Supermolecular solvent system of perfluorinated sulfonic acid resin and low-temperature dissolving method of supermolecular solvent system

Abstract

The invention belongs to the technical field of high polymer material processing, and particularly relates to a supramolecular solvent system of perfluorinated sulfonic acid resin and a low-temperature dissolving method of the supramolecular solvent system. The solvent system is composed of a fluorocrown ether main solvent, a hyperbranched fluorine-containing polymer cosolvent and a Lewis acid-alkali pair catalyst, and efficient dissolution of the perfluorosulfonic acid resin at 40-80 DEG C is achieved through interaction of supermolecule subjects and objects. Compared with a traditional method, the dissolution temperature is obviously reduced, the dissolution time is shortened by 80%, the solution concentration can reach 30wt%, and the molecular structure of the resin is not damaged. The method is suitable for processing Nafion and other perfluorinated sulfonic acid resins, and a new solution is provided for preparation of a high-performance proton exchange membrane.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polymer material processing, and particularly relates to a supramolecular solvent system of perfluorosulfonic acid resin and a low-temperature dissolving method thereof. BACKGROUND

[0002] As a kind of fluorine-containing polymer material with excellent chemical stability and proton conduction performance, perfluorosulfonic acid resin has an irreplaceable important position in the field of energy conversion and storage. This kind of material represented by Nafion has the molecular structure feature that sulfonic acid groups are distributed on the perfluorocarbon main chain. This unique structure makes it exhibit excellent performance in electrochemical devices such as fuel cells and flow batteries. However, this special molecular structure also brings great technical challenges to the processing of the material.

[0003] The main technical route for processing perfluorosulfonic acid resin in the current industry has many defects. In terms of solvent selection, the existing technology relies on high-boiling polar aprotic solvents such as dimethyl sulfoxide and N,N-dimethylformamide, which have certain solubility but need to be heated above 200℃ to effectively dissolve the resin. Not only is the energy consumption large, but also the molecular chain of the resin is broken and the sulfonic acid group is decomposed. Experiments show that after 200℃ treatment for 4 hours, the molecular weight of Nafion resin decreases by 15-20%, and the loss rate of sulfonic acid group reaches 12%. Moreover, the maximum solubility of the traditional solvent system for perfluorosulfonic acid resin does not exceed 15wt%, and the low-efficiency dissolution process limits the efficiency and quality of the subsequent film forming process. Continuous stirring for 6-8 hours during dissolution aggravates the performance degradation of the material. Studies have shown that the Nafion solution prepared by the traditional method has obvious phase separation after 72 hours of room temperature storage, and the viscosity change rate exceeds 10%, which brings difficulties to the subsequent process control. Most solvents are highly toxic and volatile, which threatens the health of operators and pollutes the environment. In addition, most solvents are difficult to completely recover, and the treatment cost is high.

[0004] In view of the technical bottlenecks in the dissolution of perfluorosulfonic acid resin, academia and industry have carried out various explorations. For example, the 1-ethyl-3-methyl imidazole tetrafluoroborate system reported in the literature can reduce the dissolution temperature to 150℃, but the high viscosity of the ionic liquid itself leads to the need for stronger mechanical stirring and increases the energy consumption, and the residual substances that are difficult to completely remove will reduce the product properties. There are reports that supercritical CO2 is used as an auxiliary solvent, but the equipment investment is huge, and it can only realize surface modification and cannot completely dissolve. The above methods have not fundamentally solved the technical problems in the dissolution of perfluorosulfonic acid resin.

[0005] In summary, developing a novel solvent system capable of efficiently dissolving perfluorosulfonic acid resins under mild conditions while preserving the intrinsic properties of the material has become a critical technical challenge that urgently needs to be addressed in this field. A breakthrough in this area will directly drive innovation in proton exchange membrane manufacturing processes and will be of great significance to the development of clean energy technologies. Summary of the Invention

[0006] To address the technical bottlenecks of high temperature, low efficiency, and high energy consumption in the dissolution process of perfluorosulfonic acid resins in existing technologies, this invention proposes a supramolecular solvent system for perfluorosulfonic acid resins and its low-temperature dissolution method, based on the principle of supramolecular interaction. The core innovation of this invention lies in the first-time construction of a ternary synergistic solvent system of "fluorinated crown ether-hyperbranched fluorinated polymer-Lewis acid-base pair," which achieves efficient dissolution of perfluorosulfonic acid resins under mild conditions through multi-level molecular recognition and interaction.

[0007] The technical solution of this invention is: This invention discloses a supramolecular solvent system for perfluorosulfonic acid resin, which consists of a fluorinated crown ether as the main solvent, a hyperbranched fluorinated polymer as the co-solvent, and a Lewis acid-base pair catalyst. The solvent system achieves efficient dissolution of perfluorosulfonic acid resin at 40-80℃ through supramolecular host-guest interactions, and the resin molecular weight retention rate after dissolution is greater than 98%, and the sulfonic acid group retention rate is greater than 98%.

[0008] Furthermore, in the aforementioned supramolecular solvent system, the fluorocrown ether is selected from at least one of perfluoro-12-crown-4, perfluoro-15-crown-5, and perfluoro-18-crown-6. The fluorocrown ether is a crown ether compound with a specific cavity size, the cavity diameter (1.2-3.2 Å) of which is highly matched with the size of the sulfonic acid group in the perfluorosulfonic acid resin. The precise "lock-key" matching relationship allows the crown ether molecule to form a stable inclusion complex with the sulfonic acid group through host-guest interaction, thereby disrupting the intermolecular forces of the resin. Molecular dynamics simulations show that the binding energy of this interaction is as high as -25 kJ / mol, which is much higher than the interaction energy between traditional solvents and resins (approximately -10 kJ / mol).

[0009] Furthermore, in the aforementioned supramolecular solvent system, the hyperbranched fluoropolymer has a molecular weight of 2000-5000 and a branching degree of 0.3-0.5. Its fluorinated segments are compatible with the resin backbone and can effectively penetrate into the resin interior. The steric hindrance effect generated by the hyperbranched structure promotes resin swelling, and the terminal hydroxyl groups form a hydrogen bond network with the sulfonic acid groups in the perfluorosulfonic acid resin, synergistically enhancing the dissolution effect.

[0010] Furthermore, in the supramolecular solvent system described above, the Lewis acid-base pair catalyst is selected from any one of AlCl3 / TPPO, BF3 / DMSO, and FeCl3 / pyridine, which disrupts the resin crystallization region through synergistic action.

[0011] Furthermore, in the supramolecular solvent system described above, the mass percentages of each component are as follows: 60-80% fluorinated crown ether main solvent, 15-30% hyperbranched fluorinated polymer co-solvent, and 5-10% Lewis acid-base pair catalyst.

[0012] This invention also discloses a low-temperature dissolution method for perfluorosulfonic acid resin, comprising the following steps: (1) Mix the perfluorosulfonic acid resin with the above-mentioned supramolecular solvent system; (2) Stir at 40-80℃ for 0.5-2 hours to obtain a homogeneous solution.

[0013] Furthermore, in the above-mentioned low-temperature dissolution method, step (2) adopts a step-by-step heating strategy to achieve staged dissolution by precisely controlling the temperature gradient, including the 40-50℃ crystallization zone destruction stage, the 60-70℃ molecular chain de-entanglement stage, and the 70-80℃ complete dissolution stage. This step-by-step heating strategy can reduce energy consumption by more than 60%.

[0014] Furthermore, in the aforementioned low-temperature dissolution method, the stirring process employs pulsed stirring at a specific frequency (50-100Hz) to ensure uniform mixing while avoiding molecular chain breakage caused by mechanical shearing.

[0015] Furthermore, in the aforementioned low-temperature dissolution method, the perfluorosulfonic acid resin is selected from any one of Nafion, Aquivion, or Flemion resins, and the dissolution process is carried out under inert gas protection.

[0016] Furthermore, the above-mentioned low-temperature dissolution method yields a solution with a solid content of 10-30 wt%. By adding 0.1-0.5 wt% graphene quantum dots as a stabilizer to the solution, their huge specific surface area can adsorb free solvent molecules, inhibit phase separation, and allow the solution to be stored stably at room temperature for more than 30 days.

[0017] The present invention also discloses the application of the perfluorosulfonic acid resin solution obtained by the above-mentioned low-temperature dissolution method in the preparation of proton exchange membranes.

[0018] Advantages and beneficial effects of the present invention: This invention not only solves key technical problems in the processing of perfluorosulfonic acid resins, but also provides new research ideas for the science of polymer dissolution. The concept of achieving mild processing of specific functional polymers through precise control of supramolecular interactions can be extended to the processing of other poorly soluble polymers, showing broad application prospects. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating the mechanism by which the supramolecular solvent system of the present invention dissolves perfluorosulfonic acid resin. In the figure, 1-resin crystallization region, 2-dissolved perfluorosulfonic acid resin, 3-fluorocrown ether main solvent, 4-hyperbranched fluorinated polymer co-solvent, and 5-Lewis acid-base pair catalyst. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be used to limit the scope of the present invention.

[0021] Example 1 In this embodiment, Nafion NR211 resin was dissolved, wherein the hyperbranched fluoropolymer co-solvent had a molecular weight of 2000 and a branching degree of 0.3; the mass composition of the solvent system was: 75% fluorocrown ether main solvent, 18.75% hyperbranched fluoropolymer co-solvent, and 6.25% Lewis acid-base pair catalyst; the dissolution initiation temperature was 40°C; the total stirring time was 0.5 hours; the target solution solid content was 10 wt%; and the amount of graphene quantum dots added was 0.1 wt% of the total solution mass.

[0022] The specific operation is as follows: Take 5.0g of Nafion NR211 resin and mix it with a solvent system consisting of 33.75g of perfluorinated-15-crown-5 (75% of the solvent system mass), 8.44g of a hyperbranched fluoropolymer with a molecular weight of 2000 and a branching degree of 0.3 (18.75%), 2.81g of AlCl3 / TPPO catalyst (6.25%), and 0.05g of graphene quantum dots. Under nitrogen protection, use a stepwise temperature increase program of 40℃ (10 minutes), 60℃ (10 minutes), and 70℃ (10 minutes), and pulse stirring for 0.5 hours (frequency 100 Hz).

[0023] Performance testing: Solubility: The solubility rate, determined by gravimetric method, was 99.0%. Resin structural integrity: The molecular weight retention rate was 99.0% as determined by gel permeation chromatography (ASTM D5296-20). The retention rate of sulfonic acid groups was 98.5% as determined by acid-base titration (ASTM D2187-17). Solution stability: After being sealed and allowed to stand for 30 days at 25°C, no gel or precipitation was observed.

[0024] Example 2 In this embodiment, Aquivion D98-25BS resin was dissolved using a hyperbranched fluoropolymer co-solvent with a molecular weight of 5000 and a branching degree of 0.5. The solvent system consisted of 60% fluorocrown ether as the main solvent, 30% hyperbranched fluoropolymer co-solvent, and 10% Lewis acid-base pair catalyst. The temperature at which complete dissolution was achieved was 80°C. The total stirring time was 2 hours. The solid content of the solution was 30 wt%. The amount of graphene quantum dots added as a stabilizer was 0.5 wt%.

[0025] Take 15.0 g of Aquivion resin and mix it with a solvent system consisting of 20.85 g of perfluorinated-18-crown-6 (60% of the solvent system mass), 10.425 g of a hyperbranched fluoropolymer with a molecular weight of 5000 and a branching degree of 0.5 (30%), 3.475 g of BF3 / DMSO catalyst (10%), and 0.25 g of graphene quantum dots. Under argon protection, use a stepped temperature program of 50℃ (40 min), 70℃ (40 min), and 80℃ (40 min), and pulse stirring for 2 hours (frequency 50 Hz).

[0026] As attached Figure 1 As shown, Lewis acid-base catalyst 5 acts as a "molecular crowbar" to synergistically disrupt the resin crystallization region 1 and open the dissolution channel; fluorinated crown ether main solvent 3 disassembles the ionic cross-linking network through host-guest recognition and shielding; hyperbranched fluorinated polymer co-solvent 4 plays a "wedge-in and stabilize" role, and its fluorinated segments are compatible with the resin, ultimately achieving complete dissolution of the resin segments to obtain dissolved perfluorosulfonic acid resin 2.

[0027] Performance testing: Solubility: The solubility was 99.8% as determined by gravimetric method. Resin structural integrity: The molecular weight retention rate was 98.3% as determined by gel permeation chromatography (ASTM D5296-20). The retention rate of sulfonic acid groups was 98.1% as determined by acid-base titration (ASTM D2187-17). Film-forming properties: After solution casting, the proton conductivity at 80°C and 100%RH was 0.118 S / cm, as measured by the relevant test procedures of the U.S. Department of Energy (DOE); the tensile strength was 27.5 MPa, as measured by ASTM D882-18.

[0028] Example 3 In this embodiment, 10.0 g of perfluorosulfonic acid resin Flemion 850 was dissolved, resulting in a target solution solid content of 20 wt%. The fluorocrown ether main solvent was a mixture of perfluoro-12-crown-4 and perfluoro-15-crown-5 in a 1:1 mass ratio, totaling 35.0 g, accounting for 70% of the total solvent system mass. The hyperbranched fluoropolymer co-solvent had a molecular weight of 3500 and a branching degree of 0.4, with a dosage of 10.0 g, accounting for 20% of the total solvent system mass. The Lewis acid-base pair catalyst was FeCl3 / pyridine (molar ratio 1:1.5), with a dosage of 5.0 g, accounting for 10% of the total solvent system mass. The total mass of the solvent system was 50.0 g, and no graphene quantum dot stabilizer was added. The dissolution process was carried out under nitrogen protection, using a stepped heating strategy of 45℃ (crystallization destruction stage, maintained for 1 hour), 65℃ (molecular chain de-entanglement stage, maintained for 0.5 hours), and 75℃ (complete dissolution stage, maintained for 0.5 hours), with pulse stirring time of 2 hours (frequency 80 Hz).

[0029] Performance testing: Solubility: The solubility was 99.7% as determined by gravimetric method. Resin structural integrity: The molecular weight retention rate was 99.1% as determined by gel permeation chromatography (ASTM D5296-20). The retention rate of sulfonic acid groups was 99.2% as determined by acid-base titration (ASTM D2187-17).

[0030] Example 4 In this embodiment, Aquivion D98-25BS resin was dissolved using the same formulation as in Example 2. Specifically: 15.0 g of perfluorosulfonic acid resin Aquivion D98-25BS was used; 28.0 g of perfluoro-18-crown-6 was used as the main solvent, accounting for 80% of the total mass of the solvent system; 5.25 g of hyperbranched fluoropolymer co-solvent with a molecular weight of 5000 and a branching degree of 0.5 was used, accounting for 15% of the total mass of the solvent system; and 1.75 g of BF3 / DMSO (molar ratio 1:2) was used as the Lewis acid-base pair catalyst, accounting for 5% of the total mass of the solvent system. The key difference was the absence of any graphene quantum dot stabilizer. The dissolution process was exactly the same as in Example 2, using a stepped temperature increase program of 50°C (40 minutes), 70°C (40 minutes), and 80°C (40 minutes) under argon protection, with pulse stirring for 2 hours (frequency 60 Hz).

[0031] Performance testing: The solubility was determined to be greater than 99.5% by gravimetric method, proving that efficient dissolution can still be achieved without stabilizers; Solution stability: The obtained solution was sealed and placed in a 25°C environment for observation. The results showed that the viscosity of the solution increased significantly after 7 days, and visible flocculent precipitate appeared after 15 days, indicating that the long-term storage stability of the high solid content solution was poor under 0wt% stabilizer conditions, thus proving the necessity of adding 0.1-0.5wt% stabilizer (as in Example 2).

[0032] Example 5 This embodiment uses Nafion NR211 resin. Specifically: Nafion NR211 perfluorosulfonic acid resin, 5.0 g; fluorocrown ether main solvent, perfluoro-15-crown-5, 30.0 g, accounting for 72.7% of the total solvent system mass (calculated after adjusting for solid content and catalyst ratio); hyperbranched fluoropolymer co-solvent with a molecular weight of 2000 and a branching degree of 0.3, 7.5 g, accounting for 18.2% of the total solvent system mass; Lewis acid-base pair catalyst, AlCl3 / TPPO (molar ratio 1:1), adjusted to 3.76 g, accounting for 9.1% of the total solvent system mass; no graphene quantum dot stabilizer was added. The total solvent system mass was 47.0 g. The dissolution process was simplified; under nitrogen protection, stepwise heating was not used, only single-stage isothermal pulse stirring at 60°C for 1 hour (frequency 80 Hz).

[0033] Performance testing: Solubility: Determined by gravimetric method, the solubility is greater than 98.5%; Resin structural integrity: The molecular weight retention rate was 98.8%, as determined by gel permeation chromatography (ASTM D5296-20). The retention rate of sulfonic acid groups was determined to be 98.2% using acid-base titration (ASTM D2187-17).

[0034] The results show that, under conditions of low solid content (10 wt%) and appropriate increase of catalyst ratio (8%), a simplified single-stage dissolution process can still achieve high dissolution efficiency and effectively protect the resin structure.

[0035] Comparative Example 1 This comparative example uses Nafion NR211 resin and employs a traditional high-temperature dissolution method as a comparison.

[0036] 5.0 g of Nafion resin was mixed with 50 g of dimethylformamide (DMF) / propylene glycol methyl ether (1:1) and refluxed at 180 °C for 8 hours. Tests showed the solution was dark brown with a solubility of approximately 95%. Gel chromatography (ASTM D5296-20) analysis indicated a molecular weight retention of only 85%, and titration (ASTM D2187-17) showed a sulfonic acid group retention of only 88%, indicating that high temperature caused severe resin degradation.

[0037] Comparative Example 2 This comparative example uses Aquivion D98-25BS resin.

[0038] The same formulation as in Example 1 (containing a co-solvent with a molecular weight of 2000 and a branching degree of 0.3, 60% main solvent and 15% co-solvent) and a stepped temperature program (40 / 60 / 70°C) were used, but the AlCl3 / TPPO catalyst was removed. The resin only swelled and failed to dissolve. Even with stirring at 80°C for 6 hours, the solubility was still below 20%, demonstrating the system's failure without the catalyst.

[0039] This invention addresses the challenges of degradation and sulfonic acid group detachment in perfluorosulfonic acid resins during traditional high-temperature dissolution processes. It designs a multi-component synergistic supramolecular solvent system and its accompanying low-temperature dissolution process. This system organically combines three functional components: a Lewis acid-base pair catalyst, a fluorocrown ether main solvent, and a hyperbranched fluorinated polymer co-solvent. Through a synergistic mechanism, it achieves efficient dissociation of the resin aggregates under mild conditions. This invention achieves selective dissolution at the molecular level, rather than traditional strong solvation or thermal destruction, reducing energy consumption while solving the structural damage problem during resin processing. It provides a revolutionary solution processing method for the manufacture of high-performance perfluorosulfonic acid proton exchange membranes and also has significant universal guiding significance for the green processing of other high-performance polymers.

Claims

1. A supramolecular solvent system for a perfluorosulfonic acid resin, characterized in that, The solvent system consists of a fluorinated crown ether as the main solvent, a hyperbranched fluorinated polymer as a co-solvent, and a Lewis acid-base pair catalyst. The solvent system achieves efficient dissolution of perfluorosulfonic acid resin at 40-80℃ through supramolecular host-guest interactions, and the molecular weight retention rate of the resin after dissolution is greater than 98%, and the sulfonic acid group retention rate is greater than 98%.

2. The supramolecular solvent system according to claim 1, characterized in that, The fluorocrown ether is selected from at least one of perfluoro-12-crown-4, perfluoro-15-crown-5, and perfluoro-18-crown-6, and its crown ether molecule matches the sulfonic acid group in the perfluorosulfonic acid resin to form a stable inclusion compound.

3. The supramolecular solvent system according to claim 1, characterized in that, The hyperbranched fluoropolymer has a molecular weight of 2000-5000 and a branching degree of 0.3-0.

5. Its fluorinated segments are compatible with the resin backbone, and its terminal hydroxyl groups form a hydrogen bond network with the sulfonic acid groups in the perfluorosulfonic acid resin.

4. The supramolecular solvent system according to claim 1, characterized in that, The Lewis acid-base pair catalyst is selected from any one of AlCl3 / TPPO, BF3 / DMSO, and FeCl3 / pyridine, and it disrupts the resin crystallization region through synergistic effect.

5. The supramolecular solvent system according to claim 1, characterized in that, The mass percentages of each component in a supramolecular solvent system for a perfluorosulfonic acid resin are as follows: 60-80% fluorocrown ether main solvent, 15-30% hyperbranched fluoropolymer co-solvent, and 5-10% Lewis acid-base pair catalyst.

6. A method for low-temperature dissolution of perfluorosulfonic acid resin, characterized in that, Includes the following steps: (1) Mix the perfluorosulfonic acid resin with the supramolecular solvent system according to any one of claims 1-5; (2) Stir at 40-80℃ for 0.5-2 hours to obtain a homogeneous solution.

7. The low-temperature dissolution method according to claim 6, characterized in that, Step (2) adopts a step-by-step heating strategy, including a 40-50℃ crystallization zone destruction stage, a 60-70℃ molecular chain de-entanglement stage, and a 70-80℃ complete dissolution stage.

8. The low-temperature dissolution method according to claim 6, characterized in that, The perfluorosulfonic acid resin is selected from any one of Nafion, Aquivion, or Flemion resins, and the dissolution process is carried out under inert gas protection.

9. The low-temperature dissolution method according to claim 6, characterized in that, The resulting solution has a solid content of 10-30 wt%. By adding 0.1-0.5 wt% graphene quantum dots as a stabilizer, the solution can be stored stably at room temperature for more than 30 days.

10. The use of the perfluorosulfonic acid resin solution obtained by the method of any one of claims 6-9 in the preparation of proton exchange membranes.

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