Method for manufacturing fluoropolymers

Abstract

The invention pertains to a process for manufacturing a (per)fluoropolymer, said process comprising polymerizing one or more fluorinated monomers in the presence of a multi-phase medium, said medium comprising: (A) a water phase [phase (W)]; (B) at least one fluorinated surfactant [surfactant (FS)] having formula (I) here below:
R.sub.f—(OCF.sub.2CF.sub.2).sub.k-1—O—CF.sub.2—COOX.sub.a  (I) wherein R.sub.f is a C.sub.1-C.sub.3 perfluoroalkyl group comprising, optionally, one or more ether oxygen atoms, k is 2 or 3 and X.sub.a is a selected from a monovalent metal and an ammonium group of formula NR.sup.N.sub.4, wherein R.sup.N, equal or different at each occurrence, is a hydrogen atom or a C.sub.1-C.sub.3 alkyl group; (C) an oil phase [phase (O)] comprising: at least one non-functional (per)fluoropolyether (non-functional PFPE) comprising at least one (per)fluoropolyoxyalkylene chain [chain (R.sub.F)] and at least one functional (per)fluoropolyether (functional PFPE) comprising at least one (per)fluoropolyoxyalkylene chain [chain (R′.sub.F)] and having a number average molecular weight of at least 1000 and a solubility of less than 1% by weight in water at 25° C.

Claims

1. A process for manufacturing a (per)fluoropolymer, said process comprising polymerizing one or more fluorinated monomers in the presence of a multi-phase medium, said medium comprising: (A) a water phase (W); (B) at least one fluorinated surfactant (FS) having formula (I) here below:
R.sub.f—(OCF.sub.2CF.sub.2).sub.k-1—O—CF.sub.2—COOX.sub.a  (I) wherein R.sub.f is a C.sub.1-C.sub.3 perfluoroalkyl group comprising, optionally, one or more ether oxygen atoms, k is 2 or 3 and X.sub.a is selected from the group consisting of a monovalent metal and an ammonium group of formula NR.sup.N.sub.4, wherein R.sup.N, equal or different at each occurrence, is a hydrogen atom or a C.sub.1-C.sub.3 alkyl group; (C) an oil phase (O) comprising: at least one non-functional (per)fluoropolyether (non-functional PFPE) comprising at least one (per)fluoropolyoxyalkylene chain (R.sub.F) and free from functional end-groups, and at least one functional (per)fluoropolyether (functional PFPE) comprising at least one (per)fluoropolyoxyalkylene chain (R′.sub.F)] and having a number average molecular weight of at least 1000 and a solubility of less than 1% by weight in water at 25° C.; wherein the at least one non-functional (per)fluoropolyether is present in an amount ranging from 0.01% to less than 30% by weight of the total weight of the multi-phase medium.

2. The process of claim 1, wherein the surfactant (FS) complies with formula (II) here below:
R.sub.f′O—CF.sub.2CF.sub.2—O—CF.sub.2—COOX.sub.a′  (II) wherein: R.sub.f′ is a C.sub.1-C.sub.3 perfluoroalkyl group; X.sub.a′ is selected from the group consisting of Li, Na, K, NH.sub.4 and NR.sup.N′.sub.4, wherein R.sup.N′ is a C.sub.1-C.sub.3 alkyl group.

3. The process of claim 1, wherein the surfactant (FS) complies with formula (III) here below:
CF.sub.3CF.sub.2O—CF.sub.2CF.sub.2—O—CF.sub.2—COOX.sub.a′  (III) wherein X.sub.a′ is selected from the group consisting of Li, Na, K, NH.sub.4 and NR.sup.N′.sub.4, wherein R.sup.N′ is a C.sub.1-C.sub.3 alkyl group.

4. The process of claim 1, wherein the non-functional PFPE is selected from the group consisting of:
T.sub.1-O—[CF(CF.sub.3)CF.sub.2O].sub.b1′(CFYO).sub.b2′-T.sup.1′  (1) wherein: T.sup.1 and T.sup.1′, equal to or different from each other, are independently selected from the group consisting of —CF.sub.3, —C.sub.2F.sub.5 and —C.sub.3F.sub.7 groups; Y, equal or different at each occurrence, is selected from the group consisting of a fluorine atom and a —CF.sub.3 group; b.sup.1′ and b.sup.2′, equal to or different from each other, are independently integers ≧0 such that the b1′/2′ ratio is comprised between 20 and 1000 and the (b1′+b2′) sum is comprised between 5 and 250; should b1′ and b2′ be both different from zero, the different recurring units are generally statistically distributed along the perfluoropolyoxyalkylene chain;
T.sup.1-O—[CF(CF.sub.3)CF.sub.2O].sub.c1′(C.sub.2F.sub.4O).sub.c2′(CFYO).sub.c3′-T.sup.1′  (2) wherein: T.sup.1 and T.sup.1′ equal to or different from each other, have the same meaning as defined above; Y, equal or different at each occurrence, has the same meaning as defined above; c.sup.1′, c.sup.2′ and c.sup.3′, equal to or different from each other, are independently integers ≧0 such that the (c1′+c2′+c3′) sum is comprised between 5 and 250; should at least two of c.sup.1′, c2′ and c3′ be different from zero, the different recurring units are generally statistically distributed along the perfluoropolyoxyalkylene chain;
T.sup.1-O—(C.sub.2F.sub.4O).sub.d1′(CF.sub.2O).sub.d2′-T.sup.1′  (3) wherein: T.sup.1 and T.sup.1′, equal to or different from each other, have the same meaning as defined above; d.sup.1′ and d.sup.2′, equal to or different from each other, are independently integers ≧0 such that the d1′/d2′ ratio is comprised between 0.1 and 5 and the (d1′+(d2′) sum is comprised between 5 and 250; should d1′ and d2′ be both different from zero, the different recurring units are generally statistically distributed along the perfluoropolyoxyalkylene chain;
T.sup.2-O—[CF(CF.sub.3)CF.sub.2O].sub.e′-T.sup.2′  (4) wherein: T.sup.2 and T.sup.2′, equal to or different from each other, are independently selected from the group consisting of —C.sub.2F.sub.5 and —C.sub.3F.sub.7 groups; e′ is an integer comprised between 5 and 250
T.sup.2-O—(CF.sub.2CF.sub.2O).sub.f′-T.sup.2′  (5) wherein: T.sup.2 and T.sup.2′, equal to or different from each other, have the same meaning as defined above; f′ is an integer comprised between 5 and 250;
T1-O—(CF.sub.2CF.sub.2C(Hal′).sub.2O).sub.g1′—(CF.sub.2CF.sub.2CH.sub.2O).sub.g2′—(CF.sub.2CF.sub.2CH(Hal′).sub.g3′-T.sup.1′  (6) wherein: T.sup.1 and T.sup.1′, equal to or different from each other, have the same meaning as defined above; Hal′ is fluorine; g1′, g2′, and g3′, equal to or different from each other, are independently integers ≧0 such that the (g1′+g2′+g3′) sum is comprised between 5 and 250; should at least two of g1′, g2′ and g3′ be different from zero, the different recurring units are generally statistically distributed along the (p)fluoropolyoxyalkylene chain; and
R.sup.1.sub.f—{C(CF.sub.3).sub.2—O—[C(R.sup.2.sub.f).sub.2].sub.j1′C(R.sup.2f).sub.2—O}.sub.j2′—R.sup.1.sub.f  (7) wherein: R.sup.1.sub.f, equal or different at each occurrence, is a C.sub.1-C.sub.6 perfluoroalkyl group; R.sup.2.sub.f, equal or different at each occurrence, is selected from the group consisting of a fluorine atom and a C.sub.1-C.sub.6 perfluoroalkyl group; j1′ is equal to 1 or 2; j2′ is an integer comprised between 5 and 250.

5. The process of claim 1, wherein the functional PFPE comprises at least one functional end-group selected from the group consisting of carboxylic acid, phosphonic acid and sulphonic acid groups.

6. The process of claim 5, wherein the functional PFPE complies with formula (IV) here below:
T.sub.1-(CFW.sub.1).sub.p1—O—R.sub.F—(CFW.sub.2).sub.p2-T.sub.2  (IV) wherein; R.sub.F is a (per)fluoropolyoxyalkylene chain (chain R′.sub.F) such that the number average molecular weight of the functional PFPE is at least 1000; T.sub.1 and T.sub.2, equal to or different from each other, are selected from the group consisting of: i) functional end-groups selected from the group consisting of carboxylic acid, phosphoric acid and sulphonic acid groups, and ii) non-functional end-groups selected from the group consisting of a fluorine atom and a C.sub.1-C.sub.3 (per)fluoroalkyl group, with the proviso that at least one of T.sub.1 and T.sub.2 is a functional end-group; W.sub.1 and W.sub.2, equal to or different from each other, independently represent a fluorine atom or a —CF.sub.3 group; p.sub.1 and p.sub.2, equal to or different from each other, are independently integers comprised between 1 and 3.

7. The process of claim 1, wherein the functional PFPE is a bifunctional PFPE complying with formula (VI) here below;
HOOC—CF.sub.2—O—(CF.sub.2).sub.n′(CF.sub.2CF.sub.2O).sub.m′—CF.sub.2—COOH  (VI) wherein n′ and m′ are independently integers 0 such that the number average molecular weight of the bifunctional PFPE is at least 1000, the recurring units being generally statistically distributed along the perfluoropolyoxyalkylene chain.

8. The process of claim 1, wherein the weight ratio of said at least one surfactant (FS) having said formula (I) to said at least one functional PFPE ranges between 1:0.3 and 1:0.9.

9. The process of claim 1, wherein R.sub.f is a (per)fluoropolyoxyalkylene chain (R′.sub.F) such that the number average molecular weight of the functional PFPE is at least 1500.

10. The process of claim 7, wherein n′ and m′ are independently integers >0 such that the number average molecular weight of the bifunctional PFPE is at least 1500.

11. The process of claim 1, wherein the fluorinated surfactant (FS) and the functional PFPE are present in a weight ratio of between 1:0.1 and 1:1.

12. The process of claim 1, wherein the fluorinated surfactant (FS) and the functional PFPE are present in a weight ratio of between 1:0.3 and 1:0.9.

Description

EXAMPLE 1

(1) Manufacture of Multi-Phase Composition (1)

(2) In a glass flask, equipped with a stirrer, were mixed under stirring 15.00 g of compound having formula CF.sub.3CF.sub.2OCF.sub.2CF.sub.2OCF.sub.2COOH, 8.02 g of a 10% by weight aqueous solution of ammonia and 6.98 g of demineralised water, 11.25 g of FLUOROLINK® C10 functional PFPE and 4.08 g of GALDEN® D02 non-functional PFPE. The pH was adjusted to about 2.2. A multi-phase composition was spontaneously obtained at room temperature which appeared as a limpid, thermodynamically stable solution containing 33.1% by weight of water, 9.0% by weight of GALDEN® D02 non-functional PFPE, 33.1% by weight of fluorinated surfactant having formula CF.sub.3CF.sub.2OCF.sub.2CF.sub.2OCF.sub.2COONH.sub.4 and 24.8% by weight of FLUOROLINK® C10 functional PFPE, wherein the weight ratio of CF.sub.3CF.sub.2OCF.sub.2CF.sub.2OCF.sub.2COONH.sub.4 to FLUOROLINK® C10 functional PFPE was 1/0.75 [multi-phase composition (1)].

(3) The average size of the homogeneously dispersed droplets was found to be 9.5 nm, as measured according to ISO 13321.

EXAMPLE 2

(4) Manufacture of Multi-Phase Composition (2)

(5) In a glass flask, equipped with a stirrer, were mixed under stirring 26.49 g of compound having formula CF.sub.3CF.sub.2OCF.sub.2CF.sub.2OCF.sub.2COOH, 14.17 g of a 10% by weight aqueous solution of ammonia and 0.09 g of demineralised water, 13.25 g of FLUOROLINK® C10 functional PFPE and 6.00 of GALDEN® D02 non-functional PFPE. The pH was adjusted to about 2.0. A multi-phase composition was spontaneously obtained at room temperature which appeared as a limpid, thermodynamically stable solution containing 23.8% by weight of water, 10.0% by weight of GALDEN® D02 non-functional PFPE, 44.1% by weight of fluorinated surfactant having formula CF.sub.3CF.sub.2OCF.sub.2CF.sub.2OCF.sub.2COONH.sub.4 and 22.1% by weight of FLUOROLINK® C10 functional PFPE, wherein the weight ratio of CF.sub.3CF.sub.2OCF.sub.2CF.sub.2OCF.sub.2COONH.sub.4 to FLUOROLINK® C10 functional PFPE was 1/0.5 [multi-phase composition (2)].

(6) The average size of the homogeneously dispersed droplets was found to be 13.5 nm, as measured according to ISO 13321.

(7) The multi-phase compositions (1) and (2) of Examples 1 and 2 of the invention could be successfully diluted with water at room temperature to yield a kinetically-stable, optically transparent, isotropic dispersion of nano-sized droplets to be suitably used in the process of the invention.

EXAMPLE 3 (COMPARATIVE)

(8) Thermodynamically stable multi-phase compositions of a water phase and an oil phase with droplets having an average size of more than 100 nm, as measured according to ISO 13321, were obtained at room temperature by addition of a fluorinated surfactant having formula CF.sub.3CF.sub.2OCF.sub.2CF.sub.2OCF.sub.2COONH.sub.4 (see Table 1 here below).

(9) TABLE-US-00001 TABLE 1 GALDEN ® D02 Average Water PFPE C.sub.2F.sub.5OCF.sub.2CF.sub.2OCF.sub.2COONH.sub.4 size 42.0% wt. 30.0% wt. 28.0% wt. 136 nm 47.0% wt. 40.0% wt. 13.0% wt. 108 nm

(10) As compared with multi-phase compositions of Examples 1 and 2 of the invention, these compositions, lacking functional PFPE, were found to give rapid coalescence of droplets towards larger size when diluted with water. As a consequence, these compositions, when used as polymerizing media, were found not to be suitable for obtaining nano-sized (per)fluoropolymer dispersed particles.

EXAMPLE 4 (COMPARATIVE)

(11) A multi-phase composition was obtained at room temperature containing 33.5% by weight of water, 8.0% by weight of GALDEN® D02 non-functional PFPE, 33.4% by weight of fluorinated surfactant having formula CF.sub.3CF.sub.2OCF.sub.2CF.sub.2OCF.sub.2COONH.sub.4 and 25.1% by weight of FLUOROLINK® C07 functional PFPE, wherein the weight ratio of CF.sub.3CF.sub.2OCF.sub.2CF.sub.2OCF.sub.2COONH.sub.4 to FLUOROLINK® C07 functional PFPE was 1/0.75.

(12) The average size of the homogeneously dispersed droplets was found to be 26 nm, as measured according to ISO 13321.

EXAMPLE 5 (COMPARATIVE)

(13) A multi-phase composition was obtained at room temperature containing 33.6% by weight of water, 7.5% by weight of GALDEN® D02 non-functional PFPE, 33.6% by weight of fluorinated surfactant having formula CF.sub.3CF.sub.2OCF.sub.2CF.sub.2OCF.sub.2COONH.sub.4 and 25.2% by weight of a functional PFPE having formula HOOC—CF.sub.2O(CF.sub.2CF.sub.2O).sub.n′(CF.sub.2O).sub.m′CF.sub.2—COOH, wherein n′ and m′ are integers such that the number average molecular weight is about 460, wherein the weight ratio of CF.sub.3CF.sub.2OCF.sub.2CF.sub.2OCF.sub.2COONH.sub.4 to the functional PFPE was 1/0.75.

(14) As compared with multi-phase compositions of Examples 1 and 2 of the invention, the compositions of comparative Examples 4 and 5 comprising functional PFPE of lower number average molecular weight could not be successfully diluted with water at room temperature to yield a kinetically-stable, optically transparent, isotropic dispersion of nano-sized droplets. As a consequence, these compositions could not be used as polymerizing medium for obtaining nano-sized (per)fluoropolymer dispersed particles with high reaction rates.

EXAMPLE 6 (COMPARATIVE)

(15) Same procedures as detailed in Examples 1 and 2 were followed but using an ammonium salt of FLUOROLINK® C10 functional PFPE having a solubility in water at 25° C. largely exceeding 1% by weight.

(16) As compared with multi-phase compositions of Examples 1 and 2 of the invention, the so obtained compositions were found to lack stability: rapid coalescence of droplets towards larger size was observed upon mixing. As a consequence, these compositions were found not to be suitable for being used as polymerizing media for obtaining nano-sized (per)fluoropolymer dispersed particles.

EXAMPLE 7

Polymerization of Tetrafluoroethylene (TFE) and Perfluoropropyl Vinyl Ether (PPVE)

(17) A reactor having an inner volume of 5 lt., equipped with a mechanical stirrer (470 rpm), was charged with 3 lt. of demineralised water and 33 g of the multi-phase composition (1) prepared as in Example 1.

(18) The reactor was heated to 75° C. and vented for a few minutes.

(19) The reactor was then charged with 50 g of PPVE, pressurized with ethane to a pressure of 250 mbar and finally pressurized with TFE to a set-point pressure of 20 bar.

(20) Polymerization was initiated by addition of ammonium persulfate (0.3 g introduced at the beginning and 0.84 g further injected in seven portions in combination with further additions of PPVE to a total of 80 g).

(21) Polymerization was pursued until reaching overall monomers consumption of 1500 g after 147 min, then the reactor was depressurized, vented and cooled.

(22) A latex having a solid content of 34% by weight was obtained comprising particles having an average size of 77 nm, as measured according to ISO 13321, of a TFE/PPVE copolymer (PPVE: 5.2% by weight of copolymer) having a melt flow index of 13 g/10 min (372° C./5 Kg, measured according to ASTM D 1238), a melting point of 300.5° C., as measured by DSC analysis, and a heat of crystallization of −28.5 J/g, as measured according to ASTM D 3418.

EXAMPLE 8

(23) Polymerization of TFE, Vinylidene Fluoride (VDF) and Hexafluoropropylene (HFP)

(24) Same procedure as detailed in Example 7 was followed but charging the reactor with 3.5 lt. of demineralised water and 35 ml of the multi-phase composition (1) prepared as in Example 1.

(25) The reactor was heated to 80° C.

(26) The reactor was then pressurized with HFP to a pressure of 8.56 bar and finally pressurized with a feed gas mixture of VDF (70% by moles), HFP (19% by moles) and TFE (11% by moles) to a set-point pressure of 26 bar. The reactor was then charged with 0.66 ml of 1,4-diiodoperfluorobutane and 0.23 ml of H.sub.2C═CH—(CF.sub.2).sub.6—CH═CH.sub.2.

(27) Polymerization was initiated by addition of ammonium persulfate (0.36 g introduced at the beginning and 0.17 g further injected after 20% by weight of monomer conversions in combination with further additions of the 1,4-diiodoperfluorobutane to a total of 4.13 ml and of H.sub.2C═CH—(CF.sub.2).sub.6—CH═CH.sub.2 to a total of 3.38 ml).

(28) Polymerization was pursued until reaching overall monomers consumption of 1500 g after 97 min.

(29) A latex having a solid content of 30.8% by weight was obtained comprising particles having an average size of 57 nm, as measured according to ISO 13321, of a VDF/HFP/TFE copolymer (VDF:HFP:TFE 70.6:17.7:11.7% by moles).

EXAMPLE 9

(30) Polymerization of TFE, VDF and HFP

(31) Same procedure as detailed in Example 8 was followed but charging the reactor with 35 ml of the multi-phase composition (2) prepared as in Example 2 and pursuing polymerization until reaching overall monomers consumption of 1500 g after 100 min.

(32) A latex having a solid content of 31.5% by weight was obtained comprising particles having an average size of 57 nm, as measured according to ISO 13321, of a VDF/HFP/TFE copolymer (VDF:HFP:TFE 70.6:17.7:11.7% by moles).

EXAMPLE 10 (COMPARATIVE)

(33) Polymerization of TFE, VDF and HFP

(34) Same procedure as detailed in Example 8 was followed but charging the reactor with 35 ml of a multi-phase composition prepared by mixing 50.0% by weight of an aqueous solution of ammonia, 20.0% by weight of GALDEN® D02 non-functional PFPE and 30.0% by weight of FLUOROLINK® 7850 fluorinated surfactant, wherein the average size of the homogeneously dispersed droplets was found to be 10 nm, as measured according to ISO 13321, and the pH was adjusted to about 8.5. A latex having a solid content of 29.3% by weight was obtained comprising particles having an average size of 79 nm, as measured according to ISO 13321, of a VDF/HFP/TFE copolymer (VDF:HFP:TFE 70.6:17.8:11.6% by moles).

(35) Recirculation tests showed an improved mechanical stability of the latexes prepared as detailed in Examples 8 and 9 of the invention with respect to latex so obtained while operating in the presence of a multi-phase medium stabilized by FLUOROLINK® 7850 fluorinated surfactant having lower number average molecular weight (see Table 2 here below).

(36) TABLE-US-00002 TABLE 2 Time Loss [%] Loss [%] Loss [%] [min] (Example 8) (Example 9) (Example 10) 0 — — — 15 0% 0% −1% 30 0% 0% −1% 60 0% 0% −1% 90 0% 0% −1% 120 0% −1%   −2%