Preparation method for improving yield and purity of perfluoropolyether ester

Abstract

The invention discloses a preparation method for improving the yield and purity of perfluoropolyether ester, which is different from the prior art that perfluoropolyether carboxylic acid and alcohol are directly reacted to generate perfluoropolyether ester, and is characterized in that perfluoropolyether carboxylic acid with the molecular weight of 1500-4000 is firstly converted into perfluoropolyether acyl chloride with high reaction activity, and then the perfluoropolyether acyl chloride is reacted with alcohol; the conversion rate of carboxylic acid can be improved. In the reaction process, the solubility of the fluorine-containing solvent 1, the perfluoropolyether carboxylic acid, the alcohol and other raw materials is considered, so that the selected fluorine-containing solvent contains more C-H bonds, the conversion rate of the perfluoropolyether carboxylic acid is greater than or equal to 98%, a post-treatment secondary extraction method is combined, the separation effect of a crude perfluoropolyether ester product is improved, and the purity of the product perfluoropolyether ester is greater than or equal to 98.5%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of perfluoropolyether ester, in particular to a preparation method for improving the yield and purity of perfluoropolyether ester. BACKGROUND

[0002] Y-type perfluoropolyether ester is a perfluoropolyether derivative, which is widely used in lubricating oil additives, lithium battery electrolytes, underwater sealing materials and other fields. As an intermediate, it is widely used in the preparation of anti-fingerprint coatings, etc. One-step reaction with 3-aminopropyltrimethoxysilane can obtain anti-fingerprint coating. When the molecular weight is between 1500 and 3500, the anti-fingerprint agent has better performance. The side chain of Y-type anti-fingerprint agent accounts for a relatively smaller proportion than the commonly seen K-type in the market, and has better wear resistance. In the preparation process of Y-type perfluoropolyfluoride, inert end-capped substances are produced, which need to be separated first and then esterified.

[0003] In the prior art, the anti-fingerprint coating requires water content in the system to be ≤100 ppm. When perfluoropolyether ester contains perfluoropolyether acid, the acid will react with 3-aminopropyltrimethoxysilane to produce water, which in turn hydrolyzes the terminal trimethoxyl group, reducing the performance of the anti-fingerprint coating. Therefore, as an intermediate, the carboxylic acid content in the perfluoropolyether ester should be ≤1.5%. Perfluoropolyether acid and perfluoropolyether ester have large molecular weights, and the only difference between them is the terminal group. It is difficult to separate them by general methods. Therefore, when synthesizing perfluoropolyether ester as an intermediate for anti-fingerprint coating, the conversion rate of the reaction raw material should be ≥98.0% to reduce the subsequent separation of perfluoropolyether acid. The purity of the product after separation should be ≥98.5%.

[0004] Chinese patent document with publication number CN115725065A discloses a preparation method of a non-ionic surfactant prepared by treating perfluoropolyether carboxylic acid. Perfluoropolyether carboxylic acid with an average molecular weight of 500-1000 in the production of anionic perfluoropolyether surfactant is reacted with polyethylene glycol and / or polyethylene glycol monomethyl ether to obtain perfluoropolyether polyethylene glycol / polyethylene glycol monomethyl ether ester perfluoropolyether non-ionic surfactant. The reaction temperature is 105-200 ℃, the reaction time is 4-10 h, and the post-treatment adopts saturated sodium carbonate solution and saturated sodium chloride solution washing, drying, and suction filtration to obtain the product. This method directly reacts carboxylic acid with alcohol to obtain perfluoropolyether ester crude product. However, due to the high reaction temperature, the product conversion rate is low. Moreover, the product is obtained after post-treatment of perfluoropolyether ester crude product with saturated sodium carbonate solution and saturated sodium chloride solution, which reduces the yield of the post-treatment step. The highest conversion rate of the raw material is 81.24%.

[0005] The Chinese patent document with the publication number CN116731329A discloses a fluorine-containing block copolymer and a method for finishing cotton fabric, wherein PS-OH and perfluoropolyether carboxylic acid are coupled under the activation of N,N'-dicyclohexyl carbodiimide (DCC) in the presence of a pyridine compound to obtain a fluorine-containing block copolymer PS-bPFPE (i.e., a carboxylate compound), wherein the number average molecular weight of the perfluoropolyether carboxylic acid is 200-1000. After the reaction is completed, the white precipitate is filtered out, the solvent is removed by rotary evaporation, and then the product is obtained by recrystallization in anhydrous methanol after being dissolved in THF and drying. The reaction condition is mild, but the reaction time is long, the post-treatment is complex, the raw material conversion rate is low, and the product yield is about 85.6%.

[0006] There are few studies on the esterification and post-treatment of perfluoropolyether acids with a molecular weight of 1500-4000. Therefore, it is necessary to continue to find a method suitable for the esterification of perfluoropolyether acids with a molecular weight of 1500-4000.

[0007] In the prior art, there are mainly two problems in the high-conversion-rate, high-efficiency synthesis and high-yield obtaining of perfluoropolyether esters with a molecular weight of 1500-4000. Firstly, the perfluoropolyether acid with a molecular weight of 1500-4000 has a longer main chain length and a lower reactivity of the terminal carboxylic acid group than the perfluoropolyether with a relatively low molecular weight, and has a higher viscosity. The raw material conversion rate and the reaction efficiency are relatively lower by using the method in the foregoing patent, and a suitable solvent system and a reaction with a highly reactive substance are needed to improve the reaction rate and the raw material conversion rate. Secondly, the viscosity of the perfluoropolyether used is high, and there are unreacted alcohol, organic salt, catalyst, acid-binding agent and unreacted perfluoropolyether carboxylic acid in the product. It is necessary to screen a better solvent system for the high-efficiency and high-yield separation of the perfluoropolyether carboxylic ester.

[0008] Therefore, it is a problem to be solved to use the perfluoropolyether acid with a molecular weight of 1500-4000 as a raw material, to synthesize the perfluoropolyether ester with a molecular weight of 1500-4000 with high conversion rate and high efficiency, and to obtain the perfluoropolyether ester with high purity and high yield by post-treatment. SUMMARY

[0009] In order to solve the above technical problems, the present application provides a preparation method for improving the yield and purity of perfluoropolyether ester, which converts the perfluoropolyether carboxylic acid with a molecular weight of 1500-4000 into highly reactive perfluoropolyether acid chloride and then reacts with alcohol, so as to improve the conversion rate of the perfluoropolyether carboxylic acid.

[0010] A preparation method for improving the yield and purity of perfluoropolyether ester, comprising the following steps: (1) Dissolve perfluoropolyether carboxylic acid with a number average molecular weight of 1500~4000 in fluorinated solvent 1, and react with dichlorosulfoxide under the action of catalyst and acid-binding agent 1 to obtain perfluoropolyether acyl chloride; wherein the fluorinated solvent 1 is at least one of ethyl nonafluorobutyl ether (CF3CF2CF2CF2OCH2CH3, i.e. HFE-7200), 1,1,2,2-tetrafluoroethyl ethyl ether (CH3CH2OCF2CF2H, i.e. HFE-374), and m-difluorotoluene; (2) The perfluoropolyether acyl chloride obtained in step (1) is reacted with an alcohol under the action of acid binding agent 2 to obtain crude perfluoropolyether ester, and then post-processed to obtain perfluoropolyether ester.

[0011] The specific route is as follows: Unlike existing technologies that directly react perfluoropolyether carboxylic acids with alcohols to form perfluoropolyether esters, this invention first converts perfluoropolyether carboxylic acids with a molecular weight of 1500-4000 into highly reactive perfluoropolyether acyl chlorides before reacting them with alcohols, thereby improving the conversion rate of perfluoropolyether carboxylic acids. Considering the solubility of fluorinated solvent 1 with the perfluoropolyether carboxylic acids, alcohols, and other raw materials during the reaction, the selected fluorinated solvent contains a large number of CH bonds, increasing reaction efficiency and conversion rate.

[0012] The structural formula of the perfluoropolyether carboxylic acid is: R f -(CFCF3CF2O) m -(C2F4O) n -CF2COOH, where R f The values ​​are (CF3)2CFO, CF3CF2CF2O, CF3CF2O, or CF3O, and the ratio of n to m is 0.01 to 0.05.

[0013] Perfluoropolyether carboxylic acid can be prepared by the method disclosed in Chinese patent document CN115651186A, or it can be purchased from Zhejiang Juhua Technology Center Co., Ltd. In most cases, R in this perfluoropolyether carboxylic acid... f The four groups (CF3)2CFO, CF3CF2CF2O, CF3CF2O, and CF3O) can be arbitrarily substituted and are difficult to separate. Therefore, the perfluoropolyether carboxylic acid of this invention is also suitable for various R... f The substituted mixture is specifically defined by its number-average molecular weight.

[0014] Preferably, in step (1), the mass ratio of the perfluoropolyether carboxylic acid and the fluorinated solvent 1 is 1:1~5.

[0015] Further preferably, the fluorine-containing solvent 1 is ethyl nonafluorobutyl ether or m-di-trifluoromethylbenzene, and the mass ratio of the perfluoropolyether carboxylic acid and the fluorine-containing solvent 1 is 1:1-2.

[0016] Preferably, in step (1), the catalyst is pyridine or 2-methylpyridine.

[0017] Preferably, the acid-binding agent 1 and the acid-binding agent 2 are at least one of pyridine, 2-methylpyridine, 2,4-dimethylpyridine, and triethylamine.

[0018] Further preferably, the catalyst is pyridine, and the acid-binding agent 1 is pyridine, 2-methylpyridine, or triethylamine.

[0019] In the present application, the catalyst and the acid-binding agent 1 can both be pyridine or can be different.

[0020] Preferably, in step (1), the molar ratio of the perfluoropolyether carboxylic acid, the catalyst, the acid-binding agent 1, and the thionyl chloride is 1:0.05-0.5:1-2:1-4.

[0021] Preferably, in step (2), the molar ratio of the perfluoropolyether carboxylic acid, the acid-binding agent 2, and the alcohol is 1:1-10:1-8.

[0022] Preferably, in step (2), the alcohol is a C1-C10 alcohol.

[0023] Preferably, the reaction temperature with the thionyl chloride is 20-50 ℃, and the reaction temperature with the alcohol is 30-60 ℃, and the reaction time is 0.5-6 h.

[0024] Compared with the prior art, in the present application, the perfluoropolyether carboxylic acid is converted into a highly reactive perfluoropolyether carbonyl chloride, and then reacted with an alcohol, which can significantly reduce the reaction with the alcohol, shorten the reaction time, and prepare the perfluoropolyether ester at a relatively low temperature (30-60 ℃), and the conversion rate of the perfluoropolyether carboxylic acid is ≥98%.

[0025] Preferably, in step (2), the post-treatment is adding an extraction agent to the crude perfluoropolyether ester, collecting the lower fluorine-containing organic phase after one extraction, adding a sodium chloride aqueous solution thereto, collecting the lower layer after two extractions, and obtaining the perfluoropolyether ester after reduced-pressure distillation. The extraction agent is a saturated sodium carbonate aqueous solution or a mixed solution of a fluorine-containing solvent 2 and a pyridine aqueous solution, and the fluorine-containing solvent 2 is 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (CF3CH2OCF2CF2H, HFE-347) or methyl nonafluorobutyl ether (CF3CF3CF2CF2OCH3, HFE-7100).

[0026] In the present application, the extractant uses saturated sodium carbonate aqueous solution or mixed solution of fluorine-containing solvent 2 and pyridine aqueous solution, and both can realize the purification of perfluoropolyether ester.

[0027] Further preferably, the concentration of the pyridine aqueous solution is 0.01-10.0 wt%.

[0028] Further preferably, the extractant is a mixed solution of HFE-347 and pyridine aqueous solution.

[0029] In the present application, when the extractant is selected as the above mixed solution, the solubility of fluorine-containing solvent 2 and perfluoropolyether ester is high, and the solubility of other non-fluorine compounds is low, and at the same time, the complex reaction of pyridine aqueous solution and unreacted perfluoropolyether carboxylic acid can effectively extract the unreacted perfluoropolyether carboxylic acid from the upper aqueous phase, thereby improving the purity of perfluoropolyether ester in the lower fluorine-containing organic phase, so that the purity of perfluoropolyether ester product is ≥98.5%.

[0030] Further preferably, the mass ratio of perfluoropolyether carboxylic acid, HFE-347 and pyridine aqueous solution is 1:1-3:1-5.

[0031] Preferably, the conversion rate of perfluoropolyether carboxylic acid is ≥98%, and the purity of perfluoropolyether ester is ≥98.5%.

[0032] Compared with the prior art, the present application has the following beneficial effects: In the present application, the perfluoropolyether carboxylic acid with a molecular weight of 1500-4000 is first converted into highly reactive perfluoropolyether acid chloride, and then reacts with alcohol, which can improve the conversion rate of carboxylic acid. In the reaction process, the solubility of fluorine-containing solvent 1, perfluoropolyether carboxylic acid, alcohol and other raw materials is considered, so the selected fluorine-containing solvent contains more C-H bonds, so that the conversion rate of perfluoropolyether carboxylic acid is ≥98%, and then the secondary extraction method of post-treatment is used to improve the separation effect of perfluoropolyether ester crude product, so that the purity of the product perfluoropolyether ester is ≥98.5%. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The fluorine spectrum comparison chart of perfluoropolyether ester and perfluoropolyether carboxylic acid raw materials prepared in Example 2, Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0034] The present application will be further described in detail below in combination with examples, but the embodiments of the present application are not limited to the following examples.

[0035] The raw materials used in the present application are all commercially available.

[0036] Example 1 (1) Dissolve 200 g of perfluoropolyether carboxylic acid (0.08 mol, Mn=2500) in 400 g of HFE-7200, add 9.48 g of pyridine, stir for 5 min, add 14.28 g of thionyl chloride (0.12 mol) under N2 protection, and react at 25°C for 2 h to obtain perfluoropolyether acid chloride; (2) Add 12.64 g of pyridine and 7.68 g of methanol (0.24 mol) to the perfluoropolyether acid chloride obtained in step (2), and react at 50°C for 3 h to obtain crude perfluoropolyether ester; (3) Add 300 g of HFE-347 and 200 g of pyridine aqueous solution (1.0 wt%) to the crude product, stir thoroughly for 20 min, stand, extract the lower fluorine-containing organic phase once, add 300 g of sodium chloride aqueous solution (0.05 wt%), stir thoroughly for 2 h, stand, extract the lower layer twice, first distill off HFE-347 at 60°C under normal pressure, then distill off HFE-7200 at 80°C under normal pressure, and obtain 198 g of perfluoropolyether ester, with a product yield of 99.0%. The conversion rate of perfluoropolyether carboxylic acid is 98.7%, and the purity of the product perfluoropolyether ester is 99.5%.

[0037] Example 2 (1) Dissolve 320 g of perfluoropolyether carboxylic acid (0.08 mol, Mn=4000) in 320 g of m-trifluorotoluene, add 0.32 g of pyridine (0.004 mol) and 8.10 g of triethylamine (0.08 mol), stir for 5 min, add 9.52 g of thionyl chloride (0.08 mol) under N2 protection, and react at 20°C for 4 h to obtain perfluoropolyether acid chloride; (2) Add 6.32 g of pyridine (0.08 mol) and 2.60 g of methanol (0.08 mol) to the perfluoropolyether acid chloride obtained in step (2), and react at 30°C for 6 h to obtain crude perfluoropolyether ester; (3) Add 320 g of HFE-347 and 320 g of pyridine aqueous solution (0.01 wt%) to the crude product, stir thoroughly for 20 min, stand, extract the lower fluorine-containing organic phase once, add 120 g of sodium chloride aqueous solution (10 wt%), stir thoroughly for 1 h, stand, extract the lower layer twice, first distill off HFE-347 at 60°C under normal pressure, then distill off m-trifluorotoluene at 80°C under reduced pressure of -0.097 MPa, and obtain 314.2 g of perfluoropolyether ester, with a product yield of 98.2%. The conversion rate of perfluoropolyether carboxylic acid is 98.4%, and the purity of the product perfluoropolyether ester is 99.3%.

[0038] Example 3 (1) 120 g of perfluoropolyether carboxylic acid (0.08 mol, Mn=2500) was dissolved in 600 g of m-trifluorotoluene, 3.2 g of pyridine (0.04 mol) and 16.19 g of triethylamine (0.16 mol) were added, stirred for 30 min, 38.08 g of thionyl chloride (0.32 mol) was added under N2 protection, and reacted at 50°C for 0.5 h to obtain perfluoropolyether acid chloride; (2) Perfluoropolyether acid chloride obtained in step (2) was added with 12.64 g of pyridine (0.16 mol), 22.08 g of ethanol (0.48 mol), and reacted at 60°C for 2 h to obtain perfluoropolyether ester crude product; (3) 360 g of HFE-347 and 600 g of pyridine aqueous solution (10.0 wt%) were added to the crude product, stirred thoroughly for 30 min, and then allowed to stand, the lower fluorine-containing organic phase was obtained by one-time extraction, 600 g of sodium chloride aqueous solution (0.01 wt%) was further added, stirred thoroughly for 2 h, and then allowed to stand, the lower layer was obtained by two-time extraction, the lower layer was first distilled at 60°C under normal pressure to separate out HFE-347, and then m-trifluorotoluene was distilled out at 80°C under reduced pressure, to obtain 118.7 g of perfluoropolyether ester, the product yield was 98.9%. The conversion rate of perfluoropolyether carboxylic acid was 98.6%, and the purity of the product perfluoropolyether ester was 99.4%.

[0039] Example 4 (1) 200 g of perfluoropolyether carboxylic acid (0.08 mol, Mn=2500) was dissolved in 400 g of m-trifluorotoluene, 9.48 g of pyridine (0.12 mol) was added, stirred for 30 min, 14.28 g of thionyl chloride (0.12 mol) was added under N2 protection, and reacted at 25°C for 2 h to obtain perfluoropolyether acid chloride; (2) Perfluoropolyether acid chloride obtained in step (2) was added with 12.64 g of pyridine (0.16 mol), 24.00 g of polyethylene glycol (Mn=200), and reacted at 50°C for 3 h to obtain perfluoropolyether ester crude product; (3) 300 g of HFE-7100 and 200 g of pyridine aqueous solution (0.60 wt%) were added to the crude product, stirred thoroughly for 20 min, and then allowed to stand, the lower fluorine-containing organic phase was obtained by one-time extraction, 300 g of sodium chloride aqueous solution (0.05 wt%) was further added, stirred thoroughly for 2 h, and then allowed to stand, the lower layer was obtained by two-time extraction, the lower layer was first distilled at 80°C under normal pressure to separate out HFE-7100, and then m-trifluorotoluene was distilled out at 80°C under reduced pressure, to obtain 196.0 g of perfluoropolyether ester, the product yield was 98.0%. The conversion rate of perfluoropolyether carboxylic acid was 98.3%, and the purity of the product perfluoropolyether ester was 99.3%.

[0040] Example 5 (1) Dissolve 200 g of perfluoropolyether carboxylic acid (0.08 mol, Mn=2500) in 200 g of m-trifluorotoluene, add 9.48 g of pyridine (0.12 mol), stir for 5 min, add 14.28 g of thionyl chloride (0.12 mol) under N2 protection, and react at 25°C for 2 h to obtain perfluoropolyether acid chloride; (2) Add 12.64 g of pyridine (0.16 mol) and 7.68 g of methanol (0.24 mol) to the perfluoropolyether acid chloride obtained in step (2) and react at 50°C for 3 h to obtain perfluoropolyether ester crude product; (3) Add 200 g of saturated sodium carbonate aqueous solution to the crude product, stir thoroughly for 20 min, stand, extract the lower layer containing fluorine organic phase once, add 300 g of saturated sodium chloride aqueous solution, stir thoroughly for 2 h, stand, extract the lower layer twice, distill m-trifluorotoluene from the lower layer at 80°C under reduced pressure to obtain 190.0 g of perfluoropolyether ester, with a product yield of 95.0%. The conversion rate of perfluoropolyether carboxylic acid is 98.7%, and the purity of the product perfluoropolyether ester is 98.8%.

[0041] Comparative Example 1 Referring to the method for synthesizing perfluoropolyether ester in Chinese patent document with publication number CN116731329A, the specific process is as follows: Dissolve 41.2 g of dicyclohexyl carbodiimide (DCC) in 400 g of super dry tetrahydrofuran (THF) and 200 g of m-trifluorotoluene in a three-necked flask, then add 200 g of perfluoropolyether carboxylic acid (0.08 mol, Mn=2500) and react for 1 h, then add 7.68 g of methanol (0.24 mol) and 0.6 g of dimethylaminopyridine (DMAP), react at 25°C for 24 h under nitrogen protection to obtain perfluoropolyether ester crude product. Filter the perfluoropolyether ester crude product through a 5 micron PTFE nanofiltration membrane to remove white solid precipitate, rotary evaporate the filtrate at 55°C to remove the solvent, add m-trifluorotoluene to the concentrated liquid to precipitate the by-product, separate the liquid, and repeat 2-3 times. The product yield is 80.5%. The conversion rate of perfluoropolyether carboxylic acid is 95.0%, and the purity of the product perfluoropolyether ester is 94.6%.

[0042] Comparative Example 2 Referring to the method for synthesizing perfluoropolyether ester in Chinese patent document with publication number CN115725065A, the post-treatment adopts the post-treatment method of the present patent, and the specific process is as follows: (1) 7.68 g of methanol (0.24 mol) was added into the reaction bottle, the stirring was started and gradually heated to 110°C, 200 g of perfluoropolyether carboxylic acid (0.08 mol, Mn=2500) was weighed and reserved; methanol and perfluoropolyether carboxylic acid were added into the feeding device according to the molar ratio of 3:1, and slowly introduced into the reaction bottle, the dropwise adding speed was controlled at 15~40 g / min, and the stirring was continued for 8 h under this condition. After the reaction was completed, the crude perfluoropolyether ester was obtained; (2) 300 g of HFE-7100 and 200 g of pyridine aqueous solution (0.60 wt%) were added into the crude product, stirred thoroughly for 20 min, and then the lower fluorine-containing organic phase was obtained by one-time extraction. Then, 300 g of sodium chloride aqueous solution (0.05 wt%) was added, stirred thoroughly for 2 h, and then the lower layer was obtained by standing. The lower layer was first distilled at 80°C under normal pressure to separate HFE-7100, and then the m-xylene was distilled out at 80°C under reduced pressure, and 170.2 g of perfluoropolyether ester was obtained, with a product yield of 85.1%. The conversion rate of perfluoropolyether carboxylic acid was 85.0%, and the purity of the product perfluoropolyether ester was 99.3%.

[0043] Figure 1 The fluorine spectrum comparison chart of the perfluoropolyether ester and the perfluoropolyether carboxylic acid raw material prepared in Example 2, Comparative Examples 1 and 2 is shown in the figure. As shown in the figure, using the preparation method of the present application, the F peak of "CF2COOH" of the perfluoropolyether carboxylic acid is not found in the perfluoropolyether ester product, while in Comparative Examples 1 and 2, the perfluoropolyether ester product is synthesized without using the method of the present application, and the perfluoropolyether carboxylic acid still exists in the perfluoropolyether ester product. Therefore, it can be seen that the conversion rate of perfluoropolyether carboxylic acid in the preparation method of the present application is higher.

[0044] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for improving the yield and purity of perfluoropolyether esters, characterized in that, The method comprises the following steps: (1) dissolving perfluoropolyether carboxylic acid with a number average molecular weight of 1500-4000 in fluorine-containing solvent 1, and reacting with dichlorosulfoxide under the action of a catalyst and an acid-binding agent 1 to obtain perfluoropolyether acyl chloride; the fluorine-containing solvent 1 is at least one of ethyl nonafluorobutyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, and m-di-trifluorotoluene; (2) reacting the perfluoropolyether acyl chloride obtained in step (1) with alcohol under the action of an acid-binding agent 2 to obtain perfluoropolyether ester crude product, and obtaining perfluoropolyether ester through post-treatment.

2. The preparation method for improving the yield and purity of perfluoropolyether ester according to claim 1, characterized in that, In step (1), the perfluoropolyether carboxylic acid has the formula: R f -(CFCF3CF2O) m -(C2F4O) n -CF2COOH, wherein R f is (CF3)2CFO, CF3CF2CF2O, CF3CF2O or CF3O, and the ratio of n to m is 0.01 to 0.

05.

3. The method of claim 1, wherein the method is performed in the presence of a base. In step (1), the mass ratio of the perfluoropolyether carboxylic acid to the fluorine-containing solvent 1 is 1:1-5. ​ 4. The method of claim 3, wherein the method is performed in the presence of a base. 5 The fluorine-containing solvent 1 is ethyl nonafluorobutyl ether or m-di-trifluorotoluene, and the mass ratio of the perfluoropolyether carboxylic acid to the fluorine-containing solvent 1 is 1:1-2.

5. The method of claim 1, wherein the method is performed in the presence of a base. The catalyst is pyridine or 2-methylpyridine; The acid-binding agent 1 and the acid-binding agent 2 are at least one of pyridine, 2-methylpyridine, 2,4-dimethylpyridine, and triethylamine.

6. The method of claim 1, wherein the method is performed in the presence of a base. In step (1), the molar ratio of the perfluoropolyether carboxylic acid, the catalyst, the acid-binding agent 1, and dichlorosulfoxide is 1:0.05-0.5:1-2:1-4.

7. The method of claim 1, wherein the method is performed in the presence of a base. In step (2), the molar ratio of the perfluoropolyether carboxylic acid, the acid-binding agent 2, and alcohol is 1:1-10:1-8.

8. The method of claim 1, wherein the method is performed in the presence of a base. The reaction temperature with dichlorosulfoxide is 20-50 ℃, and the reaction temperature with alcohol is 30-60 ℃, and the reaction time is 0.5-6 h.

9. The method of claim 1, wherein the method is performed in the presence of a base. In step (2), the post-treatment is adding an extractant to the perfluoropolyether ester crude product, collecting the lower fluorine-containing organic phase after one extraction, adding sodium chloride aqueous solution to the lower fluorine-containing organic phase, collecting the lower layer after two extractions, and obtaining perfluoropolyether ester through reduced-pressure distillation; The extractant is saturated sodium carbonate aqueous solution or a mixed solution of fluorine-containing solvent 2 and pyridine aqueous solution, and the fluorine-containing solvent 2 is 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether or methyl nonafluorobutyl ether.

10. The method of claim 9, wherein the method is performed in the presence of a base. 10 The extractant is a mixed solution of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and pyridine aqueous solution, and the mass ratio of the perfluoropolyether carboxylic acid, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and pyridine aqueous solution is 1:1-3:1-5.

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