Specific phosphonated copolymers and inorganic particles grafted by said copolymers

Abstract

The invention relates to copolymers comprising a chain of siloxane repeat units of at least two different types, a first type of siloxane repeat unit comprising at least one OH group on the silicon atom of the siloxane repeat unit and a second type of repeat unit comprising at least one pendant chain on the silicon atom of said repeat unit, this pendant chain consisting of a polymer chain comprising a chain of repeat units carrying at least one group of formula PO.sub.3R.sup.1R.sup.2 wherein R.sup.1 and R.sup.2 independently represent a hydrogen atom, an alkyl group or a cation.

Claims

1. A copolymer, comprising a chain of siloxane repeat units of at least two different types: a first siloxane repeat unit comprising at least one OH group on the silicon atom of the siloxane repeat unit; and a second repeat unit comprising at least one pendant chain on the silicon atom of the said repeat unit, this pendant chain consisting of a polymer chain comprising a chain of repeat units, wherein each of the repeat units carry at least one group of formula PO.sub.3R.sup.1R.sup.2, wherein R.sup.1 and R.sup.2 independently of each other represent a hydrogen atom, an alkyl group or a cation.

2. The copolymer according to claim 1, wherein the first repeat unit is represented by formula (I): ##STR00026## wherein one of R.sup.3 and R.sup.4 represents an OH group and the other group represents an alkyl group.

3. The copolymer according to claim 1, wherein the first repeat unit is represented by formula (II): ##STR00027##

4. The copolymer according to claim 1, wherein the second repeat unit is represented by formula (III): ##STR00028## wherein one of R.sup.5 and R.sup.6 represents a polymer chain comprising a chain of at least one repeat unit carrying at least one of the PO.sub.3R.sup.1R.sup.2 group, and the other group represents an alkyl group.

5. The copolymer according to claim 4, wherein R.sup.6 represents a polymer chain comprising a chain of repeat units derived from the polymerisation of at least one vinyl monomer carrying the PO.sub.3R.sup.1R.sup.2 group, R.sup.1 and R.sup.2 being such as defined in claim 1.

6. The copolymer according to claim 5, wherein the vinyl monomer is represented by formula (IV): ##STR00029## and a repeat unit derived from the polymerisation of said monomer is represented by formula (V): ##STR00030##

7. The copolymer according to claim 5, wherein the vinyl monomer is an ester of vinylphosphonic acid.

8. The copolymer according to claim 7, wherein the ester of vinylphosphonic acid is the diethyl vinylphosphonate or the dimethyl vinylphosphonate.

9. The copolymer according to claim 1, further comprising at least one siloxane repeat unit represented by formula (VIII): ##STR00031## wherein R.sup.7 and R.sup.8 represent an alkyl group.

10. The copolymer according to claim 1, which is a block copolymer.

11. The copolymer according to claim 1, which is represented by formula (IX): ##STR00032## wherein: R.sup.1 and R.sup.2 independently of each other represent a hydrogen atom, an alkyl group or a cation; R.sup.3 represents an OH group or an alkyl group; one of R.sup.5 and R.sup.6 represents a polymer chain comprising a chain of at least one repeat unit carrying at least one of the PO.sub.3R.sup.1R.sup.2 group, and the other group represents an alkyl group; R.sup.7 and R.sup.8 represent an alkyl group; R.sup.9, R.sup.10, R.sup.11, R.sup.12, R.sup.13 and R.sup.14 independently of each other represent an alkyl group; q, r, s and u represent the number of repeats of the repeat unit between brackets, with the proviso that q, r and u are higher than 1 and s is equal to or higher than 0.

12. The copolymer according to claim 1, represented by formula (X): ##STR00033## wherein q and r represents the number of repeats of the repeat unit between brackets and the sum (q+r) equals 8; u represents the number of repeats of the repeat unit between brackets and is higher than 1; R.sup.1 and R.sup.2 independently of each other represent a hydrogen atom, an alkyl group or a cation.

13. A method for preparing the copolymer of claim 1, the method comprising reacting, in the presence of water and at least one organic solvent, a base (co)polymer comprising a chain of repeat units comprising a first siloxane repeat unit having at least one hydrogen atom on the silicon atom of said repeat unit, in the presence of a Lewis acid comprising a borane, with a vinyl monomer comprising a PO.sub.3R.sup.1R.sup.2 group, to form a copolymer, wherein: R.sup.1 and R.sup.2 independently of each other represent a hydrogen atom, an alkyl group or a cation; after which the copolymer comprises a chain of at least two siloxane repeat units of which a first siloxane repeat unit comprises at least one OH group directly bound to the silicon atom of said repeat unit and of which a second siloxane repeat unit comprises at least one pendant chain directly bound to the silicon atom of the said repeat unit, the said pendant chain consisting of a polymer chain comprising a chain of repeat units, wherein each of the repeat units comprises at least one PO.sub.3RR.sup.2 group.

14. The method according to claim 13, wherein the base (co)polymer comprises a chain of repeat units comprising first siloxane represented by formula (XI): ##STR00034## wherein R.sup.15 is a hydrogen atom or an alkyl group.

15. The method according to claim 13, wherein the base (co)polymer further comprises a repeat unit of formula (XII): ##STR00035## wherein R.sup.7 and R.sup.8 represent an alkyl group.

16. The method according to claim 13, wherein the base (co)polymer is represented by formula (XIII): ##STR00036## wherein: R.sup.7 and R.sup.8 represent an alkyl group; R.sup.9, R.sup.10, R.sup.11, R.sup.12, R.sup.13 and R.sup.14 independently of each other represent an alkyl group; R.sup.15 is a hydrogen atom or an alkyl group; and v and w represent the number of repeats of the repeat unit between brackets.

17. The method according to claim 13, wherein the base (co)polymer is represented by formula (XIV): ##STR00037##

18. The method according to claim 13, further comprising adding a monosilane compound to a reaction medium comprising an organic solvent, water and Lewis acid comprising borane, before adding the base (co)polymer.

19. The method according to claim 13, wherein the Lewis acid is a triarylborane compound.

20. An inorganic particle grafted by at least one copolymer according to claim 1 at least one SiOH group of said copolymer to form a SiO bonding group between said copolymer and said particle.

21. The inorganic particle according to claim 20, which is an oxide particle.

22. The inorganic particle according to claim 20, which is a silica particle.

23. A fuel cell membrane, comprising the inorganic particle of claim 20.

24. A fuel cell device, comprising at least one electrode membrane-electrode assembly comprising the membrane of claim 23.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a .sup.29Si NMR spectrum of silica particles before grafting (curve a) and after grafting (curve b) obtained according to Example 4.

(2) FIG. 2 illustrates a .sup.13C NMR spectrum of silica particles obtained after grafting according to Example 4.

(3) FIG. 3 illustrates a .sup.31P NMR spectrum of silica particles obtained after grafting according to Example 4.

(4) FIG. 4 gives a thermogram illustrating the trend in weight loss P (%) as a function of temperature T ( C.) (curves a, b, c respectively for the particles grafted with the copolymer of Example 1, the copolymer of Example 2 and the copolymer of Example 3).

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

(5) In the following examples, the following reagents were used:

(6) diethyl vinylphosphonate (symbolised by the abbreviation DEVP) and toluene supplied by Aldrich;

(7) pentadimethylsiloxane, poly(hydromethyl-co-dimethyl)siloxane (symbolised by the abbreviation PHM-co-DMS) and tris (pentafluorophenyl)borane supplied by ABCR.

(8) The toluene was dried for 24 hours under calcium hydride and then distilled.

(9) The polymerisation steps were performed in mL Schlenk tubes in an inert argon atmosphere, fitted with a magnetic stirrer and a septum. Three vacuum/argon cycles were performed before adding the reagents.

Example 1

(10) This example relates to the preparation of a polymer conforming to the invention resulting from the polymerisation of diethyl vinylphosphonate having the following formula:

(11) ##STR00018##
from a base copolymer: poly(hydromethyl-co-dimethyl)siloxane having the following formula:

(12) ##STR00019##

(13) Diethyl vinylphosphonate (0.704 g; 4.310.sup.3 mol) is added to the tube. In parallel, tris (pentafluorophenyl)borane (210 mg; 4.310.sup.4 mol) is solubilised in toluene. The solution is then added to the tube. Next, pentadimethylsiloxane (0.190 g; 1.2810.sup.3 mol) is added. The temperature is then set at 50 C. About 15 minutes after adding the pentadimethylsiloxane, a strong release of gas is observed which starts to fade about 30 minutes later. Poly(hydromethyl-co-dimethyl)siloxane (1 g; 2.1310.sup.3 mol) is added at this precise moment. The reaction takes place for 16 hours at 85 C. On completion of the reaction, the reaction mixture is stored.

Example 2

(14) This example relates to the preparation of a polymer conforming to the invention resulting from the polymerisation of diethyl vinylphosphonate having the following formula:

(15) ##STR00020##
from a base copolymer: poly(hydromethyl-co-dimethyl)siloxane of following formula:

(16) ##STR00021##

(17) Diethyl vinylphosphonate (0.704 g; 4.310.sup.3 mol) is added to the tube. In parallel, tris(pentafluorophenyl)borane (210 mg; 4.310.sup.4 mol) is solubilised in toluene. The solution is then added to the tube. Next, pentadimethylsiloxane (0.190 g; 1.2810.sup.3 mol) is added. The temperature is then set at 50 C. About 15 minutes after adding the pentadimethylsiloxane, a strong gas release is observed which starts to fade about 30 minutes later. The poly(hydromethyl-co-dimethyl)siloxane (2 g; 4.2610.sup.3 mol) is added at this precise moment. The reaction takes place for 16 hours at 85 C. On completion of the reaction, the reaction mixture is stored.

Example 3

(18) This example relates to the preparation of a polymer conforming to the invention resulting from the polymerisation of diethyl vinylphosphonate having the following formula:

(19) ##STR00022##
from a base copolymer: poly(hydromethyl-co-dimethyl)siloxane having the following formula:

(20) ##STR00023##

(21) The diethyl vinylphosphonate (0.704 g; 4.310.sup.3 mol) is added to the tube. In parallel tris (pentafluorophenyl)borane (210 mg; 4.310.sup.4 mol) is solubilised in toluene. The solution is then added to the tube. Next, pentadimethylsiloxane (0.190 g; 1.2810.sup.3 mol) is added. The temperature is then set at 50 C. About 15 minutes after adding the pentadimethylsiloxane, a strong gas release is observed which starts to fade about 30 minutes alter. The poly(hydromethyl-co-dimethyl)siloxane (4 g; 4.5610.sup.3 mol) is added at this precise moment. The reaction takes place for 16 hours at 85 C. On completion of the reaction, the reaction medium is stored.

Example 4

(22) This example illustrates the preparation of silica particles grafted by the copolymers prepared according to examples 1 and 3 described above.

(23) For this purpose, a suspension of 2 g of silica nanoparticles (previously dried at 130 C. for 24 hours under nitrogen) in 120 mL of toluene is prepared in a three-necked flask under mechanical and ultrasound agitation. The suspension is placed under reflux in an oil bath for 1 hour under agitation. The reaction mixture obtained on completion of the reaction of the DEVP on PHM-co-DMS conforming to Examples 1 to 3 is added and the reflux is maintained for 16 additional hours. The functionalised silica nanoparticles are collected and washed in toluene (twice) using centrifuging cycles to remove the polymer which has not reacted. The sample obtained (3.3 g) is dried at 90 C. for 24 hours in vacuo.

(24) The particles obtained after the different experiments were characterized by solid-state .sup.29Si CP/MAS NMR. The spectra obtained with the copolymers resulting from Examples 1 to 3 do not exhibit any significant differences.

(25) The spectra obtained are illustrated in FIG. 1, spectrum (a) corresponding to the spectrum obtained with the silica particles before any modification, and spectrum (b) corresponding to the spectrum obtained with the silica particles after the grafting reaction.

(26) The particles obtained after grafting can be illustrated by the following formula:

(27) ##STR00024##
n, r, q and p representing the number of repeats of the repeat units between brackets, Et corresponding to an ethyl group, the silicon atom linked to three bonds shown as dotted lines corresponding to a silicon atom belonging to a silica particle.

(28) In comparison with spectrum (a), on spectrum (b) the disappearance is observed of the signal corresponding to the silicon atoms of type Q.sup.2 occurring at around 85 ppm combined with the occurrence of a signal of type Q.sup.4 at around 105 ppm. The Q.sup.4 silicon atoms correspond to those on the surface of the silica particles bound to the phosphonated copolymer i.e. those indicated by the FIG. 1 in the above formula. A resonance signal occurs at around 65 ppm corresponding to the silicon atoms of type T.sup.3 (these being indicated by the FIG. 2 in the above formula), a signal characteristic of the silicon atoms bound to 3 oxygen atoms. The signal occurring a 35 ppm corresponds to the silicon atoms of type D (these being indicated by the FIG. 3 in the above formula), a signal characteristic of the silicon atoms bound to two oxygen atoms. Finally, the signal which is observed at around 15 ppm corresponds to the silicon atoms of type M (these being indicated by the FIG. 4 in the above formula), a signal characteristic of the silicon atoms bound to one oxygen atom.

(29) The particles derived from the different experiments were characterized by solid-state .sup.13C CP/MAS NMR. The spectra obtained with the copolymers obtained according to Examples 1 to 3 do not exhibit any significant differences.

(30) The spectra obtained are illustrated in FIG. 2.

(31) The formula given above is that of the particles obtained after grafting with specific numbering of the carbon atoms:

(32) ##STR00025##
n, r, q and p representing the number of repeats of the repeat units between brackets, the silicon atom bound to three bonds shown as dotted lines corresponding to a silicon atom belonging to a silica particle.

(33) A resonance signal at 62 ppm corresponding to the carbon atoms numbered 1 is observed. The signal at 36 pppm corresponds to carbon atoms numbered 2 of the aliphatic chain. The signal which occurs at 18 ppm corresponds to the carbon atoms numbered 3. Finally, the signal at 0 ppm corresponds to the carbon atoms numbered 4, a signal characteristic of carbon atoms belonging to a siloxane sequence. This spectrum therefore evidences grafting of the silica particles by the copolymers in Examples 1 to 3.

(34) The particles derived from the different experiments were characterized by solid-state .sup.31P CP/MAS NMR. The spectra obtained with the copolymers obtained according to Examples 1 to 3 do not exhibit any significant differences.

(35) The spectrum obtained is illustrated in FIG. 3.

(36) A broad resonance signal is observed in this spectrum centred at 30 ppm, characteristic of diethyl phosphonate groups.

(37) The isolated particles were also characterized by TGA, the results being given in FIG. 4 in graph form showing the trend in weight loss P (%) as a function of temperature T ( C.) (curves a, b and c respectively for the particles grafted with the copolymer of Example 1, the copolymer of Example 2 and the copolymer of Example 3). The weight fraction at 850 C. is attributable to the inorganic part formed by the silica particles as such. The remainder at 100 is attributable to the organic part grafted onto the silica particles.

(38) For the particles obtained from the copolymers in Examples 1, 2 and 3, the organic part represents 35 weight %.

(39) The weight loss within the zone lying between 150 and 350 C. corresponds to the departure of the ethyl functions of the phosphonate groups, these functions representing 55 weight % of the diethylvinylphosphonate repeat unit. On the basis of these data, it is possible to deduce the weight percentage of the diethylvinylphosphonate repeat units in the products obtained.

(40) For example, for the particles obtained by grafting the copolymers of Example 1, the weight loss in the zone lying between 150 and 350 C. is evaluated at about 22%. Starting from the above-mentioned principle according to which the ethyl functions represent 55 weight % of the diethylvinylphosphonate repeat unit, the total fraction of the copolymer chains grafted onto the silica particles is then evaluated at 40 weight %. Bearing in mind that there remains 65 weight % on completion of thermogravimetric analysis, and that the contribution of this fraction derives solely from inorganic part alone (in this case the silica), the % of copolymer on each particle can be estimated at 5%. On the basis of these different fractions, the number of repeats of the diethyl vinylphosphonate repeat unit can be estimated at 60, which allows ion exchange capacity to be estimated at 2.31 meq.Math.g.sup.1.

Example 5

(41) This example illustrates the preparation of a membrane from products obtained in Example 4 using a so-called evaporative casting method of a solution of said products. The solvent used is dimethylformamide. After casting the solution onto a glass plate, the membrane is obtained after drying for 24 hours at 60 C. It is then immersed in distilled water and collected. To obtain hydrolysis of the phosphonate groups to phosphonic groups the membrane is immersed in an aqueous 12 M hydrochloric acid solution for about 70 hours. The assay of the carbon element before and after hydrolysis indicates that the conversion rate is 95%. To remove all traces of acid the membrane is washed several times in distilled water.