Fluorenyl Ether Research Articles

Rationally designed poly(propylene carbonate)-based electrolyte for dendrite-free all solid-state lithium metal batteries

Solid polymer electrolytes (SPEs)-based lithium metal batteries (LMBs) perform tremendous potential due to their high energy density and increased safety in comparison to conventional lithium-ion batteries. However, narrow electrochemical stability window (ESW), poor mechanical properties and confining current densities of traditional polyethylene oxide (PEO)-based electrolytes limit their ability to be compatible with high-energy density cathode materials. To tackle these challenges, a novel scalable SPE is hence designed for LMBs. This SPE is primarily composed of an allyl glycidyl ether modified poly(propylene carbonate) (PPCAGE) produced through metal-free polymerization method, an electrospun sulfonated poly(fluorenyl ether ketone) (SPFEK) framework and LiTFSI, which shows good mechanical property (tensile strength = 6.70 MPa and modulus of elasticity (MOE) = 82.5 MPa), high ionic conductivity (2.62 × 10−4 S cm−1 at 60 °C) and wide ESW (5.1 V). The all-solid-state batteries (ASSBs) are assembled with three different cathode materials including LFP, NCM811, and LCO to evaluate the application prospects of this SPE. The Li/LFP ASSB demonstrates a capacity of 101 mAh g−1 at 1 C, maintaining 78 % capacity retention after 500 loops. Even in the Li/LCO cell with a high cut off voltage of 4.5 V, the ASSB still achieves 132 mAh g−1 at 0.5 C, with 91 % capacity retention after 500 cycles. This SPFEK-PPCAGE/LiTFSI based electrolyte has promising application in energy-dense ASSBs.

Enhancing interfacial solvent resistance and mechanical properties of carbon fiber/polyether ether ketone composites with water‐borne sizing agents based on cross‐linkable polyphthalonitrile

AbstractThe inherent structural properties and elevated processing temperatures of thermoplastic resins present new challenges in the realm of carbon fiber (CF) sizing agents. Consequently, a water‐based cross‐linkable nitro‐phthalonitrile capped polyfluorenyl ether ketone sizing agent was meticulously designed. The sizing agent exhibits superior storage stability, encapsulating particles spanning dimensions from 66.51 to 87.71 nm. The inherent mechanism during the hot‐pressing stage involves a self‐crosslinking of nitrile groups toward stable structures with unparalleled resistance to solvents. The crosslinked sizing agent boasts a remarkable glass‐transition temperature of 290°C. Noteworthy, significance is the consequential 40.1% augmentation in maximum flexural strength, along with a commendable 35% increase in interlaminar shear strength for CF‐1.5/PEEK composites in contrast to their unsized CF/PEEK counterparts. In summary, the focal aspiration of this research endeavor lies in offering a straightforward and viable methodology for the exploration of cross‐linkable sizing agents, strategically catering to both “thermoplastic processing” and “thermosetting applications.”Highlights Bulky fluorenyl unit increases the intermolecular volume of copolymer poly(fluorenyl ether ketone). The introduction of the BPF unit to the molecular elevates the thermal stability of the copolymer. Unique electron‐donating proclivity of the fluorenyl group drastically improved its reactivity. The polymerization was accomplished at a relatively low temperature of 150°C for practical applications. The ILSS, IFSS, and bending strength were noteworthy increased by 35%, 74.02%, and 40.1%

Poly(fluorenyl ether ketone)s with densely distributed multi-cationic side chains for anion exchange membranes

The anion conductivity is one of the key properties of anion exchange membranes (AEMs), which is affected by the content and distribution of ionic groups in the ionomers. Herein, a series of poly(fluorenyl ether ketone)s with multiple phenylmethyl groups were synthesized. After bromination, the phenylmethyl groups were attached with linear tri- and di-quaternary ammonium side chains. As a result, the quaternary ammonium groups were tethered closely at the aliphatic side chains which emanate from the specific segments of the aromatic backbone. The ion exchange capacity, water affinity, Br− conductivity, morphology, thermal property, mechanical property, oxidative stability, and VO2+ permeability of the obtained AEMs were studied. It has been found that both types of AEMs have well-developed hydrophilic-hydrophobic phase separation. When comparing at similar ion exchange capacity (IEC), the AEMs bearing tri-quaternary ammonium side chains have higher Br− conductivity than the AEMs bearing di-quaternary ammonium side chains, presumably because of the better phase separation in the former. All of the AEMs have significantly reduced VO2+ permeability than Nafion 212, owing to the positive effect of Donnan repulsion. Along with the other characterizations, the obtained AEMs were proven to be promising candidates for potential vanadium redox flow battery applications.

Ionically Crosslinked Composite Membranes from Polybenzimidazole and Sulfonated Poly (fluorenyl ether ketone) for High-Temperature PEM Fuel Cells

A series of composite polymer membranes composed of poly [2,2″-(p-oxydiphenylene)-5,5″-benzimidazole] (OPBI) and sulfonated poly (fluorenyl ether ketone) (SPFEK) were developed with enhanced mechanical integrity and superior oxidative stability. The phosphonic acid (PA) doped OPBI-SPFEK membranes were then fabricated for the high temperature-proton exchange membrane fuel cells (HT-PEMFCs) application. It is suggested that an ionically crosslinked structure can be formed by the intense interaction among the protonated benzimidazolium, sulfonate groups, and PA molecules. With lower acid content and swelling ratio, the composite membranes afforded satisfactory proton conductivity and much higher tensile strength than the pristine OPBI. A maximum conductivity of 0.050 S cm−1 was reached by OPBI-SPFEK-10% at 180 °C, with tensile strength as high as 24.7 MPa. The single fuel cell from the optimized OPBI-SPFEK-10% exhibited the highest peak power density of 727 mW cm−2 at 160 °C, which was 21% higher than that from the pristine OPBI.

Densely Quaternized Fluorinated Poly(fluorenyl ether)s with Excellent Conductivity and Stability for Vanadium Redox Flow Batteries.

Cationic group distribution and elemental composition are two key factors determining the conductivity and stability of anion exchange membranes (AEMs) for vanadium redox flow batteries (VRFBs). Herein, fluorinated tetra-dimethylaminomethyl-poly(fluorenyl ether)s (TAPFE)s were designed as the polymer precursors, which were reacted with 6-bromo-N,N,N-trimethylhexan-1-aminium bromide to introduce di-quaternary ammonium (DQA) containing side chains. The resultant DQA-TAPFEs with a rigid fluorinated backbone and flexible multi-cationic side chains exhibited distinct micro-phase separation as probed by small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). DQA-TAPFE-20 with an ion exchange capacity (IEC) of 1.55 mmol g-1 exhibited a SO42- conductivity of 10.1 mS cm-1 at room temperature, much higher than that of a control AEM with an identical backbone but spaced out cationic groups, which had a similar IEC of 1.60 mmol g-1 but a SO42- conductivity of only 3.2 mS cm-1. Due to the Donnan repulsion effect, the DQA-TAPFEs exhibited significantly lower VO2+ permeability than Nafion 212. The VRFB assembled with DQA-TAPFE-20 achieved an energy efficiency of 80.4% at 80 mA cm-1 and a capacity retention rate of 82.9% after the 50th cycling test, both higher than those of the VRFB assembled with Nafion 212 and other AEMs in the literature. Therefore, the rationally designed DQA-TAPFEs are promising candidates for VRFB applications.

A Robust Composite Proton Exchange Membrane of Sulfonated Poly (Fluorenyl Ether Ketone) with an Electrospun Polyimide Mat for Direct Methanol Fuel Cells Application.

As a key component of direct methanol fuel cells, proton exchange membranes with suitable thickness and robust mechanical properties have attracted increasing attention. On the one hand, a thinner membrane gives a lower internal resistance, which contributes highly to the overall electrochemical performance of the cell, on the other hand, strong mechanical strength is required for the application of proton exchange membranes. In this work, a sulfonated poly (fluorenyl ether ketone) (SPFEK)-impregnated polyimide nanofiber mat composite membrane (PI@SPFEK) was fabricated. The new composite membrane with a thickness of about 55 μm exhibited a tensile strength of 35.1 MPa in a hydrated state, which is about 65.8% higher than that of the pristine SPFEK membrane. The antioxidant stability test in Fenton’s reagent shows that the reinforced membrane affords better oxidation stability than does the pristine SPFEK membrane. Furthermore, the morphology, proton conductivity, methanol permeability, and fuel cell performance were carefully evaluated and discussed.

Sulfonated poly(fluorene ether ketone) (SPFEK)/α-zirconium phosphate (ZrP) nanocomposite membranes for fuel cell applications

Methanol crossover through polymer electrolyte membranes (PEMs) is a major concern in fuel cell research. In order to address this problem, a sulfonated poly(fluorenyl ether ketone) (SPFEK)/α-zirconium phosphate (ZrP) nanocomposite membrane containing 2.0 wt. % of ZrP nanosheets was prepared by casting a dimethylacetamide (DMAc) dispersion containing SPFEK and exfoliated ZrP nanosheets. The membrane was characterized and tested as a PEM in a single direct methanol fuel cell (DMFC) at 80 °C. The introduction of ZrP nanosheets improved the oxidative stability and reduced methanol permeability and water uptake of the PEM. The SPFEK/ZrP nanocomposite membrane led to the best cell performance among the single cells using SPFEK/ZrP nanocomposite membrane, SPFEK, and Nafion® 117. The maximum power densities obtained for the cells composed of the above three membranes were 51.3, 41.4, and 43.6 mW/cm2, respectively.

Sulfonated poly(fluorenyl ether ketone)/Sulfonated α-zirconium phosphate Nanocomposite membranes for proton exchange membrane fuel cells

Sulfonated poly(aryl ether) (SPAE) membranes have attracted significant attention as polymer electrolyte membranes due to their superior mechanical properties and low cost. However, the poor chemical stability and methanol barrier property of SPAE membranes limit the fuel cell performance. It is necessary to improve the proton conductivity, methanol barrier property, and stability of SPAE for high-performance fuel cells. Herein, a novel proton conductive filler, sulfonated α-zirconium phosphate (ZrP-SO3H), was synthesized and introduced to sulfonated poly(fluorenyl ether ketone) (SPFEK) to fabricate advanced nanocomposite membranes. The oxidative stability, methanol permeability, water uptake, and proton conductivity of the as-prepared nanocomposite membranes were characterized. The nanocomposite membranes exhibited comparable performance as Nafion® 117 membrane in H2/O2 fuel cell and higher performance than Nafion® 117 in direct methanol fuel cell. These results suggest that ZrP-SO3H-doped SPFEK membrane is a promising candidate as a proton exchange membrane in high-performance fuel cells.

Sulfonated poly (fluorenyl ether ketone nitrile) membranes used for high temperature PEM fuel cell

A series of sulfonated poly (fluorenyl ether ketone nitrile)s with different equivalent weights (EW) ranging from 681 to 369 g mequiv.−1 were used to assemble a series of single proton exchange membrane fuel cells (PEMFC) in their turns. The mechanical strength and morphology of the copolymer were studied systematically. This paper mainly evaluated and compared their cell performance. The polarization curves showed that the prepared films have good performance at low temperature and high relative humidity. Due to the increase of temperature, dehydration seriously deteriorated the performance of the cell, especially for the membrane with high electron flow and low proton conductivity. However, at 100 °C, the cell performance of the membrane containing 441 g mequiv.- 1 was even better than that of Nafion@117 membrane. It could even be used at 125 °C. In the short life test, the output power density was stable at about 0.24 W•cm−2 within 24 h. These results show that our membranes were suitable for the applications of PEM fuel cell at high temperature.

Fluorinated poly(fluorenyl ether)s with linear multi-cationic side chains for vanadium redox flow batteries

The cationic group distribution along the polymeric backbones of anion exchange membranes (AEMs) has significant influence on their microscopic morphology and anion conductivity. To develop high-performance AEMs for vanadium redox flow batteries (VRFBs), a series of poly (fluorenyl ether) samples bearing di- and tri-quaternary ammonium side chains with similar ion exchange capacities (IECs) were synthesized by grafting cationic alkyl chains with tertiary amine-containing poly(fluorenyl ether) precursors. The experimental results indicate that the introduction of the multi-cationic side chains facilitates the formation of micro-phase-separated morphologies and enhances anion conductivity. Moreover, the number of spacer atoms between the quaternary ammonium groups on the side chains affects the water uptake of the membranes, thus complicating the relationship between the density of cationic group distribution and anion conductivity. The poly(fluorenyl ether)s with dicationic side chains and six spacing atoms (DQA-PFE-C6) showed the highest anion conductivity. A VRFB assembled with DQA-PFE-C6 exhibited a maximum power density of 239.80 mW cm−2 at 250 mA cm−2, which is significantly higher than a VRFB assembled with Nafion 212. Therefore, side chain engineering is an effective chemical approach to enhance the properties of AEMs for VRFB applications.

Synthesis of novel poly(phthalazinone fluorenyl ether ketone ketone)s with improved thermal stability and processability

In this study, a series of poly(phthalazinone fluorenyl ether ketone ketone) (PPFEKK) copolymers were designed and synthesized via nucleophilic aromatic substitution polymerization of 1,4-bis(4-fluorobenzoyl)benzene (BFBB), 4-(4-hydroxyphenyl)(2 H)-phthalazin-1-one (DHPZ) and 9,9-bis(4-hydroxyphenyl)fluorene (BHPF) to investigate the effects of bulky fluorene units on the processability and thermal degradation behavior of the polymers. The structures of the PPFEKKs were investigated and confirmed by FTIR, 1H NMR, wide-angle X-ray diffraction (WAXD) and gel permeation chromatography (GPC) techniques. Traditional thermal measurements showed that the Td5% and Td10% values of the copolymers increased as the content of BHPF units increased from 0 to 100 mol%, while their glass transition temperatures gradually decreased. The rheological measurements showed that the processability of the copolymers significantly improved upon incorporation of BHPF units; the poly(aryl ether)s were less viscous and thus more processable. The thermal degradation kinetics were clarified using TGA with Kissinger’s method. The copolymer undergoes two thermal degradation processes: as the content of BHPF units in the copolymers increased from 0 to 100 mol%, the activation energy of the first degradation reaction increased from 228 to 254 kJ mol−1, and the activation energy of the second degradation reaction increased from 271 to 298 kJ mol−1. The resulting films displayed excellent tensile strength (higher than 76 MPa), and their Young’s modulus values were inversely proportional to their BHPF contents. Dynamic mechanical analysis showed storage modulus values at 30 °C of approximately 2662, 2826, 2698, 2791 and 2830 MPa for the prepared polymers. Furthermore, the PPFEKKs were soluble in a variety of organic solvents, making them suitable for film casting.

Densely quaternized anion exchange membranes synthesized from Ullmann coupling extension of ionic segments for vanadium redox flow batteries

Membranes with high ion conductivity and selectivity are important for vanadium redox flow batteries. Herein, densely quaternized anion exchange membranes based on quaternary ammonium functionalized octa-benzylmethyl-containing poly(fluorenyl ether ketone)s (QA-OMPFEKs) were prepared from the (i) condensation polymerization of a newly developed octa-benzylmethyl-containing bisphenol monomer via Ullmann coupling, (ii) bromination at the benzylmethyl sites using N-bromosuccinimide, and (iii) quaternization of the bromomethyl groups using trimethylamine. The QA-OMPFEK-20 with an ion exchange capacity (IEC) of 1.66 mmol g−1 exhibited a higher SO42− conductivity (9.62 mS cm−1) than that of the QA-TMPFEK-40 (4.82 mS cm−1) at room temperature, which had a slightly higher IEC of 1.73 mmol g−1 but much lower QA density. The enhanced SO42− conductivity of QA-OMPFEK-20 was attributed to the ion-segregated structure arising from the densely anchored QA groups, which was validated by SAXS observation. Furthermore, the QA-OMPFEK-20 showed much lower VO2+ permeability (1.24×10−14 m2 s−1) than QA-TMPFEK-40 (5.40×10−13 m2 s−1) and Nafion N212 (5.36×10−12 m2 s−1), leading to improved Coulombic and energy efficiencies in Vanadium redox flow batteries (VRFBs). Therefore, the Ullmann coupling extension is a valuable approach for the development of high performance anion exchange membranes for VRFBs.

Carbon felt interlayer derived from rice paper and its synergistic encapsulation of polysulfides for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have remarkably high theoretical specific capacity as promising candidates for next-generation energy storage. However, the “polysulfides shuttle” effect hampers its commercial application. Here, we use a kind of rice paper as a raw material to get inorganic oxides doping carbon felt by the facile carbonization method, and then modified by a simple coating process using poly (fluorenyl ether ketone) and Super P slurry. The special structure of the carbon felt derived from rice paper and its modified layer endow the final electronic conductive interlayer with inherent polysulfides absorbents and ion Coulombic repulsion functions, respectively, which show synergistic effect for trapping polysulfides. As an interlayer of Li-S batteries, the obtained carbon felt/poly (fluorenyl ether ketone)& Super P (CFSS) interlayer shows excellent electrochemical performance in improving specific capacity and decreasing polarization. The batteries with CFSS interlayer exhibit a high capacity of 837 mA h g−1 at 2.0 C and a high initial capacity of 1073.4 mA h g−1 and good capacity retention of 824.5 mA h g−1 after 500 cycles at 0.5 C. CFSS interlayer also shows excellent anti-self-discharge performance. Therefore, the simple and economical CFSS interlayer can be considered as a promising component for high performance Li-S batteries.

High performance blend membranes based on densely sulfonated poly(fluorenyl ether sulfone) block copolymer and imidazolium-functionalized poly(ether sulfone)

AbstractNovel physically crosslinked polymer membranes were prepared by simply blending densely sulfonated poly(fluorenyl ether sulfone) with imidazolium-functionalized poly(ether sulfone). The blend showed well-defined ionic channels originating from the densely sulfonated structure and was physically crosslinked by ionic interactions. These two factors combined to enhance the physical stability and chemical stability of the prepared membranes while offering a conductivity over 0.24 S/cm at 80 °C for various amounts of crosslinker in the blend. The influence of this crosslinker amount on the chemophysical properties of the blend membranes was studied in a systematic way.

The effect of adjusting the hydrophilic–hydrophobic block length in densely sulfonated poly(fluorenyl ether sulfone) block copolymer membranes

Densely sulfonated poly(fluorenyl ether sulfone) block copolymers (DS-PFESs) of various hydrophilic and hydrophobic oligomer block lengths were prepared, and the effect of the block length on the membranes' physicochemical and electrical properties was systematically investigated. Although the conductivity increased with the block length, a morphological analysis identified an optimal chain length. Further increases in the chain length resulted in the formation of larger ionic cluster clumps that caused a significant loss in the phase separation and, hence the dimensional/mechanical stability. The DS-9-32 membrane, prepared with a hydrophilic and hydrophobic block length of 9:32, displayed a well-balanced hydrophilic/hydrophobic phase separation and a high conductivity, together with a high dimensional/mechanical stability.

Development and Characterization of Highly Conducting Nonfluorinated Di and Triblock Copolymers for Polymer Electrolyte Membranes

To achieve stable polymer electrolyte membranes (PEMs) with efficient ionic nano-channels, novel fully aromatic AB or ABA copolymers composed of poly(fluorenyl ether sulfone biphenyl)s (PFESBs) and poly(arylene ether sulfone)s (PAESs) were synthesized via polymerization and post-sulfonation methods, and were explored as fuel cell membranes. The structural analysis of synthesized copolymers and the corresponding membranes were ascertained by gel permeation chromatography (GPC), Fourier transform infrared (FTIR), and 1H nuclear magnetic resonance (NMR) techniques. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis showed that the prepared membranes were thermally stable, so that elevated temperature fuel cell operation would be possible. High hydrophilic and hydrophobic nano-phase separation and obvious ionic aggregate block morphology was observed in both triblock and diblock copolymers in atomic force microscopy (AFM) phase images, which may be highly related to their proton transport ability. A sulfonated AB diblock copolymer membrane with an ion-exchange capacity (IEC) of 2.06 meq g−1 has a maximum proton conductivity of 184 mS cm−1, which is higher than that of a perfluorosulfonic acid membrane under the same measurement conditions.

Highly branched sulfonated poly(fluorenyl ether ketone sulfone)s membrane for energy efficient vanadium redox flow battery

A series of highly branched sulfonated poly (fluorenyl ether ketone sulfone)s (HSPAEK) are synthesized by direct polycondensation reactions. The HSPAEK with 8% degree of branching is further investigated as membrane for vanadium redox flow battery (VRFB). The HSPAEK membrane prepared by solution casting method exhibits smooth, dense and tough morphology. It possesses very low VO2+ permeability and high ion selectivity compared to those of Nafion 117 membrane. When applied to VRFB, this novel membrane shows higher coulombic efficiency (CE, 99%) and energy efficiency (EE, 84%) than Nafion 117 membrane (CE, 92% and EE, 78%) at current density of 80 mA cm−2. Besides, the HSPAEK membrane shows super stable CE and EE as well as excellent discharge capacity retention (83%) during 100 cycles life test. After being soaked in 1.5 mol L−1 VO2+ solution for 21 days, the weight loss of HSPAEK membrane and the amount of VO2+ reduced from VO2+ are only 0.26% and 0.7%, respectively, indicating the superior chemical stability of the membrane.

Sulfonated Poly(Fluorenyl Ether Ketone) Membranes with Suppressed Semi-Interpenetrating Crossover and Enhanced Proton Selectivity for Vanadium Redox Flow Batteries

A series of hybrid membranes with special microstructure, based on sulfonated poly (fluorenyl ether ketone) ionomer (SPFEK, IEC=1.74 mequiv.g-1) and secondary amine group containing SiO2 (SiO2–NH–NH2), has been successfully designed and prepared for vanadium redox flow battery (VRB) application. The hybrid membranes are prepared by simply adding KH792 into the SPFEK solution in N,N’-dimethylacetamide (DMAc), followed by dispersion, co-condensation and solvent casting. The water uptake, mechanical property, proton conductivity, (VO)2+ permeability and single cell performance are investigated in order to understand the relationship between morphology and property of the membranes. The hybrid membranes show dramatically improved proton selectivity when compared with SPFEK. The vanadium ion (VO)2+ permeability through the hybrid membrane is about 10 times lower than that of virgin SPFEK. The columbic efficiency and energy efficiency of the single cell of the hybrid membrane are higher than the SPFEK membrane. The results inidicate that hybrid membranes of this type are promising for VRBs.

Amphoteric ion exchange membrane synthesized by direct polymerization for vanadium redox flow battery application

Novel sulfonated poly (fluorenyl ether ketone) with pendant quaternary ammonium groups (SPFEKA) was successfully synthesized by one-pot copolymerization of bis(4-fluoro-3-sulfophenyl)sulfone disodium salt, 4,4′-difluorobenzophenone, bisphenol fluorene and 2,2′-dimethylaminemethylene-9,9′-bis(4-hydroxyphenyl) fluorene (DABPF). The chemical structures were confirmed by FT-IR, and 1H NMR. The thermal properties were fully investigated by TGA. The synthesized copolymers SPFEKAs are soluble in aprotic solvents, and can be cast into membranes on a glass plate from their N,N′-dimethylacetamide (DMAc) solution. A new kind of amphoteric ion exchange membrane (AIEM) was obtained by immersed SPFEKA into 1 M sulfuric acid. The proton conductivities of these membranes are comparable to the most reported sulfonated polymers under the same conditions. The permeability of vanadium ions in vanadium redox flow battery (VRB) was effectively suppressed by introducing quaternary ammonium groups for Donnan exclusion effect. AIEM-20% possess a only 4.4% vanadium ion permeability of Nafion 115. Cell performance tests showed that the VRB assembled with AIEM-20% shows the highest coulombic efficiency (CE) at the current density of 50 mA/cm2, because of its lowest VO2+ permeability. In conclusion, these ionomers could be promising candidates for ion-exchange membranes for VRB applications.

Synthesis of highly branched sulfonated polymers and the effects of degree of branching on properties of branched sulfonated polymers as proton exchange membranes

Branched sulfonated polymers exhibit excellent properties as proton exchange membranes (PEMs). However, very few highly branched sulfonated polymers are reported as PEMs. The highly branched polymer, including the method to increase degree of branching (DB) and the effects of DB on the properties of PEMs, should be further studied. In this work, novel branched sulfonated poly(fluorenyl ether ketone sulfone)s with different DB value are synthesized by direct polycondensation reactions from bisphenol fluorene (A2), sulfonated 4,4′-difluorobenzphenone, 1,3,5-tris(4-(4-fluorophenylsulfonyl)phenyl)benzene (B3-3) and 4,4′-difluorodiphenyl sulfone. The highest DB with 10% branching agent is obtained using the B3-3 monomer. The method to increase the DB is discussed. It is found that B3 scaffold with long and hard arms can effectively increase the DB value. The effects of DB on the properties, including oxidative stability, proton conductivity, water uptake, swelling ratio, thermal stability, mechanical property and microstructure, are investigated. With increasing DB value, oxidative stability and proton conductivity of the membranes increase remarkably, but swelling ratio and tensile strength decrease slowly. The membrane with the highest DB value (10%) exhibits high proton conductivity (0.42 S cm−1) and oxidative stability (327 min), as well as relatively low swelling ratio (16.2%) at 80 °C.