WO2008003635A1

WO2008003635A1 - (per)fluoroelastomeric compositions

Info

Publication number: WO2008003635A1
Application number: PCT/EP2007/056478
Authority: WO
Inventors: Milena Stanga; Giovanni Comino; Margherita Albano
Original assignee: Solvay Solexis S.P.A.
Priority date: 2006-07-03
Filing date: 2007-06-28
Publication date: 2008-01-10
Also published as: ITMI20061291A1

Abstract

A (per)fluoroelastomeric composition curable by peroxidic way comprising for 100 phr of (per)fluoroelastomer: - as filler, from 2 to 70 phr of silica unwettable with water; - as crosslinking agent, from 0.5 to 10 phr of a bis-olefin having general formula: (I) wherein: R1, R2, R3, R4, R5, R6, equal to or different from each other, are H or C1-C5 alkyls; Z is selected between a C1-C18 linear or branched alkylene or cycloalkylene radical, optionally containing oxygen atoms, preferably at least partially fluorinated, or a (per)fluoropolyoxyalkylene radical; the total residual content of metals in the (per)fluoroelastomeric composition being lower than 1,500 ppm, preferably lower than 1,000 ppm.

Description

(PER)FLUOROELASTOMERIC COMPOSITIONS

The present invention relates to (per)fluoroelastomeric compositions having an improved vapour resistance at high temperatures, for example from 230°C to 320°C, in particular from 250°C to 300°C. With vapour resistance it is meant the combination of good sealing properties (compression set) and low variations of the mechanical properties, after vapour treatment at the above mentioned high temperatures. Said combination of properties is maintained even for long treatment times, for example even higher than 150 hours.

More specifically the invention refers to (per)fluoroelastomeric compositions maintaining good mechanical properties, as pointed out by the variation of mechanical properties as stress at break, elongation at break, hardness and swelling by volume, even after long times of vapour treatment at the above mentioned high temperatures.

In the preparation of sealing manufactured articles, in particular for the electronic, pharmaceutical and oil industry, (per)fluoroelastomeric compositions having the following combination of properties are required: high vapour resistance at high temperatures, for example up to 320°C, preferably up to 300°C, even for long treatment times, for example even of 150 hours or longer times, as pointed out by the substantial maintenance of the following properties: good sealing properties (compression set); limited variations of the mechanical properties as stress at break, elongation at break, hardness and swelling by volume; total residual content of metals after calcination at the temperature of 800°C lower than 1 ,500 ppm, preferably lower than 1 ,000 ppm.

It has been surprisingly and unexpectedly found by the Applicant that it is possible to solve the above mentioned technical problem by using a particular (per)fluoroelastomeric composition, as described below.

An object of the present invention are (per)fluoroelastomeric compositions curable by peroxidic way comprising per 100 phr of (per)fluoroelastomer: as filler, from 2 to 70 phr of silica not wettable with water according to the test described hereinbelow; as crosslinking agent, from 0.5 to 10 phr of a bis-olefin having general formula:

wherein:

R-i, R₂, R3, R₄, R5, Re, equal to or different from each other, are H or C_rC₅ alkyls;

Z is selected between a C1-C18 linear or branched alkylene or cycloalkylene radical, optionally containing oxygen atoms, preferably at least partially fluorinated, or a (per)fluoropolyoxyalkylene radical; the total metal residual content in the (per)fluoroelastomeric composition being lower than 1 ,500 ppm, preferably lower than 1 ,000 ppm: the test for the silica wettability with water being the following: a volume of silica equal to 200 ml is poured in a beaker containing an equal volume of water at room temperature (25°C), it is mixed with a glass rod for 3 seconds, the silica must form a separated layer over the aqueous phase to indicate that the silica is not wettable by the water.

The filler amount ranges from 5 to 50 phr, more preferably from 10 to 30 phr.

The bis-olefin amount ranges from 0.6 to 5, preferably from 0.6 to 1.8 phr, still more preferably from 0.9 to 1.5 phr.

As said, the silica suitable to be used in the (per)fluoroelastomeric compositions of the invention must not be wetted by water according to the above test.

If instead the silica does not pass the test, that is, it precipitates on the beaker bottom, it cannot be used to obtain the improved results according to the present invention, since in this case the silica would be hydrophilic and not hydrophobic (not wettable). The silica which can be used according to the present invention can have any pH, determined according to the DIN ISO 787-9 standard. Silica having a pH higher than 7 according to this standard are also suitable, provided that they are not wettable in water according to the above test. The latter class of silica, i.e., having pH higher than 7 according to said standard provided that they are not wettable in water according to the above mentioned test, if necessary can be disclaimed from the general class of silicas usable according to the present invention. However the use of the compositions of the invention for obtaining improved vapour resistance comprises also this particular kind of silica, that is, having a pH higher than 7 according to the above standard and that it is not wettable in water according to the mentioned test.

In the (per)fluoroelastomeric compositions of the present invention, as silicas not wettable in water according to the present invention, silicas which have been subjected to dehydration processes such as to substantially reduce the presence of the ≡Si-OH (silanols) on the surface, can be used. The maximum amount of silanol groups which can remain after the dehydration process is such as to render anyway the silica not wettable according to the above described test. The skilled in the field is capable to easily determine the maxi-mum amount of silanol present so that the silica is usable according to the present invention. Another process which can be mentioned to obtain not wettable silicas according to the above described test is that to treat silicas physically, for example with silicone, or chemically, for example with silanes.

Preferably the silica used in the (per)fluoroelastomeric composition according to the present invention has a SiO₂ content not lower than 98% by weight, referred to the substance previously ignited (calcined), determined according to the ISO 3262-19 method.

Examples of silicas usable in the compositions according to the present invention are the following, commercially available: Sipernat®D17, Cabot®TS720.

In formula (I) of the bis-olefin, Z is preferably a C₄-Ci₂, more preferably C₄-C₈, perfluoroalkylene radical; when Z is a (per)fluoropolyoxyalkylene radical, it can comprise units selected from the following: -CF₂CF₂O-, -CF₂CF(CF₃)O-, -CFX₁O- wherein X₁ = F, CF₃, -CF₂CF₂CF₂O-, -CF₂-CH₂CH₂O-, -C₃F₆O-; while R₁, R₂, R₃, R₄, R₅, R₆ are preferably hydrogen.

Preferably Z has formula:

-(Q)p-CF₂O-(CF₂CF₂O)_m(CF₂O)_n-CF₂-(Q)p- (II) wherein: Q is a C1-C10 alkylene or oxyalkylene radical; p is 0 or 1 ; m and n are numbers such that the m/n ratio is comprised between 0.2 and 5 and the number average molecular weight of said (per)fluoropolyoxyalkylene radical is in the range 300-10,000, preferably 700-2,000.

Preferably -Q- in the bis-olefin is selected from:

-CH₂OCH₂-; -CH₂O(CH₂CH₂O)SCH₂-, s = 1-3.

Preferably the bis-olefin has formula: CH₂=CH-(CF₂)_to-CH=CH₂, wherein to is an integer from 6 to 10.

The bis-olefins of formula (I) wherein Z is an alkylene or cycloalkylene radical can be prepared according to what described, for example, by I. L. Knunyants et al. in "Izv. Akad. Nauk. SSSR", Ser. Khim., 1964(2), 384-6, while the bis-olefins containing (per)fluoropolyoxyalkylene sequences are described in USP 3,810,874.

The (per)fluoroelastomers curable by peroxidic way with the crosslinking system according to the present invention are those containing peroxidic crosslinking sites. Preferably these sites are represented by iodine and/or bromine atoms, preferably iodine. See for example the perfluoroelastomers described in EP 769,521. The iodine and/or bromine atoms can be present along the chain and/or in end position. The amount of iodine and/or bromine is generally between 0.001% and 5% by weight, preferably between 0.01% and 2.5% by weight with respect to the total weight of the polymer. To introduce iodine atoms along the chain, the polymerization of the fluoroelastomer monomers is carried out with a suitable fluorinated comonomer containing iodine (cure-site monomers). See for example USP 4,745,165, USP 4,831 ,085, USP 4,214,060, EP 683,149. The cure-site can be selected for example from the following compounds:

(a) iodo(per)fluoroalkyl-perfluorovinylethers of formula: 1-RrO-CF=CF₂ (III) wherein Rf is a CrCi₂ (per)fluoroalkylene, optionally containing chlorine and/or ether oxygen atoms; for example: ICF₂-O-CF=CF₂, ICF₂CF₂-O-CF=CF₂, ICF₂CF₂CF-O-CF=CF₂,

CF₃CFICF₂-O-CF=CF₂, and the like; (b) iodo-(per)fluoroolefins of formula:

1-RVCF=CF₂ (IV) wherein R'_f is a C1-C12 (per)fluoroalkylene, optionally containing chlorine atoms; for example: iodotrifluoroethylene, 1-iodo-2,2-difluoroethylene, iodo- 3,3,4,4-tetrafluorobutene-1 , 4-iodo-perfluorobutene-1 , and the like;

(c) iodo-(per)fluoroolefins of formula:

CHR₀=CH-Z₀-CH₂CHR₀-I (V) wherein: R₀ is H or -CH₃; Z₀ is a C1-C-18 linear or branched (per)fluoroalkylene radical, optionally containing one or more oxygen atoms, or a

(per)fluoropolyoxyalkylene radical as above defined.

Other iodinated cure-site comonomers are iodofluoroalkylvinylethers, see USP 4,745,165 and USP 4,564,662.

Alternatively, or in addition to the iodinated comonomer, the fluoroelastomer can contain iodine atoms in end position, deriving from a suitable iodinated chain transfer agent introduced in the reaction medium during the fluoroelastomer polymerization, as described in USP 4,501 ,869. Said transfer agents have formula R^Af(l)x, wherein R^A _f is a C1-C12 (per)fluoroalkyl radical, optionally containing chlorine atoms, while x is 1 or 2. Said transfer agents can be selected, for example, from: CF₂I₂, 1(CF₂JeI, I(CF₂)₄I, CF₂CII, CF₃CFICF₂I, and the like. For the iodine introduced as chain end group by addition of iodinated chain transfer agents as above mentioned see for example USP 4,243,770 and USP 4,943,622.

It is also possible to use as chain transfer agents alkaline or alkaline-earth metal iodides, according to what described in the patent application EP 407,937.

In combination with the chain transfer agents containing iodine, other known chain transfer agents of the prior art, such as ethyl acetate, diethylmalonate, etc., can be used.

The iodine amount in end position of the (per)fluoroelastomer is generally between 0.001% and 3%, preferably between 0.01% and 1% by weight with respect to the fluoroelastomer weight. See USP 4,035,565 and USP 4,694,045.

Furthermore the (per)fluoroelastomers curable by peroxidic way can contain, alternatively or in combination with iodine, also bromine, in the backbone and/or as terminal end of the backbone. The bromine in the chain can be introduced by using a cure-site comonomer according to known techniques; see for example USP 4,035,565, USP 4,745,165, EP 199,138; or as end bromine as described in USP 4,501 ,869.

The (per)fluoroelastomers of the invention are TFE polymers with at least one perfluorinated olefin having one unsaturation of ethylene type. In particular the comonomers are selected from:

(per)fluoroalkylvinylethers (PAVE) CF₂=CFOR2f , wherein R₃ is a C_rC₆ (per)- fluoroalkyl, for example trifluoromethyl, bromotrifluoromethyl, penta- fluoropropyl;

(per)fluoro-oxyalkylvinylethers CF₂=CFOX₀, wherein X₀ is a C_rCi₂ perfluorooxyalkyl, containing one or more ether groups, for example perfluoro-

2-propoxy-propyl; (per)fluorovinylethers called MOVE having general formula:

CFX₂=CX₂OCF₂OR¹V (I-B) wherein

R'V has the following meanings:

CrC₆ linear or branched (per)fluoroalkyl, C₅-C₆ cyclic (per)fluoroalkyl,

C₂-C₆ linear or branched (per)fluorooxyalkyl containing from one to three oxygen atoms, X₂ = F₁ H.

When in the (per)fluoroelastomers the comonomer is a (per)fluorovinylether of formula (I-B), it is preferably selected from the following: CF₂=CFOCF₂OCF₂CF₃ (MOVE1)

CF₂=CFOCF₂OCF₂CF₂OCF₃ (MOVE2)

CF₂=CFOCF₂OCF₃ (MOVE3).

Preferred monomeric compositions for curable (per)fluoroelastomers are the following, expressed in % by moles: TFE 50-85%, PAVE 15-50%;

TFE 20-85%, MOVE 15-80%, optionally PAVE 0-50%; the sum of the monomers being 100% by moles. The fluorinated polymers of the present invention can optionally contain also units deriving from VDF, C3-C8 fluoroolefins, optionally containing hydrogen atoms, chlorine and/or bromine and/or iodine, C₂-C₈ non fluorinated olefins (01), preferably ethylene and/or propylene. Examples of the latter are:

33-75% by moles of tetrafluoroethylene (TFE), preferably 40-60%;

15-45% by moles of a perfluorovinylether (PAVE), preferably 20-40%;

2-25% by moles of vinylidene fluoride (VDF), preferably 15-20%;

TFE 32-60%, PAVE 20-40%; Ol 10-40%; the sum of the composition moles being 100%.

As preferred perfluorovinylethers PAVE, (per)fluoromethylvinylether, per- fluoroethylvinylether, perfluoropropylvinylether can be mentioned.

In the above mentioned compositions, at the place or in combination with the vinylethers PAVE, the (per)fluorovinylethers of formula (I-B) can be used, with the proviso that the total % of the vinylethers is within the limits indicated above for the above mentioned compositions containing PAVE.

The (per)fluoroelastomers can contain also monomeric units in the chain deriving from small amounts of a bis-olefin of the above reported general formula (I), as described in USP 5,585,449, generally the bis-olefin amount in the (per)fluoro- elastomer ranges from 0.01% to 5% by moles with respect to the polymer.

To the curing blend other components can optionally be added, for example semicrystalline (per)fluoropolymers, for example selected from PTFE, or PTFE modified with comonomers.

The curable perfluoroelastomers contain the perfluoroelastomers and the curing agent. The (per)fluoroelastomers of the invention, as said, are cured by peroxidic way. This is carried out according to known techniques, by addition of peroxides capable to generate radicals by heating. Among the most commonly used there are: dialkylperoxides, as for example di-terbutyl-peroxide and 2,5-dimethyl-2,5- di(terbutylperoxy)hexane; dicumyl peroxide; dibenzoyl peroxide; diterbutyl per- benzoate; di[1 ,3-dimethyl-3-(terbutylperoxy) butyl]-carbonate. Other peroxidic systems are described, for example, in the patent applications EP 136,596 and EP 410,351.

Generally the amount of peroxide used ranges from 0.1% to 5%, preferably from 0.2% to 3% by weight with respect to the polymer weight.

The preparation of the (per)fluoroelastomers of the present invention can be carried out by copolymerization of the monomers in aqueous emulsion according to well known methods of the prior art, in the presence of radical initiators (for example alkaline or ammonium persulphates, perphosphates, perborates or percarbonates), optionally with ferrous or silver salts, or other easily oxidizable metals. Surfactants, as for example (per)fluoroalkylic carboxylates or sulphonates (for example ammonium perfluorooctanoate) or (per)fluoropolyoxyalkylenic, or others known in the prior art are also present in the reaction medium.

At the end of the polymerization, the fluoroelastomer is isolated from the emulsion by conventional methods, as coagulation by addition of electrolytes or by cooling.

Alternatively, the polymerization reaction can be carried out in mass or in suspension, in an organic liquid wherein a suitable radical initiator is present, according to well known techniques.

The polymerization reaction is generally carried out at temperatures in the range of 25°C-150°C, under pressure up to 10 MPa.

The preparation of the fluoroelastomers of the present invention is preferably carried out in aqueous emulsion in the presence of an emulsion, dispersion or microe- mulsion of perfluoropolyoxyalkylenes, as described in USP 4,789,717 and USP 4,864,006, which are herein incorporated by reference.

Optionally the (per)fluoroelastomers of the invention can be mixed with semicrystalline (per)fluoropolymers in an amount (% by weight referred to the total dry weight (per)fluoroelastomer + semicrystalline (per)fluoropolymer) from 0% to 70%, preferably from 0% to 50% by weight, still more preferably from 2% to 30% by weight. With semicrystalline (per)fluoropolymer it is meant a (per)fluoropolymer showing, besides the glass transition temperature Tg, at least a crystalline melting temperature. The semicrystalline (per)fluoropolymer is constituted by tetrafluoroethylene (TFE) homopolymers, or TFE copolymers with one or more monomers containing at least one unsaturation of ethylene type, in an amount from 0.01% to 10% by moles, preferably from 0.05% to 7% by moles. Said comonomers having an ethylene unsaturation are of both hydrogenated and fluorinated type. Among those hydrogenated, ethylene, propylene, acrylic monomers, for example methylmethacrylate, (meth)acrylic acid, butylacrylate, hydro- xyethylhexylacrylate, styrene monomers, can be mentioned.

Among fluorinated comonomers it can be mentioned:

C₃-C₈ perfluoroolefins, as hexafluoropropene (HFP), hexafluoroisobutene;

C₂-C₈ hydrogenated fluoroolefins, as vinyl fluoride (VF), vinylidene fluoride

(VDF), trifluoroethylene, perfluoroalkylethylene CH₂=CH-Rf, wherein R_f is a

CrC₆ perfluoroalkyl;

C₂-C₈ chloro- and/or bromo- and/or iodo-fluoroolefins, as chlorotrifluoroethy- lene (CTFE);

(per)fluoroalkylvinylethers (PAVE) CF₂=CFORf, wherein R_f is a C₁-C₆ (per)- fluoroalkyl, for example CF₃, C₂F₅, C₃F₇;

(per)fluoro-oxyalkylvinylethers CF₂=CFOX, wherein X is: a CrCi₂ alkyl, or a

CrCi₂ oxyalkyl, or a CrCi₂ (per)fluoro-oxyalkyl having one or more ether groups;

(per)fluorodioxoles, preferably perfluorodioxoles.

PAVEs, in particular perfluoromethyl-, perfluoroethyl-, perfluoropropylvinylether and (per)fluorodioxoles, preferably perfluorodioxoles, are preferred comonomers.

Optionally the semicrystalline (per)fluoropolymer is coated by a shell of a semicrystalline (per)fluoropolymer containing bromine and/or iodine atoms in the chain deriving from brominated and/or iodinated comonomers, in an amount from 0.1% to 10% by moles referred to the total moles of the basic monomeric units of the semicrystalline (per)fluoropolymer core + shell, the semicrystalline (per)fluoropolymer in the core and in the shell can be of different composition. See EP 1 ,031 ,606.

The preparation of said semicrystalline (per)fluoropolymers is carried out by polymerization of the monomers in aqueous emulsion in the presence of an emulsion, dispersion or microemulsion of perfluoropolyoxyalkylenes, according to what described in USP 4,789,717 and USP 4,864,006. Preferably the synthesis is carried out in the presence of a perfluoropolyoxyalkylene microemulsion.

When the (per)fluoroelastomers of the present invention contain semicrystalline (per)fluoropolymers, mixing is preferably carried out by mixing in the desired ratios the (per)fluoroelastomer latex with the semicrystalline (per)fluoropolymer latex, then co-coagulating the obtained mixture as described in USP 6,395,834 and USP 6,310,142.

Alternatively the semicrystalline (per)fluoropolymer can be polymerized and then the (per)fluoroelastomer is polymerized on the (per)fluoropolymer particles. A core-shell structure is thus obtained.

The Applicant has unexpectedly and surprisingly found that, by using as filler the silica as defined above in the (per)fluoroelastomers of the invention, an improved vapour resistance at high temperatures, for example up to 320°C, preferably up to 300°C, is obtained, this means an improved combination of good sealing properties, as measured by the compression set, and limited variations of the mechanical properties, as stress at break, elongation at break, hardness and swelling by volume. Said combination of good sealing properties and of limited variation of mechanical properties unexpectedly and surprisingly found by the Applicant is maintained even after long times of vapour treatment at the above mentioned high temperatures, for example even for treatment times longer than 150 hours.

Furthermore the (per)fluoroelatomeric compositions of the invention contain a total residual amount of metals, after calcination at the temperature of 800°C, lower than 1 ,500 ppm, preferably lower than 1 ,000 ppm, wherefore they are usable in the electronic, pharmaceutical and oil industry. The total residual amount of metals is determined according to the method indicated below.

A further object of the present invention are also cured (per)fluoroelastomeric compositions obtainable from the curable compositions of the invention.

A further object of the present invention are cured manufactured articles obtainable from the curable compositions of the invention.

A further object of the present invention is the use of the curable compositions of the present invention to obtain manufactured articles showing an improved vapour resistance at high temperatures, from 230°C to 320°C, in particular from 250°C to 300°C, even for long treatment times, even higher than 150 hours.

The following Examples are given for illustrative and not limitative purposes of the present invention.

EXAMPLES

METHODS

Non-wettabilitv test of the silica with water

A silica volume equal to 200 ml is poured in a beaker containing an equal volume of water at room temperature (25°C), it is mixed with a glass rod for 3 seconds, the silica must form a separated layer over the aqueous phase to indicate that the silica is not wettable by water.

The silica does not pass the test if it instead precipitates on the beaker buttom. This shows indeed that the silica is wettable with water. Determination of the total amount of residual metals after calcination

The quantitative determination of sodium, calcium, potassium, barium, aluminum, magnesium, iron, chromium, nickel, zinc, lead, cadmium, molybdenum, manganese, copper, cobalt, lithium and titanium impurities is carried out by ICP-MS after calcination according to the following procedure. The samples are previously cleaned with ultrapure water to remove the surface pollution. About 2 g of the sample are calcined (ignited) in a platinum crucible on a bunsen flame to remove all the organic material at the temperature of 800°C. The residue is dissolved in 2 ml of ultrapure concentrated HCI on a heating plate and evaporated up to dryness. The residue is let revive with 1 ml of ultrapure concentrated HNO₃ on a heating plate. The solution is transferred in a graduated container, the internal standard (Indio) is added and it is diluted up to 50 ml with ultrapure water. The measurement is carried out by high resolution ICP/MS (ThermoFinnigan Element®). Each sample is double analyzed. The crucibles for the blanks are measured before the sample analysis by following the same procedure. The limits of the determination are calculated as 6^*st.dev. of the blanks. EXAMPLE 1 Polymerization

In a 22 litre steel autoclave, equipped with stirrer working at 460 rpm there have been introduced, after evacuation, 14.5 litres of demineralized water and 145 ml of a microemulsion obtained by mixing:

32 ml of a perfluoropolyoxyalkylene having average molecular weight 600 g/mole, having acid end group of formula:

CF₂CIO(CF₂-CF(CF₃)O)_n(CF₂θ)_mCF₂COOH wherein n/m = 10;

32 ml of an aqueous solution of NH₃ at 30% by volume;

62 ml of demineralized water;

19 ml of Galden® D02 having average molecular weight of 450 g/mole and formula:

CF₃O(CF₂-CF(CF₃)O)_n(CF₂O^CF₃ wherein n/m = 20.

The autoclave was then heated to 80°C and maintained at said temperature for the whole time of the reaction. Then 35 g of 1 ,4-diiodoperfluorobutane (C₄F₈I₂) were introduced in the autoclave.

The mixture of monomers having the following molar composition is then fed: tetrafluoroethylene (TFE) 35%; perfluoromethylvinylether (MVE) 65%; so as to bring the pressure to 25 bar rel (2.5 MPa).

In the autoclave are then introduced:

0.7 g of ammonium persulphate (APS) as initiator;

18 g of bis-olefin of formula CH2=CH-(CF₂)6-CH=CH₂.

The bis-olefin addition was carried out in 20 portions, each of 0.9 g, starting from the polymerization beginning and for every 5% increase in the monomer conversion.

The pressure of 25 bar relative (rel) (2.5 MPa) was maintained constant for the whole duration of the polymerization by feeding a mixture having the following molar composition: tetrafluoroethylene (TFE) 60%, perfluoromethylvinylether (MVE) 40%.

After 160 minutes of the reaction, corresponding to 100% of monomer conversion, the autoclave was cooled and the latex discharged.

The so obtained latex had a concentration equal to 290 g_Poiymer/kgι_atex and was used both in the Examples of the invention and in the comparative Examples. The latex was coagulated by dripping the latex in a nitric acid solution. The obtained polymer was dried at 90°C in an air-circulating oven for 16 hours.

The dried polymer was mixed with the following ingredients: bis-olefin, having formula CH2=CH-(CF₂)6-CH=CH₂;

2,5-dimethyl-2,5-di(terbutylperoxy)hexane Luperox®101 ; silica; optionally other fillers; in the amounts (phr) indicated in Table 1 for the examples according to the invention and for the comparative ones.

The so obtained blend was molded for 10 minutes at 170°C and then characterized under the conditions indicated in Table 1.

In Examples 2 and 4, the silicas Sipernat®D17 and Cabot®TS720, respectively, were used, which met the above described non wettability test with water and had a SiO₂ titre, determined according to the ISO 3262-19 standard, not lower than 98%.

In the comparative Example 3, Carplex® 1120 was a commercial silica which did not pass the non wettability with water test according to the above reported method. Indeed in this case the silica formed a precipitate in the aqueous phase at the beaker bottom.

In the Table the term "n.d." means that the parameter value is not determinable, since the sample degrades under the conditions in which the determination is carried out.

The Applicant has furthermore found that, if a silica not complying with the present invention was used, a perfluoroelastomer was obtained, which was not vapour resistant, see example 3 comparative. As a matter of fact it was found that the mechanical properties and the compression set could not be determined under these conditions set forth in the test since the sample degraded. Table 1

Cont.ed from Tabie 1

Claims

1. (Per)fluoroelastomeric compositions curable by peroxidic way, comprising for 100 phr of (per)fluoroelastomer: as filler, from 2 to 70 phr of silica not wettable with water according to the above reported test, as crosslinking agent, from 0.5 to 10 phr of a bis-olefin having general formula:

wherein:

R-i, R2, R3, R₄, R5, Re, equal to or different from each other, are H or C₁-C₅ alkyls;

Z is selected between a Ci-Ci₈ linear or branched alkylene or cycloalkylene radical, optionally containing oxygen atoms, preferably at least partially fluorinated, or a (per)fluoropolyoxyalkylene radical; the total residual content of metals in the (per)fluoroelastomeric composition being lower than 1 ,500 ppm, preferably lower than 1 ,000 ppm, the test for the silica wettability with water being the following: a volume of silica equal to 200 ml is poured in a beaker containing an equal volume of water at room temperature (25°C), it is mixed with a glass rod for 3 seconds, the silica must form a separated layer over the aqueous phase to indicate that the silica is not wettable by the water.

2. Curable (per)fluoroelastomeric compositions according to claim 1 , wherein the silica ranges from 5 to 50 phr, preferably from 10 to 30 phr.

3. Curable (per)fluoroelastomeric compositions according to claims 1-2, wherein the bis-olefin ranges from 0.6 to 5 phr, preferably from 0.6 to 1.8 phr, more preferably from 0.9 to 1.5 phr.

4. Curable (per)fluoroelastomeric compositions according to claim 1 , wherein in formula (I) Z is a C₄-Ci₂, preferably C₄-C₈, perfluoroalkylene radical and Ri, R₂, R₃, R₄, Rs, Re are hydrogen; when Z is a (per)fluoropolyoxyalkylene radical, it comprises units selected from the following:

-CF₂CF₂O-, -CF₂CF(CF₃)O-, -CFX₁O- wherein X₁ = F, CF₃,

-CF₂CF₂CF₂O-, -CF₂-CH₂CH₂O-, -C₃F₆O-;

5. Curable (per)fluoroelastomeric compositions according to claim 4, wherein Z has formula:

-(Q)p-CF₂O-(CF₂CF₂O)_m(CF₂O)_n-CF₂-(Q)p- (II) wherein: Q is a C₁-C₁O alkylene or oxyalkylene radical; p is O or 1 ; m and n are numbers such that the m/n ratio is between 0.2 and 5 and the molecular weight of said (per)fluoropolyoxyalkylene radical is in the range 500-10,000, preferably 700-2,000.

6. Curable (per)fluoroelastomeric compositions according to claim 5, wherein Q is selected from:

-CH₂OCH₂-; -CH₂O(CH₂CH₂O)_sCH₂-, s being = 1-3.

7. Curable (per)fluoroelastomeric compositions according to claims 4-6, wherein the bis-olefin has formula:

-CH₂=CH-(CF₂)_to-CH=CH₂ wherein to is an integer from 6 to 10.

8. Curable (per)fluoroelastomeric composition according to claims 1-7, wherein the (per)fluoroelastomers contain peroxidic crosslinking sites.

9. Curable (per)fluoroelastomeric compositions according to claim 8, wherein peroxidic crosslinking sites are iodine and/or bromine atoms, preferably iodine.

10. Curable (per)fluoroelastomeric compositions according to claims 8-9, wherein the iodine and/or bromine amount is between 0.001% and 5% by weight, preferably between 0.01% and 2,5% by weight with respect to the total weight of the polymer.

11. Curable (per)fluoroelastomeric compositions according to claims 8-10, wherein in the (per)fluoroelastomers the iodine and/or bromine atoms are in the chain and/or in end position.

12. Curable (per)fluoroelastomeric compositions according to claims 1-11 , wherein the (per)fluoroelastomers are TFE copolymers with at least a perfluorinated olefin having one unsaturation of ethylene type.

13. Curable (per)fluoroelastomeric compositions according to claim 12, wherein in the (per)fluoroelastomers the comonomer is selected from:

(per)fluoroalkylvinylethers (PAVE) CF₂=CFOR2f, wherein R₃ is a C_rC₆

(per)fluoroalkyl, preferably trifluoromethyl, bromotrifluoromethyl, penta- fluoropropyl;

(per)fluoro-oxyalkylvinylethers CF₂=CFOX₀, wherein X₀ is a C_rCi₂ perfluorooxyalkyl, containing one or more ether groups;

(per)fluorovinylethers having general formula:

CFX₂=CX₂OCF₂OR¹V (I-B) wherein

R'V has the following meanings:

CrC₆ linear or branched (per)fluoroalkyl, -C₅-C₆ cyclic (per)fluoroalkyl,

14. Curable (per)fluoroelastomeric compositions according to claim 13, wherein in the (per)fluoroelastomers when the comonomer is a (per)fluorovinylether of formula (I-B), it is selected from the following: CF₂=CFOCF₂OCF₂CF₃ (MOVE1) CF₂=CFOCF₂OCF₂CF₂OCF₃ (MOVE2)

CF₂=CFOCF₂OCF₃ (MOVE3).

15. Curable (per)fluoroelastomeric compositions according to claims 12-14, wherein the (per)fluoroelastomers have the following compositions, expressed as % by moles:

TFE 50-85%, PAVE 15-50%;

TFE 20-85%, MOVE 15-80%, optionally PAVE 0-50%; the sum of the monomers being 100% by moles.

16. Curable (per)fluoroelastomeric compositions according to claims 12-15, wherein the fluorinated polymers contain units deriving from VDF, C₃-C₈ fluoroolefins, optionally containing hydrogen atoms, chlorine and/or bromine and/or iodine, C₂-Cs non fluorinated olefins (01).

17. Curable (per)fluoroelastomeric compositions according to claim 16, wherein the fluorinated polymers have the following compositions:

33-75% by moles of tetrafluoroethylene (TFE), preferably 40-60%; 15-45% by moles of a perfluorovinylether (PAVE), preferably 20-40%; 2-25% by moles of vinylidene fluoride (VDF), preferably 15-20%; TFE 32-60%, PAVE 20-40%; Ol 10-40%; the sum of the moles of the compositions being 100%.

18. Curable (per)fluoroelastomeric compositions according to claim 17, wherein at the place or in combination with PAVE, the (per)fluorovinylethers of formula (I-B) are used, the total % of the vinylethers being within the above indicated limits.

19. Curable (per)fluoroelastomeric compositions according to claims 1-18, wherein the fluorinated polymers contain in the chain monomeric units deriving from a bis-olefin of formula (I).

20. Curable (per)fluoroelastomeric compositions according to claim 19, wherein the bis-olefin amount ranges from 0.01% to 5% by moles with respect to the polymer.

21. Curable (per)fluoroelastomeric compositions according to claims 1-20, wherein the (per)fluoroelastomeric or fluoroelastomeric polymers are in admixture with a semicrystalline (per)fluoropolymer in an amount, as per cent by weight referred to the total dry weight (per)fluoroelastomer + semicrystalline (per)fluo- ropolymer, from 0% to 70%, preferably from 0% to 50% by weight, still more preferably from 2% to 30% by weight.

22. Curable (per)fluoroelastomeric compositions according to claim 21 , wherein the semicrystalline (per)fluoropolymer is constituted by tetrafluoroethylene (TFE) homopolymers, or TFE copolymers with one or more monomers containing at least one unsaturation of ethylene type, in an amount from 0.01% to 10% by moles, preferably from 0.05% to 7% by moles, said comonomers having an ethylene unsaturation being both of hydrogenated and fluorinated type.

23. Curable (per)fluoroelastomeric compositions according to claims 21-22, wherein the hydrogenated comonomers are selected from ethylene, propylene, acrylic monomers, styrene monomers.

24. Curable (per)fluoroelastomeric compositions according to claims 21-23, wherein the fluorinated comonomers are selected from the following:

C₃-C₈ perfluoroolefins;

C₂-Cs hydrogenated fluoroolefins; perfluoroalkyl-ethylene CH₂=CH-Rf, wherein R_f is a d-C₆ perfluoroalkyl;

C₂-Cs chloro- and/or bromo- and/or iodo-fluoroolefins;

(per)fluoroalkylvinylethers (PAVE) CF₂=CFORf, wherein R_f is a C_rC₆

(per)fluoroalkyl;

(per)fluoro-oxyalkylvinylethers CF₂=CFOX, wherein X is: a CrCi₂ alkyl, or a CrCi₂ oxyalkyl, or a CrCi₂ (per)fluoro-oxyalkyl having one or more ether groups;

(per)fluorodioxoles, preferably perfluorodioxoles.

25. Manufactured articles obtainable from the (per)fluoroelastomeric compositions curable according to claims 1-24.

26. Use of the (per)fluoroelastomeric compositions curable according to claims 1-24 to obtain manufactured articles having an improved vapour resistance at high temperatures, from 230°C to 320°C, in particular from 250°C to 300°C.

27. Cured (per)fluoroelastomeric compositions obtainable from the (per)fluoro- elastomeric compositions curable according to claims 1-24.