WO2015173194A1 - Fluoroelastomers - Google Patents

Abstract

The invention pertains to a (per)fluoroelastomer comprising at least one group of formula (l_x), wherein X is phosphorous or carbon, preferably carbon, and Z is a hydrocarbon group, possibly comprising one or more than one heteroatoms [fluoroelastomer (A)], to a method for its manufacture, to a curable composition comprising the same, and to cured articles therefrom.

Description

Fluoroelastomers Cross-reference to related application

This application claims priority to European or French or other] application No. 14167932.4 filed May 12, 2014, the whole content of this application being incorporated herein by reference for all purposes.

Technical Field

The invention relates to crosslinkable fluoroelastomers comprising certain sulphur-containing groups, to a method for their manufacture, to a method for curing the same, and to cured articles derived there from.

Background Art

Vulcanized (per)fluoroelastomers have been used in a variety of applications, in particular for manufacturing sealing articles such as oil seals, gaskets, shaft seals and O-rings, because of several desirable properties such as heat resistance, chemical resistance, weatherability, etc.

It is nevertheless required for “as polymerized” (per)fluoroelastomers to undergo curing/crosslinking processes (so-called “vulcanization”) in order to ensure required sealing and mechanical properties to be exhibited in final parts.

Several techniques have been developed for ensuring creation of a three-dimensional cured structure able to delivered expected performances; the underlying chemistry generally requires the “as polymerized” (per)fluoroelastomers’ chains to possess suitable cure sites, i.e. moieties which can exhibit suitable reactivity in subsequent curing process, so as to ensure appropriate inter-chain covalent bonding.

Nevertheless, these cure sites and/or the groups which are bonded/reacted thereto during the vulcanization, are often found as possible source of weakness against the otherwise outstanding chemical and thermal stability of fluoroelastomers' chains.

While techniques based on the incorporation of iodine and/or bromine atoms and/or nitrile groups, either as pendant groups or as chain ends, are presently common in the art, a continuous quest exists for new curing chemistries enabling vulcanizing (per)fluoroelastomers for providing crosslinked structures.

On the other side, certain chemical compounds, namely, RAFT/MADIX agents, have been found capable to act as a reversible chain transfer agent in free-radical polymerizations, thereby inducing reversible-addition fragmentation transfer reactions to create an equilibrium between propagating radicals (i.e. the growing polymer chain) and so-called dormant species (containing the chain transfer agent fragment) that can become active again, and hence providing polymer chains terminated with a possibly reactive end group.

These reversible addition-fragmentation chain transfer (RAFT) agents and macromolecular design via inter-exchange of xanthate (MADIX) agents have been notably described in PERRIER, S., et al, Macromolecular design via Reversible Addition-Fragmentation Chain Transfer (RAFT)/Xanthates (MADIX) polymerization, J. Polym. Sci.: Part A: Polym. Chem., 2005, 43, 5347-5393; in WO WO 98/058974 A RHODIA CHIMIE 19981230 and WO WO 98/01478 A E.I. DUPONT DE NEMOURS AND COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANIZATION 19980115 .

While the use of RAFT/MADIX agents for the polymerization of fluorinated monomers has been suggested, nowhere mention has been made of the possibility of applying this living polymerization mechanism to the manufacture of fluoroelastomer with the aim of introducing end-groups of formula –S-X(S)-Z (with X being C or P) in the fluoroelastomer chain.

Summary of invention

The Applicant has now found that RAFT/MADIX agents can be used successfully for providing (per)fluoroelastomers comprising certain functional end groups.

It is hence a first object of the present invention a (per)fluoroelastomer comprising at least one group of formula (I_x):

wherein X, equal to or different from each other at each occurrence, is phosphorous or carbon, preferably carbon, and Z, equal to or different from each other at each occurrence, is a hydrocarbon group, possibly comprising one or more than one heteroatoms [fluoroelastomer (A)].

The Applicant has surprisingly found that (per)fluoroelastomers including groups of formula (I_x), as above detailed, can be easily vulcanized under radical conditions through the chemistry of their groups of formula (I_x).

Brief description of drawings

Figure 1 shows the generally accepted mechanism of RAFT/MADIX controlled radical polymerization.

Description of invention

The expression “RAFT/MADIX agent”, which for the avoidance of doubt is intended to mean “RAFT or MADIX agent”, is used in the present specification to refer to a class of compounds containing the functional group –X(=S)-S-, wherein X is phosphorous or carbon, preferably carbon. MADIX agents are characterized by the presence of the xanthate functional group, namely the -O–C(=S)-S- group.

RAFT/MADIX agents are capable to act as a reversible chain transfer agent in free-radical polymerizations, thereby inducing reversible-addition fragmentation transfer reactions to create an equilibrium between propagating radicals (i.e. the growing polymer chain) and so-called dormant species (containing the chain transfer agent fragment) that can become active again. The generally accepted mechanism of RAFT/MADIX controlled radical polymerization is shown in Scheme I.

Any RAFT/MADIX agent known in the art may be used in the inventive method. Non-limiting examples of suitable RAFT/MADIX agents are those disclosed in WO WO 98/058974 A RHODIA CHIMIE 19981230 and in WO WO 98/01478 A (E.I. DUPONT DE NEMOURS AND COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANIZATION 19980115 and in FAVIER, A., et al, Experimental requirements for an efficient control of free-radical polymerizations via the Reversible-Addition Fragmentation chain Transfer (RAFT) process, Macromol. Rapid Commun., 2006, 27, 653-692

For the purposes of this invention, the term “(per)fluoroelastomer” [fluoroelastomer (A)] is intended to designate a fluoropolymer resin serving as a base constituent for obtaining a true elastomer, said fluoropolymer resin comprising more than 10 % wt, preferably more than 30 % wt, of 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).

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.

This generally requires the fulfilment notably of certain molecular weight requirements, being understood that oligomers, although amorphous, are not such to deliver above listed performances.

Non limitative examples of suitable (per)fluorinated monomers are notably:
- C₂-C₈ perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropene (HFP);
- C₂-C₈ hydrogen-containing fluoroolefins, such as vinyl fluoride, 1,2-difluoroethylene, vinylidene fluoride (VDF), trifluoroethylene (TrFE), , pentafluoropropylene, and hexafluoroisobutylene;
- (per)fluoroalkylethylenes complying with formula CH₂=CH-R_f0, in which R_f0 is a C₁-C₆ (per)fluoroalkyl or a C₁-C₆ (per)fluorooxyalkyl having one or more ether groups ;
- chloro- and/or bromo- and/or iodo-C₂-C₆ fluoroolefins, like chlorotrifluoroethylene (CTFE);
- fluoroalkylvinylethers complying with formula CF₂=CFOR_f1 in which R_f1 is a C₁-C₆ fluoro- or perfluoroalkyl, e.g. -CF₃, -C₂F₅, -C₃F₇ ;
- hydrofluoroalkylvinylethers complying with formula CH₂=CFOR_f1 in which R_f1 is a C₁-C₆ fluoro- or perfluoroalkyl, e.g. -CF₃, -C₂F₅, -C₃F₇ ;
- fluoro-oxyalkylvinylethers complying with formula CF₂=CFOX₀, in which X₀ is a C₁-C₁₂ oxyalkyl, or a C₁-C₁₂ (per)fluorooxyalkyl having one or more ether groups, like perfluoro-2-propoxy-propyl;
- fluoroalkyl-methoxy-vinylethers complying with formula CF₂=CFOCF₂OR_f2 in which R_f2 is a C₁-C₆ fluoro- or perfluoroalkyl, e.g. -CF₃, -C₂F₅, -C₃F₇ or a C₁-C₆ (per)fluorooxyalkyl having one or more ether groups, like -C₂F₅-O-CF₃;
- functional fluoro-alkylvinylethers complying with formula CF₂=CFOY₀, in which Y₀ is a C₁-C₁₂ alkyl or (per)fluoroalkyl, or a C₁-C₁₂ oxyalkyl or a C₁-C₁₂ (per)fluorooxyalkyl, said Y₀ group comprising a carboxylic or sulfonic acid group, in its acid, acid halide or salt form;
- fluorodioxoles, of formula :

wherein each of R_f3, R_f4, R_f5, R_f6, equal or different each other, is independently a fluorine atom, a C₁-C₆ fluoro- or per(halo)fluoroalkyl, optionally comprising one or more oxygen atom, e.g. -CF₃, -C₂F₅, -C₃F₇, -OCF₃, -OCF₂CF₂OCF₃.

Examples of hydrogenated monomers are notably C₂-C₈ non-fluorinated olefins (Ol), in particular C₂-C₈ non-fluorinated alpha-olefins (Ol), including ethylene, propylene, 1-butene; diene monomers; styrene monomers; with alpha-olefins, as above detailed, being typically used.

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 (T_g) below room temperature. In most cases, the fluoroelastomer (A) has advantageously a T_g below 10°C, preferably below 5°C, more preferably 0°C.

The fluoroelastomer (A) is preferably selected among:
(1) VDF-based copolymers, in which VDF is copolymerized with at least one comonomer chosen from the followings classes :
(a) C₂-C₈ perfluoroolefins , such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP);
(b) hydrogen-containing C₂-C₈ fluoro-olefins, such as vinyl fluoride (VF), trifluoroethylene (TrFE), perfluoroalkyl ethylenes of formula CH₂ = CH-R_f, wherein R_f is a C₁‑C₆ perfluoroalkyl group;
(c) C₂-C₈ chloro and/or bromo and/or iodo-fluoroolefins such as chlorotrifluoroethylene (CTFE);
(d) (per)fluoroalkylvinylethers (PAVE) of formula CF₂ = CFOR_f, wherein R_f is a C₁-C₆ (per)fluoroalkyl group, e.g. CF₃, C₂F₅, C₃F₇;
(e) (per)fluoro-oxy-alkylvinylethers of formula CF₂ = CFOX, wherein X is a C₁-C₁₂ ((per)fluoro)-oxyalkyl comprising catenary oxygen atoms, e.g. the perfluoro-2-propoxypropyl group;
(f) (per)fluorodioxoles having formula :

wherein R_f3, R_f4, R_f5, R_f6, equal or different from each other, are independently selected among fluorine atoms and C₁-C₆ (per)fluoroalkyl groups, optionally comprising one or more than one oxygen atom, such as notably -CF₃, -C₂F₅, -C₃F₇, -OCF₃, -OCF₂CF₂OCF₃; preferably, perfluorodioxoles;
(g) (per)fluoro-methoxy-vinylethers (MOVE, hereinafter) having formula:
CFX₂ = CX₂OCF₂OR"_f
wherein R"_f is selected among C₁-C₆ (per)fluoroalkyls , linear or branched; C₅-C₆ cyclic (per)fluoroalkyls; and C₂-C₆ (per)fluorooxyalkyls, linear or branched, comprising from 1 to 3 catenary oxygen atoms, and X₂ = F, H; preferably X₂ is F and R"_f is -CF₂CF₃ (MOVE1); -CF₂CF₂OCF₃ (MOVE2); or -CF₃ (MOVE3);
(h) C₂-C₈ non-fluorinated olefins (Ol), for example ethylene and propylene; and
(2) TFE-based copolymers, in which TFE is copolymerized with at least one comonomer selected from classes (a) (different from TFE), (c), (d), (e), (f), (g), as above detailed and the followings:
(i) perfluorovinyl ethers containing cyanide groups, such as notably those described in patents US 4281092 , US 5447993 , and US 5789489 .

Optionally, fluoroelastomer (A) of the present invention also comprises recurring units derived from at least one bis-olefin [bis-olefin (OF)] having general formula :

wherein R₁, R₂, R₃, R₄, R₅ and R₆, equal or different from each other, are H, a halogen, or a C₁-C₅ optionally halogenated group, possibly comprising one or more oxygen group; Z is a linear or branched C₁-C₁₈ optionally halogenated alkylene or cycloalkylene radical, optionally containing oxygen atoms, or a (per)fluoropolyoxyalkylene radical, e.g. as described in EP 661304 A AUSIMONT SPA 19950705 .

The bis-olefin (OF) 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 C_1-5 alkyl or (per)fluoroalkyl group;
(OF-2)

wherein each of A, equal or different from each other and at each occurrence, is independently selected from F, Cl, and H; each of B, equal or different from each other and at each occurrence, is independently selected from F, Cl, H and OR_B, wherein R_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 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 C_1-5 alkyl or (per)fluoroalkyl group.

Among specific compositions of fluoroelastomers (A) suitable for the purpose of the invention, mention can be made of fluoroelastomers having the following compositions (in mol %) :
(i) vinylidene fluoride (VDF) 35-85 %, hexafluoropropene (HFP) 10-45 %, tetrafluoroethylene (TFE) 0-30 %, perfluoroalkyl vinyl ethers (PAVE) 0-15 %, bis-olefin (OF) 0-5 %;
(ii) vinylidene fluoride (VDF) 50-80 %, perfluoroalkyl vinyl ethers (PAVE) 5‑50 %, tetrafluoroethylene (TFE) 0-20 %, bis-olefin (OF) 0-5 %;
(iii) vinylidene fluoride (VDF) 20-30 %, C₂-C₈ non-fluorinated olefins (Ol) 10‑30 %, hexafluoropropene (HFP) and/or perfluoroalkyl vinyl ethers (PAVE) 18-27 %, tetrafluoroethylene (TFE) 10-30 %, bis-olefin (OF) 0-5 %;
(iv) tetrafluoroethylene (TFE) 50-80 %, perfluoroalkyl vinyl ethers (PAVE) 20‑50 %, bis-olefin (OF) 0-5 %;
(v) tetrafluoroethylene (TFE) 45-65 %, C₂-C₈ non-fluorinated olefins (Ol) 20‑55 %, vinylidene fluoride 0-30 %, bis-olefin (OF) 0-5 %;
(vi) tetrafluoroethylene (TFE) 32-60 % mol %, C₂-C₈ non-fluorinated olefins (Ol) 10-40 %, perfluoroalkyl vinyl ethers (PAVE) 20-40 %, fluorovinyl ethers (MOVE) 0-30 %, bis-olefin (OF) 0-5 %;
(vii) tetrafluoroethylene (TFE) 33-75 %, perfluoroalkyl vinyl ethers (PAVE) 15‑45 %, vinylidene fluoride (VDF) 5-30 %, hexafluoropropene HFP 0-30 %, bis-olefin (OF) 0-5 %;
(viii) vinylidene fluoride (VDF) 35-85 %, fluorovinyl ethers (MOVE) 5-40 %, perfluoroalkyl vinyl ethers (PAVE) 0-30 %, tetrafluoroethylene (TFE) 0-40 %, hexafluoropropene (HFP) 0-30 %, bis-olefin (OF) 0-5 %;
(ix) tetrafluoroethylene (TFE) 20-70 %, fluorovinyl ethers (MOVE) 30-80 %, perfluoroalkyl vinyl ethers (PAVE) 0-50 %, bis-olefin (OF) 0-5 %.

The fluoroelastomer (A) may additionally comprise recurring units derived from one or more than one cure-site containing monomers.

Among cure-site containing monomers, mention can be notably made of :
(CSM-1) iodine or bromine containing monomers of formula:

wherein each of A_Hf, equal to or different from each other and at each occurrence, is independently selected from F, Cl, and H; B_Hf is any of F, Cl, H and OR^Hf _B, wherein R^Hf _B is a branched or straight chain alkyl radical which can be partially, substantially or completely fluorinated or chlorinated; each of W^Hf equal to or different from each other and at each occurrence, is independently a covalent bond or an oxygen atom; E_Hf is a divalent group having 2 to 10 carbon atom, optionally fluorinated; R_Hf is a branched or straight chain alkyl radical, which can be partially, substantially or completely fluorinated; and R_Hf is a halogen atom selected from the group consisting of Iodine and Bromine; which may be inserted with ether linkages; preferably E is a –(CF₂)_m- group, with m being an integer from 3 to 5;
(CSM-2) ethylenically unsaturated compounds comprising cyanide groups, possibly fluorinated.

Among cure-site containing monomers of type (CSM1), preferred monomers are those selected from the group consisting of:
(CSM1-A) iodine-containing perfluorovinylethers of formula:

with m being an integer from 0 to 5 and n being an integer from 0 to 3, with the provisio that at least one of m and n is different from 0, and R_fi being F or CF₃; (as notably described in patents US 4745165 AUSIMONT SPA 19880517 , US 4564662 MINNESOTA MINING & MFG [US] 19860114 and EP 199138 A DAIKIN IND LTD 19861029 ); and
(CSM-1B) iodine-containing ethylenically unsaturated compounds of formula:
CX¹X²=CX³-(CF₂CF₂)_p-I
wherein each of X¹, X² and X³, equal to or different from each other, are independently H or F; and p is an integer from 1 to 5; among these compounds, mention can be made of CH₂=CHCF₂CF₂I, I(CF₂CF₂)₂CH=CH₂, ICF₂CF₂CF=CH₂, I(CF₂CF₂)₂CF=CH₂;
(CSM-1C) iodine-containing ethylenically unsaturated compounds of formula:
CHR=CH-Z-CH₂CHR-I
wherein R is H or CH₃, Z is a C₁-C₁₈ (per)fluoroalkylene radical, linear or branched, optionally containing one or more ether oxygen atoms, or a (per)fluoropolyoxyalkylene radical; among these compounds, mention can be made of CH₂=CH-(CF₂)₄CH₂CH₂I, CH₂=CH-(CF₂)₆CH₂CH₂I, CH₂=CH-(CF₂)₈CH₂CH₂I, CH₂=CH-(CF₂)₂CH₂CH₂I;
(CSM-1D) bromo and/or iodo alpha-olefins containing from 2 to 10 carbon atoms such as bromotrifluoroethylene or bromotetrafluorobutene described, for example, in US 4035565 DU PONT 19770712 or other compounds bromo and/or iodo alpha-olefins disclosed in US 4694045 DU PONT 19870915 .

Among cure-site containing monomers of type (CSM2), preferred monomers are those selected from the group consisting of:
(CSM2-A) perfluorovinyl ethers containing cyanide groups of formula CF₂=CF-(OCF₂CFX^CN)_m-O-(CF₂)_n-CN, with X^CN being F or CF₃, m being 0, 1, 2, 3 or 4; n being an integer from 1 to 12;
(CSM2-B) perfluorovinyl ethers containing cyanide groups of formula CF₂=CF-(OCF₂CFX^CN)_m’-O-CF₂—CF(CF₃)-CN, with X^CN being F or CF₃, m’ being 0, 1, 2, 3 or 4.
Specific examples of cure-site containing monomers of type CSM2-A and CSM2-B suitable to the purposes of the present invention are notably those described in patents US 4281092 DU PONT 19810728 , US 4281092 DU PONT 19810728 , US 5447993 DU PONT 19950905 and US 5789489 DU PONT 19980804

The fluoroelastomer (A) possesses a number-averaged molecular weight (M_n) of at least 10 000, preferably of at least 12 000, more preferably at least 15 000, when determined according to GPC technique.

Polymers possessing a molecular weight of less than 10 000 are not such to deliver elastomeric properties when cured and cannot be qualified as fluoroelastomers.

While upper boundaries of number-averaged molecular weight (M_n) are not particularly restricted, it is nevertheless generally understood that the Mn will be of at most 500 000, preferably at most 350 000, more preferably at most 250 000, to the sake of processability.

The fluoroelastomer (A) of the present invention advantageously possess at least one group of formula (I_x) at one of its chain ends.

Generally, if the fluoroelastomer (A) has a linear structure, the fluoroelastomer (A) is made of a polymer chain possessing two chain ends, one of which is a group of formula (I_x) as above detailed.

According to certain other embodiments, notably when the fluoroelastomer (A) comprises recurring units derived e.g. from the bis-olefin, as above detailed, the fluoroelastomer (A) advantageously possesses a branched structure, including more than two chain ends; in this case, it is possible for the fluoroelastomer (A) to include more than one chain end of formula (I_x), as above detailed.

It is not excluded, within the frame of the present invention, that the fluoroelastomer (A) may possess a chain end different from group of formula (I_x) which is substituted by a iodine and/or a bromine atom.

In formula (I_x) above Z may be selected among optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkyl, optionally substituted aryl, optionally substituted heterocyclyl, optionally substituted arylalkyl, optionally substituted alkylthio, optionally substituted arylalkylthio, dialkoxy- or diaryloxy- phosphinyl [-P(=O)(OR⁴)₂], dialkyl- or diaryl- phosphinyl [-P(=O)R⁴ ₂], where R⁴ is selected from the group consisting of optionally substituted C₁-C₁₈ alkyl, optionally substituted C₂-C₁₈ alkenyl, optionally substituted aryl, optionally substituted heterocyclyl, optionally substituted arylalkyl, optionally substituted alkaryl, optionally substituted acylamino, optionally substituted acylimino, optionally substituted amino, a polymer chain formed by any mechanism, for example polyalkylene oxide polymers such as water soluble polyethylene glycol or polypropylene glycol, and alkyl end capped derivatives thereof. Optional substituents for R⁴ and Z groups include epoxy, hydroxy, alkoxy, acyl, acyloxy, carboxy (and its salts), sulfonic acid (and its salts), alkoxy- or aryloxy- carbonyl, isocyanato, cyano, silyl, halo, and dialkylamino.

Preferably, Z is selected among optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkylthio, optionally substituted arylalkylthio, dialkoxy- or diaryloxy- phosphinyl [-P(=O)(OR⁴)₂], dialkyl- or diaryl- phosphinyl [-P(=O)R⁴ ₂], where R⁴ is as defined above.

More preferably Z is selected, without limitation, from the group consisting of: -OR⁵, -SR⁵, where R⁵ is an optionally substituted C₁-C₂₀ alkyl, -NR⁶ ₂ wherein each of R⁶, equal to or different from each other, is selected from optionally substituted C₁-C₂₀ and alkyl optionally substituted aryl, and

wherein e is an integer from 2 to 4.

Most preferably, Z is selected, without limitation, from the group consisting of -SCH₂(C₆H₅), -S(CH₂)_uCO₂H wherein u is an integer from 2 to 11, -SC_zH_2z+1 , -OC_zH_2z+1, wherein z is an integer from 1 to 12, preferably from 2 to 12, such as 2, 3, 4, 6, 8, 10,12 , -SCH₂CH₂OH, -OCH₂CF₃, -OCH₂CH₃, -N(C₆H₅)(CH₃)_.

As used herein, the terms "aryl" and "heteroaryl" refer to any substituent which includes or consists of one or more aromatic or heteroaromatic ring respectively, and which is attached via a ring atom. The rings may be mono or polycyclic ring systems, although mono or bicyclic 5 or 6 membered rings are preferred. The term "alkyl", used either alone or in combination, as in "alkenyloxyalkyl", "alkylthio", "alkylamino" and "dialkylamino" denotes straight chain, branched or cyclic alkyl, preferably C_1-C₂₀ alkyl or cycloalkyl. The term "alkoxy" denotes straight chain or branched alkoxy, preferably C_1-C₂₀ alkoxy. Examples of alkoxy include methoxy, ethoxy, n-propoxy, isopropoxy and the different butoxy isomers. The term "alkenyl" denotes groups formed from straight chain, branched or cyclic alkenes including ethylenically mono-, di- or poly-unsaturated alkyl or cycloalkyl groups as previously defined, preferably C_2-C₂₀ alkenyl. The term "acyl" either alone or in combination, as in "acyloxy", "acylthio", "acylamino" or "diacylamino", denotes carbamoyl, aliphatic acyl group and acyl group containing an aromatic ring, which is referred to as aromatic acyl or a heterocyclic ring which is referred to as heterocyclic acyl, preferably C_1-C₂₀ acyl.

The invention further pertains to a method for manufacturing the fluoroelastomer (A), as above defined, said method including polymerizing a monomers mixture [mixture (M)] in the presence of a RAFT/MADIX agent of any general formulae (I) and (II):

wherein X is carbon or phosphorous, preferably carbon; R_a is a monovalent organic group optionally substituted with one or more hydrophilic groups, R_b is a divalent organic group optionally substituted with one or more hydrophilic groups, and Z is any group that can promote sufficient reactivity of the thiocarbonyl group towards radical addition.

The monomers of the mixture (M) are those as above detailed constituting the recurring units of the fluoroelastomer (A).

In formulae (I) and (II), Z has preferably the meaning, as above defined for group of formula (I_x).

In formulae (I) and (II), X is preferably a carbon atom, that is to say that the RAFT/MADIX agent complies with any general formulae (I’) and (II’) herein below:

with R_a, R_b and Z being as above detailed.

In formula (I), R_a may be selected from C₁-C₁₂ alkyl, C₁-C₁₂ alkoxy, aryl or heteroaryl, each of which may be substituted with one or more hydrophilic groups selected from -CO₂H, -CO₂R, -CN, -SO₃H, -OSO₃H, -SOR, -SO₂R, -OP(OH)₂, -P(OH)₂, -PO(OH)₂, -OH, -OR, -(OCH₂-CHR⁰)_w-OH, -(OCH₂-CHR⁰)_w-OR, -CONH₂, -CONHR¹, -CONR¹R², -NR¹R², -NR¹R²R³, where R is selected from C₁-C₁₂ alkyl; w is an integer from 1 to 10; R⁰ is selected from hydrogen or R; R¹, R² and R³ are independently selected from C₁-C₁₂ alkyl and aryl which are optionally substituted with one or more hydrophilic substituent selected from -CO₂H, -CO₂R, -CN, -SO₃H, -OSO₃H, -SO₂R, -OH, -(OCH₂CHR⁰)_w-OH, -CONH₂, -SOR and SO₂R, and salts thereof, wherein R, R⁰ and w are as defined above.

Preferably R_a is selected, without limitation, from the group consisting of: -CH(CH₃)CO₂H, -CH(CH₃)CO₂CH₃, -CH(CH₃)CO₂CH₂CH₃, -CH(CH₃)CO₂CH(CH₃)₂, -CH(CO₂H)CH₂CO₂H, -CH(CO₂CH₃)CH₂CO₂CH₃, -CH(CO₂CH₂CH₃)CH₂CO₂CH₂CH₃, -CH(CO₂CH(CH₃)₂)CH₂CO₂CH(CH₃)₂, -C(CH₃)₂CO₂H, -C(CH₃)₂CO₂CH₃, -C(CH₃)₂CO₂CH₂CH₃, -C(CH₃)₂CO₂CH(CH₃)₂, -CH₂(C₆H₅), -C(CN)(CH₃)CO₂H, -C(CN)(CH₃)CO₂CH₃, -C(CN)(CH₃)CO₂CH₂CH₃, -C(CN)(CH₃)CO₂CH(CH₃)₂, -C(CN)(CH₃)(CH₂)₂CO₂H, -C(CN)(CH₃)(CH₂)₂CO₂CH₃, -C(CN)(CH₃)(CH₂)₂CO₂CH₂CH₃, and -C(CN)(CH₃)(CH₂)₂CO₂CH(CH₃)₂.

In formula (II), R_b may be selected from divalent C₁-C₁₂ aliphatic, aryl or heteroaryl groups, each of which may be substituted with one or more hydrophilic groups selected from -CO₂H, -CO₂R, -CN, -SO₃H, -OSO₃H, -SOR, -SO₂R, -OP(OH)₂, -P(OH)₂, -PO(OH)₂, -OH, -OR, -(OCH₂-CHR⁰)_w-OH, -(OCH₂-CHR⁰)_w-OR, -CONH₂, -CONHR¹, -CONR¹R², -NR¹R², -NR¹R²R³, where R is selected from C₁-C₁₂ alkyl; w is an integer from 1 to 10; R⁰ is selected from hydrogen or R; R¹, R² and R³ are independently selected from C₁-C₁₂ alkyl and aryl which are optionally substituted with one or more hydrophilic substituent selected from -CO₂H, -CO₂R, -CN, -SO₃H, -OSO₃H, -SO₂R, -OH, -(OCH₂CHR⁰)_w-OH, -CONH₂, -SOR and SO₂R, and salts thereof, wherein R, R⁰ and w are as defined above.

Preferably R_b is selected, without limitation, from the group consisting of: -(CH₂)_p-, with p being an integer of 1 to 12, preferably of 1 to 6, -CH(CH₃)-CH₂-CH₂-, –CH(C₂H₅)-CH₂-, -CHCO₂H-CH₂-, -CH(CO₂CH₃)-CH₂-, -CH(CO₂CH₂CH₃)-CH₂-, -CH(CO₂CH(CH₃)₂)-CH₂-, -CH(CO₂H)CH(CO₂H)-, -CH(CO₂CH(CH₃)₂)CH(CO₂CH(CH₃)₂)-, -CH(CO₂CHCH₃)CH(CO₂CHCH₃)-, -CH(CO₂CH₂CH₃)CH(CO₂CH₂CH₃)-, -(CH₂)_p’-CH(C₆H₅)-(CH₂)_p”- with p’ and p”, equal to or different from each other, being 0 or an integer of 1 to 6, -(CH₂)_q’-CH(CN)-(CH₂)_q”-, -(CH₂)_q’-C(CN)(CH₃)-(CH₂)_q”-, with q’ and q”, equal to or different from each other, being 0 or an integer of 1 to 6.

The polymerization can be carried out in any manner known to those skilled in the art, notably in solution or in aqueous emulsion.

Methods wherein the mixture (M) is polymerized in aqueous emulsions are generally preferred.

According to these embodiments, the method includes polymerizing the mixture (M) in aqueous emulsion in the presence of at least one surfactant.

The surfactant used in the method of the invention is generally a fluorinated surfactant. More specifically, fluorinated surfactant [surfactant (FS)] of formula :
R_f§ (X^-)_j (M⁺)_j
wherein R_f§ is a C₃–C₃₀ (per)fluoroalkyl chain, which can possibly be linear, cyclic of branched, a C₃–C₃₀ (per)fluoro(poly)oxyalkylenic chain, which can possibly be linear, cyclic of branched, X^- is -COO^- , -PO₃ ^- or -SO₃ ^-, M⁺ is selected from H⁺, NH₄ ⁺, an alkaline metal ion and j can be 1 or 2 can be used.

As non limitative examples of surfactants (FS), mention may be made of ammonium and/or sodium perfluorocarboxylates, and/or (per)fluoropolyoxyalkylenes having one or more carboxylic end groups.

Other examples of fluorinated surfactants are (per)fluorooxyalkylenic surfactants described in US 2007015864 3M INNOVATIVE PROPERTIES 20070108 , US 2007015865 3M INNOVATIVE PROPERTIES CO 20070118 , US 2007015866 3M INNOVATIVE PROPERTIES CO 20070118 , US 2007025902 3M INNOVATIVE PROPERTIES CO 20070201 .

More preferably, the surfactant (FS) selected from the group consisting of:
- CF₃(CF₂)_n1COOM’, in which n₁ is an integer ranging from 4 to 10, preferably from 5 to 7, and more preferably being equal to 6 ; M’ represents H, NH₄, Na, Li or K, preferably NH₄ ;
- T(C₃F₆O)_n0(CFXO)_m0CF₂COOM” [formula (FS₁)], in which T represents Cl or a perfluoroalkoxyde group of formula C_kF_2k+1O with k is an integer from 1 to 3, one F atom being optionally substituted by a Cl atom ; n₀ is an integer ranging from 1 to 6 ; m₀ is an integer ranging from 0 to 6 ; M” represents H, NH₄, Na, Li or K ; X represents F or CF₃ ;
- F-(CF₂—CF₂)_n2—CH₂—CH₂—RO₃M”’, in which R is P or S, preferably S, M’” represents H, NH₄, Na, Li or K, preferably H ; n₂ is an integer ranging from 2 to 5, preferably n₂=3 ;
- A-R_f-B bifunctional fluorinated surfactants, in which A and B, equal to or different from each other, are -(O)_pCFX—COOM* ; M* represents H, NH₄, Na, Li or K, preferably M* represents NH₄ ; X = F or CF₃ ; p is an integer equal to 0 or 1; R_f is a linear or branched perfluoroalkyl chain, or a (per)fluoropolyether chain such that the number average molecular weight of A-R_f-B is in the range 300 to 3,000, preferably from 500 to 2,000;
- R’_f-O-(CF₂)_r-O-L-COOM’, wherein R’_f is a linear or branched perfluoroalkyl chain, optionally comprising catenary oxygen atoms, M’ is H, NH₄, Na, Li or K, preferably M’ represents NH₄ ; r is 1 to 3; L is a bivalent fluorinated bridging group, preferably –CF₂CF₂- or –CFX-, X = F or CF₃ ;
- R”_f-(OCF₂)_u-O-(CF₂)_v-COOM”, wherein R”_f is a linear or branched perfluoroalkyl chain, optionally comprising catenary oxygen atoms, M” is H, NH₄, Na, Li or K, preferably M” represents NH₄ ; u and v are integers from 1 to 3;
- R”’_f-(O)_t-CHQ-L-COOM’”, wherein R’”_f is a linear or branched perfluoroalkyl chain, optionally comprising catenary oxygen atoms, Q = F or CF₃, t is 0 or 1, M’” is H, NH₄, Na, Li or K, preferably M’” is NH₄; L is a bivalent fluorinated bridging group, preferably –CF₂CF₂- or –CFX-, X = F or CF₃ ;
- cyclic fluorocompounds of the following formula (I_Cy):

wherein X₁, X₂, X₃, equal or different from each other are independently selected among H, F, and C_1-6 (per)fluoroalkyl groups, optionally comprising one or more catenary or non-catenary oxygen atoms; L represents a bond or a divalent group, in particular a divalent fluorinated aliphatic group; R_F is a divalent fluorinated C_1-3 bridging group; Y is a hydrophilic function selected from the group consisting of those of formulae:

wherein X_a is H, a monovalent metal (preferably an alkaline metal) or an ammonium group of formula –N(R’_n)₄, wherein R’_n, equal or different at each occurrence, represents a hydrogen atom or a C_1-6 hydrocarbon group (preferably an alkyl group); these cyclic fluorocompounds being notably described in WO WO 2010/003929 , the content of which is hereby incorporated by reference;
- and mixtures thereof.

In certain particularly preferred embodiments of the method of the invention, the method includes polymerizing the mixture (M) in aqueous emulsion further in the presence of at least one additional non-functional fluorinated fluid.

This technique is particularly advantageous as the addition of certain particular non-functional fluorinated fluid(s) [fluid (F)] can provide for an emulsion comprising dispersed droplets of said fluid having an average size of preferably less than 50 nm, more preferably of less than 40 nm, even more preferably of less than 30 nm. Said nanometric size of droplets is particularly advantageous in that it ensure higher polymerization rates and small fluoropolymer particles.

Said non-functional fluorinated fluids which can be used according to this embodiment are preferably (per)fluoropolyethers comprising recurring units (R1), said recurring units comprising at least one ether linkage in the main chain and at least one fluorine atom (fluoropolyoxyalkene chain). Preferably the recurring units R1 of the (per)fluoropolyether are selected from the group consisting of :
(I) –CFX-O-, wherein X is –F or –CF₃; and
(II) –CF₂-CFX-O-, wherein X is –F or –CF₃; and
(III) –CF₂-CF₂-CF₂-O-; and
(IV) –CF₂-CF₂-CF₂-CF₂-O-; and
(V) –(CF₂)_j-CFZ-O- wherein j is an integer chosen from 0 and 1 and Z is a fluoropolyoxyalkene chain comprising from 1 to 10 recurring units chosen among the classes (I) to (IV) here above; and mixtures thereof.

Should the (per)fluoropolyether comprise recurring units R1 of different types, advantageously said recurring units are randomly distributed along the fluoropolyoxyalkene chain.

Preferably the (per)fluoropolyether is a compound complying with formula (I-p) here below :
T₁-(CFX)_p-O-R_f-(CFX)_p’-T₂ ( I-p)
wherein :
- each of X is independently F or CF₃;
- p and p’, equal or different each other, are integers from 0 to 3;
- R_f is a fluoropolyoxyalkene chain comprising repeating units R°, said repeating units being chosen among the group consisting of :
(i) -CFXO-, wherein X is F or CF₃,
(ii) -CF₂CFXO-, wherein X is F or CF₃,
(iii) -CF₂CF₂CF₂O-,
(iv) -CF₂CF₂CF₂CF₂O-,
(v) –(CF₂)_j-CFZ-O- wherein j is an integer chosen from 0 and 1 and Z is a group of general formula –OR_f’T₃, wherein R_f’ is a fluoropolyoxyalkene chain comprising a number of repeating units from 0 to 10, said recurring units being chosen among the followings : -CFXO- , -CF₂CFXO-, ‑CF₂CF₂CF₂O-, -CF₂CF₂CF₂CF₂O-, with each of each of X being independently F or CF₃; and T₃ is a C₁ – C₃ perfluoroalkyl group, and mixtures thereof;
- T₁ and T₂, the same or different each other, are H, halogen atoms, C₁ – C₃ fluoroalkyl groups, optionally comprising one or more H or halogen atoms different from fluorine.

Particularly preferred embodiments are those wherein the aqueous emulsion comprises at least one surfactant (FS), as above detailed, and at least one fluid (F), as above detailed, and even more preferably those wherein the aqueous emulsion includes:
- at least one surfactant (FS) of formula (FS₁):
T(C₃F₆O)_n0(CFXO)_m0CF₂COOM”, as above detailed; and
- at least one fluid (F) of formula (I-p) T₁-(CFX)_p-O-R_f-(CFX)_p’-T₂ ( I-p)
as above detailed.

The aqueous emulsion polymerization may be carried out at a temperature between 10 to 150°C, preferably 20°C to 110°C and the pressure is typically between 2 and 35 bar, in particular 15 to 30 bar.

The reaction temperature may be varied during the polymerization e.g. for influencing the molecular weight distribution, i.e., to obtain a broad molecular weight distribution or to obtain a bimodal or multimodal molecular weight distribution.

The pH of the polymerization media may be in the range of pH 2-10, preferably 3-9, most preferably 4-8.

The aqueous emulsion polymerization is typically initiated by a radical initiator including any of the initiators known for initiating a free radical polymerization of fluorinated monomers. Suitable initiators include peroxides and azo compounds and redox based initiators. Specific examples of peroxide initiators include hydrogen peroxide, sodium or barium peroxide, diacylperoxides such as diacetylperoxide, disuccinyl peroxide, dipropionylperoxide, dibutyrylperoxide, dibenzoylperoxide, benzoylacetylperoxide, diglutaric acid peroxide and dilaurylperoxide, and further per-acids and salts thereof such as e.g. ammonium, sodium or potassium salts. Examples of per-acids include peracetic acid. Esters of the peracid can be used as well and examples thereof include tert.-butylperoxyacetate and tert.-butylperoxypivalate. Examples of inorganic include for example ammonium-alkali- or earth alkali salts of persulfates, permanganic or manganic acid or manganic acids. A persulfate initiator, e.g. ammonium persulfate (APS), can be used on its own or may be used in combination with a reducing agent. Suitable reducing agents include bisulfites such as for example ammonium bisulfite or sodium metabisulfite, thiosulfates such as for example ammonium, potassium or sodium thiosulfate, hydrazines, azodicarboxylates and azodicarboxyldiamide (ADA). Further reducing agents that may be used include sodium formaldehyde sulfoxylate (Rongalit ) or fluoroalkyl sulfinates, e.g. as disclosed in US 5285002 . The reducing agent typically reduces the half-life time of the persulfate initiator. Additionally, a metal salt catalyst such as for example copper, iron or silver salts may be added.

The amount of radical initiator is not particularly limited; nevertheless in order to ensure adequate polymerization kinetics control, it is generally understood that the amount of initiator will be selected so as to achieve a molar ratio between the amount of RAFT/MADIX agent and of radical initiator of between 0.1 to 20, preferably of between 0.5 to 10, most preferably of 0.5 to 5 moles/moles.

The invention further pertains to a curable (per)fluoroelastomer composition [composition (C)] comprising:
- at least one fluoroelastomer (A), as above defined;
- from 0.1 to 15 weight parts, per 100 parts by weight of said fluoroelastomer (A), of at least one cross-linking co-agent;
- from 0.1 to 10 weight parts, per 100 parts by weight of said fluoroelastomer (A), of at least one peroxide.

The composition (C) of the invention comprises at least one peroxide, typically an organic peroxide.

Among most commonly used 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-methylpropyl)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.

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

For achieving reasonable curing rates, it is generally preferred to have in the composition (C) amounts of peroxide of at least 0.5, preferably at least 1 weight parts per 100 parts by weight of fluoroelastomer (A).

The composition (C) of the invention comprises at least one crosslinking co-agents.

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

For achieving reasonable curing rates, it is generally preferred to have in the composition (C) amounts of crosslinking co-agent of at least 0.5, preferably at least 1 weight parts per 100 parts by weight of fluoroelastomer (A).

The crosslinking co-agent is generally selected from the group consisting of polyunsaturared compounds, i.e. from compounds comprising more than one ethylenic unsaturations.

Among these crosslinking co-agents, the following are commonly used : triallyl cyanurate; triallyl isocyanurate (TAIC); tris(diallylamine)-s-triazine; triallyl phosphite; N,N‑diallylacrylamide; N,N,N',N'-tetraallylmalonamide; trivinyl isocyanurate; 2,4,6-trivinyl methyltrisiloxane; bis-olefins (OF), as above detailed; triazines substituted with ethylenically unsaturated groups, such as notably those described in EP 860436 A AUSIMONT SPA 19980826 and WO WO 97/05122 DU PONT (US) 19970213 ; among above mentioned crosslinking co-agents, TAIC and bis-olefins (OF), as above detailed, and more specifically those of formula (OF-1), as above detailed, have been found to provide particularly good results

The composition (C) of the invention may additionally comprise other ingredients, such as notably:
(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) an acid acceptor of non-metal oxide/hydroxide type, selected from the group consisting of 1,8‑bis(dimethylamino)naphthalene, octadecylamine, oxiranes, glycidyl resins obtained by condensation of bisphenol A and epichlorhydrine, organosilances (such as 3-glycidoxypropyl trimethoxy silane);
(c) conventional additives, selected generally from the group consisting of fillers (e.g. carbon black), thickeners, pigmen­ts, 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).

It is generally understood that the composition (C) of the invention comprises no other ingredients beside those above listed; in other terms, the inventive composition (C) generally consists essentially of the fluoroelastomer (A), the peroxide, the crosslinking co-agent, and optionally metal compounds, acid acceptors and conventional additives, as above detailed.

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

The composition (C) 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.

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

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

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.

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

The invention will be now described with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention.

EXAMPLES

Example 1

In a 5 liters reactor equipped with a mechanical stirrer operating at 630 rpm, 3.1 l of demineralized water and 31 ml of a microemulsion, previously obtained by mixing 6.8 ml of a perfluoropolyoxyalkylene having acidic end groups of formula: CF₂ClO(CF₂-CF(CF₃)O)_n(CF₂O)_mCF₂COOH, wherein n/m = 10, having average molecular weight of 600, 4.3 ml of a 30 % v/v NH₄OH aqueous solution, 15.6 ml of demineralized water and 4.3 ml of GALDEN^® D02 perfluoropolyether of formula: CF₃O(CF₂CF(CF₃)O)_n(CF₂O)_mCF₃ with n/m = 20, having average molecular weight of 450, were introduced.
Then 0.25 g of O-ethyl S-(1-methoxycarbonyl ethyl)dithiocarbonate (Rhodixan® A1) as chain transfer agent were introduced, and the reactor was heated and maintained at a set-point temperature of 80°C; a mixture of tetrafluoroethylene (TFE) (7.5% moles), vinylidene fluoride (VDF) (47.5% moles) and hexafluoropropene (HFP) (45%moles) was then added to reach a final pressure of 19 bar (1.9 MPa). 2.6 g of ammonium persulfate (APS) as initiator were then introduced. Pressure was maintained at set-point of 19 bar by continuous feeding of a gaseous mixture of TFE (11.0% moles), VDF (70.0% moles) and HFP (19.0% moles) up to a total of 500 g, for a total reaction time of 104 minutes, during which additional amounts of O-ethyl S-(1-methoxycarbonyl ethyl)dithiocarbonate in equal portions of 0.25 g, at 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90% conversion of gaseous mixture, were fed to the reactor, hence totaling 2.5 g of MADIX agent. Then the reactor was cooled, vented and the latex recovered. The latex was frozen at a temperature of -20°C for 24 hours, recovered at room temperature, separated from the aqueous phase, washed with demineralized water and dried in a convection oven at 90°C for 16 hours. The composition of the obtained polymer by NMR was found to be the following: 11.5 % moles of recurring units derived from TFE; 69.9 % moles of recurring units derived from VDF, and 18.6 % moles of recurring units derived from HFP. Molecular weight distribution data (Mn, PDI, Mw) as obtained by GPC are summarized in table 2.

Example 2

Same procedure of example 1 was followed, but introducing the entire amount (2.5 g) of O-ethyl S-(1-methoxycarbonyl ethyl)dithiocarbonate before heating the mixture and initiating the reaction by addition of initiator.

Example 3

Same procedure as in Ex. 1 was followed, but initially adding 0.75 g of O-ethyl S-(1-methoxycarbonyl ethyl)dithiocarbonate before heating and initiating the polymerization, adding 0.75 g of O-ethyl S-(1-methoxycarbonyl ethyl)dithiocarbonate at 50% conversion of gaseous mixture, and continuing reaction for 66 minutes, until a conversion of 150 g of monomers mixture.

Example 4

Same procedure as in Ex. 3 was followed, but initially adding 0.75 g of O-ethyl S-(1-methoxycarbonyl ethyl)dithiocarbonate before heating and initiating the polymerization, adding 3 additional portions of 0.75 g of O-ethyl S-(1-methoxycarbonyl ethyl)dithiocarbonate at 25%, 50% and 75% conversion of gaseous mixture, and continuing reaction for 128 minutes, until a conversion of 300 g of monomers mixture.

Example 5

Same procedure as in Ex. 3 was followed, but initially adding 0.75 g of O-ethyl S-(1-methoxycarbonyl ethyl)dithiocarbonate before heating and initiating the polymerization, adding 6 additional portions of 0.75 g of O-ethyl S-(1-methoxycarbonyl ethyl)dithiocarbonate at 15%, 30%, 45%, 60%, 75% and 90% conversion of gaseous mixture, and continuing reaction for 128 minutes, until a conversion of 500 g of monomers mixture.

Example 6

Same procedure as in example 1 was followed, but further feeding during polymerization a total of 1.8 g of CH₂=CH-(CF₂)₆-CH=CH₂, divided in 8 equal portions, each at 13.5% increase in conversion.

Example 7

In a 5 litres reactor equipped with a mechanical stirrer operating at 630 rpm, 3.1 l of demineralized water and 31 ml of same microemulsion as used in Example 1, were introduced.
Then 0.25 g of 1,7-dithio-2,6-dithia-heptanedioicacid O,O'-diethyl ester were introduced, and the reactor was heated and maintained at a set-point temperature of 80°C; a mixture of tetrafluoroethylene (TFE) (7.5% moles), vinylidene fluoride (VDF) (47.5% moles) and hexafluoropropene (HFP) (45%moles) was then added to reach a final pressure of 19 bar (1.9 MPa). 2.6 g of ammonium persulfate (APS) as initiator were then introduced. Pressure was maintained at set-point of 19 bar by continuous feeding of a gaseous mixture of TFE (11.0% moles), VDF (70.0% moles) and HFP (19.0% moles) up to a total of 500 g, for a total reaction time of 51 minutes, during which additional amounts of 1,7-dithio-2,6-dithia-heptanedioicacid O,O'-diethyl ester in equal portions of 0.25 g, at 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90% conversion of gaseous mixture, were fed to the reactor, hence totalling 2.5 g of MADIX agent. Then the reactor was cooled, vented and the latex recovered. The latex was frozen at a temperature of -20°C for 24 hours, recovered at room temperature, separated from the aqueous phase, washed with demineralized water and dried in a convection oven at 90°C for 16 hours. Molecular weight distribution data (Mn, PDI, Mw) as obtained by GPC are summarized in table 2.

GPC determinations

Fluoroelastomers were characterized by GPC using instrumentation and conditions as detailed in the Table 1 below, and relevant parameter were determined based on polystyrene standards, taking into account polymer/solvent Mark-Houwink parameters for relevant standard and for fluoroelastomers. Table 1

Mobile phase	Tetrahydrofuran (THF)
Flow rate	1.0 mL/min
Temperature	35 °C
Injection system	Autosampler mod. Waters 717plus
Injection volume	200 mL
Pump	Waters mod. 515 HPLC
Column set	Precolumn + 4 Waters Styragel HR: 106, 105, 104 and 103 Å
Detector	Waters Refractive Index mod. 2414
Software for data acquisition and processing	Waters Empower 3

Table 2

Ex.	Time	MADIX/ I*	MADIX/ monomers**	Reaction rate	Molecular weight distribution
N°	min	mol/mol	(%mol)	(g/min)	Mn	PDI	Mw
1	104	1.1	0.20	4.8	78792	2.5	196980
2	282	1.1	0.20	1.8	44274	6.2	274499
3	66	0.6	0.40	2.3	26208	2.8	73382
4	128	1.3	0.40	2.3	38296	3.3	126377
5	211	2.2	0.40	2.4	81147	3.2	259670
6	90	1.1	0.20	5.5	117805	4.4	518342
7	51	0.8		9.8	n.d.	n.d.	n.d.

*molar ratio between total amount of MADIX agent and total amount of radical initiator, expressed as ratio mol/mol
**molar ratio between total amount of MADIX agent and total amount of monomers converted, expressed as molar percentage.

Crosslinking of sample produced in Example 1

Crosslinking experiment has been performed according to the conditions in Table 3.

Table 3

Example 1 polymer	100 phr
DRIMIX® TAIC 75(*)	4 phr
Luperox® 101XL 45 Atofina	3 phr
Curing rate 160°C
ML (lb x inch)	0.4
MH (lb x inch)	2.1
t02 (sec)	48
t50 (sec)	105
t90 (sec)	307

(*) dispersion of triallylisocyanurate in silica at 75 % wt/wt commercially available from Finco Srl;
(**) 2,5-bis(terbutylperoxy)-2,5-dimethylhexanesupported on silica at 45 % wt, commercially available from Atofina.

In order to evaluate the reactivity of Example 1 in a standard peroxidic system a solubility test was performed on Example 1 (raw polymer) on compounded Example 1 and on the crosslinked specimen after molding in specified conditions (molding conditions 10 min 160°C, no postcure) :

Conditions:

• Solvent: THF samples have been dissolved for 2 hrs under stirring at RT
• Samples spinning: 20000rpm (Sovrall RC-6 Plus centrifuge)
• Insoluble samples after centrifuge spinning were dried for 48h at 70°C, before weighting

Results are summarized in Table 4:

Table 4

samples	Unsoluble % (w/w)
Example 1 raw polymer	>3%
Example 1 compounded	4%
Example 1 molded	61%

Crosslinking of sample produced in Example 6

Crosslinking experiment has been performed according to the conditions in Table 5.

Table 5

Example 6 polymer	100 phr
DRIMIX® TAIC 75(*)	4 phr
Luperox® A70S(**)	2 phr
Curing rate 120°C
ML (lb x inch)	1.2
MH (lb x inch)	3.7
t02 (sec)	53
t50 (sec)	140
t90 (sec)	389

(*) dispersion of triallylisocyanurate in silica at 75 % wt/wt commercially available from Finco Srl;
(**) Dibenzoyl peroxide (70 %, remainder: water) commercially available from Aldrich.

In order to evaluate network formation of Example 6 in a standard peroxidic system a solubility/swelling test was performed on molded Example 6 compound (molding conditions 10 min 140°C, no postcure). Conditions - Solvent: MEK. Samples have been dissolved for 3 days under stirring at RT. Results are summarized in Table 6.

Table 6

Samples	Unsoluble % (w/w)	Swelling (w/w)
Example 6 molded	71%	710%

The experiment confirms that network formation occurred.

Crosslinking of sample produced in Example 7

Crosslinking experiment has been performed according to the conditions in Table 7. Table 7

Example 7 polymer	100 phr
DRIMIX® TAIC 75(*)	4 phr
Luperox® A70S(**)	2 phr
Curing rate 120°C
ML (lb x inch)	1.5
MH (lb x inch)	4.5
t02 (sec)	54
t50 (sec)	133
t90 (sec)	365

(*) dispersion of triallylisocyanurate in silica at 75 % wt/wt commercially available from Finco Srl;
(**) Dibenzoyl peroxide (70 %, remainder: water) commercially available from Aldrich.

Claims (14)

1. A (per)fluoroelastomer comprising at least one group of formula (I_x):

   

   wherein X, equal to or different from each other at each occurrence, is phosphorous or carbon, preferably carbon, and Z, equal to or different from each other at each occurrence, is a hydrocarbon group, possibly comprising one or more than one heteroatoms [fluoroelastomer (A)].
2. The fluoroelastomer (A) of claim 1, said fluoroelastomer (A) possessing a number-averaged molecular weight (M_n) of at least 10 000, preferably of at least 12 000, more preferably at least 15 000, when determined according to GPC technique.
3. The fluoroelastomer (A) of claim 1 or 2, said fluoroelastomer comprising more than 10 % wt, preferably more than 30 % wt, of recurring units derived from at least one ethylenically unsaturated monomer comprising at least one fluorine atom (hereafter, (per)fluorinated monomer) , said (per)fluorinated monomer being selected from the group consisting of:

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

   - C₂-C₈ hydrogen-containing fluoroolefins, such as vinyl fluoride, 1,2-difluoroethylene, vinylidene fluoride (VDF), trifluoroethylene (TrFE), , pentafluoropropylene, and hexafluoroisobutylene;

   - (per)fluoroalkylethylenes complying with formula CH₂=CH-R_f0, in which R_f0 is a C₁-C₆ (per)fluoroalkyl or a C₁-C₆ (per)fluorooxyalkyl having one or more ether groups ;

   - chloro- and/or bromo- and/or iodo-C₂-C₆ fluoroolefins, like chlorotrifluoroethylene (CTFE);

   - fluoroalkylvinylethers complying with formula CF₂=CFOR_f1 in which R_f1 is a C₁-C₆ fluoro- or perfluoroalkyl, e.g. -CF₃, -C₂F₅, -C₃F₇ ;

   - hydrofluoroalkylvinylethers complying with formula CH₂=CFOR_f1 in which R_f1 is a C₁-C₆ fluoro- or perfluoroalkyl, e.g. -CF₃, -C₂F₅, -C₃F₇ ;

   - fluoro-oxyalkylvinylethers complying with formula CF₂=CFOX₀, in which X₀ is a C₁-C₁₂ oxyalkyl, or a C₁-C₁₂ (per)fluorooxyalkyl having one or more ether groups, like perfluoro-2-propoxy-propyl;

   - fluoroalkyl-methoxy-vinylethers complying with formula CF₂=CFOCF₂OR_f2 in which R_f2 is a C₁-C₆ fluoro- or perfluoroalkyl, e.g. -CF₃, -C₂F₅, -C₃F₇ or a C₁-C₆ (per)fluorooxyalkyl having one or more ether groups, like -C₂F₅-O-CF₃;

   - functional fluoro-alkylvinylethers complying with formula CF₂=CFOY₀, in which Y₀ is a C₁-C₁₂ alkyl or (per)fluoroalkyl, or a C₁-C₁₂ oxyalkyl or a C₁-C₁₂ (per)fluorooxyalkyl, said Y₀ group comprising a carboxylic or sulfonic acid group, in its acid, acid halide or salt form;

   - fluorodioxoles, of formula :

   

   wherein each of R_f3, R_f4, R_f5, R_f6, equal or different each other, is independently a fluorine atom, a C₁-C₆ fluoro- or per(halo)fluoroalkyl, optionally comprising one or more oxygen atom, e.g. -CF₃, -C₂F₅, -C₃F₇, -OCF₃, -OCF₂CF₂OCF₃.
4. The fluoroelastomer (A) of anyone of claims 1 to 3, which is selected from the group consisting of:

   (1) VDF-based copolymers, in which VDF is copolymerized with at least one comonomer chosen from the followings classes :

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

   (b) hydrogen-containing C₂-C₈ fluoro-olefins, such as vinyl fluoride (VF), trifluoroethylene (TrFE), perfluoroalkyl ethylenes of formula CH₂ = CH-R_f, wherein R_f is a C₁‑C₆ perfluoroalkyl group;

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

   (d) (per)fluoroalkylvinylethers (PAVE) of formula CF₂ = CFOR_f, wherein R_f is a C₁-C₆ (per)fluoroalkyl group, e.g. CF₃, C₂F₅, C₃F₇;

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

   (f) (per)fluorodioxoles having formula :

   

   wherein R_f3, R_f4, R_f5, R_f6, equal or different from each other, are independently selected among fluorine atoms and C₁-C₆ (per)fluoroalkyl groups, optionally comprising one or more than one oxygen atom, such as notably -CF₃, -C₂F₅, -C₃F₇, -OCF₃, -OCF₂CF₂OCF₃; preferably, perfluorodioxoles;

   (g) (per)fluoro-methoxy-vinylethers (MOVE, hereinafter) having formula:

   CFX₂ = CX₂OCF₂OR"_f

   wherein R"_f is selected among C₁-C₆ (per)fluoroalkyls , linear or branched; C₅-C₆ cyclic (per)fluoroalkyls; and C₂-C₆ (per)fluorooxyalkyls, linear or branched, comprising from 1 to 3 catenary oxygen atoms, and X₂ = F, H; preferably X₂ is F and R"_f is -CF₂CF₃ (MOVE1); -CF₂CF₂OCF₃ (MOVE2); or -CF₃ (MOVE3);

   (h) C₂-C₈ non-fluorinated olefins (Ol), for example ethylene and propylene; and

   (2) TFE-based copolymers, in which TFE is copolymerized with at least one comonomer selected from classes (a) (different from TFE), (c), (d), (e), (f), (g), as above detailed and the followings:

   (i) perfluorovinyl ethers containing at least one cyanide group.
5. The fluoroelastomer (A) of anyone of the preceding claims, further comprising recurring units derived from at least one bis-olefin [bis-olefin (OF)] having general formula :

   

   wherein R₁, R₂, R₃, R₄, R₅ and R₆, equal or different from each other, are H, a halogen, or a C₁-C₅ optionally halogenated group, possibly comprising one or more oxygen group; Z is a linear or branched C₁-C₁₈ optionally halogenated alkylene or cycloalkylene radical, optionally containing oxygen atoms, or a (per)fluoropolyoxyalkylene radical.
6. The fluoroelastomer (A) of anyone of the preceding claims, wherein in formula (I_x) Z is selected from the group consisting of optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkyl, optionally substituted aryl, optionally substituted heterocyclyl, optionally substituted arylalkyl, optionally substituted alkylthio, optionally substituted arylalkylthio, dialkoxy- or diaryloxy- phosphinyl [-P(=O)(OR⁴)₂], dialkyl- or diaryl- phosphinyl [-P(=O)R⁴ ₂], where R⁴ is selected from the group consisting of optionally substituted C₁-C₁₈ alkyl, optionally substituted C₂-C₁₈ alkenyl, optionally substituted aryl, optionally substituted heterocyclyl, optionally substituted arylalkyl, optionally substituted alkaryl, optionally substituted acylamino, optionally substituted acylimino, optionally substituted amino, a polymer chain formed by any mechanism, for example polyalkylene oxide polymers such as water soluble polyethylene glycol or polypropylene glycol, and alkyl end capped derivatives thereof; optional substituents for R⁴ and Z groups include epoxy, hydroxy, alkoxy, acyl, acyloxy, carboxy (and its salts), sulfonic acid (and its salts), alkoxy- or aryloxy- carbonyl, isocyanato, cyano, silyl, halo, and dialkylamino.
7. A method for manufacturing the fluoroelastomer (A) according to anyone of claims 1 to 6, said method including polymerizing a monomers mixture [mixture (M)] in the presence of a RAFT/MADIX agent of any general formulae (I) and (II):

   

   wherein X is carbon or phosphorous, preferably carbon; R_a is a monovalent organic group optionally substituted with one or more hydrophilic groups, R_b is a divalent organic group optionally substituted with one or more hydrophilic groups, and Z is any group that can promote sufficient reactivity of the thiocarbonyl group towards radical addition.
8. The method of claim 7, wherein the RAFT/MADIX agent complies with any general formulae (I’) and (II’) herein below:

   

   wherein:

   - Z, equal to or different from each other at each occurrence, is selected from the group consisting of optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkyl, optionally substituted aryl, optionally substituted heterocyclyl, optionally substituted arylalkyl, optionally substituted alkylthio, optionally substituted arylalkylthio, dialkoxy- or diaryloxy- phosphinyl [-P(=O)(OR⁴)₂], dialkyl- or diaryl- phosphinyl [-P(=O)R⁴ ₂], where R⁴ is selected from the group consisting of optionally substituted C₁-C₁₈ alkyl, optionally substituted C₂-C₁₈ alkenyl, optionally substituted aryl, optionally substituted heterocyclyl, optionally substituted arylalkyl, optionally substituted alkaryl, optionally substituted acylamino, optionally substituted acylimino, optionally substituted amino, a polymer chain formed by any mechanism, for example polyalkylene oxide polymers such as water soluble polyethylene glycol or polypropylene glycol, and alkyl end capped derivatives thereof; optional substituents for R⁴ and Z groups include epoxy, hydroxy, alkoxy, acyl, acyloxy, carboxy (and its salts), sulfonic acid (and its salts), alkoxy- or aryloxy- carbonyl, isocyanato, cyano, silyl, halo, and dialkylamino;

   - R_a is selected from C₁-C₁₂ alkyl, C₁-C₁₂ alkoxy, aryl or heteroaryl, each of which may be substituted with one or more hydrophilic groups selected from -CO₂H, -CO₂R, -CN, -SO₃H, -OSO₃H, -SOR, -SO₂R, -OP(OH)₂, -P(OH)₂, -PO(OH)₂, -OH, -OR, -(OCH₂-CHR⁰)_w-OH, -(OCH₂-CHR⁰)_w-OR, -CONH₂, -CONHR¹, -CONR¹R², -NR¹R², -NR¹R²R³, where R is selected from C₁-C₁₂ alkyl; w is an integer from 1 to 10; R⁰ is selected from hydrogen or R; R¹, R² and R³ are independently selected from C₁-C₁₂ alkyl and aryl which are optionally substituted with one or more hydrophilic substituent selected from -CO₂H, -CO₂R, -CN, -SO₃H, -OSO₃H, -SO₂R, -OH, -(OCH₂CHR⁰)_w-OH, -CONH₂, -SOR and SO₂R, and salts thereof, wherein R, R⁰ and w are as defined above; preferably R_a is selected, without limitation, from the group consisting of: -CH(CH₃)CO₂H, -CH(CH₃)CO₂CH₃, -CH(CH₃)CO₂CH₂CH₃, -CH(CH₃)CO₂CH(CH₃)₂, -CH(CO₂H)CH₂CO₂H, -CH(CO₂CH₃)CH₂CO₂CH₃, -CH(CO₂CH₂CH₃)CH₂CO₂CH₂CH₃, -CH(CO₂CH(CH₃)₂)CH₂CO₂CH(CH₃)₂, -C(CH₃)₂CO₂H, -C(CH₃)₂CO₂CH₃, -C(CH₃)₂CO₂CH₂CH₃, -C(CH₃)₂CO₂CH(CH₃)₂, -CH₂(C₆H₅), -C(CN)(CH₃)CO₂H, -C(CN)(CH₃)CO₂CH₃, -C(CN)(CH₃)CO₂CH₂CH₃, -C(CN)(CH₃)CO₂CH(CH₃)₂, -C(CN)(CH₃)(CH₂)₂CO₂H, -C(CN)(CH₃)(CH₂)₂CO₂CH₃, -C(CN)(CH₃)(CH₂)₂CO₂CH₂CH₃, and -C(CN)(CH₃)(CH₂)₂CO₂CH(CH₃)_2;

   - R_b is selected from divalent C₁-C₁₂ aliphatic, aryl or heteroaryl groups, each of which may be substituted with one or more hydrophilic groups selected from -CO₂H, -CO₂R, -CN, -SO₃H, -OSO₃H, -SOR, -SO₂R, -OP(OH)₂, -P(OH)₂, -PO(OH)₂, -OH, -OR, -(OCH₂-CHR⁰)_w-OH, -(OCH₂-CHR⁰)_w-OR, -CONH₂, -CONHR¹, -CONR¹R², -NR¹R², -NR¹R²R³, where R is selected from C₁-C₁₂ alkyl; w is an integer from 1 to 10; R⁰ is selected from hydrogen or R; R¹, R² and R³ are independently selected from C₁-C₁₂ alkyl and aryl which are optionally substituted with one or more hydrophilic substituent selected from -CO₂H, -CO₂R, -CN, -SO₃H, -OSO₃H, -SO₂R, -OH, -(OCH₂CHR⁰)_w-OH, -CONH₂, -SOR and SO₂R, and salts thereof, wherein R, R⁰ and w are as defined above; preferably R_b is selected, without limitation, from the group consisting of: -(CH₂)_p-, with p being an integer of 1 to 12, preferably of 1 to 6, -CH(CH₃)-CH₂-CH₂-, –CH(C₂H₅)-CH₂-, -CHCO₂H-CH₂-, -CH(CO₂CH₃)-CH₂-, -CH(CO₂CH₂CH₃)-CH₂-, -CH(CO₂CH(CH₃)₂)-CH₂-, -CH(CO₂H)CH(CO₂H)-, -CH(CO₂CH(CH₃)₂)CH(CO₂CH(CH₃)₂)-, -CH(CO₂CHCH₃)CH(CO₂CHCH₃)-, -CH(CO₂CH₂CH₃)CH(CO₂CH₂CH₃)-, -(CH₂)_p’-CH(C₆H₅)-(CH₂)_p”- with p’ and p”, equal to or different from each other, being 0 or an integer of 1 to 6, -(CH₂)_q’-CH(CN)-(CH₂)_q”-, -(CH₂)_q’-C(CN)(CH₃)-(CH₂)_q”-, with q’ and q”, equal to or different from each other, being 0 or an integer of 1 to 6.
9. A curable (per)fluoroelastomer composition [composition (C)] comprising:

   - at least one fluoroelastomer (A) according to anyone of claims 1 to 6;

   - from 0.1 to 15 weight parts, per 100 parts by weight of said fluoroelastomer (A), of at least one cross-linking co-agent;

   - from 0.1 to 10 weight parts, per 100 parts by weight of said fluoroelastomer (A), of at least one peroxide.
10. The composition of claim 9, wherein said peroxide is an organic peroxide selected from the group consisting 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-methylpropyl)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.
11. The composition of claim 9 or 10, wherein said crosslinking co-agent is selected from the group consisting of polyunsaturared compounds, i.e. from compounds comprising more than one ethylenic unsaturations, generally selected from the group consisting of triallyl cyanurate; triallyl isocyanurate (TAIC); tris(diallylamine)-s-triazine; triallyl phosphite; N,N‑diallylacrylamide; N,N,N',N'-tetraallylmalonamide; trivinyl isocyanurate; 2,4,6-trivinyl methyltrisiloxane; bis-olefins (OF) having general formula :

    

    wherein R₁, R₂, R₃, R₄, R₅ and R₆, equal or different from each other, are H, a halogen, or a C₁-C₅ optionally halogenated group, possibly comprising one or more oxygen group; Z is a linear or branched C₁-C₁₈ optionally halogenated alkylene or cycloalkylene radical, optionally containing oxygen atoms, or a (per)fluoropolyoxyalkylene radical; and triazines substituted with ethylenically unsaturated groups.
12. A method of using the composition (C) according to anyone of claims 9 to 11, for fabricating shaped articles.
13. The method of claim 12 wherein composition (C) is fabricated by any of moulding (injection moulding, extrusion moulding), calendering, or extrusion, into the desired shaped article, which is subjected to vulcanization (curing) during the processing itself and/or in a subsequent step (post-treatment or post-cure).
14. A cured article obtained from the composition (C), according to anyone of claims 9 to 11, said cured article being preferably selected from the group consisting of pipes, joints, O-ring, hose, and the like.

Images