Fluorine-containing anionic surfactant and method for preparing fluorine-containing polymer from fluorine-containing anionic surfactant

Abstract

The invention discloses a fluorine-containing anionic surfactant and a method for preparing a fluorine-containing polymer from the fluorine-containing anionic surfactant, and relates to the technical field of fluororesin, the fluorine-containing anionic surfactant comprises ammonium perfluorohexanoate and ammonium perfluoro-2, 5-dimethyl-3, 6-dioxononanoate according to a mass ratio of (0.3-1.0): (0.5-1.5), and the fluorine-containing anionic surfactant comprises ammonium perfluorohexanoate and ammonium perfluoro-2, 5-dimethyl-3, 6-dioxononanoate according to a mass ratio of (0.3-1.0): (0.5-1.5). Tetrafluoroethylene, a second monomer, a fluorine-containing anionic surfactant, an initiator and a polymerization medium are mixed and subjected to a polymerization reaction, and the fluorine-containing polymer is obtained. The fluorine-containing surfactant is a compound of ammonium perfluorohexanoate and ammonium perfluoro-2, 5-dimethyl-3, 6-dioxononanoate, is high-purity 9 carbon, 6 carbon, does not contain 7 carbon and octocarbonic acid, and is a straight-chain product, so that a product containing a large number of branched chains by adopting an electrolytic process is avoided, and the performance consistency of the produced fluorine-containing polymer is favorably improved.

Description

Technical Field

[0001] This invention relates to the field of fluoropolymer technology, specifically to a fluorinated anionic surfactant and a method for preparing fluorinated polymers therefrom. Background Technology

[0002] Following the global restrictions on the use of PFOA (perfluorooctanoic acid) surfactants in the production of polytetrafluoroethylene (PTFE) dispersion resins, multiple different process routes for PFOA alternatives have emerged in the industry. International companies such as DuPont, Asahi Glass, and Daikin have their own unique process routes, while domestic companies are also developing and producing alternatives. In China, there are various PFOA (perfluorooctanoic acid) alternative routes, with perfluoropolyethers seeing the most widespread adoption, gradually replacing the market share of the original trimer acid. Due to the large variety of fluoropolymers, the demand for PFOA alternatives is greatest in the PTFE dispersion polymerization process, and the actual demand for alternatives to other fluoropolymers is also increasing. Many domestic anionic surfactant alternatives in fluoropolymer polymerization processes employ single-formulation solutions. Therefore, we propose a method for preparing fluorinated anionic surfactants and fluoropolymers. Summary of the Invention

[0003] The purpose of this invention is to provide a fluorinated anionic surfactant and a method for preparing fluorinated polymers thereto, so as to solve the problems mentioned in the background art.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a fluorinated anionic surfactant, comprising ammonium perfluorohexanoate and ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate (CAS No.: 13043-05-5).

[0005] Furthermore, the perfluoro-2,5-dimethyl-3,6-dioxanonanoate ammonium is obtained by hydrolysis and saponification of perfluoro-2,5-dimethyl-3,6-dioxanonanoyl fluoride (CAS No.: 2641-34-1);

[0006] The perfluoro-2,5-dimethyl-3,6-dioxanenonyl fluoride is obtained by telomerization of hexafluoropropylene oxide (CAS No.: 428-59-1).

[0007] Furthermore, the ammonium perfluorohexanoate is produced by reacting hexafluoropropylene oxide (HFPO, CF2-CF-CF2O) with perfluoroiodoalkane via a telomerization reaction to generate perfluorohexanoyl fluoride (C5F). 11 COF is obtained through hydrolysis and saponification.

[0008] Furthermore, the mass ratio of ammonium perfluorohexanoate to ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate is 1:(1.5 to 2.0).

[0009] In the above technical solution, the fluorinated surfactant in this application is a compound of ammonium perfluorohexanoate and ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate, which is high-purity 9-carbon and 6-carbon, and does not contain 7-carbon or octacarbonate. It is a linear product, which avoids the products containing a large number of branched chains that are produced by the electrolytic process, and helps to improve the consistency of the performance of the fluorinated polymer.

[0010] The mixed-type fluorinated anionic surfactant has an adjustable surface tension, close to that of PFOA (perfluorooctanoic acid), and can be used as a substitute in polymerization process formulations. The dosage and method of use are the same as those of the original PFOA, and there is no need to adjust the dosage of polymerization formulations and additives or the addition steps in the polymerization process.

[0011] A method for preparing fluoropolymers from fluorinated anionic surfactants includes the following process: mixing tetrafluoroethylene, a second monomer, a fluorinated anionic surfactant, an initiator, and a polymerization medium, and performing a polymerization reaction to obtain a fluoropolymer.

[0012] Furthermore, the initiator is a perfluorinated peroxide initiator;

[0013] The initiator is one of perfluorobenzoyl peroxide, perfluorobutyryl peroxide, peroxydicarbonate-4,4-bis(tert-butylcyclohexyl) ester, and peroxybis(perfluoro-2-npropoxypropionyl).

[0014] Furthermore, the polymerization medium is one of trifluorotrichloroethane, perfluoroheptane, hexafluorobenzene, perfluorocyclohexane, supercritical CO2, or deionized water.

[0015] Furthermore, the second monomer is one or a mixture of hexafluoropropylene, trifluorochloroethylene, vinylidene fluoride, fluoroethylene, ethylene, perfluoroalkyl vinyl ether monomers, and perfluorodioxane pentene monomers.

[0016] Furthermore, the perfluoroether monomers include one of the following: perfluoropropyl vinyl ether, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, sulfonated perfluorovinyl ether, and 2-perfluoropropoxyperfluoropropyltrifluorovinyl ether.

[0017] Furthermore, the perfluorodioxane monomers include one of the following: perfluoro-2,2-dimethyl-1,3-dioxane, 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxane, 2,2,4-trifluoro-5-trifluoromethyl-1,3-dioxane, perfluoro-2-methyl-2-ethyl-1,3-dioxane, perfluoro-2-methylene-4-methyl-1,3-dioxane, perfluoro-2-methylene-1,3-dioxane, and perfluoro(4-methyl-3,6-dioxane-7-octene)sulfonyl fluoride.

[0018] Furthermore, the fluoropolymer is prepared by the following process:

[0019] The reactor was evacuated and purged with nitrogen three times. Tetrafluoroethylene and fluorinated anionic surfactant were added to deionized water and ultrasonically dispersed for 10-15 minutes to form an emulsion. The emulsion was then added together with the initiator into a high-pressure reactor, heated to 60-80°C, and the pressure was adjusted to 2-5 MPa. The reaction was carried out at a stirring rate of 300-500 rpm for 4-6 hours.

[0020] Then, the second monomer is added, and the reaction is continued for 2 to 4 hours with a stirring rate of 400 to 600 rpm to obtain the fluoropolymer.

[0021] Furthermore, after the reaction, the reaction was terminated by cooling to room temperature, slowly releasing the pressure to atmospheric pressure at a rate ≤0.3 MPa / min, and collecting the polymer.

[0022] Purification: Centrifuge the polymer emulsion, wash it three times with deionized water, or dynamically extract it with supercritical CO2 (60℃, 10MPa) for 2 hours to remove unreacted monomers and surfactants;

[0023] Drying: Vacuum drying at 60℃ for 12 hours.

[0024] Furthermore, the fluoropolymer comprises the following components by weight: 80-90 parts tetrafluoroethylene, 10-20 parts second monomer, 0.8-2.5 parts fluorinated anionic surfactant, 0.05-0.20 parts initiator, and 30-50 parts deionized water.

[0025] Furthermore, the second monomer is mixed with 0.1-0.3 wt% ammonium perfluorohexanoate (PFHxA) and dissolved in deionized water (second monomer to water mass ratio = 1:3), ultrasonically dispersed for 5 min, and injected into the reactor at a rate of 0.5-1.0 mL / min through a high-pressure metering pump, maintaining pressure fluctuation <0.3 MPa;

[0026] If the second stage reaction time is >3 hours, 0.02–0.05 wt% of initiator needs to be added to maintain activity;

[0027] Hexafluoropropylene (HFP) (1-3 wt%) can be added in the later stage of the second reaction to further improve processability.

[0028] In the above technical solution, based on short-chain ammonium perfluorohexanoate, long-chain ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate is compounded as a fluorinated anionic surfactant to synergistically optimize reaction uniformity and ensure monomer dispersion and initiation efficiency. The short-chain surfactant has a smaller molecular weight, enabling rapid adsorption at the tetrafluoroethylene (TFE) / water interface, reducing the initial interfacial tension and promoting TFE dispersion in water. Its short-chain structure can fill the gaps in the micelles of ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate, increasing micelle packing density and preventing small particle aggregation. The anion (COO-) can also reduce the probability of free radical termination through electrostatic repulsion, prolonging the active chain lifetime, increasing molecular weight, and indirectly affecting the reaction rate and polymer chain growth. Perfluorinated peroxides decompose more uniformly in the presence of ammonium perfluorohexanoate, reducing the risk of localized explosive polymerization. Ammonium perfluorohexanoate has a small hydrophilic head group, enabling rapid adsorption at the interface, while ammonium perfluoro-2,5-dimethyl-3,6-dioxanonanoate has a long hydrophobic tail, providing steric hindrance. Together, they can reduce the dynamic tension at the water / monomer interface.

[0029] The long-chain perfluoropolyether structure (containing compliant segments of ether bonds) makes micelles less prone to rupture under high pressure, maintaining reaction homogeneity and forming a steric barrier on the outer layer of the micelles. In water, it forms a more stable micelle core, encapsulating hydrophobic monomers (tetrafluoroethylene, secondary monomer), providing a homogeneous reaction environment and enhancing monomer contact efficiency. The polarity of the ether bonds enhances the interaction with water, extending micelle lifetime; the resulting steric hindrance prevents latex particle aggregation under high temperature or shear, avoiding latex particle agglomeration and resulting in a narrower particle size distribution, thus forming smaller, narrower micelles. This increases the local monomer concentration, improving polymerization rate and conversion. Under high pressure and high temperature conditions, the long-chain perfluoro-2,5-dimethyl-3,6-dioxanonanoate ammonium salt exhibits stronger shear resistance, preventing monomer aggregation caused by micelle rupture, improving dynamic stability, preventing polymer particle aggregation, ensuring uniform polymer dispersion, facilitating subsequent purification, improving the homogeneity of the reaction system, avoiding local overheating or explosive polymerization, and resulting in a narrower polymer molecular weight distribution (PDI). The lone pair electrons of the ether bond can complex free radical initiators, slowing down the free radical decomposition rate and prolonging the growth time of active chains. The electrostatic repulsion of the anionic head group (COO-) can reduce the probability of free radical termination and improve chain growth efficiency. By stabilizing free radical intermediates and lowering the initiator decomposition energy barrier, the efficiency of the initiator and the stability of free radicals are improved, thus increasing the initiation efficiency and the utilization rate of the initiator. This allows for a reduction in the amount of initiator used, resulting in an increase in the molecular weight (Mw) of the fluoropolymer, with an increase of 10–20%. Flexible ether segments may partially embed into the polymer side chains, disrupting the regularity of the PTFE backbone, reducing crystallinity, increasing the melt index, and improving processing performance. The compound system promotes the directional alignment of the perfluoroether side chains (-CF2-O-CF2- of the second monomer) on the polymer surface, further reducing the surface energy and increasing the water contact angle. The resulting polymer exhibits both low-temperature flexibility and excellent water and oil repellency. Polar ether bonds can enhance the compatibility of the second monomer, making it more uniformly embedded in the backbone and reducing local compositional fluctuations.

[0030] Short-chain fluorinated anionic surfactants rapidly reduce interfacial tension, forming small-sized micelle cores, while long chains provide outer protection, extending micelle lifetime and balancing dispersion speed and stability. This avoids excessively short chains leading to overly small micelles (easily broken) or excessively long chains leading to excessively high viscosity, thus balancing emulsification speed and stability. The resulting fluorinated polymer exhibits improved TFE conversion, a narrower molecular weight distribution (PDI), and excellent surface properties.

[0031] Perfluorinated perbutyroyl (PFPO) exhibits the best synergistic effect with compound surfactants.

[0032] Furthermore, the second monomer is obtained by the following process:

[0033] Catechol, 2,2-dibromohexafluoropropane, potassium carbonate, and catalyst were mixed in solvent A, heated to 80–100 °C, and reacted for 7–10 h. The mixture was then cooled to room temperature, allowed to stand in an ice bath, and the liquid phase was separated. The organic phase was dried and then distilled to obtain benzodioxane.

[0034] Under a nitrogen atmosphere at -70 to -30°C, lithium catalyst and solvent B were mixed; benzodioxane obtained in the previous step was added over 0.5 to 2 hours, followed by a reaction at this temperature for 3 to 4 hours; perfluoro-3,5-dioxane methyl ether was added over 1.5 to 2 hours, followed by a reaction at this temperature for 1 to 2 hours; the mixture was then allowed to return to room temperature and reacted for another 2 to 3 hours; the pH was adjusted to neutral, and the mixture was extracted with a hexane / diethyl ether mixed solvent (v / v = 3:1). The molecular sieve is dried, concentrated under reduced pressure, filtered, and dried again to obtain the second monomer.

[0035] Furthermore, the molar ratio of catechol, 2,2-dibromohexafluoropropane, and potassium carbonate is 1:(1.1–1.3):(1.5–1.6);

[0036] The catalyst is tetrabutylammonium bromide (TBAB), and the amount used is 1% of the mass of catechol;

[0037] Solvent A is one of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or sulfolane, and its amount is 3.6 to 4.0 times the mass of catechol.

[0038] Furthermore, the mass ratio of benzodioxane to perfluoro-3,5-dioxane (CAS No.: 2245171-87-1) is 1:(1.3~1.6);

[0039] The lithium catalyst is one of tert-butyllithium and n-butyllithium, and the amount used is 0.20 to 0.27 of the mass of benzodioxane.

[0040] The preferred lithium catalyst is n-butyllithium;

[0041] Solvent B is anhydrous tetrahydrofuran (THF), and the amount used is 3.0 to 3.5 times the mass of benzodioxane.

[0042] In the above technical solution, potassium carbonate provides alkalinity, catechol undergoes deprotonation to generate phenoxyfluoride ions, which attack the carbon atoms in 2,2-dibromohexafluoropropane, resulting in nucleophilic substitution of bromine by catechol oxygen, forming a benzodioxane structure, denoted as benzodioxane. During the reaction, the catalyst promotes ion transfer between potassium carbonate and the solvent, leading to phase transfer.

[0043] The lithium catalyst reacts with the aromatic ring of benzodioxane obtained in the previous step to generate an aryllithium intermediate, forming a C-Li bond. The aryllithium intermediate attacks the α-position of the ether bond in perfluoro-3,5-dioxane methyl ether, forming a C-C bond and introducing a perfluoroether side chain to obtain the second monomer. The reaction is carried out at low temperature to suppress side reactions and prevent over-lithiation or decomposition.

[0044] A second monomer was prepared by introducing a rigid-flexible hybrid structure through nucleophilic substitution and lithiation reactions, which was then used to copolymerize and modify tetrafluoroethylene (PTFE). The second monomer contains a rigid benzodioxane ring and a flexible perfluoroether chain. When it participates in the polymerization of PTFE to prepare fluoropolymers, it can improve the thermal stability and mechanical strength of the resulting fluoropolymers, enhance their hydrophobic / oleophobic properties and chemical inertness, and improve low-temperature flexibility. The second monomer is a side chain of the fluoropolymer; its perfluoroether chain reduces crystallinity, improves melt flowability, and avoids the difficult processing problems of PTFE. It also introduces polar sites, improving compatibility and adhesion with other materials. The terminal -CF3 groups of the perfluoroether side chain are densely arranged on the polymer surface, significantly reducing surface energy, similar to a "self-assembly" effect, thus enhancing the polymer's water and oil repellency. By adjusting crystallinity and introducing functional side chains, the second monomer balances the mechanical properties, processing properties, and surface characteristics of PTFE, making it suitable for high-end fluorinated materials such as corrosion-resistant coatings, flexible seals, medical catheters, antifouling coatings, and lithium battery separators.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] The fluorinated surfactant in this invention is a blend of ammonium perfluorohexanoate and ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate, which is high-purity 9-carbon and 6-carbon, free of 7-carbon and 8-carbon compounds, and is a linear product. This avoids the problem of producing products with a large number of branched chains using electrolytic processes, thus helping to improve the consistency of the properties of the fluorinated polymers produced. The blended fluorinated anionic surfactant has an adjustable surface tension, close to that of PFOA (perfluorooctanoic acid), and can be used as a substitute in polymerization formulations. The dosage and method of use are consistent with the original PFOA, and there is no need to separately adjust the polymerization formulation dosage and additive steps in the polymerization process. Detailed Implementation

[0047] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] In the following specific implementation,

[0049] Ammonium perfluorohexanoate, ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate (CAS No.: 13043-05-5): Purity > 99.9%;

[0050] The initiator is perfluorobutyryl peroxide, which is dissolved in perfluoroheptane before addition. The mass ratio of perfluorobutyryl peroxide to perfluoroheptane is 1:8.

[0051] Perfluoro-3,5-dioxane: CAS No.: 2245171-87-1.

[0052] Example 1: A fluorinated anionic surfactant comprising ammonium perfluorohexanoate and ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate in a mass ratio of 1:1.5;

[0053] A method for preparing fluoropolymers from fluorinated anionic surfactants includes the following processes:

[0054] Step 1: Catechol, 2,2-dibromohexafluoropropane, potassium carbonate, and catalyst were mixed in solvent A, heated to 80°C, and reacted for 10 hours. The mixture was then cooled to room temperature, allowed to stand in an ice bath, and the liquid phase was separated and dried. The organic phase was then distilled to obtain benzodioxane. The molar ratio of cadmium, 2,2-dibromohexafluoropropane, and potassium carbonate was 1:1.1:1.5. The catalyst was tetrabutylammonium bromide, used at 1% of the mass of cadmium. Solvent A was sulfolane, used at 4.0 times the mass of cadmium.

[0055] Under a nitrogen atmosphere at -30°C, lithium catalyst and solvent B were mixed; benzodioxane obtained in the previous step was added over 0.5 h, followed by a reaction at this temperature for 3 h; perfluoro-3,5-dioxane methyl ether was added over 1.5 h, followed by a reaction at this temperature for 1 h; the mixture was then allowed to return to room temperature and reacted for another 2 h; the pH was adjusted to neutral, and the mixture was extracted with a hexane / diethyl ether mixed solvent (v / v = 3:1). Molecular sieve drying, vacuum concentration, filtration, and drying yielded the second monomer; the mass ratio of benzodioxane to perfluoro-3,5-dioxane methyl ether was 1:1.3; the lithium catalyst was n-butyllithium, used in an amount of 0.20 times the mass of benzodioxane; solvent B was anhydrous tetrahydrofuran, used in an amount of 3.0 times the mass of benzodioxane.

[0056] Step 2: Evacuate the reactor and replace it with nitrogen three times; add tetrafluoroethylene and fluorinated anionic surfactant to deionized water, and ultrasonically disperse for 10 minutes to form an emulsion; add the emulsion and initiator together to the high-pressure reactor, heat to 60°C, adjust the pressure to 2 MPa, and react for 6 hours with a stirring rate of 300 rpm;

[0057] Then, the second monomer was added, and the reaction was continued for 2 hours with a stirring rate of 400 rpm to obtain a fluoropolymer. The fluoropolymer consisted of the following components by mass: 90 parts tetrafluoroethylene, 10 parts second monomer, 0.8 parts fluorinated anionic surfactant, 0.05 parts initiator, and 30 parts deionized water. After the reaction, the mixture was cooled to room temperature and slowly depressurized to atmospheric pressure at a rate ≤0.3 MPa / min. The polymer was collected. The polymer emulsion was separated by centrifugation and washed three times with deionized water. The mixture was then vacuum dried at 60°C for 12 hours. The second monomer was mixed with 0.1 wt% ammonium perfluorohexanoate and dissolved in deionized water (second monomer to water mass ratio = 1:3). The mixture was ultrasonically dispersed for 5 minutes and injected into the reactor at a rate of 0.5 mL / min using a high-pressure metering pump, maintaining a pressure fluctuation of <0.3 MPa.

[0058] Example 2: A fluorinated anionic surfactant comprising ammonium perfluorohexanoate and ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate in a mass ratio of 1:1.8;

[0059] A method for preparing fluoropolymers from fluorinated anionic surfactants includes the following processes:

[0060] Step 1: Catechol, 2,2-dibromohexafluoropropane, potassium carbonate, and catalyst were mixed in solvent A, heated to 90°C, and reacted for 8 hours. After cooling to room temperature, the mixture was allowed to stand in an ice bath and separated. The organic phase was dried and then distilled to obtain benzodioxane. The molar ratio of cadmium, 2,2-dibromohexafluoropropane, and potassium carbonate was 1:1.2:1.55. The catalyst was tetrabutylammonium bromide, and its amount was 1% of the mass of cadmium. Solvent A was sulfolane, and its amount was 3.8 times the mass of cadmium.

[0061] Under a nitrogen atmosphere at -50°C, lithium catalyst and solvent B were mixed; benzodioxane obtained in the previous step was added over 1.2 h, followed by a reaction at this temperature for 3.5 h; perfluoro-3,5-dioxane methyl ether was added over 1.8 h, followed by a reaction at this temperature for 1.5 h; the mixture was then allowed to return to room temperature and reacted for another 2.5 h; the pH was adjusted to neutral, and the mixture was extracted with a hexane / diethyl ether mixed solvent (v / v = 3:1). Molecular sieve drying, vacuum concentration, filtration, and drying yielded the second monomer; the mass ratio of benzodioxane to perfluoro-3,5-dioxane methyl ether was 1:1.4; the lithium catalyst was n-butyllithium, used in an amount of 0.23 times the mass of benzodioxane; solvent B was anhydrous tetrahydrofuran, used in an amount of 3.2 times the mass of benzodioxane.

[0062] Step 2: Evacuate the reactor and replace it with nitrogen three times; add tetrafluoroethylene and fluorinated anionic surfactant to deionized water, and ultrasonically disperse for 12 minutes to form an emulsion; add the emulsion and initiator together to the high-pressure reactor, heat to 70°C, adjust the pressure to 3.5 MPa, and react for 5 hours with a stirring rate of 400 rpm;

[0063] Then, the second monomer was added, and the reaction was continued for 3 hours with a stirring rate of 500 rpm to obtain a fluoropolymer. The fluoropolymer consisted of the following components by mass: 85 parts tetrafluoroethylene, 15 parts second monomer, 1.6 parts fluorinated anionic surfactant, 0.1 parts initiator, and 40 parts deionized water. After the reaction, the mixture was cooled to room temperature and slowly depressurized to atmospheric pressure at a rate ≤0.3 MPa / min. The polymer was collected. The polymer emulsion was separated by centrifugation and washed three times with deionized water. The mixture was then vacuum dried at 60°C for 12 hours. The second monomer was mixed with 0.2 wt% ammonium perfluorohexanoate and dissolved in deionized water (second monomer to water mass ratio = 1:3). The mixture was ultrasonically dispersed for 5 minutes and injected into the reactor at a rate of 0.8 mL / min using a high-pressure metering pump, maintaining a pressure fluctuation of <0.3 MPa.

[0064] Example 3: A fluorinated anionic surfactant comprising ammonium perfluorohexanoate and ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate in a mass ratio of 1:2.0;

[0065] A method for preparing fluoropolymers from fluorinated anionic surfactants includes the following processes:

[0066] Step 1: Catechol, 2,2-dibromohexafluoropropane, potassium carbonate, and catalyst were mixed in solvent A, heated to 100℃, and reacted for 7 hours. After cooling to room temperature, the mixture was allowed to stand in an ice bath and separated. The organic phase was dried and then distilled to obtain benzodioxane. The molar ratio of cadmium, 2,2-dibromohexafluoropropane, and potassium carbonate was 1:1.3:1.6. The catalyst was tetrabutylammonium bromide, and its amount was 1% of the mass of cadmium. Solvent A was sulfolane, and its amount was 3.6 times the mass of cadmium.

[0067] Under a nitrogen atmosphere at -70°C, lithium catalyst and solvent B were mixed; benzodioxane obtained in the previous step was added, with the addition completed over 2 hours, followed by a reaction at this temperature for 4 hours; perfluoro-3,5-dioxane methyl ether was added, with the addition completed over 2 hours, followed by a reaction at this temperature for 2 hours; the mixture was then allowed to return to room temperature and reacted for another 3 hours; the pH was adjusted to neutral, and extraction was performed using a hexane / diethyl ether mixed solvent (v / v = 3:1). Molecular sieve drying, vacuum concentration, filtration, and drying yielded the second monomer; the mass ratio of benzodioxane to perfluoro-3,5-dioxane methyl ether was 1:1.6; the lithium catalyst was n-butyllithium, used in an amount of 0.27 times the mass of benzodioxane; solvent B was anhydrous tetrahydrofuran, used in an amount of 3.5 times the mass of benzodioxane.

[0068] Step 2: Evacuate the reactor and replace it with nitrogen three times; add tetrafluoroethylene and fluorinated anionic surfactant to deionized water, and ultrasonically disperse for 15 minutes to form an emulsion; add it together with the initiator into the high-pressure reactor, heat it to 80°C, adjust the pressure to 5 MPa, and react it for 4 hours with a stirring rate of 500 rpm;

[0069] Then, the second monomer was added, and the reaction was continued for 4 hours with a stirring rate of 600 rpm. During the reaction, 2 wt% hexafluoropropylene was added to obtain a fluoropolymer. The fluoropolymer consisted of the following components by mass: 80 parts tetrafluoroethylene, 20 parts second monomer, 2.5 parts fluorinated anionic surfactant, 0.20 parts initiator, and 50 parts deionized water. After the reaction, the mixture was cooled to room temperature and slowly depressurized to atmospheric pressure at a rate ≤0.3 MPa / min. The polymer was collected. The polymer emulsion was separated by centrifugation and washed three times with deionized water. The mixture was then vacuum dried at 60°C for 12 hours. The second monomer was mixed with 0.3 wt% ammonium perfluorohexanoate and dissolved in deionized water (second monomer to water mass ratio = 1:3). The mixture was ultrasonically dispersed for 5 minutes and injected into the reactor at a rate of 1.0 mL / min using a high-pressure metering pump, maintaining a pressure fluctuation <0.3 MPa. 0.03 wt% initiator was added to maintain activity.

[0070] Comparative Example 1: A fluorinated anionic surfactant comprising ammonium perfluorohexanoate and ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate in a mass ratio of 1:1.5;

[0071] A method for preparing fluoropolymers from fluorinated anionic surfactants, wherein the second monomer is 2-perfluoropropoxyperfluoropropyltrifluorovinyl ether;

[0072] The other process steps are the same as in Example 1, and a fluoropolymer is obtained.

[0073] Comparative Example 2: A fluorinated anionic surfactant comprising ammonium perfluorohexanoate and ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate in a mass ratio of 1:1.5;

[0074] A method for preparing fluoropolymers from a fluorinated anionic surfactant, wherein the second monomer is perfluoro-2-methylene-4-methyl-1,3-dioxacyclopentene;

[0075] The other process steps are the same as in Example 1, and a fluoropolymer is obtained.

[0076] Comparative Example 3: A fluorinated anionic surfactant is perfluoro-2,5-dimethyl-3,6-dioxanonanoate ammonium;

[0077] A method for preparing fluoropolymers from fluorinated anionic surfactants, wherein the second monomer is 2-perfluoropropoxyperfluoropropyltrifluorovinyl ether;

[0078] The other process steps are the same as in Example 1, and a fluoropolymer is obtained.

[0079] Comparative Example 4: A fluorinated anionic surfactant comprising ammonium perfluorohexanoate;

[0080] A method for preparing fluoropolymers from fluorinated anionic surfactants, wherein the second monomer is 2-perfluoropropoxyperfluoropropyltrifluorovinyl ether;

[0081] The other process steps are the same as in Example 1, and a fluoropolymer is obtained.

[0082] Comparative Example 5: A fluorinated anionic surfactant comprising perfluorooctanoic acid;

[0083] A method for preparing fluoropolymers from fluorinated anionic surfactants includes the following processes:

[0084] The reactor was evacuated and purged with nitrogen three times. Tetrafluoroethylene and a fluorinated anionic surfactant were added to deionized water and ultrasonically dispersed for 10 min to form an emulsion. The emulsion, along with the initiator, was added to a high-pressure reactor, heated to 60°C, and the pressure was adjusted to 2 MPa. The reaction was carried out at a stirring rate of 300 rpm for 6 h to obtain a fluoropolymer. The fluoropolymer consisted of the following components by mass: 100 parts tetrafluoroethylene, 0.8 parts fluorinated anionic surfactant, 0.05 parts initiator, and 30 parts deionized water. After the reaction, the mixture was cooled to room temperature and slowly depressurized to atmospheric pressure at a rate ≤0.3 MPa / min. The polymer was collected. The polymer emulsion was separated by centrifugation and washed three times with deionized water. The mixture was then vacuum dried at 60°C for 12 h.

[0085] Experiment: Fluorinated anionic surfactants and fluoropolymers (injection molded) obtained in Examples 1-3 and Comparative Examples 1-5 were used to prepare samples. Their properties were tested, and the results were recorded.

[0086] Surface tension testing: The surface tension of fluorinated anionic surfactants was tested using the platinum plate method of GB / T 22237 as the reference standard at an experimental temperature of 25±0.1℃.

[0087] Detection of fluoropolymers: Using GB / T 21863 as the reference standard, the molecular weight (Mw) and molecular weight distribution (PDI) of the sample are detected. For GPC (PL-GPC 220, THF as the mobile phase, PS standard for calibration): Using GB / T 19077 as the reference standard, the particle size distribution of the sample is detected. The amount of unreacted TFE residue is determined by gas chromatography, and the TFE conversion rate is calculated.

[0088] Surface performance testing: The water and oil (hexadecane) contact angles of the samples were tested using GB / T 30693 as the reference standard; the surface energy of the samples was tested using GB / T 24368 as the reference standard.

[0089] Mechanical property testing: The low-temperature flexibility of the specimen was tested with ASTM D256 as the reference standard, and the cantilever beam impact strength of the specimen at -40℃ was used as the performance index, with a pendulum energy of 2.75J; the tensile properties of the specimen were tested with GB / T1040.2 as the reference standard.

[0090] Thermal stability test: The thermal stability of the sample was tested with reference to GB / T 19466.2, and the decomposition temperature at 5% weight loss was used as the performance index.

[0091] Table 1. Surface tension test data of fluorinated anionic surfactants

[0092]

[0093] Table 2. Molecular weight, molecular weight distribution, particle size distribution, TFE conversion rate, and thermal stability test data of fluoropolymers.

[0094]

[0095] Table 3. Test data on water contact angle, oil (hexadecane) contact angle, surface energy, tensile properties, and low-temperature flexibility of fluoropolymers.

[0096]

[0097] Based on the data in the table above, the following conclusions can be clearly drawn:

[0098] The fluorinated anionic surfactants and fluorinated polymers obtained in Examples 1-3 were compared with those obtained in Comparative Examples 1-5. The test results show that...

[0099] The fluorinated anionic surfactants obtained in Examples 1-3 have surface tensions similar to perfluorooctanoic acid (PFOA) in Comparative Example 5, and can replace PFOA in the polymerization process. The combination of surfactant and second monomer in Examples 1-3 increases the molecular weight (Mw) and narrows the polydispersity index (PDI) of the prepared fluoropolymers, which is superior to single-component or unmodified PTFE. The fluoropolymers obtained in Examples 1-3 exhibit superior hydrophobic and oleophobic properties and mechanical properties. This fully demonstrates that the present invention achieves a comprehensive improvement in the hydrophobic, oleophobic, mechanical, and thermal stability properties of the prepared fluoropolymers.

[0100] Compared to Example 1, the second monomer in Comparative Example 1 was 2-perfluoropropoxy-perfluoropropyltrifluorovinyl ether; the second monomer in Comparative Example 2 was perfluoro-2-methylene-4-methyl-1,3-dioxane; the second monomer in Comparative Example 3 was 2-perfluoropropoxy-perfluoropropyltrifluorovinyl ether, and the fluorinated anionic surfactant was ammonium perfluoro-2,5-dimethyl-3,6-dioxanenoate; the second monomer in Comparative Example 4 was 2-perfluoropropoxy-perfluoropropyltrifluorovinyl ether, and the fluorinated anionic surfactant was ammonium perfluorohexanoate; and Comparative Example 5 used perfluorooctanoic acid as a surfactant to prepare a polytetrafluoroethylene dispersion. The performance data of the fluoropolymers obtained in Comparative Examples 1-5 deteriorated. It can be seen that the selection of the fluorinated anionic surfactant and the setting of the second monomer preparation process in this invention can promote the comprehensive improvement of the amphiphilic properties, mechanical properties, and thermal stability of the prepared fluoropolymers.

[0101] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A fluorinated anionic surfactant, characterized in that: Including ammonium perfluorohexanoate and ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate.

2. The fluorinated anionic surfactant according to claim 1, characterized in that: The mass ratio of ammonium perfluorohexanoate to ammonium perfluoro-2,5-dimethyl-3,6-dioxanonate is 1:(1.5-2.0).

3. A method for preparing fluoropolymers from a fluorinated anionic surfactant according to any one of claims 1-2, characterized in that: The process includes the following steps: mixing tetrafluoroethylene, a second monomer, a fluorinated anionic surfactant, an initiator, and a polymerization medium, followed by a polymerization reaction to obtain a fluorinated polymer.

4. The method for preparing fluoropolymers from a fluorinated anionic surfactant according to claim 3, characterized in that: The initiator is a perfluorinated peroxide.

5. The method for preparing fluoropolymers from a fluorinated anionic surfactant according to claim 3, characterized in that: The second monomer is one or a mixture of hexafluoropropylene, trifluorochloroethylene, vinylidene fluoride, fluorinated vinylidene ethylene, perfluoroalkyl vinyl ether monomers, and perfluorodioxane pentene monomers.

6. The method for preparing fluoropolymers from a fluorinated anionic surfactant according to claim 3, characterized in that: The polymerization medium is one of trifluorotrichloroethane, perfluoroheptane, hexafluorobenzene, perfluorocyclohexane, supercritical CO2, or deionized water.

7. The method for preparing fluoropolymers from a fluorinated anionic surfactant according to claim 6, characterized in that: The fluoropolymer is prepared by the following process: The reactor was evacuated and purged with nitrogen three times. Tetrafluoroethylene and fluorinated anionic surfactant were added to deionized water and ultrasonically dispersed for 10-15 minutes to form an emulsion. The emulsion was then added together with the initiator into a high-pressure reactor, heated to 60-80°C, and the pressure was adjusted to 2-5 MPa. The reaction was carried out at a stirring rate of 300-500 rpm for 4-6 hours. Then, the second monomer is added, and the reaction is continued for 2 to 4 hours with a stirring rate of 400 to 600 rpm to obtain the fluoropolymer.

8. The method for preparing fluoropolymers from a fluorinated anionic surfactant according to claim 7, characterized in that: The fluoropolymer comprises the following components by weight: 80-90 parts tetrafluoroethylene, 10-20 parts second monomer, 0.8-2.5 parts fluorinated anionic surfactant, 0.05-0.20 parts initiator, and 30-50 parts deionized water.

9. The method for preparing fluoropolymers from a fluorinated anionic surfactant according to claim 7, characterized in that: The second monomer is obtained by the following process: Catechol, 2,2-dibromohexafluoropropane, potassium carbonate, and catalyst are mixed in solvent A, heated to 80-100℃, and reacted for 7-10 hours to obtain benzodioxane. Under a nitrogen atmosphere at -70 to -30°C, lithium catalyst and solvent B were mixed; benzodioxane obtained in the previous step was added over 0.5 to 2 hours, and then the reaction was maintained at this temperature for 3 to 4 hours; perfluoro-3,5-dioxane methyl ether was added over 1.5 to 2 hours, and then the reaction was maintained at this temperature for 1 to 2 hours; the temperature was then restored to room temperature, and the reaction was continued for 2 to 3 hours to obtain the second monomer.

10. The method for preparing fluoropolymers from a fluorinated anionic surfactant according to claim 9, characterized in that: The molar ratio of catechol, 2,2-dibromohexafluoropropane, and potassium carbonate is 1:(1.1-1.3):(1.5-1.6). The mass ratio of benzodioxane to perfluoro-3,5-dioxane methyl ether is 1:(1.3 to 1.6).

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