Polybenzimidazole containing benzimidazole side groups for high-temperature fuel cell applications

A polybenzimidazole (PBI) containing bulky basic benzimidazole side groups, poly[2,2′-(2-benzimidazole-p-phenylene)-5,5′-bibenzimidazole] (BIpPBI), was prepared via the condensation polymerization of 3,3′-diaminobenzidine tetrahydrochloride dihydrate with 2-benzimidazole terephthalic acid in PPA. BIpPBI was found to be soluble in aprotic polar solvents without the addition of inorganic salts, such as lithium chloride, and the BIpPBI film also showed very good acid retention capability as well as very high proton conductivity. The maximum acid content of the BIpPBI film was approximately 81 wt.% and the proton conductivity value of the acid-doped BIpPBI membrane was 0.16 S cm⁻¹ at 180 °C and a 0% relative humidity. For comparison, the maximum proton conductivity of the most commonly used polymer for the high-temperature fuel cell membrane, poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (mPBI) membrane, is approximately 0.06 S·cm⁻¹ at 180 °C under anhydrous conditions at a 65 wt.% acid content, which is the maximum acid content that a mPBI membrane can have.     

Proton conducting membranes based on semi-interpenetrating polymer network of Nafion and polybenzimidazole

A new strategy to prepare the reinforced composite membranes for polymer electrolyte membrane fuel cells (PEMFCs), which can work both in humidified and anhydrous state, was proposed via constructing semi-interpenetrating polymer network (semi-IPN) structure from polybenzimidazole (PBI) and Nafion^®212, with N-vinylimidazole as the crosslinker. The crosslinkable PBI was synthesized from poly(2,2′-(m-phenylene)-5,5′-bibenzimidazole) and p-vinylbenzyl chloride. The semi-IPN structure was formed during the membrane preparation. The composite membranes exhibit excellent thermal stability, high-dimensional stability, and significantly improved mechanical properties compared with Nafion^®212. The proton transport in the hydrated composite membranes is mainly contributed by the vehicle mechanism, with proton conductivity from ∼10⁻² S/cm to ∼10⁻¹ S/cm. When the temperature exceeds 100 °C, the proton conductivity of the semi-IPN membranes decreases quickly due to the dehydration of the membranes. Under anhydrous condition, the proton conductivity of the membranes will drop to ∼10⁻⁴ S/cm, which is also useful for intermediate temperature (100-200 °C) PEMFCs. The benzimidazole structure of PBI and the acidic component of Nafion^® provide the possibility for the proton mobility via structure diffusion involving proton transfer between the heterocycles with a corresponding reorganization of the hydrogen bonded network.     

Morphology control of poly(2,2′-phenylene-5,5′-bibenzimidazole) by reaction-induced crystallization during polymerization

Morphology control of polybenzimidazoles was examined by reaction-induced phase separation during polymerization. Polymerizations of 3,3′-diaminobenzidine with terephthalic acid or diphenyl terephthalate were carried out in poor solvents. The morphology of the precipitated poly[2,2′-(1,4-phenylene)-5,5′-bibenzimidazole] (PpBBI) was significantly influenced by the polymerization conditions, and the aggregates of nano-scale PpBBI fibers were obtained by the polymerization at a concentration of 3-5% and 320-350 °C in dibenzyltoluene. The average diameter of the fibers was ca. 50 nm and inherent viscosities of the precipitates were 0.35-0.58 dL g⁻¹. They possessed high crystallinity and thermal stability. The oligomers were precipitated first by the reaction-induced crystallization to form the highly crystalline lath-like crystals at an initial stage of polymerization. Then the lath-like crystals were split into disentangled aggregates of fine fibers with maintaining the high crystallinity. The polymerization mainly proceeded when the oligomers were registered into the crystals. The obtained aggregates of nano-scale fibers could be recognized as nonwoven fabrics. Morphology control of poly[2,2′-(1,3-phenylene)-5,5′-bibenzimidazole] was also examined and particles were mainly formed.     

Synthesis and properties of novel sulfonated poly(phenylquinoxaline)s as proton exchange membranes

Two series of sulfonated poly(phenylquinoxaline)s (SPPQ-x and SPPQ(O)-x, x refers to molar percentage of sulfonated tetraamine monomer) were first synthesized from a sulfonated tetraamine (4,4′-bis(3,4-diaminophenoxy)biphenyl-3.3′-disulfonic acid) and two aromatic bisbenzils (4-phenylglyoxalylbenzil and p,p′-oxydibenzil) in a mild condition. The structures of SPPQ-x and SPPQ(O)-x were characterized by IR and ¹H NMR spectra. The properties of these polymer films, such as water uptake, water swelling ratio, proton conductivity, thermal properties, methanol permeability, hydrolytic and oxidative stability were also investigated. The resulting polymers generally showed good solubility in DMAc and DMSO. Flexible and tough membranes with high mechanical strength were prepared. They show very high thermal, thermooxidative, hydrolytic stabilities and low methanol permeability. SPPQ-100 with the IEC value (2.41 mmol/g) displays the conductivity of 0.1 S/cm and a swelling ratio of 7.3% at 100 °C. The low swelling was attributed to the high rigid of polymer backbones and the strong intermolecular interaction between the basic nitrogen atoms of quinoxaline units and sulfonic acid groups. Moreover, we found that the conductivities of SPPQ(O)-x membranes were higher than SPPQ-x membranes at the similar IEC value. The highest conductivity of 0.2 S/cm was obtained for SPPQ(O)-100 at 140 °C. A combination of excellent dimensional and hydrolytic stabilities indicated that the SPPQ ionomers were good candidate materials for proton exchange membrane in fuel cell applications.     

Synthesis and characterization of sulfonated polyimides bearing sulfonated aromatic pendant group for DMFC applications

A novel side-chain-type sulfonated aromatic diamine, 5-[1,1-bis(4-aminophenyl)-2,2,2- trifluoroethyl]-2-(4-sulfophenoxy)benzenesulfonic acid (BABSA) was synthesized and characterized. Two series of sulfonated polymides (SPI-N and SPI-B) were prepared from 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) or 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride (BNTDA), sulfonated diamine BABSA and various non-sulfonated aromatic diamines. The resulting sulfonated polyimide (SPI) membranes exhibited good dimensional stability with isotropic swelling of 7-22% and high thermal stability with desulfonation temperature of 283-330 °C. These membranes also displayed excellent oxidation stability and good water stability. The SPI membranes exhibited better permselectivity than Nafion 115 membrane due to their much lower methanol permeability. The ratios of proton conductivity to methanol permeability (Ф) for the SPI membranes were almost two to three times of that for Nafion 115. The SPI-N membranes exhibited excellent conducting performance with the proton conductivity higher than Nafion 115 as the temperature over 40 °C, which attributed to their good hydrophobic/hydrophilic microphase separation structure.     

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 1000 h, while its proton conductivity was still at a high level (compared to that of Nafion 117).     

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 1.5-2.8 meq g⁻¹ showed high reduced viscosity of 3-10 dL g⁻¹ and high desulfonation temperature of 320 °C. The SPI membranes were tough and flexible, having high stress at break of more than 80 MPa 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 1.77 meq g⁻¹ exhibited σ values of 120 and 260 mS cm⁻¹ at 60 and 120 °C, respectively, in water. They also showed fairly high water stability.     

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 800 h. The proton conductivity of these SPIs was 0.0250-0.3565 S/cm at 20 °C and 100% relative humidity (RH), and increased to 0.1149-0.9470 S/cm at 80 °C and 100% RH. The methanol permeability values of these SPIs were in the range of 0.99-2.36 × 10⁻⁷ cm²/s, which are much lower than that of Nafion 117 (2 × 10⁻⁶ cm²/s).     

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

A novel sulfonated diamine bearing sulfophenyl pendant groups, namely, 4,4′-bis (4-aminophenoxy)-3,3′-bis(4-sulfophenyl) biphenyl and a series of sulfonated polyimides (SPIs) based on it were successfully synthesized. The SPIs had high viscosity and gave tough, flexible and transparent membranes. The SPI membranes showed anisotropic membrane swelling in water with 2.5-4 times larger swelling in thickness direction than in plane one. They displayed reasonably high proton conductivity. For example, the conductivities for the SPI with an ion exchange capacity of 1.80 mequiv/g were 104 and 7.3 mS/cm in water and 50% RH, respectively, at 60 °C. They maintained high mechanical strength and proton conductivity even after aging in water at 130 °C for 500 h, showing the high water stability comparable to the best SPI reported so far. In polymer electrolyte fuel cells (PEFCs) operated at 90 °C and 50% RH, they showed fairly high cell performances and have high potential for PEFC applications.     

Semi-interpenetrating polymer networks of Nafion and fluorine-containing polyimide with crosslinkable vinyl group

Fluorine-containing polyimide with crosslinkable vinyl group (FPI) was synthesized from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), and 4-amino styrene (AS). The reinforced composite membranes based on semi-interpenetrating polymer networks (semi-IPN) were prepared via solution casting of FPI and Nafion^®212, and crosslinking thereafter. The water uptake, swelling ratio, mechanical properties, thermal behavior, proton conductivity, and oxidative stability of the composite membranes were investigated. Compared with the recast Nafion^® 212, the composite membrane shows better mechanical properties and improved dimensional stability. The tensile strength of the composite membranes ranges from 39.0 MPa to 80.0 MPa, which is higher than that of the recast Nafion^® 212 membrane (26.6 MPa). The dimensional stability of the composite membranes increases with increasing FPI content in the membranes, whereas the proton conductivity decreases. The composite membranes show considerable proton conductivity from 2.0 × 10⁻² S cm⁻¹ to 8.9 × 10⁻² S cm⁻¹ at a temperature from 30 °C to 100 °C, depending on the FPI contents. The composite membranes with semi-IPN from FPI and Nafion^®212 have considerable high proton conductivity, excellent mechanical properties, thermal and dimensional stabilities.     

Preparation and DMFC performance of a sulfophenylated poly(arylene ether ketone) polymer electrolyte membrane

A sulfonated poly(aryl ether ether ketone ketone) (PEEKK) having a well-defined rigid homopolymer-like chemical structure was synthesized from a readily prepared PEEKK by post-sulfonation with concentrated sulfuric acid at room temperature within several hours. The polymer electrolyte membrane (PEM) cast from the resulting polymer exhibited an excellent combination of thermal resistance, oxidative and dimensional stability, low methanol fuel permeability and high proton conductivity. Furthermore, membrane electrode assemblies (MEAs) were successfully fabricated and good direct methanol fuel cell (DMFC) performance was observed. At 2 M MeOH feed, the current density at 0.5 V reached 165 mA/cm, which outperformed our reported similarly structured analogues and MEAs derived from comparative Nafion^® membranes.     

Organosoluble and optically transparent fluorine-containing polyimides based on 4,4′-bis(4-amino-2-trifluoromethylphenoxy)-3,3′,5,5′-tetramethylbiphenyl

A novel fluorinated diamine monomer, 4,4′-bis(4-amino-2-trifluoromethylphenoxy)-3,3′,5,5′-tetramethylbiphenyl, was prepared by a nucleophilic chloro-displacement reaction of 3,3′,5,5′-tetramethyl-4,4′-biphenol with 2-chloro-5-nitrobenzotrifluoride and subsequent reduction of the intermediate dinitro compound. The diamine was reacted with aromatic dianhydrides to form polyimides via a two-step polycondensation method; formation of poly(amic acid)s, followed by thermal imidization. All the resulting polyimides were readily soluble in many organic solvents and exhibited excellent film forming ability. The polyimides exhibited high T_g (312-351 °C), good thermal stability, and good mechanical properties. Low moisture absorptions (0.2-1.1 wt%), low dielectric constants (2.54-3.64 at 10 kHz), and low color intensity were also observed.     

Synthesis of sulfonated poly(arylene-co-naphthalimide)s as novel polymers for proton exchange membranes

A series of novel sulfonated poly(arylene-co-binaphthalimide)s (SPPIs) were successfully synthesized via Ni(0) catalytic coupling of sodium 3-(2,5-dichlorobenzoyl)benzenesulfonate and bis(chloronaphthalimide)s. Bis(chloronaphthalimide)s were conveniently prepared from 5-chloro-1,8-naphthalic anhydride and various diamines. Tough and transparent SPPI membranes were prepared and the electrolyte properties of the copolymers were intensively investigated as were the effects of different diamine structures on the copolymer characterisitics. The copolymer membrane Ia-80, with an ion exchange capacity (IEC) of 2.50 meq g⁻¹, displayed a higher proton conductivity, i.e. 0.135 S cm⁻¹ at 20 °C, as compared to Nafion 117 (0.09 S cm⁻¹, 20 °C). The copolymer membrane Id-70, containing 3,3′-dimethyl-4,4′-methylenedianiline (DMMDA) units, exhibited excellent stability toward water and oxidation due to the introduction of hydrophobic methyl groups on the ortho-position of the imido bond in the copolymer. The mechanical property of Id-70 remained virtually unchanged after immersing membrane in pressured water at 140 °C for 24 h. Furthermore, the introduction of aliphatic segment a hexane-1,6-diamine (HDA) in copolymer led to a significant increase in proton conductivity and water uptake with increasing temperature; the proton conductivity of the Ic-70 membrane reached 0.212 S cm⁻¹ at 80 °C, which was higher than Nafion 117 as well as of the membranes based on aromatic diamines at equivalent IEC values. Consequently, these materials proved to be promising as proton exchange membranes.     

Synthesis, proton conductivity and methanol permeability of a novel sulfonated polyimide from 3-(2′,4′-diaminophenoxy)propane sulfonic acid

A novel sulfonated diamine monomer, 3-(2′,4′-diaminophenoxy)propane sulfonic acid (DAPPS), was successfully synthesized and the sulfonated polyimide (SPI) was prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA) and DAPPS. The resulting SPI, NTDA-DAPPS, was soluble in common organic solvents. The SPI membrane displayed proton conductivity σ values of 0.12-0.35 S/cm at temperatures ranging from 35 to 90 °C in liquid water, which were similar to or higher than those of Nafion 117 and sulfonated hydrocarbon polymers. The σ of the SPI membrane decreased significantly with decreasing relative humidity (RH) and became much lower than that of Nafion 117 at 30% RH. The SPI membrane displayed good water stability at 80 °C and was thermally stable up to 240 °C. It showed reasonable mechanical strength of a modulus of 1.3 GPa at 90 °C and 90% RH. Its methanol permeability P_M was 0.57×10⁻⁶ cm²/s at 30 °C and 8.6 wt% methanol in feed, which was a fourth of that of Nafion 117. As a result, its ratio of σ/P_M was 21×10⁴ S cm⁻³ s, which was about 4 times larger than that of Nafion 117, suggesting potential application of the SPI membrane for direct methanol fuel cell.     

Studies on anhydrous proton conducting membranes based on imidazole derivatives and sulfonated polyimide

Anhydrous proton conducting membranes based on sulfonated polyimide (sPI) and imidazole derivatives were prepared. The acid-base composite membranes show a good chemical oxidation stability and high thermal stability. The addition of imidazole derivatives in sPIs can improve the chemical oxidation stability of the composite membranes enormously, and even much better than that of pure sPI. The proton conductivity of a typical sPI/xUI(2-undecylimidazole) composite membrane can reach 10⁻³ S cm⁻¹ at 180 °C under the anhydrous condition. The proton conductivity of the acid-base composite membranes increases significantly with increasing content of UI. Moreover, UI in sPI/xUI composite membrane is difficult to be brought out by the vapor due to the existence of long hydrophobic moiety, which will improve the stability and lifetime of the membranes in the fuel cells.     

Synthesis and properties of new sulfonated poly(p-phenylene) derivatives for proton exchange membranes. I

Several high molecular weight poly(2,5-benzophenone) derivatives were synthesized by high yield nickel-catalyzed coupling polymerization of 2,5-dichloro-4′-substituted benzophenones. The monomers were prepared by Friedel-Crafts catalyzed reaction of 2,5-dichlorobenzoyl chloride and several aromatic compounds. The resulting polymers are organosoluble and show no evidence of crystallinity by differential scanning calorimetry (DSC). The temperatures of 5% weight loss of the polymers via dynamic thermogravimetric analysis in air were above 480 °C. Sulfonation of selected polymers utilizing concentrated or fuming sulfuric acid at room temperature introduced sulfonic acid moieties to the aromatic side group. Activated fluoro aryl groups were also used to generate pendent sulfonated functionalities. The sulfonated polymers were examined for ion exchange capacities, water absorption capacities and proton conductivities. The sulfonated polymers were not good film formers, but could be demonstrated to show high values of proton conductivity in the range of 0.06-0.11 S/cm when supported on glass fabrics or via polymer blending strategies.     

Structure-property relationships for a series of polyimide copolymers with sulfonated pendant groups

A series of high molecular weight, sulfonated polyimide copolymers (8a-f) with controlled acid contents have been obtained using 2,2′-bis(4-sulfobenzyloxy)benzidine (14) prepared via a flexible synthetic route. This series of novel sulfonated polyimide membranes were found to possess higher hydrolytic stability than polyimides in which the sulfonic acid groups are bound directly to the polymer main chain. An in-depth analysis of conductivity data was also performed for 8 and compared to the results for Nafion^® (1), sulfonated poly(ether ether ketone) (2) and a main-chain sulfonated polyimide (3). In order to remove the influence of acid strength, the proton mobility value for 8 at infinite dilution was calculated and found to be 1.2(±0.6) × 10⁻³ cm² s⁻¹ V⁻¹. A catalyst-coated membrane (CCM)-MEA based on a polyimide incorporating 60% sulfonated monomer (8d) was found to exhibit comparable beginning-of-life fuel cell performance as a Nafion^®-based CCM MEA at 50 °C.     

New multiblock copolymers of sulfonated poly(4′-phenyl-2,5-benzophenone) and poly(arylene ether sulfone) for proton exchange membranes. II

Rigid-rod poly(4′-phenyl-2,5-benzophenone) telechelics were synthesized by Ni(0) catalytic coupling of 2,5-dichloro-4′-phenylbenzophenone and the end-capping agent 4-chloro-4′-fluorobenzophenone. The degree of polymerization was determined by ¹³C NMR. The telechelics produced were selectively sulfonated by concentrated sulfuric acid at 50 °C. The degree of sulfonation was controlled by varying the reaction time and was determined by titration. The nucleophilic step copolymerization of the fluoroketone activated sulfonated poly(4′-phenyl-2,5-benzophenone) oligomer (M_n=3.05×10³ g/mol) with hydroxyl terminated biphenol based polyarylethersulfone (M_n=4.98×10³ g/mol) afforded an alternating multiblock sulfonated copolymer that formed flexible transparent films, in contrast to the high molecular weight rigid rod homopolymers. They were tested for water absorption and proton conductivity by specific impedance. The synthesis and characterization of these multiblock copolymers are reported.     

Low-swelling proton-conducting copoly(aryl ether nitrile)s containing naphthalene structure with sulfonic acid groups meta to the ether linkage

Wholly aromatic poly(aryl ether ether nitrile)s containing naphthalene structure with sulfonic acid groups meta to ether linkage (m-SPAEEN), intended for fuel cells applications as proton conducting membrane materials, were prepared via nucleophilic substitution polycondensation reactions. The incorporation of rigid naphthalene structure with meta-sulfonic acid groups was with the intent of improving the aggregation of hydrophilic and hydrophobic domains and to increase the acidity and conductivities. m-SPAEEN copolymers were readily synthesized by potassium carbonate mediated nucleophilic polycondensation reactions of commercially available monomers: 2,6-difluorobenzonitrile (2,6-DFBN), 2,8-dihydroxynaphthalene-6-sulfonate sodium salt (2,8-DHNS-6), and 4,4′-biphenol (4,4′-BP) in dimethylsulfoxide (DMSO) at 160-170 °C. The sulfonic acid group content (SC), expressed as a number per repeat unit of polymer, ranged from 0 to 0.6 and was readily controlled by changing the feed ratio of 2,8-DHNS-6 to 2,6-DFBN. High thermal stability of m-SPAEEN copolymers was indicated by observed glass transition temperatures (T_gs) ranging from 223 to 335 °C in sodium salt form and from 230 to 260 °C in acid form (m-SPAEENH) and decomposition temperatures (T_d)s over 250 °C in acid form and over 350 °C in sodium form in both nitrogen and air. All m-SPAEENH copolymers exhibited reasonable flexibility and tensile strength in the range of 39-78 MPa, indicating they were mechanically stronger than Nafion^®117, which had an approximate value of 10 MPa under the same test conditions. As expected, m-SPAEENH copolymers showed considerably reduced moisture absorption compared to previously prepared sulfonated hydroquinone based poly(aryl ether nitrile). m-SPAEENH copolymers also showed improved proton conductivities. Proton conductivity curves parallel to that of Nafion 117 were obtained with proton conductivity of 10⁻¹ S/cm at equivalent ion exchange capacities (IEC) of 1.6 and 1.9, comparable to Nafion^®117. The best compromise combining PEM mechanical strength, water swelling and proton conductivity, was achieved at SC of 0.5 and 0.6.     

Graphene oxide/polybenzimidazole composites fabricated by a solvent-exchange method

Homogenous organic dispersion of graphene oxide (GO) sheets was prepared by a solvent-exchange method. This method enabled the simultaneous achievement of full exfoliation and high concentration of GO in several organic solvents such as dimethyl sulfoxide, which would facilitate the fabrication of individual graphene reinforced polymer composites through a solution-based process. To this end, poly [2,2′-(p-oxydiphenylene)-5,5′-bibenzimidazole] (OPBI)/GO composites were fabricated. X-ray diffraction characterization showed that the GO sheets were individually incorporated into the OPBI matrix. Scanning electron microscope images that taken of the fracture surface of the composites revealed that the GO sheets were spontaneous aligned parallel to the surface of the composite films as the content of GO exceeded 0.3 wt.%. The incorporation of GO also showed profound effects on the macroscopic properties of OPBI. Compared to pure OPBI, the composites showed a 17% increase in Young’s modulus, 33% increase in tensile strength and 88% improvement in toughness by the addition of only 0.3 wt.% of GO. Moreover, although the thermal stability of GO is far inferior to OPBI, it is found the thermal stability of OPBI is still improved by the addition of GO.