Hydrophilic fluoropolymer

Abstract

The present invention pertains to a process for the manufacture of a grafted fluoropolymer [polymer (Fg)], said process comprising reacting: A) at least one fluoropolymer comprising at least one functional group selected from the group consisting of a hydroxyl group and a carboxylic acid group [polymer (F)], B) at least one polyoxyalkylene (POA) of formula (I): R.sub.B(CH.sub.2O).sub.x(CH.sub.2CHR.sub.AO).sub.n(CH.sub.2O).sub.xR.sub.C, wherein at least one of R.sub.B and R.sub.C is a reactive group comprising at least one heteroatom selected from oxygen and nitrogen different from the hydroxyl group, the remaining, if any, being a [O].sub.zCH.sub.3 alkyl group, wherein z is 0 or 1, R.sub.A is a hydrogen atom or a C.sub.1-C.sub.5 alkyl group, x and x, equal to or different from each other, are independently 0 or 1, and n is an integer comprised between 2 and 1000, preferably between 5 and 200, C) optionally, in the presence of at least one catalyst, and D) optionally, in the presence of at least one organic solvent (S). The present invention also pertains to grafted fluoropolymers obtained from said process and to uses of said grafted fluoropolymers for manufacturing porous membranes.

Claims

1. A process for the manufacture of a grafted fluoropolymer [polymer (Fg)], said process comprising reacting: (A) at least one fluoropolymer comprising at least one functional group selected from the group consisting of a hydroxyl group and a carboxylic acid group [polymer (F)], and (B) at least one polyoxyalkylene (POA) of formula (I):
R.sub.B(CH.sub.2O).sub.x(CH.sub.2CHR.sub.AO).sub.n(CH.sub.2O).sub.xR.sub.C(I) wherein at least one of R.sub.B and R.sub.C is a reactive group comprising at least one heteroatom selected from oxygen and nitrogen wherein the reactive group is not a hydroxyl group, and wherein the remaining of R.sub.B and R.sub.C, if any, are selected from [O].sub.zCH.sub.3 alkyl groups, wherein z is 0 or 1, R.sub.A is a hydrogen atom or a C.sub.1-C.sub.5 alkyl group, x and x, equal to or different from each other, are independently 0 or 1, and n is an integer comprised between 2 and 1000, (C) optionally, in the presence of at least one catalyst, and (D) optionally, in the presence of at least one organic solvent (S).

2. The process according to claim 1, wherein polymer (F) comprises recurring units derived from at least one fluorinated monomer and from at least one hydrogenated monomer comprising at least one functional group selected from the group consisting of a hydroxyl group and a carboxylic acid group [monomer (H)].

3. The process according to claim 2, wherein monomer (H) is a (meth)acrylic monomer [monomer (MA)] of formula (II): ##STR00015## wherein: R.sub.1, R.sub.2 and R.sub.3, equal to or different from each other, are independently selected from a hydrogen atom and a C.sub.1-C.sub.3 hydrocarbon group, and R.sub.X is a hydrogen atom or a C.sub.1-C.sub.5 hydrocarbon group comprising at least one hydroxyl group.

4. The process according to claim 3, wherein monomer (H) is acrylic acid (AA) or hydroxyethyl acrylate (HEA).

5. The process according to claim 1, wherein polymer (F) is selected from the group consisting of: a fluoropolymer [polymer (F.sub.1)] comprising recurring units derived from vinylidene fluoride (VDF), from at least one monomer (MA) of formula (II) and, optionally, from one or more fluorinated monomers different from VDF, and a fluoropolymer [polymer (F.sub.2)] comprising recurring units derived from at least one hydrogenated monomer selected from ethylene, propylene and isobutylene, from a fluorinated monomer selected from tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE) and mixtures thereof, and from at least one monomer (MA) of formula (II): ##STR00016## wherein: R.sub.1, R.sub.2 and R.sub.3, equal to or different from each other, are independently selected from a hydrogen atom and a C.sub.1-C.sub.3 hydrocarbon group, and R.sub.X is a hydrogen atom or a C.sub.1-C.sub.5 hydrocarbon group comprising at least one hydroxyl group.

6. The process according to claim 1, wherein polymer (F) is a polymer (F.sub.1) comprising: (a) at least 60% by moles of vinylidene fluoride (VDF); (b) optionally, from 0.1% to 15% by moles of a fluorinated monomer selected from vinylfluoride (VF.sub.1), chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), perfluoromethylvinylether (PMVE) and mixtures therefrom; and (c) from 0.01% to 20% by moles of at least one monomer (MA) of formula (II): ##STR00017## wherein: R.sub.1, R.sub.2 and R.sub.3, equal to or different from each other, are independently selected from a hydrogen atom and a C.sub.1-C.sub.3 hydrocarbon group, and R.sub.x is a hydrogen atom or a C.sub.1-C.sub.5 hydrocarbon group comprising at least one hydroxyl group.

7. The process according to claim 6, wherein polymer (F) is a polymer (F.sub.1) comprising: (a) at least 85% by moles of vinylidene fluoride (VDF); (b) optionally, from 0.1% to 10% by moles of a fluorinated monomer selected from vinylfluoride (VF.sub.1), chlorotrifluoroethylene (CTFE), hexafluoropropene (HFP), tetrafluoroethylene (TFE), trifluoroethylene (TrFE), perfluoromethylvinylether (PMVE) and mixtures therefrom; and (c) from 0.1% to 10% by moles of at least one monomer (MA) of formula (II).

8. The process according to claim 1, wherein the polyoxyalkylene (POA) of formula (I) is selected from the group consisting of: a monofunctional POA of formula (I-A):
R.sub.B(CH.sub.2O).sub.x(CH.sub.2CHR.sub.AO).sub.n(CH.sub.2O).sub.xCH.sub.3(I-A) wherein R.sub.B is a reactive group comprising at least one heteroatom selected from oxygen and nitrogen wherein the reactive group is not a hydroxyl group, R.sub.A is a hydrogen atom or a C.sub.1-C.sub.5 alkyl group, x and x, equal to or different from each other, are independently 0 or 1, and n is an integer comprised between 2 and 1000, and a difunctional POA of formula (I-B):
R.sub.B(CH.sub.2O).sub.x(CH.sub.2CHR.sub.AO).sub.n(CH.sub.2O).sub.xR.sub.C(I-B) wherein both R.sub.B and R.sub.C are reactive groups comprising at least one heteroatom selected from oxygen and nitrogen wherein the reactive group is not a hydroxyl group, R.sub.A is a hydrogen atom or a C.sub.1-C.sub.5 alkyl group, x and x, equal to or different from each other, are independently 0 or 1, and n is an integer comprised between 2 and 1000.

9. The process according to claim 1, wherein the polyoxyalkylene (POA) of formula (I) is a polyoxyethylene (POE) complying with formula (I):
R.sub.B(CH.sub.2O).sub.x(CH.sub.2CH.sub.2O).sub.n(CH.sub.2O).sub.xR.sub.C(I) wherein at least one of R.sub.B and R.sub.C is a reactive group comprising at least one heteroatom selected from oxygen and nitrogen wherein the reactive group is not a hydroxyl group, and wherein the remaining of R.sub.B and R.sub.C, if any, are selected from [O].sub.zCH.sub.3 alkyl groups, wherein z is 0 or 1, x and x, equal to or different from each other, are independently 0 or 1, and n is an integer comprised between 2 and 1000.

10. The process according to claim 1, wherein at least one reactive group of the POA of formula (I) is selected from the group consisting of: a sulfonic ester group of formula [O].sub.zSO.sub.2R, wherein R is a C.sub.1-C.sub.8 fluorinated or hydrogenated group optionally comprising one or more aromatic rings and z is 0 or 1, a carboxylic acid group, an epoxide functional group, and a hydrocarbon group comprising at least one isocyanate functional group of formula: ##STR00018## wherein E is a divalent hydrocarbon group, linear or branched, optionally comprising one or more aromatic or cycloaliphatic groups and/or one or more functional groups and z is 0 or 1.

11. The process according to claim 1, wherein the equivalent ratio of the polyoxyalkylene (POA) of formula (I) to the polymer (F) is comprised between 1.0 and 10.0.

12. The process according to claim 11, wherein the equivalent ratio of the polyoxyalkylene (POA) of formula (I) to the polymer (F) is comprised between 1.0 and 2.0.

13. The process according to claim 1, said process being further carried out in the presence of at least one polyoxyalkylene (POA) of formula (III):
ZO(CH.sub.2CHR.sub.AO).sub.n(CH.sub.2O).sub.wH(III) wherein Z is a hydrogen atom or a C.sub.1-C.sub.5 alkyl group, R.sub.A is a hydrogen atom or a C.sub.1-C.sub.5 alkyl group, w is 0 or 1, and n is an integer comprised between 2 and 1000.

14. The process according to claim 1, wherein the process is carried out in liquid phase in the presence of one or more organic solvents (S).

15. The process according to claim 1, wherein the process is carried out in molten phase.

16. The process according to claim 1, wherein n is an integer comprised between 5 and 200.

17. A fluoropolymer composition [composition (F)] comprising at least one grafted fluoropolymer [polymer (Fg)], said polymer (Fg) comprising: at least one fluorinated backbone selected from the group consisting of: (A) a fluorinated backbone comprising recurring units derived from a fluoropolymer [polymer (F.sub.1)], said fluorinated backbone comprising recurring units derived from vinylidene fluoride (VDF), from at least one hydrogenated monomer comprising at least one functional group selected from the group consisting of a hydroxyl group and a carboxylic acid group [monomer (H)] and, optionally, from one or more fluorinated monomers different from VDF, said recurring units being randomly distributed along the fluorinated backbone, and (B) a fluorinated backbone comprising recurring units derived from a fluoropolymer [polymer (F.sub.2)], said fluorinated backbone comprising recurring units derived from at least one hydrogenated monomer selected from ethylene, propylene and isobutylene, from a fluorinated monomer selected from tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE) and mixtures thereof, and from at least one hydrogenated monomer comprising at least one functional group selected from the group consisting of a hydroxyl group and a carboxylic acid group [monomer (H)], said recurring units being randomly distributed along the fluorinated backbone, and at least one pendant side chain linked to one or two fluorinated backbones of the polymer (Fg) through one or two functional groups, said pendant side chain having formula:
[X].sub.y(CH.sub.2O).sub.x(CH.sub.2CHR.sub.AO).sub.n(CH.sub.2O).sub.x[X].sub.y wherein X and X, equal to or different from each other, are independently bridging groups comprising at least one heteroatom selected from oxygen and nitrogen, or one of X or X is a [O].sub.zCH.sub.3 group wherein z is 0 or 1, R.sub.A is a hydrogen atom or a C.sub.1-C.sub.5 alkyl group, x and x, equal to or different from each other, are independently 0 or 1, y and y, equal to or different from each other, are independently 0 or 1, and n is an integer comprised between 2 and 1000.

18. The fluoropolymer composition according to claim 17, wherein said fluoropolymer composition is obtained by reacting: (A) at least one fluoropolymer comprising at least one functional group selected from the group consisting of a hydroxyl group and a carboxylic acid group [polymer (F)], and (B) at least one polyoxyalkylene (POA) of formula (I):
R.sub.B(CH.sub.2O).sub.x(CH.sub.2CHR.sub.AO).sub.n(CH.sub.2O).sub.xR.sub.C(I) wherein at least one of R.sub.B and R.sub.C is a reactive group comprising at least one heteroatom selected from oxygen and nitrogen wherein the reactive group is not a hydroxyl group, and wherein the remaining of R.sub.B and R.sub.C, if any, are selected from [O].sub.zCH.sub.3 alkyl groups, wherein z is 0 or 1, R.sub.A is a hydrogen atom or a C.sub.1-C.sub.5 alkyl group, x and x, equal to or different from each other, are independently 0 or 1, and n is an integer comprised between 2 and 1000 (C) optionally, in the presence of at least one catalyst, and (D) optionally, in the presence of at least one organic solvent (S).

19. The fluoropolymer composition according to claim 17, wherein at least one pendant side chain of the polymer (Fg) is linked to one or two fluorinated backbones of the polymer (Fg) through one or two ester functional group, said pendant side chain having one of the following formulae:
CH.sub.2CH.sub.2OC(O)(CH.sub.2O)(CH.sub.2CH.sub.2O).sub.n(1)
CH.sub.2CH.sub.2O(CH.sub.2CH.sub.2O).sub.n(2)
CH.sub.2CH.sub.2O(CH.sub.2O)(CH.sub.2CH.sub.2O).sub.n(3)
CH.sub.2CH.sub.2OCH.sub.2CH(OH)(CH.sub.2O)(CH.sub.2CH.sub.2O).sub.n(4)
CH.sub.2CH(OH)(CH.sub.2O)(CH.sub.2CH.sub.2O).sub.n(5)
CH.sub.2CH.sub.2OOC(O)NH-E-NHC(O)O(CH.sub.2CH.sub.2O).sub.n(6) wherein n is an integer comprised between 2 and 1000 and E is a divalent hydrocarbon group, linear or branched, optionally comprising one or more aromatic or cycloaliphatic groups and/or one or more functional groups.

20. A process for the manufacture of a porous membrane, said process comprising: processing the fluoropolymer composition [composition (F)] according to claim 17 thereby providing a fluoropolymer film, and processing the fluoropolymer film thereby providing a porous membrane.

Description

EXAMPLE 1Manufacture of Grafted Fluoropolymer (1)

(1) 60 g of polymer (F-A) and 4 g of POE-1 were mixed in a roll mill for 30 minutes and then fed to Brabender 50 EHT mixer. The test conditions were the followings: temperature=240 C., mixing time=7 minutes, rotation speed=40 rpm.

EXAMPLE 2Manufacture of Grafted Fluoropolymer (2)

(2) The same procedure as detailed under Example 1 was followed but setting a temperature of 220 C. and a mixing time of 20 minutes.

(3) The weight amount of oxyethylene recurring units of formula CH.sub.2CH.sub.2O was 1.4% by weight, relative to the total weight of the grafted fluoropolymer.

EXAMPLE 3Manufacture of Grafted Fluoropolymer (3)

(4) 55 g of polymer (F-A) and 10 g of POE-2a were mixed in a roll mill for 30 minutes and then fed to Brabender 50 EHT mixer. The test conditions were the followings: temperature=230 C., mixing time=20 minutes, rotation speed=40 rpm.

EXAMPLE 4A)Manufacture of POE-4

(5) In a dried 3-necked round-bottom flask equipped with a reflux condenser, a dripping funnel, a thermometer and a magnetic stirrer, 5.00 g (2.5 meq) of POE-3a were dissolved in 40 ml of dichloromethane under inert atmosphere. The mixture was heated to 40 C. and a mixture of 0.38 g (3.75 meq) of Et.sub.3N, 2.27 g (7.5 meq) of C.sub.4F.sub.9SO.sub.2F in 10 ml of dichloromethane were dripped during 15 minutes and the reaction mixture was stirred at 1000 rpm and 60 C. for 5 hours.

(6) The crude reaction mixture was first washed 3 times with 1,1,2-trichlorotrifluoroethane and then stripped from its solvent and unreacted Et.sub.3N and C.sub.4F.sub.9SO.sub.2F. POE-4 was recovered as a solid with a yield of 85% by moles and a purity of 99% by moles, as measured by .sup.19 F-NMR and .sup.1H-NMR techniques.

EXAMPLE 4B)Manufacture of Grafted Fluoropolymer (4)

(7) 5 g of polymer (F-A) were dissolved in 30 ml of N-methyl-2-pyrrolidone (NMP) at 60 C. This homogeneous solution was first cooled to room temperature and then 14 equivalents of POE-4 and 14 equivalents of anhydrous Et.sub.3N were added. The reaction mixture was stirred for 10 hours at 60 C. The homogeneous reaction mixture so obtained was heated to 80 C. and stirred for 10 hours.

(8) A grafted fluoropolymer was isolated by precipitating it from NMP with 600 ml of distilled water and washed on a Buchner filtering funnel with an additional 600 ml of distilled water. The functional fluoropolymer was then dried in an oven at 60 C. and 10 mm Hg of residual pressure for 5 hours.

EXAMPLE 5A)Manufacture of POE-5

(9) In a dried 3-necked round-bottom flask equipped with a reflux condenser, a dripping funnel, a thermometer and a magnetic stirrer, 5.00 g (2.5 meq) of POE-3a were dissolved in 40 ml of anhydrous methylethylketone (MEK) under inert atmosphere. The mixture was heated to 50 C. and a catalytic amount (0.1% by moles vs. POE-3a) of Stannous t-butyl laurate catalyst was added thereto. 2.78 g (12.5 meq) of isophoron diisocyanate were dripped during 15 minutes and the reaction mixture was stirred at 1000 rpm and 60 C. for 2 hours.

(10) The crude reaction mixture was stripped from its solvent and washed 3 times with 1,1,2-trichlorotrifluoroethane. POE-5 was recovered as a fine white powder with a yield of 75% by moles and a purity of 96% by moles, as measured by .sup.1H-NMR.

EXAMPLE 5B)Manufacture of Grafted Fluoropolymer (5)

(11) 2.0 grams of polymer (F-A) were dissolved in 16 ml of MEK at 80 C. and placed in a previously dried 3-necked round-bottomed flask equipped with a reflux condenser, a dripping funnel, a thermometer and a magnetic stirrer. 1.20 g of POE-5 (0.49 mmol) and a catalytic amount (0.1% by moles vs. POE-5) of Stannous t-butyl laurate catalyst previously dissolved in 10 ml of MEK were dripped during 15 minutes. A clear homogeneous solution was obtained that was stirred at 75 C. and 800 rpm for 10 hours. The crude mixture was then washed with 500 ml of luke-warm (30 C.) distilled water in order to eliminate MEK and unreacted POE-5. The resulting polymer was dried in a heating oven at 50 C. and 0.02 residual mbar for 8 hours, thus obtaining 2.5 g of a filamentous white polymeric solid. Conversion was 100% by moles, based on FT-IR quantitative calculations on the residual NCO stretching band employing the CH.sub.2 and CH.sub.3 stretching bands as internal standard.

EXAMPLE 6Manufacture of Grafted Fluoropolymer (6)

(12) 60 g of polymer (F-B) and 4 g of POE-2b were mixed in a roll mill for 30 minutes and then fed to Brabender 50 EHT mixer. The test conditions were the followings: temperature=230 C., mixing time=20 minutes, rotation speed=40 rpm.

EXAMPLE 7Manufacture of Grafted Fluoropolymer (7)

(13) 60 g of polymer (F-B), 2 g of POE-1 and 6 g of POE-3b were mixed in a roll mill for 30 minutes and then fed to Brabender 50 EHT mixer. The test conditions were the followings: temperature=230 C., mixing time=20 minutes, rotation speed=40 rpm.

(14) The weight amount of oxyethylene recurring units of formula CH.sub.2CH.sub.2Owas 1.45% by weight, relative to the total weight of the grafted fluoropolymer.

COMPARATIVE EXAMPLE 1

(15) The same procedure as detailed under Example 3 was followed but using only 60 g of polymer (F-A) having a contact angle towards water of 90.

COMPARATIVE EXAMPLE 2

(16) 60 g of polymer (F-A) and 4 g of POE-1 were mixed in a roll mill for 30 minutes. The blend so obtained was not fed to the Brabender 50 EHT mixer.

COMPARATIVE EXAMPLE 3

(17) The same procedure as detailed under Example 3 was followed but using only 60 g of polymer (F-B) having a contact angle towards water of 90.

(18) Manufacture of Porous Membranes

(19) Flat-sheet membranes were prepared using the phase inversion method as follows: dope solutions were prepared dissolving the fluoropolymer compositions (18% by weight) in NMP (82% by weight) for one day at room temperature. Before membrane casting, the solutions were ultrasonicated for 30 minutes to eliminate bubbles. An appropriate amount of the dope was casted on a glass plate (gate opening=250 mm) and immediately immersed in a bath to induce phase separation. The coagulation bath consisted of deionized water for Examples 1 to 5 and Comparative Examples 1 and 2. The coagulation bath consisted of a 70:30 by weight mixture of deionized water and isopropanol for Examples 6 and 7 and Comparative Example 3. The coagulation bath was kept at 25 C. When the membranes were fully solidified, they were taken out and rinsed in deionized water several times in order to remove the remaining solvent.

(20) Washing Procedure

(21) In order to clean the fluoropolymer compositions from unreacted species (and residual traces of solvent which could disturb the analytical measurements) the following procedure was adopted: 1. Preparation of solution in NMP with a concentration of 10% by weight. 2. Casting of said solution (gate thickness=200 micron) and immediate immersion in pure water to induce phase separation. 3. Transferring and storing the flat sheet membranes in an another deionized water bath which was refreshed frequently for one night. 4. Cutting of D=47 mm items and fluxing on each of them a volume of 0.5 liters of pure water in a permeability holder. 5. Storing of these items for another night in a deionized water bath and successive drying in a vacuum oven at 35 C. for some hours.

(22) For the grafted fluoropolymers prepared according to Examples 1 to 7, this procedure (points 1 to 5) was repeated three times to assure a progressive removal of free polyoxyalkylenes in the polymer matrix. After each step the samples were analyzed by FT-IR and .sup.1H-NMR techniques.

(23) FT-IR spectroscopic analyses of washed films of the grafted fluoropolymers prepared according to Examples 1 to 7 showed ester bands at 1730-1740 cm.sup.1.

(24) The amount of oxyalkylene recurring units of formula CH.sub.2CHR.sub.AO in the grafted fluoropolymers prepared according to Examples 1 to 7 was determined by .sup.1H-NMR technique as detailed above. The weight amount of oxyalkylene recurring units of formula CH.sub.2CHR.sub.AO was measured relative to the total weight of the grafted fluoropolymer.

(25) As shown in Table 1 here below, the water permeability values of the membranes obtained from the grafted fluoropolymers prepared according to Examples 1, 3 and 6 are significantly higher than those of membranes obtained using polymers (F) as such or blends of these polymers (F) with polyoxyalkylenes such as polyoxyethylenes.

(26) Also, the contact angle value towards water of the grafted fluoropolymer prepared according to Example 4b) is significantly lower than that of polymer (F) as such.

(27) TABLE-US-00001 TABLE 1 Water POE permeability Contact angle Porosity Thickness [% wt.] [L/h m2] [] [%] [m] Ex. 1 1.1 428 82.7 147 Ex. 3 0.2 481 81.0 149 Ex. 4 5.8 69.9 Ex. 6 1.2 375 74.0 70 C. Ex. 1 239 90.0 80.4 152 C. Ex. 2 232 82.5 148 C. Ex. 3 72 75.9 87