Fabrication of fluoropolymer latex with dual surfactants

Abstract

A process for preparing a fluoropolymer is disclosed, the process comprising reacting a fluoromonomer in the presence of at least one acrylic-diol surfactant and at least one sulfur-containing surfactant or a mixture thereof. A polymer prepared by the method is also disclosed. Also disclosed is a polymer composition comprising at least one sulfur-containing surfactant and at least one acrylic-diol surfactant and at least one fluoropolymer.

Description

Technical Field

[0001] The present invention describes a fluoropolymer latex and a method for preparing the fluoropolymer latex. The particle size of the fluoropolymer is controlled by the method. Background of the Invention

[0003] Emulsion processes for preparing fluoropolymers typically utilize surfactants to stabilize the fluoropolymer latex during polymerization. See, for example, U.S. Patents 7,122,610, 8,080,621, 8,124,699, 8,697,822, and 9,068,071. However, none of these discloses that particle size can be controlled based on the weight ratio of the surfactants by utilizing a dual surfactant system during emulsion polymerization.

[0004] The prior art does not disclose a method for controlling the average particle size of fluoropolymer latex using a dual surfactant system in emulsion polymerization. No teaching has been found to control the particle size of fluoropolymer using two types of surfactants as used in the present invention in emulsion polymerization of fluoropolymer.

[0005] This work presents the first method for controlling the particle size of fluoropolymer latexes in PVDF latexes during the polymerization process. The applicants discovered that by varying the weight ratio of two surfactants (sulfur-containing surfactant and acrylic acid-diol surfactant) during the emulsion polymerization process, the particle size of the fluoropolymer in the latex can be adjusted. The fluoropolymer particle size in the latex exhibits a linear correlation with the surfactant ratio used in the emulsion polymerization. This correlation can be used to determine the target particle size in PVDF latex preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 A linear relationship between surfactant ratio and fluoropolymer particle size in the latex is shown. Summary of the Invention

[0007] The present invention describes a fluoropolymer latex and a method for preparing the fluoropolymer latex using at least two surfactants during an emulsion polymerization process. The use of two surfactants during the emulsion polymerization process allows for control of the average particle size of the fluoropolymer in the resulting latex. The fluoropolymer latex is prepared by emulsion polymerization using one or more fluoromonomers, two surfactants, and a persulfate initiator. Surprisingly, it has been discovered that the particle size of the fluoropolymer in the latex can be adjusted by varying the weight ratio of the two surfactants.

[0008] The method comprises:

[0009] a) contacting an aqueous mixture comprising a first surfactant, a second surfactant, and a monomer feed comprising one or more fluoromonomers, and optional additives (e.g., chain transfer agents, buffers, etc.) with a free radical initiator;

[0010] b) polymerizing one or more fluoromonomers to form a fluoropolymer latex.

[0011] The first surfactant includes a sulfur-containing surfactant, and the second surfactant includes an alkyl-diol-containing surfactant.

[0012] Embodiments of the present invention:

[0013] Embodiment 1 of the present invention is a method for preparing a fluorine-containing polymer, the method comprising:

[0014] a) providing an aqueous reaction medium, at least one fluorinated monomer, and optionally a chain transfer agent in a reaction vessel;

[0015] i) an acrylic acid-glycol surfactant having at least one segment selected from polyethylene glycol segments, polypropylene glycol segments and / or polytetramethylene glycol segments, and having 2 to 200 repeating units in each segment, and

[0016] ii) a sulfur-containing surfactant, wherein the sulfur-containing surfactant is non-fluorinated and comprises at least one of an alkyl sulfonate, an alkyl sulfate surfactant, or a mixture thereof,

[0017] b) adding at least one free radical initiator to the reaction vessel, and

[0018] c) initiating emulsion polymerization of the fluorinated monomer,

[0019] To provide a fluoropolymer latex,

[0020] The total amount of surfactant in the method is at least 110 ppm based on the total weight of the fluorinated monomers fed to the polymerization reaction.

[0021] Embodiment 2: The method of embodiment 1, wherein the weight ratio of the sulfur-containing surfactant to the acrylic acid-diol-containing surfactant is between 0.1 and 500 (by weight).

[0022] Embodiment 3: The method of embodiment 1, wherein the weight ratio of the sulfur-containing surfactant to the acrylic acid-diol-containing surfactant is between 0.4 and 150 (by weight).

[0023] Embodiment 4: The method of any one of the above embodiments, wherein the amount of sulfur-containing surfactant is from 100 ppm to less than 5000 ppm based on the total fluoromonomer fed to the emulsion polymerization reaction.

[0024] Embodiment 5: The method of any of the above embodiments, wherein the amount of sulfur-containing surfactant is 200 ppm to 3500 ppm based on the total fluoromonomers fed to the emulsion polymerization reaction.

[0025] Embodiment 6: The method of any of the above embodiments, wherein the amount of acrylic acid-diol surfactant is from about 10 ppm to about 1000 ppm based on the total fluoromonomer fed to the emulsion polymerization reaction.

[0026] Embodiment 7: The method of any one of embodiments 1-5, wherein the amount of acrylic acid-diol surfactant is from about 10 ppm to about 600 ppm based on the total fluoromonomer fed to the emulsion polymerization reaction.

[0027] Embodiment 8: The method of any one of Embodiments 1-7, wherein the volume average particle size of the fluoropolymer is in the range of 110 nm to 350 nm.

[0028] Embodiment 9: The method of any one of Embodiments 1-9, wherein the surfactant is present in a total amount of at least 110 ppm and at most 6000 ppm based on the total weight of the fluoromonomers fed to the emulsion polymerization reaction.

[0029] Embodiment 10: The method of any one of embodiments 1-9, wherein the surfactant is present in a total amount of 200 ppm to 5000 ppm based on the total weight of the fluoromonomers fed to the emulsion polymerization reaction.

[0030] Embodiment 11: The method of any one of Embodiments 1-10, wherein the acrylic acid-diol surfactant has 2 to 100 repeating diol units, preferably ethylene glycol or propylene glycol.

[0031] Embodiment 12: A method as described in any of embodiments 1-11, wherein the acrylic acid-glycol-containing surfactant is selected from the following group: polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEGMA), polypropylene glycol acrylate (PPGA), polypropylene glycol methacrylate (PPGMA), polypropylene glycol polyethylene glycol acrylate, polypropylene glycol polyethylene glycol methacrylate and polypropylene glycol dimethacrylate.

[0032] Embodiment 13: The method of any one of Embodiments 1-11, wherein the acrylic acid-diol containing surfactant comprises polypropylene glycol methacrylate (PPGMA).

[0033] Embodiment 14: The method of any one of Embodiments 1-13, wherein the alkyl group on the sulfur-containing surfactant comprises a C6-C18 alkyl group.

[0034] Embodiment 15: A method as described in any of embodiments 1-13, wherein the sulfur-containing surfactant includes a non-fluorinated alkyl sulfonate, and the non-fluorinated alkyl sulfonate is selected from the following group: octyl sulfonate, octyl disulfonate, decyl sulfonate, decyl disulfonate, dodecyl sulfonate, dodecyl disulfonate and combinations thereof.

[0035] Embodiment 16: The method of any one of Embodiments 1-13, wherein the sulfur-containing surfactant comprises at least one of octyl sulfonate, octyl disulfonate, or decyl sulfonate.

[0036] Embodiment 18: A method as described in any of embodiments 1-13, wherein the sulfur-containing surfactant includes at least one of sodium lauryl sulfate, potassium lauryl sulfate, ammonium lauryl sulfate, lithium lauryl sulfate, sodium laureth sulfate, sodium octyl sulfate, potassium octyl sulfate, ammonium octyl sulfate, lithium octyl sulfate, and combinations thereof.

[0037] Embodiment 19: The method of any one of Embodiments 1-10, wherein the acrylic acid-glycol-containing surfactant comprises polypropylene glycol methacrylate (PPGMA) and the sulfur-containing surfactant comprises octyl sulfonate.

[0038] Embodiment 20: The method of any one of Embodiments 1-19, wherein the free radical initiator comprises a persulfate.

[0039] Embodiment 21: The method of any one of Embodiments 1-20, wherein the at least one fluorine-containing monomer is selected from the group consisting of vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and combinations thereof.

[0040] Embodiment 22: The method of any of Embodiments 1-21, wherein at least 65 weight percent of the added fluoromonomer comprises vinylidene fluoride monomer.

[0041] Embodiment 23: The method of any one of Embodiments 1-20, wherein the fluorine-containing monomer consists of vinylidene fluoride monomer.

[0042] Embodiment 24: The method of any one of Embodiments 1-22, wherein the fluoropolymer is a vinylidene fluoride copolymer comprising at least one comonomer selected from the group consisting of tetrafluoroethylene, trifluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, vinyl fluoride, and combinations thereof.

[0043] Embodiment 25: The method as described in Embodiment 21, wherein the fluorine-containing monomer consists of vinylidene fluoride and hexafluoropropylene.

[0044] Embodiment 26: A fluoropolymer composition comprising:

[0045] a) at least one sulfur-containing surfactant and at least one acrylic acid-diol surfactant, and

[0046] b) at least one fluoropolymer.

[0047] Embodiment 27: The fluoropolymer latex composition of Embodiment 26, wherein the acrylic-diol surfactant has 2 to 100 repeating diol units, preferably ethylene glycol or propylene glycol.

[0048] Embodiment 28: A fluoropolymer latex composition as described in embodiment 26, wherein the acrylic acid-glycol-containing surfactant is selected from the group consisting of polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEGMA), polypropylene glycol acrylate (PPGA), polypropylene glycol methacrylate (PPGMA), polypropylene glycol polyethylene glycol acrylate, polypropylene glycol polyethylene glycol methacrylate, and polypropylene glycol dimethacrylate.

[0049] Embodiment 29: The fluoropolymer latex composition of Embodiment 26, wherein the acrylic-glycol containing surfactant comprises polypropylene glycol methacrylate (PPGMA).

[0050] Embodiment 30: The fluoropolymer latex composition of any of Embodiments 26-29, wherein the sulfur-containing surfactant comprises a C6-C18 alkyl group.

[0051] Embodiment 31: A fluoropolymer latex composition as described in any of Embodiments 26-29, wherein the sulfur-containing surfactant comprises a non-fluorinated alkyl sulfonate selected from the group consisting of octyl sulfonate, octyl disulfonate, decyl sulfonate, decyl disulfonate, dodecyl sulfonate, dodecyl disulfonate, and combinations thereof.

[0052] Embodiment 32: The fluoropolymer latex composition of any of Embodiments 26-29, wherein the sulfur-containing surfactant comprises at least one of octyl sulfonate, octyl disulfonate, or decyl sulfonate.

[0053] Embodiment 33: A fluoropolymer latex composition as described in any of embodiments 26-29, wherein the sulfur-containing surfactant includes at least one of sodium lauryl sulfate, potassium lauryl sulfate, ammonium lauryl sulfate, lithium lauryl sulfate, sodium laureth sulfate, sodium octyl sulfate, potassium octyl sulfate, ammonium octyl sulfate, lithium octyl sulfate, and combinations thereof.

[0054] Embodiment 34: The fluoropolymer latex composition of Embodiment 26, wherein the acrylic-glycol surfactant comprises polypropylene glycol methacrylate (PPGMA) and the sulfur-containing surfactant comprises octyl sulfonate.

[0055] Embodiment 35: The fluoropolymer latex composition of any of Embodiments 26-36, wherein the fluoropolymer comprises fluoromonomer units selected from the group consisting of vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and combinations thereof.

[0056] Embodiment 36: The fluoropolymer latex composition of any of Embodiments 26-34, wherein the fluoropolymer is polyvinylidene fluoride comprising at least 65 weight percent vinylidene fluoride.

[0057] Embodiment 37: The fluoropolymer latex composition of any of Embodiments 26-34, wherein the fluoropolymer is a polyvinylidene fluoride homopolymer.

[0058] Embodiment 38: A fluoropolymer latex composition as described in any of Embodiments 26-34, wherein the fluoropolymer is a polyvinylidene fluoride copolymer, which comprises at least 65 weight percent vinylidene fluoride and at least one comonomer selected from the group consisting of tetrafluoroethylene, trifluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, vinyl fluoride, and combinations thereof.

[0059] Embodiment 39: The fluoropolymer latex composition of any of Embodiments 26-34, wherein the fluoropolymer is a polyvinylidene fluoride / hexafluoropropylene copolymer comprising at least 65 weight percent vinylidene fluoride. DETAILED DESCRIPTION

[0060] All references cited in this application are hereby incorporated by reference.

[0061] As used herein, percentages are by weight (wt %) unless otherwise indicated.

[0062] Melt viscosity according to ASTM D3835 at 230°C and 100 seconds- 1 Measured by capillary rheometer.

[0063] Solids refers to the material remaining after the fluoropolymer latex has been dried.Solids of the fluoropolymer latex were measured gravimetrically using an HG63 moisture analyzer from Mettler Toledo.

[0064] The term "fluoropolymer" refers to polymers and copolymers (including polymers having two or more different monomers, including, for example, terpolymers) containing at least 50 mole percent of fluorinated monomer units. These polymers may be homogeneous, heterogeneous, or random, and may have a gradient distribution of comonomer units.

[0065] The term "fluoropolymer latex" refers to an aqueous dispersion of a fluoropolymer obtained by emulsion polymerization of a fluoromonomer.

[0066] "Copolymer" is used to refer to polymers having two or more different monomer units, including terpolymers and higher polymers. "Polymer" can refer to either a homopolymer or a copolymer.

[0067] "PVDF" means vinylidene fluoride, and unless otherwise specified, this includes both homopolymers and copolymers.

[0068] Olefinic refers to monomers having polymerizable carbon-carbon double bonds.

[0069] The present invention provides a method for preparing a fluoropolymer from a fluoromonomer using at least two surfactants in an emulsion polymerization. The fluoropolymer is prepared in an aqueous mixture comprising a fluoromonomer, a surfactant 1 (a sulfur-containing surfactant), a surfactant 2 (an acrylic acid-glycol-containing surfactant), an optional chain transfer agent, an optional buffer, and an initiator. The surfactant is non-fluorinated. Optionally, the polymerization process of the present invention can be carried out in the presence of a chain transfer agent, a buffer (to maintain a desired pH range during polymerization), and an antifouling agent (to reduce or eliminate adhesion of the polymer to the inner surface of the polymerization vessel). The resulting product of the emulsion polymerization is a fluoropolymer latex.

[0070] The applicant surprisingly found that by controlling the weight ratio of the first surfactant to the second surfactant in the emulsion polymerization of the fluorinated monomer, the particle size of the fluorinated polymer in the latex can be controlled. Generally speaking, the particle size of the fluorinated polymer in the latex can be adjusted within the range of 100 nm to 400 nm.

[0071] Polymerization process

[0072] A general emulsion polymerization procedure can be followed: first, deionized water, surfactant 1 and surfactant 2, optional chain transfer agent, optional antifouling agent and / or optional buffer are added to the reactor, followed by deoxygenation (removal of oxygen). Water is usually added to the reactor before the reactor reaches the desired starting temperature, but other materials can be added before or after the reactor reaches the desired temperature. No oil phase, such as chloroform, is used. The reactor can be a pressurized polymerization reactor equipped with an agitator and heat control components. Agitation can be constant or adjusted to optimize process conditions during the polymerization process. After the reactor reaches the desired temperature, a certain amount of monomer and / or comonomer is added to the reactor. The ratio of monomer and comonomer can be selected. At least one free radical initiator is added to start and maintain the polymerization reaction. The initiator solution and optional buffer solution and optional chain transfer agent are fed to the reactor at a suitable flow rate. Additional monomer can optionally be added to replenish the consumed monomer, and other materials can optionally be added during the polymerization process to maintain the reaction and adjust the properties of the final product. The monomer feed can be stopped after the desired total monomer feed is reached. Unreacted monomers can be discharged and the resulting fluoropolymer latex collected through a drain or other collection means. The fluoropolymer latex can be retained in an aqueous medium for subsequent application or use. Alternatively, it can be converted to a dry form.

[0073] The pressure used for polymerization can be selected from a wide range of pressures, from about 280 to about 20,000 kPa, depending on the capacity of the reaction equipment, the selected initiator system, and the monomer composition used. Polymerization pressures are typically from about 2,000 to about 11,000 kPa, most typically from about 2,750 to about 9,000 kPa. The polymerization temperature, depending on the selected initiator system, can range from about 20°C to about 160°C, typically from about 35°C to about 130°C, and most typically from about 65°C to about 100°C.

[0074] Fluoropolymers

[0075] As used herein, the term "fluoropolymer" refers to a polymeric material comprising at least 65 weight percent vinylidene fluoride units, with the remainder being one or more fluorinated monomers. The fluoropolymer may consist essentially of vinylidene fluoride and optionally other fluorinated monomer units, or it may also contain other comonomer units.

[0076] Fluoropolymer can be homopolymer, copolymer, terpolymer or higher polymer (more than three different monomers). Fluoropolymer can be thermoplastic, wherein " thermoplastic " refers to can be formed into shape by applying heat and (usually) pressure (such as in molding and extrusion process). Exemplary polymer prepared by the method of the present invention includes polyvinylidene fluoride homopolymer, copolymer, vinylidene fluoride content is at least 65 weight % and typically at least 75 weight % terpolymer and higher polymer. According to the present invention, specific fluoropolymer includes for example: copolymer of vinylidene fluoride and hexafluoropropylene, tetrafluoroethylene or trifluoroethylene, and terpolymer of vinylidene fluoride and tetrafluoroethylene and hexafluoropropylene or with tetrafluoroethylene and trifluoroethylene. Other copolymers and terpolymers can contain fluorine-containing monomers different from those listed above, combined with vinylidene fluoride.

[0077] Fluoromonomers are used to prepare the fluoropolymers of the present invention. As used herein, the term "fluoromonomer" refers to a fluorinated, ethylenically unsaturated monomer capable of participating in a free radical polymerization reaction. Suitable fluoromonomers for use in accordance with the present invention include at least one fluorine atom and may, for example, contain fluoroalkyl, fluoroalkoxy, or vinyl fluorine atoms.

[0078] In addition to vinylidene fluoride, exemplary fluorine-containing monomers suitable for use in the present invention may be any one or more of the following: vinyl fluoride, trifluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), partially or fully fluorinated α-olefins (e.g., 3,3,3-trifluoro-1-propene, 1,2,3,3,3-pentafluoropropylene, 3,3,3,4,4-pentafluoro-1-butene), partially fluorinated olefin hexafluoroisobutylene, perfluorinated vinyl ethers (e.g., perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoro-n-propyl vinyl ether, and perfluoro-2-propoxypropyl vinyl ether), fluorinated dioxoles (e.g., perfluoro(1,3-dioxole) and perfluoro(2,2-dimethyl-1,3-dioxole)), and partially or fully fluorinated allyl monomers based on, for example, 2-hydroxyethyl allyl ether or 3-allyloxypropylene glycol.

[0079] The fluoropolymer of the present invention may comprise a vinylidene fluoride polymer having at least 65 weight percent VDF monomer units.

[0080] The copolymer may be composed of at least about 65 and up to 99 weight percent vinylidene fluoride, and correspondingly 1 to 35 percent of comonomers such as tetrafluoroethylene, hexafluoropropylene, and trifluoroethylene. The copolymer may be a copolymer of vinylidene fluoride and hexafluoropropylene.

[0081] surfactants

[0082] The present invention utilizes at least two types of surfactants, Surfactant 1 and Surfactant 2.

[0083] The first class of surfactants (surfactant 1) is a type of molecule that has both a hydrophobic portion and a hydrophilic portion, which allows it to be stable in aqueous media and to disperse hydrophobic molecules and aggregates of hydrophobic molecules. Examples of surfactants include alkyl or (alkyl) aryl groups connected to sulfonate groups or sulfate groups. A preferred group of first class surfactants for use in the fluoropolymer latexes of the present invention includes alkyl sulfate and alkyl sulfonate surfactants ("sulfur-containing surfactants"). The term "alkyl sulfate surfactant" or "alkyl sulfonate surfactant" refers to an alkyl group having an alkyl group as its hydrophobic portion, preferably comprising a C6 to C18 alkyl group. The alkyl group of these alkyl sulfate and alkyl sulfonate surfactants is functionalized with one or two sulfate and / or sulfonate groups as its hydrophilic portion. The hydrocarbon group does not contain any fluorine. The hydrocarbon group comprises a C6 to C18 alkyl group. Preferred first class surfactants are in salt form, preferably having an alkali metal (e.g., lithium, sodium, or potassium), an ammonium ion, or an alkyl-substituted ammonium ion as a counterion.

[0084] Examples of alkyl sulfate surfactants include, but are not limited to, C6 to C18 alkyl sulfates. Examples include, but are not limited to, lauryl sulfate and octyl sulfate. Examples include, but are not limited to, sodium lauryl sulfate, potassium lauryl sulfate, ammonium lauryl sulfate, lithium lauryl sulfate, sodium laureth sulfate, sodium octyl sulfate, and mixtures thereof.

[0085] Examples of alkyl sulfonate surfactants include, but are not limited to, C6-C18 alkyl sulfonates, and C6-C18 alkyl disulfonates, and mixtures thereof. Examples of typical counterions of alkyl sulfonate surfactants include, but are not limited to, sodium, potassium, lithium, ammonium, or alkyl-substituted ammonium. For example, C8-C12 alkyl sulfonates can be used, such as octyl sulfonate, octyl disulfonate, decyl sulfonate, decyl disulfonate, dodecyl sulfonate, dodecyl disulfonate, and combinations thereof. For example, octyl sulfonate can be sodium octyl sulfonate, potassium octyl sulfonate, ammonium octyl sulfonate, alkyl-substituted ammonium octyl sulfonate, or lithium octyl sulfonate.

[0086] The second type of surfactant suitable for use in the present invention (Surfactant 2) is a non-fluorinated nonionic acrylic-glycol surfactant (also known as acrylic-glycol surfactant) containing a vinyl double bond, preferably an acrylate or methacrylate group attached to a polyglycol segment, such as polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene glycol (PTMG), or any combination of these polyglycol segments, wherein the repeating glycol unit is preferably 3 to 100 repeating units, more preferably 3 to 50 repeating units.

[0087] Acrylic-glycol surfactants used in the present invention include, but are not limited to, polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEGMA), polypropylene glycol acrylate (PPGA), polypropylene glycol methacrylate (PPGMA), polypropylene glycol polyethylene glycol acrylate, polypropylene glycol polyethylene glycol methacrylate, polyethylene glycol dimethacrylate, and polypropylene glycol dimethacrylate.

[0088] Preferably, the acrylic-diol surfactant comprises polypropylene glycol methacrylate (PPGMA) or polypropylene glycol acrylate (PPGA).

[0089] In the present invention, PPGMA and / or PPGA may be used together with octyl sulfonate to control the particle size.

[0090] The first type of surfactant may be used in an amount of at least 100 ppm, and may be used in an amount of from about 100 ppm to less than 5000 ppm based on the total fluoromonomer fed to the polymerization reaction. Preferably, the first type of surfactant is used in an amount of from about 100 ppm to 4000 ppm based on the total fluoromonomer fed to the polymerization reaction, and more preferably, from 200 ppm to 3500 ppm based on the total fluoromonomer fed to the polymerization reaction. The second type of surfactant may be used in an amount of at least 10 ppm, and may be used in an amount of from about 10 ppm to about 2000 ppm or more based on the total fluoromonomer fed to the polymerization reaction, preferably, from 10 ppm to 1000 ppm based on the total fluoromonomer fed to the polymerization reaction, and more preferably, from 10 ppm to 800 ppm based on the total fluoromonomer fed to the polymerization reaction.

[0091] During the polymerization process, the surfactant of the present invention can be fully pre-added before the polymerization, continuously fed during the polymerization, or partially fed before the polymerization and then fed during the polymerization.

[0092] The ratio of surfactant

[0093] Smaller particle sizes can be achieved by adding more acrylic acid-glycol-containing surfactant (Surfactant 2) and less sulfur-containing surfactant (Surfactant 1) (the lower the weight ratio of surfactant, the smaller the resulting fluoropolymer particle size). The weight ratio of sulfur-containing surfactant (SCS, Surfactant 1) to acrylic acid-glycol-containing surfactant (AGS, Surfactant 2) (by weight) is 0.1 to 500. The present invention can be practiced at a weight ratio between 0.4 and 150.

[0094] It is envisioned that the two surfactants can be fed at different feed rates so that the weight ratio during the polymerization can be varied, thereby obtaining a controllable particle size distribution. Peak values ​​of different average particle sizes can be obtained, thereby providing a multimodal particle size distribution, which can be determined using the weight ratio of the surfactants fed to the polymerization reaction.

[0095] initiator

[0096] The terms "initiator" and the expressions "radical initiator" and "free radical initiator" refer to chemicals that can provide a source of free radicals that can be induced spontaneously or by exposure to heat or light. The free radical initiator can include a persulfate, such as sodium persulfate, potassium persulfate (KPS), lithium persulfate, or ammonium persulfate. The amount of persulfate added to the reaction mixture (based on the total weight of monomers added to the reaction mixture) can be, for example, from about 0.005 to about 1.0 weight percent. The terms "radical" and the expressions "free radical" refer to a chemical substance containing at least one unpaired electron. The free radical initiator is added to the reaction mixture in an amount sufficient to initiate and maintain the polymerization reaction rate. The order of addition can vary depending on the desired process and latex emulsion properties.

[0097] The free radical initiator may comprise a redox system. It will be understood by those skilled in the art that a "redox system" refers to a system comprising an oxidant, a reducing agent, and an optional promoter as an electron transfer mediator. Oxidants include, for example, persulfates, peroxides, and oxidizing metal salts (e.g., ferric sulfate). Reducing agents include, for example, sodium formaldehyde sulfoxylate, sodium sulfite and potassium sulfite, ascorbic acid, bisulfite, pyrosulfite, and reducing metal salts. The promoter is a component of the redox system that can react with both the oxidant and the reducing agent under different oxidation states, thereby accelerating the entire reaction. Promoters include, for example, transition metal salts, such as ferrous sulfate. In a redox system, based on the total monomers added to the polymerization process, the oxidant and reducing agent can be used in an amount of about 0.01 to about 0.5 weight %. Based on the total monomers added to the polymerization process, an optional promoter can be used in an amount of about 0.005 to about 0.025 weight %. Redox systems are described, for example, in GSMisra and UDN Baypai, Prag. Polym. Sci., 1982, 8(1-2), pp. 61-131.

[0098] Chain transfer agent

[0099] A chain transfer agent may be used in the polymerization reaction. The chain transfer agent may be added to the aqueous reaction mixture. The chain transfer agent may be added to the polymerization reaction in a single addition at the start of the reaction, or may be added gradually or continuously throughout the reaction. When used, the amount and manner of addition of the chain transfer agent will depend on the activity of the specific chain transfer agent used and the desired molecular weight of the polymer product. The amount of chain transfer agent added to the polymerization reaction may be up to 5 weight percent, preferably from 0.05 to about 3 weight percent, and more preferably from about 0.1 to about 2 weight percent, based on the total weight of the fluoropolymer added to the reaction mixture. Examples of chain transfer agents useful in the present invention include, but are not limited to, oxygen-containing compounds such as alcohols (preferably having 3 to 10 carbon atoms), carbonates, ketones, esters, and ethers, such as acetone, ethyl acetate, diethyl ether, methyl tert-butyl ether, and isopropanol; di(alkyl) carbonates in which the alkyl group has 1 to 9 carbon atoms (e.g., di(ethyl) carbonate, di(isobutyl) carbonate); ethane, propane, and compounds described in US2018 / 0072829; low molecular weight (less than 20,000 g / mol, preferably less than 10,000 g / mol) polymer chain transfer agents containing one or more different functional groups, including but not limited to polyacrylic acid, polylactic acid, polyphosphonic acid, polysulfonic acid, and polymaleic acid.

[0100] If desired, a paraffin antifoulant may be used, although this is not preferred and any long chain saturated hydrocarbon wax or oil may be used. The amount of paraffin added to the reactor may be from 0.01 wt % to 0.3 wt % based on the weight of the total fluoromonomer added to the polymerization process.

[0101] Buffer:

[0102] The polymerization reaction mixture may optionally contain a buffer to maintain a controlled pH throughout the polymerization reaction. The pH is preferably controlled within the range of about 3 to about 8 to minimize undesirable color development in the product.

[0103] The buffering agent may comprise an organic or inorganic acid or an alkali metal salt thereof, or a base or salt of such an organic or inorganic acid having at least one pK in the range of about 4 to about 10, preferably in the range of about 4.5 to about 9.5. a Value and / or pK b Value. Preferred buffers in the practice of the present invention include, for example, phosphate buffer and acetate buffer. "Phosphate buffer" is one or more salts of phosphoric acid. "Acetate buffer" is a salt of acetic acid, such as sodium acetate trihydrate (SAT).

[0104] product

[0105] Fluoropolymer latexes produced by emulsion polymerization typically contain from 10 to 60 weight percent solids, preferably from 20 to 50 weight percent.

[0106] The product of emulsion polymerization is fluoropolymer latex, which can be used in this form, optionally after filtering the solid by-products (e.g., coagulated polymer) of the polymerization process. When used in latex form, the fluoropolymer latex can optionally be stabilized by adding additional surfactants, ionic surfactants, or nonionic surfactants, which can be the same or different from the surfactants used in the emulsion polymerization. Alternatively, the fluoropolymer latex can be coagulated to separate the solid fluoropolymer, then washed and dried. Coagulation methods are well known in the art.

[0107] use

[0108] These fluoropolymer latexes can be used as components of battery separator coatings to improve adhesion properties.

[0109] The polymers of the present invention are useful as components in architectural coatings, water purification membranes, or high purity piping for water supply to the semiconductor industry.

[0110] Example

[0111] The synthesis procedures and characterization of the fluoropolymer latexes are summarized below.

[0112] Light scattering test method for latex particle size: The particle size of latex particles was measured using a Nicomp CW380 particle size analyzer (light scattering), and the volume average particle size was used.

[0113] Examples 1-2. Preparation of Fluoropolymer Latex in a 2 Gallon Reactor

[0114] 4400g of deionized water, PPGA, poly(propylene glycol) acrylate, Mn=475, n=7 (available from Arkema Co., Ltd.) and / or SOS (sodium octyl sulfonate) were added to a 2-gallon autoclave. The autoclave was stirred at 72rpm, heated to 83°C, and pressurized to 4475kPa with vinylidene fluoride. An aqueous solution of 1.0 wt% KPS / 1.0 wt% SAT was started at 240g / h. As the pressure began to drop, the feed rate of KPS / SAT was adjusted to maintain the pressure and the feed rate of VDF at about 500g / h (within the range of 5-20g / h). The pressure was maintained by additional VDF feeding. When the VDF feed amount reached 900g, 23g of ethyl acetate solution (8 wt% aqueous solution) was fed at 1500ml / h. After the ethyl acetate solution feed was complete, the KPS / SAT rates were adjusted to maintain pressure and the VDF feed rate was maintained at approximately 500 g / h. Feeding continued in this manner until a total of 1900 g of VDF had been fed into the reactor. The reaction temperature was maintained at 83°C for an additional 30 minutes. The pressure was then allowed to decrease spontaneously over 10 minutes, at which point the reactor was vented to atmospheric pressure and cooled to room temperature. The product was then discharged from the reactor.

[0115] Table 1

[0116]

[0117] Example 3. Preparation of Fluoropolymer Latex in an 80 Gallon Reactor

[0118] An 80-gallon autoclave was charged with 166 kg of deionized water, 135.0 g of SOS, and 4.0 g of PPGMA. The autoclave was stirred at 21 rpm, heated to 83°C, and pressurized to 44,750 kPa with 3.2 kg of HFP and 15.5 kg of vinylidene fluoride. A 2.0 wt% KPS / 2.0 wt% SAT aqueous solution was fed at 4.5 kg / h. When the pressure began to drop, the KPS / SAT feed rate was reduced to 136 g / h, and the pressure was maintained by feeding additional VDF. When the total amount of VDF reached 36.4 kg, a 10.0 wt% PAA solution was fed at 3.9 kg / h. The KPS / SAT feed rate was then increased to 1.8 kg / h. Feeds were continued in this manner until a total of 72.7 kg of VDF had been fed to the reactor. The reaction temperature was maintained at 90°C for an additional 30 minutes. The pressure was then allowed to decrease spontaneously for 10 minutes, at which time the reactor was vented to atmospheric pressure and cooled to room temperature.The product was discharged from the reactor.

[0119] Examples 4-6 were prepared in the same manner as Example 3, except that the amounts of SOS and PPGMA listed in Table 2 were used. The amount of surfactant added (in ppm) was based on the total fluoromonomer added to the polymerization reaction. Figure 1 is a graph of Table 2, where the surfactant ratio is the SCS / AGS ratio.

[0120] Table 2. Latex particle size data in 80 gallon reactor

[0121]

[0122] These examples show that by varying the weight ratio of the two surfactants, the particle size of the resulting polymer can be controlled. Reducing the amount of acrylic acid-diol surfactant results in an increase in particle size.

Claims

1. A method for preparing a fluoropolymer, the method comprising: a) providing an aqueous reaction medium, at least one fluoromonomer, and optionally a chain transfer agent in a reaction vessel, i) at least one acrylic-glycol surfactant having at least one segment selected from polyethylene glycol segments, polypropylene glycol segments and / or polytetramethylene glycol segments, and having 2 to 200 repeating units in each segment, and ii) at least one sulfur-containing surfactant, wherein the sulfur-containing surfactant is non-fluorinated and comprises at least one of an alkyl sulfonate, an alkyl sulfate surfactant, or a mixture thereof, and b) adding at least one free radical initiator to the reaction vessel, c) initiating emulsion polymerization of the fluorinated monomer; To provide a fluoropolymer latex, The total amount of surfactant in the method is at least 110 ppm based on the total weight of the fluorinated monomers fed to the polymerization reaction.

2. The method of claim 1, wherein the weight ratio of the sulfur-containing surfactant to the acrylic acid-diol-containing surfactant is between 0.1 and 500 (by weight).

3. The method of claim 1, wherein the weight ratio of the sulfur-containing surfactant to the acrylic acid-diol-containing surfactant is between 0.4 and 150 (by weight).

4. The method of claim 1, wherein the amount of the sulfur-containing surfactant is from 100 ppm to less than 5000 ppm based on the total fluorinated monomers fed to the emulsion polymerization reaction.

5. The method of claim 1, wherein the amount of the sulfur-containing surfactant is 200 ppm to 3500 ppm based on the total fluorinated monomers fed to the emulsion polymerization reaction.

6. The method of claim 1, wherein the amount of acrylic acid-diol surfactant in the method is from about 10 ppm to about 1000 ppm based on the total fluoromonomer fed to the emulsion polymerization reaction.

7. The method of claim 1, wherein the amount of acrylic acid-diol surfactant in the method is from about 10 ppm to about 600 ppm based on the total fluoromonomer fed to the emulsion polymerization reaction.

8. The method of claim 1, wherein the volume average particle size of the fluoropolymer is in the range of 110 nm to 350 nm.

9. The process of claim 1 wherein the surfactant is present in a total amount of at least 110 ppm and at most 6000 ppm based on the total weight of the fluoromonomers fed to the emulsion polymerization reaction.

10. The process of claim 1 wherein the total amount of surfactant present in the process is between 200 ppm and 5000 ppm based on the total weight of fluoromonomer fed to the emulsion polymerization reaction.

11. The method of claim 1, wherein the acrylic-diol surfactant has 2 to 100 repeating glycol units, preferably ethylene glycol or propylene glycol.

12. The method of claim 1, wherein the acrylic acid-glycol containing surfactant is selected from the group consisting of polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEGMA), polypropylene glycol acrylate (PPGA), polypropylene glycol methacrylate (PPGMA), polypropylene glycol polyethylene glycol acrylate, polypropylene glycol polyethylene glycol methacrylate, and polypropylene glycol dimethacrylate.

13. The method of claim 1, wherein the acrylic-glycol containing surfactant comprises polypropylene glycol methacrylate (PPGMA).

14. The method of claim 1, wherein the alkyl groups on the sulfur-containing surfactant comprise C6-C18 alkyl groups.

15. The method of claim 1, wherein the sulfur-containing surfactant comprises a non-fluorinated alkyl sulfonate selected from the group consisting of octyl sulfonate, octyl disulfonate, decyl sulfonate, decyl disulfonate, dodecyl sulfonate, dodecyl disulfonate, and combinations thereof.

16. The method of claim 1, wherein the sulfur-containing surfactant comprises at least one of octyl sulfonate, octyl disulfonate, or decyl sulfonate.

17. The method of claim 1, wherein the sulfur-containing surfactant comprises at least one of sodium lauryl sulfate, potassium lauryl sulfate, ammonium lauryl sulfate, lithium lauryl sulfate, sodium laureth sulfate, sodium octyl sulfate, potassium octyl sulfate, ammonium octyl sulfate, lithium octyl sulfate, and combinations thereof.

18. The method of claim 1, wherein the acrylic acid-glycol surfactant comprises polypropylene glycol methacrylate (PPGMA) and the sulfur-containing surfactant comprises octyl sulfonate.

19. The method of claim 1, wherein the free radical initiator comprises a persulfate.

20. The method of claim 1, wherein the at least one fluorine-containing monomer is selected from the group consisting of vinylidene fluoride, hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, chlorotrifluoroethylene, vinyl fluoride, and combinations thereof.

21. The method of claim 1, wherein at least 65 weight percent of the added fluoromonomer comprises vinylidene fluoride monomer.

22. The method of claim 1, wherein the fluorine-containing monomer consists of vinylidene fluoride monomer.

23. The method of claim 1, wherein the fluoropolymer is a vinylidene fluoride copolymer comprising at least one comonomer selected from the group consisting of tetrafluoroethylene, trifluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, vinyl fluoride, and combinations thereof.

24. The method of claim 21, wherein the fluorine-containing monomer consists of vinylidene fluoride and hexafluoropropylene.

25. A fluoropolymer latex composition comprising: a) at least one sulfur-containing surfactant and at least one acrylic acid-diol surfactant and b) at least one fluoropolymer, preferably a polyvinylidene fluoride fluoropolymer, comprising at least 65% by weight of vinylidene fluoride monomer units.

26. The fluoropolymer latex composition of claim 25, wherein the acrylic-glycol surfactant is selected from the group consisting of polyethylene glycol acrylate (PEGA), polyethylene glycol methacrylate (PEGMA), polypropylene glycol acrylate (PPGA), polypropylene glycol methacrylate (PPGMA), polypropylene glycol polyethylene glycol acrylate, polypropylene glycol polyethylene glycol methacrylate, and polypropylene glycol dimethacrylate, preferably polypropylene glycol methacrylate (PPGMA).

27. The fluoropolymer latex composition of claim 25, wherein the sulfur-containing surfactant comprises a C6-C18 alkyl group, preferably a non-fluorinated alkyl sulfonate.

28. The fluoropolymer latex composition of claim 25, wherein the sulfur-containing surfactant comprises a C6-C18 alkyl group, preferably a non-fluorinated alkyl sulfate.

29. The fluoropolymer latex composition of claim 25, wherein the acrylic-glycol surfactant comprises polypropylene glycol methacrylate (PPGMA) and the sulfur-containing surfactant comprises octyl sulfonate.

30. A fluoropolymer composition prepared by the process of any one of claims 1 to 24.

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