Phosphonylated unfluorinated and partially fluorinated polymers formed from sulfonated polymers

Abstract

This invention includes new types of substances, namely highly phosphonylated and lowly phosphonylated aryl polymers and polymeric perfluorophosphonic acids, the raw materials of which are in sulfonated form, and also includes a general method for preparing phosphonylated polymers from sulfonated form and their use in electrical membrane methods.

Description

[0001] Existing technology

[0002] The most commonly described phosphonylation systems are based on aryl polymers synthesized by nucleophilic substitution of aryl halides and di- or trialkyl phosphites (Michaelis-Arbusow rearrangement and Michaelis-Becker rearrangement).

[0003] These phosphonylated aryl polymers exhibit high thermal and chemical stability. Furthermore, they demonstrate good proton conductivity even in the unwetted state. [1-5]

[0004] For example, as described in DE 102011015 212 A1, a disadvantage of these phosphonylated aryl polymers is that they are very brittle in the undried (i.e., dry) state and therefore cannot be used to prepare properly functioning membranes. This brittleness increases with increasing temperature and decreasing humidity, leading to mechanical failure of the membrane. This makes it impossible to use these polymers as membranes for electrical membrane methods exceeding a temperature range of 100°C.

[0005] Kyoji Kimoto's patent US6680346B1 describes the direct synthesis of phosphonylated perfluorophosphonic acid. The claims therein relate to the following structure (Figure 2), where m is 0 or 1, n is 2 or 3, X and Y are H or C6H4SO3H, and the ratio A / B is 1.5 to 15.

[0006] As seen in EP2514773A1, the synthesized polymer in US6680346B1 undergoes cyclization due to the difficulty in controlling polymerization conditions. This leads to chain transfer during polymerization, resulting in a decrease in molecular weight and material mechanical strength. Increasing the molar ratio of short-chain phosphonoacyl monomers to tetrafluoroethylene monomers further favors side reactions, limiting improvements in ion exchange capacity and material stability.

[0007] The method claimed in this article is not subject to such limitations because polymeric perfluorosulfonic acid can now be prepared with unchanged quality, as can be seen in Figure 1.

[0008] The described phosphonylation reaction thus produces a new, stable class of polymeric perfluorophosphonic acids without the drawbacks described in US6680346B1. The same behavior is observed in sulfonated aryl polymers, where the base polymers already possess good mechanical properties, which are retained in these new forms of phosphonylated polymers. Summary of the Invention

[0009] The objective of this invention is to find and synthesize novel phosphonylated polymers that are protonally conductive even in a dry state and are chemically and mechanically stable. This is achieved by first converting a sulfonated polymer with good mechanical properties and a sulfonic acid group to the -SO₂Cl form using thionyl chloride via chlorosulfonation. Trialkyl phosphites, such as tris(trimethylsilyl)phosphites (TTMSP), can be used as a trigger for phosphonylation, or the -SO₂Cl form can be converted to -SO₂Na (sodium sulfonate) using sodium sulfite and then phosphonylated, or the -SO₂Na form can be further converted to -SO₂Li (lithium sulfonate) and then phosphonylated. Using this method, phosphonylated polymers with high mechanical flexibility, chemical stability, and high proton conductivity can be synthesized from all polymers with sulfonic acid groups. Polymers that already possess good mechanical and chemical properties in their sulfonated form retain these properties after phosphonylation and, unlike sulfonic acid-containing polymers, exhibit very good proton conductivity above 100°C. Figure 3 )

[0010] This reaction should be as efficient and simple as possible, and that is exactly what it is.

[0011] Phosphonylated polymers should be soluble in common solvents so that films can be prepared from them.

[0012] Using the synthetic methods described in this paper, phosphonylated polymers can theoretically be synthesized from all sulfonated polymers.

[0013] The present invention is based on the introduction of a reactive group -X (which can be -SO2Cl, -SO2Na, or -SO2Li) into a sulfonated polymer and the reaction of the reactive group with a trialkyl phosphite, such as tris(trimethylsilyl)phosphite (TTMSP).

[0014] Depending on the degree of phosphonylation, phosphonylated polymers may also contain free reactive groups -X. These free groups can be used to subsequently covalently crosslink the phosphonylated polymer or to convert unreacted groups back into the -SO3H form, thus obtaining polymers that contain both sulfonylation and phosphonylation groups.

[0015] Phosphonylation can be carried out in solution. For this purpose, polymers with the reactive group -X can be dissolved in solvents such as N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), etc. TTMSP can be selectively added beforehand, directly before the dissolution process, or after the polymer has been dissolved. Depending on the desired degree of phosphonylation, 0.1% by weight (wt%) (for lower degrees of phosphonylation) to 5000% by weight (for higher degrees of phosphonylation) is added relative to the polymer weighing amount.

[0016] This reaction proceeds best and fastest in high-boiling solvents such as NMP, DMAc, and DMSO. During the reaction, gas formation can be observed, indicating when the reaction begins, or the cessation of gas formation indicates the end of the reaction.

[0017] Maintain this reaction at the reaction temperature (60-200°C) until gas formation ceases, regardless of the polymer used, its molecular weight, and the solvent. Then continue maintaining the temperature for 2 to 8 hours to ensure complete reaction.

[0018] The reaction byproducts and excess TTMSP were then removed by distillation, while the phosphonylated polymer in its trimethylsilyl ester form remained in the solvent.

[0019] The polymer solution is now poured into water and either precipitates as a solid (low phosphonylation) or enters the solution (high phosphonylation) depending on the degree of phosphonylation. By heating the water / polymer mixture, the phosphonylated polymer is hydrolyzed from its trimethylsilyl ester form to free polymeric phosphonic acid.

[0020] To completely separate the hydrolysis byproducts, the polymer can be simply washed with water according to the degree of phosphonylation. The water-insoluble portion can be washed out and filtered off, or the water-soluble portion can be purified by dialysis.

[0021] Another variation is to not allow the polymer solution to precipitate in water, but instead to further process the polymer solution directly from

[0015] into a film after removing excess TTMSP and then hydrolyze it in hot to boiling water or perform subsequent treatment with hot steam.

[0022] Figure 4 shows an overview of the exemplary reactions corresponding to the non-limiting embodiments.

[0023] The obtained polymer can be blended with basic polymers, such as polybenzimidazole or anion exchange polymers, to form acid-base blend membranes, covalently cross-linked membranes, and covalently cross-linked acid-base blend membranes.

[0024] The mixing ratio between phosphonylated polymer and basic polymer can be between 99 mol% phosphonylated polymer / 1 mol% basic polymer and 1 mol% phosphonylated polymer / 99 mol% basic polymer.

[0025] Alternatively, any sulfonated polymer can be added to the polymer or blend in any amount.

[0026] The obtained polymer can be blended with basic polymers such as polybenzimidazole or anion exchange polymers to form acid-base blend membranes, covalently cross-linked membranes, and covalently cross-linked acid-base blend membranes.

[0027] The mixing ratio between phosphonylated polymer and basic polymer can be between 99 mol% phosphonylated polymer / 1 mol% basic polymer and 1 mol% phosphonylated polymer / 99 mol% basic polymer.

[0028] Alternatively, any sulfonated polymer can be added to the polymer or blend in any amount.

[0029] Alternatively, the blend film can be doped with any amount of phosphoric acid. A preferred phosphoric acid doping degree is between 40% by weight and 500% by weight.

[0030] The obtained polymer can be used in electrochemical cells. Preferably, it can be used in low-temperature or medium-temperature fuel cells in a temperature range of -30°C to 250°C, or in low-temperature or medium-temperature electrolytic cells in a temperature range of 0°C to 250°C. Furthermore, it can be used in chemical synthesis reactors in a temperature range of -70°C to 250°C. The obtained polymer can also be used as a separator in primary and secondary batteries, or as a binder in electrodes, primary and secondary batteries.

[0031] Non-limiting embodiments:

[0032] 2 g of sulfonated polyetherketone (sPEKEKK) was mixed with 55 g of thionyl chloride, heated to 90°C, and refluxed to boiling. DMF (dimethylformamide) was then added and heated until no more gas formation was observed. The reaction temperature was maintained for 2 hours to ensure complete reaction. Excess thionyl chloride and byproducts were distilled off, and the product was slurried with THF (tetrahydrofuran). The solution / suspension could now be precipitated in isopropanol or water. The product was washed until neutral and then dried. The previously sulfonated polymer now existed as -SO₂Cl. The product in a 2M sodium sulfite solution was then converted to -SO₂Na. The polymer was then filtered off and washed again with water to remove excess sodium sulfite. The -SO₂Na polymer was then mixed with a 10% by weight LiCl solution to convert it to -SO₂Li. The polymer was then washed again with water to remove excess salt. The polymer was then dried.

[0033] Phosphonylation can be performed using TTMSP in all three forms: -SO2Cl, -SO2Na, and -SO2Li, with the -SO2Li form being preferred.

[0034] Currently, polymers with -SO2Cl, -SO2Na, or -SO2Li groups can be mixed with organic solvents such as DMAc, NMP, DMSO, etc., and TTMSP and then phosphonylated.

[0035] In the case of polymeric perfluorosulfonic acid, polymer granules, powders, etc., from the reactions described in

[0019] to

[0021] can be used, or a perfluorosulfonic acid membrane can be used directly. For this purpose, the perfluorosulfonic acid membrane is passed through a hot thionyl chloride / DMF bath (in which chlorosulfonation is performed), and then through a water bath for rinsing. The membrane, now in the form of -SO2Cl, is then passed through a sodium sulfite bath, where the -SO2Na form is produced, and then again through a water bath for rinsing. The membrane in the form of -SO2Na is then passed through a LiCl bath and converted to the -SO2Li form, and then washed again in a water bath. All three forms of the membrane, namely -SO2Cl, -SO2Na, and -SO2Li, can be passed through a heated TTMSP bath and then through a hot / boiling water bath to obtain the phosphonic acid form by hydrolysis. This can be achieved either in a continuous roll-to-roll process or in a batch process. The membrane can now be dried and reused directly. The -SO2Cl form is preferred for phosphonylation.

[0036] Analysis of the experiment:

[0037] This section exemplifies one of these phosphonyl polymers, its ion exchange capacity, and its conductivity up to 180°C. Figure 3 ).

[0038] Determination of ion exchange capacity

[0039] 100 mg of the treated polymer was covered with a saturated NaCl solution, stirred for approximately 2 hours, and 2 drops of bromothymol blue were added as an indicator. Here, the protons of the phosphonylated polymer exchanged for Na ions, producing HCl. This HCl could be detected by titration with 0.1 mol NaOH. This allows for the determination of IEC. 直接 To determine the total IEC 总 Add 3 ml of excess 0.1 M NaOH to the same solution, stir again for 2 hours, and then titrate with HCl in the reverse direction.

[0040] For the experiment in

[0019] , IEC was obtained for phosphonylated PEKEKK (pPEKEKK). 直接 = 0.95 mmol / g and IEC 总 = 2.2 mmol / g. In Figure 3The conductivity measurements clearly demonstrate excellent proton conductivity, even above 100°C. In contrast, a decrease in conductivity is observed in Nafion 212 under the same measurement conditions, from 50% indoor humidity at 30°C to 0.2% indoor humidity at 180°C.

[0041] Therefore, the high conductivity at high temperatures can be attributed to the strong electron-withdrawing effect of the SO2 group on the electrons of the phosphonic acid group.

[0042] literature

[0043] [1] Vladimir Atanasov and Jochen Kerres Highly PhosphonatedPolypentafluorostyrene; Macromolecules 2011, 44, 16, 6416-6423

[0044] [2] Vladimir Atanasov, Dietrich Gudat, Bastian Ruffmann, JochenKerres,Highly phosphonated polypentafluorostyrene: Characterization and blends with polybenzimidazole,European Polymer Journal, Volume 49, Issue 12,2013, Pages 3977-3985,

[0045] [3] Vladimir Atanasov, Matthias Bürger, Sandrine Lyonnard, Lionel Porcar, Jochen Kerres,Sulfonated poly(pentafluorostyrene): Synthesis &characterization,Solid State lonics, Volume 252, 2013, Pages 75-83,

[0046] [4] Vladimir Atanasov, Jochen Kerres,ETFE-g-pentafluorostyrene:Functionalization and proton conductivity,European Polymer Journal, Volume63, 2015, Pages 168-176,

[0047] [5] Vladimir Atanasov, Andrey Oleynikov, Jiabing Xia, SandrineLyonnard, Jochen Kerres,Phosphonic acid functionalized poly(pentafluorostyrene) as polyelectrolyte membrane for fuel cell applicationJournal of Power Sources, Volume 343, 2017, Pages 364-372.

Claims

1. A method for preparing a phosphonylated polymer from an initial polymer containing sulfonic acid groups, the method comprising the following steps: a) The initial polymer is converted to the -SO2Cl form using thionyl chloride by chlorosulfonation. b) The initial polymer to be converted to the -SO2Cl form is converted to a phosphonylated polymer using tris(trimethylsilyl) phosphite. The initial polymer is selected from the group consisting of: polyimide, polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketone etherketone ketone (PEKEKK), polycarbonate, polysulfone, polysulfone, polysulfide, unfluorinated and partially fluorinated polyethersulfone, unfluorinated and partially fluorinated polyetherethersulfone, polyester, and polystyrene.

2. The method of claim 1, wherein, Following step a), it is first converted to the sodium-containing form -SO2Na by reacting with sodium sulfite.

3. The method of claim 2, wherein, After being converted to sodium form, it is first converted to lithium-containing form -SO2Li by reacting with lithium chloride or lithium hydroxide or other lithium salts.

4. The method according to any one of claims 1 to 3, characterized in that, Step b) is carried out in a solvent.

5. The method of claim 4, wherein, During step b), the solvent is heated to boiling temperature.

6. The method of claim 5, wherein, The reaction mixture is heated to the boiling point of the solvent for at least 2 hours.

7. The method according to claim 1, characterized in that, After step b), the unreacted active group is reverse-reacted into a sulfonic acid group, wherein the active group is -SO2Cl, sodium-containing form, or lithium-containing form.

8. The method according to claim 1, characterized in that, The amount of tris(trimethylsilyl)phosphite is 0.1 to 5000 weight percent of the initial polymer that has been converted to the -SO2Cl form.

9. The method according to claim 1, characterized in that, The initial polymer exists as a membrane, and the method steps a) and b) are carried out by immersion in the respective reactants, wherein the membrane is rinsed by immersion in water after each method step.

10. The phosphonylated polymer prepared by the method according to any one of claims 1-9, characterized in that, The polymer contains both sulfonyl groups and phosphonic acid groups.

11. The phosphonylated polymer according to claim 10, characterized in that, The polymer is a phosphonylated polyetherketone (sPEKEKK).

12. Use of the polymer according to claim 10 or 11 in an electrochemical battery.

13. The use of the polymer according to claim 12, in low-temperature or medium-temperature fuel cells in a temperature range of -30°C to 250°C.

14. The use of the polymer according to claim 12, in a low-temperature or medium-temperature electrolytic cell in a temperature range of 0°C to 250°C.

15. The use of the polymer according to claim 12, in a chemical synthesis reactor at -70 to 250°C.

16. Use of the polymer according to claim 12 as a separator in primary and secondary batteries.

17. Use of the polymer according to claim 12 as a binder in electrodes, primary batteries and secondary batteries.

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