ARYL-ETHER-FREE POLYAROMATIC POLYMERS WITH BRANCHED STRUCTURES FOR ANION EXCHANGE MEMBRANES

Abstract

The present invention relates to a polyaromatic polymer that comprises multifunctional aromatic moieties MA, cationic groups CG and bifunctional aromatic moieties BA, wherein one or more CG and one or more BA form a linear unit L, and MA is connected to 3 to 6 linear units L. MA, CG and BA are defined as described in the specification. Furthermore, the present invention relates to a neutral precursor of the polyaromatic polymer and to an anion exchange membrane that comprises a polyaromatic polymer according to the invention.

Claims

1. A polyaromatic polymer comprising at least one multifunctional aromatic moiety MA that comprises, particularly consists of, 2 to 6, particularly 2 to 4, cyclic hydrocarbon moieties, wherein MA may be unsubstituted or substituted by one or more substituents independently selected from a C.sub.1-20-alkyl, particularly a C.sub.1-6-alkyl, cationic groups CG that are independently selected from a moiety of formula 1 or 4, ##STR00022## wherein R.sup.1 is a fully or partly fluorinated C.sub.1-6-alkyl, particularly CF.sub.3, R.sup.12 and R.sup.13 are independently of each other selected from H, C.sub.1-12-alkyl, phenyl, and C.sub.3-10-cycloalkyl, or R.sup.12 and R.sup.13 are connected to each other to form a cycloalkyl comprising 4 to 10 C atoms, D is selected from N.sup.+(R.sup.2).sub.3, P.sup.+(R.sup.2).sub.4 or a cation of piperidyl, pyrrolidinyl, imidazolyl, pyrazolyl, imidazolidinyl, particularly from N.sup.+(R.sup.2).sub.3, P.sup.+(R.sup.2).sub.4 or a cation of imidazolyl, pyrazolyl, imidazolidinyl, more particularly N.sup.+(R.sup.2).sub.3 or a cation of imidazolyl, wherein the cation of piperidyl, pyrrolidinyl, imidazolyl, pyrazolyl or imidazolidinyl is unsubstituted or substituted by one or more substituents independently selected from C.sub.1-12-alkyl, phenyl, each R.sup.2 is independently of any other R.sup.2 selected from H, C.sub.1-12-alkyl, phenyl, particularly H, C.sub.1-6-alkyl, phenyl, y is 0 or 1, x is an integer between 0 and 12, particularly 0 and 8, more particularly 6 and 8, z is 0 or 1, particularly 1, bifunctional aromatic moieties BA that are independently selected from a moiety that comprises 2 to 5, particularly 2 to 3, cyclic hydrocarbon moieties, wherein BA may be unsubstituted or substituted by one or more substituents independently selected from C.sub.1-10-alkyl, OC.sub.1-10-alkyl, a fully or partly fluorinated C.sub.1-10-alkyl, wherein one or more CG and one or more BA form a linear unit L, and MA is connected to 3 to 6, particularly 3 to 4, more particularly 3, linear units L.

2. The polyaromatic compound according to claim 1, wherein the cyclic hydrocarbon moieties of BA and MA are not connected by O, particularly the cyclic moieties of BA and MA are connected by a single bond, sharing one or more covalent bonds (fused rings), sharing a single atom (spirocyclic), and/or an alkyl.

3. The polyaromatic compound according to claim 1, wherein BA and CG alternate within the linear unit L.

4. The polyaromatic polymer according claim 1, wherein the multifunctional moiety MA is independently selected from 1,3,5-triphenylbenzene, naphthalene, biphenylene, 1H-phenalene, anthracene, phenanthrene, 1,6-dihydropyrene, 10b,10c-dihydropyrene, pyrene, 9,9-spirobi[fluorene].

5. The polyaromatic polymer according to claim 1, wherein the multifunctional moiety MA is independently selected from ##STR00023## ##STR00024## ##STR00025## ##STR00026## wherein (L) or (L.sub.m) indicates a bond to the linear unit L, each m is independently selected from 0, 1 and 2, and the sum of all m is 3, 4, 5 or 6, particularly 3 or 4, more particularly 3.

6. The polyaromatic polymer according to claim 1, wherein each bifunctional aromatic moiety BA is independently selected from a moiety of formula 2 or 3, particularly from a moiety of formula 2a, 2b or 3, ##STR00027## wherein R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are independently of each other selected from H, F, C.sub.1-6-alkyl, partly or fully fluorinated C.sub.1-6-alkyl, R.sup.7 and R.sup.8 are independently of each other selected from H, F, C.sub.1-6-alkyl, partly or fully fluorinated C.sub.1-6-alkyl, s and t are independently of each other an integer between 0 and 4, r is an integer between 0 and 3, particularly 0 and 2, more particularly 0 and 1, particularly each bifunctional aromatic moiety BA is independently selected from ##STR00028##

7. The polyaromatic polymer according to claim 1, wherein the cationic group CG is selected from a moiety of formula 1a, 1b, 1c, 1d, or 4, ##STR00029## wherein R.sup.1 is a fully or partly fluorinated C.sub.1-6-alkyl, particularly a fully fluorinated C.sub.1-6-alkyl, more particularly a fully fluorinated C.sub.1-3-alkyl, even more particularly CF.sub.3, R.sup.9, R.sup.10, R.sup.11, R.sup.14, R.sup.15 and R.sup.16 are independently of each other selected from H, C.sub.1-6-alkyl, phenyl, R.sup.12 and R.sup.13 are independently of each other selected from H, C.sub.1-6-alkyl, phenyl, C.sub.3-10-cycloalkyl, or R.sup.12 and R.sup.13 are connected to each other to form a cycloalkyl comprising 4 to 10 C atoms, R.sup.17 and R.sup.18 are independently selected from C.sub.1-6-alkyl, p and q are an integer between 0 and 3, particularly 0, R.sup.19 and R.sup.20 are independently selected from H and C.sub.1-6-alkyl, x is an integer between 0 and 12, particularly between 0 and 8, more particularly between 6 and 8, z is 0 or 1, particularly 1.

8. A precursor comprising at least one multifunctional aromatic moiety MA that comprises, particularly consists of, 2 to 6, particularly 2 to 4, cyclic hydrocarbon moieties, wherein MA may be unsubstituted or substituted by one or more substituents independently selected from a C.sub.1-20-alkyl, particularly a C.sub.1-6-alkyl, neutral groups NG that are independently selected from a moiety of formula 1 or 4, ##STR00030## wherein R.sup.1 is a fully or partly fluorinated C.sub.1-6-alkyl, particularly CF.sub.3, R.sup.12 is selected from H, C.sub.1-12-alkyl, phenyl, C.sub.3-10-cycloalkyl, D is a leaving group, particularly a leaving group selected from I, Br, Cl and OH, y is 0 or 1, x is an integer between 0 and 12, particularly 0 and 8, more particularly 6 and 8, z is 0 or 1, particularly 1, bifunctional aromatic moieties BA that are independently selected from a moiety that comprises 2 to 5, particularly 2 to 3, cyclic hydrocarbon moieties, wherein BA may be unsubstituted or substituted by one or more substituents independently selected from C.sub.1-10-alkyl, OC.sub.1-10-alkyl, a fully or partly fluorinated C.sub.1-10-alkyl, wherein one or more CG and one or more BA form a linear unit L, and MA is connected to 3 to 6, particularly 3 to 4, more particularly 3, linear units L.

9. The precursor according to claim 11, wherein the neutral group NG is independently selected from a moiety of formula 1, 1 or 4, ##STR00031## wherein R.sup.1 is a fully or partly fluorinated C.sub.1-6-alkyl, particularly CF.sub.3, R.sup.12 is selected from H, C.sub.1-6-alkyl, phenyl, C.sub.3-10-cycloalkyl, particularly C.sub.1-4-alkyl, x is an integer between 0 and 12, particularly 0 and 8, more particularly 6 and 8.

10. A precursor obtained by a reaction of a reaction mixture comprising at least one multifunctional aromatic moiety MA that comprises, particularly consist of, 2 to 6, particularly 2 to 4, cyclic hydrocarbon moieties, wherein MA may be unsubstituted or substituted by one or more substituents independently selected from a C.sub.1-20-alkyl, particularly a C.sub.1-6-alkyl, a ketone independently selected from a moiety of formula 1k or 4k, ##STR00032## wherein R.sup.1 is a fully or partly fluorinated C.sub.1-6-alkyl, particularly CF.sub.3, D is a leaving group, particularly a leaving group selected from I, Br, Cl and OH, R.sup.12 is selected from H, C.sub.1-12-alkyl, phenyl, C.sub.3-10-cycloalkyl, y is 0 or 1, x is an integer between 0 and 12, particularly 0 and 8, more particularly 6 and 8, z is 0 or 1, particularly 1, bifunctional aromatic moieties BA that are independently selected from a moiety that comprises 2 to 5, particularly 2 to 3, cyclic hydrocarbon moieties, wherein BA may be unsubstituted or substituted by one or more substituents independently selected from C.sub.1-10-alkyl, OC.sub.1-10-alkyl, a fully or partly fluorinated C.sub.1-10-alkyl wherein the reaction mixture has a pH<1.

11. The precursor according to claim 13, wherein the ratio of the sum of the molar amounts of BA and MA to the molar amount of the ketone is between 0.8 and 1.2, particularly 1:1, and/or the ratio of the molar amount of BA to the molar amount of the ketone is between 50:100 and 100:100, particularly between 95:100 and 99.5:100, and/or the ratio of the molar amount of MA to the sum of the molar amounts of the ketone and BA is between 0.1:100 and 50:100, particularly between 0.5:100 and 5:100, more particularly 1:100.

12. A polyaromatic polymer obtained by a reaction of a reaction mixture comprising the precursor according to claim 8, and a reactant selected from a halogenated C.sub.1-12-alkyl, a halogenated phenyl, or a halogenated C.sub.3-10-cycloalkyl, or N(R.sup.2).sub.3, P(R.sup.2).sub.3, with R.sup.2 being defined as above, or piperidyl, pyrrolidinyl, imidazolyl, pyrazolyl or imidazolidinyl.

13. The polyaromatic polymer according to claim 12, wherein the ratio of the molar amount of the reactant to the molar amount of the neutral group NG or to the molar amount of the ketone is 1:1 to 3:1, particularly 1.5:1 to 3:1, more particularly 3:1.

14. An anion exchange membrane comprising a polyaromatic compound according to claim 1 and a suitable counterion.

15. The polyaromatic polymer according to claim 1, wherein the polyaromatic polymer comprises one or more counterions, particularly selected from OH.sup., Cl.sup., Br.sup., I.sup., CO.sub.3.sup.2, HCO.sub.3.sup., TFA.sup. (CF.sub.3CO.sub.2.sup.), TFSA.sup. (CF.sub.3SO.sub.3.sup.), BF.sub.4.sup., PF.sub.6.sup., more particularly OH.sup. and Cl.sup., or the anion exchange membrane according to claim 14, wherein the counterion is selected from OH.sup., Cl.sup., Br.sup., I.sup., CO.sub.3.sup.2, HCO.sub.3.sup., TFA.sup. (CF.sub.3CO.sub.2.sup.), TFSA.sup. (CF.sub.3SO.sub.3.sup.), BF.sub.4.sup., PF.sub.6.sup., particularly OH.sup. and Cl.sup..

Description

DESCRIPTION OF THE FIGURES

[0277] FIG. 1 shows a section of a polymer (branched poly(terphenyl-triphenyl benzene-piperidine). The multifunctional aromatic moiety MA, the bifunctional moieties BA and the cationic groups CG are indicated.

[0278] FIG. 2 shows the preparation method of aryl-ether-free polyaromatics with branched structures. The moiety Ar in the polymer corresponds to the moiety BA, the ketone in the structure corresponds to the neutral group NG, n indicates that the polymer comprises several multifunctional moieties MA.

[0279] FIG. 3 shows possible bifunctional aromatic moieties BA.

[0280] FIG. 4 shows possible multifunctional aromatic moieties MA.

[0281] FIG. 5 shows possible ketones.

[0282] FIG. 6 shows possible cationic groups CG. Wavy lines indicate bonds to adjacent moieties of the polymer.

[0283] FIG. 7 shows the chemical structure of a branched poly(terphenyl-triphenyl benzene-piperidine).

[0284] FIG. 8 shows .sup.1H spectra of (a) a branched poly(terphenyl-triphenyl benzene-piperidine) (protonated by TFA) and (b) a branched poly(terphenyl-triphenyl benzene-piperidinium).

[0285] FIG. 9 shows stress-strain curve of PTP and b-PTP-x.

[0286] FIG. 10 shows OH.sup. conductivity remaining of b-PTP-2.5 after treatment in 1 M or 3M KOH at 80 C.

EXAMPLES

Example 1: Polymer and Membrane Preparation

[0287] A series of aryl-ether-free polyaromatics with branch structures (see the example shown in FIG. 1) was prepared. The polyaromatics comprise multifunctional aromatic moieties MA, bifunctional aromatic moieties BA and cationic groups CG. The branching degree ranges from 3 to 20.

[0288] The preparation of aryl-ether-free polyaromatics with branch structures is shown in FIG. 2. A bifunctional aromatic, a multifunctional aromatic, and a ketone were dissolved in dichloromethane. Trifluoromethanesulfonic acid (TFSA) were added to form an ether-free polyaromatic precursor. The reaction of the polyaromatic precursor with trialkyl amine (NR.sub.3) or a halogenated alkane gives a branching polyaromatic with cationic groups.

[0289] In FIG. 2, the bifunctional aromatic compound is selected from FIG. 3.

[0290] In FIG. 2, the multifunctional aromatic compound is selected from FIG. 4.

[0291] In FIG. 2, the ketone compound is selected from FIG. 5, where n is from 1 to 20, R is H or alkyl group.

[0292] After reacting with an amine or a halogenated alkane, the cationic groups (CG) of the aryl-ether-free polyaromatics are one of the groups listing in FIG. 6, where n is from 1 to 20, R1, R2, R3, R4 and R5 are alkyl groups.

[0293] One example of aryl-ether-free polyaromatics with branched structures is shown in FIG. 7.

Polymer Preparation

[0294] p-terphenyl (1 equiv.), 1,3,5-triphenylbenzene, and 1-methyl-4-piperidone (1 equiv.) were dissolved into dichloromethane. Different equivalents for 1,3,5-triphenylbenzene were used as follows: Polymers that were obtained by using 0.01 equivalents 1,3,5-triphenylbenzene are noted as b-PTP-1. Polymers that were obtained by using 0.025 equivalents 1,3,5-triphenylbenzene are noted as b-PTP-2.5. Polymers that were obtained by using 0.05 equivalents 1,3,5-triphenylbenzene are noted as b-PTP-5. PTP relates to linear polymers without 1,3,5-triphenylbenzene.

[0295] The solution was stirred at 0 C. Trifluoroacetic acid (1.5 equiv.) and trifluoromethanesulfonic acid (10 equiv.) were added. After 6 hours, the solution became viscous and was stirred for another 1 hour. The resulting dark blue gel was slowly poured into excessive water, forming a white fiber. The fiber was further washed with a 1 M KOH solution and water for three times. A branched poly(terphenyl-triphenyl benzene-piperidine) (yield 92%) was obtained after drying under vacuum at 120 C. overnight. FIG. 8(a) shows .sup.1H spectra of a branched poly(terphenyl-triphenyl benzene-piperidine) (protonated by TFA). A branch poly(terphenyl-triphenyl benzene-piperidine) was suspended in dimethyl sulfoxide. CH.sub.3I (3 equiv. to piperidone group) and K.sub.2CO.sub.3 (2 equiv. to piperidone group) were added. The solution was stirred at room temperature in a dark environment for 1 day. The resulted viscous solution was precipitated from dichloromethane, washed with water twice, and completely dried at 80 C. under vacuum. The yield of the branch poly(terphenyl-triphenyl benzene-piperidinium) is around 100%. FIG. 8(b) shows .sup.1H spectra of branch poly(terphenyl-triphenyl benzene-piperidinium).

Membrane Preparation

[0296] The polymers were dissolved in dimethyl sulfoxide, filtered through a 0.45 m PTFE filter and casted onto a glass plate. AEMs (in iodide form) were peeled off from the glass plate in contact with deionized water. AEMs in chloride ion form were obtained by ion exchanging in 1 M KCl solution at 80 C. AEMs in hydroxide form was obtained by ion exchanging in 1 M KOH solution at 80 C. The AEMs is noted as b-PTP-x, where x is the percent of triphenyl benzene to p-terphenyl.

[0297] FIG. 9 showed the stress-strain curves of PTP and b-PTP-x at ambient conditions. As comparison, PTP is the AEM with a linear structure and has 48 MPa stress and 17% strain at break under 50% RH and room temperature. The b-PTP-2.5 exhibits 58 MPa stress and 14% strain at break, thanks to the branching structure.

[0298] Table 1 shows the ion exchange capacity (IEC), water uptake, swelling ratio and OH-conductivity of PTP and b-PTP-x. b-PTP-2.5 showed high OH.sup. conductivity compared with other reported aromatic AEMs (e.g., quaternized poly(phenylene oxide)s, poly(arylene ether ketone)s and poly(arylene ether sulfone)s). The conductivity increases with temperature, due to the faster migration of ions and higher diffusivity with increasing temperature. b-PTP-2.5 has similar IEC and OH.sup. conductivity with PTP, while it has less water uptake and swelling ratio. These advantages may be beneficial for building membrane electrode assembly (MEA) in AEM fuel cells/water electrolyzers.

TABLE-US-00001 TABLE 1 Ion exchange capacity (IEC), water uptake, swelling ratio and OH.sup. conductivity of PTP and b-PTP-x IEC (mmol/g) Water uptake Swelling ration OH conductivity (%) (%) (%) (mS/cm) AEMs .sup.1H NMR titration 40 C. 80 C. 40 C. 80 C. 40 C. 80 C. PTP 2.79 2.75 95.4 109.8 30.7 33.2 81.4 137.7 b-PTP-1 2.80 2.80 85.1 98.3 25.0 30.3 84.9 138.6 b-PTP-2.5 2.80 2.84 69.5 79.5 22.7 25.9 87.1 146.7 b-PTP-5 2.81 2.87 91.4 107.4 28.5 32.5 82.2 136.3

[0299] FIG. 10 showed the remaining OH conductivity of b-PTP-2.5 after treatment in 1 M or 3M KOH at 80 C. b-PTP-2.5 showed nearly no loss of conductivity in 1 M KOH at 80 C. over 1500 h, which indicate that our AEMs has excellent ex-situ durability. The degradation of 20% conductivity can be observed in 3M KOH at 1500 h.

Example 2: Comparison to Known Polymers

[0300] The polymers according to the invention are characterized by a high molecular weight as measured by the intrinsic viscosity. A comparison to known polymers is shown in Table 2. The polymer according to the invention has higher intrinsic viscosity than others, indicating a higher molecular weight. Improved mechanical properties are associated with the high molecular weight.

TABLE-US-00002 TABLE 2 Comparison of viscosity with reported poly(aryl piperidinium)s. POLYMERS VISCOSITY (DL G.sup.1) REF. b-PTP-2.5 6.18 This work PFTP-13 4.08 Chen, Wang, Kim et al. (2021) PDTP-75 5 Chen, Hu, Wang et al. (2021) PAP-TP-x 4.71 Wang et al. (2019) PTPipQ1 0.39 (30 C.) Olsson et al. (2018) PBPA 2.18 (30 C.) Lee, Mohanty, Bae (2015) b-PTP-2.5: branched poly(terphenyl piperidinium), where X is the molar ratio of 1,3,5-triphenyl benzene to all aryl monomers in percent.

REFERENCES

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