Ferroelectric fluoropolymer

Abstract

The present invention pertains to a ferroelectric fluoropolymer, to a process for manufacturing said fluoropolymer and to uses of said fluoropolymer in electric and/or electronic applications.

Claims

1. A fluoropolymer [polymer (F)] comprising: recurring units derived from vinylidene fluoride, recurring units derived from trifluoroethylene, and recurring units derived from 1,2-dichloro-1,2-difluoroethylene.

2. The polymer (F) according to claim 1, wherein the recurring units derived from 1,2-dichloro-1,2-difluoroethylene are recurring units derived from cis-1,2-dichloro-1,2-difluoroethylene or trans-1,2-dichloro-1,2-difluoroethylene.

3. The polymer (F) according to claim 1, said polymer (F) comprising from 15% to 30% by moles of recurring units derived from trifluoroethylene, with respect to the total moles of recurring units in said polymer (F).

4. The polymer (F) according to claim 1, said polymer (F) comprising from 0.1% to 10% by moles of recurring units derived from 1,2-dichloro-1,2-difluoroethylene, with respect to the total moles of recurring units in said polymer (F).

5. The polymer (F) according to claim 1, said polymer (F) further comprising recurring units derived from at least one fluorinated monomer selected from chlorotrifluoroethylene and 1,1-chlorofluoroethylene.

6. A process for manufacturing the polymer (F) according to claim 1, said process comprising polymerizing vinylidene fluoride, trifluoroethylene and 1,2-dichloro-1,2-difluoroethylene in the presence of at least one radical initiator.

7. The process according to claim 6, said process being carried out in the presence of an aqueous medium.

8. The process according to claim 6, said process being carried out by aqueous emulsion polymerization or by aqueous suspension polymerization.

9. The process according to claim 6, said process being carried out by aqueous emulsion polymerization in an aqueous medium comprising: at least one surfactant (S), at least one radical initiator, optionally, at least one non-functional perfluoropolyether (PFPE) oil, and optionally, at least one chain transfer agent.

10. The process according to claim 6, wherein the surfactant (F) is a cyclic fluorocompound of formula (II): ##STR00008## wherein X.sub.1, X.sub.2 and X.sub.3, equal to or different from each other, are independently selected from the group consisting of H, F and C.sub.1-C.sub.6 (per)fluoroalkyl groups, optionally comprising one or more catenary or non-catenary oxygen atoms, L is a bond or a divalent group, R.sub.F is a divalent fluorinated C.sub.1-C.sub.3 bridging group, and Y is an anionic functionality.

11. A composition (C) comprising at least one polymer (F) according to claim 1.

12. The composition (C) according to claim 11, said composition (C) further comprising one or more additives.

13. A fluoropolymer film (F) comprising the composition (C) according to claim 11.

14. A process for manufacturing the film (F) according to claim 13, said process comprising processing the composition (C) into a film.

15. An electric and/or electronic device comprising the polymer (F) according to claim 1.

16. The polymer (F) according to claim 2, wherein the recurring units derived from 1,2-dichloro-1,2-difluoroethylene are recurring units derived from trans-1,2-dichloro-1,2-difluoroethylene.

17. The polymer (F) according to claim 3, said polymer (F) comprising from 19% to 28% by moles of recurring units derived from trifluoroethylene, with respect to the total moles of recurring units in said polymer (F).

18. The polymer (F) according to claim 4, said polymer (F) comprising from 0.5% to 8.5% by moles of recurring units derived from 1,2-dichloro-1,2-difluoroethylene, with respect to the total moles of recurring units in said polymer (F).

19. The polymer (F) according to claim 18, said polymer (F) comprising from 1% to 6% by moles of recurring units derived from 1,2-dichloro-1,2-difluoroethylene, with respect to the total moles of recurring units in said polymer (F).

20. The polymer (F) according to claim 19, said polymer (F) comprising from 1% to 5% by moles of recurring units derived from 1,2-dichloro-1,2-difluoroethylene, with respect to the total moles of recurring units in said polymer (F).

Description

(1) Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

(2) The invention will be now described in more detail with reference to the following examples whose purpose is merely illustrative and not limitative of the scope of the invention.

(3) Raw Materials

(4) Polymer (F-a): VDF (69.9% by moles)-TrFE (27.9% by moles)-1112 (2.2% by moles).

(5) Polymer (F-b): VDF (68.2% by moles)-TrFE (26.4% by moles)-1112 (5.4% by moles).

(6) Polymer (F-c): VDF (66.2% by moles)-TrFE (25.6% by moles)-1112 (8.2% by moles).

(7) Polymer (F-d): VDF (67.1% by moles)-TrFE (24.2% by moles)-CTFE (7.1% by moles)-1112 (1.6% by moles).

(8) Polymer (a): VDF (76.1% by moles)-TrFE (23.9% by moles).

(9) Polymer (b): VDF (57.5% by moles)-TrFE (34.8% by moles)-CTFE (7.7% by moles).

(10) Manufacture of the Polymer (F-a)

(11) In an AISI 316 steel horizontal autoclave, equipped with baffles and a stirrer working at 90 rpm, 14.2 liter of demineralized water were introduced. The temperature was then brought to reaction temperature of 70° C. When this temperature was reached, 335 g of a 35% w/w aqueous solution of cyclic surfactant of formula (VI) as defined above, with X.sub.a═NH.sub.4, 7 bar of vinylidene fluoride and 4 ml of trans-1,2-dichloro-1,2-difluoroethylene were introduced.

(12) A gaseous mixture of VDF-TrFE in the molar ratio of 70/30 was subsequently added via a compressor until reaching a pressure of 30 bar. By a metering pump, 200 ml of a 3% by weight aqueous solution of sodium persulfate (NaPS) was fed. The polymerization pressure was maintained constant by feeding the above mentioned monomeric mixture; 2 ml of trans-1,2-dichloro-1,2-difluoroethylene were fed every 28 g of synthesized polymer to a total amount of 42 ml. When 560 g of the mixture were fed, the pressure was let fall down up to 15 bar and the reactor was cooled to room temperature. The latex was discharged, frozen for 48 hours and, once unfrozen, the coagulated polymer was washed with demineralized water and dried at 80° C. for 48 hours.

(13) The properties of the polymer (F-a) are set forth in Table 1.

(14) Manufacture of the Polymer (F-b)

(15) The same conditions under the general procedure for the manufacture of the polymer (F-a) were followed but introducing the following modifications: using 150 ml of a 3% by weight aqueous solution of sodium persulfate (NaPS), feeding 6 ml of trans-1,2-dichloro-1,2-difluoroethylene before pressurizing the reactor with the monomeric mixture, and feeding 6 ml of trans-1,2-dichloro-1,2-difluoroethylene every 56 g of synthesized polymer to a total amount of 60 ml.

(16) The properties of the polymer (F-b) are set forth in Table 1.

(17) Manufacture of the Polymer (F-c)

(18) The same conditions under the general procedure for the manufacture of the polymer (F-a) were followed but introducing the following modifications: using 160 ml of a 3% by weight aqueous solution of sodium persulfate (NaPS), feeding 8 ml of trans-1,2-dichloro-1,2-difluoroethylene before pressurizing the reactor with the monomeric mixture, feeding 8 ml of trans-1,2-dichloro-1,2-difluoroethylene every 52 g of synthesized polymer to a total amount of 80 ml, and feeding 20 g of ethyl acetate as chain transfer agent.

(19) The properties of the polymer (F-c) are set forth in Table 1.

(20) Manufacture of the Polymer (F-d)

(21) The same conditions under the general procedure for the manufacture of the polymer (F-a) were followed but introducing the following modifications, at a reaction temperature of 80° C.: feeding a gaseous mixture of VDF-TrFE-CTFE in molar ratio of 63/28/9, feeding 5 bar of VDF, feeding 0.5 bar of CTFE, using 60 ml of a 3% by weight aqueous solution of sodium persulfate (NaPS), feeding a total amount of 5 ml of trans-1,2-dichloro-1,2-difluoroethylene before pressurizing the reactor with the monomeric mixture, and feeding 20 g of ethyl acetate as chain transfer agent.

(22) The properties of the polymer (F-d) are set forth in Table 1.

(23) Manufacture of the Polymer (a)

(24) The same conditions under the general procedure for the manufacture of the polymer (F-a) were followed but introducing the following modifications, without adding trans-1,2-dichloro-1,2-difluoroethylene: feeding a gaseous mixture of VDF-TrFE in a molar ratio of 75/25, using 180 ml of a 3% by weight aqueous solution of sodium persulfate (NaPS), and using 50 g of ethyl acetate as chain transfer agent.

(25) The properties of the polymer (a) are set forth in Table 1.

(26) Manufacture of the Polymer (b)

(27) The same conditions under the general procedure for the manufacture of the polymer (F-a) were followed but introducing the following modifications, without adding trans-1,2-dichloro-1,2-difluoroethylene: feeding a gaseous mixture of VDF-TrFE-CTFE in a molar ratio of 63/28/9, feeding 5 bar of VDF, feeding 0.5 bar of CTFE, using 180 ml of a 3% by weight aqueous solution of sodium persulfate (NaPS), and using 20 grams of ethyl acetate as chain transfer agent.

(28) The properties of the polymer (b) are set forth in Table 1.

(29) General Procedure for the Manufacture of a Fluoropolymer Film

(30) A solution of the polymer in methylethylketone having a concentration of 20% w/w was prepared and a film was casted therefrom by doctor blade technique, using an Elcometer automatic film applicator, model 4380, onto a glass substrate.

(31) The polymer layer so casted was dried at 70° C. for 2 hours under vacuum. On the so obtained dried film, 12 patterns of 1 cm×1 cm were printed by inkjet printing technique as electrodes on both sides of the films using as conductive material a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) purchased by Agfa-Gevaert under the trademark name ORGACON®.

(32) The thickness of the sample was measured using a Mitutoyo micrometer.

(33) Annealing of the Fluoropolymer Film

(34) The annealing temperature was selected for each fluoropolymer film according to the melting temperature of each fluoropolymer: T.sub.annealing=T.sub.melting−5° C.

(35) Annealing was performed leaving the fluoropolymer film for one hour at a constant temperature (T.sub.annealing) in a conventional oven, following by slow cooling until room temperature. Slow cooling was performed switching-off the oven and leaving the whole system to reach room temperature.

(36) Poling of the Fluoropolymer Film

(37) A LC Precision poling equipment equipped with a High Voltage Interface with 10 KV maximum field generated by RADIANT was used for poling of the fluoropolymer film. The annealed film was placed in the polarization cell where a variable field from 80 V/μm to 250 V/μm was applied trough the sample.

(38) Determination of the Dielectric Constant of the Fluoropolymer Film

(39) The value of dielectric permittivity [k] was derived from the direct measurement of dielectric capacitance by a piezo meter system provided by Piezotest. The capacitance values were all measured at 110 Hz. The measurements were also used to check the electrical homogeneity and electrical conductivity of the electrodes.

(40) $\mathrm{Dielectric}\mathrm{permittivity}\left[k\right]=\frac{\mathrm{Capacitance}\left[F\right]\times \mathrm{Thickness}\left[m\right]}{{\mathrm{.Math.}}_0\left[F/m\right]\times \mathrm{Area}\left[m^2\right]}$
Determination of the Piezoelectric Coefficient of the Fluoropolymer Film

(41) The value of the piezoelectric coefficient (d33) was measured using a PiezoMeter PM 300 system (PiezoTest Inc.) by placing the poled sample in the instrument strain gouge where the film is stimulated under a vibration at 110 Hz at room temperature. The d33 value is reported as μC/N.

(42) The results are shown in Table 1 here below:

(43) TABLE-US-00001 TABLE 1 Dielectric Piezoelectric permittivity coefficient [k] [μC/N] T.sub.Curie T.sub.melting before after before after Polymer [° C.] [° C.] annealing annealing annealing annealing (F-a) 67.4 122.4 18.5 20.5 21.0 25.0 (F-b) 52.7 116.0 16.0 18.0 20.0 17.3 (F-c) 30.3 105.2 18.5 20.3 7.4 6.5 (F-d) 21.6 118.8 53.0 59.0 0 0 (a) 119.8 147.0 9.0 9.0 2.0 27.0 (b) 33.4 122.6 29.0 24.0 0 1.4

(44) As shown in Table 1, the polymer (F) of the present invention as notably embodied by any of the polymers (F-a), (F-b), (F-c) and (F-d) according to the invention has advantageously a Curie temperature (T.sub.Curie) below which its retains its ferroelectric properties.

(45) Also, as shown in Table 1, the polymer (F) of the present invention as notably embodied by any of the polymers (F-a), (F-b) and (F-c) according to the invention is endowed with a higher dielectric constant as compared to the polymer (a) either before annealing or after annealing.

(46) In particular, the polymer (F-d) according to the invention is endowed with a higher dielectric constant as compared to the polymer (b) either before annealing or after annealing.

(47) Further, as shown in Table 1, the polymer (F) of the present invention as notably embodied by any of the polymers (F-a), (F-b) and (F-c) according to the invention is endowed with a higher piezoelectric coefficient as compared to any of the polymer (a) and the polymer (b) even before annealing.

(48) In view of the above, it has been found that the polymer (F) of the present invention or any films thereof is particularly suitable for use in electric and/or electronic devices.