A long-short branched perfluorosulfonic acid resin, proton membrane, and preparation method and application thereof

Abstract

The present invention belongs to the field of polymer materials, and relates to a kind of long and short branched perfluorosulfonic acid resin, proton membrane and its preparation method and application, the resin structure has both long branched perfluorosulfonic acid and short branched perfluorosulfonic acid structural units, and retains the structural advantage of perfluorosulfonic acid resin.The introduction of long branched perfluorosulfonic acid structure can regulate the water absorption rate of resin and membrane, improve dimensional stability; In addition, the cationic group in the structure can effectively improve the dissociation of terminal sulfonic acid group, improve the ionic conductivity of proton membrane, and solve the contradiction between "long side chain" and "low conductivity". The sulfonic acid group in the short branched perfluorosulfonic acid structure can form an acid-base ion pair with the amino group (N) in the long branched perfluorosulfonic acid structure, effectively limiting the strong water absorption of the sulfonic acid group in the proton membrane, and can greatly enhance the mechanical properties of the membrane; In addition, the ion pair formed can also carry out ion conduction, solve the contradiction between "short side chain" and "high swelling".

Description

Technical Field

[0001] The invention belongs to the field of polymer materials and relates to a long- and short-chain branched perfluorosulfonic acid resin, a proton membrane, and a preparation method and application thereof. Background Art

[0002] The traditional homogeneous perfluorosulfonic acid proton exchange membrane (PFSA) is prepared by an ion exchange resin with a single cation exchange function. Its main chain structure is a strongly hydrophobic polytetrafluoroethylene (Teflon) skeleton, and the side chain has a single hydrophilic cation exchange group (-SO3 - , negatively charged groups) side chains. The hydrophilic cationic groups on the side chains of perfluorosulfonic acid resins will undergo affinity / disappearance microphase separation with the hydrophobic main chain structure, thereby forming nanoscale sulfonic acid ion clusters that are evenly distributed in the continuous CF lattice (polymer crystal region). Under working conditions, the transfer of ions in PFSA is conducted by the sulfonic acid groups reacting with water to form hydrated protons. The high water absorption rate of a single sulfonic acid group causes an expansion-de-expansion process in the PFSA proton membrane, which leads to serious swelling problems, causing the membrane to deform and even cause problems such as pinholes or cracks, significantly reducing the mechanical strength of the membrane. In addition, severe swelling problems lead to a reduction in the ion selective permeability of the ion exchange membrane, such as the permeation of hydrogen in fuel cells, the permeation of methanol, the permeation of vanadium ions in vanadium batteries, etc., which leads to a reduction in the selectivity of cations, thereby reducing the energy efficiency of the battery.

[0003] To address the aforementioned issues with current PFSA membranes, currently used methods include compounding polytetrafluoroethylene (PTFE) membranes with PFSA to improve the tensile strength and reduce swelling of proton exchange membranes, and this method has achieved some success. For example, CN101692487A uses a combined ultrasonic impregnation-spraying method to compound PFSA resin onto the surface of an expanded PTFE microporous membrane. Ultrasonic impregnation involves ultrasonically immersing the expanded PTFE microporous membrane in a PFSA solution, while spraying involves repeatedly coating the ultrasonically impregnated expanded PTFE membrane with a coating to produce a proton exchange membrane of a predetermined thickness. CN101667648A discloses a method for compounding a PTFE membrane. Perfluorosulfonic acid resin and silica components are impregnated into the micropores of an expanded PTFE microporous membrane through impregnation, and the thickness of the composite proton exchange membrane is controlled by spraying the perfluorosulfonic acid resin and silica components. However, due to the poor compatibility between hydrophobic PTFE and hydrophilic PFSA, surface treatment is required, making the compounding process relatively complex. In addition, PTFE itself does not have proton conduction function, and the resulting composite membrane will inevitably lose its ion conduction performance and face the problem of low conductivity.

[0004] Research has found that extending the side chain length can also reduce PFSA's water absorption, effectively limiting excessive membrane swelling. However, simply extending the chain length can reduce PFSA's ion exchange capacity, leading to problems such as low membrane ion conductivity and decreased mass transfer performance. Furthermore, shortening the side chain length can increase PFSA's conductivity. However, shortening the side chain length increases PFSA's ion exchange capacity, leading to problems such as excessive water absorption and high membrane swelling. Maintaining high conductivity while ensuring membrane material stability remains a significant challenge. Summary of the Invention

[0005] In order to solve the excessive swelling problem of perfluorosulfonic acid proton exchange membrane (PFSA), the present invention provides a long and short branched perfluorosulfonic acid resin, a proton membrane and a preparation method and application thereof from the perspective of resin structure.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The long-short branched perfluorosulfonic acid resin is characterized in that the resin structure includes a perfluoroethylene structural unit, a short-chain branched perfluorosulfonic acid structural unit (A) and a long-chain branched perfluorosulfonic acid structural unit (B), and the resin has a structure shown in the following formula I:

[0008]

[0009] wherein ad is an integer from 0 to 30, x is 0 or 1; y, z are integers from 0 to 3, preferably a, c are 1 to 10; b, d = 1; x = 1; y, z = 0, 1; e is the number of repeating units, and e is 50 to 10000; a+b / (a+b+c+d) = 0.30 to 0.90; c+d / (a+b+c+d) = 0.40 to 0.80; preferably a+b / (a+b+c+d) = 0.45 to 0.70; c+d / (a+b+c+d) = 0.30 to 0.55; further preferably a+b / (a+b+c+d) = 0.50 to 0.65; c+d / (a+b+c+d) = 0.35 to 0.50;

[0010] In the structural unit B, m is an integer ≥2, and preferably m is an integer of 2-6.

[0011] Ar in the structural unit B is a cationic group.

[0012] Preferably, the cationic group is H + Or it is composed of a cationic structure and a counterion containing one of the structures in Formula II:

[0013]

[0014] The counter ions are Cl-, SO4 2- , HSO4 - , one of the OH-.

[0015] More preferably, the Ar is H+ or One of them.

[0016] Preferably, the molar percentages of the polymer units in the resin are as follows: the molar percentage of the tetrafluoroethylene structural unit is 35-85%, the molar percentage of the short-chain branched perfluorosulfonic acid structural unit is 10-60%, and the molar percentage of the long-chain branched perfluorosulfonic acid structural unit is 5-55%.

[0017] Further preferably, the molar percentage of each polymer unit in the resin is: the molar percentage of tetrafluoroethylene structural unit is 40-60%, the molar percentage of short-chain branched perfluorosulfonic acid structural unit is 20-35%, and the molar percentage of long-chain branched perfluorosulfonic acid structural unit is 20-35%.

[0018] More preferably, the molar proportion of tetrafluoroethylene structural units is 45-49%, the molar proportion of short-chain branched perfluorosulfonic acid structural units is 21-28%, and the molar proportion of long-chain branched perfluorosulfonic acid structural units is 23-30%.

[0019] The resin has both cation exchange capacity and anion exchange capacity, and the ion exchange capacity is 0.9 to 2.0 mmol / g, more preferably 1.0 to 1.5 mmol / g.

[0020] The present invention also provides a method for preparing the long and short branched perfluorosulfonic acid resin, comprising the following steps:

[0021] Step 1: PFSO2F is pre-swelled in an organic solvent and reacted with an ammonia reagent to convert part of the -SO2F group into -SO2NH2. Then, the remaining -SO2F groups are converted into sulfonate -SO3M (M is K) through an alkaline ion exchange process. + , Na + ), washing and drying to obtain a long and short branched chain intermediate product, the reaction formula is as follows:

[0022]

[0023] Step 2:

[0024] Method (1), when Ar is H + When the intermediate product is directly reacted with Q-Ar2 reagent to graft long-chain -SO3 - , forming -SO3 - ·····HN +HSO2-zwitterionic groups, and then undergo acid ion exchange to obtain long and short branched chain sulfonic acid groups, which are then washed and dried to obtain long and short branched chain perfluorosulfonic acid resin;

[0025] Method (2): When Ar is a cationic group with other positively charged groups, the intermediate product is subjected to a grafting reaction with a Q-Ar2 reagent and a Q-Ar1 reagent with a cationic group in an organic solvent to graft a long branched chain -SO 3- and cationic groups; the product finally undergoes an acid ion exchange process to obtain long and short branched sulfonic acid groups, and after washing and drying, a long and short branched perfluorosulfonic acid resin is obtained.

[0026] The above reaction formula is as follows:

[0027]

[0028] Preferably, the Q-Ar1 reagent is composed of one of the cationic structures and a counter ion in the structure shown in Formula III:

[0029]

[0030] Preferably, the cationic structure in the Q-Ar1 reagent is One of them.

[0031] Preferably, when the counter ion in the Q-Ar1 reagent is Cl - Br - , I - When alkali and acid ion exchange is carried out, the ion is exchanged for OH - , [(CF3SO2)2N] - , (H2PO3) - wait.

[0032] The Q-Ar2 reagent is a reagent with a sultone structure, and its general structural formula is shown in Formula IV, wherein m is an integer ≥ 2;

[0033]

[0034] According to the preferred embodiment of the present invention, the organic solvent in the preparation method is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, ethanol, isopropanol, dichloromethane, acetone, dimethyl sulfoxide or ethyl acetate.

[0035] The ammonia reagent is aqueous ammonia or liquid ammonia. According to the preferred embodiment of the present invention, the molar ratio of PFSO2F resin to ammonia in the method is 1:5-20, preferably 1:10-15; the molar ratio of the intermediate product to the Q-Ar1 and Q-Ar2 reagents is 1:5-12, preferably 1:6-10.

[0036] According to the preferred embodiment of the present invention, the temperature of the grafting reaction in step 2 is 70-90° C., preferably 80° C.; and the reaction time is 10-15 hours, preferably 12 hours.

[0037] According to a preferred embodiment of the present invention, the pre-swelling in step 1 is to swell the perfluorosulfonyl fluoride resin in an organic solvent at 45-55° C. for 50-70 minutes.

[0038] The ion exchange capacity and the ratio of short-chain to long-chain branched perfluorosulfonic acid structural units of the long- and short-chain branched perfluorosulfonic acid resin prepared above can be determined through acid-base titration. Depending on product performance requirements, the ratio of long- and short-chain branches can be adjusted by controlling the reaction time, reaction temperature, and raw material ratio during the preparation process, thereby adjusting the ion exchange capacity of the resin and the ratio of each functional unit.

[0039] Another object of the present invention is to provide a proton membrane containing the long and short chain branched perfluorosulfonic acid resin.

[0040] Preferably, the mass content percentage of the long and short branched perfluorosulfonic acid resin is 1 to 100%.

[0041] The present invention also provides the use of the long- and short-chain branched perfluorosulfonic acid resin in a fuel cell.

[0042] Technical effects of the present invention:

[0043] Compared with the prior art, the present invention has at least the following advantages:

[0044] (1) The long- and short-chain branched perfluorosulfonic acid resin and proton membrane provided by the present invention have a side chain structure combining a short-chain branched perfluorosulfonic acid structure with a long-chain branched perfluorosulfonic acid structure, and have high dimensional stability and high ion conductivity.

[0045] (2) The introduction of long-chain perfluorosulfonic acid structure can regulate the water absorption rate of resin and membrane and improve dimensional stability; in addition, the cationic group in the structure can effectively increase the dissociation of terminal sulfonic acid group, improve ionic conductivity, and resolve the contradiction between "long side chain" and "low conductivity".

[0046] (3) The sulfonic acid groups in the short-chain perfluorosulfonic acid structure can form acid-base ion pairs with the amino groups (-N-) in the long-chain perfluorosulfonic acid structure, thereby enhancing the intermolecular interaction force and effectively limiting the strong water absorption of the sulfonic acid groups in the proton membrane, which can greatly enhance the mechanical properties of the membrane. In addition, the formed ion pairs can also conduct ions, resolving the contradiction between "short side chains" and "high swelling".

[0047] (4) Benefiting from the Donnan exclusion effect (positive charges repel each other), the introduction of cationic structural units into the resin and membrane structure can effectively inhibit the penetration of positively charged ions in the zwitterionic membrane, and has excellent alcohol and vanadium resistance properties.

[0048] (5) The long and short branched structural units in the perfluorosulfonic acid resin provided by the present invention have the function of regulating the crystallinity and water absorption of the polymer and improving the mechanical properties and ionic conductivity of the resin. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 : is the infrared test spectrum of each resin in the example, wherein A is PFSO2F resin, B is intermediate product A1, C is target product A2, and D is target product A3;

[0050] Figure 2 It is a device for testing the vanadium ion permeability of membranes. DETAILED DESCRIPTION

[0051] To further help understand the technical solution of the present invention, the technical solution of the present invention is described in more detail below by providing several specific implementation examples.

[0052] Unless otherwise specified, the raw materials and reagents involved in the examples are common commercially available products; the experimental methods involved in the examples are conventional technical means in the art unless otherwise specified.

[0053] The wavy line of the present invention represents an alkyl chain or perfluoroalkyl chain of any length or H. The length is for reference only and does not represent the actual length.

[0054] Example 1

[0055] Preparation of a long and short branched perfluorosulfonic acid resin, wherein a grafting reaction is performed according to a preparation method to graft long and short branched perfluorosulfonic acid groups. PFSO2F resin (a'=4, b'=1; x', y', z'=1, number average molecular weight of 420,000, molar equivalent E w =869g / mol), the specific steps are as follows:

[0056] (1) A 500 mL sealed reactor was cleaned, evacuated, and replaced with high-purity nitrogen three times. 50 g of PFSO2F resin and 150 mL of dry N,N-dimethylacetamide were added. The stirring device was turned on and the mixture was slowly heated to 50 °C and maintained for 60 min. The product was filtered and washed repeatedly with deionized water three times to obtain a pre-swollen resin.

[0057] (2) The reactor was cleaned and evacuated again, and then replaced with high-purity nitrogen three times. The pre-swollen resin and 200 ml of 10% ammonia solution were added, and the molar ratio of PFSO2F resin to ammonia was 1:10; the stirring device was turned on, and the mixture was slowly heated to 30°C and maintained for 100 minutes. The pressure in the reactor was controlled below 0.15 MPa, and part of the -SO2F group was converted into -SO2NH2 (the reaction degree was controlled by the reaction time, and then the -SO2F reaction degree was determined by titration IEC). The product was filtered and washed three times with deionized water, and then immersed in 15% KOH at 70°C for 24 hours to complete ion exchange, and the remaining -SO2F was converted into -SO3K. The product was washed with deionized water; finally, it was dried at 60°C to obtain a long-short branched chain intermediate product, recorded as A1, and the reaction formula is as follows:

[0058]

[0059] Figure 1 PFSO2F( Figure 1 , A) and A1( Figure 1 , B) infrared transmission spectrum was measured. It can be seen in the figure that at 1467cm -1 The infrared absorption peak of -SO2F group in the intermediate product A1 disappeared, and the infrared absorption peak of -SO2F group in the intermediate product A1 disappeared. -1 and 1548cm -1 The characteristic peak of -SO2NH2 primary amine (-NH2 group) appeared at 1390cm -1 and 1060cm -1 SN bond and -SO3 appeared nearby - The characteristic peak (-SO3K group) of

[0060] (3) 10 g of the obtained A1 was added to 200 mL of dry N, N-dimethylacetamide, the stirring device was turned on, and the mixture was slowly heated to 80 ° C. After it was completely dissolved, 0.025 g of allyl trimethyl ammonium chloride was added. The molar ratio of A1 to allyl trimethyl ammonium chloride (Q-Ar1 reagent) was about 1:8. After the addition was completed, -SO2NH2 was used to react with the double bond under mechanical stirring at 80 ° C to graft the quaternary ammonium cationic group. After the reaction for 12 hours, it was cooled to room temperature, the product was filtered, and the unreacted allyl trimethyl ammonium chloride was removed by washing with deionized water several times. It was dried at 60 ° C. The product was then subjected to a ring-opening reaction with tetrafluorosulfone (Q-Ar2 reagent, m = 2) to graft SO3 -Cationic group (the reaction process is the same as the reaction process of A1 and Q-Ar1, and the reactants react in the same molar ratio), and finally washed three times with deionized water, and then soaked in 15% sulfuric acid for 20 hours to complete ion exchange. The product is washed with deionized water; finally, it is dried at 60°C to obtain a long and short branched perfluorosulfonic acid resin, recorded as A2. The reaction formula is shown in the figure below:

[0061]

[0062] The product A2( Figure 1 , C) Infrared transmission spectrum was measured, and it can be seen that at 3304~3400cm -1 and 1548cm -1 The characteristic peak (-NH2 group) of -SO2NH2 primary amine disappears, and at 3300cm -1 The characteristic peak of -NH- appears near 3038~3110cm -1 The characteristic peaks of -CH2 and -CH3 appeared at 1478 cm -1 There was a strong The characteristic peak at 1060cm -1 -SO3 - The above results prove that the target product A2 was successfully obtained.

[0063] After ion exchange capacity (IEC) measurement, the IEC of the obtained target product A2 was 1.05 mmol / g, the molar proportion of tetrafluoroethylene structural units in the copolymer was 49.00%, the molar proportion of short-chain branched perfluorosulfonic acid structures was 27.50%, and the molar proportion of long-chain branched perfluorosulfonic acid structural units was 23.50%.

[0064] Example 2

[0065] A long and short branched perfluorosulfonic acid resin was prepared. First, the intermediate product A1 was prepared according to the method of Example 1, except that the PFSO2F resin (E w =800g / mol) and ammonia in a molar ratio of 1:15; the reaction time was extended from 100min to 200min to prepare a long-short-chain branched intermediate product, 1-allyl-3-methylimidazolium chloride was used as the Q-Ar1 reagent, and the other components, material ratios and synthesis methods were the same as in Example 1 to obtain a long-short-chain branched perfluorosulfonic acid resin, denoted as A3, and the reaction formula is shown below:

[0066]

[0067] The ion exchange capacity (IEC) was measured and the IEC of the obtained target product A3 was 1.20 mmol / g.

[0068] The molar proportion of tetrafluoroethylene structural units in the copolymer is 46.00%, the molar proportion of short-chain branched perfluorosulfonic acid structural units is 26.50%, and the molar proportion of long-chain branched perfluorosulfonic acid structural units is 27.50%.

[0069] Example 3

[0070] A long- and short-chain branched perfluorosulfonic acid resin was prepared. First, the intermediate product A1 was prepared according to the method of Example 1, except that the reaction time of PFSO2F resin (Ew = 680 g / mol) and NH3 was extended from 100 min to 300 min to prepare the long- and short-chain branched intermediate product; in addition, only tetrafluorosulfone was used as the Q-Ar2 reagent to directly react with A1 for a ring-opening addition reaction to prepare the long- and short-chain branched perfluorosulfonic acid resin. The remaining components, material ratios, and synthesis methods were the same as those of Example 1. The obtained product was recorded as A4, and the reaction formula is shown below:

[0071]

[0072] The ion exchange capacity (IEC) was determined to be 1.40 mmol / g for the target product A4.

[0073] The molar proportion of tetrafluoroethylene structural units in the copolymer is 48.00%, the molar proportion of short-chain branched perfluorosulfonic acid structural units is 25.50%, and the molar proportion of long-chain branched perfluorosulfonic acid structural units is 26.50%.

[0074] Example 4

[0075] A long- and short-chain branched perfluorosulfonic acid resin was prepared. First, the intermediate product A1 was prepared according to the method of Example 1, except that the reaction time of PFSO2F resin (Ew=680g / mol) and NH3 was extended from 100 min to 500 min to prepare the long- and short-chain branched intermediate product; in addition, only perfluorobutane sultone (m=4) was used as the Q-Ar2 reagent to directly react with A1 for a ring-opening addition reaction to prepare the long- and short-chain branched perfluorosulfonic acid resin. The remaining components, material ratios and synthesis methods were the same as those of Example 1. The obtained product was recorded as A5, and the reaction formula is shown below:

[0076]

[0077] The ion exchange capacity (IEC) of the obtained target product A5 was 1.42 mmol / g. The reaction formula is shown in the figure below:

[0078] The molar proportion of tetrafluoroethylene structural units in the copolymer is 45.00%, the molar proportion of short-chain branched perfluorosulfonic acid structural units is 26.50%, and the molar proportion of long-chain branched perfluorosulfonic acid structural units is 28.50%.

[0079] Example 5

[0080] Preparation of a long and short branched perfluorosulfonic acid resin, which is different from Example 1 in that PFSO2F resin (a'=4, b'=1; x', z'=1; y'=0, molar equivalent E w =680g / mol) to prepare a long and short branched intermediate; the other components, material ratios and synthesis methods are the same as those in Example 1. The obtained product is recorded as A6, and the reaction formula is shown in the figure below:

[0081]

[0082] The ion exchange capacity (IEC) was determined to be 1.45 mmol / g for the target product A6.

[0083] The molar proportion of tetrafluoroethylene structural units in the copolymer is 46.00%, the molar proportion of short-chain branched perfluorosulfonic acid structural units is 26.50%, and the molar proportion of long-chain branched perfluorosulfonic acid structural units is 27.50%.

[0084] Example 6

[0085] Preparation of a long and short branched perfluorosulfonic acid resin, which is different from Example 1 in that PFSO2F resin (a'=4, b'=1; x', z'=1; y'=0, molar equivalent E w =680g / mol) to prepare a long and short branched intermediate product; in addition, only tetrafluorosulfone was used as the Q-Ar2 reagent to directly react with A1 to perform a ring-opening addition reaction to prepare a long and short branched perfluorosulfonic acid resin. The other components, material ratios and synthesis methods were the same as those in Example 1. The obtained product was recorded as A7, and the reaction formula is shown below:

[0086]

[0087] The ion exchange capacity (IEC) was determined to be 1.45 mmol / g for the target product A7.

[0088] The molar proportion of tetrafluoroethylene structural units in the copolymer is 47.50%, the molar proportion of short-chain branched perfluorosulfonic acid structural units is 26.50%, and the molar proportion of long-chain branched perfluorosulfonic acid structural units is 26.00%.

[0089] Example 7

[0090] A long- and short-chain branched perfluorosulfonic acid resin was prepared using the same method as in Example 4, except that the reaction time between PFSO₂F resin (Ew = 680 g / mol) and NH₃ was extended from 100 minutes to 1000 minutes to produce the long- and short-chain branched intermediate. All other components, material ratios, and synthesis methods were the same as in Example 4. The resulting product, designated A8, had the same structural formula as A5. Ion exchange capacity (IEC) analysis revealed that the IEC of the obtained target product A8 was 1.35 mmol / g.

[0091] The molar proportion of tetrafluoroethylene structural units in the obtained copolymer is 48.50%, the molar proportion of short-chain branched perfluorosulfonic acid structural units is 21.50%, and the molar proportion of long-chain branched perfluorosulfonic acid structural units is 30.00%.

[0092] Example 8

[0093] Preparation of a long and short branched perfluorosulfonic acid resin, which is different from Example 1 in that PFSO2F resin (a'=4, b'=1; x', z'=1, y'=0, molar equivalent E w =680g / mol) to prepare a long and short branched intermediate product; the difference is that the reaction time of PFSO2F resin (Ew = 680g / mol) and NH3 is shortened from 100min to 50min to prepare the long and short branched intermediate product; the other components, material ratios and synthesis methods are the same as those in Example 6. The obtained product is recorded as A9, and its structural formula is the same as A7. The ion exchange capacity (IEC) of the obtained target product A9 is 1.47mmol / g

[0094] The molar proportion of tetrafluoroethylene structural units in the obtained copolymer is 48.30%, the molar proportion of short-chain branched perfluorosulfonic acid structural units is 31.00%, and the molar proportion of long-chain branched perfluorosulfonic acid structural units is 20.70%.

[0095] Example 9

[0096] Prepare the resin into a proton membrane:

[0097] A homogeneous long and short branched perfluorosulfonic acid proton membrane was prepared by solution casting method, and the specific steps were as follows: first, resin A2, resin A3, resin A4, resin A5, resin A6, resin A7, resin A8, and resin A9 were dissolved in N, N-dimethylformamide respectively, stirred and dispersed evenly to prepare a 10 wt% homogeneous membrane liquid, and coated on a polytetrafluoroethylene reinforced mesh (2 layers, porosity 80%, gram weight 3.2 g / m 2 ), pre-dried at 80°C, placed in an oven at 145°C for 90 minutes, taken out and demoulded, to prepare 15 μm homogeneous proton membranes, which were respectively recorded as M2 to M9.

[0098] Comparative Example 1

[0099] The PFSO2F resin in Example 1 was immersed in 15% KOH and 25wt% sulfuric acid solutions at 80°C for 30h to complete ion exchange, thereby converting all -SO2F groups into -SO3H to obtain a short-chain branched perfluorosulfonic acid resin PFSA (the molar proportion of tetrafluoroethylene polymer structural units is 55.0%, and the molar proportion of perfluorosulfonic acid structural units is 45.0%), which is recorded as resin B1. The reaction formula is as follows:

[0100]

[0101] Comparative Example 2

[0102] The PFSO2F resin in Example 1 was reacted with ammonia to convert all -SO2F groups to -SO2NH2. The resulting product was recorded as perfluorosulfonamide (PFSO2NH2). Tetrafluorosulfone was then used as the Q-Ar2 reagent to directly react with PFSO2NH2 in a ring-opening addition reaction to prepare a long-chain branched perfluorosulfonic acid resin (the molar ratio of tetrafluoroethylene polymer structural units was 52.0% and the molar ratio of perfluorosulfonic acid structural units was 48.0%). The remaining components, material ratios, and synthesis methods were the same as in Example 1, recorded as resin B2, and the reaction formula is as follows:

[0103]

[0104] Comparative Example 3

[0105] The resin in Comparative Example 1 was selected to have a molar content of 50.00% and the resin in Comparative Example 2 was selected to have a molar content of 50.00% to prepare a long- and short-chain branched mixed resin, which was recorded as resin B3.

[0106] Comparative Example 4

[0107] The perfluorosulfonic acid resins B1, B2, and B3 obtained in Comparative Examples 1, 2, and 3 were selected to prepare long-chain perfluorosulfonic acid proton exchange membranes according to the steps of Example 7, and were designated as D-1, D-2, and D-3, respectively.

[0108] Test method:

[0109] Titration of ion exchange capacity (IEC): Accurately weigh a certain amount of dry target product, and then perform ion exchange with a 1M NaCl aqueous solution for 12 hours to convert the counter ions of the perfluorinated anion groups in the product into Cl - , collect the ion exchange solution, use phenolphthalein as an indicator, and titrate with 0.1M NaOH standard solution until the solution turns pink. The ion exchange capacity (IEC) value of the target product can be calculated according to the following formula:

[0110] IEC=(V NaOH ×C NaOH ) / m

[0111] Where: V NaOH ——The volume of NaOH standard solution consumed, mL; C NaOH ——molar concentration of NaOH standard solution, mmol / mL; m——mass of dry target product, g.

[0112] The mechanical properties test of the ion membrane is carried out in accordance with GB / T20042.3-2009.

[0113] The ion membrane conductivity test was carried out in accordance with GB / T20042.3-2009 (test conditions were room temperature and 120°C).

[0114] Thermal degradation temperature (defined as the temperature at which the polymer degrades by 5%): The test was conducted using a thermogravimetric analyzer (TAQ50) manufactured by Perkin Elmer, USA, with an N2 atmosphere, a heating rate of 10°C / min, and a temperature range of 50-800°C. The samples were dried at 60°C for 24 hours before testing.

[0115] Water absorption and swelling: Soak the sample in deionized water at the test temperature (test conditions are room temperature and 80 ° C) for 24 hours to ensure complete swelling. Take out the sample, quickly wipe off the water on the sample surface, and record the sample weight (M w ) and length (L w Then dry the sample thoroughly at 80℃ and record the sample weight (M d ) and length (L d ), water absorption and swelling degree are calculated by the following formula:

[0116] Water absorption % = [(M w -M d ) / M d ]×100%, swelling degree %=[(L w -L d ) / L d ]×100%.

[0117] Crystallinity: This test was conducted using a DSC2910 manufactured by TA Instruments (USA) under nitrogen atmosphere according to GB / T 19466.3-2004. The sample was first heated from room temperature to 150°C at a rate of 10°C / min, held constant for 5 minutes, and then cooled to room temperature. The temperature was then scanned from room temperature to 150°C at a rate of 10°C / min, and the DSC curve was recorded.

[0118] Crystallinity X i =(ΔH f / 293)×100%

[0119] Where: ΔH f is the melting enthalpy of the sample polymer, in Jg -1 293 is the melting enthalpy of polyethylene when the crystallinity is 100%, the unit is Jg -1 .

[0120] Vanadium ion permeability of ion membrane: Figure 2 The device shown (refer to Chinese patent CN114835842A) tests the vanadium ion permeability of the membrane. The two sides of the container are 3MH2SO4 / 1.5MVOSO4 and 3MH2SO4 / 1.5MMgSO4, respectively, with the ion membrane to be tested in the middle. Mechanical stirring is auxiliary on both sides of the container to prevent concentration polarization. As time goes by, samples are taken from the right electrode solution at regular intervals to test the VOSO4 concentration, and an equal amount of stock solution is added. The VOSO4 concentration test is tested by an ultraviolet spectrophotometer (JASCO, FT-IR4100, Japan), and the vanadium ion permeability is calculated with reference to the literature (Journal of Membrane Science 525 (2017) 229-239).

[0121] The water absorption, thermal stability, IEC and crystallinity of the resins obtained in the examples and comparative examples were tested. The test results are shown in Table 1.

[0122] Table 1

[0123]

[0124]

[0125] As can be seen from the above table, compared with long-chain branched perfluorosulfonic acid resin PFSA, short-chain branched perfluorosulfonic acid resin PFSA, and long-chain and short-chain branched mixed resins, the long-chain and short-chain branched perfluorosulfonic acid resin prepared by the present invention has high thermal stability and high crystallinity. In addition, because the sulfonic acid group in the short-chain branched perfluorosulfonic acid structure can form an acid-base ion pair with the amino group (-N-) in the long-chain branched perfluorosulfonic acid structure, the intermolecular interaction force is enhanced, the water absorption rate of the sulfonic acid resin is effectively limited (less than 30%), and the stability of the resin is improved.

[0126] The conductivity, swelling degree, tensile strength, and vanadium ion permeability of the exchange membranes obtained in the examples and comparative examples were tested. The test results are shown in Table 2.

[0127] Table 2

[0128]

[0129] As can be seen from the table above, the long- and short-chain branched perfluorosulfonic acid proton membrane disclosed in the embodiments of the present invention has superior mechanical properties, dimensional stability, and lower vanadium ion permeation compared to proton membranes in the prior art. Furthermore, by regulating the proportion of long- and short-chain branched structural units in the resin, the vanadium barrier properties of the proton membrane can be improved while maintaining the electrical conductivity and mechanical properties. This can address the shortcomings of ion membranes, such as poor vanadium barrier properties and high swelling, and is suitable for use in fuel cells, chlor-alkali electrolyzers, and water electrolysis hydrogen production electrolyzers.

Claims

1. Long and short branched perfluorosulfonic acid resin, characterized in that: The resin structure includes a perfluoroethylene structural unit, a short-chain branched perfluorosulfonic acid structural unit (A) and a long-chain branched perfluorosulfonic acid structural unit (B), and the resin has a structure shown in the following formula I: ， Wherein a, c are independently selected from 1 to 10, b, d are 1; x is 1; y, z are independently 0 or 1, e is 50 to 10000, m is an integer from 2 to 6, Ar is a cationic group, and the cationic group is H + or a cationic structure containing one of the structures of formula II and a counter ion composition: Formula (II); The counter ion is Cl - , SO4 2- , HSO4 - , OH - One of them.

2. The perfluorosulfonic acid resin according to claim 1, characterized in that (a+b) / (a+b+c+d)=0.45~0.70; (c+d) / (a+b+c+d)=0.30~0.

55.

3. The perfluorosulfonic acid resin according to claim 1, characterized in that The molar percentages of the polymer units in the resin are as follows: the molar percentage of the tetrafluoroethylene structural unit is 35-85%, the molar percentage of the short-chain branched perfluorosulfonic acid structural unit is 10-60%, and the molar percentage of the long-chain branched perfluorosulfonic acid structural unit is 5-55%.

4. The perfluorosulfonic acid resin according to claim 1, characterized in that The resin has both cation exchange capacity and anion exchange capacity, and the ion exchange capacity is 0.9-2.0 mmol / g.

5. The perfluorosulfonic acid resin according to claim 4, characterized in that The ion exchange capacity is 1.0-1.5 mmol / g.

6. The method for preparing the resin according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: PFSO2F is pre-swelled in an organic solvent and reacted with an ammonia reagent to convert part of the -SO2F group into -SO2NH2. Then, the remaining -SO2F groups are converted into sulfonate -SO3M through an alkaline ion exchange process, where M is K + Or Na + , after washing and drying, long and short branched chain intermediates are obtained; Step 2: Follow one of the following methods: Method (1), when Ar is H + When the intermediate product is directly reacted with Q-Ar2 reagent to graft long-chain -SO3 - , forming -SO3 - ·····HN + HSO2-zwitterionic groups, and then undergo acid ion exchange to obtain long and short branched chain sulfonic acid groups, which are then washed and dried to obtain long and short branched chain perfluorosulfonic acid resin; Method (2), when Ar is + When the cationic group is other than a positively charged group, the intermediate product is grafted with a Q-Ar2 reagent and a Q-Ar1 reagent with a cationic group in an organic solvent to graft a long branched chain -SO3 - and cationic groups; the product finally undergoes an acid ion exchange process to obtain long and short branched sulfonic acid groups, and after washing and drying, a long and short branched perfluorosulfonic acid resin is obtained.

7. The preparation method according to claim 6, characterized in that The Q-Ar1 reagent is composed of a cationic structure and a counter ion in the structure shown in Formula III. composition: Formula (III); The Q-Ar2 reagent is a reagent with a sultone structure, and its general structural formula is shown in Formula IV, wherein m is an integer of 2-6; Formula (IV).

8. The preparation method according to claim 6, characterized in that The organic solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, ethanol, isopropanol, dichloromethane, acetone, dimethyl sulfoxide or ethyl acetate.

9. The preparation method according to claim 6, characterized in that The molar ratio of PFSO2F resin to ammonia is 1:5~20; the molar ratio of the intermediate product to Q-Ar1 and Q-Ar2 reagents is 1:5~12.

10. The preparation method according to claim 6, characterized in that The grafting reaction temperature in step 2 is 70-90° C., and the reaction time is 10-15 hours.

11. The preparation method according to claim 6, characterized in that The pre-swelling in step 1 is to swell the perfluorosulfonyl fluoride resin in an organic solvent at 45-55° C. for 50-70 minutes.

12. A proton membrane comprising the perfluorosulfonic acid resin according to any one of claims 1 to 5 or the perfluorosulfonic acid resin prepared by the method according to any one of claims 6 to 11.

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