Ultra-high molecular weight polyglutamic acid and preparation method therefor

Abstract

The present invention provides an ultra-high molecular weight polyglutamic acid and a preparation method therefor, preparing a polyglutamic acid having a molecular weight of 1,500-4,000 kDa by means of a metal hydride-promoted initiator-initiated polymerization technique, using a γ-protecting group-L-glutamic acid-N-carboxyanhydride (i.e. glutamate ester-N-carboxyanhydride) as a raw material. The present invention adopts an anionic active ring-opening polymerization process, which has low production costs and mild reaction conditions. The obtained polyglutamic acid has a high molecular weight, and can be used in the fields of drug delivery, tissue engineering materials and soft tissue repair.

Description

Ultra-high molecular weight polyglutamic acid and preparation method thereof Technical Field

[0001] The invention belongs to the technical field of biomedical material preparation, and particularly relates to ultra-high molecular weight polyglutamic acid and a preparation method thereof. Background Art

[0002] Polyglutamic acid (PGA) is a polymer composed of glutamic acid as its structural unit. Its structure is similar to that of polypeptides in living organisms, resulting in excellent biocompatibility, biodegradability, and biosafety. Furthermore, the presence of a large number of free carboxyl groups on the polyglutamic acid molecular chain allows it to be modified into active molecules for drug delivery or cross-linked with polyhydroxy or polyamine cross-linkers to form gels for use in tissue engineering. Furthermore, the carboxyl groups' ability to bind water gives polyglutamic acid high water absorption and moisturizing properties, making it useful as a moisturizing ingredient in cosmetics. These numerous advantages have made polyglutamic acid one of the most actively researched biomedical polymers.

[0003] Currently, there are three main methods for synthesizing polyglutamic acid: extraction, microbial fermentation, and chemical synthesis. The extraction method extracts polyglutamic acid from natto. Due to the low polyglutamic acid content in natto, the extraction process is complex, the production cost is high, and large-scale production is difficult. Microbial fermentation is a currently industrialized method for preparing polyglutamic acid, which can produce polyglutamic acid of 10-2000 kDa. However, its production process is complex, the molecular weight is difficult to control, and the production capacity is low. The chemical synthesis method using γ-protected group-L-glutamic acid-N-carboxyl cyclic anhydride (i.e., glutamate ester NCA, the same below) through ring-opening polymerization is an important method for synthesizing kilogram-scale polyglutamic acid. Its process is simple, the product is easy to purify, and the resulting polyglutamic acid has a controllable molecular weight and a small distribution coefficient.

[0004] In the prior art, in chemical synthesis, often under inert gas protection, alkaline reagents (such as triethylamine, sodium borohydride, sodium hydride, etc.) are used as initiators to prepare polyglutamic acid, and the preparation process usually needs to be carried out in a closed glove box. For example, patent documentation CN102666566A discloses that under argon protection, glutamate monomer is used as raw material, triethylamine, sodium borohydride or its combination is used as initiator to prepare starting polyglutamic acid benzyl ester, and then hydrolysis is performed to obtain a method for product polyglutamic acid having a molecular weight of 12-72kDa, but its product molecular weight is relatively low, and there is still a large gap with the molecular weight of microbial fermentation products obtained, and it is necessary to provide an anhydrous and oxygen-free environment, complex process, harsh reaction conditions, and higher preparation cost.

[0005] In the preparation of polyglutamic acid using ring-opening polymerization, previous work has focused on developing novel initiators to produce high-molecular-weight polyglutamate (PBG), which is then deprotected by removing the ester groups to obtain polyglutamic acid of the corresponding molecular weight. Amine compounds such as sodium hydride, potassium hydride, primary and secondary amines, transition metal complexes, hexamethyldisilazane, trimethylsilyl derivatives, Al-Schiff base complexes, rare earth metal complexes, ammonium salts, and amine-borane Lewis acid-base pairs have been developed. These initiators, used alone or in combination, have significantly increased the molecular weight of polyglutamic acid. US Patent No. 4161948A reports the use of triethylamine and sodium hydride to initiate the polymerization of polyglutamic acid and leucine NCA monomers, producing a 25 kDa polymer. Patent No. CN101511862A also reports the use of potassium hydride, sodium hydride, and cyclohexylamine to initiate the preparation of amino acid NCA copolymers, resulting in copolymers with molecular weights up to 25 kDa. Recently, Lv Hua et al. from Peking University published "J Yuan, Z Yi, Z Li, Y Wang, & L Hua. (2018). A s-sn Lewis pair-mediated ring-opening polymerization of α-amino acid n-carboxyanhydrides: fast kinetics, high molecular weight, and facile bioconjugation. ACS Macro Letters, 7, 892-897." They reported the use of trimethyltin-thiophenol as an initiator to prepare poly(benzyl glutamate) with a molecular weight of up to 800 kDa. However, the initiator thiophenol is a highly toxic compound, and the resulting polyglutamic acid is unsuitable for biomedical applications. Furthermore, the molecular weight of the resulting product is still somewhat lower than that of products obtained through microbial fermentation.

[0006] In addition, the monomer of γ-protected-L-glutamic acid-N-carboxyl ring anhydride (glutamate NCA) is sensitive to water vapor, which leads to its synthesis being mostly carried out in a glove box or using a vacuum line with experimental equipment. In order to solve this problem, Liu Runhui et al. from East China University of Science and Technology published "Wu Y, Zhang D, Ma P, et al. Lithium hexamethyldisilazide initiated superfast ring opening polymerization of alpha-amino acid N-carboxyanhydrides[J]. Nature Communications, 2018, 9(1)." which used lithium bis(trimethylsilylamide) as an initiator to react in an open system to prepare polyglutamic acid with a molecular weight of 280 kDa, solving the problem of synthesizing polyglutamic acid in an air atmosphere. However, the molecular weight of the product obtained was relatively low, which was still far behind the molecular weight of the product obtained by microbial fermentation.

[0007] Summary of the Invention

[0008] To solve the above problems, the present invention provides a method for preparing ultrahigh molecular weight polyglutamic acid by forming a composite initiation system in an air atmosphere using hydrides corresponding to highly electronegative metals (such as magnesium hydride, calcium hydride, and cuprous hydride) and initiators (such as triethylamine and pyridine) to initiate a ring-opening polymerization reaction.

[0009] The first aspect of the present invention provides an ultra-high molecular weight polyglutamic acid, which is obtained by a ring-opening polymerization reaction initiated by a composite initiation system formed by a metal hydride and an initiator and a monomer.

[0010] Furthermore, the metal hydride is selected from one or more of magnesium hydride, calcium hydride, and cuprous hydride.

[0011] Furthermore, the initiator is an organic amine compound and / or a heterocyclic compound.

[0012] Preferably, the organic amine compound is selected from one or more of triethylamine, dimethylamine, diethylamine, di-n-propylamine, diisopropylamine, N-ethylmethylamine, di-n-butylamine, diisobutylamine, di-sec-butylamine, di-tert-butylamine, dipentylamine, di-n-octylamine, diallylamine, dicyclohexylamine, and diphenylamine.

[0013] Preferably, the heterocyclic compound is selected from one or more of pyridine, aziridine, pyrrole, pyrrolidine, imidazole, indole, piperidine and purine.

[0014] In some embodiments of the present invention, the initiator is triethylamine.

[0015] In some embodiments of the present invention, the initiator is pyridine.

[0016] Furthermore, in the polymerization reaction, the molar ratio of the monomer to the initiator is (1-50):1; in the composite initiation system, the content of the metal hydride is 1-30wt% of the initiator, specifically 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, preferably 1%, 2%, 5%, 10%, 15%, 20%, 25%, 30%.

[0017] Furthermore, the monomer is glutamate-N-carboxyl cyclic anhydride.

[0018] Furthermore, the glutamate-N-carboxyl ring anhydride is a γ-alkyl-L-glutamate-N-carboxyl ring anhydride or a γ-aryl-L-glutamate-N-carboxyl ring anhydride, wherein the alkyl group is selected from methyl, ethyl, tert-butyl, allyl or tert-butyldimethyl; the aryl group is selected from benzyl, or benzyl containing a halogen atom, a phenolic hydroxyl group, a nitro group, a sulfonic acid group or other substituents, or diphenylmethyl, triphenylmethyl, ethylphenylbenzene, naphthylmethyl, anthracenemethyl, etc., and the above groups can all serve as the carboxyl protecting group at the γ position of glutamic acid.

[0019] In some embodiments of the present invention, the glutamate-N-carboxyl ring anhydride is γ-benzyl-L-glutamate-N-carboxyl ring anhydride, γ-tert-butyl-L-glutamate-N-carboxyl ring anhydride or γ-ethyl-L-glutamate-N-carboxyl ring anhydride.

[0020] Furthermore, the molecular weight of the ultra-high molecular weight polyglutamic acid is 1500-4000 kDa, and its molecular weight distribution coefficient is 1 <PD<2。

[0021] The second aspect of the present invention provides a method for preparing ultra-high molecular weight polyglutamic acid, comprising the following steps:

[0022] (1) Synthesis of polyglutamate: glutamate-N-carboxyl cyclic anhydride monomer (glutamate NCA), organic solvent A, metal hydride, and initiator are mixed and reacted to obtain polyglutamate;

[0023] (2) Synthesis of polyglutamic acid: The polyglutamate obtained in step (1), organic solvent B, and a deprotecting agent are mixed and reacted to obtain ultrahigh molecular weight polyglutamic acid;

[0024] Wherein, the molecular weight of the ultra-high molecular weight polyglutamic acid is 1500-4000 kDa, specifically 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, and 4000 kDa.

[0025] Furthermore, the glutamate-N-carboxyl ring anhydride monomer is γ-alkyl-L-glutamate-N-carboxyl ring anhydride or γ-aryl-L-glutamate-N-carboxyl ring anhydride;

[0026] Preferably, the alkyl group is selected from methyl, ethyl, tert-butyl, allyl or tert-butyldimethyl; the aryl group is selected from benzyl, benzyl containing halogen atoms, phenolic hydroxyl groups, nitro groups, sulfonic acid groups as substituents, diphenylmethyl, triphenylmethyl, ethylphenylbenzene, naphthylmethyl or anthracenemethyl;

[0027] More preferably, the glutamate-N-carboxyl ring anhydride monomer is γ-benzyl-L-glutamate-N-carboxyl ring anhydride, γ-tert-butyl-L-glutamate-N-carboxyl ring anhydride or γ-ethyl-L-glutamate-N-carboxyl ring anhydride.

[0028] The present invention finds that metal hydrides are selective. During the ring-opening polymerization process, the metal and the monomer anion (i.e., the glutamate NCA anion) form MN and MO bond-type ion pairs. The stronger the electronegativity of the metal in the metal hydride, such as calcium (1.00), magnesium (1.31), and copper (1.90) in the present invention, the weaker the ionic bond energy formed and the more inclined to covalent bonds. The ion pairs formed at this time are loose ion pairs, which have higher ion pair stability and good solubility in the system, and can better promote the chain transfer process of the initiator, thereby preparing ultra-high molecular weight polyglutamic acid. The loose ion pair chain initiation and transfer process are shown in formula (I).

[0029] And the weaker the electronegativity of metal, the easier it is to form ionic bond, and the ion pair formed is a tight ion pair, and this ion pair has poor solubility in the system, and the metal ion and monomer anion force are stronger, and are tightly combined, which is unfavorable for the carrying out of the chain transfer process. For example, the use of sodium hydride or potassium hydride and initiator triethylamine etc. reported in the patents US4161948A and CN101511862A mentioned in the background technology is smaller alone or in combination with the resulting polymer molecular weight, and the highest is only 25kDa. This may be because it has adopted sodium metal (0.93) and potassium (0.82) with weak electronegativity, formed a tight ion pair, which is unfavorable for chain transfer, and the polyglutamic acid polymerization degree of preparation is small, and molecular weight is lower. Tight ion pair chain initiation and transfer process are shown in formula (II).

[0030] Formula (I):

[0031] Formula (II):

[0032] Furthermore, in step (1), glutamate-N-carboxyl cyclic anhydride monomer is first dissolved in organic solvent A, and then a premix of metal hydride and initiator is added and mixed to react to obtain polyglutamate;

[0033] In step (2), the polyglutamate obtained in step (1) is first dissolved in an organic solvent B, and then a deprotecting agent is added and mixed to react to obtain ultra-high molecular weight polyglutamic acid.

[0034] Furthermore, in step (1), the organic solvent A is selected from one or more of dioxane, n-hexane, cyclohexane, dichloromethane, chloroform, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, ether, diisopropyl ether, acetonitrile, methanol, ethanol, ethyl acetate, benzene, and toluene, preferably dioxane.

[0035] Furthermore, in step (1), the metal hydride is selected from one or more of magnesium hydride, calcium hydride, and cuprous hydride.

[0036] Furthermore, in step (1), the initiator is an organic amine compound and / or a heterocyclic compound.

[0037] Preferably, the organic amine compound is selected from one or more of triethylamine, dimethylamine, diethylamine, di-n-propylamine, diisopropylamine, N-ethylmethylamine, di-n-butylamine, diisobutylamine, di-sec-butylamine, di-tert-butylamine, dipentylamine, di-n-octylamine, diallylamine, dicyclohexylamine, and diphenylamine.

[0038] Preferably, the heterocyclic compound is selected from one or more of pyridine, aziridine, pyrrole, pyrrolidine, imidazole, indole, piperidine and purine.

[0039] In some embodiments of the present invention, the initiator is triethylamine.

[0040] In some embodiments of the present invention, the initiator is pyridine.

[0041] Furthermore, in step (1), the molar ratio of the glutamate-N-carboxyl intracyclic anhydride monomer to the initiator is (1-50):1, specifically 1:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, preferably (5-20):1.

[0042] Furthermore, in step (1), the content of the metal hydride is 1-30wt% of the initiator, specifically 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, preferably 1%, 2%, 5%, 10%, 15%, 20%, 25%, 30%.

[0043] Furthermore, in step (1), the reaction is carried out at room temperature, specifically 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30° C.; and the reaction time is 1-5 days, specifically 1, 2, 3, 4, or 5 days.

[0044] Furthermore, the step (1) further comprises the steps of alcohol precipitation and drying of the polyglutamate.

[0045] Furthermore, the solvent used in the alcohol precipitation is ethanol.

[0046] Furthermore, in step (2), the organic solvent B is selected from one or more of dichloromethane, chloroform, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, dioxane, n-hexane, cyclohexane, ether, diisopropyl ether, acetonitrile, methanol, ethanol, ethyl acetate, benzene, and toluene, preferably dichloromethane.

[0047] Furthermore, in step (2), the deprotecting agent is a silane protecting agent selected from one or more of trimethylsilyl iodide, trimethylsilane, tert-butyldimethylsilyl chloride, triisopropylsilyl chloride, tert-butyldimethylsilyl trifluorosulfonate, and triisopropylsilyl trifluorosulfonate, preferably trimethylsilyl iodide.

[0048] Furthermore, in step (2), the molar ratio of the polyglutamate to the deprotecting agent is 1:(1-3), specifically 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, 1:2.5, 1:3, preferably 1:(1-2.5), more preferably 1:1.6.

[0049] Furthermore, in step (2), the reaction is carried out at room temperature, specifically 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30°C; and the reaction time is 12-24h, specifically 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24h.

[0050] Furthermore, the step (2) further comprises the steps of hydrolyzing the polyglutamate, layering, washing, adjusting the pH of the system, alcohol precipitation, redissolving, dialysis and freeze-drying.

[0051] Furthermore, the solvent used in the hydrolysis is water.

[0052] Furthermore, the detergent used in the washing is dichloromethane.

[0053] Furthermore, the pH value of the adjustment system is adjusted to 7-9, specifically 7, 7.2, 7.4, 7.6, 7.8, 8, 8.2, 8.4, 8.6, 8.8, and 9.

[0054] Furthermore, the solvent used in the alcohol precipitation is ethanol.

[0055] Furthermore, the solvent used for the re-dissolution is water.

[0056] The technical principle of the present invention is as follows (taking the case where the initiator is triethylamine and the protective agent is trimethyl iodosilane as an example):

[0057] Polyglutamate solution polymerization mechanism:

[0058] Chain initiation:

[0059] Chain transfer and termination:

[0060] Triethylamine, acting as a basic initiator, first protonates the glutamate-N-carboxyl ring anhydride monomer amide, forming an active initiating ion pair. This ion pair then reacts with the solid-phase metal hydride in the system at the interface, generating a metal ion-monomer active intermediate ion pair. This ion pair then attacks the NCA monomer to form a dimer. The glutamate NCA anion in the dimer forms a loose ion pair with the metal ion. This loose ion pair not only stabilizes the glutamate NCA active intermediate, but also prevents side reactions. Furthermore, the loose ion pair is highly soluble in organic solvents, and the interaction between the metal ion and the glutamate NCA anion is weak, facilitating the NCA anion's end-to-end attack on new monomers, forming a monomer active intermediate and promoting chain transfer. This allows the preparation of ultrahigh molecular weight polyglutamate.

[0061] In one embodiment of the present invention, the steps of synthesizing polybenzyl glutamate include: cleaning a Schneck tube with chromic acid and capping it with trimethylsilyl chloride, first adding γ-benzyl-L-glutamic acid-N-carboxyl ring anhydride, then adding dioxane, and then adding triethylamine containing a metal hydride, shaking well, reacting at room temperature for 3 days, and then diluting the resulting viscous solution with dioxane, adding ethanol dropwise to precipitate, and drying the precipitate to obtain polybenzyl glutamate.

[0062] In one embodiment of the present invention, the steps of synthesizing polyglutamic acid include: adding the obtained polyglutamic acid benzyl ester to dichloromethane, then adding trimethylsilyl iodide and stirring at room temperature overnight, wherein the molar ratio of trimethylsilyl iodide to polyglutamic acid benzyl ester is 1.6:1, adding water and stirring the next day to hydrolyze the trimethylsilyl polyglutamate, separating the lower layer to remove impurities, washing with dichloromethane multiple times to remove impurities in the system, using starch potassium iodide solution to test whether the iodine in the system is completely removed, adjusting the pH of the system to 7-9, and then using 5 times the volume of ethanol for precipitation, re-dissolving the obtained precipitate with purified water, dialyzing for three days to remove salt, and then freeze-drying to obtain polyglutamic acid.

[0063] In another embodiment of the present invention, the steps of synthesizing poly(tert-butyl glutamate) include: cleaning a Schneck tube with chromic acid and capping it with trimethylsilyl chloride, first adding γ-tert-butyl-L-glutamic acid-N-carboxyl ring anhydride, then adding dioxane, and then adding pyridine containing a metal hydride, shaking well, reacting at room temperature for 3 days, then diluting the resulting viscous solution with dioxane, adding ethanol dropwise to precipitate, and drying the precipitate to obtain poly(tert-butyl glutamate).

[0064] In another embodiment of the present invention, the steps of synthesizing polyglutamic acid include: adding the obtained polyglutamic acid tert-butyl ester to dichloromethane, then adding trimethylsilyl iodide and stirring at room temperature overnight, wherein the molar ratio of trimethylsilyl iodide to polyglutamic acid tert-butyl ester is 2.8:1, adding water and stirring the next day to hydrolyze the trimethylsilyl polyglutamic acid tert-butyl ester, separating the lower layer to remove impurities, washing with dichloromethane multiple times to remove impurities in the system, using starch potassium iodide solution to test whether the iodine in the system is completely removed, adjusting the pH of the system to 7-9, and then using 5 times the volume of ethanol for precipitation, re-dissolving the obtained precipitate with purified water, dialyzing for three days to remove salt, and then freeze-drying to obtain polyglutamic acid.

[0065] The third aspect of the present invention provides an application of the ultra-high molecular weight polyglutamic acid described in the first aspect or the ultra-high molecular weight polyglutamic acid prepared by the preparation method described in the second aspect in drug delivery, tissue engineering material preparation, and soft tissue repair.

[0066] Compared with the prior art, the present invention has the following outstanding features:

[0067] (1) The present invention selects specific magnesium hydride, calcium hydride, cuprous hydride metal hydride and initiator (such as organic amine or heterocyclic compound) to form a composite initiation system, and utilizes anionic active ring-opening polymerization (AARP) technology to prepare polyglutamic acid. During the ring-opening polymerization process, the metal forms MN and MO bond-type ion pairs with the monomer anion. By utilizing the strong electronegativity of the metal in the metal hydride, a loose ion pair of metal ion-monomer active intermediate can be formed with the monomer active intermediate. On the one hand, it is beneficial to stabilize the glutamate ester NCA active intermediate and avoid the occurrence of side reactions; on the other hand, the loose ion pair has good solubility in organic solvents, and the interaction between the metal ion and the polyglutamate ester NCA anion is relatively weak, which is beneficial for the glutamate ester NCA anion end to attack new monomers, forming monomer active intermediates, promoting chain transfer, and thus being able to prepare ultra-high molecular weight polyglutamic acid.

[0068] (2) The loose ion pair intermediates formed by the metal hydride-promoting initiation system used in the present invention can exist stably in non-polar solvents. After the monomers in the system have completely reacted, the monomers can be added continuously without terminating the chain growth, and the chain growth reaction can be further carried out to expand the molecular weight. The anionic living ring-opening polymerization technology of the present invention can promote chain growth and chain transfer continuously and with high stability. The molecular weight of the prepared polyglutamic acid can reach 1500-4000 kDa, providing more possibilities for the application scenarios of polyglutamic acid.

[0069] (3) The present invention utilizes a composite initiation system using a metal hydride-promoted initiator, which can be carried out in an open system at room temperature and pressure. Under glove box-free synthesis conditions, ultrahigh molecular weight polyglutamic acid (1500-4000 kDa) can be obtained, which is much higher than the molecular weight of polyglutamic acid synthesized using existing glove box ring-opening polymerization technology (30-280 kDa). The polyglutamic acid synthesis process of the present invention can be carried out outside the glove box, under mild reaction conditions, and significantly reduces production costs.

[0070] (4) The molecular weight of the polyglutamic acid prepared by the present invention is superior to that of the polyglutamic acid produced by the traditional microbial fermentation method, the molecular weight is controllable, and the molecular distribution coefficient is small; and compared with the microbial fermentation method, the process of the present invention is simple to operate and the product is easy to purify.

[0071] (5) The ultra-high molecular weight polyglutamic acid synthesized by the present invention has a wide range of uses and can be used in the fields of drug delivery, tissue engineering materials, and soft tissue repair. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] FIG1 shows a GPC molecular weight chart of poly-γ-benzyl L-glutamate prepared in Example 4 of the present invention.

[0073] FIG2 shows a GPC test molecular weight diagram of poly-L-glutamic acid prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0074] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention relates.

[0075] In the present invention, the term "room temperature" refers to a temperature close to or the same as the temperature of the space (e.g., the location of the fume hood in which the article is located). Typically, room temperature is about 20°C to about 30°C, or about 22°C to 27°C, or about 25°C.

[0076] In the present invention, the term "air atmosphere" refers to the mixed gas surrounding the earth, mainly including oxygen, carbon dioxide, nitrogen, rare gases and other substances (such as water vapor, etc.).

[0077] As used herein, the term "PD" refers to the polydispersity index, which describes the molecular weight distribution of a polymer. PD is a quantitative measure of the molecular weight distribution in a polymer and is calculated by dividing the weight-average molecular weight (Mw) by the number-average molecular weight (Mn). A smaller PD value indicates a narrower molecular weight distribution, meaning the differences between individual molecular weights are smaller. Conversely, a larger PD value indicates a wider molecular weight distribution, meaning the differences between individual molecular weights are greater. Generally, PD values ​​range from 1 to 10, with preferred polymer materials typically having a PD between 1 and 2.

[0078] The main raw materials used in this article, such as metal hydride, triethylamine, γ-benzyl-L-glutamic acid-N-carboxyl ring anhydride, γ-tert-butyl-L-glutamic acid-N-carboxyl ring anhydride, γ-ethyl-L-glutamic acid-N-carboxyl ring anhydride, and dioxane, are all commercially available products.

[0079] The disclosures of various publications, patents, and published patent specifications cited herein are incorporated by reference in their entirety.

[0080] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0081] Example 1: Preparation of Poly-L-Glutamic Acid 1 by Triethylamine Promoted by 1% Magnesium Hydride

[0082] 1. Preparation of Poly-γ-benzyl L-glutamate 1

[0083] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and a premix of ultra-dry triethylamine and magnesium hydride (0.1537 g of triethylamine and 1% of the weight of the triethylamine, magnesium hydride added to the triethylamine). The molar ratio of monomer to initiator triethylamine was 5:1. The mixture was then shaken and allowed to react at room temperature for three days. After three days, the solution became viscous. The solution was diluted with dioxane and then added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-benzyl-L-glutamic acid ester 1.

[0084] 2. Preparation of Poly-L-Glutamate 1

[0085] The obtained polyglutamate benzyl ester is added to dichloromethane, and then trimethylsilyl iodide is stirred at room temperature overnight, wherein the molar ratio of polyglutamate benzyl ester to trimethylsilyl iodide is 1:1.6. Then, water is added and stirred the next day to hydrolyze the trimethylsilyl polyglutamate. Then, the lower layer is separated to remove impurities, and dichloromethane is used for washing to remove impurities in the system several times. Then, starch potassium iodide solution is used to test whether the iodine in the system is completely removed. The pH of the system is adjusted to 7-9, and then 5 volumes of ethanol are used for precipitation. The precipitate is re-dissolved with purified water, dialyzed for three days to remove salt, and then freeze-dried to obtain poly-L-glutamic acid 1.

[0086] Example 2: Preparation of Poly-L-Glutamic Acid 2 by Triethylamine Promoted by 5% Magnesium Hydride

[0087] 1. Preparation of Poly-γ-benzyl L-glutamate 2

[0088] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and a premix of ultra-dry triethylamine and magnesium hydride (magnesium hydride was added to triethylamine to form a premix). The mixture was stirred and allowed to react at room temperature for three days. After three days, the solution became viscous and was diluted with dioxane before being added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-benzyl-L-glutamic acid ester 2.

[0089] 2. Preparation of Poly-L-Glutamate 2

[0090] The same method as step 2 in Example 1 was used to finally obtain poly-L-glutamic acid 2.

[0091] Example 3: Preparation of Poly-L-Glutamic Acid 3 by Triethylamine Promoted by 10% Magnesium Hydride

[0092] 1. Preparation of Poly-γ-benzyl L-glutamate 3

[0093] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and a premix of ultra-dry triethylamine and magnesium hydride (magnesium hydride was added to triethylamine to form a premix). The mixture was stirred and allowed to react at room temperature for three days. After three days, the solution became viscous and was diluted with dioxane before being added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-benzyl-L-glutamic acid ester 3.

[0094] 2. Preparation of Poly-L-Glutamate 3

[0095] The same method as step 2 in Example 1 was used to finally obtain poly-L-glutamic acid 3.

[0096] Example 4: Preparation of Poly-L-Glutamic Acid 4 by Triethylamine Promoted by 20% Magnesium Hydride

[0097] 1. Preparation of Poly-γ-benzyl L-glutamate 4

[0098] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and a premix of ultra-dry triethylamine and magnesium hydride (magnesium hydride was added to triethylamine to form a premix). The mixture was stirred and allowed to react at room temperature for three days. After three days, the solution became viscous and was diluted with dioxane before being added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-benzyl-L-glutamic acid ester 4.

[0099] 2. Preparation of Poly-L-Glutamate 4

[0100] The same method as step 2 in Example 1 was used to finally obtain poly-L-glutamic acid 4.

[0101] Example 5: Preparation of Poly-L-Glutamic Acid 5 by Triethylamine Promoted by 30% Magnesium Hydride

[0102] 1. Preparation of Poly-γ-benzyl L-glutamate 5

[0103] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and a premix of ultra-dry triethylamine and magnesium hydride (magnesium hydride was added to triethylamine to form a premix). The mixture was stirred and allowed to react at room temperature for three days. After three days, the solution became viscous and was diluted with dioxane before being added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-benzyl-L-glutamic acid ester 5.

[0104] 2. Preparation of Poly-L-Glutamate 5

[0105] The same method as step 2 in Example 1 was used to finally obtain poly-L-glutamic acid 5.

[0106] Example 6: Preparation of Poly-L-Glutamic Acid 6 by Triethylamine Promoted by 2% Calcium Hydride

[0107] 1. Preparation of Poly-γ-benzyl L-glutamate 6

[0108] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and a premix of ultra-dry triethylamine and calcium hydride (calcium hydride was added to triethylamine to form a premix). The mixture contained 0.1537 g of triethylamine and 2% of the mass of calcium hydride per unit weight of triethylamine, with a molar ratio of monomer to initiator of 5:1. The mixture was then shaken and allowed to react at room temperature for three days. After three days, the solution became viscous and was diluted with dioxane before being added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-benzyl-L-glutamic acid ester 6.

[0109] 2. Preparation of Poly-L-Glutamate 6

[0110] The same method as step 2 in Example 1 was used to finally obtain poly-L-glutamic acid 6.

[0111] Example 7: Preparation of Poly-L-Glutamic Acid 7 by Triethylamine Promoted by 2% Cuprous Hydride

[0112] 1. Preparation of Poly-γ-benzyl L-glutamate 7

[0113] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and a premix of ultra-dry triethylamine and cuprous hydride (0.1537 g triethylamine, 2% of the mass of triethylamine, and a molar ratio of 5:1). The mixture was shaken and allowed to react at room temperature for one day. After one day, the solution became viscous and was diluted with dioxane before being added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and dried under vacuum for 24 hours to yield poly-γ-benzyl-L-glutamic acid ester 7.

[0114] 2. Preparation of Poly-L-Glutamate 7

[0115] The same method as step 2 in Example 1 was used to finally obtain poly-L-glutamic acid 7.

[0116] Example 8: Preparation of Poly-L-Glutamic Acid 8 by Pyridine Promoted by 25% Calcium Hydride

[0117] 1. Preparation of Poly-γ-tert-butyl L-glutamate

[0118] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-tert-butyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and a premix of ultra-dry pyridine and calcium hydride (calcium hydride was added to pyridine to form a premix). The mixture contained 0.1381 g of pyridine and 25% of the pyridine mass, with a molar ratio of monomer to initiator of 5:1. The mixture was then shaken and allowed to react at room temperature for three days. After three days, the solution became viscous and was diluted with dioxane before being added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-tert-butyl-L-glutamate.

[0119] 2. Preparation of Poly-L-Glutamate 8

[0120] The obtained poly(tert-butyl glutamate) was added to dichloromethane, and then trimethylsilyl iodide was stirred at room temperature overnight, wherein the molar ratio of poly(tert-butyl glutamate) to trimethylsilyl iodide was 1:2.8. Water was then added and stirred the next day to hydrolyze the trimethylsilyl polyglutamate. The lower layer was then separated to remove impurities, and dichloromethane was used for multiple washings to remove impurities in the system. A starch potassium iodide solution was then used to test whether the iodine in the system was completely removed. The pH of the system was adjusted to 7-9, and then 5 times the volume of ethanol was used for precipitation. The precipitate was re-dissolved with purified water, dialyzed for three days to remove salt, and then freeze-dried to obtain poly-L-glutamic acid 8.

[0121] Example 9: Preparation of poly-L-glutamic acid 9 by triethylamine promoted by 2% calcium hydride, secondary monomer addition

[0122] 1. Preparation of Poly-γ-benzyl L-glutamate 8

[0123] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added to a Schneck tube under air atmosphere. 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride was then added. This was followed by 50 ml of ultra-dry dioxane and a premix of ultra-dry triethylamine and calcium hydride (calcium hydride was added to triethylamine to form a premix). The triethylamine was added in an amount of 0.1537 g and the calcium hydride was added in an amount equal to 2% of the mass of triethylamine. The molar ratio of monomer to initiator triethylamine was 5:1. The mixture was then shaken and allowed to react at room temperature for three days. After three days, the solution became viscous. Without terminating the reaction, 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride monomer was dissolved in ultra-dry dioxane and added to the reaction system. The reaction continued for an additional two days. The resulting product was diluted with dioxane and precipitated by dropwise addition to anhydrous ethanol. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-benzyl-L-glutamic acid ester 8.

[0124] 2. Preparation of Poly-L-Glutamate 9

[0125] The same method as step 2 in Example 1 was followed to finally obtain poly-L-glutamic acid 9.

[0126] Example 10: Preparation of Poly-L-Glutamic Acid 10 by Triethylamine Promoted by 10% Magnesium Hydride

[0127] 1. Preparation of Poly-γ-ethyl L-glutamate

[0128] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-ethyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and a premix of ultra-dry triethylamine and magnesium hydride (0.2008 g of triethylamine and 10% of the weight of the triethylamine). The molar ratio of monomer to initiator triethylamine was 20:1. The mixture was then shaken and allowed to react at room temperature for three days. After three days, the solution became viscous. The solution was diluted with dioxane and then added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-ethyl-L-glutamate.

[0129] 2. Preparation of Poly-L-Glutamic Acid 10

[0130] The obtained poly(ethyl glutamate) was added to dichloromethane, and then trimethylsilyl iodide was stirred at room temperature overnight, wherein the molar ratio of poly(ethyl glutamate) to trimethylsilyl iodide was 1:1.6. Then, water was added and stirred the next day to hydrolyze the trimethylsilyl poly(glutamate). Then, the lower layer was separated to remove impurities. Dichloromethane was used to wash the system several times to remove impurities. Then, starch potassium iodide solution was used to test whether the iodine in the system was completely removed. The pH of the system was adjusted to 7-9. Then, 5 volumes of ethanol were used for precipitation. The precipitate was redissolved with purified water, dialyzed for three days to remove salt, and then freeze-dried to obtain poly-L-glutamic acid 10.

[0131] Comparative Example 1: Preparation of Poly-L-Glutamic Acid 11 by Triethylamine Promoted by 35% Magnesium Hydride

[0132] 1. Preparation of Poly-γ-benzyl L-glutamate 9

[0133] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and a premix of ultra-dry triethylamine and magnesium hydride (magnesium hydride was added to triethylamine to form a premix). The mixture was stirred and allowed to react at room temperature for three days. After three days, the solution became viscous and was diluted with dioxane before being added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-benzyl-L-glutamic acid ester 9.

[0134] 2. Preparation of Poly-L-Glutamic Acid 11

[0135] The same method as step 2 in Example 1 was followed to finally obtain poly-L-glutamic acid 11.

[0136] Comparative Example 2: Preparation of Poly-L-Glutamic Acid 12 Catalyzed by Triethylamine

[0137] 1. Preparation of Poly-γ-benzyl L-glutamate 10

[0138] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and 0.1537 g of ultra-dry triethylamine (a molar ratio of monomer to initiator, triethylamine, was 5:1). The mixture was shaken and allowed to react at room temperature for three days. After three days, the solution became viscous. The solution was diluted with dioxane and then added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-benzyl-L-glutamic acid ester 10.

[0139] 2. Preparation of Poly-L-Glutamic Acid 12

[0140] The same method as step 2 in Example 1 was used to finally obtain poly-L-glutamic acid 12.

[0141] Comparative Example 3: Preparation of Poly-L-Glutamic Acid 13 by Magnesium Hydride Catalysis

[0142] 1. Preparation of Poly-γ-benzyl L-glutamate 11

[0143] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and 0.0399 g of magnesium hydride (a molar ratio of 5:1). The mixture was shaken and allowed to react at room temperature for three days. After three days, the solution became viscous. The solution was diluted with dioxane and then added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-benzyl-L-glutamic acid ester 11.

[0144] 2. Preparation of Poly-L-Glutamic Acid 13

[0145] The same method as step 2 in Example 1 was used to finally obtain poly-L-glutamic acid 13.

[0146] Comparative Example 4: Preparation of Poly-L-Glutamic Acid 14 Catalyzed by Triethylamine Containing (2%) Potassium Hydride

[0147] 1. Preparation of Poly-γ-benzyl L-glutamate 12

[0148] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and a premix of ultra-dry triethylamine and potassium hydride (0.1537 g of triethylamine, 2% of the mass of triethylamine, and a molar ratio of 5:1). The mixture was then shaken and allowed to react at room temperature for three days. After three days, the solution became viscous and was diluted with dioxane before being added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-benzyl-L-glutamic acid ester 12.

[0149] 2. Preparation of Poly-L-Glutamic Acid 14

[0150] The same method as step 2 in Example 1 was used to finally obtain poly-L-glutamic acid 14.

[0151] Comparative Example 5: Preparation of Poly-L-Glutamic Acid 15 Catalyzed by Triethylamine Containing (2%) Sodium Hydride

[0152] 1. Preparation of Poly-γ-benzyl L-glutamate 13

[0153] A Schneck tube cleaned with chromic acid and capped with trimethylsilyl chloride was added under air to 2.0 g of γ-benzyl-L-glutamic acid-N-carboxylic anhydride. This was followed by 50 ml of ultra-dry dioxane and a premix of ultra-dry triethylamine and sodium hydride (sodium hydride was added to triethylamine to form a premix). The mixture was stirred and allowed to react at room temperature for three days. After three days, the solution became viscous and was diluted with dioxane before being added dropwise to anhydrous ethanol for precipitation. The precipitate was filtered and vacuum dried for 24 hours to yield poly-γ-benzyl-L-glutamic acid ester 13.

[0154] 2. Preparation of Poly-L-Glutamic Acid 15

[0155] The same method as step 2 in Example 1 was used to finally obtain poly-L-glutamic acid 15.

[0156] Molecular weight performance test

[0157] The molecular weight of the polyglutamate obtained in the above examples and comparative examples was tested by GPC / SEC using 0.1 M LiBr in DMF as the mobile phase, the test temperature was 45° C., and polystyrene was used as the internal standard.

[0158] The obtained poly-L-glutamic acid 1-15 was further tested for its molecular weight using a GPC / SEC triple detector with 0.1 M sodium hydrogen phosphate / sodium dihydrogen phosphate buffer as the mobile phase and a test temperature of 45°C.

[0159] The test results are shown in Table 1.

[0160] Table 1: Molecular weight test of polyglutamate and poly-L-glutamic acid

[0161] Based on the above experimental data, it can be seen from Comparative Example 1-5 and Comparative Example 1 that the polymer molecular weight increases with the increase in the mass fraction of metal magnesium hydride, and the increase is significant before 20%, and is substantially unchanged between 20-30%. This is because when the mass fraction is below 30%, magnesium hydride can react with the activity of triethylamine to initiate an ion pair reaction, forming magnesium ions and NCA active intermediate ion pairs, achieving a good ion balance, and with the increase in the number of ion pairs, it is beneficial to accelerate the chain transfer process and reduce side reactions. Therefore, the molecular weight of the prepared polyglutamic acid is relatively large, and it has reached a plateau phase of equilibrium between 20% and 30%. The increase in the number of ion pairs can no longer dominate the reaction. When the ratio exceeds 30%, the introduction of excessive magnesium ions into the system will destroy the original ion balance. The destruction of the ion balance will cause free metal ions to attack the NCA monomer, forming too many active ends, and there are more side reactions, resulting in a decrease in the molecular weight of the resulting product.

[0162] As can be seen from Examples 6-7 and Comparative Examples 4-5, under the same conditions of metal hydride content (2%), the molecular weight of the polyglutamic acid product prepared in the Examples is much higher than that of the polyglutamic acid obtained in the Comparative Examples. This indicates that the reaction system is selective for metal hydrides. By selecting hydrides of highly electronegative metal ions, such as calcium and copper, these metal ions can form loose ion pairs with the NCA active intermediate, promoting chain transfer, thereby obtaining high-molecular-weight polyglutamic acid. In contrast, hydrides of less electronegative metal ions, such as sodium and potassium, form tight ion pairs with the NCA active intermediate, which is not conducive to the chain growth process, resulting in a low-molecular-weight polyglutamic acid.

[0163] As can be seen from Example 8, by screening specific metal hydrides, a composite initiation system can be formed with different organic base initiators, such as the heterocyclic compound pyridine, and glutamate ester NCA with different carboxyl protecting agents, such as γ-tert-butyl-L-glutamic acid-N-carboxyl ring anhydride, can be used as a monomer to obtain polyglutamic acid with a higher molecular weight (greater than 2000 KDa).

[0164] As can be seen from Example 9, the use of metal hydride to promote triethylamine-initiated polymerization forms a stable loose ion pair in a non-polar organic solvent. Without terminating the system, continued addition of monomers can further extend the chain and expand the molecular weight.

[0165] As can be seen from Example 2 and Comparative Examples 2 and 3, neither the metal hydride-only nor triethylamine-only comparative examples can produce high-molecular-weight polyglutamic acid. This is because magnesium hydride is in a solid state in the reaction system and, without the effect of triethylamine, it is difficult to form active initiating ion pairs, resulting in limited chain transfer and chain growth. Consequently, the molecular weight of the prepared polyglutamic acid is relatively low. Furthermore, in Comparative Example 3, which contains only triethylamine but no calcium hydride, it is impossible to form loose active intermediate ion pairs, and thus, it is impossible to produce higher-molecular-weight polyglutamic acid.

[0166] Therefore, the preparation of ultra-high polyglutamic acid is based on the use of organic amine as an initiator and the use of hydride catalysis corresponding to highly electronegative metal ions to form a composite initiation system, which can prepare ultra-high molecular weight polyglutamic acid while ensuring ion balance.

[0167] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An ultra-high molecular weight polyglutamic acid, characterized in that: The composite initiator system formed by metal hydride and initiator initiates a ring-opening polymerization reaction with monomers to obtain ultra-high molecular weight polyglutamic acid; The metal hydride is selected from one or more of magnesium hydride, calcium hydride and cuprous hydride; The initiator is an organic amine compound and / or a heterocyclic compound.

2. The ultra-high molecular weight polyglutamic acid according to claim 1, characterized in that The organic amine compound is selected from one or more of triethylamine, dimethylamine, diethylamine, di-n-propylamine, diisopropylamine, N-ethylmethylamine, di-n-butylamine, diisobutylamine, di-sec-butylamine, di-tert-butylamine, dipentylamine, di-n-octylamine, diallylamine, dicyclohexylamine and diphenylamine; Preferably, the heterocyclic compound is selected from one or more of pyridine, aziridine, pyrrole, pyrrolidine, imidazole, indole, piperidine and purine; More preferably, the initiator is triethylamine or pyridine; Preferably, the monomer is glutamate-N-carboxyl cyclic anhydride; Preferably, in the polymerization reaction, the molar ratio of the monomer to the initiator is (1-50):1; And / or, in the composite initiation system, the content of the metal hydride is 1-30wt% of the initiator.

3. A method for preparing ultra-high molecular weight polyglutamic acid, characterized in that: The steps include: (1) Synthesis of polyglutamate: glutamate-N-carboxyl ring anhydride monomer, organic solvent A, metal hydride, and initiator are mixed and reacted to obtain polyglutamate; (2) Synthesis of polyglutamic acid: the polyglutamate obtained in step (1), an organic solvent B, and a deprotecting agent are mixed and reacted to obtain ultrahigh molecular weight polyglutamic acid; The metal hydride is selected from one or more of magnesium hydride, calcium hydride and cuprous hydride.

4. The preparation method according to claim 3, characterized in that: In step (1), the content of the metal hydride is 1-30wt% of the initiator.

5. The preparation method according to claim 3, characterized in that: In step (1), the glutamate-N-carboxyl ring anhydride monomer is γ-alkyl-L-glutamate-N-carboxyl ring anhydride or γ-aryl-L-glutamate-N-carboxyl ring anhydride; Preferably, the alkyl group is selected from methyl, ethyl, tert-butyl, allyl or tert-butyldimethyl; the aryl group is selected from benzyl, benzyl containing halogen atoms, phenolic hydroxyl, nitro, sulfonic acid substituents, diphenylmethyl, triphenylmethyl, ethylphenylbenzene, naphthylmethyl or anthracenemethyl; More preferably, the glutamate-N-carboxyl ring anhydride monomer is γ-benzyl-L-glutamate-N-carboxyl ring anhydride, γ-tert-butyl-L-glutamate-N-carboxyl ring anhydride or γ-ethyl-L-glutamate-N-carboxyl ring anhydride.

6. The preparation method according to claim 3, characterized in that: In step (1), the initiator is an organic amine compound and / or a heterocyclic compound; Preferably, the organic amine compound is selected from one or more of triethylamine, dimethylamine, diethylamine, di-n-propylamine, diisopropylamine, N-ethylmethylamine, di-n-butylamine, diisobutylamine, di-sec-butylamine, di-tert-butylamine, dipentylamine, di-n-octylamine, diallylamine, dicyclohexylamine, and diphenylamine; Preferably, the heterocyclic compound is selected from one or more of pyridine, aziridine, pyrrole, pyrrolidine, imidazole, indole, piperidine and purine; More preferably, the initiator is triethylamine or pyridine.

7. The preparation method according to claim 3, characterized in that: In step (1), the molar ratio of the glutamate-N-carboxyl intracyclic anhydride monomer to the initiator is (1-50):1, preferably (5-20):1; And / or, in step (1), the reaction is carried out at room temperature for 1-5 days.

8. The preparation method according to claim 3, characterized in that: In step (2), the molar ratio of the polyglutamate to the deprotecting agent is 1:(1-3).

9. The preparation method according to claim 3, characterized in that: The organic solvent A is selected from one or more of dioxane, n-hexane, cyclohexane, dichloromethane, chloroform, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, ether, diisopropyl ether, acetonitrile, methanol, ethanol, ethyl acetate, benzene, and toluene, preferably dioxane; And / or, the deprotecting agent is a silane protecting agent selected from one or more of trimethylsilyl iodide, trimethylsilane, tert-butyldimethylsilyl chloride, triisopropylsilyl chloride, tert-butyldimethylsilyl trifluorosulfonate, triisopropylsilyl trifluorosulfonate, preferably trimethylsilyl iodide; And / or, the organic solvent B is selected from one or more of dichloromethane, chloroform, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, dioxane, n-hexane, cyclohexane, ether, diisopropyl ether, acetonitrile, methanol, ethanol, ethyl acetate, benzene and toluene, preferably dichloromethane.

10. Use of the ultra-high molecular weight polyglutamic acid according to any one of claims 1 to 2 or the ultra-high molecular weight polyglutamic acid prepared by the preparation method according to any one of claims 3 to 9 in drug delivery, preparation of tissue engineering materials, and soft tissue repair.

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