Alcohol amine lithium complex and preparation method and use thereof

Abstract

The present application relates to a kind of alcohol amine lithium complex and preparation method, purposes, belong to catalytic synthesis field.The preparation method of alcohol amine lithium complex of the present application includes the following steps: 1) nitrogen protection, hexane solution of n-butyl lithium is injected into anhydrous N, N-dimethyl aniline, solvent is extracted dry, reaction after warming, after reaction is finished, solid powder is obtained after processing;2) nitrogen protection, anhydrous ether is added to the solid powder prepared in step 1), ultrasonic treatment, subsequently at 0 ℃, the ethyl ether solution of carbonyl compound is added dropwise, and reaction is carried out after being warmed to room temperature, after reaction is finished, alcohol amine lithium complex is obtained after processing.The preparation method used in the present application is simple and efficient, low in cost, high in yield, the alcohol amine lithium complex prepared is applied to lactide ring-opening polymerization reaction, and shows extremely high activity, and the polymeric product with narrow molecular weight distribution and controllable can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of catalytic synthesis, specifically relating to an alcoholamine lithium complex, its preparation method, and its uses. Background Technology

[0002] Polylactide (PLA) has shown great potential in fields such as fibers, food packaging, and biomedical materials due to its excellent biodegradability and biocompatibility. In the fiber industry, environmentally friendly fibers made from PLA possess high strength and abrasion resistance, making them suitable for a variety of products, including clothing, household goods, and industrial materials. In food packaging, PLA is widely used in food packaging films and containers because it is non-toxic and non-irritating to food and has excellent transparency and barrier properties. In the medical field, PLA also plays an important role. For example, surgical sutures made from PLA can effectively reduce postoperative scarring and promote wound healing. In medical devices, catheters and stents made from PLA help doctors accurately locate and dilate blood vessels or other cavities, facilitating treatment. Furthermore, with the rapid development of 3D printing technology, PLA is extremely suitable for printing complex structures or personalized products due to its outstanding mechanical strength and morphological stability.

[0003] However, current lactide ring-opening polymerization technology mainly relies on stannous octoate catalysts. While these catalysts play an important role in promoting the polymerization reaction, their catalytic activity is relatively low, and they are also quite expensive. Furthermore, due to the neurotoxicity of tin, the application of the final product may be affected to some extent. Therefore, there is an urgent need to develop inexpensive, environmentally friendly, and efficient lactide ring-opening polymerization catalysts to address these issues.

[0004] Lithium complexes are important catalysts widely used in organic synthesis, possessing advantages such as high efficiency, good selectivity, and mild reaction conditions. They can promote the construction and functionalization of complex molecules, improving reaction rates and yields. Therefore, developing a highly active and inexpensive lithium complex catalyst is of great significance for improving the efficiency of lactide ring-opening polymerization and reducing production costs. Summary of the Invention

[0005] The purpose of this invention is to provide an alcoholamine lithium complex, its preparation method, and its uses, which can effectively solve the problems of low catalytic activity, high cost, difficult preparation, and unavailable raw materials in the prior art for the ring-opening polymerization of lactide.

[0006] To achieve the above or other objectives, the present invention is implemented through the following technical solutions.

[0007] A lithium alcoholamine complex, the structural formula of which is shown in Formula 1:

[0008]

[0009] Among them, R1 and R2 satisfy the following conditions: R1 and R2 are both phenyl, or R1 is phenyl and R2 is hydrogen, or R1 is phenyl and R2 is methyl, or R1 is o-fluorophenyl and R2 is hydrogen.

[0010] This invention provides a method for preparing the above-mentioned lithium alcoholamine complex, comprising the following steps:

[0011] 1) Under nitrogen protection, a hexane solution of n-butyllithium was injected into anhydrous N,N-dimethylaniline, the solvent was dried, the temperature was raised and the reaction was carried out. After the reaction was completed, the solid powder was obtained by treatment.

[0012] 2) Under nitrogen protection, anhydrous diethyl ether is added to the solid powder prepared in step 1), and the mixture is ultrasonically treated. Then, a diethyl ether solution of the carbonyl compound is added dropwise at 0°C, and the temperature is raised to room temperature for reaction. After the reaction is completed, the mixture is post-treated to obtain a lithium alkanolamine complex. The carbonyl compound is selected from benzaldehyde, o-fluorobenzaldehyde, acetophenone, and benzophenone.

[0013] Further, the concentration of the hexane solution of n-butyllithium used in step 1) is 1.6M to 2.5M. Preferably, the concentration of the hexane solution of n-butyllithium used in step 1) is 1.6M.

[0014] Furthermore, in step 1), the molar ratio of n-butyllithium to N,N-dimethylaniline is (1-1.1):1.

[0015] Further, the reaction temperature in step 1) is 50℃~80℃. Preferably, the reaction temperature in step 1) is 60℃.

[0016] Further, the reaction time in step 1) is 1 hour to 12 hours. Preferably, the reaction time in step 1) is 4 hours.

[0017] Further, the processing in step 1) includes washing with anhydrous n-hexane, filtering, and vacuum drying. Preferably, the obtained solid powder is washed with n-hexane 1 to 3 times, and the vacuum drying temperature is 25°C to 35°C. More preferably, it is washed with n-hexane 3 times, and the vacuum drying temperature is 30°C.

[0018] Further, in step 2), the mass ratio of anhydrous diethyl ether to solid powder is (5-20):1.

[0019] Further, the ultrasonic treatment time in step 2) is 10 min to 30 min. Preferably, the ultrasonic treatment time in step 2) is 30 min.

[0020] Furthermore, in step 2), the rate of adding the carbonyl compound in diethyl ether solution is ensured to be completed within 10 to 30 minutes.

[0021] Furthermore, the molar ratio of the carbonyl compound to N,N-dimethylaniline is 1:1.

[0022] Furthermore, in step 2), the heating rate is 3℃ / min.

[0023] Further, the reaction time in step 2) is 1 hour to 12 hours. Preferably, the reaction time in step 2) is 10 hours.

[0024] Further, the post-processing in step 2) includes: filtering to remove the solvent, washing with anhydrous n-hexane, filtering, and vacuum drying. Preferably, after removing the solvent, the obtained product is washed with anhydrous n-hexane 1 to 3 times, and vacuum dried at a temperature of 25°C to 35°C. More preferably, it is washed with anhydrous n-hexane 3 times, and vacuum dried at a temperature of 30°C.

[0025] The present invention also provides the application of the above-mentioned lithium alkanolamine complex in the catalytic ring-opening polymerization of lactide to prepare polylactide.

[0026] A catalytic ring-opening polymerization reaction of lactide is proposed, using a lithium alkanolamine complex as a catalyst.

[0027] Further, the method includes the following steps: adding lithium alcoholamine complex, benzyl alcohol, and lactide to anhydrous toluene, carrying out a ring-opening polymerization reaction under nitrogen protection, quenching the reaction with water after the reaction is completed, and performing post-treatment to obtain polylactide.

[0028] Preferably, the lactide is selected from one or more of L-lactide, D-lactide, mesolactide, and racemic lactide.

[0029] Preferably, the molar ratio of lactide to lithium alkanolamine complex is (100-1000):1, and the molar ratio of benzyl alcohol to lithium alkanolamine complex is (1-4):1.

[0030] Preferably, the mass ratio of anhydrous toluene to the total mass of the reactants lithium alcoholamine complex, benzyl alcohol, and lactide is (5-20):1.

[0031] Preferably, the reaction temperature is 10℃~60℃ and the reaction time is 0.5min~30min.

[0032] Preferably, after the reaction is complete, dichloromethane is added to dissolve the product, and a small amount of water is added to quench the reaction.

[0033] Preferably, the post-treatment includes recrystallization with ethanol, filtration, and vacuum drying at room temperature.

[0034] This invention provides a lithium alkanolamine complex, its preparation method, and its applications. The preparation method is simple, efficient, low-cost, and yields high output, showing potential for industrial-scale production. The lithium metal center of this catalyst has a small ionic radius and high electron affinity, enabling it to effectively adsorb reactant molecules, thereby improving reaction rate and selectivity. Applying the lithium alkanolamine catalyst of this invention to the ring-opening polymerization of lactide not only achieves highly efficient catalysis but also allows for control of the polymer molecular weight, yielding polymer products with a narrow molecular weight distribution to meet the performance requirements of various fields. Furthermore, this catalyst is easily removed and converted into non-toxic substances during post-processing, providing a more economical, green, and sustainable solution for the ring-opening polymerization of lactide. Attached Figure Description

[0035] Figure 1 The catalyst ① in Example 1 1 H NMR spectrum;

[0036] Figure 2 The catalyst ② in Example 2 1 H NMR spectrum;

[0037] Figure 3 The catalyst ③ in Example 3 1 H NMR spectrum;

[0038] Figure 4 The catalyst ④ in Example 4 1 H NMR spectrum;

[0039] Figure 5 For the polylactide prepared in Example 1 1 H NMR spectrum;

[0040] Figure 6 The GPC curve of the polylactide prepared in Example 6 is shown. Detailed Implementation

[0041] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0042] It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. It should also be understood that the terminology used in the embodiments of this invention is for describing specific implementations and not for limiting the scope of protection of this invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0043] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention.

[0044] In this embodiment of the invention, proton nuclear magnetic resonance spectroscopy (NMR) is used. 1 The composition of lithium alcoholamine catalyst and polymer was analyzed by ¹H NMR (Bruker Avance III 400 MHz); the molecular weight (multiplied by a correction factor of 0.58, Nat. Commun. 2023, 14, 4783) and molecular weight distribution (PDI) of polymer were measured by gel permeation chromatography (GPC, WATERS 1515, with polystyrene as a standard).

[0045] The present invention will be further illustrated below with specific embodiments, but the present invention is not limited thereto, and the specific scope of protection is as described in the foregoing claims.

[0046] The reaction formula for the preparation of lithium alcoholamine complexes is as follows:

[0047]

[0048] Example 1

[0049] Under nitrogen protection, 7.8 mL of n-butyllithium hexane solution (1.6 M) was injected into 1.5 mL of anhydrous N,N-dimethylaniline. The solvent was removed by vacuum, and the mixture was heated to 60 °C and reacted for 4 h. After the reaction was completed, anhydrous n-hexane was added to wash the mixture three times, and the mixture was filtered and dried under vacuum at 30 °C. Subsequently, 20 mL of anhydrous diethyl ether was added to the solid powder obtained in step 1), and the mixture was sonicated for 30 min. 2.0 mL of benzophenone was added dropwise at 0 °C. After the addition was completed, the mixture was slowly heated to room temperature and the reaction was continued for 10 h. After the reaction was completed, the solvent was removed by filtration, and the mixture was washed three times with anhydrous n-hexane and dried under vacuum at 30 °C to obtain the lithium alcoholamine complex (catalyst ①) with a yield of 77.2%.

[0050] The prepared catalyst ① was subjected to 1H NMR spectroscopy (NMR spectroscopy). 1Detection was performed using ¹H NMR (Bruker Avance III 400MHz), and the results are as follows: Figure 1 As shown: 1 HNMR (400MHz, CDCl3) δ7.33 (dd, J=49.3, 6.1Hz, 10H), 7.24 (dd, J=8.6, 4.3Hz, 2H), 7.06 (t, J=7.5Hz, 1H), 6.70 (d, J=7.8Hz, 1H), 2.40 (s, 6H).

[0051] Example 2

[0052] Under nitrogen protection, 8.0 mL of n-butyllithium hexane solution (1.6 M) was injected into 1.5 mL of anhydrous N,N-dimethylaniline. The solvent was removed by vacuum, and the mixture was heated to 50 °C and reacted for 12 h. After the reaction was completed, anhydrous n-hexane was added to wash the mixture three times, and the mixture was filtered and dried under vacuum at 30 °C. Subsequently, 25 mL of anhydrous diethyl ether was added to the solid powder obtained in step 1), and the mixture was sonicated for 20 min. 1.2 mL of benzaldehyde was added dropwise at 0 °C. After the addition was completed, the mixture was slowly heated to room temperature and the reaction was continued for 8 h. After the reaction was completed, the solvent was removed by filtration, and the mixture was washed three times with anhydrous n-hexane and dried under vacuum at 30 °C to obtain the lithium alcoholamine complex (catalyst ②) with a yield of 81.5%.

[0053] The prepared catalyst ② was subjected to 1H NMR spectroscopy (NMR spectroscopy). 1 Detection was performed using ¹H NMR (Bruker Avance III 400MHz), and the results are as follows: Figure 2 As shown: 1 HNMR(400MHz, CDCl3) δ7.59(d,J=6.3Hz,1H),7.40(d,J=7.7Hz,2H),7.34(dd,J=7.0,1.6Hz,2 H),7.31-7.27(m,2H),7.12(s,1H),7.04(d,J=7.6Hz,1H),5.97(d,J=6.2Hz,1H),2.58(s,6H).

[0054] Example 3

[0055] Under nitrogen protection, 6.5 mL of n-butyllithium hexane solution (2.0 M) was injected into 1.5 mL of anhydrous N,N-dimethylaniline. The solvent was removed by vacuum, and the mixture was heated to 60 °C and reacted for 5 h. After the reaction was completed, anhydrous n-hexane was added to wash the mixture three times, and the mixture was filtered and dried under vacuum at 30 °C. Subsequently, 25 mL of anhydrous diethyl ether was added to the solid powder obtained in step 1), and the mixture was sonicated for 15 min. 1.2 mL of o-fluorobenzaldehyde was added dropwise at 0 °C. After the addition was completed, the mixture was slowly heated to room temperature and the reaction was continued for 6 h. After the reaction was completed, the solvent was removed by filtration, and the mixture was washed three times with anhydrous n-hexane and dried under vacuum at 30 °C to obtain the lithium alcoholamine complex (catalyst ③) with a yield of 81.0%.

[0056] The prepared catalyst ③ was subjected to 1H NMR spectroscopy (NMR spectroscopy 3). 1 Detection was performed using ¹H NMR (Bruker Avance III 400MHz), and the results are as follows: Figure 3 As shown: 1 HNMR(400MHz, CDCl3)δ7.75(d,J=4.5Hz,1H),7.56-7.52(m,1H),7.32(dd,J=8.0,1.3Hz,1H),7.30-7.27(m,1 H),7.18(dd,J=7.5,1.0Hz,1H),7.10-7.01(m,2H),6.94(d,J=7.8Hz,1H),6.37(d,J=4.5Hz,1H),2.73(s,6H).

[0057] Example 4

[0058] Under nitrogen protection, 5.0 mL of n-butyllithium hexane solution (2.5 M) was injected into 1.5 mL of anhydrous N,N-dimethylaniline. The solvent was removed by vacuum, and the mixture was heated to 80 °C and reacted for 4 h. After the reaction was completed, anhydrous n-hexane was added to wash the mixture three times, and the mixture was filtered and dried under vacuum at 30 °C. Subsequently, 30 mL of anhydrous diethyl ether was added to the solid powder obtained in step 1), and the mixture was sonicated for 30 min. 1.4 mL of acetophenone was added dropwise at 0 °C. After the addition was completed, the mixture was slowly heated to room temperature and the reaction was continued for 12 h. After the reaction was completed, the solvent was removed by filtration, and the mixture was washed three times with anhydrous n-hexane and dried under vacuum at 30 °C to obtain the lithium alcoholamine complex (catalyst ④) with a yield of 83.4%.

[0059] The prepared catalyst ④ was subjected to 1H NMR spectroscopy (NMR spectroscopy 4). 1 Detection was performed using ¹H NMR (Bruker Avance III 400MHz), and the results are as follows: Figure 4 As shown: 1HNMR(400MHz, CDCl3) δ7.50(dd,J=15.1,7.4Hz,1H),7.37(dd,J=28.8,5.8Hz,2H),7.26(d,J =8.8Hz, 2H), 7.18 (d, J = 7.3Hz, 2H), 6.76 (dd, J = 14.1, 7.6Hz, 2H), 2.97 (s, 6H), 1.87 (s, 3H).

[0060] Application Example 1

[0061] Under nitrogen protection, 0.3 g of catalyst ①, 0.1 mL of benzyl alcohol, 14.4 g of lactide, and 75 mL of toluene were sequentially added to an ampoule that had been purged with nitrogen and baked at high temperature. The reaction was carried out at 25 °C for 1 min. Subsequently, dichloromethane was added to dissolve the product, and a small amount of water was added to terminate the reaction. The filtrate was slowly poured into ethanol for recrystallization (3 times), filtered, collected, and dried at room temperature to obtain 13.2 g of polylactide, with a yield of 91.7% and a molecular weight of 11.4 × 10⁻⁶. 3 The PDI is 1.27.

[0062] The prepared polylactide was analyzed by 1H NMR spectroscopy (Bruker Avance III 400MHz NMR spectrometer, CDCl3) and the results are as follows. Figure 5 As shown in the figure, δ = 5.15 ppm is the signal peak of the methylene group in polylactide. Figure 5 As shown in the annotation 'a'; δ = 1.58 ppm is the signal peak of methyl groups in polylactide, as shown in the figure. Figure 5 As shown by the label b.

[0063] Application Example 2

[0064] Under nitrogen protection, 0.2 g of catalyst ②, 0.1 mL of benzyl alcohol, 14.4 g of lactide, and 100 mL of toluene were sequentially added to an ampoule that had been purged with nitrogen and baked at high temperature. The reaction was carried out at 30 °C for 2 min. Subsequently, dichloromethane was added to dissolve the product, and a small amount of water was added to terminate the reaction. The filtrate was slowly poured into ethanol for recrystallization (3 times), filtered, collected, and dried at room temperature to obtain 13.8 g of polylactide, with a yield of 95.8% and a molecular weight of 13.2 × 10⁻⁶. 3 The PDI is 1.24.

[0065] Application Example 3

[0066] Under nitrogen protection, 0.3 g of catalyst ③, 0.1 mL of benzyl alcohol, 14.4 g of lactide, and 80 mL of toluene were sequentially added to an ampoule that had been purged with nitrogen and baked at high temperature. The reaction was carried out at 60 °C for 0.5 min. Subsequently, dichloromethane was added to dissolve the product, and a small amount of water was added to terminate the reaction. The filtrate was slowly poured into ethanol for recrystallization (3 times), filtered, collected, and dried at room temperature to obtain 12.8 g of polylactide, with a yield of 88.9% and a molecular weight of 14.1 × 10⁻⁶. 3 The PDI is 1.33.

[0067] Application Example 4

[0068] Under nitrogen protection, 0.2 g of catalyst ④, 0.1 mL of benzyl alcohol, 14.4 g of lactide, and 80 mL of toluene were sequentially added to an ampoule that had been purged with nitrogen and baked at high temperature. The reaction was carried out at 10 °C for 30 min. Subsequently, dichloromethane was added to dissolve the product, and a small amount of water was added to terminate the reaction. The filtrate was slowly poured into ethanol for recrystallization (3 times), filtered, collected, and dried at room temperature to obtain 13.6 g of polylactide, with a yield of 94.4% and a molecular weight of 13.3 × 10⁻⁶. 3 The PDI is 1.35.

[0069] Application Example 5

[0070] Under nitrogen protection, 0.3 g of catalyst ①, 0.2 mL of benzyl alcohol, 144 g of lactide, and 800 mL of toluene were sequentially added to an ampoule that had been purged with nitrogen and baked at high temperature. The reaction was carried out at 25 °C for 5 min. Subsequently, dichloromethane was added to dissolve the product, and a small amount of water was added to terminate the reaction. The filtrate was slowly poured into ethanol for recrystallization (3 times), filtered, collected, and dried at room temperature to obtain 135 g of polylactide, with a yield of 93.8% and a molecular weight of 138 × 10⁻⁶. 3 The PDI is 1.24.

[0071] Application Example 6

[0072] Under nitrogen protection, 0.2 g of catalyst ②, 0.3 mL of benzyl alcohol, 28.8 g of lactide, and 150 mL of toluene were sequentially added to an ampoule that had been purged with nitrogen and baked at high temperature. The reaction was carried out at 25 °C for 1 min. Subsequently, dichloromethane was added to dissolve the product, and a small amount of water was added to terminate the reaction. The filtrate was slowly poured into ethanol for recrystallization (3 times), filtered, collected, and dried at room temperature to obtain 26.5 g of polylactide, with a yield of 92.0% and a molecular weight of 27.2 × 10⁻⁶. 3 The PDI is 1.17 (the measured GPC curve is shown below). Figure 6 (As shown).

[0073] Application Example 7

[0074] Under nitrogen protection, 0.3 g of catalyst ③, 0.2 mL of benzyl alcohol, 43.2 g of lactide, and 500 mL of toluene were sequentially added to an ampoule that had been purged with nitrogen and baked at high temperature. The reaction was carried out at 40 °C for 5 min. Subsequently, dichloromethane was added to dissolve the product, and a small amount of water was added to terminate the reaction. The filtrate was slowly poured into ethanol for recrystallization (3 times), filtered, collected, and dried at room temperature to obtain 41.8 g of polylactide, with a yield of 96.8% and a molecular weight of 41.2 × 10⁻⁶. 3 The PDI is 1.24.

[0075] Application Example 8

[0076] Under nitrogen protection, 0.2 g of catalyst ④, 0.1 mL of benzyl alcohol, 72.0 g of lactide, and 400 mL of toluene were sequentially added to an ampoule that had been purged with nitrogen and baked at high temperature. The reaction was carried out at 20 °C for 10 min. Subsequently, dichloromethane was added to dissolve the product, and a small amount of water was added to terminate the reaction. The filtrate was slowly poured into ethanol for recrystallization (3 times), filtered, collected, and dried at room temperature to obtain 69.4 g of polylactide, with a yield of 96.4% and a molecular weight of 68.1 × 10⁻⁶. 3 The PDI is 1.27.

[0077] Application Example 9

[0078] Under nitrogen protection, 0.3 g of catalyst ①, 0.1 mL of benzyl alcohol, 86.4 g of lactide, and 450 mL of toluene were sequentially added to an ampoule that had been purged with nitrogen and baked at high temperature. The reaction was carried out at 25 °C for 1 min. Subsequently, dichloromethane was added to dissolve the product, and a small amount of water was added to terminate the reaction. The filtrate was slowly poured into ethanol for recrystallization (3 times), filtered, collected, and dried at room temperature to obtain 82.2 g of polylactide, with a yield of 95.1% and a molecular weight of 81.1 × 10⁻⁶. 3 The PDI is 1.32.

[0079] Application Example 10

[0080] Under nitrogen protection, 0.3 g of catalyst ①, 0.1 mL of benzyl alcohol, 100.8 g of lactide, and 600 mL of toluene were sequentially added to an ampoule that had been purged with nitrogen and baked at high temperature. The reaction was carried out at 30 °C for 1 min. Subsequently, dichloromethane was added to dissolve the product, and a small amount of water was added to terminate the reaction. The filtrate was slowly poured into ethanol for recrystallization (3 times), filtered, collected, and dried at room temperature to obtain 93.2 g of polylactide, with a yield of 92.5% and a molecular weight of 94.6 × 10⁻⁶. 3 The PDI is 1.20.

[0081] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A lithium alcoholamine complex, characterized in that, Its structural formula is shown in Equation 1: Among them, R1 and R2 satisfy the following conditions: R1 and R2 are both phenyl, or R1 is phenyl and R2 is hydrogen, or R1 is phenyl and R2 is methyl, or R1 is o-fluorophenyl and R2 is hydrogen.

2. A method for preparing the lithium alcoholamine complex according to claim 1, characterized in that, Includes the following steps: 1) Under nitrogen protection, a hexane solution of n-butyllithium was injected into anhydrous N,N-dimethylaniline, the solvent was dried, the temperature was raised and the reaction was carried out. After the reaction was completed, the solid powder was obtained by treatment. 2) Under nitrogen protection, anhydrous diethyl ether was added to the solid powder prepared in step 1), and the mixture was sonicated. Then, a diethyl ether solution of the carbonyl compound was added dropwise at 0°C, and the temperature was raised to room temperature for reaction. After the reaction was completed, the lithium alcoholamine complex was obtained through post-treatment. The carbonyl compound is selected from one of benzaldehyde, o-fluorobenzaldehyde, acetophenone, and benzophenone.

3. The preparation method according to claim 2, characterized in that, Includes one or more of the following technical features: In step 1), the molar ratio of n-butyllithium to N,N-dimethylaniline is (1-1.1):1; In step 1), the reaction temperature is 50℃~80℃ and the reaction time is 1h~12h.

4. The preparation method according to claim 2, characterized in that, Includes one or more of the following technical features: In step 2), the mass ratio of anhydrous diethyl ether to solid powder is (5-20):1; The ultrasonic treatment time in step 2) is 10 min to 30 min; The molar ratio of the carbonyl compound to N,N-dimethylaniline is 1:1; The reaction time in step 2) is 1h to 12h.

5. The application of the lithium alkanolamine complex as described in claim 1 in the catalytic ring-opening polymerization of lactide to prepare polylactide.

6. A catalytic ring-opening polymerization reaction of lactide, characterized in that, The lithium alkanolamine complex described in claim 1 is used as a catalyst.

7. The catalytic ring-opening polymerization reaction of lactide as described in claim 6, characterized in that, Includes the following steps: Lithium alcoholamine complex, benzyl alcohol, and lactide were added to anhydrous toluene and subjected to ring-opening polymerization under nitrogen protection. After the reaction was completed, the reaction was quenched with water and post-treated to obtain polylactide.

8. The catalytic ring-opening polymerization reaction of lactide as described in claim 7, characterized in that, The lactide is selected from one or more of L-lactide, D-lactide, mesolactide, and racemic lactide.

9. The catalytic ring-opening polymerization reaction of lactide as described in claim 7, characterized in that, The molar ratio of lactide to lithium alkanolamine complex is (100-1000):1, and the molar ratio of benzyl alcohol to lithium alkanolamine complex is (1-4):

1.

10. The catalytic ring-opening polymerization reaction of lactide as described in claim 7, characterized in that, The reaction temperature is 10–60℃, and the reaction time is 0.5 min–30 min.

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