Process for manufacture of fluoroelastomers in aqueous emulsions without use of fluorinated surfactants

Abstract

The invention relates to a method for producing fluoroelastomers via emulsion polymerization in the absence of fluorinated surfactants and in the presence of one or more polycarboxylic acids having 2 to 22 carbon atoms. The invention also relates to aqueous fluoroelastomer latices and fluoroelastomers, which can be obtained by the process.

Description

Technical Field

[0001] The present invention relates to a process for producing fluoroelastomers, in particular fluoroelastomers based on vinylidene fluoride (VDF), in emulsion polymerization, wherein no addition of fluorosurfactants is required and wherein very stable fluoropolymer latexes can be obtained. Background Art

[0002] This application claims the benefit of European patent application No. 2210470.5 filed on November 30, 2022, the entire contents of which are incorporated herein by reference for all purposes.

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

[0004] A common process for making curable fluoroelastomers involves the aqueous emulsion polymerization of one or more fluorinated monomers. This type of polymerization is typically carried out in the presence of fluorinated surfactants, which are required to ensure latex stability, improve kinetics, and avoid reactor buildup or fouling.

[0005] For example, US2007 / 0100062 (DuPont Performance Elastomers LLC) discloses fluoroelastomers prepared by emulsion polymerization. Although surfactants are widely disclosed as optional ingredients, all examples require the use of fluorinated surfactants (e.g., perfluorohexyl ethyl sulfonic acid). Recently, due to the increasing problems associated with the use of fluorinated surfactants, reactions requiring non-fluorinated surfactants have been disclosed in the art, such as in US2018 / 0237628 and US2018 / 0148527 (both in the name of Asahi Glass Company, Limited and describing TFE-based fluoroelastomers).

[0006] While the goal is to produce stable latexes of fluoroelastomers based on VDF in the absence of added fluorinated surfactants, the prior art still does not provide a method for making such fluoroelastomers as latexes with excellent stability.

[0007] Now, surprisingly, the Applicant has found that this problem can be effectively solved by the process of the present invention. Such a process also allows obtaining fluoroelastomer latexes with very small average particle sizes, which results in latexes that are easier to handle and fluoroelastomers with excellent chemical resistance, especially towards polar solvents. Summary of the Invention

[0008] The present invention relates to a method for preparing a fluorinated elastomer [fluorinated elastomer A] in an aqueous reaction medium free of fluorinated surfactants, the method comprising:

[0009] a: forming an aqueous emulsion comprising:

[0010] i) one or more polycarboxylic acids having from 2 to 22 carbon atoms in acid or salt form,

[0011] iii) a free radical initiator,

[0012] ii) monomers comprising vinylidene fluoride (VDF) and one or more fluorinated monomers different from VDF,

[0013] iv) optionally a chain transfer agent;

[0014] b: Initiating polymerization of the monomers to form fluoroelastomer A as a stable latex, wherein:

[0015] The fluoroelastomer A comprises from 30% to 80% by mole of recurring units derived from vinylidene fluoride (VDF) and from 20% to 70% by mole of recurring units derived from one or more fluorinated monomers different from VDF.

[0016] The present invention also relates to an aqueous latex free of fluorinated surfactants, comprising one or more polycarboxylic acids having from 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 measured according to ISO 13321, and wherein the fluoroelastomer A:

[0017] - contains 30% to 80% by mole of repeating units derived from VDF, 20% to 70% by mole of repeating units derived from one or more fluorinated monomers different from VDF,

[0018] - having a Mooney viscosity (ML1+10 (121° C.)) of at least 10 MU;

[0019] - contains -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.

[0020] The present invention also relates to a fluoroelastomer having a Mooney viscosity (ML1+10 (121° C.)) of at least 10 MU and comprising:

[0021] - 30% to 80% by mole of repeating units derived from VDF, 20% to 70% by mole of repeating units derived from one or more fluorinated monomers different from VDF,

[0022] -- 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;

[0023] - hydrogen-containing chain ends selected from the group consisting of -CF2H and -CF2CH3, the amount of such chain ends being from 15 to 100 mmol / kg of fluoroelastomer A.

[0024] In another aspect, the present invention relates to a curable composition comprising a fluoroelastomer A and one or more curing agents.

[0025] Additional objects of the present invention are a method for making a cured part and a cured part obtained from the above curable composition. DETAILED DESCRIPTION

[0026] For the purposes of this specification and the following claims:

[0027] - the use of parentheses around an identifying symbol or number, for example in expressions like "fluoroelastomer (A)", etc., has the sole purpose of making this symbol or number better distinguishable from the rest of the text, and said parentheses may therefore also be omitted;

[0028] - the expression "consisting essentially of" when used in combination with repeating units of fluoroelastomer A is intended to indicate that a minor amount of end chains, defects, irregularities, and monomer rearrangements are tolerated in fluoroelastomer A, provided that the amount thereof is less than 5 mol%, more preferably less than 2 mol%, even more preferably less than 1 mol%, based on the total moles of fluoroelastomer A;

[0029] - the term "fluoroelastomer" is intended to indicate a substantially amorphous polymer, preferably having a low degree of 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, as measured by ASTM D-3418. Fluoroelastomers advantageously have a Tg below 10°C, preferably below 5°C, more preferably below 0°C;

[0030] - Expressions "fluorinated surfactant", "fluorinated monomer" etc. are intended to cover both partially and fully fluorinated compounds, unless otherwise stated.

[0031] The process of the present invention is suitable for preparing fluoroelastomers using emulsion polymerization in an environment free of fluorosurfactants, these fluoroelastomers having 30% to 80%, preferably 35% to 75%, more preferably 40% to 70%, even more preferably 45% to 65% by mole of repeating units derived from vinylidene fluoride (VDF), and 20% to 70%, 25% to 65%, more preferably 30% to 40%, even more preferably 35% to 55% by mole of repeating units derived from one or more fluorinated monomers other than vinylidene fluoride (VDF).

[0032] Non-limiting examples of suitable fluorinated monomers other than VDF are in particular:

[0033] (a) C2-C8 perfluoroolefins, such as tetrafluoroethylene (TFE) and hexafluoropropylene (HFP);

[0034] (b) Hydrogen-containing C2-C8 olefins other than VDF, such as vinyl fluoride (VF), trifluoroethylene (TrFE), olefins having the formula CH2=CH-R f Perfluoroalkylethylene, where R f is a C1-C6 perfluoroalkyl group;

[0035] (c) C2-C8 chloro- and / or bromo- and / or iodo-fluoroolefins, such as chlorotrifluoroethylene (CTFE);

[0036] (d) having the formula CF2=CFOR f (per)fluoroalkyl vinyl ether (PAVE), wherein R f is a C1-C6 (per)fluoroalkyl group, such as -CF3, -C2F5, -C3F7;

[0037] (e) (per)fluoro-oxy-alkyl vinyl ethers of the formula CF2=CFOX, wherein X is a C1-C ... 12 [(Per)fluoro]-oxyalkyl, for example perfluoro-2-propoxypropyl;

[0038] (f) (per)fluorodioxoles having the formula:

[0039]

[0040] where R f3 、R f4 、R f5 、R f6 Identical or different from each other, independently selected from fluorine atoms and C1-C6 (per)fluoroalkyl groups, optionally containing one or more oxygen atoms, such as especially -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3; preferably, perfluorodioxole;

[0041] (g) (per)fluoro-methoxy-vinyl ether (MOVE, hereinafter) having the formula: CFX2=CX2OCF2OR f , where R" f is selected from a linear or branched C1-C6 (per)fluoroalkyl group; a C5-C6 cyclic (per)fluoroalkyl group; and a linear or branched C2-C6 (per)fluorooxyalkyl group containing 1 to 3 chain oxygen atoms, and X2=F, H; preferably X2 is F and R" f It is -CF2CF3(MOVE1); -CF2CF2OCF3(MOVE2); or -CF3(MOVE3).

[0042] It is generally preferred that the fluoroelastomer A comprises, in addition to recurring units derived from VDF, recurring units derived from HFP.

[0043] In this case, fluoroelastomer A typically comprises, relative to all the repeating units of fluoroelastomer A, at least 10 mol %, preferably at least 12 mol %, more preferably at least 15 mol %, of repeating units derived from HFP.

[0044] Furthermore, the fluoroelastomer A typically comprises, relative to all the recurring units of the fluoroelastomer A, at most 55 mol %, preferably at most 45 mol %, more preferably at most 35 mol %, of recurring units derived from HFP.

[0045] Furthermore, in some embodiments, in addition to the repeating units derived from VDF and HFP monomers, such fluoroelastomer (A) may also contain repeating units derived from TFE and / or CTFE. In this case, fluoropolymer A typically contains at least 2 mol%, preferably at least 4 mol%, more preferably at least 7 mol% and at most 25 mol%, preferably at most 20 mol%, more preferably at most 15 mol% of repeating units selected from TFE and CTFE.

[0046] In addition to repeating units derived from VDF, HFP, TFE and CTFE, the fluoroelastomer A may also comprise one or more of the following:

[0047] - recurring units derived from at least one diolefin [diolefin (OF)] having the general formula:

[0048]

[0049] wherein R1, R2, R3, R4, R5 and R6 are the same as or different from each other and are H, halogen, or a C1-C5 optionally halogenated group that may contain one or more oxygen groups; Z is a linear or branched C1-C18 optionally halogenated alkylene or cycloalkylene group that optionally contains an oxygen atom, or a (per)fluoropolyoxyalkylene group;

[0050] - repeating units derived from at least one fluorinated monomer different from VDF, HFP, TFE and CTFE; and

[0051] - repeating units derived from at least one hydrogenated monomer;

[0052] - repeating units derived from one or more cure site-containing monomers.

[0053] Examples of hydrogenated monomers that can be used herein are especially non-fluorinated α-olefins, including ethylene, propylene, 1-butene, diene monomers, styrene monomers, typically α-olefins. C2-C8 non-fluorinated α-olefins (O1), and more particularly ethylene (E) and propylene (F), will be selected to achieve increased alkali resistance.

[0054] The diene (OF) is preferably selected from the group consisting of dienes conforming to formula (OF-1), (OF-2) and (OF-3):

[0055] (OF-1)

[0056]

[0057] wherein j is an integer between 2 and 10, preferably between 4 and 8, and R1, R2, R3, R4 are the same as or different from each other and are H, F or C 1-5 Alkyl or (per)fluoroalkyl; preferred dienes of type (OF-1) are

[0058] H2C=CH-(CF2)6-CH=CH2.

[0059] (OF-2)

[0060]

[0061] in

[0062] Each A is the same as or different from each other and, at each occurrence, is independently selected from F, Cl and H;

[0063] Each B is the same as or different from each other and, at each occurrence, is independently selected from F, Cl, H and OR B , where R B is a branched or linear alkyl chain which may be partially, substantially or fully fluorinated or chlorinated;

[0064] E is an optionally fluorinated divalent group having 2 to 10 carbon atoms, which may be interrupted by an ether bond; preferably E is -(CF2) m - group, wherein m is an integer from 3 to 5;

[0065] A preferred diene of the (OF-2) type is F2C=CF-O-(CF2)5-O-CF=CF2.

[0066] (OF-3)

[0067]

[0068] wherein E, A and B have the same meanings as defined above; R5, R6, R7 are the same as or different from each other and are H, F or C 1-5 Alkyl or (per)fluoroalkyl.

[0069] When one or more dienes are employed, the resulting fluoroelastomer A typically comprises from 0.01% to 5% by mole of units derived from the one or more dienes, relative to the total amount of units of said fluoroelastomer A.

[0070] Alternatively, the fluoroelastomer A may comprise repeating units containing cure sites, ie units derived from monomers having cure sites.

[0071] Among the repeating units containing the curing sites, mention may especially be made of:

[0072] (CSM-1) an iodine-containing or bromine-containing monomer having the formula:

[0073]

[0074] Each of A Hf are the same as or different from each other and are independently selected at each occurrence from F, Cl and H; B Hf It is F, Cl, H and OR Hf B Any one of the following, where R Hf B is a branched or straight chain alkyl group which may be partially, substantially or fully fluorinated or chlorinated; each W Hf are the same as or different from each other and, at each occurrence, are independently a covalent bond or an oxygen atom; E Hf is an optionally fluorinated divalent group having 2 to 10 carbon atoms; R Hf is a branched or straight chain alkyl group which may be partially, substantially or fully fluorinated; and 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;

[0075] (CSM-2) An ethylenically unsaturated compound containing a cyano group which may be fluorinated.

[0076] Among the cure site-containing monomers of type (CSM1), preferred monomers are those selected from the group consisting of: (CSM1-A) iodine-containing perfluorovinyl ethers having the formula:

[0077]

[0078] wherein m is an integer from 0 to 5 and n is an integer from 0 to 3, with the proviso that at least one of m and n is different from 0, and Rfi is F or CF3; (as described, inter alia, in patents US 4745165 (AUSIMONT SPA), US 4564662 (MINNESOTA MINING) and EP 199138A (DAIKIN IND., LTD.)); and

[0079] (CSM-1B) an iodine-containing ethylenically unsaturated compound having the formula:

[0080] CX1X2=CX3-(CF2CF2) p -I

[0081] wherein each of X1, X2 and X3 is the same as or different from each other and is independently H or F; and p is an integer from 1 to 5; among these compounds, CH2=CHCF2CF2I, I(CF2CF2)2CH=CH2, ICF2CF2CF=CH2, I(CF2CF2)2CF=CH2 may be mentioned;

[0082] (CSM-1C) an iodine-containing ethylenically unsaturated compound having the formula:

[0083] CHR=CH-Z-CH2CHR-I

[0084] wherein R is H or CH3, Z is a linear or branched C1-C18 (per)fluoroalkylene group, optionally containing one or more ether oxygen atoms, or a (per)fluoropolyoxyalkylene group; among these compounds, mention may be made of CH2=CH-(CF2)4CH2CH2I, CH2=CH-(CF2)6CH2CH2I, CH2=CH-(CF2)8CH2CH2I, CH2=CH-(CF2)2CH2CH2I;

[0085] (CSM-1D) contains brominated and / or iodinated α-olefins of 2 to 10 carbon atoms, such as, for example, bromotrifluoroethylene or bromotetrafluorobutene as described in US Pat. No. 4,035,565 (Du Pont de Nemours and Company), or other brominated and / or iodinated α-olefins disclosed in US Pat. No. 4,694,045 (Du Pont de Nemours and Company).

[0086] Among the cure site-containing monomers of type (CSM2), preferred monomers are those selected from the group consisting of:

[0087] (CSM2-A) has the formula CF2=CF-(OCF2CFX CN ) m -O-(CF2) n -CN containing cyano perfluorovinyl ether, where X CN is F or CF3, m is 0, 1, 2, 3 or 4; n is an integer from 1 to 12;

[0088] (CSM2-B) has the formula CF2=CF-(OCF2CFX CN ) m’ -O-CF2-CF(CF3)-CN containing cyano perfluorovinyl ether, wherein X CN is F or CF3, and m' is 0, 1, 2, 3 or 4.

[0089] Specific examples of cure-site-containing monomers of the CSM2-A and CSM2-B types suitable for the purposes of the present invention are those described, inter alia, in patents US 4,281,092 (DuPont), US 5,447,993 (DuPont) and US 5,789,489 (DuPont).

[0090] When one or more cure site containing monomers are employed, the resulting fluoroelastomer A typically comprises from 0.01 to 5 mol% of units derived from the one or more cure site containing monomers relative to the total amount of units of said fluoroelastomer A.

[0091] More preferred fluoroelastomers A are those comprising 35%-80% vinylidene fluoride (VDF), 10%-45% hexafluoropropylene (HFP), 0-30% tetrafluoroethylene (TFE), 0-15% perfluoroalkyl vinyl ether (PAVE), 0-5% diene (OF), and 0-5% cure site-containing monomers.

[0092] Even more preferably, the fluoroelastomer (A) has iodine and / or bromine chain ends and does not comprise cure site containing monomers, since the iodine / bromine chain ends are typically derived from chain transfer agents (as explained below) and already provide effective cure sites for crosslinking.

[0093] The method of the present invention comprises a step wherein an aqueous emulsion is formed in the absence of a fluorinated surfactant, said aqueous emulsion comprising:

[0094] i) one or more polycarboxylic acids having 2 to 22, preferably 2 to 16, more preferably 2 to 12, even more preferably 2 to 10 carbon atoms, in acid or salt form

[0095] iii) Free radical initiator

[0096] ii) vinylidene fluoride (VDF) and one or more fluorinated monomers other than VDF

[0097] iv) optionally a chain transfer agent.

[0098] The first essential component of the emulsion of the present invention is one or more polycarboxylic acids having 2 to 22, preferably 2 to 16, more preferably 2 to 12, and even more preferably 2 to 10 carbon atoms. Preferably, the one or more polycarboxylic acids are selected from dicarboxylic acids and tricarboxylic acids, and even more preferably from dicarboxylic acids. A polycarboxylic acid is an organic acid having more than one carboxyl group. Any polycarboxylic acid having 2 to 22 carbon atoms can be used in the present invention. It can be used equally in acid form or as an alkali metal or ammonium salt, so that whenever a polycarboxylic acid (including tricarboxylic acids and dicarboxylic acids) is cited in this patent application, the citation is intended to also cover its corresponding salt form. Generally speaking, it is preferred that the pH of the aqueous emulsion is 7 or lower, typically such a pH is obtained directly by mixing the required components when the polycarboxylic acid is in acid form, however, in the case where the polycarboxylic acid is introduced in salt form, the pH of the emulsion can also be adjusted as needed using conventional methods.

[0099] Preferred tricarboxylic acids are in particular citric acid and aconitic acid. Preferred dicarboxylic acids are compounds according to formula (I)

[0100] HOOC-R-COOH

[0101] Wherein R is a covalent bond or a C1-20 saturated or unsaturated carbochain, and this carbochain can carry a substituent such as -OH group.Preferably, R is a covalent bond or a C1-C16 carbochain, more preferably a covalent bond or a C1-C12 carbochain, most preferably a covalent bond or a C1-C8 carbochain.In certain embodiments, it is a C1-C8 carbochain.Unsaturation can exist in the chain R, but preferably the chain is saturated to reduce the interference to the polymerization reaction.Substituents can be present on the chain R, but preferably they do not exist or are -OH.The example of suitable dicarboxylic acids is for example oxalic acid, adipic acid, malonic acid, glutaric acid, fumaric acid, pimelic acid, azelaic acid, fumaric acid, maleic acid, suberic acid, sebacic acid.

[0102] Without wishing to be bound by theory, it is believed that the polycarboxylic acid allows the emulsion polymerization to proceed rapidly and also helps to stabilize the resulting latex and not exhibit telogenic behavior.

[0103] Typically, the effective total amount of one or more polycarboxylic acids in the aqueous emulsions of the present invention is at least 0.05 g, preferably 0.1 g, more preferably 0.2 g per litre of emulsion and at most 20 g, preferably at most 15 g, more preferably at most 10 g per litre of emulsion.

[0104] Another essential component of the aqueous emulsion of the present invention is a free radical initiator. Although the choice of free radical initiator is not particularly limited, it is understood that those free radical initiators suitable for use in the process according to the present invention are selected from compounds capable of initiating and / or accelerating the polymerization process.

[0105] Inorganic free radical initiators may be used and include, but are not limited to, persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate, and permanganates such as potassium permanganate.

[0106] In addition, organic free radical initiators may be used, and these include, but are not limited to, the following: acetylcyclohexanesulfonyl peroxide; diacetyl peroxydicarbonate; dialkyl peroxydicarbonate, 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-cyanobutane; dibenzoyl peroxide; tert-butyl-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.

[0107] Other suitable free radical initiators include, inter alia, halogenated free radical initiators, such as chlorocarbon-based and fluoroalkane-based acyl peroxides, such as trichloroacetyl peroxide, bis(perfluoro-2-propoxypropionyl) peroxide, [CF3CF2CF2OCF(CF3)COO]2, perfluoropropionyl peroxide, (CF3CF2CF2COO)2, (CF3CF2COO)2, {(CF3CF2CF2)-[CF(CF3)CF2O] m -CF(CF3)-COO}2 (wherein m=0-8), [ClCF2(CF2) n COO]2, and [HCF2(CF2) nCOO]2 (wherein n = 0-8); perfluoroalkylazo compounds, such as perfluoroazoisopropyl, [(CF3)2CFN=]2, RN=NR¤ (wherein R¤ is a linear or branched perfluorocarbon group having 1-8 carbons); stable or hindered perfluoroalkane radicals, such as hexafluoropropylene trimer radical, [(CF3)2CF]2(CF2CF2)C● radical and perfluoroalkanes.

[0108] It is also possible to use redox systems comprising at least two components forming a redox couple, such as dimethylaniline-benzoyl peroxide, diethylaniline-benzoyl peroxide and diphenylamine-benzoyl peroxide, as free radical initiators to initiate the polymerization process.

[0109] The initiator is preferably chosen from inorganic peroxides, and in particular from persulfates.

[0110] As stated, in the process of the present invention, the amount of initiator (O) is at least 1.50 and at most 100.00 mmol of O2 per kg of fluoroelastomer (A).

[0111] This amount is expressed as mmol (millimoles) of the -OO- (peroxide) moiety in the initiator (O) and represents the amount of active oxygen atoms that contribute to the generation of free radical species.

[0112] For any initiator (O) that does not contain any peroxide moieties, the number of millimoles of -OO-(peroxide) moieties in said initiator (O) can likewise be determined based on the decomposition mechanism leading to the generation of free radical species; in particular, it is known that an organic azo group decomposes, eliminating nitrogen and generating two free radical species, and therefore, it is equivalent to the -OO-(peroxide) moiety with respect to the generation of free radical species.

[0113] Another optional component of the aqueous emulsion of the present invention is a chain transfer agent. However, the choice of chain transfer agent is not particularly limited because the resulting polymer is a fluoroelastomer and it is typically beneficial for the fluoroelastomer to contain cure sites so that the fluoroelastomer can be vulcanized.

[0114] One way to introduce cure sites into fluoroelastomers is to create end groups of the fluoroelastomer (A) chains that contain iodine or bromine atoms, preferably iodine. As is known in the art, such iodine and / or bromine chain ends are obtained by adding at least one iodinated / brominated chain transfer agent [agent (CTA-X)] to the polymerization medium during the manufacture of the fluoroelastomer. Said agent (CTA-X) is preferably selected from the group consisting of:

[0115] - iodinated and / or brominated organic chain transfer agents; suitable organic chain transfer agents are typically of formula R f (I) x(Br) y Those, among which R f is a (per)fluoroalkyl group or a (per)fluorochloroalkyl group containing 1 to 8 carbon atoms, and x and y are integers between 0 and 2, wherein 1≤x+y≤2 (see, for example, US 4243770 (Daikin Industries, Ltd.) and US 4943622 (NIPPON MEKTRON KK.); and

[0116] - Alkali metal or alkaline earth metal iodides and / or bromides, as described inter alia in US Pat. No. 5,173,553 (AUSIMONT SRL.).

[0117] That is, the preferred reagent (CTA-X) is an iodinated and / or brominated organic chain transfer agent, more preferably having the formula R f (I) x (Br) y Those, among which R f is a (per)fluoroalkyl or (per)fluorochloroalkyl group containing 1 to 8 carbon atoms, while x and y are integers between 0 and 2, wherein 1≤x+y≤2; and most preferably has the formula R' f (I) x '(Br) y 'Those, where R' f is a perfluoroalkyl group containing 1 to 8 carbon atoms, while x' and y' are integers between 0 and 2, wherein 1≤x'+y'≤2, most preferably x'=2 and y'=0.

[0118] In the process of the present invention, the iodinated reagent (CTA-X) is preferably used, in particular the reagent having the formula R f (I)2 or R' f (I) 2, wherein R f and R' f As detailed above.

[0119] As is known in the art and as mentioned above, another way to introduce cure sites into fluoroelastomers is to copolymerize cure site monomers with the desired fluoromonomers. In this case, or where 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.

[0120] When a chain transfer agent is used, typically an amount of 1 to 100 mmol of I and / or Br per kg of fluoroelastomer is used.

[0121] The aqueous emulsion of the invention also contains monomers comprising VDF and one or more fluorinated monomers different from VDF, the composition of the monomers being variable during the polymerization process as known to the skilled person and being chosen in such a way as to obtain the desired fluoroelastomer A comprising 30% to 80% by moles of repeating units derived from vinylidene fluoride (VDF) and 20% to 70% by moles of repeating units derived from one or more fluorinated monomers different from vinylidene fluoride (VDF) as described above.

[0122] The other step in the method of the present invention is to initiate the polymerization of the monomers. This is typically achieved by contacting the monomers with a free radical initiator through a water-based reaction medium (typically the aqueous emulsion described above), which is kept stirred in a sealed reactor at a set pressure and temperature. As is common in free radical polymerization, after initiation of polymerization, the monomers and optionally the initiator and / or chain transfer agent are typically continuously fed in the reactor until the polymerization reaction is complete, so that at the end of the polymerization process, the total amount of free radical initiator and chain transfer agent (if present) is loaded into the reactor.

[0123] Once the polymerization reaction is complete, a stable latex comprising particles of fluoroelastomer A is obtained.

[0124] As mentioned above, in the process of the present invention, the emulsion polymerization is carried out in the absence of any added fluorinated surfactant.

[0125] Examples of fluorinated surfactants not used in the present invention are fluorinated surfactants that conform to the following formula:

[0126] R * -X B- (T + )

[0127] in

[0128] R * is a C5-C16 (per)fluoroalkyl chain or a (per)fluoropolyoxyalkylene chain containing one or more than one ether oxygen,

[0129] X B- Yes-COO - or -SO3 - ,

[0130] T + Selected from: H + NH4 + , and alkali metal ions.

[0131] In particular, the fluorinated surfactants used herein are those corresponding to the following general formula:

[0132]

[0133] Wherein X1, X2, and X3 are the same as or different from each other and are independently selected from H, F, and a C1-6 (per)fluoroalkyl group optionally containing one or more chain or non-chain 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 nonionic functional groups.

[0134] Exemplary embodiments of fluorinated surfactants which are not added in the process of the invention are, in particular: ammonium perfluorooctanoate; (per)fluoropolyoxyalkylenes terminated with one or more carboxyl groups, optionally salted with sodium, ammonium and alkali metals; and partially fluorinated alkyl sulfonates and compounds of the formula:

[0135]

[0136] wherein Xa is an alkali metal or ammonium moiety.

[0137] In a preferred embodiment, the method 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 sulfur-containing surfactants are not preferred because they may reduce the color quality of the resulting fluoroelastomer.

[0138] More generally, in order to obtain better color quality, it is preferred that the aqueous emulsions of the invention are substantially free of any compounds containing sulphur atoms, these compounds being considered both surfactant and non-surfactant compounds.

[0139] Anionic surfactants, cationic surfactants and nonionic surfactants can all be used herein provided that they do not contain fluorine atoms. Preferred surfactants for use herein are anionic surfactants and nonionic surfactants, more preferably nonionic surfactants and in particular surfactants based on polyethylene glycol (PEG) and polypropylene glycol (PPG) repeating units. Particularly preferred nonionic surfactants are PEG / PPG block copolymers, such as those manufactured by BASF under the trademark and by Solvay under the trade name Those that are sold.

[0140] When non-fluorinated surfactants are used, it is preferred that such non-fluorinated surfactants be passivated. The use of passivated surfactants allows for higher molecular weight polymers and faster initiation and polymerization times.

[0141] 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 previously. A preferred way to carry out the deactivation of the surfactant is to heat the surfactant together with the oxidizing agent in aqueous solution at a temperature at which the oxidizing agent is effective to generate free radicals. Preferably, at least at a temperature T h The surfactant is heated at a temperature T wherein the oxidant h The half-life of oxidants as a function of temperature can be found in the technical literature, for example in https: / / polymerdatabase.com / polymer%20chemistry / t-alf2.html .

[0142] More preferably, the surfactant is added at least h The temperature is maintained for 10 minutes or longer, preferably 10-120 minutes, more preferably 20-60 minutes.

[0143] Preferably, the deactivation of the surfactant is carried out before initiation of polymerization.

[0144] One method that can be used is to passivate the non-fluorinated surfactant prior to introduction into the aqueous emulsion of the present invention, either as a neat material or mixed with the other components of the emulsion, provided that no monomer is present during the passivation process.

[0145] A preferred method for forming the aqueous emulsion of the present invention containing a passivated surfactant comprises:

[0146] - first forming an aqueous mixture comprising said one or more dicarboxylic acids, said non-fluorinated surfactant and said oxidizing agent, wherein said aqueous mixture does not comprise monomers,

[0147] - then at least at temperature T h The aqueous mixture is heated at a temperature T wherein the oxidant is at the temperature T h and maintaining the temperature for 10 minutes or more, preferably 10-120 minutes, more preferably 20-60 minutes, thereby forming a passivated aqueous mixture, and then

[0148] - forming an aqueous emulsion comprising the passivating aqueous mixture, a free radical initiator, monomers comprising vinylidene fluoride (VDF) and one or more fluorinated monomers different from VDF, and optionally a chain transfer agent, wherein all components are as described above, and wherein the free radical initiator may be the same as or different from the oxidizing agent used in the passivation step.

[0149] Typically, the effective total amount of non-fluorinated surfactant in the aqueous emulsion of the present invention is at least 0.05 g, preferably 0.1 g, more preferably 0.2 g per liter of emulsion and at most 20 g, preferably at most 15 g, more preferably at most 10 g per liter of emulsion.

[0150] Advantageously, the process of the invention comprises polymerizing VDF and at least one further fluorinated monomer different from VDF as defined above in aqueous emulsion.

[0151] The process according to the invention can preferably be carried out continuously, or semi-batch or batchwise.

[0152] The process of the invention is carried out at a temperature which can be selected by a person skilled in the art, in particular based on the free radical initiator employed. Preferably, the process of the invention is carried out at a temperature of 40 to 120°C, more preferably 50 to 100°C.

[0153] The process of the present invention is preferably carried out at a pressure of between 10 and 60 bar, more preferably from 20 to 55 bar.

[0154] As stated, another object of the present invention is an aqueous latex free of fluorinated surfactants, comprising one or more dicarboxylic acids in acid or salt form, and particles of fluoroelastomer A, wherein the particles of fluoroelastomer A have an average particle size measured according to ISO 13321 of less than 400 nm, preferably less than 350 nm, more preferably less than 300, even more preferably less than 270 nm, most preferably less than 220 nm, and wherein the fluoroelastomer A:

[0155] - comprising 30% to 80% by mole of repeating units derived from VDF, 20% to 70% by mole of repeating units derived from one or more fluorinated monomers other than VDF

[0156] - having a Mooney viscosity (ML1+10 (121° C.)) of at least 10 MU;

[0157] - comprising -CH2OH chain ends in an amount of 0 to less than 10, preferably less than 5 mmol / kg of fluoroelastomer A.

[0158] In some embodiments, the 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 / kg of fluoroelastomer.

[0159] The latex can be produced by emulsion polymerization without the addition of any fluorinated surfactant as described above.

[0160] As described, 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), and / or a Mooney viscosity (ML1+10) at 121°C of at most 80, preferably at most 75, more preferably at most 70 MU, as determined according to ASTM D1646. In other words, fluoroelastomer (A) is a high molecular weight polymer, rather than a fluorowax or fluororubber having a finite molecular weight. This is an important feature, as techniques for making fluororubbers without the addition of fluorosurfactants may not provide a way to obtain such high molecular weight materials.

[0161] Furthermore, in another aspect, the present invention relates to a fluoroelastomer (A), wherein the fluoroelastomer (A):

[0162] - comprising 30% to 80% by mole of repeating units derived from VDF, 20% to 70% by mole of repeating units derived from one or more fluorinated monomers other than VDF

[0163] - having a Mooney viscosity (ML1+10 (121° C.)) of at least 10 MU;

[0164] - contains -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;

[0165] - comprising hydrogen-containing chain ends selected from the group consisting of -CF2H and -CF2CH3, said chain ends being present in an amount of 15 to 100 mmol / kg of fluoroelastomer A.

[0166] The fluoroelastomer can be produced by emulsion polymerization without adding any fluorinated surfactant.

[0167] Such fluoroelastomer (A) is advantageously obtained by coagulation according to standard techniques of a latex (comprising particles of fluoroelastomer (A) as described above), typically resulting in fluoroelastomer pellets or crumbs.

[0168] In yet another aspect, the present invention relates to a curable composition comprising such a fluoroelastomer (A), and a curing agent.

[0169] The curing agent may be chosen from all agents typically used for curing elastomers, for example it may be chosen from peroxides and in particular organic peroxides having at least two peroxide groups in their molecule.

[0170] The organic peroxide is selected from those capable of generating free radicals under curing conditions.

[0171] Among the commonly used organic peroxides, mention may be made of dialkyl peroxides such as, for example, di-tert-butyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane; dicumyl peroxide; dibenzoyl peroxide; di-tert-butyl perbenzoate; di[1,3-dimethyl-3-(tert-butylperoxy)butyl] carbonate.

[0172] The curable composition of the present invention may further comprise:

[0173] (a) a curing aid, the amount of which is generally in the range of 0.5-10 phr, preferably 1-7 phr, relative to the fluoroelastomer (A); among which 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-methyltrisiloxane; N,N'-bisallyldicyclo-oct-7-ene-disuccinimide (BOSA); a diene (OF) as described above, in particular a diene having the formula CH2=CH-(CF2) n -CH=CH2 dienes, triazines having the following general formula:

[0174] wherein X can independently be hydrogen, chlorine, fluorine, C1-C3 alkyl or perfluoroalkyl; n is an integer in the range of 2-20, preferably 4-12, more preferably 4-8. TAIC is particularly preferred as a curing aid;

[0175] (b) a metal compound in an amount ranging from 1 to 15 phr, 2 to 10 phr relative to the fluoroelastomer (A), chosen for example from oxides or hydroxides of divalent metals such as Mg, Zn, Ca or Pb, optionally in combination with a weak acid salt such as stearates, benzoates, carbonates, oxalates or phosphites of Ba, Na, K, Pb, Ca;

[0176] (c) Other conventional additives, such as thickeners, pigments, antioxidants, reinforcing agents (e.g. carbon black), stabilizers, etc.

[0177] Additional objects of the present invention are a method for making a cured part and a cured part obtained from the above curable composition.

[0178] The solidifying part may especially be selected from tubes, fittings, O-rings, hoses and the like.

[0179] In another aspect, the present invention relates to a method for making a cured part, said method comprising processing and curing a curable composition comprising at least one fluoroelastomer (A) and at least one organic peroxide.

[0180] The curable composition comprising the fluoroelastomer (A) can be manufactured into a desired shaped article, for example, by molding (injection molding, extrusion molding), calendaring or extrusion. The cured part can be subjected to vulcanization (or curing) during its own processing and / or in a subsequent step (post-treatment or post-curing).

[0181] Should the disclosure of any patents, patent applications, and publications incorporated herein by reference conflict with the description of the present application to the extent that a term may be unclear, the description of the present application shall take precedence.

[0182] The present invention will now be described in more detail with reference to the following examples, the purpose of which are merely illustrative and not limiting on the scope of the present invention.

[0183] Experimental part

[0184] Materials used

[0185] All polycarboxylic acids were from Sigma-Aldrich.

[0186] Galden D02, VDF, HFP, and TFE were obtained from Solvay Specialty Polymers Italia SpA.

[0187] Pluronic PE6200 is a commercial material from BASF.

[0188] Mooney viscosity:

[0189] Mooney viscosity (ML1+10) at 121° C. is measured according to ASTM D1646.

[0190] Determination of average particle size

[0191] The average particle size of the latex particles is measured according to ISO 13321 via light scattering.

[0192] End group determination

[0193] The end groups were identified and quantified by NMR and / or by infrared spectroscopy according to the method described in PIANCA, M., et al. J. Fluor. Chem. 1999, pp. 95-71. In the following tables, the qualifier "nd" is used to mean "not detectable", relating to chain ends having a concentration below the detection limit (i.e., below 0.05 mmol / Kg).

[0194] Example 1

[0195] After evacuation, in a 2.2 L vertical autoclave equipped with baffles and a stirrer operating at 650 rpm were introduced: 1.3 L of demineralized water, 1.3 g of pimelic acid, 1.8 grams of C4F8I2 (3 ml of a 33% w solution of C4F8I2 in Galden D02).

[0196] Then the autoclave is sealed and heated to 80 ℃ and keeps the whole duration of reaction at this temperature.By charging HFP monomer, the pressure of autoclave is increased by 9 bar.The gaseous mixture of following monomers is fed to autoclave so that pressure reaches 22 bar: by mole 70% vinylidene fluoride (VDF), by mole 19% hexafluoropropylene (HFP) and by mole 11% tetrafluoroethylene (TFE).Then the concentration of adding 35ml is 50g / l ammonium persulfate aqueous solution (corresponding to the elastomer of 14mmol 00 / kg).After initiation, continuously feed VDF / HFP / TFE mixture to keep constant pressure.Continue polymerization, until reaching the total monomer consumption of 550g.Then the autoclave is depressurized, vented and cooled.

[0197] Example 2

[0198] 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 of elastomer).

[0199] Example 3

[0200] 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 / kg of elastomer).

[0201] Example 4

[0202] 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 OO / kg of elastomer).

[0203] Example 5

[0204] 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.

[0205] Example 6

[0206] 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 OO / kg of elastomer).

[0207] Example 7

[0208] After evacuation, a 2.2 L vertical autoclave equipped with baffles and a stirrer operating at 650 rpm was 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 resulting mixture was heated at 70° C. for 60 minutes, after which 3 ml of a 33% w solution of C4F8I2 in Galden D02 was added.

[0209] Then the autoclave is sealed and heated to 80 ℃ and keeps the whole duration of reaction at this temperature.By charging HFP monomer, the pressure of autoclave is increased by 9 bar.The gaseous mixture of following monomers is fed to autoclave so that pressure reaches 22 bar: by mole 70% vinylidene fluoride (VDF), by mole 19% hexafluoropropylene (HFP) and by mole 11% tetrafluoroethylene (TFE).Then the concentration of adding 50ml is 50g / l ammonium persulfate aqueous solution (corresponding to the elastomer of 20mmol 00 / kg).After starting polymerization, continuously feed VDF / HFP / TFE mixture to keep constant pressure.Continue polymerization, until reaching the total monomer consumption of 550g.Then the autoclave is depressurized, vented and cooled.

[0210] Example 8c (comparative)

[0211] The same procedure as Example 1 was followed except that no dicarboxylic acid was added.

[0212] A portion of the latex obtained from Examples 1-9 was then coagulated to extract fluoropolymer crumb according to the following procedure:

[0213] In a glass beaker, 3 liters of demineralized water were heated to 60°C by means of a hot plate, and then 6 grams of aluminum sulfate [Al2(SO4)3] were added and mixed until completely dissolved. 250 ml of the latex obtained according to the procedure in Example 1 were then added to the beaker using a dropping funnel stirred by an overhead stirrer. Once all the latex had been added, the solution was left under stirring until the polymer had completely coagulated. The polymer was then washed with water and dried to obtain fluoroelastomer crumbs. The Mooney viscosity of the fluoroelastomer was measured on the dried fluoroelastomer crumbs.

[0214] The results shown in Table 1 below highlight how the process of the invention allows obtaining fluoroelastomer latexes having very low particle size and excellent stability, if compared with a reference product having the same composition and manufactured with a prior art process. The Mooney viscosity values ​​obtained confirm that the fluoroelastomers obtained in the process of the invention are suitable for use in many common applications of fluoroelastomers.

[0215] Table 1

[0216]

Claims

1. A method for producing a fluoroelastomer [fluoroelastomer A] in an aqueous reaction medium free of fluorinated surfactants, The method comprises: a: forming an aqueous emulsion comprising: i) one or more polycarboxylic acids having 2 to 22 carbon atoms in acid or salt form, iii) a free radical initiator, ii) monomers comprising vinylidene fluoride (VDF) and one or more fluorinated monomers different from VDF, iv) optionally a chain transfer agent; b: initiating polymerization of the monomers to form a fluoroelastomer [fluoroelastomer A] as a stable latex, in: The fluoroelastomer A comprises from 30% to 80% by mole of recurring units derived from vinylidene fluoride (VDF) and from 20% to 70% by mole of recurring units derived from one or more fluorinated monomers different from VDF.

2. The method according to claim 1, wherein The aqueous emulsion also includes one or more non-fluorinated surfactants.

3. The method according to claim 2, wherein: The one or more non-fluorinated surfactants are selected from nonionic surfactants, and wherein the aqueous emulsion does not contain a sulfur-containing surfactant.

4. The method according to claim 2 or 3, wherein: The one or more non-fluorinated surfactants are deactivated.

5. The method according to claim 3 or 4, wherein: The surfactant is a polyethylene glycol-polypropylene glycol block copolymer.

6. A method as claimed in any preceding claim, wherein The free radical initiator is selected from inorganic free radical initiators, preferably from persulfates.

7. A method as claimed in any preceding claim, wherein The one or more fluorinated monomers other than VDF are selected from hexafluoropropylene (HFP), tetrafluoroethylene (TFE), perfluoroalkyl vinyl ether (PAVE), and chlorotrifluoroethylene (CTFE).

8. The method of any preceding claim further comprising the additional step of coagulating the fluoroelastomer A and separating it from the latex as fluoroelastomer crumb.

9. An aqueous latex free of fluorinated surfactants, comprising one or more polycarboxylic acids having from 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 measured according to ISO 13321, and wherein the fluoroelastomer A: - contains 30% to 80% by mole of repeating units derived from VDF, 20% to 70% by mole of repeating units derived from one or more fluorinated monomers different from VDF, - having a Mooney viscosity (ML1+10 (121° C.)) of at least 10 MU, - contains -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.

10. The aqueous latex according to claim 9, wherein The fluoroelastomer A comprises hydrogen-containing chain ends selected from the group consisting of -CF2H and -CF2CH3, the amount of the chain ends being from 15 to 100 mmol / kg of the fluoroelastomer A.

11. A fluoroelastomer A having a Mooney viscosity (ML1+10 (121° C.)) of at least 10 MU; And includes: - 30% to 80% by mole of repeating units derived from VDF, 20% to 70% by mole of repeating units derived from one or more fluorinated monomers different from VDF, - 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, - hydrogen-containing chain ends selected from the group consisting of -CF2H and -CF2CH3, the amount of such chain ends being from 15 to 100 mmol / kg of fluoroelastomer A.

12. The fluoroelastomer of claim 11 produced by emulsion polymerization without the addition of any fluorinated surfactant.

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

14. A method for making a cured part, the method comprising processing and curing the curable composition of claim 13.

15. A cured part obtained by the method according to claim 14.

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