A block sulfonated polybenzimidazole and its preparation method

Abstract

The present invention belongs to the technical field of fuel cell proton exchange membrane materials and relates to a block sulfonated polybenzimidazole and a preparation method thereof. This block sulfonated polybenzimidazole is made from aromatic dicarboxylic acid, sulfonated 4,4-dicarboxyl diphenyl ether and 3,3-diaminobenzidine. Amino-terminated and carboxyl-terminated prepolymers are first synthesized separately, and then block polymerization is carried out. The block copolymer can form a microphase-separated structure in the membrane, thereby enhancing the internal connectivity of the block, helping to form a continuous proton transport channel, which is beneficial to proton conduction. Sulfonic acid groups are introduced into PBI through covalent bonds to achieve rapid proton conduction and solve the acid leakage problem well. The presence of ether bonds in the main chain of the molecule can increase the flexibility of the polymer chain, which is beneficial to improving the solubility of PBI and the toughness of the proton exchange membrane. At the same time, the introduction of sulfone groups allows the membrane to maintain good mechanical properties when the water absorption content is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cell proton exchange membrane materials, and particularly relates to a block sulfonated polybenzimidazole and a preparation method thereof. The prepared block sulfonated polybenzimidazole can be used to prepare proton exchange membrane materials. Background Art

[0002] Proton exchange membranes (PEMs) are the core material of PEM fuel cells (PEMFCs). Polybenzimidazole (PBI) is an excellent PEM material due to its excellent thermal stability, good film-forming properties, and exceptional chemical stability. PBI is typically produced by copolymerizing a diacid monomer with a tetraamine monomer. The PBI backbone contains repeating benzimidazole units. Phosphoric acid doping weakens the interaction between the -NH and -N=C groups on the imidazole ring, making the PBI membrane brittle. This limits the level of phosphoric acid doping and its application in high-temperature PEMFCs (HT-PEMFCs). Furthermore, phosphoric acid is readily soluble in water and easily leaks, resulting in a decrease in proton conductivity. To improve the proton conductivity and mechanical properties of PBI membranes, researchers have conducted extensive research on PBI, primarily through chemical structure modification, blending, and crosslinking. Sulfonic acid groups can also be introduced into PBI via covalent bonds, enabling rapid proton conduction and effectively addressing the acid leakage problem. However, most currently developed PBIs are obtained through random copolymerization and often suffer from low proton conductivity and poor mechanical properties. The study found that the microstructure of microphase separation has an important influence on proton conduction, and block copolymers can form a microphase separation structure due to the thermodynamic incompatibility between the blocks, thereby enhancing the internal connectivity of the blocks, helping to form a continuous proton transport channel, and facilitating proton conduction. Summary of the Invention

[0003] In order to overcome the above problems in the prior art, the present invention provides a block sulfonated polybenzimidazole from the perspective of improving polymer properties. The proton exchange membrane prepared using the block sulfonated polybenzimidazole has good mechanical strength and proton conductivity.

[0004] To achieve the purpose of the present invention, the technical solution adopted by the present invention is: a block sulfonated polybenzimidazole, the general structural formula of the block sulfonated polybenzimidazole is:

[0005]

[0006] Wherein: R is any one of an oxy group or a sulfone group, and m:n=3~7:3~7.

[0007] The method for preparing the above-mentioned block sulfonated polybenzimidazole comprises the following steps:

[0008] (1) Under nitrogen protection, 3,3-diaminobenzidine was fully dissolved in polyphosphoric acid as a solvent and added to a three-necked flask (specifically, polyphosphoric acid was added to a three-necked flask as a solvent, heated to 120°C and stirred to expel the air in the polyphosphoric acid, 3,3-diaminobenzidine was first added and heated to 140°C and stirred to fully dissolve 3,3-diaminobenzidine), and then aromatic dicarboxylic acid was added Wherein: R is either an oxy group or a sulfone group, and the temperature is raised to 190℃~200℃ for reaction for 10~12h to obtain an amino-terminated prepolymer PBI-Am. After the reaction is completed, the reaction liquid is reserved for the next reaction. Its general structural formula is as follows:

[0009]

[0010] (2) Under nitrogen protection, 3,3-diaminobenzidine was fully dissolved in polyphosphoric acid as a solvent and added to a three-necked flask (specifically, polyphosphoric acid was used as a solvent, mechanically stirred at 120°C to expel the air in the polyphosphoric acid, and then a certain molar mass of 3,3-diaminobenzidine was added, and mechanically stirred at 140°C for 1 hour to dissolve the 3,3-diaminobenzidine). Then, a certain molar mass of sulfonated 4,4-dicarboxydiphenyl ether was added, and the temperature was raised to 170°C, stirred for 1 hour, and left for the next reaction. Its structural formula is as follows:

[0011]

[0012] (3) Under nitrogen protection, the amino-terminated PBI-Am obtained in step (1) is poured into the three-necked flask containing the carboxyl-terminated SOPBI-Ac obtained in step (2), and the reaction is continued at 200°C for 12 hours. After the reaction is completed, it is poured into ice water. The filtered product is poured into a carbonate or bicarbonate solution of a certain concentration (for neutralizing polyphosphoric acid, but it is necessary to avoid the system from being alkaline), stirred overnight in a water bath (generally 80°C), then filtered and washed with water and ethanol, and finally dried (specifically, the dark green product is placed in a 120°C oven and dried for 12 hours).

[0013] Furthermore, the content of the reactant in step (1) in the polyphosphoric acid is 3 wt% to 8 wt%.

[0014] Furthermore, the 3,3-diaminobenzidine in step (1) is in an excess of 3 wt % to 6 wt % relative to the aromatic dicarboxylic acid.

[0015] Furthermore, the sulfonated 4,4-dicarboxydiphenyl ether in step (2) is in excess of 3 wt % to 6 wt % relative to 3,3-diaminobenzidine.

[0016] Furthermore, in step (3), the system is washed to a pH of 7.0 to 8.0.

[0017] Furthermore, the carbonate in step (3) is sodium carbonate or sodium bicarbonate, and its concentration is 5wt% to 8wt%.

[0018] The beneficial effects of the present invention are as follows: the block sulfonated polybenzimidazole and block copolymer of the present invention can form a nanophase-separated structure in the membrane by changing factors such as the chemical composition and the volume fraction of each block, thereby enhancing the internal connectivity of the block, helping to form a continuous proton transport channel, and facilitating proton conduction. Most importantly, the block directly improves the proton conductivity without increasing the level of phosphoric acid doping, so it solves the problem of balancing phosphoric acid doping with mechanical properties. Sulfonic acid groups are introduced into PBI through covalent bonds to achieve rapid proton conduction. The presence of ether bonds in the main chain of the molecule can increase the flexibility of the polymer chain, which is beneficial to improving the solubility of PBI and the toughness of the proton exchange membrane. At the same time, the introduction of sulfone groups allows the membrane to maintain good mechanical properties even when the water absorption content is high. The block sulfonated polybenzimidazole of the present application, and the use of this block sulfonated polybenzimidazole to prepare a proton exchange membrane can improve the mechanical properties and proton conductivity of the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The sulfonated 4,4'-dicarboxyl diphenyl ether prepared in step (1) of Example 1 1 H NMR (DMSO-d6).

[0020] Figure 2 The block and random sulfonated polybenzimidazole prepared in Examples 2 to 5 1 H NMR (DMSO-d6).

[0021] Figure 3 Graph showing the proton conductivity of the block and random sulfonated polybenzimidazole prepared in Example 7 as a function of temperature. DETAILED DESCRIPTION

[0022] The following is further described in conjunction with specific embodiments:

[0023] Example 1

[0024] Synthesis of sulfonated 4,4'-dicarboxydiphenyl ether

[0025] 45mL of fuming sulfuric acid (30% SO3) and 15.000g of 4,4'-dicarboxyldiphenyl ether (58.0mmol) were added to a 250mL three-necked flask equipped with a magnetic stirrer and a nitrogen inlet and outlet. The mixture was reacted at 110°C for 2h, and the final brown uniform solution was slowly poured into ice water. Then, after the ice melted, it was salted out with sodium chloride to obtain a crude product. The resulting precipitate was filtered and recrystallized twice in water with a yield of 75%. After vacuum drying at 120°C for 20h, the product sulfonated 4,4'-dicarboxyldiphenyl ether was obtained. The product was subjected to 1 H NMR characterization, see Figure 1 The attribution of each peak is marked in the spectrum, proving the synthesis of sulfonated 4,4'-dicarboxydiphenyl ether.

[0026] Example 2

[0027] (1) Synthesis of carboxyl-terminated prepolymer SOPBI-Ac

[0028] Under nitrogen, add 50.000g of polyphosphoric acid to a 250mL three-necked flask and mechanically stir at 120°C. Then add 2.928g (7.0mmol) of sulfonated 4,4'-dicarboxydiphenyl ether and 1.499g (7.0mmol) of 3,3'-diaminobenzidine. The actual amount added is 3.106g of sulfonated 4,4'-dicarboxydiphenyl ether, a 3% excess. Stir the heterogeneous mixture until a homogeneous solution is formed. Incubate at 170°C for 1h before proceeding to the next step.

[0029] (2) Synthesis of amino-terminated prepolymer SO2-PBI-Am

[0030] Under nitrogen, add 52.000 g of polyphosphoric acid to a 100 mL three-necked flask and mechanically stir at 120°C. Then add 0.918 g (3.0 mmol) of 4,4'-dicarboxydiphenylsulfone and 0.642 g (3.0 mmol) of 3,3'-diaminobenzidine. The actual amount of 3,3'-diaminobenzidine added is 0.662 g, a 3% excess. The heterogeneous mixture is stirred until a homogeneous solution is formed and then reacted at 200°C for 12 hours before being used for the next reaction.

[0031] (3) Synthesis of block sulfonated polybenzimidazole (SO2-b-SOPBI)

[0032] Under nitrogen protection, the amino-terminated SO2-PBI-Am obtained in step (2) was poured into a three-necked flask containing the carboxyl-terminated SOPBI-Ac obtained in step (1), and the reaction was continued at 200°C for 10 hours. After the reaction was completed, it was poured into ice water, and the filtered product was poured into a 5wt% sodium bicarbonate solution, stirred in an 80°C water bath for 12 hours, then filtered and washed with water and ethanol to pH = 7, and finally the dark green product was placed in a 120°C oven and dried for 12 hours to obtain the product block sulfonated polybenzimidazole with a yield of 81%. The product was subjected to 1 H NMR characterization, see Figure 2 The attribution of each peak is marked in the spectrum, proving the synthesis of block sulfonated polybenzimidazole.

[0033] Example 3

[0034] (1) Synthesis of carboxyl-terminated prepolymer SOPBI-Ac

[0035] Under nitrogen, add 32.000 g of polyphosphoric acid to a 100 mL three-necked flask and mechanically stir at 120°C. Then, add 1.255 g (3.0 mmol) of sulfonated 4,4'-dicarboxydiphenyl ether and 0.642 g (3.0 mmol) of 3,3'-diaminobenzidine. The actual amount added is 1.330 g of sulfonated 4,4'-dicarboxydiphenyl ether, a 6% excess. Stir the heterogeneous mixture until a homogeneous solution forms. Incubate at 170°C for 1 h before proceeding to the next step.

[0036] (2) Synthesis of amino-terminated prepolymer SO2-PBI-Am

[0037] Under nitrogen, add 26.000 g of polyphosphoric acid to a 100 mL three-necked flask and mechanically stir at 120°C. Then, add 0.918 g (3.0 mmol) of 4,4'-dicarboxydiphenylsulfone and 0.642 g (3.0 mmol) of 3,3'-diaminobenzidine. The actual amount of 3,3'-diaminobenzidine added is 0.681 g, a 6% excess. The heterogeneous mixture is stirred until a homogeneous solution is formed and then reacted at 200°C for 12 hours before being used for the next reaction.

[0038] (3) Synthesis of block sulfonated polybenzimidazole (SO2-b-SOPBI)

[0039] Under nitrogen protection, the amino-terminated SO2-PBI-Am obtained in step (2) was poured into a three-necked flask containing the carboxyl-terminated SOPBI-Ac obtained in step (1), and the reaction was continued at 200°C for 10 hours. After the reaction was completed, it was poured into ice water, and the filtered product was poured into 8wt% sodium carbonate solution, stirred in an 80°C water bath for 12 hours, then filtered and washed with water and ethanol to pH = 7, and finally the dark green product was placed in a 120°C oven and dried for 12 hours to obtain the product block sulfonated polybenzimidazole. The product was subjected to 1 H NMR characterization, see Figure 2 The attribution of each peak is marked in the spectrum, proving the synthesis of block sulfonated polybenzimidazole.

[0040] Example 4

[0041] (1) Synthesis of carboxyl-terminated prepolymer SOPBI-Ac

[0042] Under nitrogen, add 30.000 g of polyphosphoric acid to a 250 mL three-necked flask and mechanically stir at 120°C. Then, add 1.255 g (3.0 mmol) of sulfonated 4,4'-dicarboxydiphenyl ether and 0.642 g (3.0 mmol) of 3,3'-diaminobenzidine. The actual amount added is 1.305 g of sulfonated 4,4'-dicarboxydiphenyl ether, a 4% excess. Stir the heterogeneous mixture until a homogeneous solution forms. Incubate at 170°C for 1 h before proceeding to the next step.

[0043] (2) Synthesis of amino-terminated prepolymer SO2-PBI-Am

[0044] Under nitrogen, add 125.000 g of polyphosphoric acid to a 250 mL three-necked flask and mechanically stir at 120°C. Then, add 2.144 g (7.0 mmol) of 4,4'-dicarboxydiphenylsulfone and 1.499 g (7.0 mmol) of 3,3'-diaminobenzidine. The actual amount of 3,3'-diaminobenzidine added is 1.559 g, a 4% excess. The heterogeneous mixture is stirred until a homogeneous solution is formed and then reacted at 200°C for 12 hours before being used for the next reaction.

[0045] (3) Synthesis of block sulfonated polybenzimidazole (SO2-b-SOPBI)

[0046] Under nitrogen protection, the amino-terminated SO2-PBI-Am obtained in step (2) was poured into a three-necked flask containing the carboxyl-terminated SOPBI-Ac obtained in step (1), and the reaction was continued at 200°C for 10 hours. After the reaction was completed, it was poured into ice water, and the filtered product was poured into a 6wt% sodium bicarbonate solution, stirred in an 80°C water bath for 12 hours, then filtered and washed with water and ethanol to pH = 7, and finally the dark green product was placed in a 120°C oven and dried for 12 hours to obtain the product block sulfonated polybenzimidazole. The product was subjected to 1 H NMR characterization, see Figure 2 The attribution of each peak is marked in the spectrum, proving the synthesis of block sulfonated polybenzimidazole.

[0047] Example 5

[0048] Synthesis of random sulfonated polybenzimidazole

[0049] Under nitrogen protection, 80.000g of polyphosphoric acid was added to a 250mL three-necked flask, mechanically stirred at 120°C, 1.285g (6.0mmol) of 3,3-diaminobenzidine was added and the temperature was raised to 140°C, mechanically stirred for 1h to dissolve it, 0.918g (3.0mmol) of 4,4-dicarboxyldiphenyl sulfone and 1.255g (3.0mmol) of sulfonated 4,4-dicarboxyldiphenyl ether were added and the temperature was raised to 170°C. The heterogeneous mixture was stirred and reacted at 200°C for 24h after forming a homogeneous solution. After the reaction, it was poured into ice water, and the obtained filamentous product was filtered, then immersed in 7wt% sodium bicarbonate solution, placed in an 80°C water bath overnight, then filtered and washed with water and ethanol, and finally placed in a 120°C oven to dry for 12h to obtain the product. The product was subjected to 1 H NMR characterization, see Figure 2 The attribution of each peak is marked in the spectrum, proving the synthesis of random sulfonated polybenzimidazole.

[0050] Example 6

[0051] (1) Synthesis of carboxyl-terminated prepolymer SOPBI-Ac

[0052] Under nitrogen, add 32.000 g of polyphosphoric acid to a 100 mL three-necked flask and mechanically stir at 120°C. Then, add 1.331 g (3.0 mmol) of sulfonated 4,4'-dicarboxydiphenyl ether and 0.642 g (3.0 mmol) of 3,3'-diaminobenzidine. Stir the heterogeneous mixture until a homogeneous solution forms. Incubate at 170°C for 1 h before reserving for the next reaction.

[0053] (2) Synthesis of amino-terminated prepolymer OPBI-Am

[0054] Under nitrogen, add 26.000 g of polyphosphoric acid to a 100 mL three-necked flask and mechanically stir at 120°C. Then add 0.918 g (3.0 mmol) of 4,4'-dicarboxydiphenyl ether and 0.642 g (3.0 mmol) of 3,3'-diaminobenzidine. Stir the heterogeneous mixture until a homogeneous solution forms. Incubate at 200°C for 12 hours before reserving for the next reaction.

[0055] (3) Synthesis of block sulfonated polybenzimidazole (Ob-SOPBI)

[0056] Under nitrogen protection, the amino-terminated OPBI-Am obtained in step (2) was poured into a three-necked flask containing the carboxyl-terminated SOPBI-Ac obtained in step (1), and the reaction was continued at 200°C for 10 hours. After the reaction was completed, it was poured into ice water. The filtered product was poured into a 5wt% sodium carbonate solution and stirred in an 80°C water bath for 12 hours. Then, it was filtered and washed with water and ethanol until the pH was 7. Finally, the dark green product was placed in a 120°C oven and dried for 12 hours to obtain the product block sulfonated polybenzimidazole.

[0057] Example 7

[0058] 0.5 g of a block polymer prepared with a 3:7 molar ratio of aromatic dicarboxylic acid to sulfonated 4,4-dicarboxydiphenyl ether (Example 2), a block polymer prepared with a 1:1 molar ratio of aromatic dicarboxylic acid to sulfonated 4,4-dicarboxydiphenyl ether (Example 3), a block polymer with a 7:3 molar ratio (Example 4), and a random copolymer with a 1:1 molar ratio (Example 5) were weighed and added to 10 g of DMSO. The mixture was magnetically stirred at 120°C for 2 hours. After cooling to room temperature, the solution was centrifuged to remove undissolved particles. The resulting homogeneous solution was poured onto a smooth glass plate and smoothed with a spatula to obtain a proton exchange membrane with a thickness of 40 μm. The membrane was then placed in a vacuum drying oven at 80°C for 12 hours. Finally, the membrane was peeled off and immersed in anhydrous methanol for 24 hours to remove residual DMSO. The membrane was then transferred to a 1M H2SO4 solution and soaked for 24 hours to ensure sufficient proton exchange. Finally, it was rinsed with a large amount of deionized water until it was neutral and moved to a vacuum drying oven at 80°C for 10 hours. The membrane was tested for proton conductivity at 30°C to 180°C and 100% relative humidity. Figure 3 , the proton conductivity of all membranes increases steadily with increasing temperature.

[0059] The SO2-b-SOPBI (3:7) membrane exhibited excellent proton conductivity (0.27 S / cm at 160°C) and good mechanical strength of 64.0 MPa. The weight loss rate after immersion in Fenton's reagent for 60 hours was 65.9%. The weight loss rate of the SO2-b-SOPBI (1:1) membrane after immersion in Fenton's reagent for 60 hours was 42.1%. The proton conductivity at 160°C was 0.24 S / cm, which was higher than that of the Random-SOPBI (1:1) membrane (0.15 S / cm at 160°C). The tensile strength was 61.4 MPa, which was much higher than that of the Random-SOPBI (1:1) membrane. 212 membrane (DuPont, USA) (12.9 MPa). In contrast, SO2-b-SOPBI (7:3) has a proton conductivity of only 0.09 S / cm at 160°C, a tensile strength of 60.8 MPa, and a weight loss of 19.5% after immersion in Fenton's reagent for 60 hours.

[0060] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent replacement or modification made by a person skilled in the art according to the technical solution and concept of the present invention within the technical scope disclosed by the present invention shall be covered by the scope of protection of the present invention. It should be noted that the embodiments and features of the embodiments of the present invention may be combined with each other unless there is a conflict.

Claims

1. A block sulfonated polybenzimidazole, characterized in that: The general structural formula of the block sulfonated polybenzimidazole is: Wherein: R=O group or sulfone group; m:n=3~7:3~7.

2. A method for preparing the block sulfonated polybenzimidazole according to claim 1, characterized in that: The steps include: (1) Under nitrogen protection, 3,3-diaminobenzidine was fully dissolved in polyphosphoric acid solvent, and then aromatic dicarboxylic acid was added. Wherein: R = either oxy or sulfone group, the temperature is raised to 190℃~200℃ and the reaction is carried out for 10~12h to obtain amino-terminated prepolymer PBI-Am. After the reaction is completed, the reaction liquid is reserved for the next reaction. The general structural formula is as follows: (2) Under nitrogen protection, 3,3-diaminobenzidine is fully dissolved in polyphosphoric acid as a solvent, and then sulfonated 4,4-dicarboxydiphenyl ether is added. The temperature is raised to 180°C to 200°C and stirred for 1 to 2 hours to obtain a carboxyl-terminated prepolymer SOPBI-Ac, which is reserved for the next reaction. Its structural formula is as follows: (3) Under nitrogen protection, the amino-terminated PBI-Am obtained in step (1) is poured into the carboxyl-terminated prepolymer SOPBI-Ac obtained in step (2), and the reaction is continued at 190° C. to 200° C. for 10 to 12 hours. After the reaction is completed, the mixture is poured into ice water. The filtered product is poured into a carbonate solution of a certain concentration to neutralize the polyphosphoric acid, and then filtered and washed with water and ethanol for at least three times. Finally, the dark green product is dried to obtain the block sulfonated polybenzimidazole.

3. The method for preparing the block sulfonated polybenzimidazole according to claim 2, wherein: The reactant in step (1) has a content of 3 wt% to 8 wt% relative to the polyphosphoric acid.

4. The method for preparing the block sulfonated polybenzimidazole according to claim 2, wherein: The 3,3-diaminobenzidine in step (1) is in excess of 3 wt% to 6 wt% relative to the aromatic dicarboxylic acid.

5. The method for preparing the block sulfonated polybenzimidazole according to claim 2, wherein: The sulfonated 4,4-dicarboxydiphenyl ether in step (2) is in excess of 3 wt % to 6 wt % relative to 3,3-diaminobenzidine.

6. The method for preparing the block sulfonated polybenzimidazole according to claim 2, wherein: In step (3), the solution is washed to a pH of 7.0 to 8.

0.

7. The method for preparing the block sulfonated polybenzimidazole according to claim 2, wherein: The carbonate described in step (3) is sodium carbonate or sodium bicarbonate, and its concentration is 5wt% to 8wt%.

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