METHOD OF MANUFACTURING FLUOROELASTOMERS

Abstract

The invention pertains to a method for manufacturing a (per)fluoroelastomer [fluoroelastomer (A)] comprising the following steps: step (a): polymerizing in an aqueous emulsion in the presence of a surfactant by feeding in a first reactor comprising feeding the following ingredients: (i) a monomer mixture [mixture (M1)] comprising at least one fluoromonomer [monomer (F)], (ii) at least one iodinated and/or brominated chain-transfer agent(s), (iii) at least one branching agent possessing at least two ethylenic unsaturations; and (iv) at least one radical initiator, so as to obtain a pre-polymer latex [latex (P)]; step (b): recovering the said latex (P) from the said first reactor and storing the same in a storage tank; and step (c): feeding the said latex (P) from the said storage tank to a second reactor; step (d): polymerizing in the said second reactor at least a second monomer mixture [mixture (M2)] comprising at least one monomer (F) in the presence of a radical initiator, so as to obtain a final latex [latex (F)]; and step (d): recovering the (per)fluoroelastomer from the said latex (F).

Claims

1. A method for manufacturing fluoroelastomer (A), wherein fluoroelastomer (A) is a (per)fluoroelastomer, the method comprising: (a): polymerizing in an aqueous emulsion in the presence of a surfactant by feeding the following ingredients into a first reactor: (i) a monomer mixture (M1) comprising at least one monomer (F), wherein monomer (F) is a fluoromonomer, (ii) at least one iodinated and/or brominated chain-transfer agent(s), (iii) at least one branching agent possessing at least two ethylenic unsaturations; and (iv) at least one radical initiator, so as to obtain a pre-polymer latex (P); (b): recovering latex (P) from the first reactor and storing the recovered latex (P) in a storage tank; (c): feeding the recovered latex (P) from the storage tank into a second reactor; (d): polymerizing in the second reactor at least a second monomer mixture (M2) comprising at least one monomer (F) in the presence of a radical initiator, so as to obtain a final latex (F); and (e): recovering fluoroelastomer (A) from latex (F).

2. The method of claim 1, wherein monomer mixture (M1) comprises at least one fluoromonomer selected from the group consisting of: C.sub.2-C.sub.8 perfluoroolefins; C.sub.2-C.sub.8 hydrogen-containing fluoroolefins; (per)fluoroalkylethylenes complying with formula CH.sub.2CHR.sub.f0, in which R.sub.f0 is a C.sub.1-C.sub.6 (per)fluoroalkyl or a C.sub.1-C.sub.6 (per)fluorooxyalkyl having one or more ether groups; chloro- and/or bromo- and/or iodo-C.sub.2-C.sub.6 fluoroolefins; fluoroalkylvinylethers complying with formula CF.sub.2CFOR.sub.f1 in which R.sub.f1 is a C.sub.1-C.sub.6 fluoro- or perfluoroalkyl; hydrofluoroalkylvinylethers complying with formula CH.sub.2CFOR.sub.f1 in which R.sub.f1 is a C.sub.1-C.sub.6 fluoro- or perfluoroalkyl; fluoro-oxyalkylvinylethers complying with formula CF.sub.2CFOX.sub.0, in which X.sub.0 is a C.sub.1-C.sub.12 oxyalkyl, or a C.sub.1-C.sub.12 (per)fluorooxyalkyl having one or more ether groups; fluoroalkyl-methoxy-vinylethers complying with formula CF.sub.2CFOCF.sub.2OR.sub.f2 in which R.sub.f2 is a C.sub.1-C.sub.6 fluoro- or perfluoroalkyl, or a C.sub.1-C.sub.6 (per)fluorooxyalkyl having one or more ether groups; functional fluoro-alkylvinylethers complying with formula CF.sub.2CFOY.sub.0, in which Y.sub.0 is a C.sub.1-C.sub.12 alkyl or (per)fluoroalkyl, or a C.sub.1-C.sub.12 oxyalkyl or a C.sub.1-C.sub.12 (per)fluorooxyalkyl, said Y.sub.0 group comprising a carboxylic or sulfonic acid group, in its acid, acid halide or salt form; fluorodioxoles, of formula: ##STR00009## wherein each of R.sub.f3, R.sub.f4, R.sub.f5, R.sub.f6, equal or different each other, is independently a fluorine atom, a C.sub.1-C.sub.6 fluoro- or per(halo)fluoroalkyl, optionally comprising one or more oxygen atom.

3. The method of claim 2, wherein mixture (M1) is selected from the group consisting of: (1) vinylidene fluoride (VDF) containing monomers mixtures, in which VDF is mixed with at least one comonomer different from VDF and selected from the group consisting of: (a) C.sub.2-C.sub.8 perfluoroolefins; (b) hydrogen-containing C.sub.2-C.sub.8 fluoro-olefins or perfluoroalkyl ethylenes of formula CH.sub.2CHR.sub.f, wherein R.sub.f is a C.sub.1-C.sub.6 perfluoroalkyl group; (c) C.sub.2-C.sub.8 chloro and/or bromo and/or iodo-fluoroolefins; (d) (per)fluoroalkylvinylethers (PAVE) of formula CF.sub.2CFOR.sub.f, wherein R.sub.f is a C.sub.1-C.sub.6 (per)fluoroalkyl group; (e) (per)fluoro-oxy-alkylvinylethers of formula CF.sub.2CFOX, wherein X is a C.sub.1-C.sub.12 ((per)fluoro)-oxyalkyl comprising catenary oxygen atoms; (f) (per)fluorodioxoles having formula: ##STR00010## wherein R.sub.f3, R.sub.f4, R.sub.f5, R.sub.f6, equal or different from each other, are independently selected from fluorine atoms and C.sub.1-C.sub.6 (per)fluoroalkyl groups, optionally comprising one or more than one oxygen atom; (g) (per)fluoro-methoxy-vinylethers (MOVE, hereinafter) having formula:
CFX.sub.2CX.sub.2OCF.sub.2OR.sub.f wherein R.sub.f is selected among C.sub.1-C.sub.6 (per)fluoroalkyls, linear or branched; C.sub.5-C.sub.6 cyclic (per)fluoroalkyls; and C.sub.2-C.sub.6 (per)fluorooxyalkyls, linear or branched, comprising from 1 to 3 catenary oxygen atoms, and X.sub.2 is F or H; (h) C.sub.2-C.sub.8 non-fluorinated olefins (Ol); (i) ethylenically unsaturated compounds comprising nitrile (CN) groups, optionally (per)fluorinated; and (2) tetrafluoroethylene (TFE) containing monomers mixtures, in which TFE is mixed with at least one comonomer different from TFE and selected from the group consisting of monomers of classes (a), (c), (d), (e), (f), (g), and (i), as above detailed.

4. The method according to claim 1, wherein step (a) comprises polymerizing the mixture (M1) in an aqueous emulsion in the presence of a fluorinated surfactant (FS) selected from the group consisting of: CF.sub.3(CF.sub.2).sub.n1COOM, in which n.sub.1 is an integer ranging from 4 to 10; and M represents H, NH.sub.4, Na, Li or K; T(C.sub.3F.sub.6O).sub.n0(CFXO).sub.m0CF.sub.2COOM [formula (FS.sub.1)], in which T represents Cl or a perfluoroalkoxyde group of formula C.sub.kF.sub.2k+1O wherein k is an integer from 1 to 3, one F atom being optionally substituted by a Cl atom; n.sub.0 is an integer ranging from 1 to 6; m.sub.0 is an integer ranging from 0 to 6; M represents H, NH.sub.4, Na, Li or K; and X represents F or CF.sub.3; F(CF.sub.2CF.sub.2).sub.n2CH.sub.2CH.sub.2RO.sub.3M, in which R is P or S, M represents H, NH.sub.4, Na, Li or K; and n.sub.2 is an integer ranging from 2 to 5; A-R.sub.fB bifunctional fluorinated surfactants, in which A and B, equal to or different from each other, are (O).sub.pCFXCOOM*; M* represents H, NH.sub.4, Na, Li or K; X is F or CF.sub.3; p is an integer equal to 0 or 1; and R.sub.f is a linear or branched perfluoroalkyl chain, or a (per)fluoropolyether chain such that the number average molecular weight of A-R.sub.fB is in the range 300 to 3,000; R.sub.fO(CF.sub.2).sub.rO-L-COOM, wherein R.sub.f is a linear or branched perfluoroalkyl chain, optionally comprising catenary oxygen atoms, M is H, NH.sub.4, Na, Li or K; r is 1 to 3; L is a bivalent fluorinated bridging group; R.sub.f(OCF.sub.2).sub.uO(CF.sub.2).sub.vCOOM, wherein R.sub.f is a linear or branched perfluoroalkyl chain, optionally comprising catenary oxygen atoms, M is H, NH.sub.4, Na, Li or K; u and v are integers from 1 to 3; R.sub.f(O).sub.tCHQ-L-COOM, wherein R.sub.f is a linear or branched perfluoroalkyl chain, optionally comprising catenary oxygen atoms, Q is F or CF.sub.3, t is 0 or 1, M is H, NH.sub.4, Na, Li or K; L is a bivalent fluorinated bridging group; cyclic fluorocompounds of the following formula (I): ##STR00011## wherein X.sub.1, X.sub.2, X.sub.3, equal or different from each other are independently selected from H, F, and C.sub.1-6 (per)fluoroalkyl groups, optionally comprising one or more catenary or non-catenary oxygen atoms; L represents a bond or a divalent group; R.sub.F is a divalent fluorinated C.sub.1-3 bridging group; Y is a hydrophilic function selected from the group consisting of those of formulae: ##STR00012## wherein X.sub.a is H, a monovalent metal or an ammonium group of formula N(R.sub.n).sub.4, wherein R.sub.n, equal or different at each occurrence, represents a hydrogen atom or a C.sub.1-6 hydrocarbon group; and mixtures thereof.

5. The method of claim 4, wherein the aqueous emulsion of step (a) further includes an additional non-functional fluorinated fluid selected from (per)fluoropolyethers complying with formula (I-p):
T.sub.1(CFX).sub.pOR.sub.f(CFX).sub.p-T.sub.2(I-p) wherein: each of X is independently F or CF.sub.3; p and p, equal or different each other, are integers from 0 to 3; R.sub.f is a fluoropolyoxyalkene chain comprising repeating units R.sup.o, said repeating units being selected from the group consisting of: (i) CFXO, wherein X is F or CF.sub.3, (ii) CF.sub.2CFXO, wherein X is F or CF.sub.3, (iii) CF.sub.2CF.sub.2CF.sub.2O, (iv) CF.sub.2CF.sub.2CF.sub.2CF.sub.2O, (v) (CF.sub.2).sub.jCFZO wherein j is an integer chosen from 0 and 1 and Z is a group of general formula OR.sub.fT.sub.3, wherein R.sub.f is a fluoropolyoxyalkene chain comprising a number of repeating units from 0 to 10, said recurring units being selected from: CFXO, CF.sub.2CFXO, CF.sub.2CF.sub.2CF.sub.2O, CF.sub.2CF.sub.2CF.sub.2CF.sub.2O, with each of X being independently F or CF.sub.3; and T.sub.3 is a C.sub.1-C.sub.3 perfluoroalkyl group, and mixtures thereof; T.sub.1 and T.sub.2, the same or different from each other, are H, halogen atoms, or C.sub.1-C.sub.3 fluoroalkyl groups, optionally comprising one or more H or halogen atoms different from fluorine.

6. The method according to claim 1, wherein the iodinated and/or brominated chain-transfer agent is selected from the group consisting of 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, x and y are integers between 0 and 2, with 1x+y2 and wherein the amount of iodinated and/or brominated chain-transfer agent(s) fed during Step (a) is of at least 1.0 weight part per 100 weight parts of pre-polymer manufactured in Step (a) and/or is of at most 4.0 weight parts per 100 weight parts of pre-polymer manufactured in Step (a).

7. The method according to claim 1, wherein the branching agent possessing at least two ethylenic unsaturations is generally a bis-olefin (OF) having general formula: ##STR00013## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6, equal or different from each other, are H or C.sub.1-C.sub.5 alkyl; Z is a linear or branched C.sub.1-C.sub.18 alkylene or cycloalkylene radical, optionally containing oxygen atoms, optionally at least partially fluorinated, or a (per)fluoropolyoxyalkylene radical and wherein the amount of branching agent possessing at least two ethylenic unsaturations fed in Step (a) is of at most 1% wt, with respect to the total weight of pre-polymer obtained in Step (a).

8. The method according to claim 1, wherein pre-polymer latex (P) comprises particles of a pre-polymer having a number-averaged molecular weight of at least 1000 and/or at most 40000, and/or having a PDI of at least 1.2 and/or of at most 3.5.

9. The method according to claim 1, wherein pre-polymer latex (P) comprises particles of a pre-polymer having a iodine and/or bromine content of at least 0.5%, with respect to the weight of the pre-polymer and/or of at most 3.0%, with respect to the weight of the pre-polymer.

10. The method according to claim 1, wherein in step (b), latex (P) is recovered from the first reactor in a storage tank for a storage time of at least 1 hour.

11. The method according to claim 1, wherein the second reactor is different from the first reactor, which is not equipped for metering branching agent and/or for metering iodinated and/or brominated chain transfer agent.

12. The method according to claim 1, wherein monomer mixture (M2) comprises at least one fluoromonomer selected from the group consisting of: C.sub.2-C.sub.8 perfluoroolefins, C.sub.2-C.sub.8 hydrogen-containing fluoroolefins, (per)fluoroalkylethylenes complying with formula CH.sub.2CHR.sub.f0, in which R.sub.f0 is a C.sub.1-C.sub.6 (per)fluoroalkyl or a C.sub.1-C.sub.6 (per)fluorooxyalkyl having one or more ether groups; chloro- and/or bromo- and/or iodo-C.sub.2-C.sub.6 fluoroolefins, fluoroalkylvinylethers complying with formula CF.sub.2CFOR.sub.f1 in which R.sub.f1 is a C.sub.1-C.sub.6 fluoro- or perfluoroalkyl, hydrofluoroalkylvinylethers complying with formula CH.sub.2CFOR.sub.f1 in which R.sub.f1 is a C.sub.1-C.sub.6 fluoro- or perfluoroalkyl, fluoro-oxyalkylvinylethers complying with formula CF.sub.2CFOX.sub.0, in which X.sub.0 is a C.sub.1-C.sub.12 oxyalkyl, or a C.sub.1-C.sub.12 (per)fluorooxyalkyl having one or more ether groups, fluoroalkyl-methoxy-vinylethers complying with formula CF.sub.2CFOCF.sub.2OR.sub.f2 in which R.sub.f2 is a C.sub.1-C.sub.6 fluoro- or perfluoroalkyl, or a C.sub.1-C.sub.6 (per)fluorooxyalkyl having one or more ether groups, functional fluoro-alkylvinylethers complying with formula CF.sub.2CFOY.sub.0, in which Y.sub.0 is a C.sub.1-C.sub.12 alkyl or (per)fluoroalkyl, or a C.sub.1-C.sub.12 oxyalkyl or a C.sub.1-C.sub.12 (per)fluorooxyalkyl, said Y.sub.0 group comprising a carboxylic or sulfonic acid group, in its acid, acid halide or salt form, fluorodioxoles, of formula: ##STR00014## wherein each of R.sub.f3, R.sub.f4, R.sub.f5, R.sub.f6, equal or different each other, is independently a fluorine atom, a C.sub.1-C.sub.6 fluoro- or per(halo)fluoroalkyl, optionally comprising one or more oxygen atom.

13. The method according to claim 1, wherein the weight ratio between the amount of mixture (M2) converted in Step (d) and the amount of pre-polymer fed to the second reactor as latex (P) is of at least 2 weight parts of mixture (M2) converted per weight part of pre-polymer, and/or at most 20 weight parts of mixture (M2) converted per weight part of pre-polymer and/or wherein the weight fraction of fluoroelastomer (A) produced in Step (a) is less than 33% weight, with respect to the total weight of fluoroelastomer (A).

14. The method according to claim 1, wherein fluoroelastomer (A) possesses a number-averaged molecular weight of at least 40000 and/or of at most 150000.

15. The method according to claim 1, wherein the iodine and/or bromine content of fluoroelastomer (A) is reduced by a factor equal to the weight of fluoroelastomer (A) over the weight of pre-polymer obtained from Step (a) and/or wherein the branching agent content in fluoroelastomer (A) is reduced by a factor equal to the weight of fluoroelastomer (A) over the weight of pre-polymer obtained from Step (a).

16. The method of claim 12, wherein mixture (M2) is selected from the group consisting of: (1) vinylidene fluoride (VDF) containing monomers mixtures, in which VDF is mixed with at least one comonomer different from VDF and selected from the group consisting of: (a) C.sub.2-C.sub.8 perfluoroolefins; (b) hydrogen-containing C.sub.2-C.sub.8 fluoro-olefins or perfluoroalkyl ethylenes of formula CH.sub.2CHR.sub.f, wherein R.sub.f is a C.sub.1-C.sub.6 perfluoroalkyl group; (c) C.sub.2-C.sub.8 chloro and/or bromo and/or iodo-fluoroolefins; (d) (per)fluoroalkylvinylethers (PAVE) of formula CF.sub.2CFOR.sub.f, wherein R.sub.f is a C.sub.1-C.sub.6 (per)fluoroalkyl group; (e) (per)fluoro-oxy-alkylvinylethers of formula CF.sub.2CFOX, wherein X is a C.sub.1-C.sub.12 ((per)fluoro)-oxyalkyl comprising catenary oxygen atoms; (f) (per)fluorodioxoles having formula: ##STR00015## wherein R.sub.f3, R.sub.f4, R.sub.f5, R.sub.f6, equal or different from each other, are independently selected from fluorine atoms and C.sub.1-C.sub.6 (per)fluoroalkyl groups, optionally comprising one or more than one oxygen atom; (g) (per)fluoro-methoxy-vinylethers (MOVE, hereinafter) having formula:
CFX.sub.2CX.sub.2OCF.sub.2OR.sub.f wherein R.sub.f is selected among C.sub.1-C.sub.6 (per)fluoroalkyls, linear or branched; C.sub.5-C.sub.6 cyclic (per)fluoroalkyls; and C.sub.2-C.sub.6 (per)fluorooxyalkyls, linear or branched, comprising from 1 to 3 catenary oxygen atoms, and X.sub.2 is F or H; (h) C.sub.2-C.sub.8 non-fluorinated olefins (OI); (i) ethylenically unsaturated compounds comprising nitrile (CN) groups, optionally (per)fluorinated; and (2) tetrafluoroethylene (TFE) containing monomers mixtures, in which TFE is mixed with at least one comonomer different from TFE and selected from the group consisting of monomers of classes (a), (c), (d), (e), (g), and (i), as above detailed.

17. The method according to claim 8, wherein pre-polymer latex (P) comprises particles of a pre-polymer having a number-averaged molecular weight of at least 10000 and at most 20000, and/or having a PDI of at least 1.5 and of at most 2.8.

18. The method according to claim 9, wherein pre-polymer latex (P) comprises particles of a pre-polymer having a iodine and/or bromine content of at least 1.2% wt, with respect to the weight of the pre-polymer and of at most 2.0% wt, with respect to the weight of the pre-polymer.

19. The method according to claim 13, wherein the weight ratio between the amount of mixture (M2) converted in Step (d) and the amount of pre-polymer fed to the second reactor as latex (P) is of at least 5 weight parts of mixture (M2) converted per weight part of pre-polymer, and at most 15 weight parts of mixture (M2) converted per weight part of pre-polymer and/or wherein the weight fraction of fluoroelastomer (A) produced in Step (a) is less than 18% weight, with respect to the total weight of fluoroelastomer (A).

20. The method according to claim 14, wherein fluoroelastomer (A) possesses a number-averaged molecular weight of at least 80000 and of at most 120000.

Description

EXAMPLES

Example 1

Example 1aPreparation of Pre-Polymer Latex

[0159] In a 10 liters reactor equipped with a mechanical stirrer operating at 545 rpm, 5.4 l of demineralized water and 175 ml of a microemulsion, previously obtained by mixing 38.5 ml of a perfluoropolyoxyalkylene having acidic end groups of formula: CF.sub.2ClO(CF.sub.2CF(CF.sub.3)O).sub.n(CF.sub.2O).sub.mCF.sub.2COOH, wherein n/m=10, having average molecular weight of 600, 24.6 ml of a 30% v/v NH.sub.4OH aqueous solution, 87.7 ml of demineralized water and 24.2 ml of GALDEN D02 perfluoropolyether of formula: CF.sub.3O(CF.sub.2CF(CF.sub.3)O).sub.n(CF.sub.2O).sub.mCF.sub.3 with n/m=20, having average molecular weight of 450, were introduced.

[0160] The reactor was heated and maintained at a set-point temperature of 80 C.; a mixture of vinylidene fluoride (VDF) (78.5% moles) and hexafluoropropene (HFP) (21.5% moles) was then added to reach a final pressure of 25 bar. Then 102 g of 1,4-diiodioperflurobutane (C.sub.4F.sub.8I.sub.2) as chain transfer agent were introduced, and 2.0 g of ammonium persulfate (APS) as initiator were introduced. Pressure was maintained at set-point of 25 bar by continuous feeding of a gaseous mixture of vinylidene fluoride (VDF) (78.5% moles) and hexafluoropropene (HFP) (21.5% moles) up to a total of 3150 g. Simultaneously, 6.8 g of CH.sub.2CH(CF.sub.2).sub.6CHCH.sub.2 were fed to the reactor in a controlled manner following the consumption of monomers, by 20 identical step-wise additions at the onset of the polymerization and at each 5% increase in target conversion. Then the reactor was cooled, vented and the latex recovered and stored in a tank for duration of more than 1 day. A specimen of this pre-polymer was taken for analytical/mechanical determinations

Example 1bPreparation of Final Fluoroelastomer

[0161] In a 21 liters reactor equipped with a magnetic stirrer operating at 60 rpm, 12.9 l of demineralized water and 1776 g of latex produced in Example 1, having a solids content of about 36% wt, were introduced.

[0162] The reactor was heated and maintained at a set-point temperature of 80 C.; a mixture of vinylidene fluoride (VDF) (78.5% moles) and hexafluoropropene (HFP) (21.5% moles) was then added to reach a final pressure of 25 bar. 2.6 g of ammonium persulfate (APS) as initiator were then introduced. Pressure was maintained at set-point of 25 bar by continuous feeding of a gaseous mixture of vinylidene fluoride (VDF) (78.5% moles) and hexafluoropropene (HFP) (21.5% moles) up to a total of 4170 g. Then the reactor was cooled, vented and the latex recovered. The latex was coagulated by addition of aluminum sulphate; coagulated fluoroelastomer was separated from the aqueous phase, washed with demineralized water and dried in a convection oven at 90 C. for 16 hours.

[0163] Raw polymer characterization data are reported in Table 1 and 2.

Comparative Example 2

[0164] In a 10 liters reactor equipped with a mechanical stirrer operating at 545 rpm, 5.4 l of demineralized water and 40 ml of a microemulsion, previously obtained by mixing 8.8 ml of a perfluoropolyoxyalkylene having acidic end groups of formula: CF.sub.2ClO(CF.sub.2CF(CF.sub.3)O).sub.n(CF.sub.2O).sub.mCF.sub.2COOH, wherein n/m=10, having average molecular weight of 600, 5.6 ml of a 30% v/v NH.sub.4OH aqueous solution, 20.0 ml of demineralized water and 5.5 ml of GALDEN D02 perfluoropolyether of formula: CF.sub.3O(CF.sub.2CF(CF.sub.3)O).sub.n(CF.sub.2O).sub.mCF.sub.3 with n/m=20, having average molecular weight of 450, were introduced.

[0165] The reactor was heated and maintained at a set-point temperature of 80 C.; a mixture of vinylidene fluoride (VDF) (78.5% moles) and hexafluoropropene (HFP) (21.5% moles) was then added to reach a final pressure of 25 bar. Then 13.5 g of 1,4-diiodioperflurobutane (C.sub.4F.sub.8I.sub.2) as chain transfer agent were introduced, and 2.0 g of ammonium persulfate (APS) as initiator were introduced. Pressure was maintained at set-point of 25 bar by continuous feeding of a gaseous mixture of vinylidene fluoride (VDF) (78.5% moles) and hexafluoropropene (HFP) (21.5% moles) up to a total of 3150 g. Moreover, 1.2 g of CH.sub.2CH(CF.sub.2).sub.6CHCH.sub.2, fed in 20 equivalent portions, at the onset of the polymerization and then each 5% increase in conversion, were introduced. Then the reactor was cooled, vented and the latex recovered. The latex was treated with aluminum sulphate, separated from the aqueous phase, washed with demineralized water and dried in a convection oven at 90 C. for 16 hours. Raw polymer characterization data are reported in Table 1 and 2.

[0166] GPC Determinations

[0167] Fluoroelastomers were characterized by GPC using instrumentation and conditions as detailed in the Table 1 below, and relevant parameters were determined based on polystyrene standards, taking into account polymer/solvent Mark-Houwink parameters for relevant standard and for fluoroelastomers.

TABLE-US-00001 TABLE 6 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: 10.sup.6, 10.sup.5, 10.sup.4 and 10.sup.3 Detector Waters Refractive Index mod. 2414 Software for data Waters Empower 3 acquisition and processing

TABLE-US-00002 TABLE 1 Molecular Reaction Composition weight Example time % mol distribution N.sup.o min VDF HFP Mn PDI 1a 148 78.9 21.1 12734 2.1 1b 107 78.9 21.1 91966 2.8 2C 122 79.0 21.0 98997 2.8

TABLE-US-00003 TABLE 2 Other chain ends Ex. I [mmol/kg of polymer] N.sup.o [% g/gpol] CF2H CF2CH3 CF2CH2OH 1a 1.55 20 4 1 1b 0.20 29 10 1 2C 0.21 31 10 1

[0168] Mechanical and Sealing Property Determination on Cured Samples

[0169] Fluoroelastomer of Example 1 (final fluoroelastomer from Ex.1b) and comparative fluoroelastomer of Example 2 were pre-compounded using a Brabender mixer with the crosslinking ingredients as listed in the table:

TABLE-US-00004 TABLE 5 Compound recipe [phr] Polymer 100 Drimix TAIC 75 - 3.0 Finco(*) Luperox 101XL 45 1.5 peroxide - Atofina(**) VULCAN 1391 - 10.0 Cabot(***) ZnO 3.0 (*)TAIC: Drimix TAIC 75: triallylisocyanurate 75% wt dispersion in silica; (**)Luperox 101 XL 45 peroxide is a 45% dispersion of 2,5 Dimethyl 2,5 Di(tert-butylperoxyl) hexane in calcium carbonate; (***)Carbon Black

[0170] Cure behaviour was determined according to ASTM D-6601, at a temperature of 170 C. for 12 minutes, by determining the following properties:

[0171] M.sub.L=Minimum torque (lb*in)

[0172] M.sub.H=Maximum torque (lb*in)

M=M.sub.HM.sub.L

[0173] t.sub.90=Time to 90% state of cure (sec)

[0174] Mooney viscosity (MU) of raw rubbers has been determined according to ASTM D1646-07 as ML (1+10) at 121 C.

[0175] Plaques and O-rings (size class=214) have been cured in a pressed mould for 10 minutes at 170 C. and then post-treated in an air circulating oven ((1+4) h at 230 C.)

[0176] The tensile properties have been determined on specimens punched out from the plaques, according to the DIN 53504 Standard.

[0177] M.sub.100 is the modulus in MPa at an elongation of 100%;

[0178] T.S. is the tensile strength in MPa;

[0179] E.B. is the elongation at break in %.

[0180] The Shore A hardness (3) (HDS) has been determined on 3 pieces of plaque piled according to the ASTM D 2240 method.

TABLE-US-00005 TABLE 6 ML MH M t90 Example MU [lb * in] [lb * in] [lb * in] [sec] 1 44 0.9 13.1 12.2 305 2C 48 0.9 12.7 11.8 293

TABLE-US-00006 TABLE 7 T.S. E.B. M100 HDS Example [MPa] [%] [Mpa] [Shore A] 1 32.3 503 2.1 63 2C 31.8 460 2.2 63