A method for removing the end groups of perfluoropolyether acyl fluoride

Abstract

This invention discloses a method for removing acyl fluoride end groups from perfluoropolyether. The method includes the following steps: adding perfluoropolyether acyl fluoride, a fluorinating agent, a catalyst, and a solvent to a photochemical reactor, reacting at room temperature and pressure under ultraviolet light for 2-12 hours to remove the acyl fluoride end groups, yielding perfluoropolyether, which can be used as a perfluoropolyether vacuum pump oil; the fluorinating agent is a fluorinated aromatic compound. This invention features simple operation steps, readily available reaction equipment, and mild reaction conditions, avoiding the decomposition and loss of perfluoropolyether products due to high temperatures, and has the advantages of safety and energy saving.

Description

Technical Field

[0001] This invention relates to the field of fluorochemical technology, and specifically to a method for removing the end groups of perfluoropolyether acyl fluoride. Background Technology

[0002] Perfluoropolyether oil (PFPE) is a new type of synthetic lubricant. Its molecules contain only C, F, and O atoms, and the molecular chain is saturated. It has excellent thermal stability, chemical inertness, non-flammability, resistance to strong oxidants, strong acids, and strong alkalis, and stable performance at high temperatures. Compared with conventional vacuum oils, it is safer and has a longer service life. It can also maintain long-term stability in environments containing corrosive gases, making it a high-performance vacuum pump oil.

[0003] However, after the polymerization of perfluoropolyethers, the polymer molecular chains always contain highly unstable acyl fluoride end groups (-COF), which react with water to release hydrogen fluoride and simultaneously convert into carboxylic acid groups (-COOH). Neither the acyl fluoride groups nor the carboxyl groups are stable. During use, the perfluoropolymer decomposes from the end groups, producing volatile substances, resulting in bubbles or voids in the finished product. This limits the further application of PFPE products in high-tech fields such as semiconductor silicon wafer processing, anti-sticking of photocopier hot rollers, and anti-corrosion thick film coatings. Therefore, developing and optimizing technologies for removing unstable end groups from perfluoropolymers to reduce PFPE production costs is beneficial to the development of the chemical, mechanical, aerospace, and electronics industries.

[0004] Currently, the main processes for removing the end groups of perfluoropolyether acyl fluoride are as follows:

[0005] One method involves end-group fluorination of perfluoropolyether fluoride (PFPE-COF) using fluorine gas or a fluorine-nitrogen mixture to obtain stable perfluoropolyether products. However, this method suffers from drawbacks such as the high toxicity and corrosiveness of fluorine gas, high requirements for production equipment, and significant safety risks during operation. For example, patent CN103111253A discloses a method and equipment for fluorinating perfluoropolyethers, but its disadvantage is that the reaction requires high temperatures, which not only leads to the decomposition and loss of low-boiling-point perfluoropolyethers but also shortens the lifespan of production equipment. Patents CN110092901A and CN110467723A disclose methods for preparing perfluoropolyether oil by fluorinating it using fluorine gas and a fluorine-nitrogen mixture, but these methods suffer from low fluorine utilization, high toxicity to humans, and strong corrosiveness to equipment. These factors significantly increase production costs, hindering industrial-scale production.

[0006] Secondly, metal fluorides such as Al, Ti, and V are used as catalysts to cap the acyl fluoride end groups of perfluoropolyethers. However, this method also faces some problems, such as high reaction energy consumption and low perfluoropolyether yield. To address these shortcomings, patents CN115364875A and CN117362626A both utilize carbon-based supported fluorides prepared by calcination or impregnation as fluorinating agents to cap perfluoropolyethers. Compared to the former method that directly uses metal fluorides as catalysts, this method has lower energy consumption and higher product yield, but it still suffers from drawbacks such as higher reaction temperature, longer reaction time, and more complex reaction operation.

[0007] Thirdly, there is the hydrolysis-decarboxylation method, where the acyl fluoride end groups of perfluoropolyethers are converted into carboxylic acid groups and removed under the action of water and alkali. Patents such as CN111892705A and CN113150262A use water and a mixture of inorganic alkali or organic amine compounds with inorganic alkali for decarboxylation and end-capping reactions. However, these end-capping methods suffer from low reaction efficiency, and the molecular weight of the perfluoropolyether decreases after decarboxylation. Furthermore, the decarboxylation-treated end groups are inert -CF2H groups, not the highly stable -CF3 molecular structure. The product is impure after the reaction, requiring purification, which increases energy consumption and production costs.

[0008] Therefore, the development of a highly efficient, safe, green, environmentally friendly, low-energy-consumption, and high-yield end-capping method for perfluoropolyethers has significant application value. Summary of the Invention

[0009] The primary objective of this invention is to address the shortcomings of existing technologies by providing a method for removing fluorinated acyl fluoride end groups from perfluoropolyethers. This method utilizes a fluorinated aromatic compound as a fluorinating agent, a transition metal and its complexes as catalysts, and employs ambient temperature and pressure ultraviolet irradiation. The active carbon-fluorine bonds of the fluorinated aromatic compound provide fluorine atoms to fluorinate the acyl fluoride end groups. The transition metal and its complexes, acting as catalysts, coordinate and complex with the carboxyl groups of the fluorinated aromatic compound to activate these carbon-fluorine bonds, thereby achieving the removal of the fluorinated acyl fluoride end groups from the perfluoropolyether under ultraviolet light irradiation. This invention features simple operation steps, readily available reaction equipment, and mild reaction conditions, avoiding the decomposition and loss of perfluoropolyether products due to high temperatures, and offers advantages in safety and energy conservation.

[0010] The technical solution of this invention is as follows:

[0011] A method for removing the end groups of perfluoropolyether acyl fluoride, the method comprising the following steps:

[0012] Perfluoropolyether acyl fluoride, fluorinating agent, catalyst and solvent are added to a photochemical reactor and reacted at room temperature and pressure under ultraviolet light for 2-12 hours to remove acyl fluoride end groups and obtain perfluoropolyether;

[0013] Wherein, the mass ratio of the perfluoropolyether fluoride to the solvent is 1:(1-1000); the mass ratio of the perfluoropolyether fluoride to the fluorinating agent is 1:(0.005-0.5); and the mass ratio of the perfluoropolyether fluoride to the catalyst is 1:(0.005-0.5).

[0014] The ultraviolet light wavelength is 100-400nm;

[0015] The solvent is a polar solvent such as an alcohol, an aliphatic solvent, or an ether, amide, nitrile, sulfone, or ketone containing an aromatic group; the polar solvent is one or more of ethanol, methanol, dimethyl sulfoxide, ethylene glycol dimethyl ether, acetonitrile, phenylacetonitrile, dimethyl sulfoxide, dimethylformamide, and N-methylpyrrolidone.

[0016] The fluorinating agent is a fluorinated aromatic compound;

[0017] The catalyst is a transition metal and its complex; the transition metal is Fe, Co, Ni, Cu, Ru, Rh, Pd or Pt;

[0018] The fluorinated aromatic compound is one or more of the following: 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, methyl 2,3,4,5-tetrafluorobenzoate, 1,2,3,4,5-pentafluorobenzene, pentafluorobenzoic acid, pentafluorophenol, methyl pentafluorobenzoate, and hexafluorobenzene.

[0019] The transition metals and their complexes are one or more of palladium on carbon, platinum on carbon, Fe / Co / Ni complexes, triphenylphosphine palladium chloride, triphenylphosphine ruthenium chloride, triphenylphosphine rhodium chloride, triphenylphosphine nickel chloride, and triphenylphosphine cobalt chloride.

[0020] The photochemical reactor includes a long-arc mercury lamp with a constant current power supply, a quartz reactor, a multi-position photochemical reactor, a coolant circulation pump, and a dark chamber.

[0021] The removal method yields a perfluoropolyether with removed acyl fluoride end groups, which is used as vacuum pump oil.

[0022] The index system of the aforementioned perfluoropolyether lubricating oil meets the following requirements:

[0023] Degree of polymerization range: 18-35;

[0024] Yield: ≥90%;

[0025] Average molecular weight: 3000-10000 g / mol;

[0026] Vapor pressure at 25℃: ≤1 x 10 -6 Pa;

[0027] Vapor pressure at 100℃: ≤1×10 -4 Pa;

[0028] Ultimate vapor pressure: ≤1×10 -3 Pa;

[0029] Thermal decomposition temperature: 300-500℃;

[0030] Pour point: ≤-35℃.

[0031] The essential features of this invention are:

[0032] In this invention, the fluorinating agent is crucial for the removal of the acyl fluoride group, and this invention uses a fluorinated aromatic compound as the fluorinating agent. In fluorinated aromatic compounds, the substitution of fluorine and carboxyl groups on the benzene ring of the fluorinated aromatic carboxylic acid has a significant impact on the removal of the acyl fluoride end group from the perfluorinated polyether: the carboxyl group on the benzene ring has a strong electron-withdrawing effect, making the carbon-fluorine bond in the fluorinated aromatic carboxylic acid molecule more reactive and weakening its polarity. This allows the fluorine atom to easily approach the carbon atom attached to the acyl fluoride end group, thereby attacking the reactive acyl fluoride end group and causing the removal reaction.

[0033] Transition metals and their complexes can coordinate with deprotonated carboxylic acids in fluorinated aromatic carboxylic acids. Under mild conditions of ambient temperature, ambient pressure, and ultraviolet light, they can act as catalysts to activate the carbon-fluorine bonds in fluorinated aromatic carboxylic acids, which is conducive to the attack of fluorine atoms on acyl fluoride end groups. The covalent bond breaking of acyl fluoride end groups in perfluoropolyethers is similar to the decarboxylation reaction, that is, it undergoes heterolytic cleavage according to the ionic reaction mechanism, thereby improving the efficiency of removing acyl fluoride end groups from perfluoropolyethers.

[0034] This invention utilizes a mercury lamp to irradiate a photochemical reactor at room temperature and pressure with ultraviolet light. It features simple operation steps, readily available reaction equipment, and mild reaction conditions.

[0035] The beneficial effects of this invention are:

[0036] In this invention, the utilization rate of fluorinated aromatic compound fluorinating agent and transition metal complex catalyst is extremely high. The mass ratio of perfluoropolyether fluoride to solvent is 1: (1-1000), the mass ratio of perfluoropolyether fluoride to fluorinating agent is 1: (0.005-0.5), and the mass ratio of perfluoropolyether fluoride to catalyst is 1: (0.005-0.5). The amount of fluorinating agent and catalyst used is very low, the reaction time is short, and the reaction conditions are mild, avoiding the use of high temperature. This invention does not require fluorine gas or high-energy-consuming equipment, and has the advantages of low energy consumption and high added value.

[0037] Furthermore, this invention utilizes the coordination of transition metal catalysts with the carboxyl groups of fluorinating agents to activate carbon-fluorine bonds, greatly improving the efficiency of removing acyl fluoride end groups and achieving a perfluoropolyether product yield of over 90%, thus possessing the advantages of high efficiency and economy. This invention also utilizes a photochemical reactor under ultraviolet light at room temperature, with simple operation steps, readily available reaction equipment, and mild reaction conditions, avoiding the decomposition and loss of perfluoropolyether products due to high temperatures, thus possessing the advantages of safety and environmental protection. Attached Figure Description

[0038] Figure 1 The UV-Vis absorption spectra of perfluoropolyether fluoride at concentrations of 0.1wt%, 1wt%, 2wt%, and 4wt% using ethanol as a solvent.

[0039] Figure 2 The UV-Vis absorption spectra of 0.1wt% PFPE, 0.1wt% PFPE-COF, and 0.1wt% PFPE-COF with added 2,3,5,6-tetrafluoroterephthalic acid are shown in the figure.

[0040] Figure 3 These are the Fourier transform infrared (FT-IR) spectra of PFPE, PFPE-COF, and PFPE-COF with different catalysts and fluorinating agents added.

[0041] Figure 4 This is a schematic diagram of the carbon-oxygen double bond and carbon-oxygen triple bond structure of perfluoropolyether fluoride and their corresponding infrared wavenumbers. Detailed Implementation

[0042] The technical solution of the present invention will be further clearly and completely described below with reference to the embodiments and accompanying drawings. Through these descriptions, the features and advantages of this application will become clearer and more explicit. The described embodiments are merely some embodiments of the present invention, and not all embodiments.

[0043] This invention utilizes an ionic reaction mechanism for heterolytic cleavage, as follows:

[0044]

[0045] Example 1

[0046] Prepare a 0.1 wt% PFPE-COF solution using ethanol as the solvent. Add 10 ml of ethanol to a container, add 0.0079 g of PFPE-COF, stir well, and prepare for testing.

[0047] Examples 2-4

[0048] The other steps are the same as in Example 1, except that the mass concentration of the PFPE-COF solution is replaced by 1wt%, 2wt%, and 4wt% respectively instead of 0.1wt%, that is, the amount of PFPE-COF added is changed from 0.0079g to 0.0797g, 0.1610g, and 0.3288g respectively.

[0049] 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; from Figure 1 It can be seen that the absorbance values ​​are: 4wt% > 2wt% > 1wt% > 0.1wt%, meaning that as the concentration of the perfluoropolyether acyl fluoride solution increases, the concentration of the acyl fluoride end groups is higher, and the absorbance is also greater.

[0050] Example 5

[0051] Prepare a 0.1 wt% PFPE solution using ethanol as the solvent. Add 10 ml of ethanol to a container, add 0.0079 g of PFPE, stir well, and prepare for testing.

[0052] Examples 6-7

[0053] The other steps are the same as in Example 1, except that 0.0079g of PFPE is replaced with 0.0079g of PFPE-COF, and a mixture of 0.0079g of PFPE-COF and 0.0039g of 2,3,5,6-tetrafluoroterephthalic acid.

[0054] The samples obtained in Examples 5-7 were subjected to ultraviolet-visible absorption spectroscopy (UV-vis) testing to quantitatively analyze the content of acyl fluoride end groups in perfluorinated polyether acyl fluoride solutions with and without fluorinating agents. Figure 2 As shown.

[0055] from Figure 2 As shown, the absorbance ranking is: pure PFPE-COF > PFPE-COF containing 2,3,5,6-tetrafluoroterephthalic acid > pure PFPE. This indicates that compared to pure PFPE-COF, the content of acyl fluoride end groups is reduced in PFPE-COF containing 2,3,5,6-tetrafluoroterephthalic acid, suggesting that the fluorinating agent of 2,3,5,6-tetrafluoroterephthalic acid effectively removes the acyl fluoride end groups.

[0056] Example 8

[0057] Add 2.1894g of PFPE-COF, 0.0252g of 2,3,5,6-tetrafluoroterephthalic acid, and 45ml of ethanol to a 100ml quartz reaction tube. Seal the side arm with a rubber stopper. Then, insert a disposable dropper into the bottom of the solution and bubble with N2 for 10 minutes to expel dissolved air from the solution. After bubbling, place the tube in a photochemical reaction chamber and install a condenser to seal the reaction system. Connect a cooling circulation pump and turn on the mercury lamp condenser and reaction solution condenser sequentially. After confirming the cooling circulation pump is running smoothly, turn on the mercury lamp to begin the photochemical reaction. The mercury lamp has an irradiation power of 500W and an irradiation distance of approximately 15cm. The temperature is maintained between 15-30℃ through condensation. After 6.5 hours of reaction, turn off the mercury lamp to stop the reaction and shut off the cooling devices. Take 1 ml of the reaction solution after 2 h and 6.5 h of reaction, respectively, and concentrate it under vacuum by rotary evaporation for 30 min-60 min at room temperature to remove residual solvent and obtain solid samples. Then add 0.5 ml of acetonitrile to dissolve it completely. Aspirate the obtained solution with a syringe, filter it through a filter membrane to remove residual catalyst particles, and place it in a sample tube for analysis.

[0058] Example 9

[0059] Similar to the preparation method in Example 8, the difference is that after the entire reaction system in Example 8 has reacted for 6.5 hours, 0.013 g of palladium on carbon catalyst is added to the reactor and the reaction continues for another 2.5 hours. After the reaction is complete, 1 ml of the reaction solution is taken and processed in the same way as in Example 8. The resulting solution is drawn out with a syringe, filtered through a filter membrane to remove residual catalyst particles, and then placed in a sample tube for analysis.

[0060] Example 10

[0061] 1.7370 g of PFPE-COF, 0.1745 g of 2,3,5,6-tetrafluoroterephthalic acid, 0.1540 g of palladium on carbon catalyst, and 45 ml of ethanol were added to a 100 ml quartz reaction tube. After all the apparatus was connected, the reaction was started under light irradiation for 6 hours. After 6 hours of reaction, the mercury lamp was turned off to stop the reaction, and the cooling device was shut off. 1 ml of the reaction solution after 6 hours of reaction was taken and processed in the same way as in Example 8. The resulting solution was drawn out with a syringe, filtered through a filter membrane to remove residual catalyst particles, and then placed in a sample tube for analysis.

[0062] Example 11

[0063] Add 1.3435g PFPE-COF, 0.0444g o-fluorobenzoic acid, and 45ml ethanol to a 100ml quartz reaction tube, and react under light for 4 hours. Take 1ml of the reaction solution after 4 hours of reaction, dissolve it by rotary evaporation at room temperature, filter it, and place the resulting solution in a sample tube for analysis. Continue the reaction for 2 hours, and after the reaction is complete, turn off the mercury lamp and cooling device. Take 1ml of the reaction solution after 6 hours of reaction, and process it in the same way as in Example 8. Draw the resulting solution out with a syringe, filter it through a filter membrane to remove residual catalyst particles, and place it in a sample tube for analysis.

[0064] Example 12

[0065] Add 1.3435g PFPE-COF, 0.0444g o-fluorobenzoic acid, 0.0183g triphenylphosphine rhodium catalyst, and 45ml ethanol to a 100ml quartz reaction tube, and react under light for 4 hours. Take 1ml of the reaction solution after 4 hours of reaction, dissolve it by rotary evaporation at room temperature, and filter the resulting solution into a sample tube for analysis. Continue the reaction for 2 hours, then take 1ml of the reaction solution after 6 hours of reaction, dissolve it by rotary evaporation at room temperature, and filter the resulting solution into a sample tube for analysis. Continue the reaction for 6 hours, and after the reaction is complete, turn off the mercury lamp and cooling device. Take 1ml of the reaction solution after 12 hours of reaction, and process it in the same way as in Example 8. Draw the resulting solution out with a syringe, filter it through a filter membrane to remove residual catalyst particles, and then place it into a sample tube for analysis.

[0066] Comparative Example 1

[0067] Add 1.5755g of PFPE-COF and 45ml of ethanol to a 100ml quartz reaction tube and react under light for 2 hours. Take 1ml of the reaction solution after 2 hours of reaction, dissolve and filter it by rotary evaporation at room temperature, and place the resulting solution in a sample tube for analysis. Continue the reaction for another 2 hours, then take 1ml of the reaction solution after 4 hours of reaction, dissolve and filter it by rotary evaporation at room temperature, and place the resulting solution in a sample tube for analysis. Continue the reaction for another 2 hours, and after the reaction is complete, turn off the mercury lamp and cooling device. Take 1ml of the reaction solution after 6 hours of reaction, and process it in the same way as in Example 8. Draw the resulting solution out with a syringe, filter it through a filter membrane to remove residual catalyst particles, and place it in a sample tube for analysis.

[0068] Test Examples 8-12, Comparative Example 1

[0069] Fourier transform infrared (FT-IR) tests were performed on the test samples obtained from the above embodiments and comparative examples, such as... Figure 3 As shown. From Figure 4 We can obtain the structural diagrams and infrared wavenumbers of the carbon-oxygen double and triple bonds of perfluoropolyether fluoride.

[0070] pass Figure 3 , Figure 4 It can be seen that the above is at 1897 cm -1 1780cm -1 The characteristic absorption peaks are attributed to the vibrations of the carbon-oxygen triple bond and the carbon-oxygen double bond, respectively. Compared with pure PFPE-COF, the absorption peak of the carbon-oxygen triple bond completely disappears in the PFPE-COF system with added fluorinated aromatic carboxylic acid fluorinating agents and transition metals and their complex catalysts, indicating that the carbon-oxygen triple bond in PFPE-COF has been completely eliminated; the absorption peak of the carbon-oxygen double bond is weakened, indicating that the carbon-oxygen double bond in PFPE-COF is partially eliminated, resulting in a perfluoropolyether vacuum pump oil with partially removed acyl fluoride end groups.

[0071] Experiments have shown that the rate of de-acyl fluoride removal from fluorinated aromatic compounds with different substitution structures varies with the structure and number of electron-withdrawing groups. The de-acyl fluoride removal rates are: 2,3,5,6-tetrafluoroterephthalic acid > 2,3,4,5-tetrafluorobenzoic acid > methyl 2,3,4,5-tetrafluorobenzoate > 1,2,3,5-tetrafluorobenzene > terephthalic acid.

[0072] The obtained perfluoropolyether was purified by rotary evaporation. Before rotary evaporation, a vacuum pump was used to provide a negative pressure environment to accelerate the evaporation rate. The controlled conditions were: evaporation temperature 120-200℃, evaporation time 120-360 min, rotor speed 250-350 r / min, and condensation temperature 15-25℃.

[0073] The performance indicators of the perfluoropolyether vacuum pump oil obtained by the above method were tested:

[0074] The average molecular weight of perfluoropolyethers was determined by end-group back titration.

[0075] The total fluorine content of perfluoropolyethers was quantitatively analyzed by ion chromatography.

[0076] The decomposition temperature of perfluoropolyethers was determined by thermogravimetric analysis.

[0077] Pour point was tested using a fully automated pour point and freezing point tester;

[0078] The degree of polymerization was measured using a lubricating oil tester;

[0079] Vapor pressure is measured using a vapor pressure measuring instrument.

[0080] By removing the acyl fluoride end groups of perfluoropolyether acyl fluoride under ambient temperature, pressure, and ultraviolet light with a catalyst and fluorinating agent, and then evaporating the solvent by rotary evaporation, a perfluoropolyether vacuum pump oil with the following performance characteristics was obtained:

[0081] Degree of polymerization range: 18-35;

[0082] Yield: ≥90%;

[0083] Average molecular weight: 3000-10000 g / mol;

[0084] Vapor pressure at 25℃: ≤1 x 10 -6 Pa;

[0085] Vapor pressure at 100℃: ≤1×10 -4 Pa;

[0086] Ultimate vapor pressure: ≤1×10 -3 Pa;

[0087] Thermal decomposition temperature: 300-500℃;

[0088] Pour point: ≤-35℃.

[0089] Matters not covered in this invention are common knowledge.

Claims

1. A method for removing end groups of perfluoropolyether acyl fluoride, characterized in that the method includes the following steps: Perfluoropolyether acyl fluoride, fluorinating agent, catalyst and solvent are added to a photochemical reactor and reacted at room temperature and pressure under ultraviolet light for 2-12 hours to remove acyl fluoride end groups and obtain perfluoropolyether; in, The mass ratio of the perfluoropolyether fluoride to the solvent is 1:(1-1000); the mass ratio of the perfluoropolyether fluoride to the fluorinating agent is 1:(0.005-0.5); the mass ratio of the perfluoropolyether fluoride to the catalyst is 1:(0.005-0.5). The ultraviolet light wavelength is 100-400nm; The solvent is an alcohol, an aliphatic solvent, or an ether, amide, nitrile, sulfone, or ketone containing an aromatic group; The fluorinating agent is o-fluorobenzoic acid or 2,3,5,6-tetrafluoroterephthalic acid; 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 described in claim 1, characterized in that the solvent is one or more of ethanol, methanol, dimethyl sulfoxide, ethylene glycol dimethyl ether, acetonitrile, phenylacetonitrile, dimethylformamide, and N-methylpyrrolidone.

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

4. The method for removing perfluoropolyether acyl fluoride end groups as described in claim 1, characterized in that the photochemical reactor includes a long-arc mercury lamp constant current power supply, a quartz reactor, a multi-position photochemical reactor, a coolant circulation pump, and a dark chamber.

5. The method for removing the perfluoropolyether acyl fluoride end groups as described in claim 1, characterized in that, The obtained perfluoropolyether was purified by rotary evaporation. The solvent was evaporated by rotary evaporation to obtain a perfluoropolyether with the following properties: Degree of polymerization range: 18-35; Yield: ≥90%; Average molecular weight: 3000-10000 g / mol; Vapor pressure at 25℃: ≤1 x 10 -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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