Method for preparing ultra-pure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin

Abstract

The embodiment of the invention provides a preparation method of ultra-pure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin. The preparation method comprises the following steps: carrying out devolatilization on tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer by using liquid or supercritical fluid; carrying out end group passivation on the devolatilized tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer under a swelling condition, and removing a passivation medium; and washing, dehydrating and drying the passivated tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and then removing magnetic particle impurities to obtain the ultra-pure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, so that the problems that unstable end groups are easily generated in the preparation process, fluorine ions are difficult to dissolve out and the like are solved; and the stability and the product quality of the prepared product are improved.

Description

Technical Field

[0001] The present application relates to the technical field of fluororesins, and in particular to a method for preparing ultrapure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin. Background Art

[0002] Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA for short) not only retains almost all the excellent properties of polytetrafluoroethylene (PTFE), but also can be melt processed. PFA has chemical and thermal stability. However, the chemical and thermal stability is adversely affected by the presence of terminal groups (e.g., -CH2OH, -COF, -COOH type terminal groups) in the polymer chain. For example, -COF and -COOH type terminal groups can trigger the "unzipping reaction" of the polymer.

[0003] The average particle size of the primary particles of the emulsion obtained by emulsion polymerization is about 200nm, and the average particle size of the dried powder after condensation is in the range of 0.1-1.0mm. If the devolatilization and end group passivation reaction of the dried powder are controlled by the mass transfer process, the following problems will occur: First, the end group passivation reaction mainly occurs on the outer surface of the particles, and the unstable end groups inside the particles will also have an adverse effect during the subsequent mixing and extrusion process; second, when the existing process is dried and devolatilized at high temperature, if the diffusion within the particles is the controlling step, there are still residual volatiles, which are not conducive to the passivation process and affect the quality of subsequent products; third, the dissolution of fluoride ions during washing is difficult to control, resulting in the products being unsuitable for use in semiconductor processes in many cases.

[0004] Based on this, the present application provides an improved method for preparing ultrapure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin. Summary of the invention

[0005] In view of this, the embodiments of this specification provide a method for preparing an ultra-pure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, which improves the problem of unstable end groups easily generated during the preparation process, controls the amount of fluoride ion dissolution, and improves the stability of the copolymer and the product quality.

[0006] The embodiments of this specification provide the following technical solutions:

[0007] The method for preparing ultrapure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin provided in the embodiments of this specification comprises the following steps:

[0008] Devolatilize tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer powder using liquid or supercritical fluid;

[0009] Passivating the end groups of the devolatilized tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer under swelling conditions, and removing the passivation medium;

[0010] The passivated tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is washed, dehydrated and dried to remove magnetic particle impurities, thereby obtaining an ultra-pure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin.

[0011] Optionally, before devolatilization, the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is obtained by emulsion polymerization of tetrafluoroethylene and perfluoroalkyl vinyl ether.

[0012] Optionally, the perfluoroalkyl vinyl ether includes perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether.

[0013] Optionally, during fluorination, the cumulative amount of fluorination medium introduced per unit mass of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is 1-10 g / kg polymer, and during amination, the cumulative amount of amination medium introduced is 1-10 g / kg polymer.

[0014] Optionally, a tetrafluoroethylene-perfluoroalkyl vinyl ether polymer emulsion obtained by polymerizing 90-99 parts by mass of tetrafluoroethylene and 1-10 parts by mass of perfluoroalkyl vinyl ether is diluted, stirred and condensed, washed with ultrapure water at 90-98° C., and vacuum dried at 200-280° C. to obtain tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer micropowder.

[0015] Optionally, before diluting and stirring the emulsion, the pH of the emulsion is adjusted to between 8 and 10.

[0016] Optionally, the liquid or supercritical fluid is N2 or CO2.

[0017] Optionally, the liquid or supercritical fluid contains an entrainer, and the entrainer is ethanol or methanol at 0%-4% of the mass of N2 or CO2.

[0018] Optionally, during devolatilization, the temperature of the liquid or supercritical fluid is 40-85°C and the pressure is 8-20MPa, and maintained for 2-10 hours. Finally, liquid or supercritical fluid is used for purging, and the apparent flow rate of the liquid or supercritical fluid is 0.02-0.08m / s. The devolatilization process is stopped when the detected organic matter concentration is less than 0.01mg / kg.

[0019] Optionally, the duration of swelling tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer with fluid or supercritical fluid is 0.5-2 hours.

[0020] Optionally, the swelling condition is to perform fluorination treatment after replacing the fluid or supercritical fluid with a gas flow containing a fluorinating agent.

[0021] Optionally, the end group passivation includes fluorination and amination, and the unreacted fluorinating agent is removed after fluorination and then the amination reaction is carried out.

[0022] Optionally, the fluorinating agent used in the fluorination is one of F2 and NF3 or a mixture of the two; the mass proportion of F2 in the fluorinating agent is 10-30%, and the balance gas is N2 or CO2.

[0023] Optionally, the aminating agent used in the amination is NH3; the mass proportion of NH3 in the aminating agent is 10-60%, and the balance gas is N2.

[0024] Optionally, the passivation temperature of the fluorination is 80-280°C; the reaction temperature of the amination is 60-80°C.

[0025] Optionally, the passivated tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is washed with ultrapure water at 90-98° C., wherein the resistivity of the ultrapure water is ≥18.2 MΩ·cm.

[0026] Optionally, a high gradient magnetic field is used to remove magnetic particle impurities, the high gradient magnetic field strength is 4000-8000 Oe, the magnetic medium separation chamber is filled with magnetically conductive stainless steel, the diameter of the stainless steel mesh wire is 5-300 μm, and the filling rate is 15-25%.

[0027] Optionally, the number of unstable end groups of the final product of the ultrapure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin is ≤2ppm, the total metal ion content after immersion in ultrapure water is ≤200ppb, and the extracted fluoride ion content is less than 0.5ppm.

[0028] Compared with the prior art, the at least one technical solution adopted in the embodiments of this specification can achieve the following beneficial effects:

[0029] Ultrapure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin is obtained by subjecting tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin to liquid or supercritical fluid devolatilization and then end group passivation treatment under swelling conditions. According to detection, unstable end groups -COOF and -COF are reduced by more than 90% and become stable end groups -CONH2 and -CF3, the stability of the prepared polymer is greatly improved and the metal ion content in the polymer is reduced. According to the test, the total metal ion concentration is less than 200ppb after immersion in ultrapure water for one month; and the thermal stability of the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer treated with devolatilization and end group passivation is significantly improved, and even if the processing and molding temperature is not reduced, the dissolution amount of fluoride ions can be greatly reduced, and the extracted fluoride ion content is less than 0.5ppm, which reduces the corrosion of the dissolved fluoride ions to the metal and reduces the pollution of high-purity water and high-purity reagents in the semiconductor process; in addition, the prepared product does not change color when exposed to high temperature and oxidizing environment during subsequent processing and use, and its products can be used in high-clean semiconductor processes. DETAILED DESCRIPTION

[0030] The embodiments of the present application are described in detail below.

[0031] The following describes the implementation methods of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific implementation methods, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present application.

[0032] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present application, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number and aspect described herein can be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this device and / or practice this method.

[0034] Additionally, in the following description, specific details are provided to facilitate a thorough understanding of the examples. However, it will be understood by those skilled in the art that the examples can be practiced without these specific details.

[0035] The method for preparing ultrapure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin provided in the embodiment of the present application comprises the following steps:

[0036] S1. Devolatilizing tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer powder using a liquid or a supercritical fluid;

[0037] S2, passivating the end groups of the devolatilized tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer under swelling conditions, and removing the passivation medium;

[0038] S3, washing, dehydrating and drying the passivated tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer to remove magnetic particle impurities and obtain ultra-pure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin.

[0039] Optionally, before devolatilization, the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is obtained by emulsion polymerization of tetrafluoroethylene and perfluoroalkyl vinyl ether.

[0040] Optionally, the perfluoroalkyl vinyl ether includes perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether.

[0041] Optionally, during fluorination, the cumulative amount of fluorination medium introduced per unit mass of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is 1-10 g / kg polymer, and during amination, the cumulative amount of amination medium introduced is 1-10 g / kg polymer.

[0042] Optionally, a tetrafluoroethylene-perfluoroalkyl vinyl ether polymer emulsion obtained by polymerizing 90-99 parts by mass of tetrafluoroethylene and 1-10 parts by mass of perfluoroalkyl vinyl ether is diluted, stirred and condensed, washed with ultrapure water at 90-98° C., and vacuum dried at 200-280° C. to obtain tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer micropowder.

[0043] Optionally, before diluting and stirring the emulsion, the pH of the emulsion is adjusted to between 8 and 10.

[0044] Optionally, the liquid or supercritical fluid is N2 or CO2.

[0045] Optionally, the liquid or supercritical fluid contains an entrainer, and the entrainer is ethanol or methanol at 0%-4% of the mass of N2 or CO2.

[0046] Optionally, during devolatilization, the temperature of the liquid or supercritical fluid is 40-85°C and the pressure is 8-20MPa, and maintained for 2-10 hours. Finally, liquid or supercritical fluid is used for purging, and the apparent flow rate of the liquid or supercritical fluid is 0.02-0.08m / s. The devolatilization process is stopped when the detected organic matter concentration is less than 0.01mg / kg.

[0047] Optionally, the duration of swelling tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer with fluid or supercritical fluid is 0.5-2 hours.

[0048] Optionally, the swelling condition is to perform fluorination treatment after replacing the fluid or supercritical fluid with a gas flow containing a fluorinating agent.

[0049] Optionally, the end group passivation includes fluorination and amination, and the unreacted fluorinating agent is removed after fluorination and then the amination reaction is carried out.

[0050] Optionally, the fluorinating agent used in the fluorination is one of F2 and NF3 or a mixture of the two; the mass proportion of F2 in the fluorinating agent is 10-30%, and the balance gas is N2 or CO2.

[0051] Optionally, the aminating agent used in the amination is NH3; optionally, the mass proportion of NH3 in the aminating agent is 10-60%, and the balance gas is N2.

[0052] Optionally, the passivation temperature of the fluorination is 80-280°C; the reaction temperature of the amination is 60-80°C.

[0053] Optionally, the passivated tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is washed with ultrapure water at 90-98° C., wherein the resistivity of the ultrapure water is ≥18.2 MΩ·cm.

[0054] Optionally, a high gradient magnetic field is used to remove magnetic particle impurities, the high gradient magnetic field strength is 4000-8000 Oe, the magnetic medium separation chamber is filled with magnetically conductive stainless steel, the diameter of the stainless steel mesh wire is 5-300 μm, and the filling rate is 15-25%.

[0055] Optionally, the number of unstable end groups of the ultrapure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin is ≤2ppm, the total metal ion content after immersion in ultrapure water is ≤200ppb, and the extracted fluoride ion content is less than 0.5ppm.

[0056] In some embodiments, in the above-mentioned step S1, the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer emulsion prepared by aqueous emulsion polymerization is subjected to condensation, washing and centrifugal dehydration treatment, so that the condensation is dispersed into particles, while preventing the formation of agglomerates, and the average particle size range of the generated polymer powder is 0.1-1.0 mm, which is conducive to removing the free water and part of the bound water contained in the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and keeping most of the particles from adhering to each other. Then, the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is vacuum dried, and then the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is devolatilized using a liquid or a supercritical fluid, for example, CO2, the devolatilization temperature is 25-80°C, and the pressure is 7-12MPa. Since the supercritical fluid molecules have a strong permeability, when the supercritical fluid molecules are dissolved in the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, the polymer will swell. During the devolatilization process, the volatile solute diffuses from the inside to the outside at the beginning, and the supercritical fluid molecules diffuse from the outside to the inside, and then gradually reach mass transfer equilibrium. The volume of the polymer phase will change as the mass transfer process proceeds.

[0057] In some embodiments, the liquid or supercritical fluid CO2 contains an entrainer, which includes ethanol and methanol, and the amount of the entrainer is 0%-4% of the mass of CO2. The use of an entrainer can enhance the selectivity, solubility and devolatilization efficiency of the CO2 devolatilization process, and can be miscible with the fluid solvent and have a volatility between the devolatilized substance and the supercritical component to improve its selectivity and solubility for the devolatilization component. At the same time, the unstable end group reacts with alcohols to generate a relatively stable ester end group, for example, the unstable end group reacts with methanol to generate a relatively stable methyl ester end group. Since the concentration of the components is low during the devolatilization process, the error caused by the adhesion of the pipeline and the container after the decompression release is large, the mass difference of the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer before and after the devolatilization can be taken to estimate the mass of the volatile matter.

[0058] In some embodiments, in the above-mentioned S2 step, the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is end-group passivated by fluorination and amination under swelling conditions. In some embodiments, the swelling temperature of the swelling conditions is 30-70°C and the pressure is 9-12MPa. In some embodiments, the fluorinating agent used in the fluorination process includes one or a mixture of two of F2 and NF3. Preferably, a fluorinating agent with a concentration of 1%-10% (v / v) F2 is used, the balance gas is N2 or CO2, and the temperature of fluorination passivation is 80-280°C. The amination agent in the amination process uses NH3, preferably 10-60% (v / v) NH3, the balance gas is N2, and the amination reaction temperature is 60-80°C.

[0059] Exemplarily, the initial temperature of the fluorination passivation is set at 80°C. As the passivation process proceeds, the bed temperature gradually increases, and the peak gradually moves toward the outlet. The temperature rise is related to the concentration and flow rate of the fluorinating agent. Generally, the bed temperature is controlled by limiting the concentration and flow rate of the fluorinating agent so that it is lower than 280°C to prevent local agglomeration of the polymer powder. The decomposition temperature of ammonium carbonate is 58°C, and the initial temperature of the amination temperature is set at 60°C to prevent unreacted NH3 from reacting with CO2 to form ammonium carbonate particles during the passivation process.

[0060] After the devolatilized tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is passivated under swelling conditions, the cumulative amount of passivation medium introduced per unit mass of polymer is 1-10 g / kg polymer, and the cumulative amount of amination medium introduced after removing the passivation medium is 1-10 g / kg polymer.

[0061] The thermal stability of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer after devolatilization and end group passivation treatment is significantly improved. Even if the processing temperature is not lowered, the dissolution of fluoride ions can be greatly reduced, and the metal content caused by metal corrosion during molding can be reduced, thereby reducing the pollution of high-purity water and high-purity reagents in the semiconductor industry.

[0062] The preparation method of the ultra-pure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin provided in the embodiments of the present application is further described below in conjunction with specific examples and comparative examples.

[0063] Example 1

[0064] First, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) is prepared.

[0065] In a 5L autoclave reactor, 3L ultrapure water (resistivity ≥ 18.2MΩ·cm), 720g (7.2mol; 97.32% by mass) tetrafluoroethylene (MW 100.01); 19.8g (0.074mol; 2.68% by mass) perfluoropropyl vinyl ether PPVE (MW 266.04); 0.21g initiator ammonium persulfate (APS; MW 228.2); 3.1g surfactant ammonium perfluorooctanoate; 2g ammonium carbonate (MW 96) buffer substance; and 0.2mL chain transfer agent methanol were added. The polymerization pressure (TFE pressure) was 2.1MPa, the temperature was 75°C, PPVE was added once, and the reaction pressure of the polymerization process was controlled by continuous addition of TFE.

[0066] When the final reaction pressure drops to 0.1 MPa, the reaction is terminated, the unreacted TFE monomer is recovered, and the material is discharged after cooling. The emulsion is diluted with deionized water to a solid content of about 10%, and ammonia water is added to adjust the pH of the emulsion to 9.0. The mixture is coagulated at a stirring speed of 120 rpm (r / min) and 30° C. for 10 minutes to separate the coagulant.

[0067] The above-mentioned condensate was washed with ultrapure water until the resistivity of the washing water was ≥17.5 MΩ·cm, and centrifuged for dehydration to obtain about 1370 g of wet tetrafluoroethylene-perfluoropropyl vinyl ether copolymer powder with an average particle size of 0.32 mm.

[0068] The wet tetrafluoroethylene-perfluoropropyl vinyl ether copolymer powder was dried in a vacuum drying oven at 200° C. for 24 h. The absolute pressure of the drying oven was 0.01 MPa. The mass of the dried polymer powder was about 712 g.

[0069] S1. Put 350 g of the vacuum-dried powder into a stainless steel inner cylinder. The cylinder body uses a 2000-mesh stainless steel screen (Tyler mesh, about 6.5 μm). The inner cylinder is placed in an extraction device. The gap between the inner cylinder and the extraction device is sealed with a PTFE sealing gasket.

[0070] Supercritical CO2 was used as the extractant, and a plunger pump was used to add methanol entrainer, the mass of which was 2% of the mass of CO2. The supercritical CO2 temperature was 85°C, the pressure was 12MPa, and the apparent flow rate of CO2 was 0.05m / s. Finally, CO2 was used for purging, and the concentration of organic matter in the tail gas was detected by GC-MS (Agilent 8860-5977B). When the concentration of organic matter was less than 0.01mg / kg, the devolatilization process was stopped; the extraction temperature and pressure were maintained for 2h to allow the swelling to approach equilibrium.

[0071] S2, after the system pressure is reduced to about 4MPa, the CO2 fluid is switched to a fluid containing a fluorinating agent at a pressure of 4MPa, and a fluorination treatment is carried out under swelling conditions, the concentration of the fluorinating agent F2 is 5.0% (v / v) (N2 balance; Shanghai Fubon Chemical Co., Ltd.), the fluorination temperature is 80°C, the flow rate is 0.3L / min, and after the fluorination treatment, N2 is replaced to purge and remove the fluorine-containing gas in the gaps to obtain a devolatilized and fluorinated tetrafluoroethylene-perfluoropropyl vinyl ether copolymer. The cumulative amount of fluorine gas per unit mass of the polymer reaction is about 4.8g / kg polymer.

[0072] Then, the fluid was further switched to an NH3-containing fluid at a pressure of 4 MPa for amination treatment, the amination agent concentration was 5.0% (v / v) (N2 balance; Shanghai Fubon Chemical Co., Ltd.), the amination temperature was 60°C, the flow rate was 0.2 L / min, and after the amination treatment, N2 was replaced to purge and remove the NH3-containing gas in the gaps to obtain a tetrafluoroethylene-perfluoropropyl vinyl ether copolymer that was devolatilized and end-group passivated (including fluorination and amination), and the cumulative NH3 reacted per unit mass of the polymer was approximately 4.8 g / kg of the polymer.

[0073] S3. The tetrafluoroethylene-perfluoropropyl vinyl ether copolymer product which has been subjected to devolatilization and end group passivation treatment is placed in deionized water at 90° C. for washing, and after centrifugal dehydration, is dried in a vacuum drying oven at 200° C. to obtain a tetrafluoroethylene-perfluoropropyl vinyl ether copolymer with devolatilization end group passivation.

[0074] Then, the dried material is treated by a high gradient magnetic field, wherein the high gradient magnetic field strength is 6000 Oe (A / m), and the magnetic medium separation chamber is filled with magnetic conductive stainless steel 430, the stainless steel mesh wire diameter is 80 μm, and the filling rate is 10%.

[0075] Finally, the corresponding parameters were measured by the corresponding instruments. The functional group parameters of the tetrafluoroethylene-perfluoropropyl vinyl ether copolymer surface were detected by microscopy-infrared (Shimadzu ATM9000), and the metal ion content after ashing and ultrapure water immersion was tested by ICP-MS (PE Nexlon2200). The weight loss parameters were measured by a balance (Shimadzu, accuracy 0.1 mg).

[0076] The mass change Q before and after devolatilization is

[0077] Q=(m1-m2) / m1

[0078] Wherein m1 and m2 are the masses of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer before and after devolatilization, respectively.

[0079] Determination of fluoride ion concentration: Fluoride ions were extracted with a solution prepared with 5 mL of methanol and 10 mL of buffer solution for determination. The buffer solution consisted of 500 g of NaCl, 500 g of acetic acid, 320 g of NaOH, and 5 g of sodium citrate dissolved in ultrapure water. A fluoride ion electrode (Mettler, SD50 F-ion Kid) was used to measure the fluoride ion content.

[0080] Example 2

[0081] The difference between this embodiment and embodiment 1 is that there is no entrainer during the extraction and devolatilization process, the fluorination temperature is 100°C, and the amination temperature is 80°C.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 1 is that no swelling is performed. After the supercritical CO2 is devolatilized and cooled to room temperature, fluorination and amination are performed at a certain temperature and pressure.

[0084] Comparative Example 2

[0085] The difference between this comparative example and Example 2 is that no swelling is performed. After the supercritical CO2 is devolatilized and cooled to room temperature, fluorination and amination are performed at a certain temperature and pressure.

[0086] Table 1 below shows the test results of unstable end groups and the number of extracted fluoride ions before and after fluorination of Examples 1-2 and Comparative Examples 1-2.

[0087]

[0088] Table 2 below shows the results of the metal ion content measurement of tetrafluoroethylene-perfluoropropyl vinyl ether copolymer particles after immersion * .

[0089]

[0090]

[0091] *: Q / SMS002-2024 Immersion and liquid resistance test method for perfluoroether elastomers and rubber seals;

[0092] **: indicates the number of micrograms (μg) of extractables per kg of elastomer or rubber;

[0093] ***: Conductivity ≤ 0.055μS / cm.

[0094] By comparison in Table 1, it can be seen that the entrainer methanol is added during the devolatilization process, and part of the unstable end groups are partially converted into methyl esters -CO2CH3. After the end group passivation treatment, the unstable end groups are reduced by more than 90% and become stable end groups -CONH2. Swelling treatment is also helpful in reducing the metal ion content of the polymer, as shown in Table 2. By comparing the examples 1-2 and comparative examples 1-2 in Tables 1 and 2, it can be seen that the present application applies technology to tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, and further adopts the end group passivation method to solve the problem of many unstable end groups and poor stability of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, that is, the stability of the prepared polymer has been greatly improved. After immersion in ultrapure water for 1 month, the total metal ion concentration is less than 200ppb, which shows that the metal ion content of the polymer is also reduced, and the extracted fluoride ion content is less than 0.5ppm, which meets the semiconductor process with high cleanliness and harsh conditions.

[0095] In this specification, the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the product embodiment described later, since it corresponds to the method, the description is relatively simple, and the relevant parts can be referred to the partial description of the system embodiment.

[0096] At the same time, this specification uses specific words to describe the embodiments of this specification. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of this specification. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more in different positions in this specification does not necessarily refer to the same embodiment. In addition, certain features, structures or characteristics in one or more embodiments of this specification can be appropriately combined.

[0097] In addition, unless explicitly stated in the claims, the order of the processing elements and sequences described in this specification, the use of alphanumeric characters, or the use of other names are not intended to limit the order of the processes and methods of this specification. Although the above disclosure discusses some invention embodiments that are currently considered useful through various examples, it should be understood that such details are only for illustrative purposes, and the attached claims are not limited to the disclosed embodiments. On the contrary, the claims are intended to cover all modifications and equivalent combinations that are consistent with the essence and scope of the embodiments of this specification. For example, although the system components described above can be implemented by hardware devices, they can also be implemented only by software solutions, such as installing the described system on an existing processing device or mobile device.

[0098] The basic concepts have been described above. Obviously, for those skilled in the art, the above detailed disclosure is only for example and does not constitute a limitation of this specification. Although not explicitly stated here, those skilled in the art may make various modifications, improvements and corrections to this specification. Such modifications, improvements and corrections are suggested in this specification, so such modifications, improvements and corrections still belong to the spirit and scope of the exemplary embodiments of this specification.

Claims

1. A method for preparing ultrapure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin, characterized in that: include: Devolatilize tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer powder using liquid or supercritical fluid; Passivating the end groups of the devolatilized tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer under swelling conditions, and removing the passivation medium; The passivated tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is washed, dehydrated and dried to remove magnetic particle impurities, thereby obtaining an ultra-pure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin.

2. The preparation method according to claim 1, characterized in that: Before devolatilization, the tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is obtained by emulsion polymerization of tetrafluoroethylene and perfluoroalkyl vinyl ether.

3. The preparation method according to claim 2, characterized in that: The perfluoroalkyl vinyl ether includes perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and perfluoropropyl vinyl ether.

4. The preparation method according to claim 2, characterized in that: The tetrafluoroethylene-perfluoroalkyl vinyl ether polymer emulsion obtained by polymerizing 90-99 parts by mass of tetrafluoroethylene and 1-10 parts by mass of perfluoroalkyl vinyl ether is diluted, stirred and condensed, washed with ultrapure water at 90-98°C, and vacuum dried at 200-280°C to obtain tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer micropowder.

5. The preparation method according to claim 4, characterized in that: Before dilution, stirring and coagulation, adjust the pH of the emulsion to between 8 and 10.

6. The preparation method according to claim 1, characterized in that: During fluorination, the cumulative amount of fluorination medium introduced per unit mass of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is 1-10 g / kg polymer, and during amination, the cumulative amount of amination medium introduced is 1-10 g / kg polymer.

7. The preparation method according to claim 1, characterized in that: The liquid or supercritical fluid is N2 or CO2.

8. The preparation method according to claim 7, characterized in that: The liquid or supercritical fluid contains an entrainer, and the entrainer is ethanol or methanol at 0%-4% of the mass of N2 or CO2.

9. The preparation method according to claim 1, characterized in that: During devolatilization, the temperature of the liquid or supercritical fluid is 40-85°C and the pressure is 8-20MPa, which is maintained for 2-10 hours. Finally, liquid or supercritical fluid is used for purging. The apparent flow rate of the liquid or supercritical fluid is 0.02-0.08m / s. The devolatilization process is stopped when the detected organic matter concentration is less than 0.01mg / kg.

10. The preparation method according to claim 1, characterized in that: The duration of swelling tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer with fluid or supercritical fluid is 0.5-4 hours.

11. The preparation method according to claim 1, characterized in that: The end group passivation includes fluorination and amination, and the unreacted fluorinating agent is removed after fluorination and then the amination reaction is carried out.

12. The preparation method according to claim 11, characterized in that: The fluorinating agent used in the fluorination is one of F2 and NF3 or a mixture of the two; the mass proportion of F2 in the fluorinating agent is 10-30%, and the balance gas is N2 or CO2.

13. The preparation method according to claim 11, characterized in that: The aminating agent used in the amination is NH3; the mass proportion of NH3 in the aminating agent is 10-60%, and the balance gas is N2.

14. The preparation method according to claim 11, characterized in that: The passivation temperature of the fluorination is 80-280°C; the reaction temperature of the amination is 60-80°C.

15. The preparation method according to claim 1, characterized in that: The passivated tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is washed with ultrapure water at 90-98° C., wherein the resistivity of the ultrapure water is ≥18.2 MΩ·cm.

16. The preparation method according to claim 1, characterized in that: Magnetic particle impurities are removed by using a high gradient magnetic field, the high gradient magnetic field strength is 4000-8000 Oe, the magnetic medium separation chamber is filled with magnetically conductive stainless steel, the diameter of the stainless steel mesh wire is 5-300 μm, and the filling rate is 15-25%.

17. The preparation method according to claim 1, characterized in that: The number of unstable end groups of the ultrapure tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin is ≤2ppm, the total metal ion content after being soaked in ultrapure water is ≤200ppb, and the extracted fluoride ion content is less than 0.5ppm.

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