Preparation method of peroxide vulcanized raw fluororubber

Abstract

The invention provides a preparation method of peroxide vulcanized raw fluororubber, which comprises the following steps: in the presence of an initiator, contacting an aqueous solution of an emulsifier with a mixed monomer to carry out polymerization reaction, and adding a chain transfer agent into the reaction system in batches, ensuring that the pH value of the reaction system is relatively stable, and obtaining the raw rubber after the reaction is finished. The preparation method has the beneficial effects that the operation is simple, the reaction condition is mild, the polymerization reaction rate is effectively improved, the vulcanization points on the fluororubber molecular chain are uniformly distributed, and the peroxide vulcanized fluororubber raw rubber with small permanent compression deformation is prepared. Meanwhile, the obtained peroxide vulcanized raw fluororubber has good vulcanization performance and good oil resistance, and can be applied to various industrial fields, especially the automobile industry, including sealing elements, lubricating oil pipes and the like.

Description

Technical Field

[0001] The present invention belongs to the field of fluororubber synthesis, and particularly relates to a preparation method of peroxide-cured fluororubber raw rubber. Background Art

[0002] Fluororubbers have high temperature resistance, oil resistance, resistance to a variety of chemical agents, and excellent sealing properties, and are indispensable materials for modern aerospace, military, space navigation and other cutting-edge science and technologies. In recent years, with the continuous improvement of the requirements of the automotive industry for reliability, safety, etc., the consumption of fluororubbers in automobiles has also increased rapidly. Fluororubber products prepared with peroxide-type high-fluorine-content fluoroelastomers as the skeleton material are particularly favored in the new energy vehicle industry, especially peroxide-type fluororubber products with a high fluorine content, a narrow molecular weight distribution, and low permanent compression set.

[0003] The excellent functions of fluororubbers are necessarily related to chemical crosslinking. The crosslinking mechanism is mainly divided into ionic and free radical types. The ionic type includes amine vulcanization and bisphenol vulcanization, while the free radical type includes organic peroxide vulcanization and radiation crosslinking vulcanization. Peroxide-type fluororubbers are vulcanized in the form of free radical crosslinking, including the following two processes: (1) Free radicals are generated by heating the peroxide, and then H on the tertiary carbon atom in the polymer chain or the active site on the crosslinking point monomer is absorbed to form a polymer free radical; (2) The polymer free radical directly or through the mediation of a free radical scavenger forms a crosslinking bond.

[0004] Peroxide-type fluororubbers have higher fluorine content (fluorine content greater than 70%), and compared with fluororubbers vulcanized with vulcanizing agent No. 3 and bisphenol vulcanization systems, they have more excellent sealing properties, chemical resistance and other properties. However, they have the following disadvantages: due to their high Mooney viscosity and difficult dispersion, resulting in poor processing performance, high compression set and other factors. In addition, due to low production efficiency and high price, peroxide-type fluororubbers have not become the preferred choice for people.

[0005] Chinese Patent Publication No. CN104448095A discloses a preparation method of a peroxide-curable fluororubber, and the steps are as follows: 1) Add deionized water, a pH buffer, and an emulsifier into a reaction kettle, perform a vacuum pumping operation on the reaction kettle, and raise the temperature in the kettle to 50 - 120 °C; 2) Add polymerization monomer A and polymerization monomer B into the reaction kettle until the pressure in the kettle reaches 0.3 - 5 MPa, add a free radical initiator to initiate the polymerization reaction, add a chain transfer agent after the reaction starts, and simultaneously replenish polymerization monomer A and polymerization monomer B to maintain the pressure at the pressure in the kettle; 3) As the reaction proceeds, replenish the free radical initiator every 4 h until the reaction is completed; 4) Obtain an elastomer emulsion, add a coagulant for coagulation, washing, and vacuum drying to obtain a peroxide-curable fluororubber. However, the fluororubber raw rubber obtained by this method has a low density, and the cured rubber has poor heat resistance and liquid resistance. Moreover, this method has a cumbersome process and a too long production time, which is not conducive to realizing efficient industrial production.

[0006] Patent CN201210307846.0 discloses a preparation method of an alkali-resistant cured fluororubber. The disadvantage of this method is that the polymerization reaction rate is slow, the polymerization time is long, and the industrial production cost is high. Patent CN201310293100.3 discloses a preparation method of a peroxide-curable fluorine-containing elastomer, using an alkyl iodide as a chain transfer agent. During the reaction, an I atom is introduced into the molecular structure of the polymer, which can play the role of a crosslinking point in peroxide curing. The permanent compression set of the peroxide-cured fluororubber synthesized by this method is relatively high, which limits the application range. Summary of the Invention

[0007] To solve the above problems, the present invention improves the preparation method and increases the reaction rate by improving the configuration method of the reaction mixture monomers, adjusting the addition time and addition method of the initiator, adjusting the addition time and addition method of the chain transfer agent, adjusting the pH value of the emulsion during the reaction, etc., so as to improve the curing performance of the peroxide-curable fluororubber, that is, to improve the compression set permanent deformation, etc.

[0008] In the first aspect of the present invention, there is provided a preparation method of a peroxide-curable fluororubber raw rubber, comprising the following steps:

[0009] (1) In the presence of an initiator, bring an aqueous solution of an emulsifier into contact with a mixed monomer for a polymerization reaction, and the mixed monomer is prepared by mixing vinylidene fluoride, tetrafluoroethylene, perfluoropropylene, and a vulcanization point monomer;

[0010] (2) To the reaction system described in step (1), a chain transfer agent is added in batches. When the reaction amount of the mixed monomers in the reaction system reaches 8%-15% of their cumulative reaction total, the first batch of the chain transfer agent is added. When the reaction amount of the mixed monomers in the reaction system reaches 45%-75% of their cumulative reaction total, the second batch of the chain transfer agent is added, and the pH of the reaction system is ensured to be relatively stable. After the reaction is completed, the raw rubber is obtained.

[0011] The vulcanization point monomer is uniformly mixed with vinylidene fluoride, tetrafluoroethylene, and perfluoropropylene before the reaction and then continuously added to the reactor, which is beneficial to the uniform distribution of vulcanization points on the molecular chain and improves the reaction rate. If the vulcanization point monomer is added during the reaction and the local concentration is too high, the system distribution is uneven, and the unreacted vulcanization point monomer in the rubber has an adverse effect on the chemical resistance and heat resistance of the rubber and affects the reaction rate.

[0012] In some embodiments of the preparation method according to the present invention, in step (1), in every 100 g of the reaction system, the amount of the emulsifier is 0.1-1 g (for example: 0.1 g, 0.3 g, 0.5 g, 0.6 g, 0.8 g, 1.0 g).

[0013] In some embodiments of the preparation method according to the present invention, in every 100 g of the reaction system, the amount of the initiator is 0.01-0.1 g (for example: 0.01 g, 0.03 g, 0.05 g, 0.06 g, 0.08 g, 0.1 g).

[0014] In some embodiments of the preparation method according to the present invention, in every 100 g of the reaction system, the mixed monomers are continuously supplemented. When the cumulative reaction total of the mixed monomers reaches 35-55 g, such as 35 g, 40 g, 45 g, 50 g, 55 g, the reaction is stopped, preferably 40-45 g.

[0015] In some embodiments of the preparation method according to the present invention, in step (1), the initiator is a water-soluble initiator.

[0016] In some embodiments of the preparation method according to the present invention, the initiator is selected from one or more of persulfates, peroxosuccinic acid, or azodiisobutyramidine dihydrochloride; preferably selected from ammonium persulfate and / or potassium persulfate. As the reaction proceeds, the effect of the initiator weakens and the reaction gradually slows down. By continuously adding the initiator all the time, the reaction rate is kept relatively constant.

[0017] In some embodiments of the preparation method according to the present invention, the initiator is an aqueous solution of persulfate with a mass percentage concentration of 1%-8% (for example: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%).

[0018] In some embodiments of the preparation method according to the present invention, the emulsifier is perfluorocarboxylate, alkyl sulfonate, higher fatty acid salt, alkyl sulfate ester, fluorinated ether carboxylic acid, perfluoroether carboxylate, preferably perfluoroether carboxylate.

[0019] In some embodiments of the preparation method according to the present invention, the molar ratio of vinylidene fluoride, tetrafluoroethylene, perfluoropropylene and sulfurization point monomer in the mixed monomers is: (18 - 45):(6 - 34):(28 - 49):(0.1 - 1), for example: 18:6:28:0.1, 25:10:30:0.3, 35:21:32:0.5, 45:34:49:1.

[0020] In some embodiments of the preparation method according to the present invention, the sulfurization point monomer is a halogenated fluorinated olefin.

[0021] In some embodiments of the preparation method according to the present invention, the sulfurization point monomer is selected from one or more of CF2=CFOCF2CF2CF2OCF2Br, 1-bromo-2,2-difluoroethylene, 3-bromo-perfluoro(propyl vinyl) ether, trifluorobromoethylene, trifluoroiodoethylene, perfluoroiodoalkyl vinyl ether, perfluorobromoalkyl vinyl ether and 3,3,4,4-tetrafluoro-4-bromo-1-butene.

[0022] In some embodiments of the preparation method according to the present invention, the sulfurization point monomer is trifluorobromoethylene or 3,3,4,4-tetrafluoro-4-bromo-1-butene.

[0023] In some embodiments of the preparation method according to the present invention, the temperature for mixing the mixed monomers is 50 - 110 °C (for example: 50 °C, 60 °C, 80 °C, 100 °C, 110 °C), preferably, the temperature is 55 - 90 °C.

[0024] In some embodiments of the preparation method according to the present invention, in step (1), the pH of the reaction system is 2 - 6 and the oxygen content < 30 ppm (for example: 5 ppm, 10 ppm, 15 ppm, 20 ppm, 25 ppm).

[0025] The reaction temperature of the reaction system is 80 - 120 °C (for example: 80 °C, 90 °C, 100 °C, 110 °C, 120 °C), preferably 85 - 105 °C; the reaction pressure is 2.0 - 5.0 MPa, preferably 2.0 - 4.5 MPa. During the polymerization process, in order to stabilize the polymerization rate, the polymerization temperature can be appropriately increased.

[0026] In some embodiments of the preparation method according to the present invention, in step (2), in every 100 g of the reaction system, the addition amount of the chain transfer agent is 0.1 - 2.0 g (for example: 0.1 g, 0.3 g, 0.5 g, 1 g, 1.2 g, 1.5 g, 1.8 g, 2.0 g, 2.6 g, 3.0 g).

[0027] In some embodiments of the preparation method according to the present invention, the ratio of the addition amount of the first batch of the chain transfer agent to the addition amount of the second batch of the chain transfer agent is: (6 - 8) : (4 - 2), for example: 6:4, 6:3, 7:4, 7:3, 7:2, 8:3, 8:2.

[0028] In some embodiments of the preparation method according to the present invention, the chain transfer agent is selected from one or more of methylene iodide, diiodomethane, perfluoroalkyl iodide, and 1,4 - diiodoperfluoro - butane.

[0029] In some embodiments of the preparation method according to the present invention, the chain transfer agent is selected from one or more of diiodomethane, perfluoroalkyl iodide, and 1,4 - diiodoperfluoro - butane.

[0030] In radical polymerization, bromine - or iodine - containing compounds are more preferably selected as the chain transfer agent, and then bromine or iodine atoms are attached to the ends of the polymer. During the polymerization process, this chain transfer agent must react with the salt of Br - / I - together. The copolymer synthesized using bromine - or iodine - containing perfluoroalkane as the chain transfer agent has good fluidity and processing performance. During vulcanization, the peroxide vulcanizing agent undergoes a cross - linking reaction with highly reactive bromine or iodine.

[0031] In some embodiments of the preparation method according to the present invention, in step (2), when the reaction amount of the mixed monomers in the reaction system reaches 60% - 80% of their cumulative total reaction amount, a pH regulator is added to ensure the relative stability of the pH of the reaction system. Maintaining the pH value in the reactor within a suitable range is beneficial to the progress of the polymerization reaction.

[0032] In some embodiments of the preparation method according to the present invention, the pH regulator is selected from one or more of phosphates, hydrogen phosphates, dihydrogen phosphates, hydrogen diphosphates, carbonates, and bicarbonates.

[0033] In some embodiments of the preparation method according to the present invention, the pH regulator is dipotassium hydrogen phosphate.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows: The preparation method of the present invention is simple in operation and mild in reaction conditions. By adjusting measures such as the configuration method of the reaction mixture monomers, the addition time and addition method of the chain transfer agent, and the pH value of the emulsion during the reaction, the polymerization reaction rate and the uniform distribution of vulcanization sites on the fluororubber molecular chain are effectively improved, and a peroxide-cured fluororubber raw rubber with a small permanent compression set is prepared. At the same time, the obtained peroxide-cured fluororubber raw rubber has good vulcanization properties and good oil resistance, and can be applied to a variety of industrial fields, especially in the automotive industry, including seals, lubricating oil pipes, etc. Detailed Embodiments

[0035] To make the objectives, technical solutions and advantages of the present invention clearer, the following further details the present invention with reference to embodiments. The specific embodiments described herein are only used to explain the present invention and do not constitute any limitation to the present invention. In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessarily confusing the concepts of the present disclosure. Such structures and technologies have also been described in many publications.

[0036] Example 1

[0037] Vinylidene fluoride, tetrafluoroethylene, perfluoropropylene, and trifluorobromoethylene were mixed evenly at a molar ratio of (31:26.5:42:0.5) at a temperature of 70 °C to prepare a homogeneous and stable mixed monomer.

[0038] Free radical emulsion polymerization was carried out in a 50 L reaction kettle to prepare a peroxide-type fluororubber raw rubber. 30 Kg of deionized water, 150 g of perfluoroether ammonium acid, and 75 g of pH regulator dipotassium hydrogen phosphate were added to the reaction kettle. The air in the vapor space of the reaction kettle was first replaced with nitrogen and then with the mixed monomer to make the oxygen content less than 30 ppm and the system pH 8 - 9. The stirring of the reaction kettle was started and heated to 95 °C. The prepared mixed monomer was added to the reaction kettle by a compressor to raise the pressure to 3.0 MPa, and then 200 g of initiator solution (4.5 wt%, potassium persulfate) was added to start the reaction. When the cumulative reaction amount of the mixed monomer was 1.2 Kg, 12 g of chain transfer agent (diiodomethane) was added, and the initiator solution (1 wt%, potassium persulfate) was continuously added at 60 ml / 10 min until the reaction ended. During the reaction, the pressure of the reaction kettle was maintained at 3.0 MPa and the temperature at 95 °C with the mixed monomer all the time. When the cumulative reaction amount of the mixed monomer was 6 Kg, 8 g of chain transfer agent (diiodomethane) was added. When the cumulative reaction amount of the mixed monomer was 9 Kg, 75 g of pH regulator dipotassium hydrogen phosphate was added to keep the system pH at 3 - 5, which was beneficial to the progress of the reaction. The reaction continued until the predetermined feed amount of 12 Kg was reached, then the stirring was stopped and the product was recovered and discharged.

[0039] The obtained polymer was subjected to electrolyte coagulation, washed, dried in vacuum, and rolled and formed on an open mill. More than 11 Kg of the polymer was obtained, and its performance characteristics are shown in Table 1.

[0040] Table 1 Performance test results of fluororubber raw rubber

[0041]

[0042] Example 2

[0043] Vinylidene fluoride, tetrafluoroethylene, perfluoropropylene, and trifluorobromoethylene were mixed evenly at a molar ratio of (31:26.7:42:0.3) at a temperature of 70 °C to prepare a homogeneous and stable mixed monomer.

[0044] Free radical emulsion polymerization was carried out in a 50 L reaction kettle to prepare peroxide-type fluororubber raw rubber. 30 Kg of deionized water, 150 g of perfluoroether ammonium acid, and 75 g of pH regulator dipotassium hydrogen phosphate were added to the reaction kettle. The air in the vapor space of the reaction kettle was first replaced with nitrogen and then with the mixed monomer to make the oxygen content less than 30 ppm and the system pH 8-9. The stirring of the reaction kettle was started and the temperature was raised to 95 °C. The prepared mixed monomer was added to the reaction kettle by a compressor to raise the pressure to 3.0 MPa, and then 200 g of initiator solution (4.5 wt%, potassium persulfate) was added to start the reaction. When the cumulative reaction amount of the mixed monomer was 1.2 Kg, 12 g of chain transfer agent (diiodomethane) was added, and the initiator solution (1 wt%, potassium persulfate) was continuously added at 60 ml / 10 min until the reaction ended. During the reaction process, the pressure of the reaction kettle was maintained at 3.0 MPa and the temperature at 95 °C with the mixed monomer. When the cumulative reaction amount of the mixed monomer was 6 Kg, 8 g of chain transfer agent (diiodomethane) was added. When the cumulative reaction amount of the mixed monomer was 9 Kg, 75 g of pH regulator dipotassium hydrogen phosphate was added to keep the system pH at 3-5, which was beneficial to the progress of the reaction. The reaction was continued until the predetermined feeding amount of 12 Kg was reached, then the stirring was stopped and the product was recovered and discharged.

[0045] Example 3

[0046] Vinylidene fluoride, tetrafluoroethylene, perfluoropropylene, and trifluorobromoethylene were mixed evenly at a molar ratio of (31:26:42:1.0) at a temperature of 70 °C to prepare a homogeneous and stable mixed monomer.

[0047] Free radical emulsion polymerization was carried out in a 50 L reactor to prepare peroxide type fluororubber raw rubber. 30 Kg of deionized water, 150 g of ammonium perfluoroetherate, and 75 g of pH regulator dipotassium hydrogen phosphate were added to the reactor. The air in the vapor space of the reactor was first replaced with nitrogen and then with the mixed monomer to make the oxygen content less than 30 ppm, and the system pH was 8 - 9. The reactor stirrer was turned on and the temperature was raised to 95 °C. The prepared mixed monomer was added to the reactor with a compressor to raise the pressure to 3.0 MPa, and then 200 g of initiator solution (4.5 wt%, potassium persulfate) was added to start the reaction. When the cumulative reaction amount of the mixed monomer reached 1.2 Kg, 12 g of chain transfer agent (diiodomethane) was added, and the initiator solution (1 wt%, potassium persulfate) was continuously added at a rate of 60 ml / 10 min until the reaction ended. During the reaction, the reactor pressure was maintained at 3.0 MPa and the temperature at 95 °C with the mixed monomer all the time. When the cumulative reaction amount of the mixed monomer reached 6 Kg, 8 g of chain transfer agent (diiodomethane) was added. When the cumulative reaction amount of the mixed monomer reached 9 Kg, 75 g of pH regulator dipotassium hydrogen phosphate was added to keep the system pH at 3 - 5, which was beneficial to the progress of the reaction. The reaction was continued until the predetermined feed amount of 12 Kg was reached, then the stirring was stopped and the product was recovered and discharged.

[0048] Comparative Example 1

[0049] Vinylidene fluoride, tetrafluoroethylene, and perfluoropropylene were mixed evenly at a molar ratio of (31:27:42) at a temperature of 70 °C to prepare a homogeneous and stable mixed monomer.

[0050] Free radical emulsion polymerization was carried out in a 50 L reactor to prepare peroxide type fluororubber raw rubber. 30 Kg of deionized water, 150 g of ammonium perfluoroetherate, and 75 g of pH regulator dipotassium hydrogen phosphate were added to the reactor. The air in the vapor space of the reactor was first replaced with nitrogen and then with the mixed monomer. After the oxygen content was less than 30 ppm, 60 g of bromotrifluoroethylene was added to the reactor. The reactor stirrer was turned on and the temperature was raised to 95 °C. The prepared mixed monomer was added to the reactor with a compressor to raise the pressure to 3.0 MPa, and then 200 g of initiator solution (4.5 wt%, potassium persulfate) was added to start the reaction. When the cumulative reaction amount of the mixed monomer reached 1.2 Kg, 12 g of chain transfer agent (diiodomethane) was added, and the initiator solution (1 wt%, potassium persulfate) was continuously added at a rate of 60 ml / 10 min until the reaction ended. During the reaction, the reactor pressure was maintained at 3.0 MPa and the temperature at 95 °C with the mixed monomer all the time. When the cumulative reaction amount of the mixed monomer reached 6 Kg, 8 g of chain transfer agent (diiodomethane) was added. When the cumulative reaction amount of the mixed monomer reached 9 Kg, 75 g of pH regulator dipotassium hydrogen phosphate was added to keep the system pH at 3 - 5, which was beneficial to the progress of the reaction. The reaction was continued until the predetermined feed amount of 12 Kg was reached, then the stirring was stopped and the product was recovered and discharged.

[0051] The obtained polymer is coagulated with electrolyte, washed, dried in vacuum, and rolled and formed on an open mill. More than 11 Kg of polymer is obtained, and its performance characteristics are shown in Table 2.

[0052] Table 2 Performance test results of raw fluororubber

[0053]

[0054]

[0055] Comparative Example 2

[0056] Vinylidene fluoride, tetrafluoroethylene, perfluoropropylene, and trifluorobromoethylene are mixed evenly at a molar ratio of (31:26.5:42:0.5) at a temperature of 70 °C to prepare a uniform and stable mixed monomer.

[0057] Free radical emulsion polymerization is carried out in a 50 L reaction kettle to prepare peroxide-type raw fluororubber. 30 Kg of deionized water, 150 g of ammonium perfluoroetherate, and 75 g of pH regulator dipotassium hydrogen phosphate are added to the reaction kettle. The air in the vapor space of the reaction kettle is first replaced with nitrogen, and then replaced with the mixed monomer. After the oxygen content is less than 30 ppm, the stirring of the reaction kettle is started and the temperature is raised to 95 °C. The prepared mixed monomer is added to the reaction kettle by a compressor to raise the pressure to 3.0 MPa, and then 200 g of initiator solution (4.5 wt%, potassium persulfate) and 20 g of chain transfer agent (diiodomethane) are added to start the reaction. The initiator solution (1 wt%, potassium persulfate) is continuously added at 60 ml / 10 min until the reaction ends. When the cumulative reaction amount of the mixed monomer is 9 Kg, 75 g of pH regulator dipotassium hydrogen phosphate is added to keep the pH of the system at 3-5, which is beneficial to the progress of the reaction. Continue the reaction until the predetermined feed amount of 12 Kg is reached, stop stirring, and recover the product.

[0058] The obtained polymer is coagulated with electrolyte, washed, dried in vacuum, and rolled and formed on an open mill. More than 11 Kg of polymer is obtained, and its performance characteristics are shown in Table 3.

[0059] Table 3 Performance test results of raw fluororubber

[0060]

[0061]

[0062] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including the combination of each technical feature in any other suitable manner. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A preparation method of peroxide-cured fluororubber raw rubber, comprising the following steps: (1) In the presence of an initiator, contacting an aqueous solution of an emulsifier with a mixed monomer for a polymerization reaction, wherein the mixed monomer is prepared by mixing vinylidene fluoride, tetrafluoroethylene, perfluoropropylene and a vulcanization site monomer; (2) Adding a chain transfer agent to the reaction system described in step (1) in batches. When the reaction amount of the mixed monomer in the reaction system reaches 8%-15% of its cumulative reaction total amount, add the first batch of chain transfer agent. When the reaction amount of the mixed monomer in the reaction system reaches 45%-75% of its cumulative reaction total amount, add the second batch of chain transfer agent, and ensure that the pH of the reaction system is relatively stable. After the reaction is completed, obtain the rubber raw rubber.

2. The preparation method according to claim 1, characterized in that, In step (1), in every 100 g of the reaction system, the amount of the emulsifier is 0.1-1 g; And / or, in every 100 g of the reaction system, the amount of the initiator is 0.01-0.1 g; And / or, in every 100 g of the reaction system, continuously supplement the mixed monomer. When the cumulative reaction total amount of the mixed monomer reaches 35-55 g, stop the reaction, preferably 40-45 g.

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the initiator is a water-soluble initiator; preferably, the initiator is selected from one or more of persulfates, peroxosuccinic acid or azobisisobutyramidine dihydrochloride; preferably selected from ammonium persulfate and / or potassium persulfate; Preferably, the initiator is an aqueous solution of persulfate with a mass percentage concentration of 1%-8%.

4. The preparation method according to any one of claims 1-3, characterized in that, The emulsifier is perfluorocarboxylate, alkyl sulfonate, higher fatty acid salt, alkyl sulfate ester, fluoroether carboxylic acid, perfluoropolyether carboxylate, preferably perfluoropolyether carboxylate.

5. The preparation method according to any one of claims 1 to 3, characterized in that, The molar ratio of vinylidene fluoride, tetrafluoroethylene, perfluoropropylene and the vulcanization site monomer in the mixed monomer is: (18-45):(6-34):(28-49):(0.1-1); Preferably, the vulcanization site monomer is a halogenated fluorinated olefin; Preferably, the vulcanization site monomer is selected from one or more of CF2=CFOCF2CF2CF2OCF2Br, 1-bromo-2,2-difluoroethylene, 3-bromo-perfluoro(propyl vinyl ether), trifluorobromoethylene, trifluoroiodoethylene, perfluoroiodoalkyl vinyl ether, perfluorobromoalkyl vinyl ether and 3,3,4,4-tetrafluoro-4-bromo-1-butene, preferably trifluorobromoethylene or 3,3,4,4-tetrafluoro-4-bromo-1-butene; The temperature for mixing the mixed monomer is 50-110 °C, preferably 55-90 °C.

6. The preparation method according to any one of claims 1-5, characterized in that, In step (1), the pH of the reaction system is 2-6, and the oxygen content < 30 ppm; The reaction temperature of the reaction system is 80-120 °C, preferably 85-105 °C; the reaction pressure is 2.0-5.0 MPa, preferably 2.0-4.5 MPa.

7. The preparation method according to claim 1, characterized in that In step (2), in every 100 g of the reaction system, the addition amount of the chain transfer agent is 0.1-2.0 g; Preferably, the ratio of the addition amount of the first batch of chain transfer agent to the addition amount of the second batch of chain transfer agent is: (6-8):(4-2); Preferably, the chain transfer agent is selected from one or more of methylene iodide, diiodomethane, perfluoroalkyl iodide, and 1,4-diiodoperfluorobutane, preferably one or more of diiodomethane and 1,4-diiodoperfluorobutane.

8. The preparation method according to claim 1 or 7, characterized in that In step (2), when the reaction amount of the mixed monomers in the reaction system reaches 60%-80% of their cumulative total reaction amount, a pH regulator is added to ensure the relative stability of the pH of the reaction system.

9. The preparation method according to claim 8, characterized in that, The pH regulator is selected from one or more of phosphates, hydrogen phosphates, dihydrogen phosphates, hydrogen diphosphates, carbonates, and bicarbonates.

10. The preparation method according to claim 8, characterized in that, The pH regulator is dipotassium hydrogen phosphate.

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