Crosslinkable fluoropolymers

Abstract

The present invention pertains to a process for the manufacture of a crosslinkable fluoropolymer, to said crosslinkable fluoropolymer and the crosslinked fluoropolymer obtainable therefrom, to a film comprising said crosslinkable fluoropolymer or said crosslinked fluoropolymer and to uses of said crosslinked fluoropolymer film in various applications.

Claims

1. A crosslinkable fluoropolymer [polymer (FC)] comprising: first recurring units derived from vinylidene fluoride (VDF), and from 0.01% to 10% by moles, with respect to the total moles of recurring units of said polymer (FC), of second recurring units derived from at least one functional hydrogenated monomer (H.sub.F), said second recurring units comprising a pendant side chain comprising an end group (E) of any of formulae (III-A) to (V-A):
OC(O)C(R.sub.3)CR.sub.1R.sub.2(III-A)
OC(O)NHC(O)C(R.sub.3)CR.sub.1R.sub.2(IV-A)
OC(O)ZC(R.sub.3)CR.sub.1R.sub.2(V-A) wherein each of R.sub.1, R.sub.2 and R.sub.3, equal to or different from each other, is independently a hydrogen atom or a C.sub.1-C.sub.3 hydrocarbon group, and Z is a bonding group of any of formulae (j) and (jj):
NHXOC(O)(j), and
NHXNHC(O)OXOC(O)(jj) wherein X and X, equal to or different from each other, are independently hydrocarbon groups selected from the group consisting of C.sub.1-C.sub.20 aliphatic groups, C.sub.5-C.sub.40 cycloaliphatic groups and C.sub.6-C.sub.50 aromatic, alkylaromatic and heteroaromatic groups.

2. The crosslinkable fluoropolymer [polymer (FC)] according to claim 1, wherein the pendent side chain of at least one monomer (H.sub.F) is a pendant side chain of any of formulae (VI) to (X):
C(O)OYE(VI)
C(O)NHYE(VII)
[C(O)].sub.nOROYE(VIII)
[C(O)].sub.nOROC(O)NHYE(IX)
[C(O)].sub.nOROC(O)OYE(X) wherein Y is a C.sub.1-C.sub.10 hydrocarbon bonding group, optionally comprising at least one functional group, R is a C.sub.1-C.sub.5 hydrocarbon group, optionally comprising at least one hydroxyl group, n is 0 or 1, and E is an end group of any of formulae (III-A) to (V-A).

3. A process for the manufacture of the crosslinkable fluoropolymer [polymer (FC)] according to claim 1, said process comprising reacting: (A) at least one fluoropolymer [polymer (F)] comprising: first recurring units derived from vinylidene fluoride (VDF), and from 0.01% to 10% by moles, with respect to the total moles of recurring units of said polymer (F), of second recurring units derived from at least one functional hydrogenated monomer (H.sub.F), said second recurring units comprising a pendant side chain comprising an end group of any of formulae (I) and (II):
C(O)OR.sub.x(I)
OR.sub.x(II) wherein R.sub.x is a hydrogen atom or a C.sub.1-C.sub.5 hydrocarbon group comprising at least one hydroxyl group, and (B) at least one (meth)acrylic compound (MA) of any of formulae (III) to (V):
R.sub.1R.sub.2CC(R.sub.3)C(O)OT(III)
R.sub.1R.sub.2CC(R.sub.3)C(O)NHC(O)OT(IV)
R.sub.1R.sub.2CC(R.sub.3)ZC(O)OT(V) wherein each of R.sub.1, R.sub.2 and R.sub.3, equal to or different from each other, is independently a hydrogen atom or a C.sub.1-C.sub.3 hydrocarbon group, T is a C.sub.1-C.sub.10 hydrocarbon end group comprising at least one functional group, and Z is a bonding group of any of formulae (j) and (jj):
NHXOC(O)(j), and
NHXNHC(O)OXOC(O)(jj) wherein X and X, equal to or different from each other, are independently hydrocarbon groups selected from the group consisting of C.sub.1-C.sub.20 aliphatic groups, C.sub.5-C.sub.40 cycloaliphatic groups and C.sub.6-C.sub.50 aromatic, alkylaromatic and heteroaromatic groups.

4. The process according to claim 3, wherein monomer (H.sub.F) is selected from the group consisting of (meth)acrylic monomers of formula (I-A) and vinyl ether monomers of formula (II-A): ##STR00006## wherein each of R.sub.4, R.sub.5 and R.sub.6, equal to or different from each other, is independently a hydrogen atom or a C.sub.1-C.sub.3 hydrocarbon group, R.sub.X is a hydrogen atom or a C.sub.1-C.sub.5 hydrocarbon group comprising at least one hydroxyl group, and R.sub.x is a C.sub.1-C.sub.5 hydrocarbon group comprising at least one hydroxyl group.

5. The process according to claim 3, wherein T is a C.sub.1-C.sub.10 hydrocarbon end group comprising at least one functional group selected from the group consisting of hydroxyl groups, cyclic alkyl ether groups, isocyanate groups, carboxylic acid groups, amine groups, aryl ether groups and alkoxy silane groups.

6. The process according to claim 3, said process being carried out in a liquid medium comprising at least one organic solvent (S).

7. The process according to claim 3, wherein monomer (H.sub.F) comprises an end group of formula (I), wherein R.sub.x is a hydrogen atom, and compound (MA) has any of formulae (III) to (V), wherein T is a C.sub.1-C.sub.10 hydrocarbon end group comprising at least one functional group selected from the group consisting of hydroxyl groups, cyclic alkyl ether groups, and amine groups.

8. The process according to claim 7, wherein compound (MA) has any of formulae (III) to (V), wherein T is a C.sub.1-C.sub.10 hydrocarbon end group comprising at least one hydroxyl group, said process being carried out in the presence of at least one activating agent selected from the group consisting of N,N-dicyclohexylcarbodiimide, thionyl chloride, oxalyl dichloride and inorganic acids.

9. The process according to claim 3, wherein monomer (H.sub.F) comprises an end group of any of formulae (I) and (II), wherein R.sub.x is a C.sub.1-C.sub.5 hydrocarbon group comprising at least one hydroxyl group, and compound (MA) has any of formulae (III) to (V), wherein T is a C.sub.1-C.sub.10 hydrocarbon end group comprising at least one functional group selected from the group consisting of hydroxyl groups, cyclic alkyl ether groups, isocyanate groups and carboxylic acid groups.

10. The process according to claim 9, wherein compound (MA) has any of formulae (III) to (V), wherein T is a C.sub.1-C.sub.10 hydrocarbon end group comprising at least one isocyanate group, said process being carried out in the presence of at least one activating agent selected from the group consisting of organic tin compounds.

11. A crosslinkable composition (CC) comprising: at least one crosslinkable fluoropolymer [polymer (FC)] according to claim 1, and at least one additive selected from the group consisting of crosslinking co-agents and crosslinking initiators.

12. A crosslinkable fluoropolymer film [film (FC)] comprising at least one crosslinkable fluoropolymer [polymer (FC)] according to claim 1.

13. The crosslinkable fluoropolymer film [film (FC)] according to claim 12, said film (FC) being free from any organic solvent (S).

14. The crosslinkable fluoropolymer film [film (FC)] according to claim 12, said film (FC) further comprising at least one organic solvent (S).

15. The film (FC) according to claim 14, wherein the solvent (S) is selected from the group consisting of diesters of formula (DE-I) and ester-amides of formula (EA-I):
R.sub.AOOCZ.sub.deCOOR.sub.B(DE-I)
R.sub.AOOCZ.sub.eaCONR.sub.CR.sub.D(EA-I) wherein: R.sub.A and R.sub.B, equal to or different from each other, are independently selected from the group consisting of C.sub.1-C.sub.20 hydrocarbon groups, R.sub.C and R.sub.D, equal to or different from each other, are independently selected from the group consisting of hydrogen, C.sub.1-C.sub.36 hydrocarbon groups, optionally substituted, wherein R.sub.C and R.sub.D are optionally part of a cyclic moiety including the nitrogen atom to which they are bound, said cyclic moiety being optionally substituted and/or optionally comprising one or more than one additional heteroatom, and mixtures thereof, and Z.sub.de and Z.sub.ea, equal to or different from each other, are independently a linear or branched C.sub.3-C.sub.10 divalent alkylene group.

16. The crosslinkable fluoropolymer film [film (FC)] according to claim 14, said film (FC) further comprising at least one electrolytic salt.

17. A process for the manufacture of a crosslinked fluoropolymer film [film (FCC)], said process comprising crosslinking, either by UV treatment under UV radiation or by thermal treatment, the crosslinkable fluoropolymer film [film (FC)] according to claim 12.

18. A crosslinked fluoropolymer film [film (FCC)] obtainable by the process according to claim 17, said film (FCC) comprising at least one crosslinked fluoropolymer [polymer (FCC)].

19. A solar cell module comprising the crosslinked fluoropolymer film [film (FCC)] according to claim 18.

20. An electrochemical device comprising a polymer electrolyte which comprises the crosslinked fluoropolymer film [film (FCC)] obtainable by the process according to claim 17, said process comprising crosslinking, either by UV treatment under UV radiation or by thermal treatment, a crosslinkable fluoropolymer film [film (FC)] that further comprises at least one electrolytic salt.

Description

EXAMPLE 1

Manufacture of a Crosslinkable Fluoropolymer [Polymer (FC-1)]

(1) The polymer (F-1) (25 g) having EW of 9280 g/eq (2.7 meq. CH.sub.2CH.sub.2OH; 10.8 acrylate chains/100000 g/mole) was dissolved in 350 ml of methyl ethyl ketone at 85 C. and placed in a previously flame-dried 3-necked round-bottomed flask equipped with a reflux condenser, a dripping funnel, a thermometer and a mechanical stirrer. The solution was heated to 75 C. and then 2-isocyanatoethyl methacrylate (420 mg, 2.7 mmol free NCO) and a catalytic amount (0.1 mol % vs. free NCO) of di-tert-butyl tin bislaurate (previously dissolved in 10 ml methyl ethyl ketone) were dripped thereto in 1 minute. A clear homogeneous solution was obtained which was stirred at 75 C. and 800 rpm for 15 hours. The progress of the reaction was monitored by FT-IR quantitatively measuring the residual NCO groups. Once the conversion was completed, the crude mixture was poured in 1 lt. of distilled H.sub.2O. The polymer precipitated as a white solid. The polymer so obtained was then washed with an additional 2 lt. of distilled H.sub.2O on a Bchner funnel. The polymer was finally dried in a heating oven at 60 C. and 20 mm Hg residual pressure for 5 hours thereby providing 24.1 g of a powdery, white solid.

(2) Conversion (of starting acrylate co-monomer): 96.6% by moles based on FT-IR measurements.

(3) Active sites: 10.4 acrylate sites/100000 g/mol of polymer (FC-1).

(4) EW: 9430 g/eq.

(5) Urethane-acrylate modification: 2.78% w/w

(6) Isolated yield: 95%.

EXAMPLE 2

Manufacture of a Crosslinkable Fluoropolymer [Polymer (FC-2)]

(7) The polymer (F-2) (2.0 g) having EW of 9259 g/eq (0.216 meq COOH; 8 acrylate chains/100000 g/mole) was dissolved in 20 ml of ethyl acetate in a 250 ml 4-necked glass reaction flask equipped with a magnetic stirrer, a condenser, a thermometer and a dripping funnel. The reactor was placed in an inert atmosphere (N.sub.2) with vigorous stirring and heated to 55 C. until the polymer (F-2) was completely dissolved. The reactor was then cooled to 20 C. and a mixture of thionyl chloride (0.256 g, 2.16 mmols) and pyridine (17 l, 0.216 mmols) in ethyl acetate (5 ml) was dripped thereto in 10 minutes. The mixture was then heated to 75 C. with vigorous stirring for 3 hours under an inert atmosphere (N.sub.2), following the conversion of PVDF's carboxylic groups to acyl chloride groups by measuring the volume of HCl gas evolved employing a micro-gas collector. Once the conversion was completed, the crude mixture so obtained was filtered under pressure on a 0.2 m PFPE membrane so as to remove side-products and then evaporated in a rotary evaporator at 70 C. and 100 mm Hg residual pressure. The evaporated solid was dissolved in 15 ml of ethyl acetate and heated to 75 C. with vigorous stirring for 3 hours under an inert atmosphere (N.sub.2). A mixture of hydroxy propyl acrylate isomers (0.28 g, 2.16 mmol) dissolved in 2 ml of ethyl acetate was dripped thereto in about 5 minutes. Once HCl evolution stopped, the crude mixture was stirred at 75 C. for additional 5 hours. The crude polymer mixture was then evaporated at 70 C. and 18 mm Hg of residual pressure. The solid polymer obtained was finally washed with ethyl acetate and CH.sub.2Cl.sub.2 and dried in a vacuum oven at 65 C. for 4 hours thereby providing 1.66 g of a pale-yellow, powdery polymer.

(8) Conversion (of starting acrylic co-monomer): 60% by moles.

(9) Isolated yield: 83%

(10) EW: 9401 g/eq.

(11) Active sites: 6.5 acrylate sites/100000 g/mol

(12) Urethane-acrylate modification: 1.67% w/w

COMPARATIVE EXAMPLE 1

(13) The polymer (F-1) (0.5 g) was dissolved in 20 ml of ethyl acetate at 20 C. The mixture was placed in a Petri dish to which 50 ml of a 10% v/v solution of methylene-4-4biscyclohexylisocyanate (0.02 mmol, 0.04 meq NCO) and 10 ml of a 2% solution of di-tert-butyl tin bislaurate as catalyst were added. The mixture so obtained was heated in an oven at 55 C. for 3 hours at atmospheric pressure. Following the thermal reaction, the solvent was evaporated and a film made from a crosslinked polymer with covalent urethane bonds was recovered from the Petri dish by adding 10 ml of distilled H.sub.2O. The wet film was dried in a vacuum oven at 50 C. and 10 mm Hg residual pressure. The film thereby provided was not soluble in ethyl acetate and other solvents such as acetone in which the polymers (F-1) was soluble, thus confirming that the polymer forming the film is suitably crosslinked.

(14) Manufacture of Films and Crosslinking Thereof Using Polymers (FC-1) and (FC-2) of Examples 1 and 2

(15) Specimens of any of the polymers obtained according to Examples 1 and 2 were dissolved in a mixture containing triethyl phosphate, propylene glycol monomethyl ether acetate and cyclopentanone so as to provide, after 3 hours of stirring at a temperature of 40 C., solutions having a concentration of 10% by weight.

(16) (A) Spin Coating

(17) The solutions so obtained were loaded into a Laurell WS-650 LITE SERIES spin coater and spin-coated at a speed of 2000 rpm onto silicon wafer substrates in order to obtain very thin polymeric layers on silicon wafer as substrate. The polymer layers so obtained were dried at 85 C. for 20 minutes. For each example, two polymeric films on silicon wafer were prepared.

(18) The samples thereby obtained were all homogeneous. The thickness of the samples has been measured using a Filmetrics F20 unit.

(19) (B) Crosslinking

(20) The polymer films so obtained were submitted to crosslinking either by UV treatment or by thermal treatment.

(21) Thermal treatment consisted in maintaining samples of films so obtained in a ventilated oven at a temperature of about 125 C. for 20 minutes.

(22) For UV treatment, samples of films obtained according to procedure (A) but using a composition comprising any of the polymers obtained according to Examples 1 and 2 and at least one additive selected from the group consisting of crosslinking initiators were passed through a semi-automatic crosslinker device based on a UV lamp and equipped with a moving belt carrying the samples for 30 seconds equivalent to 3 steps of 10 seconds each.

(23) The crosslinking initiator was selected from the group consisting of photoinitiators (PI).

(24) (C) Chemical Resistance Test

(25) In order to verify if the samples were crosslinked, pure acetone was poured on the films after crosslinking treatment: insolubility in such conditions was considered to be a clear evidence of suitable crosslinking.

(26) Results are summarized in Table 1 here below.

(27) TABLE-US-00001 TABLE 1 Solubility in acetone Thermal Film before treatment UV treatment treatment Ex. 1 soluble insoluble insoluble Ex. 1 + PI soluble insoluble insoluble Ex. 2 soluble insoluble insoluble Ex. 2 + PI soluble insoluble insoluble Polymer (F-1) soluble soluble soluble Polymer (F-2) soluble soluble soluble

(28) Results in Table 1 here above well demonstrate that polymers (FC) according to the invention such as those obtained according to Examples 1 and 2 are effective in crosslinking either by UV treatment or by thermal treatment to the same extent as the crosslinked polymer obtained according to Comparative Example 1. On the contrary, VDF-HEA and VDF-AA polymers, said polymers being free from (meth)acrylic end groups, do not undergo crosslinking.