Fluoroelastomer composition for high thermal rating

Abstract

The invention pertains to a fluoroelastomer composition comprising one or more fluoroelastomer (A) comprising recurring units derived from tetrafluoroethylene (TFE) in an amount of from 40% to 69%, recurring units derived from one or more perfluoro alkyl-vinyl ether (PAVE) in an amount of from 30 to 59% by moles, recurring units derived from cure-site containing monomers having at least a nitrile group (CS-N) in an amount below 1,5% by moles, and one or more curing agent (B) comprising a cation and an anion of formula: An q -Qp n+ wherein m, n, p, and q are positive integers, wherein m * p = n * q, wherein Qn+ is a cation, and Aq- is an anion according to the formula (I), wherein each R independently is H, halo, alkyl, aryl, aralkyl, or cycloalkyl, and which also may be halogenated, fluorinated, or perfluorinated, wherein two or more of R and R' groups may together form a ring, wherein each R group independently may contain one or more heteroatom(s), wherein R' can be the same as R, with the proviso that R' cannot be halo. The composition of the invention is able to provide for cured parts having ability to retain outstanding sealing performances at very high temperatures. The invention also relates to a method of curing the same and to cured articles obtained therefrom, which are useful as sealing parts in semi-conductors industry.

Description

DescriptionFluoroelastomer composition for high thermal ratingTechnical Field

[0001] The invention pertains to a fluoroelastomer composition able to provide for cured parts having ability to retain outstanding sealing performances at very high temperatures, to a method of curing the same and to cured articles obtained therefrom, which are notably useful as sealing parts in semi-conductors industry. This application claims priority from the European Patent Application 24171158.9 filed on 2024-04-18, the whole content of this application being incorporated herein by reference for all purposes.

[0002] Background Art

[0003] Fluoroelastomers, and more specifically tetrafluoroethyelene-based fluoroelastomers, have long been used in a variety of applications that require excellent resistance to several rash conditions, including high temperature, chemical attack, and exposure to plasma, including in particular in the semi-conductors’ manufacturing industry. Especially in this area, the possibility of providing cured parts having ability to withstand routinely temperatures as high as 320-330°C, and up to about 350°C, and yet possessing all other advantageous attributes of perfluororubbers, is a long-felt need in this area.

[0004] A variety of curing agents is available commercially and described in the literature. US7402630 from 3M describes curing agents comprising a cation and an anion of formula:Anq’Qpn+wherein m, n, p, and q are positive integers, wherein m * p = n * q, wherein Qn+ is an organo onium, and Aq- is an anion according to the formula:wherein each R independently is H, halo, alkyl, aryl, aralkyl, or cycloalkyl, and which also may be halogenated, fluorinated, or perfluorinated, wherein two or more of R and R' groups may together form a ring, wherein each R group independently may contain one or more heteroatom(s), wherein R' can be the same as R, with the proviso that R' cannot be halo.

[0005] Such curing agents are described as effective in the curing of fluoroelastomer compositions and in providing satisfying properties for the resulting fluoroelastomer in terms of sealing at high temperature.

[0006] There is however a need for even more performing materials which show an even higher performance at high temperatures in order to be used as sealing elements in a more broad variety of applications.

[0007] The Applicant surprisingly found that the use of these curing agents in combination with a selected fluoroelastomer having a carefully controlled level of PAVE comonomers and of nitrile containing curing site monomers results in a cured fluoroelastomer having outstanding thermal resistance properties.Summary of invention

[0008] The present invention relates to a fluoroelastomer composition comprising: A: one or more fluoroelastomer (A) comprising:- recurring units derived from tetrafluoroethylene (TFE) in an amount of from 40% to 69%, preferably 49-65% by moles with respect to the total moles of recurring units of the fluoroelastomer (A);- recurring units derived from one or more perfluoro alkyl-vinyl ether (PAVE) of formula CF2 = CFORf, wherein Rf is a C1-C6 perfluoroalkyl group, in an amount of from 30 to 59% by moles, preferably from 34 to 50%by moles with respect to the total moles of recurring units of the fluoroelastomer (A);- recurring units derived from cure-site containing monomers having at least a nitrile group (CS-N) in an amount below 1 ,5% by moles, preferably from 0.1 to 1 .4% by moles, more preferably from 0.5 to 1 .3% by moles, most preferably between 1 and 1 .3% by moles with respect tothe total moles of recurring units of the fluoroelastomer (A); andB: one or more curing agent (B) comprising a cation and an anion of formula:Anq'Qpn+wherein m, n, p, and q are positive integers, wherein m * p = n * q, whereinQn+is a cation, and Aq_is an anion according to the formula:wherein each R independently is H, halo, alkyl, aryl, aralkyl, or cycloalkyl, and which also may be halogenated, fluorinated, or perfluorinated, wherein two or more of R and R' groups may together form a ring, wherein each R group independently may contain one or more heteroatom (s), wherein R' can be the same as R, with the proviso that R' cannot be halo.Detailed description of the invention

[0009] For the purposes of this invention, the term “(per)fluoroelastomer” is intended to designate a fluoropolymer resin serving as a base constituent for obtaining a true elastomer, said fluoropolymer resin comprising recurring units derived from at least one ethylenically unsaturated monomer comprising at least one fluorine atom (hereafter, (per)fluorinated monomer) and, optionally, recurring units derived from at least one ethylenically unsaturated monomer free from fluorine atom (hereafter, hydrogenated monomer).

[0010] 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.

[0011] The present invention relates to a fluoroelastomer composition a selected fluoroelastomer (A) and a selected curing agent (B).

[0012] A fluoroelastomer (A) for use in the present invention comprises:- recurring units derived from tetrafluoroethylene (TFE) in an amount of from 40% to 69% by moles with respect to the total moles of recurring units of the fluoroelastomer (A);- recurring units derived from one or more perfluoro alkyl-vinylether (PAVE) of formula CF2 = CFORf, wherein Rf is a C1-C6 perfluoroalkyl group, in an amount of from 30 to 59% by moles, preferably from 34 to 50%by moles with respect to the total moles of recurring units of the fluoroelastomer (A);- recurring units derived from cure-site containing monomers having at least a nitrile group (CS-N) in an amount below 1 ,5% by moles, preferably from 0.1 to 1 .4% by moles, more preferably from 0.5 to 1 .3% by moles, most preferably between 1 and 1 .3% by moles with respect to the total moles of recurring units of the fluoroelastomer (A).

[0013] Among perfluoro alkyl-vinylethers (PAVE) monomers it is preferred to use alkyl vinyl ethers selected from perfluoro methyl vinyl ether, perfluoro ethyl vinyl ether, perfluoro propyl vinyl ether, perfluoro butyl vinyl ether and mixtures thereof. More preferably the perfluoro alkyl-vinyl ether monomers are selected from perfluoro methyl vinyl ether, perfluoro propyl vinyl ether and mixtures thereof. Most preferably the perfluoro alkyl-vinylethers monomers are perfluoro methyl vinyl ether.

[0014] Among cure-site containing monomers of type (CS-N), as above detailed, comprised in fluoroelastomer (A), preferred monomers are fluorinated, more preferably perfluorinated, and are especially those selected from the group consisting of:(CS-N1 ) perfluorovinyl ethers containing nitrile groups of formula CF2=CF-[OCF2CFXCN(CF2)ai]m-O-(CF2)n-CN, with XCNbeing F or CF3, a1 being 0, 1 or 2; m being 0, 1 , 2, 3 or 4; n being an integer from 1 to 12;(CS-N2) perfluorovinyl ethers containing nitrile groups offormula CF2=CF-(OCF2CFXCN(CF2)a2)m -O-CF2— CF(CF3)-CN, with XCNbeing F or CF3, a2 being 0, 1 or 2; m’ being 0, 1 , 2, 3 or 4.Specific examples of cure-site containing monomers of type CS-N1 and CS-N2 suitable to the purposes of the present invention are notably those described in patents US 4281092 (DU PONT ) 28 / 07 / 1981 , US 4281092 (DU PONT) 28 / 07 / 1981 , US 5447993 (DU PONT) 5 / 09 / 1995 and US 5789489 (DU PONT) 4 / 08 / 1998.

[0015] Most preferred cure-site monomers (CS-N) are notably perfluoro(8-cyano- 5-methyl-3,6-dioxa-1 -octene) of formula: CF2=CF-O-CF2-CF(CF3)-O-CF2- CF2-CN (8-CNVE) and the monomer of formula CF2=CF-O-CF2-CF2-CF2- O-CF2-CF(CF3)-CN. Most preferably, monomer (CS-N) is 8-CNVE, as described above. When increased chemical resistance is required, monomer of formula CF2=CF-O-CF2-CF2-CF2-O-CF2-CF(CF3)-CN may be most preferred.

[0016] Fluoroelastomer (A) in addition to recurring units derived from tetrafluoroethylene, recurring units derived from PAVE monomers and recurring units derived from (CS-N) monomers, may also comprise recurring units derived from one or more additional (per)fluorinated monomer. Such one or more additional perfluorinated monomer can be preferably selected from the group consisting of:(a) C3-C8 perfluoroolefins, such as hexafluoropropylene (HFP);(b) C2-C8 fluoroolefins comprising at least one of iodine, chlorine and bromine, such as chlorotrifluoroethylene (CTFE);(c) C2-C8 hydrogen-containing fluoroolefins, such as vinyl fluoride;1 ,2-difluoroethylene, vinylidene fluoride (VDF), trifluoroethylene (TrFE), pentafluoropropylene, and hexafluoroisobutylene;(d) (per)fluoroalkylethylenes complying with formula CH2=CH-Rro, in which Rro is a Ci-Ce (per)fluoroalkyl or a Ci-Ce (per)fluorooxyalkyl having one or more ether groups ;(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; among these monomers, preferred are (e’) (per)fluoro-methoxy-vinylethers (MOVE, hereinafter) having formula:CF2=CFOCF2ORf2 wherein Fte is selected from the group consisting of Ci-Ce (per)fluoroalkyls; Cs-Ce cyclic (per)fluoroalkyls; and C2-C6 (per)fluorooxyalkyls, comprising at least one catenary oxygen atom; Fte is preferably -CF2CF3 (M0VE1 ); - CF2CF2OCF3 (M0VE2); or -CF3 (M0VE3);(f) (per)fluorodioxoles having formula :wherein each of Rf3, Rf4, Rfs, Rf6, 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.

[0017] More preferably, such one or more additional perfluorinated monomer are selected from the group consisting of:(a1 ) hexafluoropropylene (HFP);(e1 ) perfluoro-oxy-alkylvinylethers of formula CF2=CFOX, wherein X is a C1-C12 perfluoro-oxyalkyl comprising catenary oxygen atoms; and more preferably (e’1 ) perfluoro-methoxy-vinylethers (MOVE, hereinafter) having formula: CF2=CFOCF2OR1f2 wherein R>2 is selected from the group consisting of C1-C3 perfluoroalkyls; and C2-C6 perfluorooxyalkyls, comprising at least one catenary oxygen atom; R1f2 is preferably selected from -CF2CF3; -CF2CF2OCF3; or -CF3.

[0018] Fluoroelastomer (A) may also include recurring units derived from fluorine- free monomers, which will be hereunder referred to as hydrogenated monomers. Examples of hydrogenated monomers are notablyhydrogenated alpha-olefins, including ethylene, propylene, 1 -butene, diene monomers, styrene monomers, alpha-olefins being typically used.

[0019] Fluoroelastomer (A) of the present invention may also comprise recurring units derived from a bis-olefin [bis-olefin (OF)] having general formula :wherein Ri , R2, R3, R4, Rs and Re, equal or different from each other, are independently selected from the group consisting of F, Cl, H, C1-C5 (fluoro)alkyl groups, and groups -ORB, wherein RB is a branched or straight chain alkyl radical which can be partially, substantially or completely fluorinated or chlorinated; 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.

[0020] The 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 selectedfrom 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] If present, a more preferred bis-olefin (OF) is a bis-olefin of formula (OF- 1 ), as above detailed, and most preferably it is divinylperfluorohexane.

[0022] For embodiments wherein the fluoroelastomer (A) comprises recurring units derived from a bis-olefin (OF), as detailed above, the amount of the said bis-olefin (OF) is generally of at least 0.04, preferably of at least 0.05 and / or of at most 0.25, preferably of at most 0.20 % moles, with respect to the total moles of recurring units of fluoroelastomer (A).

[0023] The introduction of bis-olefin recurring units in fluoroelastomer A, as known to the skilled person, increases the level of branching of the fluoroelastomer A. For the present invention fluoroelastomer (A) is preferably selected among linear fluoroelastomers or among fluoroelastomers having a low level of branching, therefore fluoroelastomer A is preferably free from recurring units derived from bis olefins.

[0024] Exemplary preferred 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) : tetrafluoroethylene (TFE): 40-69 %; (per)fluoroalkylvinylethers (PAVE): 30-59 %; monomer (CS-N).

[0025] Fluoroelastomers (A) are in general amorphous products or products having a low degree of crystallinity (crystalline phase less than 20 % by volume) and a glass transition temperature (Tg) below room temperature. In most cases, the fluoroelastomer (A) has advantageously a Tgbelow 10°C, preferably below 5°C, more preferably 0°C.

[0026] End chains, defects or minor amounts of monomer impurities leading to recurring units different from those above mentioned (typically, <0.1 % moles, with respect to the total amount of recurring units) can be still present in the exemplary preferred fluoroelastomers (A), without this affecting properties of the material.

[0027] The composition of the present invention also comprises one or more curing agent (B). Curing agent B comprises a cation and an anion of formula:Anq'Qpn+

[0028] wherein m, n, p, and q are positive integers, wherein m * p = n * q, wherein Qn+is a cation, and Aq_is an anion according to the formula:wherein each R independently is H, halo, alkyl, aryl, aralkyl, or cycloalkyl, and which also may be halogenated, fluorinated, or perfluorinated, wherein two or more of R and R' groups may together form a ring, wherein each R group independently may contain one or more heteroatom(s), wherein R' can be the same as R, with the proviso that R' cannot be halo.For example, each R can be F such that the central carbon of the anion is bonded to two perfluoromethyl groups. In addition, R' can be selected from the group consisting of H, phenyl, methoxyphenyl toluyl, phenoxy, fluorophenyl, trifluoromethylphenyl, and CF3. Preferably each R is F and R’ is a substituted on non substituted aromatic ring, more preferably R’ is an aromatic ring substituted with one or more C1-C3 alkyl, even morepreferably R’ is an aromatic ring substituted with one, two or three -CF3 groups.

[0029] The choice of the cation Qn+is not particularly limited, metal ions can be used although preferably the cation is selected from ammonium, phosphonium and organo onium ions and more preferably is an organo onium ion.

[0030] Preferred organo onium ions are mono-, bi-, tri- and tetra-alkyl ammonium ions, and mono-, bi-, tri- and tetra-alkyl phosphonium ions, more preferred cations are tetra-alkyl ammonium and tetra-alkyl phosphonium, most preferred cations are tetra-butyl ammonium and tetra-butyl phosphonium

[0031] Examples of curing agent B include tetra-alkyl ammonium 2-phenyl-1 , 1 ,1 .3.3-hexafluoroisopropanolate, tetra-alkyl ammonium 1 , 1 , 1 ,3,3- hexafluoroisopropanolate, tetra-butyl phosphonium 2-phenyl-1 , 1 , 1 , 3,3,3- hexafluoroisopropanolate, tetra-butyl phosphonium 1 , 1 , 1 , 3,3,3- hexafluoroisopropanolate, tetra-butyl phosphonium 2-methoxyphenyl-1 , 1 ,1 .3.3.3-hexafluoroisopropanolate, and tetra-butyl phosphonium 2-p-toluyl- 1 , 1 , 1 ,3,3,3-hexafluoroisopropanolate.

[0032] Most preferred curing agent B is 2-p-toluy 1-1 , 1 , 1 ,3,3,3- hexafluoroisopropanolate.

[0033] Curing agent (B) is an agent able to promote the cross-linking of the fluoroelastomer (A) through reaction with the cure sites of monomers (CS-N). Such curing agent may be introduced in the composition of the invention in pure form or preferably supported on an inert carrier such as e.g. a SiO2 carrier.

[0034] One or more than one curing agent (B) can be used in the composition of the present invention.

[0035] The fluoroelastomer composition of the invention may further additionally comprise ingredients which maybe commonly used in curable compositions, for example:(a) one or more metallic basic compound, in amounts generally of from 0.5 to 15 phr, and preferably of from 1 to 10 phr, relative to 100 weight parts of fluoroelastomer (A); metallic basic compounds are generallyselected from the group consisting of (i) oxides or hydroxides of divalent metals, for instance oxides or hydroxides of Mg, Zn, Ca or Pb, and (ii) metal salts of a weak acid, for instance Ba, Na, K, Pb, Ca stearates, benzoates, carbonates, oxalates or phosphites;(b) one or more acid acceptor which is not a metallic basic compound, in amounts generally of from 0.5 to 15 phr, and preferably of from 1 to 10 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 ;(c) other conventional additives, such as fillers, thickeners, pigments, antioxidants, stabilizers, processing aids, and the like.

[0036] Among fillers, fluorinated reinforcing fillers consisting of fluoroplastic, in particular of nanometric size, can be advantageously used. Hence, the composition of the invention, according to certain embodiments, may comprise at least one semi-crystalline fluoropolymer, generally in an amount of from 10 to 70 weight parts, preferably from 12 to 60 weight parts, relative to 100 weight parts of fluoroelastomer (A); the said semicrystalline fluoropolymer is generally selected from the group consisting of tetrafluoroethylene (TFE) homopolymers and copolymers of TFE with one or more monomers containing at least one unsaturation of ethylenic type, in an amount of from 0.01 to 10 mol % and preferably from 0.05 to 7 mol %. Within this frame, particularly preferred are semi-crystalline TFE copolymers comprising recurring units derived from at least one (per)fluoroalkylvinylethers (PAVE) of formula CF2 = CFORf, wherein Rf is a C1-C6 (per)fluoroalkyl group, preferably CF3, C2F5, C3F7. From morphological perspective, the semi-crystalline fluoropolymers preferred for these embodiment’s are those which possess an average particle size of between 10 and 400 nm, preferably of 10 to 250 nm, even more preferably of 10 to 100 nm.

[0037] The invention also pertains to a method for making shaped articles comprising curing the fluoroelastomer composition of the invention.

[0038] The fluoroelastomer composition of the invention can be used to make shaped articles with conventional techniques such as e.g. molding(injection molding, extrusion molding), calendering, or extrusion into the desired shaped article, which is advantageously subjected to vulcanization (curing) during the processing itself and / or in a subsequent step (posttreatment 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.

[0039] The invention also pertains to cured articles obtained from the fluoroelastomer composition of the invention. Said cured articles are generally obtained by molding and curing the fluoroelastomer composition, as above detailed. These cured articles may be for example sealing articles, including O(square)-rings, packings, gaskets, door sleeves, diaphragms, shaft seals, valve stem seals, piston rings, crankshaft seals, cam shaft seals, and oil seals or maybe piping and tubings, in particular sealing parts or other items includes in semi-conductor manufacturing devices.

[0040] Further in addition, the invention also pertains to a method for processing the fluoroelastomer composition of the invention, according any of injection molding, compression molding, extrusion molding, coating, screen printing technique, form-in-place technique.

[0041] 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.

[0042] 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.

[0043] Raw materialsCuring agent B: Tetrabutvlphosphonium 2-p-toluyl-l 1 ,1 ,3,3 — hexafluoroisopropanoate, 34%wt on a SiO2 carrier supplied by 3M.Comparative curing agent: Bis-aminophenol AF (BOAP, herein after) was supplied from Apollo Scientific and used as received.Fluoroelastomer A1 : TFE 64.7 %mol, MVE 34.3 %mol, 8-CNVE 1.1 %mol, and the Mooney viscosity at 121 °C is 101 MU.Fluoroelastomer A2 TFE 61.7 %mol, MVE 37.1 %mol, 8-CNVE 1.2 %mol, and the Mooney viscosity at 121 °C is 60 MUFluoroelastomer A3 (Comparative ): TFE 65.1 %mol, MVE 33.1 %mol, CN 1 .8 %mol, and the Mooney viscosity at 121 °C is 60 MU.The fluoroelastomers were provided by Solvay Specialty Polymers.

[0044] Compression set value measurement

[0045] Compression set (CS) is the amount of permanent deformation (as % of the original dimension) that occurs when a material is compressed to a specific deformation, for a specified time, at a specific temperature. The lower is the CS value the more the material has a better ability to maintain seal pressure over time, preventing leaks, product failure, and hazards. Compression set (CS) values have been determined on O-rings obtained by molding preformed extruded cords (#214 class) according to the ASTM D 395-B method at temperatures ranging from 200°C to 325°C; values in the table are the average of determinations made on 4 specimens. The qualification “broken” is representative of determinations where all specimens experienced critical failures and were not suitable for determining residual deformation.

[0046] ExamplesExample 1 .A fluoroelastomer composition was formed compounding in a two rolls open mill Fluoroelastomer A1 with 20 phr of carbon black Cancarb N 990 MT and 2.25phr of curing agent B. O-rings were cured in a pressed mold (15 min 188°C) and then post-treated in an air circulating oven (16hours 250°C).The O-rings were subject to CS measurement after 70 hours of storage at different temperatures. Results are shown in the table below.Example 2The same procedure of Example 1 was followed using Fluoroelastomer A2 instead of Fluoroelastomer A1 .Example C3 (comparative)The same procedure of Example 1 was followed using Fluoroelastomer A3 instead of Fluoroelastomer A1 .Example C4 (comparative)The same procedure of Example 1 was followed using 1 phr of BOAP as curing agent instead of 2.25 phr of curing agent B.Example C5 (comparative)The same procedure of Example 2 was followed using 1 phr of BOAP as curing agent instead of 2.25 phr of curing agent B.Table 1C set measured at a deflection of 25% after 30 min relax time

Claims

ClaimsClaim 1A fluoroelastomer composition comprising:A: one or more fluoroelastomer (A) comprising:- recurring units derived from tetrafluoroethylene (TFE) in an amount of from 40% to 69%, preferably 49-65% by moles with respect to the total moles of recurring units of the fluoroelastomer (A);- recurring units derived from one or more perfluoro alkyl-vinyl ether (PAVE) of formula CF2 = CFORf, wherein Rf is a C1-C6 perfluoroalkyl group, in an amount of from 30 to 59% by moles, preferably from 34 to 50%by moles with respect to the total moles of recurring units of the fluoroelastomer (A);- recurring units derived from cure-site containing monomers having at least a nitrile group (CS-N) in an amount below 1 ,5% by moles, preferably from 0.1 to 1 .4% by moles, more preferably from 0.5 to 1 .3% by moles, most preferably between 1 and 1.3% by moles with respect to the total moles of recurring units of the fluoroelastomer (A); andB: one or more curing agent (B) comprising a cation and an anion of formula: Anq’Qpn+wherein m, n, p, and q are positive integers, wherein m * p = n * q, wherein Qn+is a cation, and Aq- is an anion according to the formula:wherein each R independently is H, halo, alkyl, aryl, aralkyl, or cycloalkyl, and which also may be halogenated, fluorinated, or perfluorinated, wherein two or more of R and R' groups may together form a ring, wherein each R group independently may contain one or more heteroatom(s), wherein R' can be the same as R, with the proviso that R' cannot be halo.Claim 2A fluoroelastomer composition according to claim 1 wherein said one or more perfluoro alkyl-vinyl ether (PAVE) monomers selected from perfluoro methyl vinyl ether, perfluoro ethyl vinyl ether, perfluoro propyl vinyl ether, perfluoro butyl vinyl ether and mixtures thereof.Claim 3A fluoroelastomer composition according to claim 2 wherein said one or more perfluoro alkyl-vinylether (PAVE) monomers are perfluoro methyl vinyl ether.Claim 4A fluoroelastomer composition according to claim 1 wherein said cure-site containing monomers having at least a nitrile group (CS-N) are selected from the group consisting of:- (CS-N1 ) perfluorovinyl ethers containing nitrile groups of formula CF2=CF-[OCF2CFXCN(CF2)ai]m-O-(CF2)n-CN, with XCNbeing F or CF3, a1 being 0, 1 or 2; m being 0, 1 , 2, 3 or 4; n being an integer from 1 to 12;- (CS-N2) perfluorovinyl ethers containing nitrile groups of formula CF2=CF-(OCF2CFXCN(CF2)a2)m -O-CF2— CF(CF3)-CN, with XCNbeing F or CF3, a2 being 0, 1 or 2; m’ being 0, 1 , 2, 3 or 4.Claim 5A fluoroelastomer composition according to claim 1 or 2 wherein said cure-site containing monomers having at least a nitrile group (CS-N) are selected from the group consisting of :- CF2=CF-O-CF2-CF(CF3)-O-CF2-CF2-CN (8-CNVE) and - CF2=CF-O-CF2-CF2-CF2-O-CF2-CF(CF3)-CN, and mixtures thereof.Claim 6A fluoroelastomer composition according to any preceding claim wherein said fluoroelastomer (A) comprises recurring units derived from one or more (per)fluorinated monomer, in addition to recurring units derived from tetrafluoroethylene, and recurring units derived from monomer (CS-N), whereinsaid (per)fluorinated monomer is selected from the group consisting of:(a) Cs-Cs perfluoroolefins, such as hexafluoropropylene (HFP);(b) C2-C8 fluoroolefins comprising at least one of iodine, chlorine and bromine, such as chlorotrifluoroethylene (CTFE);(c) C2-C8 hydrogen-containing fluoroolefins, such as vinyl fluoride;1 ,2-difluoroethylene, vinylidene fluoride (VDF), trifluoroethylene (TrFE), pentafluoropropylene, and hexafluoroisobutylene;(d) (per)fluoroalkylethylenes complying with formula CH2=CH-Rfo, in which Rro is a Ci-Ce (per)fluoroalkyl or a Ci-Ce (per)fluorooxyalkyl having one or more ether groups ;(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; among these monomers, preferred are (e’) (per)fluoro- methoxy-vinylethers (MOVE, hereinafter) having formula:CF2=CFOCF2ORf2 wherein Rf2 is selected from the group consisting of Ci-Ce (per)fluoroalkyls; Cs-Ce cyclic (per)fluoroalkyls; and C2-C6 (per)fluorooxyalkyls, comprising at least one catenary oxygen atom; Rf2 is preferably -CF2CF3 (M0VE1 ); -CF2CF2OCF3 (M0VE2); or -CF3 (M0VE3);(f) (per)fluorodioxoles having formula :wherein each of Rf3, Rf4, Rfs, Rf6, 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.Claim 7A fluoroelastomer composition according to any preceding claim wherein said cation Qn+is selected from ammonium, phosphonium and organo onium ions and more preferably is an organo onium ion.Claim 8A fluoroelastomer composition according to any preceding claim wherein said cation Qn+is selected from tetra-alkyl ammonium, and tetra-alkyl phosphonium, preferably from tetra-butyl ammonium, and tetra-butyl phosphonium.Claim 9A fluoroelastomer composition according to any preceding claim wherein, in said anion, each R is F and R’ is a substituted or unsubstituted aromatic ring.Claim 10A fluoroelastomer composition according to claim 9 wherein, in said anion, R’ is an aromatic ring substituted with one, two or three C1-C3 alkyl groups, preferably one two or three CF3 groups.Claim 11A fluoroelastomer composition according to any preceding claim wherein said curing agent B is selected from tetra-alkyl ammonium 2-phenyl-1 , 1 , 1 ,3,3- hexafluoroisopropanolate, tetra-alkyl ammonium 1 , 1 , 1 ,3,3- hexafluoroisopropanolate, tetra-butyl phosphonium 2-phenyl-1 , 1 , 1 , 3,3,3- hexafluoroisopropanolate, tetra-butyl phosphonium 1 , 1 , 1 , 3,3,3- hexafluoroisopropanolate, tetra-butyl phosphonium 2-methoxyphenyl-1 , 1 , 1 , 3,3,3- hexafluoroisopropanolate, and tetra-butyl phosphonium 2-p-toluyl-1 , 1 , 1 , 3,3,3- hexafluoroisopropanolate.Claim 12A fluoroelastomer composition according to any preceding claim wherein said curing agent B is 2-p-toluyl-1 , 1 , 1 ,3,3,3-hexafluoroisopropanolate.Claim 13A fluoroelastomer composition according to any preceding claim wherein said curing agent B is supported on a carrier, preferably a SiO2 carrier.Claim 14A method for fabricating a shaped article, said method comprising curing the composition according to anyone of Claims 1 to 13Claim 15Cured articles obtained from the fluoroelastomer composition according to anyone of Claims 1 to 13, said cured articles being sealing articles, including O(square)- rings, packings, gaskets, diaphragms, shaft seals, valve stem seals, piston rings, crankshaft seals, cam shaft seals, and oil seals, piping and tubings.

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