Bimetallic aluminum complex and method for preparing ultra-high molecular weight polycaprolactone by using bimetallic aluminum complex

Abstract

The invention designs and synthesizes a bimetallic aluminum complex and a method for preparing ultrahigh molecular weight polycaprolactone by using the bimetallic aluminum complex based on earlier-stage research and aiming at the limitation of the prior art. Through theoretical calculation and experimental verification, when aluminum is screened as a metal center, the bimetallic ligand shows an optimal synergistic catalysis effect. The catalyst can efficiently catalyze ring opening polymerization of epsilon-caprolactone in a wide temperature range of 25-150 DEG C, and an ultra-high molecular weight polycaprolactone material with the molecular weight exceeding two millions is successfully prepared. The ultra-high molecular weight polycaprolactone not only has more excellent thermal properties and mechanical properties, can meet the requirements of high-end fields such as biomedical treatment and the like on high-performance polyester materials, but also has the following advantages that the metal residual quantity is low, the molecular weight can be regulated and controlled within a certain range, and the production process is suitable for large-scale industrial production and has wide application prospects. The obvious practical value and market prospect are shown.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials, and particularly relates to a bimetallic aluminum complex and its use in the preparation of ultra-high molecular weight (number average molecular weight up to 2100.0 kg / mol) polycaprolactone. Background Art

[0002] Polycaprolactone is an aliphatic polyester with broad application prospects. Due to its excellent biocompatibility and biodegradability, it has attracted much attention in the fields of biomedicine, packaging materials, and reinforced composite materials. However, the commonly used stannous octoate catalyst in industry has the problem of heavy metal residue, and the molecular weight of the prepared polyester is relatively low, which is difficult to meet the requirements of the biomedical field for high-quality polyester materials. For example, in vivo scaffolds require ultra-high molecular weight polycaprolactone to provide sufficient mechanical properties and stability. In addition, the properties such as melting point, tensile strength, and flexural modulus of polycaprolactone increase significantly with the increase of molecular weight, but it is difficult to efficiently prepare high molecular weight polyester by traditional methods. Therefore, developing new catalysts to achieve the preparation of ultra-high molecular weight polyester materials can not only break through the existing technical bottlenecks but also further expand its applications in the fields of high-end medical treatment and high-performance materials, which has important scientific and practical significance.

[0003]

[0004] In view of the above problems, scientific researchers have developed various efficient catalysts to achieve the ring-opening polymerization of ε-caprolactone and prepare polycaprolactone. For example, Patent CN112851918A discloses a single-metal magnesium catalyst (Formula 1), which can efficiently achieve the self-polymerization reaction of ε-caprolactone at a certain catalyst ratio. However, with the increase of the catalyst ratio, an obvious catalyst concentration effect appears in the polymerization system, and the preparation of high molecular weight polyester cannot be achieved. Yao. Inorg. Chem. 2015, 54, 4699. introduces a bimetallic aluminum catalyst (Formula 2), which can prepare polycaprolactone materials with a number average molecular weight up to 172.8 kg / mol. Wang. Macromolecules 2024, 57, 5720. introduces a highly active bimetallic magnesium catalyst (Formula 3), which greatly reduces the catalyst ratio by utilizing the synergistic effect between the two metals. However, the highest number average molecular weight of the prepared polycaprolactone is only 480.6 kg / mol, still unable to meet the preparation of polycaprolactone materials with a number average molecular weight exceeding one million. Summary of the Invention

[0005] Based on previous research and aiming at the limitations of the existing technology, the present invention designs and synthesizes a brand-new bimetallic ligand. Through theoretical calculations and experimental verification, when aluminum is used as the metal center, the bimetallic ligand exhibits the best synergistic catalytic effect. This catalyst can efficiently catalyze the ring-opening polymerization of ε-caprolactone in a wide temperature range of 25-150 °C, and successfully prepares ultra-high molecular weight polycaprolactone materials with a molecular weight exceeding two million. This ultra-high molecular weight polycaprolactone not only has more excellent thermal and mechanical properties, meeting the requirements of high-performance polyester materials in high-end fields such as biomedicine, but also has the following advantages: low metal residue, the molecular weight can be regulated within a certain range, and the production process is suitable for large-scale industrial production, showing significant practical value and market prospects.

[0006] The technical solution of the present invention:

[0007] A bimetallic aluminum complex, which is a catalyst for the ring-opening polymerization of ε-caprolactone to prepare ultra-high molecular weight polycaprolactone, and the specific structural formula is as follows:

[0008]

[0009] Furthermore, the synthesis reaction equation of the bimetallic aluminum complex is:

[0010]

[0011] where n is a positive integer;

[0012] The specific preparation method of the bimetallic aluminum complex:

[0013] Under the protection of an inert gas, 2,4-di-tert-butylphenol and paraformaldehyde with a molar ratio of 1:1.1-1.3 are mixed, glacial acetic acid with a mass ratio to 2,4-di-tert-butylphenol of 3.5-4:1 is added, and after reacting at 15-25 °C for 10-12 h, a hydrobromic acid acetic acid solution with a molar ratio to 2,4-di-tert-butylphenol of 2-2.2:1 is added, and the reaction is continued while maintaining the temperature for 4-6 h, and then purified by recrystallization to obtain Intermediate 1.

[0014] Under the protection of inert gas, anhydrous tetrahydrofuran and triethylene glycol with a mass ratio of 10 - 16:1 are mixed evenly, and sodium hydride with a molar ratio of 6 - 6.5:1 to triethylene glycol is slowly added at -5 - 0 °C. After addition, the temperature is raised to 50 - 60 °C, and the reaction is kept for 10 - 12 h to obtain System 1. Intermediate 1 is dissolved in anhydrous tetrahydrofuran with a mass ratio of anhydrous tetrahydrofuran to Intermediate 1 of 3.5 - 4:1, and is added dropwise into System 1 at a constant speed through a constant pressure funnel within 2 - 3 h. The reaction is kept for 10 - 14 h. After the reaction ends, water is added to quench the reaction, and the pH value of the solution is adjusted to 3 - 4 by adding hydrochloric acid aqueous solution. Dichloromethane with a mass ratio of 3 - 5:1 to the solution is added for extraction, the organic phase is collected, the solvent is removed by vacuum distillation to obtain the crude product of the bimetallic aluminum ligand, and the pure product of the bimetallic ligand is obtained by column chromatography purification.

[0015] Under the protection of inert gas, the bimetallic ligand is dissolved in anhydrous tetrahydrofuran with a mass ratio of 2 - 5:1 to it, and is dropped into triethylaluminum with a molar ratio of 5 - 10:1 to the bimetallic ligand at a constant speed within 1 - 3 h at -15 - -10 °C. After dropping, the temperature is raised to 20 - 25 °C, and the reaction is kept for 20 - 24 h. After the reaction ends, the solvent is removed by vacuum distillation, and then anhydrous n-hexane with a mass ratio of 3 - 5:1 to the bimetallic ligand is added, and a white precipitate is precipitated. Stir for 1 - 2 h, wash, filter, collect the filter cake, repeat the operation 3 - 5 times, and dry to obtain the bimetallic aluminum complex.

[0016] Using one of the above bimetallic aluminum complexes, the specific polymerization reaction process is as follows: Under the protection of inert gas, the bimetallic aluminum complex and the initiator are added into the reactor, and an organic solvent is selectively added. After stirring for a period of time at the reaction temperature, ε-caprolactone with a molar ratio of 15000:1 to the bimetallic aluminum complex is added, and the reaction is continued with stirring at the reaction temperature; after the reaction is completed, the crude product is first dissolved in dichloromethane, and then methanol is added, and stirred vigorously to precipitate the polymer. The precipitation process is repeated to obtain polycaprolactone.

[0017] Furthermore, the molar ratio of the bimetallic aluminum complex to the initiator is 1:0.5 - 4;

[0018] Furthermore, the mixing and stirring time of the bimetallic aluminum complex and the initiator is 20 - 30 min.

[0019] Furthermore, the molar ratio of ε-caprolactone to the bimetallic aluminum complex is 12000 - 15000:1;

[0020] Furthermore, the reaction temperature is 25 - 150 °C; the reaction time is 4.0 - 12.0 h.

[0021] Further, the initiator is one of methanol, 1,4-butanediol, p-xylene glycol, glycerol, erythritol, xylitol, sorbitol, sucrose, and polypropylene glycol, and the number-average molecular weight of the polypropylene glycol is 2.0 to 10.0 kg / mol.

[0022] Further, the organic solvent is one of ultra-dry tetrahydrofuran, ultra-dry toluene, ultra-dry acetonitrile, and ultra-dry dichloromethane.

[0023] Further, the number-average molecular weight of the ultra-high molecular weight polycaprolactone is 400.0 to 2100.0 kg / mol; the molecular weight distribution is 1.20 to 2.20.

[0024] Advantages of the present invention:

[0025] (1) The present invention designs and synthesizes a novel bimetallic aluminum complex. Through the synergistic catalytic effect of the bimetal, the efficient ring-opening polymerization of ε-caprolactone is achieved, and polycaprolactone with a number-average molecular weight of up to 2100.0 kg / mol is prepared.

[0026] (2) The bimetallic aluminum complex designed and synthesized by the present invention has a wide range of initiator applicability and can efficiently prepare polycaprolactone materials with a functionality between 1 and 8. Specific embodiments

[0027] The technical solutions of the present invention are further described below through examples.

[0028] The terms used in the present invention generally have the meanings commonly understood by those of ordinary skill in the art unless otherwise specified.

[0029] In the following examples, various processes and methods not described in detail are conventional methods well known in the art. To further illustrate the differences between the monometallic aluminum complex, the bimetallic aluminum complexes with different ligand skeletons, and other bimetallic complexes with the same ligand skeleton and the present invention, the corresponding complex structures were prepared and compared with the examples in the comparative examples.

[0030] Example 1 is an example of the preparation method of the bimetallic aluminum complex of the present invention, and Comparative Examples 1 to 4 are respectively examples of the preparation methods of the bimetallic magnesium complex, the bimetallic zinc complex, the bimetallic aluminum complex with different ligand skeletons, and the monometallic aluminum complex. Examples 2 to 5 are examples of the method for preparing polycaprolactone using the above complexes.

[0031] For ease of expression and description, the catalyst structure, name, and the structure of ε-caprolactone are shown below.

[0032]

[0033] Example 1

[0034] Synthesis reaction equation of the bimetallic aluminum complex:

[0035]

[0036] Specific preparation steps of the bimetallic aluminum complex:

[0037] Under nitrogen protection, 2,4 - di - tert - butylphenol (30.0 g, 145.40 mmol) and paraformaldehyde (5.2 g, 178.48 mmol) with a molar ratio of 1:1.2 were mixed, acetic acid (120.0 g) with a mass ratio of 4:1 to 2,4 - di - tert - butylphenol was added. After reacting at 25 °C for 12 h, a hydrobromic acid acetic acid solution (72.7 ml, 290.80 mmol, 4 mol / L) with a molar ratio of 2:1 to 2,4 - di - tert - butylphenol was added, and the reaction continued for 6 h. After the reaction was completed, the solvent was removed by rotary evaporation, and then n - hexane (90.0 g) with a mass ratio of 3:1 to 2,4 - di - tert - butylphenol was added for recrystallization purification to obtain Intermediate 1 (27.50 g, 91.92 mmol, yield 63%). 1 HNMR(400MHz,CDCl 3 )δ7.35(d,J=2.4Hz,1H),7.11(d,J=2.4Hz,1H),5.29(s,1H),4.59(s,2H),1.45(s,9H),1.31(s,9H).

[0038] Under nitrogen protection, anhydrous tetrahydrofuran (18.0 g) and triethylene glycol (1.2 g, 8.15 mmol) with a mass ratio of 15:1 were mixed. Sodium hydride (2.0 g, 48.9 mmol) with a molar ratio of 6:1 to triethylene glycol was slowly added at - 5 °C, and the system temperature was controlled not to exceed 0 °C during the slow addition. After addition, the temperature was raised to 50 °C and the reaction was kept for 12 h to obtain System 1. Intermediate 1 (5.00 g, 16.71 mmol) was dissolved in anhydrous tetrahydrofuran (20.0 g) with a mass ratio of 4:1 to it, and was added dropwise into System 1 at a constant speed through a constant - pressure funnel within 3 h. The reaction was kept for 12 h. After the reaction ended, water was added to quench the reaction, and 3M hydrochloric acid aqueous solution was slowly added to adjust the pH value of the solution to 3.5. Dichloromethane (65.0 g) with a mass ratio of 3 - 5:1 to the solution was added for extraction, and the organic phase was collected three times. After adding a desiccant to remove water, the solvent was removed under reduced pressure to obtain the crude bimetallic ligand. The crude product was separated and purified by column chromatography (silica gel column; eluent: petroleum ether / ethyl acetate = 20 / 1) to obtain the pure bimetallic ligand (3.0 g, 5.1 mmol, yield 63%). 11H NMR (400 MHz, CDCl3) δ 7.61 (s, 2H), 7.25 (d, J = 2.3 Hz, 2H), 6.88 (d, J = 2.3 Hz, 2H), 4.69 (s, 4H), 3.72 (d, J = 3.9 Hz, 12H), 1.41 (s, 9H), 1.27 (s, 9H).

[0039] Under nitrogen protection, the bimetallic ligand (0.5 g, 0.85 mmol) was dissolved in anhydrous tetrahydrofuran (2.0 g) with a mass ratio of 4:1. At -15 °C, it was uniformly added dropwise into triethylaluminum (4.3 ml, 8.5 mmol, 2 mol / L in n-hexane solution) with a molar ratio of 10:1 to the bimetallic ligand within 2 h. After the addition, the temperature was raised to 20 °C and the reaction was kept for 24 h. After the reaction was completed, the solvent was removed under reduced pressure. Then, anhydrous n-hexane (2.5 g) with a mass ratio of 5:1 to the bimetallic ligand was added. A white precipitate was formed, stirred for 1 h, washed, filtered, and the filter cake was collected. The operation was repeated 3 times, and the filter cake was collected and dried to obtain the bimetallic aluminum complex (0.48 g, 0.64 mmol, yield 76%).

[0040] Comparative Example 1

[0041] Synthesis reaction equation of the bimetallic magnesium complex:

[0042]

[0043] Specific preparation process of the bimetallic magnesium complex:

[0044] Under nitrogen protection, the bimetallic ligand (0.5 g, 0.85 mmol) was dissolved in anhydrous tetrahydrofuran (2.0 g) with a mass ratio of 4:1. At -15 °C, it was uniformly added dropwise into diethylmagnesium (8.5 ml, 8.5 mmol, 1 mol / L in n-hexane solution) with a molar ratio of 10:1 to the bimetallic ligand within 2 h. After the addition, the temperature was raised to 20 °C and the reaction was kept for 24 h. After the reaction was completed, the solvent was removed under reduced pressure. Then, n-hexane (2.5 g) with a mass ratio of 5:1 to the bimetallic ligand was added. A white precipitate was formed, stirred for 1 h, washed, filtered, and the filter cake was collected. The operation was repeated 3 times, and the filter cake was collected and dried to obtain the bimetallic magnesium complex (0.47 g, 0.68 mmol, yield 80%).

[0045] Comparative Example 2

[0046] Synthesis reaction equation of the bimetallic zinc complex:

[0047]

[0048] Specific preparation process of the bimetallic zinc complex:

[0049] Under nitrogen protection, the bimetallic ligand (0.5 g, 0.85 mmol) was dissolved in anhydrous tetrahydrofuran (2.0 g) with a mass ratio of 4:1. At -15 °C, diethylzinc (8.5 ml, 8.5 mmol, 1 mol / L in hexane solution) with a molar ratio of 10:1 to the bimetallic ligand was added dropwise evenly within 2 h. After the addition was completed, the temperature was raised to 20 °C and the reaction was kept for 24 h. After the reaction ended, the solvent was removed under reduced pressure. Then, hexane (2.5 g) with a mass ratio of 5:1 to the bimetallic ligand was added, and a white precipitate was formed. After stirring for 1 h, it was washed, filtered, and the filter cake was collected. The operation was repeated 3 times, and the filter cake was collected and dried to obtain the bimetallic zinc complex (0.42 g, 0.54 mmol, yield 64%).

[0050] Comparative Example 3

[0051] Synthesis reaction equation of bimetallic aluminum complexes with different ligand structures:

[0052]

[0053] Specific preparation process of bimetallic aluminum complexes with different ligand structures:

[0054] Under nitrogen protection, ligand A (0.52 g, 0.85 mmol) was dissolved in anhydrous tetrahydrofuran (2.0 g) with a mass ratio of 4:1. At -15 °C, triethylaluminum (4.3 ml, 8.5 mmol, 2 mol / L in hexane solution) with a molar ratio of 10:1 to ligand A was added dropwise evenly within 2 h. After the addition was completed, the temperature was raised to 20 °C and the reaction was kept for 24 h. After the reaction ended, the solvent was removed under reduced pressure. Then, hexane (2.5 g) with a mass ratio of 5:1 to ligand A was added, and a white precipitate was formed. After stirring for 1 h, it was washed, filtered, and the filter cake was collected. The operation was repeated 3 times, and the filter cake was collected and dried to obtain the bimetallic aluminum complex with different ligand structures (0.48 g, 0.61 mmol, yield 72%).

[0055] Comparative Example 4

[0056] Synthesis reaction equation of monometallic aluminum complex:

[0057]

[0058] Specific preparation steps of the monometallic aluminum complex are as follows:

[0059] Under nitrogen protection, anhydrous tetrahydrofuran (20.0 g) and ethylene glycol methyl ether (1.91 g, 25.06 mmol) with a mass ratio of 10.5:1 were mixed. Sodium hydride (1.34 g, 33.42 mmol) with a molar ratio of 1:1.3 to ethylene glycol methyl ether was added at -5 °C. It was added slowly while controlling the system temperature not to exceed 0 °C. After addition, the temperature was raised to 50 °C and the reaction was carried out under insulation for 12 h to obtain System 2. The intermediate 1 (5.00 g, 16.71 mmol) prepared in Example 1 was dissolved in anhydrous tetrahydrofuran (20.0 g) with a mass ratio of 4:1 to it, and was added dropwise into System 2 uniformly within 3 h through a constant pressure funnel. The reaction was carried out under insulation for 12 h. After the reaction ended, water was added to quench the reaction, and 3M hydrochloric acid aqueous solution was slowly added to adjust the pH value of the solution to 3. Dichloromethane (65.0 g) with a mass ratio of 3:1 to the solution was added for extraction. The organic phase was collected and repeated three times. After adding a desiccant to remove water, the solvent was removed under reduced pressure to obtain a crude product of the monometallic ligand. The crude product was separated and purified by column chromatography (silica gel column; eluent: petroleum ether / ethyl acetate = 20 / 1) to obtain a pure product of the monometallic ligand (4.30 g, 14.60 mmol, yield 87%). 1 H NMR (400 MHz, CDCl3) δ 7.56 (s, 1H), 7.28 (d, J = 2.4 Hz, 1H), 6.91 (d, J = 2.4 Hz, 1H), 4.72 (s, 2H), 3.72 (m, 2H), 3.60 (m, 2H), 3.42 (s, 3H), 1.43 (s, 9H), 1.29 (s, 9H).

[0060] Under nitrogen protection, the monometallic ligand (0.5 g, 1.70 mmol) was dissolved in anhydrous tetrahydrofuran (2.0 g) with a mass ratio of 4:1 to it. At -10 °C, triethylaluminum (4.3 ml, 8.52 mmol, 2 mol / L in n - hexane solution) with a molar ratio of 5:1 to the monometallic ligand was added dropwise uniformly within 2 h. After addition, the temperature was raised to room temperature and the reaction was carried out under insulation for 24 h. After the reaction ended, the solvent was removed under reduced pressure. Then, n - hexane (2.5 g) with a mass ratio of 5:1 to the monometallic ligand was added, and stirred for 1 h. Recrystallization was carried out at -15 °C. The supernatant was poured off and the operation was repeated 3 times. After drying, a monometallic aluminum complex (0.53 g, 1.39 mmol, yield 82%) was obtained.

[0061] Example 2

[0062] A 100 mL reaction flask equipped with a magnetic stir bar was dried at 120 °C for more than 12 h, evacuated, and allowed to cool to room temperature. Nitrogen was flushed in and it was ready for use. Under nitrogen protection, a bimetallic aluminum complex (6.30 mg, 8.33 μmol) and p-xylene glycol (3.45 mg, 24.99 μmol) were added to the reaction flask. Ultra-dry tetrahydrofuran (20.00 g) was added, and the mixture was stirred at 25 °C for 30 min. Then, ε-caprolactone (11.41 g, 100.00 mmol) with a molar ratio of 12000:1 to the bimetallic aluminum complex was added, and the reaction was carried out at a constant temperature for 12 h and then stopped. The crude product was first dissolved in dichloromethane, then methanol was added, and the mixture was stirred vigorously to precipitate the polymer. The precipitation process was repeated to obtain polycaprolactone (10.95 g, yield 96%). Gel permeation chromatography showed that the number-average molecular weight of the polycaprolactone was 400.0 kg / mol and the molecular weight distribution was 1.20.

[0063] Example 3

[0064] A 100 mL reaction flask equipped with a magnetic stir bar was dried at 120 °C for more than 12 h, evacuated, and allowed to cool to room temperature. Nitrogen was flushed in and it was ready for use. Under nitrogen protection, a bimetallic aluminum complex (5.04 mg, 6.67 μmol) and sorbitol (0.61 mg, 3.34 μmol) were added to the reaction flask. The mixture was stirred at 150 °C for 30 min. Then, ε-caprolactone (11.41 g, 100.00 mmol) with a molar ratio of 15000:1 to the bimetallic aluminum complex was added, and the reaction was carried out at a constant temperature for 4 h and then stopped. The crude product was first dissolved in dichloromethane, then methanol was added, and the mixture was stirred vigorously to precipitate the polymer. The precipitation process was repeated to obtain polycaprolactone (10.73 g, yield 94%). Gel permeation chromatography showed that the number-average molecular weight of the polycaprolactone was 2100.0 kg / mol and the molecular weight distribution was 2.20.

[0065] Example 4

[0066] A 100 mL reaction flask equipped with a magnetic stir bar was dried at 120 °C for more than 12 h, evacuated, allowed to cool to room temperature, and purged with nitrogen for use. Under nitrogen protection, a bimetallic aluminum complex (5.04 mg, 6.67 μmol) and polypropylene glycol with a number-average molecular weight of 8.0 kg / mol (0.11 g, 13.34 μmol) were added to the reaction flask. Ultra-dry toluene (10.00 g) was added, and the mixture was stirred at 100 °C for 30 min. Then, ε-caprolactone (11.41 g, 100.00 mmol) with a molar ratio of 15000:1 to the bimetallic aluminum complex was added, and the reaction was carried out at a constant temperature for 6 h before stopping the reaction. The crude product was first dissolved in dichloromethane, then methanol was added, and the mixture was stirred vigorously to precipitate the polymer. The precipitation process was repeated to obtain polycaprolactone (11.06 g, yield 96%). Gel permeation chromatography showed that the number-average molecular weight of the polycaprolactone was 750.0 kg / mol and the molecular weight distribution was 1.65.

[0067] Example 5

[0068] A 100 mL reaction flask equipped with a magnetic stir bar was dried at 120 °C for more than 12 h, evacuated, allowed to cool to room temperature, and purged with nitrogen for use. Under nitrogen protection, a bimetallic aluminum complex (5.04 mg, 6.67 μmol) and erythritol (0.82 mg, 6.67 μmol) were added to the reaction flask. Ultra-dry toluene (5.00 g) was added, and the mixture was stirred at 120 °C for 30 min. Then, ε-caprolactone (11.41 g, 100.00 mmol) with a molar ratio of 15000:1 to the bimetallic aluminum complex was added, and the reaction was carried out at a constant temperature for 5 h before stopping the reaction. The crude product was first dissolved in dichloromethane, then methanol was added, and the mixture was stirred vigorously to precipitate the polymer. The precipitation process was repeated to obtain polycaprolactone (10.95 g, yield 96%). Gel permeation chromatography showed that the number-average molecular weight of the polycaprolactone was 1530.0 kg / mol and the molecular weight distribution was 1.83.

[0069] Table 1 Experimental results of the ring-opening polymerization of ε-caprolactone to prepare polycaprolactone

[0070]

[0071] The experimental procedures of Comparative Examples 5-1 to 5-4 in Table 1 were the same as those of Example 5. ε-Caprolactone was used as the raw material. The molar ratios of ε-caprolactone to the bimetallic magnesium complex of Comparative Example 1, the bimetallic zinc complex of Comparative Example 2, and the bimetallic aluminum complex with different ligand structures of Comparative Example 3 were all 15,000:1. The molar ratio of ε-caprolactone to the monometallic aluminum complex of Comparative Example 4 was 7,500:1. Erythritol was used as the initiator, and the molar ratio of erythritol to the metal complex was 1:1. The solvent was ultra-dry toluene, and the mass ratio of the solvent to ε-caprolactone was 5:11.41. The reaction temperature was 120 °C, and the reaction time was 5 h. The differences were the types of catalysts, the molecular weight, molecular weight distribution, and yield of the corresponding polycaprolactone at 5 h of reaction.

Claims

1. A bimetallic aluminum complex, characterized in that: The bimetallic aluminum complex is a catalyst for preparing ultrahigh molecular weight polycaprolactone by ring-opening polymerization of ε-caprolactone, and the specific structural formula is as follows:

2. The method for preparing the bimetallic aluminum complex according to claim 1, characterized in that: The synthesis reaction equation of the bimetallic aluminum complex is: Wherein, n is a positive integer; The specific preparation method of the bimetallic aluminum complex is: Under the protection of inert gas, 2,4-di-tert-butylphenol and paraformaldehyde in a molar ratio of 1:1.1-1.3 are mixed, glacial acetic acid in a mass ratio of 3.5-4:1 to 2,4-di-tert-butylphenol is added, and after reacting at 15-25° C. for 10-12 hours, a hydrogen bromide acetic acid solution in a molar ratio of 2-2.2:1 to 2,4-di-tert-butylphenol is added, the reaction is continued for 4-6 hours under heat preservation, and recrystallization is performed to purify to obtain intermediate 1; Under the protection of inert gas, anhydrous tetrahydrofuran and triethylene glycol in a mass ratio of 10 to 16:1 are uniformly mixed, and sodium hydride in a molar ratio of 6 to 6.5:1 to triethylene glycol is slowly added at -5 to 0°C, and the temperature is raised to 50 to 60°C after the addition, and the reaction is kept warm for 10 to 12 hours to obtain system 1; intermediate 1 is dissolved in anhydrous tetrahydrofuran, and the mass ratio of anhydrous tetrahydrofuran to intermediate 1 is 3.5 to 4:1, and is uniformly added to system 1 through a constant pressure funnel within 2 to 3 hours, and the reaction is kept warm for 10 to 14 hours. After the reaction is completed, water is added to quench the reaction, and a hydrochloric acid aqueous solution is added to adjust the pH value of the solution to 3 to 4, and dichloromethane in a mass ratio of 3 to 5:1 to the solution is added for extraction, and the organic phase is collected, and the solvent is removed by reduced pressure distillation to obtain a crude product of the bimetallic aluminum ligand, and the bimetallic ligand is purified by column chromatography to obtain a pure product; Under the protection of inert gas, the bimetallic ligand is dissolved in anhydrous tetrahydrofuran in a mass ratio of 2 to 5:1 with the bimetallic ligand, and triethylaluminum in a molar ratio of 5 to 10:1 with the bimetallic ligand is uniformly added dropwise at -15 to -10°C over 1 to 3 hours. After the addition is completed, the temperature is raised to 20 to 25°C, and the reaction is kept warm for 20 to 24 hours. After the reaction is completed, the solvent is removed by distillation under reduced pressure, and anhydrous n-hexane in a mass ratio of 3 to 5:1 with the bimetallic ligand is added to precipitate a white precipitate. The precipitate is stirred for 1 to 2 hours, washed, filtered, and the filter cake is collected. The operation is repeated 3 to 5 times and dried to obtain a bimetallic aluminum complex.

3. A method for preparing ultrahigh molecular weight polycaprolactone using a bimetallic aluminum complex according to claim 1 or a bimetallic aluminum complex prepared by the preparation method according to claim 2, characterized in that: The specific polymerization reaction process is: under the protection of inert gas, add bimetallic aluminum complex and initiator into the reactor, selectively add organic solvent, stir at the reaction temperature for a period of time, then add ε-caprolactone with a molar ratio of 15000:1 to the bimetallic aluminum complex, and continue to stir and react at the reaction temperature; after the reaction is completed, first dissolve the crude product in dichloromethane, then add methanol, and stir vigorously to precipitate the polymer, and repeat the precipitation process repeatedly to obtain polycaprolactone.

4. The method according to claim 3, characterized in that The molar ratio of the bimetallic aluminum complex to the initiator is 1:0.5-4.

5. The method according to claim 3, characterized in that: The mixing and stirring time of the bimetallic aluminum complex and the initiator is 20 to 30 minutes.

6. The method according to claim 3, characterized in that The molar ratio of ε-caprolactone to the bimetallic aluminum complex is 12000-15000:

1.

7. The method according to claim 3, characterized in that The reaction temperature is 25-150° C. and the reaction time is 4.0-12.0 h.

8. The method according to claim 3, characterized in that The initiator is one of methanol, 1,4-butanediol, terephthalic acid, glycerol, erythritol, xylitol, sorbitol, sucrose and polypropylene glycol, and the number average molecular weight of the polypropylene glycol is 2.0-10.0 kg / mol.

9. The method according to claim 3, characterized in that: The organic solvent is one of super dry tetrahydrofuran, super dry toluene, super dry acetonitrile and super dry dichloromethane.

10. The method according to any one of claims 3 to 9, characterized in that: The number average molecular weight of the ultra-high molecular weight polycaprolactone is 400.0-2100.0 kg / mol, and the molecular weight distribution is 1.20-2.20.

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