Preparation method of high-strength PCTFE resin

Abstract

The invention relates to a high-strength PCTFE resin preparation method, belongs to the field of fluorine-containing polymer preparation, and provides a high-strength PCTFE resin preparation method for solving the problems that in the prior art, a preparation process is complex, and the performance of an obtained product is insufficient, the high-strength PCTFE resin preparation method comprises the following steps that perfluorooxaalkanoyl peroxide is adopted as an initiator and dissolved in a fluorine-containing solvent, and the perfluorooxaalkanoyl peroxide is obtained; the preparation method comprises the following steps: adding a chlorotrifluoroethylene monomer once or multiple times under an anaerobic condition, carrying out a polymerization reaction, and washing and drying after the reaction is completed, thereby obtaining the high-strength PCTFE resin. According to the invention, the perfluorinated oxaalkanoyl peroxide is used as an initiator, the perfluorinated oxaalkanoyl peroxide has relatively high activity, can effectively initiate polymerization reaction under relatively mild conditions, and is beneficial to control of the structure and performance of a polymerization product, and the prepared PCTFE does not need to be subjected to post-blocking, so that the complexity of the process is greatly reduced, and the production cost is reduced. And the safety is improved.

Description

Technical Field

[0001] The invention patent relates to a preparation process of fluorine-containing polymers, and in particular to a preparation method of high-strength PCTFE (polychlorotrifluoroethylene) resin. Background Art

[0002] Polychlorotrifluoroethylene (PCTFE) is a homopolymer of chlorotrifluoroethylene, with a structure containing fluorine atoms and chlorine atoms around the main carbon chain, and its general chemical structure formula is: [CF2CFCl]n. Due to the introduction of C-Cl bonds in the molecular structure of PCTFE, except that its heat resistance and chemical inertness are slightly worse than those of polytetrafluoroethylene and tetrafluoroethylene-hexafluoropropylene copolymer, its hardness, rigidity, creep resistance are better, and its permeability, melting point and melt viscosity are relatively low; and the presence of chlorine atoms in the molecular structure gives the polymer good processing fluidity, transparency and hardness characteristics.

[0003] PCTFE has excellent gas barrier capability, and its film products have the lowest water vapor permeability among all transparent plastic films. PCTFE also has outstanding low temperature resistance, and will not crack or creep in liquid nitrogen, liquid oxygen, and liquefied natural gas. Under certain conditions, it can be used at temperatures close to absolute zero (-273°C). Because of its unique characteristics, it is widely used, especially as packaging diaphragms and low-temperature sealing materials, so its strength performance is of particular concern.

[0004] CN201010542727.4 proposes to use azo initiators for suspension polymerization and then use cobalt fluoride for end-capping treatment. Although high-temperature resistant and highly transparent polytrifluorochloroethylene resin is obtained, high temperature and high pressure are required for end-capping, which increases costs and safety risks; similarly, CN20111044061.4 also needs to use F2 / N2 mixed gas to perform fluorination end-capping treatment on PCTFE at 160-200°C. CN201410647902.4 proposes a secondary reaction method of first synthesizing an initiator in situ and then initiating the polymerization of trifluorochloroethylene. First, the acyl halide solution is dissolved in a fluorine-containing organic solvent, a mixed solution of hydrogen peroxide and an inorganic alkali solution is added to stir the reaction, and then an aqueous solution of a dispersant, trifluorochloroethylene monomer and a molecular weight regulator are added to carry out polymerization reaction to obtain polytrifluorochloroethylene. Hydrogen peroxide is used to provide the free radicals required for redox polymerization, and the inorganic alkali can maintain the stability of hydrogen peroxide. Although this method reduces the end-capping process, the process is complicated and various additives are added, which increases the burden of subsequent purification. The presence of impurities affects thermal stability and will affect strength at high temperatures. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing a high-strength PCTFE resin. The process method has the advantages of simple process, high adjustability, good reproducibility, no need to use fluorine gas for tail end group treatment, and high strength of the prepared polytrifluorochloroethylene polymer.

[0006] To achieve the above purpose, the technical scheme adopted is: a method for preparing high-strength PCTFE resin, comprising the following steps: using perfluorooxoalkanoyl peroxide as an initiator, dissolving it in a fluorine-containing solvent, adding chlorotrifluoroethylene monomer once or multiple times under anaerobic conditions, carrying out a polymerization reaction, and washing and drying after the reaction is completed to obtain a high-strength PCTFE resin.

[0007] The present application does not require an in situ synthetic initiator. The molecular structure of perfluorooxoalkanoyl peroxide contains oxygen atoms (i.e., oxygen atoms serve as bridging atoms in the carbon chain), and is highly symmetrical with the peroxide bond as the center. It has high activity and can effectively initiate polymerization reactions under relatively mild conditions, which is beneficial for controlling the structure and properties of the polymerized product. Compared with ordinary hydrocarbon peroxide initiators, polymers initiated by perfluorooxoalkanoyl peroxide have more stable end groups. These stable end groups can prevent the polymer from generating bubbles due to thermal instability during processing and use, resulting in problems such as uneven product surfaces. In addition, the preparation process in the present application does not require complex end-capping treatment, the process is relatively simple and easy to operate, the initiator is dissolved in a fluorinated solvent, and a polymerization reaction is carried out by adding trifluorochloroethylene monomer. There are fewer additives, and fewer impurities are generated, which reduces the burden of impurity removal, and the fluorinated solvent can also be recycled.

[0008] The introduction of inert gas can prevent oxygen from inhibiting polymerization and reduce the occurrence of side reactions. The preparation needs to be carried out under anaerobic conditions. The common anaerobic method is to replace the air in the reactor with inert gas, and achieve an anaerobic reaction environment through one or more replacements. There are no special requirements for inert gas, and the most common nitrogen can be selected.

[0009] After the polymerization reaction is completed, the polymer is separated from the solvent. There is no special regulation on the separation method. Centrifugation, screen filtration, membrane filtration, distillation and other separation methods can be used. It is only necessary to separate the solid polymer from the residual liquid. The separated solid can be obtained by simple water washing and drying to obtain high-strength PCTFE resin, without the need to use wet heat method, fluorine gas, cobalt fluoride and other end-capping methods.

[0010] This application is very friendly to the reactor and has no special regulations. Either a horizontal reactor or a vertical reactor can be used.

[0011] The system is initially in a solution state. As the polymer is generated, the polymer is suspended from the fluorinated solvent and gradually forms a swollen state.

[0012] Furthermore, the added amount of each substance is calculated by weight: perfluorooxaalkanoyl peroxide is 1, fluorine-containing solvent is 100-1000 (preferably 500-1000, particularly preferably 500-800); chlorotrifluoroethylene monomer (CTFE monomer) is 100-5000.

[0013] Furthermore, the initiator has the structural formula R f -OOR f , or ; Where Rf is CF3CF2[OCF2CF(CF3)] n , n is 1 to 8. The perfluorooxoalkanoyl peroxide has a peroxy structure of a conventional initiator, and the molecule is highly symmetrical with the peroxy bond as the center, and does not contain a carbon-hydrogen bond.

[0014] As another preferred embodiment, R f The structural formula is (CF3CF2CF2O) a (CF2CF2O) b (CF2O) c , a+b+c is 3-16.

[0015] Further, the fluorine-containing solvent includes one of a polyfluoroalkane, a hydrofluoroether or a fluoroether oil, the polyfluoroalkane specifically includes but is not limited to one of octafluorocyclobutane, decafluorocyclopentane, octafluorooctane, tetradecafluorohexane, and decafluorobutane; the hydrofluoroether includes but is not limited to one of hexafluoropropyl methyl ether, hexafluoropropyl ethyl ether, tetrafluoroethyl methyl ether, and tetrafluoroethyl ethyl ether; the fluoroether oil adopts one of the following structures: K-type structure CF3CF2CF2O[CF(CF3)CF2O]nCF(CF3)CF3; Y-type structure CF3O(C3F6O)m(CF2O)nCF3; Z-type structure CF3(C2F4O)m(CF2O)nCF3; D-type structure C3F7O(CF2CF2CF2O)mC2F5; The value range of m and n is 10 4 -5×10 7 .

[0016] Fluorinated alkane compounds have high chemical stability, are not easy to react to most acids, alkalis, solvents and chemicals, are usually colorless and transparent liquids or gases at room temperature and pressure, have low melting points and boiling points, usually have low global warming potential (GWP) and ozone depletion potential (ODP), and have little impact on the environment; hydrofluoroethers contain fluorine atoms and ether bonds (COC). The presence of fluorine atoms makes these compounds have high chemical stability and thermal stability, and the introduction of ether bonds makes these compounds have good solubility and permeability. Hydrofluoroethers usually have low global warming potential (GWP) and ozone depletion potential (ODP), and have little impact on the environment; fluoroether oils have oxygen atoms connected to the main chain, which can improve the flexibility of the molecule. In addition, fluoroether oils have outstanding chemical stability and are not easily corroded and oxidized by chemicals, but their prices are slightly higher.

[0017] The molecular weight of the fluorinated solvent used is about 100, and the molecular weight of the fluorinated ether oil is 10 4 -5×10 5 However, it should be noted that there is no particular regulation on the molecular weight of the fluorinated solvent, as long as it meets the use requirements, that is, it can dissolve CTFE and fluorinated peroxides but cannot dissolve PCTFE resin. However, it is preferred to be a substance with a low molecular weight and a boiling point between 35-235°C.

[0018] Further, the reaction temperature is -10°C to 100°C, preferably 20-65°C.

[0019] Furthermore, the stirring intensity is 300-1300 rpm, preferably 1000-1200 rpm.

[0020] Furthermore, the reaction time is 1 h-48 h, preferably 3-5 h, so as to achieve a balance in manufacturing efficiency.

[0021] Furthermore, the fluorinated solvent is also added with a chain transfer agent, and the chain transfer agent includes one of alcohols, esters, halogenated hydrocarbons, alkanes or cyclohexane. The substance containing one or two H atoms or non-fluorine halogen atoms in the molecular structure is ideal when used as a chain transfer agent, and may also contain one or more hydroxyl groups. Specifically, the alcohols that can be used include one of methanol, ethanol, propanol, tert-butyl alcohol, and thiol; the esters that can be used include one of dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate, and dimethyl succinate; the halogenated hydrocarbon that can be used is carbon tetrachloride, and the alkane that can be used isopentane, methane, ethane, and propane. According to the chain transfer constant, a suitable chain transfer agent can be selected, and more preferably, alkanes containing only CH bonds, and most preferably, methane and isopentane.

[0022] Furthermore, the amount of chain transfer agent added is 1-5% of the chlorotrifluoroethylene monomer.

[0023] In the production method of the present invention, the fluorinated monomer may be polymerized in the presence of a chain transfer agent as required. The use of a chain transfer agent can adjust the polymerization rate and molecular weight.

[0024] Beneficial effects of the invention: (1) The present invention uses perfluorooxaalkanoyl peroxide as an initiator, and the prepared PCTFE does not need to be post-terminated, which greatly reduces the complexity of the process and improves safety.

[0025] (2) The present invention can improve the adjustability of the process according to the activity of perfluoroalkanoyl peroxide to obtain a high molecular weight, high strength PCTFE resin.

[0026] (3) The present invention uses a fluorinated solvent as a heat transfer medium, which can effectively dissolve the monomer and precipitate the polymer, making it very easy to achieve separation treatment after the reaction without adding surfactants, cleaning agents, etc., making it easier to obtain high-purity PCTFE resin, thereby improving its thermal stability, that is, its strength at high temperatures. DETAILED DESCRIPTION

[0027] Specific embodiments of the present invention will be described in detail below, but the present invention is not limited to the following embodiments.

[0028] Example 1 After nitrogen replacement in a 2L polymerization reactor equipped with electromagnetic stirring, 800g of octafluorocyclobutane and 1g of R f -OOR f Perfluoroperoxide, where R f CF3CF2OCF2CFCF3. At a stirring rate of 700rmp, 200g of chlorotrifluoroethylene monomer was added, the reaction temperature was controlled to be 35°C, and the reaction was carried out for 6h. After the reaction was completed, the polymerization kettle was opened, the solvent and polymer mixture were released, filtered, and the obtained resin was washed twice with 50°C distilled water and then washed three times with normal temperature distilled water under stirring, and finally dried at 120°C for 12h, and the product was recovered to obtain PCTFE resin.

[0029] Example 2 After nitrogen replacement of a 2L polymerization kettle with electromagnetic stirring, 800g of octafluorocyclobutane and 1g of di(perfluorobutyryl)peroxide were added, and 200g of chlorotrifluoroethylene monomer was added at a stirring rate of 700rmp. The reaction temperature was controlled to be 28°C and the reaction was carried out for 20h. After the reaction was completed, the polymerization kettle was opened, the solvent and polymer mixture were released, filtered, and the obtained resin was washed twice with 50°C distilled water and then washed three times with room temperature distilled water under stirring, and finally dried at 120°C for 12h, and the product was recovered to obtain PCTFE resin.

[0030] Example 3 After nitrogen replacement of a 2L polymerization kettle with electromagnetic stirring, 1000g of tetrafluoroethyl methyl ether and 1g of di(perfluorovaleryl) peroxide were added, and 200g of trifluorochloroethylene monomer was added at a stirring rate of 700rmp. The reaction temperature was controlled to be 28°C and the reaction was carried out for 20h. After the reaction was completed, the polymerization kettle was opened, the solvent and polymer mixture were released, filtered, and the obtained resin was washed twice with 50°C distilled water and then washed three times with room temperature distilled water under stirring, and finally dried at 120°C for 12h, and the product was recovered to obtain PCTFE resin.

[0031] Example 4 After nitrogen replacement in a 2L polymerizer with electromagnetic stirring, 500g of K-type fluoroether oil (structural formula: C3F7O[CF(CF3)CF2O]) was added. m CF2CF3, boiling range 100-110℃), then add 2g of molecular formula R f -OOR f Perfluoroperoxide, where R f CF3CF2[OCF2CF(CF3)]8,5g methanol, under the stirring rate of 700rmp, add 200g trifluorochloroethylene monomer, control the reaction temperature to 28℃, react for 20h. After the reaction is completed, open the polymerization kettle, release the solvent and polymer mixture, filter, and wash the obtained resin with 50℃ distilled water twice, then wash it with room temperature distilled water for 3 times under stirring, and finally dry it at 120℃ for 12h, recover the product to obtain PCTFE resin.

[0032] Example 5 After nitrogen replacement in a 2L polymerization reactor with electromagnetic stirring, 100 g of D-type fluoroether oil (structural formula: C3F7O(C3F6O) was added. m CF2CF3, boiling range 100-110℃), then add 1g of the structural formula peroxide, wherein Rf is (CF3CF2CF2O)(CF2CF2O)CF2O, at a stirring rate of 300 mp, 100 g of chlorotrifluoroethylene monomer is added, the reaction temperature is controlled to be 100°C, the reaction is carried out for 1 hour, after the reaction is completed, the polymerization kettle is opened, the solvent and the polymer mixture are released, filtered, and the obtained resin is washed twice with 50°C distilled water and then washed three times with room temperature distilled water under stirring, and finally dried at 120°C for 12 hours, and the product is recovered to obtain PCTFE resin.

[0033] Example 6 After nitrogen replacement in a 2L polymerization reactor with electromagnetic stirring, 100 g of Y-type fluoroether oil (structural formula: CF3O(C3F6O)) was added. p (CF2O) q CF3, boiling range 95-110℃), then add 1g of the structural formula Peroxide, where R f (CF3CF2CF2O)3(CF2CF2O) 12 CF2O, under the stirring rate of 1000rmp, 5000g of chlorotrifluoroethylene monomer was metered in, the reaction temperature was controlled to be -10℃, the reaction was carried out for 48h. After the reaction was completed, the polymerization kettle was opened, the solvent and polymer mixture were released, filtered, and the obtained resin was washed twice with 50℃ distilled water and then washed three times with room temperature distilled water under stirring, and finally dried at 120℃ for 12h, and the product was recovered to obtain PCTFE resin.

[0034] Example 7 A 2L polymerization kettle with electromagnetic stirring was first purged with nitrogen, and then 100g of hexafluoropropyl ethyl ether (boiling point 52°C) and 2g of the structural formula Peroxide, where R f CF3CF2[OCF2CF(CF3)]8,5g methane, under the stirring rate of 700rmp, 2000g chlorotrifluoroethylene monomer was added, the reaction temperature was controlled at 35℃, the reaction was carried out for 6h. After the reaction was completed, the polymerization kettle was opened, the solvent and polymer mixture were released, filtered, and the obtained resin was washed twice with 50℃ distilled water and then washed three times with room temperature distilled water under stirring, and finally dried at 120℃ for 12h, and the product was recovered to obtain PCTFE resin.

[0035] Example 8 After nitrogen replacement in a 2L polymerization reactor with electromagnetic stirring, 100 g of D-type fluoroether oil (structural formula: C3F7O(C3F6O) was added. m CF2CF3, boiling range 100-120℃), then add 2g of the structural formula Peroxide, where R f CF3CF2[OCF2CF(CF3)]8,5g cyclopentane, under the stirring rate of 700rmp, 3000g chlorotrifluoroethylene monomer was added, the reaction temperature was controlled to 65℃, the reaction was carried out for 6h. After the reaction was completed, the polymerization kettle was opened, the solvent and polymer mixture were released, filtered, and the obtained resin was washed twice with 50℃ distilled water and then washed three times with room temperature distilled water under stirring, and finally dried at 120℃ for 12h, and the product was recovered to obtain PCTFE resin.

[0036] Performance Test: (1) Tensile strength test standard The tensile strength of PCTFE resin was determined according to the national standard of the People's Republic of China GB / T 1040.1-2006 "Determination of tensile properties of plastics Part 1: General principles".

[0037] (2) Thermal stability According to the national standard of the People's Republic of China GB / T 19466.3-2004, the T of the polymer was determined by DSC method using a thermal analyzer. G ; (3) Loss of strength time test standard Determine the polymer loss time according to the American standard ASTM1430-03; The test results of various embodiments are shown in Table 1.

[0038] Table 1

[0039] It can be seen from the examples that although the final products of each process are different, they all achieve a tensile strength of >40MPa, meeting the use requirements. According to the actual processing requirements, PCTFE resins with various processing fluidities can be prepared, thereby meeting the high production efficiency of PCTFE production.

[0040] Compared with Example 2, Example 1 uses different reaction times and temperatures, and the performance of the obtained PCTFE resin is also equivalent. Compared with Example 2, Example 3 uses the same reaction time and temperature, but uses a different fluorinated solvent, and the performance of the obtained PCTFE resin is equivalent. Compared with Example 2, Example 4 uses methanol as a chain transfer agent, and uses the same reaction time and temperature, and the performance of the obtained PCTFE resin is equivalent. In Example 5, Example 6, and Example 8, the stirring rate, reaction temperature and time used are all different, but the performance of the obtained PCTFE resin can meet the requirements, especially Example 6 can react at a lower temperature; Example 7 uses a different chain transfer agent from Example 4, and the performance of the obtained PCTFE resin can also meet the requirements.

[0041] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a high-strength PCTFE resin, characterized in that: The method comprises the following steps: using perfluorooxoalkanoyl peroxide as an initiator, dissolving it in a fluorine-containing solvent, adding chlorotrifluoroethylene monomer once or multiple times under anaerobic conditions to carry out polymerization reaction, and washing and drying after the reaction is completed to obtain high-strength PCTFE resin.

2. The method for preparing high-strength PCTFE resin according to claim 1, characterized in that: The added amount of each substance is calculated by weight: 1 part for perfluorooxaalkanoyl peroxide, 100-1000 for fluorine-containing solvent, and 100-5000 for chlorotrifluoroethylene monomer.

3. The method for preparing a high-strength PCTFE resin according to claim 1 or 2, characterized in that: The initiator has the structural formula R f -OOR f , or ; where R f CF3CF2[OCF2CF(CF3)] n , n is 1-8.

4. The method for preparing a high-strength PCTFE resin according to claim 1 or 2, characterized in that: The initiator structural formula is (CF3CF2CF2O) a (CF2CF2O) b (CF2O) c , a+b+c is 3-16.

5. The method for preparing a high-strength PCTFE resin according to claim 1 or 2, characterized in that: The fluorine-containing solvent includes one of a polyfluoroalkane, a hydrofluoroether or a fluoroether oil, wherein the polyfluoroalkane specifically includes but is not limited to one of octafluorocyclobutane, decafluorocyclopentane, octafluorooctane, tetradecafluorohexane and decafluorobutane; the hydrofluoroether includes but is not limited to one of hexafluoropropyl methyl ether, hexafluoropropyl ethyl ether, tetrafluoroethyl methyl ether and tetrafluoroethyl ethyl ether; the fluoroether oil adopts one of the following structures: K-type structure CF3CF2CF2O[CF(CF3)CF2O]nCF(CF3)CF3; Y-type structure CF3O(C3F6O)m(CF2O)nCF3; Z-type structure CF3(C2F4O)m(CF2O)nCF3; D-type structure C3F7O(CF2CF2CF2O)mC2F5; The value range of m and n is 10 4 -5×10 7 .

6. The method for preparing a high-strength PCTFE resin according to claim 1 or 2, characterized in that: The reaction temperature is -10°C to 100°C.

7. The method for preparing a high-strength PCTFE resin according to claim 1 or 2, characterized in that: The stirring intensity is 300-1300 rpm.

8. The method for preparing a high-strength PCTFE resin according to claim 1 or 2, characterized in that: The reaction time is 1h-48h.

9. The method for preparing a high-strength PCTFE resin according to claim 1 or 2, characterized in that: A chain transfer agent is also added to the fluorine-containing solvent, and the chain transfer agent includes one of alcohols, esters, halogenated hydrocarbons, alkanes or cyclohexane.

10. The method for preparing high-strength PCTFE resin according to claim 9, characterized in that: The added amount of the chain transfer agent is 1-5% of the mass of the chlorotrifluoroethylene monomer.

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