Method for producing fluoroelastomers in aqueous emulsions without the use of fluorinated surfactants - Patent Application 20070122997

Abstract

The present invention relates to a process for preparing fluoroelastomers by fluorinated surfactant-free emulsion polymerization in the presence of one or more polycarboxylic acids having from 2 to 22 carbon atoms. The present invention also relates to aqueous fluoroelastomer latexes and fluoroelastomers obtained from this process.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a fluoroelastomer, particularly a vinylidene fluoride (VDF)-based fluoroelastomer, by emulsion polymerization, which does not require the addition of a fluorine-based surfactant and can produce a highly stable fluoropolymer latex. [Background technology]

[0002] This application claims priority to European Patent Application Publication No. 2210470.5, filed November 30, 2022, the entire contents of which are incorporated herein by reference for all purposes.

[0003] Due to several desirable properties such as heat resistance, chemical resistance and weather resistance, vulcanized fluoroelastomers have been used in a variety of applications, especially for the manufacture of sealing products such as oil seals, gaskets, shaft seals and O-rings.

[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. Although surfactants are generally disclosed as optional, all examples require the use of fluorinated surfactants (e.g., perfluorohexyl ethyl sulfonic 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 Co., Ltd., describing TFE-based fluoroelastomers).

[0006] If the goal is to produce stable latexes of VDF-based fluoroelastomers without the addition of fluorinated surfactants, the current state of the art does not yet provide a method for producing such fluoroelastomers as stable latexes.

[0007] The applicant has now surprisingly found that this problem can be effectively solved by the method of the present invention, which also makes it possible to obtain fluoroelastomer latexes with very small average particle sizes, thereby producing latices that are easy to handle and fluoroelastomers with good chemical resistance, especially to polar solvents. Summary of the Invention

[0008] The present invention relates to a process for the preparation of a fluoroelastomer [fluoroelastomer A] in an aqueous reaction medium free of fluorinated surfactants, comprising: a: an aqueous emulsion, i) one or more polycarboxylic acids having 2 to 22 carbon atoms in acid or salt form; iii) a free radical initiator; and ii) a monomer comprising vinylidene fluoride (VDF) and one or more fluorinated monomers different from VDF; iv) an optional chain transfer agent; and forming an aqueous emulsion containing b) initiating polymerization of said monomers, thereby forming fluoroelastomer A as a stable latex, - the fluoroelastomer A contains 30 to 80 mol % of repeating units derived from vinylidene fluoride (VDF) and 20 to 70 mol % of repeating units derived from one or more fluorinated monomers other than VDF, The present invention relates to a method comprising:

[0009] The present invention also provides a fluorinated surfactant-free aqueous latex comprising one or more polycarboxylic acids having 2 to 22 carbon atoms in acid or salt form and particles of fluoroelastomer A, wherein the particles of fluoroelastomer A have an average particle size of less than 400 nm as measured in accordance with ISO 13321, and the fluoroelastomer A is -containing 30 to 80 mol % of repeating units derived from VDF and 20 to 70 mol % of repeating units derived from one or more fluorinated monomers other than VDF, - 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 per kg of fluoroelastomer A, preferably less than 5 mmol per kg of fluoroelastomer A, It also relates to water-based latex.

[0010] The present invention also provides a lubricant having a Mooney viscosity (ML1+10 (121°C)) of at least 10MU, -containing 30 to 80 mol % of repeating units derived from VDF and 20 to 70 mol % of repeating units derived from one or more fluorinated monomers other than VDF, -CH2OH chain ends in an amount of 0 to less than 10 mmol per kg of fluoroelastomer A, preferably less than 5 mmol per kg of fluoroelastomer A, containing hydrogen-containing chain ends selected from the group consisting of -CF2H and -CF2CH3 in an amount of 15 to 100 mmol per kg of fluoroelastomer A, It also relates to fluoroelastomers.

[0011] In another aspect, the present invention relates to a curable composition comprising fluoroelastomer A and one or more curing agents.

[0012] Methods for making cured articles and cured articles obtained from the above curable compositions are further objects of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] For purposes of this specification and the claims that follow: - the use of parentheses around symbols or numbers identifying a formula, such as in expressions such as "fluoroelastomer (A)", has the sole purpose of making the symbols or numbers more distinguishable from the rest of the text, and therefore such parentheses may also be omitted; - the expression "consisting essentially of", when used in combination with repeating units of fluoroelastomer A, is intended to indicate that small amounts of chain ends, defects, irregularities and monomer rearrangements are permitted in fluoroelastomer A, provided that the amount thereof 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 crystallinity (having a heat of fusion of less than 5 J / g, preferably less than 3 J / g, more preferably less than 1 J / g, as measured by ASTM D-3418) and a glass transition temperature (Tg) below room temperature, the fluoroelastomer advantageously having a Tg of less than 10°C, preferably less than 5°C, more preferably less than 0°C; - Expressions such as "fluorinated surfactant", "fluorinated monomer" and the like are intended to encompass partially and fully fluorinated compounds, unless otherwise specified.

[0014] The method of the present invention is suitable for preparing a fluoroelastomer having 30 to 80 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 vinylidene fluoride (VDF) and 20 to 70 mol %, 25 to 65 mol %, more preferably 30 to 40 mol %, and even more preferably 35 to 55 mol % of repeating units derived from one or more fluorinated monomers other than vinylidene fluoride (VDF), using emulsion polymerization in a fluorosurfactant-free environment.

[0015] Non-limiting examples of suitable fluorinated monomers different from VDF include, inter alia: (a) C2-C8 perfluoroolefins such as tetrafluoroethylene (TFE) and hexafluoropropylene (HFP); (b) Vinyl fluoride (VF), trifluoroethylene (TrFE), formula CH2=CH - R f (In the formula, R f hydrogen-containing C2-C8 olefins different from VDF, such as perfluoroalkylethylenes in which: (wherein is a C1-C6 perfluoroalkyl group); (c) C2-C8 chloro- and / or bromo- and / or iodo-fluoroolefins such as chlorotrifluoroethylene (CTFE); (d) Formula CF2=CFOR f (In the formula, R f is a C1-C6 (per)fluoroalkyl group, for example, -CF3, -C2F5, -C3F7), (per)fluoroalkyl vinyl ether (PAVE); (e) 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; (f) Formula: [ka] (In the formula, R f3 , R f4 , R f5 , R f6 are the same or different from one another and optionally contain a fluorine atom and one or more oxygen atoms, such as -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3, among others. ~ (per)fluorodioxoles, preferably perfluorodioxoles, having C6 (per)fluoroalkyl groups (independently selected from among C6 (per)fluoroalkyl groups); (g) Formula: CFX2=CX2OCF2OR'' f (In the formula, R'' f is a linear or branched C1 ~ C6 (per)fluoroalkyl; C5-C6 cyclic (per)fluoroalkyl; and linear or branched C2-C6 (per)fluorooxyalkyl containing 1-3 catenary oxygen atoms, where X2 = F, H; preferably, X2 is F and R'' f (per)fluoromethoxyvinyl ether (hereinafter referred to as MOVE) having -CF2CF3 (MOVE1); -CF2CF2OCF3 (MOVE2); or -CF3 (MOVE3).

[0016] It is usually preferred that the fluoroelastomer A contains repeating units derived from HFP in addition to repeating units derived from VDF.

[0017] In this case, fluoroelastomer A typically contains at least 10 mol %, preferably at least 12 mol %, more preferably at least 15 mol %, of repeat units derived from HFP, based on all repeat units of fluoroelastomer A.

[0018] Furthermore, fluoroelastomer A typically contains at most 55 mol %, preferably at most 45 mol %, more preferably at most 35 mol %, of repeat units derived from HFP, based on all repeat units of fluoroelastomer A.

[0019] Furthermore, in some embodiments, such fluoroelastomer (A) may contain repeating units derived from TFE and / or CTFE in addition to repeating units derived from VDF and HFP monomers. In this case, fluoropolymer A typically contains at least 2 mol%, preferably at least 4 mol%, more preferably at least 7 mol%, and up to 25 mol%, preferably up to 20 mol%, more preferably up to 15 mol% of repeating units selected from TFE and CTFE.

[0020] Fluoroelastomer A may contain, in addition to repeat units derived from VDF, HFP, TFE, and CTFE, one or more of the following: of the following general formula: [ka] wherein R1, R2, R3, R4, R5, and R6 are the same or different from one another and are selected from H, halogen, or optionally halogenated C1 ~ C5 group; and Z is a linear or branched C1-C18 alkylene or cycloalkylene radical, or a (per)fluoropolyoxyalkylene radical, optionally containing oxygen atoms and optionally halogenated; - repeat units derived from at least one fluorinated monomer other than VDF, HFP, TFE, and CTFE; - repeat units derived from at least one hydrogen-containing monomer; - Repeat units derived from one or more cure site monomers.

[0021] Examples of hydrogen-containing 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.

[0022] 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 from each other and are H, F, or C 1~5 alkyl or (per)fluoroalkyl group; (OF -1 ) type of preferred screws - Olefins are H2C=CH - (CF2)6 - (CH=CH2). (OF-2) [ka] (In the formula, each A is the same or different from each other and at each occurrence and is independently selected from F, Cl, and H; Each B is the same or different from each other and in each occurrence and is selected from the group consisting of F, Cl, H, and OR. B are independently selected from R B is a branched or linear alkyl chain which may be partially, substantially or fully fluorinated or chlorinated; E is a divalent group having 2 to 10 carbon atoms which may contain an ether linkage and which may be optionally fluorinated; preferably E is -(CF2) m - group, wherein m is an integer of 3 to 5; 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; R, R, R 7 are the same or different from each other and are H, F, or C 1~5 alkyl or (per)fluoroalkyl groups).

[0023] One or more types of screws - When olefins are employed, 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.

[0024] Optionally, said fluoroelastomer A may contain repeating units, ie cure sites, which include units derived from cure site-bearing monomers.

[0025] Among the cure site-containing repeat units are those of the following formula: (CSM-1) [ka] (In the formula, A Hf are the same or different from each other and at each occurrence and are independently selected from any of F, Cl, and H; Hf is F, Cl, H and OR Hf B (where R Hf Bis a branched or straight chain alkyl radical which may be partially, substantially or fully fluorinated or chlorinated; W Hf are the same or different from one another and at each occurrence and are independently a covalent bond or an oxygen atom; E Hf is an optionally fluorinated divalent radical having 2 to 10 carbon atoms; R Hf is a branched or linear alkyl radical 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 be interrupted by an ether bond; preferably E is -(CF2) m - group (wherein m is an integer from 3 to 5); (CSM-2) Ethylenically unsaturated compounds containing cyanide groups, optionally fluorinated.

[0026] Among the cure site monomers of type (CSM1), preferred monomers are those of the following formula: (CSM1-A) [ka] iodine-containing perfluorovinyl ethers of the formula (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 (such as those described in U.S. Pat. No. 4,745,165 (AUSIMONT SPA), U.S. Pat. No. 4,564,662 (MINNESOTA MINING), and EP 199138A (DAIKIN IND., LTD.) among others); (CSM-1B) formula: CX1X2=CX3-(CF2CF2) p -I (wherein X1, X2 and X3 are the same or different from one another and independently represent H or F; and p is 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 iodine-containing ethylenically unsaturated compounds of the formula (wherein R is H or CH3 and Z is a linear or branched C1-C18 (per)fluoroalkyl radical or a (per)fluoropolyoxyalkylene radical, optionally containing one or more ether oxygen atoms) (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). is selected from the group consisting of:

[0027] Among the (CSM2) type cure site monomers, preferred monomers are: (CSM2-A) formula CF2=CF-(OCF2CFX CN ) m -O-(CF2) n -CN(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-(OCF2CFX CN ) m’ -O-CF2-CF(CF3)-CN(XCN is F or CF3, and m' is 0, 1, 2, 3, or 4); is selected from the group consisting of:

[0028] 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. Nos. 4,281,092 (DU PONT), 5,447,993 (DU PONT), and 5,789,489 (DU PONT).

[0029] 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 the one or more cure site monomers, based on the total amount of units of the fluoroelastomer A.

[0030] A more preferred fluoroelastomer A contains 35-80% vinylidene fluoride (VDF), 10-45% hexafluoropropene (HFP), 0-30% tetrafluoroethylene (TFE), 0-15% perfluoroalkyl vinyl ether (PAVE), 0-5% bis-olefin (OF), and 0-5% cure site-containing monomer.

[0031] Further preferred fluoroelastomers (A) are those that 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.

[0032] The method of the present invention comprises forming an aqueous emulsion in an aqueous reaction medium without a fluorinated surfactant, said aqueous emulsion comprising: i) one or more polycarboxylic acids in acid or salt form having 2 to 22, preferably 2 to 16, more preferably 2 to 12, and even more preferably 2 to 10 carbon atoms; iii) a free radical initiator; and ii) vinylidene fluoride (VDF) and one or more fluorinated monomers different from VDF; iv) an optional chain transfer agent; and Contains:

[0033] The first essential component of the emulsion of the present invention is one or more polycarboxylic acids having 2 to 22 carbon atoms, preferably 2 to 16 carbon atoms, more preferably 2 to 12 carbon atoms, and even more preferably 2 to 10 carbon atoms. Preferably, the one or more polycarboxylic acids are selected from dicarboxylic acids and tricarboxylic acids, more preferably dicarboxylic acids. The polycarboxylic acid is an organic acid having one or more carboxyl groups. Any polycarboxylic acid having 2 to 22 carbon atoms can be used in the present invention. It can be used equally well in its acid form or as an alkali metal salt or ammonium salt. Therefore, when a polycarboxylic acid (including a tricarboxylic acid and a dicarboxylic acid) is mentioned in this patent application, the reference is intended to encompass its corresponding salt form. Generally, the pH of the aqueous emulsion is preferably 7 or less. Typically, when the polycarboxylic acid is in its acid form, such a pH can be achieved directly by mixing the necessary components. However, when the polycarboxylic acid is introduced in its salt form, the pH of the emulsion can be adjusted as desired using conventional methods.

[0034] Preferred tricarboxylic acids are, in particular, citric acid and aconitic acid. Preferred dicarboxylic acids are those of formula (I) HOOC-R-COOH (wherein R is a covalent bond or a C1-20 saturated or unsaturated carbon chain optionally bearing a substituent such as an -OH group). Preferably, R is a covalent bond or a C1-C16 carbon chain, more preferably a covalent bond or a C1-C12 carbon chain, and most preferably a covalent bond or a C1-C8 carbon chain. In some embodiments, it is a C1-C8 carbon chain. While unsaturation may be present in the R chain, the chain is preferably saturated to reduce interference with the polymerization reaction. Substituents may be present on the R chain, but are preferably absent or -OH. Examples of suitable dicarboxylic acids include oxalic acid, adipic acid, malonic acid, glutaric acid, fumaric acid, pimelic acid, azelaic acid, fumaric acid, maleic acid, suberic acid, and sebacic acid.

[0035] Without being bound by theory, it is believed that the polycarboxylic acid promotes rapid emulsion polymerization and also contributes to the stabilization of the resulting latex, which does not exhibit telogenic behavior.

[0036] Typically, the effective total amount of one or more polycarboxylic acids in the aqueous emulsions of the present invention is at least 0.05 grams per liter of emulsion, preferably at least 0.1 grams per liter, more preferably at least 0.2 grams per liter of emulsion, and up to 20 grams per liter of emulsion, preferably up to 15 grams per liter, more preferably up to 10 grams per liter of emulsion.

[0037] Another essential component of the aqueous emulsion 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 method according to the present invention are selected from compounds capable of initiating and / or accelerating the polymerization process.

[0038] Inorganic radical initiators may also be used, including, but not limited to, persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate, and permanganates such as potassium permanganate.

[0039] 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-butyl azo tert-butylperoxyisopropylcarbonate; tert-butylperacetate; 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.

[0040] 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(m=0~8), [ClCF2(CF2) n COO]2, and [HCF2(CF2) n COO]2 (n=0-8); perfluoroalkyl azo compounds, such as perfluoroazoisopropane, [(CF3)2CFN=]2, TIFF2025538879000008.tif12170Stable or sterically hindered perfluoroalkane radicals, such as the hexafluoropropylene trimer radical, the [(CF3)2CF]2(CF2CF2)C· radical, and perfluoroalkanes.

[0041] Redox systems containing at least two components that form a redox pair, such as dimethylaniline-benzoyl peroxide, diethylaniline-benzoyl peroxide, and diphenylamine-benzoyl peroxide, may be used as radical initiators to start the polymerization process.

[0042] The initiator is preferably chosen from among the inorganic peroxides, in particular from among the persulfates.

[0043] 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 mmol (millimoles) of -OO- (peroxide) moieties in the initiator (O) and represents the amount of active oxygen atoms contributing to the generation of radical species.

[0044] For any initiator (O) that does not contain any peroxide moieties, the millimoles of -OO- (peroxide) moieties in the initiator (O) can be equivalently determined based on the decomposition mechanism that results in the generation of radical species; organic azo groups are known, among others, 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.

[0045] A further optional component of the aqueous emulsion 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 usually beneficial for the fluoroelastomer to contain cure sites so that the fluoroelastomer can be vulcanized.

[0046] One way to introduce cure sites into fluoroelastomers is to form end groups on the fluoroelastomer (A) chains that contain 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 is known in the art. The reagent (CTA-X) is preferably one of the following: - 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 having 1 to 8 carbon atoms, and x and y are integers from 0 to 2, with 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.);

[0047] This means that 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, with 1≦x+y≦2, most preferably those of formula R′ f (I) x’ (Br) y’ (In the formula, R' fis a perfluoroalkyl containing 1 to 8 carbon atoms, while x' and y' are integers from 0 to 2, with 1≦x'+y'≦2, and most preferably x'=2 and y'=0.

[0048] 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 above.

[0049] As is 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 fluoroelastomer that does not contain cure sites is desired, the process of the present invention can be carried out without the addition of a chain transfer agent.

[0050] When chain transfer agents are used, the amount typically used is 1 to 100 mmol of I and / or Br per kg of fluoroelastomer.

[0051] The aqueous emulsion of the present invention also contains monomers including VDF and one or more fluorinated monomers different from VDF, and the monomer composition can be varied during the polymerization process as known to those skilled in the art and is selected so as to obtain the desired fluoroelastomer A containing 30 to 80 mol % of repeating units derived from vinylidene fluoride (VDF) and 20 to 70 mol % of repeating units derived from one or more fluorinated monomers other than vinylidene fluoride (VDF).

[0052] An additional step in the process of the present invention is to initiate polymerization of the monomers. This is typically accomplished by contacting the monomers with a free radical initiator via an aqueous reaction medium, typically the aqueous emulsion described above, maintained under stirring in a sealed reactor at a set pressure and temperature. As is common in radical polymerizations, after initiation of polymerization, the monomers and optional 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 radical initiator and, if present, the chain transfer agent, are introduced into the reactor.

[0053] Once the polymerization reaction is complete, a stable latex containing particles of fluoroelastomer A is obtained.

[0054] As previously mentioned, in the process of the present invention, the emulsion polymerization is carried out without the addition of a fluorinated surfactant.

[0055] 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 (per)fluoropolyoxyalkylene chain containing one or more etheric oxygen atoms, X B- -COO - or -SO3 - and T + is H + , NH4 + and alkali metal ions).

[0056] Specific fluorinated surfactants for use in the present invention are of the general formula: [ka] (wherein X1, X2, and X3 are the same or different and independently selected from H, F, and a C1-6 (per)fluoroalkyl group which may optionally contain 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 anionic functional groups, cationic functional groups, and non-ionic functional groups).

[0057] Exemplary embodiments of fluorinated surfactants that are not added in the process of the present invention are, 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, as well as compounds of the formula: [ka] where Xa is an alakaline metal or ammonium moiety.

[0058] In a preferred embodiment, the process of the present invention is carried out in the presence of one or more non-fluorinated surfactants. Preferably, such non-fluorinated surfactants do not contain sulfur-containing groups, such as sulfate and sulfonate surfactants. Such S-containing surfactants are not preferred because they may reduce the color quality of the resulting fluoroelastomer.

[0059] More generally, to obtain better color quality, it is preferred that the aqueous emulsions of the present invention be substantially free of compounds containing sulfur atoms, taking into account both surfactant and non-surfactant compounds.

[0060] As long as they do not contain fluorine atoms, any of anionic surfactants, cationic surfactants, and nonionic surfactants can be used herein, and preferred surfactants for use herein are anionic and nonionic surfactants, more preferred are nonionic surfactants, especially surfactants based on polyethylene glycol (PEG) and polypropylene glycol (PPG) repeating units.Particularly preferred nonionic surfactants are PEG / PPG block copolymers, such as those commercially available from BASF under the brand name PLURONIC® and from Solvay under the brand name ANTAROX®.

[0061] When non-fluorinated surfactants are used, it is preferred that such non-fluorinated surfactants be deactivated, as the use of deactivated surfactants can result in higher molecular weight polymers and faster initiation and polymerization times.

[0062] The deactivation of the non-fluorinated surfactant is preferably carried out by reacting the surfactant with an oxidizing agent. Preferably, the oxidizing agent is hydrogen peroxide or a free radical initiator selected from the list presented above. A preferred method for deactivating the surfactant is to heat the surfactant together with the oxidizing agent in aqueous solution at a temperature effective for the oxidizing agent to generate radicals. Preferably, the surfactant is heated to a temperature of at least T h is heated to the temperature T h The oxidizing agent at T has a half-life of 1 hour. The half-life of oxidizing agents as a function of temperature can be found in the technical literature, for example, https: / / polymerdatabase.com / polymer%20chemistry / t-alf2.html. More preferably, the surfactant has a half-life of at least T h The temperature is maintained for 10 minutes or more, preferably 10 to 120 minutes, and more preferably 20 to 60 minutes.

[0063] Preferably, deactivation of the surfactant is carried out before the start of polymerization.

[0064] One method that can be used is to deactivate the non-fluorinated surfactant before introducing it into the aqueous emulsion of the present invention either as a pure material or mixed with the other components of the emulsion, provided that no monomer is present during the deactivation process.

[0065] A preferred method for forming the aqueous emulsions of the present invention containing deactivated surfactants is to: - first forming an aqueous mixture containing said one or more dicarboxylic acids, said non-fluorinated surfactant, and said oxidizing agent, said aqueous mixture being free of monomers; The aqueous mixture is then heated to at least a temperature T h (preferably said temperature is maintained for 10 minutes or more, preferably 10 to 120 minutes, more preferably 20 to 60 minutes) to form an inactivated aqueous mixture, h wherein the oxidizing agent has a half-life of 1 hour; forming an aqueous emulsion containing the deactivated aqueous mixture, a free radical initiator, monomers comprising vinylidene fluoride (VDF) and one or more fluorinated monomers different from VDF, and an optional chain transfer agent, all components as described above, and wherein the free radical initiator may be the same as or different from the oxidizing agent used in the deactivation step.

[0066] The effective total amount of non-fluorinated surfactant in the aqueous emulsions of the present invention is typically at least 0.05 grams per liter of emulsion, preferably at least 0.1 grams, more preferably at least 0.2 grams per liter of emulsion, and up to 20 grams per liter of emulsion, preferably up to 15 grams, more preferably up to 10 grams per liter of emulsion.

[0067] Advantageously, the process of the invention comprises polymerizing, in aqueous emulsion, VDF with at least one additional fluorinated monomer different from VDF as defined above.

[0068] The process according to the invention can preferably be carried out continuously, or in semi-batch or batch mode.

[0069] The process of the present invention is carried out at a temperature selectable 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 from 40°C to 120°C, more preferably from 50°C to 100°C.

[0070] The process of the present invention is preferably carried out at a pressure of from 10 to 60 bar, more preferably from 20 to 55 bar.

[0071] As mentioned above, another object of the present invention is a fluorinated surfactant-free aqueous latex comprising one or more dicarboxylic acids in acid or salt form and particles of fluoroelastomer A, said particles having an average particle size, measured according to ISO 13321, of less than 400 nm, preferably less than 350 nm, more preferably less than 300 nm, even more preferably less than 270 nm and most preferably less than 220 nm, said fluoroelastomer A being -containing 30 to 80 mol % of repeating units derived from VDF and 20 to 70 mol % of repeating units derived from one or more fluorinated monomers other than VDF, - has a Mooney viscosity (ML1+10 (121 ° C)) of at least 10 MU, - Contains from 0 to less than 10 mmol, preferably less than 5 mmol, of -CH2OH chain ends per kg of fluoroelastomer A.

[0072] In some embodiments, fluoroelastomer A in the aqueous latex according to the present invention comprises hydrogen-containing chain ends selected from the group consisting of -CF2H and -CF2CH3 in an amount of 15 to 100 mmol per kg of fluoroelastomer. The latex can be produced by emulsion polymerization without the addition of fluorinated surfactants as described above.

[0073] As mentioned above, the fluoroelastomer (A) has a Mooney viscosity (ML1+10) at 121°C of at least 10, preferably at least 15, more preferably at least 20 Mooney units (MU), as determined according to ASTM D1646, and / or a Mooney viscosity (ML1+10) at 121°C of at most 80 MU, preferably at most 75 MU, more preferably at most 70 MU. 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 characteristic, since techniques for producing fluororubbers without adding fluorosurfactants may not be able to provide such high molecular weight materials.

[0074] In yet a further aspect, the present invention relates to a fluoroelastomer (A), -containing 30 to 80 mol % of repeating units derived from VDF and 20 to 70 mol % of repeating units derived from one or more fluorinated monomers other than VDF, - has a Mooney viscosity (ML1+10 (121 ° C)) of at least 10 MU, -CH2OH chain ends in an amount of 0 to less than 10 mmol per kg of fluoroelastomer A, preferably less than 5 mmol per kg of fluoroelastomer A, -CF2H and -CF2CH3 hydrogen-containing chain ends in an amount of 15 to 100 mmol per kg of fluoroelastomer A; Regarding the fluoroelastomer (A).

[0075] The fluoroelastomers can be prepared by emulsion polymerization without the addition of fluorinated surfactants.

[0076] Such fluoroelastomer (A) is advantageously obtained by coagulating the above-mentioned latex comprising particles of fluoroelastomer (A) according to standard techniques, typically to obtain fluoroelastomer granules or crumbs.

[0077] In yet another aspect, the present invention relates to a curable composition containing such a fluoroelastomer (A) and a curing agent.

[0078] The curing agent can be chosen from all the agents typically used to cure elastomers, for example, it can be chosen from peroxides, in particular organic peroxides having at least two peroxide groups in the molecule.

[0079] The organic peroxide is selected from those capable of generating radicals under curing conditions.

[0080] Among the commonly used organic peroxides, mention may be made of dialkyl peroxides (such as di-tertbutyl peroxide and 2,5-dimethyl-2,5-di(tertbutylperoxy)hexane); dicumyl peroxide; dibenzoyl peroxide; di-tertbutyl perbenzoate; and di[1,3-dimethyl-3-(tertbutylperoxy)butyl]carbonate.

[0081] The curable compositions of the present invention may further comprise: (a) A curing coagent, generally in an amount ranging from 0.5 to 10 phr, preferably from 1 to 7 phr, relative to the fluoroelastomer (A); among these, those commonly used are triallyl cyanurate; triallyl isocyanurate (TAIC); tris(diallylamine)-s-triazine; triallyl phosphite; N,N-diallyl acrylamide; N,N,N',N'-tetraallyl malonamide; trivinyl isocyanurate; 2,4,6-trivinyl methyl trisiloxane; N,N'-bisallyl bicyclo-oct-7-ene-disuccinimide (BOSA); the above-mentioned bis-olefins (OF), in particular those of the formula CH═CH—(CF) n -CH=CH2 bis-olefins, general formula: [ka] (wherein X may independently be hydrogen, chlorine, fluorine, C1-C3 alkyl or perfluoroalkyl; n is an integer ranging from 2 to 20, preferably from 4 to 12, more preferably from 4 to 8), and TAIC is particularly preferred as the curing coagent; (b) a metal compound in an amount ranging from 1 to 15 phr, from 2 to 10 phr, relative to the fluoroelastomer (A), selected from oxides or hydroxides of divalent metals such as Mg, Zn, Ca or Pb, optionally in combination with a weak acid salt such as, for example, Ba, Na, K, Pb, Ca stearates, benzoates, carbonates, oxalates or phosphites; (c) Other conventional additives such as thickeners, pigments, antioxidants, reinforcing agents (e.g., carbon black), stabilizers, etc.

[0082] A method for making a cured article and a cured article obtained from the above curable composition are further objects of the present invention. The cured article may be selected from pipes, joints, O-rings, hoses, etc., among others.

[0083] In a further aspect, the present invention relates to a method for producing a cured article, comprising processing and curing a curable composition containing at least one fluoroelastomer (A) and at least one organic peroxide.

[0084] The curable compositions containing fluoroelastomer (A) can be fabricated into desired shaped articles, for example by molding (injection molding, extrusion), calendering, or extrusion. The cured articles may be subjected to vulcanization (or curing) during the processing itself and / or in a subsequent step (post-treatment or post-cure).

[0085] To the extent that the disclosure of any patents, patent applications, and publications incorporated herein by reference conflicts with the statements of this application to the extent that a term may be unclear, the statements of this application shall control.

[0086] The present 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.

[0087] Experimental section Materials used All polycarboxylic acids were sourced from Sigma-Aldrich. Galden D02, VDF, HFP, and TFE were obtained from Solvay Specialty Plymers Italia SpA. Pluronic PE6200 is a commercial material from BASF.

[0088] Mooney Viscosity: Mooney viscosity (ML1+10) at 121°C was measured according to ASTM D1646.

[0089] Determination of average particle size The average particle size of the latex particles is measured by light scattering according to ISO 13321.

[0090] 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.

[0091] Example 1 A 2.2 L vertical autoclave equipped with baffles and a stirrer operating at 650 rpm was evacuated and then charged with 1.3 L of demineralized water, 1.3 g of pimelic acid, 1.8 g of C4F8I2 (3 ml of a 33% by weight solution of C4F8I2 in Galden D02).

[0092] The autoclave was then sealed and heated to 80 °C and maintained at that temperature for the entire reaction time. The pressure in the autoclave increased by 9 bar by feeding the HFP monomer. The following gaseous monomer mixture was fed into the autoclave to a pressure of 22 bar: 70 mol% vinylidene fluoride (VDF), 19 mol% hexafluoropropene (HFP), and 11 mol% tetrafluoroethylene (TFE). Then, 35 ml of an aqueous ammonium persulfate solution with a concentration of 50 g / l was added (corresponding to 14 mmol of OO per kg of elastomer). After initiation, a constant pressure was maintained by continuously feeding the VDF / HFP / TFE mixture. The polymerization continued until a total monomer consumption of 550 g was reached. The reactor was then depressurized, vented, and cooled.

[0093] Example 2 The same procedure as in Example 1 was followed, except that azelaic acid was used instead of pimelic acid and the amount of APS was adjusted to 60 ml of a 50 g / l solution (corresponding to 24 mmol OO / kg elastomer).

[0094] Example 3 The same procedure as in Example 1 was followed, except that oxalic acid was used instead of pimelic acid and the amount of APS was adjusted to 50 ml of a 50 g / l solution (corresponding to 20 mmol OO per kg elastomer).

[0095] Example 4 The same procedure as in Example 1 was followed, except that 0.65 g of malonic acid was used instead of 1 g of pimelic acid and the amount of APS was adjusted to 105 ml of a 50 g / l solution (corresponding to 42 mmol of OO per kg of elastomer).

[0096] Example 5 The same procedure as in Example 1 was followed, except that 0.65 g of fumaric acid was used instead of 1 g of pimelic acid.

[0097] Example 6 The same procedure as in Example 1 was followed, except that 0.65 g of itaconic acid was used instead of 1 g of pimelic acid and the amount of APS was adjusted to 78 ml of a 50 g / l solution (corresponding to 31 mmol of OO per kg of elastomer).

[0098] Example 7 A 2.2 L vertical autoclave equipped with baffles and a stirrer operating at 650 rpm was evacuated and then charged with 1.3 L of demineralized water, 1.3 g of oxalic acid, 0.65 g of Pluronic PE6200, and 20 ml of a 50 g / L APS solution. The mixture was heated at 70°C for 60 minutes, after which 3 ml of a 33 wt% C4F8I2 solution in Galden D02 was added.

[0099] The autoclave was then sealed and heated to 80 °C and maintained at that temperature throughout the reaction. The pressure in the autoclave increased by 9 bar by feeding the HFP monomer. The following gaseous monomer mixture was fed into the autoclave to a pressure of 22 bar: 70 mol% vinylidene fluoride (VDF), 19 mol% hexafluoropropene (HFP), and 11 mol% tetrafluoroethylene (TFE). 50 ml of an aqueous ammonium persulfate solution with a concentration of 50 g / l was then added (corresponding to 20 mmol of OO per kg of elastomer). After the polymerization had started, a constant pressure was maintained by continuously feeding the VDF / HFP / TFE mixture. The polymerization was continued until a total monomer consumption of 550 g was reached. The reactor was then depressurized, vented, and cooled.

[0100] Example 8c (Comparative Example) The same procedure as in Example 1 was followed, except that no dicarboxylic acid was added.

[0101] A portion of the latex obtained in Examples 1 to 9 was then coagulated and the fluoropolymer crumbs were extracted according to the following process: In a glass becker, 3 liters of demineralized water were heated to 60°C using a heating plate, after which 6 grams of aluminum sulfate (Al2(SO4)3) were added and mixed until completely dissolved. Then, using a dropping funnel, 250 ml of the latex obtained according to the procedure of Example 1 was added to the becker while stirring with an overhead stirrer. After all the latex had been 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 was measured on a crumb of the dried fluoroelastomer.

[0102] The results shown in Table 1 below clearly demonstrate that the process of the present invention results in fluoroelastomer latexes with very small particle size and excellent stability when compared to reference products of the same composition produced by prior art processes. The Mooney viscosity values ​​obtained confirm that the fluoroelastomers obtained by the process of the present invention are suitable for many common applications of fluoroelastomers.

[0103] [Table 1]

Claims

1. 1. A process for the preparation of a fluoroelastomer [fluoroelastomer A] in an aqueous reaction medium free of fluorinated surfactants, comprising: a: an aqueous emulsion, i) one or more polycarboxylic acids having from 2 to 22 carbon atoms in acid or salt form; iii) a free radical initiator; and ii) a monomer comprising vinylidene fluoride (VDF) and one or more fluorinated monomers different from VDF; iv) an optional chain transfer agent; and forming an aqueous emulsion containing b) initiating polymerization of said monomers, thereby forming a fluoroelastomer [fluoroelastomer A] as a stable latex, During the ceremony, - said fluoroelastomer A comprises 30 to 80 mol % of repeating units derived from vinylidene fluoride (VDF) and 20 to 70 mol % of repeating units derived from one or more fluorinated monomers other than VDF, A method comprising:

2. The method of claim 1 , wherein the aqueous emulsion also comprises one or more non-fluorinated surfactants.

3. 3. The method of claim 2, wherein the one or more non-fluorinated surfactants are selected from non-ionic surfactants, and the aqueous emulsion does not contain sulfur-containing surfactants.

4. 4. The method of claim 2 or 3, wherein the one or more non-fluorinated surfactants are deactivated.

5. The method of claim 3 or 4, wherein the surfactant is a polyethylene glycol-polypropylene glycol block copolymer.

6. The method according to any one of claims 1 to 5, wherein the free radical initiator is selected from inorganic free radical initiators, preferably persulfates.

7. 7. The method according to any one of claims 1 to 6, wherein the one or more fluorinated monomers different from VDF are selected from hexafluoropropylene (HFP), tetrafluoroethylene (TFE), perfluoroalkyl vinyl ethers (PAVE), chlorotrifluoroethylene (CTFE).

8. The method of any one of claims 1 to 7, also comprising the additional step of coagulating said fluoroelastomer A and separating it from said latex as a fluoroelastomer crumb.

9. 1. A fluorinated surfactant-free aqueous latex comprising one or more polycarboxylic acids having 2 to 22 carbon atoms in acid or salt form and particles of fluoroelastomer A, said particles of fluoroelastomer A having an average particle size of less than 400 nm as measured in accordance with ISO 13321, said fluoroelastomer A comprising: - containing 30 to 80 mol % of repeating units derived from VDF and 20 to 70 mol % of repeating units derived from one or more fluorinated monomers other than VDF, - has a Mooney viscosity (ML1+10(121°C)) of at least 10MU, -CH in an amount of from 0 to less than 10 mmol per kg of fluoroelastomer A, preferably less than 5 mmol per kg of fluoroelastomer A ２ A water-based latex containing OH chain ends.

10. The fluoroelastomer A is —CF ２ H and -CF ２ CH ３ 10. The aqueous latex of claim 9, comprising hydrogen-containing chain ends selected from the group consisting of CH3 in an amount of 15 to 100 mmol per kg of fluoroelastomer A.

11. having a Mooney viscosity (ML1+10(121°C)) of at least 10MU; - containing 30 to 80 mol % of repeating units derived from vinylidene fluoride (VDF) and 20 to 70 mol % of repeating units derived from one or more fluorinated monomers other than VDF, -CH in an amount of from 0 to less than 10 mmol per kg of fluoroelastomer A, preferably less than 5 mmol per kg of fluoroelastomer A ２ containing OH chain ends, -CF ２ H and -CF ２ CH ３ in an amount of 15 to 100 mmol per kg of fluoroelastomer A selected from the group consisting of: Fluoroelastomer A.

12. 12. The fluoroelastomer of claim 11, produced by emulsion polymerization without the addition of fluorinated surfactants.

13. A curable composition comprising the fluoroelastomer A according to claim 11 or 12 and one or more curing agents.

14. 14. A method for producing a cured article comprising processing and curing the curable composition of claim 13.

15. A cured article obtained from the method of claim 14.

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