阅读说明：本技术 一种膦酸化聚烯烃接枝苯并咪唑类聚合物质子交换膜及其制备方法和应用 (Phosphonated polyolefin grafted benzimidazole polymer proton exchange membrane and preparation method and application thereof ) 是由 莫肇华 李素丽 李俊义 徐延铭 于 2020-05-28 设计创作，主要内容包括：本发明提供一种膦酸化聚烯烃接枝苯并咪唑类聚合物质子交换膜及其制备方法和应用。本发明所述材料由于使用聚烯烃类为主链,以HBPBI和LPBI为支链合成接枝共聚物。利用两种性质的聚合物将发生微观相分离形态构建质子传输通道,从而提高质子电导率；另外,在高温下聚烯烃类柔性主链带动HBPBI和LPBI支链运动以降低质子迁移活化能,促进磷酸或质子的迁移,提高质子电导率。利用超支化结构不仅可以容纳更多的磷酸,且超支化结构中的大量活性位点可以接枝大量的有机膦酸,双管齐下达到降低磷酸流失和提高质子电导率保持率的作用,通过本发明可以在较低的磷酸掺杂水平和低的体积溶胀率时获得高质子电导率和较高的质子电导率保持率的高温质子交换膜。(The invention provides a phosphonated polyolefin grafted benzimidazole polymer proton exchange membrane and a preparation method and application thereof. The material of the invention uses polyolefin as a main chain and uses HBPBI and LPBI as branched chains to synthesize a graft copolymer. The polymer with two properties is utilized to construct a proton transmission channel in a micro phase separation state, so that the proton conductivity is improved; in addition, the polyolefin flexible main chain drives HBPBI and LPBI branched chains to move at high temperature so as to reduce proton migration activation energy, promote migration of phosphoric acid or protons and improve proton conductivity. The hyperbranched structure can contain more phosphoric acid, a large number of active sites in the hyperbranched structure can be grafted with a large number of organic phosphonic acids, and the effects of reducing phosphoric acid loss and improving the proton conductivity retention rate are achieved by double pipes.)

1. A graft copolymer is prepared by mixing and reacting an amino-containing linear benzimidazole polymer, an amino-containing hyperbranched benzimidazole polymer, a partially phosphonated olefin polymer with a side chain containing carboxyl and carboxyl-containing phosphonic acid.

2. The graft copolymer of claim 1, wherein the partially phosphonated olefin polymer has a degree of phosphonated extent of 5% to 95%.

3. The graft copolymer according to claim 1, wherein the graft copolymer is prepared by condensation reaction of terminal amino groups in amino-containing linear benzimidazole polymers and amino-containing hyperbranched benzimidazole polymers with carboxyl groups on side chains to obtain side chains amino-containing polyolefin graft (hyperbranched and linear) benzimidazole polymers; and then, further grafting phosphonic acid containing carboxyl on the polyolefin graft (hyperbranched and linear) benzimidazole polymer with the side chain containing amino to obtain the graft copolymer, which is marked as a phosphonated (polyolefin graft (hyperbranched and linear) benzimidazole polymer) graft copolymer.

4. The graft copolymer according to any one of claims 1 to 3, wherein the graft copolymer contains a structural unit represented by the following formula (I):

in the formula (I), R' is selected from H and alkyl; r' is selected from the group consisting of absent, substituted or unsubstituted arylene, substituted or unsubstituted alkylene, wherein the substituents may be selected from the group consisting of alkyl, carboxyl, halogen; r₁Through a terminal amino group (-NH)₂) Linear benzimidazole polymer chain segments containing amino groups grafted to the main chain of the partially phosphonated olefin polymer after undergoing a condensation reaction with-COOH on R'; r₂Through a terminal amino group (-NH)₂) A phosphorylated hyperbranched benzimidazole polymer chain segment grafted to a partially phosphorylated olefin polymer backbone after undergoing a condensation reaction with-COOH on R'; r₅A residue selected from carboxyl-containing phosphonic acids; r₆A residue selected from amino-containing phosphonic acids; m is an integer between 100 and 50000;

when R' is absent, z is 0, 1 is more than or equal to x1+ x2>0, y1+ y2 is 1-x1-x 2; when R' is arylene or alkylene, 1> z ≧ 0, 1 ≧ x1+ x2>0, y1+ y2 ═ 1-z-x1-x 2.

5. The graft copolymer according to any one of claims 1 to 4, wherein the polyolefin graft (hyperbranched and linear) benzimidazole polymer having amino groups in its side chains comprises structural units of formula (I'):

in the formula (I '), R', R₁、R₆M, x1, x2, y1, y2, z are as defined above, R is₂' is through terminal amino group (-NH)₂) And (3) the hyperbranched benzimidazole polymer containing amino groups grafted to the main chain of the partially phosphonated olefin polymer after undergoing a condensation reaction with-COOH on R'.

6. The graft copolymer of any one of claims 1 to 5, wherein the hyperbranched benzimidazole polymer is selected from at least one of the following structures of formula (VI) to formula (VII):

in formulae (VI) to (VII), X is as defined above; n2 is an integer between 1 and 100; represents a branch point; r₃At least one selected from the following structures:

denotes a connection point;

the linear benzimidazole polymer is selected from at least one of the following structures of formula (VIII), formula (IX) or formula (X):

in the formulae (VIII) to (X), X is selected from,-S-, -O-, halogen substituted or unsubstituted C_1-6An alkyl group; r₄Selected from halogen substituted or unsubstituted C_1-8Alkylene, halogen substituted orUnsubstituted C_6-20An arylene group; n1 is an integer between 1 and 5000.

7. The graft copolymer according to any one of claims 1 to 6, wherein the amino group-containing hyperbranched benzimidazole polymer has the following structure:

wherein, n2 and R₃And X is as defined above, n' is an integer between 1 and 100, and X is a branching point.

8. The graft copolymer according to any one of claims 1 to 7, wherein the partially phosphonated olefin-based polymer having a carboxyl group in a side chain has a structural formula (VIII) below:

in formula (VIII), t ═ x1+ x2+ y1, R', R₆M, z, x1, x2, y1, y2 are as defined above. Further, y2/(y2+ t) is 0.05 to 0.95.

9. The graft copolymer of any one of claims 1 to 8, wherein the amino group-containing phosphonic acid is selected from at least one of 4-amino-1-hydroxybutylidene-1, 1-diphosphonic acid (alendronic acid), 4-aminobutylphosphonic acid, 2-aminoethylphosphonic acid, 3-aminobutylphosphonic acid, 3-aminopropylphosphonic acid, (1-aminoethyl) phosphonic acid, (1-aminopropyl) phosphonic acid, (1-aminobutyl) phosphonic acid, 2-amino-5-phosphonovaleric acid, 5-aminopentylphosphonic acid, 4-aminopentylphosphonic acid, 3-aminopentylphosphonic acid, (4-aminophenyl) phosphonic acid, (3-aminophenyl) phosphonic acid, (2-aminophenyl) phosphonic acid; preferably, at least one selected from the group consisting of 4-amino-1-hydroxybutylidene-1, 1-diphosphonic acid (alendronic acid), 4-aminobutylphosphonic acid, 2-aminoethylphosphonic acid, 3-aminobutylphosphonic acid;

the carboxyl group-containing phosphonic acid is selected from phosphonoacetic acid, phosphonopropionic acid, phosphonobutyric acid, 5-phosphonovaleric acid, 6-phosphonohexanoic acid, 7-phosphonoheptanoic acid, 8-phosphonooctanoic acid, 9-phosphonononanoic acid, 10-phosphonodecanoic acid, 11-phosphonoundecanoic acid, 16-phosphonohexadecanoic acid, 3-phosphonopropionic acid, 4-phosphonobutyric acid, DL-2-amino-3-phosphonopropionic acid, DL-2-amino-4-phosphonobutyric acid, DL-2-amino-5-phosphonovaleric acid, DL-2-amino-6-phosphonohexanoic acid, DL-2-amino-7-phosphonoheptanoic acid, N-phosphono-2-amino-4-phosphono-butanoic acid, N-, 4-phosphobutyric acid, 2- (phosphomethyl) pentanedioic acid, 4-phosphorylbenzoic acid, 3-phosphorylbenzoic acid, and glyphosate.

10. A proton exchange membrane comprising the graft copolymer of any one of claims 1-9. Preferably, the proton exchange membrane is also doped with phosphoric acid; and/or the doping level ADL of the phosphoric acid is less than 10; and/or the volume swelling ratio of the proton exchange membrane is less than 200%.

Technical Field

The invention relates to a high-temperature proton exchange membrane, in particular to a phosphonated polyolefin grafted benzimidazole polymer proton exchange membrane and a preparation method and application thereof.

Background

Benzimidazole Polymers (PBIs) are polymers containing benzimidazole rings in a main chain structure, have excellent physicochemical properties such as chemical stability, thermal stability, flame retardance, mechanical property and the like, and are widely applied to high-temperature-resistant fabrics, fireproof flame-retardant materials, industrial product filter materials and the like. With the development of fuel cell research, the conventional perfluorosulfonic acid proton exchange membrane cannot meet the operation of the fuel cell under the conditions of high temperature and low humidity due to the defects of proton conductivity, mechanical property reduction and the like under the conditions of high temperature and low humidity, and researchers begin to search and research novel proton exchange membrane materials. PBIs are favored because of their excellent chemical and thermal stability, and researchers have found that although PBIs are not proton conductive, PBIs exhibit basicity due to their specific imidazole ring structure, and protonate with inorganic acids, especially Phosphoric Acid (PA), to form ion pairs, resulting in certain ionic conductivity.

In the field of high temperature proton exchange membranes, the proton conductivity of PBIs-based proton exchange membranes is strongly dependent on their phosphoric acid doping level (ADL, number of moles of phosphoric acid incorporated per mole of polymer repeat unit), and the high proton conductivity of such membranes requires the incorporation of large amounts of phosphoric acid, which leads to a significant reduction in the mechanical properties of the membrane, and for this reason the mechanical properties of the membrane are significantly reducedBalance between proton conductivity and mechanical properties is required; in addition, more phosphoric acid is easy to run off along with water generated by the cathode in the using process, and the proton conductivity of the membrane is reduced. The conventional solution to the above problems is crosslinking, incorporation of proton carriers such as zirconium phosphate, heteropoly acid, ionic liquid, etc., or introduction of SiO₂、TiO₂Clay, zeolite, and montmorillonite. In the prior art, a cross-linking type high-temperature proton exchange membrane is formed by self-crosslinking by taking polybenzimidazole as a polymer framework and triazole ionic liquid-based polyethylene as a cross-linking agent; in the prior art, it has also been reported that 0.1-30% of acid modified ordered mesoporous SiO is doped into the composite high-temperature proton exchange membrane₂The proton transfer is promoted, and the proton conductivity is improved; or doping inorganic porous materials in the PBIs membrane to prepare the composite membrane.

Therefore, how to reduce the phosphoric acid doping level in the PBIs matrix proton exchange membrane doped with phosphoric acid and obtain high proton conductivity and high conductivity retention rate under the high-temperature anhydrous condition is a very challenging research direction and has a very good research and application prospect.

Disclosure of Invention

As mentioned above, the benzimidazole polymer as a proton exchange membrane material has the problem of how to achieve higher proton conductivity and conductivity retention rate under the condition of less phosphoric acid. Therefore, the invention designs and synthesizes the graft copolymer which takes the polyolefin as the main chain and takes the linear benzimidazole polymer (LPBI) and the Hyperbranched Benzimidazole Polymer (HBPBI) as the branched chain, and the graft copolymer can construct a proton transmission channel through the phase separation structure of two chain segments, thereby improving the proton conductivity. A large amount of organic phosphonic acid can be introduced through the multi-terminal group characteristic of the hyperbranched structure. The hyperbranched benzimidazole polymer is a dispersed spherical molecule, intermolecular entanglement is less, so that intermolecular action is weak, swelling is increased after phosphoric acid is soaked, mechanical property is reduced, linear benzimidazole polymer is introduced, protons can be conducted, intermolecular action can be formed between the linear benzimidazole polymer and the hyperbranched polybenzimidazole, swelling resistance of the membrane is improved, and the mechanical property is improved, so that the high-temperature proton exchange membrane (the highest proton conductivity can reach 0.09S/cm) and the high proton conductivity retention rate (the highest proton conductivity can reach 90%) can be obtained under the conditions of lower phosphoric acid doping level (ADL <10) and lower volume swelling rate (less than 200%) (the test temperature reaches 180 ℃).

Specifically, the invention provides the following technical scheme:

a graft copolymer is prepared by mixing and reacting an amino-containing linear benzimidazole polymer, an amino-containing hyperbranched benzimidazole polymer, a partially phosphonated olefin polymer with a side chain containing carboxyl and carboxyl-containing phosphonic acid.

The graft copolymer is prepared by condensation reaction of terminal amino in linear benzimidazole polymer containing amino and hyperbranched benzimidazole polymer containing amino and carboxyl of partially phosphonated olefin polymer with side chain containing carboxyl to obtain polyolefin graft (hyperbranched and linear) benzimidazole polymer with side chain containing amino; and then, further grafting phosphonic acid containing carboxyl on the polyolefin graft (hyperbranched and linear) benzimidazole polymer with the side chain containing amino to obtain the graft copolymer, which is marked as a phosphonated (polyolefin graft (hyperbranched and linear) benzimidazole polymer) graft copolymer.

The invention also provides a preparation method of the graft copolymer, which comprises the following steps:

(1) mixing olefin polymer with side chain containing carboxyl and phosphonic acid containing amino, and reacting to obtain partially phosphonated olefin polymer with side chain containing carboxyl;

(2) dissolving linear benzimidazole polymer containing amino, hyperbranched benzimidazole polymer containing amino, olefin polymer with partial phosphonic acid containing carboxyl on side chains and phosphonic acid containing carboxyl in an organic solvent, mixing, and reacting under a heating condition to prepare the graft copolymer.

The invention also provides a proton exchange membrane which comprises the graft copolymer.

Wherein, the proton exchange membrane is also doped with phosphoric acid.

The invention also provides a preparation method of the proton exchange membrane, which comprises the following steps:

(s1) mixing the olefin polymer having carboxyl in the side chain and phosphonic acid having amino group, and reacting to obtain partially phosphonated olefin polymer having carboxyl in the side chain;

dissolving linear benzimidazole polymer containing amino, hyperbranched benzimidazole polymer containing amino, olefin polymer with partial phosphonic acid containing carboxyl on side chains and phosphonic acid containing carboxyl in an organic solvent, mixing, and reacting under heating;

(s2) after the reaction is finished, pouring the solution into the surface of the base material for tape casting while the solution is hot, volatilizing the solvent at the temperature of 60-120 ℃, and obtaining a polymer film after the solvent is completely volatilized;

(s3) soaking the polymer membrane obtained in the step (s2) in a phosphoric acid solution, taking out and drying to obtain the phosphoric acid doped proton exchange membrane.

The invention also provides the application of the proton exchange membrane in the fields of fuel cells, flow batteries and the like.

It is to be understood that the above-described technical features of the present invention and the respective technical features described in detail hereinafter may be combined with each other to constitute a new or preferred technical solution.

The invention has the beneficial effects that:

the material of the invention uses polyolefin as a main chain and uses HBPBI and LPBI as branched chains to synthesize a graft copolymer. The polymer with two properties is utilized to construct a proton transmission channel in a micro phase separation state, so that the proton conductivity is improved; in addition, the polyolefin flexible main chain drives HBPBI and LPBI branched chains to move at high temperature so as to reduce proton migration activation energy, promote migration of phosphoric acid or protons and improve proton conductivity. The hyperbranched structure can contain more phosphoric acid, a large number of active sites in the hyperbranched structure can be grafted with a large number of organic phosphonic acids, and the effects of reducing phosphoric acid loss and improving the proton conductivity retention rate can be achieved under double conditions, so that the high-temperature proton exchange membrane (the test temperature reaches 180 ℃) with high proton conductivity (0.09S/cm) and high proton conductivity retention rate (the highest proton conductivity can reach 90%) can be obtained at a lower phosphoric acid doping level (ADL < 10%) and a low volume swelling rate (less than 200%).

Drawings

FIG. 1 is a schematic representation of the molecular structure of examples 1-6.

FIG. 2 is a schematic representation of the molecular structure of examples 7-12.

Detailed Description

< graft copolymer >

A graft copolymer is prepared by mixing and reacting an amino-containing linear benzimidazole polymer, an amino-containing hyperbranched benzimidazole polymer, a partially phosphonated olefin polymer with a side chain containing carboxyl and carboxyl-containing phosphonic acid.

According to the invention, the partially phosphonated olefin polymer has a degree of phosphonated content of 5% to 95%, for example 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 88%, 90% or 95%.

According to the invention, the graft copolymer is firstly a condensation reaction of terminal amino groups in amino-containing linear benzimidazole polymers and amino-containing hyperbranched benzimidazole polymers and carboxyl groups of partially phosphonated olefin polymers with side chains containing carboxyl groups to obtain polyolefin graft (hyperbranched and linear) benzimidazole polymers with side chains containing amino groups; and then, further grafting phosphonic acid containing carboxyl on the polyolefin graft (hyperbranched and linear) benzimidazole polymer with the side chain containing amino to obtain the graft copolymer, which is marked as a phosphonated (polyolefin graft (hyperbranched and linear) benzimidazole polymer) graft copolymer.

Specifically, the graft copolymer contains a structural unit represented by the following formula (I):

in the formula (I), R' is selected from H and alkyl; r' is selected from the group consisting of absent, substituted or unsubstituted arylene, substituted or unsubstituted alkylene, wherein the substituents may be selected from the group consisting of alkyl, carboxyl, halogen; r₁Through a terminal amino group (-NH)₂) Linear benzimidazole polymer chain segments containing amino groups grafted to the main chain of the partially phosphonated olefin polymer after undergoing a condensation reaction with-COOH on R'; r₂Through a terminal amino group (-NH)₂) A phosphorylated hyperbranched benzimidazole polymer chain segment grafted to a partially phosphorylated olefin polymer backbone after undergoing a condensation reaction with-COOH on R'; r₅A residue selected from carboxyl-containing phosphonic acids; r₆A residue selected from amino-containing phosphonic acids; m is an integer between 100 and 50000;

when R' is absent, z is 0, 1 is more than or equal to x1+ x2>0, y1+ y2 is 1-x1-x 2; when R' is arylene or alkylene, 1> z ≧ 0, 1 ≧ x1+ x2>0, y1+ y2 ═ 1-z-x1-x 2.

Wherein x1+ x2 is preferably 0.05 to 0.5, more preferably 0.1 to 0.4, and even more preferably 0.15 to 0.3.

Wherein x1/x2 is 1/18-9/1.

Wherein y2 is 0.05-0.95.

Wherein z is 0 to 0.8.

Specifically, the R' is selected from H, C_1-6An alkyl group; still more specifically, said R "is selected from H, methyl.

Specifically, R' is selected from the group consisting of absent, substituted or unsubstituted alkylene, substituted or unsubstituted phenylene, wherein the substituent may be selected from the group consisting of alkyl, carboxyl. For example, the R' is selected from absent, or one or more of the following:

wherein denotes the connection point.

Specifically, the polyolefin grafted (hyperbranched and linear) benzimidazole polymer with the side chain containing amino contains a structural unit shown as the following formula (I'):

in the formula (I '), R', R₁、R₆M, x1, x2, y1, y2, z are as defined above, R is₂' is through terminal amino group (-NH)₂) And (3) the hyperbranched benzimidazole polymer containing amino groups grafted to the main chain of the partially phosphonated olefin polymer after undergoing a condensation reaction with-COOH on R'.

More specifically, the molecular structural formula of the polyolefin grafted (hyperbranched and linear) benzimidazole polymer with the side chain containing amino is one of the following:

wherein, x1, x2, y1, y2, z, m, R₁And R₂' is as defined above; ar is selected from one or more of the following groups:

denotes the connection point.

Specifically, the linear benzimidazole polymer is a linear benzimidazole polymer which contains benzimidazole rings in a main chain structure and does not contain branched chains. More specifically, the linear benzimidazole polymer containing amino groups is a linear benzimidazole polymer containing benzimidazole rings in a main chain structure, and one end of the linear benzimidazole polymer is connected with amino (-NH)₂) Linear benzimidazole polymers containing no side chain. The polymerization degree n1 of the linear benzimidazole polymer can be 1-5000 according to requirements.

Specifically, the hyperbranched benzimidazole polymer is a polymer with a main chain structure containing benzimidazole rings and a side chain containing a branched structure. In still another embodiment, the composition comprisesThe hyperbranched benzimidazole polymer of amino is a main chain structure containing benzimidazole ring, the side chain contains branched structure, and one end of the main chain and one end of the branched structure are connected with amino (-NH)₂) The polymer of (1). According to requirements, the polymerization degree n2 of the hyperbranched benzimidazole polymer can be 1-100.

Specifically, the hyperbranched benzimidazole polymer is prepared by taking a compound containing three carboxyl groups and a compound containing four amino groups as monomers and performing solution condensation reaction.

Wherein, the compound containing three carboxyl groups is, for example, a six-membered ring compound containing three carboxyl groups; substituted or unsubstituted, straight or branched chain aliphatic compounds containing three carboxyl groups (e.g., alkanes); or at least one compound having a structure represented by the following formula (III):

in formula (III), Y is selected from absent,-S-、-O-、

Wherein the six-membered ring compound may be benzene, pyridine or imidazole; the aliphatic compound may be C_3-10An alkane; the substituent may be H₂PO₃、C_1-6An alkyl group.

Specifically, the compound containing three carboxyl groups is selected from:

specifically, the compound containing four amino groups is selected from at least one of the following structures of formula (IV) or formula (V):

in the formula (IV), X is selected from,-S-、-O-、Halogen substituted or unsubstituted C_1-6An alkyl group.

Specifically, the hyperbranched benzimidazole polymer is selected from at least one of the following structures of formula (VI) to formula (VII):

in formulae (VI) to (VII), X is as defined above; n2 is an integer between 1 and 100; represents a branch point; r₃Selected from the group consisting of residues of compounds containing three carboxyl groups.

In particular, R₃At least one selected from the following structures:

denotes the connection point.

In one embodiment of the invention, X is selected from absent,-S-、-O-、-C(CH₃)₂-、-C(CF₃)₂-、-CH₂-。

Illustratively, the hyperbranched benzimidazole polymer is selected from at least one of the following structures:

wherein n2 and R₃As defined above, is a branch point.

Specifically, the linear benzimidazole polymer is selected from at least one of the following structures of formula (VIII), formula (IX) or formula (X):

in the formulae (VIII) to (X), X is selected from,-S-, -O-, halogen substituted or unsubstituted C_1-6An alkyl group; r₄Selected from halogen substituted or unsubstituted C_1-8Alkylene, halogen substituted or unsubstituted C_6-20An arylene group; n1 is an integer between 1 and 5000.

In one embodiment of the present invention, R is₄Selected from halogen substituted or unsubstituted C_3-8Alkylene, halogen substituted or unsubstituted C_6-16Arylene radicals, e.g. selected from-C₆H₄-、-C₆H₄-C₆H₄-、-C₆H₄-O-C₆H₄-、-C₆H₄-C(CH₃)₂-C₆H₄-、-C₆H₄-C(CF₃)₂-C₆H₄-、-C₆H₄-CH₂-C₆H₄-、-CH₂-C₆H₄-CH₂-、-(CH₂)_4-8-、-(CF₂)_3-6-。

Illustratively, the linear benzimidazole polymer is selected from at least one of the following structures:

wherein n1 is an integer between 1 and 5000; r₄Selected from the following structuresOne of them is:

denotes the connection point.

Also illustratively, the structure of the amino group-containing hyperbranched benzimidazole polymer is shown as follows:

wherein, n2 and R₃And X is as defined above, n' is an integer between 1 and 100, and X is a branching point.

According to the present invention, the structural formula of the partially phosphonated olefin-based polymer having a carboxyl group in a side chain is shown as the following formula (VIII):

in formula (VIII), t ═ x1+ x2+ y1, R', R₆M, z, x1, x2, y1, y2 are as defined above. Further, y2/(y2+ t) is 0.05 to 0.95.

According to the invention, the partially phosphonated olefin polymer with side chain containing carboxyl is prepared after the grafting reaction of the olefin polymer with side chain containing carboxyl and phosphonic acid containing amino.

Wherein the molar ratio of the amino-containing phosphonic acid to the carboxyl functional groups in the olefin polymer with the side chains containing carboxyl groups is 0.05-0.95: 1.

Specifically, the olefin polymer having a carboxyl group in a side chain is at least one selected from polyacrylic acid (PAA), polymethacrylic acid (PMAA), and carboxylated polystyrene.

Specifically, the structural formula of the amino-containing phosphonic acid is NH₂-R₆-H₂PO₃(ii) a Wherein R is₆Is as defined above.

Still more specifically, the amino group-containing phosphonic acid is selected from at least one of 4-amino-1-hydroxybutylidene-1, 1-diphosphonic acid (alendronic acid), 4-aminobutylphosphonic acid, 2-aminoethylphosphonic acid, 3-aminobutylphosphonic acid, 3-aminopropylphosphonic acid, (1-aminoethyl) phosphonic acid, (1-aminopropyl) phosphonic acid, (1-aminobutyl) phosphonic acid, 2-amino-5-phosphonovaleric acid, 5-aminopentylphosphonic acid, 4-aminopentylphosphonic acid, 3-aminopentylphosphonic acid, (4-aminophenyl) phosphonic acid, (3-aminophenyl) phosphonic acid, (2-aminophenyl) phosphonic acid; preferably, it is selected from at least one of 4-amino-1-hydroxybutylidene-1, 1-diphosphonic acid (alendronic acid), 4-aminobutylphosphonic acid, 2-aminoethylphosphonic acid, 3-aminobutylphosphonic acid.

Specifically, the structural formula of the phosphonic acid containing carboxyl is COOH-R₅-H₂PO₃(ii) a Wherein R is₅Is as defined above.

Still more specifically, the carboxyl group-containing phosphonic acid is selected from phosphonoacetic acid, phosphonopropionic acid, phosphonobutyric acid, 5-phosphonovaleric acid, 6-phosphonohexanoic acid, 7-phosphonoheptanoic acid, 8-phosphonooctanoic acid, 9-phosphonononanoic acid, 10-phosphonodecanoic acid, 11-phosphonoundecanoic acid, 16-phosphonohexadecanoic acid, 3-phosphonopropionic acid, 4-phosphonobutyric acid, DL-2-amino-3-phosphonopropionic acid, DL-2-amino-4-phosphonobutyric acid, DL-2-amino-5-phosphonovaleric acid, DL-2-amino-6-phosphonohexanoic acid, DL-2-amino-7-phosphonoheptanoic acid, DL-2-amino-6-phosphono-hexanoic acid, DL-4-phosphono-1, 4-phosphobutyric acid, 2- (phosphomethyl) pentanedioic acid, 4-phosphorylbenzoic acid, 3-phosphorylbenzoic acid, and glyphosate.

According to the invention, from the design of a polymer structure, firstly, partial phosphorylation is carried out on an olefin polymer with a side chain containing carboxyl by using phosphonic acid containing amino, and the partially phosphorylated olefin polymer with the side chain containing carboxyl is obtained; then, carrying out condensation reaction on terminal amino groups in the amino-containing linear benzimidazole polymers and amino-containing hyperbranched benzimidazole polymers and carboxyl groups of the partially-phosphonated olefin polymers with carboxyl groups on side chains to obtain amino-containing linear benzimidazole polymers and polymers grafted to the main chains of the partially-phosphonated olefin polymers with carboxyl groups on side chains, wherein the polymers are polyolefin grafted (hyperbranched and linear) benzimidazole polymers with amino groups on side chains; and then, further grafting phosphonic acid containing carboxyl on the polyolefin graft (hyperbranched and linear) benzimidazole polymer with the side chain containing amino to obtain the graft copolymer, and marking as a phosphonated (polyolefin graft (hyperbranched and linear) benzimidazole polymer) graft copolymer. Researches show that the proton exchange membrane containing the phosphonated graft copolymer is suitable for being used as a high-temperature proton exchange membrane, and has higher proton conductivity (up to 0.09S/cm) and higher proton conductivity retention rate (up to 90%) under the condition of lower phosphoric acid doping level (ADL <10), thereby achieving the aim of the invention.

The "halogen" in the invention refers to fluorine, chlorine, bromine or iodine.

"alkyl" used herein alone or as suffix or prefix, is intended to include both branched and straight chain saturated aliphatic hydrocarbon groups having from 1 to 20, preferably from 1 to 6, carbon atoms. For example, "C_1-6Alkyl "denotes straight-chain and branched alkyl groups having 1,2, 3, 4, 5 or 6 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, and hexyl.

"aryl" used herein alone or as a suffix or prefix, refers to an aromatic ring structure made up of 5 to 20 carbon atoms. For example: the aromatic ring structure containing 5, 6, 7 and 8 carbon atoms may be a monocyclic aromatic group such as phenyl; the ring structure containing 8, 9, 10, 11, 12, 13 or 14 carbon atoms may be polycyclic, for example naphthyl. The aromatic ring may be substituted at one or more ring positions with substituents such as alkyl, carboxyl and the like, for example tolyl.

The "alkylene" in the present invention is a group obtained by substituting one H with the "alkyl".

The "arylene" of the present invention is a group obtained by substituting one H with the "aryl".

< preparation of graft copolymer >

The invention also provides a preparation method of the graft copolymer, which comprises the following steps:

(1) mixing olefin polymer with side chain containing carboxyl and phosphonic acid containing amino, and reacting to obtain partially phosphonated olefin polymer with side chain containing carboxyl;

(2) dissolving linear benzimidazole polymer containing amino, hyperbranched benzimidazole polymer containing amino, olefin polymer with partial phosphonic acid containing carboxyl on side chains and phosphonic acid containing carboxyl in an organic solvent, mixing, and reacting under a heating condition to prepare the graft copolymer.

In one embodiment of the present invention, in the step (1), the olefin-based polymer having carboxyl groups in side chains is, for example, at least one selected from polyacrylic acid (PAA), polymethacrylic acid (PMAA), and carboxylated polystyrene.

In one embodiment of the present invention, in step (1), the molar ratio of the amino-containing phosphonic acid to the carboxyl functional groups in the side chain carboxyl-containing olefin-based polymer is 0.05 to 0.95: 1.

In one embodiment of the present invention, in the step (1), the temperature of the reaction is 100-150 ℃, and the time of the reaction is 6-24 h; the reaction is carried out under an inert atmosphere.

In one embodiment of the present invention, in the step (2), the organic solvent is one or a combination of more of the following: DMF (N, N-dimethylformamide), DMAc (N, N-dimethylacetamide), DMSO (dimethyl sulfoxide), NMP (N, N-dimethylpyrrolidone).

In one embodiment of the present invention, in step (2), the amino group-containing hyperbranched benzimidazole polymer may be commercially available or may be prepared by the following method:

and mixing a compound containing three carboxyl groups, a compound containing four amino groups and polyphosphoric acid, and reacting to prepare the amino-containing hyperbranched benzimidazole polymer.

For example, when the molar ratio of the compound containing four amino groups to the compound containing three carboxyl groups is 1.6:1 to 2.5:1, the hyperbranched benzimidazole polymer containing the amino groups is prepared.

Wherein the compound containing three carboxyl groups and the compound containing four amino groups account for 0.5-3% of the total solution by mass.

The preparation method of the amino-containing hyperbranched benzimidazole polymer specifically comprises the following steps:

dissolving a compound containing three carboxyl groups and a compound containing four amino groups in polyphosphoric acid, wherein the molar ratio of the compound containing four amino groups to the compound containing three carboxyl groups is 1.6:1-2.5:1, and reacting at 150-250 ℃ for 6-24h to prepare the amino-containing hyperbranched benzimidazole polymer.

Wherein, still include after the reaction stops: the solution is precipitated in water, then washed with deionized water for 2 times, added with sodium bicarbonate to be alkaline, and then washed with deionized water to be neutral. And collecting the solid, and drying the solid in vacuum at the temperature of 60 ℃ to obtain the hyperbranched benzimidazole polymer.

In one embodiment of the present invention, in step (2), the amino group-containing linear benzimidazole polymer may be commercially available or may be prepared by the following method:

dissolving a compound containing two carboxyl groups and a compound containing four amino groups in polyphosphoric acid according to a molar ratio of 1:1, and reacting to prepare the amino-containing linear benzimidazole polymer.

In one embodiment of the invention, in the step (2), the reaction is carried out under the protection of inert gas under the heating condition of 120-160 ℃; specifically, the reaction time is 6-24 h.

In a specific embodiment of the invention, in the step (2), the mass ratio of the amino-containing hyperbranched benzimidazole polymer to the amino-containing linear benzimidazole polymer is 90: 5-10: 90.

In one embodiment of the present invention, in the step (2), the mass ratio of the sum of the mass of the amino group-containing hyperbranched benzimidazole polymer and the amino group-containing linear benzimidazole polymer to the mass of the partially phosphonated olefin polymer having a carboxyl group in a side chain is 9 to 0.8:1, for example, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1, and 0.8: 1.

In one embodiment of the invention, in the step (2), the amount of the phosphonic acid containing carboxyl is 0.15 to 0.8 times of the molar amount of the four amino compounds used for preparing the amino-containing hyperbranched benzimidazole polymer.

In one embodiment of the present invention, in the step (2), the method specifically includes the following steps:

(2-1) simultaneously dissolving an amino-containing hyperbranched benzimidazole polymer and an amino-containing linear benzimidazole polymer in an organic solvent to obtain a solution a, and dissolving a partially phosphonated olefin polymer with a side chain containing carboxyl in the organic solution to obtain a solution b;

(2-2) dissolving a phosphonic acid containing a carboxyl group in an organic solvent to obtain a solution c;

(2-3) mixing the solution a and the solution b, reacting for 2-10 h at 120-150 ℃, then slowly dripping the solution c, and reacting for 5-12 h at the temperature.

< proton exchange Membrane and preparation thereof >

The invention also provides a proton exchange membrane which comprises the graft copolymer.

Furthermore, the proton exchange membrane is also doped with phosphoric acid.

Further, the doping level ADL of phosphoric acid is less than 10.

Further, the volume swelling ratio of the proton exchange membrane is less than 200%.

The invention also provides a preparation method of the proton exchange membrane, which comprises the following steps:

mixing olefin polymer with side chain containing carboxyl and phosphonic acid containing amino, and reacting to obtain partially phosphonated olefin polymer with side chain containing carboxyl; dissolving linear benzimidazole polymer containing amino, hyperbranched benzimidazole polymer containing amino, olefin polymer with partial phosphonic acid containing carboxyl on side chains and phosphonic acid containing carboxyl in an organic solvent, mixing, and reacting under heating;

(s2) after the reaction is finished, pouring the solution into the surface of the base material for tape casting while the solution is hot, volatilizing the solvent at the temperature of 60-120 ℃, and obtaining a polymer film after the solvent is completely volatilized;

(s3) soaking the polymer membrane obtained in the step (s2) in a phosphoric acid solution, taking out and drying to obtain the phosphoric acid doped proton exchange membrane.

In the present invention, the specific conditions in step (s1) are the same as in step (1) and step (2) in the above-mentioned production method of a graft copolymer.

In the step (s2), the base material is one of copper foil, aluminum foil, glass plate, polypropylene, polyester, polytetrafluoroethylene, and polyvinylidene fluoride.

In the step (s3), the concentration of phosphoric acid is 60 to 90 wt%.

In step (s3), the immersion time is 6 to 30 hours, for example 12 to 24 hours.

In the step (s3), the drying temperature is 60-90 ℃.

The invention also provides the application of the proton exchange membrane in the fields of fuel cells, flow batteries and the like.

The preparation method of the present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.

The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.