A process for the preparation of a fluorine-containing polyether

Abstract

The application provides a preparation method of a fluorine-containing polyether. The preparation method comprises the following steps: reacting a fluorine-containing olefin gas, oxygen and a dilution gas through a pipeline with ultraviolet light transmittance under ultraviolet light irradiation to generate the fluorine-containing polyether. The preparation method provided by the application has high production efficiency and high conversion rate, the product is easy to separate, the reaction can be continuously carried out, and the safety is good, and the method is suitable for industrialized continuous large-scale production of the fluorine-containing polyether.

Description

Technical Field

[0001] This invention belongs to the field of chemical production technology, and specifically relates to a method for preparing fluorinated polyether. Background Technology

[0002] Perfluoropolyethers (PFPEs) are a special class of high-molecular-weight perfluoropolymers containing only carbon, phosphorus, and oxygen (C, F, and O) elements. At room temperature, they are colorless, odorless, and transparent oily liquids, soluble only in perfluorinated organic solvents. PFPEs possess properties such as heat resistance, oxidation resistance, radiation resistance, corrosion resistance, low volatility, and non-flammability. They also exhibit excellent compatibility with plastics, elastomers, and metals, making them highly reliable lubricants in harsh environments (such as for aerospace mechanical components). They are widely used in chemical, electronics, electrical, mechanical, magnetic media, nuclear, and aerospace industries.

[0003] Industrially, most perfluoropolyethers are obtained through oxidative polymerization using tetrafluoroethylene (TFE), hexafluoropropylene (HFP), or a mixture of both as raw materials, under ultraviolet light and with oxygen at low temperature. Their structural formulas are as follows:

[0004] TO-[CF(CF3)CF2O] m -(CF2O) n -(CF2CF2O) p -(O) q -T'

[0005] Wherein: T and T' are independently -CF3, -COF, -CF2COF, or -CF(CF3)COF, etc.; n≠0, q≠0; when p=0, it is a pure HFP polymer; when m=0, it is a pure TFE polymer; when p≠0 and m≠0, it is a mixed polymer of HFP and TFE. The various groups are randomly arranged on the main chain.

[0006] Because the reaction between tetrafluoroethylene and oxygen is extremely violent and uncontrollable, and highly prone to explosion, the reaction of tetrafluoroethylene, hexafluoropropylene, and oxygen is usually carried out in a fluorinated solvent liquid phase at extremely low temperatures. The reactor is cylindrical and equipped with a UV lamp port. For example, US3715378 describes the preparation of perfluoropolyethers in a 600cc cylindrical glass reactor under UV irradiation in a CFCl2CF2Cl solvent at a low temperature of -80°C, using a mixture of tetrafluoroethylene and oxygen. The -COF end groups are then treated at high temperature in a KOH aqueous solution to obtain perfluoropolyethers with end groups of -OCF3 and -OCHF2, with a molecular weight of 1500–5000.

[0007] US4451646 uses tetrafluoroethylene and oxygen as raw materials to prepare an amorphous, high-viscosity, high-molecular-weight perfluoropolyether in a 600cc cylindrical glass reactor in a fluorinated solvent such as CF2Cl2 at -80℃ to 35℃ under 330nm ultraviolet light irradiation. The repeating units -CF2CF2O- and -CF2O- are greater than 200, and the peroxide value of the product is 4.15wt%.

[0008] US2006 / 0205982Al uses tetrafluoroethylene and oxygen as raw materials to prepare perfluoropolyether peroxide products in a 30L cylindrical reactor at -80℃ to -40℃, with a mixture of pentafluoroethane / heptafluoropropane / perfluoropropane as the solvent. The prepared products have a molecular weight of 35,000 to 45,000 and a peroxide value exceeding 1.2%.

[0009] US5783789 discloses the oxidation of tetrafluoroethylene into perfluoropolyether peroxide in a cylindrical reactor at -80 to -50°C in pentafluoroethane under ultraviolet light, with a high peroxide value of 1 to 3.5 wt%.

[0010] The aforementioned methods employ complex reactor structures with stringent requirements. Not only must the apparatus be equipped with a very low-temperature refrigerant, but it also contains ultraviolet lamps with significant heat release. Furthermore, due to the inherent characteristics of the reaction, the products are highly corrosive, necessitating excellent corrosion resistance from the apparatus and frequent replacement of vulnerable components, such as quartz glass. Additionally, the reaction between tetrafluoroethylene and oxygen is typically intermittent, requiring the release and separation of materials and solvents after each reaction, a complex process unsuitable for large-scale production. Moreover, due to the inherent reaction mechanism, tetrafluoroethylene typically does not fully participate in the reaction, with a maximum conversion rate not exceeding 80%. This results in the exhaust gas containing a mixture of tetrafluoroethylene and oxygen, a highly explosive and hazardous mixture.

[0011] Therefore, there is a need in this field to research a method for preparing fluorinated polyethers that is simpler to operate, requires less equipment, is safer, and has higher production efficiency. Summary of the Invention

[0012] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing fluorinated polyethers. The preparation method provided by the present invention features high production efficiency, high conversion rate, continuous reaction, and good safety, making it suitable for large-scale, continuous industrial production of fluorinated polyethers.

[0013] To achieve this objective, the present invention adopts the following technical solution:

[0014] In a first aspect, the present invention provides a method for preparing a fluorinated polyether, the method comprising the following steps:

[0015] Fluorinated olefin gas, oxygen, and diluent gas are passed through a pipe with ultraviolet light transmittance and reacted under ultraviolet light irradiation to produce fluorinated polyether.

[0016] It should be noted that the diluent gas described in this invention serves to dilute fluorinated olefins and oxygen. Those skilled in the art can select the type of diluent gas according to actual needs. It should be understood that this diluent gas cannot react with fluorinated olefins or oxygen, nor can it promote the reaction between fluorinated olefins and oxygen.

[0017] This invention improves reaction safety by diluting the fluorinated olefin gas and oxygen with a dilution gas and conducting the reaction under flowing, gas-phase conditions, thereby reducing the reaction rate and increasing heat dissipation. Since the reaction can proceed continuously, production efficiency is higher. Because the reaction takes place in the gas phase, the fluorinated polyether product can be separated with a simple condensation operation, avoiding the complex operations of separating solvent and product in liquid-phase reactions. Furthermore, the reaction of this invention can be carried out at relatively higher temperatures, reducing the energy consumption required for cooling.

[0018] In some embodiments of the present invention, the fluorinated olefin is selected from one or more of tetrafluoroethylene, trifluorochloroethylene, vinylidene fluoride, and hexafluoropropylene. Among these, the reaction between tetrafluoroethylene and oxygen under ultraviolet light irradiation is extremely violent and uncontrollable, and is very prone to explosion, while the reaction of other fluorinated olefins with oxygen is relatively safer. Therefore, the method provided by the present invention is particularly suitable for the reaction of tetrafluoroethylene with oxygen.

[0019] In some embodiments of the present invention, the volume ratio of the fluorinated olefin gas to oxygen is 1:0.5 to 2; for example, it can be 1:0.5, 1:0.6, 1:0.8, 1:1, 1:1.2, 1:1.3, 1:1.5, 1:1.6, 1:1.8 or 1:2, etc.

[0020] In some embodiments of the present invention, the volume ratio of the diluent gas to the total volume of the fluorinated olefin gas and oxygen is 5-100:1, for example, it can be 5:1, 8:1, 10:1, 12:1, 15:1, 18:1, 20:1, 25:1, 30:1, 35:1, 40:1, 50:1, 60:1, 80:1 or 100:1, etc.; preferably 10 to 40:1.

[0021] In this invention, the proportion of the diluent gas needs to be maintained within a suitable range. If there is too little diluent gas, a large amount of byproducts will be generated, or even no target product will be produced. Moreover, the reaction rate will be too fast, which may easily lead to an explosion and reduce reaction safety. If there is too much diluent gas, it may cause fluorinated olefins to fail to react with oxygen, or the reaction may produce highly toxic and corrosive phosgene, resulting in an extremely low conversion rate of the target product. At the same time, due to the low conversion rate, explosive mixtures (fluorinated olefins and oxygen) will accumulate in the tail gas, which may easily cause an explosion in the tail gas absorption system, reducing production safety.

[0022] In some embodiments of the present invention, the diluting gas is selected from one or more of nitrogen, helium, SF6, CF4, NF5, fluorinated alkanes, and fluorinated ethers. Fluorinated alkanes and fluorinated ethers have better miscibility with fluorinated olefins, which is beneficial for improving the dispersion uniformity of fluorinated olefins, with fluorinated ethers showing the best effect. Therefore, the diluting gas is preferably selected from one or more of fluorinated alkanes and fluorinated ethers, and more preferably fluorinated ethers.

[0023] In some embodiments of the present invention, the fluorinated alkane is selected from perfluoroethane, pentafluoroethane, and heptafluoropropane.

[0024] In some embodiments of the present invention, the fluorinated ether is selected from CF3OCF3, CF3OCHF2, CF3OCFHCF3, and CF3OCF2CF3.

[0025] In this invention, the larger the diameter of the pipe, the smaller its specific surface area, which is less conducive to receiving ultraviolet light energy and releasing reaction heat. Therefore, the inner diameter of the pipe in this invention is preferably less than 5 mm; for example, it can be 5 mm, 4.5 mm, 4 mm, 3.5 mm, 3 mm, 2.5 mm, 2 mm, 1.5 mm, 1 mm, or 0.5 mm, etc.

[0026] In this invention, to ensure the reaction proceeds fully, the shorter the pipe, the lower the required gas flow rate and the lower the production efficiency. Therefore, the length of the pipe in this invention is preferably 0.5m or more; for example, it can be 0.5m, 1m, 1.5m, 2m, 3m, 5m, 8m, 10m, etc.

[0027] The pipes used in this invention can be arranged in any manner. For the purpose of facilitating ultraviolet light irradiation and reducing the space occupied by the pipes, a disc-type or folded arrangement can be used. The pipes need to have sufficient length to ensure that the reaction proceeds fully.

[0028] In some embodiments of the present invention, the material of the pipe is quartz or fluororesin, preferably fluororesin, more preferably F46 resin or PFA resin.

[0029] The reaction of fluorinated olefins with oxygen produces a large amount of highly corrosive substances, such as various fluorinated products with acyl fluoride end groups. These substances are corrosive to quartz glass in long-term contact, leading to decreased transparency, reduced ultraviolet light transmittance, and decreased reaction efficiency. Therefore, a better choice for pipe materials is a corrosion-resistant, transparent resin material, ideally a fluoropolymer, such as F46 resin and PFA resin. Furthermore, resins offer excellent flexibility, making pipes easier to bend and coil, less prone to damage, and ensuring a long service life.

[0030] In some embodiments of the present invention, the residence time of the fluorinated olefin gas, oxygen and diluent gas in the pipeline is 0.1 to 2 seconds; for example, it can be 0.1 seconds, 0.3 seconds, 0.5 seconds, 0.8 seconds, 1 second, 1.2 seconds, 1.5 seconds, 1.8 seconds or 2 seconds, etc.

[0031] In some embodiments of the invention, the pipe is immersed in a solvent that is transparent to ultraviolet light.

[0032] Immersing the pipes in the solvent facilitates the timely absorption of heat generated during the reaction, thereby improving the stability of the reaction. In this invention, the solvent can be water or a fluorinated polyether solvent with ultraviolet light transmittance, preferably a fluorinated polyether.

[0033] In some embodiments of the present invention, the fluorinated polyether used as a solvent has the following structural formula:

[0034] AO—(CF2O) n —(CFX-CF2O) m —OB;

[0035] In this structure, A and B are independently -CF3, -CF2CF3, -CHF2, -CHFCF3, -CClF2, or -CClFCF3, X is -F, -CF3, or -CClCF2, and n and m are independently integers from 2 to 10. Fluorinated polyethers with this structure have better thermal conductivity and ultraviolet light transmittance.

[0036] In some embodiments of the present invention, the wavelength of the ultraviolet light is 200–380 nm. A wavelength concentrated around 360 nm is more effective. The power of the ultraviolet lamp used to provide the ultraviolet light can be 10–1000 W.

[0037] In some embodiments of the present invention, the reaction temperature is -30 to 30°C, for example, it can be -30°C, -25°C, -20°C, -15°C, -10°C, -8°C, -5°C, -2°C, 0°C, 2°C, 5°C, 8°C, 10°C, 15°C, 20°C, 25°C or 30°C, etc.; preferably -20 to 5°C.

[0038] In this invention, different reaction temperatures can be selected depending on the diluent gas. For example, when the diluent gas is pentafluoroethane, the reaction temperature can be -20 to -15°C; when the diluent gas is CF3OCF3, the reaction temperature can be -10 to -5°C; when the diluent gas is CF3OCFHCF3, the reaction temperature can be -5 to 5°C, etc., but it is not limited to these ranges.

[0039] In some embodiments of the present invention, the preparation method includes the following steps:

[0040] Fluorinated olefin gas, oxygen, and dilution gas are continuously passed into a pipe that is transparent to ultraviolet light. The pipe is immersed in a solvent that is transparent to ultraviolet light. The reaction takes place under ultraviolet light irradiation conditions, and the fluorinated polyether is collected by condensation from the end of the pipe.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] This invention improves reaction safety by diluting fluorinated olefin gas and oxygen with a diluent gas and conducting the reaction under flowing, gas-phase conditions, thereby reducing the reaction rate and increasing heat dissipation. Since the reaction can proceed continuously, production efficiency is higher. Because the reaction takes place in the gas phase, the fluorinated polyether product can be separated with a simple condensation operation, avoiding the complex operations of separating solvent and product in liquid-phase reactions. Furthermore, the reaction of this invention can be carried out at relatively higher temperatures, reducing the energy consumption required for cooling. This makes the method provided by this invention suitable for the industrial-scale, continuous production of fluorinated polyethers. Detailed Implementation

[0043] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the specific embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0044] Example 1

[0045] This embodiment provides a method for preparing fluorinated polyether, the steps of which are as follows:

[0046] A disc-shaped tubular quartz glass reactor (total length 0.8 m, inner diameter 3 mm) was immersed in a fluorinated polyether solvent (prepared by photo-oxidation of hexafluoropropylene, number average molecular weight 600) at a constant temperature of -15 °C. A 30 W UV lamp was placed in the center of the disc-shaped tube, and a condenser (condensation temperature 20 °C) and a collection bottle were connected to the end of the reactor. Tetrafluoroethylene, oxygen, and pentafluoroethane were mixed in a volume ratio of 0.8:1:30 and introduced into the disc-shaped tubular quartz glass reactor at a pressure of 0.1 MPa and a flow rate of 500 mL / min. After continuous introduction for 6 hours, the reaction was stopped, yielding 23 g of a transparent liquid.

[0047] Example 2

[0048] This embodiment provides a method for preparing fluorinated polyether, the steps of which are as follows:

[0049] A disc-shaped tubular quartz glass reactor (total length 0.8 m, inner diameter 3 mm) was immersed in a fluorinated polyether solvent (prepared by photo-oxidation of hexafluoropropylene, number average molecular weight 600) at a constant temperature of -5 °C. A 30 W UV lamp was placed in the center of the disc-shaped tube, and a condenser (condensation temperature 20 °C) and a collection bottle were connected to the end of the reactor. Tetrafluoroethylene, oxygen, and heptafluoropropane were mixed in a volume ratio of 1:1:20 and introduced into the disc-shaped tubular quartz glass reactor at a pressure of 0.1 MPa and a flow rate of 500 mL / min. After continuous introduction for 6 hours, the reaction was stopped, yielding 43 g of a transparent liquid.

[0050] Example 3

[0051] This embodiment provides a method for preparing fluorinated polyether, the steps of which are as follows:

[0052] A disc-shaped tubular F46 resin reactor (total length 1m, inner diameter 2mm) was immersed in a fluorinated polyether solvent (prepared by photo-oxidation of hexafluoropropylene, number average molecular weight 600) at a constant temperature of -5℃. A 30W UV lamp was placed in the center of the disc-shaped tube, and a condenser (condensation temperature 20℃) and a collection bottle were connected to the end of the reactor. Tetrafluoroethylene, oxygen, pentafluoroethane, and CF3OCF3 were mixed in a volume ratio of 1:1:15:15 and introduced into the disc-shaped tubular F46 resin reactor at a pressure of 0.1 MPa and a flow rate of 500 mL / min. After continuous introduction for 6 hours, the reaction was stopped, yielding 28g of a transparent liquid.

[0053] Example 4

[0054] This embodiment provides a method for preparing fluorinated polyether, the steps of which are as follows:

[0055] A disc-shaped tubular PFA resin reactor (total length 1m, inner diameter 2mm) was immersed in a fluorinated polyether solvent (prepared by photo-oxidation of hexafluoropropylene, number average molecular weight 600) at a constant temperature of -5℃. A 30W UV lamp was placed in the center of the disc-shaped tube, and a condenser (condensation temperature 10℃) and a collection bottle were connected to the end of the reactor. Tetrafluoroethylene, oxygen, and CF3OCFHCF3 were mixed at a volume ratio of 1.2:1:15 and introduced into the disc-shaped tubular PFA resin reactor at a pressure of 0.1 MPa and a flow rate of 500 mL / min. After continuous introduction for 6 hours, the reaction was stopped, yielding 59g of a transparent liquid.

[0056] Example 5

[0057] This embodiment provides a method for preparing fluorinated polyether, the steps of which are as follows:

[0058] A disc-shaped tubular PFA resin reactor (total length 3m, inner diameter 5mm) was immersed in a fluorinated polyether solvent (prepared by photo-oxidation of hexafluoropropylene, number average molecular weight 600) at a constant temperature of 2℃. A 500W UV lamp was placed in the center of the disc-shaped tube, and a condenser (condensation temperature 10℃) and a collection bottle were connected to the end of the reactor. Tetrafluoroethylene, oxygen, and CF3OCFHCF3 were mixed at a volume ratio of 1:1:25 and introduced into the disc-shaped tubular PFA resin reactor at a pressure of 0.2 MPa and a flow rate of 4000 mL / min. After continuous introduction for 12 hours, the reaction was stopped, yielding 1010 g of a transparent liquid.

[0059] Example 6

[0060] This embodiment provides a method for preparing fluorinated polyether, the steps of which are as follows:

[0061] A disc-shaped tubular PFA resin reactor (total length 1.5 m, inner diameter 1 mm) was immersed in a fluorinated polyether solvent (prepared by photo-oxidation of hexafluoropropylene, number average molecular weight 600) at a constant temperature of -30℃. A 100W UV lamp was placed in the center of the disc-shaped tube, and a condenser (20℃) and a collection bottle were connected to the end of the reactor. Tetrafluoroethylene, oxygen, and CF3OCF2CF3 were mixed at a volume ratio of 1:1:10 and introduced into the disc-shaped tubular PFA resin reactor at a pressure of 0.1 MPa and a flow rate of 300 mL / min. After continuous introduction for 6 hours, the reaction was stopped, yielding 44 g of a transparent liquid.

[0062] Example 7

[0063] This embodiment provides a method for preparing fluorinated polyether, the steps of which are as follows:

[0064] A disc-shaped tubular PFA resin reactor (total length 1m, inner diameter 2mm) was immersed in a fluorinated polyether solvent (prepared by photo-oxidation of hexafluoropropylene, number average molecular weight 600) at a constant temperature of 10℃. A 30W UV lamp was placed in the center of the disc-shaped tube, and a condenser (condensation temperature 10℃) and a collection bottle were connected to the end of the reactor. Tetrafluoroethylene, oxygen, and CF3OCHF2 were mixed at a volume ratio of 1:1:100 and introduced into the disc-shaped tubular PFA resin reactor at a pressure of 0.1 MPa and a flow rate of 500 mL / min. After continuous introduction for 6 hours, the reaction was stopped, yielding 2g of a transparent liquid.

[0065] Example 8

[0066] This embodiment provides a method for preparing fluorinated polyether, the steps of which are as follows:

[0067] A disc-shaped tubular PFA resin reactor (total length 1m, inner diameter 2mm) was immersed in a fluorinated polyether solvent (prepared by photo-oxidation of hexafluoropropylene, number average molecular weight 600) at a constant temperature of -10℃. A 30W UV lamp was placed in the center of the disc-shaped tube, and a condenser (condensation temperature 10℃) and a collection bottle were connected to the end of the reactor. Tetrafluoroethylene, oxygen, and CF3OCFHCF3 were mixed at a volume ratio of 1:1:200 and introduced into the disc-shaped tubular PFA resin reactor at a pressure of 0.1 MPa and a flow rate of 500 mL / min. After continuous introduction for 6 hours, the reaction was stopped, yielding 0.8 g of a transparent liquid.

[0068] Comparative Example 1

[0069] This comparative example provides a method for preparing fluorinated polyether. The only difference from Example 4 is that the volume ratio of tetrafluoroethylene, oxygen and CF3OCFHCF3 is 1.2:1:5, and the tail gas contains a large amount of acidic gas, so the target product was not obtained.

[0070] Comparative Example 2

[0071] This comparative example provides a method for preparing a fluorinated polyether. The only difference from Example 4 is that the volume ratio of tetrafluoroethylene, oxygen, and CF3OCFHCF3 is 1.2:1:250, and the target product was not obtained.

[0072] The molecular weight of the fluorinated polyethers prepared in the above examples and comparative examples was tested by liquid chromatography, the peroxide value was detected by the starch-potassium iodide method, and the conversion rate was calculated. The results are shown in Table 1 below.

[0073] Table 1

[0074]

[0075]

[0076] As can be seen from the experimental results in Table 1, the method provided by this invention successfully prepared fluorinated polyethers with a molecular weight below 1500 and a peroxide value of 0.1–0.35%. By optimizing the ratio of fluorinated olefin gas, oxygen, and diluent gas, the product yield can reach over 80%.

[0077] In Comparative Example 1, the proportion of diluent gas was too low, leading to excessive side reactions between tetrafluoroethylene and oxygen, resulting in no target product being formed. In Comparative Example 2, the proportion of diluent gas was too high, preventing the reaction between tetrafluoroethylene and oxygen, also resulting in no target product being formed.

[0078] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a fluorinated polyether, characterized in that, The preparation method includes the following steps: Fluorinated olefin gas, oxygen, and diluent gas are passed through a pipe with ultraviolet light transmittance and reacted under ultraviolet light irradiation to produce fluorinated polyether; The volume ratio of the fluorinated olefin gas to oxygen is 1:0.5~2; The volume ratio of the diluent gas to the total volume of the fluorinated olefin gas and oxygen is 5~20:1; The diluent gas is selected from one or more of nitrogen, helium, SF6, CF4, fluorinated alkanes, and fluorinated ethers; The reaction temperature is -30~10℃.

2. The preparation method according to claim 1, characterized in that, The fluorinated olefin is selected from one or more of tetrafluoroethylene, trifluorochloroethylene, vinylidene fluoride, and hexafluoropropylene.

3. The preparation method according to claim 1, characterized in that, The diluting gas is selected from one or more of fluorinated alkanes and fluorinated ethers.

4. The preparation method according to claim 3, characterized in that, The diluent gas is a fluorinated ether.

5. The preparation method according to claim 3, characterized in that, The fluorinated alkanes are selected from perfluoroethane, pentafluoroethane, and heptafluoropropane.

6. The preparation method according to claim 4, characterized in that, The fluorinated ether is selected from CF3OCF3, CF3OCHF2, CF3OCFHCF3, and CF3OCF2CF3.

7. The preparation method according to any one of claims 1-6, characterized in that, The inner diameter of the pipe is less than 5 mm.

8. The preparation method according to claim 7, characterized in that, The length of the pipe is more than 0.5 m.

9. The preparation method according to claim 7, characterized in that, The pipe is made of quartz or fluoropolymer.

10. The preparation method according to claim 9, characterized in that, The pipe is made of fluoropolymer resin.

11. The preparation method according to claim 9, characterized in that, The pipe is made of F46 resin or PFA resin.

12. The preparation method according to any one of claims 1-6, characterized in that, The residence time of the fluorinated olefin gas, oxygen, and diluent gas in the pipeline is 0.1 to 2 seconds.

13. The preparation method according to any one of claims 1-6, characterized in that, The pipe is immersed in a solvent that is transparent to ultraviolet light.

14. The preparation method according to claim 13, characterized in that, The solvent is water or fluorinated polyether.

15. The preparation method according to claim 13, characterized in that, The solvent is a fluorinated polyether.

16. The preparation method according to claim 15, characterized in that, The fluorinated polyether used as a solvent has the following structural formula: AO—(CF2O) n —(CFX-CF2O) m —OB; Where A and B are independently -CF3, -CF2CF3, -CHF2, -CHFCF3, -CClF2 or -CClFCF3, X is -F or -CF3, and n and m are independently integers from 2 to 10.

17. The preparation method according to any one of claims 1-6, characterized in that, The wavelength of the ultraviolet light is 200~380nm.

18. The preparation method according to any one of claims 1-6, characterized in that, The reaction temperature is -20~5℃.

19. The preparation method according to any one of claims 1-6, characterized in that, The preparation method includes the following steps: Fluorinated olefin gas, oxygen, and diluent gas are continuously passed through a pipe that is transparent to ultraviolet light. The pipe is immersed in a solvent that is transparent to ultraviolet light. The reaction takes place under ultraviolet light irradiation conditions, and the fluorinated polyether is collected by condensation from the end of the pipe.

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