Controlled free-radical copolymerization of trifluoroethylene

Abstract

The invention concerns a method for preparing block copolymers, comprising a step of controlled free-radical copolymerisation of trifluoroethylene with at least one additional monomer, different from trifluoroethylene, in the presence of a chain transfer agent, said chain transfer agent being a xanthate compound, a trithiocarbonate compound or a monoiodide compound. The invention also concerns the block copolymers likely to be obtained by this method.

Claims

1. A thermoplastic block copolymer, comprising: a poly(vinylidene fluoride) homopolymer block and a copolymer block comprising vinylidene fluoride and trifluoroethylene units and optionally additional units; or a copolymer block comprising vinylidene fluoride and trifluoroethylene units and a copolymer block comprising vinylidene fluoride and trifluoroethylene units and additional units, said thermoplastic block copolymer having a xanthate or trithiocarbonate or monoiodinated end group.

2. A thermoplastic block copolymer according to claim 1 having trifluoroethylene and vinylidene fluoride units and additional units, and having a xanthate or trithiocarbonate or monoiodinated end group.

3. The copolymer as claimed in claim 2, in which the xanthate or trithiocarbonate end group is an SC(S)Z group, Z representing an OR.sub.2 group in which R.sub.2 represents an alkyl or aryl group comprising from 1 to 10 carbon atoms or Z representing an SR.sub.3 group in which R.sub.3 represents an aliphatic group comprising from 1 to 20 carbon atoms.

4. The copolymer as claimed in claim 3, in which the xanthate or trithiocarbonate end group is an SC(S)OC.sub.2H.sub.5 or SC(S)SC.sub.12H.sub.25 group.

5. A process for preparing a copolymer (c), comprising reacting a copolymer (a) as claimed in claim 2 with at least one comonomer (b).

6. The process as claimed in claim 5, in which the comonomer (b) is a fluorinated monomers or a combination thereof.

7. The process according to claim 6, wherein the comonomer (b) is 2,3,3,3-tetrafluoropropene, vinyl fluoride, 2-chloro-1,1-difluoroethylene, 2-bromo-1,1-difluoroethylene, hexafluoropropene, 3,3,3-trifluoropropene, 3,3,3-trifluoro-2-chloropropene, 1,1,1,3-tetrafluoropropene, 3,3,3-trifluoro-2-bromopropene, 1H-pentafluoropropene, 2H-pentafluoropropene, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, -trifluoromethacrylic acid and its derivatives; vinyl acetate, N-vinylpyrrolidone, methacrylates, acrylates, acrylamide, N-vinylcarbazole, acrylonitrile, allyl alcohol, allyl acetate, allyl halide or allyl glycidyl ether units; or are combinations thereof.

8. The process as claimed in claim 5, comprising preparing the copolymer (a) by controlled free-radical copolymerization, comprising copolymerization of a trifluoroethylene monomer with at least one additional monomer, different than trifluoroethylene, in the presence of an initiator and of a chain transfer agent, said chain transfer agent being a xanthate compound, a trithiocarbonate compound or a monoiodinated compound, in which the copolymer prepared is a block copolymer and in which the molar ratio of the amount of chain transfer agent to the amount of monomers is from 0.001 to 0.020, and the initial molar ratio of the amount of the TrFE monomer to the amount of the comonomers is from 10% to 90%, preferably from 20% to 50%.

9. A film or membrane comprising at least one copolymer as claimed in claim 2.

10. A piezoelectric device comprising a film as claimed in claim 9.

11. A ferroelectric device comprising a film as claimed in claim 9.

12. A pyroelectric device comprising a film as claimed in claim 9.

13. A coating comprising a film as claimed in claim 9.

14. The copolymer as claimed in claim 1, in which the additional units are fluorinated units or combinations thereof.

15. The block copolymer as claimed in claim 14, in which: the additional units are 2,3,3,3-tetrafluoropropene, vinyl fluoride, 2-chloro-1,1-difluoroethylene, 2-bromo-1,1-difluoroethylene, hexafluoropropene, 3,3,3-trifluoropropene, 3,3,3-trifluoro-2-chloropropene, 1,1,1,3-tetrafluoropropene, 3,3,3-trifluoro-2-bromopropene, 1H-pentafluoropropene, 2H-pentafluoropropene, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, -trifluoromethacrylic acid and its derivatives; vinyl acetate, N-vinylpyrrolidone, methacrylates, acrylates, acrylamide, N-vinylcarbazole, acrylonitrile, allyl alcohol, allyl acetate, allyl halide or allyl glycidyl ether units; or are combinations thereof.

16. The block copolymer as claimed in claim 1, comprising: a poly(vinylidene fluoride) homopolymer block and a copolymer block comprising vinylidene fluoride, trifluoroethylene and 2,3,3,3-tetrafluoropropene units; or a copolymer block comprising vinylidene fluoride and trifluoroethylene units and a copolymer block comprising vinylidene fluoride, trifluoroethylene and 2,3,3,3-tetrafluoropropene units; or a poly(vinylidene fluoride) homopolymer block and a copolymer block consisting of vinylidene fluoride and trifluoroethylene units.

17. The process for preparing a copolymer according to claim 1 by controlled free-radical copolymerization, comprising copolymerization of a trifluoroethylene monomer with at least one additional monomer, different than trifluoroethylene, in the presence of an initiator and of a chain transfer agent, said chain transfer agent being a xanthate compound, a trithiocarbonate compound or a monoiodinated compound, in which the copolymer prepared is a block copolymer and the monomers present during the copolymerization step comprise vinylidene fluoride, trifluoroethylene, and at least one additional monomer, and in which the molar ratio of the amount of chain transfer agent to the amount of monomers is from 0.001 to 0.020, and the initial molar ratio of the amount of the TrFE monomer to the amount of the comonomers is from 10% to 90%.

18. The process as claimed in claim 1, in which the additional monomers are 2,3,3,3-tetrafluoropropene, vinyl fluoride, 2-chloro-1,1-difluoroethylene, 2-bromo-1,1-difluoroethylene, hexafluoropropene, 3,3,3-trifluoropropene, 3,3,3-trifluoro-2-chloropropene, 1,1,1,3 tetrafluoropropene, 3,3,3-trifluoro-2-bromopropene, 1H-pentafluoropropene, 2H-pentafluoropropene, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, -trifluoromethacrylic acid or its derivatives; vinyl acetate, N-vinylpyrrolidone, methacrylates, acrylates, acrylamide, N-vinylcarbazole, acrylonitrile, allyl alcohols, allyl acetate, allyl halides, allyl glycidyl ether; or are combinations thereof.

19. The process as claimed in claim 1, in which the chain transfer agent is a xanthate or trithiocarbonate compound which is a compound of formula R.sub.1SC(S)Z, in which R.sub.1 represents an aliphatic group comprising from 1 to 20 carbon atoms, Z represents an OR.sub.2 group in which R.sub.2 represents an alkyl or aryl group comprising from 1 to 10 carbon atoms or Z represents an SR.sub.3 group in which R.sub.3 represents an aliphatic group comprising from 1 to 20 carbon atoms.

20. The process as claimed in claim 19, in which the xanthate or trithiocarbonate compound is O-ethyl-S-(1-methyloxycarbonyl)ethyl xanthate.

21. The process as claimed in claim 1, in which the chain transfer agent is a monoiodinated compound which is a 1-iodofluoroalkane.

22. The process according to claim 21, wherein the monoiodinated compound is a compound of formula R.sub.F(CH.sub.2CF.sub.2).sub.NI, in which n is an integer ranging from 1 to 500, and R.sub.F represents a perfluorocarbon group.

23. The process according to claim 22, wherein R.sub.F is CF.sub.3, C.sub.2F.sub.5, C.sub.3F.sub.7 or C.sub.mF.sub.2m+1, m being an even integer ranging from 4 to 20.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 represents a .sup.1H NMR spectrum in deuterated acetone of a PVDF-b-poly(VDF-ter-TrFE-ter-1234yf) block copolymer (see example 1).

(2) FIG. 2 represents a .sup.19F NMR spectrum in deuterated acetone of the same block copolymer.

(3) FIG. 3 represents a .sup.1H NMR spectrum in deuterated acetone of a poly(VDF-co-TrFE) copolymer (see example 2) with a xanthate end group.

(4) FIG. 4 represents a .sup.19F NMR spectrum in deuterated acetone of the same copolymer.

(5) FIG. 5 represents a .sup.1H NMR spectrum in deuterated acetone of a poly(VDF-co-TrFE)-b-poly(VDF-ter-TrFE-ter-1234yf) block copolymer with a xanthate end group (see example 3).

(6) FIG. 6 represents a .sup.19F NMR spectrum in deuterated acetone of the same block copolymer.

(7) FIG. 7 represents a .sup.1H NMR spectrum in deuterated acetone of a poly(VDF-co-TrFE)-b-PVDF block copolymer with a xanthate end group (see example 4).

(8) FIG. 8 represents a .sup.19F NMR spectrum in deuterated acetone of the same block copolymer.

(9) In the above figures, the chemical shift in ppm is indicated along the x-axis.

(10) FIG. 9 represents a size exclusion chromatogram (SEC or GPC) of a poly(VDF-co-TrFE) copolymer (see example 2) with a xanthate end group, and of a poly(VDF-co-TrFE)-b-poly(VDF-ter-TrFE-ter-1234yf) block copolymer with a xanthate end group (see example 3).

(11) FIG. 10 represents a size exclusion chromatogram (SEC or GPC) of a poly(VDF-co-TrFE) copolymer (see example 2) with a xanthate end group, and of a poly(VDF-co-TrFE)-b-PVDF block copolymer with a xanthate end group (see example 4).

(12) In the above figures, the retention time in minutes appears along the x-axis, and the intensity in mV appears along the y-axis. The highest molar masses correspond to the shortest retention times.

(13) FIG. 11 represents a thermogram of thermogravimetric analysis, carried out under air, of a PVDF-b-poly(VDF-ter-TrFE-ter-1234yf) copolymer with a monoiodinated end group (see example 1), a poly(VDF-co-TrFE) copolymer with a xanthate end group (see example 2), a poly(VDF-co-TrFE)-b-poly(VDF-ter-TrFE-ter-1234yf) copolymer with a xanthate end group (see example 3) and a poly(VDF-co-TrFE)-b-PVDF copolymer with a xanthate end group (see example 4). The numbers indicated on the figure correspond to the numbers of the examples. The temperature in C. is indicated along the x-axis, and the % residual mass is indicated along the y-axis.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(14) The invention is now described in greater detail and in a nonlimiting manner in the description which follows.

(15) Throughout the description, TrFE or VF.sub.3 denote trifluoroethylene, VDF denotes vinylidene fluoride, PVDF denotes poly(vinylidene fluoride), and 1234yf denotes 2,3,3,3-tetrafluoropropene.

(16) The invention provides for preparing a thermoplastic block copolymer by means of a copolymerization reaction between TrFE and at least one additional monomer, optionally several additional monomers, in the presence of a xanthate or trithiocarbonate compound or of a monoiodinated compound as chain transfer agent, making it possible to control the copolymerization reaction.

(17) If a single additional monomer denoted X is used, a copolymer having TrFE units and units corresponding to the additional monomer X is obtained. The copolymer obtained is denoted poly(TrFE-co-X) or poly(X-co-TrFE).

(18) It is particularly advantageous to use VDF as additional monomer, in which case the copolymer obtained is denoted poly(VDF-co-TrFE) or poly(TrFE-co-VDF).

(19) Alternatively, it is possible to use another additional monomer, for example chosen from fluorinated monomers, and preferably from 2,3,3,3-tetrafluoropropene (1234yf), vinyl fluoride, 2-chloro-1,1-difluoroethylene, 2-bromo-1,1-difluoroethylene, hexafluoropropene, 3,3,3-trifluoropropene, 3,3,3-trifluoro-2-chloropropene, 1,1,1,3-tetrafluoropropene, 1H-pentafluoropropene, 2H-pentafluoropropene, 3,3,3-trifluoro-2-bromopropene, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, -trifluoromethacrylic acid and its derivatives; or chosen from hydrogenated monomers, and preferably from vinyl acetate, N-vinylpyrrolidone, methacrylates, acrylates, acrylamide, N-vinylcarbazole, acrylonitrile and allyl monomers of allyl alcohol, allyl acetate, allyl halide or allyl glycidyl ether type, for example.

(20) It is also possible to use two, three or more than three different additional monomers. In this case, one of these monomers is preferably VDF.

(21) These additional monomers are preferably chosen from the list above.

(22) By way of example, the invention makes it possible to attain the poly(VDF-ter-TrFE-ter-1234yf) copolymer.

(23) Preferably, the xanthate or trithiocarbonate compound is a compound of formula (I):
R.sub.1SC(S)Z,(I)

(24) in which R.sub.1 represents an aliphatic (preferably alkyl) group comprising from 1 to 20 carbon atoms, Z represents an OR.sub.2 group in which R.sub.2 represents an alkyl or aryl group comprising from 1 to 10 carbon atoms (in this case, it is a xanthate compound) or Z represents an SR.sub.3 group in which R.sub.3 represents an aliphatic (preferably alkyl) group comprising from 1 to 20 carbon atoms (in this case, it is a trithiocarbonate compound).

(25) It has been noted that the absence of aromatic groups in R.sub.1, R.sub.2 and/or R.sub.3 has a tendency to improve the reaction yield.

(26) The R.sub.1, R.sub.2 and R.sub.3 groups can be substituted or unsubstituted, preferably unsubstituted. Preferably, R.sub.1, R.sub.2 and R.sub.3 are linear or branched groups, and they are preferably saturated groups.

(27) The copolymers obtained according to the process of the invention then have a xanthate or trithiocarbonate end group, i.e. an SC(S)Z group, or Z has the meaning above, located at the chain end.

(28) It is possible to use a monoiodinated compound in place of the xanthate or trithiocarbonate compound. The xanthate or trithiocarbonate compound has the advantage of producing inverted end groups (CF.sub.2CH.sub.2SC(S)R, with R=alkyl or SR, R alkyl) which are active, just like the normal end groups (CH.sub.2CF.sub.2SC(S)R, with R=alkyl or SR, R alkyl), which is not the case with the monoiodinated compound.

(29) Moreover, improved thermostability can be obtained with the copolymers prepared from a xanthate or trithiocarbonate compound, compared with the copolymers prepared from a monoiodinated compound (see FIG. 11 in this regard).

(30) The monoiodinated compound is a compound comprising a single iodine atom. It can in particular be a 1-iodofluoroalkane, and in particular a compound of formula R.sub.F(CH.sub.2CF.sub.2).sub.nI, in which n is an integer ranging from 1 to 500, and R.sub.F represents a perfluorocarbon group, preferably chosen from the groups CF.sub.3, C.sub.2F.sub.5, C.sub.3F.sub.7 and C.sub.mF.sub.2m+1, m being an even integer ranging from 4 to 20.

(31) The copolymers obtained according to the process of the invention then have a (single) monoiodinated end group, i.e. a single end iodine atom.

(32) The copolymerization reaction is carried out in the presence of an initiator. Said initiator may, for example, be tert-butyl peroxypivalate, tert-amyl peroxypivalate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, sodium persulfate, ammonium persulfate, potassium persulfate, benzoyl peroxide, tert-butyl hydroxyperoxide, tert-butyl peroxide or 2,5-bis(tert-butylperoxy)-2,5-di methyl hexane.

(33) The reaction is carried out in a solvent, which is, for example, chosen from 1,1,1,3,3-pentafluorobutane, acetonitrile, methyl ethyl ketone, 2,2,2-trifluoroethanol, hexafluoroisopropanol, methyl acetate, ethyl acetate, cyclohexanone and water, and mixtures thereof.

(34) The reaction is preferably carried out at a temperature of from 10 to 200 C., preferably from 35 to 170 C., and at a pressure of from 10 to 120 bar, preferably from 20 to 80 bar. The choice of the optimum temperature depends on the initiator which is used. Generally, the reaction is carried out for at least 6 hours, at a temperature at which the half-life time of the initiator is approximately 1 hour.

(35) The molar ratio of the amount of chain transfer agent to the amount of monomers makes it possible to control the molar mass of the copolymer. Preferably, this ratio is from 0.001 to 0.020, more preferentially from 0.005 to 0.010.

(36) The initial molar ratio of the amount of the TrFE monomer to the amount of the comonomers can be, for example, from 10% to 90%, preferably from 20% to 50%. A copolymer containing approximately 65% of VDF and 35% of TrFE (in molar proportions) is particularly advantageous.

(37) The molar mass of the copolymer obtained is preferably from 10 000 to 400 000 g/mol, more preferentially from 40 000 to 300 000 g/mol. The higher the molar mass, the better the properties of the materials obtained.

(38) The polydispersity index of the copolymer obtained is preferably from 1.2 to 1.9, more preferentially from 1.4 to 1.7.

(39) The copolymer obtained by this synthesis technique can, owing to its xanthate or trithiocarbonate end group or to its monoiodinated end group, in turn be reacted with one (or more) comonomer for the preparation of another block copolymer.

(40) The comonomer(s) can in particular be chosen from those listed above.

(41) The block copolymer thus obtained can comprise (or consist of) a first block and a second block.

(42) The first block can in particular be a copolymer comprising blocks of vinylidene fluoride and of trifluoroethylene or a terpolymer based on vinylidene fluoride, on trifluoroethylene and on 2,3,3,3-tetrafluoropropene (1234yf).

(43) The second block can be a homopolymer, copolymer or terpolymer block.

(44) For example, the second block can be a poly(vinylidene fluoride) block, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on 2,3,3,3-tetrafluoropropene, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on vinyl fluoride, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on de 2-chloro-1,1-difluoroethylene, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on 2-bromo-1,1-difluoroethylene, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on hexafluoropropene, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on de 3,3,3-trifluoropropene, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on 3,3,3-trifluoro-2-chloropropene, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on 1,1,1,3-tetrafluoropropene, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on 3,3,3-trifluoro-2-bromopropene, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on perfluoromethyl vinyl ether, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on 2H-pentafluoropropene, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on 1H-pentafluoropropene, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on perfluoroethyl vinyl ether, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on -trifluoromethacrylic acid, a terpolymer based on vinylidene fluoride, on trifluoroethylene and on perfluoropropyl vinyl ether, a copolymer based on VDF, on -trifluoromethacrylic acid or on an -trifluoromethacrylic acid derivative, or a poly(vinyl acetate), polyvinylpyrrolidone, poly(alkyl methacrylate), poly(alkyl acrylate), polyacrylamide, polyvinylcarbazole or polyacrylonitrile block.

(45) Conditions analogous to those described above can be used for this reaction for producing block copolymers. The molar ratio of the amount of comonomer to the amount of copolymer with a xanthate or trithiocarbonate or monoiodinated end group is preferably from 1 to 200, more preferentially from 5 to 100.

(46) The copolymers obtained according to the invention are of use in particular for the production of electrolytes or for the production of membranes. They are also of use for the production of piezoelectric, ferroelectric or pyroelectric devices and also of coatings.

EXAMPLES

(47) The following examples illustrate the invention without limiting it.

Example 1

Synthesis of PVDF-b-poly(VDF-ter-TrFE-ter-1234yf)

(48) The synthesis of the PVDF-b-poly(VDF-ter-TrFE-ter-1234yf) block polymer was carried out in two steps, as follows:

(49) ##STR00001##

(50) First of all, the C.sub.6F.sub.131 controlled free-radical polymerization of the VDF was carried out according to the protocol described in the article entitled Iodine transfer polymerization (ITP) of vinylidene fluoride (VDF)Influence of the defect of VDF chaining on the control of ITP published in Macromolecules, 38, 10353-10362 (2005).

(51) The free-radical copolymerization is carried out in a 100 mL Parr Hastelloy autoclave equipped with a manometer, with a rupture disk and with gas-introduction and release valves. A regulated electronic device controls both the stirring and the heating of the autoclave. The VDF-based telomers C.sub.6F.sub.13(VDF).sub.nI (6.2 g, 0.026 mol, 2%, DP.sub.n=26) are introduced into the autoclave. It is then pressurized to 30 bar of nitrogen for 1 h in order to verify the leaktightness thereof. Once the nitrogen has been evacuated, the reactor is placed under vacuum for 40 min, then t-butyl peroxypivalate TBPPI (0.60 g, 3.47 mmol) and 60 mL of 1,1,1,3,3-pentafluorobutane are introduced therein. The reactor is then cooled to 60 C. (acetone/liquid nitrogen mixture), then 1,1,2-trifluoroethylene or TrFE (7.47 g, 0.091 mol), 2,3,3,3-tetrafluoro-2-propene or 1234yf (1.49 g, 0.013 mol) and vinylidene fluoride or VDF (10 g, 0.156 mmol) are then successively introduced therein.

(52) The reactor is gradually heated to 74 C., and the changes in pressure and in temperature are recorded. During the polymerization, an increase in the pressure inside the reactor is observed, due to the exothermicity of the reaction, followed by a decrease in said pressure, caused by the conversion of the gaseous fluorinated monomers into the desired polymer. At 74 C., the pressure is close to 35 bar (a rapid increase in the temperature to 78 C. is observed, thereby showing that the reaction is exothermic). During the hour following this exotherm, the pressure decreases from 35 bar to 12 bar with a temperature maintained at 74 C. After reaction and cooling, the reactor is left in ice for 30 min and then degassed (release of the unreacted fluorinated monomers). After the reactor has been opened, the solvent is eliminated by distillation and then the product is precipitated from cold pentane, filtered and dried under vacuum (10.sup.2 bar, 60 C.) until the weight is constant. The PVDF-b-poly(VDF-ter-TrFE-ter-1234yz) block copolymer, in the form of a white powder, is characterized by .sup.1H NMR (FIG. 1) and .sup.19F NMR (FIG. 2) spectroscopy. The calculated yield is 78%.

(53) In FIG. 1, the reference A denotes the CFH group of TrFE; the reference B denotes the CF.sub.2CH.sub.2I group; the reference C denotes the normal diads CH.sub.2CF.sub.2CH.sub.2CF.sub.2 of VDF and CH.sub.2 of 1234yf; and the reference D denotes the inverse diads CF.sub.2CH.sub.2CH.sub.2CF.sub.2 of VDF. The calculated proportion of TrFE is 20 mol %.

(54) In FIG. 2, the reference E denotes 1234yf.

(55) The TGA thermogram (carried out under air) of the copolymer is visible in FIG. 11 (curve no. 1).

(56) ##STR00002##

Example 2

Synthesis of poly(VDF-co-TrFE)-SC(S)OEt

(57) This copolymerization is carried out as previously in a 100 mL HC-276 reactor by introducing therein respectively t-butyl peroxypivalate (0.904 g, 5.2 mmol), 2-mercaptopropionic acid methyl ester O-ethyl dithiocarbonate (Rhodixan; 0.811 g, 3.9 mmol) and 50 mL of 1,1,1,3,3-pentafluorobutane. The reactor is then cooled to 60 C. (acetone/liquid nitrogen mixture), then the TrFE (12.81 g, 0.156 mol) followed by the VDF (15 g, 0.234 mmol) are then successively introduced therein.

(58) The reactor is gradually heated to 74 C., and the changes in pressure and in temperature are recorded. During the polymerization, an increase in the pressure inside the reactor is observed, due to the exothermicity of the reaction, and then a decrease in said temperature, caused by the consumption of the gaseous fluorinated monomers to give the desired polymer. At 74 C., the pressure is close to 22 bar (linked to the exothermicity up to 76 C.).

(59) During the hour following this exotherm, the pressure drops to 7 bar for a temperature maintained at 74 C. As previously, after reaction and cooling, the reactor is left in ice for 30 min and then degassed. After the reactor has been opened, the solvent is distilled off. The product is precipitated from cold pentane, filtered and dried under vacuum (10.sup.2 bar, 60 C.) for 14 hours. The poly(VDF-co-TrFE)-SC(S)OEt copolymer, in the form of a white powder, is characterized by .sup.1H NMR (FIG. 3) and .sup.19F NMR (FIG. 4) spectroscopy. The calculated yield is 75%.

(60) In FIG. 3, the reference A denotes the CHF group; the reference B denotes the CF.sub.2CH.sub.2SC(S)OEt group; the reference C denotes CH.sub.2CF.sub.2CH.sub.2CF.sub.2; and the reference D denotes the tBu-VDF group. Moreover, the references a, b, c and d correspond to the positions indicated on the illustrated formula of the copolymer.

(61) ##STR00003##

(62) In FIG. 4, the reference E denotes CH.sub.2CF.sub.2CH.sub.2. Moreover, the references a, b, c, d, e, f, g, h and h correspond to the positions indicated on the illustrated formula of the copolymer.

(63) The GPC chromatogram of the copolymer can be seen in FIGS. 9 and 10. The molar mass of this copolymer is 40 000 g/mol (PMMA equivalent) and its polydispersity index DPI is 1.61.

(64) The TGA thermogram of the copolymer can be seen in FIG. 11 (curve no. 2).

Example 3

Synthesis of poly(VDF-co-TrFE)-b-poly(VDF-ter-TrFE-ter-1234) Block Polymer

(65) This copolymerization is carried out by introducing the copolymers based on VDF and TrFE of example 2 (6.2 g, 0.026 mol, 2%) into the autoclave. The reactor is placed under vacuum for 40 min, then t-butyl peroxypivalate (0.60 g, 3.47 mmol) and 60 mL of 1,1,1,3,3-pentafluorobutane are introduced therein. The reactor is then cooled to 60 C., and the TrFE (7.47 g, 0.091 mol), the 1234yf (1.49 g, 0.013 mol), and, finally, the VDF (10 g, 0.156 mmol) are then respectively introduced therein. The reactor is gradually heated to 74 C., and the changes in pressure and temperature are reported.

(66) During the polymerization, an increase in the pressure inside the reactor is observed, due to the exothermicity of the reaction, then a decrease in said pressure, caused by the conversion of the gaseous fluorinated monomers into the desired polymer in solution. At 74 C., the pressure is close to 42 bar (a rapid increase in the temperature to 79 C. is observed). During the hour following this exotherm, the pressure decreases from 42 bar to 11 bar with a temperature maintained at 74 C. After reaction and cooling, the reactor is left in ice for 30 min and then degassed.

(67) After the reactor has been opened, the solvent is completely eliminated by distillation, and the copolymer is precipitated from ice-cold pentane, filtered and dried under vacuum (10.sup.2 bar, 60 C.) for 14 hours. The desired copolymer, in the form of a white powder, is characterized by .sup.1H NMR (FIG. 5) and .sup.19F NMR (FIG. 6) spectroscopy. The calculated yield is 81%.

(68) In FIG. 6, the double reference A indicates the presence of 1234yf.

(69) The GPC chromatogram of the copolymer can be seen in FIG. 9. The molar mass of the block copolymer is 55 000 g/mol (PMMA equivalent) and the DPI is 1.71. The TGA thermogram of the copolymer can be seen in FIG. 11 (curve no. 3).

Example 4

Synthesis of poly(VDF-co-TrFE)-b-PVDF Block Copolymer

(70) ##STR00004##

(71) This copolymerization is carried out by introducing the copolymer based on VDF and TrFE, with a xanthate end group, synthesized in example 2 (6.2 g, 0.026 mol, 2%) into the autoclave. The reactor is placed under vacuum for 40 min, then t-butyl peroxypivalate (0.43 g, 1.87 mmol) and 60 mL of 1,1,1,3,3-pentafluorobutane are introduced therein. The reactor is then cooled to 60 C. (acetone/liquid nitrogen mixture), then the VDF (12 g, 0.187 mmol) is introduced therein. The reactor is gradually heated to 74 C., and the changes in pressure and temperature are recorded.

(72) During the polymerization, an increase in the pressure inside the reactor is observed, due to the exothermicity of the reaction, then a decrease in said pressure, caused by the consumption of the gaseous VDF to give the desired polymer. At 74 C., the pressure is close to 25 bar (a rapid increase in the temperature to 76 C. is observed), and then down to 7 bar (the temperature being maintained at 74 C.). After reaction and cooling, the reactor is left in ice for 30 min and then degassed. After the reactor has been opened, the solvent is eliminated by distillation and then the residue is precipitated from cold pentane, filtered and dried under vacuum (10.sup.2 bar, 60 C.) until the weight is constant.

(73) The desired copolymer, in the form of a white powder, is characterized by .sup.1H NMR (FIG. 7) and .sup.19F NMR (FIG. 8) spectroscopy. The calculated yield is 79%.

(74) The GPC chromatogram of the copolymer can be seen in FIG. 10. The molar mass of this block copolymer is 43 000 g/mol (PMMA equivalent) and the DPI is 1.72.

(75) The TGA thermogram of the copolymer can be seen in FIG. 11 (curve no. 4).