Stabilizing treatment method for unstable end group of fusible polytetrafluoroethylene and application

Abstract

The invention provides a stabilizing treatment method for an unstable end group of fusible polytetrafluoroethylene and application. The stabilizing treatment method comprises the following steps: obtaining fusible polytetrafluoroethylene resin RfCOOH containing carboxyl; the method comprises the following steps: carrying out reduction reaction on carboxyl-containing meltable polytetrafluoroethylene resin and a first reducing agent in a first solvent under the action of a halogenated salt catalyst to obtain fluoroalcohol RfCH2OH; a second reducing agent and halogenated fluoroalkyl carboxylate X (CF2) m + 1COOM are added into the RfCH2OH for a reaction, and carboxyl-terminated perfluoroether RfCH2O (CF2) m + 1COOH is obtained; adding a selective fluorination reagent and a noble metal acid salt into the carboxyl-terminated perfluoroether RfCH2O (CF2) m + 1COOH, and reacting to obtain a fusible polytetrafluoroethylene resin RfCH2O (CF2) mCF3 of which the terminal group is perfluoroether; and treating the fusible polytetrafluoroethylene resin of which the terminal group is perfluoro ether by fluorine-nitrogen mixed gas to obtain the perfluoro fusible polytetrafluoroethylene resin RfCF2O (CF2) mCF3. According to the method, regeneration of unstable end groups in the subsequent processing process is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of fluororesin synthesis, and specifically relates to a method for stabilizing unstable end groups of soluble polytetrafluoroethylene and its application. Background Art

[0002] In fluororesin materials, tetrafluoroethylene (TFE) and perfluoroalkyl vinyl ether (PAVE) are copolymerized by free radical copolymerization technology to produce products with excellent heat resistance, solvent resistance, high purity and other characteristics, so they are widely used in chemical industry, electronics, medical and other fields.

[0003] In the above application fields, especially in the field of electronic semiconductors, there are high requirements for the extraction rate of fluoride ions and the content of metal ions, that is, low fluoride ion extraction rate and low metal ion content. However, in the current general polymerization process, coagulation washing, extrusion granulation and other processes, due to the influence of the polymerization process, including factors such as the selection of initiator, solvent, emulsifier, etc., a large number of unstable end groups are generated, and the treatment of these end groups is basically concentrated after granulation. By performing fluorination treatment, hydrothermal treatment, oxidation treatment, methyl esterification treatment, ammonium salt or ammonia treatment to remove unstable end groups, these treatment methods can only solve the unstable end groups on the surface of PFA pellets, and the unstable end groups existing inside the PFA pellets are not removed. During the secondary melting process, due to the secondary rearrangement of molecular chains by heat, the unstable end groups inside the PFA pellets are re-exposed or the chains are broken, and unstable end groups are re-formed, generating HF, -CF 2 -CF 2 、CO 2 etc., which pollute the sample secondarily, corrode the processing equipment, and bring metal pollutants into the soluble polytetrafluoroethylene products, resulting in a reduction in product performance and a limited application range. Summary of the Invention

[0004] Aiming at the problem of incomplete removal of unstable end groups in soluble polytetrafluoroethylene in the prior art, the present invention provides a method for stabilizing unstable end groups of soluble polytetrafluoroethylene and its application.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0006] The present invention provides a method for stabilizing unstable end groups of soluble polytetrafluoroethylene and its application, including the following steps:

[0007] Obtain a soluble polytetrafluoroethylene resin R containing carboxyl groups f COOH;

[0008] The fusible polytetrafluoroethylene resin containing carboxyl groups undergoes a reduction reaction with a first reducing agent in a first solvent under the action of a halogenated salt catalyst to obtain a fluoroalcohol R f CH 2 OH;

[0009] To the R f CH 2 OH, a second reducing agent and a haloalkyl fluoroacetate X(CF 2 ) m+1 COOM are added for reaction to obtain a perfluoroether with a terminal carboxyl group R f CH 2 O(CF 2 ) m+1 COOH, where X is a halogen, M is a metal ion or an ammonium ion, and m is a positive integer from 0 to 5;

[0010] To the perfluoroether with a terminal carboxyl group R f CH 2 O(CF 2 ) m+1 COOH, a selective fluorination reagent and a noble metal acid salt are added for reaction to obtain a fusible polytetrafluoroethylene resin with a perfluorinated ether terminal group R f CH 2 O(CF 2 ) m CF 3 ;

[0011] The fusible polytetrafluoroethylene resin with a perfluorinated ether terminal group is treated with a fluorine-nitrogen mixed gas to obtain a perfluorinated fusible polytetrafluoroethylene resin R f CF 2 O(CF 2 ) m CF 3 .

[0012] Optionally, the perfluoroalkyl vinyl ether has the general formula CF 2 =CF(OC n F 2n+1 ), where n - 1 = m.

[0013] Optionally, the steps of the pretreatment are demulsification, pickling, washing, and drying. The demulsification is physical demulsification and / or electrolyte demulsification. The electrolyte in the electrolyte demulsification is selected from one or more of alkalis or organic or inorganic salts that hydrolyze to be alkaline; the acid used in the pickling is selected from one or more of formic acid, acetic acid, hydrochloric acid, nitric acid, and sulfuric acid.

[0014] Optionally, the first reducing agent includes one or more of borane, borohydride salts, and ammonia borane;

[0015] The halogenated salt includes one or more of Ti salt, Fe salt, Cu salt, and Zr salt, and the halogen in the halogenated salt includes one or more of Cl, Br, and I;

[0016] The first solvent includes one or more of diethyl ether, dimethyl ether, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0017] Optionally, the second reducing agent includes metal hydride; the halogenated fluoroalkane carboxylate includes ammonium bromofluoroalkane carboxylate; the selective fluorination reagent includes 1-fluoro-4-methyl-1,4-diazabicyclo[2.2.2]octane tetrafluoroborate; the noble metal acid salt includes soluble salts of gold, silver, and platinum metals;

[0018] The terminal carboxyl perfluoroether and the fusible polytetrafluoroethylene resin with a terminal perfluorinated ether are respectively dissolved in a second solvent at 25-30 °C and obtained by refluxing. The second solvent includes one or more of dioxane, dichloromethane, chloroform, N,N-dimethylformamide, and water.

[0019] Optionally, the molar ratio of the halogenated salt catalyst, the first reducing agent, and the fusible polytetrafluoroethylene resin containing a carboxyl group is (0.1-10):1:(2000-20000);

[0020] The molar ratio of the second reducing agent, the halogenated fluoroalkane carboxylate, and the fluoroalcohol is (0.1-10):1:(2000-20000);

[0021] The molar ratio of the selective fluorination reagent, the noble metal acid salt, and the terminal carboxyl perfluoroether is (0.1-10):1:(10000-100000).

[0022] Optionally, the step of obtaining the fusible polytetrafluoroethylene resin R f COOH includes:

[0023] Polymerize perfluoroalkyl vinyl ether and tetrafluoroethylene to prepare a fusible polytetrafluoroethylene emulsion with -COF. After pretreatment, convert -COF into a carboxyl group to obtain the fusible polytetrafluoroethylene resin R f COOH.

[0024] Optionally, the steps of the pretreatment are demulsification, pickling, washing, and drying. The demulsification is physical demulsification and / or electrolyte demulsification. The electrolyte in the electrolyte demulsification includes one or more of alkalis or organic or inorganic salts that hydrolyze to be alkaline; the acids used in the pickling include one or more of formic acid, acetic acid, hydrochloric acid, nitric acid, and sulfuric acid.

[0025] Optionally, the step of preparing the fusible polytetrafluoroethylene emulsion with -COF and -COOH further includes the following steps:

[0026] Add water, emulsifier, chain transfer agent and the perfluoroalkyl vinyl ether into a reaction vessel to obtain a mixed solution;

[0027] Heat up to the reaction temperature, introduce tetrafluoroethylene into the mixed solution until the reaction pressure is reached, and then add an initiator into the mixed solution for reaction;

[0028] Supplement tetrafluoroethylene and initiator to the mixed solution, maintain the pressure in the reaction vessel within the reaction pressure range until the reaction ends, and obtain a fusible polytetrafluoroethylene emulsion with -COF and -COOH.

[0029] Optionally, the emulsifier includes perfluoropolyether carboxylic acid or perfluoropolyether carboxylate;

[0030] The chain transfer agent includes one or more of methane, ethane, propane, cyclohexane, methanol, ethanol, hydrogen;

[0031] The initiator includes a peroxide initiator, and the peroxide initiator includes persulfate and / or perfluoroalkyl peroxide.

[0032] On the other hand, the present invention also provides an application of the stabilization treatment method of the unstable end groups of the fusible polytetrafluoroethylene as described in any one of the above in the fluorinated capping of fluorinated thermoplastic polymers.

[0033] According to the stabilization treatment method of the unstable end groups of the fusible polytetrafluoroethylene provided by the present invention, after converting -COF generated during the reaction into a carboxyl group, it is first reduced to a hydroxyl group, and then the hydroxyl group is etherified to generate a perfluorinated ether end group, thereby achieving capping treatment, realizing a good end group stabilization effect of the fusible polytetrafluoroethylene, avoiding the re-generation of unstable end groups during subsequent processing, and expanding the application range of the material. And compared with the existing end group treatment methods, the treatment method of the present invention significantly reduces the content of fluoride ions and heavy metal ions in the product, making it applicable to the semiconductor field. Description of the Drawings

[0034] Figure 1 It is the infrared spectrum of the fusible polytetrafluoroethylene resin with perfluorinated ether end groups in Example 1 and Comparative Example 1. Detailed Embodiments

[0035] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to 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.

[0036] An embodiment of the present invention provides a method for stabilizing unstable end groups of soluble polytetrafluoroethylene and its application, including the following operation steps:

[0037] Obtain soluble polytetrafluoroethylene resin R containing carboxyl groups f COOH.

[0038] The soluble polytetrafluoroethylene resin containing carboxyl groups undergoes a reduction reaction with a first reducing agent in a first solvent under the action of a halogenated salt catalyst to obtain fluoroalcohol R f CH 2 OH.

[0039] Add a second reducing agent and halogenated fluoroalkane carboxylate X(CF f CH 2 ) 2 ) m+1 COOM to react with R f CH 2 O(CF 2 ) m+1 COOH is obtained, where X is a halogen, M is a metal ion or an ammonium ion, and m is a positive integer from 0 to 5.

[0040] Add a selective fluorination reagent and a noble metal acid salt to the end-carboxyl perfluoroether R f CH 2 O(CF 2 ) m+1 COOH to react to obtain a soluble polytetrafluoroethylene resin with end groups of perfluorinated ethers R f CH 2 O(CF 2 ) m CF 3 .

[0041] Treat the soluble polytetrafluoroethylene resin with end groups of perfluorinated ethers through a fluorine-nitrogen mixed gas to obtain a perfluorinated soluble polytetrafluoroethylene resin R f CF 2 O(CF 2 ) m CF 3 .

[0042] In this embodiment, after converting -COF generated during the reaction process into a carboxyl group, it is first reduced to a hydroxyl group, and then the hydroxyl group is etherified to form the end group of perfluoroether, thereby achieving end-capping treatment, realizing a good end-group stabilization effect of soluble polytetrafluoroethylene, avoiding the re-generation of unstable end groups during subsequent processing, and expanding the application range of the material. Moreover, compared with the existing end-group treatment methods, the treatment method of the present invention significantly reduces the content of fluoride ions and heavy metal ions in the product, making it applicable to the semiconductor field.

[0043] In some embodiments, a soluble polytetrafluoroethylene resin R containing a carboxyl group is obtained f The steps of COOH include:

[0044] Perfluoroalkyl vinyl ether is polymerized with tetrafluoroethylene to prepare a soluble polytetrafluoroethylene emulsion with -COF. After pretreatment, -COF is converted into a carboxyl group to obtain a soluble polytetrafluoroethylene resin R containing a carboxyl group f COOH.

[0045] The unstable end groups are -COOH and -COF, and -COF is converted into -COOH through pretreatment. The specific reaction steps are shown in Formula I

[0046]

[0047] In some embodiments, the steps of the pretreatment are demulsification, pickling, washing, and drying. The demulsification is physical demulsification and / or electrolyte demulsification. The electrolyte in the electrolyte demulsification includes one or more of alkalis or organic or inorganic salts that hydrolyze to be alkaline. The acids used in the pickling include one or more of formic acid, acetic acid, hydrochloric acid, nitric acid, and sulfuric acid.

[0048] The molar ratio of the addition amount of the electrolyte to the addition amount of the emulsifier is 0.01 - 0.5:1.

[0049] In some embodiments, the steps of preparing the soluble polytetrafluoroethylene emulsion with -COF and -COOH further include the following steps:

[0050] Water, an emulsifier, a chain transfer agent, and the perfluoroalkyl vinyl ether are added to a reaction vessel to obtain a mixed solution.

[0051] The temperature is raised to the reaction temperature. After introducing tetrafluoroethylene into the mixed solution to the reaction pressure, an initiator is added to the mixed solution for reaction.

[0052] Tetrafluoroethylene and the initiator are replenished to the mixed solution, and the pressure in the reaction vessel is maintained within the reaction pressure range until the reaction ends to obtain a soluble polytetrafluoroethylene emulsion with -COF and -COOH.

[0053] Specifically, the reaction temperature is 20-90 °C, the reaction pressure is 0.6-5.0 Mpa, and the reaction time is 5-50 h. Preferably, the reaction time is 8-10 h.

[0054] In some embodiments, the addition amount of the emulsifier is 0.01-2 wt% of the mass of water, and the amount of the initiator used is 0.0001-0.5 wt% of the mass of water. The total addition amount of the initiator replenished multiple times is 0.00001-0.05 wt% of the mass of water.

[0055] In some embodiments, the perfluoroalkyl vinyl ether has the general formula CF 2 =CF(OC n F 2n+1 ), where n-1 = m, such that the ends of the generated perfluoroether with terminal carboxyl groups have the same structure as the side groups of soluble polytetrafluoroethylene, which is beneficial to improving the thermal stability and crystallization properties of soluble polytetrafluoroethylene.

[0056] In some embodiments, the steps of the pretreatment are demulsification, pickling, washing, and drying. The demulsification is physical demulsification and / or electrolyte demulsification. The electrolyte in the electrolyte demulsification is selected from one or more of alkalis or organic or inorganic salts that hydrolyze to be alkaline. The acid used in the pickling is selected from one or more of formic acid, acetic acid, hydrochloric acid, nitric acid, and sulfuric acid.

[0057] The molar ratio of the addition amount of the electrolyte to the addition amount of the emulsifier is 0.01-0.5:1.

[0058] In some embodiments, the first reducing agent includes one or more of borane, borohydride salts, and ammonia borane. Preferably, the first reducing agent includes ammonia borane.

[0059] The halogenated salt includes one or more of Ti salts, Fe salts, Cu salts, and Zr salts. The halogen in the halogenated salt includes one or more of Cl, Br, and I. Preferably, the halogenated salt includes TiCl 4 .

[0060] The first solvent includes one or more of diethyl ether, dimethyl ether, N,N-dimethylformamide, and N,N-dimethylacetamide. Preferably, the first solvent includes diethyl ether.

[0061] In some embodiments, the second reducing agent includes metal hydrides. Preferably, the second reducing agent includes sodium hydride. The halogenated fluoroalkyl carboxylate includes ammonium bromofluoroalkyl carboxylate. The selective fluorinating agent includes 1-fluoro-4-methyl-1,4-diazabicyclo[2.2.2]octane tetrafluoroborate, and the structural formula is The noble metal acid salts include soluble salts of gold, silver, and platinum metals. Preferably, the noble metal acid salts include silver nitrate.

[0062] In some embodiments, the terminal carboxyl perfluoroether and the fusible polytetrafluoroethylene resin with a perfluorinated ether end group are respectively obtained by dissolving in a second solvent at 25 - 30 °C and refluxing. The second solvent includes one or more of dioxane, dichloromethane, chloroform, N,N - dimethylformamide, and water.

[0063] Specifically, the second solvent for refluxing to prepare the terminal carboxyl perfluoroether at room temperature includes dioxane, and the second solvent for refluxing to prepare the fusible polytetrafluoroethylene resin with a perfluorinated ether end group at room temperature includes a mixed solvent of dichloromethane and water.

[0064] In some embodiments, taking the tetrafluoroethylene added to the fusible polytetrafluoroethylene resin as 15 kg, i.e., 150 mol, the molar ratio of the halogenated salt catalyst, the first reducing agent, and the fusible polytetrafluoroethylene resin containing a carboxyl group is (0.1 - 10):1:(2000 - 20000).

[0065] The molar ratio of the second reducing agent, the halogenated fluoroalkane carboxylate, and the fluoroalcohol is (0.1 - 10):1:(2000 - 20000).

[0066] The molar ratio of the selective fluorination reagent, the noble metal acid salt, and the terminal carboxyl perfluoroether is (0.1 - 10):1:(10000 - 100000).

[0067] In some embodiments, the emulsifier includes perfluoropolyether carboxylic acid or perfluoropolyether carboxylate. Specifically, the emulsifier includes ammonium perfluoropolyether formate and perfluoropolyether formic acid.

[0068] The chain transfer agent includes one or more of methane, ethane, propane, cyclohexane, methanol, ethanol, and hydrogen.

[0069] The initiator includes a peroxide initiator, and the peroxide initiator includes persulfate and / or perfluoroalkyl peroxide. Specifically, the peroxide includes ammonium persulfate, [R 1 C(=O)O] 2 ,R 1 is a perfluoroalkyl group with 1 - 6 carbon atoms.

[0070] In some embodiments, the number of supplementary additions is 1 - 5 times.

[0071] On the other hand, an embodiment of the present invention also provides an application of the method for stabilizing the unstable end groups of the fusible polytetrafluoroethylene as described in any one of the above in the fluorination capping of fluorine - containing thermoplastic polymers.

[0072] The present invention will be further described below by way of examples.

[0073] Example 1

[0074] In a 100 L polymerization kettle, 60 L of pure water and 300 g of CF 3 O(CF 2 O) 3 CF 2 COONH 4 3 are added. After evacuating and purging with nitrogen, when the oxygen content in the polymerization kettle is less than 10 ppm, 32 g of methane and 765 g of perfluoropropyl vinyl ether (PPVE) are added. The temperature is raised to 70 °C, and tetrafluoroethylene is added until the pressure reaches 1.8 MPa. 22.8 g of ammonium persulfate is added to start the reaction, and tetrafluoroethylene monomer and PPVE monomer are continuously added in a mass ratio of 100:2. When the added amount of tetrafluoroethylene is 5000 g and the added amount of PPVE is 100 g, 2.13 g of [CF 3 CF 2 CF 2 C(=O)O] 2 is added at one time; when the added amount of tetrafluoroethylene is 10000 g and the added amount of PPVE is 200 g, 2.13 g of [CF 3 CF 2 CF 2 C(=O)O] 2 is added at one time; when the added amount of tetrafluoroethylene is 15000 g and the added amount of PPVE is 300 g, 2.13 g of [CF 3 CF 2 CF 2 C(=O)O] 2 is added at one time. After 10 h from the start of the polymerization reaction, a total of 15000 g of tetrafluoroethylene, 300 g of PPVE, and 6.39 g of [CF 3 CF 2 CF 2 C(=O)O] 2 are added. The reaction is stopped, the temperature is lowered, the unreacted gas in the kettle is vented, and the mixture is transferred to a coagulation kettle. 8.26 g of 25 wt% concentrated ammonia water is added, diluted 10 times and then added to the coagulation kettle for electrolyte-stirring mechanical demulsification. The powder formed by demulsification is pickled with 1 mol / L acetic acid, washed thoroughly and dried. 9.26 g of ammonia borane and 56.90 g of titanium tetrachloride are added, and the mixture is refluxed thoroughly in an ether solvent to convert the terminal carboxyl group into a terminal hydroxyl group. The terminal hydroxyl group material is washed thoroughly and dried in an ether solvent, 0.72 g of sodium hydride and 4.83 g of Br(CF 2 ) 3COONa reacts at room temperature in the solvent dioxane, is then thoroughly washed and dried with dioxane, and then 9.59 g of 1-fluoro-4-methyl-1,4-diazabicyclo[2.2.2]octane tetrafluoroborate and 1.70 g of silver nitrate are added. The reaction is carried out at room temperature in a water and dichloromethane solution with a mass ratio of 1:10 to eliminate the terminal carboxylic acid, and a PFA resin with a perfluorinated ether end group is formed by treatment with a 10% fluorine-nitrogen mixed gas.

[0075] Example 2

[0076] This example is basically the same as Example 1, except that 13.89 g of ammonia borane and 85.35 g of titanium tetrachloride are added and refluxed thoroughly in an ether solvent to convert the terminal carboxyl group into a terminal hydroxyl group. The terminal hydroxyl group material is thoroughly washed and dried in an ether solvent, and 1.08 g of sodium hydride and 7.25 g of Br(CF 2 ) 3 COONa reacts at room temperature in the solvent dioxane, is then thoroughly washed and dried with dioxane, and then 14.385 g of 1-fluoro-4-methyl-1,4-diazabicyclo[2.2.2]octane tetrafluoroborate and 2.55 g of silver nitrate are added. The reaction is carried out at room temperature in a water and dichloromethane solution with a mass ratio of 1:10 to eliminate the terminal carboxylic acid, and a PFA resin with a perfluorinated ether end group is formed by treatment with a 10% fluorine-nitrogen mixed gas.

[0077] Example 3

[0078] This example is basically the same as Example 1, except that 4.63 g of ammonia borane and 28.45 g of titanium tetrachloride are added and refluxed thoroughly in an ether solvent to convert the terminal carboxyl group into a terminal hydroxyl group. The terminal hydroxyl group material is thoroughly washed and dried in an ether solvent, and 0.36 g of sodium hydride and 2.42 g of Br(CF 2 ) 3 COONa reacts at room temperature in the solvent dioxane, is then thoroughly washed and dried with dioxane, and then 4.80 g of 1-fluoro-4-methyl-1,4-diazabicyclo[2.2.2]octane tetrafluoroborate and 0.85 g of silver nitrate are added. The reaction is carried out at room temperature in a water and dichloromethane solution with a mass ratio of 1:10 to eliminate the terminal carboxylic acid, and a PFA resin with a perfluorinated ether end group is formed by treatment with a 10% fluorine-nitrogen mixed gas.

[0079] Example 4

[0080] This example is basically the same as Example 1, except that when the additional amount of tetrafluoroethylene is 5000 g and the additional amount of PPVE is 100 g, 2.28 g of ammonium persulfate is added at one time; when the additional amount of tetrafluoroethylene is 10000 g and the additional amount of PPVE is 200 g, 3.47 g of bis(2-ethylhexyl) peroxydicarbonate is added at one time; when the additional amount of tetrafluoroethylene is 15000 g and the additional amount of PPVE is 300 g, 3.99 g of dilauroyl peroxide is added at one time. 10 h after the start of the polymerization reaction, a total of 15000 g of tetrafluoroethylene, 300 g of PPVE, 2.28 g of ammonium persulfate, 3.47 g of bis(2-ethylhexyl) peroxydicarbonate, and 3.99 g of dilauroyl peroxide are added.

[0081] Example 5

[0082] This example is basically the same as Example 1, except that the halogenated fluoroalkane carboxylate is Br(CF 2 ) 4 COONa.

[0083] Comparative Example 1

[0084] In a 100 L polymerization kettle, 60 L of pure water, 300 g of CF 3 O(CF 2 O) 3 CF 2 COONH 4 are added, evacuated, and replaced with nitrogen. After the oxygen content in the polymerization kettle is less than 10 ppm, 32 g of methane and 765 g of perfluoropropyl vinyl ether (PPVE) are added. The temperature is raised to 70 °C, tetrafluoroethylene is added until the pressure reaches 1.8 MPa, and 22.8 g of ammonium persulfate is added to start the reaction. Tetrafluoroethylene monomer and PPVE monomer are continuously added in a mass ratio of 100:2. When the additional amount of tetrafluoroethylene is 5000 g and the additional amount of PPVE is 100 g, 2.13 g of [CF 3 CF 2 CF 2 C(=O)O] 2 is added at one time; when the additional amount of tetrafluoroethylene is 10000 g and the additional amount of PPVE is 200 g, 2.13 g of [CF 3 CF 2 CF 2 C(=O)O] 2 is added at one time; when the additional amount of tetrafluoroethylene is 15000 g and the additional amount of PPVE is 300 g, 2.13 g of [CF 3 CF 2 CF 2 C(=O)O] 2 is added at one time. 10 h after the start of the polymerization reaction, a total of 15000 g of tetrafluoroethylene, 300 g of PPVE, and 6.39 g of [CF3 CF 2 CF 2 C(=O)O] 2 Stop the reaction, cool down, vent the unreacted gas in the autoclave, transfer it to the coagulation kettle, and stir for mechanical demulsification. Wash and dry the powder formed by demulsification to obtain PFA resin.

[0085] Comparative Example 2

[0086] In a 100 L polymerization kettle, add 60 L of pure water and 300 g of CF 3 O(CF 2 O) 3 CF 2 COONH 4 300 g, evacuate, replace with nitrogen. After the oxygen content in the polymerization kettle is less than 10 ppm, add 32 g of methane and 765 g of perfluoropropyl vinyl ether (PPVE). Heat up to 70 °C, add tetrafluoroethylene until the pressure reaches 1.8 MPa, add 22.8 g of ammonium persulfate, start the reaction, and add tetrafluoroethylene monomer in batches. The amount of tetrafluoroethylene added in one batch is 5000 g. After 10 h from the start of the polymerization reaction, a total of 15000 g of tetrafluoroethylene is added. Stop the reaction, cool down, vent the unreacted gas in the autoclave, transfer it to the coagulation kettle, and stir for mechanical demulsification. Wash and dry the powder formed by demulsification to obtain PFA resin.

[0087] Comparative Example 3

[0088] In a 100 L polymerization kettle, add 60 L of pure water and 300 g of CF 3 O(CF 2 O) 3 CF 2 COONH 4 300 g, evacuate, replace with nitrogen. After the oxygen content in the polymerization kettle is less than 10 ppm, add 32 g of methane and 765 g of perfluoropropyl vinyl ether (PPVE). Heat up to 70 °C, add tetrafluoroethylene until the pressure reaches 1.8 MPa, add 22.8 g of ammonium persulfate, start the reaction, and add tetrafluoroethylene monomer in batches. The amount of tetrafluoroethylene added in one batch is 5000 g. After 10 h from the start of the polymerization reaction, a total of 15000 g of tetrafluoroethylene is added. Stop the reaction, cool down, vent the unreacted gas in the autoclave, transfer it to the coagulation kettle, and stir for mechanical demulsification. Wash and dry the powder formed by demulsification, and then obtain PFA resin through sintering, crushing, granulation, and end-group treatment with a fluorine-nitrogen mixed gas containing 10% fluorine gas.

[0089] Performance Test

[0090] Test Examples 1 - 5, and the metal ion content, fluoride ion content, and spherulite size in the soluble polytetrafluoroethylene resin in Comparative Examples 1 - 3 were tested. The results are shown in Table 1.

[0091] Testing method: The metal ion content is detected by ICP-MS, and the pretreatment method is to sample and detect after soaking in 10% nitric acid at 85°C for 168 h;

[0092] The fluoride ions are soaked in a methanol / water 1:1 solution for 48 h and then detected by an ion chromatograph;

[0093] The spherulite size is detected by the small-angle laser diffraction method.

[0094] Table 1

[0095] Metal ion content Fluoride ion content Spherulite size (μm) Example 1 203 ppt 31 ppb 2.8 Example 2 92 ppt 16 ppb 1.9 Example 3 356 ppt 45 ppb 3.2 Example 4 714 ppt 63 ppb 1.6 Example 5 208 ppt 30 ppb 4.6 Comparative Example 1 1380 ppb 3150 ppb 58 Comparative Example 2 1454 ppb 3654 ppb 65 Comparative Example 3 69 ppb 198 ppb 52

[0096] From the test data of Examples 1-5 and Comparative Examples 1-3, it can be seen that the treatment method of the unstable end groups in this example makes the metal ion content and fluoride ion content in the soluble polytetrafluoroethylene resin much lower than those in the comparative examples. And with the increase of the dosages of the first reducing agent, halogenated salt, second reducing agent, haloalkanoate, selective fluorination reagent and noble metal acid salt, the metal ion content and fluoride ion content in the soluble polytetrafluoroethylene resin are significantly further reduced, and the spherulite size is also further reduced, effectively improving the mechanical properties and thermal stability of the soluble polytetrafluoroethylene resin. It can be seen from Example 1 and Example 4 that the spherulite size is regulated by adjusting the use of different types of initiators. Further, the unstable end groups: -COF(1883 cm -1 ), -COOH(1811 cm -1 ), -COOH(H)(1766 cm -1 ), -CF=CF 2 (1792 cm -1 ). It can be seen from Figure 1 that through the treatment with the first reducing agent and the second reducing agent and the fluorine gas treatment in Example 1, most of the unstable groups disappear.

[0097] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for stabilizing unstable end groups of fusible polytetrafluoroethylene, characterized in that: The following steps are involved: Obtaining Fusible Polytetrafluoroethylene Resin R Containing Carboxyl Groups f COOH; The fusible polytetrafluoroethylene resin containing carboxyl groups is subjected to a reduction reaction with a first reducing agent in a first solvent under the action of a halogenated salt catalyst to obtain a fluoroalcohol R f CH2OH; To the R f Add the second reducing agent and the halofluoroalkane carboxylate X(CF2) to CH2OH m+1 COOM to obtain carboxyl-terminated perfluoroether R f CH2O(CF2) m+1 COOH, wherein X is a halogen, M is a metal ion or an ammonium ion, and m is a positive integer from 0 to 5; To the carboxyl-terminated perfluoroether R f CH2O(CF2) m+1 A fusible polytetrafluoroethylene resin R with a perfluoroether end group is obtained by adding a selective fluorination agent and a noble metal acid salt to COOH. f CH2O(CF2) m CF3; The fusible polytetrafluoroethylene resin having a perfluoroether terminal group is treated with a fluorine-nitrogen mixed gas to obtain a perfluoro fusible polytetrafluoroethylene resin R f CF2O(CF2) m CF3.

2. The method for stabilizing unstable end groups of fusible polytetrafluoroethylene according to claim 1, characterized in that: The general formula of the perfluoroalkyl vinyl ether is CF2=CF(OC n F 2n+1 ), where n-1=m.

3. The method for stabilizing unstable end groups of fusible polytetrafluoroethylene according to claim 1, characterized in that: The first reducing agent includes one or more of borane, borohydride salts and ammonia borane; The halogenated salt includes one or more of Ti salt, Fe salt, Cu salt and Zr salt, and the halogen in the halogenated salt includes one or more of Cl, Br and I; The second reducing agent comprises a metal hydride; The halogenated fluoroalkane carboxylate includes ammonium bromofluoroalkane carboxylate; the selective fluorination agent includes 1-fluoro-4-methyl-1,4-diazabicyclo[2.2.2]octane tetrafluoroborate; the noble metal acid salt includes soluble salts of gold, silver and platinum metals; The first solvent is selected from one or more of diethyl ether, dimethyl ether, N,N-dimethylformamide, and N,N-dimethylacetamide.

4. The method for stabilizing unstable end groups of fusible polytetrafluoroethylene according to claim 1, characterized in that: The carboxyl-terminated perfluoroether and the fusible polytetrafluoroethylene resin with a terminal perfluoroether are respectively dissolved in a second solvent at 25-30° C. and refluxed to obtain the obtained resin. The second solvent includes one or more of dioxane, dichloromethane, chloroform, N,N-dimethylformamide and water.

5. The method for stabilizing unstable end groups of fusible polytetrafluoroethylene according to claim 1, characterized in that: The molar ratio of the halogenated salt catalyst, the first reducing agent and the fusible polytetrafluoroethylene resin containing a carboxyl group is (0.1-10):1:(2000-20000); The molar ratio of the second reducing agent, the halogenated fluoroalkane carboxylate and the fluoroalcohol is (0.1-10):1:(2000-20000); The molar ratio of the selective fluorination agent, the noble metal acid salt and the carboxyl-terminated perfluoroether is (0.1-10):1:(10000-100000).

6. The method for stabilizing unstable end groups of fusible polytetrafluoroethylene according to claim 1, characterized in that: Obtaining Fusible Polytetrafluoroethylene Resin R Containing Carboxyl Groups f The steps of COOH include: The perfluoroalkyl vinyl ether is polymerized with tetrafluoroethylene to prepare a fusible polytetrafluoroethylene emulsion with -COF. After pretreatment, the -COF is converted into a carboxyl group to obtain a fusible polytetrafluoroethylene resin R containing a carboxyl group. f COOH.

7. The method for stabilizing unstable end groups of fusible polytetrafluoroethylene according to claim 6, characterized in that: The pretreatment steps include demulsification, pickling, washing and drying. The demulsification is physical demulsification and / or electrolyte demulsification. The electrolyte in the electrolyte demulsification includes one or more alkalis or organic or inorganic salts that are alkaline when hydrolyzed. The acid used in the pickling includes one or more of formic acid, acetic acid, hydrochloric acid, nitric acid and sulfuric acid.

8. The method for stabilizing unstable end groups of fusible polytetrafluoroethylene according to claim 7, characterized in that: The step of preparing a fusible polytetrafluoroethylene emulsion with -COF and -COOH also includes the following steps: Adding water, an emulsifier, a chain transfer agent and the perfluoroalkyl vinyl ether into a reaction container to obtain a mixed solution; Raising the temperature to the reaction temperature, introducing tetrafluoroethylene into the mixed solution until the reaction pressure is reached, and then adding an initiator into the mixed solution to react; Tetrafluoroethylene and initiator are added to the mixed solution, and the pressure of the reaction container is maintained within the reaction pressure range until the reaction is completed, thereby obtaining a fusible polytetrafluoroethylene emulsion with -COF and -COOH.

9. The method for stabilizing unstable end groups of fusible polytetrafluoroethylene according to claim 8, characterized in that: The emulsifier includes perfluoropolyether carboxylic acid or perfluoropolyether carboxylate; The chain transfer agent includes one or more of methane, ethane, propane, cyclohexane, methanol, ethanol, and hydrogen; The initiator includes a peroxide initiator, and the peroxide initiator includes a persulfate and / or a perfluoroalkyl peroxide.

10. Use of the stabilization treatment method of unstable end groups of fusible polytetrafluoroethylene as claimed in any one of claims 1 to 9 in fluorination end-capping of fluorine-containing thermoplastic polymers.

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