Sulfonic-phosphonic bis-acid cage silsesquioxane, and method of preparation and use thereof

Abstract

The application discloses a sulfonic acid-phosphonic acid double-acid cage-type silsesquioxane and a preparation method and application thereof, belongs to the application of a nano filler modified sulfonated polyarylene ether sulfone composite ion exchange membrane, and utilizes a nucleophilic ring-opening reaction to well obtain a controllable active sulfonic acid group for a sulfonation reaction, a part of amino groups on a POSS surface is subjected to a sulfonation reaction, a certain number of unreacted amino groups are reserved on the POSS surface while the sulfonic acid groups are introduced, and a sulfonic acid functionalized POSS is obtained, and the application has the beneficial effects that the sulfonic acid and the phosphonic acid cooperatively construct a double channel, and the proton conductivity in a high-humidity environment and a low-humidity environment is better than that of a single acid POSS modified membrane; a'sulfonation first and then phosphonation' step-by-step route is matched with a N,N-dimethylacetamide / sodium hydroxide / cyclic lactone sulfonation system, which is the only scheme that can realize covalent synchronous grafting of double acids, and a new functionalized filler that integrates two active centers is obtained and used for ion exchange membrane preparation.

Description

Technical Field

[0001] This invention belongs to the field of organic-inorganic hybrid proton conduction functional materials technology, specifically relating to a method for preparing sulfonic acid-phosphonic acid dual-acid functionalized cage-type silsesquioxane, and its application as a nanofiller to modify sulfonated polyarylene ether sulfone composite ion exchange membrane. Background Technology

[0002] Proton exchange membranes (PEMs) are a type of ion exchange membrane and are the core electrolyte component of proton exchange membrane fuel cells, directly determining the proton conductivity, stability, and mechanical properties of the battery. While commercial perfluorosulfonic acid membranes (Nafion) offer excellent proton conductivity, they suffer from drawbacks such as rapid moisture loss under high temperature and low humidity conditions, proton transport channel collapse, significant conductivity degradation, and high cost. Non-fluorinated aromatic proton exchange membranes such as sulfonated polyarylether sulfones (SPAES) are low in cost and have good thermal stability, but they rely solely on the main chain sulfonic acid groups to construct proton transport channels. Their proton hopping conduction ability is insufficient under low humidity conditions, and their mechanical strength decreases significantly during high-temperature operation, limiting their further application.

[0003] To improve the overall performance of proton exchange membranes, existing technologies incorporate cage-like silsesquioxanes (POSS) as inorganic-organic hybrid nanofillers into polymer matrices. POSS possesses a three-dimensional Si-O-Si cage-like rigid framework, which enhances the thermal stability and mechanical strength of the membrane material. Furthermore, additional proton transport sites can be constructed through chemical grafting of acidic functional groups. Currently, modified POSS fillers are mainly classified into two categories: single sulfonic acid modified POSS and single phosphonic acid modified POSS. 1. Single sulfonic acid functionalized POSS: It relies on the hydration carrier of sulfonic acid group to conduct protons. The conductivity is significantly improved in high humidity environment, but the water holding capacity is poor and the proton conduction is greatly reduced in low humidity. Moreover, the strong hydrophilicity of sulfonic acid will cause the membrane to have excessive water absorption rate, serious size swelling, and deterioration of mechanical properties. 2. Single phosphonic acid functionalized POSS: Phosphonic acid groups can achieve anhydrous proton hopping conduction through intermolecular hydrogen bonds, which has a significant advantage in low humidity conditions. However, the upper limit of proton conduction in high humidity environments is lower than that of sulfonic acid groups, and the improvement in ion exchange capacity is limited.

[0004] Existing technologies make it difficult to simultaneously covalently graft sulfonic acid and phosphonic acid bifunctional groups onto the surface of the same POSS cage. Furthermore, existing sulfonation modification processes have many drawbacks: poor POSS dispersion, severe side reactions, and extremely low sulfonic acid grafting rate, making it impossible to prepare highly functionalized dual-acid POSS nanofillers.

[0005] Based on the above problems, there is an urgent need in this field to develop a novel POSS functionalization strategy that can integrate the advantages of both sulfonic acid and phosphonic acid functional groups, is applicable to a variety of polymer matrices, and has a mild and simple preparation process. Summary of the Invention

[0006] This invention aims to overcome the defects of the prior art and provide a sulfonic acid-phosphonic acid dual-acid functionalized cage-type silsesquioxane, its preparation method and application. The technical problem to be solved is that it is difficult to covalently graft sulfonic acid and phosphonic acid dual-functional groups onto the same POSS cage surface at the same time. The existing sulfonation modification process has poor POSS dispersion, serious side reactions and extremely low sulfonic acid grafting rate, which makes it impossible to prepare highly functionalized dual-acid POSS nanofillers.

[0007] The specific technical solution of the present invention to solve the above-mentioned technical problems is as follows: A sulfonic acid-phosphonic acid dual-acid functionalized cage-type silsesquioxane is prepared using an octaamino cage-type silsesquioxane as the backbone. The amino groups on the cage surface are first nucleophilically and covalently grafted with alkyl sulfonic acid side chains, and the remaining amino groups are grafted with phosphonic acid groups via a pyridoxal phosphate Schiff base reaction. This yields a cage-type silsesquioxane simultaneously loaded with both sulfonic acid and phosphonic acid proton-conducting active functional groups. Its preferred structural formula is Formula 1.

[0008] Formula 1 The preparation method of the sulfonic acid-phosphonic acid bis-acid functionalized cage-type silsesquioxane includes the following steps: (1) Preparation of octaaminoPOSS: Using (3-aminopropyl)triethoxysilane as a raw material, hydrolysis and condensation were carried out in a methanol system catalyzed by hydrochloric acid, and high-purity octaaminoPOSS powder was obtained by recrystallization from tetrahydrofuran. Its preferred structural formula is Formula 2.

[0009] Formula 2 (2) Preparation of sulfonic acid-functionalized POSS (SPOSS): Eighty-amino POSS was dispersed in N,N-dimethylacetamide, and sulfonating agent 1,3-propanesulfonic acid lactone was added. Nucleophilic ring-opening reaction was carried out in the presence of a basic catalyst. Nucleophilic ring-opening reactions can effectively yield controllable, active sulfonic acid groups for sulfonation. This allows for the controlled sulfonation of some amino groups on the POSS surface. Simultaneously, a certain number of unreacted amino groups are retained on the POSS surface, resulting in sulfonic acid-functionalized POSS (denoted as SPOSS). The structural formula of SPOSS is shown as compound II in Formula 3. This step involves a nucleophilic ring-opening reaction, and the chemical reactions involved are shown in Formula 3 below.

[0010] Formula 3 (3) Preparation of sulfonic acid-phosphonic acid dual-acid functionalized PSPOS: First, a Schiff base pre-reaction is carried out between pyridoxal phosphate and the remaining amino group of SPOSS. Then, the SPOSS is activated by diethyl phosphite silyl group and deprotected by trimethylbromosilane hydrolysis. Phosonic acid groups are covalently grafted onto the remaining amino group of SPOSS. The structural formula of PPSOSS is shown as compound III in formula 4.

[0011] Formula 4 Further, in step (1), the volume ratio of (3-aminopropyl)triethoxysilane to methanol is 1:15, and the volume ratio of (3-aminopropyl)triethoxysilane to hydrochloric acid is 1:1.

[0012] Further, the concentration of hydrochloric acid in step (1) is 36%; the reaction process is heated to 90°C at a rate of 3°C / min and refluxed for 18 h.

[0013] Further, the reaction solvent in step (2) is N,N-dimethylacetamide, the sulfonating agent is 1,3-propanesulfonate lactone or 1,4-butanesulfonate lactone, and the catalyst is sodium hydroxide.

[0014] Further, in step (2), the mass ratio of the sulfonating agent 1,3-propanesulfonate lactone to octaaminoPOSS is 1:1 to 1:2; the volume ratio of 1,3-propanesulfonate lactone to N,N-dimethylacetamide is 1:25 to 1:50; and the volume ratio of 1,3-propanesulfonate lactone to sodium hydroxide is 1:1.

[0015] Furthermore, the reaction process described in step (2) is heated to 105°C at a heating rate of 3°C / min and kept at that temperature for 4–6 hours.

[0016] Further, in step (3), the mass ratio of SPOSS to pyridoxal phosphate is 1:72; the mass ratio of pyridoxal phosphate to anhydrous magnesium sulfate is 12:13. Furthermore, the Schiff base reaction conditions in step (3) are stirring at room temperature for 48 hours; Further, the activator in step (3) is trimethylchlorosilane, and its molar ratio with diethyl phosphite is 2:1; in a specific embodiment, the preferred volume ratio of trimethylchlorosilane to diethyl phosphite is 4:1.

[0017] The present invention also provides a proton exchange composite membrane comprising a sulfonated polymer matrix and the PPSPOSS dispersed therein; wherein the doping amount of the PPSPOSS is 3 wt% of the polymer matrix.

[0018] The present invention also provides the application of the PSPOSS or the composite membrane in fuel cells.

[0019] The beneficial effects of this invention are: (1) The sulfonic acid and phosphonic acid proposed in this invention synergistically construct a dual-channel structure, and the proton conductivity in high and low humidity environments is better than that of a single acidic POSS modified membrane; at the same time, the rigid POSS skeleton improves the tensile strength of the membrane, the phosphonic acid groups inhibit water absorption and swelling, and the power density of the fuel cell is significantly improved.

[0020] (2) The stepwise route of “sulfonate first, then phosphine” combined with the N,N-dimethylacetamide / sodium hydroxide / cyclic lactone sulfonation system of this invention is the only scheme that can achieve simultaneous covalent grafting of two acids. The reagents and reaction order are irreplaceable. The reaction conditions are mild and the parameters are adjustable. The filler is compatible with a variety of sulfonated polymers and is easy to scale up.

[0021] (3) By utilizing nucleophilic ring-opening reaction, controllable active sulfonic acid groups can be obtained for sulfonation reaction. Some amino groups can be sulfonated in a controllable manner on the POSS surface. While introducing sulfonic acid groups, a certain number of unreacted amino groups are reserved on the POSS surface to obtain phosphonic acid functionalized POSS. This achieves synchronous and efficient grafting of sulfonic acid groups and phosphonic acid groups, thus obtaining a new type of functionalized filler that integrates two active centers. Attached Figure Description

[0022] Appendix Figure 1 This is an HRTEM image of the octaamino POSS of Example 1 of the present invention; Appendix Figure 2 This is the HRTEM diagram of the PSPOSS in Embodiment 1 of the present invention; Appendix Figure 3 The infrared spectra of octaaminoPOSS, SPOSS and PSPOSS in Example 1 of this invention are shown. Appendix Figure 4 These are the XPS spectra of octaaminoPOSS and PSPOS from Example 1 of this invention; Appendix Figure 5 These are HRTEM and EDS elemental surface scans of the comparative product of the first phosphonate reaction followed by sulfonation in Comparative Example 1 of this invention. Appendix Figure 6 This is the infrared spectrum of the product of Comparative Example 2 of the present invention. Detailed Implementation

[0023] The specific details in the description of this invention are merely for the purpose of fully understanding the embodiments of the invention. However, those skilled in the art should know that the implementation of the invention is not limited to these details. In addition, well-known structures and functions have not been described or shown in detail to avoid obscuring the key points of the embodiments of the invention. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0024] Specific embodiments of the present invention: To better understand the present invention, specific embodiments are described. It is worth emphasizing that the effects of these embodiments are not substantially different from those of various embodiments within the scope of protection of the present invention, including their respective reagents and reagent content ratios. All of them can achieve the effects described in the present invention and solve the above-mentioned problems. Other combinations are not described here. Example 1: (1) Obtaining octaaminoPOSS: It can be obtained by purchasing or by preparation. Preparation includes: 10 mL of (3-aminopropyl)triethoxysilane was added to 150 mL of methanol and stirred. 10 mL of 36% hydrochloric acid was slowly added dropwise, and the temperature was raised to 90 °C at a rate of 3 °C / min. The mixture was then refluxed and kept at that temperature for 18 h. After naturally cooling to room temperature, 180 mL of tetrahydrofuran was added to precipitate a white precipitate. The precipitate was then filtered under vacuum, washed repeatedly with tetrahydrofuran, and dried under vacuum at 60 °C for 24 h to finally obtain 1.58 g of octaaminoPOSS powder. Figure 1 HRTEM image of octaamino POSS; Figure 3 Including the infrared spectrum of octaaminoPOSS; Figure 4 XPS spectrum including octaaminoPOSS; (2) Preparation of sulfonic acid functionalized POSS (SPOSS) In a three-necked flask equipped with a magnetic stirrer and nitrogen protection, 10 mL of N,N-dimethylacetamide was added, followed by the addition of 0.4 g of octaaminoPOSS under stirring. The mixture was stirred at room temperature for 2 h to disperse the precipitate. Then, 0.2 mL of 1,3-propanesulfonic acid lactone and 0.2 g of sodium hydroxide were added sequentially and stirred until homogeneous. The temperature was increased to 105 °C at a rate of 3 °C / min and maintained at this temperature for 4 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, centrifuged, washed multiple times with ethanol, and dried under vacuum at 80 °C for 12 h to obtain 0.42 g of SPOSS product. (3) Preparation of sulfonic acid-phosphonic acid bis-acid functionalized POSS (PSPOSS) 0.1 g SPOSS was dispersed in 10 mL of N,N-dimethylacetamide and sonicated for 45 min. Then, 0.78 g of anhydrous magnesium sulfate and 0.72 g of pyridoxal phosphate were added, and the mixture was stirred at room temperature for 48 h to complete the Schiff base pre-reaction. The product was washed with methanol, dried, and dispersed in 3 mL of acetonitrile to obtain the pre-reaction system. 1.59 mL of trimethylchlorosilane and 0.39 mL of diethyl phosphite were dissolved in 2 mL of acetonitrile and activated at room temperature for 4 h to obtain the activated solution. The pre-reaction system was added dropwise to the activated solution and stirred at room temperature for 36 h. Then, 5 mL of methanol and 2 mL of deionized water were added, and the mixture was allowed to stand at 4 °C for 48 h. After centrifugation, washing with methanol, and drying, the PSPOSS intermediate was obtained. The obtained intermediate was dispersed in 15 mL of anhydrous dichloromethane, and 0.66 mL of trimethylbromosilane was added dropwise under nitrogen protection. The mixture was stirred at room temperature in the dark for 28 h. After removing impurities by rotary evaporation under reduced pressure, the product was hydrolyzed with anhydrous methanol, quenched with deionized water, washed multiple times with methanol, and dried under vacuum to obtain 0.06 g of PSPOSS product. Figure 2 For the HRTEM diagram of PSPOSS; Figure 3 Including the infrared spectra of SPOSS and PSPOSS; Figure 4 It includes the XPS spectrum of PSPOS.

[0025] Example 2: Step (1) is the same as in Example 1; (2) Preparation of sulfonic acid functionalized POSS (SPOSS) In a three-necked flask equipped with a magnetic stirrer and nitrogen protection, 10 mL of N,N-dimethylacetamide was added, followed by the addition of 0.4 g of octaaminoPOSS under stirring. The mixture was stirred at room temperature for 2 h to disperse the precipitate. Then, 0.3 mL of 1,3-propanesulfonic acid lactone and 0.3 g of sodium hydroxide were added sequentially and stirred until homogeneous. The temperature was increased to 105 °C at a rate of 3 °C / min and maintained at this temperature for 4 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, centrifuged, washed multiple times with ethanol, and dried under vacuum at 80 °C for 12 h to obtain 0.48 g of SPOSS product. Step (3) is the same as in Example 1.

[0026] Example 3: Step (1) is the same as in Example 1; (2) Preparation of sulfonic acid functionalized POSS (SPOSS) In a three-necked flask equipped with a magnetic stirrer and nitrogen protection, 10 mL of N,N-dimethylacetamide was added, followed by the addition of 0.4 g of octaaminoPOSS under stirring. The mixture was stirred at room temperature for 2 h to disperse the precipitate. Then, 0.4 mL of 1,3-propanesulfonic acid lactone and 0.4 g of sodium hydroxide were added sequentially and stirred until homogeneous. The temperature was increased to 105 °C at a rate of 3 °C / min and maintained at this temperature for 6 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, centrifuged, washed multiple times with ethanol, and dried under vacuum at 80 °C for 12 h to obtain 0.52 g of SPOSS product. Step (3) is the same as in Example 1.

[0027] Example 4: Step (1) is the same as in Example 1; (2) Preparation of sulfonic acid functionalized POSS (SPOSS) In a three-necked flask equipped with a magnetic stirrer and nitrogen protection, 10 mL of N,N-dimethylacetamide was added, followed by the addition of 0.4 g of octaaminoPOSS under stirring. The mixture was stirred at room temperature for 2 h to disperse the precipitate. Then, 0.4 mL of 1,4-butyryl lactone and 0.4 g of sodium hydroxide were added sequentially and stirred until homogeneous. The temperature was increased to 105 °C at a rate of 3 °C / min and maintained at this temperature for 6 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, centrifuged, washed multiple times with ethanol, and dried under vacuum at 80 °C for 12 h to obtain 0.52 g of SPOSS product. Step (3) is the same as in Example 1.

[0028] To more intuitively demonstrate the technological advantages of this invention, a comparative example is provided. Comparative Example 1: Step (1) is the same as in Example 1; (2) First, functionalize with phosphonic acid: Take 0.1 g of octaaminoPOSS and follow the complete set of steps (3) in Example 1 to obtain monophosphonic acid modified POSS intermediate; (3) Try sulfonate functionalization: Take 0.4 g of the above monophosphonate POSS intermediate and follow the sulfonation process in step (2) of Example 1 to obtain a solid product; The TEM and EDS elemental distributions of the product of Comparative Example 1 are as follows: Figure 4As shown: the distribution of C, O, and Si elements completely overlaps with the particle morphology, proving that the POSS framework is intact; the P element signal, representing phosphonic acid groups, is uniformly distributed throughout the particle area, proving that the pyridoxal phosphate macromolecule has been extensively grafted onto the surface of the POSS cage; the S element, representing sulfonic acid groups, only exists as instrument background noise and has no obvious characteristic distribution signal; the results show that after the large volume of pyridoxal phosphate is preferentially grafted, it occupies most of the amino active sites in the POSS cage, generating strong steric hindrance, which prevents 1,3-propanesulfonic acid lactone from undergoing nucleophilic ring opening with the remaining amino groups, and cannot simultaneously introduce sulfonic acid and phosphonic acid bifunctional groups, confirming that the stepwise modification sequence of sulfonation followed by phosphonation in this invention has significant advantages.

[0029] Comparative Example 2: Step (1) is the same as in Example 1; (2) Sulfonic acid modification step: Refer to all process parameters of step (2) in Example 1, except that 0.2 mL of 1,3-propanesulfonic acid lactone is replaced with an equal amount of methanesulfonyl chloride, and the remaining solvent, sodium hydroxide dosage, heating program, reaction time and post-treatment process remain completely unchanged. After vacuum drying at 80°C, a solid product is obtained. Figure 5 Infrared characterization showed that the product of Comparative Example 2 was in the range of 1000–1250 cm⁻¹. - ¹The absence of alkyl sulfonate S=O stretching characteristic peaks indicates that methanesulfonyl chloride only forms sulfonamide structures with amino groups and cannot introduce alkyl sulfonate side chains via ring-opening reactions. Furthermore, methanesulfonyl chloride is easily hydrolyzed, and the high-temperature reaction environment of 105°C will cause it to decompose in large quantities, resulting in a significant decrease in the effective reactant concentration. In contrast, 1,3-propanesulfonate lactone has good thermal stability and can stably undergo ring-opening grafting at high temperatures. This demonstrates that cyclic sulfonate lactones are essential reagents for achieving nucleophilic ring-opening sulfonation in this invention.

[0030] Comparative Example 3: Step (1) is the same as in Example 1; (2) Sulfonic acid modification step: Refer to all process parameters in step (2) of Example 1, except that 0.2 mL of 1,3-propanesulfonic acid lactone is replaced with its completely ring-opening product, sodium 3-hydroxypropanesulfonate. The remaining solvent, sodium hydroxide dosage, heating program, reaction time, and post-treatment process remain completely unchanged. After the reaction was completed, the system was naturally cooled to room temperature. The system remained a homogeneous mixture with no obvious color change, no change in viscosity, and no new substance formation. Then, the same post-processing process as step (2) in Example 1 was used: centrifugation, multiple washing with ethanol, and vacuum drying at 80°C for 12 hours. Finally, only a small amount of unreacted octaamino POSS raw material powder was obtained, and no target sulfonic acid functionalized POSS product was generated. This may be due to the ternary strained ring structure of 1,3-propanesulfonic acid lactone, which is the key active structure for its nucleophilic ring-opening and covalent grafting of sulfonyl propionate with octaaminoPOSS. Its ring-opening product, sodium 3-hydroxypropanesulfonate, is structurally stable and non-reactive, and cannot undergo covalent grafting with octaaminoPOSS. Under the same reaction conditions, the ring-opening intermediate cannot replace 1,3-propanesulfonic acid lactone to achieve PSS sulfonic acid functionalization modification, confirming the necessity and uniqueness of the process route using cyclic lactone monomers in this invention, and effectively verifying the rationality and effectiveness of this technical solution.

[0031] Comparative Example 4: Step (1) is the same as in Example 1; (2) Sulfonic acid modification step: Refer to all process parameters of step (2) in Example 1, except that 0.2 g of sodium hydroxide is replaced with an equal amount of triethylamine, and the remaining solvents, the amount of 1,3-propanesulfonic acid lactone, the heating program, the reaction time and the post-treatment process remain completely unchanged. After vacuum drying at 80°C, a solid product is obtained. The final product of this system has a sulfonation grafting rate of only 15% of that in Example 1, with almost no detectable effective sulfonic acid groups incorporated, which completely fails to meet the minimum grafting threshold requirement for highly functionalized SPOSS. The reason may be that triethylamine is an organic weak base, and its basicity is much lower than that of the inorganic strong base sodium hydroxide. It cannot fully activate the active amino group on the surface of the octaamino POSS, making it difficult to drive the ring-opening grafting reaction between the amino group and 1,3-propanesulfonic acid lactone. Furthermore, the steric hindrance of the triethylamine molecule will further hinder the contact between the sulfonating agent and the active site. This proves that the inorganic strong base sodium hydroxide is a necessary catalytic component for achieving high grafting rate sulfonation modification.

[0032] Comparative Example 5: Step (1) is the same as in Example 1; (2) Sulfonic acid modification step: Refer to all process parameters of step (2) in Example 1, except that 10 mL of N,N-dimethylacetamide is replaced with 10 mL of anhydrous ethanol, and the amount of 1,3-propanesulfonic acid lactone, sodium hydroxide, heating program, reaction time and post-treatment process remain completely unchanged. After vacuum drying at 80°C, a solid product is obtained. The final product obtained by this system is a completely hardened, blocky aggregate. This is because: octaaminoPOSS readily aggregates and obscures its active sites in anhydrous ethanol through amino hydrogen bonds; ethanol will undergo alcoholysis with 1,3-propanesulfonate lactone, consuming raw materials; and sodium hydroxide has extremely low solubility in ethanol, resulting in insufficient alkalinity of the system, making efficient sulfonation grafting impossible. Therefore, it is clear that N,N-dimethylacetamide is a necessary reaction solvent for the preparation of highly functionalized SPOSS.

[0033] Comparative Example 6: Monosulfonic Acid Type POSS SPOSS was prepared according to steps (1) and (2) of Example 1, without step (3), and served as a single sulfonic acid type POSS control sample for subsequent composite membrane performance comparison; Comparative Example 7: Single Phosphonic Acid Type POSS A single phosphonic acid type POSS (PPOSS) was prepared according to steps (1) and (3) of Example 1, without step (2), and served as a single phosphonic acid type POSS control sample for subsequent composite membrane performance comparison; Application Example 1: Preparation and Performance Testing of Composite Proton Exchange Membranes 0.65 g of sulfonated polyarylene ether sulfone (SPAES) with a sulfonation degree of 50% was dissolved in 13 mL of N,N-dimethylacetamide and stirred at room temperature for 24 h to obtain a polymer solution. 19.5 mg each of PSPOS obtained in Example 1, SPOSS obtained in Comparative Example 5, and PPOSS obtained in Comparative Example 6 were dispersed in 3 mL of N,N-dimethylacetamide, sonicated for 1 h, and stirred at room temperature for 12 h to obtain filler dispersions. The different filler dispersions were then mixed with the polymer solution and stirred at room temperature for 24 h to obtain casting solutions. The casting solutions were slowly poured into an ultra-flat casting pan and heated in an oven according to a programmed temperature rise (80 °C / 10 h; 100 °C / 2 h) to form a film. After removal, the film was immersed in 1 mol / L hydrochloric acid solution for 72 h and washed with deionized water until neutral, yielding three composite membranes: SPAES / PSPOSS-3.0 wt%, SPAES / SPOSS-3.0 wt%, and SPAES / PPOSS-3.0 wt%. wt%; and at the same time, an undoped pure SPAES film was prepared as a blank control using the same method.

[0034] The performance of four membrane samples was tested, and the results are shown in Table 1. Table 1. Performance comparison of electrolyte membranes prepared in different embodiments and comparative examples.

[0035] Analysis of the data in Table 1 shows that: Under high humidity conditions of 80°C / 100%RH, the conductivity improvement of single sulfonic acid POSS (188.6 mS / cm) is superior to that of single phosphonic acid POSS (170.3 mS / cm), demonstrating the superiority of the sulfonic acid carrier mechanism; while under medium humidity conditions of 80°C / 50%RH, single phosphonic acid POSS (52.4 mS / cm) is significantly superior to that of single sulfonic acid POSS (32.1 mS / cm), demonstrating the unique advantage of phosphonic acid hopping conduction. The dual-acid PSSOS of this invention exhibits conductivity of 210.3 mS / cm and 68.7 mS / cm under two conditions, respectively, both surpassing the conductivity of the two single-acid systems. Furthermore, its performance gain exceeds the difference between the single-acid systems, directly demonstrating that sulfonic acid and phosphonic acid form a synergistic enhancement effect on the same PSS nanoparticle surface. In addition, the tensile strength (30.7 MPa) of the dual-acid composite membrane is superior to that of the pure membrane and the two single-acid composite membranes, while its water absorption rate (34.8%) is significantly lower than that of the single sulfonic acid type (41.2%). Its maximum output power (728.5 mW / cm²) is 32.9% higher than that of the pure membrane, and 13.2% and 23.2% higher than that of the single sulfonic acid and single phosphonic acid composite membranes, respectively, fully verifying the significant superiority of this invention in terms of overall performance. Comparing Examples 1-7, we can see that: Existing technologies make it difficult to covalently graft sulfonic acid and phosphonic acid bifunctional groups onto the same POSS cage surface simultaneously. If a large volume phosphonic acid macromolecule is introduced first, it will generate extremely strong steric hindrance on the POSS cage surface, blocking most of the amino active sites, making it impossible to complete the subsequent sulfonic acid grafting. If sulfonating agents such as methanesulfonyl chloride are directly used to replace cyclic sulfonyl lactones, only sulfonamide structures without proton conduction ability can be generated, and alkyl sulfonic acid side chains cannot be introduced. Through the above embodiments and performance comparisons, it can be confirmed that the dual-acid modification strategy proposed in this invention, while maintaining the advantages of POSS nanofillers, achieves improved proton conductivity and optimized comprehensive mechanical properties of the composite membrane under a wide humidity window through the synergistic integration of sulfonic acid and phosphonic acid functional groups, demonstrating significant technological advancement and practical value.

[0036] In summary: (1) The sulfonic acid and phosphonic acid proposed in this invention synergistically construct a dual-channel structure, and the proton conductivity in high and low humidity environments is better than that of a single acidic POSS modified membrane; at the same time, the rigid POSS skeleton improves the tensile strength of the membrane, the phosphonic acid groups inhibit water absorption and swelling, and the power density of the fuel cell is significantly improved.

[0037] (2) The stepwise route of “sulfonate first, then phosphine” combined with the N,N-dimethylacetamide / sodium hydroxide / cyclic lactone sulfonation system of this invention is the only scheme that can achieve simultaneous covalent grafting of two acids. The reagents and reaction order are irreplaceable. The reaction conditions are mild and the parameters are adjustable. The filler is compatible with a variety of sulfonated polymers and is easy to scale up.

[0038] (3) By utilizing nucleophilic ring-opening reaction, controllable active sulfonic acid groups can be obtained for sulfonation reaction. Some amino groups can be sulfonated in a controllable manner on the POSS surface. While introducing sulfonic acid groups, a certain number of unreacted amino groups are reserved on the POSS surface to obtain phosphonic acid functionalized POSS. This achieves synchronous and efficient grafting of sulfonic acid groups and phosphonic acid groups, thus obtaining a new type of functionalized filler that integrates two active centers.

Claims

1. A sulfonic acid-phosphonic acid bis-acid cage-type silsesquioxane, characterized in that... The structural formula is: 。 2. A method for preparing a sulfonic acid-phosphonic acid bis-acid cage-type silsesquioxane, characterized in that... The process includes the following steps: using an octaaminocage-type silsesquioxane as the backbone substrate, firstly, alkyl sulfonic acid side chains are covalently grafted via nucleophilic ring-opening, and then phosphonic acid groups are grafted onto the remaining amino groups via a pyridoxal phosphate Schiff base reaction, thus obtaining a sulfonic acid-phosphonic acid bis-acid cage-type silsesquioxane simultaneously loaded with both sulfonic acid and phosphonic acid proton-conducting active functional groups.

3. The method for preparing sulfonic acid-phosphonic acid bis-acid cage-type silsesquioxane according to claim 2, characterized in that... Includes the following steps: (1) Preparation of sulfonic acid functionalized POSS: Eighty-amino POSS was dispersed in N,N-dimethylacetamide, and sulfonating agent 1,3-propanesulfonic acid lactone was added. Nucleophilic ring-opening reaction was carried out in the presence of a basic catalyst, and some amino groups on the POSS surface were sulfonated to obtain sulfonic acid functionalized POSS. (2) Preparation of sulfonic acid-phosphonic acid bis-acid cage-type silsesquioxanes: First, a Schiff base pre-reaction is carried out between pyridoxal phosphate and the remaining amino group. Then, the phosphonic acid group is activated by diethyl phosphite and deprotected by trimethylbromosilane hydrolysis. Finally, sulfonic acid-phosphonic acid bisacrylic silsesquioxane is obtained by covalently grafting phosphonic acid groups onto the remaining amino site of SPOSS.

4. The method for preparing sulfonic acid-phosphonic acid bis-acid cage-type silsesquioxane according to claim 3, characterized in that... The reaction solvent is N,N-dimethylacetamide, the sulfonating agent is 1,3-propanesulfonate lactone or 1,4-butanesulfonate lactone, and the catalyst is sodium hydroxide.

5. The method for preparing the sulfonic acid-phosphonic acid bisacrylic silsesquioxane according to claim 3, characterized in that... The mass ratio of the sulfonating agent 1,3-propanesulfonate lactone to octaaminoPOSS is 1:1 to 1:2; the volume ratio of 1,3-propanesulfonate lactone to N,N-dimethylacetamide is 1:25 to 1:

50.

6. The method for preparing the sulfonic acid-phosphonic acid bisacrylic silsesquioxane according to claim 3, characterized in that... The reaction process described in step (1) is heated to 105℃ at a heating rate of 3℃ / min and kept at that temperature for 4 to 6 hours.

7. The method for preparing sulfonic acid-phosphonic acid bisacrylic silsesquioxane according to claim 3, characterized in that... In step (2), the mass ratio of SPOSS to pyridoxal phosphate is 1:72; the mass ratio of pyridoxal phosphate to anhydrous magnesium sulfate is 12:

13.

8. The method for preparing sulfonic acid-phosphonic acid bis-acid cage-type silsesquioxane according to claim 3, characterized in that... The activator in step (2) is trimethylchlorosilane, and the molar ratio of trimethylchlorosilane to diethyl phosphite is 2:1; the preferred volume ratio of trimethylchlorosilane to diethyl phosphite is 4:

1.

9. The use of a sulfonic acid-phosphonic acid bisacrylic silsesquioxane, comprising the preparation method of the sulfonic acid-phosphonic acid bisacrylic silsesquioxane according to any one of claims 2-8, wherein the prepared sulfonic acid-phosphonic acid bisacrylic silsesquioxane is characterized in that... Used to prepare proton exchange composite membranes The proton exchange composite membrane comprises a sulfonated polymer matrix and the sulfonic acid-phosphonic acid bisacrylic silsesquioxane dispersed therein; the doping amount of the sulfonic acid-phosphonic acid bisacrylic silsesquioxane is 3 wt% of the polymer matrix mass.

10. The use of the sulfonic acid-phosphonic acid bisacrylic cage-type silsesquioxane according to claim 9, characterized in that... Application of the proton exchange composite membrane in fuel cells.

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