Preparation method of perfluoroether rubber

Abstract

The preparation method of the perfluoroether rubber comprises the following steps: mixing a solvent, a pH regulator, a cosolvent and an emulsifier to obtain a mixed solution, adding an initial mixed monomer and an initiator into the mixed solution to carry out emulsion polymerization reaction, continuously adding and supplementing the mixed monomer in the emulsion polymerization reaction process to maintain the reaction pressure constant, and after the polymerization reaction is finished, obtaining an emulsion, and carrying out post-treatment on the emulsion to obtain the perfluoroether rubber. The initial mixed monomer comprises tetrafluoroethylene and perfluoroalkyl vinyl ether; the supplemented mixed monomer comprises tetrafluoroethylene, perfluoroalkyl vinyl ether and an iodine-containing vulcanization site monomer; the cosolvent comprises one or two of perfluorobutyl tetrahydrofuran and perfluoro (tetradecahydrophenanthrene); the initiator includes a diacyl peroxide. According to the preparation method provided by the invention, the added cosolvent and initiator cooperate with each other, so that the pressure and temperature required by the emulsion polymerization of the perfluoroether rubber can be greatly reduced, and the batch stability of the perfluoroether rubber is improved.

Description

Technical Field

[0001] The invention relates to the technical field of perfluoroether rubber, and in particular to a method for preparing perfluoroether rubber. Background Art

[0002] Perfluoroether rubber has been widely made into O-rings, valve stem seals, shaft seals, gaskets and other products due to its excellent heat resistance, chemical resistance and permeation resistance. These products are used in various fields with harsh application conditions.

[0003] At present, perfluoroether rubber is generally prepared by emulsion polymerization under high temperature and high pressure conditions. For example, Chinese patent CN104530292 discloses a method for preparing low-temperature resistant perfluoroether rubber under the conditions of 70-125°C and 2.0-4.5MPa. Patent CN117946316A discloses a method for preparing high-temperature resistant perfluoroether rubber under the conditions of 85-90°C and 2.5-3MPa.

[0004] However, in the emulsion polymerization process of perfluoroether rubber, the comonomer perfluoroalkyl vinyl ether used is prone to uncontrollable free radical rearrangement reaction at a polymerization temperature higher than 70°C. The free radical rearrangement may lead to an increase in chain transfer reactions during the polymerization reaction, forming short-chain molecules, which reduces the molecular weight of the polymer; the free radical rearrangement may also produce new active sites, which can trigger new chain growth reactions, thereby forming branches, resulting in an increase in the degree of branching. Because the free radical rearrangement is uncontrollable, the location and length of the branching also become unpredictable. Unlike the relatively regular branching under normal polymerization conditions, this abnormal reaction will make the branching unevenly distributed on the molecular chain. Some molecules may have more branches, while others have very few, resulting in an increase in the difference in the degree of branching between molecules, which in turn affects the batch stability of perfluoroether rubber.

[0005] In addition, higher polymerization pressure places higher requirements on the equipment used in emulsion polymerization and is prone to cause safety accidents during the polymerization process, which has an adverse impact on the large-scale production of perfluoroether rubber. Summary of the invention

[0006] In view of the problems that the existing emulsion polymerization method for preparing perfluoroether rubber has high reaction temperature affecting the batch stability of perfluoroether rubber and high reaction pressure having high requirements on equipment, the present application provides a method for preparing perfluoroether rubber.

[0007] The present invention provides a method for preparing perfluoroether rubber, comprising the following steps: A solvent, a pH regulator, a cosolvent and an emulsifier are mixed to obtain a mixed solution, an initial mixed monomer and an initiator are added to the mixed solution to carry out an emulsion polymerization reaction, additional mixed monomers are continuously added during the emulsion polymerization reaction to maintain a constant reaction pressure, an emulsion is obtained after the polymerization reaction is completed, and the emulsion is post-treated to obtain the perfluoroether rubber; The initial mixed monomers include tetrafluoroethylene and perfluoroalkyl vinyl ether; The additional mixed monomers include tetrafluoroethylene, perfluoroalkyl vinyl ether and iodine-containing vulcanization site monomers; The cosolvent includes one or two of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene); The initiator includes a diacyl peroxide.

[0008] Preferably, the cosolvent is perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene), The mass ratio of perfluorobutyltetrahydrofuran to perfluoro(tetradecahydrophenanthrene) is 1:(1-5); The mass ratio of the co-solvent to the solvent is (5-30):100.

[0009] Preferably, the mass ratio of the initiator to the solvent is (0.00025-0.4):100.

[0010] Preferably, the diacyl peroxide comprises CF3CH2CH2CF2(CO)OO(CO)CF2CH2CH2CF3; And / or, the pH adjuster is selected from one or more of ammonium carbonate, ammonium bicarbonate, dipotassium hydrogen phosphate, and disodium hydrogen phosphate, and the added amount of the pH adjuster is 0.01% to 0.5% of the mass of the solvent.

[0011] Preferably, the reaction temperature of the emulsion polymerization reaction is 30-50° C., and the reaction pressure is 0.5-1 MPa.

[0012] Preferably, in the initial mixed monomers, the molar ratio of tetrafluoroethylene to perfluoroalkyl vinyl ether is (30-50): (50-70).

[0013] Preferably, in the additional mixed monomer, the molar ratio of the tetrafluoroethylene, the perfluoroalkyl vinyl ether and the iodine-containing sulfurization site monomer is (60-70): (25-40): (1-2); And / or, the iodine-containing vulcanization site monomer includes one or more of perfluoroiodoethyl vinyl ether, perfluoro-4-iodo-1-butene, trifluoroiodoethylene, and I-(CF2)2OCF=CF2.

[0014] Preferably, the emulsifier is a perfluoropolyether carboxylate, and the mass ratio of the emulsifier to the solvent is (0.0025-1.25):100; And / or, the perfluoropolyether carboxylate comprises ammonium perfluoropolyether carboxylate.

[0015] Preferably, the solid content of the emulsion is 20% to 30%; The post-treatment of the emulsion to obtain the perfluoroether rubber comprises the following steps: The emulsion is sequentially subjected to coagulation, washing and drying to obtain the perfluoroether rubber; The drying temperature is 95-105°C.

[0016] Preferably, the solvent is deionized water, and the resistivity of the deionized water is ≥18MΩ·m; The perfluoroalkyl vinyl ether includes a compound represented by Formula 1, CF2=CFOR1, Formula 1 Wherein, R1 is selected from a C1~C5 perfluoroalkyl group.

[0017] The present application provides a method for preparing perfluoroether rubber, wherein the cosolvent comprises one or two of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene), and the initiator comprises diacyl peroxide. The added cosolvent and initiator can synergistically greatly reduce the pressure and temperature required for the emulsion polymerization of the perfluoroether rubber, and can achieve emulsion polymerization at a temperature below 70°C, thereby avoiding uncontrollable free radical rearrangement reaction of the monomer perfluoroalkyl vinyl ether and improving the batch stability of the perfluoroether rubber; at the same time, the reaction pressure is low, which reduces the requirements for equipment and improves the safety of the polymerization process. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0019] In order to illustrate the technical solution of the present invention, specific embodiments are provided below for illustration.

[0020] In one embodiment of the present invention, a method for preparing perfluoroether rubber comprises the following steps: A solvent, a pH regulator, a cosolvent and an emulsifier are mixed to obtain a mixed solution, an initial mixed monomer and an initiator are added to the mixed solution to carry out an emulsion polymerization reaction, additional mixed monomers are continuously added during the emulsion polymerization reaction to maintain a constant reaction pressure, an emulsion is obtained after the polymerization reaction is completed, and the emulsion is post-treated to obtain the perfluoroether rubber; The initial mixed monomers include tetrafluoroethylene and perfluoroalkyl vinyl ether; The additional mixed monomers include tetrafluoroethylene, perfluoroalkyl vinyl ether and iodine-containing vulcanization site monomers; The cosolvent includes one or two of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene); The initiator includes a diacyl peroxide.

[0021] Specifically, the solvent has the functions of a dispersing cosolvent, an emulsifier, and a pH regulator. The emulsifier increases the solubility of the gas phase monomer in the reaction system, ensures that the produced polymer can be evenly dispersed in the system, and maintains the stability of the emulsion during the polymerization process.

[0022] During the reaction, the mixed monomer is continuously added to maintain the reaction pressure constant so that the reaction temperature and reaction pressure are maintained within a certain range, thereby promoting the emulsion polymerization reaction, making the polymerization reaction more controllable and the obtained product more uniform.

[0023] Tetrafluoroethylene is the main component of the main chain of perfluoroether rubber. Its large amount of polymerization forms the basic skeleton of the rubber molecule, giving the rubber a certain strength and stability, making the perfluoroether rubber have better physical and mechanical properties, while improving the chemical stability of the perfluoroether rubber.

[0024] Perfluoroalkyl vinyl ether is a branched monomer. Its perfluoroalkyl group has a large spatial volume and low surface energy, which can increase the distance between molecular chains and reduce the intermolecular forces, thereby providing better flexibility and elasticity for the rubber molecular chain. The perfluoroether rubber has good chemical corrosion resistance while also having elasticity and flexibility similar to ordinary rubber, and can maintain good sealing performance under different temperature and pressure conditions.

[0025] Iodine-containing vulcanization site monomers can introduce active vulcanizable sites during the polymerization reaction. These sites can react chemically with the vulcanizing agent during the vulcanization process to form cross-linked bonds, thereby transforming the linear rubber molecular chain into a three-dimensional network structure, giving the perfluoroether rubber good elasticity and strength.

[0026] The cosolvent used is a mixed solution of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene), which has the following effects: first, the cosolvent has the characteristics of low surface tension and low dielectric constant, which can make the initial mixed monomers and the additional mixed monomers dispersed better in the solution, forming smaller and more uniform emulsion particles, increasing the number of micelles and improving the reaction efficiency; second, the cosolvent can effectively reduce the viscosity of the reaction system. In emulsion polymerization, the lower viscosity is conducive to the diffusion and collision of the initial mixed monomers, the additional mixed monomers and the initiator, making the reaction easier to proceed; third, the solubility of the reaction gas in the liquid phase can be increased, thereby increasing the reaction speed.

[0027] The initiator includes diacyl peroxide, which has the following effects: First, compared with other initiators, diacyl peroxide has a lower decomposition temperature and higher initiation efficiency, which means that it can generate enough free radicals to initiate the polymerization reaction at a relatively low temperature, thereby reducing the temperature required for the polymerization reaction.

[0028] The present application provides a method for preparing perfluoroether rubber, wherein the cosolvent comprises one or two of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene), and the initiator comprises diacyl peroxide. The added cosolvent and initiator can synergistically greatly reduce the pressure and temperature required for the emulsion polymerization of the perfluoroether rubber, and can achieve emulsion polymerization at a temperature below 70°C, thereby avoiding uncontrollable free radical rearrangement reaction of the monomer perfluoroalkyl vinyl ether and improving the batch stability of the perfluoroether rubber; at the same time, the reaction pressure is low, which reduces the requirements for equipment and improves the safety of the polymerization process.

[0029] The specific principle of the co-solvent and the initiator synergistically reducing the temperature and pressure required for the emulsion polymerization of perfluoroether rubber is as follows: emulsion polymerization is controlled by mass transfer and heat transfer. In the emulsion polymerization of perfluoroether rubber, the comonomer is a gas, and the reaction site is in the liquid phase. The solubility of the gas in the liquid phase increases with the increase of the gas pressure, so high pressure is required to increase the mass transfer capacity. The effect of the above-mentioned co-solvent increases the mass transfer capacity of the emulsion polymerization. Therefore, the use of the co-solvent mentioned in the present invention can make the emulsion polymerization proceed under low pressure. In general perfluoroether rubber emulsion polymerization, inorganic peroxides such as ammonium persulfate are generally used as initiators. The initiator needs to be at a higher temperature to obtain a satisfactory free radical generation rate. The generation rate of the initiator will affect the reaction time. The initiator used in the present invention can have a faster free radical generation rate at a lower temperature. At the same time, compared with high temperature, at low temperature, the solubility of the reaction gas in the liquid phase is higher, which further improves the mass transfer effect. The combination of the two offsets the effect of the reaction monomer collision number reduction at low temperature on the reaction, thereby realizing the emulsion polymerization of perfluoroether rubber under low temperature and low pressure conditions.

[0030] In some embodiments, the co-solvent is perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene), The mass ratio of perfluorobutyltetrahydrofuran to perfluoro(tetradecahydrophenanthrene) is 1:(1-5).

[0031] Specifically, in a preferred embodiment, the co-solvent is perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene), and the mass ratio of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene) in the co-solvent added at the same time is 1:(1-5), which is beneficial to reduce the viscosity of the reaction system, promote the diffusion and collision of the initial mixed monomers, the additional mixed monomers and the initiator, and make the reaction easier to proceed.

[0032] Specifically, the mass ratio of perfluorobutyltetrahydrofuran to perfluoro(tetradecahydrophenanthrene) can be 1:1, 1:2, 1:3, 1:4, 1:5, etc., as long as the mass ratio of perfluorobutyltetrahydrofuran to perfluoro(tetradecahydrophenanthrene) is within the range of 1: (1~5).

[0033] In some preferred embodiments, the mass ratio of perfluorobutyltetrahydrofuran to perfluoro(tetradecahydrophenanthrene) is 1:(2-3); within this preferred range, it is more conducive to reducing the viscosity of the reaction system, and the material transfer resistance is also smaller, which is more conducive to the initial mixed monomers and the additional mixed monomers to carry out emulsion polymerization under lower temperature conditions and the action of an initiator.

[0034] In some embodiments, the mass ratio of the co-solvent to the solvent is (5-30): 100 Specifically, limiting the mass ratio of the co-solvent to the solvent to (5-30):100 helps reduce the viscosity of the mixed solution, accelerates the diffusion rate of the monomer and the initiator in the reaction system, and facilitates the collision between them, so that the polymerization reaction can be carried out at a lower temperature.

[0035] The mass ratio of the co-solvent to the solvent can be 5:100, 10:100, 12:100, 15:100, 18:100, 20:100, 23:100, 25:100, 30:100, etc., as long as the mass ratio of the co-solvent to the solvent is within the range of (5~30):100.

[0036] It should be noted that the type and amount of the co-solvent mainly affect the rate of the polymerization reaction. Compared with the co-solvent being perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene), within the same reaction time, the co-solvent is selected from perfluorobutyltetrahydrofuran or perfluoro(tetradecahydrophenanthrene), and the yield of the generated perfluoroether rubber is low.

[0037] Similarly, the amount of co-solvent added affects the rate of the polymerization reaction. If the amount of co-solvent added is too little, the yield of the generated perfluoroether rubber will be extremely low within the same reaction time; if the amount of co-solvent added is too much, the improvement in the polymerization reaction rate will not be obvious, and the cost and separation difficulty will increase.

[0038] In some preferred embodiments, the mass ratio of the co-solvent to the solvent is (10-20): 100. When the mass ratio of the co-solvent to the solvent is in the range of (10-20): 100, it is more conducive to reducing the viscosity of the mixed solution, accelerating the collision of the monomers tetrafluoroethylene, perfluoroalkyl vinyl ether and iodine-containing sulfurization site monomers, and increasing the reaction rate, so that the emulsion polymerization reaction can be initiated at a lower temperature.

[0039] In some embodiments, the mass ratio of the initiator to the solvent is (0.00025-0.4):100.

[0040] Specifically, the mass ratio of the initiator to the solvent is in the range of (0.00025~0.4):100. In the emulsion polymerization reaction, the initiator decomposes to generate free radicals that react with tetrafluoroethylene, perfluoroalkyl vinyl ether, and sulfurization site monomers to initiate a chain growth reaction, thereby starting the polymerization reaction. If the amount of initiator added is too much, the number of decomposed free radicals is too large, the reaction is not easy to control and is prone to violent polymerization. At the same time, the product has a wide molecular weight distribution and a low molecular weight, which does not meet the requirements. If the amount of initiator added is too little, the polymerization reaction rate decreases, reducing production efficiency. The mass ratio of the initiator to the solvent can be in the following ranges: (0.00025~0.001):100, (0.00125~0.01):100, (0.001~0.1):100, (0.1~0.25):100, (0.25~0.3):100 or (0.3~0.4):100.

[0041] In some preferred embodiments, the mass ratio of the initiator to the solvent is (0.00125-0.25): 100. The mass ratio of the initiator to the solvent in the range of (0.00125-0.25): 100 is conducive to the control of the emulsion polymerization, and the obtained perfluoroether rubber has a uniform molecular weight, a fast reaction rate, good mechanical properties, good flexibility, chemical resistance and high temperature resistance.

[0042] In some embodiments, the diacyl peroxide includes CF3CH2CH2CF2(CO)OO(CO)CF2CH2CH2CF3, which is more conducive to initiating the polymerization reaction at a lower temperature.

[0043] In some embodiments, the reaction temperature of the emulsion polymerization reaction is 30-50° C., and the reaction pressure is 0.5-1 MPa.

[0044] The preparation method of the present application uses one or two of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene) as cosolvents and diacyl peroxide as initiator, which can reduce the reaction temperature of the emulsion polymerization reaction to 30-50°C and the reaction pressure to 0.5-1MPa. The low reaction temperature avoids uncontrollable free radical rearrangement reaction of the monomer perfluoroalkyl vinyl ether, thereby improving the batch stability of the perfluoroether rubber; the low reaction pressure improves the safety during the reaction.

[0045] Specifically, the polymerization reaction temperature can be 30°C, 35°C, 40°C, 45°C, 50°C, etc., and the reaction pressure can be 0.5 MPa, 0.6 MPa, 0.8 MPa, 0.9 MPa, 1.0 MPa, etc.

[0046] In some embodiments, a solvent, a pH regulator, a cosolvent, and an emulsifier are mixed to obtain a mixed solution, and an initial mixed monomer and an initiator are added to the mixed solution to carry out an emulsion polymerization reaction, comprising the following steps: First, a solvent, a pH adjuster, a co-solvent, and an emulsifier are added to a reaction container, and evacuated and replaced until the oxygen content in the reaction container is less than 20 ppm. Then stirring is started to obtain a mixed solution, which is heated to a temperature of 30-50° C., and initial mixed monomers are added to the reaction container until the pressure in the reaction container reaches 0.5-1 MPa. An initiator is added to the reaction container, and the mixed monomers dissolved in the mixed solution undergo an emulsion polymerization reaction under the action of the initiator.

[0047] In some embodiments, the continuous addition of mixed monomers during the emulsion polymerization reaction to maintain a constant reaction pressure comprises the following steps: during the reaction, continuous addition of mixed monomers to the reaction vessel to maintain the pressure in the reaction vessel at 0.5-1 MPa, and to maintain a constant pressure in the reaction vessel.

[0048] In some embodiments, in the initial mixed monomers, the molar ratio of tetrafluoroethylene to perfluoroalkyl vinyl ether is (30-50): (50-70).

[0049] In the initial mixed monomers, the molar ratio of tetrafluoroethylene and perfluoroalkyl vinyl ether is (30-50): (50-70). Tetrafluoroethylene is the main component of the main chain of perfluoroether rubber. A large amount of polymerization forms the basic skeleton of the rubber molecule. Perfluoroalkyl vinyl ether, as a branching monomer, can increase the distance between molecular chains and improve flexibility.

[0050] In some embodiments, in the additional mixed monomer, the molar ratio of the tetrafluoroethylene, the perfluoroalkyl vinyl ether and the iodine-containing sulfurization site monomer is (60-70): (25-40): (1-2).

[0051] Specifically, in the additional mixed monomer, the molar ratio of tetrafluoroethylene, the perfluoroalkyl vinyl ether and the iodine-containing vulcanization site monomer is (60-70): (25-40): (1-2). The content of the iodine-containing vulcanization site monomer that meets the above range can adjust the crosslinking density of the rubber. The appropriate crosslinking density can make the perfluoroether rubber have good elasticity while maintaining a certain hardness and mechanical strength; thereby forming a perfluoroether rubber with high strength, good flexibility, chemical resistance and high temperature resistance. If the content of the iodine-containing vulcanization site monomer is too low, the elasticity of the obtained perfluoroether rubber is reduced; if the content of the iodine-containing vulcanization site monomer is too high, the mechanical strength of the formed perfluoroether rubber is reduced.

[0052] In some embodiments, the iodine-containing curing site monomer includes one or more of perfluoro iodoethyl vinyl ether, perfluoro-4-iodo-1-butene, trifluoroiodoethylene, and I-(CF2)2OCF=CF2.

[0053] Specifically, the iodine-containing vulcanization site monomer is selected from the above types, has good polymerization reaction activity, high scorch safety during the mixing process, high vulcanization rate, and within the appropriate chain length and dosage range, its effect on the glass transition temperature of perfluoroether rubber is usually controllable and will not adversely affect the low-temperature properties of the rubber.

[0054] In some embodiments, the emulsifier is a perfluoropolyether carboxylate.

[0055] Specifically, the emulsifier is selected from perfluoropolyether carboxylate, which increases the solubility of the gas phase monomer, makes the generated polymer particles evenly dispersed in the system, and maintains the stability of the system.

[0056] In some embodiments, the perfluoropolyether carboxylate salt comprises ammonium perfluoropolyether carboxylate.

[0057] In some embodiments, the mass ratio of the emulsifier to the solvent is (0.0025~1.25):100.

[0058] Specifically, the mass ratio of emulsifier to solvent is (0.0025~1.25):100, which is conducive to the emulsifier being able to significantly reduce the interfacial tension at the gas-liquid interface, increase the solubility of the gas-phase monomer, and make the generated polymer particles evenly dispersed in the system to maintain the stability of the system. If the amount of emulsifier added is too low, it is difficult to maintain the stability of the system; if the amount of emulsifier added is too high, it will affect demulsification, increase the difficulty of separation and purification steps, and increase the impurity residues of perfluoroether rubber.

[0059] The mass ratio of the emulsifier to the solvent may be in the following ranges: (0.0025-0.005):100, (0.005-0.01):100, (0.01-0.1):100, (0.1-0.5):100, (0.5-0.75):100 or (0.75-1.25):100.

[0060] In some preferred embodiments, the mass ratio of the emulsifier to the solvent is (0.005-0.75): 100. The mass ratio of the emulsifier to the solvent is in the range of (0.005-0.75): 100, which is conducive to forming a stable emulsion and improving the reaction rate while reducing the cost.

[0061] In some embodiments, the solid content of the emulsion is 20% to 30%.

[0062] Specifically, the solid content of the emulsion obtained after the reaction is 20% to 30%, and the amount of monomer to be included can be calculated according to the solid content range of the emulsion to carry out the emulsion polymerization reaction. The solidification amount of the emulsion can be 20%, 22%, 23%, 25%, 26%, 27%, 28%, 29%, 30%, etc., as long as the solid content of the emulsion is within the range of 20% to 30%.

[0063] In some preferred embodiments, the solid content of the emulsion is 25%.

[0064] In some embodiments, post-processing the emulsion to obtain the perfluoroether rubber comprises the following steps: The emulsion is sequentially subjected to coagulation, washing and drying to obtain the perfluoroether rubber; The drying temperature is 95-105°C.

[0065] Specifically, the content of the monomer to be included is calculated based on the solid content of the emulsion. When the feeding is stopped, the reaction is completed and cooled to room temperature (25±5°C), the monomer is recovered, and the emulsion obtained after the reaction is discharged. The emulsion is sequentially condensed, washed, and dried to obtain the perfluoroether rubber.

[0066] Drying removes deionized water on the surface of perfluoroether rubber to improve purity. The specific drying temperature can be 95°C, 96°C, 98°C, 100°C, 101°C, 102°C, 103°C, 105°C, etc., as long as the drying temperature is within the range of 95°C~105°C.

[0067] The drying time can be limited according to the specific situation, such as 5 to 20 hours of drying time.

[0068] In some embodiments, the coagulation method is to coagulate the latex with a 3 wt % magnesium chloride aqueous solution.

[0069] Specifically, using a 3 wt % magnesium chloride aqueous solution to coagulate the latex is beneficial for separating the perfluoroether rubber from the emulsion system, while reducing the residual impurities such as emulsifiers and cosolvents, and facilitating the subsequent processing steps of the perfluoroether rubber.

[0070] In some embodiments, deionized water is used for washing to remove impurities, such as emulsifiers, co-solvents and the like.

[0071] In some preferred embodiments, the drying method is vacuum drying.

[0072] More preferably, the drying temperature is 100°C.

[0073] In some embodiments, the perfluoroalkyl vinyl ether includes a compound represented by Formula 1, CF2=CFOR1, Formula 1 Wherein, R1 is selected from a C1~C5 perfluoroalkyl group.

[0074] Specifically, R1 is selected from a perfluoroalkyl group having 1 to 5 carbon atoms, including a perfluoro C1 to C5 straight-chain alkyl group and a perfluoro C1 to C5 branched alkyl group. For example, R1 can be a perfluoromethyl group, a perfluorobutyl group, a perfluoropentyl group, a perfluoroisobutyl group, a perfluoroisopropyl group, and the like.

[0075] The perfluoroalkyl vinyl ether is selected from the compounds shown in Formula 1, which is conducive to the emulsion polymerization reaction with tetrafluoroethylene and iodine-containing vulcanization sites to form perfluoroether rubber.

[0076] In some embodiments, the perfluoroalkyl vinyl ether includes perfluoropropyl vinyl ether (PPVE), perfluoroethyl vinyl ether (PEVE), and perfluoromethyl vinyl ether (PMVE).

[0077] In some preferred embodiments, the perfluoroalkyl vinyl ether is perfluoromethyl vinyl ether (PMVE).

[0078] In some embodiments, the resistivity of the deionized water is ≥18 MΩ·m.

[0079] Specifically, the solvent used is deionized water, and the resistivity of the deionized water is limited to ≥18 MΩ·m. The ion impurity content in the deionized water is extremely low, which prevents the impurities in the deionized water from affecting the emulsion polymerization reaction and avoids the introduction of impurities into the generated polymer.

[0080] In some embodiments, the amount of solvent added is 40% to 60% of the volume of the reaction container.

[0081] Specifically, the volume of deionized water added to the reaction container is 40% to 60% of the volume of the reaction container. For example, the volume of deionized water added to the reaction container can be 40%, 42%, 45%, 48%, 50%, 55%, 60%, etc. of the volume of the reaction container.

[0082] Specifically, the reaction container may be a reaction kettle, etc., which is not limited in this application.

[0083] In some embodiments, the pH adjuster is selected from one or more of ammonium carbonate, ammonium bicarbonate, dipotassium hydrogen phosphate, and disodium hydrogen phosphate, and the added amount of the pH adjuster is 0.01% to 0.5% of the mass of the solvent.

[0084] Specifically, the pH adjuster is used to adjust the pH value of the entire reaction system. The above-mentioned type of pH adjuster is added, and the amount of the pH adjuster added is controlled to be in the range of 0.01% to 0.5% of the mass of the solvent, so that the pH value of the entire reaction system is in the range of 3-6, which is conducive to the polymerization reaction.

[0085] The present invention is further described below by way of examples.

[0086] Example 1 S1: Add 29L deionized water, 3.0kg perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene) cosolvent in a mass ratio of 1:3, 55g perfluoropolyether carboxylic acid ammonium and 25g ammonium carbonate into a 55L stainless steel reactor, and evacuate and replace until the oxygen content is ≤20ppm. Start stirring, mix evenly to obtain a mixed solution, add TFE and PMVE initial mixed monomers in a molar ratio of 45:55 to the mixed solution, and then heat to 40°C, continue to add TFE and PMVE initial mixed monomers in a molar ratio of 45:55 until the reaction pressure reaches 0.75MPa, add 5gCF3CH2CH2CF2(CO)OO(CO)CF2CH2CH2CF3 to initiate emulsion polymerization, the temperature of the emulsion polymerization reaction is 40°C, and the reaction pressure is 0.75MPa. Subsequently, a mixed monomer of perfluoroethyl iodide vinyl ether, TFE and PMVE in a molar ratio of 1.5:65:35 was continuously added to keep the reaction pressure unchanged, and the emulsion polymerization reaction was continued until the feed amount reached a preset value, and the feed was stopped. The polymerization reaction was terminated to obtain an emulsion containing perfluoroether rubber with a solid content of 25%. The emulsion was cooled to room temperature (25±5°C), and the gas phase monomer was recovered.

[0087] S2: The emulsion obtained in step S1 is then coagulated with a 3 wt % magnesium chloride aqueous solution, washed with deionized water, and dried in a 100° C. forced air oven for 10 hours to obtain the final product, perfluoroether rubber.

[0088] Example 2 S1: Add 29L deionized water, 5.0kg of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene) cosolvent in a mass ratio of 1:2, 55g of ammonium perfluoropolyether carboxylate and 21g of ammonium carbonate into a 55L stainless steel reactor, and evacuate and replace until the oxygen content is ≤20ppm. Start stirring, mix evenly to obtain a mixed solution, add the initial mixed monomer of TFE and PMVE in a molar ratio of 40:60 to the mixed solution, and then heat to 50°C, continue to add the initial mixed monomer of TFE and PMVE in a molar ratio of 40:60 until the reaction pressure reaches 0.5MPa, add 5gCF3CH2CH2CF2(CO)OO(CO)CF2CH2CH2CF3 to initiate emulsion polymerization, the temperature of the emulsion polymerization reaction is 50°C, and the reaction pressure is 0.5MPa. Subsequently, a mixed monomer of perfluoroiodoethyl vinyl ether, TFE and PMVE in a molar ratio of 1.7:60:40 was continuously added to keep the reaction pressure unchanged, and the emulsion polymerization reaction was continued until the feed amount reached a preset value, and the feed was stopped. The polymerization reaction was terminated to obtain an emulsion containing perfluoroether rubber with a solid content of 23%. The emulsion was cooled to room temperature (25±5°C), and the gas phase monomer was recovered.

[0089] S2: The emulsion obtained in step S1 is then coagulated with a 3 wt % magnesium chloride aqueous solution, washed with deionized water, and dried in a blast vacuum oven at 100° C. for 10 hours to obtain the final product, perfluoroether rubber.

[0090] Example 3 S1: Add 29L deionized water, 4.8kg of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene) cosolvent in a mass ratio of 2:5, 55.5g of perfluoropolyether carboxylic acid ammonium and 15g of ammonium carbonate into a 55L stainless steel reactor, and evacuate and replace until the oxygen content is ≤20ppm. Start stirring, mix evenly to obtain a mixed solution, add the initial mixed monomer of TFE and PMVE in a molar ratio of 45:55 to the mixed solution, and then heat to 45°C, continue to add the initial mixed monomer of TFE and PMVE in a molar ratio of 45:55 until the reaction pressure reaches 0.8MPa, add 5gCF3CH2CH2CF2(CO)OO(CO)CF2CH2CH2CF3 to initiate emulsion polymerization, the temperature of the emulsion polymerization reaction is 45°C, and the reaction pressure is 0.8MPa. Subsequently, a mixed monomer of perfluoroiodoethyl vinyl ether, TFE and PMVE in a molar ratio of 1.2:65:35 was continuously added to keep the reaction pressure unchanged, and the emulsion polymerization reaction was continued until the feed amount reached a preset value, and the feed was stopped. The polymerization reaction was terminated to obtain an emulsion containing perfluoroether rubber with a solid content of 28%. The emulsion was cooled to room temperature (25±5°C), and the gas phase monomer was recovered.

[0091] S2: The emulsion obtained in step S1 is then coagulated with a 3 wt % magnesium chloride aqueous solution, washed with deionized water, and dried in a blast vacuum oven at 100° C. for 10 hours to obtain the final product, perfluoroether rubber.

[0092] Example 4 S1: Add 29L deionized water, 4.0kg perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene) cosolvent in a mass ratio of 1:2, 33g perfluoropolyether carboxylic acid ammonium and 20g ammonium carbonate into a 55L stainless steel reactor, and evacuate and replace until the oxygen content is ≤20ppm. Start stirring, mix evenly to obtain a mixed solution, add the initial mixed monomer of TFE and PMVE in a molar ratio of 45:55 to the mixed solution, and then heat to 48°C, continue to add the initial mixed monomer of TFE and PMVE in a molar ratio of 45:55 until the reaction pressure reaches 1.0MPa, add 5gCF3CH2CH2CF2(CO)OO(CO)CF2CH2CH2CF3 to initiate emulsion polymerization, the temperature of the emulsion polymerization reaction is 48°C, and the reaction pressure is 1.0MPa. Subsequently, a mixed monomer of perfluoroethyl iodide vinyl ether, TFE and PMVE in a molar ratio of 2.0:63:37 was continuously added to keep the reaction pressure unchanged, and the emulsion polymerization reaction was continued until the feed amount reached a preset value, and the feed was stopped. The polymerization reaction was terminated to obtain an emulsion containing perfluoroether rubber with a solid content of 26%. The emulsion was cooled to room temperature (25±5°C), and the gas phase monomer was recovered.

[0093] S2: The emulsion obtained in step S1 is then coagulated with a 3 wt % magnesium chloride aqueous solution, washed with deionized water, and dried in a blast vacuum oven at 100° C. for 10 hours to obtain the final product, perfluoroether rubber.

[0094] Example 5 S1: Add 29L deionized water, 4.5kg of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene) cosolvent in a mass ratio of 1:2, 33g of ammonium perfluoropolyether carboxylate and 20g of ammonium carbonate into a 55L stainless steel reactor, and evacuate and replace until the oxygen content is ≤20ppm. Start stirring, mix evenly to obtain a mixed solution, add the initial mixed monomer of TFE and PMVE in a molar ratio of 45:55 to the mixed solution, and then heat to 46°C, continue to add the initial mixed monomer of TFE and PMVE in a molar ratio of 45:55 until the reaction pressure reaches 0.8MPa, add 5gCF3CH2CH2CF2(CO)OO(CO)CF2CH2CH2CF3 to initiate emulsion polymerization, the temperature of the emulsion polymerization reaction is 46°C, and the reaction pressure is 0.8MPa. Subsequently, a mixed monomer of perfluoroethyl iodide vinyl ether, TFE and PMVE in a molar ratio of 1.5:65:35 was continuously added to keep the reaction pressure unchanged, and the emulsion polymerization reaction was continued until the feed amount reached a preset value, and the feed was stopped. The polymerization reaction was terminated to obtain an emulsion containing perfluoroether rubber with a solid content of 23%. The emulsion was cooled to room temperature (25±5°C), and the gas phase monomer was recovered.

[0095] S2: The emulsion obtained in step S1 is then coagulated with a 3 wt % magnesium chloride aqueous solution, washed with deionized water, and dried in a blast vacuum oven at 100° C. for 10 hours to obtain the final product, perfluoroether rubber.

[0096] Example 6 Most of the steps in this embodiment are the same as those in embodiment 1, except that the co-solvent in this embodiment is perfluorobutyltetrahydrofuran. The rest is the same as in embodiment 1.

[0097] Example 7 Most of the steps in this embodiment are the same as those in embodiment 1, except that the co-solvent in this embodiment is perfluoro(tetradecahydrophenanthrene). The rest is the same as in embodiment 1.

[0098] Example 8 Most of the steps in this embodiment are the same as those in embodiment 1, except that the amount of co-solvent added in this embodiment is 2 kg.

[0099] Example 9 Most of the steps in this embodiment are the same as those in embodiment 1, except that the amount of co-solvent added in this embodiment is 6 kg.

[0100] Example 10 Most of the steps in this example are the same as those in Example 1, except that the amount of co-solvent added in this example is 8.5 Kg.

[0101] Embodiment 11 Most of the steps of this embodiment are the same as those of embodiment 1, except that the co-solvent in this embodiment is 5.0 kg of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene) in a mass ratio of 1:2, and the rest is the same as embodiment 1.

[0102] Example 12 Most of the steps of this embodiment are the same as those of embodiment 1, except that the co-solvent in this embodiment is 5.0 kg of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene) in a mass ratio of 1:6, and the rest is the same as embodiment 1.

[0103] Example 13 Most of the steps of this embodiment are the same as those of embodiment 1, except that the co-solvent in this embodiment is 5.0 kg of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene) in a mass ratio of 2:1, and the rest is the same as embodiment 1.

[0104] It should be noted that the solid content of the emulsions of Examples 6 to 13 is the same as that of Example 1. The emulsion polymerization reaction is carried out under the conditions of a reaction pressure of 0.75 MPa and a reaction pressure of 40° C. When the solid content of the emulsions prepared in Examples 6 to 13 reaches 25%, the reaction is terminated, and the reaction time of Examples 6 to 13 is recorded to determine the speed of the reaction. The specific reaction time of Examples 6 to 13 is shown in Table 2.

[0105] Comparative Example 1 Add 28L of deionized water to a 55L stainless steel reactor. Add 180g of ammonium perfluoropolyether carboxylate and 20g of potassium dihydrogen phosphate, and evacuate and replace. After heating to 90°C, add a mixed monomer of TFE and PMVE at a molar ratio of 40:60 until the pressure reaches 1.7MPa, add 5g of ammonium persulfate to initiate the polymerization reaction, then add perfluoroiodoethyl vinyl ether, TFE and PMVE at a molar ratio of 1:60:40 to keep the pressure in the reactor unchanged until the feed amount reaches the preset value, stop feeding, recover the gas phase monomer, and cool down to obtain a perfluoroether rubber latex with a solid content of 30%.

[0106] Step S2 is the same as in Example 1.

[0107] Comparative Example 2 Most of the steps in this comparative example are the same as those in Example 1, except that the initiator in this comparative example is ammonium persulfate, and the rest is the same as in Example 1.

[0108] The perfluoroether rubber obtained in the above embodiments and comparative examples was vulcanized. The types and components added during vulcanization are shown in Table 1. Two-stage vulcanization treatment was performed. The first stage vulcanization temperature was 170° C., the first stage vulcanization time was 10 min, and the second stage vulcanization temperature was 232° C., and the second stage vulcanization time was 4 h.

[0109] Table 1 Performance Testing The rubber vulcanized in the above-mentioned embodiments and comparative examples was tested for tensile strength, elongation, hardness and permanent compression set.

[0110] GB / T 528 (ISO 37) was used to test the tensile strength and elongation.

[0111] The hardness is tested according to GB / T 531.1-2008.

[0112] GB / T 7759 ISO 815-1 was used to test the permanent compression deformation. The test temperature was maintained at 200°C for 70 hours, and then the compression was released. The height of the sample after recovery was measured, and the compression permanent deformation rate was calculated. The test results under specific temperature and time conditions are shown in Table 2.

[0113] The above test results are shown in Table 2.

[0114] Table 2 From the test results of Table 1 and Table 2, it can be seen that, compared with Example 1 and Comparative Example 1, Comparative Example 1 is prepared by the existing method for preparing perfluoroether rubber, indicating that by adding a cosolvent and a diacyl peroxide initiator by the preparation method of the present application, it is possible to react to form perfluoroether rubber at a reaction temperature of 30-50°C and a reaction pressure of 0.5-1MPa, and the tensile strength and hardness of the obtained perfluoroether rubber are close to those of Comparative Example 1, the permanent compression deformation rate is lower than that of Comparative Example 1, the reaction time is lower than that of Comparative Example 1, and the elongation is also relatively similar to that of Comparative Example 1, indicating that by adopting the preparation method provided by the present application, the perfluoroether rubber obtained also has high tensile strength and hardness, good permanent compression deformation, good toughness, and is close to the performance of the existing perfluoroether rubber, and the preparation method of the present application has low temperature, low pressure, high safety and low cost.

[0115] Comparing Example 1 with Comparative Example 2, the ammonium persulfate used as the initiator in Comparative Example 2 basically does not react at a low temperature of 50°C, indicating that in the process of preparing perfluoroether rubber, the added cosolvent and initiator can synergistically greatly reduce the pressure and temperature required for the emulsion polymerization of perfluoroether rubber, and the emulsion polymerization reaction can be carried out at a temperature below 70°C, avoiding the uncontrollable free radical rearrangement reaction of the monomer perfluoroalkyl vinyl ether, and improving the batch stability of the perfluoroether rubber; at the same time, the reaction pressure is low, which reduces the requirements for equipment and improves the safety of the polymerization process.

[0116] Comparison between Example 1 and Examples 6 and 7 shows that, when the solid content of the emulsion is limited to be the same, if the co-solvent is perfluorobutyltetrahydrofuran or perfluoro(tetradecahydrophenanthrene), the reaction time is long, and the obtained perfluoroether rubber has low tensile strength, low elongation, and low hardness; it shows that when the co-solvent is perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene), the reaction time is short, the polymerization reaction rate is high, and the obtained perfluoroether rubber has high tensile strength and hardness, good permanent compression set, and good toughness.

[0117] Comparing Examples 1, 8-10, when the mass ratio of the co-solvent to the solvent is in the range of (5-30):100, as the content of the co-solvent increases, the reaction rate is not significantly improved, the preparation cost is increased, and the separation difficulty is increased.

[0118] Comparison between Examples 1-5 and 11 and Examples 12 and 13 shows that when the mass ratio of perfluorobutyltetrahydrofuran to perfluoro(tetradecahydrophenanthrene) is lower or higher than 1: (1-5), the reaction time increases, and the tensile strength and elongation of the perfluoroether rubber decrease, indicating that when the mass ratio of the added co-solvent perfluorobutyltetrahydrofuran to perfluoro(tetradecahydrophenanthrene) is within the range of 1: (1-5), the polymerization reaction rate is fast, and the content of the obtained perfluoroether rubber is higher within the same reaction time. Comparison between Examples 1-5 and Comparative Example 1 shows that the performance of the perfluoroether rubber obtained by the preparation method of the perfluoroether rubber provided in the present application is basically maintained at the same level as that of the perfluoroether rubber obtained under high temperature and high pressure, and the successful preparation of the perfluoroether rubber under low temperature and low pressure conditions is achieved.

[0119] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A method for preparing perfluoroether rubber, characterized in that: The following steps are involved: A solvent, a pH regulator, a cosolvent and an emulsifier are mixed to obtain a mixed solution, an initial mixed monomer and an initiator are added to the mixed solution to carry out an emulsion polymerization reaction, additional mixed monomers are continuously added during the emulsion polymerization reaction to maintain a constant reaction pressure, an emulsion is obtained after the polymerization reaction is completed, and the emulsion is post-treated to obtain the perfluoroether rubber; The initial mixed monomers include tetrafluoroethylene and perfluoroalkyl vinyl ether; The additional mixed monomers include tetrafluoroethylene, perfluoroalkyl vinyl ether and iodine-containing vulcanization site monomers; The cosolvent comprises one or two of perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene); The initiator includes a diacyl peroxide.

2. The method for preparing perfluoroether rubber according to claim 1, characterized in that: The cosolvent is perfluorobutyltetrahydrofuran and perfluoro(tetradecahydrophenanthrene), The mass ratio of perfluorobutyltetrahydrofuran to perfluoro(tetradecahydrophenanthrene) is 1:(1-5); The mass ratio of the co-solvent to the solvent is (5-30):

100.

3. The method for preparing perfluoroether rubber according to claim 1, characterized in that: The mass ratio of the initiator to the solvent is (0.00025-0.4):

100.

4. The method for preparing perfluoroether rubber according to claim 1 or 3, characterized in that: The diacyl peroxide comprises CF3CH2CH2CF2(CO)OO(CO)CF2CH2CH2CF3; And / or, the pH adjuster is selected from one or more of ammonium carbonate, ammonium bicarbonate, dipotassium hydrogen phosphate, and disodium hydrogen phosphate, and the added amount of the pH adjuster is 0.01% to 0.5% of the mass of the solvent.

5. The method for preparing perfluoroether rubber according to claim 1, characterized in that: The reaction temperature of the emulsion polymerization reaction is 30-50° C., and the reaction pressure is 0.5-1 MPa.

6. The method for preparing perfluoroether rubber according to claim 1, characterized in that: In the initial mixed monomers, the molar ratio of tetrafluoroethylene to perfluoroalkyl vinyl ether is (30-50): (50-70).

7. The method for preparing perfluoroether rubber according to claim 1, characterized in that: In the additional mixed monomer, the molar ratio of the tetrafluoroethylene, the perfluoroalkyl vinyl ether and the iodine-containing sulfurization site monomer is (60-70): (25-40): (1-2); And / or, the iodine-containing vulcanization site monomer includes one or more of perfluoroiodoethyl vinyl ether, perfluoro-4-iodo-1-butene, trifluoroiodoethylene, and I-(CF2)2OCF=CF2.

8. The method for preparing perfluoroether rubber according to claim 1, characterized in that: The emulsifier is perfluoropolyether carboxylate, and the mass ratio of the emulsifier to the solvent is (0.0025-1.25):100; And / or, the perfluoropolyether carboxylate comprises ammonium perfluoropolyether carboxylate.

9. The method for preparing perfluoroether rubber according to claim 1, characterized in that: The solid content of the emulsion is 20% to 30%; The post-treatment of the emulsion to obtain the perfluoroether rubber comprises the following steps: The emulsion is sequentially subjected to coagulation, washing and drying to obtain the perfluoroether rubber; The drying temperature is 95-105°C.

10. The method for preparing perfluoroether rubber according to claim 1, characterized in that: The solvent is deionized water, and the resistivity of the deionized water is ≥18MΩ·m; The perfluoroalkyl vinyl ether includes a compound represented by Formula 1, CF2=CFOR1, Formula 1 Wherein, R1 is selected from a C1~C5 perfluoroalkyl group.

Images