Method for removing perfluoropolyether acyl fluoride end group

Abstract

The invention relates to a method for removing a perfluoropolyether acyl fluoride end group. The method comprises the following steps: adding perfluoropolyether acyl fluoride, a fluorinating agent, a catalyst and a solvent into a photochemical reactor, reacting for 2-12 hours under the conditions of normal temperature and normal pressure and ultraviolet irradiation, and removing acyl fluoride end groups to obtain perfluoropolyether which can be used as perfluoropolyether vacuum pump oil, the fluorinating agent is a fluorine-containing aromatic compound. The method has the advantages of simple operation steps, easy realization of reaction equipment, mild reaction conditions, avoiding of decomposition loss of the perfluoropolyether product due to high temperature, safety and energy saving.

Description

Technical Field

[0001] The invention relates to the technical field of fluorine chemical industry, and in particular to a method for removing the end group of perfluoropolyether acyl fluoride. Background Art

[0002] Perfluoropolyether oil (PFPE) is a new type of synthetic lubricant. It contains only three types of atoms, C, F, and O, in its molecules. Its molecular chain is saturated. It has excellent thermal stability, chemical inertness, and non-flammability. It is resistant to strong oxidants, strong acids, and strong alkalis, and has stable high-temperature performance. Compared with conventional vacuum oils, it is safer and has a longer service life. It can also remain stable for a long time in an environment containing corrosive gases. It is a vacuum pump oil with excellent performance.

[0003] However, after the polymerization of perfluoropolyether is completed, there are always extremely unstable acyl fluoride end groups (-COF) in the molecular chain segments of this type of polymer, which will react with water to release hydrogen fluoride and convert into carboxylic acid groups (-COOH). Both the acyl fluoride group and the carboxyl group are unstable. During use, the perfluoropolymer will begin to decompose from the end group and produce volatile substances, which will cause the finished product to contain bubbles or voids, thereby limiting the further application of PFPE products in high-tech fields such as semiconductor silicon wafer processing, photoelectric copying hot roller anti-sticking and anti-corrosion thick film coating. Therefore, developing and optimizing the removal technology of unstable end groups of perfluoropolymers and reducing the production cost of PFPE will be beneficial to the development of the chemical industry, mechanical industry, aerospace industry and electronic industry.

[0004] At present, the removal processes of perfluoropolyether acyl fluoride end groups mainly include the following: One is to use fluorine gas or fluorine-nitrogen mixed gas to fluorinate the end groups of perfluoropolyether acyl fluoride (PFPE-COF) to obtain a stable perfluoropolyether product. However, this method has the disadvantages of high toxicity and strong corrosiveness of fluorine gas, high requirements for production equipment, and high safety risks during operation. For example, patent CN103111253A discloses a method and equipment for fluorination of perfluoropolyether, the disadvantage of which is that the reaction conditions require high temperature, which not only causes the decomposition and loss of low-boiling perfluoropolyether, but also the high temperature easily shortens the life of the production equipment. Patents CN110092901A and CN110467723A respectively disclose a preparation method for fluorinating perfluoropolyether oil using fluorine gas and fluorine-nitrogen mixed gas, which has the disadvantages of low fluorine gas utilization, high toxicity to the human body, and strong corrosiveness to equipment. The above factors have caused a substantial increase in production costs, which is not conducive to industrialized and large-scale production.

[0005] The second is to use metal fluorides such as Al, Ti, and V as catalysts to cap the end groups of perfluoropolyether acyl fluoride. However, this method also faces some problems, such as high reaction energy consumption and low perfluoropolyether yield. In order to solve the above shortcomings, patents CN115364875A and CN117362626A both use carbon-based supported fluorides prepared by calcination or impregnation as fluorinating agents to cap perfluoropolyether. Compared with the former capping method that directly uses metal fluorides as catalysts, this method has lower energy consumption and higher product yield, but it still has disadvantages such as high reaction temperature, long reaction time, and complex reaction operation.

[0006] The third is the hydrolysis-decarboxylation method, that is, the acyl fluoride end group of the perfluoropolyether is converted into a carboxylic acid group and removed under the action of water and alkali. Patents such as CN111892705A and CN113150262A use water and an inorganic base or a mixture of an organic amine compound and an inorganic base for decarboxylation end-capping reaction. However, these end-capping methods have low reaction efficiency, and the molecular weight of the perfluoropolyether decreases after decarboxylation. And the rear end group after decarboxylation treatment is an inert group -CF2H, not a highly stable -CF3 molecular structure. After the reaction is completed, the product is impure and needs to be purified, which increases energy consumption and production costs.

[0007] Therefore, the research and development of a highly efficient, safe, green, environmentally friendly, low-energy consumption, and high-yield perfluoropolyether end-capping method has important application value. Summary of the invention

[0008] The first purpose of the present invention is to provide a method for removing the end groups of perfluoropolyether acyl fluoride in view of the deficiencies of the prior art. The method uses fluorine-containing aromatic compounds as fluorinating agents, transition metals and their complexes as catalysts, and adopts ultraviolet irradiation at room temperature and pressure to provide fluorine atom fluorinated acyl fluoride end groups through the active carbon-fluorine bonds of the fluorine-containing aromatic compounds, and uses transition metals and their complexes as catalysts to coordinate and complex with the carboxyl groups of the fluorine-containing aromatic compounds to activate the carbon-fluorine bonds of the fluorine-containing aromatic compounds, and remove the end groups of perfluoropolyether acyl fluoride under ultraviolet light. The present invention has simple operating steps, easy-to-implement reaction equipment, mild reaction conditions, avoids the decomposition loss of perfluoropolyether products due to high temperature, and has the advantages of safety and energy saving.

[0009] The technical solution of the present invention is: A method for removing perfluoropolyether acyl fluoride end groups, the method comprising the following steps: Adding perfluoropolyether acyl fluoride, a fluorinating agent, a catalyst and a solvent into a photochemical reactor, reacting for 2-12 hours at room temperature and pressure under ultraviolet light, and removing the acyl fluoride end group to obtain perfluoropolyether; Wherein, the mass ratio of the perfluoropolyether acyl fluoride to the solvent is 1: (1-1000); the mass ratio of the perfluoropolyether acyl fluoride to the fluorinating agent is 1: (0.005-0.5); the mass ratio of the perfluoropolyether acyl fluoride to the catalyst is 1: (0.005-0.5); The wavelength of the ultraviolet light is 100-400nm; The solvent is a polar solvent such as alcohol, aliphatic or aromatic ether, amide, nitrile, sulfone, ketone, etc.; the polar solvent is one or more of ethanol, methanol, dimethyl sulfoxide, ethylene glycol dimethyl ether, acetonitrile, benzyl cyanide, dimethyl sulfoxide, dimethylformamide, and N-methylpyrrolidone.

[0010] The fluorinating agent is a fluorine-containing aromatic compound; The catalyst is a transition metal and its complex; the transition metal is Fe, Co, Ni, Cu, Ru, Rh, Pd or Pt; The fluorine-containing aromatic compound is one or more of o-fluorobenzoic acid, m-fluorobenzoic acid, p-fluorobenzoic acid, 1,2,4-trifluorobenzene, sodium 2, 4,5-trifluorobenzoate, 1,2,3,5-tetrafluorobenzene, 2,6-difluorobenzoic acid, 2,3,4,5-tetrafluorobenzoic acid, 2,3,5,6-tetrafluoroterephthalic acid, 2,3,4,5-tetrafluorobenzoic acid methyl ester, 1,2,3,4,5-pentafluorobenzene, pentafluorobenzoic acid, pentafluorophenol, methyl pentafluorobenzoate, and hexafluorobenzene.

[0011] The transition metal and its complex are one or more of palladium carbon, platinum carbon, Fe / Co / Ni complex, triphenylphosphine palladium chloride, triphenylphosphine ruthenium chloride, triphenylphosphine rhodium chloride, triphenylphosphine nickel chloride, and triphenylphosphine cobalt chloride.

[0012] The photochemical reactor comprises a long arc mercury lamp regulated current power supply, a quartz reactor, a multi-position photochemical reactor, a cooling liquid circulation pump and a dark box.

[0013] The removal process obtains a perfluoropolyether from which the acyl fluoride end groups have been removed for use as a vacuum pump oil.

[0014] The index system of the perfluoropolyether lubricant meets the following requirements: Degree of polymerization range: 18-35; Yield: ≥90%; Average molecular weight: 3000-10000 g / mol; Vapor pressure at 25℃: ≤1x10 -6 Pa; Vapor pressure at 100℃: ≤1×10 -4 Pa; Ultimate vapor pressure: ≤1×10 -3Pa; Thermal decomposition temperature: 300-500℃; Pour point: ≤-35℃.

[0015] The essential features of the present invention are: In the present invention, the fluorinating agent is crucial for the removal of the acyl fluoride group, and the present invention adopts a fluorinated aromatic compound as the fluorinating agent. In the fluorinated aromatic compound, the substitution of fluorine and carboxyl groups on the benzene ring of the fluorinated aromatic carboxylic acid has a great influence on the reaction of removing the acyl fluoride end group of the perfluoropolyether: the carboxyl group on the benzene ring has a strong electron-withdrawing effect, which makes the carbon-fluorine bond in the fluorinated aromatic carboxylic acid molecule more active, and weakens the polarity of the carbon-fluorine bond, so that the fluorine atom is easy to approach the carbon atom connected to the acyl fluoride end group, thereby attacking the active acyl fluoride end group to cause the acyl fluoride end group removal reaction.

[0016] Transition metals and their complexes can coordinate with the deprotonated carboxylic acid in the fluorinated aromatic carboxylic acid, and can act as catalysts under mild conditions of ultraviolet light at room temperature and pressure to activate the carbon-fluorine bonds in the fluorinated aromatic carboxylic acid, which is beneficial for the fluorine atoms to attack the acyl fluoride end groups. The covalent bond breaking of the acyl fluoride end groups of the perfluoropolyether is similar to the decarboxylation reaction, that is, the heterolytic cleavage is carried out according to the ionic reaction process, thereby improving the efficiency of removing the acyl fluoride end groups of the perfluoropolyether.

[0017] The invention utilizes a mercury lamp to perform ultraviolet irradiation on a photochemical reactor at room temperature and pressure, and has the characteristics of simple operation steps, easy realization of reaction equipment, mild reaction conditions, and the like.

[0018] Beneficial effects of the present invention: In the present invention, the utilization rate of the fluorinated aromatic compound fluorinating agent and the transition metal complex catalyst is extremely high, the mass ratio of perfluoropolyether acyl fluoride to the solvent is 1: (1-1000), the mass ratio of perfluoropolyether acyl fluoride to the fluorinating agent is 1: (0.005-0.5), and the mass ratio of perfluoropolyether acyl fluoride to the catalyst is 1: (0.005-0.5), the dosage of the fluorinating agent and the catalyst is very low, the reaction time is short, and the reaction conditions are mild to avoid the use of high temperature. The present invention does not require fluorine gas or equipment with high energy consumption, and has the advantages of low energy consumption and high added value; In addition, the present invention utilizes the coordination effect of the transition metal catalyst and the carboxyl group of the fluorinating agent to activate the carbon-fluorine bond, which greatly improves the efficiency of removing the acyl fluoride end group, so that the yield of the perfluoropolyether product is above 90%, and has the advantages of high efficiency and economy; the present invention utilizes ultraviolet light in a photochemical reactor at room temperature, and the operation steps are simple, the reaction equipment is easy to implement, and the reaction conditions are mild, which avoids the decomposition loss of the perfluoropolyether product due to high temperature, and has the advantages of safety and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1The ultraviolet visible absorption spectra (UV-vis) of perfluoropolyether acyl fluoride at concentrations of 0.1wt%, 1wt%, 2wt%, and 4wt% using ethanol as solvent; Figure 2 The UV-visible absorption spectra (UV-vis) of 0.1wt% PFPE, 0.1wt% PFPE-COF, and 0.1wt% PFPE-COF with 2,3,5,6-tetrafluoroterephthalic acid added using ethanol as solvent; Figure 3 It is the Fourier transform infrared spectra (FT-IR) of PFPE, PFPE-COF and PFPE-COF with different catalysts and fluorinating agents; Figure 4 It is a structural diagram of the carbon-oxygen double bond and carbon-oxygen triple bond of perfluoropolyether fluoride and their corresponding infrared wavenumbers. DETAILED DESCRIPTION

[0020] The technical scheme of the present invention is further clearly and completely described below in conjunction with the embodiments and the accompanying drawings. Through these descriptions, the characteristics and advantages of the present application will become clearer and more specific. The described embodiments are only part of the embodiments of the present invention, not all of them.

[0021] The present invention performs heterolytic cleavage according to the ionic reaction process, and the process is as follows:

[0022] Example 1 Use ethanol as solvent to prepare a 0.1wt% PFPE-COF solution. Add 10ml of ethanol to a container, add 0.0079g of PFPE-COF, stir evenly, and wait for testing.

[0023] Embodiment 2-4 The other steps are the same as those in Example 1, except that the mass concentration of the PFPE-COF solution is replaced from 0.1wt% to 1wt%, 2wt%, and 4wt%, respectively, that is, the amount of PFPE-COF added is changed from 0.0079g to 0.0797g, 0.1610g, and 0.3288g.

[0024] The samples obtained in Examples 1-4 were subjected to ultraviolet visible absorption spectroscopy (UV-vis) testing to quantitatively analyze the content of acyl fluoride end groups in perfluoropolyether acyl fluoride solutions of different concentrations; Figure 1 It can be seen that the absorbance is: 4wt% > 2wt% > 1wt% > 0.1wt%, that is, as the concentration of perfluoropolyether acyl fluoride solution increases, the higher the concentration of acyl fluoride end groups, the greater the absorbance.

[0025] Example 5 Use ethanol as solvent to prepare 0.1wt% PFPE solution. Add 10ml ethanol to the container, add 0.0079g PFPE, stir evenly, and wait for testing.

[0026] Embodiment 6-7 The other steps were the same as those of Example 1, except that 0.0079 g of PFPE was replaced by 0.0079 g of PFPE-COF and a mixture of 0.0079 g of PFPE-COF and 0.0039 g of 2,3,5,6-tetrafluoroterephthalic acid.

[0027] The samples obtained in Examples 5-7 were subjected to UV-visible absorption spectroscopy (UV-vis) test, and the content of acyl fluoride end groups in the perfluoropolyether acyl fluoride solution with or without the fluorinating agent was quantitatively analyzed, such as Figure 2 shown.

[0028] from Figure 2 As shown in the figure, the absorbance is: pure PFPE-COF > PFPE-COF containing 2,3,5,6-tetrafluoroterephthalic acid > pure PFPE. This indicates that compared with pure PFPE-COF, the content of acyl fluoride end groups in PFPE-COF containing 2,3,5,6-tetrafluoroterephthalic acid is reduced, and the 2,3,5,6-tetrafluoroterephthalic acid fluorination agent has the effect of removing acyl fluoride end groups.

[0029] Example 8 Add 2.1894g PFPE-COF, 0.0252g 2,3,5,6-tetrafluoroterephthalic acid and 45ml ethanol to a 100ml quartz reaction tube, plug the branch tube with a rubber stopper, and then insert a disposable dropper into the bottom of the solution, and bubble N2 for 10 minutes to empty the dissolved air in the solution in the test tube. After the bubbling is completed, put the test tube into a photochemical reaction box, and install a condenser to make the reaction system airtight, connect the cooling circulation pump, turn on the mercury lamp condensation device and the reaction liquid condensation device in turn, confirm that the cooling circulation pump is running smoothly, and turn on the mercury lamp to start the light reaction. Among them, the irradiation power of the mercury lamp is 500W, the irradiation distance is about 15cm, and the temperature is maintained at 15-30℃ by condensation. After 6.5h of reaction, turn off the mercury lamp to stop the reaction, and turn off the cooling device. Take 1 ml of the reaction solution after 2 hours and 6.5 hours of reaction respectively, and vacuum concentrate it by rotary evaporation at room temperature for 30 minutes to 60 minutes to remove the residual solvent to obtain a solid sample, and then add 0.5 ml of acetonitrile to fully dissolve it. The obtained solution is sucked out with a syringe, and the residual catalyst particles are filtered out with a filter membrane and placed in a sample tube for testing.

[0030] Example 9 The preparation method is similar to that in Example 8, except that after the entire reaction system of Example 8 reacts for 6.5 hours, 0.013 g of palladium carbon catalyst is added to the reactor and the reaction is continued for 2.5 hours. After the reaction is completed, 1 ml of the reaction solution is taken and the treatment method is the same as that of Example 8. The obtained solution is sucked out with a syringe, and the residual catalyst small particles are filtered out with a filter membrane and placed in a sample tube for testing.

[0031] Example 10 1.7370g PFPE-COF, 0.1745g 2,3,5,6-tetrafluoroterephthalic acid, 0.1540g palladium carbon catalyst and 45ml ethanol were added to a 100ml quartz reaction tube, and the light reaction was started after the various devices were connected. The reaction was carried out under light for 6h. After the reaction was allowed to proceed for 6h, the mercury lamp was turned off to stop the reaction, and the cooling device was turned off. 1ml of the reaction solution after the reaction for 6h was taken, and the treatment method was the same as that of Example 8. The obtained solution was aspirated with a syringe, and the residual catalyst particles were filtered out with a filter membrane and placed in a sample tube for testing.

[0032] Embodiment 11 Add 1.3435g PFPE-COF, 0.0444g o-fluorobenzoic acid and 45ml ethanol to a 100ml quartz reaction tube, and react under light for 4h. Take 1ml of the reaction solution after 4h of reaction, dissolve it by rotary evaporation, filter it at room temperature, and place the solution in a sample tube for testing. Continue to react for 2h, and turn off the mercury lamp and cooling device after the reaction is complete. Take 1ml of the reaction solution after 6h of reaction, and treat it in the same way as in Example 8. The obtained solution is aspirated with a syringe, and the residual catalyst particles are filtered out with a filter membrane and placed in a sample tube for testing.

[0033] Example 12 1.3435g PFPE-COF, 0.0444g o-fluorobenzoic acid, 0.0183g triphenylphosphine rhodium catalyst and 45ml ethanol were added to a 100ml quartz reaction tube and reacted for 4h under illumination. Take 1ml of the reaction solution when it reacted for 4h, and place the solution obtained by rotary evaporation, dissolution and filtration at room temperature in a sample tube for testing. The whole system continued to react for 2h, and 1ml of the reaction solution when it reacted for 6h was taken, and the solution obtained by rotary evaporation, dissolution and filtration at room temperature was placed in a sample tube for testing. The system continued to react for 6h, and the mercury lamp and cooling device were turned off after the reaction was completely completed. Take 1ml of the reaction solution when it reacted for 12h, and its treatment method was the same as Example 8. The obtained solution was sucked out with a syringe, and the residual catalyst small particles were filtered out with a filter membrane and placed in a sample tube for testing.

[0034] Comparative Example 1 Add 1.5755g PFPE-COF and 45ml ethanol to a 100ml quartz reaction tube and react for 2h under light. Take 1ml of the reaction solution after 2h of reaction, dissolve and filter the solution at room temperature and place it in a sample tube for testing. The whole system continues to react for 2h, take 1ml of the reaction solution after 4h of reaction, dissolve and filter the solution at room temperature and place it in a sample tube for testing. The system continues to react for 2h, and after the reaction is complete, turn off the mercury lamp and the cooling device. Take 1ml of the reaction solution after 6h of reaction, and treat it in the same way as Example 8. The obtained solution is aspirated with a syringe, filtered with a filter membrane to remove the residual small catalyst particles, and placed in a sample tube for testing.

[0035] Test Examples 8 to 12, Comparative Example 1 The samples obtained in the above embodiments and comparative examples were subjected to Fourier transform infrared (FT-IR) test. Figure 3 As shown. Figure 4 It can be learned that the structural diagram and infrared wavenumber of the carbon-oxygen double bond and carbon-oxygen triple bond of perfluoropolyether acyl fluoride.

[0036] pass Figure 3 , Figure 4 It can be seen that the above -1 、1780cm -1 The characteristic absorption peaks are attributed to the vibration of carbon-oxygen triple bond and carbon-oxygen double bond. Compared with pure PFPE-COF, the absorption peak of carbon-oxygen triple bond in PFPE-COF system with fluorinated aromatic carboxylic acid fluorinating agent and transition metal and its complex catalyst completely disappears, indicating that carbon-oxygen triple bond in PFPE-COF has been completely eliminated; the absorption peak of carbon-oxygen double bond is weakened, indicating that carbon-oxygen double bond in PFPE-COF is partially eliminated, and perfluoropolyether vacuum pump oil with partially removed acyl fluoride end group is obtained.

[0037] Experiments show that the deacylfluorination rate of fluorinated aromatic compounds with different substitution structures varies with the structure and number of electron-withdrawing groups. The deacylfluorination rate is: 2,3,5,6-tetrafluoroterephthalic acid>2,3,4,5-tetrafluorobenzoic acid>2,3,4,5-tetrafluorobenzoic acid methyl ester>1,2,3,5-tetrafluorobenzene>terephthalic acid.

[0038] The obtained perfluoropolyether is purified by rotary evaporation. Before rotary evaporation, a vacuum pump is used to provide a negative pressure environment to accelerate the evaporation speed. The control conditions are evaporation temperature of 120-200°C, evaporation time of 120-360min, rotor speed of 250-350r / min, and condensation temperature of 15-25°C.

[0039] The perfluoropolyether vacuum pump oil obtained by the above method was tested for its performance indicators: The average molecular weight of perfluoropolyether was determined by end group back titration; The total fluorine content of perfluoropolyether was quantitatively analyzed by ion chromatography; The decomposition temperature of perfluoropolyether was tested by thermogravimetry; The pour point is tested using a fully automatic pour point tester; The degree of polymerization was measured using a lubricating oil tester; The vapor pressure is measured using a vapor pressure measuring device.

[0040] By removing the acyl fluoride end group of perfluoropolyether acyl fluoride under the conditions of catalyst, fluorinating agent and ultraviolet light at normal temperature and pressure, and evaporating the solvent by rotary evaporation, a perfluoropolyether vacuum pump oil with the following performance indicators is obtained: Degree of polymerization range: 18-35; Yield: ≥90%; Average molecular weight: 3000-10000 g / mol; Vapor pressure at 25℃: ≤1x10 -6 Pa; Vapor pressure at 100℃: ≤1×10 -4 Pa; Ultimate vapor pressure: ≤1×10 -3 Pa; Thermal decomposition temperature: 300-500℃; Pour point: ≤-35℃.

[0041] Matters not covered by the present invention are known technologies.

Claims

1. A method for removing the end group of perfluoropolyether acyl fluoride, characterized in that the method comprises the following steps: Adding perfluoropolyether acyl fluoride, a fluorinating agent, a catalyst and a solvent into a photochemical reactor, reacting for 2-12 hours at room temperature and pressure under ultraviolet light, and removing the acyl fluoride end group to obtain perfluoropolyether; in, The mass ratio of the perfluoropolyether acyl fluoride to the solvent is 1: (1-1000); the mass ratio of the perfluoropolyether acyl fluoride to the fluorinating agent is 1: (0.005-0.5); the mass ratio of the perfluoropolyether acyl fluoride to the catalyst is 1: (0.005-0.5); The wavelength of the ultraviolet light is 100-400nm; The solvent is an alcohol, an aliphatic, or an ether, an amide, a nitrile, a sulfone, or a ketone containing an aromatic group; The fluorinating agent is a fluorine-containing aromatic compound; The catalyst is a transition metal and its complex; the transition metal is Fe, Co, Ni, Cu, Ru, Rh, Pd or Pt.

2. The method for removing the end groups of perfluoropolyether acyl fluoride as claimed in claim 1, wherein the fluorine-containing aromatic compound is one or more of o-fluorobenzoic acid, m-fluorobenzoic acid, p-fluorobenzoic acid, 1,2,4-trifluorobenzene, 2, 4,5-sodium trifluorobenzoate, 1,2,3,5-tetrafluorobenzene, 2,6-difluorobenzoic acid, 2,3,4,5-tetrafluorobenzoic acid, 2,3,5,6-tetrafluoroterephthalic acid, 2,3,4,5-tetrafluorobenzoic acid methyl ester, 1,2,3,4,5-pentafluorobenzene, pentafluorobenzoic acid, pentafluorophenol, methyl pentafluorobenzoate and hexafluorobenzene.

3. The method for removing the end groups of perfluoropolyether acyl fluoride as claimed in claim 1, characterized in that the solvent is one or more of ethanol, methanol, dimethyl sulfoxide, ethylene glycol dimethyl ether, acetonitrile, benzyl cyanide, dimethyl sulfoxide, dimethylformamide, and N-methylpyrrolidone.

4. The method for removing the end group of perfluoropolyether acyl fluoride as claimed in claim 1, characterized in that the transition metal and its complex are one or more of palladium carbon, platinum carbon, Fe / Co / Ni complex, triphenylphosphine palladium chloride, triphenylphosphine ruthenium chloride, triphenylphosphine rhodium chloride, triphenylphosphine nickel chloride, and triphenylphosphine cobalt chloride.

5. The method for removing the end group of perfluoropolyether acyl fluoride as claimed in claim 1, characterized in that the photochemical reactor comprises a long arc mercury lamp constant current power supply, a quartz reactor, a multi-position photochemical reactor, a coolant circulation pump and a dark box.

6. Use of the perfluoropolyether obtained by the removal method as claimed in claim 1, characterized in that it is used as a perfluoropolyether lubricating oil for vacuum pump oil.

7. The use according to claim 6, characterized in that the index system of the perfluoropolyether lubricant meets: Degree of polymerization range: 18-35; Yield: ≥90%; Average molecular weight: 3000-10000 g / mol; Vapor pressure at 25℃: ≤1x10 -6 Pa; Vapor pressure at 100℃: ≤1×10 -4 Pa; Ultimate vapor pressure: ≤1×10 -3 Pa; Thermal decomposition temperature: 300-500℃; Pour point: ≤-35℃.

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