Chiral zinc-based catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of polymer synthesis, and discloses a chiral zinc-based catalyst and a preparation method and application thereof.The preparation method comprises the steps that a phenylenediamine derivative and a halogenated carboxylic acid compound are taken to react, and a halogenated benzimidazole derivative is obtained; carrying out nucleophilic substitution reaction on the halogenated benzimidazole derivative and an aminophenol compound in an organic solvent to obtain a tridentate ligand; the tridentate ligand and a zinc source compound are subjected to a complexation reaction in an organic solvent to obtain the chiral zinc-based catalyst. The chiral zinc-based catalyst has a tridentate chiral active center with an adjustable coordination environment, and can induce the monomer to be inserted in a specific stereoregularity mode in the ring-opening polymerization process of the lactone monomer, so that the stereoregularity of the polyhydroxyalkanoate is improved; according to the invention, on the premise of ensuring high monomer conversion rate, collaborative regulation of polymer molecular weight and molecular weight distribution is realized, and preparation of polyhydroxyalkanoate with high molecular weight, narrow molecular weight distribution and high stereoregularity is facilitated.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis technology, specifically to a chiral zinc-based catalyst, its preparation method, and its application. Background Technology

[0002] Plastic materials are widely used in packaging, medical, agricultural, and electronics fields due to their excellent processing performance and low cost. However, their difficulty in natural degradation leads to continuously increasing environmental pressure. Global plastic production has remained high for a long time, while the actual effective recycling rate is low. A large amount of waste plastic enters the ecosystem through incineration, open dumping, or improper landfilling, causing serious "white pollution." To reduce the environmental burden caused by traditional plastics, countries have successively introduced policies to restrict single-use plastic products and promote the development of environmentally friendly biodegradable materials.

[0003] Currently, widely used biodegradable plastics include polylactic acid (PLA) and polybutylene terephthalate (PBAT). However, these materials typically require industrial composting conditions for effective degradation and are highly dependent on temperature and humidity, limiting their degradation efficiency in natural environments. In contrast, polyhydroxyalkanoates (PHA) can spontaneously degrade in various natural environments such as soil, seawater, and freshwater. Their degradation products are small-molecule hydroxy acids, which can be directly utilized by microorganisms or plants and animals, and are non-toxic to the environment, better meeting the needs of green and sustainable development. However, existing PHA production mainly relies on microbial fermentation, which involves long fermentation cycles, demanding cultivation conditions, and high costs, making it less price-competitive with materials like PLA and PBAT.

[0004] To reduce the production cost of PHA, the chemical synthesis route for PHA has attracted increasing attention. Chemical methods offer significant advantages such as high controllability, tunable product structure, high process stability, and ease of scalability. Developing an economical and efficient synthesis method would greatly contribute to the widespread application of PHA in the field of biodegradable plastics.

[0005] The main existing chemical methods for preparing polyhydroxy fatty acid esters include ring-opening polymerization of racemic β-butyrolactone, dehydration condensation polymerization of β-hydroxybutyric acid, and transesterification polymerization of β-hydroxybutyrate. However, the former usually relies on chiral rare earth catalysts with complex structures and high costs, making the construction of catalytic systems difficult and hindering process scale-up, and there are still shortcomings in controlling the stereoregularity of polymers; dehydration condensation polymerization is limited by equilibrium reaction characteristics, making it difficult to obtain high molecular weight products, and it is even more impossible to achieve effective construction of stereo sequences through reaction pathways; transesterification polymerization is prone to eliminating side reactions at high temperatures, which leads to inhibited chain growth, and the products mostly remain at the oligomer level and have almost no stereoselectivity.

[0006] In summary, existing technologies have significant limitations in terms of catalyst availability, catalytic efficiency, polymer molecular weight enhancement, and stereoregularity construction, making it difficult to achieve efficient preparation of high molecular weight, narrow distribution, and high stereoregularity PHA materials. Summary of the Invention

[0007] This invention provides a chiral zinc-based catalyst, its preparation method, and its application, to solve the problems in the prior art where the catalyst has a complex structure, high cost, and difficulty in achieving effective stereoselectivity control over racemic β-butyrolactone, resulting in the difficulty in efficiently preparing high molecular weight, narrow molecular weight distribution, and highly stereoregular polyhydroxy fatty acid esters.

[0008] In a first aspect, the present invention provides a chiral zinc-based catalyst, the structural formula (I) of which is as follows:

[0009] Wherein, Bn is benzyl, SiMe3 is trimethylsilyl, and R is selected from C1 to C2. 30 Straight-chain or branched alkyl groups, C1-C 30 alkoxy groups, C3-C 12 Substituted or unsubstituted cycloalkyl, substituted or unsubstituted phenyl, substituted or unsubstituted benzyl; Preferably, R is selected from C1-C5 straight-chain or branched alkyl groups and C1-C5 alkoxy groups; Preferably, R is selected from methyl, benzyl, or tert-butyl.

[0010] Among them, C1~C 30 Straight-chain or branched alkyl groups, including but not limited to methyl, ethyl, n-propyl, isopropyl, n-butyl, and tert-butyl; C1~C 30 Alkyl groups, including but not limited to methoxy, ethoxy, isopropoxy, tert-butoxy, etc. C3~C 12 The substituted or unsubstituted cycloalkyl group, including but not limited to cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, etc., may be further substituted by alkyl, halogen or other conventional substituents to adjust the rigidity and stereoconfiguration of the ligand; Substituted or unsubstituted phenyl groups, i.e. aromatic ring structures, can be further introduced with alkyl, halogen, alkoxy and other substituents to enhance the aromaticity and steric hindrance effect of the ligand. Substituted or unsubstituted benzyl groups, i.e. aromatic groups linked by methylene groups, can have their substitution forms occurring on the aromatic ring.

[0011] The present invention provides a chiral zinc-based catalyst that constructs a tridentate chiral coordination environment by introducing benzimidazole structural units, nitrogen-oxygen multi-coordination sites, and adjustable substituents R into the ligand framework. This enables the zinc center to form stable active sites with significant stereoselectivity during the catalytic reaction. The synergistic effect of benzimidazole and oxygen-containing coordinating atoms enhances the interaction between the metal and the ligand, improving the stability of the catalyst. Furthermore, the type and volume of the R group can be adjusted within a wide range, thereby achieving precise control over the steric hindrance and electronic environment around the metal center.

[0012] This catalyst can effectively induce stereoselective insertion of monomers during the ring-opening polymerization of racemic β-butyrolactone. While maintaining high catalytic activity, it achieves synergistic control over polymer molecular weight, molecular weight distribution, and stereoregularity, which is beneficial for preparing high molecular weight, narrow distribution, and high stereoregularity polyhydroxy fatty acid esters. In addition, this chiral zinc-based catalyst does not rely on complex or expensive rare earth metal systems, has a relatively simple structure, and has a wide range of raw material sources, which helps to reduce the synthesis cost of the catalyst and improve its feasibility in practical applications.

[0013] Secondly, the present invention provides a method for preparing a chiral zinc-based catalyst, comprising the following steps: (1) React the phenylenediamine derivative with a halocarboxylic acid compound to obtain a halobenzimidazole derivative; (2) The halobenzimidazole derivative reacts with the aminophenol compound in an organic solvent to undergo a nucleophilic substitution reaction to obtain a tridentate ligand; (3) Tridentate ligands and zinc source compounds undergo a complexation reaction in an organic solvent to obtain a chiral zinc-based catalyst.

[0014] The method for preparing chiral zinc-based catalysts provided by this invention constructs tridentate chiral ligands through stepwise reactions of phenylenediamine derivatives, halocarboxylic acid compounds, and aminophenol compounds, and further complexes them with zinc source compounds to form chiral zinc-based catalysts. This synthetic route has clear reaction steps, mild conditions, and readily available raw materials, enabling efficient construction of the ligand framework and stable coordination of the metal center with fewer reaction steps. By first constructing a benzimidazole heterocyclic structure and introducing oxygen-containing coordination sites, a stable and tunable multi-coordination environment is formed at the molecular level, thus providing a clear chiral inducible structure for subsequent catalytic reactions. The overall preparation process does not require complex separation and purification, has good reproducibility, is suitable for large-scale scale-up, and helps reduce the preparation cost of chiral zinc-based catalysts and improve their industrial application feasibility.

[0015] In one optional embodiment, in step (1), the molar ratio between the phenylenediamine derivative and the halocarboxylic acid compound is 1:(1 to 1.1). In an optional embodiment, in step (2), the molar ratio between the halobenzimidazole derivative and the aminophenol compound is 1:(1 to 1.1). In one optional embodiment, in step (3), the molar ratio between the tridentate ligand and the zinc source compound is 1:(1 to 1.1). Preferably, the phenylenediamine derivative includes one or more of N1-(tert-butyl)phenyl-1,2-diamine, o-aminodiphenylamine, mono-N-methylphenylenediamine, and mono-N-substituted phenylphenylenediamine; Among them, mono-N-methylphenylenediamine and mono-N-substituted phenylphenylenediamine include, but are not limited to, the following substances; ; In an optional embodiment, in step (3), the zinc source compound is selected from Zn(HMDS)2.

[0016] In one optional embodiment, the reaction in step (1) is carried out in an alkaline solution under reflux conditions; preferably, 80 to 140 mL of alkaline solution is added for each mole of phenylenediamine derivative. Preferably, the temperature of the heating reflux in step (1) is 100℃~120℃ and the time is 4h~8h.

[0017] In one alternative embodiment, in step (1), after the reaction is completed, the pH of the reaction system is adjusted to neutral, and the halobenzimidazole derivative is obtained by recrystallization.

[0018] In an optional embodiment, in step (2), the organic solvent includes one or two of N,N-dimethylformamide and dimethyl sulfoxide; preferably, 200 to 400 mL of organic solvent is added for each mole of halobenzimidazole derivative. In one optional embodiment, in step (2), the reaction temperature is 60℃~90℃ and the reaction time is 3h~12h.

[0019] In an optional embodiment, in step (3), the organic solvent includes one or two of tetrahydrofuran and diethyl ether; preferably, 65 to 71 mL of organic solvent is added for each mole of tridentate ligand. Thirdly, the present invention provides the application of a chiral zinc-based catalyst in the ring-opening polymerization of lactone monomers to prepare stereoregular polyhydroxy fatty acid esters.

[0020] In one optional embodiment, the lactone monomer includes one or more of racemic β-butyrolactone, chiral β-butyrolactone, racemic β-valerolactone, chiral β-valerolactone, racemic β-caprolactone, and chiral β-caprolactone.

[0021] In one optional embodiment, the molar ratio of the lactone monomer to the chiral zinc-based catalyst is (1000-10000):1.

[0022] The technical solution of this invention has the following advantages: The chiral zinc-based catalyst of this invention constructs a well-defined and spatially controllable tridentate chiral coordination environment by introducing benzimidazole units, nitrogen / oxygen multicoordinating atoms, and tunable substituents R into the ligand framework. This allows the zinc center to form stable chiral active sites during the catalytic reaction. The introduction of benzyl (Bn) and trimethylsilyl (SiMe3) groups helps to regulate the steric hindrance and electronic environment of the ligand, while the R group can be selected from a wide range, allowing for fine control of the stereostructure and electronic effects around the metal center as needed. This structural design helps to effectively induce stereoselective insertion of monomers during the ring-opening polymerization of lactone monomers, achieving synergistic control over polymer molecular weight, molecular weight distribution, and stereoregularity while maintaining high catalytic activity. This is beneficial for obtaining high molecular weight, narrow distribution, and highly stereoregular polyhydroxy fatty acid esters.

[0023] The chiral zinc-based catalyst of this invention can be used for the ring-opening polymerization of various lactone monomers. By constructing a stable chiral catalytic system under a wide range of monomer types and monomer / catalyst molar ratios, lactone monomers can be polymerized at high conversion rates, and the stereoregular sequence can be effectively induced during the polymerization process. This application method is not only applicable to racemic and chiral β-butyrolactone, but can also be extended to lactone monomers with different ring sizes such as β-valerolactone and β-caprolactone, demonstrating good applicability and versatility. At the same time, under high monomer / catalyst molar ratios, polyhydroxy fatty acid esters with high stereoregularity and controllable molecular weight characteristics can still be obtained, which is beneficial to improving catalytic efficiency and reducing catalyst dosage. Thus, it provides a technical approach with practical application value for the efficient preparation of stereoregular polyhydroxy fatty acid esters. Detailed Implementation

[0024] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0025] (1) The test methods involved in the embodiments and comparative examples of the present invention are as follows: The catalytic activity of β-butyrolactone ring-opening polymerization was characterized by the number-average molecular weight, molecular weight distribution, and stereoregularity of the synthesized PHA. The conditions of the GPC and NMR analyzers used are as follows: GPC instrument model: Agilent 1260 Infinity II; Chromatographic columns: Plgel mixed C (PL1110-6500), Plgel mixed D (PL1110-6504), Plgel mixed E (PL1110-6300), guard column (PL1110-1520); Mobile phase: chromatographically pure dichloromethane, brand Inokai; NMR instrument model: AVANCE NEO 600M; (2) The raw materials involved in the embodiments and comparative examples of the present invention are as follows: Racemic β-butyrolactone: synthesized according to the method in the patent "A method for preparing β-butyrolactone by asymmetric hydrogenation of diketene" (application number: 202310000401.6); phenylenediamine derivative: 99% purity, derived from Inokai; Chloroacetic acid: 99% purity, sourced from Inokai; Aminophenol: 99% purity, from Inokai, CAS number 128307-92-6; Zn(HMDS)2, with a purity of 99%, is derived from Sigma-Aldrich; The chiral zinc-based catalyst was prepared by using phenylenediamine derivatives as starting materials.

[0026] Unless otherwise specified, the experimental steps or conditions in the examples were performed in accordance with conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0027] In the embodiments of this invention, unless otherwise specified, all operations were carried out under anhydrous and oxygen-free conditions, and all solvents and reagents used were dehydrated and deoxygenated.

[0028] Example 1 Preparation of chiral zinc-based catalyst L1; (1) 16.42 g N1-(tert-butyl)phenyl-1,2-diamine (CAS No. 28458-68-6), 26.5 g anhydrous sodium carbonate, 40 mL water, 80 mL ethanol and 10.4 g chloroacetic acid were added sequentially to the reaction flask, and a reflux condenser was connected to the reaction flask. Then, stirring was turned on and the mixture was heated to reflux at 105 °C for 6 hours. Dilute hydrochloric acid was added to the system to adjust the pH of the reaction solution to neutral, and the resulting mixture was recrystallized to obtain the halobenzimidazole derivative.

[0029] (2) 17.91 g of halobenzimidazole derivative, 19.32 g of aminophenol, and 29.36 g of anhydrous potassium carbonate were added sequentially to a reaction flask. Then, 300 mL of N,N-dimethylformamide was added as a solvent. The stirring was turned on and the mixture was heated to maintain the reaction at 80 °C for 6 h. After the reaction was completed, the system was cooled to room temperature and neutralized with dilute hydrochloric acid. After neutralization, the reaction solution was extracted with dichloromethane. After extraction, the solution was dried with anhydrous sodium sulfate. The solvent was removed from the dried extract by rotary evaporation. The crude product was purified by column chromatography to obtain 24.24 g of tridentate ligand.

[0030] (3) In a glove box, weigh 24.24 g of the tridentate ligand into a reaction flask, add 400 mL of anhydrous tetrahydrofuran solvent, and stir. Then slowly add 68 mL of Zn(HMDS)2 solution dropwise into the reaction flask. After the addition is complete, react at room temperature for 2 hours. After the reaction is complete, remove the solvent under reduced pressure in a glove box to obtain 42.65 g of dark brown chiral zinc-based catalyst L1.

[0031] The preparation route is as follows:

[0032] The NMR characterization data of the chiral zinc-based catalyst L1 are as follows: 1 H NMR (δ, ppm): 7.45 (m, 5H), 7.35 (m, 5H), 7.20 (m, 3H), 4.10 (m, 1H), 3.70 (m, 4H), 1.70 (S, 9H), 1.60 (t, J = 7.5 Hz, 3H), 0.30 (s, 18H); 13 C NMR (δ, ppm): 150.0, 142.6, 137.7, 128.5, 127.3, 126.1, 125.5, 60.4, 42.4, 36.2, 25.6, 20.7, 1.5.

[0033] Ring-opening polymerization process: Inside the glove box, 50g of racemic β-butyrolactone monomer was added to the reactor, followed by 117mg of chiral zinc-based catalyst L1. For every 3000 mol of β-butyrolactone monomer, 1 mol of chiral zinc-based catalyst L1 was added.

[0034] Under a nitrogen atmosphere, the temperature of the reactor was adjusted to 90℃, and the stirring speed was maintained at 400 rpm for 3 hours to carry out the polymerization reaction. After the reaction was completed, the temperature was lowered to room temperature (25℃), the reactor was opened, and a small amount of product was taken for testing.

[0035] The ring-opening polymerization process is as follows:

[0036] Characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR), the obtained polyhydroxyalkanoate (PHA) had a number-average molecular weight (Mn) of 180,000, a molecular weight distribution (PDI) of 1.25, and a stereoregularity (Pm) of 0.82. Meanwhile, by comparing the changes in the integral area of ​​characteristic peaks before and after the reaction using 1H NMR spectroscopy, the monomer conversion rate could be quantitatively calculated, and the results showed that the conversion rate was greater than 99%.

[0037] Example 2 This embodiment uses the same chiral zinc-based catalyst L1 as in Example 1; The ring-opening polymerization process is as follows: Inside a glove box, 50 g of racemic β-butyrolactone monomer was added to the reactor, followed by 71 mg of chiral zinc-based catalyst L1. For every 5000 mol of β-butyrolactone monomer, 1 mol of chiral zinc-based catalyst L1 was added. Under a nitrogen atmosphere, the reactor temperature was adjusted to 90°C, and the stirring speed was maintained at 400 rpm for 3 h. After the reaction, the temperature was lowered to room temperature (25°C), the reactor was opened, and a small amount of product was taken for testing.

[0038] Characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR), the obtained polyhydroxyalkanoate (PHA) had a number-average molecular weight (Mn) of 150,000, a molecular weight distribution (PDI) of 1.37, and a stereoregularity (Pm) of 0.76. Meanwhile, by comparing the changes in the integral area of ​​characteristic peaks before and after the reaction using 1H NMR spectroscopy, the monomer conversion rate could be quantitatively calculated, and the results showed that the conversion rate was greater than 99%.

[0039] Example 3 This embodiment uses the same chiral zinc-based catalyst L1 as in Example 1; The ring-opening polymerization process is as follows: Inside a glove box, 50 g of racemic β-butyrolactone monomer was added to the reactor, followed by 50 mg of chiral zinc-based catalyst L1. For every 5000 mol of β-butyrolactone monomer, 1 mol of chiral zinc-based catalyst L1 was added. Under a nitrogen atmosphere, the reactor temperature was adjusted to 90°C, and the stirring speed was maintained at 400 rpm for 3 h for polymerization. After the reaction, the temperature was lowered to room temperature (25°C), the reactor was opened, and a small amount of product was taken for testing. It is recommended to provide 1H NMR spectroscopy data; otherwise, there is a risk of insufficient disclosure. Characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR), the obtained polyhydroxyalkanoate (PHA) had a number-average molecular weight (Mn) of 130,000, a molecular weight distribution (PDI) of 1.31, and a stereoregularity (Pm) of 0.70. Meanwhile, by comparing the changes in the integral area of ​​characteristic peaks before and after the reaction using 1H NMR spectroscopy, the monomer conversion rate could be quantitatively calculated, and the results showed that the conversion rate was greater than 99%.

[0040] Example 4 Preparation of chiral zinc-based catalyst L2; The difference between the preparation of the chiral zinc-based catalyst L2 in this embodiment and that in Example 1 is that N1-(tert-butyl)phenyl-1,2-diamine is replaced with o-aminodiphenylamine (CAS number 534-85-0).

[0041] The preparation route is as follows:

[0042] The following are the NMR characterization data of the chiral zinc-based catalyst L2: 1 H NMR (δ, ppm): 7.45 (m, 5H), 7.35 (m, 9H), 7.25 (m, 4H), 4.10 (m, 1H), 3.80 (m, 2H), 3.70 (m, 2H), 1.60 (s, 3H), 0.30 (s, 18H); 13 C NMR (δ, ppm): 180.5, 150.2, 141.8, 135.0, 130.1, 128.5, 128.0, 127.2, 125.5, 122.0, 65.4, 25.2, 20.5, 1.8.

[0043] Ring-opening polymerization process: Inside a glove box, 50 g of racemic β-butyrolactone monomer was added to the reactor, followed by 117 mg of chiral zinc-based catalyst L2. For every 3000 mol of β-butyrolactone monomer, 1 mol of chiral zinc-based catalyst L2 was added. Under a nitrogen atmosphere, the reactor temperature was adjusted to 90 °C, and the stirring speed was maintained at 400 rpm for 3 h. After the reaction, the temperature was lowered to room temperature (25 °C), the reactor was opened, and a small amount of product was taken for testing.

[0044] The ring-opening polymerization process is as follows:

[0045] Characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR), the obtained polyhydroxyalkanoate (PHA) had a number-average molecular weight (Mn) of 210,000, a molecular weight distribution (PDI) of 1.18, and a stereoregularity (Pm) of 0.88. Meanwhile, by comparing the changes in the integral area of ​​characteristic peaks before and after the reaction using 1H NMR spectroscopy, the monomer conversion rate could be quantitatively calculated, and the results showed that the conversion rate was greater than 99%.

[0046] Example 5 This embodiment uses the same chiral zinc-based catalyst L2 as in Example 4; The ring-opening polymerization process is as follows: Inside the glove box, 50g of racemic β-butyrolactone monomer was added to the reactor, followed by 70mg of chiral zinc-based catalyst L2. For every 5000 mol of β-butyrolactone monomer, 1 mol of chiral zinc-based catalyst L2 was added.

[0047] Under a nitrogen atmosphere, the temperature of the reactor was adjusted to 90℃, and the stirring speed was maintained at 400 rpm for 3 hours to carry out the polymerization reaction. After the reaction was completed, the temperature was lowered to room temperature (25℃), the reactor was opened, and a small amount of product was taken for testing.

[0048] Characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR), the obtained polyhydroxyalkanoate (PHA) had a number-average molecular weight (Mn) of 190,000, a molecular weight distribution (PDI) of 1.28, and a stereoregularity (Pm) of 0.83. Meanwhile, by comparing the changes in the integral area of ​​characteristic peaks before and after the reaction using 1H NMR spectroscopy, the monomer conversion rate could be quantitatively calculated, and the results showed that the conversion rate was greater than 99%.

[0049] Example 6 This embodiment uses the same chiral zinc-based catalyst L2 as in Example 4; The ring-opening polymerization process is as follows: Inside the glove box, 50g of racemic β-butyrolactone monomer was added to the reactor, followed by 50mg of chiral zinc-based catalyst L2. For every 7000 mol of β-butyrolactone monomer, 1 mol of chiral zinc-based catalyst L2 was added.

[0050] Under a nitrogen atmosphere, the temperature of the reactor was adjusted to 90℃, and the stirring speed was maintained at 400 rpm for 3 hours to carry out the polymerization reaction. After the reaction was completed, the temperature was lowered to room temperature (25℃), the reactor was opened, and a small amount of product was taken for testing.

[0051] Characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR), the obtained polyhydroxyalkanoate (PHA) had a number-average molecular weight (Mn) of 160,000, a molecular weight distribution (PDI) of 1.32, and a stereoregularity (Pm) of 0.77. Meanwhile, by comparing the changes in the integral area of ​​characteristic peaks before and after the reaction using 1H NMR spectroscopy, the monomer conversion rate could be quantitatively calculated, and the results showed that the conversion rate was greater than 99%.

[0052] Example 7 This embodiment uses the same chiral zinc-based catalyst L2 as in Example 4; The ring-opening polymerization process is as follows: Inside a glove box, 50 g of racemic β-butyrolactone monomer was added to the reactor, followed by 350 mg of chiral zinc-based catalyst L2. For every 1000 mol of β-butyrolactone monomer, 1 mol of chiral zinc-based catalyst L2 was added. Under a nitrogen atmosphere, the reactor temperature was adjusted to 90 °C, and the stirring speed was maintained at 400 rpm for 3 h. After the reaction was complete, the temperature was lowered to room temperature (25 °C), the reactor was opened, and a small amount of product was taken for testing.

[0053] Characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR), the obtained polyhydroxyalkanoate (PHA) had a number-average molecular weight (Mn) of 230,000, a molecular weight distribution (PDI) of 1.15, and a stereoregularity (Pm) of 0.86. Meanwhile, by comparing the changes in the integral area of ​​characteristic peaks before and after the reaction using 1H NMR spectroscopy, the monomer conversion rate could be quantitatively calculated, and the results showed that the conversion rate was greater than 99%.

[0054] Example 8 This embodiment uses the same chiral zinc-based catalyst L2 as in Example 4; The ring-opening polymerization process is as follows: Inside a glove box, 50 g of racemic β-butyrolactone monomer was added to the reactor, followed by 35 mg of chiral zinc-based catalyst L2. For every 10,000 mol of β-butyrolactone monomer, 1 mol of chiral zinc-based catalyst L2 was added. Under a nitrogen atmosphere, the reactor temperature was adjusted to 90 °C, and the stirring speed was maintained at 400 rpm for 3 h. After the reaction was complete, the temperature was lowered to room temperature (25 °C), the reactor was opened, and a small amount of product was taken for testing.

[0055] Characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR), the obtained polyhydroxyalkanoate (PHA) had a number-average molecular weight (Mn) of 90,000, a molecular weight distribution (PDI) of 2.5, and a stereoregularity (Pm) of 0.62. Meanwhile, by comparing the changes in the integral area of ​​characteristic peaks before and after the reaction using 1H NMR spectroscopy, the monomer conversion rate could be quantitatively calculated, and the results showed that the conversion rate was 74%.

[0056] Example 9 This embodiment uses the same chiral zinc-based catalyst L2 as in Example 4; The ring-opening polymerization process is as follows: Inside a glove box, 58 g of racemic β-valerol monomer was added to the reactor, followed by 117 mg of chiral zinc-based catalyst L2. For every 3000 mol of racemic β-valerol monomer, 1 mol of chiral zinc-based catalyst L2 was added. Under a nitrogen atmosphere, the reactor temperature was adjusted to 90 °C, and the stirring speed was maintained at 400 rpm for 3 h. After the reaction, the temperature was lowered to room temperature (25 °C), the reactor was opened, and a small amount of product was taken for testing.

[0057] Characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR), the obtained polyhydroxyalkanoate (PHA) had a number-average molecular weight (Mn) of 130,000, a molecular weight distribution (PDI) of 1.9, and a stereoregularity (Pm) of 0.75. Meanwhile, by comparing the changes in the integral area of ​​characteristic peaks before and after the reaction using 1H NMR spectroscopy, the monomer conversion rate could be quantitatively calculated, and the results showed that the conversion rate was 89%.

[0058] Comparative Example 1 The only difference between this comparative example and Example 1 is that: Zinc-based catalyst L3 was used as the catalyst for the ring-opening polymerization reaction. The structural formula of zinc-based catalyst L3 is as follows:

[0059] Inside a glove box, 50 g of racemic β-butyrolactone monomer was added to the reactor, followed by 112 mg of zinc-based catalyst L3. For every 3000 mol of β-butyrolactone monomer, 1 mol of zinc-based catalyst L3 was added. Under a nitrogen atmosphere, the reactor temperature was adjusted to 90°C, and the stirring speed was maintained at 400 rpm for 3 h to carry out the polymerization reaction. After the reaction was completed, the temperature was lowered to room temperature (25°C), the reactor was opened, and a small amount of product was taken for testing.

[0060] Characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR), the obtained polyhydroxyalkanoate (PHA) had a number-average molecular weight (Mn) of 170,000, a molecular weight distribution (PDI) of 1.56, and a stereoregularity (Pm) of 0.07. Meanwhile, by comparing the changes in the integral area of ​​characteristic peaks before and after the reaction using 1H NMR spectroscopy, the monomer conversion rate could be quantitatively calculated, and the results showed that the conversion rate was greater than 99%.

[0061] Test Example 1 This test example demonstrates and compares the catalytic performance of the catalysts prepared in the embodiments and comparative examples of this invention in the ring-opening polymerization of lactone monomers. The number-average molecular weight, molecular weight distribution, stereoregularity, and monomer conversion rate of the polyhydroxyalkanoates (PHAs) obtained from the polymerization reaction were characterized to evaluate the differences in molecular weight control ability, stereoselectivity, and catalytic activity among different catalyst systems. The results are shown in Table 1 below. Table 1: Test results of catalysts in the embodiments and comparative examples of the present invention

[0062] As shown in Table 1, the chiral zinc-based catalysts used in Examples 1 to 9 of this invention all exhibited good catalytic performance in the ring-opening polymerization of racemic lactone monomers. Specifically, most examples achieved high number-average molecular weight and narrow molecular weight distribution while maintaining high monomer conversion rates, indicating that the catalyst system has strong chain growth capability and good molecular weight regulation effect.

[0063] From the perspective of stereoregularity (Pm), the polyhydroxyalkanoates obtained in Examples 1 to 9 of this invention all exhibit high stereoregularity, significantly higher than that of Comparative Example 1. This indicates that the chiral zinc-based catalyst used in this invention can effectively induce the lactone monomer to insert in a specific stereoregular manner, thereby achieving regulation of the polymer stereostructure sequence. In contrast, although Comparative Example 1 can achieve a high monomer conversion rate, its stereoregularity is significantly reduced, indicating that the non-chiral catalyst system is difficult to effectively control the stereoselectivity during the polymerization process.

[0064] The chiral zinc-based catalyst provided by this invention can achieve synergistic regulation of monomer conversion, polymer molecular weight and stereoregularity within a wide range of reaction conditions in the ring-opening polymerization of lactone monomers, and its overall performance is significantly better than that of non-chiral zinc-based catalyst systems.

[0065] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A chiral zinc-based catalyst, characterized in that, Its structural formula (Ⅰ) is as follows: Wherein, Bn is benzyl, SiMe3 is trimethylsilyl, and R is selected from C1 to C2. 30 Straight-chain or branched alkyl groups, C1-C 30 alkoxy groups, C3-C 12 Substituted or unsubstituted cycloalkyl, substituted or unsubstituted phenyl, substituted or unsubstituted benzyl; Preferably, R is selected from C1-C5 straight-chain or branched alkyl groups and C1-C5 alkoxy groups; Preferably, R is selected from methyl, benzyl, or tert-butyl.

2. A method for preparing a chiral zinc-based catalyst, characterized in that, Includes the following steps: (1) React the phenylenediamine derivative with a halocarboxylic acid compound to obtain a halobenzimidazole derivative; (2) The halobenzimidazole derivative reacts with the aminophenol compound in an organic solvent to undergo a nucleophilic substitution reaction to obtain a tridentate ligand; (3) Tridentate ligands and zinc source compounds undergo a complexation reaction in an organic solvent to obtain a chiral zinc-based catalyst.

3. The method for preparing a chiral zinc-based catalyst according to claim 2, characterized in that, In step (1), the molar ratio between the phenylenediamine derivative and the halocarboxylic acid compound is 1:(1 to 1.1). And / or, in step (2), the molar ratio between the halobenzimidazole derivative and the aminophenol compound is 1:(1 to 1.1). And / or, in step (3), the molar ratio between the tridentate ligand and the zinc source compound is 1:(1 to 1.1). Preferably, the phenylenediamine derivative includes one or more of N1-(tert-butyl)phenyl-1,2-diamine, o-aminodiphenylamine, mono-N-methylphenylenediamine, and mono-N-substituted phenylphenylenediamine; And / or, in step (3), the zinc source compound is selected from Zn(HMDS)2.

4. The method for preparing a chiral zinc-based catalyst according to claim 2 or 3, characterized in that, The reaction in step (1) is carried out in an alkaline solution under reflux conditions; Preferably, the temperature of the heating reflux in step (1) is 100℃~120℃ and the time is 4h~8h.

5. A method for preparing a chiral zinc-based catalyst according to any one of claims 2-4, characterized in that, In step (1), after the reaction is completed, the pH of the reaction system is adjusted to neutral, and the halobenzimidazole derivative is obtained by recrystallization.

6. A method for preparing a chiral zinc-based catalyst according to any one of claims 2-5, characterized in that, In step (2), the organic solvent includes one or both of N,N-dimethylformamide and dimethyl sulfoxide; And / or, in step (2), the reaction temperature is 60℃~90℃ and the reaction time is 3h~12h.

7. A method for preparing a chiral zinc-based catalyst according to any one of claims 2-6, characterized in that, In step (3), the organic solvent includes one or both of tetrahydrofuran and diethyl ether.

8. The use of a chiral zinc-based catalyst as described in any one of claims 1-7 in the preparation of stereoregular polyhydroxy fatty acid esters by ring-opening polymerization of lactone monomers.

9. The application according to claim 8, characterized in that, The lactone monomer includes one or more of racemic β-butyrolactone, chiral β-butyrolactone, racemic β-valerolactone, chiral β-valerolactone, racemic β-caprolactone, and chiral β-caprolactone.

10. The application according to claim 8 or 9, characterized in that, The molar ratio of the lactone monomer to the chiral zinc-based catalyst is (1000-10000):1.

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