Phosphonated non-fluorinated and semi-fluorinated aryl polymers from sulfated aryl polymers and polymeric perfluorophosphonic acids from polymeric perfluorosulfonic acids, their manufacturing process and application in electromembrane applications

Description

State of the art:

[0001] The most frequently described phosphonated systems are based on aryl polymers synthesized by nucleophilic substitution (Michaelis-Arbusow and Michaelis-Becker rearrangement) of aryl halides and di- or trialkyl phosphite.

[0002] These phosphonated aryl polymers exhibit high thermal and chemical stability. They also exhibit good proton conductivity even in the non-humidified state. [1-5]

[0003] The disadvantage of these phosphonated aryl polymers, e.g., from DE 10 2011 015 212 A1, is that they are extremely brittle in the non-hydrogenated, i.e., dry, state, making it impossible to produce functional membranes. This brittle behavior increases with increasing temperature and decreasing humidity, leading to mechanical failure of the membrane. This makes the use of these polymers as membranes for electromembrane processes at temperatures above 100°C impossible.

[0004] Patent US6680346B1 by Kyoji Kimoto describes a direct synthesis of a phosphonated perfluorophosphonic acid. The claim refers to the following structure ( Fig. 2 ) with the ratios m is 0 or 1, n is 2 or 3, X,Y is H or C6H4SO3H and the ratio of A / B is 1.5 to 15.

[0005] EP2514773A1 reveals that the synthesized polymers in US6680346B1 are subject to cyclization due to difficult-to-control polymerization conditions, which leads to chain transfer during polymerization and thus causes a decrease in the molecular weight and mechanical strength of the materials. With increasing molar ratios of short-chain phosphonyl-containing monomer to tetrafluoroethylene monomer, this side reaction is further promoted, limiting the increase in ion exchange capacity and material stability.

[0006] WO 2007 / 101415 A2 relates to polymeric materials for the production of membranes in electrochemical cells and, among other things, aims to achieve the highest possible proton conductivity even under reduced humidity. The polymers used – preferably polyaryl ethers – can, among other things, carry sulfonic and phosphonic acid groups (claim 1; Figures 12, 22, and 27).

[0007] The process claimed here does not have this limitation, since polymeric perfluorosulfonic acids can nowadays be produced in consistent quality, examples of which are described in Fig. 1 to see.

[0008] The described phosphonation reaction thus leads to a new, stable class of polymeric perfluorophosphonic acids and does not have the disadvantages of US6680346B1. The same applies to sulfonated aryl polymers: if the base polymer already has good mechanical properties, it retains these properties in its new form as a phosphonated polymer. Description of the invention

[0009] The inventive step is based on finding and synthesizing new phosphonated polymers that are proton-conducting and chemically and mechanically stable even in the dry state. This is achieved by first converting sulfonated polymers, which already exhibit good mechanical properties and possess sulfonic acid groups, into the -SO 2 Cl form by sulfochlorination with thionyl chloride. Starting from the -SO 2 Cl form, one can already phosphonate with trialkyl phosphites such as tris(trimethylsilyl)phosphite (TTMSP), or convert the -SO 2 Cl form into the -SO 2 Na (sodium sulfonate) form with sodium sulfite and phosphonate this form, or further convert the -SO 2 Na form into the -SO 2 Li (lithium sulfonate) form and phosphonate this form in turn. Using this process, phosphonated polymers with high mechanical flexibility, chemical stability and high proton conductivity can be synthesized from all polymers containing sulfonic acid groups.The polymers, which already possess good mechanical and chemical properties in their sulfonated form, retain these properties after phosphonation and, unlike the sulfonic acid-containing polymers, are also very good proton conductors above 100°C. Fig. 3 )

[0010] The reaction should be as efficient and simple as possible, which is the case here.

[0011] The phosphonated polymers should be soluble in common solvents so that they can be used to produce membranes.

[0012] With the synthesis method described here, the phosphonated polymer can in principle be synthesized from all sulfonated polymers.

[0013] The invention is based on the insertion of a reactive group -X into a sulfonated polymer (-X can be -SO 2 Cl, -SO 2 Na, -SO 2 Li) and the reaction of the reactive group with trialkyl phosphites such as tris(trimethylsilyl)phosphite (TTMSP).

[0014] Depending on the degree of phosphonation, the phosphonated polymers may still contain free reactive groups -X. These free groups can be used to subsequently covalently crosslink the phosphonated polymers or to convert the unreacted groups back to the -SO 3 H form, thus obtaining a polymer containing both sulfonated and phosphonated groups.

[0015] Phosphonation can take place in solution. For this purpose, the polymers with the reactive -X group can be dissolved in solvents such as N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), etc. TTMSP can be added either before, directly during the dissolution process, or after the polymers have dissolved. Depending on the desired degree of phosphonation, 0.1 wt.% (weight percent) for a low degree of phosphonation, up to 5000 wt.% for a high degree of phosphonation, based on the polymer weight, is added.

[0016] The reaction works best and fastest in high-boiling solvents such as NMP, DMAc, and DMSO. During the reaction, gas evolution is observed, indicating when the reaction starts or ends. Gas evolution is no longer observed.

[0017] The reaction is maintained at reaction temperature (60-200°C), depending on the polymer used, its molecular mass, and solvent, until gas evolution stops. The reaction is then maintained at temperature for another 2-8 hours to ensure complete reaction.

[0018] Subsequently, reaction by-products and excess TTMSP are removed by distillation and the phosphonated polymer, in the form of its trimethylsilyl ester, remains in the solvent.

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

[0020] To completely remove hydrolysis byproducts, the polymer can simply be washed with water, depending on the degree of phosphonation. Non-water-soluble components can be washed out with water and filtered off, or water-soluble components can be purified by dialysis.

[0021] Another variant is not to precipitate the polymer solution in water, but after separating the excess TTMSP, to process the polymer solution from

[0015] directly into a membrane and then to hydrolyze it in hot to boiling water or to treat it with hot steam.

[0022] A corresponding exemplary reaction overview of a non-limiting embodiment is shown in Fig. 4 shown.

[0023] The resulting polymers 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 phosphonated and basic polymer can be between 99 mol% phosphonated polymer / 1 mol% basic polymer and 1 mol% phosphonated polymer / 99 mol% basic polymer.

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

[0026] The obtained polymers 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 phosphonated and basic polymer can be between 99 mol% phosphonated polymer / 1 mol% basic polymer and 1 mol% phosphonated polymer / 99 mol% basic polymer.

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

[0029] The blend membrane can be additionally doped with phosphoric acid in any desired amount. Phosphoric acid doping levels between 40 wt.% and 500 wt.% are preferred.

[0030] The resulting polymers can be used in electrochemical cells. The resulting polymers can preferably be used in low- or medium-temperature fuel cells operating in the temperature range from -30°C to 250°C or in low- or medium-temperature electrolyzers operating in the temperature range from 0°C to 250°C. Furthermore, the resulting polymers can be used in chemical synthesis reactors operating in the temperature range from -70°C to 250°C. The resulting polymers can also be used as separators in primary and secondary batteries or as binders in electrodes, primary and secondary batteries. Non-limiting example:

[0031] 2 g of a sulfonated polyether ketone ether ketone ketone (sPEKEKK) are mixed with 55 g of thionyl chloride, heated to 90°C, and refluxed. DMF (dimethylformamide) is then added, and the mixture is heated until gas evolution has ceased. The reaction is then held at temperature for a further 2 hours to ensure the reaction is complete. Excess thionyl chloride and by-products are distilled off, and the product is slurried with THF (tetrahydrofuran). The solution / suspension can then be precipitated in isopropanol or water. The product is washed until neutral and then dried. The previously sulfonated polymer is now in the -SO 2 Cl form. The product is then converted into the -SO 2 Na form in a 2 M sodium sulfite solution. The polymer is then filtered off and washed again with water to remove excess sodium sulfite.The polymer in the -SO 2 Na form is then treated with a 10 wt% LiCl solution to convert it to the -SO 2 Li form. The polymer is then washed with water to remove excess salts. Finally, the polymer is dried.

[0032] Phosphonation with TTMSP can be carried out with all three forms, -SO 2 Cl, -SO 2 Na and -SO 2 Li, with the -SO 2 Li form being preferred.

[0033] The polymer with -SO 2 Cl, -SO 2 Na or -SO 2 Li groups can now be treated with an organic solvent such as DMAc, NMP, DMSO etc. and TTMSP and phosphonated.

[0034] With polymeric perfluorosulfonic acids, the reaction can be carried out either from the polymer granules, powder, etc., as described in

[0019] to

[0021] , or the perfluorosulfonic acid membrane can be used directly. For this purpose, the perfluorosulfonic acid membrane is drawn through a hot thionyl chloride / DMF bath, in which the sulfochlorination takes place, and then drawn through a water bath for rinsing. The membrane, which is now in the -SO 2 Cl form, is then drawn through a sodium sulfite bath, forming the -SO 2 Na form, and is then drawn through a water bath again for rinsing. The membrane in the -SO 2 Na form is then drawn through a LiCl bath and converted into the -SO 2 Li form, and then washed again in a water bath.All three membrane forms, -SO2Cl, -SO2Na, and -SO2Li, can be drawn through a heated TTMSP bath and then drawn through a hot / boiling water bath to obtain the phosphonic acid form by hydrolysis. This can be done in a continuous roll-to-roll process, but is also possible in a batch process. The membrane can then be dried and reused directly. The -SO2Li form is preferred for phosphonation. Analysis of the experiment:

[0035] Here, one of the phosphonated polymers is described as an example, whose ion exchange capacity, conductivity up to 180°C ( Fig. 3 ). Determination of ion exchange capacity

[0036] 100 mg of the prepared polymer is covered with a saturated NaCl solution, stirred for approximately 2 hours, and 2 drops of bromothymol blue are added as an indicator. The protons of the phosphonated polymer exchange with the Na ions, producing HCl. This HCl can be detected by titration with 0.1 mol NaOH. From this, the IEC can be directly determined. To determine the total IEC, 3 ml of excess 0.1 M NaOH is added to the same solution, stirred for another 2 hours, and then back-titrated with HCl.

[0037] For the experiment in

[0019] , the IEC direct = 0.95 mmol / g and the IEC total = 2.2 mmol / g are obtained for the phosphonated PEKEKK (pPEKEKK). The very good proton conductivity, even above 100°C, can be seen in the conductivity measurement in Fig. 3 can be seen very clearly. In comparison, you can also see a Nafion 212 and its decrease in conductivity under the same measurement conditions at 50% RH at 30°C, dropping to 0.2% RH at 180°C.

[0038] The high conductivity at high temperatures may be due to the fact that the SO 2 group has a strong attracting effect on the electrons of the phosphonic acid group. literature

[0039] [1] Vladimir Atanasov and Jochen Kerres Highly Phosphonated Polypentafluorostyrene; Macromolecules 2011, 44, 16, 6416-6423 [2] Vladimir Atanasov, Dietrich Gudat, Bastian Ruffmann, Jochen Kerres, Highly phosphonated polypentafluorostyrene: Characterization and blends with polybenzimidazole, European Polymer Journal, Volume 49, Issue 12, 2013, Pages 3977-3985, [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, [4] Vladimir Atanasov, Jochen Kerres, ETFE-g-pentafluorostyrene: Functionalization and proton conductivity, European Polymer Journal, Volume 63, 2015, Pages 168-176, [5] Vladimir Atanasov, Andrey Oleynikov, Jiabing Xia, Sandrine Lyonnard, Jochen Kerres, Phosphonic acid functionalized poly(pentafluorostyrene) as polyelectrolyte membrane for fuel cell application Journal of Power Sources, Volume 343, 2017, Pages 364-372

Claims

1. Process for the preparation of phosphonated polymers from raw polymers containing sulfonic acid groups, comprising the following process steps: a) the raw polymer is converted to the -SO2Cl form by sulphochlorination with thionyl chloride, b) the intermediate is reacted with tris(trimethylsilyl)phosphite to form the phosphonated polymer, wherein the raw polymer is a member selected from the group consisting of polyimides, polyether ketones (PEK), polyether ether ketones (PEEK), polyetherketoneetherketoneketone (PEKEKK), polycarbonates, polysulfones, polysulphoxides, polysulphides, non- and partially fluorinated polyether sulphones, non- and partially fluorinated polyether ether sulphones, polyesters, polystyrenes, polymeric perfluorosulfonic acids.

2. Process according to claim 1, characterized in that, after process step a) conversion to the sodium form (-SO2Na) is first carried out by reaction with sodium sulphite.

3. Process according to claim 2, characterized in that, after the conversion to the sodium form, a conversion to the lithium form (-SO2Li) is first carried out by reaction with lithium chloride or lithium hydroxide or another lithium salt.

4. Process according to any one of the preceding claims, characterized in that, the method step b) is carried out in a solvent, preferably a high boiling solvent, which is a least one member selected from the group consisting of N-methylpyrolidone (NMP), dimethylacetamide (DMAc), dimethylsulfxide (DMSO).

5. Process according to claim 4, characterized in that, the solvent is heated to boiling temperature during process step b).

6. Process according to claim 5, characterized in that, the reaction mixture is heated to boiling temperature of the solvent for at least 2 hours, preferably at least 8 hours.

7. Process according to any one of the preceding claims, characterized in that, after process step b), the unreacted active groups (-SO2Cl, sodium form or lithium form) are reacted back into the sulfonic acid group.

8. Process according to any one of the preceding claims, characterized in that, the amount of tris(trimethylsilyl)phosphite is 0.1 wt-% to 5000 wt-% of the intermediate.

9. Process according to any one of the preceding claims, characterized in that, the original polymer is in the form of a membrane, the process steps a) and b) are carried out by immersion in the respective reagent, the process steps each are followed by rinsing of the membrane by immersion in water.

10. Phosphonated polymers and membranes optainable according to any of the preceding claims, characterized in that the polymer contains both sulfonic groups and phosphonic acid groups.

11. Phosphonated polymers and membranes optainable according to any one of the preceding claims, characterized in that it is a phosphonated polyetherketoneetherketoneketone (pPEKEKK).

12. Use of the polymers and membranes according to any one of claim 10 or claim 11 in electrochemical cells.

13. Use of the membranes according to claim 12 in low or medium temperature fuel cells in the temperature range from -30 °C to 250 °C.

14. Use of the membranes according to claim 12 in low or medium temperature electrolysers in the temperature range from 0 °C to 250 °C.

15. Use of the membranes according to claim 12 in chemical synthesis reactors from -70 °C to 250 °C.

16. Use of the membranes according to claim 12 as separators in primary and secondary batteries.

17. Use of the polymers according to claim 12 as binders in electrodes, primary and secondary batteries.