A process for the preparation of a fluorine-containing copolymer and the resulting copolymer

Abstract

The application belongs to the field of fluorine-containing polymer preparation, and relates to a preparation method of a fluorine-containing copolymer and the obtained copolymer. The preparation method comprises the following steps: (1) in the presence of water and a dispersing agent, the oxygen content is controlled to be less than 20 ppm, initial mixed monomers of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene are introduced into a reaction pressure, and an initiator is added to initiate a polymerization reaction; (2) during the polymerization process, the mixed monomers of tetrafluoroethylene and vinylidene fluoride, the mixed monomers of tetrafluoroethylene and hexafluoropropylene are alternately supplemented, and the initiator is continuously supplemented. The application adopts the mode of alternately supplementing mixed monomers, so that different monomers are more uniformly distributed in the polymer chain, the probability of monomer insertion is greater, the product performance is greatly improved, and the whole process does not need to add a cosolvent for compounding, the impurities are less, the operation is simple, and the feasibility is strong.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of preparation method of fluorine-containing copolymer and the copolymer obtained, belong to fluorine-containing polymer preparation field. BACKGROUND

[0002] Polyfluoroethylene propylene (FEP) is a linear structure of macromolecular compound, which is copolymerized by tetrafluoroethylene (TFE) and hexafluoropropylene (HFP), and has excellent chemical stability, which can resist corrosion of almost all kinds of organic acids, bases and alcohols, ketones, hydrocarbons, halogenated hydrocarbons, aromatic hydrocarbons, etc. FEP resin has good heat resistance, weather resistance and corrosion resistance, excellent mechanical properties and creep resistance, good corrosion resistance, hydrophobicity and non-stick properties below 200℃. In the process of processing and use, the melt viscosity is low and the flowability of the melt is good, which can be processed normally at 250-360℃.

[0003] However, FEP lacks flexibility, and it is not easy to bend when processed into oil pipelines, which leads to bending and blocking of the pipeline during bending. In view of the above shortcomings, the flexibility can be improved by blending other resins such as PTFE, PFA, PVDF, ETFE, etc., but the blending modification is to improve the performance of the product by physical mixing, which is unstable and unevenly blended, which also affects the performance of the product.

[0004] Chinese patent CN104479061A uses vinylidene fluoride to modify polyfluoroethylene propylene to prepare polyfluoroethylene propylene products with a melting point of 120-270℃. However, due to the different reactivity of the three monomers, the block distribution of the copolymer obtained by this method is very uneven, and the molar composition of the copolymer is also difficult to control, which leads to poor flexibility and transparency of the obtained vinylidene fluoride modified polyfluoroethylene propylene copolymer, affecting the processing performance. In addition, MgCl2 is used for demulsification in the reaction process, which can affect the dielectric properties and color of the product, and also uses non-environmental friendly perfluorooctanoate dispersant. SUMMARY

[0005] In view of the shortcomings of the prior art, the purpose of the present application is to provide a preparation method of fluorine-containing copolymer and the copolymer obtained.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] A preparation method of fluorine-containing copolymer, comprising the following steps:

[0008] (1) in the presence of water and dispersant, control the oxygen content to be less than 20ppm, and pass the initial mixed monomers of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene to the reaction pressure, and add initiator to initiate polymerization reaction;

[0009] (2) Alternately adding tetrafluoroethylene and vinylidene fluoride mixed monomers, tetrafluoroethylene and hexafluoropropylene mixed monomers, and continuously adding initiators during the polymerization process.

[0010] Preferably, the mass ratio of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene in the initial mixed monomers in step (1) is 1:1-5:1-3, and further preferably 1:1.5-4.5:1-2.5.

[0011] Preferably, the reaction temperature in step (1) is 50-90℃, and the reaction pressure is 1.5-4.5 MPa, and further preferably the reaction temperature is 60-80℃, and the reaction pressure is 2-4 MPa.

[0012] Preferably, the dispersing agent in step (1) is one or a mixture of two of perfluoropolyether dispersing agent, perfluorohexanoic acid and HFPO trimer (hexafluoroepoxy propane trimer), and the mass ratio of the dispersing agent to the total monomers is 1:100-200. Further preferably, the dispersing agent is CF3-O-[-CF(OCF3)-CF2-O-]2-CF2-O-COONH4 or a mixed dispersing agent of CF3-O-[-CF(OCF3)-CF2-O-]2-CF2-O-COONH4 and perfluorohexanoic acid at a mass ratio of 1:1.

[0013] Preferably, the initiator in step (1) or (2) is one or more of perfluoroacyl peroxide, potassium persulfate, ammonium persulfate, or a mixture of potassium permanganate and ammonium oxalate, and further preferably the initiator is ammonium persulfate or a mixture of potassium permanganate and ammonium oxalate. The amount of the initial initiator is 0.002-0.006% of the amount of water.

[0014] Preferably, the mass ratio of tetrafluoroethylene to hexafluoropropylene in the mixed monomers in step (2) is 1-1.5:0.2-0.6, and further preferably 2.5-5:1, and the mass ratio of tetrafluoroethylene to vinylidene fluoride in the mixed monomers is 1-1.5:0.3-0.7, and further preferably 2-3.5:1. The amount of the added initiator is 0.01-0.03% of the amount of water.

[0015] Preferably, the method of alternately adding mixed monomers in step (2) is as follows: when the reaction pressure drops by 0.1 MPa, add tetrafluoroethylene and vinylidene fluoride mixed monomers to the reaction pressure, and when the reaction pressure drops by 0.1 MPa, add tetrafluoroethylene and hexafluoropropylene mixed monomers to the reaction pressure, and so on.

[0016] Preferably, the method further comprises step (3): when the total amount of added tetrafluoroethylene and hexafluoropropylene mixed monomers and tetrafluoroethylene and vinylidene fluoride mixed monomers reaches 30-40% of the amount of water, the reaction is ended.

[0017] The polymerization method also includes the coagulation, washing and drying of the emulsion after the polymerization reaction.

[0018] The method for preparing the fluorine-containing copolymer provided by the application can obtain a vinylidene fluoride modified polyfluoroethylene propylene copolymer with uniform block distribution by changing the adding mode of the supplemented monomers, and can overcome the problems of difficult control of the molar composition of the copolymer and uneven block distribution by alternately supplementing two kinds of mixed monomers, so that the product has high flexibility while retaining high transparency.

[0019] Another object of the application is to provide a fluorine-containing copolymer with high flexibility and high transparency, which is composed of 50-70 wt% of tetrafluoroethylene structural units, 10-20 wt% of hexafluoropropylene structural units and 20-30 wt% of vinylidene fluoride structural units.

[0020] Preferably, the fluorine-containing copolymer is composed of 54-59 wt% of tetrafluoroethylene structural units, 16-20 wt% of hexafluoropropylene structural units and 21-30 wt% of vinylidene fluoride structural units.

[0021] The vinylidene fluoride modified polyfluoroethylene propylene copolymer provided by the application has a melt index of 9-11 g / 10 min, a melting point of 130-220℃, a tensile strength of ≥28.5 MPa, an elongation at break of ≥470%, a refractive index of ≤1.36, a thermal decomposition temperature of greater than 440℃ and a bonding property with a polyimide film of ≥16 N / 2.5 cm.

[0022] The fluorine-containing copolymer provided by the application improves the flexibility and bonding property of the polyfluoroethylene propylene copolymer while ensuring the transparency of the polyfluoroethylene propylene copolymer.

[0023] The application also provides the use of the copolymer in the preparation of plastic products, such as oil pipes and sheaths.

[0024] Compared with the prior art, one or more specific embodiments provided by the application have at least the following beneficial effects:

[0025] (1) The application uses the method of alternately supplementing mixed monomers to make the different monomers more uniformly distributed in the polymer chain, and the probability of the insertion of monomers is greater, so that the performance of the product is greatly improved, and the whole process does not need to add a cosolvent for compounding, introduces less impurities, is simple to operate and has high feasibility.

[0026] (2) The present application adjusts the proportion of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene in the fluorine-containing polymer by balancing the initial mixed monomers and the two kinds of additional mixed monomers, so that the polymer with flexibility and transparency is obtained, which can be processed into films, pipes and cables, and is applied to some fields with higher requirements for flexibility. The introduction of vinylidene fluoride enables the polymer to form a covalent bond with a hydrocarbon-based material, and has good adhesion.

[0027] (3) The melt index of the polymer obtained by the present application is in the range of 9-11 g / 10 min, the melting point temperature range is wide to 120-220 ℃, the high temperature resistance and thermal stability are better, the processing and use range of the fluorine-containing polymer is widened, the common plastic can be co-extruded, and pipes, sheaths and the like can be made. DETAILED DESCRIPTION

[0028] The present application will be further described below in combination with examples, but it does not limit the implementation of the present application.

[0029] The raw materials used in the examples are all commercially available products, which can be obtained by purchase or prepared by using the prior art, except for special instructions.

[0030] The polymerization method of the fluorine-containing copolymer provided by the present application comprises the following steps:

[0031] (1) In a stainless steel polymerization kettle, water and a dispersing agent are added, and the oxygen content of the polymerization kettle is treated to be less than 20 ppm, at the reaction temperature, the initial mixed monomers of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene are added to the kettle pressure to the reaction pressure, the mass ratio of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene is 1:1-5:1-3, and the initiator is added for polymerization reaction;

[0032] (2) During the polymerization reaction, the mixed monomers of tetrafluoroethylene and vinylidene fluoride with a mass ratio of 1-1.5:0.3-0.7, the mixed monomers of tetrafluoroethylene and hexafluoropropylene with a mass ratio of 1-1.5:0.2-0.5 and the initiator are continuously and alternately added to the polymerization kettle;

[0033] (3) When the total amount of the additional mixed monomers reaches 30-40% of the weight of water, the reaction is ended, the obtained emulsion is coagulated, washed and dried, and the fluorine-containing copolymer is obtained.

[0034] Example 1

[0035] In a 10 L stainless steel polymerization kettle, 5.5 L of deionized water and 40 g (50 wt%) of perfluoropolyether dispersant (CF3-O-[-CF(OCF3)-CF2-O-]2-CF2-O-COONH4) were added, the polymerization kettle was treated to an oxygen content of less than 20 ppm, the polymerization kettle was started to stir, and the temperature was raised to 60 °C. An initial mixture of monomers having a mass ratio of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride of 1:1.5:1 was added to the reactor to a pressure of 2.0 MPa. 10 g of 2.5 wt% ammonium persulfate initiator was added, and the reaction was started. When the reaction pressure dropped to 1.9 MPa, a mixture of tetrafluoroethylene and vinylidene fluoride having a mass ratio of 1:0.3 was added to a pressure of 2.0 MPa. When the reaction pressure dropped again to 1.9 MPa, a mixture of tetrafluoroethylene and hexafluoropropylene having a mass ratio of 1:0.2 was added to a pressure of 2.0 MPa. The above operation was repeated until the total weight of the added monomers was 2 kg. During the addition of the monomers, 50 g of 2.5 wt% ammonium persulfate initiator was continuously added. After about 3.5 hours of reaction, the stirring was stopped, the polymerization kettle was cooled and vented, and the resulting emulsion was mechanically coagulated, washed, dried, and granulated at 80 °C to obtain the target fluoropolymer. The fluoropolymer included 59 wt% tetrafluoroethylene structural units, 20 wt% hexafluoropropylene structural units, and 21 wt% vinylidene fluoride structural units. The results of the relevant performance tests are shown in Table 1 below.

[0036] Example 2

[0037] In a 10L stainless steel polymerization reactor, 5.5L of deionized water and 30g (50wt%) of perfluoropolyether dispersant (CF3-O-[-CF(OCF3)-CF2-O-]2-CF2-O-COONH4) were added, the polymerization reactor was treated to an oxygen content of less than 20ppm, the polymerization reactor was started stirring, and the temperature was raised to 70°C. The initial mixed monomers were added to the polymerization reactor to a pressure of 3.0MPa, and the mass ratio of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride in the initial mixed monomers was 1:2.5:1.5. 10g of 2.5wt% ammonium persulfate initiator was added, and the reaction was started. When the reaction pressure dropped to 2.9MPa, the mixed monomers of tetrafluoroethylene and vinylidene fluoride with a mass ratio of 1.2:0.5 were added to a pressure of 3.0MPa. When the reaction pressure dropped again to 2.9MPa, the mixed monomers of tetrafluoroethylene and hexafluoropropylene with a mass ratio of 1.2:0.5 were added to a pressure of 3.0MPa. The above-mentioned operation was alternately repeated until the total weight of the reaction monomers reached 2kg. During the addition of the additional monomers, 50g of 2.5wt% ammonium persulfate initiator was continuously added. After about 3.5 hours of reaction, the stirring was stopped, the polymerization reactor was cooled and vented, and the resulting emulsion was mechanically coagulated, washed, dried, and granulated at 80°C to obtain the target fluorine-containing polymer. The composition of the fluorine-containing polymer was 56wt% tetrafluoroethylene structural units, 17wt% hexafluoropropylene structural units, and 27wt% vinylidene fluoride structural units. The relevant performance test results are shown in Table 1 below.

[0038] Example 3

[0039] In a 10 L stainless steel polymerization kettle, 5.5 L of deionized water and 20 g (50 wt%) of perfluoropolyether dispersant (CF3-O-[-CF(OCF3)-CF2-O-]2-CF2-O-COONH4) were added, the polymerization kettle was treated to an oxygen content of less than 20 ppm, the polymerization kettle was started to stir, and the temperature was raised to 80 °C. Then the initial mixed monomers were added until the pressure of the polymerization kettle reached 4.0 MPa. The mass ratio of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride in the initial mixed monomers was 1:4.5:2.5. 10 g of 2.5 wt% ammonium persulfate initiator was added to start the reaction. When the reaction pressure drop decreased to 3.9 MPa, the mixed monomers of tetrafluoroethylene and vinylidene fluoride with a mass ratio of 1.5:0.7 were added to 4.0 MPa. When the reaction pressure dropped again to 3.9 MPa, the mixed monomers of tetrafluoroethylene and hexafluoropropylene with a mass ratio of 1.5:0.6 were added to 4.0 MPa. The above-mentioned operation was alternately carried out until the total weight of the reaction monomers reached 2 kg. During the addition of the additional monomers, 50 g of 2.5 wt% ammonium persulfate initiator was continuously added. After about 3.5 hours of reaction, the stirring was stopped, the polymerization kettle was cooled and vented, and the obtained emulsion was mechanically coagulated, washed, dried, and granulated at 80 °C to obtain the target fluorine-containing polymer. The composition of the fluorine-containing polymer was 54 wt% of tetrafluoroethylene structural units, 16 wt% of hexafluoropropylene structural units, and 30 wt% of vinylidene fluoride structural units. The relevant performance test results are shown in Table 1 below.

[0040] Example 4

[0041] In a 10 L stainless steel polymerization reactor, 5.5 L of deionized water, 40 g (50 wt%) of CF3-O-[-CF(OCF3)-CF2-O-]2-CF2-O-COONH4 and perfluorohexanoic acid mixed dispersant with a mass ratio of 1:1 were added, the polymerization reactor was treated to an oxygen content of less than 20 ppm, and the temperature was raised to 60°C. The polymerization reactor was then stirred, and the initial monomer mixture was added to the polymerization reactor until the pressure reached 2.0 MPa. The initial monomer mixture contained tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride in a mass ratio of 1:1.5:1. 10 g of a 2.5 wt% mixed aqueous solution of potassium permanganate and ammonium oxalate (mass ratio of potassium permanganate to ammonium oxalate: 1:100) was added as an initiator, and the reaction was started. When the reaction pressure dropped to 1.9 MPa, the mixed monomers of tetrafluoroethylene and vinylidene fluoride in a mass ratio of 1:0.3 were added to the pressure of 2.0 MPa. When the reaction pressure dropped again to 0.9 MPa, the mixed monomers of tetrafluoroethylene and hexafluoropropylene in a mass ratio of 1:0.2 were added to the pressure of 2.0 MPa. The above-mentioned monomer addition was alternately repeated until the total weight of the reaction monomers reached 2 kg. During the addition of the monomers, 50 g of a 2.5 wt% mixed aqueous solution of potassium permanganate and ammonium oxalate (mass ratio of potassium permanganate to ammonium oxalate: 1:100) was continuously added. After about 3.5 hours of reaction, the stirring was stopped, the polymerization reactor was cooled and vented, and the obtained emulsion was mechanically coagulated, washed, dried, and granulated at 80°C to obtain the target fluorine-containing polymer. The composition of the fluorine-containing polymer was 58 wt% of tetrafluoroethylene structural units, 19 wt% of hexafluoropropylene structural units, and 23 wt% of vinylidene fluoride structural units. The test results of the related properties are shown in Table 1.

[0042] Example 5

[0043] In a 10 L stainless steel polymerization reactor, 5.5 L of deionized water, 40 g (50 wt%) of CF3-O-[-CF(OCF3)-CF2-O-]2-CF2-O-COONH4 and perfluorohexanoic acid mixed dispersant with a mass ratio of 1:1 were added, the polymerization reactor was treated to an oxygen content of less than 20 ppm, and the temperature was raised to 60°C. The polymerization reactor was then stirred, and the initial monomer mixture was added to the polymerization reactor until the pressure reached 2.0 MPa. The initial monomer mixture contained tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride in a mass ratio of 1:1.5:1. 10 g of a 2.5 wt% mixed aqueous solution of potassium permanganate and ammonium oxalate (mass ratio of potassium permanganate to ammonium oxalate: 1:100) was added as an initiator, and the reaction was started. When the reaction pressure dropped to 1.9 MPa, the mixed monomers of tetrafluoroethylene and vinylidene fluoride in a mass ratio of 1:0.3 were added to the pressure of 2.0 MPa. When the reaction pressure dropped again to 0.9 MPa, the mixed monomers of tetrafluoroethylene and hexafluoropropylene in a mass ratio of 1:0.2 were added to the pressure of 2.0 MPa. The above-mentioned monomer addition was alternately repeated until the total weight of the reaction monomers reached 2 kg. During the addition of the monomers, 50 g of a 2.5 wt% mixed aqueous solution of potassium permanganate and ammonium oxalate (mass ratio of potassium permanganate to ammonium oxalate: 1:100) was continuously added. After about 3.5 hours of reaction, the stirring was stopped, the polymerization reactor was cooled and vented, and the obtained emulsion was mechanically coagulated, washed, dried, and granulated at 80°C to obtain the target fluorine-containing polymer. The composition of the fluorine-containing polymer was 58 wt% of tetrafluoroethylene structural units, 19 wt% of hexafluoropropylene structural units, and 23 wt% of vinylidene fluoride structural units. The test results of the related properties are shown in Table 1.

[0044] The reaction was initiated by adding 10 g of a 2.5 wt% aqueous solution of a mixture of potassium permanganate and ammonium oxalate (mass ratio of potassium permanganate to ammonium oxalate of 1:100) as an initiator. When the reaction pressure drop fell to 2.9 MPa, the addition of a mixture of tetrafluoroethylene and hexafluoropropylene monomers with a mass ratio of 1.2:0.5 was started to 3.0 MPa, and when the reaction pressure dropped again to 2.9 MPa, the addition of a mixture of tetrafluoroethylene and hexafluoropropylene monomers with a mass ratio of 1.2:0.4 was started to 3.0 MPa. The above-mentioned addition of monomers was alternately repeated until the total weight of the reaction monomers reached 2 kg. During the addition of the monomers, 50 g of a 2.5 wt% aqueous solution of a mixture of potassium permanganate and ammonium oxalate (mass ratio of potassium permanganate to ammonium oxalate of 1:100) was continuously added as an initiator. After about 3.5 hours of reaction, the stirring was stopped, the polymerization kettle was cooled and vented, and the obtained emulsion was mechanically coagulated, washed, dried, and granulated at 80°C to obtain the target fluorine-containing polymer. The composition of the fluorine-containing polymer was 55 wt% tetrafluoroethylene structural units, 18 wt% hexafluoropropylene structural units, and 27 wt% vinylidene fluoride structural units. The relevant performance test results are shown in Table 1 below.

[0045] Example 6

[0046] In a 10 L stainless steel polymerization kettle, 5.5 L of deionized water and 20 g (50 wt%) of a mixed dispersant of perfluoropolyether CF3-O-[-CF(OCF3)-CF2-O-]2-CF2-O-COONH4 and perfluorohexanoic acid with a mass ratio of 1:1 were added, and the polymerization kettle was treated until the oxygen content was less than 20 ppm. The polymerization kettle was started and stirred, and the temperature was raised to 80°C. Then, the initial monomer mixture was added until the pressure in the polymerization kettle reached 4.0 MPa. The mass ratio of tetrafluoroethylene, vinylidene fluoride, and hexafluoropropylene in the initial monomer mixture was 1:4.5:2.5.

[0047] The reaction was initiated by adding 10 g of a 2.5 wt% aqueous solution of a mixture of potassium permanganate and ammonium oxalate (mass ratio of potassium permanganate to ammonium oxalate of 1:100) initiator. When the reaction pressure drop decreased to 3.9 MPa, a mixture of tetrafluoroethylene and hexafluoropropylene monomers with a mass ratio of 1.5:0.7 was added to increase the pressure to 4.0 MPa. When the pressure decreased again to 3.9 MPa, a mixture of tetrafluoroethylene and hexafluoropropylene monomers with a mass ratio of 1.5:0.6 was added to increase the pressure to 4.0 MPa. The monomers were alternately added according to the above procedure until the total weight of the reaction monomers reached 2 kg. During the addition of the additional monomers, 50 g of a 2.5 wt% aqueous solution of a mixture of potassium permanganate and ammonium oxalate (mass ratio of potassium permanganate to ammonium oxalate of 1:100) was continuously added as an additional initiator. After about 3.5 hours of reaction, the stirring was stopped, the polymerization kettle was cooled and vented, and the resulting emulsion was mechanically coagulated, washed, dried, and granulated at 80°C to obtain the target fluoropolymer. The composition of each structural unit of the fluoropolymer was 54 wt% tetrafluoroethylene structural units, 17 wt% hexafluoropropylene structural units, and 29 wt% vinylidene fluoride structural units. The results of the relevant performance tests are shown in Table 1 below.

[0048] Comparative Example 1

[0049] In a 10 L stainless steel polymerization kettle, 5.5 L of deionized water and 20 g (50 wt%) of a perfluoropolyether dispersant (CF3-O-[-CF(OCF3)-CF2-O-]2-CF2-O-COONH4) were added, the polymerization kettle was treated to an oxygen content of less than 20 ppm, and the polymerization kettle was started with stirring. Then, an initial monomer mixture was added, the mass ratio of tetrafluoroethylene to hexafluoropropylene in the initial monomer mixture was 1:2.5, and the temperature was raised to 80°C. The constant reaction pressure was 4.0 MPa.

[0050] 10 g of a 2.5 wt% aqueous solution of ammonium persulfate initiator was added, and then additional monomers were continuously fed into the polymerization kettle, the mass ratio of tetrafluoroethylene to hexafluoropropylene in the additional monomers was 1.5:0.5, and the total weight was 2 kg. During the addition of the additional monomers, 50 g of a 2.5 wt% aqueous solution of ammonium persulfate was continuously added as an additional initiator. After about 3.5 hours of reaction, the stirring was stopped, the polymerization kettle was cooled and vented, and the resulting emulsion was mechanically coagulated, washed, dried, and granulated at 80°C to obtain the target fluoropolymer. The composition of each structural unit of the fluoropolymer was 82 wt% tetrafluoroethylene structural units and 18 wt% hexafluoropropylene structural units. The results of the relevant performance tests are shown in Table 1 below.

[0051] Comparative Example 2

[0052] In a 10 L stainless steel polymerization kettle, 6.4 L of deionized water was added, 7 g of sodium perfluorooctanoate was added, and the polymerization kettle was treated to an oxygen content of less than 20 ppm. The polymerization kettle was opened for stirring, and the temperature was raised to 60 °C. Then the initial monomer mixture was added to the reaction pressure of 3.0 MPa. The molar ratio of vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene in the initial monomer mixture was 6:11:3.

[0053] 3 g of ammonium persulfate initiator and 5 g of diethyl malonate were added to initiate the reaction. During the reaction, the additional monomer was continuously fed into the polymerization kettle to maintain the reaction pressure. The molar ratio of vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene in the additional monomer was 7:11:2. The reaction was stopped when the emulsion solid content was about 30% (mass percent). The stirring was stopped, and the polymerization kettle was cooled and vented. The obtained emulsion was coagulated, washed, dried, and granulated with 5% MgCl2 to obtain the target fluoropolymer. The composition of each structural unit of the fluoropolymer was 57 wt% of tetrafluoroethylene structural units, 24 wt% of hexafluoropropylene structural units, and 19 wt% of vinylidene fluoride structural units. The relevant performance test results are shown in Table 1.

[0054] Comparative Example 3

[0055] In a 10 L stainless steel polymerization kettle, 5.5 L of deionized water was added, 40 g (50 wt%) of perfluoropolyether dispersant (CF3-O-[-CF(OCF3)-CF2-O-]2-CF2-O-COONH4) was added, and the polymerization kettle was treated to an oxygen content of less than 20 ppm. The polymerization kettle was opened for stirring, and the temperature was raised to 60 °C. The initial monomer mixture was added to the pressure of the polymerization kettle to 2.0 MPa. The mass ratio of tetrafluoroethylene, vinylidene fluoride, and hexafluoropropylene in the initial monomer mixture was 1:1.5:1. 10 g of 2.5 wt% ammonium persulfate initiator was added to initiate the reaction. During the reaction, the additional monomer was continuously fed to maintain the reaction pressure of 2.0 MPa. The mass ratio of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride in the additional monomer was 1:0.2:0.3. The total weight of the additional monomer was 2 kg. During the addition of the additional monomer, 50 g of 2.5 wt% ammonium persulfate was continuously added. After about 3.5 hours of reaction, the stirring was stopped, and the polymerization kettle was cooled and vented. The obtained emulsion was coagulated, washed, dried, and granulated at 80 °C to obtain the target fluoropolymer. The composition of each structural unit of the fluoropolymer was 76 wt% of tetrafluoroethylene structural units, 16 wt% of hexafluoropropylene structural units, and 8 wt% of vinylidene fluoride structural units. The relevant performance test results are shown in Table 1.

[0056] Performance Test:

[0057] The bending modulus test is performed according to GB / T 9341-2000, using the recommended sample specification, and using an injection molding method to prepare the sample. The thermal decomposition temperature (0.4% weight loss) is measured using a thermal gravimetric analyzer. The adhesion test method: refer to GB / T2791-1995 for testing. Refractive index test: the obtained fluoropolymer is prepared into a film with a thickness of 100 μm. Component test: element analysis, 1 HNMR、 19 F NMR and infrared spectroscopy analysis of each structural unit.

[0058] Table 1 performance test results

[0059]

[0060] The vinylidene fluoride modified perfluoroethyl propylene copolymer provided by the application has a melt index of 9-11 g / 10 min, a melting point of 130-220℃, a tensile strength of ≥28.5 MPa, an elongation at break of ≥470%, a refractive index of ≤1.36; a thermal decomposition temperature of greater than 440℃; and an adhesion to polyimide film of ≥16 N / 2.5 cm. The method of the application improves the flexibility of the perfluoroethyl propylene copolymer while retaining its high transparency, and also significantly improves its mechanical strength, thermal stability and adhesion performance.

Claims

1. A process for the preparation of a fluorine-containing copolymer, characterized by, The method comprises the following steps: (1) introducing initial mixed monomers of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene into the reaction pressure in the presence of water and dispersant, controlling the oxygen content to be less than 20 ppm, and adding an initiator to initiate the polymerization reaction; the mass ratio of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene in the initial mixed monomers is 1:1-5:1-3; the amount of the initial mixed monomers added is 85-93% of the amount added to the reaction pressure; the reaction temperature is 50-90°C, and the reaction pressure is 1.5-4.5 MPa; the dispersant is one or a mixture of two of perfluoropolyether dispersant, perfluorohexanoic acid and hexafluoropropylene oxide trimer; (2) alternately supplementing the mixed monomers of tetrafluoroethylene and vinylidene fluoride, the mixed monomers of tetrafluoroethylene and hexafluoropropylene, and continuously supplementing the initiator during the polymerization process; the mass ratio of the two in the mixed monomers of tetrafluoroethylene and hexafluoropropylene in step (2) is 1-1.5:0.2-0.6; the mass ratio of the two in the mixed monomers of tetrafluoroethylene and vinylidene fluoride is 1-1.5:0.3-0.7; the method for alternately supplementing the mixed monomers is that when the reaction pressure drops by 0.1 MPa, the mixed monomers of tetrafluoroethylene and vinylidene fluoride are supplemented to the reaction pressure, and then when the reaction pressure drops by 0.1 MPa, the mixed monomers of tetrafluoroethylene and hexafluoropropylene are supplemented to the reaction pressure, and the two kinds of mixed monomers are alternately supplemented in this way.

2. The production method according to claim 1, characterized by, The mass ratio of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene in the initial mixed monomers in step (1) is 1:1.5-4.5:1-2.5; the reaction temperature in step (1) is 60-80°C, and the reaction pressure is 2-4 MPa.

3. The preparation method according to claim 1, characterized in that, The amount of the dispersant used in step (1) is 1:100-200 of the total mass of the monomers.

4. The preparation method according to claim 3, characterized in that The dispersant is CF3-O-[-CF(OCF3)-CF2-O-]2-CF2-O-COONH4 or a mixed dispersant of CF3-O-[-CF(OCF3)-CF2-O-]2-CF2-O-COONH4 and perfluorohexanoic acid with a mass ratio of 1:

1.

5. The preparation method according to claim 1, characterized in that, The initiator in step (2) is one or more of perfluoroacyl peroxide, potassium persulfate, ammonium persulfate, or a mixture of potassium permanganate and ammonium oxalate.

6. The production method according to claim 5, wherein The initiator in step (2) is ammonium persulfate or a mixture of potassium permanganate and ammonium oxalate; the mass ratio of the two in the mixed monomers of tetrafluoroethylene and hexafluoropropylene in step (2) is 2.5-5:

1.

7. A fluorine-containing copolymer produced by the process according to any one of claims 1 to 6, characterized in that, The fluorine-containing copolymer is composed of 50-70 wt% of tetrafluoroethylene structural units, 10-20 wt% of hexafluoropropylene structural units and 20-30 wt% of vinylidene fluoride structural units.

8. The fluorine-containing copolymer according to claim 7, characterized in that, The fluorine-containing copolymer is composed of 54-59 wt% of tetrafluoroethylene structural units, 16-20 wt% of hexafluoropropylene structural units and 21-30 wt% of vinylidene fluoride structural units.

9. The fluorine-containing copolymer according to claim 8, characterized in that, The said vinylidene fluoride modified perfluoro-ethyl propylene copolymer has a melt index of 9-11 g / 10 min, a melting point of 130-220 DEG C, a tensile strength of > 28.5 MPa, an elongation at break of > 470%, a refractive index of < 1.36, a thermal decomposition temperature of > 440 DEG C, and a bonding property with a polyimide film of > 16 N / 2.5 cm.

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