High-melt-strength ethylene-tetrafluoroethylene copolymer and preparation method thereof

Abstract

The invention discloses a high-melt-strength ethylene-tetrafluoroethylene copolymer and a preparation method thereof, and the preparation method comprises the following steps: preparing the ethylene-tetrafluoroethylene copolymer by adopting an emulsion polymerization mode, and introducing a reaction type functional group into an ethylene-tetrafluoroethylene copolymer molecular chain through a polymerization process to obtain the high-melt-strength ethylene-tetrafluoroethylene copolymer. The ethylene-tetrafluoroethylene copolymer containing the reaction type functional group is obtained; and carrying out a micro-crosslinking reaction on the ethylene-tetrafluoroethylene copolymer containing the reactive functional group and a micro-crosslinking assistant containing more than three degrees of functionality under the action of a catalyst to obtain the ethylene-tetrafluoroethylene copolymer with high melt strength. A reaction type functional group is introduced in the polymerization process, the high-melt-strength ETFE copolymer with a high molecular weight and a long branch chain structure is obtained in a micro-crosslinking reaction mode, the good heat resistance and mechanical performance of a linear ETFE copolymer are considered, meanwhile, the high-melt-strength ETFE copolymer has higher melt strength and higher critical shear rate, processing is more stable, and the high-melt-strength ETFE copolymer is suitable for industrial production. The method is suitable for various processing modes.

Description

Technical Field

[0001] The invention belongs to the technical field of fluorine-containing polymers, and in particular relates to an ethylene-tetrafluoroethylene copolymer with high melt strength and a preparation method thereof. Background Art

[0002] Ethylene tetrafluoroethylene copolymer (ETFE) is a polymer material with excellent chemical corrosion resistance, heat resistance and electrical insulation properties, and is widely used in the electrical field and wire and cable industry. However, the ETFE copolymer currently prepared still has the defects of low melt strength and poor sag resistance.

[0003] First, the molecular structure of ETFE is a linear chain structure, showing a partial crystal state, which leads to its low melt strength. The existence of partial crystal state makes ETFE material have lower fluidity and viscosity in the molten state, thus affecting its performance in processing such as high-speed extrusion; secondly, the softening point and melting point of ETFE are very close. When the processing temperature exceeds its melting point, the melt strength and viscosity of ETFE will drop rapidly. This limits the processing and molding of ETFE under high temperature conditions. In addition, in the molten state, ETFE material has almost no strain hardening effect, and its mechanical properties cannot be enhanced by the molecular arrangement inside the material, which also limits the application of ETFE in the field of high-speed extrusion.

[0004] At present, the preparation method of high melt strength ETFE is mainly through broadening the molecular weight distribution and filler reinforcement method. However, the wide molecular weight distribution requires a molecular chain regulator, the preparation process is difficult to control, and the wide molecular weight distribution will affect the heat resistance of ETFE; the filler reinforcement method is prone to uneven dispersion of additives, which limits the processing performance of ETFE; so traditional modification methods often cannot achieve high melt strength, heat resistance and good mechanical properties at the same time. Therefore, a new method is needed to prepare ETFE copolymers with high melt strength, high heat resistance and excellent mechanical properties. Summary of the invention

[0005] In order to solve the above-mentioned drawbacks of the prior art, the present invention discloses a method for preparing an ethylene-tetrafluoroethylene copolymer with high melt strength, which adopts the following technical scheme:

[0006] A method for preparing an ethylene-tetrafluoroethylene copolymer with high melt strength, wherein the ethylene-tetrafluoroethylene copolymer is prepared by emulsion polymerization, and reactive functional groups are introduced into the molecular chains of the ethylene-tetrafluoroethylene copolymer through the polymerization process to obtain an ethylene-tetrafluoroethylene copolymer containing reactive functional groups;

[0007] The ethylene-tetrafluoroethylene copolymer containing reactive functional groups and a micro-crosslinking auxiliary agent containing trifunctionality or more are subjected to micro-crosslinking reaction under the action of a catalyst to obtain an ethylene-tetrafluoroethylene copolymer with high melt strength.

[0008] The present invention introduces reactive functional groups into ETFE molecular chains, and then carries out micro-crosslinking reaction with micro-crosslinking auxiliary agents containing trifunctionality or more to prepare ethylene-tetrafluoroethylene copolymers, which have micro-crosslinking structures with long-chain branches. The micro-crosslinking structures with long-chain branches ensure that the ETFE copolymers have good processing fluidity and heat resistance. The highly entangled branched structures simultaneously improve the interaction between molecular chains, improve the shear resistance during processing, show as stretching hardening in elongation flow, and play a reinforcing role on melt strength. Therefore, compared with the method for improving melt strength by widening molecular weight distribution and filler reinforcement method in the prior art, the present invention, while making the ETFE copolymers have higher melt strength and better critical shear rate, also takes into account the good heat resistance and mechanical properties of linear ETFE copolymers. Therefore, the ETFE copolymers prepared by the present invention have more stable processing properties and are suitable for multiple molding processing modes such as extrusion processing and injection molding processing.

[0009] In the ethylene-tetrafluoroethylene copolymer emulsion containing reactive functional groups prepared by emulsion polymerization, the copolymer has a nanometer particle size, a large specific surface area and good dispersibility. Therefore, no post-treatment is required, and the ethylene-tetrafluoroethylene copolymer emulsion obtained by the reaction can be directly subjected to micro-crosslinking reaction with a micro-crosslinking auxiliary agent under the action of a catalyst to obtain an ETFE copolymer with long chain branches, and the preparation process is simple and easy to operate.

[0010] Furthermore, the high melt strength ethylene-tetrafluoroethylene copolymer comprises 35-55 mol% of ethylene repeating units, 35-55 mol% of tetrafluoroethylene repeating units and 0.1-10 mol% of a third monomer repeating unit. The third monomer is one or a combination of perfluoroolefin ether and perfluoroalkylethylene, the perfluoroolefin ether is preferably perfluoro-n-propyl vinyl ether, perfluoromethyl vinyl ether or perfluoroethyl vinyl ether; the perfluoroalkylethylene is preferably perfluoromethylethylene or perfluorobutylethylene.

[0011] Furthermore, the reactive functional group is one or a combination of a carbonyl group and anhydride group.

[0012] Further, the micro-crosslinking auxiliary agent is one or a combination of alcohols, amines and isocyanates. Preferably, the micro-crosslinking auxiliary agent is one or a combination of tris(2-aminoethyl)amine, tris(3-aminopropyl)amine, 1,2,4-butanetriol, 1,3,5-cyclohexanetriol, meso-erythritol, 2-aminoethanol, N-(3-aminopropyl)diethanolamine, 1,3-diamino-2-propanol, N,N,N,N'-tetrakis(2-hydroxyethyl)ethylenediamine, 2-(2-aminoethoxy)ethanol, DL-arabitol, 3-amino-1,2-propanediol, 2-amino-1,3-propanediol, α-thioglycerol and 2,3-dimercapto-1-propanol.

[0013] Furthermore, the catalyst is an organic tin catalyst, and preferably, the catalyst is one or a combination of dibutyltin dilaurate, stannous octoate, dibutyltin didodecylsulfide and dibutyltin diacetate.

[0014] Furthermore, the specific method of introducing reactive functional groups into the molecular chain of ethylene-tetrafluoroethylene copolymer through the polymerization process is: introducing reactive functional groups into the molecular chain of ethylene-tetrafluoroethylene copolymer through initiator and / or reactive chain transfer agent during the polymerization process.

[0015] Furthermore, the initiator is one or a combination of peroxycarbonate and peroxyester; the reactive chain transfer agent is one or a combination of carboxylic acid and acid anhydride.

[0016] Furthermore, the initiator is one or a combination of diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, tert-butyl peroxyisopropyl carbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate and di-2-ethylhexyl peroxydicarbonate; and the reactive chain transfer agent is one or a combination of acetic acid, propionic acid, butyric acid, acetic anhydride, propionic anhydride, butyric anhydride and isobutyric anhydride.

[0017] Furthermore, the specific preparation process of the high melt strength ethylene-tetrafluoroethylene copolymer is as follows:

[0018] 1) Add the polymerization monomer, surfactant and chain transfer agent into the reactor, add the initial monomer into the reactor until the pressure in the reactor is 0.5MPa-4MPa, and heat the reactor to 25-80°C;

[0019] 2) adding an initiator into a reactor to carry out a polymerization reaction, adding mixed monomers into the reactor during the polymerization process to maintain the pressure in the reactor at 0.5 MPa-4 MPa, reacting for 3-10 hours, and obtaining an ethylene-tetrafluoroethylene copolymer emulsion containing reactive functional groups;

[0020] 3) adding a micro-crosslinking auxiliary agent to an ethylene-tetrafluoroethylene copolymer emulsion containing a reactive functional group, and adding a catalyst to carry out a micro-crosslinking reaction, the reaction temperature is 30 to 80° C., and the reaction time is 0.2 to 5 hours to obtain a micro-crosslinked ethylene-tetrafluoroethylene copolymer emulsion;

[0021] 4) filtering, washing, drying, and melt-processing the slightly cross-linked ethylene-tetrafluoroethylene copolymer emulsion to obtain a high melt strength ethylene-tetrafluoroethylene copolymer;

[0022] Among them, the surfactant is one or a combination of ether bond and methylene fluorocarbon surfactants. Preferably, the surfactant is perfluoro-2,5-dimethyl-3,6-dioxaoctanoic acid and its salts, perfluoro-2,5-dimethyl-3,6-dioxaheptanoic acid and its salts, perfluoro-2,5-dimethyl-3,6-dioxanononanoic acid and its salts, and other linear perfluoropolyether fluorocarbonic acid and its salts. One or more.

[0023] Wherein, the chain transfer agent includes a reactive chain transfer agent.

[0024] Furthermore, the content of the chain transfer agent accounts for 0.5-5% of the total polymerized monomer content, and the content of the initiator accounts for 0.2-3% of the total polymerized monomer content, calculated by mass fraction.

[0025] The molar amount of the micro-crosslinking auxiliary agent is 0.8 to 3 times the molar amount of the reactive functional groups in the ethylene-tetrafluoroethylene copolymer emulsion containing reactive functional groups obtained in step 2).

[0026] The mass of the total polymerized monomers is the total mass of the polymerized monomers (ethylene, tetrafluoroethylene, and fluorinated third monomer) participating in the polymerization reaction, and the total mass of the polymerized monomers consumed in the polymerization reaction can be calculated based on the solid content of the ETFE copolymer to be prepared in actual production.

[0027] Furthermore, the chain transfer agent includes a reactive chain transfer agent and a non-reactive chain transfer agent, and the mass ratio of the reactive chain transfer agent to the non-reactive chain transfer agent is 0.1 to 15:1, preferably 0.5 to 8:1.

[0028] When the content of reactive chain transfer agent is too high or the content of non-reactive chain transfer agent is too low, the content of low molecular weight polymer in the prepared ETFE copolymer will be high and the thermal stability will be poor; when the content of reactive chain transfer agent is too low or the content of non-reactive chain transfer agent is too high, the content of reactive functional groups in the prepared ETFE copolymer will be too low and the improvement effect on melt strength will be insufficient.

[0029] Furthermore, the non-reactive chain transfer agent is one or a combination of alkanes, alcohols and ethers, preferably methanol, cyclohexane and methyl ether; the reactive chain transfer agent is one or a combination of carboxylic acids and anhydrides, preferably, the reactive chain transfer agent is one or a combination of carboxylic acids and anhydrides with a molecular weight of 20-500, further preferably one or a combination of acetic acid, propionic acid, butyric acid, acetic anhydride, propionic anhydride, butyric anhydride and isobutyric anhydride.

[0030] Furthermore, the initiator is a free radical initiator, including inorganic peroxides, organic peroxides and redox systems. Among them, the inorganic peroxide is preferably ammonium persulfate; the organic peroxide is preferably peroxycarbonate or peroxyester, and the initiator is preferably diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, tert-butyl peroxyisopropyl carbonate, di(4-tert-butylcyclohexyl) peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, etc.

[0031] The invention also discloses an ethylene-tetrafluoroethylene copolymer with high melt strength, which is prepared by any of the above-mentioned preparation methods.

[0032] By adopting the above technical solution, the beneficial effects of the present invention are:

[0033] The present invention introduces reactive functional groups during the polymerization process and utilizes a micro-crosslinking reaction to obtain a high-molecular-weight, long-chain branched structure, high-melt-strength ETFE copolymer. While taking into account the good heat resistance and mechanical properties of the linear ETFE copolymer, the copolymer also has higher melt strength and higher critical shear rate, and is more stable in processing, and is suitable for various molding processing methods such as extrusion processing and injection molding processing. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with the embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0035] The test methods of various properties of the ETFE copolymers prepared in the embodiments and comparative examples are as follows:

[0036] 1. Melt index (MFI, g / 10min) is carried out in accordance with the provisions of GB / T3682.1-2018, with a test load of 5kg and a temperature of 297°C.

[0037] 2. Melting point (Tm, ℃) is carried out in accordance with the provisions of GB / T19466.3-2004. Accurately weigh 10 mg ± 0.5 mg of the sample, and heat it to 320 ℃ at a heating rate of 20 ℃ / min in a nitrogen atmosphere to completely melt the ETFE resin. The top temperature of the melting peak is taken as the melting point of the polymer.

[0038] 3. The tensile strength and elongation at break shall be tested in accordance with the provisions of GB / T2918-2018. The test environment temperature shall be 23°C±2°C, the tensile speed shall be 50mm / min±5mm / min, the lengths of the two ends of the specimen clamped by the fixture shall be equal, and the distance between the fixtures shall be 24mm.

[0039] 4. The content of reactive functional groups in ethylene-tetrafluoroethylene copolymers can be characterized by Fourier transform infrared spectroscopy.

[0040] 5. Heat resistance test: use an electronic balance to weigh 2.5±0.2g of the sample, put it into a container made of 5cm*5cm aluminum foil, sinter it at 315℃ in a sintering furnace for 40min, and observe the color change visually.

[0041] 6. Cable extrusion evaluation test, cable wall thickness 0.25mm, evaluate the cable forming process.

[0042] 7. Melt strength: The melt strength of the sample is tested using a Gottfort tensile rheometer. The device is equipped with a capillary tube, from which the polymer melt flows. The melt moves downward under the force of the roller, and the tensile force can be measured by a sensor, which is the melt strength. The test temperature is 300°C, and the roller rotation acceleration is 6mm / s 2 .

[0043] The raw materials used in the examples and comparative examples of the present invention are all common commercially available products, wherein the surfactant in the examples and comparative examples is perfluoro-2,5-dimethyl-3,6-dioxanononanoic acid.

[0044] Example 1

[0045] 1) To a 4m2 vessel with a mixer, valve, pressure gauge, and thermometer 3 2.4 tons of pure water were added to the high-pressure polymerization kettle, and by mass fraction, 4‰ of the surfactant, 0.3% of the total polymerization monomer content of non-reactive chain transfer agent methanol, and 0.6% of the total polymerization monomer content of reactive chain transfer agent acetic anhydride were added. The air was fully replaced with nitrogen and then evacuated. While stirring, tetrafluoroethylene, ethylene, and perfluoro-(propyl vinyl ether) initial mixed monomers were added to make the pressure in the high-pressure polymerization kettle reach 1.5MPa, and the temperature in the system was maintained at 50°C.

[0046] 2) Pressurize the initiator ammonium persulfate with nitrogen in an amount of 1% of the total polymerization monomer content by mass, start the reaction, maintain the reaction pressure and temperature, continuously add the mixed monomers tetrafluoroethylene, ethylene, and perfluoro-(propyl vinyl ether), stop the reaction after 6 hours, cool the high-pressure polymerization autoclave, recover the unreacted monomers, and obtain an ETFE copolymer emulsion containing reactive functional groups.

[0047] 3) After the copolymer emulsion is treated, FTIR is used to test the content of its reactive functional groups.

[0048] 4) adding 1.5 times molar equivalent of tri(3-aminopropyl)amine of reactive functional groups to the ETFE copolymer emulsion containing reactive functional groups obtained in step 2), adding catalyst stannous octoate and heating to 50° C. to carry out micro-crosslinking reaction, and obtaining micro-crosslinked ETFE copolymer emulsion with long-chain branched structure after reacting for 1 hour.

[0049] 5) filtering, washing and drying the ETFE copolymer emulsion obtained in step 4) to obtain a crude product of ethylene-tetrafluoroethylene copolymer.

[0050] 6) The crude ethylene-tetrafluoroethylene copolymer obtained in step 5) is melt-processed and granulated in a devolatilizing granulator to obtain an ethylene-tetrafluoroethylene copolymer with high melt strength.

[0051] The performance test results of the high melt strength ethylene-tetrafluoroethylene copolymer prepared in this example are shown in Table 1.

[0052] Example 2

[0053] 1) Add 2 tons of pure water, 4‰ of the mass of the pure water, 0.3% of the total polymerization monomer content of methanol as a non-reactive chain transfer agent, and 0.6% of the total polymerization monomer content of acetic anhydride as a reactive chain transfer agent to a high-pressure polymerization reactor equipped with a stirrer, a valve, a pressure gauge, and a thermometer, and evacuate the system after fully replacing the gas with nitrogen. While stirring, add an initial mixed monomer of tetrafluoroethylene, ethylene, and perfluoro-(propyl vinyl ether) to make the pressure in the high-pressure polymerization reactor reach 0.7 MPa, and keep the temperature in the system at 35°C.

[0054] 2) Using nitrogen to pressurize the initiator di-n-propyl peroxydicarbonate in an amount of 1% by mass of the total polymerization monomer content, the reaction was started, the reaction pressure and temperature were maintained, tetrafluoroethylene, ethylene, and perfluoro-(propyl vinyl ether) mixed monomers were continuously added, the reaction was stopped after 10 hours, the high-pressure polymerization autoclave was cooled, and the unreacted monomers were recovered to obtain an ETFE copolymer emulsion containing reactive functional groups.

[0055] 3) After the copolymer emulsion is treated, FTIR is used to test the content of its reactive functional groups.

[0056] 4) Add 2 times the molar equivalent of tri(2-aminoethyl)amine to the ETFE copolymer emulsion containing reactive functional groups obtained in step 2), add stannous octoate as a catalyst and heat to 50° C. to carry out a micro-crosslinking reaction, and after reacting for 1 hour, obtain an ETFE copolymer emulsion with a micro-crosslinked long-chain branched structure.

[0057] 5) filtering, washing and drying the ETFE copolymer emulsion obtained in step 4) to obtain a crude product of ethylene-tetrafluoroethylene copolymer.

[0058] 6) The crude ethylene-tetrafluoroethylene copolymer obtained in step 5) is melt-processed and granulated in a devolatilizing granulator to obtain an ethylene-tetrafluoroethylene copolymer with high melt strength.

[0059] The performance test results of the high melt strength ethylene-tetrafluoroethylene copolymer prepared in this example are shown in Table 1.

[0060] Example 3

[0061] In step 1), methanol, a non-reactive chain transfer agent, accounting for 2% of the total polymerization monomer content, and acetic anhydride, a reactive chain transfer agent, accounting for 1% of the total polymerization monomer content, are added.

[0062] The rest is the same as Example 2.

[0063] Example 4

[0064] The third monomer in steps 1) and 2) is perfluorobutylethylene monomer.

[0065] The rest is the same as in Example 1.

[0066] Example 5

[0067] In step 1), methanol, a non-reactive chain transfer agent, accounting for 0.5% of the total polymerization monomer content, and propionic anhydride, a reactive chain transfer agent, accounting for 4% of the total polymerization monomer content, are added; and in step 3), 2-aminoethanol is added as a micro-crosslinking aid.

[0068] The rest is the same as in Example 1.

[0069] Example 6

[0070] In step 1), methanol, a non-reactive chain transfer agent, accounting for 1% of the total polymer monomer content, and acetic anhydride, a reactive chain transfer agent, accounting for 4% of the total polymer monomer content, are added. In step 3), 2-aminoethanol is added as a micro-crosslinking auxiliary agent.

[0071] The rest is the same as in Example 1.

[0072] Example 7

[0073] The rest is the same as in Example 1.

[0074] Comparative Example 1

[0075] In step 1), methanol, a non-reactive chain transfer agent, accounting for 0.9% of the total polymerization monomer content, is added, and no reactive chain transfer agent is added.

[0076] Others are the same as in Example 1

[0077] Comparative Example 2

[0078] In step 1),

[0079] Acetic anhydride, a reactive chain transfer agent, was added in an amount of 0.9% of the total polymerized monomer content, and no non-reactive chain transfer agent was added.

[0080] Others are the same as in Example 1

[0081] Comparative Example 3

[0082] Step 4) Add 0.2 times the molar equivalent of tris(3-aminopropyl)amine to the ETFE copolymer emulsion containing reactive functional groups obtained.

[0083] Others are the same as in Example 1

[0084] Comparative Example 4

[0085] Step 4) Add 4 times the molar equivalent of tris(3-aminopropyl)amine to the ETFE copolymer emulsion containing reactive functional groups obtained.

[0086] Others are the same as in Example 1

[0087] Comparative Example 5

[0088] In step 3), the micro-crosslinking auxiliary agent added is ethylenediamine.

[0089] Comparative Example 6

[0090] In step 1), methanol, a non-reactive chain transfer agent, accounting for 0.85% of the total polymerization monomer content, and acetic anhydride, a reactive chain transfer agent, accounting for 0.05% of the total polymerization monomer content, are added.

[0091] The rest is the same as in Example 1.

[0092] Comparative Example 7

[0093] In step 1), methanol, a non-reactive chain transfer agent, accounting for 0.05% of the total polymerization monomer content, and acetic anhydride, a reactive chain transfer agent, accounting for 0.85% of the total polymerization monomer content, are added.

[0094] The rest is the same as in Example 1.

[0095] Comparative Example 8

[0096] In step 1), the reactive chain transfer agent is polysebacic anhydride.

[0097] The rest is the same as in Example 1.

[0098] Table 1 Performance test results of high melt strength ethylene-tetrafluoroethylene copolymers prepared in Examples and Comparative Examples

[0099]

[0100] It can be seen from Table 1 that the high melt strength ethylene-tetrafluoroethylene copolymers prepared in Examples 1-7 have good heat resistance and mechanical properties. After processing and extrusion evaluation, the line speed is as high as 100-135 m / min, and the number of glue breakage and breakdown is greatly reduced, and even no glue breakage and no breakdown can be achieved, which solves the problems of glue breakage and breakdown of high-speed extruded cables and improves the molding efficiency and cable quality.

[0101] In Comparative Example 1, only a non-reactive chain transfer agent was used for polymerization, resulting in the prepared ethylene-tetrafluoroethylene copolymer having a linear structure. The extrusion evaluation result was poor, the line speed was only 70 m / min, and the rubber breaking was serious.

[0102] In Comparative Example 2, only a reactive chain transfer agent was used for polymerization, resulting in a polymer with a lower molecular weight, a larger melt index and poorer thermal stability.

[0103] In Comparative Example 3, the amount of micro-crosslinking agent added is too low, resulting in the ethylene tetrafluoroethylene copolymer prepared therefrom being not much different from that in Comparative Example 1. In Comparative Example 4, due to the excessive addition of micro-crosslinking agent, the degree of crosslinking is too high, and the extrusion molding processability is reduced, and the thermal stability is reduced.

[0104] Comparative Example 5 uses a difunctional micro-crosslinking auxiliary agent, which results in insufficient molecular chain entanglement and insignificant improvement in molecular melt strength.

[0105] Although the chain transfer agents added in Comparative Examples 6 and 7 include non-reactive chain transfer agents and reactive chain transfer agents, the content of the non-reactive chain transfer agent in Comparative Example 6 is too high and the content of the reactive chain transfer agent is too low, resulting in insufficient improvement in melt strength. The content of the non-reactive chain transfer agent in Comparative Example 7 is too low and the content of the reactive chain transfer agent is too high, resulting in a lower polymer molecular weight and poor thermal stability.

[0106] The molecular weight of the reactive chain transfer agent in Comparative Example 8 is relatively large, resulting in the introduction of too many hydrocarbon segments, poor melt fluidity and stability, and branch chain degradation during high-temperature processing, leading to bubbles, yellowing, poor processability, and inability to perform normal cable extrusion.

[0107] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in this field can still modify the technical solutions recorded in the above embodiments, or replace part or all of the technical features therein with equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A method for preparing a high melt strength ethylene-tetrafluoroethylene copolymer, characterized in that: The ethylene-tetrafluoroethylene copolymer is prepared by emulsion polymerization, and reactive functional groups are introduced into the molecular chain of the ethylene-tetrafluoroethylene copolymer through the polymerization process to obtain the ethylene-tetrafluoroethylene copolymer containing reactive functional groups; The ethylene-tetrafluoroethylene copolymer containing reactive functional groups and a micro-crosslinking auxiliary agent containing trifunctionality or more are subjected to micro-crosslinking reaction under the action of a catalyst to obtain an ethylene-tetrafluoroethylene copolymer with high melt strength.

2. The preparation method according to claim 1, characterized in that: The reactive functional group is one or a combination of a carbonyl group and an anhydride group; The micro-crosslinking auxiliary agent is one or a combination of alcohols, amines and isocyanates.

3. The preparation method according to claim 2, characterized in that: The micro-crosslinking auxiliary agent is one or a combination of tris(2-aminoethyl)amine, tris(3-aminopropyl)amine, 1,2,4-butanetriol, 1,3,5-cyclohexanetriol, meso-erythritol, 2-aminoethanol, N-(3-aminopropyl)diethanolamine, 1,3-diamino-2-propanol, N,N,N,N'-tetrakis(2-hydroxyethyl)ethylenediamine, 2-(2-aminoethoxy)ethanol, DL-arabitol, 3-amino-1,2-propylene glycol, 2-amino-1,3-propylene glycol, a-thioglycerol and 2,3-dimercapto-1-propanol; And / or, the catalyst is an organic tin catalyst, preferably, the catalyst is one or a combination of dibutyltin dilaurate, stannous octoate, dibutyltin didodecylsulfide and dibutyltin diacetate.

4. The preparation method according to claim 1, characterized in that: The specific method of introducing reactive functional groups into the molecular chain of ethylene-tetrafluoroethylene copolymer through the polymerization process is: During the polymerization process, reactive functional groups are introduced into the molecular chains of the ethylene-tetrafluoroethylene copolymer through an initiator and / or a reactive chain transfer agent.

5. The preparation method according to claim 4, characterized in that: The initiator is one or a combination of peroxycarbonate and peroxyester; The reactive chain transfer agent is one or a combination of carboxylic acid and acid anhydride. Preferably, the reactive chain transfer agent is one or a combination of carboxylic acid and acid anhydride with a molecular weight of 20 to 500.

6. The preparation method according to claim 5, characterized in that: The initiator is one or a combination of diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, tert-butyl peroxyisopropyl carbonate, bis(4-tert-butylcyclohexyl) peroxydicarbonate and di-2-ethylhexyl peroxydicarbonate; And / or, the reactive chain transfer agent is one or a combination of acetic acid, propionic acid, butyric acid, acetic anhydride, propionic anhydride, butyric anhydride and isobutyric anhydride.

7. The preparation method according to claim 1, characterized in that: The specific preparation process is as follows: 1) Add the polymerization monomer, surfactant and chain transfer agent into the reactor, add the initial monomer into the reactor until the pressure in the reactor is 0.5MPa-4MPa, and heat the reactor to 25-80°C; 2) adding an initiator into a reactor to carry out a polymerization reaction, adding mixed monomers into the reactor during the polymerization process to maintain the pressure in the reactor at 0.5 MPa-4 MPa, reacting for 3-10 hours, and obtaining an ethylene-tetrafluoroethylene copolymer emulsion containing reactive functional groups; 3) adding a micro-crosslinking auxiliary agent to an ethylene-tetrafluoroethylene copolymer emulsion containing a reactive functional group, and adding a catalyst to carry out a micro-crosslinking reaction, the reaction temperature is 30 to 80° C., and the reaction time is 0.2 to 5 hours to obtain a micro-crosslinked ethylene-tetrafluoroethylene copolymer emulsion; 4) filtering, washing, drying, and melt-processing the slightly cross-linked ethylene-tetrafluoroethylene copolymer emulsion to obtain a high melt strength ethylene-tetrafluoroethylene copolymer.

8. The preparation method according to claim 7, characterized in that: The content of the chain transfer agent accounts for 0.5 to 5% of the total polymerization monomer content by mass fraction; The initiator content accounts for 0.2-3% of the total polymerization monomer content; The molar amount of the micro-crosslinking auxiliary agent is 0.8 to 3 times the molar amount of the reactive functional groups in the ethylene-tetrafluoroethylene copolymer emulsion containing reactive functional groups obtained in step 2).

9. The preparation method according to claim 7, characterized in that: The chain transfer agent includes a non-reactive chain transfer agent and a reactive chain transfer agent, and the mass ratio of the non-reactive chain transfer agent to the reactive chain transfer agent is 0.1 to 15:1, preferably 0.5 to 8:

1.

10. A high melt strength ethylene-tetrafluoroethylene copolymer, characterized in that: The method is prepared by any one of claims 1 to 9.

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