Method for producing a fluoroelastomer

Abstract

The present invention relates to a method for producing a fluoroelastomer [fluoroelastomer A] in an aqueous reaction medium free of fluorinated surfactants, comprising the steps of: a) forming a mixture comprising: i) water; ii) one or more fluorinated solvents having less than 0.1 mmol of ionic functional groups per kg of solvent, preferably free of ionic functional groups; iii) a free radical initiator; iv) monomers comprising tetrafluoroethylene (TFE) and one or more perfluoroalkyl vinyl ethers (PAVE); v) optionally one or more chain transfer agents; b) initiating polymerization of the monomers, thereby forming a fluoroelastomer [fluoroelastomer A] as a stable latex; - the mixture is free of fluorinated surfactants; - the weight ratio between the one or more fluorinated solvents and the water is between 0.1 and 10; and - the fluoroelastomer A comprises 30 to 85 mol % of repeat units derived from tetrafluoroethylene and 5 to 50 mol % of repeat units derived from one or more PAVEs.

Description

[Technical Field]

[0001] This application claims priority from European Patent Application Publication No. 23155071.6, filed February 6, 2023, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to a method for producing fluoroelastomers, particularly tetrafluoroethylene (TFE)-based fluoroelastomers, under mild pressure conditions, which does not require the addition of fluorosurfactants and can result in highly stable fluoropolymer latexes. [Background technology]

[0003] Vulcanized fluoroelastomers are used in a variety of applications, particularly in the manufacture of sealing articles such as oil seals, gaskets, shaft seals and O-rings, due to several desirable properties such as heat resistance, chemical resistance and weather resistance.

[0004] A commonly used method for producing curable fluoroelastomers involves the aqueous emulsion polymerization of one or more fluorinated monomers. This type of polymerization is generally carried out in the presence of a fluorinated surfactant, which is required to ensure latex stability, increase the reaction rate, and prevent reactor deposits or fouling.

[0005] For example, U.S. Patent Application Publication No. 2007 / 0100062 (DuPont Performance Elastomers LLC) discloses fluoroelastomers prepared by emulsion polymerization. While it is generally disclosed that surfactants are optional components, all examples require the use of fluorinated surfactants (e.g., perfluorohexylethylsulfonic acid). More recently, due to growing concerns related to the use of fluorinated surfactants, reactions requiring non-fluorinated surfactants have been disclosed in the art, such as U.S. Patent Application Publication No. 2018 / 0237628 and U.S. Patent Application Publication No. 2018 / 0148527 (both in the name of Asahi Glass Company, Limited, which describe TFE-based fluoroelastomers).

[0006] When the goal is to produce stable latexes of TFE-based fluoroelastomers without adding fluorinated surfactants, the prior art still does not provide a method for producing such fluoroelastomers as latexes with excellent stability.

[0007] Now, surprisingly, the Applicant has discovered that this problem can be effectively solved by the method of the present invention, which also makes it possible to obtain stable fluoroelastomer latexes that are easier to handle and that are free of fluorinated surfactants both during production and in the final product in latex or solid form. Summary of the Invention

[0008] The present invention relates to a process for producing a fluoroelastomer [fluoroelastomer A] in an aqueous reaction medium free from fluorinated surfactants, said process comprising the steps of: a: a mixture, i) water, ii) one or more fluorinated solvents having less than 0.1 mmol of ionic functional groups per kg of solvent, preferably free of ionic functional groups; iii) a free radical initiator; iv) a monomer comprising tetrafluoroethylene (TFE) and one or more perfluoroalkyl vinyl ethers (PAVE); v) optionally, one or more chain transfer agents forming a mixture comprising: b) initiating the polymerization of said monomers, thereby forming the fluoroelastomer [fluoroelastomer A] as a stable latex. Including, - the mixture does not contain a fluorinated surfactant, the weight ratio between the one or more fluorinated solvents and the water is between 0.1 and 10; - said fluoroelastomer A comprises 30 to 85 mol % of repeating units derived from tetrafluoroethylene and 5 to 50 mol % of repeating units derived from one or more PAVEs;

[0009] In another aspect, the present invention relates to an aqueous latex comprising one or more fluorinated solvents that are free of fluorinated surfactants and have less than 0.1 mmol of ionic functional groups per kg of solvent, and particles of Fluoroelastomer A, wherein said particles of Fluoroelastomer A have an average particle size of less than 800 nm, measured according to ISO 13321; the weight ratio between said one or more fluorinated solvents and said water is between 0.1 and 10, preferably between 0.2 and 5, more preferably between 0.3 and 1, and even more preferably between 0.5 and 0.8, The fluoroelastomer A is - 30 to 85 mol%, preferably 35 to 75 mol%, more preferably 40 to 70 mol%, even more preferably 45 to 65 mol% of repeating units derived from tetrafluoroethylene and 5 to 50 mol%, preferably 10 to 45 mol%, more preferably 15 to 40 mol%, even more preferably 20 to 35 mol% of repeating units derived from one or more PAVEs, - has a Mooney viscosity (ML1+10 (121 ° C)) of at least 10 MU, - containing -CH2OH chain ends in an amount of 0 to less than 10 mmol / kg of fluoroelastomer A, preferably less than 5 mmol / kg of fluoroelastomer A; DETAILED DESCRIPTION OF THE INVENTION

[0010] For purposes of this specification and the claims that follow: the use of parentheses around symbols or numbers identifying a formula, for example in expressions such as "fluoroelastomer (A)", has the sole purpose of better distinguishing the symbols or numbers from the rest of the text, and so said parentheses may also be omitted, - the expression "consisting essentially of" is intended to indicate that, when used in combination with repeating units of fluoroelastomer A, trace amounts of chain ends, defects, irregularities and monomer rearrangements are permitted in fluoroelastomer A, provided that the amount is less than 5 mol %, more preferably less than 2 mol %, and even more preferably less than 1 mol %, based on the total number of moles of fluoroelastomer A; - the term "fluoroelastomer" is intended to denote an essentially amorphous polymer, preferably having a low degree of crystallinity (heat of fusion measured by ASTM D-3418 of less than 5 J / g, preferably less than 3 J / g, more preferably less than 1 J / g) and a glass transition temperature (Tg) measured by ASTM D-3418 of less than room temperature. Fluoroelastomers advantageously have a Tg of less than 10°C, preferably less than 5°C, more preferably less than 0°C; The expressions "fluorinated surfactants", "fluorinated monomers" are intended to encompass partially fluorinated compounds and fully fluorinated compounds, unless otherwise specified.

[0011] The method of the present invention is suitable for preparing a fluoroelastomer (A) having 30 to 85 mol%, preferably 35 to 75 mol%, more preferably 40 to 70 mol%, and even more preferably 45 to 65 mol% of repeating units derived from tetrafluoroethylene (TFE) and 5 to 50 mol%, preferably 10 to 45 mol%, more preferably 15 to 40 mol%, and even more preferably 20 to 35 mol% of repeating units derived from one or more perfluoroalkyl vinyl ethers (PAVE) under mild pressure conditions and in a fluorosurfactant-free environment.

[0012] Perfluoroalkyl vinyl ether (PAVE) monomers suitable for the present invention have the general formula: (I)CF2=CFOR f (In the formula, R f is a C1-C6 (per)fluoroalkyl group, such as -CF3, -C2F5, -C3F7, preferably R f is selected from -CF3 and -C2F5, more preferably -CF3) It has.

[0013] In addition to TFE and PAVE, the fluoroelastomers of the present invention may optionally contain 1 to 50 mole % of repeat units derived from other fluorinated monomers different from TFE and PAVE; non-limiting examples of suitable fluorinated monomers are, inter alia: (a) C2-C8 perfluorinated fluoroolefins other than TFE, such as hexafluoropropylene (HFP), (b) vinylidene fluoride (VDF), vinyl fluoride (VF), trifluoroethylene (TrFE), formula CH 2 =CH - R f (In the formula, R f hydrogen-containing C2-C8 olefins such as perfluoroalkylethylenes in the formula (wherein each of the formulas is a C1-C6 perfluoroalkyl group); (c) C2-C8 chloro- and / or bromo- and / or iodo-fluoroolefins such as chlorotrifluoroethylene (CTFE); (d) Formula CF2 = CFOX (wherein X is a C1-C 12 (per)fluoro-oxy-alkyl vinyl ethers of [(per)fluoro]-oxyalkyl, for example perfluoro-2-propoxypropyl group; (e) Formula: [ka] (In the formula, R f3 , R f4 , R f5 , R f6 are the same or different and are fluorine atoms and in particular -CF3, -C2F5, -C3F7, - -OCF3, -OCF2CF2OCF3, and C1-C6 (per)fluoroalkyl groups optionally containing one or more oxygen atoms, such as (Per)fluorodioxoles, preferably perfluorodioxoles, having the formula (f) Formula: CFX2=CX2OCF2OR'' f (In the formula, R'' f is selected from linear or branched C1-C6 (per)fluoroalkyl, C5-C6 cyclic (per)fluoroalkyl and linear or branched C2-C6 (per)fluorooxyalkyl containing 1 to 3 catenary oxygen atoms; X 2 = F, H, preferably X 2 is F and R'' f is -CF2CF3(MOVE 1 ), -CF2CF2OCF3(MOVE 2 ) or -CF3(MOVE 3 )) having a (per)fluoro-methoxy-vinyl ether (hereinafter MOVE) is.

[0014] Fluoroelastomer A may contain, in addition to the fluorinated repeat units described above, one or more of the following: - General formula: [ka] (wherein R1, R2, R3, R4, R5 and R6 are the same or different and are H, halogen or an optionally halogenated C1-C5 group optionally containing one or more oxygen groups, and Z is an optionally halogenated linear or branched C1-C18 alkylene or cycloalkylene group optionally containing an oxygen atom or a (per)fluoropolyoxyalkylene group.) repeat units derived from at least one bis-olefin [bis-olefin (OF)] having the formula - repeat units derived from at least one hydrogenated monomer, - Repeat units derived from one or more cure site-containing monomers.

[0015] Examples of hydrogenated monomers that can be used herein are non-fluorinated alpha-olefins, including ethylene, propylene, 1-butene, diene monomers, styrene monomers, among others, with alpha-olefins typically being used. C2-C8 non-fluorinated alpha-olefins (O1), more specifically ethylene (E) and propylene (F), may be selected to achieve improved base resistance.

[0016] The bis-olefins (OF) are preferably selected from the group consisting of those according to formula (OF-1), formula (OF-2) and formula (OF-3): (OF-1) [ka] (wherein j is an integer of 2 to 10, preferably an integer of 4 to 8, and R 1 , R 2 , R 3 , R 4 are the same or different and are H, F or C 1~5 alkyl or (per)fluoroalkyl groups, a preferred bis-olefin of type (OF-1) is H2C=CH-(CF2)6-CH=CH2), (OF-2) [ka] wherein each A at each occurrence is the same or different from one another and is independently selected from F, Cl, and H; Each B is the same or different from each other at each occurrence and is selected from the group consisting of F, Cl, H, and OR. B (In the formula, R B are branched or straight chain alkyl groups which may be partially, substantially or fully fluorinated or chlorinated; E is an optionally fluorinated divalent group having 2 to 10 carbon atoms, into which an ether bond may be inserted, and preferably E is —(CF ) where m is an integer from 3 to 5. m - group, A preferred bis-olefin of the (OF-2) type is F2C=CF-O-(CF2)5-O-CF=CF2), (OF-3) [ka] (wherein E, A and B have the same meanings as defined above, and R, R, R 7 are the same or different and are H, F or C 1~5 alkyl or (per)fluoroalkyl groups).

[0017] When one or more bis-olefins are used, the resulting fluoroelastomer A typically contains from 0.01 mol % to 5 mol % of units derived from one or more bis-olefins relative to the total amount of units of said fluoroelastomer A.

[0018] Optionally, the fluoroelastomer A may contain cure sites comprising repeat units, ie, units derived from cure site-containing monomers.

[0019] Among the cure site-containing repeat units are: (CSM-1) formula: [ka] (In the formula, A Hfare the same or different from each other at each occurrence and are independently selected from F, Cl and H; B fHf is F, Cl, H and OR Hf B (In the formula, R Hf B is a branched or straight chain alkyl group which may be partially, substantially or fully fluorinated or chlorinated; W Hf are the same or different from each other at each occurrence and are independently a covalent bond or an oxygen atom; Hf is an optionally fluorinated divalent group having 2 to 10 carbon atoms, and R Hf is a branched or straight chain alkyl group which may be partially, substantially or fully fluorinated; R Hf is a halogen atom selected from the group consisting of iodine and bromine, which may have an ether bond inserted therein, and preferably E is -(CF 2 ) m -base) an iodine- or bromine-containing monomer of the formula (CSM-2) optionally fluorinated ethylenically unsaturated compounds containing cyanide groups Examples include:

[0020] Of the cure site monomers of type (CSM1), preferred monomers are those selected from the group consisting of: (CSM1-A) formula: [ka] (wherein m is an integer of 0 to 5, n is an integer of 0 to 3, provided that at least one of m and n is different from 0, and Rfi is F or CF3 (e.g., those described in U.S. Pat. No. 4,745,165 (AUSIMONT SPA), U.S. Pat. No. 4,564,662 (MINNESOTA MINING), and European Patent Application Publication No. 199138A (DAIKIN IND., LTD.)). an iodine-containing perfluorovinyl ether of (CSM-1B) formula: CX1X2=CX3-(CF2CF2) p -I (In the formula, X1, X2, and X3 are the same or different and independently represent H or F, and p represents an integer of 1 to 5.) iodine-containing ethylenically unsaturated compounds (among these compounds, mention may be made of CH2=CHCF2CF2I, I(CF2CF2)2CH=CH2, ICF2CF2CF=CH2, I(CF2CF2)2CF=CH2), (CSM-1C) formula: CHR=CH-Z-CHCHR-I (wherein R is H or CH3, and Z is a linear or branched C1 to C18 (per)fluoroalkyl or (per)fluoropolyoxyalkylene group optionally containing one or more ether oxygen atoms). iodine-containing ethylenically unsaturated compounds (among these compounds, mention may be made of CH₂═CH—(—F₂)₄CH₂CH₂I, CH₂═CH—(CF₂)₆CH₂CH₂I, CH₂═CH—(CF₂)₈CH₂CH₂I, CH₂═CH—(CF₂)₂CH₂CH₂I), (CSM-1D) Bromo and / or iodo alpha-olefins containing 2 to 10 carbon atoms, such as bromotrifluoroethylene or bromotetrafluorobutene as described in U.S. Pat. No. 4,035,565 (DU PONT) or other compounds disclosed in U.S. Pat. No. 4,694,045 (DU PONT), bromine and / or iodo alpha-olefins.

[0021] Among the (CSM2) type cure site monomers, preferred monomers are: (CSM2-A) Formula CF2=CF-(OCF2CFX CN ) m -O-(CF2) n -CN(wherein, X CN is F or CF3, m is 0, 1, 2, 3 or 4, and n is an integer of 1 to 12), (CSM2-B) Formula CF2=CF-(OCF2CFXCN ) m '-O-CF2-CF(CF3)-CN (where X CN is F or CF3, and m' is 0, 1, 2, 3, or 4) is selected from the group consisting of:

[0022] Specific examples of cure site monomers of type CSM2-A and CSM2-B suitable for the purposes of the present invention are those described in, inter alia, U.S. Pat. No. 4,281,092 (DU PONT), U.S. Pat. No. 5,447,993 (DU PONT) and U.S. Pat. No. 5,789,489 (DU PONT).

[0023] When one or more cure site monomers are used, the resulting fluoroelastomer A typically contains 0.01 mol % to 5 mol % of units derived from one or more cure site monomers, based on the total amount of units of said fluoroelastomer A.

[0024] Even more preferred fluoroelastomers (A) have iodine and / or bromine chain ends and do not contain cure site monomers, since the iodine / bromine chain ends typically come from chain transfer agents (discussed below) and already provide available cure sites for crosslinking.

[0025] The method of the present invention comprises providing a mixture comprising: i) water, ii) one or more fluorinated solvents having less than 0.1 mmol of ionic functional groups per kg of solvent, and more preferably no ionic functional groups; iii) a free radical initiator; iv) Monomers including tetrafluoroethylene (TFE) and one or more perfluoroalkyl vinyl ether (PAVE) containing monomers; v) optionally, one or more chain transfer agents forming a mixture comprising: - the mixture does not contain a fluorinated surfactant, the weight ratio between said one or more fluorinated solvents and said water is between 0.1 and 10, preferably between 0.2 and 5, more preferably between 0.3 and 1, and even more preferably between 0.5 and 0.8;

[0026] An essential component of the aqueous mixture of the present invention is one or more fluorinated solvents having less than 0.1 mmol of ionic functional groups per kg of solvent, and preferably no ionic functional groups.

[0027] By "ionic functional group" is intended all functional groups that are ionic or can be made ionizable through a pH change in the range of 1 to 14, in particular sulfate, sulfonate, carboxylate, phosphate, phosphonate, ammonium, etc. In other words, functional groups are those that are ionic in their salt form (e.g., -COO - ) and / or its conjugate acid / base form (e.g., —COOH).

[0028] For use in the present invention, the fluorinated solvent used must have a very low level of ionic groups, less than 0.1 mmol / kg of solvent, and preferably the fluorinated solvent does not contain ionic groups. Such fluorinated solvents provide effective and rapid polymerization of fluoroelastomers in the method of the present invention and, surprisingly, have been found to be very effective in forming a stable latex at the end of the polymerization process, despite being immiscible with water. In the early stages of polymerization, water and solvent form two separate phases, but surprisingly, as the polymerization reaction progresses and the fluoroelastomer is formed, a uniform, stable latex is formed that does not show separation. Without being bound by theory, it is believed that the polymer latex particles, while dispersed in the aqueous phase, absorb the fluorinated solvent until the separate solvent phase disappears, thus forming a uniform, stable latex.

[0029] Apart from the required small number of ionic groups, the choice of fluorinated solvent is not particularly limited. Among partially fluorinated solvents, hydrofluoroethers such as those sold by 3M under the brand name Novec® can be used. However, partially fluorinated solvents can cause undesirable chain transfer effects. For this reason, it is preferable to use fully fluorinated solvents. In the case of non-polymer solvents (e.g., perfluoroalkanes), "fully fluorinated solvent" refers to a solvent in which all hydrogen atoms in the molecule are replaced with fluorine atoms. In the case of polymer solvents (e.g., perfluoropolyethers) among fully fluorinated solvents, it refers to a solvent in which at least all hydrogen atoms in the polymer backbone are replaced with fluorine atoms, but the chain ends may or may not be fully fluorinated.

[0030] All perfluorinated solvents commonly used in the production of fluoropolymers can be used herein, with particular preference given to perfluoroalkanes, perfluorinated ethers, perfluoropolyether solvents (such as those sold by Solvay Specialty Polymers SpA under the brand name Galden®) and perfluoroamines such as perfluorobutylimine sold by 3M under the brand name Fluorinert®. Due to their manufacturing process, perfluoropolyethers often have a fully fluorinated backbone and partially fluorinated chain ends. Some commercially available perfluoropolyether materials have partially fluorinated chain ends, while other materials are sold with fully fluorinated chain ends. Both classes of perfluoropolyethers are considered "perfluorinated solvents" according to the definition of the present invention and are suitable as fluorinated solvents in the process of the present invention.

[0031] Another essential component of the aqueous mixture of the present invention is a free radical initiator. While the choice of radical initiator is not particularly limited, it is understood that those suitable for the process according to the present invention are selected from compounds capable of initiating and / or accelerating the polymerization process.

[0032] Inorganic radical initiators may be used, including, but not limited to, persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate, and permanganates such as potassium permanganate.

[0033] Organic radical initiators may also be used, including, but not limited to, acetylcyclohexanesulfonyl peroxide, diacetyl peroxydicarbonate, dialkyl peroxydicarbonates such as diethyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, tert-butyl perneodecanoate, 2,2'-azobis(4-methoxy-2,4 dimethylvaleronitrile), tert-butyl perpivalate, dioctanoyl peroxide, dilauroyl peroxide, 2,2'-azobis(2,4-dimethylvaleronitrile), tert-butylazo-2- Examples of peroxides include cyanobutane, dibenzoyl peroxide, tert-butyl per-2-ethylhexanoate, tert-butyl permaleate, 2,2'-azobis(isobutyronitrile), bis(tert-butylperoxy)cyclohexane, tert-butylperoxyisopropyl carbonate, tert-butyl peracetate, 2,2'-bis(tert-butylperoxy)butane, dicumyl peroxide, di-tert-amyl peroxide, di-tert-butyl peroxide (DTBP), p-methane hydroperoxide, pinane hydroperoxide, cumene hydroperoxide, and tert-butyl hydroperoxide.

[0034] Other suitable radical initiators include, in particular, halogenated radical initiators, such as chlorocarbon and fluorocarbon acyl peroxides, e.g., trichloroacetyl peroxide, bis(perfluoro 2-propoxypropionyl) peroxide, [CFCFCFOCF(CF)COO], perfluoropropionyl peroxide, (CFCFCFCOO), (CFCFCOO), {(CFCFCF)-[CF(CF)CFO] m —CF(CF3)—COO}2 (wherein m=0 to 8), [ClCF2(CF2) n COO]2 and [HCF2(CF2) n COO]2 (wherein n=0-8), perfluoroalkyl azo compounds such as perfluoroazoisopropane, [(CF3)2CFN=]2, TIFF2026504211000008.tif71701-8 carbon atoms), stable or sterically hindered perfluoroalkane groups, such as hexafluoropropylene trimer group, [(CF3)2CF]2(CF2CF2)C· group, and perfluoroalkanes.

[0035] Redox systems containing at least two components that form a redox pair, such as dimethylaniline-benzoyl peroxide, diethylaniline-benzoyl peroxide, and diphenylamine-benzoyl peroxide, can be used as radical initiators to start the polymerization process.

[0036] The initiator is preferably chosen from inorganic peroxides, especially persulfates.

[0037] As mentioned above, in the method of the present invention, the amount of initiator (O) is at least 1.50 mmol and at most 100.00 mmol of O per kg of fluoroelastomer (A). Such amount is expressed in millimoles (mmoles) of -OO- (peroxide) moieties in the initiator (O) and represents the amount of active oxygen atoms contributing to the generation of radical species.

[0038] For any initiator (O) that does not contain any peroxide moieties, the millimoles of -OO- (peroxide) moieties in said initiator (O) can be equally determined based on the decomposition mechanism that results in the generation of radical species; organic azo groups are particularly known to decompose with the elimination of nitrogen to produce two radical species, and are therefore equivalent to -OO- (peroxide) moieties with respect to the generation of radical species.

[0039] A further optional component of the aqueous mixture of the present invention is a chain transfer agent. The choice of chain transfer agent is not particularly limited, but since the resulting polymer is a fluoroelastomer, it is typically beneficial for the fluoroelastomer to contain cure sites so that the fluoroelastomer can be vulcanized.

[0040] One way to introduce cure sites into a fluoroelastomer is to form end groups on the fluoroelastomer (A) chains containing iodine or bromine atoms, preferably iodine. Such iodine and / or bromine chain ends are obtained by adding at least one iodinated / brominated chain transfer agent [reagent (CTA-X)] to the polymerization medium during the preparation of the fluoroelastomer, as known in the art. The reagent (CTA-X) is preferably: - iodinated and / or brominated organic chain transfer agents (suitable organic chain transfer agents are typically of the formula R f (I) x (Br) y wherein R f is a (per)fluoroalkyl or (per)fluorochloroalkyl containing 1 to 8 carbon atoms, and x and y are integers from 0 to 2, where 1≦x+y≦2 (see, for example, U.S. Pat. No. 4,243,770 (DAIKIN IND., LTD.) and U.S. Pat. No. 4,943,622 (NIPPON MEKTRON KK.)), and alkali metal or alkaline earth metal iodides and / or bromides, such as those described in particular in US Pat. No. 5,173,553 (AUSIMONT SRL.); is selected from the group consisting of:

[0041] Nevertheless, the preferred reagent (CTA-X) is an iodinated and / or brominated organic chain transfer agent, more preferably a compound of formula R f (I) x (Br) y (In the formula, R f is (per)fluoroalkyl or (per)fluorochloroalkyl containing 1 to 8 carbon atoms, while x and y are integers from 0 to 2, where 1≦x+y≦2), most preferably those of formula R′ f (I) x’ (Br) y’ (In the formula, R' f is a perfluoroalkyl containing 1 to 8 carbon atoms, while x' and y' are integers from 0 to 2, where 1≦x'+y'≦2, and most preferably x'=2 and y'=0.

[0042] In the method of the present invention, iodinated reagents (CTA-X), in particular compounds of formula R f (I) 2 or R' f (I)2 is preferred, wherein R f and R' f is as described above.

[0043] As known in the art and as already mentioned above, another method of introducing cure sites into fluoroelastomers is to copolymerize a cure site monomer with the required fluoromonomer. In that case, or if a cure site-free fluoroelastomer is desired, the process of the present invention can be carried out without the addition of a chain transfer agent.

[0044] When chain transfer agents are used, the amount typically used is 1 to 100 mmol of I and / or Br per kg of fluoroelastomer.

[0045] The aqueous mixture of the present invention also contains monomers including TFE and one or more PAVE monomers, the composition of the monomers being variable during the polymerization process as known to those skilled in the art and selected to obtain the desired fluoroelastomer A containing 30 to 85 mol %, preferably 35 to 75 mol %, more preferably 40 to 70 mol %, and even more preferably 45 to 65 mol % of repeating units derived from tetrafluoroethylene and 5 to 50 mol %, preferably 10 to 45 mol %, more preferably 15 to 40 mol %, and even more preferably 20 to 35 mol % of repeating units derived from one or more PAVE monomers as described above.

[0046] Preferably, the fluoroelastomer A of the latex contains -CH2OH chain ends in an amount of 0 to less than 10 mmol, preferably less than 5 mmol per kg of fluoroelastomer A.

[0047] A further step in the process of the present invention is to initiate polymerization of the monomers. This is typically achieved by contacting the monomers with a free radical initiator via an aqueous reaction medium, typically the aqueous mixture described above, maintained under agitation in a sealed reactor at a set pressure and temperature. As is common in radical polymerizations, after initiation of polymerization, the monomers and optionally the initiator and / or chain transfer agent are typically continuously fed into the reactor until the polymerization reaction is complete, so that at the end of the polymerization process, the entire amount of the free radical initiator and, if present, the chain transfer agent, are introduced into the reactor.

[0048] Once the polymerization reaction is complete, a stable latex containing particles of fluoroelastomer A is obtained.

[0049] As mentioned above, in the process of the present invention, the polymerization is carried out without the addition of a fluorinated surfactant.

[0050] Examples of fluorinated surfactants that are not used in the present invention include those of the following formula: R * -X B- (T + ) (In the formula, R * is a C5-C16 (per)fluoroalkyl chain or a (per)fluoropolyoxyalkylene chain containing one or more ether oxygens, X B- -COO - or -SO3 - and T + is H + , NH4 + and alkali metal ions) It is a fluorinated surfactant according to

[0051] Specific fluorinated surfactants for use in the present invention are of the general formula: [ka]

[0052] In the formula, X1, X2, and X3 are the same or different and are independently selected from H, F, and a C1-6 (per)fluoroalkyl group optionally containing one or more catenary or non-catenary oxygen atoms; L represents a bond or a divalent group; RF is a divalent fluorinated C1-3 bridging group; and Y is a hydrophilic functional group selected from an anionic functional group, a cationic functional group, and a non-ionic functional group.

[0053] Exemplary embodiments of fluorinated surfactants that are not added in the process of the present invention include, inter alia, ammonium perfluorooctanoate, (per)fluoropolyoxy-alkylenes terminated with one or more carboxylic acid groups, optionally in the form of salts with sodium, ammonium and alkali metals, and partially fluorinated alkylsulfonates, and compounds of the formula: [ka] wherein Xa is an alkali metal or ammonium moiety. is a compound of

[0054] Although not preferred, the process of the present invention can be carried out optionally in the presence of one or more non-fluorinated surfactants.If used, such non-fluorinated surfactants preferably do not contain sulfur-containing groups, such as sulfate surfactants and sulfonate surfactants.Such S-containing surfactants are not preferred because they may reduce the color quality of the resulting fluoroelastomer.

[0055] More generally, to obtain better color quality, it is preferred that the aqueous mixtures of the present invention be substantially free of compounds containing sulfur atoms, taking into account both surfactant and non-surfactant compounds.

[0056] When non-fluorinated surfactants exist, both anionic, cationic and non-ionic surfactants can be used herein, provided that they do not contain fluorine atoms.Preferred surfactants for use herein are anionic and non-ionic surfactants, and more preferred are non-ionic surfactants, especially surfactants based on polyethylene glycol (PEG) and polypropylene glycol (PPG) repeating units.Particularly preferred non-ionic surfactants are PEG / PPG block copolymers, such as those sold by BASF under the brand name PLURONIC® and by Solvay under the brand name ANTAROX®.

[0057] Typically, the effective total amount of non-fluorinated surfactant in the aqueous mixture of the present invention is at least 0.05 grams per liter of mixture, preferably at least 0.1 grams, more preferably at least 0.2 grams per liter of mixture, and at most 20 grams per liter of mixture, preferably at most 15 grams, more preferably at most 10 grams per liter of mixture.

[0058] However, as mentioned above, it is preferred to carry out the process of the present invention without the addition of non-fluorinated surfactants.

[0059] Advantageously, the process of the invention comprises polymerizing, in an aqueous medium, TFE with one or more PAVE monomers as defined above.

[0060] The process according to the invention can preferably be carried out continuously or semi-batchwise or batchwise.

[0061] The process of the present invention is carried out at a temperature that can be selected by one skilled in the art, based inter alia on the free radical initiator used. Preferably, the process of the present invention is carried out at a temperature of 40°C to 120°C, more preferably 50°C to 100°C.

[0062] The process of the present invention is preferably carried out at moderate pressures of between 10 and 60 bar, more preferably between 20 and 55 bar.

[0063] As mentioned above, another object of the present invention is an aqueous latex that is free of fluorinated surfactants and that comprises one or more fluorinated solvents, preferably one or more perfluorinated solvents, and particles of fluoroelastomer A, said particles of fluoroelastomer A having an average particle size, measured according to ISO 13321, of less than 800 nm, preferably less than 600 nm, more preferably less than 400 nm, the weight ratio between said one or more fluorinated solvents and said water is between 0.1 and 10, preferably between 0.2 and 5, more preferably between 0.3 and 1, and even more preferably between 0.5 and 0.8, The fluoroelastomer A is - 30 to 85 mol%, preferably 35 to 75 mol%, more preferably 40 to 70 mol%, even more preferably 45 to 65 mol% of repeating units derived from tetrafluoroethylene and 5 to 50 mol%, preferably 10 to 45 mol%, even more preferably 20 to 35 mol% of repeating units derived from one or more PAVEs, - have a Mooney viscosity (ML1+10 (121°C)) of at least 10 MU; Preferably, the fluoroelastomer A of the latex contains -CH2OH chain ends in an amount of 0 to less than 10 mmol, preferably less than 5 mmol per kg of fluoroelastomer A.

[0064] As mentioned above, the fluoroelastomer (A) has a Mooney viscosity (ML1+10) of at least 10, preferably at least 15, more preferably at least 20 Mooney units (MU) at 121°C, as determined according to ASTM D1646, and / or a Mooney viscosity (ML1+10) of at most 120 MU, preferably at most 100 MU, more preferably at most 80 MU at 121°C. In other words, the fluoroelastomer (A) is a high molecular weight polymer and is not a molecular weight limited fluorowax or fluororubber. In fact, this is an important feature, since other techniques for producing fluororubbers without adding fluorosurfactants may not be able to provide such high molecular weight materials.

[0065] In a further step, the fluoroelastomer A can be extracted from the latex by coagulation using conventional coagulation techniques for fluoroelastomers, such as increasing the ionic strength of the latex addition salts or acids, such as aluminum sulfate, nitric acid, or mixtures thereof.

[0066] To the extent that the disclosure of any patents, patent applications, and publications incorporated herein by reference contradicts the statements of this application to the extent that a term may be unclear, the statements of this application shall control.

[0067] The invention will now be described in more detail with reference to the following examples, the purpose of which is merely illustrative and not intended to limit the scope of the invention. [Example]

[0068] Materials used Galden® HT135, TFE, PMVE obtained from Solvay Specialty Polymers Italia SpA. C4F8I2, ammonium persulfate were obtained from Sigma Aldrich.

[0069] Mooney Viscosity: Mooney viscosity (ML1+10) at 121°C was measured according to ASTM D1646.

[0070] Determination of average particle size The average particle size of the latex particles is measured by light scattering according to ISO 13321.

[0071] End group determination The end groups were identified and quantified by NMR and / or infrared spectroscopy according to the method described in PIANCA, M., et al., J. Fluor. Chem., 1999, pp. 95-71. In the tables below, the term "nd" is used to mean "not detectable" in reference to chain ends present below the detection limit, i.e., at a concentration below 0.05 mmol / kg.

[0072] Tg Tg was measured by DSC according to ASTM D 3418.

[0073] Example 1 A 5 L vertical autoclave equipped with baffles and a stirrer operating at 650 rpm was evacuated and then charged with the following ingredients: 2.74 L of demineralized water, 0.61 L of the fluorinated solvent Galden® HT135, and 1.8 g of pure C4F8I2. The autoclave was then sealed and heated to 85 °C and maintained at that temperature throughout the reaction. The pressure of the autoclave was increased by 7.5 bar by feeding perfluorinated methyl vinyl ether (PMVE) monomer. A gaseous mixture of 57 mol% tetrafluoroethylene (TFE) and 43 mol% PMVE was then fed into the autoclave, increasing the pressure to 21 bar. 100 ml of an aqueous ammonium persulfate solution with a concentration of 50 g / L was then added. After initiation, a constant pressure was maintained by continuously feeding the TFE / MVE mixture. The polymerization was continued until a total monomer consumption of 1400 g was reached. The autoclave was then depressurized, evacuated, and cooled. The resulting latex has an average particle size of 194 and is still stable and single-phase after 30 days of storage at 25° C. A portion of the resulting latex was then coagulated and the fluoropolymer crumbs extracted according to the following procedure: - 3 liters of demineralized water were heated to 60°C in a glass beaker using a heating plate, then 6 g of aluminum sulfate [Al2(SO4)3] was added and mixed until completely dissolved, and 25 ml of pure nitric acid [HNO3] was obtained. Then, using a dropping funnel, 250 ml of the latex obtained according to the above procedure was added to the beaker while stirring with an overhead stirrer. After all the latex was added, the solution was left stirring until the polymer was completely coagulated. The polymer was then washed with water and dried to obtain a fluoroelastomer crumb. The Mooney viscosity of the fluoroelastomer (ML1+10 (121°C)) was measured on a dried fluoroelastomer crumb and found to be 25 MU. The resulting fluoroelastomer had 30 mol% PMVE and 70 mol% TFE. Tg=-7.

[0074] Example 2 The same procedure as in Example 1 was followed with the following exceptions: - 90 ml of an aqueous solution of ammonium persulfate at a concentration of 50 g / l was added instead of 100 ml. - 1.5g of pure C4F8I2 was used instead of 1.8g. The resulting latex had an average particle size of 226 nm. The Mooney viscosity (ML1+10 (121°C)) of the fluoroelastomer was measured on a dried fluoroelastomer crumb and found to be 63 MU. The resulting fluoroelastomer had 30 mol% PMVE and 70 mol% TFE. Tg=-5.6.

[0075] Example 3 The same procedure as in Example 1 was followed with the following exceptions: - 115 ml of an aqueous solution of ammonium persulfate at a concentration of 50 g / l was added instead of 100 ml. - 1.3g of pure C4F8I2 was used instead of 1.8g. The resulting latex had an average particle size of 196 nm. The Mooney viscosity (ML1+10 (121°C)) of the fluoroelastomer was measured on a dried fluoroelastomer crumb and found to be 102 MU. The resulting fluoroelastomer had 30 mol% PMVE and 70 mol% TFE. Tg=-5.6.

[0076] The method of the present invention makes it possible to obtain fluoroelastomer latexes with small particle size and excellent stability without using fluorinated surfactants, or even without using any surfactants at all. The obtained Mooney viscosity values ​​confirm that the fluoroelastomers obtained by the method of the present invention are suitable for many common applications of fluoroelastomers.

Claims

1. 1. A process for producing a fluoroelastomer [fluoroelastomer A] in an aqueous reaction medium free of fluorinated surfactants, comprising the steps of: a: A mixture, i) water, ii) one or more fluorinated solvents having less than 0.1 mmol of ionic functional groups per kg of solvent, preferably free of ionic functional groups; iii) a free radical initiator; iv) a monomer comprising tetrafluoroethylene (TFE) and one or more perfluoroalkyl vinyl ethers (PAVE); v) optionally, one or more chain transfer agents forming a mixture comprising: b) initiating the polymerization of said monomers, thereby forming the fluoroelastomer [fluoroelastomer A] as a stable latex. Including, - the mixture does not contain a fluorinated surfactant, the weight ratio between said one or more fluorinated solvents and said water is between 0.1 and 10; - a process wherein said fluoroelastomer A comprises from 30 to 85 mol % of repeating units derived from tetrafluoroethylene and from 5 to 50 mol % of repeating units derived from one or more PAVEs.

2. The method of claim 1 , wherein the fluorinated solvent is a perfluorinated solvent.

3. 3. The method according to claim 1 or 2, wherein the fluorinated solvent is selected from perfluorinated alkanes, perfluorinated ethers, perfluoropolyethers, perfluoroamines and mixtures thereof.

4. 4. The method according to any one of claims 1 to 3, wherein the PAVE is selected from perfluoromethyl vinyl ether, perfluoroethyl vinyl ether and perfluoropropyl vinyl ether, preferably perfluoromethyl vinyl ether.

5. 5. The method according to any one of claims 1 to 4, wherein said fluoroelastomer A comprises 35 to 75 mol%, preferably 40 to 70 mol%, more preferably 45 to 65 mol% of repeating units derived from TFE and 10 to 45 mol%, preferably 15 to 40 mol%, more preferably 20 to 35 mol% of repeating units derived from one or more PAVEs.

6. The method according to any one of claims 1 to 5, wherein said fluoroelastomer A comprises 1 to 50 mol % of repeating units derived from other fluorinated monomers different from TFE and PAVE.

7. The method according to any one of claims 1 to 6, wherein said fluoroelastomer A comprises from 0.01 mol % to 5 mol % of units derived from one or more bis-olefins.

8. The method of any one of claims 1 to 7, wherein said fluoroelastomer A comprises from 0.01 mol % to 5 mol % of units derived from cure site monomers.

9. 9. The method according to any one of claims 1 to 8, wherein the weight ratio between the one or more fluorinated solvents and the water is from 0.2 to 5, more preferably from 0.3 to 1, even more preferably from 0.5 to 0.

8.

10. 10. The method of any one of claims 1 to 9, also comprising the additional step of coagulating said fluoroelastomer A and separating it from said latex as a fluoroelastomer crumb.

11. The fluoroelastomer A may contain from 0 to less than 10 mmoles of —CH 3 per kg of fluoroelastomer A, preferably less than 5 mmoles of —CH 3 per kg of fluoroelastomer A. ２ 11. The method of any one of claims 1 to 10, comprising OH chain ends.

12. The method of any one of claims 1 to 11, wherein the mixture comprises one or more chain transfer agents selected from iodine- or bromine-containing chain transfer agents.

13. 1. An aqueous latex free of fluorinated surfactants, comprising one or more fluorinated solvents and particles of fluoroelastomer A, said particles of fluoroelastomer A having an average particle size of less than 800 nm, measured according to ISO 13321; the weight ratio between said one or more fluorinated solvents and said water is between 0.1 and 10, preferably between 0.2 and 5, more preferably between 0.3 and 1, and even more preferably between 0.5 and 0.8; The fluoroelastomer A is - 30 to 85 mol%, preferably 35 to 75 mol%, more preferably 40 to 70 mol%, even more preferably 45 to 65 mol% of repeat units derived from tetrafluoroethylene and 5 to 50 mol%, preferably 10 to 45 mol%, more preferably 15 to 40 mol%, even more preferably 20 to 35 mol% of repeat units derived from one or more PAVEs, - an aqueous latex having a Mooney viscosity (ML1+10 (121°C)) of at least 10MU.

14. The fluoroelastomer A may contain from 0 to less than 10 mmoles of —CH 3 per kg of fluoroelastomer A, preferably less than 5 mmoles of —CH 3 per kg of fluoroelastomer A. ２ 14. The latex of claim 13 comprising OH chain ends.

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