Fluoropolymers produced using alkenyl sulfonates

Abstract

A fluoropolymer composition comprising at least one alkenyl sulfonate and a method of making the fluoropolymer composition is provided

Description

FLUOROPOLYMERS PRODUCED USING ALKENYL SULFONATES

[0001] FIELD OF THE INVENTION

[0002] The invention relates to fluoropolymers, preferably vinylidene fluoride (“VDF”) based, and their preparation. More particularly, it relates to alkenyl sulfonates as surfactants for use in preparing such fluoropolymers.

[0003] BACKGROUND

[0004] Many fluoropolymers are produced via aqueous polymerization (typical emulsion polymerization) processes by reacting a polymerization initiator in the presence of the fluorinated monomers and at least one surfactant (also referred to as emulsifier). Perfluorinated surfactants, such as ammonium perfluorooctanoate, are very effective in fluoropolymer polymerization. Unfortunately, due to their high stability, they present an environmental concern related to bio-persistence.

[0005] Due to governmental regulation the perfluorinated surfactants are being phased out. There is a need to find surfactants that can stabilize a fiuoropolymer emulsion system and produce a stable fluoropolymer latex.

[0006] Processes for making fluoropolymers by an emulsion process commonly use surfactants to stabilize the fluoropolymer latex during the polymerization reaction. See, for example, US patents: US7122610, US 8080621, US8124699, US8697822, and US9068071.

[0007] US7122610 discloses a process for making fluoropolymers using of alkane sulfonates but never discloses the use of alkenyl sulfonates.

[0008] The applicant found that by conducting an emulsion polymerization process containing fluoromonomer, using alkenyl sulfonates, fiuoropolymer shear stability and latexes with % solids in excess of 20 wt% can be prepared.

[0009] Summary of Invention

[0010] The invention provides a fluoropolymer composition comprising fluoropolymer and alkenyl sulfonate.

[0011] The invention provides a method of making a fluoropolymer.

[0012] The invention provides a method of making a vinylidene fluoride (VDF) based fluoropolymer. The method comprises polymerizing vinylidene fluoride, optionally in the presence of at least one other comonomer, in an aqueous emulsion in the presence of an alkenyl sulfonate (as a surfactant) and a radical initiator.

[0013] Various Aspects of the Invention

[0014] In a first aspect provided is a fluoropolymer composition comprising at least one alkenyl sulfonate; and at least one fluoropolymer, wherein the alkenyl sulfonate comprises between 2 and 20 carbon atoms.

[0015] The fluoropolymer composition of the invention can be a vinylidene fluoride homopolymer or a vinylidene fluoride copolymer comprising at least one comonomer.

[0016] A fluorinated comonomer of the vinylidene fluoride copolymer may be selected from the group consisting of hexafluoropropene, chlorotrifluoroethylene, perfluoromethyl vinyl ether (PMVE), perfluoropropyl vinyl ether (PPVE), perfluorobutylvinyl ether (PBVE), tetrafluoroethylene, trifluoroethylene, vinyl fluoride, trifluoropropylene, tetrafluoropropylene , 2,3,3,3-tetrafluoropropene and combinations thereof.

[0017] Monomers known to copolymerizate with vinylidene fluoride may also be comonomers. Such monomers include, but are not limited to, acrylates, methacrylates, acrylic acids, and methacrylic acids. Additional comonomers may include those mentioned in US5415958, US8337725, andUS20130273424, and WO2019199753, such monomers are herein incorporated by reference.

[0018] The fluoropolymer in the invention may comprise vinylidene fluoride monomer units.

[0019] The fluoropolymer composition of any one or more of the above aspects may comprise a fluoropolymer having hexafluoropropylene monomer units.

[0020] The fluoropolymer composition of any one or more of the above aspects, may comprise and from 0.001 to 3.0 weight percent of at least one alkenyl sulfonate based on the weight of the fluoropolymer in the invention.

[0021] The fluoropolymer composition of any one or more of the above aspects, wherein the alkenyl sulfonate comprises from 6 to 18 carbon atoms.

[0022] The fluoropolymer composition of any one or more of the above aspects, wherein the alkenyl sulfonate comprises from 10 to 18 carbons atoms.

[0023] The fluoropolymer composition of any one or more of the above aspects, wherein the alkenyl sulfonate comprises a sodium, potassium, lithium or ammonium alkenyl sulfonate, or a mixture thereof.

[0024] The fluoropolymer composition of any one or more of the above aspects, wherein the fluoropolymer composition is in latex form.

[0025] Further disclosed is a method for preparing a fluoropolymer composition in an aqueous reaction medium comprising: a) forming an aqueous mixture comprising at least one surfactant, and at least one fluoromonomerb) adding at least one radical initiator, c) polymerizing said fluoromonomers, thereby forming a fluoropolymer dispersion; wherein the surfactant comprises at least one alkenyl sulfonate comprising from 2 and 20 carbon atoms.

[0026] In the method, the at least one fluoromonomer can be selected from the group consisting of vinylidene fluoride, hexafluoropropene, ch loro trifluoroethylene, perfluoromethyl vinyl ether (PMVE), perfluoropropyl vinyl ether (PPVE), perfluorobutylvinyl ether (PBVE), tetrafluoroethylene, trifluoroethylene, vinyl fluoride, trifluoropropylene, tetrafluoropropylene, 2,3,3,3-tetrafluoropropene, and combinations thereof.

[0027] In the method of the invention, the at least one fluoromonomer may comprise vinylidene fluoride.

[0028] In the method of the invention, the fluoropolymer may comprise at least 40 wt % vinylidene fluoride of the total monomer units in the fluoropolymer.

[0029] In the method of the invention, in some embodiments, the fluoropolymer may comprise at least 75 wt % vinylidene fluoride of the total monomer units in the fluoropolymer.

[0030] In method of the invention, the alkenyl sulfonate can be in a sodium, potassium, or ammonium alkenyl sulfonate salt form.

[0031] In any of the methods of the invention the alkenyl sulfonate comprises from 6 to 18 carbon atoms.

[0032] in any of the methods of the invention, the alkenyl sulfonate comprises from 10 to 18 carbon atoms.

[0033] In any of the methods of the invention, the alkenyl sulfonate can be present at from 0.001 to 3.0 weight percent based on the total weight of monomer added to the polymerization reaction.

[0034] In any of the methods of the invention, the alkenyl sulfonate can be present at from 0.001 to 2 weight percent based on the total weight of monomer added to the polymerization reaction.

[0035] In any of the methods of the invention, the alkenyl sulfonate can be present at from 0.001 to 3.0 weight percent, based on the total weight of monomer and the fluoropolymer dispersion that result from the method constitutes, after step (c) at least 20 wt. % fluoropolymer based on total weight of the dispersion.

[0036] Any of the methods of the invention can further comprise adding alkenyl sulfonate to the fluoropolymer dispersion after step c (forming of the fluoropolymer dispersion).

[0037] In any of the methods of the invention, the fluoromonomer can comprise vinylidene fluoride, the alkenyl sulfonate can comprise from 12 to 18 carbon atoms and the radical initiator can comprise a persulfate initiator.

[0038] In the fluoropolymer composition of any one or more of the above aspects, the fluoropolymer may comprise at least 40 wt % vinylidene fluoride based on the total monomer units in the fluoropolymer.

[0039] In the fluoropolymer composition of any one or more of the above aspects, the fluoropolymer may comprise at least 50 wt % vinylidene fluoride based on the total monomer units in the fluoropolymer.

[0040] Detailed Description of the Invention

[0041] The references cited in this application are incorporated herein by reference.

[0042] Unless stated otherwise, all percentages, parts, ratios, etc. are by weight.

[0043] The term fluoropolymer refers to homopolymers, copolymers with other fluorinated hydrocarbon monomers and to copolymers having functional acrylic comonomers containing acrylic comonomer units. The copolymers formed may have a monomer distribution and / or molecular weight distribution that is homogeneous or heterogeneous. The morphology of the fluoropolymer is not limited; for instance it may be linear or branched, it can have a random, alternating or gradient distribution of monomer units or can be a block copolymer.

[0044] The terms latex and dispersion are used interchangeable.

[0045] Alkenyl sulfonates, also called alkene sulfonates, means a molecule having at least one sulfonate group and an alkene chain having at least one carbon-carbon double bond and is not aromatic. The term alkenyl sulfonate as used herein includes both the alkenyl sulfonic acid and the salts thereof.

[0046] Shear stable or shear stability means that the Brookfield viscosity is below 1000 cp (at 1500 rpm, room temperature and spindle LV-4).

[0047] The invention provides a suitable method to prepare fluoropolymers from fluoromonomers. The fluoropolymers are prepared in an aqueous emulsion polymerization reaction mixture that includes an alkenyl sulfonate as a surfactant and an inorganic initiator (preferably a persulfate) or an organic initiator. Optionally, polymerizations to prepare the fluoropolymers may be performed in the presence of chain transfer agents to regulate molecular weight, buffering agents to maintain a desired pH range during the polymerization, and antifoulants to reduce or eliminate adhesion of the polymer to the inside surfaces of the polymerization vessels.

[0048] The vinylidene fluoride-based polymers of the invention are conveniently made by aqueous polymerization, preferably emulsion polymerization. The polymerization process can be a batch, semibatch, or continuous polymerization process.

[0049] The polymerization process preferably contains no other fluorine containing compounds or molecules except for the monomers and the resulting polymerization products. No fluorinated surfactants are used.

[0050] Fluoromonomer

[0051] The term “vinylidene fluoride polymer” used herein includes both homopolymers and copolymers within its meaning.

[0052] The copolymers include those containing at least 40 weight percent of vinylidene fluoride, preferably at least 50 wt % or at least 75 wt % vinylidene fluoride, copolymerized with at least one comonomer.

[0053] The comonomer may be selected from the group consisting of, tetrafluoroethylene (TFE), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), perfluorobutylethylene (PFBE), hexafluoropropene (HFP), vinyl fluoride (VF), pentafluoropropene, 2,3,3,3-tetrafluoropropene, trifluoropropene, fluorinated (alkyl) vinyl ethers, such as, perfluoroethyl vinyl ether (PEVE), and perfluoro-2-propoxypropyl vinyl ether, perfluoromethyl vinyl ether (PMVE), perfluoropropyl vinyl ether (PPVE), perfluorobutylvinyl ether (PBVE), longer chain perfluorinated vinyl ethers, one or more of partly or fully fluorinated alpha-olefins such as 3,3,3-trifluoro-l-propene, 2-trifluoromethyl-3,3,3- trifluoropropene, 1 ,2,3,3,3-pentafluoropropene, 3,3,3,4,4-pentafluoro-l-butene, hexafluoroisobutylene (HFIB), fluorinated dioxoles, such as perfluoro(l,3-dioxole) and perfluoro(2,2-dimethyl-l,3-dioxole) (PDD), partially- or per-fluorinated alpha olefins of C4 and higher, partially- or per-fluorinated cyclic alkenes of C3 and higher, partly fluorinated allylic, or fluorinated allylic monomers, and combinations thereof.

[0054] Monomers known to copolymerizate with vinylidene fluoride may be comonomers. Such monomers include, but are not limited to, acrylates, methacrylates, acrylic acids, methacrylic acids. Preferably such monomers have a hydrophilic group. Additional monomers include those mentioned in US5415958, US8337725, and US20130273424, and WO2019199753, such monomers are herein incorporated by reference.

[0055] Surfactant

[0056] The term "surfactant" means a type of molecule, which has both hydrophobic and hydrophilic portions, which allows it to stabilize and disperse hydrophobic molecules and aggregates of hydrophobic molecules in aqueous systems. A preferred group of surfactants for stabilization of fluoropolymer dispersion of the present invention includes alkenyl sulfonates also referred to as alkene sulfonate. Theterm "alkenyl sulfonate" means surfactants having an alkene group containing one or more double bond (DB) as their hydrophobic portion, preferably linear or branched and containing from 2 to 20 carbons. The hydrocarbon groups of these alkenyl sulfonate have one or two sulfonate groups as their hydrophilic portion. The hydrocarbon group does not contain any fluorine (F) and does not contain an aromatic group. Examples of such alkenyl sulfonates include, but are not limited to, Rhodacal A246 (from Solvay) and Bio Terge AS 40 (Stepan Company). Mixtures of different alkenyl sulfonates may be employed.

[0057] Preferred alkenyl sulfonates are in salt form. The alkenyl sulfonate used in the invention can be the ammonium, lithium, sodium, or potassium alkenyl sulfonate salts.

[0058] In accordance with an embodiment of the invention, there is provided a fluoropolymer composition comprising fluoropolymer, preferably a polyvinylidene fluoride, and alkenyl sulfonate. The alkenyl sulfonate may be represented by formula (1)

[0059] wherein: R is an alkenyl group having from 2 to 20 carbon atoms and having at least one carbon-carbon double bond; x is an integer ranging from 1 to 2, M is a cation or H. For avoidance of doubt, when x is 2, the additional sulfonate group is connected to a carbon in the R group.

[0060] There are no aromatic groups in the alkenyl sulfonate. The alkenyl sulfonate is does not contain fluorine.

[0061] Preferably the alkenyl group has from 6 to 18 carbon atoms. In one particular embodiment the alkenyl group has from 10 to 18 carbon atoms and one sulfonate group.

[0062] The alkenyl sulfonate may comprise an alkenyl group having from 12 to 18 carbon atoms and one sulfonate group.

[0063] In accordance with an embodiment of the invention, there is provided a process for preparing a fluoropolymer in an aqueous dispersion wherein the surfactant comprises an alkenyl sulfonate surfactant. It may be represented by formula ( 1)

[0064] In accordance with another embodiment of the invention, there is provided a process for preparing a fluoropolymer in an emulsion polymerization, said process comprising the steps of:1. forming an aqueous solution comprising an alkenyl sulfonate in a polymerization reactor, ii. pressurizing the polymerization reactor with fluoromonomer, andiii. initiating a polymerization reaction of the fluoromonomer by adding an initiator into the polymerization reactor, wherein the alkenyl sulfonate comprises between 2 to 20 carbon atoms.

[0065] The alkenyl sulfonates are added to the polymerization process in an amount from about 0.001 to about 3 weight percent based on total monomer fed to the reaction. Preferably alkenyl sulfonate is used in an amount from about 0.001 to about 2 weight percent on total monomer and more preferably from about 0.005 to 1 wt%.

[0066] The composition of the invention will have from 0.0005 to about 3 weight percent alkenyl sulfonate based on polymer weight.

[0067] The polymerization reaction is generally terminated after consumption of a preset quantity of fluoromonomers.

[0068] The addition of the alkenyl sulfonate can be done entirely before the addition of the initiator begins, after the addition of the initiator begins or cofed during the addition of the initiator. In one embodiment, the alkenyl sulfonate is also added after the termination of the polymerization to stabilize the latex (post polymerization addition).

[0069] Initiator

[0070] The reaction is started and maintained by the addition of a radical initiator. Inorganic radical initiators include inorganic peroxides, such as persulfates. The present invention preferably uses inorganic persulfate as the initiator. Typical inorganic persulfates, including sodium, potassium or ammonium persulfate, have useful activity in the 50°C to 140°C temperature range. Organic peroxides can also be used as the radical initiator in the present invention.

[0071] Preferably, the inorganic radical initiator is selected from the group comprising, hydrogen peroxide, persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate, preferably potassium persulfate in conjunction with sodium acetate or sodium acetate trihydrate.

[0072] The total amount of inorganic initiator used is from 0.01 wt% to 4.0 wt%, preferable from 0.04 wt%-3 wt%, based on the total monomer weight added to the reactor. A mixture of one or more inorganic initiators as defined above, can be used to conduct the polymerization. Typically, sufficient initiator is added at the beginning to start the reaction and then additional initiator may be optionally added to maintain the polymerization at a preset rate (fluoromonomer consumption rate).

[0073] CHAIN TRANSFER AGENT

[0074] A chain-transfer agent may be added to the polymerization to regulate the molecular weight of the product. They may be added to a polymerization in a single portion at the beginning of the reaction, or incrementally or continuously throughout the reaction. The amount and mode of addition of chain-transfer agent depend on the activity of the chain-transfer agent employed, and on the desired molecular weight of the polymer product. The amount of chain-transfer agent added to the polymerization reaction is from about 0 to 5 wt%, preferably 0.05 to about 5 weight percent, more preferably from about 0.1 to about 2 weight percent based on the total weight of monomer added to the reaction mixture. Examples of chain transfer agents useful in the present invention include, but are not limited to oxygenated compounds such as alcohols (preferably having 3 to 10 carbons), carbonates, ketones, esters, and ethers may serve as chain-transfer agents such as acetone, ethyl acetate, diethyl ether, methyl-ter-butyl ether, isopropyl alcohol; bis(alkyl)carbonates wherein the alkyl has from 1 to 5 carbon atoms, such as bis(ethyl)carbonate, bis(isobutyl)- carbonate; ethane and propane and low molecular weight functional polymers as defined in US 1 1643484.

[0075] BUFFERING AGENT

[0076] The polymerization reaction mixture may optionally contain a buffering agent to maintain a controlled pH throughout the polymerization reaction. The pH is preferably controlled within the range of from about 3 to about 8, to minimize undesirable color development in the product.

[0077] Buffering agents may comprise an organic or inorganic acid or alkali metal salt thereof, or base or salt of such organic or inorganic acid, that has at least one pKavalue and / or pKb value in the range of from about 3 to about 10, preferably from about 4.5 to about 9.5. Preferred buffering agents in the practice of the invention include, for example, phosphate buffers and acetate buffers. A “phosphate buffer” is a salt or salts of phosphoric acid. An “acetate buffer” is a salt of acetic acid.

[0078] A paraffin antifoulant may be employed, if desired, although it is not preferred, and any long- chain, saturated, hydrocarbon wax or oil may be used. Reactor loadings of the paraffin may be from 0.01% to 0.3% by weight on the total monomer weight used.

[0079] The fluoropolymer can be isolated using standard methods such as oven drying, spray diying, shear or chemica coagulation followed by drying or the fluoropolymer can be kept in the aqueous media for subsequent application or use.

[0080] In a further aspect, the present invention also relates to an article made from a composition comprising the fluoropolymer composition as defined herein.

[0081] In a further aspect, the present invention relates to a method for the manufacture of shaped article, said method comprising processing a composition comprising the fluoropolymer composition as defined herein.

[0082] Said fluoropolymer composition can be fabricated, e.g. by molding (injection molding, extrusion molding), calendaring, or extrusion, into the desired shaped article. If necessary, the article is then subjected to vulcanization (or curing) during the processing itself and / or in a subsequent step (posttreatment or post-cure).

[0083] The following general emulsion process may be followed: to a reactor is initially added deionized water with a surfactant (also referred to as an emulsifier), followed by deoxygenation (removal of oxygen). The reactor is brought to desired preset reaction temperature. Optionally chain transfer agent, antifoulant and buffering agent may be added to the reactor, preferably before deoxygenation. Fluoromonomer, such as vinylidene fluoride and optional other comonomer(s) is added to the reactor to reach a preset reaction pressure. When the preset reaction pressure is reached, a radical initiator is added to start and maintain the polymerization reaction. Additional monomer may be optionally added to replenish monomer that is consumed, and the other materials may be optionally added during the polymerization. After feeding the preset monomer amount to the reactor, the feed of the monomers can be stopped. However, the charging of initiator can be stopped or continued to consume the unreacted monomers. After the initiator charging is stopped, the reactor may be cooled, and agitation stopped. The unreacted monomers can be vented, and the prepared polymer can be collected through a drain port or by other collection means.

[0084] The reactor used in the polymerization is a pressurized polymerization reactor. The reactor usually is equipped with a stirrer and heat control means. The stirring may be constant or may be varied to optimize process conditions during the course of the polymerization. The method according to the present invention can be preferably performed in continuous, or semi-batch or batch.

[0085] The temperature of the polymerization is typically from 50°C to 140°C, preferably of 50 °C to 130 °C, more preferably from 60°C to 125 °C. The temperature can be varied during the reaction, preferably the temperature is kept constant at + / - 0.5°C.

[0086] The pressure of the polymerization may vary from 1380 to 12,500 kPa, depending on the capabilities of the reaction equipment, the initiator system chosen, and the monomer selection. The polymerization pressure is preferably from 2,000 to 9,000 kPa.

[0087] CHARACTERISTICS OF THE POLYMER AND DISPERSION

[0088] The fluoropolymer comprises at least 40 wt % fluoromonomer, or at least 50 wt% by weight fluoromonomer or at least 75% by weight fluoromonomer. The fluoropolymer can comprise up to 100 weight percent fluoromonomer.

[0089] The fluoropolymer can be a vinylidene fluoride polymer wherein the fluoropolymer comprises at least 40 wt% vinylidene fluoride (VDF), or at least 50 wt% by weight VDF or at least 75% by weight VDF. The fluoropolymer comprises up to 100 weight percent VDF.

[0090] The melt viscosity of the inventive polymer is generally in the range of from 0.1 to 65, preferably 5 kPoise to 65 kPoise, (ASTM D3835 at 230°C and 100 sec -1)

[0091] Preferably, the dispersion of the invention has a solids level of from 20 to 60 weight percent, more preferably from 28-60 weight percent.

[0092] The fluoropolymer particles in the dispersion have a particle size in the range of 50 to 500 nm, and preferable from 100-300 nm (volume average particle size).ANALYTICAL METHODS

[0093] The fluoropolymer particle size (volume average particle size) of the dispersion was determined using a Nicomp Model 380 Sub-Micron Particle Sizer including single mode 35 mW Laser diode with wavelength of 639 nm.

[0094] Melt viscosity measurements of fluoropolymer were performed with a DYNISCO LCR-7000 according to ASTM D3835 by a capillary rheometry at 230° C. and 100 sec-1.

[0095] Shear stability of the aqueous fluoropolymer dispersion was measured as produced by the polymerization reaction using a dispersion blade of 48 mm model Al 64 (by Caframo Lab Solution) at room temperature. 750 ml of dispersion was placed in a 1 -liter wide-mouth jar, the dispersion blade was lowered to 1 / 3 of the dispersion height from the bottom of the jar. The stability time is recorded when Brookfield viscosity rises above 1000 cp (Brookfield viscosity at 1500 rpm, room temperature and spindle LV-4). When the Brookfield viscosity is 1000 cp or greater, the dispersion is no longer fluid and behaves like a gel, and is considered unstable.

[0096] Solid content as measured by gravimetry on the latex produced by the reaction.

[0097] EXAMPLES

[0098] Examples 1-5 PVDF homopolymer

[0099] The experiments were carried out in a 7.5 L stainless steel reactor in which were added 4000 g of D. I. water and the desirable amount of surfactant (as indicated in the table). Examples 1-5 used Rhodacal A 246 MBA as the surfactant. Comparative example 1 used Bioterge PAS-8S (sodium octyl sulfonate, “SOS”). The reactor was purged with nitrogen gas. The reactor was then sealed, and agitation is started at 72 RPM. 72 RPM agitation was maintained throughout the whole reaction. The reactor was heated to desired temperature. The reactor was charged with vinylidene fluoride to reach the desired pressure of 4481 kPa. After pressurization, the reactor was charged with initiator solution. Initiator solution was aqueous initiator solution of 1% potassium persulfate (from EMD Chemicals, ACS grade) and 1% sodium acetate trihydrate (from Mallinckrodt Chemicals, ACS grade). A continuous feed of the aqueous initiator solution was added to the reaction to obtain consumption rate of between 600-800 g / h VDF. The reaction temperature was held, and the reaction pressure was maintained at 4481 kPa by adding vinylidene fluoride as needed. When the amount of VDF consumed reached the desired level, the VDF and initiator feed were stopped. For a period of 30 minutes, agitation was continued, and temperature was maintained. Then the agitation and heating were discontinued. After cooling to room temperature, surplus gas was vented. The latex produced by the reaction was drained into a suitable receiving vessel. Gravimetric solids measurement of the latex was done. The fluoropolymer was recovered by drying the latex in a convection oven at 1 10 C overnight.

[0100] The particle size, melt viscosities, and solids were measured and reported in Table 1 , “I” means initiator. In the example below potassium persulfate was used as the initiator.Table 1 Examples 1-5

[0101] In table 1, the comparative sample (Comp. 1) using SOS as the surfactant provided lower solids in the latex as compared to the samples using alkenyl sulfonate as the surfactant and the latex of comp 1 was more viscous such that it did not freely flow.

[0102] Example 6 Pilot sample

[0103] Into an 80-gallon stainless steel reactor was charged, 345 lbs of deionized water, desirable amount of surfactant (as in Table 2). Example 6 used Rhodacal A 246 as the surfactant. Comparative example 2 used Plutonic 31R1 (BASF) as the surfactant. Following evacuation, agitation was begun at 23 rpm and the reactor was heated. After reactor temperature reached the desired set point of 83°C., VDF charge was started. Reactor pressure was then raised to 4500 kP by charging 40 lbs VDF into the reactor. After reactor pressure was stabilized, the reactor was charged with initiator solution to initiate polymerization. Initiator solution was aqueous initiator solution of 1% potassium persulfate (from EMD Chemicals, ACS grade) and 1% sodium acetate trihydrate (from Mallinckrodt Chemicals, ACS grade). The rate of further addition of initiator solution was adjusted to obtain and maintain a VDF polymerization rate of roughly between 60-120 pounds per hour. The VDF polymerization was continued until predetermined weight of VDF was introduced into the reactor. The VDF feed was stopped, and the batch was allowed to react-out at the reaction temperature and by feeding initiator to consume residual monomer at decreasing pressure. After 30 minutes, the agitation was stopped, and the reactor was vented and the latex recovered. Polymer resin was isolated by coagulating the latex, washing the latex with deionized water, and drying. The data for example 6 is in table 2

[0104] Example 6, having a solids level of 28.6%, had a 16 min stability, whereas, comparative 3 (Comp 3) with similar solids level, had only a 1 min and 49 seconds stability.

[0105] Examples 7-8 VDF-HFP copolymer

[0106] The experiments were carried out in a 7.5 L stainless steel reactor in which were added 4000 g of D. I. water and 1 g of surfactant Rhodacal A 246 MBA. The reactor was purged with nitrogen gas. The reactor was then sealed, and agitation is started at 72 RPM. 72 RPM agitation was maintained throughout the whole reaction. The reactor was heated to desired temperature. The reactor was charged with vinylidene fluoride and comonomer, to reach the desired pressure of 4481 kPa. After pressurization, the reactor was charged with initiator solution. Initiator solution was aqueous initiator solution of 1% potassium persulfate (from EMD Chemicals, ACS grade) and 1% sodium acetate trihydrate (from Mallinckrodt Chemicals, ACS grade). A continuous feed of the aqueous initiator solution was added to the reaction to obtain adequate polymerization rate. The reaction temperature was held, and the reaction pressure was maintained at 4481 kPa by adding vinylidene fluoride and comonomer as needed. When the amount of VDF consumed reached the desired level, the VDF and comonomer feed was stopped. For a period of 30 minutes, agitation was continued, and temperature was maintained. Then the agitation and heating were discontinued. After cooling to room temperature, surplus gas was vented, and latex produced by reaction was drained into a suitable receiving vessel. Gravimetric solids measurement of the latex was done. The fluoropolymer was recovered by drying the latex in a convection oven at 110 C overnight.

[0107] The particle size, melt viscosities, and solids were measured and reported in Table 3.

[0108] I / VDF means the quantity of initiator added to the polymerization in relation to the total VDF monomer added to the polymerization.

Claims

Claims1. A fluoropolymer composition comprising: at least one alkenyl sulfonate; and at least one fluoropolymer, wherein the alkenyl sulfonate comprises between 2 and 20 carbon atoms.

2. The fluoropolymer composition of claim 1 or 2, wherein the fluoropolymer comprises vinylidene fluoride monomer units.

3. The fluoropolymer composition of claim 1, wherein the fluoropolymer comprises a vinylidene fluoride homopolymer or a vinylidene fluoride copolymer.

4. The fluoropolymer composition of claim 3, wherein the vinylidene fluoride copolymer comprises at least one comonomer unit selected from the group consisting of hexafluoropropene, chlorotrifluoroethylene, perfluoromethyl vinyl ether (PMVE), perfluoropropyl vinyl ether (PPVE), perfluorobutylvinyl ether (PBVE), tetrafluoroethylene, trifluoroethylene, vinyl fluoride, trifluoropropylene, tetrafluoropropylene (such as 2,3,3,3-tetrafluoropropene) and combinations thereof.

5. The fluoropolymer composition of any one or more of claims 1 to 3, wherein the fluoropolymer comprises hexafluoropropylene monomer units.

6. The fluoropolymer composition of any one or more of claims 1 to 3, wherein the fluoropolymer composition comprises from 0.001 to 3.0 weight percent of at least one alkenyl sulfonate based on the weight of the fluoropolymer.

7. The fluoropolymer composition of any one or more of claims 1 to 3, wherein the alkenyl sulfonate comprises from 6 to 18 carbon atoms.

8. The fluoropolymer composition of any one or more of claims 1 to 6, wherein the alkenyl sulfonate comprises from 10 to 18 carbons atoms.

9. The fluoropolymer composition of any one or more of claims 1 to 8, wherein the alkenyl sulfonate comprises a sodium, potassium, lithium or ammonium alkenyl sulfonate, or a mixture thereof.

10. The fluoropolymer composition of any one or more of claims I to 9, wherein the fluoropolymer composition is in latex form.

11. A method for preparing a fluoropolymer in an aqueous reaction medium comprising: a) forming an aqueous mixture comprising at least one surfactant, and at least one fluoromonomer b) adding at least one radical initiator, c) polymerizing said fluoromonomers, thereby forming a fluoropolymer dispersion; wherein the surfactant comprises at least one alkenyl sulfonate comprising from 2 and 20 carbon atoms.

12. The method of claim 11, wherein said at least one fluoromonomer comprises vinylidene fluoride.

13. The method of claim 11, wherein said at least one fluoromonomer is selected from the group consisting of vinylidene fluoride, hexafluoropropene, chlorotri fluoroethylene, perfluoromethyl vinylether (PMVE), perfluoropropyl vinyl ether (PPVE), perfluorobutylvinyl ether (PBVE), tetrafluoroethylene, trifluoroethylene, vinyl fluoride, trifluoropropylene, tetrafluoropropylene, 2, 3,3,3- tetrafluoropropene, and combinations thereof.

14. The method of any one or more of claims 11 to 13, wherein the fluoropolymer comprises at least 40 wt % vinylidene fluoride.

15. The method of any one or more of claims 11 to 13, wherein the fluoropolymer comprises at least 50 wt % vinylidene fluoride.

16. The method of any one or more of claims 11 to 13, wherein said one alkenyl sulfonate comprises a sodium, potassium, or ammonium alkenyl sulfonate salt.

17. The method of any one or more of claims 1 1 to 16, wherein said one alkenyl sulfonate comprises from 6 to 18 carbon atoms.

18. The method of any one or more of claims 11 to 16, wherein said alkene group has from 10 to 18 carbon atoms.

19. The method of any one or more of claims 1 1 to 18, wherein said alkenyl sulfonate is present at from 0.001 to 3.0 weight percent, based on the total weight of monomer.

20. The method of any one or more of claims 11 to 18, wherein said alkenyl sulfonate is present at from 0.001 to 2 weight percent, based on the total weight of monomer.

21. The method of any one or more of claims 11 to 20, wherein the fluoropolymer dispersion constitutes, after step (c) at least 20 wt. % fluoropolymer based on total weight of the dispersion.

22. The method of any one or more of claims 11 to 21 , further comprising adding alkenyl sulfonate to the fluoropolymer dispersion after step c.

23. The method of any one or more of claims 1 Ito 22, wherein the fluoromonomer comprises vinylidene fluoride, wherein the alkenyl sulfonate comprises from 12 to 18 carbon atoms, wherein the radical initiator comprises a persulfate initiator.

24. The fluoropolymer composition of any one or more of claims 1 to 3, wherein the fluoropolymer comprises at least 40 wt % vinylidene fluoride.

25. The fluoropolymer composition of any one or more of claims I to 9, wherein the fluoropolymer comprises at least 50 wt % vinylidene fluoride.

26. The fluoropolymer composition of any one or more of claims 1 to 3, wherein the alkenyl sulfonate comprises a sodium, potassium, lithium or ammonium alkenyl sulfonate, or a mixture thereof.

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