDADS as a hydrophilic component were prepared. The copolymers showed excellent solubility and good film‐forming capability. Atomic force microscopy phase images clearly showed hydrophilic/hydrophobic microphase separation. The relationship between the proton conductivity and degree of sulfonation was examined. The sulfonated polyimide copolymer with 60 mol % BNDADS showed higher proton conductivity (0.0945–0.161 S/cm) at 20–80 °C in liquid water. The membranes exhibited methanol permeability from 9 × 10^?8 to 5 × 10^?7 cm²/s at 20 °C, which was much lower than that of Nafion (2 × 10^?6cm²/s). The copolymers were thermally stable up to 300 °C. The sulfonated polyimide copolymers with 30–60 mol % BNDADS showed reasonable mechanical strength; for example, the maximum tensile strength at break of the sulfonated polyimide copolymer with 40 mol % BNDADS was 80.6 MPa under high moisture conditions. The optimum concentration of BNDADS was found to be 60 mol % from the viewpoint of proton conductivity, methanol permeability, and membrane stability. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 222–231, 2007     

Locally sulfonated poly(ether sulfone)s with highly sulfonated units as proton exchange membrane

Novel locally sulfonated poly(ether sulfone)s with highly sulfonated units were successfully synthesized for fuel cell applications. Poly(ether sulfone)s were prepared by the nucleophilic substitution of bis(4‐fluorophenyl) sulfone with 1,2,4,5‐tetrakis([1,1′‐biphenyl]‐2‐oxy)‐3,6‐bis(4‐hydroxyphenoxy)benzene and bis(4‐hydroxyphenyl) sulfide, followed by oxidation using m‐chloroperoxybenzoic acid. The desired highly sulfonated units were easily introduced by postsulfonation and each one had ten sulfonic acid groups. The sulfonated polymers gave tough, flexible, and transparent membranes by solvent casting. The high contrast in polarity between highly sulfonated units and hydrophobic poly(ether sulfone) units enabled the formation of defined phase‐separated structures and well‐connected proton paths. The sulfonated polymers exhibited excellent proton conductivity over a wide range of relative humidities. The proton conductivity of the sulfonated polymer with an ion exchange capacity value of 2.38 mequiv/g was comparable to that of Nafion 117 even at 30% relative humidity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3444–3453, 2009     

Synthesis and properties of novel sulfonated polyimides containing phthalazinone moieties for PEMFC

A novel sulfonated diamine, 1,2-dihydro-2-(3-sulfonic-4-aminophenyl)-4-[4-(3-sulfonic-4-aminophenoxy)-phenyl]-phthalazin-1-one(S-DHPZDA), was successfully synthesized and two series of six-membered sulfonated polyimides (SPIs) were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), S-DHPZDA, and nonsulfonated diamines DHPZDA or 4,4′-diaminodiphenyl ether (ODA). The chemical structure of the S-DHPZDA and the SPIs were characterized by ¹H NMR and FT-IR. Tough, brownish and transparent membranes were cast from SPIs’ solution in NMP. The water uptake, swelling ratio, chemical and thermal stability, hydrolytic and oxidative stability as well as proton conductivity of these new polymers were investigated systematically. Compared with Nafions, the obtained SPI membranes have onset decomposed temperatures of these two series SPIs were above 318 °C and decomposed temperature of main chain were 565 °C and excellent dimension stabilities on similar IECs. Introduction of phthalazinone moieties had improved the copolyimides’ solubility in polar aprotic organic solvents like m-cresol, NMP, DMSO, DMF etc. The SPIs had high proton conductivity (σ) in the order of magnitude of 10⁻³ to 10⁻² S cm⁻¹ depending on the degree of sulfonation (DS) of the polymers.     

Substituents effect on the properties of sulfonated polyimide copolymers

A series of sulfonated polyimide (SPI) copolymers containing methyl, methoxy, or fluorine groups were synthesized to elucidate the substituents effect on their proton conducting properties as well as thermal, hydrolytic, and oxidative stability for polymer electrolyte membrane fuel cell applications. SPIs of high molecular weight (M_w > 200 kDa, M_n > 80 kDa) along with the ion exchange capacity (IEC) varying between 1.34 and 1.91 mequiv/g were obtained, which gave tough, ductile, and flexible membranes by solution casting. The thermal properties of the SPIs were dominated by the electronic structure of the sulfonated aromatic rings. The electron‐donating methyl groups lowered the thermal decomposition temperature. The hydrolytic and oxidative stability was roughly in the order of IEC (the higher IEC membranes were less stable). Fluorine groups, either as ? F or ? CF₃, had negative effect on the hydrolytic and oxidative stability. In the water uptake and proton conductivity, hydrophobic components are rather more influential than the substituents. It was found out that the SPI(5, 8, 0.7) containing bis(phenoxy)biphenylene sulfone moieties as a rigid hydrophobic component showed the best balanced properties in terms of the stability and the proton conductivity for its rather low IEC. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4469–4478, 2008     

Synthesis and positive‐imaging photosensitivity of soluble polyimides having pendant carboxyl groups

Polyimides having pendant carboxyl groups were prepared by a direct one‐pot polycondensation of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 3,5‐diaminobenzoic acid (DABz) and bis[4‐(3‐aminophenoxy)phenyl]sulfone (m‐BAPS) in the presence of a γ‐valerolactone/pyridine catalyst system using N‐methyl‐2‐pyrrolidone (NMP)/toluene mixture as a solvent at 180 °C. The obtained polyimides were soluble in dipolar aprotic solvents such as dimethylformamide, dimethyl sulfoxide, and NMP as well as in tetrahydrofuran and aqueous basic solution. The solubility of the polyimides was dependent on the diamine composition. Photosensitve polyimide (PSPI) systems composed of the polyimides and diazonaphthoquinone compound as a photosensitive material gave positive‐tone behavior by UV irradiation, followed by development with aqueous tetramethylammonium hydroxide (TMAH) solution. The scanning electron microscopic photograph of the resulting image showed 10‐μm line/space resolution with about 15 μm of film thickness. The PSPIs baked at 350 °C for a short time had excellent thermal resistance comparable to the original polyimides. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 934–946, 2001     

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.     

Synthesis and characterization of sulfonated homo‐ and co‐polyimides based on 2,4 and 2,5‐diaminobenzenesulfonic acid for proton exchange membranes

A series of sulfonated homo‐ and random co‐polyimides (co‐SPI) based on 2,4‐diaminobenzenesulfonic acid (2,4‐DABS) and 2,5‐diaminobenzenesulfonic acid (2,5‐DABS) has been synthesized via conventional two‐step polyimidization method. 2,4‐DABS and 2,5‐DABS were used as sulfonated diamine compounds, 4,4′‐oxydianiline (ODA) and 4,4′‐diaminodiphenyl sulfone (DDS) were used as non‐sulfonated diamine compounds. Mixtures of sulfonated and non‐sulfonated diamine compounds were reacted with benzophenonetetracarboxylic dianhydride (BTDA) to obtain co‐SPI membranes. Molar ratios of sulfonated to non‐sulfonated diamine were systematically varied to produce copolymers of controlled compositions. The co‐SPIs were evaluated for thermal oxidative stability, ion exchange capacity (IEC), water uptake, proton conductivity, solubility, and hydrolytic stability. Proton conductivity and hydrolytic stability of the co‐SPIs were compared with the fully aromatic polyimide, homo‐SPIs (BTDA/2,4‐DABS and BTDA/2,5‐DABS). Regarding thermogravimetric analysis (TGA) analysis, it is concluded that desulfonation temperature in the range of 200–350°C suggests high stability of sulfonic acid groups. co‐SPIs with 40 mol% of 2,4‐DABS showed similar or higher proton conductivity than Nafion® 117 in water. Proton conductivity values of the co‐SPIs were mainly a function of IEC and water uptake. Consequently, the optimum concentration of 2,4‐DABS was found to be in the range of 30–40 mol% from the viewpoint of proton conductivity, IEC, and hydrolytic stability. Copyright © 2008 John Wiley & Sons, Ltd.