Controllable anionic polymerization of perfluoropolyether oils and methods of making the same

Abstract

The application belongs to the technical field of perfluoropolyether oil preparation, and particularly relates to a controllable anionic polymerization perfluoropolyether oil and a preparation method thereof. The preparation method of the controllable anionic polymerization perfluoropolyether oil comprises the following steps: adding a metal fluoride catalyst and an aprotic polar solvent into a reaction kettle, adding an end group fluorocarbon compound under cooling, and then introducing hexafluoropropylene oxide for reaction; continuously cooling, and then introducing hexafluoropropylene oxide for chain growth for the second time; and finally, performing fluorination reaction to obtain the perfluoropolyether oil. The application provides the preparation method of the controllable anionic polymerization perfluoropolyether oil, relies on the differences of different initiation end groups in initiation activity, steric hindrance and anti-chain transfer capacity, and cooperates with the mode of introducing hexafluoropropylene oxide in sections to realize the controllable synthesis of perfluoropolyether products with different molecular weights, and the actual number average molecular weight deviation of the obtained product is low; meanwhile, the overall preparation process is simple and does not need complex operation steps.

Description

Technical Field

[0001] This invention belongs to the field of perfluoropolyether oil preparation technology, specifically, it relates to a controllable anionic polymerized perfluoropolyether oil and its preparation method. Background Technology

[0002] Perfluoropolyethers (PFPEs) are linear polymers whose main molecular chain consists only of carbon, fluorine, and oxygen. They possess extremely low surface tension, excellent thermal stability, chemical inertness, non-flammability, and wide-temperature-range lubrication properties, making them irreplaceable special lubricants and functional materials in high-end equipment, aerospace, semiconductor, and precision manufacturing fields. Among them, K-type perfluoropolyether oils, obtained by anionic ring-opening polymerization of hexafluoropropylene oxide (HFPO, also known as perfluoropropylene oxide), are the most widely used due to their branched molecular chain structure, higher viscosity at the same molecular weight, and superior overall performance.

[0003] Depending on the degree of polymerization, K-type perfluoropolyether oils can be graded into low molecular weight products (typically n≈3-5) and high molecular weight products (n≈5-70 and above). These two types exhibit significant differences in performance and applications, requiring drastically different levels of precision in their preparation processes. Low molecular weight PFPE fluorinated oils have low viscosity, excellent fluidity and permeability, moderate volatility, outstanding low-temperature performance, and good insulation. Besides being suitable for micro-lubrication and corrosion protection in precision instruments, miniature bearings, and electronic components, they can also be used as high-end insulating coolants and temperature control media for precision equipment. Their molecular chains contain active acyl fluoride groups, making them easy to modify and prepare key intermediates such as fluorinated surfactants and fluorinated fine chemicals. High molecular weight PFPE fluorinated oils have high molecular chain regularity, significantly improved thermal stability, oxidation resistance, friction resistance, and aging resistance. They also exhibit excellent viscosity and film-forming properties, forming a stable lubricating protective film under extreme conditions such as high temperature, high vacuum, and strong corrosion. They are widely used in aerospace, semiconductor, and heavy-duty chemical equipment. A systematic study of the two types of fluorinated oils can enable the gradient preparation and rational selection of PFPE materials, solving the problem of the limitation of single fluorinated oils in suitable application scenarios.

[0004] Currently, HFPO-based K-type perfluoropolyether fluorinated oils have achieved initial industrialization. The industrial preparation of HFPO-based K-type perfluoropolyethers generally employs anionic polymerization initiation systems using alkali metal fluorides (typically cesium fluoride, CsF) in aprotic polar solvents (such as ethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether). This initiates the ring-opening polymerization of HFPO to generate oligomers containing acyl fluoride end groups. After end-group stabilization treatment, fluorinated oils meeting basic application scenarios such as low-to-mid-range lubrication and general equipment cooling are obtained. However, high-end products still heavily rely on imports, exhibiting significant technological shortcomings. The core challenge lies in the imbalance between high and low molecular weight product preparation control. Low molecular weight PFPE fluorinated oils are core raw materials for high-end cooling media and fine fluorochemical intermediates. Currently, the purity of these products is poor, and the polymerization reaction easily generates multi-component oligomer byproducts. Conventional distillation processes struggle to completely separate impurities, resulting in high volatility and insufficient insulation stability, severely limiting their application in high-end precision fields. High molecular weight PFPE fluorooils face the critical challenge of uncontrollable degree of polymerization. The chain growth stability during the polymerization process is poor, and phenomena such as premature termination and overpolymerization are prone to occur. This results in a wide molecular weight distribution of the product and large batch-to-batch performance differences, leading to insufficient film-forming properties and thermal stability of the product, making it unsuitable for the application requirements of aerospace, high-end semiconductor and other working conditions.

[0005] Patent CN115975168A discloses a method for controlled polymerization of hexafluoropropylene oxide at room temperature. This method uses an alkali metal fluoride, ether solvent, and carbonyl fluoride in a high-boiling-point fluorinated solvent to prepare an anionic initiator, which then initiates the polymerization of hexafluoropropylene oxide into a polymer. The advantages of this method are room-temperature polymerization, mild operating conditions, and easy solvent separation. However, as the chain lengthens, HFPO accumulates in the reaction system, increasing the viscosity. Although a fluorinated solvent is introduced, it only provides physical viscosity reduction and cannot suppress side reactions at the active chain ends. Furthermore, this method makes chain transfer more likely at the active chain ends, continuously generating new CF3O. - The continuous generation of a large number of short chains makes it difficult to control their molecular weight, resulting in a wider molecular weight distribution of the product and making it difficult to obtain high molecular weight perfluoropolyether products.

[0006] Patent CN121449876A discloses a production process for perfluoropolyether oil. The process involves activating a metal fluoride catalyst, an aprotic polar solvent, and a co-catalyst in a polymerization reactor. Hexafluoropropylene oxide is then added to prepare a perfluoropropylene oxide oligomer containing acyl fluoride end groups. The oligomer is then stabilized using a fluorinating agent. The resulting product is subjected to vacuum distillation and dehydration with an adsorbent to obtain the perfluoropolyether oil. This method improves the solubility of hexafluoropropylene oxide and the catalyst, increases the conversion rate of hexafluoropropylene oxide, and increases the product yield. However, during the subsequent fluorination process, a large number of CH bonds, benzimidazole aromatic rings, secondary amines, and ester groups in the co-catalyst molecule are easily destroyed by fluorination, generating a large amount of nitrogen- and oxygen-containing, difficult-to-remove fluorinated fragment impurities that interfere with product purity and thermal stability.

[0007] Patent CN105273178A discloses a method for preparing hexafluoropropylene oxide homopolymer. This method uses potassium fluoride as a catalyst to initiate the ring-opening polymerization of hexafluoropropylene oxide. A saturated solution of tetraethylene glycol dimethyl ether containing cesium fluoride and a fluorinated solvent is added in batches. The reaction temperature is gradually lowered to maintain the reactivity of the terminal groups of the hexafluoropropylene oxide homopolymer. Hexafluoropropylene oxide monomer is then added continuously. By controlling the number of additions of hexafluoropropylene oxide and cesium fluoride solution, a homopolymer with an average degree of polymerization of up to 50 can be synthesized. This method produces fluoropropylene oxide homopolymers and allows for control of the average degree of polymerization according to actual production requirements. However, it is only suitable for the polymerization of high-molecular-weight PFPE, and the reaction process is cumbersome, requiring repeated cycles of catalyst replenishment, cooling, feeding, and pressure stirring. Multiple additions of saturated cesium fluoride solution to the sealed reactor are necessary, requiring a high degree of anhydrous and oxygen-free protection of the system. It is also prone to introducing trace amounts of water vapor, resulting in poor batch stability. Furthermore, the repeated additions of catalyst solution continuously introduce new active initiation sites into the system, easily generating byproducts and resulting in a wide molecular weight distribution of the products.

[0008] Patent CN122404691A discloses a liquid catalyst for synthesizing high molecular weight K-type perfluoropolyethers and its preparation and use methods. This patent utilizes the coordination dissolution of alkali metal fluorides by a non-protic polar solvent, followed by reaction with perfluoroalkyl acyl fluorides or perfluoroalkyl epoxy compounds to synthesize the liquid catalyst. The liquid catalyst has a high content of effective active components and a large contact area with hexafluoropropylene oxide gas in subsequent reactions, resulting in a complete and uniform reaction. However, this method involves releasing the entire catalytic system midway and then filtering it, which may not only filter out a large amount of active cesium acyl fluoride salts but also increases the risk of moisture absorption upon contact with air. Highly active catalysts are prone to deactivation upon contact with moisture, making large-scale production operations difficult. Finally, the separation of catalyst preparation from the polymerization unit increases the risk of process steps and impurity introduction.

[0009] In summary, existing PFPE polymerization processes struggle to controllably prepare both low- and high-molecular-weight products. They generally suffer from difficulties in controlling the degree of polymerization, wide molecular weight distributions, complex operating procedures, and stringent requirements for anhydrous and oxygen-free conditions. Furthermore, some processes are prone to introducing impurities that negatively impact product quality. Therefore, developing a simple, gradient-polymerizable perfluoropolyether oil that produces high-purity and stable products is of significant practical importance. Summary of the Invention

[0010] The purpose of this invention is to overcome the aforementioned defects in the prior art and provide a method for preparing controllable anionic polymerized perfluoropolyether oil without the introduction of other substances. This method uses fluorocarbon end-groups with different carbon chain lengths as initiating end groups, combined with a segmented polymerization method involving the introduction of hexafluoropropylene oxide. By relying on the differences in initiation activity, steric hindrance, and anti-chain transfer ability of different initiating end groups, controllable synthesis of perfluoropolyether products with different molecular weights can be achieved, resulting in products with a narrow molecular weight distribution. At the same time, the overall preparation process is simple and does not require complex operating steps.

[0011] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing a controllable anionic polymerized perfluoropolyether oil includes the following steps: (1) The dehydrated metal fluoride catalyst and aprotic polar solvent are added to the reactor, and after cooling, terminal fluorocarbon compounds are added to initiate the chain. Then, hexafluoropropylene oxide is introduced and stirred to form an initiator. (2) Continue to lower the reaction temperature and introduce hexafluoropropylene oxide a second time to promote chain growth; (3) After the chain growth is completed, a fluorination reaction is carried out to obtain perfluorinated polyether oil.

[0012] When the number-average molecular weight of the perfluoropolyether oil is <3500 g / mol, the terminal fluorocarbon compound is one of carbamate fluoride or trifluoroacetyl fluoride; when the number-average molecular weight of the perfluoropolyether oil is 3500-6000 g / mol, the terminal fluorocarbon compound is pentafluoropropionyl fluoride; when the number-average molecular weight of the perfluoropolyether oil is >6000 g / mol, the terminal fluorocarbon compound is one of heptafluorobutyryl fluoride or heptafluoroisobutyryl fluoride; furthermore, the number-average molecular weight is the theoretical number-average molecular weight.

[0013] The metal fluoride catalyst is one of sodium fluoride (NaF), cesium fluoride (CsF), and potassium fluoride (KF).

[0014] The aprotic polar solvent is one of tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, acetonitrile, 15-crown ether-5, 21-crown ether-7, and 18-crown ether-6. Preferably, the aprotic polar solvent is one of tetraethylene glycol dimethyl ether, acetonitrile, and 18-crown ether-6.

[0015] The molar ratio of the terminal fluorocarbon compound to the metal fluoride catalyst is (1-1.5):1, and the amount of aprotic polar solvent is 5-30 times the mass of the metal fluoride catalyst; preferably, the molar ratio of the terminal fluorocarbon compound to the metal fluoride catalyst is 1:1.

[0016] The total amount of hexafluoropropylene oxide and the molar ratio of the terminal fluorocarbon compound are (3-50):1, and the flow rate of hexafluoropropylene oxide is 50-600 sccm; preferably, in step (1), the molar ratio of hexafluoropropylene oxide to the terminal fluorocarbon compound is 2:1.

[0017] In step (1), the reaction temperature is -5~25℃ and the reaction time is 1-3h, wherein the reaction time is calculated after the hexafluoropropylene oxide is introduced.

[0018] In step (2), the reaction temperature for chain growth is -40 to -20°C, and the reaction time is 1-3 hours. The reaction time is calculated after the hexafluoropropylene oxide is introduced.

[0019] In step (3), the specific process of the fluorination reaction is as follows: after the chain growth reaction is completed, post-processing is performed, and then the reaction liquid is transferred to the reaction vessel. F2 / N2 mixed gas is introduced at 80-200℃, and the perfluorinated polyether oil is obtained after fluorination reaction for 10-80h.

[0020] Preferably, the post-treatment can adopt conventional processes in the art. The post-treatment process parameters can be adjusted adaptively according to the different molecular weights of the obtained perfluoropolyethers. Specifically, for perfluoropolyether oils with a number average molecular weight ≤1000g / mol, the post-treatment process is as follows: after the chain growth reaction is completed, it is added dropwise to an equimolar amount of 20wt.% NaOH aqueous solution for alkalization to generate PFPE-COONa. Then, an equimolar amount of 20wt.% sulfuric acid aqueous solution is added. After being discharged, it is washed three times with an equimolar amount of 20wt.% sulfuric acid aqueous solution to generate PFPE-COOH. After standing and separating the liquid in the reactor, the lower layer material is transferred to the reaction vessel and fluorinated at 80-150℃ for 10-80h to complete the fluorination reaction. For perfluoropolyether oils with a number average molecular weight >1000 g / mol, the post-treatment process is as follows: the reaction solution after chain growth is completed is directly filtered, then the solvent is removed by separation, and then the material is directly added to the reactor and fluorinated at 150-200℃ for 10-80 h to complete the fluorination reaction.

[0021] A controllable anionic polymerizable perfluoropolyether oil is prepared by the above-described method; the general structural formula of the controllable anionic polymerizable perfluoropolyether oil is: ; Where m = 0-3, n = 1-70; preferably, the number average molecular weight is 500-900 g / mol.

[0022] In the preparation process of the controllable anionic polymerized perfluoropolyether oil of this invention, taking cesium fluoride as a catalyst as an example, the reaction mechanism involved is as follows: ; .

[0023] The anionic ring-opening polymerization of HFPO uses alkali metal fluorides as catalysts and terminal fluorocarbon compounds as initiators. The reaction consists of two main stages: chain initiation and chain propagation, accompanied by chain transfer and chain termination side reactions. Among these, α-fluorine elimination leads to the decomposition of the terminal alkoxide anion of the propagating chain into an acyl fluoride end group, releasing free fluorine. - Chain transfer is a core factor in regulating the degree of polymerization of a product. The steric hindrance of the initiator end groups directly determines the strength of chain transfer. Carbonyl fluoride has the least steric hindrance and the highest initiation activity, but chain transfer occurs very easily, resulting in a low degree of polymerization in the product. It is suitable for synthesizing low molecular weight perfluoropolyether oils. Trifluoroacetyl fluoride and pentafluoropropionyl fluoride have increasing steric hindrance as the end group carbon chain lengthens, and chain transfer is gradually suppressed, resulting in a corresponding increase in the degree of polymerization. They can be used to prepare products with low to medium degrees of polymerization. Heptafluorobutyryl fluoride and heptafluoroisobutyryl fluoride have branched, highly sterically hindered end groups, which can significantly enhance the α-fluorine elimination barrier and suppress chain transfer. Combined with low temperature and segmented feeding processes, perfluoropolyethers with high degree of polymerization and narrow molecular weight distribution can be obtained.

[0024] Preferably, the preparation method of the controllable anionic polymerized perfluoropolyether oil includes the following steps: (1) Add the dehydrated metal fluoride catalyst to the reactor, then add 5-20 times the mass of the metal fluoride catalyst and stir until homogeneous. Cool down to 0°C. Add the terminal fluorocarbon compound to carry out the chain initiation reaction according to the molar ratio of terminal fluorocarbon compound to metal fluoride catalyst of 1:1. Maintain the temperature at 5±5°C throughout the process. Then, pass HFPO with a flow rate of 300-500 sccm at a flow rate of 2 times the molar amount of terminal fluorocarbon compound. After the passage is completed, stir the reaction for 1-3 hours to form an initiator. (2) Continue to lower the reaction temperature to -30±5℃, and pass the remaining HFPO at a flow rate of 300-500 sccm to carry out chain growth. The molar ratio of total hexafluoropropylene oxide to terminal fluorocarbon compound is (3-50):1. Maintain the temperature at -30±5℃ for 1-3 hours throughout the reaction. (3) For perfluoropolyether oil with a number average molecular weight ≤1000g / mol, after the chain growth reaction is completed, it is added dropwise to an equimolar amount of 20wt.% NaOH aqueous solution for alkalization to generate PFPE-COONa, and then an equimolar amount of 20wt.% sulfuric acid aqueous solution is added. After the release, it is washed three times with an equimolar amount of 20wt.% sulfuric acid aqueous solution to generate PFPE-COOH. After standing and separating the liquid in the reactor, the lower layer material is transferred to the reactor. A 20% volume fraction of F2 / N2 mixed gas is introduced at 130℃ and fluorinated for 10-80h to obtain perfluoropolyether oil. For perfluoropolyether oils with a number average molecular weight >1000 g / mol, after the chain growth reaction is completed, the solvent is removed by filtration and separation, and the liquid is transferred to a reaction vessel. A 20% volume fraction of F2 / N2 mixed gas is introduced at 180°C, and fluorination is carried out for 10-80 h to obtain perfluoropolyether oil.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The preparation method of the controllable anionic polymerized perfluoropolyether oil of the present invention utilizes the differences in steric hindrance, nucleophilic activity and resistance to α-fluorine elimination chain transfer of different perfluoroacyl fluoride end groups to achieve polymerization control. The actual molecular weight of the product deviates little from the theoretical molecular weight, which can effectively suppress the problem of random chain breakage and generation of a large number of heterogeneous oligomers during the polymerization process, greatly reduce the separation load of distillation cutting, reduce separation operations, and obtain the target product, thus improving the problem of large performance fluctuations between batches.

[0026] (2) The preparation method of the controllable anionic polymerized perfluoropolyether oil of the present invention is simple. It only uses a non-protic polar solvent as the polymerization medium and relies on end-group fluorocarbon compounds, segmented temperature control, and two-stage introduction of hexafluoropropylene oxide to suppress side reactions. It does not require the introduction of fluorinated solvents, co-catalysts, etc., which reduces production costs, ensures product purity, and simplifies the post-processing process. Attached Figure Description

[0027] Figure 1 The GC-FID spectrum of the perfluoropolyether oil obtained in Example 2 of this invention is shown below. Figure 2 The product after chain growth in Embodiment 3 of the present invention 19 F-NMR nuclear magnetic resonance spectrum; Figure 3 The perfluoropolyether oil obtained in Example 4 of this invention 19 F-NMR nuclear magnetic resonance spectrum; Figure 4 The perfluoropolyether oil obtained in Example 5 of this invention 19 F-NMR nuclear magnetic resonance spectrum; Figure 5The infrared spectrum of the product after chain growth is completed in Embodiment 6 of the present invention; Figure 6 The infrared spectrum of the perfluoropolyether oil obtained in Example 6 of this invention; Figure 7 The perfluoropolyether oil obtained in Comparative Example 3 of this invention 19 F-NMR nuclear magnetic resonance spectrum. Detailed Implementation

[0028] The technical solution of the present invention will be further described below with reference to the embodiments and comparative examples. Unless otherwise specified, the raw materials used in the embodiments and comparative examples are all conventional commercial raw materials, and the process methods used are all conventional methods in the art unless otherwise specified.

[0029] In the embodiments and comparative examples, except for the actual number-average molecular weight of the final product, all other limitations related to number-average molecular weight and molar amount are theoretical calculation values.

[0030] Example 1 The method for preparing the controllable anionic polymerized perfluoropolyether oil includes the following steps: (1) Place 1 mol of dehydrated CsF catalyst in a reactor, then add 800 g of tetraethylene glycol dimethyl ether and stir evenly. Cool down to 0°C, add 1 mol of carbonyl fluoride to carry out chain initiation reaction, keep the temperature at 5±5°C throughout the process, then pass 2 mol of HFPO at a flow rate of 500 sccm, stir the reaction for 1 h to form an initiator. (2) Continue to lower the reaction temperature to -30±5℃, and pass the remaining HFPO at a flow rate of 500 sccm to carry out chain growth. The total amount of hexafluoropropylene oxide is 3 mol. The temperature is maintained at -30±5℃ throughout the process. After the HFPO is passed, the reaction is carried out for 1 h. (3) After the chain growth reaction is completed, it is added dropwise to an equimolar amount of 20wt.% NaOH aqueous solution to alkalize and generate PFPE-COONa. Then, an equimolar amount of 20wt.% sulfuric acid aqueous solution is added. After the reaction is released, it is washed three times with an equimolar amount of 20wt.% sulfuric acid aqueous solution to generate PFPE-COOH. After standing and separating the liquid in the reactor, the lower layer material is transferred to the reactor. A 20% volume fraction of F2 / N2 mixed gas is introduced at 130℃ and fluorinated for 15h to obtain perfluorinated polyether oil.

[0031] Example 2 The method for preparing the controllable anionic polymerized perfluoropolyether oil includes the following steps: (1) Place 1 mol of dehydrated NaF catalyst in a reactor, then add 800 g of tetraethylene glycol dimethyl ether and stir until homogeneous. Cool to 0°C, add 1 mol of trifluoroacetyl fluoride to initiate the chain reaction, and maintain the temperature at 5±5°C throughout the process. Then, pass 2 mol of HFPO at a flow rate of 500 sccm and stir for 2 h to form an initiator. (2) Continue to lower the reaction temperature to -30±5℃, and pass the remaining HFPO at a flow rate of 500 sccm to carry out chain growth. The total amount of hexafluoropropylene oxide is 3 mol. The temperature is maintained at -30±5℃ throughout the process. After the HFPO is passed, the reaction is carried out for 1 h. (3) After the chain growth reaction is completed, it is added dropwise to an equimolar amount of 20wt.% NaOH aqueous solution to alkalize and generate PFPE-COONa. Then, an equimolar amount of 20wt.% sulfuric acid aqueous solution is added. After the reaction is released, it is washed three times with an equimolar amount of 20wt.% sulfuric acid aqueous solution to generate PFPE-COOH. After standing and separating the liquid in the reactor, the lower layer material is transferred to the reactor. A 20% volume fraction of F2 / N2 mixed gas is introduced at 130℃ and fluorinated for 15h to obtain perfluorinated polyether oil.

[0032] The perfluoropolyether oil obtained in this embodiment was subjected to gas chromatography analysis. The perfluoropolyether oil obtained in this embodiment is a tetrameric fluorinated oil. The obtained GC-FID spectrum is shown below. Figure 1 , Figure 1 The corresponding gas chromatographic data are shown in Table 1. Figure 1 As shown in Table 1, the peak area of ​​the target tetramer fluorinated oil in the product accounts for 99.595%, and the proportion of impurity peaks is low, indicating that high-purity tetramer perfluorinated polyether oil was prepared in this embodiment.

[0033] Table 1 Gas Chromatography Data of Perfluoropolyether Oil in Example 2

[0034] Example 3 The method for preparing the controllable anionic polymerized perfluoropolyether oil includes the following steps: (1) Place 1 mol of dehydrated CsF catalyst in a reactor, then add 800 g of acetonitrile and stir until homogeneous. Cool to 0°C, add 1 mol of pentafluoropropionyl fluoride to carry out chain initiation reaction, and maintain the temperature at 5±5°C throughout the process. Then, pass 2 mol of HFPO at a flow rate of 500 sccm and stir for 1 h to form an initiator. (2) Continue to lower the reaction temperature to -30±5℃, and pass the remaining HFPO at a flow rate of 300sccm to carry out chain growth. The total amount of hexafluoropropylene oxide is 30mol. The temperature is maintained at -30±5℃ throughout the process. After the HFPO is passed, the reaction is carried out for 1h. (3) After the chain growth reaction is completed, the solvent is removed by filtration and separation. The liquid is then transferred to the reactor and a 20% volume F2 / N2 mixture is introduced at 180°C. Fluorination is carried out for 20 hours to obtain perfluorinated polyether oil.

[0035] Take the material that has not yet undergone fluorination treatment after the chain growth is completed in this embodiment. 19 F-NMR nuclear magnetic resonance characterization, spectrum as follows Figure 2 .

[0036] Example 4 The method for preparing the controllable anionic polymerized perfluoropolyether oil includes the following steps: (1) Place 1 mol of dehydrated KF catalyst in a reactor, then add 800 g of tetraethylene glycol dimethyl ether and stir until homogeneous. Cool down to 0°C, add 1 mol of heptafluorobutyryl fluoride to carry out chain initiation reaction, and maintain the temperature at 5±5°C throughout the process. Then, pass 2 mol of HFPO at a flow rate of 500 sccm and stir the reaction for 3 h to form an initiator. (2) Continue to lower the reaction temperature to -30±5℃, and introduce the remaining HFPO at a flow rate of 300sccm for chain growth. The total amount of hexafluoropropylene oxide is 50mol. The temperature is maintained at -30±5℃ throughout the process, and the reaction is carried out for 3h. (3) After the chain growth reaction is completed, the solvent is removed by filtration and separation. The liquid is then transferred to the reactor and a 20% volume F2 / N2 mixture is introduced at 180°C. Fluorination is carried out for 80 hours to obtain perfluorinated polyether oil.

[0037] The perfluorinated polyether oil obtained in the final fluorination of this embodiment was subjected to... 19 F-NMR characterization, spectrum shown in [reference needed] Figure 3 .

[0038] Example 5 The method for preparing the controllable anionic polymerized perfluoropolyether oil includes the following steps: (1) Place 1 mol of dehydrated CsF catalyst in a reactor, then add 800 g of 18-crown ether-6 and stir until homogeneous. Cool down to 0°C and add 1 mol of heptafluoroisobutyryl fluoride to initiate the chain reaction. Maintain the temperature at 5±5°C throughout the process. Then, pass 2 mol of HFPO at a flow rate of 500 sccm and stir for 1 h to form an initiator. (2) Continue to lower the reaction temperature to -30±5℃, and introduce the remaining HFPO at a flow rate of 300sccm for chain growth. The total amount of hexafluoropropylene oxide is 50mol. The temperature is maintained at -30±5℃ throughout the process, and the reaction is carried out for 2.5h. (3) After the chain growth reaction is completed, the solvent is removed by filtration and separation. The liquid is then transferred to the reactor and a 20% volume F2 / N2 mixture is introduced at 180°C. Fluorination is carried out for 80 hours to obtain perfluorinated polyether oil.

[0039] The perfluorinated polyether oil obtained in the final fluorination of this embodiment was subjected to... 19 F-NMR characterization, spectrum shown in [reference needed] Figure 4 .

[0040] Example 6 The method for preparing the controllable anionic polymerized perfluoropolyether oil includes the following steps: (1) Place 1 mol of dehydrated NaF catalyst in a reactor, then add 800 g of acetonitrile and stir until homogeneous. Cool down to 0°C, add 1 mol of heptafluoroisobutyryl fluoride to carry out chain initiation reaction, and maintain the temperature at 5±5°C throughout the process. Then, pass 2 mol of HFPO at a flow rate of 500 sccm and stir for 2 h to form an initiator. (2) Continue to lower the reaction temperature to -30±5℃, and introduce the remaining HFPO at a flow rate of 400sccm for chain growth. The total amount of hexafluoropropylene oxide is 35mol. The temperature is maintained at -30±5℃ throughout the process, and the reaction is carried out for 2h. (3) After the chain growth reaction is completed, the solvent is removed by filtration and separation. The liquid is then transferred to the reactor and a 20% volume F2 / N2 mixture is introduced at 180°C. Fluorination is carried out for 40 hours to obtain perfluorinated polyether oil.

[0041] Infrared analysis was performed on the PFPE acyl fluoride and perfluoropolyether oil products before and after fluorination in this embodiment. The obtained infrared spectra are shown below. Figures 5-6 Through comparison of the spectra, it was found that Figure 5 The 1884 cm corresponding to PFPE acyl fluoride -1 The characteristic peak of C=O at fluorination ( Figure 6 The disappearance of the PFPE acyl fluoride indicates that the fluorination end-capping process has been completed to obtain perfluoropolyether oil.

[0042] Example 7 The method for preparing the controllable anionic polymerized perfluoropolyether oil includes the following steps: (1) Place 1 mol of dehydrated CsF catalyst in a reactor, then add 800 g of tetraethylene glycol dimethyl ether and stir until homogeneous. Cool down to 0°C, add 1 mol of trifluoroacetyl fluoride to initiate the chain reaction, and maintain the temperature at 5±5°C throughout the process. Then, pass 2 mol of HFPO at a flow rate of 500 sccm and stir for 1 h to form an initiator. (2) Continue to lower the reaction temperature to -30±5℃, and introduce the remaining HFPO at a flow rate of 400sccm for chain growth. The total amount of hexafluoropropylene oxide is 20mol. The temperature is maintained at -30±5℃ throughout the process, and the reaction is carried out for 1h. (3) After the chain growth reaction is completed, the solvent is removed by filtration and separation. The liquid is then transferred to the reactor and a 20% volume F2 / N2 mixture is introduced at 180°C. Fluorination is carried out for 30 hours to obtain perfluorinated polyether oil.

[0043] Example 8 The method for preparing the controllable anionic polymerized perfluoropolyether oil includes the following steps: (1) Place 1 mol of dehydrated KF catalyst in a reactor, then add 800 g of tetraethylene glycol dimethyl ether and stir until uniform. Cool down to 0°C, add 1 mol of pentafluoropropionyl fluoride to carry out chain initiation reaction, and maintain the temperature at 5±5°C throughout the process. Then, pass 2 mol of HFPO at a flow rate of 500 sccm and stir the reaction for 1 h to form an initiator. (2) Continue to lower the reaction temperature to -30±5℃, and pass the remaining HFPO at a flow rate of 300sccm to carry out chain growth. The total amount of hexafluoropropylene oxide is 20mol. The temperature is maintained at -30±5℃ throughout the process. After the HFPO is passed, the reaction is carried out for 1h. (3) After the chain growth reaction is completed, the solvent is removed by filtration and separation. The liquid is then transferred to the reactor and a 20% volume F2 / N2 mixture is introduced at 180°C. Fluorination is carried out for 20 hours to obtain perfluorinated polyether oil.

[0044] Example 9 The method for preparing the controllable anionic polymerized perfluoropolyether oil includes the following steps: (1) Place 1 mol of dehydrated CsF catalyst in a reactor, then add 800 g of tetraethylene glycol dimethyl ether and stir until homogeneous. Cool down to 0°C, add 1 mol of pentafluoropropionyl fluoride to carry out chain initiation reaction, keep the temperature at 5±5°C throughout the process, then pass 2 mol of HFPO at a flow rate of 500 sccm and stir for 1 h to form an initiator. (2) Continue to lower the reaction temperature to -30±5℃, and pass the remaining HFPO at a flow rate of 300sccm to carry out chain growth. The total amount of hexafluoropropylene oxide is 35mol. The temperature is maintained at -30±5℃ throughout the process. After the HFPO is passed, the reaction is carried out for 1h. (3) After the chain growth reaction is completed, the solvent is removed by filtration and separation. The liquid is then transferred to the reactor and a 20% volume F2 / N2 mixture is introduced at 180°C. Fluorination is carried out for 20 hours to obtain perfluorinated polyether oil.

[0045] Comparative Example 1 This comparative example differs from Example 7 in that no terminal fluorocarbon compound is added, while the rest of the process and raw material amounts are the same as in Example 7.

[0046] Comparative Example 2 This comparative example differs from Example 5 in that the terminal fluorocarbon compound is changed from heptafluoroisobutyryl fluoride to carbonyl fluoride, while the rest of the process and raw material amounts are the same as in Example 5.

[0047] Comparative Example 3 This comparative example differs from Example 3 in that hexafluoropropylene oxide is added all at once, while the rest of the process and raw material amounts are the same as in Example 3. The perfluoropolyether oil finally obtained through fluorination in this comparative example was subjected to... 19 F-NMR nuclear magnetic resonance characterization, spectrum as follows Figure 7 .

[0048] Comparative Example 4 The difference between this comparative example and Example 5 is that the terminal fluorocarbon compound was changed from heptafluoroisobutyryl fluoride to carbonyl fluoride, and a fluorinated solvent (hexafluoropropylene dimer) was added between the initiation and polymerization stages. The rest of the process and the amount of raw materials were the same as in Example 5.

[0049] The products obtained in the above embodiments and comparative examples were subjected to... 19 F-NMR analysis, such as Figures 2-4 and Figure 7 As shown, the group assignments corresponding to each chemical shift are as follows: the multiplet at chemical shifts -91.0 to -81.0 represents the absorption peaks of the CF single bonds in the -CF3 and C-CF2-O groups of the product molecule; the singlet at -132.2 to -131.1 represents the absorption peaks of the CF single bonds in the C-CF2-C groups of the product molecule, and its absorption peak area is denoted as A; the singlet at -132.9 to -132.0 represents the absorption peaks of the CF single bonds in the terminal O-CF-COF groups of the product molecule, and its absorption peak area is denoted as B; the multiplet at -147.5 to -146.7 represents the absorption peaks of the CF single bonds in the repeating unit C-CF-O groups of the product molecule, and its absorption peak area is denoted as C. The actual number-average molecular weight is: M. n =2+C / B=2+C / (A / 2), that is, there exists a relationship A=2B.

[0050] For uncapped PFPE acyl fluoride intermediates after chain growth, the NMR spectrum will show obvious characteristic double peaks between -133 and -131. The active end group integral B can be directly used to calculate M. n =2+C / B to calculate the actual number-average molecular weight of the sample; For the fluorinated polyether oil product, since the -CF-COF end group is fluorinated, there is no absorption peak in the range of -132.9 to -132.0. Therefore, M can be calculated using the relationship between A and B. n ; The formula for calculating the theoretical number-average molecular weight of the product is shown below: ; The formula for calculating the deviation rate is as follows: ; In the above calculation formula, M 端 n 端 The molecular weight and molar amount of the terminal fluorocarbon compound; M HFPO n HFPO Here are the molecular weight and molar amount of HFPO; n 催 The molar amount is the metal fluoride catalyst. The product parameters obtained from the above examples and comparative examples are shown in Table 2 below.

[0051] Table 2 Product parameters for examples and comparative examples

[0052] As shown in Examples 1-9 of Table 2, the hexafluoropropylene oxide polymerization method provided in this application can effectively control the degree of polymerization of the hexafluoropropylene oxide polymer, ensuring that the number-average molecular weight deviation is within 2%. Although the introduction of end-group fluorocarbon compounds causes a change in the PFPE structure, it only alters the length of the end-group carbon chain without introducing other atoms or groups. In the low molecular weight region, the carbon chain length of PFPE can be effectively controlled, and 99% high-purity oligomer PFPE can be obtained through simple purification.

[0053] For high molecular weight PFPE, appropriate end-group fluorocarbon compounds can be used, and the chain length of PFPE can be effectively controlled by adjusting the amount of HFPO added.

[0054] In contrast, Comparative Example 1 used a conventional method to polymerize PFPE without adding end-group fluorocarbons. The actual number-average molecular weight of the resulting PFPE was 24% lower than the theoretical number-average molecular weight. This is because the method first catalytically isomerizes HFPO to pentafluoropropionyl fluoride, and then continuously introduces HFPO to initiate chain growth. The polymerization process is prone to α-fluorine elimination chain transfer side reactions, generating a large number of short-chain products, which leads to a decrease in its actual number-average molecular weight.

[0055] In the comparative example, the terminal fluorocarbon compound was changed from heptafluoroisobutyryl fluoride to carbonyl fluoride for PFPE polymer synthesis. Due to the minimal steric hindrance and highest initiation activity of carbonyl fluoride, chain transfer was very easy to occur, resulting in a low degree of polymerization of the product. The final actual number average molecular weight was 43.58% lower than the theoretical number average molecular weight.

[0056] Comparative Example 3 used a one-time addition polymerization method with hexafluoropropylene oxide, and the other conditions were kept the same as in Example 3. The actual number-average molecular weight of the product was 22.85% lower than the theoretical number-average molecular weight. One-time addition of HFPO can cause excessively high local monomer concentrations in the early stage of the reaction, which can aggravate the α-fluorine elimination chain transfer side reaction, easily generate a large number of short-chain components, broaden the molecular weight distribution of the product, and make it impossible to control the molecular weight.

[0057] In Comparative Example 4, the introduction of fluorocarbon solvents into the polymerization system can alleviate the viscosity problem and improve the molecular weight deviation to a certain extent, but the actual number-average molecular weight of the product is still 17.28% lower than the theoretical number-average molecular weight. At the same time, fluorocarbon solvents have defects such as high GWP, high waste liquid treatment cost, increased product separation difficulty, and decreased process stability, making it difficult to industrialize production.

Claims

1. A method for preparing a controllable anionic polymerized perfluoropolyether oil, characterized in that, Includes the following steps: (1) The dehydrated metal fluoride catalyst and aprotic polar solvent are added to the reactor, and after cooling, terminal fluorocarbon compounds are added to initiate the chain. Then, hexafluoropropylene oxide is introduced and stirred to form an initiator. (2) Continue to lower the reaction temperature and introduce hexafluoropropylene oxide a second time to promote chain growth; (3) After the chain growth is completed, a fluorination reaction is carried out to obtain perfluorinated polyether oil; When the number-average molecular weight of the perfluoropolyether oil is <3500 g / mol, the terminal fluorocarbon compound is one of carbamate fluoride or trifluoroacetyl fluoride; when the number-average molecular weight of the perfluoropolyether oil is 3500-6000 g / mol, the terminal fluorocarbon compound is pentafluoropropionyl fluoride; when the number-average molecular weight of the perfluoropolyether oil is >6000 g / mol, the terminal fluorocarbon compound is one of heptafluorobutyryl fluoride or heptafluoroisobutyryl fluoride.

2. The method for preparing the controllable anionic polymerized perfluoropolyether oil according to claim 1, characterized in that, The metal fluoride catalyst is one of sodium fluoride, cesium fluoride, or potassium fluoride.

3. The method for preparing the controllable anionic polymerized perfluoropolyether oil according to claim 1, characterized in that, The aprotic polar solvent is one of tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, acetonitrile, 15-crown ether-5, 21-crown ether-7, and 18-crown ether-6.

4. The method for preparing the controllable anionic polymerized perfluoropolyether oil according to claim 1, characterized in that, The molar ratio of the terminal fluorocarbon compound to the metal fluoride catalyst is (1-1.5):1, and the amount of aprotic polar solvent is 5-30 times the mass of the metal fluoride catalyst.

5. The method for preparing the controllable anionic polymerized perfluoropolyether oil according to claim 1, characterized in that, The molar ratio of total hexafluoropropylene oxide to terminal fluorocarbon compounds is (3-50):1, and the flow rate of hexafluoropropylene oxide is 50-600 sccm.

6. The method for preparing the controllable anionic polymerized perfluoropolyether oil according to claim 1, characterized in that, In step (1), the reaction temperature is -5~25℃ and the reaction time is 1-3h.

7. The method for preparing the controllable anionic polymerized perfluoropolyether oil according to claim 1, characterized in that, In step (2), the reaction temperature for chain growth is -40 to -20°C, and the reaction time is 1-3 hours.

8. The method for preparing the controllable anionic polymerized perfluoropolyether oil according to claim 1, characterized in that, In step (3), the specific process of the fluorination reaction is as follows: after the chain growth reaction is completed, post-processing is performed, and then the reaction liquid is transferred to the reaction vessel. F2 / N2 mixed gas is introduced at 80-200℃, and the perfluorinated polyether oil is obtained after fluorination reaction for 10-80h.

9. A controllable anionic polymerized perfluoropolyether oil, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

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