Method for manufacturing fluoroelastomers

1 . A method of making a fluoroelastomer (A), which is a (per)fluoroelastomer comprising Iodine and/or Bromine chain ends, said method comprising

polymerizing vinylidene fluoride (VDF), in the presence of at least one second (per)fluorinated monomer (M F ) different from VDF, in an aqueous emulsion in the presence of a chain transfer agent (CTA-X) having I and/or Br atoms and in the presence of a redox-initiating system (R) comprising at least one organic radical initiator (O) and at least one composition (CS) comprising at least one compound (S) bearing at least one sulfinic acid group,

wherein:

the amount of initiator (O) is of at least 1.50 and at most 15.00 mmol of O 2 per kg of fluoroelastomer (A);

the amount of compound(S) is of at least 0.20 and at most 2.00 g per kg of fluoroelastomer (A); and

the ratio between agent (CTA-X) and composition (CS) is of at least 2.00 and of at most 8.00 g of X/g of composition (CS), whereas X is the amount of I and/or Br in the agent (CTA-X); and

wherein said emulsion polymerization is carried out without addition of any fluorinated surfactant or hydrogenated surfactant.

2 . The method of claim 1 , wherein monomer (M F ) is selected from the group consisting of:

C 2 -C 8 perfluoroolefins;

hydrogen-containing C 2 -C 8 olefins different from VDF;

C 2 -C 8 chloro and/or bromo and/or iodo-fluoroolefins;

(per)fluoroalkylvinylethers (PAVE) of formula CF 2 ═CFOR f , wherein R f is a C 1 -C 6 (per)fluoroalkyl group;

(per)fluoro-oxy-alkylvinylethers of formula CF 2 ═CFOX, wherein X is a C 1 -C 12 [(per)fluoro]-oxyalkyl comprising catenary oxygen atoms;

(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 C 1 -C 6 (per)fluoroalkyl groups, optionally comprising one or more than one oxygen atom;

(per)fluoro-methoxy-vinylethers (MOVE) having formula: CFX 2 ═CX 2 OCF 2 OR″ f wherein R″ f is selected among linear or branched C 1 -C 6 (per)fluoroalkyls; C 5 -C 6 cyclic (per)fluoroalkyls; and C 2 -C 6 (per)fluorooxyalkyls, linear or branched, comprising from 1 to 3 catenary oxygen atoms, and X 2 ═F, H;

and/or

wherein fluoroelastomer (A) comprises, in addition to recurring units derived from VDF, recurring units derived from hexafluoropropylene (HFP), and may comprise one or more of the following:

recurring units derived from at least one bis-olefin (OF) having general formula:

wherein R 1 , R 2 , R 3 , R 4 , R 5 and R 6 , equal or different from each other, are H, a halogen, or a C 1 -C 5 optionally halogenated group, optionally comprising one or more oxygen group; Z is a linear or branched C 1 -C 18 optionally halogenated alkylene or cycloalkylene radical, optionally containing oxygen atoms, or a (per)fluoropolyoxyalkylene radical;

recurring units derived from at least one monomer (M F ) different from VDF and HFP; and

recurring units derived from at least one hydrogenated monomer.

3 . The method of claim 1 ,

wherein said agent (CTA-X) is selected from the group consisting of:

iodinated and/or brominated organic chain-transfer agent(s); and

alkali metal or alkaline-earth metal iodides and/or bromides; and/or

wherein said agent (CTA-X) is selected from the group consisting of those of formula R f (I) x (Br) y , in which R 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; and/or

wherein the ratio between agent (CTA-X) and composition (CS) is of at least 2.50 and/or of at most 7.60 g of X/g of composition (CS), whereas X is the amount of I and/or Br in the agent (CTA-X); and/or

wherein agent (CTA-X) is a iodinated chain transfer agent, and wherein the amounts of (CTA-X) and composition (CS) are such that the iodine/composition (CS) ratio is of at least 2.00 and of at most 7.60 g of I/g of composition (CS).

4 . The method of claim 1 , wherein initiator (O) is selected from the group consisting of:

(b) diacylperoxides;

(c) dialkylperoxides;

(d) hydroperoxides;

(e) per-acids esters and salts thereof;

(f) peroxydicarbonates; and/or

wherein the amount of initiator (O) is of at most 12.00 mmol of O 2 per kg of fluoroelastomer (A); and/or in an amount of at least 1.80 mmol of O 2 per kg of fluoroelastomer (A); and/or

wherein the molar ratio between the halogen content of (CTA-X) and the peroxide content of the initiator (O) is of at least 3.00 in mol of X/mol of O 2 and/or of at most 15.00 in mol of X/mol of O 2 .

5 . The method of claim 1 ,

wherein said compound(S) complies with the following formula (S-I):

wherein

M is a hydrogen atom, an ammonium ion, or a monovalent metal ion;

R 20 is —OH or —N(R 4 )(R 5 ) where each of R 4 and R 5 , identical or different from one another, are hydrogen atom or linear or branched alkyl chain having from 1 to 6 carbon atoms;

R 21 is hydrogen atom, linear or branched alkyl group having from 1 to 6 carbon atoms, 5- or 6-membered cycloalkyl group, 5- or 6-membered aryl group;

R 22 is —COOM, —SO 3 M, —C(═O)R 4 , —C(═O)N(R 4 )(R 5 ), —C(═O)OR 4 ,

and salt thereof with at least one monovalent metal ion; and/or

wherein said composition (CS) comprises at most 50 wt of a compound complying with formula (S-I), with respect to the total weight of said composition (CS); and/or

wherein said composition (CS) further comprises a compound (S 3 ) comprising at least one sulfonic acid group, said compound (S 3 ) complying with the following formula (S 3 —I):

wherein M is a monovalent metal ion; and/or

wherein said composition (CS) comprises at least 5 wt. % of a compound complying with formula (S 3 —I), with respect to the total weight of said composition (CS); and/or

wherein said composition (CS) further comprises at least one of:

sulphurous acid or a salt thereof; and

sulphuric acid or a salt thereof.

6 . The method of claim 2 , wherein monomer (M F ) is selected from the group consisting of:

C 2 -C 8 perfluoroolefins, selected from tetrafluoroethylene (TFE) and hexafluoropropylene (HFP);

hydrogen-containing C 2 -C 8 olefins different from VDF, selected from vinyl fluoride (VF), trifluoroethylene (TrFE), perfluoroalkyl ethylenes of formula CH 2 ═CH—R f , wherein R f is a C 1 -C 6 perfluoroalkyl group;

C 2 -C 8 chloro and/or bromo and/or iodo-fluoroolefins selected from chlorotrifluoroethylene (CTFE);

(per)fluoroalkylvinylethers (PAVE) of formula CF 2 ═CFOR f , wherein R f is a C 1 -C 6 (per)fluoroalkyl group selected from —CF 3 , —C 2 F 5 , —C 3 F 7 ;

(per)fluoro-oxy-alkylvinylethers of formula CF 2 ═CFOX, wherein X is a perfluoro-2-propoxypropyl group;

(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 C 1 -C 6 (per)fluoroalkyl groups, selected from —CF 3 , —C 2 F 5 , —C 3 F 7 , —OCF 3 , —OCF 2 CF 2 OCF 3 ;

(per)fluoro-methoxy-vinylethers (MOVE) having formula: CFX 2 ═CX 2 OCF 2 OR″ f wherein X 2 ═F, and R″ f is —CF 2 CF 3 (MOVE1); —CF 2 CF 2 OCF 3 (MOVE2); or —CF 3 (MOVE3);

and/or

wherein fluoroelastomer (A) comprises, in addition to recurring units derived from VDF, recurring units derived from hexafluoropropylene (HFP), and may comprise one or more of the following:

recurring units derived from at least one bis-olefin (OF) having general formula:

wherein R 1 , R 2 , R 3 , R 4 , R 5 and R 6 , equal or different from each other, are H, a halogen, or a C 1 -C 5 optionally halogenated group, possibly comprising one or more oxygen group; Z is a linear or branched C 1 -C 18 optionally halogenated alkylene or cycloalkylene radical, optionally containing oxygen atoms, or a (per)fluoropolyoxyalkylene radical; wherein bis-olefin (OF) is a bis-olefin (OF-1) of formula:

wherein j is an integer between 2 and 10, and R 1 , R 2 , R 3 , R 4 , equal or different from each other, are H, F or C 1-5 alkyl or (per)fluoroalkyl group, such as H 2 C═CH—(CF 2 ) 6 —CH═CH 2 ;

recurring units derived from at least one monomer (M F ) different from VDF and HFP; and

recurring units derived from at least one hydrogenated monomer.

7 . The method of claim 1 ,

wherein said agent (CTA-X) is selected from the group consisting of:

iodinated and/or brominated organic chain-transfer agent(s) selected from those of formula R f (I) x (Br) y , in which R 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; and

alkali metal or alkaline-earth metal iodides and/or bromides; and/or

wherein said agent (CTA-X) is selected from the group consisting of those of formula R f (I) x (Br) y , which is of formula R′ f (I) x′ (Br) y′ , in which R′ f is a perfluoroalkyl containing from 1 to 8 carbon atoms, while x′ and y′ are integers between 0 and 2, with 1≤x′+y′≤2; and/or

wherein the ratio between agent (CTA-X) and composition (CS) is of at least 3.20 and/or of at most 7.50, g of X/g of composition (CS), whereas X is the amount of I and/or Br in the agent (CTA-X); and/or

wherein agent (CTA-X) is a iodinated chain transfer agent, and wherein the amounts of (CTA-X) and composition (CS) are such that the iodine/composition (CS) ratio is of at least 2.50 and of at most 7.50 g of I/g of composition (CS).

8 . The method of claim 1 , wherein initiator (O) is selected from the group consisting of:

(b) diacylperoxides selected from diacetylperoxide, disuccinyl peroxide, dipropionylperoxide, dibutyrylperoxide, dibenzoylperoxide, dilauroyl-peroxide; benzoylacetylperoxide, diglutaric acid peroxide;

(c) dialkylperoxides selected from ditertbutylperoxide (DTBP), t-butyl cumyl peroxide; 2,5-dimethyl-2,5-di(t-butylperoxy) hexane; dicumyl peroxide; 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane; di-tertamyl peroxide;

(d) hydroperoxides selected from t-butyl hydroperoxide (TBHP), cumene hydroperoxide, tertiaryamylhydroperoxide;

(e) per-acids esters and salts thereof selected from peracetic acid, and ammonium, sodium or potassium salts thereof, tert-butyl peroxybenzoate, tert-butylperoxyacetate and tert-butylperoxypivalate;

(f) peroxydicarbonates selected from diisopropylperoxydicarbonate, tert-butyl-peroxyisopropylcarbonate; di-n-propylperoxydicarbonate, dicyclohexylperoxydicarbonate, di-n-butyl peroxydicarbonate, di-2-ethylhexylperoxydicarbonate, dimyristyl peroxydicarbonate, dicetyl peroxydicarbonate, diethylperoxydicarbonate; and/or

wherein the amount of initiator (O) is of at most 10.00 mmol of O 2 per kg of fluoroelastomer (A); and/or in an amount of at least 2.00 mmol of O 2 per kg of fluoroelastomer (A); and/or

wherein the molar ratio between the halogen content of (CTA-X) and the peroxide content of the initiator (O) is of at least 3.50 in mol of X/mol of O 2 and/or of at most 13.00 in mol of X/mol of O 2 .

9 . The method of claim 5 , wherein

sulphurous acid or a salt thereof is selected from sodium sulphite and sodium hydrogen sulphite; and

sulphuric acid or a salt thereof is selected from sodium sulphate and sodium hydrogen sulphate.