METHOD FOR MAKING FLUOROPOLYMERS

Abstract

The invention pertains to a method of making fluoropolymer dispersions using certain polyfunctional perfluoropolyether derivatives including a plurality of ionisable groups selected from the group consisting of —SO.sub.3X.sub.a, —PO.sub.3X.sub.a and —COOX.sub.a, whereas X.sub.a is H, an ammonium group or a monovalent metal, and whereas said groups are comprised as pendant groups in the perfluoropolyether chain, and to fluoropolymer dispersions therefrom.

Claims

1. A method for making a fluoropolymer, the method comprising emulsion polymerizing one or more than one fluorinated monomer in an aqueous medium wherein said aqueous emulsion polymerization is carried out in an aqueous medium in the presence of at least one radical initiator and at least one dispersant (D), wherein dispersant (D) is at least one polyfunctional perfluoropolyether dispersant comprising a plurality of ionisable groups (X) of —COOX.sub.a, wherein X.sub.a is H, an ammonium group or a monovalent metal, optionally in combination with sulfonic acid groups of formula —SO.sub.3X.sub.a and/or phosphonic acid groups of formula PO.sub.3X.sub.a, and complying with formula:
T.sup.X-O—[R.sub.f.sup.1—O].sub.n1[R.sub.f.sup.2—O].sub.n2-T.sup.X′  (I) wherein: each of R.sub.f.sup.1, equal to or different from each other at each occurrence, is a C.sub.1-C.sub.4 perfluoroalkylene group; each of R.sub.f.sup.2, equal to or different from each other at each occurrence, is a C.sub.1-C.sub.4 perfluoroalkylene group comprising at least one group (X), as above detailed; n1 and n2 are positive numbers different from zero; and T.sup.X and T.sup.X′, equal to or different from each other, are selected from the group consisting of: (j) C.sub.1-C.sub.24 (hydro)(fluoro)carbon groups free from group (X), as above detailed, possibly comprising one or more than one of H, O, and Cl; and (jj) C.sub.1-C.sub.24 (hydro)(fluoro)carbon groups comprising at least one group (X), as above detailed; and said dispersant (D) possessing a number averaged molecular weight of more than 2000.

2. The method of claim 1, wherein the amount of dispersant (D) is at least 0.05% wt and/or at most 3.20% wt, with respect to the total weight of the aqueous medium.

3. (canceled)

4. The method of claim 1, wherein the amount of said ionisable groups in dispersant (D) is at least 0.35 meq/g, with respect to the weight of dispersant (D), and/or at most 2.50 meq/g.

5. The method of claim 1, wherein repeating units —R.sub.f.sup.1—O— of the dispersant (D) are selected from the group consisting of: (a1) units —CF.sub.2CF.sub.2O— (b1) units —CFYO— (c1) units —CF.sub.2CFYO— (d1) units —CF.sub.2O— (e1) units —CF.sub.2(CF.sub.2).sub.zCF.sub.2O—, wherein: Y is a C.sub.1-C.sub.5 perfluoro(oxy)alkyl group; z is 1 or 2, and/or wherein repeating units —R.sub.f.sup.2—O— of the dispersant (D) are selected from the group consisting of: (a2) units —CF.sub.2CF(G.sub.x)O— (b2) units —CF(G.sub.x)O— (c2) units —CF.sub.2(CF.sub.2).sub.x1CF(G.sub.x(CF.sub.2).sub.x2O—, with X1 and X2 being zero or integers from 1 to 2, with the proviso that X1+X2 is at least 1, wherein: G.sub.x is a C.sub.1-C.sub.5 perfluoro(oxy)alkylene group comprising at least one group (X) selected from the group consisting of —SO.sub.3X.sub.a, —PO.sub.3X.sub.a and —COOX.sub.a, wherein X.sub.a is H, an ammonium group or a monovalent metal.

6. The method of claim 1, wherein repeating units —R.sub.f.sup.2—O— of the dispersant (D) are selected from the group consisting of: (a2′) units —CF.sub.2CF(COOX.sub.a)O— (b2′) units —CF(COOX.sub.a)O— (c2′) units —CF.sub.2(CF.sub.2).sub.x1CF(COOX.sub.a)(CF.sub.2).sub.x2O—, with X1 and X2 being zero or integers from 1 to 2, with the proviso that X1+X2 is at least 1, wherein X.sub.a is H, an ammonium group or a monovalent metal.

7. The method of claim 6, wherein dispersant (D) is a compound complying with formula:
T.sup.C-O—(CF.sub.2CF.sub.2O).sub.a′(CFYO).sub.b′(CF.sub.2CFYO).sub.c′(CF.sub.2O).sub.d′(CF.sub.2(CF.sub.2).sub.zCF.sub.2O).sub.e′(CF.sub.2CF(COOX.sub.a)O).sub.f′(CF(COOX.sub.a)O).sub.g′(CF.sub.2CF(COOX.sub.a)CF.sub.2CF.sub.2O).sub.h′(CF.sub.2CF.sub.2CF(COOX.sub.a)CF.sub.2O).sub.i′-T.sup.C′, wherein: Y is a C.sub.1-C.sub.5 perfluoro(oxy)alkyl group; z is 1 or 2; a′, b′, c′, d′, e′, f′, g′, h′, i′ are ≥0, with the proviso that a′+b′+c′+d′+e′ is >0 and f′+g′+h′+i′>0; X.sub.a is H, an ammonium group or a monovalent metal; each of T.sup.C and T.sup.C′, equal to or different from each other, are selected from the group consisting of (j) ionisable groups T.sup.x″ of any of formulae —CFZ*—COOX.sub.a, —CFZ*CH.sub.2—COOX.sub.a, and —CFZ*—CH.sub.2(OCH.sub.2CH.sub.2).sub.k—COOX.sub.a, wherein Z* is F or CF.sub.3; k is ranging from 0 to 10; X.sub.a is H, an ammonium group or a monovalent metal and (jj) non-ionisable groups C.sub.1-C.sub.3 (per)fluoroalkyl groups free from —COOX.sub.a groups, optionally comprising one or more than one of H, and Cl.

8. (canceled)

9. (canceled)

10. The method according to claim 1, wherein the fluorinated monomer is selected from the group consisting of: C.sub.2-C.sub.8 perfluoroolefins; C.sub.2-C.sub.8 hydrogen-containing fluoroolefins; C.sub.2-C.sub.8 chloro- and/or bromo- and/or iodo-containing fluoroolefins; fluoroalkylvinylethers of formula CF.sub.2═CFOR.sub.f1, wherein R.sub.f1 is a C.sub.1-C.sub.6 fluoroalkyl; fluorooxyalkylvinylethers of formula CF.sub.2—CFOX.sub.0, wherein X.sub.0 is a C.sub.1-C.sub.12 fluorooxyalkyl group comprising one or more than one ethereal oxygen atom; fluorodioxoles, of formula: ##STR00004## 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, or a C.sub.1-C.sub.6 fluoro(halo)fluoroalkyl, optionally comprising one or more oxygen atom.

11. The method according to claim 1, wherein the method comprises emulsion polymerizing vinylidene fluoride (VDF) optionally in combination with one or more than one hydrogenated and/or fluorinated monomer different from VDF.

12. The method according to claim 1, wherein the method comprises emulsion polymerizing tetrafluoroethylene (TFE) optionally in combination with one or more than one hydrogenated and/or fluorinated monomer different from TFE.

13. The method according to claim 1, wherein the method is carried out in substantial absence of fluorinated emulsifiers having a molecular weight of less than 1000, and no such fluorinated emulsifier is purposely added to the polymerization.

14. A fluoropolymer dispersion obtained from the method according to claim 1.

15. A fluoropolymer dispersion comprising fluoropolymer particles and at least one dispersant (D), wherein dispersant (D) is at least one polyfunctional perfluoropolyether dispersant comprising a plurality of ionisable groups (X) of —COOX.sub.a, whereas X.sub.a is H, an ammonium group or a monovalent metal, optionally in combination with sulfonic acid groups of formula —SO.sub.3X.sub.a and/or phosphonic acid groups of formula PO.sub.3X.sub.a, and complying with formula:
T.sup.X-O—[R.sub.f.sup.1—O].sub.n1[R.sub.f.sup.2—O].sub.n2-T.sup.X′  (I) wherein: (i) each of R.sub.f.sup.1, equal to or different from each other at each occurrence, is a C.sub.1-C.sub.4 perfluoroalkylene group; (ii) each of R.sub.f.sup.2, equal to or different from each other at each occurrence, is a C.sub.1-C.sub.4 perfluoroalkylene group comprising at least one group (X), as above detailed; and (iii) n1 and n2 are positive numbers different from zero; and T.sup.X and T.sup.X′, equal to or different from each other, are selected from the group consisting of: (j) C.sub.1-C.sub.24 (hydro)(fluoro)carbon groups free from group (X), as above detailed, optionally comprising one or more than one of H, O, and Cl; and (jj) C.sub.1-C.sub.24 (hydro)(fluoro)carbon groups comprising at least one group (X), as above detailed; and said dispersant (D) possessing a number averaged molecular weight of more than 2000.

16. The method of claim 2, wherein the amount of dispersant (D) is at least 0.10% wt and at most 3.00% wt, with respect to the total weight of the aqueous medium.

17. The method of claim 4, wherein the amount of said ionisable groups in dispersant (D) is at least 0.40 meq/g, with respect to the weight of dispersant (D), and at most 2.20 meq/g.

18. The method according to claim 10, wherein the fluorinated monomer is selected from the group consisting of: tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoroisobutylene; trifluoroethylene (TrFE), vinylidene fluoride (VDF), vinyl fluoride (VF), pentafluoropropylene, and hexafluoroisobutylene; chlorotrifluoroethylene (CTFE) and bromotrifluoroethylene; fluoroalkylvinylethers of formula CF.sub.2═CFOR.sub.f1, wherein R.sub.f1 is —CF.sub.3, —C.sub.2F.sub.5, or —C.sub.3F.sub.7; fluoromethoxyalkylvinylethers of formula CF.sub.2═CFOCF.sub.2OR.sub.f2, wherein R.sub.f2 is a C.sub.1-C.sub.3 fluoro(oxy)alkyl group; fluorodioxoles, of formula: ##STR00005## wherein each of R.sub.f3, R.sub.f4, R.sub.f5, R.sub.f6, equal or different from each other, is independently a fluorine atom, —CF.sub.3, —C.sub.2F.sub.5, —C.sub.3F.sub.7, —OCF.sub.3, or —OCF.sub.2CF.sub.2OCF.sub.3.

Description

PREPARATIVE EXAMPLE 1—PREPARATION OF DISPERSANT (D-1)

[0155] A 800 ml photochemical reactor was used, with an optical path of 10 mm, equipped with a reflux condenser kept at the temperature of −80° C. with dry ice, and a thermocouple for temperature detecting. The reactor was equipped with a system of GALDEN® HT55-cooled quartz sheaths for the insertion of the UV Lamp (HANAU type TQ 150), emitting at a wavelength comprised within the range of from 248 to 334 nm.

[0156] To the reactor, after cooling by dry ice-acetone bath, 600 ml of CF.sub.2Cl.sub.2 were charged; then the reactor being maintained at −60° C., to it, over 5 hours, 86.4 g (2.7 mol) of O.sub.2, 90 g (0.9 mol) of C.sub.2F.sub.4 and 17.0 g (0.105 mol) of C.sub.4F.sub.6 were charged. At the end, the solvent was evaporated off, and 62 g of an oil were obtained. The produced oil was found by iodometric analysis to contain 2.12% by weight of peroxidic oxygen. .sup.19F-N.M.R. spectrum, IR spectrum and peroxide content enabled demonstrating this oil being a compound made of sequences mainly of —CF.sub.2—, —CF.sub.2—CF.sub.2—, —CF.sub.2—CF(—CF(O)CF.sub.2)—, —CF(—CF(O)CF.sub.2)— —CF.sub.2CF(O)CF—CF.sub.2— units linked by ether and/or peroxy bridges. The product was found to possess a molecular weight determined by .sup.19F-NMR of 18 000. The epoxy content, calculated by the same NMR .sup.19F, was found to be 12.9 units per polymeric chain.

[0157] At this point an aliquot of the oil was submitted to a thermal treatment in order to remove peroxide moieties. 20 g of polymer were charged to a 50 cc flask equipped with thermometer and stirrer; over a 2-hour time the temperature was increased to 230° C.; the reaction mass was then kept for a further 6 hours at 230°-240° C. At the end of this thermal treatment, 14.2 g were obtained of a product which, at the iodometric analysis, comprised no detectable amount of peroxidic groups. The NMR .sup.19F spectrum failed to provide any evidence of epoxy groups, but solely of corresponding carbonyl fluoride moieties.

[0158] The product obtained so far was then hydrolyzed with water by stirring at room temperature for 4 hrs. The final mass was then separated from water phase and washed with fresh water.

[0159] The final product was recovered after drying at 100° C. in vacuum apparatus. All the acylfluorides groups were found to be converted into correspondent carboxylic acid groups.

[0160] Dispersant (D-1) was found by .sup.19F-NMR analysis to possess a number averaged molecular weight of 11 500, and was found to be composed of a majority of C1=(CF.sub.2O) and C2=(CF.sub.2CF.sub.2O) units, with a ratio C2/C1 of 1.27, and of units comprising pendant ionisable repeat units of formulae —OCF.sub.2CF(COOH)O— (predominant) and —OCF.sub.2CF(COOH)CF.sub.2— (minor) and —OCF(COOH)O— (negligible), and further including chain ends of formulae —CF.sub.2COOH (73%), —CF.sub.2Cl (21%) and —CF.sub.3 (6%) (with percentages based on overall end groups). The total amount of ionisable groups was of 6.6 moles per mole of dispersant (D-1) (corresponding to about 0.57 meq/g), of which 5.1 moles per mole of dispersant (D-1) comprised in pendant ionisable repeat units, as above detailed, the remainder in chain ends.

[0161] The above described procedure was repeated several times, in order to collect an appropriate amount of dispersant (D1), which has been used in the herein below described polymerization runs.

Working Example 2: Polymerization of Tetrafluoroethylene (TFE) with the Dispersant (D-1) of Preparative Example 1

[0162] Step 1—Salification of Dispersant (D-1)

[0163] A 1 L flask was feeded with 600 g of demineralized water and 2 g of ammonia; then 12 g of the dispersant (D-1) of Preparative Example 1 were dropped in the flask. The dispersion obtained was stirred for 5 h at 40° C. until a homogeneous dispersion was obtained.

[0164] Step 2: Polymerization of Tetrafluoroethylene (TFE)

[0165] A 5 liters autoclave was deaerated with multiple cycles of vacuum and nitrogen filling, then charged with 1.6 liters of demineralized water and 614 grams of the dispersion obtained from Preparative Ex. 1 above, corresponding to 12 g of dispersant (D-1); after heating at 68° C. (stirring at 480 rpm) the autoclave was pressurized with tetrafluoroethylene (TFE) at 20.5 Bar and the reaction was started by feeding 60 ml of a solution containing 8 g/l of ammonium persulfate (APS).

[0166] The pressure of the autoclave was maintained at constant value of 20.5 Bar by feeding TFE until a quantity of 600 grams of TFE were fed, after 150 minutes the TFE feeding was stopped. By keeping constant stirring of 480 rpm the autoclave was cooled to ambient temperature the white-latex obtained was discharged after being kept under nitrogen bubbling for 16 hours to strip away residual monomers from the polymerization, and then stored in a plastic tank. The latex was then coagulated and obtained polymer confirms to be insoluble in each tested solvent.

Working Example 3: Polymerization of Tetrafluoroethylene (TFE) with the Dispersant (D-1) of Preparative Example 1

[0167] Step 1—Salification of Dispersant (D-1) in the Presence of PFPE Fluid

[0168] A 1 L flask was feeded with 50 g of GALDEN® D02 non-functional PFPE and 1 g of ammonia; then 10 g dispersant (D-1) of Preparative Example 1 was dropped in the flask. The dispersion obtained was stirred for 5 h at room temperature.

[0169] Step 2—Polymerization of Tetrafluoroethylene (TFE)

[0170] A 5 liters autoclave was deaerated with multiple cycles of vacuum and nitrogen filling, then charged with 1.6 liters of demineralized water and 61 grams of the dispersion obtained from Preparative Ex. 1 above, corresponding to 10 g of dispersant (D-1) of Preparative Example 1; after heating at 68° C. (stirring at 480 rpm) the autoclave was pressurized with tetrafluoroethylene (TFE) at 20.5 Bar and the reaction was started by feeding 60 ml of a solution containing 8 g/l of ammonium persulfate (APS). The pressure of the autoclave was maintained at constant value of 20.5 Bar by feeding TFE until a quantity of 600 grams of TFE were fed, after 150 minutes the TFE feeding was stopped. By keeping constant stirring of 480 rpm the autoclave was cooled to ambient temperature the white-latex obtained was discharged after being kept under nitrogen bubbling for 16 hours to strip away residual monomers from the polymerization, and then stored in a plastic tank. The latex was then coagulated and obtained polymer confirms to be insoluble in each tested solvent.