Method for manufacturing fluoroelastomers

Abstract

The invention pertains to a process for manufacturing a fluoroelastomer [fluoroelastomer (A)] having a heat of fusion of less than 5 J/g as measured by ASTM D-3418-08, said method comprising emulsion polymerizing vinylidene fluoride (VDF) in the presence of at least one additional fluorinated monomer, in an aqueous polymerization medium, said method comprising polymerizing VDF and said additional fluorinated monomer(s) in the presence of a redox radical initiator system comprising: at least one organic oxidizing agent [agent (O)]; at least one organic reducing agent [agent (R)]; wherein agent (O) is fed to said polymerization medium separately from agent (R), so that agent (O) comes in contact with agent (R) exclusively in said polymerization medium comprising VDF and optional additional monomer(s), to fluoroelastomers having low amount of chain defects and low amount of polar end groups, notably obtainable from said process, and to curable compositions therefrom.

Claims

1. A fluoroelastomer (A) comprising recurring units derived from vinylidene fluoride and from at least one additional fluorinated monomer, said fluoroelastomer further comprising: end groups of formula CF.sub.2H and/or CF.sub.2CH.sub.3 in an amount of at most 60 mmoles per kg of fluoroelastomer; and polar end groups of formula CF.sub.2CH.sub.2OH in an amount of at most 5 mmoles per kg of fluoroelastomer.

2. The fluoroelastomer of claim 1, in which VDF is copolymerized with at least one comonomer selected from: (a) C.sub.2-C.sub.8 perfluoroolefins; (b) C.sub.2-C.sub.8 hydrogenated fluoroolefins; (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 group comprising catenary oxygen atoms; (f) (per)fluorodioxoles having formula: ##STR00012## wherein R.sub.f3, R.sub.f4, R.sub.f5, R.sub.f6, equal or different from each other, are independently selected among fluorine atoms and C.sub.1-C.sub.6 (per)fluoroalkyl groups, optionally comprising one or more than one oxygen atom; and (g) (per)fluoro-methoxy-vinylethers (MOVE) 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.2F, H.

3. The fluoroelastomer of claim 1, further comprising recurring units derived from: (CSM-1) iodine or bromine containing monomers of formula: ##STR00013## wherein each of A.sub.Hf, equal to or different from each other and at each occurrence, is independently selected from F, Cl, and H; B.sub.Hf is any of F, Cl, H and OR.sup.Hf.sub.B, wherein R.sup.Hf.sub.B is a branched or straight chain alkyl radical which can be partially, substantially or completely fluorinated or chlorinated; each of W.sup.Hf equal to or different from each other and at each occurrence, is independently a covalent bond or an oxygen atom; E.sub.Hf is a divalent group having 2 to 10 carbon atoms, optionally fluorinated; R.sub.Hf is a branched or straight chain alkyl radical, which can be partially, substantially or completely fluorinated; and X.sub.Hf is a halogen atom selected from the group consisting of iodine and bromine; which may be inserted with ether linkages; or (CSM-2) ethylenically unsaturated compounds comprising cyanide groups, possibly fluorinated.

4. The fluoroelastomer of claim 1, further comprising recurring units derived from a bis-olefin [bis-olefin (OF)] having general formula: ##STR00014## 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 fluorinated, or a (per)fluoropolyoxyalkylene radical.

5. The fluoroelastomer of claim 1, wherein the end groups of formula CF.sub.2H and/or CF.sub.2CH.sub.3 are present in an amount of at most 40 mmoles per kg of fluoroelastomer; and wherein the polar end groups of formula CF.sub.2CH.sub.2OH are present in an amount of at most 3 mmoles per kg of fluoroelastomer.

6. The fluoroelastomer of claim 2, wherein VDF is copolymerized with at least one comonomer selected from tetrafluoroethylene (TFE), hexafluoropropylene (HFP), hexafluoroisobutylene, vinyl fluoride (VF), trifluoroethylene (TrFE), chlorotrifluoroethylene (CTFE), CF.sub.2CFOCF.sub.3, CF.sub.2CFOC.sub.2F.sub.5, CF.sub.2CFOC.sub.3F.sub.7, CF.sub.2CFOX wherein X is a perfluoro-2-propoxypropyl group, perfluorodioxole, CF.sub.2CFOCF.sub.2OCF.sub.2CF.sub.3 (MOVE1), CF.sub.2CFOCF.sub.2OCF.sub.2CF.sub.2OCF.sub.3 (MOVE2), CF.sub.2CFOCF.sub.2OCF.sub.3 (MOVE3), ethylene and propylene.

7. The fluoroelastomer of claim 1, further comprising at least one comonomer selected from C.sub.2-C.sub.8 non-fluorinated olefins.

8. A peroxide curable composition comprising the fluoroelastomer (A) according to claim 1 and at least one peroxide.

9. A ionically curable composition comprising the fluoroelastomer (A) according to claim 1 and at least one curing agent and at least one accelerator.

10. Cured articles obtained from the fluoroelastomer (A) according to claim 1.

11. A process for manufacturing the fluoroelastomer of claim 1 having a heat of fusion of less than 5 J/g as measured by ASTM D-3418-08, said method comprising emulsion polymerizing vinylidene fluoride (VDF) in the presence of at least one additional fluorinated monomer, in an aqueous polymerization medium and-in the presence of a redox radical initiator system comprising: at least one organic oxidizing agent [agent (O)]; and at least one organic reducing agent [agent (R)]; wherein agent (O) is fed to said polymerization medium separately from agent (R), so that agent (O) comes in contact with agent (R) exclusively in said polymerization medium comprising VDF and optional additional monomer(s).

12. The process of claim 11, wherein the organic oxidizing agent [agent (O)] is selected from the group consisting of: diacylperoxides; dialkylperoxides; hydroperoxides; per-acid esters and salts thereof; and peroxydicarbonates.

13. The process of claim 12, wherein the organic oxidizing agent [agent (O)] is selected from the group consisting of diacetylperoxide, disuccinyl peroxide, dipropionylperoxide, dibutyrylperoxide, dibenzoylperoxide, benzoylacetylperoxide, diglutaric acid peroxide, dilaurylperoxide, ditertbutylperoxide (DTBP), t-butyl hydroperoxide (TBHP), cumene hydroperoxide, tertiaryamyl-hydroperoxide, an ammonium per-acid ester, a sodium per-acid ester, a potassium per-acid ester, diisopropylperoxydicarbonate, di-n-propylperoxydicarbonate and mixtures thereof.

14. The process of claim 11, wherein the organic reducing agent [agent (R)] is selected from the group consisting of oxalic acid, ascorbic acid, formic acid, malonic acid, citric acid, a reducing sugar, N-nitrosamine, hydroxylamines and mixtures thereof.

15. The process of claim 14, wherein the agent (R) is ascorbic acid.

16. The process of claim 11, wherein the redox radical initiator system comprises at least one transition metal catalyst [agent (P)].

17. The process of claim 16, wherein agent (P) comprises at least one of Fe.sup.2+, Cu.sup.+1, Co.sup.2+, Ag.sup.+, and Ti.sup.2+.

18. The process of claim 16, wherein the agent (P) is selected from salts of Fe.sup.2+.

19. The process of claim 11, wherein the redox radical initiator system comprises: at least one organic oxidizing agent [agent (O)]; at least one organic reducing agent [agent (R)]; optionally at least one inorganic oxidizing agent [agent (IO)]; and said redox radical initiator system is substantially free from any salt of Fe.sup.2+, Cu.sup.+1, Co.sup.2+, Ag.sup.+, Ti.sup.2+.

Description

EXAMPLE 1

Manufacture of a VDF/HFP Copolymer with t-Butyl Hydroperoxide, Ascorbic Acid and Ferrous Sulphate at 85 C.

(1) Fluoroelastomer of example 1 was produced according to following procedure: in a 211 horizontal autoclave, equipped with stirrer working at 60 rpm, were introduced, after evacuation 11.4 l of demineralized water and 114 ml of a perfluoropolyoxyalkylene microemulsion previously obtained by mixing:

(2) 24.79 ml of an acid terminated perfluoropolyoxyalkylene of formula: CF.sub.3O(CF.sub.2CF(CF.sub.3)O).sub.n(CF.sub.2O).sub.mCF.sub.2COOH, wherein n/m=10, and having an average molecular weight of 600;

(3) 8.71 ml of 30% by volume NH.sub.4OH aqueous solution;

(4) 65.66 ml demineralized water;

(5) 14.84 ml of GALDEN D02 PFPE of formula:
CF.sub.3O(CF.sub.2CF(CF.sub.3)O).sub.n(CF.sub.2O).sub.mCF.sub.3
wherein n/m=20, and having an average molecular weight of 450. The autoclave was then heated to 85 C. and maintained at such temperature for the entire duration of the reaction. A gazeous mixture of following monomers: vinylidene fluoride (VDF) 48% by moles and hexafluoropropene (HFP) 52% by moles was introduced in the autoclave so as to bring the pressure to 37 bar.

(6) A 0.89% w/w solution of t-butyl hydroperoxide in DI water were pumped in at a speed of 420 mL/h; simultaneously but separately, a 0.89% w/w in L-ascorbic acid and 0.22% w/w in ferrous sulphate were pumped in at the same speed. Set-point pressure of 37 bar was maintained constant during polymerization by feeding a mixture consisting of: VDF 71.5% by moles; HFP 21.5% by moles.

(7) After 158 min the autoclave was cooled, and the latex was discharged. 377.4 g/l of latex of a copolymer having molar monomer composition of 78.9% by mol of VDF and 21.1% by mol of HFP was obtained. Chain ends characterization of the obtained fluoroelastomer is provided in table 1.

COMPARATIVE EXAMPLE 2

Manufacture of a VDF/HFP Copolymer with Di-t-Butyl Peroxide at 121 C.

(8) Fluoroelastomer of comparative example 2 was produced according to following procedure:

(9) In a 21 l horizontal autoclave, equipped with stirrer working at 60 rpm, were introduced, after evacuation 15 l of demineralized water and 114 ml of a perfluoropolyoxyalkylene microemulsion previously obtained by mixing:

(10) 24.79 ml of an acid terminated perfluoropolyoxyalkylene of formula: CF.sub.3O(CF.sub.2CF(CF.sub.3)O).sub.n(CF.sub.2O).sub.mCF.sub.2COOH, wherein n/m=10, and having an average molecular weight of 600;

(11) 8.71 ml of 30% by volume NH.sub.4OH aqueous solution;

(12) 65.66 ml demineralized water;

(13) 14.84 ml of GALDEN D02 PFPE of formula:
CF.sub.3O(CF.sub.2CF(CF.sub.3)O).sub.n(CF.sub.2O).sub.mCF.sub.3
wherein n/m=20, and having an average molecular weight of 450. The autoclave was then heated to 121 C. and maintained at such temperature for the entire duration of the reaction. A gazeous mixture of following monomers: vinylidene fluoride (VDF) 48% by moles and hexafluoropropene (HFP) 52% by moles was introduced in the autoclave so as to bring the pressure to 37 bar. 33.9 g of di-t-butyl peroxide (DTBP) were then introduced in step-wise additions, 6.44 g at the beginning of polymerization and 9 equal parts, each of 3.05 g for every 5% increment in the monomer conversion (last addition at 45% of conversion). Set-point pressure of 37 bar was maintained constant during polymerization by feeding a mixture consisting of: VDF 71.5% by moles; HFP 21.5% by moles. After 230 min the autoclave was cooled, and the latex was discharged. 278.6 g/l of latex of a copolymer having molar monomer composition of 78.8% by mol of VDF and 21.2% by mol of HFP was obtained. Chain ends characterization of the obtained fluoroelastomer is provided in table 1.

COMPARATIVE EXAMPLE 3

Manufacture of a VDF/HFP Copolymer with Ammonium Persulfate at 85 C.

(14) Fluoroelastomer of comparative example 3 was produced according to following procedure:

(15) In a 10 l vertical autoclave, equipped with stirrer working at 545 rpm, were introduced, after evacuation 5.6 l of demineralized water. The autoclave was then heated to 85 C. and maintained at such temperature for the entire duration of the reaction. A gazeous mixture of following monomers: vinylidene fluoride (VDF) 48% by moles and hexafluoropropene (HFP) 52% by moles was introduced in the autoclave so as to bring the pressure to 19 bar.

(16) 40 g of di-ammonium persulfate were then introduced in 2 steps, 12 g at the beginning of polymerization and 28 g at 70% of conversion (2660 g of monomer mixture fed to the reactor). Set-point pressure of 19 bar was maintained constant during polymerization by feeding a mixture consisting of: VDF 71.5% by moles; HFP 21.5% by moles.

(17) After 77 min the autoclave was cooled, and the latex was discharged. 468 g/l of latex of a copolymer having molar monomer composition of 78.9% by mol of VDF and 21.1% by mol of HFP was obtained. Chain ends characterization of the obtained fluoroelastomer is provided in table 1.

(18) Characterization of Chain-Ends of Fluoroelastomers

(19) Chain ends were determined according to the method described in PIANCA, M., et al. End groups in fluoropolymers. Journal of Flurine Chemistry. 1999, vol. 95, p. 71-84. Concentration of relevant end chains are expressed both as mmoles per kg of polymer and as mmoles per kg of fluoroelastomer.

(20) TABLE-US-00001 TABLE 1 Run Ex. 1 Ex. 2C Ex. 3C VDF % mol 78.9 78.8 78.9 HFP % mol 21.1 21.5 21.1 Chain end (mmol) per Kg of fluoroelastomer [mmol/kg] CF.sub.2H (a) mmol/kg 22 61 41 CF.sub.2CH.sub.3 (b) mmol/kg 6 18 9 Total (a) + (b) mmol/kg 28 79 50 CF.sub.2CH.sub.2OH mmol/kg n.d.* n.d.* 7 *n.d. = non detectable (i.e. inferior to the limit of detection, said limit being 0.05 mmol/kg).

EXAMPLE 4

Manufacture of a VDF/HFP Copolymer with t-Butyl Hydroperoxide, Ascorbic Acid and Ferrous Sulphate at 85 C.

(21) In a 6483 liters horizontal reactor, equipped with stirrer working at 19 rpm, were introduced, after evacuation 3538 kg of demineralized water and 44.45 kg of perfluoropolyether microemulsion previously obtained by mixing:

(22) 13.74 kg (7.63 liters) of an acid terminated perfluoropolyoxyalkylene of formula:

(23) CF.sub.3O(CF.sub.2CF(CF.sub.3)O).sub.n(CF.sub.2O).sub.mCF.sub.2COOH, wherein n/m=10, and having an average molecular weight of 600;

(24) 2.39 kg (2.68 liters) of 30% by volume NH.sub.4OH aqueous solution;

(25) 20.23 kg of demineralized water;

(26) 8.09 kg (4.57 liters) of GALDEN D02 PFPE of formula:
CF.sub.3O(CF.sub.2CF(CF.sub.3)O).sub.n(CF.sub.2O).sub.mCF.sub.3
wherein n/m=20, and having an average molecular weight of 450. The autoclave was then heated to 85 C. HFP and VDF were then separately introduced in the autoclave so as to ensure a weight ratio HFP/VDF of 2.19 wt/wt and to bring the pressure to 37 bar.

(27) A 0.89% w/w solution of t-butyl hydroperoxide in deionized water was pumped in at an initial rate of 136 kg/h (300 lb/h); simultaneously but separately, a 0.89% w/w in L-ascorbic acid and 0.22% w/w in ferrous sulphate were pumped in at the same speed. Set-point pressure of 37 bar was maintained constant during polymerization by feeding a mixture consisting of VDF and HFP(HFP/VDF=0.6 wt/wt).

(28) Ethyl acetate chain transfer agent (190 kg; 418 lbs) was added as a 5.6 wt % solution in water stepwise as a function of VDF consumption.

(29) A very fast kinetic was observed at the beginning of the polymerization run, with temperature raising beyond 90 C.; temperature set point of 85 C. was restored after about 20-25 minutes and reaction was continued for about 4 hours, corresponding to the conversion of about 630 kg (1390 lbs) of VDF. No fouling was observed in the reactor.

EXAMPLE 5

Manufacture of a VDF/HFP Copolymer with t-Butyl Hydroperoxide, and Ascorbic Acid at 85 C.

(30) In a 6483 liters horizontal reactor, equipped with stirrer working at 19 rpm, were introduced, after evacuation 2767 kg of demineralized water and 44.45 kg of perfluoropolyether microemulsion previously obtained by mixing ingredients as detailed in Example 4. The autoclave was then heated to 85 C. Ethyl acetate chain transfer agent (183 kg) was added as a 5.6 wt % solution in water stepwise as a function of VDF consumption. HFP and VDF were then separately introduced in the autoclave so as to ensure a weight ratio HFP/VDF of 2.19 wt/wt and to bring the pressure to 37 bar.

(31) A 0.592% w/w solution of t-butyl hydroperoxide in deionized water was pumped in the reactor at a speed of 129 kg/h (285 lb/h); simultaneously but separately, a 0.592% w/w in L-ascorbic acid water solution was pumped in at the same speed. After about 25 minutes, feeding rate of both t-butyl hydroperoxide and L-ascorbic acid solutions were raised at 147 kg/h (325 lbs/h). Set-point pressure of 37 bar was maintained constant during polymerization by feeding a mixture consisting of VDF and HFP (HFP/VDF=0.6 wt/wt), with an average VDF consumption rate of about 340 kg/h (about 750 lbs/h).

(32) Reaction was continued for 174 minutes, corresponding to the conversion of about 1296 kg (2857 lbs) of VDF, with no fouling.

(33) A VDF-HFP fluoroelastomer substantially free from polar end groups, having a 22.3% moles HFP content and a Mooney viscosity (ML 1+10 at 121 C.) of 21.7 MU was obtained.