A method for preparing perfluoroether rubber by soap-free emulsion polymerization

Abstract

In order to overcome the problem that solvent-resistant peroxide-vulcanized perfluoroether rubber products are difficult to be used at high temperature above 310 DEG C for a long time and have poor heat resistance, a method for preparing perfluoroether rubber by soap-free emulsion polymerization is provided, comprising the following steps: mixing deionized water, a first monomer and a pH regulator to obtain a mixed liquid; heating the mixed liquid to a reaction temperature, introducing a second monomer and a third monomer into the mixed liquid to a reaction pressure, adding an initiator into the mixed liquid to carry out a polymerization reaction, and obtaining an emulsion after the reaction, and obtaining perfluoroether rubber through post-treatment of the emulsion; the first monomer is a compound shown in formula 1, CF2=CFO(CF2)nCOOH, formula 1, wherein n is an integer of 1-4; the second monomer is tetrafluoroethylene, and the third monomer is perfluoroalkyl vinyl ether. The perfluoroether rubber prepared by the method provided in the application can be vulcanized by peroxide without using a cross-linking aid, and solvent-resistant perfluoroether rubber products with superior heat resistance are obtained.

Description

Technical Field

[0001] This invention belongs to the field of perfluoroether rubber technology, specifically relating to a method for preparing perfluoroether rubber by soap-free emulsion polymerization. Background Technology

[0002] Perfluoroelastomer rubber, due to its excellent heat resistance, chemical resistance and impermeability, has been widely used to manufacture O-rings, valve stem seals, shaft seals, gaskets and other products, and is applied in various fields with harsh conditions.

[0003] The vulcanization system used for solvent-resistant perfluoroelastomers significantly affects the performance of the final product. Products obtained through peroxide vulcanization exhibit the broadest chemical resistance; however, the co-crosslinking agent used can impact the heat resistance of the final product. Currently used multifunctional co-crosslinking agents, such as triallyl isocyanurate (TAIC) and dienes (as disclosed in patents EP661304, EP784064, and EP769521), result in products that are difficult to use for extended periods at temperatures above 310°C, exhibiting poor heat resistance, which limits their application. Furthermore, solvent-resistant perfluoroelastomers are generally obtained through emulsion polymerization in the presence of fluorinated surfactants. However, the use of fluorinated surfactants has environmental impacts, and their residues in the perfluoroelastomer can affect its purity, electrical properties, and physical properties. Summary of the Invention

[0004] The present invention aims to solve the problem that existing solvent-resistant perfluoroether rubber products vulcanized by peroxides are difficult to use for a long time at high temperatures above 310°C and have poor heat resistance. This application provides a method for preparing perfluoroether rubber by soap-free emulsion polymerization.

[0005] To address the aforementioned technical problems, this application provides a method for preparing perfluoroether rubber via soap-free emulsion polymerization, comprising the following steps:

[0006] Deionized water, the first monomer, and the pH adjuster are mixed to obtain a mixed liquid;

[0007] The mixed liquid is heated to the reaction temperature, and the second and third monomers are introduced into the mixed liquid to the reaction pressure. An initiator is added to the mixed liquid to carry out the polymerization reaction. After the reaction is completed, an emulsion is obtained. The emulsion is then post-treated to obtain perfluoroether rubber.

[0008] The first monomer is the compound shown in Formula 1.

[0009] CF2=CFO(CF2)nCOOH, Equation 1

[0010] Where n is an integer from 1 to 4;

[0011] The second monomer is tetrafluoroethylene, and the third monomer is a perfluoroalkyl vinyl ether.

[0012] Preferably, the reaction temperature is 70–90°C and the reaction pressure is 2.0–3.0 MPa.

[0013] Preferably, the steps of introducing the second and third monomers into the mixed liquid to the reaction pressure and adding an initiator to the mixed liquid to carry out the polymerization reaction specifically include the following steps:

[0014] An initial mixed monomer containing a second monomer and a third monomer is introduced into the mixed liquid to a reaction pressure of 2.0–3.0 MPa. An initiator is added to the mixed liquid to carry out the polymerization reaction. During the reaction, an additional mixed monomer containing a second monomer and a third monomer is continuously added to maintain the pressure at 2.0–3.0 MPa.

[0015] Preferably, in the initial mixed monomers, the molar ratio of the second monomer to the third monomer is (30-50):(50-70);

[0016] In the added mixed monomers, the molar ratio of the second monomer to the third monomer is (60-70):(30-40).

[0017] Preferably, the mixing of deionized water, the first monomer, and the pH adjuster includes the following steps: adding the deionized water, the first monomer, and the pH adjuster into the reaction vessel, evacuating and replacing the contents until the oxygen content is ≤20ppm; the amount of deionized water added is 40-60% of the volume of the reaction vessel.

[0018] The resistivity of the deionized water is ≥18 MΩ·m;

[0019] The pH adjuster is selected from one or more of ammonium carbonate, ammonium bicarbonate, dipotassium hydrogen phosphate, and disodium hydrogen phosphate, and the amount of pH adjuster added is 0.01-0.5% of the mass of the deionized water;

[0020] The amount of the first monomer added is 0.05 to 0.8% of the mass of the deionized water.

[0021] Preferably, the amount of the first monomer added is 0.05 to 0.2% of the mass of the deionized water;

[0022] The pH adjuster is ammonium carbonate;

[0023] The amount of pH adjuster added is 0.05-0.1% of the mass of the deionized water.

[0024] Preferably, the perfluoroalkyl vinyl ether is selected from perfluoroalkyl vinyl ethers having 1 to 5 carbon atoms.

[0025] Preferably, the perfluoroalkyl vinyl ether includes one or more of PPVE, PEVE, and PMVE.

[0026] Preferably, the initiator is persulfate, and the amount of the initiator added is 0.01% to 0.02% of the mass of the deionized water;

[0027] The initiator may be added in one go, in batches, or continuously.

[0028] The batch addition includes the following steps: preparing the initiator into an aqueous solution to obtain an initiator aqueous solution, and adding the initiator aqueous solution every 25 min to 35 min after the start of the polymerization reaction.

[0029] Preferably, the solid content of the emulsion is 15% to 30%;

[0030] The step of obtaining perfluoroether rubber by post-processing the emulsion includes the following steps: passing the emulsion through cooling, coagulation, washing, drying and heat treatment in sequence to obtain perfluoroether rubber that can be vulcanized by peroxide;

[0031] In the cooling step, the emulsion is cooled to 20-25°C;

[0032] The coagulation method is to coagulate the emulsion using a 3wt% nitric acid aqueous solution;

[0033] The washing solvent used is deionized water, ethanol, or a mixture of ethanol and water, wherein the mass ratio of ethanol to water in the mixture is (30-70):(70-30); the drying temperature is 95-105°C, and the drying time is 24-48 hours.

[0034] The heat treatment temperature is 280–320°C, and the heat treatment time is 25–60 min.

[0035] Beneficial effects:

[0036] Compared with existing technologies, the method for preparing perfluoroether rubber via soap-free emulsion polymerization provided in this application does not involve the addition of emulsifiers. Instead, a first monomer is added during the preparation process, and perfluoroether rubber is obtained through soap-free emulsion polymerization. This avoids the environmental hazards caused by the use of fluorinated surfactants and prevents the influence of residual fluorinated surfactants on the properties of perfluoroether rubber. The perfluoroether rubber prepared by this application can be vulcanized by peroxide without the use of co-crosslinking agents. A permanent compression set test at 316°C for 70 hours shows a low permanent compression set, resulting in a solvent-resistant perfluoroether rubber product with superior heat resistance. Detailed Implementation

[0037] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0038] This application provides a method for preparing perfluoroether rubber via soap-free emulsion polymerization, comprising the following steps:

[0039] Deionized water, the first monomer, and the pH adjuster are mixed to obtain a mixed liquid;

[0040] The mixed liquid is heated to the reaction temperature, and the second and third monomers are introduced into the mixed liquid to the reaction pressure. An initiator is added to the mixed liquid to carry out the polymerization reaction. After the reaction is completed, an emulsion is obtained. The emulsion is then post-treated to obtain perfluoroether rubber.

[0041] The first monomer is the compound shown in Formula 1.

[0042] CF2=CFO(CF2)nCOOH, Equation 1

[0043] Where n is an integer from 1 to 4;

[0044] The second monomer is tetrafluoroethylene, and the third monomer is a perfluoroalkyl vinyl ether.

[0045] Specifically, n is 1 to 4, such as n being an integer of 1, 2, 3 or 4.

[0046] Compared with existing technologies, the method for preparing perfluoroether rubber provided in this application does not involve the addition of emulsifiers. Instead, a first monomer, a second monomer, and a third monomer are added during the preparation process, and perfluoroether rubber is obtained through soap-free emulsion polymerization. This avoids the environmental hazards associated with the use of fluorinated surfactants and prevents the impact of residual fluorinated surfactants on the performance of the perfluoroether rubber. The perfluoroether rubber prepared in this application can be vulcanized with peroxide without the use of co-crosslinking agents. A permanent compression set test at 316°C for 70 hours shows a low permanent compression set, resulting in a solvent-resistant perfluoroether rubber product with superior heat resistance.

[0047] In some embodiments, the reaction temperature is 70–90°C and the reaction pressure is 2.0–3.0 MPa.

[0048] Specifically, a polymerization reaction temperature in the range of 70–90°C and a polymerization reaction pressure in the range of 2.0–3.0 MPa are conducive to the polymerization reaction of the first monomer, the second monomer, and the third monomer under the action of the initiator, to produce perfluoroether rubber.

[0049] If the polymerization temperature is below 70℃, the polymer reaction is too slow; if the polymerization temperature is above 90℃, the temperature is too high and the polymerization reaction is too fast, which may cause safety accidents. If the pressure is below 2.0MPa, the resulting perfluoroether rubber, when subjected to a permanent compression set test at 316℃ for 70 hours, shows a low permanent compression set rate; if the pressure is above 3.0MPa, the polymerization reaction is too fast, the reaction process is difficult to control, and safety accidents are easily caused.

[0050] The reaction temperature can be within the following ranges, such as 70–80℃, 75–85℃, 80–90℃, or 85–90℃, as long as the reaction temperature is within the range of 70–90℃. The reaction pressure can be 2.0 MPa, 2.2 MPa, 2.5 MPa, 2.7 MPa, 2.8 MPa, or 3.0 MPa, as long as the reaction pressure is within the range of 2.0–3.0 MPa.

[0051] In some embodiments, the step of introducing a second monomer and a third monomer into the mixed liquid to a reaction pressure, and adding an initiator to the mixed liquid to carry out the polymerization reaction, specifically includes the following steps:

[0052] An initial mixed monomer containing a second monomer and a third monomer is introduced into the mixed liquid to a reaction pressure of 2.0–3.0 MPa. An initiator is added to the mixed liquid to carry out the polymerization reaction. During the reaction, an additional mixed monomer containing a second monomer and a third monomer is continuously added to maintain the pressure at 2.0–3.0 MPa.

[0053] It should be noted that in the preparation of perfluoroether rubber, the second and third monomers can be added all at once or in batches. As described above, an initial mixture of the second and third monomers is first introduced into the mixed liquid to a reaction pressure of 2.0–3.0 MPa, followed by the addition of an initiator to initiate the reaction. During the reaction, supplementary mixtures of the second and third monomers are continuously added. The method of adding the second and third monomers can be chosen in batches according to actual needs. It should be noted that this application controls the end of the reaction based on the solid content of the generated emulsion; however, other methods can also be used to control when the reaction ends, and this application does not impose any limitations on this.

[0054] In some embodiments, in the initial mixed monomers, the molar ratio of the second monomer to the third monomer is (30-50):(50-70).

[0055] In the added mixed monomers, the molar ratio of the second monomer to the third monomer is (60-70):(30-40).

[0056] The ratio of the second monomer to the third monomer in the copolymer obtained by emulsion polymerization is related to the molar ratio of the fed monomers. In the preparation method of this application, before the polymerization reaction, the amount of the second monomer added in the first addition is less than that of the third monomer, and the amount of the second monomer added in subsequent additions increases. This feeding ratio is to obtain the desired copolymer composition. Specifically, in the initial mixed monomers, the molar ratio of the second monomer to the third monomer can be (30-35):(50-55), (35-40):(50-55), (40-50):(50-55), (35-40):(55-60), (35-40):(60-65), (35-40):(65-70), etc., as long as the molar ratio of the second monomer to the third monomer is within the range of (30-50):(50-70). In the addition of mixed monomers, the molar ratio of the second monomer to the third monomer can be (60-65):30, (65-70):30, (60-65):(30-35), (60-65):(35-40), etc., as long as the molar ratio of the second monomer to the third monomer is within the range of (60-70):(30-40).

[0057] In some embodiments, the mixing of deionized water, the first monomer, and the pH adjuster includes the following steps: adding the deionized water, the first monomer, and the pH adjuster into a reaction vessel, evacuating and replacing the contents until the oxygen content is ≤20ppm; the amount of deionized water added is 40-60% of the volume of the reaction vessel.

[0058] Specifically, vacuum purging refers to first evacuating the reaction vessel to a vacuum, and then purging it with nitrogen or an inert gas, preferably nitrogen. After vacuum purging, the oxygen content in the reaction vessel is controlled to be ≤20ppm to prevent the tetrafluoroethylene from exploding.

[0059] In some embodiments, the resistivity of the deionized water is ≥18 MΩ·m.

[0060] The conductivity of deionized water is limited to ≥18 MΩ·m to avoid the metal ions in the water affecting the stability of the emulsion and the purity of the product.

[0061] 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 amount of pH adjuster added is 0.01-0.5% of the mass of the deionized water.

[0062] pH adjusters are used to adjust the pH value of the reaction system.

[0063] In some preferred embodiments, the pH adjuster is ammonium carbonate.

[0064] In some preferred embodiments, the amount of pH adjuster added is 0.05-0.1% of the mass of the deionized water.

[0065] In some embodiments, the amount of the first monomer added is 0.05 to 0.8% of the mass of the deionized water.

[0066] Compared with existing technologies, the first monomer added in the preparation method of this application is also consumed during the polymerization reaction, and the final emulsion does not contain traditional small molecule emulsifiers, belonging to soap-free emulsion polymerization. If the amount of the first monomer added is higher than 0.8% of the mass of deionized water, the compression set of the final perfluoroether rubber will increase, resulting in waste of raw materials and increased reaction costs. If the amount of the first monomer added is lower than 0.05% of the mass of deionized water, the amount of the first monomer added is too low, resulting in a high compression set and poor heat resistance of the final perfluoroether rubber product. The amount of the first monomer added is 0.05% to 0.8% of the mass of deionized water, which is conducive to the polymerization reaction of the first monomer with the second and third monomers. Perfluoroether rubber is obtained through soap-free emulsion polymerization, avoiding the environmental hazards of using fluorinated surfactants and the impact of residual fluorinated surfactants on the performance of perfluoroether rubber. At the same time, under the condition of controlling the reaction cost at a low level, solvent-resistant perfluoroether rubber products with better heat resistance can be prepared. The amount of the first monomer added can be 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 0.8% of the deionized mass, as long as the amount of the first monomer added is within the range of 0.05% to 0.8% of the deionized mass.

[0067] In some preferred embodiments, the amount of the first monomer added is 0.05 to 0.2% of the mass of the deionized water.

[0068] Specifically, the amount of the first monomer added is within the above range. Under the condition of lower cost, the first monomer can also carry out polymerization reaction with the second and third monomers. Perfluoroether rubber is obtained through soap-free emulsion polymerization, which avoids the environmental harm caused by the use of fluorinated surfactants and avoids the impact of residual fluorinated surfactants on the performance of solvent-resistant perfluoroether rubber.

[0069] In some preferred embodiments, n is 3.

[0070] In some embodiments, the perfluoroalkyl vinyl ether is selected from perfluoroalkyl vinyl ethers having 1 to 5 carbon atoms.

[0071] Specifically, the number of carbon atoms can be 1, 2, 3, 4 or 5.

[0072] In some preferred embodiments, the perfluoroalkyl vinyl ether includes one or more of PPVE (perfluoropropyl vinyl ether), PEVE (perfluoroethyl vinyl ether), and PMVE (perfluoromethyl vinyl ether).

[0073] In some embodiments, the initiator is a persulfate.

[0074] In some preferred embodiments, the initiator includes at least one selected from ammonium sulfate, potassium persulfate, and sodium persulfate. More preferably, the initiator is ammonium persulfate.

[0075] In some embodiments, the amount of initiator added is 0.01% to 0.02% of the mass of the deionized water.

[0076] In some preferred embodiments, the amount of initiator added is 0.015% to 0.02% of the mass of the deionized water.

[0077] In some embodiments, the initiator is added in a single step, in batches, or continuously.

[0078] The batch addition includes the following steps: preparing the initiator into an aqueous solution to obtain an initiator aqueous solution, and adding the initiator aqueous solution every 25 min to 35 min after the start of the polymerization reaction.

[0079] Specifically, the water in the initiator aqueous solution is also deionized water, and the resistivity of deionized water is ≥18MΩ·m.

[0080] In some embodiments, the solid content of the emulsion is 15% to 30%.

[0081] In some embodiments, the step of obtaining perfluoroether rubber by post-processing the emulsion includes the following steps: sequentially subjecting the emulsion to cooling, coagulation, washing, drying, and heat treatment to obtain perfluoroether rubber that can be peroxide-cured; in the cooling step, the emulsion is cooled to 20-25°C; the coagulation method is to coagulate the emulsion using a 3wt% nitric acid aqueous solution; the washing solvent used is deionized water, ethanol, or a mixed solution of ethanol and water, wherein the mass ratio of ethanol to water in the mixed liquid is (30-70):(70-30); the drying temperature is 95-105°C, and the drying time is 24-48 hours; the heat treatment temperature is 280-320°C, and the heat treatment time is 25-60 minutes.

[0082] In some embodiments, the cooling method includes room temperature cooling, circulating cooling water cooling, etc. Circulating cooling water cooling is preferred.

[0083] In some embodiments, the drying method is vacuum drying.

[0084] In some preferred embodiments, the drying temperature is 100°C.

[0085] In some preferred embodiments, the heat treatment specifically includes the following steps: microwave heating for 30 minutes under inert gas protection at a temperature of 280–320°C.

[0086] The first monomer is F2C=CFOCF2COOH, and the third monomer is F2C=CFOCF3. The polymerization reaction equation is as follows:

[0087]

[0088] The specific embodiments of the present invention will be further explained and illustrated below through examples, but this does not mean that the scope of protection of the present invention is limited to the scope described in the examples.

[0089] Example 1

[0090] This embodiment illustrates a method for preparing perfluoroether rubber using soap-free emulsion polymerization disclosed in this application.

[0091] In a 50L stainless steel reactor, 29L of deionized water, 20g of ammonium carbonate, and 100g of the first monomer CF2=CFOCF2COOH were added and mixed to obtain a mixed liquid. The mixture was then evacuated and purged with nitrogen until the oxygen content was ≤20ppm. The mixed liquid was heated to 80℃, and an initial mixed monomer mixture of TFE (tetrafluoroethylene) and PMVE (perfluoromethyl vinyl ether) was introduced into the mixed liquid at a molar ratio of 45:55 until the reaction pressure reached 2.5MPa. Then, 5g of ammonium persulfate initiator was added to the mixed liquid to initiate the polymerization reaction at 80℃ and 2.5MPa. Subsequently, during the reaction, a mixture of TFE and PMVE monomers in a molar ratio of 55:45 was continuously added, maintaining a constant pressure of 2.5 MPa inside the reactor. The polymerization reaction continued until the amount of added monomers reached 6.3 kg. Feeding was then stopped, and after the pressure reached equilibrium, the reaction was completed, resulting in an emulsion. The solid content of the emulsion was tested and found to be in the range of 15%–30%. The gaseous monomers were recovered, and the emulsion was then cooled to 25°C using circulating cooling water. The emulsion was then coagulated using a 3 wt% nitric acid aqueous solution. After coagulation, the emulsion was washed with water, dried, and heat-treated sequentially to obtain a solvent-resistant perfluoroether rubber that can be peroxide-cured.

[0092] The drying process employs vacuum drying at a temperature of 100℃; the heat treatment involves microwave heating for 30 minutes under inert gas protection at a temperature of 290℃.

[0093] The resistivity of deionized water is ≥18 MΩ·m.

[0094] Example 2-19

[0095] The differences between Examples 2-17 and Example 1 are as follows: the amount of pH adjuster and the first monomer added is different relative to the mass of deionized water; the molar ratio of the second and third monomers in the initial mixed monomers is different; the molar ratio of the second and third monomers in the supplemented mixed monomers is different; the polymerization reaction temperature and polymerization reaction pressure are different; and the amount of initiator added is different relative to the mass of deionized water. See Table 1 for details. The rest is the same as in Example 1.

[0096] Among them, Examples 18-19 are compared with Example 2, except that the type of the first monomer is different, while the rest are the same as Example 2. In Example 18, the first monomer is CF2=CFO(CF2)3COOH, and in Example 19, the first monomer is CF2=CFO(CF2)4COOH.

[0097] Table 1. Reaction parameter data for Examples 1-19

[0098]

[0099] Comparative Example 1

[0100] The following compound was obtained by adding 14.5 L of deionized water and 145 ml of microemulsion to a 22 L stainless steel reactor and mixing them.

[0101] 32ml of perfluoropolyoxyethylene, with an average molecular weight of 600, has the following general formula.

[0102] CF2ClO(CF2-CF(CF3)O) n (CF2O) m CF2COOH

[0103] Where n / m = 10

[0104] In Comparative Example 1, the perfluoropolyoxyethylene used had n = 2.34 and m = 0.234. The structural formula of the perfluoropolyoxyethylene is as follows:

[0105] (CF2ClO(CF2-CF(CF3)O) 2.34 (CF2O) 0.234 CF2COOH);

[0106] 32 ml of NH3 aqueous solution, concentration 30%.

[0107] 62ml softened water

[0108] 19ml Galden DO2, average molecular weight 450, its formula is:

[0109] CF3O(CF2-CF(CF3)O) n＇ (CF2O) m＇ CF3

[0110] Where n' / m' = 20

[0111] The Galden DO2 compound used in Comparative Example 1 has n' = 1.74 and m' = 0.087, and its specific structural formula is as follows:

[0112] (CF3O(CF2-CF(CF3)O) 1.74 (CF2O) 0.087 CF3);

[0113] The reactor was evacuated and heated to 80°C. 35g of 1,4-diiodoperfluorobutane was added, along with an initial mixture of TFE and PMVE monomers at a molar ratio of 35:65, until the reaction pressure reached 2.5MPa. 0.7g of ammonium persulfate initiator was then added. From the start of the polymerization reaction, for every 5% increase in monomer conversion, 0.9g of the diene CH2=CH-(CF2)6-CH=CH2 was added, totaling 18g. Subsequently, a supplementary mixture of TFE and PMVE monomers at a molar ratio of 60:40 was continuously added, maintaining a constant pressure within the reactor. The polymerization reaction continued for 160 minutes, after which feeding was stopped. After pressure equilibrium was reached, the reaction was complete, yielding an emulsion. The gaseous monomers were recovered. The emulsion was then cooled, coagulated, washed with water, and dried to obtain peroxide-curable perfluoroether rubber. The cooling, coagulation, washing, and drying processes were the same as in Example 2.

[0114] Comparative Example 2

[0115] (1) Mix the ionic surfactant CF3-CF2-CF2-O-(CF2-CF2-O)2-CF2-COOH, the nonionic surfactant (polyoxyethylene oleate), the fluoroether oil (CF3-CF2-CF2-O-(CF2-CF2-O)2-CF3), and water in a weight ratio of (15:10:5:70), gently stir and heat to 40°C to mix evenly. The weight is 500g. Add 240g of CF3CF2CF2OCF(CF3)CF2OF=CF and 3500g of CF3OCF2OCF2OCF=CF2 and mix evenly.

[0116] (2) Add 30L of deionized water and 45g of disodium hydrogen phosphate to the reaction vessel, replace the air in the reaction vessel with nitrogen to make the oxygen content less than 20ppm, raise the reaction vessel to 90℃, add the initial mixed monomers with a molar ratio of TFE to PMVE of 70:30, raise the pressure to 4.4Mpa, turn on the stirring to make the monomers in the reaction vessel fully mixed.

[0117] (3) The mixed liquid from step (1) was added to the reaction vessel, followed by 160g of a 5wt% potassium persulfate aqueous solution to initiate the polymerization reaction. Subsequently, 50g of 2-bromoperfluoro(ethyl vinyl) and 30g of 1,4-diiodoperfluorobutane were added. During the reaction, a mixture of TFE and PMVE in a molar ratio of 30:70 was continuously added to maintain the reaction vessel pressure at 4.4MPa and the temperature at 90℃. After the predetermined feed amount was reached, the emulsion was cooled, coagulated, washed with water, and dried to obtain peroxide-curable perfluoroether rubber. The cooling, coagulation, washing, and drying processes were the same as in Example 2.

[0118] Comparative Example 3

[0119] (1) Mix the ionic surfactant CF3-CF2-CF2-O-(CF2-CF2-O)2-CF2-COOH, the nonionic surfactant (polyoxyethylene oleate), the fluoroether oil (CF3-CF2-CF2-O-(CF2-CF2-O)2-CF3), and water in a weight ratio of (18:14:3:65), gently stir and heat to 40°C to mix evenly. The weight is 500g. Add 240g of CF3CF2CF2OCF(CF3)CF2OF=CF and 3500g of CF3OCF2OCF2OCF=CF2 and mix evenly.

[0120] (2) Add 30L of deionized water and 45g of disodium hydrogen phosphate to the reaction vessel, replace the air in the reaction vessel with nitrogen to make the oxygen content less than 20ppm, raise the reaction vessel to 85℃, add a mixture of TFE and PMVE in a molar ratio of 65:35, raise the pressure to 4.0Mpa, turn on the stirrer to make the monomers in the reaction vessel fully mixed.

[0121] (3) The mixed liquid from step (1) was added to the reaction vessel, followed by 160g of a 5wt% potassium persulfate aqueous solution to initiate the polymerization reaction. Subsequently, 40g of CF2=CFOCF2CF2CF2OCF2Br and 30g of 1,4-diiodoperfluorobutane were added. During the reaction, a mixture of TFE and PMVE monomers in a molar ratio of 65:35 was continuously added to maintain the pressure in the reaction vessel at 4.0MPa and the temperature at 90℃. After the predetermined feed amount was reached, the emulsion was cooled, coagulated, washed with water, and dried to obtain peroxide-curable perfluoroether rubber. The cooling, coagulation, washing, and drying processes were the same as in Example 2.

[0122] The perfluoroether rubber products prepared in Examples 1-19 and Comparative Examples 1-3 were vulcanized.

[0123] Examples 1-19 use the following vulcanization formulation by weight: 100 parts of the perfluoroether rubber prepared in Examples 1-19, 0.7 parts of bis(2,5)-5-vinyl chloride agent, 5 parts of zinc oxide, 8 parts of carbon black, 7 parts of graphene, the first vulcanization temperature is 170℃, the first vulcanization time is 10 min, the second vulcanization temperature is 290℃, and the second vulcanization time is 16 h.

[0124] Comparative Example 1 uses the following vulcanization formula in parts by weight: 100 parts of rubber prepared in Comparative Example 1, 1.0 part of diene, 0.7 parts of bis(2,5)-5, 5 parts of zinc oxide, 8 parts of carbon black, and 7 parts of graphene. The first vulcanization temperature is 170℃ and the first vulcanization time is 10 min. The second vulcanization temperature is 290℃ and the second vulcanization time is 16 h.

[0125] Comparative Example 2 uses the following vulcanization formula in parts by weight: 100 parts of rubber prepared in Comparative Example 2, 1.5 parts of diene, 0.7 parts of bis(2,5)-5, 5 parts of zinc oxide, 8 parts of carbon black, and 7 parts of graphene. The first vulcanization temperature is 170℃ and the first vulcanization time is 10 min. The second vulcanization temperature is 290℃ and the second vulcanization time is 16 h.

[0126] Comparative Example 3 uses the following vulcanization formula in parts by weight: 100 parts of the rubber prepared in Comparative Example 2, 1.5 parts of TAIC, 0.7 parts of bis(2,5)-5, 5 parts of zinc oxide, 8 parts of carbon black, and 7 parts of graphene. The first vulcanization temperature is 170℃ and the first vulcanization time is 10 min. The second vulcanization temperature is 290℃ and the second vulcanization time is 16 h.

[0127] The vulcanizates of Examples 1-19 and Comparative Examples 1-3 were subjected to permanent compression set tests (316°C, 70h) according to ASTM D395. Specific test results are shown in Table 2.

[0128] Table 2

[0129]

[0130]

[0131] As shown in Tables 1 and 2, compared with Comparative Examples 1-3, the perfluoroether rubber prepared by the method of Comparative Examples 1-3 required the addition of a crosslinking agent for vulcanization during the vulcanization process. Furthermore, the per-compression set test at 316℃ for 70 hours showed a higher per-compression set rate. This indicates that by adding the first monomer CF2=CFO(CF2)nCOOH (n is 1-4), the second monomer tetrafluoroethylene, the third monomer perfluoroalkyl vinyl ether, and an initiator, perfluoroether rubber can be obtained through soap-free emulsion polymerization. This avoids the environmental hazards caused by the use of fluorinated surfactants and the impact of residual fluorinated surfactants on the performance of perfluoroether rubber. Simultaneously, vulcanization can be carried out without the use of a crosslinking agent. The per-compression set test at 316℃ for 70 hours showed a lower per-compression set rate, resulting in a solvent-resistant perfluoroether rubber product with superior heat resistance.

[0132] Comparing Examples 2 and 6-9 with Examples 10-11, in Example 10, the amount of the first monomer added was less than 0.05% of the mass of deionized water, and the permanent compression set test was conducted at 316℃ for 70 hours, resulting in a high permanent compression set rate. In Example 11, the amount of the first monomer added was more than 0.8% of the mass of deionized water, and the permanent compression set rate was also high. This indicates that when the amount of the first monomer added is within the range of 0.05% to 0.8% of the mass of deionized water, the prepared perfluoroether rubber has a low permanent compression set rate and superior heat resistance.

[0133] A comparison of Examples 2, 14-15 and Example 16 shows that the polymerization reaction pressure in Example 16 is lower than 2.0 MPa. The permanent compression set test was conducted at 316°C for 70 hours. The permanent compression set rate was high in the permanent compression set test, indicating that the polymerization reaction pressure is in the range of 2 to 3 MPa, which is beneficial to reduce the permanent compression set rate of perfluoroether rubber and improve the heat resistance of rubber products. A comparison of Examples 2 and 17 shows that in Example 17, the molar ratio of the second and third monomers in the initial mixed monomers was not in the range of (30-50):(50-70), and the molar ratio of the second and third monomers in the supplemented mixed monomers was not in the range of (60-70):(30-40). The resulting perfluoroether rubber exhibited a significantly increased compression set. This indicates that in the preparation of perfluoroether rubber, when the molar ratio of the second and third monomers in the initial mixed monomers was in the range of (30-50):(50-70), and the molar ratio of the second and third monomers in the supplemented mixed monomers was in the range of (60-70):(30-40), solvent-resistant perfluoroether rubber products with low compression set and superior heat resistance can be obtained.

[0134] Compared with Examples 18-19, Example 2 changed the type of the first monomer. As long as the first monomer satisfies the structural formula CF2=CFO(CF2)nCOOH, where n is 1~4, it can undergo polymerization reaction with the second and third monomers to generate a perfluoroether rubber that can be vulcanized without the use of a crosslinking agent. The permanent compression set test was carried out at 316℃ for 70h, and the permanent compression set rate was low, resulting in a solvent-resistant perfluoroether rubber product with better heat resistance.

[0135] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing perfluoroether rubber via soap-free emulsion polymerization, characterized in that, Includes the following steps: Deionized water, the first monomer, and the pH adjuster are mixed to obtain a mixed liquid; The mixed liquid is heated to the reaction temperature, and the second and third monomers are introduced into the mixed liquid to the reaction pressure. An initiator is added to the mixed liquid to carry out the polymerization reaction. After the reaction is completed, an emulsion is obtained. The emulsion is then post-treated to obtain perfluoroether rubber. The first monomer is the compound shown in Formula 1. CF2=CFO(CF2)nCOOH, Equation 1 Where n is an integer from 1 to 4; The second monomer is tetrafluoroethylene, and the third monomer is a perfluoroalkyl vinyl ether.

2. The method for preparing perfluoroether rubber by soap-free emulsion polymerization according to claim 1, characterized in that, The reaction temperature is 70–90°C, and the reaction pressure is 2.0–3.0 MPa.

3. The method for preparing perfluoroether rubber by soap-free emulsion polymerization according to claim 1, characterized in that, The steps of introducing a second and a third monomer into the mixed liquid to the reaction pressure, and adding an initiator to the mixed liquid to carry out the polymerization reaction, specifically include the following steps: An initial mixed monomer containing a second monomer and a third monomer is introduced into the mixed liquid to a reaction pressure of 2.0–3.0 MPa. An initiator is added to the mixed liquid to carry out the polymerization reaction. During the reaction, an additional mixed monomer containing a second monomer and a third monomer is continuously added to maintain the pressure at 2.0–3.0 MPa.

4. The method for preparing perfluoroether rubber by soap-free emulsion polymerization according to claim 3, characterized in that, In the initial mixed monomers, the molar ratio of the second monomer to the third monomer is (30-50):(50-70); In the added mixed monomers, the molar ratio of the second monomer to the third monomer is (60-70):(30-40).

5. The method for preparing perfluoroether rubber by soap-free emulsion polymerization according to claim 1, characterized in that, The mixture of deionized water, the first monomer, and the pH adjuster is then added. The process includes the following steps: adding the deionized water, the first monomer, and the pH adjuster into the reaction vessel, evacuating and replacing the contents until the oxygen content is ≤20ppm; the amount of deionized water added is 40-60% of the volume of the reaction vessel. The resistivity of the deionized water is ≥18 MΩ·m; The pH adjuster is selected from one or more of ammonium carbonate, ammonium bicarbonate, dipotassium hydrogen phosphate, and disodium hydrogen phosphate, and the amount of pH adjuster added is 0.01-0.5% of the mass of the deionized water; The amount of the first monomer added is 0.05 to 0.8% of the mass of the deionized water.

6. The method for preparing perfluoroether rubber by soap-free emulsion polymerization according to claim 1 or 5, characterized in that, The amount of the first monomer added is 0.05 to 0.2% of the mass of the deionized water; The pH adjuster is ammonium carbonate; The amount of pH adjuster added is 0.05-0.1% of the mass of the deionized water.

7. The method for preparing perfluoroether rubber by soap-free emulsion polymerization according to claim 1, characterized in that, The perfluoroalkyl vinyl ether is selected from perfluoroalkyl vinyl ethers having 1 to 5 carbon atoms.

8. The method for preparing perfluoroether rubber by soap-free emulsion polymerization according to claim 1 or 7, characterized in that, The perfluoroalkyl vinyl ether includes one or more of PPVE, PEVE, and PMVE.

9. The method for preparing perfluoroether rubber by soap-free emulsion polymerization according to claim 1, characterized in that, The initiator is persulfate, and the amount of initiator added is 0.01% to 0.02% of the mass of the deionized water; The initiator may be added in one go, in batches, or continuously. The batch addition includes the following steps: preparing the initiator into an aqueous solution to obtain an initiator aqueous solution, and adding the initiator aqueous solution every 25 min to 35 min after the start of the polymerization reaction.

10. The method for preparing perfluoroether rubber by soap-free emulsion polymerization according to claim 1, characterized in that, The solid content of the emulsion is 15% to 30%; The step of obtaining perfluoroether rubber by post-processing the emulsion includes the following steps: passing the emulsion through cooling, coagulation, washing, drying and heat treatment in sequence to obtain perfluoroether rubber that can be vulcanized by peroxide; In the cooling step, the emulsion is cooled to 20-25°C; The coagulation method involves coagulating the emulsion using a 3wt% nitric acid aqueous solution; The washing solvent used for washing is deionized water, ethanol, or a mixture of ethanol and water, wherein the mass ratio of ethanol to water in the mixture is (30-70):(70-30). The drying temperature is 95–105°C, and the drying time is 24–48 hours. The heat treatment temperature is 280–320°C, and the heat treatment time is 25–60 min.

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