Fluoroelastomer composition

Abstract

The invention pertains to a (per)fluoroelastomer composition comprising at least one (per)fluoroelastomer comprising iodine and/or bromine atoms, at least one polyunsaturated compound, at least one organic peroxide and at least one organic compound selected from the group consisting of (thio)urea compounds, cyclic addition products of ammonia or primary amine and aldehyde; (thio)carbamates.

Claims

1. A (per)fluoroelastomer composition comprising: at least one (per)fluoroelastomer [fluoroelastomer (A)], said fluoroelastomer (A) comprising iodine and/or bromine atoms and having a backbone comprising: recurring units derived from tetrafluoroethylene (TFE); recurring units derived from at least one perfluorinated monomer selected from the group consisting of: PAVE monomers, wherein the PAVE monomers are perfluoroalkylvinylethers complying with formula CF.sub.2═CFOR.sub.f1 in which R.sub.f1 is a C.sub.1-C.sub.6 perfluoroalkyl; and MOVE monomers, wherein the MOVE monomers are perfluoro-oxyalkylvinylethers complying with formula CF.sub.2═CFOX.sub.0, in which X.sub.0 is (i) a C.sub.1-C.sub.12 perfluorooxyalkyl having one or more ether groups; or (ii) a group of formula -CF.sub.2OR.sub.f2 in which R.sub.f2 is a C.sub.1-C.sub.6 perfluoroalkyl; optionally, recurring units derived from vinylidene fluoride (VDF) in an amount of up to 30% by moles, with respect to the total moles of recurring units; optionally, recurring units derived from at least one perfluorinated C.sub.3-C.sub.8 alpha- olefin, in an amount of up to 5% moles, with respect to the total moles of recurring units; optionally, recurring units derived from at least one fluorine-free alpha-olefin, in an amount of up to 10% moles, with respect to the total moles of recurring units; and optionally, recurring units derived from at least one bis-olefin [bis-olefin (OF)]; from 0.5 to 5 weight parts, per 100 parts by weight of said fluoroelastomer (A), of at least one polyunsaturated compound selected from the group consisting of bis-olefins of formulae (OF-1), (OF-2) and (OF-3): ##STR00023## wherein j is an integer between 2 and 10, and R.sub.1, R.sub.2, R.sub.3, R.sub.4, equal or different from each other, are H, F or C.sub.1-5 alkyl or (per)fluoroalkyl-group; ##STR00024## 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 OR.sub.B, wherein R.sub.B 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 atoms, optionally fluorinated, which may be inserted with ether linkages; ##STR00025## wherein E, A and B have the same meaning as above defined; R.sub.5, R.sub.6, R.sub.7, equal or different from each other, are H, F or C.sub.1-5 alkyl or (per)fluoroalkyl group from 0.1 to 3 weight parts, per 100 parts by weight of said fluoroelastomer (A), of at least one organic peroxide; from 0.1 to 10 weight parts, per 100 parts by weight of said fluoroelastomer (A), of at least one organic compound [compound (C)] selected from the group consisting of: urea compounds of formula (U): ##STR00026## wherein E is O, and each of R.sub.u, equal to or different from each other, is independently selected from the group consisting of hydrogen and C.sub.1-C.sub.6 hydrocarbon groups; cyclic addition products of ammonia or primary amine and aldehyde; and carbamates of formula (C): ##STR00027## wherein E is oxygen; R.sub.b is a C.sub.1-C.sub.36 hydrocarbon group, and R.sub.e is H or a C.sub.1-C.sub.6 alkyl group.

2. The (per)fluoroelastomer composition of claim 1, wherein the polyunsaturated compound is present in the composition in an amount of at least 1 weight parts per 100 parts by weight of fluoroelastomer (A) and in an amount of less than 5 weight parts per 100 parts by weight of fluoroelastomer (A).

3. The (per)fluoroelastomer composition of claim 2, wherein the polyunsaturated compound is present in the composition in an amount of at least 1.2 weight parts per 100 parts by weight of fluoroelastomer (A) and/or in an amount of less than 4 weight parts per 100 parts by weight of fluoroelastomer (A).

4. The (per)fluoroelastomer composition of claim 3, wherein the polyunsaturated compound is present in the composition in an amount of less than 3 weight parts per 100 parts by weight of fluoroelastomer (A).

5. The (per)fluoroelastomer composition of claim 1, wherein fluoroelastomer (A) is selected from those having a backbone comprising: recurring units derived from TFE in an amount of 30 to 70% moles; recurring units derived from at least one perfluorinated monomer selected from the group consisting of PAVE monomers and MOVE monomers, in an amount of 25 to 40% moles; optionally, recurring units derived from VDF in an amount of 1 to 25% moles; optionally, recurring units derived from ethylene (E) in an amount from 0 to 5% moles; optionally, recurring units derived from hexafluoropropylene (HFP) in an amount from 0 to 5% moles; and optionally, recurring units derived from at least one bis-olefin (OF).

6. The (per)fluoroelastomer composition of claim 5, wherein fluoroelastomer (A) is selected from the group consisting of fluoroelastomers having any of the following monomer compositions (in mol %): (i) tetrafluoroethylene (TFE) 50-80%, perfluoroalkyl vinyl ethers (PAVE) 20-50%, bis- olefin (OF) 0-5%; (ii) tetrafluoroethylene (TFE) 20-70%, perfluoro-oxyalkylvinylether (MOVE) 30- 80%, perfluoroalkyl vinyl ethers (PAVE) 0-50%, bis-olefin (OF) 0-5%; (iii) tetrafluoroethylene (TFE) 40-70%, perfluoroalkyl vinyl ethers (PAVE) 20-50%, vinylidene fluoride (VDF): 10-30%; bis-olefin (OF): 0-5%; hexafluoropropylene (HFP): 0-5%; and (iv) tetrafluoroethylene (TFE) 40-69%, perfluoroalkyl vinyl ethers (PAVE) 20-49%, vinylidene fluoride (VDF): 10-30%; ethylene (E): 1-5%; bis-olefin (OF) 0-5%; hexafluoropropylene (HFP): 0-5%.

7. The (per)fluoroelastomer composition of claim 1, wherein the organic peroxide is selected from the group consisting of dialkyl peroxides.

8. The (per)fluoroelastomer composition of claim 7, wherein dialkyl peroxides are selected from di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, bis(1,1-diethylpropyl)peroxide, bis(1-ethyl -1-methylpropyl)peroxide, 1,1-diethylpropyl-1-ethy1-1-methylpropyl-peroxide, 2,5- dimethyl-2,5-bis(tert-amylperoxy)hexane; dicumyl peroxide; dibenzoyl peroxide; di-tert-butyl perbenzoate; and bis[1,3-dimethyl-3-(tert-butylperoxy)butyl] carbonate.

9. The (per)fluoroelastomer composition of claim 1, wherein the amount of the organic peroxide is at least 0.5 weight parts per 100 parts by weight of fluoroelastomer (A) and less than 3 weight parts per 100 parts by weight of fluoroelastomer (A).

10. The (per)fluoroelastomer composition of claim 9, wherein the amount of the organic peroxide is at least 0.8 weight parts per 100 parts by weight of fluoroelastomer (A) and/or less than 2.5 weight parts per 100 parts by weight of fluoroelastomer (A).

11. The (per)fluoroelastomer composition of claim 10, wherein the amount of the organic peroxide is at less than 2 weight parts per 100 parts by weight of fluoroelastomer (A).

12. The (per)fluoroelastomer composition of claim 1, wherein said urea compounds are selected from the group consisting of: (i-A) ureas of formula (U-2): ##STR00028## wherein E′ is O; and/or wherein said cyclic addition products of ammonia or primary amine and aldehyde are selected from the group consisting of: (ii-A) cyclic aldehyde adducts trimers of formula (T): ##STR00029## wherein each of R.sub.a, equal to or different from each other, is selected from the group consisting of hydrogen and C.sub.1-C.sub.6 hydrocarbon groups; and (ii-B) hexamethylene tetramine of formula: ##STR00030## and/or wherein said carbamates are selected from the group consisting of: carbamates of formula (C-1): ##STR00031## wherein R′.sub.d dis a C.sub.1-C.sub.36 hydrocarbon group.

13. The (per)fluoroelastomer composition of claim 1, wherein organic compound (C) is selected from the group consisting of: (C-1) Urea of formula: ##STR00032## (C-2) Acetaldehyde ammonia trimer of formula: ##STR00033## (C-3) Hexamethylenetetramine of formula: ##STR00034## and (C-4) Benzyl carbamate of formula: ##STR00035##

14. The (per)fluoroelastomer composition of claim 1, wherein the amount of organic compound (C) is at least 0.2 weight parts per 100 parts by weight of fluoroelastomer (A) and/or less than 3 weight parts per 100 parts by weight of fluoroelastomer (A).

15. The (per)fluoroelastomer composition of claim 14, wherein the amount of organic compound (C) is at least 0.5 weight parts per 100 parts by weight of fluoroelastomer (A) and/or less than 2.5 weight parts per 100 parts by weight of fluoroelastomer (A).

16. The (per)fluoroelastomer composition of claim 15, wherein the amount of organic compound (C) is less than 2 weight parts per 100 parts by weight of fluoroelastomer (A).

17. The (per)fluoroelastomer composition of claim 1, wherein the (per)fluoroelastomer composition consists essentially of: the at least one (per)fluoroelastomer [fluoroelastomer (A)], said fluoroelastomer (A) comprising iodine and/or bromine atoms and having a backbone comprising: recurring units derived from tetrafluoroethylene (TFE); recurring units derived from at least one perfluorinated monomer selected from the group consisting of: PAVE monomers, wherein the PAVE monomers are perfluoroalkylvinylethers complying with formula CF.sub.2═CFOR.sub.f1 in which R.sub.f1 is a C.sub.1-C.sub.6 perfluoroalkyl; and MOVE monomers, wherein the MOVE monomers are perfluoro-oxyalkylvinylethers complying with formula CF.sub.2═CFOX.sub.0, in which X.sub.0 is (i) a C.sub.1-C.sub.12 perfluorooxyalkyl having one or more ether groups; or (ii) a group of formula —CF.sub.2OR.sub.f2 in which R.sub.f2 is a C.sub.1-C.sub.6 perfluoroalkyl; optionally, recurring units derived from vinylidene fluoride (VDF) in an amount of up to 30% by moles, with respect to the total moles of recurring units; optionally, recurring units derived from at least one perfluorinated C.sub.3-C.sub.8 alpha- olefin, in an amount of up to 5% moles, with respect to the total moles of recurring units; optionally, recurring units derived from at least one fluorine-free alpha-olefin, in an amount of up to 10% moles, with respect to the total moles of recurring units; and optionally, recurring units derived from at least one bis-olefin [bis-olefin (OF)]; from 0.5 to 5 weight parts, per 100 parts by weight of said fluoroelastomer (A), of the at least the one polyunsaturated compound selected from the group consisting of bis-olefins of formulae (OF-1), (OF-2) and (OF-3) from 0.1 to 3 weight parts, per 100 parts by weight of said fluoroelastomer (A), of the at least one organic peroxide; from 0.1 to 10 weight parts, per 100 parts by weight of said fluoroelastomer (A), of the at least one organic compound [compound (C)] selected from the group consisting of: urea compounds of formula (U), cyclic addition products of ammonia or primary amine and aldehyde; and carbamates of formula (C).

18. The (per)fluoroelastomer composition of claim 1, wherein the at least one (per)fluoroelastomer (A) comprises iodine and/or bromine atoms and having a backbone consisting essentially of: recurring units derived from tetrafluoroethylene (TFE); recurring units derived from at least one perfluorinated monomer selected from the group consisting of: PAVE monomers, wherein the PAVE monomers are perfluoroalkylvinylethers complying with formula CF.sub.2═CFOR.sub.f1 in which R.sub.f1 is a C.sub.1-C.sub.6 perfluoroalkyl; and MOVE monomers, wherein the MOVE monomers are perfluoro-oxyalkylvinylethers complying with formula CF.sub.2═CFOX.sub.0, in which X.sub.0 is (i) a C.sub.1-C.sub.12 perfluorooxyalkyl having one or more ether groups; or (ii) a group of formula —CF.sub.2OR.sub.f2 in which R.sub.f2 is a C.sub.1-C.sub.6 perfluoroalkyl; optionally, recurring units derived from vinylidene fluoride (VDF) in an amount of up to 30% by moles, with respect to the total moles of recurring units; optionally, recurring units derived from at least one perfluorinated C.sub.3-C.sub.8 alpha-olefin, in an amount of up to 5% moles, with respect to the total moles of recurring units; optionally, recurring units derived from at least one fluorine-free alpha-olefin, in an amount of up to 10% moles, with respect to the total moles of recurring units; and optionally, recurring units derived from at least one bis-olefin [bis-olefin (OF)].

19. The (per)fluoroelastomer composition of claim 1, wherein the at least one organic compound (C) is selected from the group consisting of: urea compounds of formula (U): ##STR00036## wherein E is O, and each of R.sub.u, equal to or different from each other, is independently selected from the group consisting of hydrogen and C.sub.1-C.sub.6 hydrocarbon groups; and carbamates of formula (C): ##STR00037## wherein E is oxygen; R.sub.b is a C.sub.1-C.sub.36 hydrocarbon group, and R.sub.e is H or a C.sub.1-C.sub.6 alkyl group; optionally, a metal compound selected from the group consisting of (i) oxides and hydroxides of divalent metals, (ii) salts of a weak acid, and (iii) mixtures of (i) and (ii); and optionally, at least one filler, thickener, pigment, antioxidants stabilizer, or processing aid.

20. The (per)fluoroelastomer composition of claim 1, wherein said urea compounds are selected from the group consisting of: (i-A) ureas of formula (U-2): ##STR00038## wherein E′ is O; (ii-B) hexamethylene tetramine of formula: ##STR00039## and/or carbamates are selected from the group consisting of: carbamates of formula (C-1): ##STR00040## wherein R′.sub.d dis a C.sub.1-C.sub.36 hydrocarbon group.

21. The (per)fluoroelastomer composition of claim 1, wherein the wherein organic compound (C) is selected from the group consisting of: (C-1) Urea of formula: ##STR00041## (C-3) Hexamethylenetetramine of formula: ##STR00042## and (C-4) Benzyl carbamate of formula: ##STR00043##

22. A method for preparing a shaped article, the method comprising processing the fluoroelastomer composition according to claim 1 such that it is fabricated into a desired shape.

23. The method according to claim 22, wherein the fluoroelastomer composition fabricated into the desired shape is subjected to vulcanization, during the processing itself and/or in a subsequent step.

24. A cured article comprising the fluoroelastomer composition according to claim 1.

Description

(1) 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.

(2) 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 R.sub.f(I).sub.x(Br).sub.y, in which R.sub.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 (see, for example, U.S. Pat. No. 4,243,770 (DAIKIN IND LTD) 6 Jan. 1981 and U.S. Pat. No. 4,943,622 (NIPPON MEKTRON KK) 24 Jul. 1990); and alkali metal or alkaline-earth metal iodides and/or bromides, such as described notably in U.S. Pat. No. 5,173,553 (AUSIMONT SRL) 22 Dec. 1992.

(3) The fluoroelastomer (A) of the invention comprises advantageously iodine and/or bromine atoms in an amount of 0.001 to 10% wt, with respect to the total weight of the fluoroelastomer (A).

(4) According to this embodiment, for ensuring acceptable reactivity it is generally understood that the content of iodine and/or bromine in the fluoroelastomer (A) should be of at least 0.05% wt, preferably of at least 0.1% weight, more preferably of at least 0.15% weight, with respect to the total weight of fluoroelastomer (A).

(5) On the other side, amounts of iodine and/or bromine not exceeding preferably 7% wt, more specifically not exceeding 5% wt, or even not exceeding 4% wt, with respect to the total weight of perfluoroelastomer (A), are those generally selected for avoiding side reactions and/or detrimental effects on thermal stability.

(6) The curable composition of the invention comprises at least one organic peroxide.

(7) Among most commonly used organic peroxides, mention can be made of dialkyl peroxides, for instance di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, bis(1,1-diethylpropyl)peroxide, bis(1-ethyl-1-methyl propyl)peroxide, 1,1-diethylpropyl-1-ethyl-1-methylpropyl-peroxide, 2,5-dimethyl-2,5-bis(tert-amylperoxy)hexane; dicumyl peroxide; dibenzoyl peroxide; di-tert-butyl perbenzoate; bis[1,3-dimethyl-3-(tert-butylperoxy)butyl] carbonate.

(8) The amount of the organic peroxide ranges normally from 0.1 to 10 weight parts per 100 parts by weight of fluoroelastomer (A).

(9) For achieving reasonable curing rates, it is generally preferred to have in the composition amounts of organic peroxide of at least 0.5, preferably at least 0.8 weight parts per 100 parts by weight of fluoroelastomer (A).

(10) Equally, to the sake of efficiency, amount of organic peroxide is of generally less than 3, more preferably less than 2.5, still more preferably less than 2 weight parts per 100 parts by weight of fluoroelastomer (A).

(11) Among suitable compounds (C), (thio)urea compounds, as above detailed, are preferably selected from the group consisting of:

(12) (i-A) (thio)ureas of formula (U-2):

(13) ##STR00011##
wherein E′ is O or S;
cyclic addition products of ammonia or primary amine and aldehyde, as above detailed, are preferably selected from the group consisting of:
(ii-A) cyclic aldehyde adducts trimers of formula (T):

(14) ##STR00012##
wherein each of R.sub.a, equal to or different from each other, is selected from the group consisting of hydrogen and C.sub.1-C.sub.6 hydrocarbon groups (in particular C.sub.1-C.sub.6 alkyl groups);
(ii-B) hexamethylene tetramine of formula:

(15) ##STR00013##
(which is known to be the result of addition of ammonia on formaldehyde); (thio)carbamates, as above detailed, are preferably selected from the group consisting of carbamates of formula (C-1):

(16) ##STR00014##
wherein R′.sub.d is a C.sub.1-C.sub.36 hydrocarbon group, preferably is a optionally substituted benzyl group.

(17) Organic compounds (C) which have been found particularly useful in the composition of the present invention are the following:

(18) (C-1) Urea of formula:

(19) ##STR00015##
(C-2) Acetaldehyde ammonia trimer of formula:

(20) ##STR00016##
(C-3) Hexamethylenetetramine of formula:

(21) ##STR00017##
(C-4) Benzyl carbamate of formula:

(22) ##STR00018##

(23) The amount of the organic compound (C) ranges normally from 0.1 to 10 weight parts per 100 parts by weight of fluoroelastomer (A).

(24) Optimization of thermal resistance and sealing properties at e.g. 300° C. would generally preferably require to have in the composition amounts of organic compound (C) of at least 0.2, preferably at least 0.5 weight parts per 100 parts by weight of fluoroelastomer (A).

(25) Equally, for avoiding possible side reactions/side effects, it may be useful limiting the amount of organic compound (C) to generally less than 3, more preferably less than 2.5, still more preferably less than 2 weight parts per 100 parts by weight of fluoroelastomer (A).

(26) The fluoroelastomer composition of the invention may additionally comprise other ingredients, such as notably:

(27) (a) a metal compound, generally in amounts of between 1 and 15, and preferably between 2 and 10 weight parts per 100 parts of fluoroelastomer (A), typically selected from the group consisting of (i) oxides and hydroxides of divalent metals, for instance Mg, Zn, Ca or Pb, (ii) salts of a weak acid, for instance Ba, Na, K, Pb, Ca stearates, benzoates, carbonates, oxalates or phosphites, and (iii) mixtures of (i) and (ii);
(b) conventional additives, selected generally from the group consisting of fillers (e.g. carbon black), thickeners, pigmen-ts, antioxidants, stabilizers, processing aids, and the like, in amounts of generally 5 and 150, preferably between 10 and 100 weight parts, more preferably between 20 and 60 weight parts, per 100 parts of fluoroelastomer (A).

(28) It is generally understood that the fluoroelastomer composition of the invention comprises no other ingredients beside those above listed; in other terms, the inventive composition generally consists essentially of the fluoroelastomer (A), the organic peroxide, the polyfunctional compound, the organic compound (C), and optionally metal compounds, and conventional additives, as above detailed.

(29) The invention also pertains to a method of using the fluoroelastomer composition, as above described, for fabricating shaped articles.

(30) The fluoroelastomer composition can be fabricated, e.g. by moulding (injection moulding, extrusion moulding), 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 (post-treatment or post-cure), advantageously transforming the relatively soft, weak, fluoroelastomer (A) into a finished article made of non-tacky, strong, insoluble, chemically and thermally resistant cured fluoroelastomer.

(31) Finally, the invention pertains to cured articles obtained from the fluoroelastomer composition, as above detailed.

(32) The cured articles can be notably pipes, joints, O-ring, hose, and the like.

(33) 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.

(34) 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.

(35) Raw Materials

(36) Fluoroelastomer:

(37) (PFR95HT) TECNOFLON® PFR 95HT, a TFE/perfluoromethylvinylether perfluoroelastomer, comprising recurring units derived from a bis-olefin of formula CH.sub.2═CH—(CF.sub.2).sub.6—CH═CH.sub.2, and iodine end-chains, commercially available from Solvay Specialty Polymers Italy, S.p.A.

(38) Organic Compounds:

(39) the following organic compounds were supplied from commercial sources, and used as received:

(40) (C-1) Urea of formula:

(41) ##STR00019##
(C-2) Acetaldehyde ammonia trimer tri-hydrate of formula:

(42) ##STR00020##
(C-3) Hexamethylenetetramine of formula:

(43) ##STR00021##
(C-4) Benzyl carbamate of formula:

(44) ##STR00022##

(45) The following fillers were used:

(46) (CB-1): Austin Black, commercially available from Coal Fillers Inc;

(47) (CB-2): Carbon Black N990MT, commercially available from Cancarb;

(48) The following polyunsaturated compounds were used:

(49) (BO-1) bis-olefin of formula CH.sub.2═CH—(CF.sub.2).sub.6—CH═CHC.sub.2 commercially available from Solvay Specialty Polymers Italy, S.p.A;

(50) (TAIC) triallylisocyanurate commercially available under tradename DRIMIX®.

(51) The following organic peroxide was used:

(52) (P-1) neat 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (C.sub.16H.sub.34O.sub.4), commercially available as LUPEROX® 101 liquid from Arkema.

(53) Curing, Mechanical and Thermal Resistance Property Determination on Cured Samples

(54) Fluoroelastomer was compounded with the additives as detailed in following table in a Brabender mixer. O-rings (size class=214) have been cured from said compositions in a pressed mould 10 minutes at 170° C., and then post-treated/post-cured in an air circulating oven at 200° C. for 8+16 hours. The compression set (C-SET) has been determined on O-ring, specimen standard AS568A (type 214), according to the ASTM D 395, method B, after 70 hours at 300° C.

(55) Plaques have been molded from same composition for 5 minutes at 170° C., and then post-treated/post-cured in an air circulating oven at 200° C. for 8+16 hours. Mechanical properties were determined on specimens punched out from said plaques according to ASTM D412C at 23° C. The following properties were determined:

(56) M.sub.50 is the tensile strength in MPa at an elongation of 50%

(57) M.sub.100 is the tensile strength in MPa at an elongation of 100%

(58) T.S. is the tensile strength in MPa;

(59) E.B. is the elongation at break in %.

(60) Results are summarized in the following table.

(61) TABLE-US-00001 TABLE 1 Ingredient Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5C Ex. 6C Ex. 7C Amounts in parts by weight PFR95HT 100 100 100 100 100 100 100 CB-1 15 15 15 15 15 15 15 CB-2 15 15 15 15 15 15 15 C-1 1 0 0 0 0 0 1 C-2 0 1 0 0 0 0 0 C-3 0 0 1 0 0 0 0 C-4 0 0 0 1 0 0 0 P-1 1 1 1 1 1 0.75 0.75 BO-1 1.5 1.5 1.5 1.5 1.5 0 0 TAIC 0 0 0 0 0 1.2 1.2 C-Set on O-ring moulded 10 min at 170° C. and post-cured (8 + 16) h at 200° C. - C-set determined after 70 h at 300° C. C-Set (%) 44 54 45 54 60 >100 >100 Mechanical properties on punched specimens from plaques moulded 5 min at 170° C. and post-cured (8 + 16) h at 200° C. - determined at 23° C. T.S. (MPa) 14.6 15.3 14.2 14.5 17.9 15.8 16.7 M.sub.50 (MPa) 5.2 5.7 6.1 5.7 5.7 8.8 8.9 M.sub.100 (MPa) 11.6 11.4 11.4 10.9 11.2 15.5 16.1 E.B. (%) 149 195 155 196 180 111 110

(62) The data collected in Table 1 above well demonstrate a positive effect on C-set after compression at 300° C. when the composition comprises an organic compound, as above detailed, in combination with a bis-olefin as polyunsaturated crosslinking agent. C-set is found to be improved by 10 to 27%, which is a significant improvement, especially at these very harsh conditions (temperature of 300° C.). On the other side, the organic compounds are ineffective in delivering any improvement, when used in combination with other polyunsaturated crosslinking agents, e.g. when using TAIC.