Preparation method and application of fluorine-containing polymer emulsion

Abstract

The invention discloses a preparation method of a fluorine-containing polymer emulsion, which comprises the following steps: in the presence of a specific surfactant, polymerizing monomers in an aqueous medium to prepare the fluorine-containing polymer emulsion through a polymerization reaction, enabling an ionic compound to participate in the polymerization reaction, and enabling a shell layer of a fluorine-containing polymer to contain an ionic compound structure unit, the surfactant is a multi-block copolymer with more than 5 blocks of a hydrophobic monomer structure unit, a nonionic hydrophilic monomer structure unit and an ionic hydrophilic monomer structure unit, the block length of a single block is 1-10, and the particle size of the fluorine-containing polymer emulsion is 60-100 nm. The steric hindrance effect of the hydrophilic chain segment of the surfactant and the joint effect of the ionic group interface potential of the iontophoresis agent increase a layer of interface potential in a hydration layer interface formed by the hydrophilic chain segment with high steric hindrance, so that coalescence of emulsion particles can be better prevented, and the small-particle-size fluorine-containing polymer with the particle size ranging from 60 nm to 100 nm is obtained.

Description

Technical Field

[0001] The present invention relates to the field of polymers, and specifically relates to a preparation method and application of a fluoropolymer emulsion. Background Art

[0002] Among the current synthesis methods of fluoropolymer emulsions, emulsion polymerization is one of the most commonly used polymerization methods. Among them, surfactants (hereinafter referred to as surfactants) as dispersants are one of the most core raw materials. So far, the two types of fluorosurfactants with the most use in the polymerization of fluoromonomers are those led by PFOA and GenX. Their advantages mainly lie in: special surface activity and excellent chemical stability. However, these advantages are also the direct reasons for the extremely long degradation half-life and extremely high toxicity of fluorosurfactants. This results in not only high waste treatment costs in the production and use of fluoropolymer emulsions, but also inevitable emissions to the natural world to a certain extent. To solve the above problems, it is an urgent and important issue to develop surfactants that are easily degradable, low-toxic or even non-toxic and suitable for the polymerization of fluoromonomers.

[0003] Currently, regarding the toxicity problem of fluorosurfactants, the prior art discloses substituting with non-fluorosurfactants, and the design ideas of non-fluorosurfactants are as follows:

[0004] 1) Designing into hydrophilic monomers that can copolymerize with fluoromonomers, and using the obtained oligomers as surfactants. Patent documents CN104292374A, CN104292378A, US2847404A, and US5859123A adopt this design idea. Although the toxicity problem is solved to a certain extent, there will be hydrophilic groups that cannot be removed in the resulting fluoropolymer emulsion, resulting in a decline in product performance and limited application scope. In addition, the polymer solid content prepared by this design idea is generally relatively low.

[0005] 2) Designing into block-type amphiphilic polymer surfactants. Patent documents CN1535989A and CN111148772A adopt this design idea. This design idea brings another technical problem. The mobility of this block-type amphiphilic polymer surfactant at the surface and the gas-liquid interface of the fluoropolymer is poor, resulting in a decrease in the mass transfer rate between the interfaces.

[0006] Surfactants play a decisive role in controlling the size of emulsion particles. The size of emulsion particles affects the performance of fluoropolymers. Lower emulsion particle size can reduce molecular weight distribution, improve emulsion stability, accelerate polymer dissolution rate, enhance coating performance, increase adhesion, etc. When the particle size of emulsion particles is less than 100nm, the Brownian motion kinetic energy of the particles is equal to the stirring kinetic energy and van der Waals interaction energy, and is much greater than the sedimentation kinetic energy. At this time, the stability of the emulsion will undergo a qualitative change. Therefore, synthesizing fluoropolymer emulsions with a particle size less than 100nm is a technical problem that needs to be solved urgently.

[0007] At present, there are two public reports of fluorine-containing polymer emulsions less than 100nm. They are:

[0008] 1) Use polyethylene glycol oligomers with dithiocarbonate groups as chain transfer agents for fluoropolymer polymerization, and introduce polyethylene glycol into the end groups of fluoropolymers to reduce the surface energy of the solid-liquid interface (Fuentes-Exposito, M. et al. Polym. Chem., 2021, 12, 5640). However, this polymerization method requires the introduction of a large amount of polyethylene glycol segments (>1wt%) as end groups, and at the same time requires the addition of more than twice the initiator equivalent. The molecular weight of the fluoropolymer obtained is limited and is not enough to support most fluoropolymer application scenarios.

[0009] 2) Use C4 fluorinated small molecules as surfactants (Banerjee, S. et al. Chem. Commun., 2018, 54, 11399). Although this surfactant has a stronger degradation ability than the commonly used perfluorinated surfactants. However, due to its higher CMC (2.3mM) value, its polymerization conditions require a large amount of this surfactant and an initiator of the same order of magnitude, resulting in the resulting fluorinated polymer having a low molecular weight (<5000g / mol). Summary of the invention

[0010] In order to solve the above-mentioned technical problems, the inventors of the present invention unexpectedly found that a small-particle fluorine-containing polymer emulsion can be obtained by using a specific surfactant and an ionic compound in combination. This is due to the combined effect of the steric hindrance of the hydrophilic chain segment of the surfactant and the interfacial potential of the ionic group of the ionic compound. In the hydration layer interface formed by the high steric hindrance hydrophilic chain segment, adding a layer of interfacial potential can better prevent the aggregation of emulsion particles, and also better reduce the interfacial energy between the polymer and water.

[0011] The present invention provides a method for preparing a fluorine-containing polymer emulsion, the method comprising: polymerizing monomers in an aqueous medium in the presence of a surfactant to obtain the fluorine-containing polymer emulsion through a polymerization reaction,

[0012] Ionic compounds participate in the polymerization reaction, and the shell of the fluoropolymer contains structural units of ionic compounds.

[0013] The surfactant is a multi-block copolymer with more than 5 blocks of hydrophobic monomer structural units, non-ionic hydrophilic monomer structural units, and ionic hydrophilic monomer structural units. The block length of a single block is 1 to 10.

[0014] The particle size of the fluoropolymer emulsion is 60 to 100 nm.

[0015] In the fluoropolymer of the present invention, the content of the ionic compound structural unit is 0.005 wt% to 2.5 wt%, preferably 0.005 wt% to 1.0 wt%, and more preferably 0.01 wt% to 0.7 wt%.

[0016] The ionic compounds of the present invention are selected from at least one of acrylate, trifluoromethyl acrylate, vinyl sulfonate, vinyl phosphate, ionic acrylate, methacrylate, ionic methacrylate, ionic allyl ester, ionic allyl ether, ionic vinyl ether, monofumarate, itaconate, 10-undecenoate.

[0017] The ionic compound can be an alkali metal salt or an alkaline earth metal salt. For example, acrylate can be an alkali metal salt of acrylic acid or an alkaline earth metal salt of acrylic acid, such as sodium acrylate, potassium acrylate, ammonium acrylate, lithium acrylate, etc.

[0018] The fluoropolymer of the present invention is any polymer containing fluorine atoms, including but not limited to polyvinylidene fluoride (PVDF), polyvinyl fluoride, polytrifluoroethylene, polytrifluorochloroethylene, polytetrafluoroethylene, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene-trifluorochloroethylene copolymer, vinylidene fluoride-trifluoroethylene-fluorochloroethylene copolymer, ethylene-trifluorochloroethylene copolymer, etc.

[0019] The fluoropolymer is prepared by polymerizing fluorine-containing monomers or by polymerizing fluorine-containing monomers and non-fluorine-containing monomers.

[0020] The fluorine-containing monomer is selected from at least one of vinyl fluoride, vinylidene fluoride, trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, tetrafluoropropylene, chlorotrifluoroethylene, 1,1-chlorofluoroethylene, 1,2-chlorofluoroethylene, perfluoroalkyl ethylene, perfluoroalkyl vinyl ether, perfluoropropyl vinyl ether, perfluoromethyl vinyl ether, and perfluoro(2,2-dimethyl-1,3-dioxolene); preferably, the fluorine-containing monomer is selected from at least one of vinyl fluoride, vinylidene fluoride, trifluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, 1,1-chlorofluoroethylene, perfluoropropyl vinyl ether, perfluoromethyl vinyl ether, and perfluoro(2,2-dimethyl-1,3-dioxolene). The above perfluoroalkyl vinyl ether can be selected from perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, and perfluorobutyl vinyl ether.

[0021] The non-fluorine-containing monomer is selected from at least one of ethylene, acrylate, methyl acrylate, methacrylate, methyl methacrylate, vinyl ether, vinyl acetate, acrylonitrile, butadiene, isoprene, styrene, maleic anhydride, and itaconic acid. The non-fluorine-containing monomer accounts for 0 to 50 mol% of the total amount of the polymerization monomers.

[0022] The number-average molecular weight of the fluorine-containing polymer of the present invention is greater than 170,000, preferably greater than 200,000, and more preferably greater than 1,000,000. The number-average molecular weight of the fluorine-containing polymer is mainly affected by the polymerization process. If no ionic compound is used in the polymerization reaction of the present invention, although the emulsion particle size can be less than 100 nm when the amount of the surfactant used increases, the number-average molecular weight of the fluorine-containing polymer is relatively low, and the preparation of a fluorine-containing polymer with a high number-average molecular weight cannot be achieved.

[0023] The amount of the ionic compound used in the present invention only needs to meet the requirements. Preferably, the mass ratio of the ionic compound to the polymerization reaction initiator is 1:0.5 to 1:2, and preferably 1:1.5.

[0024] The polymerization reaction of the present invention is initiated by an initiator, which is a commonly used initiator in the field of fluorinated monomer polymerization. For example, the initiator includes persulfates, such as ammonium persulfate or potassium persulfate. The initiator can also include azo initiators, such as 2,2'-azobis-(2,4-dimethyl-4-methoxypentanenitrile) or azobisisobutyronitrile (AIBN). The initiator can also include organic peroxides, such as alkyl peroxides, dialkyl peroxides, diacyl peroxides, peroxy esters and peroxy dicarbonates; such as 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, benzoyl peroxide and its derivatives, tert-butyl peroxyneopentanoate, tert-amyl peroxyneopentanoate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, sodium peroxydicarbonate or di(n-alkyl) peroxydicarbonate, di-tert-butyl peroxide, succinic peroxide, di-n-propyl peroxydicarbonate, di-isopropyl peroxydicarbonate. The usage amount of the initiator accounts for 0.005wt% to 2.5wt% of the total amount of the polymerization monomers.

[0025] As an implementation method, the initiator for preparing the fluorinated polymer in the polymerization reaction of the present invention is a water-soluble initiator, including but not limited to water-soluble peroxides, such as succinic peroxide; persulfates, such as ammonium persulfate or potassium persulfate; water-soluble azo compounds, such as 4,4'-azobis(4-cyanopentanoic acid). The usage amount of the initiator accounts for 0.005wt% to 2.5wt% of the total amount of the polymerization monomers.

[0026] The polymerization reaction of the present invention can add a chain transfer agent to adjust the molecular weight of the fluorinated polymer. The chain transfer agent is a commonly used chain transfer agent in the field of fluorinated monomer polymerization, and the chain transfer agent is selected from at least one of small molecule compounds of alcohols, ethers, esters, thiols, and halogen-containing organic compounds. The usage amount of the chain transfer agent in the polymerization reaction accounts for 0.005wt% to 5wt% of the total amount of the polymerization monomers.

[0027] For the polymerization reaction of the present invention, the polymerization temperature is generally 5 to 130 °C and the polymerization pressure is 0.05 to 10 MPa. Preferably, the polymerization temperature is 60 to 100 °C and the polymerization pressure is 1 to 6 MPa. The polymerization temperature and polymerization pressure are appropriately determined according to the type of the fluorinated monomer used, the molecular weight of the target fluorinated polymer, and the reaction rate.

[0028] The polymerization reaction of the present invention is carried out under stirring, and the stirring rate is 50 to 700 rpm. The stirring method is preferably magnetic stirring or mechanical stirring, and other stirring methods that can achieve the corresponding stirring function can also be selected.

[0029] The fluoropolymer prepared by the present invention contains a surfactant in an amount of 0.1 ppm to 1000 ppm by mass based on the mass of the fluoropolymer. Preferably, the amount is 100 ppm or less, and more preferably, 10 ppm or less.

[0030] The surfactant in the present invention is a copolymer represented by the formula (1),

[0031]

[0032] wherein, R 1 , R 4 , R 7 are each independently selected from hydrogen, a C 1 -C 18 linear or branched alkyl group, a C 1 -C 18 linear or branched alkyl ether group, a C 1 -C 18 linear or branched haloalkyl group, a C 2 -C 18 aliphatic hydroxyl group, a C 2 -C 18 aliphatic thioether, a C 2 -C 18 aliphatic ester group, a C 2 -C 18 aliphatic cyano group;

[0033] R 2 , R 5 , R 8 are each independently selected from oxygen, sulfur, imino, a C 1 -C 18 linear or branched or cyclic alkanimino group, a C 1 -C 18 arylimino group;

[0034] R 3 is selected from phenyl, a C 1 -C 18 linear or branched alkyl group, benzyl, 2-phenyl-2-propyl, allyl;

[0035] R 6 is selected from polyethylene glycol derivatives (CH 2 CH 2 O) q A, where q is an integer greater than 4 and less than or equal to 100, and A is selected from hydrogen, a C 1 -C 3 linear or branched alkyl group;

[0036] R 9Selected from hydrogen, lithium, sodium, potassium, ammonium, lithium 2-methylpropanesulfonate, sodium 2-methylpropanesulfonate, potassium 2-methylpropanesulfonate, ammonium 2-methylpropanesulfonate, ethyltrimethylammonium chloride, ethyltrimethylammonium bromide, ethyltrimethylammonium iodide, ethyltrimethylammonium fluoride, lithium 2-sulfoethyl ester, sodium 2-sulfoethyl ester, potassium 2-sulfoethyl ester, ammonium 2-sulfoethyl ester, ammonium propane-1-sulfonate, lithium propane-1-sulfonate, sodium propane-1-sulfonate, potassium propane-1-sulfonate.

[0037] Further, in order to reduce the polymerization side reaction and improve the interfacial wetting property, preferably, R 1 , R 4 , R 7 are independently selected from hydrogen, C 1 -C 5 linear or branched alkyl, C 1 -C 5 linear or branched alkyl ether group; R 2 , R 5 , R 8 are independently selected from oxygen, imino, C 1 -C 9 linear or branched or cyclic alkylene imino, C 1 -C 9 arylene imino; R 3 is selected from phenyl, C 1 -C 4 linear or branched alkyl, benzyl, 2-phenyl-2-propyl, allyl; R 6 is selected from polyethylene glycol derivatives (CH 2 CH 2 O) q A, where q is an integer greater than 9 and less than or equal to 100, and A is selected from hydrogen, C 1 -C 3 linear or branched alkyl; R 9 is selected from hydrogen, lithium, sodium, potassium, ammonium, lithium 2-methylpropanesulfonate, sodium 2-methylpropanesulfonate, potassium 2-methylpropanesulfonate, ammonium 2-methylpropanesulfonate, ethyltrimethylammonium chloride, lithium 2-sulfoethyl ester, sodium 2-sulfoethyl ester, potassium 2-sulfoethyl ester, ammonium 2-sulfoethyl ester, ammonium propane-1-sulfonate, lithium propane-1-sulfonate, sodium propane-1-sulfonate, potassium propane-1-sulfonate. More preferably, R 1 , R 4 , R 7 are independently selected from hydrogen, methyl; R 2 , R 5 , R 8 are independently selected from oxygen, imino; R 3 is selected from phenyl, C 1 -C4 Straight-chain or single-branched alkyl; R 6 Selected from polyethylene glycol derivatives (CH 2 CH 2 O) q A, where q is an integer greater than 9 and less than or equal to 80, and A is selected from hydrogen, C 1 ~C 3 Straight-chain or branched alkyl; R 9 Selected from lithium, sodium, potassium, ammonium, lithium 2-amino-2-methylpropanesulfonate, sodium 2-amino-2-methylpropanesulfonate, potassium 2-amino-2-methylpropanesulfonate, ammonium 2-amino-2-methylpropanesulfonate, ethyltrimethylammonium chloride, lithium 2-sulfoethyl ester, sodium 2-sulfoethyl ester, potassium 2-sulfoethyl ester, ammonium 2-sulfoethyl ester, ammonium propane-1-sulfonate, lithium propane-1-sulfonate, sodium propane-1-sulfonate, potassium propane-1-sulfonate. More preferably, R 1 、R 4 、R 7 Are each independently selected from methyl; R 2 、R 5 、R 8 Are each independently selected from oxygen; R 3 Is selected from phenyl, methyl, tert-butyl; R 6 Selected from polyethylene glycol derivatives (CH 2 CH 2 O) q A, where q is an integer greater than 9 and less than or equal to 50, and A is selected from hydrogen, C 1 ~C 3 Straight-chain or branched alkyl; R 9 Selected from lithium, sodium, potassium, ammonium, lithium 2-amino-2-methylpropanesulfonate, sodium 2-amino-2-methylpropanesulfonate, potassium 2-amino-2-methylpropanesulfonate, ammonium 2-amino-2-methylpropanesulfonate, lithium 2-sulfoethyl ester, sodium 2-sulfoethyl ester, potassium 2-sulfoethyl ester, ammonium 2-sulfoethyl ester, ammonium propane-1-sulfonate, lithium propane-1-sulfonate, sodium propane-1-sulfonate, potassium propane-1-sulfonate.

[0038] In the surfactant of the present invention, the molar contents x, y, and z of each structural unit have a great influence on the performance of the surfactant and need to simultaneously meet the conditions: x / (y + z) = 1 to 9 and z / y = 0 to 3 and greater than 0. Further, x + y + z = 1. Considering multiple aspects such as improving the emulsion polymerization rate, reducing the occurrence of side reactions in emulsion polymerization, enhancing the wettability of the water-oil interface, increasing the steric hindrance of the surface hydration layer, enhancing the stability of the dispersion system, enhancing the LCST, and increasing the interfacial adsorption energy, preferably, x + y + z = 1, x / (y + z) = 1 to 5, and z / y = 1 to 3. More preferably, x + y + z = 1, x / (y + z) = 1 to 2, and z / y = 2 to 3.

[0039] When the value of x / (y + z) is too low, the structural units corresponding to y and z are distributed on the hydrophobic main chain in a block form. At the same time, the degree of polymerization of the structural unit chain segment corresponding to x is relatively low, resulting in a decrease in the adsorption force of the surfactant on the emulsion surface. In addition, it causes the surfactant to be unable to form a unimolecular micelle structure in water, and the micelle particle size formed in water is relatively large. When the value of x / (y + z) is too large, the chain segment of the structural unit corresponding to x is too long, resulting in a decrease in the mobility of the hydrophobic chain segment, making the micelle formed by the surfactant too stable and not easily adsorbed on the emulsion surface, and the emulsion stability decreases.

[0040] The ratio of y to z has a great influence on the LCST value of the surfactant. When the value of z / y is too small, the content of the ionic hydrophilic monomer structural unit is too low, resulting in too low LCST value of the surfactant, lower than 100 °C. When the value of z / y is too large, the content of the PEG chain segment is too small, resulting in a decrease in the stabilizer of the surfactant.

[0041] The HLB value (hydrophilic-lipophilic balance value) of the surfactant described in the present invention is 14-20. Considering multiple aspects such as improving the emulsion polymerization rate, reducing the occurrence of side reactions in emulsion polymerization, enhancing the wettability of the water-oil interface, increasing the steric hindrance of the surface hydration layer, enhancing the stability of the dispersion system, enhancing the LCST, and increasing the interfacial adsorption energy, preferably, the HLB value is 14-16.

[0042] The number-average molecular weight of the surfactant described in the present invention is 5000-100000. When the molecular weight is lower than the lower limit, it cannot form a stable unimolecular micelle and cannot meet the structure of the multi-block copolymer. When the molecular weight is higher than the upper limit, the micelle particle size is on the high side, and the mobility of the molecular chain segment decreases, resulting in a reduction in surface performance.

[0043] As a preferred embodiment, the lowest critical solution temperature LCST value of the surfactant described in the present invention > 100 °C, and the surfactant desolvation process can be carried out under normal pressure.

[0044] The addition amount of the surfactant described in the present invention only needs to meet the requirements of the polymerization reaction. Preferably, the addition amount of the surfactant is 0.001-5 wt% of the generated amount of the fluoropolymer, preferably 0.01-0.1 wt%. Increasing the amount of the surfactant used can reduce the emulsion particle size. When the addition amount of the surfactant is 0.3-3 wt% of the generated amount of the fluoropolymer, the emulsion particle size can be less than 100 nm. However, too much addition amount leads to a long induction period, slow polymerization rate, and high polymerization cost. Too little usage amount results in poor emulsion stability and low yield.

[0045] The surfactant described in the present invention easily forms unimolecular micelles in an aqueous medium and has no critical micelle concentration limit. Compared with existing surfactants, the polyethylene glycol chain segment of the surfactant described in the present invention can form a hydration layer with high steric hindrance, enabling the surfactant to form a stable unimolecular micelle structure in water. The content of unimolecular micelles is ≥50%, preferably ≥70%, and more preferably ≥80%. The micelle particle size formed by the surfactant in water is 1 - 90 nm. The emulsion particle size of fluoropolymers generally ranges from 100 to 300 nm. An overly large micelle particle size easily leads to a low adsorption amount of the surfactant on the emulsion surface. Preferably, the micelle particle size formed by the surfactant in water is 5 - 30 nm, and more preferably, the micelle particle size is 7 - 15 nm. The size of the micelle particle size is related to the magnitudes of the x, y, and z values and the molecular weight of the copolymer. When the micelle particle size is too large, the formed micelles are multi-molecular micelles, which is not conducive to the adsorption of the surfactant on the polymer surface. When the micelle particle size is too small, effective micelles are not formed by the polymer.

[0046] The surfactant described in the present invention has a hydrophobic main chain and hydrophilic side chains. The carbon main chain has hydrophobic properties, and the hydrophilic monomers are dispersedly distributed in the hydrophobic main chain in the form of chains. The side chains have hydrophilic properties. This special molecular chain structure enables the surfactant to form a unimolecular micelle structure in water and can also be adsorbed onto the interface of polymer particles to form an amphoteric film-like structure. The conversion between the micelle structure and the film-like structure state can be achieved only by changing some conformations of the copolymer main chain. This enables good mobility while reducing the interfacial energy, increases the mass exchange rate, and promotes the polymerization reaction. In addition, the surfactant of the present invention has the characteristics of excellently reducing the side reactions of emulsion polymerization, enhancing the wettability of the water-oil interface, increasing the steric hindrance of the surface hydration layer, enhancing the stability of the dispersion system, increasing the LCST value, and increasing the interfacial adsorption energy.

[0047] The preparation method of the surfactant described in the present invention includes the step of polymerizing at least one of the compounds shown in formula (2), formula (3), and formula (4) in a solvent,

[0048]

[0049] wherein, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 Same as claim 1.

[0050] The compound shown in formula (2) is a hydrophobic monomer, and R 1 is selected from hydrogen, C1 ~C 18 linear or branched alkyl, C 1 ~C 18 linear or branched alkyl ether group, C 1 ~C 18 linear or branched haloalkyl, C 2 ~C 18 aliphatic hydroxyl, C 2 ~C 18 aliphatic thioether, C 2 ~C 18 aliphatic ester group, C 2 ~C 18 aliphatic cyano; R 2 selected from oxygen, sulfur, imino, C 1 ~C 18 linear or branched or cyclic alkanimino, C 1 ~C 18 arylimino; R 3 selected from phenyl, C 1 ~C 18 linear or branched alkyl, benzyl, 2-phenyl-2-propyl, allyl. Considering aspects such as reducing polymerization side reactions and improving interfacial wettability, preferably, R 1 selected from hydrogen, C 1 ~C 5 linear or branched alkyl, C 1 ~C 5 linear or branched alkyl ether group; R 2 selected from oxygen, imino, C 1 ~C 9 of linear or branched or cyclic alkanimino, C 1 ~C 9 arylimino; R 3 selected from phenyl, C 1 ~C 4 linear or branched alkyl, benzyl, 2-phenyl-2-propyl, allyl. More preferably, R 1 selected from hydrogen, methyl; R 2 selected from oxygen, imino; R 3 selected from phenyl, C 1 ~C 4A straight-chain or single-branched alkyl group. When the surfactant has an active C-H bond, a chain transfer reaction will occur, resulting in the incorporation of the surfactant into the fluoropolymer. Among all C-H bonds, the C-H bonds of primary carbon and phenyl have the lowest chain transfer activity. In existing non-fluorinated surfactants, the C-H content of methyl or phenyl is generally low. For example, PLURONIC 31R1 contains a large amount of tertiary carbon, and the activity of tertiary carbon is relatively high. To further reduce the occurrence of chain transfer side reactions and prevent the surfactant from connecting to the fluoropolymer, which may affect the application performance of the fluoropolymer product, more preferably, R 1 is selected from methyl; R 2 is selected from oxygen; R 3 is selected from methyl, tert-butyl, and phenyl. When R 3 is an alkyl group with 10 or more carbon atoms and 2 or more branched chains, the hydrophobic group volume of the side chain is too large, resulting in insufficient main chain mobility and reducing the surface performance of the product. It has poor performance when used as an emulsifier for emulsion polymerization.

[0051] The hydrophobic monomer represented by the formula (2) satisfies the above conditions. Preferably, it is selected from at least one of methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, phenyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, tert-butyl acrylate, and phenyl acrylate.

[0052] The compound represented by the formula (3) is a non-ionic hydrophilic monomer, and R 4 is selected from hydrogen, C 1 to C 18 straight-chain or branched-chain alkyl group, C 1 to C 18 straight-chain or branched-chain alkyl ether group, C 1 to C 18 straight-chain or branched-chain halogenated alkyl group, C 2 to C 18 aliphatic hydroxyl group, C 2 to C 18 aliphatic thioether, C 2 to C 18 aliphatic ester group, C 2 to C 18 aliphatic cyano group; R 5 is selected from oxygen, sulfur, imino group, C 1 to C 18 straight-chain or branched-chain or cyclic alkylimino group, C 1 to C 18 arylimino group; R 6 is selected from polyethylene glycol derivatives (CH 2 CH 2O) q A, where q is an integer greater than 4 and less than or equal to 100, and A is selected from hydrogen, C 1 ~C 3 linear or branched alkyl groups. For considerations such as reducing polymerization side reactions, enhancing interfacial wettability, increasing the steric hindrance of the surface hydration layer, and improving the stability of the dispersion system, preferably, R 4 is selected from hydrogen, C 1 ~C 5 linear or branched alkyl groups, C 1 ~C 5 linear or branched alkyl ether groups; R 5 is selected from oxygen, imino, C 1 ~C 9 linear or branched or cyclic alkanimino groups, C 1 ~C 9 arylimino groups; R 6 is selected from polyethylene glycol derivatives (CH 2 CH 2 O) q A, where q is an integer greater than 9 and less than or equal to 100, and A is selected from hydrogen, C 1 ~C 3 linear or branched alkyl groups. More preferably, R 4 is selected from hydrogen, methyl; R 5 is selected from oxygen, imino; R 6 is selected from polyethylene glycol derivatives (CH 2 CH 2 O) q A, where q is an integer greater than 9 and less than or equal to 80, and A is selected from hydrogen, C 1 ~C 3 linear or branched alkyl groups. Even more preferably, R 4 is selected from methyl; R 5 is selected from oxygen; R 6 is selected from polyethylene glycol derivatives (CH 2 CH 2 O) q A, where q is an integer greater than 9 and less than or equal to 50, and A is selected from hydrogen, C 1 ~C 3 linear or branched alkyl groups.

[0053] Small molecule fluorosurfactants form thermodynamically stable particles by virtue of their extremely low surface tension. The surfactant described in the present invention can increase the kinetic stability by means of steric hindrance, and the length of the polyethylene glycol chain segment on the side chain of the surfactant is a key factor. When the degree of polymerization (q value) of polyethylene glycol in R 6 is too low, due to the too small steric hindrance of the polyethylene glycol chain segment, the emulsion particle size is large, the stability is poor, and demulsification is likely to occur during the polymerization process. When R 6When the degree of polymerization (q value) of polyethylene glycol is greater than 4, especially greater than 9, polyethylene glycol can form a highly sterically hindered hydration layer, enabling the surfactant to form a stable single-molecule micelle structure in water, obtaining a smaller micelle particle size and better surface activity performance. Preferably, R 6 the degree of polymerization (q value) of polyethylene glycol is greater than 20. R 6 the degree of polymerization (q value) of polyethylene glycol is less than or equal to 100, preferably less than or equal to 80, more preferably less than or equal to 50.

[0054] The non-ionic hydrophilic monomer represented by the formula (3) satisfies the above conditions. Preferably, the molecular weight of the non-ionic hydrophilic monomer is 400 to 2000, and it is selected from at least one of methoxypolyethylene glycol methacrylate, ethoxypolyethylene glycol methacrylate, propoxypolyethylene glycol methacrylate, and polyethylene glycol methacrylate.

[0055] The compound represented by the formula (4) is an ionic hydrophilic monomer, where R 7 is selected from hydrogen, C 1 to C 18 linear or branched alkyl, C 1 to C 18 linear or branched alkyl ether group, C 1 to C 18 linear or branched haloalkyl, C 2 to C 18 aliphatic hydroxyl, C 2 to C 18 aliphatic thioether, C 2 to C 18 aliphatic ester group, C 2 to C 18 aliphatic cyano; R 8 is selected from oxygen, sulfur, imino, C 1 to C 18 linear or branched or cyclic alkylimino, C 1 to C 18 arylimino; R 9 is selected from hydrogen, lithium, sodium, potassium, ammonium, amino-2-methylpropanesulfonic acid, lithium amino-2-methylpropanesulfonate, sodium amino-2-methylpropanesulfonate, potassium amino-2-methylpropanesulfonate, ammonium amino-2-methylpropanesulfonate, ethyltrimethylammonium chloride, ethyltrimethylammonium bromide, ethyltrimethylammonium iodide, ethyltrimethylammonium fluoride, 2-sulfoethyl ester, lithium 2-sulfoethyl ester, sodium 2-sulfoethyl ester, potassium 2-sulfoethyl ester, ammonium 2-sulfoethyl ester, propane-1-sulfonic acid ammonium, propane-1-sulfonic acid lithium, propane-1-sulfonic acid sodium, propane-1-sulfonic acid potassium. Preferably, R 7 is selected from hydrogen, C 1 to C 5 linear or branched alkyl, C1 ~C 5 a straight-chain or branched-chain alkyl ether group, R 8 selected from oxygen, imino, C 1 ~C 9 a straight-chain or branched-chain or cyclic alkylene imino, C 1 ~C 9 an arylene imino, R 9 selected from hydrogen, lithium, sodium, potassium, ammonium, amino-2-methylpropanesulfonic acid, lithium amino-2-methylpropanesulfonate, sodium amino-2-methylpropanesulfonate, potassium amino-2-methylpropanesulfonate, ammonium amino-2-methylpropanesulfonate, ethyltrimethylammonium chloride, 2-sulfoethyl ester, lithium 2-sulfoethyl ester, sodium 2-sulfoethyl ester, potassium 2-sulfoethyl ester, ammonium 2-sulfoethyl ester, ammonium propane-1-sulfonate, lithium propane-1-sulfonate, sodium propane-1-sulfonate, potassium propane-1-sulfonate. More preferably, R 7 selected from hydrogen, methyl, R 8 selected from oxygen, imino, R 9 selected from hydrogen, lithium, sodium, potassium, ammonium, amino-2-methylpropanesulfonic acid, lithium amino-2-methylpropanesulfonate, sodium amino-2-methylpropanesulfonate, potassium amino-2-methylpropanesulfonate, ammonium amino-2-methylpropanesulfonate, ethyltrimethylammonium chloride, 2-sulfoethyl ester, lithium 2-sulfoethyl ester, sodium 2-sulfoethyl ester, potassium 2-sulfoethyl ester, ammonium 2-sulfoethyl ester, ammonium propane-1-sulfonate, lithium propane-1-sulfonate, sodium propane-1-sulfonate, potassium propane-1-sulfonate. Even more preferably, R 7 selected from methyl, R 8 selected from oxygen, R 9 selected from hydrogen, lithium, sodium, potassium, ammonium, amino-2-methylpropanesulfonic acid, lithium amino-2-methylpropanesulfonate, sodium amino-2-methylpropanesulfonate, potassium amino-2-methylpropanesulfonate, ammonium amino-2-methylpropanesulfonate, 2-sulfoethyl ester, lithium 2-sulfoethyl ester, sodium 2-sulfoethyl ester, potassium 2-sulfoethyl ester, ammonium 2-sulfoethyl ester, ammonium propane-1-sulfonate, lithium propane-1-sulfonate, sodium propane-1-sulfonate, potassium propane-1-sulfonate.

[0056] The compound represented by the formula (4) satisfies the above conditions. Preferably, the compound of formula (4) is selected from potassium methacrylate, sodium methacrylate, lithium methacrylate, ammonium methacrylate, 2-(methylamino)ethyl 2-methylpropanesulfonate lithium salt, 2-(methylamino)ethyl 2-methylpropanesulfonate sodium salt, 2-(methylamino)ethyl 2-methylpropanesulfonate potassium salt, 2-(methylamino)ethyl 2-methylpropanesulfonate ammonium salt, ethyl 2-(trimethylammonio)ethyl methacrylate chloride, ethyl 2-(trimethylammonio)ethyl methacrylate bromide, ethyl 2-(trimethylammonio)ethyl methacrylate iodide, ethyl 2-(trimethylammonio)ethyl methacrylate fluoride, 2-(sulfo)ethyl methacrylate lithium salt, 2-(sulfo)ethyl methacrylate sodium salt, 2-(sulfo)ethyl methacrylate potassium salt, 2-(sulfo)ethyl methacrylate ammonium salt, 1-(sulfo)propyl methacrylate ammonium salt, 1-(sulfo)propyl methacrylate lithium salt, 1-(sulfo)propyl methacrylate sodium salt, 1-(sulfo)propyl methacrylate potassium salt, methacrylic acid, 2-(methylamino)propyl methacrylate, 2-(sulfo)ethyl methacrylate, and 1-(sulfo)propyl methacrylate, and at least one of them.

[0057] As an embodiment, the compound represented by the formula (4) is selected from potassium methacrylate, sodium methacrylate, lithium methacrylate, ammonium methacrylate, 2-(methylamino)ethyl 2-methylpropanesulfonate lithium salt, 2-(methylamino)ethyl 2-methylpropanesulfonate sodium salt, 2-(methylamino)ethyl 2-methylpropanesulfonate potassium salt, 2-(methylamino)ethyl 2-methylpropanesulfonate ammonium salt, ethyl 2-(trimethylammonio)ethyl methacrylate chloride, ethyl 2-(trimethylammonio)ethyl methacrylate bromide, ethyl 2-(trimethylammonio)ethyl methacrylate iodide, ethyl 2-(trimethylammonio)ethyl methacrylate fluoride, 2-(sulfo)ethyl methacrylate lithium salt, 2-(sulfo)ethyl methacrylate sodium salt, 2-(sulfo)ethyl methacrylate potassium salt, 2-(sulfo)ethyl methacrylate ammonium salt, 1-(sulfo)propyl methacrylate ammonium salt, 1-(sulfo)propyl methacrylate lithium salt, 1-(sulfo)propyl methacrylate sodium salt, and 1-(sulfo)propyl methacrylate potassium salt, and at least one of them. After desolvation under normal pressure, an aqueous solution of the surfactant is obtained.

[0058] As another embodiment, the compound represented by the formula (4) is selected from methacrylic acid, 2-(methylamino)propyl methacrylate, 2-(sulfo)ethyl methacrylate, and 1-(sulfo)propyl methacrylate, and at least one of them. After the polymerization is completed, an alkali or an alkaline aqueous solution is added to neutralize to a pH of 6-8, and then desolvation is carried out under normal pressure to obtain an aqueous solution of the surfactant.

[0059] The alkali described in the present invention includes, but is not limited to, sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia water, etc.

[0060] The halogenation described above in the present invention can be either fully halogenated or partially halogenated. Halogenation means being substituted by fluorine, chlorine, bromine, or iodine. For example, monofluoromethane is one hydrogen in methane being substituted by fluorine.

[0061] The CAS numbers of the above-mentioned compounds are as follows:

[0062] The CAS number of lithium 3-(acrylamido)-2-methylpropanesulfonate is 86475-33-4,

[0063] The CAS number of sodium 3-(acrylamido)-2-methylpropanesulfonate is 52825-47-5,

[0064] The CAS number of potassium 3-(acrylamido)-2-methylpropanesulfonate is 86475-32-3,

[0065] The CAS number of ammonium 3-(acrylamido)-2-methylpropanesulfonate is 86475-31-2,

[0066] The CAS number of ethyl 2-(trimethylammonio)ethyl methacrylate chloride is 5039-78-1,

[0067] The CAS number of ethyl 2-(trimethylammonio)ethyl methacrylate bromide is 56727-55-0,

[0068] The CAS number of ethyl 2-(trimethylammonio)ethyl methacrylate iodide is 52254-04-3,

[0069] The CAS number of ethyl 2-(trimethylammonio)ethyl methacrylate fluoride is 104583-98-4,

[0070] The CAS number of lithium 2-sulfoethyl methacrylate is 93890-81-4,

[0071] The CAS number of sodium 2-sulfoethyl methacrylate is 1804-87-1,

[0072] The CAS number of potassium 2-sulfoethyl methacrylate is 40074-61-1,

[0073] The CAS number of ammonium 2-sulfoethyl methacrylate is 52556-35-1,

[0074] The CAS number of ammonium 3-(acrylamido)-1-methylpropanesulfonate is 35061-69-9,

[0075] The CAS number of lithium 3-(acrylamido)-1-methylpropanesulfonate is 29364-60-1,

[0076] The CAS number of sodium 3-(acrylamido)-1-methylpropanesulfonate is 10548-16-0,

[0077] The CAS number of potassium 3-(acrylamido)-1-methylpropanesulfonate is 31098-21-2.

[0078] The non-ionic hydrophilic monomer represented by the formula (3) exhibits hydrophobicity in water at temperatures above 80°C, resulting in the insolubility of the surfactant in water, which greatly limits the applicable range of the surfactant in purification processes and operating conditions. To make up for this shortcoming, an ionic group is introduced through the compound represented by the formula (4) to raise the LCST value of the surfactant to above 100°C, enabling the surfactant desolvation process to be carried out at atmospheric pressure.

[0079] The surfactant of the present invention is a random copolymer, and the reactivity ratios of the compound represented by the formula (2), the compound represented by the formula (3), and the compound represented by the formula (4) are 0.5 to 2.5. This enables the structural units of the formula (2), the formula (3), and the formula (4) to be dispersedly distributed on the main chain of the surfactant, resulting in better surface activity performance.

[0080] From the perspective of the surfactant molecular structure, the surfactant of the present invention is a multi-block copolymer with a block number greater than 5 of the structural units of the compound represented by the formula (2), the structural units of the compound represented by the formula (3), and the structural units of the compound represented by the formula (4), and the block length of a single block is 1 to 10. This enables the structural units of the compound represented by the formula (2), the structural units of the compound represented by the formula (3), and the structural units of the compound represented by the formula (4) to be dispersedly distributed on the main chain of the surfactant, resulting in better surface activity performance.

[0081] The solvent for preparing the surfactant of the present invention contains an initiator, and there is no special limitation on the initiator as long as it can achieve monomer polymerization. Preferably, the initiator is selected from at least one of peroxides and azo compounds. The peroxides may include persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate, or may also include organic peroxides such as alkyl, dialkyl, or diacyl peroxides such as di-tert-butyl peroxide or benzoyl peroxide, peresters such as tert-amyl peroxytrimethylacetate, succinic acid peroxide, or tert-butyl peroxytrimethylacetate, or peroxydicarbonates such as di-n-propyl peroxydicarbonate or di-isopropyl peroxydicarbonate. The azo compounds may be selected from dimethyl 2,2'-azobis(2-methylpropionate), azobisisobutyronitrile, and 2,2'-azobis(2,4-dimethyl-4-methoxypentanenitrile).

[0082] There is no special limitation on the solvent for preparing the surfactant of the present invention as long as it can dissolve the polymerization monomers to achieve monomer polymerization. Preferably, the solvent is selected from at least one of small-molecule alcohol compounds, small-molecule ester compounds, and small-molecule ether compounds.

[0083] The small-molecule alcohol compounds are selected from C 1 ~C 10 alcohol compounds such as isopropyl alcohol and tert-butyl alcohol.

[0084] The small-molecule ester compounds are selected from C1 ~C 10 ester compounds such as ethyl acetate, diethyl carbonate, etc.

[0085] The small molecule ether compounds are selected from C 1 ~C 10 ether compounds such as diethyl ether.

[0086] As an implementation method, the solvent is selected from at least one of methanol, ethanol, n-propanol, isopropanol, tert-butanol, ethyl acetate, dimethyl carbonate, tetrahydrofuran, ethylene glycol dimethyl ether and 1,3-dioxolane. The prepared surfactant is used directly without separation from the solvent. When used directly, the solvent therein can play a role in adjusting the molecular weight of the polymer, that is, the role of a chain transfer agent.

[0087] In the preparation method of the surfactant, the temperature of the polymerization reaction is 50-100 °C, and the reaction time is 5-25 h.

[0088] The present invention also provides an application of the fluoropolymer emulsion. The fluoropolymer emulsion is used as a component in coatings, adhesives, rubbers, 3D printing materials, diaphragm coatings, water treatment membranes, composite material additives, microgels, and electronic product structural adhesives.

[0089] The test method for the LCST value in the present invention is as follows: Add an aqueous solution of 10 wt% surfactant into a sealed cuvette, use a spectrophotometer to measure the transmittance at 550 nm, and calibrate the transmittance of the solution at room temperature to 100% transmittance. Raise the temperature of the solution from room temperature to 100 °C at intervals of 2 °C, and record the transmittance corresponding to the temperature. Define the temperature corresponding to the intermediate value of the transmittance gradient change as the LCST value. If the transmittance is 100% uniformly, record the LCST value > 100 °C.

[0090] The definition of the HLB value in the present invention is

[0091]

[0092] The definitions of x, y, and z are as detailed above and will not be elaborated here.

[0093] Compared with the prior art, the beneficial effects of the present invention are:

[0094] 1) The fluoropolymer emulsion with a particle size of 60-100 nm in the present invention simultaneously realizes that the number average molecular weight of the fluoropolymer is greater than 170,000;

[0095] 2) The surfactant provided by the present invention replaces the PFOA-based fluorosurfactant, solving the environmental pollution pressure caused by the PFOA-based fluorosurfactant;

[0096] 3) The present invention uses ionic copolymerizable monomers to introduce trace polar groups to stabilize emulsion particles. Description of the Drawings

[0097] Figure 1 SEM image of the fluoropolymer emulsion prepared in Example 1.

[0098] Figure 2 SEM image of the fluoropolymer emulsion prepared in Example 2.

[0099] Figure 3 SEM image of the fluoropolymer emulsion prepared in Comparative Example 1. Detailed Embodiments

[0100] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternative, improved, and equivalent solutions that may be included within the scope of the claims.

[0101] In the present invention, Mn refers to the number-average molecular weight of the polymer; PDI refers to the polymer dispersity index, which describes the molecular weight distribution of the polymer.

[0102] PLURONIC 31R1: A bifunctional block copolymer surfactant with terminal secondary hydroxyl groups, a nonionic surfactant, non-toxic, from BASF.

[0103] R h R is the hydrodynamic radius. The micelle particle size (hydrodynamic radius) of the surfactant described in the present invention in an aqueous medium is similar to that in isopropanol, indicating that the vast majority of the micelles formed by the surfactant in the aqueous medium are single-molecule micelles; when the difference is large, it indicates that there is folding in the aqueous medium of the surfactant and the content of single-molecule micelles is relatively low. The hydrodynamic radius is measured using a HORIBA / SZ-100Z2 instrument.

[0104] Preparation of Surfactant A1

[0105] Add tert-butyl methacrylate (4.5 g), methoxypolyethylene glycol methacrylate (degree of polymerization 20, molecular weight about 950, 4.5 g), methacrylic acid (1.0 g), and ethyl acetate (5.0 g) into a three-necked flask that has been replaced with vacuum nitrogen, keep stirring and heat to 90 °C. After the temperature is constant, add dimethyl 2,2'-azobis(2-methylpropionate) (0.60 g), and continue heating and stirring for 8 h until the monomers and initiator are completely converted (conversion rate is greater than 99%). Add pure water (85 g) and sodium hydroxide (0.5 g) and keep stirring until completely dissolved. After heating and distilling the blended solvent until the solution boiling point is 100 °C, dilute the solution mass with water to 100 g again to obtain an aqueous solution containing surfactant. The surfactant has Mn = 55000, PDI = 2.00, the micelle particle size formed in water is 13.0 nm, and the hydrodynamic radius R in isopropanol h is 14.0 nm.

[0106] Preparation of Surfactant A2

[0107] Add tert-butyl methacrylate (4.5 g), methoxypolyethylene glycol methacrylate (degree of polymerization 9, molecular weight about 950, 4.5 g), methacrylic acid (1.0 g), and ethyl acetate (5.0 g) into a three-necked flask that has been replaced with vacuum nitrogen, keep stirring and heat to 90 °C. After the temperature is constant, add dimethyl 2,2'-azobis(2-methylpropionate) (0.60 g), and continue heating and stirring for 8 h until the monomers and initiator are completely converted (conversion rate is greater than 99%). Add pure water (85 g) and sodium hydroxide (0.5 g) and keep stirring until completely dissolved. After heating and distilling the blended solvent until the solution boiling point is 100 °C, dilute the solution mass with water to 100 g again to obtain an aqueous solution containing surfactant. The surfactant has Mn = 48200, PDI = 1.96, the micelle particle size formed in water is 10.1 nm, and the hydrodynamic radius R in isopropanol h is 12.8 nm.

[0108] The performance data of surfactants A1 - A2 are shown in Table 1.

[0109] Table 1 Performance Data of Surfactants A1 - A2

[0110]

[0111] Preparation of Fluorine-Containing Polymer

[0112] Example 1 - Preparation of Small-Particle-Size PVDF Using Surfactant A1

[0113] Add pure water (1800 g) into a 3.4 L polymerization kettle. After closing the kettle, continuously evacuate the air with an oil-sealed vacuum pump for 5 minutes, and then backfill with high-purity nitrogen to 0.15 MPa. Repeat this operation three times. After the last evacuation, add vinylidene fluoride (150 g) with a high-pressure gas cylinder, add the surfactant prepared in Example 1 (100 g, surfactant content 0.2 wt%, isopropanol content 0.2 wt%) with a plunger pump, and start stirring (700 rpm) to heat the mixture to 100 °C. After the temperature is stable for 5 minutes, add vinylidene fluoride (30 g) with a high-pressure gas cylinder to 4.50 MPa, and add 100 g of a mixed solution of ammonium persulfate (1 wt%) and sodium acrylate (1 wt%) with a plunger pump to initiate the polymerization reaction. During the polymerization reaction, maintain the temperature in the kettle at (100 ± 0.5 °C), and continuously add a mixed solution of ammonium persulfate (1 wt%) and sodium acrylate (1.5 wt%) to keep the monomer consumption rate greater than 3 g / min, and add vinylidene fluoride to maintain the pressure at (4.25 ± 0.25 MPa) until the total monomer feeding target (800 g) is reached. At this time, the consumption of sodium acrylate is 5.4 g. Stop stirring and open the pressure relief valve. After the pressure drops to atmospheric pressure, collect the emulsion (2905 g, solid content 29.8 wt%). The total content of demulsifying materials is 0.00 wt% calculated based on the mass of the polymer. The obtained polyvinylidene fluoride is observed by SEM, and the average particle size of the emulsion is 65.4 nm, its molecular weight is Mn = 472400, and PDI = 2.07.

[0114] Example 2 - Preparation of PVDF with small particle size using surfactant A1

[0115] Add pure water (1800 g) to a 3.4 L polymerization kettle. After closing the kettle, continuously evacuate with an oil-sealed vacuum pump for 5 minutes, and then backfill with high-purity nitrogen to 0.15 MPa. This operation is repeated three times. After the last evacuation, add vinylidene fluoride (150 g) with a high-pressure gas cylinder, add the surfactant prepared in Example 1 (100 g, surfactant content 0.2 wt%, isopropanol content 0.2 wt%) with a plunger pump, and start stirring (700 rpm) to heat the mixture to 100 °C. After the temperature stabilizes for 5 minutes, add vinylidene fluoride (30 g) with a high-pressure gas cylinder to 4.50 MPa, and add a mixed solution of 100 g of ammonium persulfate (1 wt%) and sodium trifluoromethacrylate (1 wt%) with a plunger pump to initiate the polymerization reaction. During the polymerization reaction, maintain the temperature in the kettle at (100 ± 0.5 °C), and continuously add a mixed solution of ammonium persulfate (1 wt%) and sodium trifluoromethacrylate (1.5 wt%) to keep the monomer consumption rate greater than 3 g / min, and add vinylidene fluoride to maintain the pressure at (4.25 ± 0.25 MPa) until the monomer reaches the total feeding target (600 g). At this time, the consumption of sodium trifluoromethacrylate is 2.0 g. Stop stirring and open the pressure relief valve. After the pressure drops to atmospheric pressure, collect the emulsion (2488 g, solid content 21.3 wt%). The total content of demulsifying materials is 0.00 wt% calculated based on the polymer mass. The obtained polyvinylidene fluoride is observed by SEM, and the average particle size of the emulsion is 80.6 nm, its molecular weight is Mn = 461800, and PDI = 2.27.

[0116] Comparative Example 1

[0117] Add pure water (1800 g) to a 3.4 L polymerization kettle. After closing the kettle, continuously evacuate with an oil-sealed vacuum pump for 5 minutes, and then backfill with high-purity nitrogen to 0.15 MPa. This operation is repeated three times. After the last evacuation, add vinylidene fluoride (150 g) with a high-pressure gas cylinder, add the surfactant solution prepared in Example 1 (100 g, surfactant content 0.2 wt%, isopropanol content 0.2 wt%) with a plunger pump, and start stirring (700 rpm) to heat the mixture to 80 °C. After the temperature stabilizes for 5 minutes, add vinylidene fluoride (50 g) with a high-pressure gas cylinder to a pressure of 4.50 MPa, and add an ammonium persulfate solution (100 g, 0.8 wt%) with a plunger pump to initiate the polymerization reaction. During the polymerization reaction, maintain the temperature in the kettle at (80 ± 0.5 °C), and add vinylidene fluoride to maintain the pressure at (4.25 ± 0.25 MPa) until vinylidene fluoride reaches the total feeding target (600 g). Stop stirring and open the pressure relief valve. After the pressure drops to atmospheric pressure, collect the emulsion (2404 g, solid content 21.3 wt%). The total content of demulsifying materials is 0.04 wt% calculated based on the polymer mass. The obtained polyvinylidene fluoride is observed by SEM, and the average particle size of the emulsion is 175.0 nm, its molecular weight is Mn = 783800, and PDI = 2.14.

[0118] Comparative Example 2

[0119] Add pure water (1400 g) into a 3.4 L polymerization kettle. After closing the kettle, continuously evacuate the air with an oil-sealed vacuum pump for 5 minutes, and then backfill with high-purity nitrogen to 0.15 MPa. This operation is repeated three times. After the last evacuation, add vinylidene fluoride (180 g) with a high-pressure gas cylinder, add a surfactant solution (150 g, containing 1.8 wt% PLURONIC 31R1 and 0.64 wt% sodium acrylate) with a piston pump, and start stirring (700 rpm) to heat the mixture to 80 °C. After the temperature is stable for 5 minutes, add vinylidene fluoride (100 g) with a high-pressure gas cylinder until the pressure reaches 4.50 MPa, and add an ammonium persulfate solution (50 g, 2 wt%) with a piston pump to initiate the polymerization reaction. During the polymerization reaction, maintain the temperature in the kettle at (80 ± 0.5 °C), and add vinylidene fluoride to maintain the pressure at (4.25 ± 0.25 MPa) until the total feeding target of vinylidene fluoride reaches 600 g. Stop stirring and open the pressure relief valve. After the pressure drops to atmospheric pressure, collect the emulsion (2018 g, solid content 23.35 wt%). The average particle size of the obtained polyvinylidene fluoride (PVDF) emulsion observed by SEM is 143 nm, its molecular weight is Mn = 485000, and PDI = 2.26.

[0120] Perform performance tests on the fluoropolymer emulsions prepared in the examples and comparative examples. The data are shown in Table 2 for details.

[0121] Table 2 Performance data of fluoropolymer emulsions in examples and comparative examples

[0122]

[0123] It can be seen from Table 2 that: In Comparative Example 1, no ionic compound was added. Compared with Example 1, the particle size of the obtained emulsion is significantly larger than that using an ionic compound. In Comparative Example 2, the surfactant PLURONIC 31R1 was used and an ionic compound was added. Even when the amount of the ionic compound used is high, the particle size of the fluoropolymer is greater than 100 nm.

Claims

1. A method for preparing a fluoropolymer emulsion, the preparation method comprising polymerizing monomers in an aqueous medium in the presence of a surfactant to obtain a fluoropolymer emulsion through a polymerization reaction. It is characterized in that: An ionic compound participates in the polymerization reaction, and the shell layer of the fluoropolymer contains structural units of the ionic compound. The surfactant is a multi-block copolymer with more than 5 blocks of hydrophobic monomer structural units, non-ionic hydrophilic monomer structural units, and ionic hydrophilic monomer structural units, and the block length of a single block is 1 to 10. The particle size of the fluoropolymer emulsion is 60 to 100 nm.

2. The method for preparing a fluoropolymer emulsion according to claim 1. It is characterized in that: The content of the structural units of the ionic compound in the fluoropolymer is 0.005 wt% to 2.5 wt%.

3. The method for preparing a fluoropolymer emulsion according to claim 1. It is characterized in that: The ionic compound is selected from at least one of acrylate, trifluoromethyl acrylate, vinyl sulfonate, vinyl phosphate, ionic acrylate, methacrylate, ionic methacrylate, ionic allyl ester, ionic allyl ether, ionic vinyl ether, monoester salt of fumaric acid, itaconate, 10-undecenoate.

4. The method for preparing a fluoropolymer emulsion according to claim 1. It is characterized in that: The mass ratio of the ionic compound to the initiator of the polymerization reaction is 1:0.5 to 1:

2.

5. The method for preparing a fluoropolymer emulsion according to claim 1. It is characterized in that: The fluoropolymer is selected from at least one of polyvinylidene fluoride, polyvinyl fluoride, polytrifluoroethylene, polytrifluorochloroethylene, polytetrafluoroethylene, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluoroethylene-trifluorochloroethylene copolymer, vinylidene fluoride-trifluoroethylene-fluorochloroethylene copolymer, and ethylene-trifluorochloroethylene copolymer.

6. The method for preparing a fluoropolymer emulsion according to claim 1. It is characterized in that: The surfactant is a copolymer represented by formula (1). Among them, R 1 , R 4 , R 7 are each independently selected from hydrogen, C 1 -C 18 linear or branched alkyl, C 1 -C 18 linear or branched alkyl ether group, C 1 -C 18 linear or branched haloalkyl, C 2 -C 18 aliphatic hydroxyl group, C 2 -C 18 aliphatic thioether, C 2 -C 18 aliphatic ester group, C 2 -C 18 aliphatic cyano group; R 2 、R 5 、R 8 are each independently selected from oxygen, sulfur, imino, C 1 to C 18 linear or branched or cyclic alkyleneimino, C 1 to C 18 aryleneimino; R 3 selected from phenyl, C 1 ~C 18 linear or branched alkyl, benzyl, 2-phenyl-2-propyl, allyl; R 6 Selected from polyethylene glycol derivatives (CH 2 CH 2 O) q A, where q is an integer greater than 4 and less than or equal to 100, and A is selected from hydrogen, C 1 ~C 3 linear or branched alkyl; R 9 selected from hydrogen, lithium, sodium, potassium, ammonium, lithium 2-methylaminopropanesulfonate, sodium 2-methylaminopropanesulfonate, potassium 2-methylaminopropanesulfonate, ammonium 2-methylaminopropanesulfonate, ethyltrimethylammonium chloride, ethyltrimethylammonium bromide, ethyltrimethylammonium iodide, ethyltrimethylammonium fluoride, lithium 2-sulfoethyl ester, sodium 2-sulfoethyl ester, potassium 2-sulfoethyl ester, ammonium 2-sulfoethyl ester, ammonium propane-1-sulfonate, lithium propane-1-sulfonate, sodium propane-1-sulfonate, potassium propane-1-sulfonate.

7. The method for preparing a fluoropolymer emulsion according to claim 6. It is characterized in that: R 1 、R 4 、R 7 are each independently selected from hydrogen, C 1 -C 5 linear or branched alkyl, C 1 -C 5 linear or branched alkyl ether group; R 2 、R 5 、R 8 are each independently selected from oxygen, imino, C 1 -C 9 linear or branched or cyclic alkylimino, C 1 -C 9 arylimino; R 3 selected from phenyl, C 1 ~C 4 linear or branched alkyl, benzyl, 2-phenyl-2-propyl, allyl; R 6 Selected from polyethylene glycol derivatives (CH 2 CH 2 O) q A, where q is an integer greater than 9 and less than or equal to 80, and A is selected from hydrogen, C 1 ~C 3 linear or branched alkyl; R 9 selected from lithium, sodium, potassium, ammonium, lithium 2-methylpropanesulfonate, sodium 2-methylpropanesulfonate, potassium 2-methylpropanesulfonate, ammonium 2-methylpropanesulfonate, ethyltrimethylammonium chloride, lithium 2-sulfoethyl ester, sodium 2-sulfoethyl ester, potassium 2-sulfoethyl ester, ammonium 2-sulfoethyl ester, ammonium propane-1-sulfonate, lithium propane-1-sulfonate, sodium propane-1-sulfonate, potassium propane-1-sulfonate.

8. The method for preparing a fluoropolymer emulsion according to claim 7. It is characterized in that: R 1 、R 4 、R 7 are each independently selected from methyl; R 2 、R 5 、R 8 are each independently selected from oxygen; R 3 selected from phenyl, methyl, tert-butyl; R 6 Selected from polyethylene glycol derivatives (CH 2 CH 2 O) q A, where q is an integer greater than 9 and less than or equal to 50, and A is selected from hydrogen, C 1 ~C 3 linear or branched alkyl; R 9 selected from lithium, sodium, potassium, ammonium, lithium 2-methylpropanesulfonate, sodium 2-methylpropanesulfonate, potassium 2-methylpropanesulfonate, ammonium 2-methylpropanesulfonate, lithium 2-ethylsulfonate, sodium 2-ethylsulfonate, potassium 2-ethylsulfonate, ammonium 2-ethylsulfonate, ammonium propane-1-sulfonate, lithium propane-1-sulfonate, sodium propane-1-sulfonate, potassium propane-1-sulfonate.

9. The method for preparing a fluoropolymer emulsion according to claim 6. It is characterized in that: x, y, and z satisfy: x + y + z = 1, x / (y + z) = 1 to 9, and z / y is 0 to 3 and greater than 0.

10. The method for preparing a fluoropolymer emulsion according to claim 6. It is characterized in that: The HLB value of the surfactant is 14 to 20.

11. The method for preparing a fluoropolymer emulsion according to claim 6. It is characterized in that: The number-average molecular weight of the surfactant is 5000 to 100000.

12. The method for preparing a fluoropolymer emulsion according to any one of claims 6 - 11. It is characterized in that: The lowest critical solution temperature (LCST) value of the surfactant is > 100 °C.

13. The method for preparing a fluoropolymer emulsion according to claim 6, wherein: The addition amount of the surfactant is 0.001 - 5 wt% of the amount of fluoropolymer produced.

14. The method for preparing a fluoropolymer emulsion according to claim 13, wherein: The addition amount of the surfactant is 0.01 - 0.1 wt% of the amount of fluoropolymer produced.

15. The method for preparing a fluoropolymer emulsion according to claim 6, wherein: The method for preparing the surfactant includes a step of polymerizing at least one compound represented by formula (2), formula (3), and formula (4) in a solvent. Among them, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 are the same as Claim 6.

16. The method for preparing a fluoropolymer emulsion according to claim 15, wherein: The compound represented by formula (2) is selected from at least one of methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, phenyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, tert-butyl acrylate, and phenyl acrylate. The molecular weight of the compound represented by formula (3) is 400 - 2000, and it is selected from at least one of methoxypolyethylene glycol methacrylate, ethoxypolyethylene glycol methacrylate, propoxypolyethylene glycol methacrylate, and polyethylene glycol methacrylate. The compound represented by formula (4) is selected from at least one of potassium methacrylate, sodium methacrylate, lithium methacrylate, ammonium methacrylate, lithium 2-(methacryloylamino)propylsulfonate, sodium 2-(methacryloylamino)propylsulfonate, potassium 2-(methacryloylamino)propylsulfonate, ammonium 2-(methacryloylamino)propylsulfonate, ethyl trimethylammonium methacrylate chloride, ethyl trimethylammonium methacrylate bromide, ethyl trimethylammonium methacrylate iodide, ethyl trimethylammonium methacrylate fluoride, lithium 2-sulfoethyl methacrylate, sodium 2-sulfoethyl methacrylate, potassium 2-sulfoethyl methacrylate, ammonium 2-sulfoethyl methacrylate, ammonium 1-sulfopropyl methacrylate, lithium 1-sulfopropyl methacrylate, sodium 1-sulfopropyl methacrylate, potassium 1-sulfopropyl methacrylate, methacrylic acid, 2-(methacryloylamino)propylsulfonic acid, 2-sulfoethyl methacrylate, and 1-sulfopropyl methacrylate.

17. The method for preparing a fluoropolymer emulsion according to claim 15, wherein: The reactivity ratios of the compounds represented by formula (2), formula (3), and formula (4) are 0.5 - 2.

5.

18. The application of the fluoropolymer emulsion according to any one of claims 1 - 17, wherein: The fluoropolymer emulsion is used as a component in coatings, adhesives, rubbers, 3D printing materials, diaphragm coatings, water treatment membranes, composite material additives, microgels, and structural adhesives for electronic products.

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