Trifluoromethyl)-4,4′-diaminobiphenyl Research Articles

Study on the Application of Fluorinated Polyimide in the Acidic Corrosion Protection of 3-nitro-1,2,4-trizole-5-one (NTO)-Based Explosive Formulations.

3-nitro-1,2,4-triazol-5-one (NTO) has been widely used as a kind of insensitive single-compound explosive owing to its excellent balance between safety and explosive energy. To reduce its possible acid corrosion and extend its application to insensitive ammunition, acid protection research on NTO-based explosives is significant. Traditionally, the acid protection effect was evaluated by metal corrosion, which is time-consuming and qualitative. An efficient and quantitative method is desirable for evaluating the acid protection effect and exploring novel protection materials. Herein, a polyimide of 4,4'-(hexafluoroisopropene)diphthalic anhydride (6FDA)/2,2-bis(trifluoromethyl)-4,4-diaminobiphenyl (TFMB) was synthesized by replacing the 4,4'-diaminodiphenyl ether (ODA) monomer with a TFMB monomer to act as an acid-protective coating material for NTO-based explosives. Compared with three other coating materials, polyvinylidene fluoride (PVDF), polyetherimide (PEI), and copolyimide (P84), the fluorinated polyimide exhibits the best acid protection effect. Moreover, a new method was constructed to obtain the pH time-dependent curve in order to evaluate efficiently the acid protection effect of the polymer materials. By the virtue of molecular dynamic simulation (Materials Studio 2023), the interfacial effects of the coating materials with NTO-based explosives were obtained. The study provides an interpretation of the acid protection effect on the molecular level, suggesting that the higher content of fluorine atoms is beneficial for stabilizing the active hydrogen atom of the NTO by forming intermolecular hydrogen bonds.

Synthesis of novel biphenyl‐fused alicyclic tetracarboxylic dianhydride and its performance in thermostable and transparent colorless polyimides

AbstractBiphenyl fused alicyclic tetracarboxylic dianhydride, 6,6′,7,7′‐tetracarboxylic dianhydride‐5,5′,6,6′,7,7′,8,8′‐octahydro‐2,2′‐binaphthalene (OHBNDA) was successfully synthesized from biphenyltetracarboxylic dianhydride (BPDA) through hydrolysis, reduction, bromination, and Diels–Alder reaction. Three OHBNDA‐based polyimides (PIs) were synthesized by one‐step polycondensation at high temperature with 9,9‐bis(4‐aminophenyl)fluorene (BAFL), 2,2′‐bis(trifluoromethyl)‐4,4′‐diaminobiphenyl (TFMB), and 4,4′‐diamino‐2,2′‐dimethyl‐1,1′‐biphenyl (m‐TolDA) diamines, respectively. These PIs have moderate molecular weights and good solubility in polar organic solvents, such as N,N‐dimethylformamide, dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO). OHBNDA‐TFMB, OHBNDA‐m‐TolDA, and OHBNDA‐BAFL display glass transition temperatures (Tgs) of 309, 329, and 377°C from differential scanning calorimetry (DSC) curves, and the decomposition temperatures at 5% weight loss (Td5) of as high as 522, 507, and 548°C under nitrogen, respectively. Meanwhile, these PI films also show good optical transparency with the cut‐off wavelength <315 nm and the transmittance >75% at 400 nm. These results confirm that aryl‐fused alicyclic tetracarboxylic dianhydrides can afford transparent/colorless PIs with high thermal stability, especially the higher decomposition temperatures than the wholly alicyclic dianhydrides.

Synthesis and properties of vat photopolymerization 3D-printing benzoxazine

Conventional benzoxazine is difficult for molding and manufacturing parts with complex structures, shaped thin walls, etc. In this work, we presented a new method of synthesizing vat photopolymerization 3D printable benzoxazine inks were proposed to produce high precision constructions with low shrinkage. A creative benzoxazine monomer with excellent printability was synthesized by 2,2′-bis(trif luoromethyl)-4,4′-diaminobiphenyl (TFDB) and Bisphenol AF grafting with isocyanoethyl methacrylate (IEM). Specially, the solvent-free benzoxazine inks have ultra-low shrinkage, line shrinkage up to 1.8%. Minimum printable feature size of 300 µm. This study has solved the problem of benzoxazine being too brittle to be machining. It can be used in aerospace and copper laminate applications.

Transparent polyimide films with ultra-low coefficient of thermal expansion

According to the application requirements of colorless transparent polyimide (CPI) film for low coefficient of thermal expansion (CTE) in the field of OLED display, the new aromatic dianhydride monomers with amide bond structure were synthesized, namely s-ABDA, i-ABDA, EADA. Furthermore, a series of CPI films were prepared by two-step method from the reaction of as-synthesized dianhydrides with 2.2′-bis (trifluoromethyl) −4.4′-diaminobiphenyl (TFMB) or trans-1.4′-cyclohexanediamine ( t-CHDA). Based on the analysis of performance results, the incorporation of amide group and biphenyl, benzene or ether bond into dianhydride monomer helped this new type of transparent polyimide film with excellent optical properties (T550 nm> 88%), great heat stability (CTE <4.4 ppm/K; Tg >314°C; Td5% >478°C) and good mechanical strength (σ > 208 MPa). The film s-ABDA/TFMB showed ultra-low CTE value at 4.4 ppm/K, aligning with the maximum birefringence, indicating that the role of hydrogen bonding was of great benefit to the regulation of thermal expansion.

Homocoupling of a Grignard Reagent toward the Synthesis of 2,2′-Bis(trifluoromethyl)-4,4′-diaminobiphenyl

A new process for the synthesis of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) comprising three steps has been industrially developed. The first step is the homocoupling of the Grignard reagent derived from 1-chloro-2-(trifluoromethyl)benzene with iron chloride(III) in the presence of an oxidizing agent to afford 2,2′-bis(trifluoromethyl)biphenyl. The second step is the nitration of this biphenyl to 2,2′-bis(trifluoromethyl)-4,4′-dinitrobiphenyl, and the third step is the reduction of this dinitrobiphenyl using hydrogen over Pd/C to afford TFMB. This process has been demonstrated on an industrial scale.

Structure‐Property Relationship of Polyimide Fibers with High Tensile Strength and Low Dielectric Constant by Introducing Benzimidazole and Trifluoromethyl Units

AbstractCopolyimide (co‐PI) fibers with high strength and low dielectric constant are synthesized and prepared by introducing 2,2′‐bis(trifluoromethyl)‐4,4′‐diaminobiphenyl (TFMB) and 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (BIA) diamines into the rigid backbones. The resultant fibers not only exhibited excellent mechanical properties with a tensile strength of 2.627 GPa and an initial modulus of 96.786 GPa, but also possessed a dielectric constant as low as 2.433 at 10 GHz. The existence of intermolecular hydrogen‐bonding interaction is confirmed by Fourier transform infrared spectroscopy, which has been considered as the leading factor responsible for the significantly improved mechanical properties of the co‐PI fibers. 2D wide‐angle X‐ray diffraction (2D WAXD) is adopted to investigate the variation on the aggregation structure of PI fibers after the incorporation of fluorine group. The fibers with more TMFB content possessed a higher orientation degree together with a larger free volume fracture due to the combined effects of enhanced flexibility and the volume effect of trifluoromethyl groups. Meanwhile, the prepared PI fibers exhibit a 5% weight loss temperature ranging from 543 to 533 °C in the nitrogen atmosphere and a glass transition temperature ranging from 334 to 317 °C, revealing high thermal stability of co‐PI fibers.

Structure-property relationship of low dielectric constant polyimide fibers containing fluorine groups

A series of copolyimide (co-PI) fibers with low dielectric constants and excellent comprehensive properties have been successfully prepared via a two-step wet-spinning method by incorporating 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) into rigid polymer backbones of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/p-phenylenediamine (p-PDA). The dielectric constant of PI fibers were substantially reduced from 3.0 to 2.48 at the frequency of 10 GHz after the introduction of trifluoromethyl (-CF3) groups. Meanwhile, the prepared PI fibers exhibited high thermal stability as well as excellent mechanical properties. The co-PI fibers possessed the optimum tensile strength of 1.4 GPa and modulus of 83.3 GPa at the p-PDA/TFMB molar ratio of 7/3. The 5% weight loss temperature in nitrogen ranged from 523 to 558 °C, and the glass transition temperature decreased from 372 °C to 295 °C with increasing TFMB contents. Both experimental and molecular simulations method were adopted to discuss the influence of fluorine group on the aggregation structure and properties of PI fibers, suggesting that the improved free volume were the crucial factor responsible for low dielectric constant. The molecular ordered degree and orientation degree of co-PI fibers decreased firstly and further increased with increasing TMFB content, which is due to the combined effects of large free volume of trifluoromethyl and polymer regularity variation caused by copolymerization.

A facile synthesis of soluble polyimides with high glass transition temperature and excellent mechanical properties due to intermolecular hydrogen bonds

An unsymmetrical heterocyclic diamine monomer containing proton donor (–NH–), 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ), which can form hydrogen bond interactions with carbonyl functional group, was copolymerized with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) through two-step synthetic methods to obtain a series of homo- and co-polyimide (PI). The corresponding homo- and co-PI both exhibited good solubility in aprotic polar solvents, such as N, N-dimethylacetamide, N-methyl-2-pyrrolidone, N, N-dimethylformamide, pyridine, and dimethyl sulfoxide. In addition, the PI-containing PABZ units showed excellent tensile strength ranging from 83 to 164 MPa, 130–260% higher than 6FDA/TFMB homo-PIa films. These PIs, especially PABZ/6FDA, showed very high glass transition temperatures, 430°C.

Preparation and characterization of highly hydrophobic fluorinated polyimide aerogels cross-linked with 2,2′,7,7′-Tetraamino- 9,9′-spirobifluorene

Highly hydrophobic fluorinated polyimide aerogels were successfully prepared using a mild sol-gel method at room temperature from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2′-bis(trifluoromethyl)- 4,4′-diaminobiphenyl (TFDB), and cross-linked with 2,2′,7,7′-tetraamino-9,9′-spirobifluorene (TASBF). The obtained polyimide aerogels had low bulky density (0.118–0.161 g/cm3), high specific surface areas (440.6–606.7 m2/g), small pore diameter (17.08–44.89 nm) and excellent mechanical property. These polyimide aerogels also exhibited high thermal stability in both nitrogen and air atmosphere, and the 5% weight loss occurred at temperatures above 530 °C. The introduction of 6FDA into polymer structures enhanced the hydrophobicity of the prepared polyimide aerogels. After replacing 50 mol % of BPDA with 6FDA in the oligomer backbone, water contact angles of the aerogels increased from 104.5° to 126.5°, and water absorption decreased from 4.3% to 2.1%. The high hydrophobicity makes these polyimide aerogels good candidates for use as thermal insulators in harsh environments and other applications.

Molecular design of interpenetrating fluorinated polyimide network with enhanced high performance for heat-resistant matrix

Novel reactive phenylethynyl-endcapped diluents were synthesized and physically mixed with fluorinated cooligoimides (molecular weights of 5000 g/mol) derived from 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 2,2′-bis(trifluoromethyl)-4,4′-diamino biphenyl (TFDB) and para-phenylenediamine (p-PDA) at 25/75 M ratio, and 4-phenylethyethynylphthalic anhydride (PEPA) to formulate blends served as matrix resins for developing high-performance composites with excellent processabilities. The uncured blend shows very low minimum melt viscosity (<1 Pa s) and extended process window achieved using molten solvation of reactive diluent to prevent intermolecular interactions and recrystallization at higher temperature. This blend was converted to interpenetrating polyimide network through thermal-curing of phenylethynyl end-groups in each constituent. The morphology, relaxation transition and mechanical property were investigated as functions of mass fraction and chemical configuration of reactive diluent. The covalent incorporation of crosslink structures restricts segmental motion while backbone linkage induces strength and toughness retention. This cooperative effect endows homogeneous networks with high glass transition temperatures (435 °C) and flexural strength (130 MPa) simultaneously.

Low dielectric constant and moisture-resistant polyimide aerogels containing trifluoromethyl pendent groups

Conventional polyimide aerogels made from biphenyl-3,3′,4,4′-tetracarboxylic dianydride (BPDA) and 4,4′-oxidianiline (ODA) exhibit poor resistance to moisture and mechanical properties. In this work, a versatile diamine, 2,2′-bis-(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB), is introduced to BPDA/ODA backbone to modify the comprehensive performance of this aerogel. Among all formulations, the resulted polyimide aerogels exhibit the lowest shrinkage and density as well as highest porosity, at the ODA/TFMB molar ratio of 5/5. Dielectric constants and loss tangents of the aerogels fall in the range of 1.29–1.33 and 0.001–0.004, respectively, and more TFMB fractions results in a slightly decrease of dielectric constant and loss tangent. In addition, moisture-resistance of the aerogels are dramatically enhanced as the water absorption decreasing from 415% for BPDA/ODA to 13% for the polyimide aerogel at the ODA/TFMB molar ratio of 7/3, and even to 4% for the homo-BPDA/TFMB polyimide aerogel, showing a superhydrophobic characteristic, which is a great advantage for polyimide aerogels used as low dielectric materials. Meanwhile, all of formulations of aerogels exhibit high absorption capacities for oils and common organic solvents, indicating that these fluorinated polyimide aerogels are good candidates for the separation of oils/organic solvents and water. Mechanical properties and thermal stability of the polyimide aerogels are also raised to varying degrees due to the rigid-rod biphenyl structure introduced by TFMB.

Towards colorless polyimide/silica hybrids for flexible substrates

Abstract In this work, we report highly transparent flexible polyimide/silica hybrids with low coefficient of thermal expansion (CTE) comparable to that of a glass, low optical birefringence and high thermal stability over 400 °C. We started from the polyimide system based on 2,2′-bis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA)/2,2′-bis-(trifluoromethyl)-4,4′-diaminobiphenyl (TFDB), which has high optical transparency for aromatic polyimides, utilized well-known simple strategy of using silane end-capped oligomeric polyamic acid and silica sol-gel reaction to increase the miscibility between PI and silica, and finely tuned the property by control of molecular weight and processing condition. The resulting hybrid film showed homogeneous surface after oxide deposition and annealing, and passed the repeated folding/unfolding test with more than 200,000 cycles. These finely tuned hybrid films are promising candidate for flexible transparent substrate especially for high temperature (>400 °C) electronic and optoelectronic manufacturing processes.

Deposition of fluorinated polyimide consisting of 6FDA and TFDB into microscale trenches using supercritical carbon dioxide

Fluorinated polyimide (PI) consisting of 2,2-bis(3,4-anhydrodicarboxyphenyl)-hexafluoropropane (6FDA) and 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFDB) were deposited on silicon wafers with patterned microscale trenches. The deposition was carried out in supercritical carbon dioxide (scCO2) with 5mol% N,N-dimethylformamide (DMF). The effects of the monomer concentration and deposition temperature on the deposition of fluorinated PI inside the microscale trenches were studied to clarify the appropriate conditions for the deposition of fluorinated PI using scCO2. The monomer concentration and deposition temperature studied were in the ranges of 0.28×10−2–1.1×10−2mol/dm3 and 150–250°C, respectively. The amount of deposited fluorinated PI inside the trenches increased with increasing monomer concentrations and deposition temperature. Moreover, the time course of the phase behavior in the reactor was also investigated during the deposition, and the time-dependent changes in the shapes and amount of deposited fluorinated PI inside the microscale trenches were also investigated. Finally, the relationship between the trench size and the deposition behavior was studied, and the trenches of width-depth sizes of 1.5–23.5, 3–26, and 5–30μm could be completely filled with fluorinated PI simultaneously.

Phase appearance during polymerization of fluorinated polyimide monomers and deposition into the microscopic‐scale trenches in supercritical carbon dioxide

ABSTRACTThe phase appearance during the synthesis of fluorinated polyamic acid (PAA) from 2,2‐bis(3,4‐anhydrodicarboxyphenyl)‐hexafluoropropane (6FDA) and 2,2′‐bis(trifluoromethyl)−4,4′‐diaminobiphenyl (TFDB) in supercritical carbon dioxide (scCO2) was investigated to obtain fundamental data for the deposition of fluorinate polyimides (PI) using scCO2. All polymerizations were carried out at 30 MPa for 60 min. The experimental temperatures ranged from 50 to 70 °C, and each of the monomer concentrations ranged from 0.67 × 10−5 to 3.3 × 10−5 mol cm−3. The holding time of the transparent phases, which was the time from the beginning of the polymerization to the appearance of a turbid phase, was increased with either a decrease in the polymerization temperature or a decrease in the initial monomer concentration. The holding time of the fluorinated PAA was longer than that of the monomers of Kapton‐type PAA. The deposition of PI into the microscopic‐scale trenches that had formed on the silicon wafer was successful in scCO2. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43334.

聚酰亚胺主链结构对液晶取向膜性能的影响

A series polyimides(PIs)were prepared by one-step method.These PIs were comprised of a functional diamine N,N-bis(4-aminophenyl)-4-(dodecylo-xy-biphenyl)-4′-amino-phenylether(C12-BAAPE),one of two commercially available diamines 2,2′-Bis(trifluoromethy-l)-4,4′-diaminobiphenyl(TFDB),4,4′-Oxydianiline(ODA)and one of two dianhydride 4,4′-(hexafluoroisopropylidene)diphthalic anhydride(6FDA)and 4,4′-Oxydiphthalic anhydride(ODPA)in order to get different backbone structures.The structures and thermo properties of these PIs were characterized by NMR,FT-IR,DSC and TGA.Pretilt angles and alignment abilities were carried out by pretilt angle tester and polarization microscope.Solubility of PIs was tested by dissolving PIs in various organic solvents.DSC and TGA curves showed that PI-2had higher glass transition temperature(Tg)and decomposition temperature(Td)than PI-1and PI-3.Three PI films presented vertical alignment before mechanical rubbing and only PI-2maintained it after rubbing process.Conformations of these PIs were simulated by Material Studio(MS).The vertical conformation existed in PI-2's backbones improvedrubbing resistance and showed vertical alignment ability after rubbing.

Hydrogen‐Bonding Interactions and Molecular Packing in Polyimide Fibers Containing Benzimidazole Units

Rigid‐rod polyimides (PI) containing benzimidazole moieties were synthesized and spun into fibers by a wet‐spinning method. The resultant fibers exhibited an optimum tensile strength of 2.15 GPa and an initial modulus of 105 GPa with a low elongation of 2.2%. The PI fibers consisting of various ratios of 2,2′‐bis(trifluoromethyl)‐4,4′‐diaminobiphenyl (TFMB) and 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (BIA) were investigated by Fourier transform infrared spectroscopy and two‐dimensional wide angle X‐ray diffraction (2D WAXD). Direct evidence of hydrogen‐bonding involving the NH groups of BIA and the imide carbonyls is presented. Qualitative and quantitative information of this molecular interaction was obtained and discussed. This has been considered as a main factor responsible for the significantly improved mechanical properties of the PI fibers. 2D WAXD and molecular mechanics modeling were used to simulate the structure of the aromatic PI fibers. As a result, the addition of BIA in the main chains is to increase the regularity of the molecule packing, which plays an important role in the enhanced strength of the PI fibers with more BIA loadings.

The curing and thermal transition behavior of epoxy resin: a molecular simulation and experimental study

Curing and thermal transition behavior of two epoxy resins i.e. 2,2′-dimethyl-4,4′-diaminobiphenyl (MTB)–4,5-epoxycyclohexyl-1,2-diglycidyl diformate (TDE85) and 2,2′-bis(trifluoromethyl)-4,4′-diamino biphenyl (TFMB)–4,5-epoxycyclohexyl-1,2-diglycidyl diformate (TDE85) with different chemical structures were experimentally and theoretically investigated via molecular simulations to establish the structure–property relationships. The slight modification in the diamine structure resulted in significant changes in the curing and glass transition behavior of epoxy resin. As the side group of the diamine was changed from methyl to trifluoromethyl, the reactivity of the diamine toward epoxy decreased and the glass transition temperature increased from about 164 °C to about 191 °C. These phenomena can be illustrated by the change of the reaction energy barrier, flexibility of chains and the cohesive energy density in the molecular simulation of the curing process. The simulated values show good agreement with experimental data, and can be used to predict the related material characteristics for the different amine curing agent–epoxy systems.

Semi-interpenetrating polymer networks based-on end-group crosslinked fluorine-containing polyimide via click chemistry

The reinforced composite membranes based on Nafion® membranes attract a lot of attention as proton exchange membrane (PEM) for polymer electrolyte membrane fuel cells (PEMFCs). Fluorine-containing polyimide (FPI), end-capped with alkynyl, is synthesized from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2,2′-bis(trifluoromethyl)- 4,4′-diaminobiphenyl (TFMB), and 3-aminophenylacetylene (APA). The chemical structure of FPI is characterized by 1H-NMR. The reinforced composite membrane based-on semi-interpenetrating polymer network (semi-IPN) is prepared via solution casting of FPI and Nafion®212, and crosslinking thereafter. During the membrane preparation, alkynyl in FPI reacts with azide and itself via click chemistry and addition polymerization. The water uptake, swelling ratio, mechanical properties, thermal behavior, proton conductivity, and oxidative stability of the composite membranes are investigated. Compared to Nafion®212, the composite membrane shows improved thermal stability, mechanical properties, and dimensional stability. The tensile strength of the composite membranes is in the range of 35.0–55.6MPa, which is much higher than that of Nafion®212 membrane. The composite membranes show considerable proton conductivity from 2.0×10−2Scm−1 to 9.9×10−2Scm−1 at a temperature range from 30°C to 100°C, depending on FPI content.

Synthesis and Properties of Fluorinated Polyimide Films Based on 1,2,3,4-Cyclobutanetetracarboxylic Dianhydride

The alicyclic dianhydrides 1,2,3,4-cyclobutanetetracarboxylic dianhydride(CBDA) was polymerized with four kinds of fluorinated aromatic diamine, 2,2’-bis(trifluoromethyl)-4,4’- diaminobiphenyl(TFDB), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene(6FAPB), 1,4-bis(4- amino-2-trifluoromethylphenoxy) diphenyl ether (6FAPE) and 1,4-bis(4-amino-2-trifluoromethyl- phenoxy)diphenyl(6FBAB) respectively, via a two-step polycondensation procedure to prepare four series of fluorinated polyimides(PIs) derived from CBDA. The obtained PIs displayed excellent solubility in aprotic polar solvents, such as NMP, DMAc, DMF and DMSO. These PIs showed good thermal stability with the 10% thermal decomposing temperatures higher than 457 in nitrogen and the glass transition temperatures higher than 267 . In addition, the PI films exhibited good optical transparency in the visible light region(400-700nm) with the transmittance higher than 80% at 450nm, and the PI films showed little absorption at the optocommunication wavelengths of 1.30µm and 1.55µm.

Proton exchange membranes based on semi-interpenetrating polymer networks of fluorine-containing polyimide and Nafion ®

A series of reinforced composite membranes as proton exchange membranes were prepared from Nafion ®212 and crosslinkable fluorine-containing polyimides (FPI). FPI was prepared from the polymerization of 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB), and 3,5-diaminobenzoic acid (DABA). Then FPI was thermally crosslinked during the membrane preparation and formed the semi-interpenetrating polymer networks (semi-IPN) structure in the composite membranes. The thermal properties of the composite membranes were characterized by thermogravimetric analysis. The crosslinking density of FPI in the composite membranes was evaluated by the gel fraction. These membranes showed excellent thermal stabilities and good oxidative stabilities. Compared with Nafion ®212, the obtained composite membranes displayed much improved mechanical properties and dimensional stabilities. The tensile strength of the composite membranes was more than twice that of Nafion ®212. The composite membranes exhibited high proton conductivity, which ranged from 2.3 × 10 −2 S cm −1 to 9.1 × 10 −2 S cm −1. All membranes showed an increase in proton conductivity with temperature elevation.