WO2024200225A1

WO2024200225A1 - Curable fluoroelastomer composition

Info

Publication number: WO2024200225A1
Application number: PCT/EP2024/057678
Authority: WO
Inventors: Terry Michael KITCHENS; Yu Shiraishi; Daniela BERTANI; Stefano Bossolo; Eliana Ieva
Original assignee: Solvay Specialty Polymers Italy SpA
Current assignee: Solvay Specialty Polymers Italy SpA
Priority date: 2023-03-27
Filing date: 2024-03-21
Publication date: 2024-10-03
Anticipated expiration: 2025-09-27
Also published as: KR20250162573A

Abstract

The invention pertains to certain fluoroelastomer compositions comprising (i) a fluoroelastomer (fluoroelastomer A), being obtained from an emulsion polymerization process performed in the absence of fluorinated surfactants, comprising iodine and/or bromine atoms and having a backbone comprising 40-80% by moles of recurring units derived from vinylidene fluoride (VDF), 20-60% by moles of recurring units derived from one or more additional fluorinated monomer different from VDF, (ii) one or more organic peroxide, (iii) one or more curing co-agent, (iv) one or more fatty acid salt. The composition results in cured parts with improved c-set performance with respect to the same compositions without the addition of a fatty acid salt.

Description

Curable fluoroelastomer composition

Technical Field

[0001] The present invention relates to novel peroxide curable fluoroelastomer compositions, based on fuoroelastomers which are manufactured without the use of fluorinated surfactants, as well as a process for producing fluoroelastomer moldings using the same.

Background Art

[0002] This application claims priority from the European Patent Application 23164295.0 filed on 2023-03-27, the whole content of this application being incorporated herein by reference for all purposes.

[0003] Fluoroelastomers based on vinylidene fluoride (also referred to as 1 ,1- difluoroethylene or VDF) are a class of high-performance materials with a diverse range of applications encompassing O-rings, valve stem seals, shaft seals, gaskets and hoses in chemical processing industry (CPI).

[0004] Typically, VDF-based fluoroelastomers are amorphous copolymers of VDF which are produced via emulsion polymerization processes, by reacting a water-soluble polymerization initiator in the presence of the fluorinated monomers and often one or more surfactant (also referred to as emulsifier). In the past fluorinated surfactants have been used as emulsifiers, however, in order to improve the environmental impact of the process, emulsion polymerization processes using non fluorinated surfactants have been developed. In more recent years also methods of making VDF based fluoroelastomers via emulsion polymerization without the use of any surfactant have been described e.g. in WO2019/002180.

[0005] The resulting fluoroelastomers are typically molded in the shape of the required object and then cured (the process being referred to also as “vulcanization”) in order to produce the final cured part.

[0006] It is understood that properties of final cured parts made from such fluoroelastomers are greatly influenced by the curing system employed, with peroxide-based curing being considered as delivering higher performances over bis-phenol-based ionic curing. [0007] In peroxide-based curing, a peroxide is added to the fluoroelastomer comprising, either as pendant groups in recurring units of the main chain, or as end-groups, certain cure sites which are able to react under radical condition, and to a polyfunctional unsaturated compound. Under the effect of heat, the peroxide generates radicals which promote reactions of the fluoroelastomer chain, activated through the cure sites, with the polyfunctional unsaturated compound for yielding a cured mass, with chemically interconnected polymer chains.

[0008] It has been observed that, in some cases, the curing of VDF based fluoroelastomers produced without the use of fluorinated surfactants, was less efficient than the curing of fluoroelastomers having the same composition in terms of monomers and cure sites but being produced with a traditional process using fluorinated surfactants. As detailed in the experimental section of this document, it has been observed in particular that the compression set (c-set) value of certain VDF based fluoroelastomers, having iodine/bromine cure sites and having being subject to peroxide based curing, was inferior when the VDF based fluoroelastomers were obtained from an emulsion process performed in the absence of fluorosurfactants.

[0009] At the moment it is unclear why this effect is observed, without being bound by theory we speculate that this effect may be due to a different distribution and type of chain end groups in the fluoroelastomer obtained from the process not employing fluorinated surfactants.

[0010] There is therefore a need to improve the curing performance of fluoroelastomer compositions wherein the fluoroelastomers are produced via emulsion polymerization without the use of fluorinated surfactants.

[0011 ] It is thus an object of the present invention to provide a fluoroelastomer composition wherein the fluoroelastomers are obtained from an emulsion polymerization process without the use of fluorinated surfactants, which, after peroxide based curing, has a comparable performance in terms of c-set value to a similar composition wherein the fluoroelastomers are obtained from a traditional emulsion process using fluorinated surfactants.

Summary of invention [0012] The present invention relates to a fluoroelastomer composition comprising:

(i) a fluoroelastomer (fluoroelastomer A), said fluoroelastomer A:

- being obtained from an emulsion polymerization process performed in the absence of fluorinated surfactants,

- comprising iodine and/or bromine atoms and

- having a backbone comprising 40-80% by moles of recurring units derived from vinylidene fluoride (VDF), 20-60% by moles of recurring units derived from one or more additional fluorinated monomer different from VDF,

(ii) one or more organic peroxide

(iii) one or more curing co-agent

(iv) one or more fatty acid salt.

[0013] The Applicant has surprisingly found that the addition of a fatty acid salt to the composition improves the c-set performance of the material after curing so that a composition containing fluoroelastomers being manufactures in the absence of fluorinated surfactant have essentially the same c-set performance as compositions containing fluoroelastomers manufactured using fluorinated surfactants.

Description of the embodiments

[0014] For the purposes of the present description and of the following claims:

- the use of parentheses around symbols or numbers identifying the formulae, for example in expressions like “fluoroelastomer (A)”, etc., has the mere purpose of better distinguishing the symbol or number from the rest of the text and, hence, said parenthesis can also be omitted;

- the expressions “fluorinated surfactant” “fluorinated monomer” and similar, are intended to encompass partially and fully fluorinated compounds, unless otherwise specified.

- the term “phr” as common in the elastomer industry means “parts per hundred rubber”, i.e. parts by weight per 100 parts by weight of elastomer. - the term “fluoroelastomer” indicates polymers serving as a base constituent for obtaining a true elastomer. Such polymers are amorphous polymers or polymers having a low degree of crystallinity (having a heat of fusion of less than 5 J/g, preferably of less than 3 J/g, more preferably of less than 1 J/g, as measured by ASTM D-3418) and a glass transition temperature (T_g) below room temperature. In most cases, the fluoroelastomer (A) has advantageously a T_g below 10°C, preferably below 5°C, more preferably 0°C.

[0015] True elastomers are defined by the ASTM, Special Technical Bulletin, No. 184 standard as materials capable of being stretched, at room temperature, to twice their intrinsic length and which, once they have been released after holding them under tension for 5 minutes, return to within 10 % of their initial length in the same time.

[0016] The compositions of the present invention comprises a fluoroelastomer A comprising 40-80% by moles of recurring units derived from vinylidene fluoride (VDF) and 20-60% by moles of recurring units derived from one or more additional fluorinated monomer different from VDF. Optionally fluoroelastomer A may also comprise recurring units derived from one or more ethylenically unsaturated monomer free from fluorine atom (hereafter, hydrogenated monomer) .

[0017] Non limitative examples of suitable fluorinated monomers different from VDF which can be used in the fluoroelastomer A of the present invention are notably:

(a) C2-C8 perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP);

(b) hydrogen-containing C2-C8 olefins, such as vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutene (HFIB), perfluoroalkyl ethylenes of formula CH2 = CH-Rf, wherein Rf is a Ci-Ce perfluoroalkyl group;

(c) C2-C8 fluoroolefins comprising at least one of iodine, chlorine and bromine, such as chlorotrifluoroethylene (CTFE);

(d) (per)fluoroalkylvinylethers (PAVE) of formula CF2 = CFORf, wherein Rf is a C1-C6 (per)fluoroalkyl group, preferably CF3, C2F5, C3F7;

(e) (per)fluoro-oxy-alkylvinylethers of formula CF2 = CFOX, wherein X is a C1-C12 ((per)fluoro)-oxyalkyl comprising catenary oxygen atoms, e.g. the perfluoro-2-propoxypropyl group;

(f) (per)fluorodioxoles having formula :

wherein each of Rf3, Rf4, Rfs, Rre, equal to or different from each other, is independently selected from the group consisting of fluorine atom and C1- Ce (per)fluoroalkyl groups, optionally comprising one or more than one oxygen atom, such as notably -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3; preferably, perfluorodioxoles;

(g) (per)fluoro-methoxy-vinylethers (MOVE, hereinafter) having formula: CF₂=CFOCF₂OR_f2 wherein Rt2 is selected from the group consisting of C-i-Ce (per)fluoroalkyls; Cs-Ce cyclic (per)fluoroalkyls; and C2-C6 (per)fluorooxyalkyls, comprising at least one catenary oxygen atom; Rt2 is -CF2CF3 (M0VE1 ); -CF2CF2OCF3 (M0VE2); or -CF3 (M0VE3).

[0018] Examples of optional hydrogenated monomers are C2-C8 non-fluorinated olefins (Ol), for example ethylene, propylene, 1 -butene, diene monomers, styrene monomers. Such optional hydrogenated monomers, if present, preferably represent less than 20%by moles, preferably less than 10% by moles, more preferably less than 5% by moles based on the total recurring units of the fluoroelastomer A.

[0019] Optionally, fluoroelastomer (A) also comprises recurring units derived from one or more bis-olefin [bis-olefin (OF)] having general formula :

wherein Ri , R2, R3, R4, Rs and Re, equal or different from each other, are H or C1-C5 alkyl; Z is a linear or branched C1-C18 hydrocarbon radical (including alkylene or cycloalkylene radical), optionally containing oxygen atoms, preferably at least partially fluorinated, or a (per)fluoropolyoxyalkylene radical, e.g. as described in EP 661304 A (AUSIMONT SPA) 5/07/1995 .

[0020] The one or more bis-olefin (OF), if present, is preferably selected from the group consisting of those complying with formulae (OF-1 ), (OF-2) and (OF-3) :

(OF-1 )

wherein j is an integer between 2 and 10, preferably between 4 and 8, and R1 , R2, R3, R4, equal or different from each other, are H, F or C1-5 alkyl or (per)fluoroalkyl group;

(OF-2)

wherein each of A, equal or different from each other and at each occurrence, is independently selected from F, Cl, and H; each of B, equal or different from each other and at each occurrence, is independently selected from F, Cl, H and ORB, wherein RB is a branched or straight chain alkyl radical which can be partially, substantially or completely fluorinated or chlorinated; E is a divalent group having 2 to 10 carbon atom, optionally fluorinated, which may be inserted with ether linkages; preferably E is a -(CF2)m- group, with m being an integer from 3 to 5; a preferred bis-olefin of (OF-2) type is F2C=CF-O-(CF2)5-O-CF=CF2. (OF-3)

wherein E, A and B have the same meaning as above defined; R5, R6, R7, equal or different from each other, are H, F or C1-5 alkyl or (per)fluoroalkyl group.

[0021] When one or more bis-olefin is employed, the resulting fluoroelastomer A typically comprises from 0.01 % to 5% by moles of units deriving from the one or more bis-olefin with respect to the total amount of units of said fluoroelastomer A.

[0022] Exemplary fluoroelastomers (A) which can be used in the composition of the present invention are those having following monomers composition (in mol %, with respect to the total moles of recurring units) :

(i) vinylidene fluoride (VDF) 40-80 %, hexafluoropropene (HFP) IQ- 45 %, tetrafluoroethylene (TFE) 0-30 %, (per)fluoroalkylvinylethers (PAVE) 0-15 %; bis-olefin (OF): 0-5 %;

(ii) vinylidene fluoride (VDF) 50-80 %, (per)fluoroalkylvinylethers (PAVE) 5-50 %, tetrafluoroethylene (TFE) 0-20 %, bis-olefin (OF): 0-5 %;

(viii) vinylidene fluoride (VDF) 40-85 %, (per)fluoro-methoxy-vinylethers (MOVE) 5-40 %, (per)fluoroalkylvinylethers (PAVE) 0-30 %, tetrafluoroethylene (TFE) 0-40 %, hexafluoropropene (HFP) 0-30 %; bis- olefin (OF): 0-5 %.

[0023] The fluoroelastomer (A) comprises iodine and/or bromine atoms; the selection among iodine/bromine is not particularly critical, provided that they ensure adequate reactivity in curing. Iodine is nevertheless generally preferred.

[0024] These iodine or bromine atoms can be comprised in the fluoroelastomer (A) as pending groups bound to the backbone of the fluoroelastomer (A) polymer chain (by means of incorporation in the fluoroelastomer (A) chain of recurring units derived from monomers having iodine and/or bromine atoms, referred to as cure-site containing recurring units) and/or can be comprised as terminal groups of said polymer chain.

[0025] Among cure-site containing recurring units, mention can be notably made of:

(CSM-1 ) iodine or bromine containing monomers of formula:

wherein each of AHT, equal to or different from each other and at each occurrence, is independently selected from F, Cl, and H; Bnf is any of F, Cl, H and OR^HfB, wherein R^HfB is a branched or straight chain alkyl radical which can be partially, substantially or completely fluorinated or chlorinated; each

equal to or different from each other and at each occurrence, is independently a covalent bond or an oxygen atom; EHT is a divalent group having 2 to 10 carbon atom, optionally fluorinated; RHT is a branched or straight chain alkyl radical, which can be partially, substantially or completely fluorinated; and RHT is a halogen atom selected from the group consisting of Iodine and Bromine; which may be inserted with ether linkages; preferably E is a -(CF2)m- group, with m being an integer from 3 to 5;

(CSM-2) ethylenically unsaturated compounds comprising cyanide groups, possibly fluorinated.

[0026] Among cure-site containing monomers of type (CSM1 ), preferred monomers are those selected from the group consisting of:

[0027] (CSM1-A) iodine-containing perfluorovinylethers of formula:

with m being an integer from 0 to 5 and n being an integer from 0 to 3, with the provision that at least one of m and n is different from 0, and Rfi being F or CF₃; (as notably described in patents US4745165 (AUSIMONT S.P.A.) US4564662 (MINNESOTA MINING) and EP199138 A (DAIKIN IND., LTD.); and [0028] (CSM-1 B) iodine-containing ethylenically unsaturated compounds of formula:

CX1X2=CX3-(CF₂CF2)_P-I wherein each of X1 , X2 and X3, equal to or different from each other, are independently H or F; and p is an integer from 1 to 5; among these compounds, mention can be made of CH2=CHCF2CF2l, l(CF₂CF₂)2CH=CH2, ICF₂CF₂CF=CH2, l(CF₂CF2)2CF=CH₂;

[0029] (CSM-1 C) iodine-containing ethylenically unsaturated compounds of formula:

CHR=CH-Z-CH₂CHR-I wherein R is H or CH3, Z is a C1-C18 (per)fluoroalkylene radical, linear or branched, optionally containing one or more ether oxygen atoms, or a (per)fluoropolyoxyalkylene radical; among these compounds, mention can be made of CH₂=CH-(CF2)4CH₂CH2l, CH₂=CH-(CF2)6CH₂CH2l, CH2=CH-(CF₂)8CH₂CH2l, CH2=CH-(CF₂)2CH₂CH2l;

[0030] (CSM-1 D) bromo and/or iodo alpha-olefins containing from 2 to 10 carbon atoms such as bromotrifluoroethylene or bromotetrafluorobutene described, for example, in US 4035565 (DU PONT) or other compounds bromo and/or iodo alpha-olefins disclosed in US 4694045 (DU PONT) .

[0031] According to a first embodiment, the iodine and/or bromine atoms are comprised as pending groups bound to the backbone of the fluoroelastomer polymer chain. The fluoroelastomer according to this embodiment generally comprises recurring units derived from iodine or bromine containing monomers (CSM-1 ) in amounts of 0.05 to 5 mol per 100 mol of all other recurring units of the fluoroelastomer (A), so as to advantageously ensure iodine and/or bromine weight content to meet requirement for achieving adequate curing rate and crosslinking density.

[0032] According to a second preferred embodiment, the iodine and/or bromine atoms are comprised as terminal groups of the fluoroelastomer (A); the perfluoroelastomer according to this embodiment is generally obtained by addition to the polymerization medium during fluoroelastomer manufacture of anyone of:

- iodinated and/or brominated chain-transfer agent(s); suitable chain-chain transfer agents are typically those of formula Rf(l)_x(Br)_y, in which Rf is a (per)fluoroalkyl or a (per)fluorochloroalkyl containing from 1 to 8 carbon atoms, while x and y are integers between 0 and 2, with 1 < x+y < 2 (see, for example, patents US 4243770 (DAIKIN IND LTD ) 6/01/1981 and US 4943622 (NIPPON MEKTRON KK ) 24/07/1990 ); and

- alkali metal or alkaline-earth metal iodides and/or bromides, such as described notably in patent US 5173553 (AUSIMONT SRL) 22/12/1992 .

[0033] This said, preferred agents (CTA-X) are iodinated and/or brominated organic chain-transfer agent(s), more preferably those of formula Rf(l)x(Br)_y, in which R_f is a (per)fluoroalkyl or a (per)fluorochloroalkyl containing from 1 to 8 carbon atoms, while x and y are integers between 0 and 2, with 1 < x+y < 2, and most preferably those of formula R’_f(l)x’(Br)y’, in which R’_f is a perfluoroalkyl containing from 1 to 8 carbon atoms, while x’ and y’ are integers between 0 and 2, with 1 < x’+y’ < 2, most preferably x’ = 2 and y’=0.

[0034] In the method of the present invention, agents (CTA-X) which are iodinated are preferred, in particular those of formula Rf(l)2 or R’f(l)2 with Rf and R’f being as above detailed.

[0035] When using a chain transfer agent the amount typically used is of from 1 to 100 mmol of I and/or Br per kg of fluoroelastomer.

[0036] The fluoroelastomer (A) of the invention comprises advantageously iodine and/or bromine atoms in an amount of 0.001 to 10% wt., preferably 0.05 to 5% wt., more preferably 0.1 to 2% wt., even more preferably from 0.1 to 1% wt with respect to the total weight of the fluoroelastomer (A).

[0037] As mentioned above the fluoroelastomer A of the present invention is obtained from an emulsion polymerization process performed in the absence of fluorinated surfactants. Preferably in the absence of surfactants including fluorinated and non fluorinated surfactants.

[0038] The preparation method for the fluoroelastomer A typically includes a step wherein an aqueous reaction medium is formed within a sealable reactor, the reaction medium being free from fluorinated surfactants, and comprising a free-radical initiator, optionally a chain transfer agent, preferably a iodine containing chain transfer agent. The reactor is typically sealed and pressurized with monomer gas comprising VDF while the other monomers are added as gas or liquids depending on the type of monomers. Typically the polymerization is performed at a temperature from 40°C to 120°C, more preferably from 50° C to 100°Cand at a pressure between 10 and 60 bars, more preferably from 20 to 55 bars.

[0039] While the choice of the radical initiator is not particularly limited, it is understood that those suitable for the process according to the invention are selected from compounds capable of initiating and/or accelerating the polymerization process.

[0040] Inorganic radical initiators may be used and include, but are not limited to, persulfates such as sodium, potassium and ammonium persulfates, permanganates such as potassium permanganate.

[0041] Also, organic radical initiators may be used and include, but are not limited to, the followings: acetylcyclohexanesulfonyl peroxide; diacetylperoxydicarbonate; dialkylperoxydicarbonates such as diethylperoxydicarbonate, dicyclohexylperoxydicarbonate, di-2- ethylhexylperoxydicarbonate; tert-butylperneodecanoate; 2,2'-azobis(4- methoxy-2,4dimethylvaleronitrile; tert-butylperpivalate; dioctanoylperoxide; dilauroyl-peroxide; 2,2'-azobis (2,4-dimethylvaleronitrile); tert-butylazo-2-cyanobutane; dibenzoylperoxide; tert-butyl-per-2ethylhexanoate; tert-butylpermaleate; 2,2'-azobis(isobutyronitrile); bis(tert-butylperoxy)cyclohexane; tert-butyl- peroxyisopropylcarbonate; 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.

[0042] Other suitable radical initiators notably include halogenated radical initiators such as chlorocarbon based and fluorocarbon based acyl peroxides such as trichloroacetyl peroxide, bis(perfluoro-2-propoxy propionyl) peroxide, [CF3CF2CF2OCF(CF3)COO]2 , perfluoropropionyl peroxides, (CF3CF₂CF₂COO)2 , (CF₃CF2COO)₂ , {(CF3CF2CF2)-[CF(CF3)CF₂O]m-CF(CF3)-COO}2 wherein m = 0-8, [CICF₂(CF₂)nCOO]2 , and [HCF₂(CF₂)nCOO]2 wherein n = 0-8; perfluoroalkyl azo compounds such as perfluoroazoisopropane, [(CF₃)₂CFN=]2 , RN=NRn , wherein Rn 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.

[0043] Redox systems, comprising at least two components forming a redox couple, such as dimethylaniline-benzoyl peroxide, diethylaniline-benzoyl peroxide and diphenylamine-benzoyl peroxide may also be used as radical initiators to initiate the polymerization process.

[0044] A particularly suitable method to prepare a fluoroelastomer A via emulsion polymerization without the use of surfactants and in particular without the use of fluorinated surfactants is the method described in WO201 9/002180 (Solvay Specialty Polymers Italy S.p.A) wherein the polymerization process is performed in the presence of a redox initiating system comprising at least one organic radical initiator and at least one compound bearing at least one sulfinic acid group..

[0045] Examples of fluorinated surfactants which are not used in the present invention are fluorinated surfactants complying with the following formula: R‘-X^B’(T⁺) wherein

R* is a C5-C16 (per)fluoroalkyl chain or a (per)fluoropolyoxyalkylenic chain including one or more than one ethereal oxygen, X^B- is -COO- or -SO3-,

T⁺ is selected from: H⁺, NH4⁺, and an alkaline metal ion.

[0046] Specifically fluorinated surfactants which are not used herein are those corresponding to the general formula:

[0047] wherein Xi, X2, X3, equal or different from each other are independently selected among H, F, and C1 -6 (per)fluoroalkyl groups, optionally comprising 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; Y is a hydrophilic function selected among anionic functionalities, cationic functionalities and non-ionic functionalities.

[0048] Exemplary embodiments of fluorinated surfactants which are not added in the method of the present invention are notably: ammonium perfluorooctanoate; (per)fluoropolyoxy-alkylenes ended with one or more carboxylic groups, optionally salified with sodium, ammonium and alkaline metals; and partially fluorinated alkylsulphonates and compounds of formula:

wherein Xa is an alkaline metal or ammonium moiety.

[0049] The composition of the invention comprises one or more organic peroxide (0), and one or more curing co-agent (II) which together form a cross linking system which is able to promote the curing of the fluoroelastomer A.

[0050] The choice said one or more organic peroxide (0) is not particularly critical provided that the same is capable of generating radicals with the assistance of a transition metal catalyst. Among most commonly used peroxides, mention can be made of:

- di(alkyl/aryl) peroxides, including for instance di-tert-butyl peroxide, 2,5- dimethyl-2,5-bis(tert-butylperoxy)hexane, di(t- butylperoxyisopropyl)benzene, dicumyl peroxide;

- diacyl peroxides, including dibenzoyl peroxide, disuccinic acid peroxide, di(4-methylbenzoyl)peroxide, di(2,4-dichlorobenzoyl)peroxide, dilauroyl peroxide, decanoyl peroxide;

- percarboxylic acids and esters, including di-tert-butyl perbenzoate, t- butylperoxy-2-ethylhexanoate, 1 ,1 ,3,3-tetramethylethylbutyl peroxy-2- ethylhexanoate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane; - peroxycarbonates including notably di(4-t- butylcyclohexyl)peroxydicarbonate, di(2-phenoxyethyl)peroxydicarbonate, bis[1 ,3-dimethyl-3-(tert-butylperoxy)butyl] carbonate, t- hexylperoxyisoproprylcarbonate, t-butylperoxyisopropylcarbonate,

- perketals such as 1 , 1-bis(tert-butylperoxy)cyclohexane and 2, 2- bis(tertbutylperoxy)butane;

- ketone peroxides such as cyclohexanone peroxide and acetyl acetone peroxide;

- organic hydroperoxides such as cumene hydroperoxide, tert-butyl hydroperoxide, methylethylketone peroxide (otherwise referred to as 2-[(2- hydroperoxybutan-2-yl)peroxy]butane-2-peroxol) and pinane hydroperoxide;

- oil-soluble azo initiators such as 2, 2'-azobis (4-methoxy-2. 4-dimethyl valeronitrile), 2, 2'-azobis (2.4-dimethyl valeronitrile), 2,2'- azobis(isobutyronitrile), 2, 2'-azobis(2-cyano-2-butane), dimethyl-2, 2'- azobisdimethyli sobutyrate, dimethyl-2, 2'-azobis(2-methylpropionate), 2,2'- azobis(2-methylbutyronitrile), 1 ,1'-azobis(cyclohexane-l-carbonitrile), 2, 2'- azobis[N-(2-propenyl)-2-methylpropionamide], 1 -[(1 -cyano-1 -methyl ethyl)azo]formamide, 2, 2'-azobis(N-cyclohexy1 -2-methylpropionamide), 2,2'-azobis(i sobutyronitrile), 2,2'-azobis(2-cyano-2-butane), dimethyl-2, 2'- azobisdimethylisobutyrate, 1 ,1'-azobis(cyclohexanecarbonitrile), 2-(t- butylazo)-2-cyanopropane, 2,2'-azobis[2-methyl-N-(1 , 1)- bis(hydroxymethyl)-2-hydroxyethyl]propionamide, 2, 2'-azobis[2-methyl-N- hydroxyethyl]-proprionamide, 2, 2'-azobis(N, N'- dimethyleneisobutyramine), 2, 2'-azobis(2-methyl-N-[1 ,1- bis(hydroxymethyl)-2-hydroxyethyl] propionamide), 2,2'-azobis(2-methyl- N-[1 ,1-bis(hydroxymethyl) ethyl] proprionamide), 2, 2'-azobis[2-5 methyl- N-(2-hydroxyethyl) propionamide], 2,2'-azobis(isobutyramide) dihydrate, 2,2'-azobis(2, 2, 4-trimethylpentane), 2, 2'-azobis(2-methylpropane).

[0051] Other suitable peroxide systems are those described, notably, in patent applications EP 136596 A (MONTEDISON SPA ) 10/04/1985 and EP 410351 A (AUSIMONT SRL ) 30/01/1991 , whose content is hereby incorporated by reference. [0052] Choice of the most appropriate peroxide depending upon curing conditions (time, temperature) will be done by one of ordinary skills in the art.

[0053] The amount of peroxide (0) in the composition of this embodiment is generally of 0.1 to 15 phr, preferably of 0.2 to 12 phr, more preferably of 1.0 to 7.0 phr, (“phr” being intended as common in the art as “parts of peroxide by weight relative to 100 parts by weight of fluoroelastomer A”).

[0054] The one or more curing co-agent II is selected from polyunsaturated compounds. The expression “polyunsaturated compound” is hereby intended to designate a compound comprising more than one carboncarbon unsaturation.

[0055] Compounds (II) may be selected from compounds comprising two carboncarbon unsaturations, compounds comprising three carbon-carbon unsaturations and compounds comprising four or more than four carboncarbon unsaturations.

[0056] Among compounds (II) comprising two carbon-carbon unsaturations, mention can be made of bis-olefins [bis-olefin (OF)], as above detailed, preferably selected from those complying with any of formulae (OF-1 ), (OF-2) and (OF-3), as above detailed.

[0057] Among compounds (II) comprising three carbon-carbon unsaturations, mention can be made of:

[0058] (i) - tri-substuituted cyanurate compounds of general formula:

wherein each of R_cy, equal to or different from each other and at each occurrence, is independently selected from H or a group -Rrcy or-ORrcy , with Rrcy being C1-C5 alkyl, possibly comprising halogen(s), and each of Jcy, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms; within this group preferred compounds are triallyl cyanurate and trivinyl cyan urate;

[0059] (ii) - tri-substuituted isocyanurate compounds of general formula:

wherein each of Risocy, equal to or different from each other and at each occurrence, is independently selected from H or a group -Rrisocyor-ORrisocy , with Rrisocy being C1-C5 alkyl, possibly comprising halogen(s), and each of Jisocy, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms; within this group preferred compounds are triallyl isocyanurate (otherwise referred to as “TAIC”), trivinyl isocyanurate, with TAIC being the most preferred;

[0060] (iii) - tri-substituted triazine compounds of general formula:

wherein each of Raz, equal to or different from each other and at each occurrence, is independently selected from H or a group -R_raz or -ORraz , with Rraz being C1-C5 alkyl, possibly comprising halogen(s), and each of J_az, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms; tri-substituted triazine compounds include notably compounds disclosed in EP 0860436 A (AUSIMONT SPA) 26/08/1998 and in WO 97/05122 (DU PONT) 13/02/1997 ;

[0061 ] (iv) - tri-substituted phosphite compounds of general formula:

wherein each of R_Ph, equal to or different from each other and at each occurrence, is independently selected from H or a group -Rrph or -ORrph, with R_rPh being C1-C5 alkyl, possibly comprising halogen(s), and each of J_Ph, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms; preferred compounds in this group include tri-allyl phosphite; [0062] (v) - tri-substituted alkyltrisiloxanes of general formula:

wherein each of Rsi, equal to or different from each other and at each occurrence, is independently selected from H or a group -Rrsi or-ORrsi, with Rrsi being C1-C5 alkyl, possibly comprising halogen(s), each of R’si, equal to or different from each other and at each occurrence, is independently selected from C1-C5 alkyl groups, possibly comprising halogen(s), and each of Jsi, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms; preferred compounds in this group include 2,4,6-trivinyl methyltrisiloxane and 2,4,6-trivinyl ethyltrisiloxane;

[0063] (vi) - N,N-disubstituted acrylamide compounds of general formula:

wherein each of Ran, equal to or different from each other and at each occurrence, is independently selected from H or a group -Rran or -ORran, with Rran being C1-C5 alkyl, possibly comprising halogen(s), and each of Jan, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms; preferred compounds in this group include N,N-diallylacrylamide.

[0064] Among compounds (II) comprising four or more carbon-carbon unsaturations, mention can be made of tris(diallylamine)-s-triazine of formula:

hexa-allylphosphoramide, N, N, N', N'-tetra-allyl terephthalamide, N,N,N',N'- tetra-allyl malonamide.

[0065] It is generally preferred for the compound (II) to be selected from the group consisting of bis olefins (OF), as above detailed, in particular olefins of (OF-1 ) type; and tri-substuituted isocyanurate compounds, as above detailed, in particular TAIC.

[0066] The amount of the compound (II) ranges normally from 0.1 to 20 phr, preferably from 1 to 15 phr, more preferably from 1 to 10 phr (“phr” being intended as common in the art as “parts of polyunsaturated compound II by weight relative to 100 parts by weight of fluoroelastomer A”).

[0067] Another component of the composition of the present invention is one or more fatty acid salt.

[0068] Preferably the one or more fatty acid salt is selected from metal salts of fatty acids. Metals for the metal salts of fatty acids are for example alkali metals, alkaline earth metals, transition metals. Preferred metals are sodium, potassium, calcium, magnesium, barium, zinc, aluminum. Suitable carbon chains for the fatty acids salts are preferably C12-28, more preferably C14-C26, even more preferably C16-C24, most preferably C16- C22.

[0069] The fatty acid metal salt may be for example a salt of behenic acid (C22 ), eicosenoic acid (C20), stearic acid (C18 ), palmitic acid (C16 ), myristic acid (C14 ) or lauric acid (C12 ). Among them, salts of stearic acid and palmitic acid are preferred, stearic acid metal salts are more preferred.

[0070] Most preferred fatty acid metal salts for use herein are sodium stearate, potassium stearate, barium stearate, calcium stearate, zinc stearate, magnesium stearate or aluminum stearate.

[0071 ] The amount of fatty acid salt which can be used in the composition of the invention is typically from 0.05 to 5 phr, preferably from 0.1 to 2 phr, more preferably from 0.1 to 1.5 phr, most preferably from 0.2 to 1 phr.

[0072] The composition of the invention may further additionally comprise ingredients which maybe commonly used for the peroxide curing of fluoroelastomers; more specifically, the composition may generally further comprise

(a) one or more than one metallic basic compound, in amounts generally of from 0.5 to 15.0 phr, and preferably of from 1 to 10 phr, more preferably 1 to 5 phr, relative to 100 weight parts of fluoroelastomer (A); metallic basic compounds are generally selected from the group consisting of (j) oxides or hydroxides of divalent metals, for instance oxides or hydroxides of Mg, Zn, Ca or Pb, and (jj) metal salts of a weak acid, for instance Ba, Na, K, Pb, Ca stearates, benzoates, carbonates, oxalates or phosphites;

(b) one or more than one acid acceptor which is not a metallic basic compound, in amounts generally of from 0.5 to 15.0 phr, and preferably of from 1 to 10.0 phr, more preferably 1 to 5 phr, relative to 100 weight parts of fluoroelastomer (A); these acid acceptors are generally selected from nitrogen-containing organic compounds, such as 1 ,8-bis(dimethylamino)naphthalene, octadecylamine, etc., as notably described in EP 708797 A (DU PONT ) 1/05/1996 .

[0073] In general the presence of metallic basic oxides is non preferred because it has been found that in certain conditions it may reduce the chemical resistance of the cured fluoroelastomer part in particular with respect to resistance to acids. [0074] The composition of the invention may comprise other conventional additives, such as fillers, thickeners, pigments, antioxidants, stabilizers, processing aids/plasticizers, and the like. Carbon black is often used as an advantageous reinforcing system.

[0075] In another aspect, the invention pertains to a method for making a composition as described above, the method including making said fluoroelastomer A, comprising iodine and/or bromine atoms and having a backbone comprising 40-80% by moles of recurring units derived from vinylidene fluoride (VDF), 20-60% by moles of recurring units derived from one or more additional fluorinated monomer different from VDF, using an emulsion polymerization process performed in the absence of fluorinated surfactants. The method also including mixing said fluoroelastomer A with one or more organic peroxide, one or more curing co-agent and one or more fatty acid salt.

[0076] In another aspect, the invention pertains to a method for fabricating shaped articles comprising curing the composition of the invention, as above described.

[0077] The composition can be fabricated, e.g. by molding (injection molding, extrusion molding), calendering, coating, screen-printing, forming-in-place, into the desired shaped article, which is advantageously subjected to vulcanization (curing) during the processing itself and/or in a subsequent step (post-treatment or post-cure), advantageously transforming the relatively soft, weak, fluoroelastomeric uncured composition into a finished article made of non-tacky, strong, insoluble, chemically and thermally resistant cured fluoroelastomer material.

[0078] The invention also pertains to cured articles obtained from the composition, as above detailed. Said cured articles are generally obtained by molding and curing the fluoroelastomer composition, as above detailed. These cured articles may be sealing articles, including O(square)-rings, packings, gaskets, diaphragms, shaft seals, valve stem seals, piston rings, crankshaft seals, cam shaft seals, and oil seals or maybe piping and tubings, in particular flexible hoses or other items, including conduits for delivery of hydrocarbon fluids and fuels.

[0079] The invention further pertains to assemblies including a substrate and at least one cured article, as above detailed.

[0080] The choice of substrate is not particularly limited: the composition of the invention is such to ensure adhesion to a variety of metal and non-metal substrates, including notably plastic and rubber substrates, among which polyamide substrates, silicone substrates can be notably mentioned.

[0081] The assemblies of the invention are generally manufactured by contacting the composition (C), as above detailed, with a substrate, and subjecting the said composition (C) to vulcanization (curing) while in contact with the said substrate, and optionally exposing the assembly to a subsequent thermal treatment step (post-treatment or post-cure).

[0082] The Applicant has surprisingly found that cured article obtained from the composition of the invention have an reduced c-set value (which reflects a more effective and improved curing process) if compared with cured articles obtained from the same composition wherein the fatty acid salt is not included.

[0083] Therefore a further aspect of the present invention is the use of fatty acid salt to reduce the c-set value of cured materials obtained from curing composition comprising:

(i) a fluoroelastomer (fluoroelastomer A), said fluoroelastomer A:

- comprising iodine and/or bromine atoms and

(ii) one or more organic peroxide,

(iii) one or more curing co-agent.

[0084] Should the disclosure of any of the patents, patent applications, and publications that are incorporated herein by reference conflict with the present description to the extent that it might render a term unclear, the present description shall take precedence.

[0085] The present invention will be now described in more detail with reference to the following examples, whose purpose is merely illustrative and not limitative of the scope of the invention.

EXAMPLES

[0086] Materials used:

[0087] Fluoroelastomer 1 - having the following molar composition VDF 70%- HFP 19%- TFE 16% and a iodine content of 0.4% by weight, being prepared as follows:

In a 22L vertical autoclave, equipped with a stirrer working at 450 rpm, were introduced after evacuation 11 .5 L of demineralized water. The autoclave was then heated at 80°C and maintained at such temperature for the entire duration of the reaction. The pressure of the autoclave was increased by 13.7 bar by feeding HFP monomer. A gaseous mixture of the following monomers was fed to the autoclave so as to bring the pressure to 26 bar: VDF 70.5% by moles, HFP 19% by moles, TFE 11 % by moles. Then 10.61 g of C4F8I2 and 0.90g of bis-olefin of formula H₂C=CH-(CF₂)6-CH=CH2 were introduced. A 8.22g/l solution of t-butyl hydroperoxide in demineralized water was pumped in the autoclave at a constant feed rate. Simultaneously, but separately, a 23.5 g/l of solution of Bruggolite type E 28 in demineralized water was pumped in the autoclave at essentially similar feed rate. After initiation, the VDF/HFP/TFE mixture was continuously fed to keep a constant pressure, and a total of 16.49 g of bis- olefin were added in 19 steps. After the instantaneous monomer conversion has exceeded 2000g/h, TBHP and Bruggolite E28 feed rate were decreased of about 25% and kept constant for the remainder of the reaction. At a monomer conversion of 1056g, 16.3 g of C4F8l₂ were added. A final aliquot of 8.98g of C4F8l₂ was introduced at a monomer conversion of 4224g.

The polymerization was continued until an overall monomer consumption of 5280g was reached after 212 minutes; then the autoclave was depressurized, vented and cooled. The obtained latex has a solid content of 26.6% by weight. After coagulation with a solution of Al2(SO4)3 and drying, a Mooney viscosity (ML) (1 +10) at 121 °C of 22 was measured on the so obtained fluoroelastomer crumbs.

[0088] Fluoroelastomer 2 - having the same molar composition and Iodine content of fluoroelastomer 1 but being prepared via emulsion polymerization in the presence of fluorosurfactant. Same procedure as in the fluoroelastomer 1 was followed, but with the use of 2.5 g of ammonium persulfate as initiator (instead of E28/TBHP redox initiator) and the use of 105ml of microemulsion, previously obtained by mixing 8.8 ml of perfluoropolyoxyalkylene having acidic end groups of formula: CF2CIO(CF2-CF(CF3)O)n(CF2O)mCF2COOH, wherein n/m = 10, having average molecular weight of 600, 5.6 ml of a 30% v/v NH4OH aqueous solution, 20.0 ml of demineralized water and 5.5 ml of GALDEN D02 perfuoropolyether of formula: CF3O(CF2CF(CF3)O)n(CF2O)mCF3 with n/m = 20, having average molecular weight of 450.

Fluoroelastomers 1-2 were obtained from Solvay Specialty Polymers Italy S.p.A

Bruqqolite E28: was obtained from Bruggermann Organic peroxide: 2,5-dimethyl-2,5-di(terbutylperoxy)hexane from Arkema. Curing co-aqent: Triallylisocianurate (TAIC) from Degussa.

Carbon black N-990: from Cancarb.

Stearic acid and all stearates: were obtained from Faci Group. Sodium Dodecylsulfate: was obtained from Sigma Aldrich

[0089] For all examples Fluoroelastomers were compounded with the additives as detailed in the following table in an open mill. O - rings ( size class = 214 ) and cured in a pressed mould for 10 minutes at 180°C and then post - treated in an air circulating oven for 4h at 230°C. The curing process was monitored by Moving Die Rheometer monitoring the torque curve until a plateau is reached at the maximum torque value.

[0090] For each composition a compression set (c-set) value has been determined on a cured o-ring spaceman standard AS568A (type 214) according to ASTM D 395, method B (after 70 hours at 200°C). [0091] The following compositions Ex. 1-6 were prepared as examples according to the invention:

Ex. 1 :

Fluoroelastomer 1 : 100 parts by weight,

Carbon black N-990: 30 parts by weight

Organic peroxide: 1 .35 parts by weight

Taic: 3 parts by weight

Calcium Stearate: 1 part by weight

Ex. 2-6:

Same composition as Ex. 1 except that instead of Calcium stearate the following were added:

Ex. 2 - Magnesium Stearate: 1 part by weight

Ex. 3 - Magnesium Stearate 0.25 parts by weight

Ex. 4 - Zinc Stearate 0.25 parts by weight

Ex. 5 - Sodium Stearate 0.25 parts by weight

Ex. 6 - Potassium Zinc Stearate 0.25 parts by weight.

[0092] The following compositions CEx. 1-3 were prepared as comparative examples:

CEx. 1:

Same composition as Ex. 1 except that no fatty acid salt is added.

CEx. 2:

Same composition as CEx. 1 except that instead of Fluoroelastomer 1 , Fluoroelastomer 2 is used.

CEx. 3:

Same composition as Ex. 3 except that instead of Fluoroelastomer 1 , Fluoroelastomer 2 is used.

CEx. 4:

Same composition as Ex. 4 except that instead of Fluoroelastomer 1 , Fluoroelastomer 2 is used.

CEx. 5:

Same composition as Ex. 5 except that instead of Fluoroelastomer 1 , Fluoroelastomer 2 is used. CEx. 6:

Same composition as Ex. 6 except that instead of Fluoroelastomer 1 , Fluoroelastomer 2 is used.

CEx. 7:

Same composition as Ex. 1 except that instead of Calcium Stearate the same amount of Stearic acid is used.

CEx. 8:

Same composition as Ex. 1 except that instead of Calcium Stearate the same amount of sodium dodecylsulfate is used.

[0093] The resulting c-set values measured as described above on spaceman o- rings obtained from the cured compositions are presented in the table below. It can be clearly noticed how, in the absence of fatty acid salts, the c-set value is higher (i.e. less desirable) for compositions comprising the Fluoroelastomer 1 (prepared without the use of fluorinated surfactants) than for compositions comprising the Fluoroelastomer 2 (prepared with the use of fluorinated surfactants). The data show how the addition of any of the fatty acid salts tested (at both tested levels of 1 and 0.25 parts by weight) brings the c-set value for compositions based on Fluoroelastomer 1 to the same level as that obtained from compositions based on Fluoroelastomer 2 thus allowing to use more environmentally friendly fluoroelastomers for the same applications.

[0094] The data also show that the addition of the same fatty acid salts to compositions based on Fluoroelastomer 2 has no effect on the c-set value of o-rings obtained by said compositions.

Comparative Examples 6 also show how fatty acids (as acids rather than as salts) added to compositions based on Fluoroelastomer 1 instead of the fatty acid salt of the invention do not have a significant effect on the c-set value. Comparative Example 7 shows the effect of the use of a dodecylsulfate sodium salt instead of a fatty acid salt. The composition could not be cured in regular curing conditions. Table 1

Claims

Claim 1

A fluoroelastomer composition comprising:

(i) a fluoroelastomer (fluoroelastomer A), said fluoroelastomer A:

- comprising iodine and/or bromine atoms and

(ii) one or more organic peroxide,

(iii) one or more curing co-agent,

(iv) one or more fatty acid salt.

Claim 2

A fluoroelastomer composition according to claim 1 wherein said fluoroelastomer comprises iodine and/or bromine atoms in an amount of 0.1 to 10.0 % wt with respect to the total weight of fluoroelastomer (A).

Claim 3

A fluoroelastomer composition according to any preceding claim wherein said one or more fatty acid salt is present in an amount of from 0.05 to 5 phr.

Claim 4

A fluoroelastomer composition according to any preceding claim wherein said one or more fatty acid salt is selected among metal salts of fatty acids, preferably among those having a C12-C28 carbon chain, more preferably a C14-C26 carbon chain, even more preferably a C16-C24 carbon chain, most preferably a C16-C22 carbon chain.

Claim 5

A fluoroelastomer composition according to any preceding claim wherein said one or more organic peroxide is selected from the group consisting of: - di(alkyl/aryl) peroxides, including for instance di-tert-butyl peroxide, 2,5- dimethyl-2,5-bis(tert-butylperoxy)hexane, di(t-butylperoxyisopropyl)benzene, dicumyl peroxide;

- diacyl peroxides, including dibenzoyl peroxide, disuccinic acid peroxide, di(4- methylbenzoyl)peroxide, di(2,4-dichlorobenzoyl)peroxide, dilauroyl peroxide, decanoyl peroxide;

- percarboxylic acids and esters, including di-tert-butyl perbenzoate, t- butylperoxy-2-ethylhexanoate, 1 ,1 ,3,3-tetramethylethylbutyl peroxy-2- ethylhexanoate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane;

- peroxycarbonates including notably di(4-t-butylcyclohexyl)peroxydicarbonate, di(2-phenoxyethyl)peroxydicarbonate, bis[1 ,3-dimethyl-3-(tert-butylperoxy)butyl] carbonate, t-hexylperoxyisoproprylcarbonate, t-butylperoxyisopropylcarbonate,

- ketone peroxides such as cyclohexanone peroxide and acetyl acetone peroxide;

- oil-soluble azo initiators such as 2, 2'-azobis (4-methoxy-2. 4-dimethyl valeronitrile), 2, 2'-azobis (2.4-dimethyl valeronitrile), 2,2'- azobis(isobutyronitrile), 2, 2'-azobis(2-cyano-2-butane), dimethyl-2, 2'- azobisdimethyli sobutyrate, dimethyl-2, 2'-azobis(2-methylpropionate), 2,2'- azobis(2-methylbutyronitrile), 1 ,1'-azobis(cyclohexane-l-carbonitrile), 2, 2'- azobis[N-(2-propenyl)-2-methylpropionamide], 1 -[(1 -cyano-1 -methyl ethyl)azo]formamide, 2, 2'-azobis(N-cyclohexy1-2-methylpropionamide), 2,2'- azobis(i sobutyronitrile), 2,2'-azobis(2-cyano-2-butane), dimethyl-2, 2'- azobisdimethylisobutyrate, 1 ,1'-azobis(cyclohexanecarbonitrile), 2-(t-butylazo)- 2-cyanopropane, 2,2'-azobis[2-methyl-N-(1 , 1)-bis(hydroxymethyl)-2- hydroxyethyl]propionamide, 2, 2'-azobis[2-methyl-N-hydroxyethyl]- proprionamide, 2, 2'-azobis(N, N'-dimethyleneisobutyramine), 2, 2'-azobis(2- methyl-N-[1 ,1-bis(hydroxymethyl)-2-hydroxyethyl] propionamide), 2,2'-azobis(2- methyl-N-[1 ,1-bis(hydroxymethyl) ethyl] proprionamide), 2, 2'-azobis[2-5 methyl- N-(2-hydroxyethyl) propionamide], 2,2'-azobis(isobutyramide) dihydrate, 2,2'- azobis(2, 2, 4-trimethylpentane), 2, 2'-azobis(2-methylpropane).

Claim 6

A fluoroelastomer composition according to any preceding claim wherein said one or more organic peroxide is comprised in an amount from 0.1 to 15 phr, preferably 0.2 to 12 phr, more preferably from 1 to 7 phr.

Claim 7

A fluoroelastomer composition according to any preceding claim wherein said one or more additional fluorinated monomer are selected from the group consisting of:

(b) hydrogen-containing C2-C8 olefins, such as vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutene (HFIB), perfluoroalkyl ethylenes of formula CH2 = CH- Rf, wherein Rf is a Ci-Ce perfluoroalkyl group;

(d) (per)fluoroalkylvinylethers (PAVE) of formula CF2 = CFORf, wherein Rf is a Ci- Ce (per)fluoroalkyl group, preferably CF3, C2F5, C3F7;

(e) (per)fluoro-oxy-alkylvinylethers of formula CF2 = CFOX, wherein X is a C1-C12 ((per)fluoro)-oxyalkyl comprising catenary oxygen atoms, e.g. the perfluoro-2- propoxypropyl group;

(f) (per)fluorodioxoles having formula :

wherein each of Rf3, Rf4, Rfs, Rre, equal to or different from each other, is independently selected from the group consisting of fluorine atom and Ci-Ce (per)fluoroalkyl groups, optionally comprising one or more than one oxygen atom, such as notably -CF3, -C2F5, -C3F7, -OCF3, -OCF2CF2OCF3; preferably, perfluorodioxoles;

(g) (per)fluoro-methoxy-vinylethers (MOVE, hereinafter) having formula: CF₂=CFOCF₂OR_f2 wherein Fta is selected from the group consisting of C-i-Ce (per)fluoroalkyls; Cs-Ce cyclic (per)fluoroalkyls; and C2-C6 (per)fluorooxyalkyls, comprising at least one catenary oxygen atom; Fte is -CF2CF3 (M0VE1 ); -CF2CF2OCF3 (M0VE2); or -CF3 (M0VE3).

Claim 8

A fluoroelastomer composition according to any preceding claim wherein said one or more curing co-agent is selected from the group consisting of:

A: compounds comprising two carbon-carbon unsaturations, preferably selected from bis-olefins having general formula :

wherein R1, R2, R3, R4, Rs and Re, equal or different from each other, are H or C1- Cs alkyl; Z is a linear or branched C1-C18 (hydro)carbon radical (including alkylene or cycloalkylene radical), optionally containing oxygen atoms, preferably at least partially fluorinated, or a (per)fluoro(poly)oxyalkylene radical comprising one or more catenary ethereal bonds;

B- compounds comprising three carbon-carbon unsaturations, preferably selected from the group consisting of :

(i) tri-substuituted cyanurate compounds of general formula:

wherein each of R_cy, equal to or different from each other and at each occurrence, is independently selected from H or a group -Rrcy or -ORrcy , with Rrcy being C1-C5 alkyl, possibly comprising halogen(s), and each of J_cy, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms;

(ii)- tri-substuituted isocyanurate compounds of general formula:

wherein each of Risocy, equal to or different from each other and at each occurrence, is independently selected from H or a group -Rrisocy or -ORrisocy , with Rrisocy being C1-C5 alkyl, possibly comprising halogen(s), and each of Jisocy, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms;

(iii) tri-substituted triazine compounds of general formula:

wherein each of Raz, equal to or different from each other and at each occurrence, is independently selected from H or a group -Rraz or -ORraz , with Rraz being C1-C5 alkyl, possibly comprising halogen(s), and each of Jaz, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms;

(iv) tri-substituted phosphite compounds of general formula:

wherein each of R_Ph, equal to or different from each other and at each occurrence, is independently selected from H or a group -Rrph or -ORr_Ph, with R_rPh being C1-C5 alkyl, possibly comprising halogen(s), and each of J_Ph, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms;

(v) tri-substituted alkyltrisiloxanes of general formula:

wherein each of Rsi, equal to or different from each other and at each occurrence, is independently selected from H or a group -Rrsi or-ORrsi, with Rrsi being C1-C5 alkyl, possibly comprising halogen(s), each of R’si, equal to or different from each other and at each occurrence, is independently selected from C1-C5 alkyl groups, possibly comprising halogen(s), and each of Jsi, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms;

(vi) N,N-disubstituted acrylamide compounds of general formula:

wherein each of Ran, equal to or different from each other and at each occurrence, is independently selected from H or a group -Rran or -ORran, with Rran being C1-C5 alkyl, possibly comprising halogen(s), and each of Jan, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms;

C: compounds (II) comprising four or more carbon-carbon unsaturations, which are preferably selected from tris(diallylamine)-s-triazine of formula:

hexa-allylphosphoram ide, N, N, N', N'-tetra-allyl terephthalamide, and N,N,N',N'- tetra-allyl malonamide.

Claim 9

A fluoroelastomer composition according to any preceding claim wherein said one or more curing co-agent, is present in an amount of from 0.1 to 20 phr, preferably from 1 to 15 phr, more preferably from 1 to 10 phr.

Claim 10

A fluoroelastomer composition according to any preceding claim wherein said fluoroelastomer A is obtained from an emulsion polymerization process performed in the absence of surfactants.

Claim 11

A fluoroelastomer composition according to claim 10, wherein said emulsion polymerization process is performed in the presence of a redox initiating system comprising at least one organic radical initiator and at least one compound bearing at least one sulfinic acid group.

Claim 12

A method for making a composition according to claims 1 -11 including the steps of

(i) making a Fluoroelastomer A as defined in claim 1 with an emulsion polymerization process performed in the absence of fluorinated surfactants, Use of the fluoroelastomer composition according to anyone of the preceding claims for fabricating shaped articles,

(ii) mixing said Fluoroelastomer A with

- one or more organic peroxide, - one or more curing co-agent and

- one or more fatty acid salt.

Claim 13

A method for fabricating shaped articles comprising curing the fluoroelastomer composition, according to any of claims 1 to 11 .

Claim 14

A cured article obtained from the composition, according to anyone of Claims 1 to 11 , said cured article being selected from the group consisting of sealing articles, including O(square)-rings, packings, gaskets, diaphragms, shaft seals, valve stem seals, piston rings, crankshaft seals, cam shaft seals, and oil seals or maybe piping and tubings, in particular flexible hoses or other items, including conduits for delivery of hydrocarbon fluids and fuels.

Claim 15

The use of one or more fatty acid salt in a composition comprising:

(i) a fluoroelastomer (fluoroelastomer A), said fluoroelastomer A:

- comprising iodine and/or bromine atoms and

(ii) one or more organic peroxide,

(iii) one or more curing co-agent, to reduce the c-set value of cured materials obtained from curing said composition.