Bimetallic magnesium catalysts and methods for the preparation of lactone, lactide homopolymer or copolymer using same

Abstract

The application belongs to the field of high polymer materials, and particularly relates to a kind of bimetallic magnesium catalyst and a preparation method of lactone, lactide self-polymer or copolymer using the bimetallic magnesium catalyst.The bimetallic magnesium catalyst is designed and synthesized, and can realize the self-polymerization and copolymerization of lactone or lactide by bimetallic synergistic catalysis.Compared with a single metal catalyst, the bimetallic catalyst can realize synergistic catalysis, and the activity is greatly improved.Meanwhile, the preparation route of the catalyst given in the application is simple, raw materials are all commercial bulk chemicals, and the process is suitable for scale-up.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, specifically relating to the use of a type of bimetallic magnesium catalyst for the preparation of lactones, lactide self-polymers or copolymers. Background Technology

[0002] Polyester materials are a class of high-performance and widely used polymers. Among the methods for preparing polyesters, the ring-opening self-polymerization of lactones or lactides is receiving increasing attention from researchers. The ring-opening self-polymerization of lactones or lactides offers advantages such as low cost, high atom utilization, and mild reaction conditions. Furthermore, polyester materials prepared from lactones or lactides often exhibit good biocompatibility and biodegradability, leading to their increasingly widespread application in the biomedical field, such as polylactic acid (PLLA) and polycaprolactone (PCL). Therefore, developing novel catalysts for the polymerization of lactones or lactides is of great significance. Currently, the industrially mature catalyst is stannous octoate; however, metallic tin easily causes heavy metal residues in polyester products, and the separation process is complex and costly, increasingly failing to meet the demands of the biomedical field for high-quality polyester materials.

[0003] To address the aforementioned issues, researchers have developed a variety of highly efficient catalysts for the polymerization of lactones or lactides, such as Lin Chu-Chich. J.Polym. Sci. In 2008, 46(19), 6466-6476, a mononuclear zinc catalyst, as shown in Formula 1, was introduced, which can realize the polymerization reaction of lactide. Patent CN112851918A disclosed a mononuclear magnesium catalyst, as shown in Formula 2, which can efficiently realize the self-polymerization or copolymerization reaction of lactone and lactide under a certain catalyst ratio.

[0004] While the aforementioned two types of catalysts exhibit high activity in catalyzing lactone or lactide polymerization, they also have certain limitations. Specifically, when the catalyst-to-monomer ratio is high, the catalytic reaction can be completed in a very short time; however, when the catalyst-to-monomer ratio is low, the catalytic activity shows a significant downward trend. Therefore, this type of catalyst remains challenging for the preparation of high molecular weight polyester materials. Furthermore, due to the high catalyst loading, the purification and separation of the metals also present complex problems. Based on these findings and considering the catalytic activity characteristics exhibited by the aforementioned catalysts, this application considers that such reactions may be bimetallic synergistic catalytic reactions. Therefore, if bimetallic catalysts with suitable ligand framework structures and controllable metal spacing can be prepared, it is hoped that the above problems can be solved.

[0005] In previous research, we designed and synthesized a class of bimetallic catalysts, which were described in the patent "A Class of Highly Active Catalysts, Preparation Methods and Their Application in Lactone or Lactose Polymerization, Publication No. CN115746283A," with the general structural formula shown in Formula 3. This type of catalyst exhibits significantly improved activity when the metal-to-monomer ratio is the same, demonstrating a synergistic effect between the bimetals. Based on this, this application further optimizes the ligand framework of the bimetals, designing and synthesizing two types of catalysts as described in this invention. The ligand structures of the two catalysts are similar, but the bridging structure of the bimetals has been altered compared to Formula 3, further optimizing the spacing and orientation of the bimetals. Simultaneously, the light metal magnesium is still used instead of the heavy metal zinc, resulting in a significantly improved catalytic activity compared to mononuclear catalysts. Summary of the Invention

[0006] The main content of this invention is to provide a type of bimetallic magnesium catalyst and its application in the preparation of lactones, lactide self-polymers or copolymers, based on the shortcomings of the prior art.

[0007] The technical solution of the present invention: A class of bimetallic magnesium catalysts, wherein the bimetallic magnesium catalyst has a general structural formula of 1 or 2.

[0008] In the formula: R is .

[0009] The catalyst 1 specifically includes the following three structures: .

[0010] The catalyst 2 specifically includes the following three structures: .

[0011] Furthermore, the synthesis reaction equation for binuclear magnesium catalyst 1 is as follows: The specific preparation steps of the dual-nuclear magnesium catalyst 1 are as follows: Under inert gas protection, a mixture of diol and potassium tert-butoxide in a molar ratio of 1:5 to 5.5 was added. A first portion of tetrahydrofuran was then added, with a tetrahydrofuran to diol mass ratio of 40 to 50:1. Chloroacetic acid was then dissolved in a second portion of tetrahydrofuran, with a chloroacetic acid to diol molar ratio of 2.3 to 2.5:1, in a mass ratio of 4 to 5:1. The mixture was heated to reflux, and the tetrahydrofuran solution of chloroacetic acid was added to the reaction system at a uniform rate over 1 to 5 hours. After the addition was complete, the reaction was maintained at this temperature for 8 to 12 hours. The tetrahydrofuran was removed by vacuum distillation to obtain crude intermediate 1, which was not purified and proceeded directly to the next reaction step.

[0012] Add methanol (40-50:1 mass ratio to diol) and concentrated sulfuric acid (2-3:1 mass ratio to diol) to the crude intermediate 1. Heat to reflux and react for 10-15 h. After the reaction is complete, cool to room temperature, filter, collect the filtrate, and rotary evaporate. First, extract with ethyl acetate and deionized water (1:1 volume ratio), collect the organic phase, then extract with ethyl acetate and saturated sodium carbonate solution (1:1 volume ratio), collect the organic phase, dry, filter, collect the filtrate, remove the solvent under reduced pressure, and obtain a dark brown liquid, which is the crude intermediate 2.

[0013] Under inert gas protection, crude intermediate 2 was dissolved in anhydrous tetrahydrofuran at a mass ratio of 2.5–3:1. Lithium aluminum hydride, with a molar ratio of 2–3:1 to crude intermediate 2, was added slowly over 1–4 hours at -5–0 °C, controlling the system temperature to not exceed 0 °C. After the addition was complete, the temperature was raised to 20–30 °C and the reaction was maintained for 12–15 hours. The reaction was then quenched with water. The mixture was filtered multiple times, the filtrate was collected, dried, filtered again, and the filtrate was collected. The solvent was removed under reduced pressure to obtain crude intermediate 3. Reduced pressure distillation yielded a colorless, viscous liquid intermediate 3.

[0014] Under inert gas protection, pyridine at a molar ratio of 2-3:1 to intermediate 3 was added, followed by 1,4-dioxane at a mass ratio of 1.5-2.5:1 to intermediate 3. The mixture was heated to 80-90 °C, and thionyl chloride at a molar ratio of 2.5:1 to intermediate 3 was added uniformly over 2-5 h through a constant pressure funnel. The reaction was maintained at this temperature for 10-14 h. After the reaction was completed, excess pyridine and thionyl chloride were removed by rotary evaporation. Methyl tert-butyl ether was added, and the mixture was stirred, washed, filtered, and the filtrate was collected. This process was repeated several times, and the filtrate was concentrated and purified by vacuum distillation to obtain intermediate 4.

[0015] Intermediate 4 was added to an aqueous solution of methylamine, with a molar ratio of methylamine to intermediate 4 of 3-10:1. The temperature was raised to 70-90 °C and the reaction was carried out for 10-12 h. After the reaction was completed, the temperature was lowered to room temperature, and sodium hydroxide was slowly added until the system no longer showed obvious exothermic reaction or bubble generation, and obvious stratification occurred. The upper layer was collected and distilled under reduced pressure to obtain intermediate 5.

[0016] Under inert gas protection, intermediate 5, 2,4-di-tert-butylphenol, and paraformaldehyde were mixed in a molar ratio of 1:2.1~2.5:2.5~3 and dissolved in ethanol at a mass ratio of 7~10:1 to intermediate 5. The mixture was then stirred at 90~120℃ for 12~16 h. After the reaction was complete, a solution of ethyl hydrochloric acid and ethyl acetate at a molar ratio of 2.3~2.5:1 to intermediate 5 was added to obtain a white precipitate. The precipitate was filtered, the filter cake was collected, and washed with ethanol. The dried filter cake was dissolved in water at a mass ratio of 3~5:1. NaHCO3 was added to adjust the pH of the solution to 6~7. Dichloromethane at a mass ratio of 3~5:1 to the filter cake was added for extraction. The organic phase was collected, and after adding a desiccant to remove water, the solvent was removed under reduced pressure to obtain intermediate 6.

[0017] Under inert gas protection, intermediate 6 was dissolved in anhydrous tetrahydrofuran at a mass ratio of 2-5:1. The solution was then added dropwise at a uniform rate to di-n-butylmagnesium at a molar ratio of 5-10:1 to intermediate 6 over 1-3 h at -15 to -10 °C. After the addition was complete, the mixture was brought to room temperature and the reaction was maintained for 20-24 h. Once the reaction was complete, the solvent was removed under reduced pressure, and then n-hexane at a mass ratio of 3-5:1 to intermediate 6 was added. A white precipitate formed. The mixture was stirred for 1-2 h, washed, filtered, and the filter cake was collected. This process was repeated 3-5 times. The filter cake was collected and dried to obtain binuclear magnesium catalyst 1.

[0018] Furthermore, the intermediate 4 is used to synthesize a binuclear magnesium catalyst 2. The synthesis reaction equation for the binuclear magnesium catalyst 2 is as follows: The specific preparation steps of the dual-nuclear magnesium catalyst 2 are as follows: Under inert gas protection, potassium phthalimide was mixed with DMF at a mass ratio of 3-4:1, heated to reflux, and stirred to dissolve. Intermediate 4, with a molar ratio of 1:2.5-3 to potassium phthalimide, was dissolved in DMF at an amount of 4-5 times the mass of intermediate 4. The solution was added to the reaction system at a uniform rate over 1-4 hours, and the reaction was refluxed for 12-15 hours. After the reaction was completed, the mixture was cooled to room temperature, and deionized water at a mass ratio of 2-3:1 to DMF was added. The mixture was stirred for 1-2 hours, filtered, the filter cake was collected, and dried to obtain crude intermediate 7.

[0019] Potassium hydroxide was added at a molar ratio of 8-12:1 to intermediate 4, and deionized water was added to dissolve the potassium hydroxide. The reaction was carried out at 70-90 °C for 10-12 h, and then at room temperature until the solution changed from a suspension to a clear and transparent solution. Water was removed under normal pressure, methyl tert-butyl ether was added, and the mixture was stirred and washed. The solution was filtered, and the filtrate was collected. The solvent was removed by rotary evaporation to obtain crude intermediate 8. Intermediate 8 was obtained by vacuum distillation.

[0020] Intermediate 8 and 3,5-di-tert-butylsalicylaldehyde in a molar ratio of 1:2 to 2.5 were added to anhydrous ethanol, with the mass ratio of anhydrous ethanol to intermediate 8 being 3 to 5:1. The mixture was heated to reflux and reacted for 3 to 5 hours. The mixture was then slowly cooled to 40 to 45 °C, filtered at this temperature, and the filter cake was collected and dried to obtain intermediate 9.

[0021] Under inert gas protection, intermediate 9 was dissolved in anhydrous tetrahydrofuran at a mass ratio of 2-5:1. The tetrahydrofuran solution of intermediate 9 was added dropwise over 1-4 h at a uniform rate to di-n-butylmagnesium at a molar ratio of 5-10:1 to intermediate 9. After the addition was complete, the temperature was raised to room temperature and the reaction was maintained for 20-24 h. After the reaction was completed, the solvent was removed under reduced pressure, and then n-hexane at a mass ratio of 3-5:1 to intermediate 9 was added, resulting in the precipitation of a white precipitate. The precipitate was stirred for 1-2 h, washed, filtered, and the filter cake was collected. This process was repeated 3-5 times. The filter cake was collected and dried to obtain binuclear magnesium catalyst 2.

[0022] A method for preparing lactone, lactone and / or lactone self-polymers or copolymers using a bimetallic magnesium catalyst, the specific reaction process being as follows: adding a bimetallic magnesium catalyst, lactone and / or lactone to a reactor, selectively adding a chain transfer agent, selectively adding an organic solvent, stirring for a certain time at a certain reaction temperature, and then stopping the reaction; adding a large amount of methanol or ethanol to the crude product and stirring vigorously to precipitate the polymer, repeating the precipitation process repeatedly to obtain a polyester.

[0023] Furthermore, the lactone is... e -caprolactone, e - Decaprolactone, butylcaprolactone d -A mixture of one or more of valproic acid lactones, wherein the lactide is one or two of lactide or glycolide, with the specific structure as follows: .

[0024] Furthermore, when only one of lactone or lactide is added, the molar ratio of the bimetallic magnesium catalyst to lactone or lactide is 1:500 to 10000; the molar ratio of the chain transfer agent to lactone or lactide is 1:30 to 5000. When only both lactone and lactide are added, the molar ratio of the bimetallic magnesium catalyst to the sum of the molar amounts of lactone and lactide is 1:500 to 10000; the molar ratio of the chain transfer agent to the sum of the molar amounts of lactone and lactide is 1:30 to 5000.

[0025] Furthermore, the reaction temperature is 0~150 ℃; the reaction time is 0.1~10.0 h.

[0026] Furthermore, the organic solvent is one of dichloromethane, dichloroethane, tetrahydrofuran, 1,4-dioxane, toluene, or n-hexane.

[0027] Furthermore, the chain transfer agent is one of methanol, ethanol, ethylene glycol, terephthalic acid, glycerol, and pentaerythritol.

[0028] The beneficial effects of this invention are: (1) This invention designs and synthesizes a bimetallic magnesium catalyst that can achieve bimetallic synergistic catalysis of the self-polymerization and copolymerization of lactones or lactones. Compared with monometallic catalysts, the activity is greatly improved.

[0029] (2) The catalyst preparation route given in this invention is simple, the raw materials are all commercially available bulk chemicals, and the process is suitable for large-scale scale-up. Detailed Implementation

[0030] The technical solution of the present invention will be further described below through embodiments.

[0031] Unless otherwise stated, the terms used in this invention generally have the meanings commonly understood by those skilled in the art.

[0032] In the following embodiments, various processes and methods not described in detail are conventional methods known in the art. Furthermore, due to the large variety of catalysts and polymer structure ratios, not all preparation methods are described in detail; typical examples are used to illustrate the specific process steps of the present invention. Additionally, to further illustrate the activity difference between mononuclear and binuclear magnesium catalysts, a corresponding mononuclear magnesium catalyst was prepared according to the binuclear magnesium catalyst structure of the present invention, and it is compared with the examples in the comparative examples.

[0033] Examples 1-3 are examples of the preparation method of binuclear magnesium catalyst 1, Example 4 is an example of the preparation method of mononuclear magnesium catalyst 3, Examples 5-7 are examples of the preparation method of binuclear magnesium catalyst 2, Example 8 is an example of the preparation method of mononuclear magnesium catalyst 4, and Examples 9-12 are examples of methods for preparing polyester using the above catalysts.

[0034] For ease of description and explanation, the catalyst number, lactone and lactone names are shown in the following formula.

[0035] Example 1 The synthesis reaction equation for binuclear magnesium catalyst 1-1 is as follows: The specific preparation steps of the aforementioned dual-nuclear magnesium catalyst 1-1 are as follows: Under nitrogen protection, ethylene glycol (30 g, 483.33 mmol) and potassium tert-butoxide (271.15 g, 2416.63 mmol) in a molar ratio of 1:5 were mixed, and tetrahydrofuran (1500 g) in a mass ratio of 50:1 to ethylene glycol was added. Chloroacetic acid (105.05 g, 1111.66 mmol) was dissolved in tetrahydrofuran (150 g) in a mass ratio of 5:1 to ethylene glycol, resulting in a molar ratio of chloroacetic acid to ethylene glycol of 2.3:1. The system was heated to reflux, and the tetrahydrofuran solution of chloroacetic acid was added uniformly to the reaction system over 2 h. After the addition was complete, the reaction was maintained at this temperature for 12 h. The tetrahydrofuran was removed by vacuum distillation to obtain crude intermediate 1-1, which was not purified and directly proceeded to the next reaction step.

[0036] Methanol (1200 g) in a mass ratio of 40:1 to ethylene glycol was added, followed by concentrated sulfuric acid (60 g) in a mass ratio of 2:1 to ethylene glycol. The mixture was heated to reflux and reacted for 15 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filtrate was collected. After rotary evaporation, ethyl acetate (150 mL) and deionized water (150 mL) in a volume ratio of 1:1 were added for extraction, and the organic phase was collected. Then, ethyl acetate and saturated sodium carbonate solution in a volume ratio of 1:1 were added for extraction, and the organic phase was collected. The mixture was dried, filtered, and the filtrate was collected. The solvent was removed under reduced pressure to obtain a dark brown liquid, which was the crude intermediate 2-1 (75.74 g, 367.68 mmol, crude product yield 76%).

[0037] Under nitrogen protection, crude intermediate 2-1 (75.74 g, 367.68 mmol) was dissolved in anhydrous tetrahydrofuran (189.35 g) at a mass ratio of 2.5:1. Lithium aluminum hydride (27.94 g, 735.36 mmol) at a molar ratio of 2:1 to crude intermediate 2-1 was added at -5 to 0 °C. The mixture was divided into 10 equal portions and added over 2 h. After the addition was complete, the temperature was raised to approximately 25 °C and the reaction was maintained at this temperature for 12 h. The reaction was then quenched with water. The mixture was filtered multiple times, and the filtrate was collected, dried, filtered again, and the solvent was removed under reduced pressure to obtain crude intermediate 3-1. Distillation under reduced pressure yielded a colorless, viscous liquid intermediate 3-1 (41.42 g, 275.76 mmol, crude product yield 75%).

[0038] Under nitrogen protection, pyridine (41.42 g, 830.28 mmol) in a molar ratio of 3:1 to intermediate 3-1 (41.42 g, 275.76 mmol) was added, along with 1,4-dioxane (82.84 g) in a mass ratio of 2:1 to intermediate 3-1. The mixture was heated to 90 °C, and thionyl chloride (82.02 g, 689.40 mmol) in a molar ratio of 2.5:1 to intermediate 3-1 was added uniformly over 3 h through a constant pressure funnel. The reaction was maintained at this temperature for 14 h. After the reaction was complete, excess pyridine and thionyl chloride were removed by rotary evaporation. Methyl tert-butyl ether was added, and the mixture was stirred, washed, filtered, and the filtrate was collected. This process was repeated several times, and the filtrate was concentrated and purified by vacuum distillation to obtain intermediate 4-1 (43.85 g, 234.40 mmol, crude product yield 85%).

[0039] An aqueous solution of methylamine (242.68 g, 2344.0 mmol, mass fraction 30%) with a molar ratio of 10:1 to intermediate 4-1 (43.85 g, 234.40 mmol) was added to intermediate 4-1. The mixture was heated to 80 °C and reacted for 10 h. After the reaction was completed, the mixture was cooled to room temperature, and sodium hydroxide was slowly added until the system no longer showed significant exothermic reaction or bubble generation, and obvious stratification occurred. The upper layer was collected and distilled under reduced pressure to obtain intermediate 5-1 (28.09 g, 159.39 mmol, crude product yield 68%).

[0040] Under nitrogen protection, intermediate 5-1 (28.09 g, 159.39 mmol), 2,4-di-tert-butylphenol (75.64 g, 366.60 mmol), and paraformaldehyde (14.35 g, 478.17 mmol) in a molar ratio of 1:2.3:3 were mixed and dissolved in ethanol (224.72 g) at a mass ratio of 8:1 to intermediate 5-1. The mixture was then stirred at 100 °C for 16 h. After the reaction was complete, an ethyl acetate hydrochloride solution (99.62 mL, 398.48 mmol) at a molar ratio of 2.5:1 to intermediate 5-1 was added. M), a white precipitate was obtained, filtered, the filter cake was collected, and the filter cake was washed with ethanol. The dried filter cake was dissolved in water at a mass ratio of 5:1. NaHCO3 was added to adjust the pH of the solution to 6-7. Dichloromethane at a mass ratio of 5:1 was added for extraction. The organic phase was collected, and after adding a desiccant to remove water, the solvent was removed under reduced pressure to obtain intermediate 6-1 (79.13 g, 129.11 mmol, crude product yield 81%).

[0041] Under nitrogen protection, intermediate 6-1 (2 g, 3.26 mmol) was dissolved in anhydrous tetrahydrofuran (8 g) at a mass ratio of 4:1. The solution was then added dropwise over 2 h at a molar ratio of 10:1 to intermediate 6-1 to di-n-butylmagnesium (32.60 mL, 32.60 mmol, 1 M in n-hexane solution) at -15 to -10 °C. After the addition was complete, the solution was brought to room temperature and the reaction was maintained for 24 h. Once the reaction was complete, the solvent was removed under reduced pressure, and then n-hexane (10 g) at a mass ratio of 5:1 to intermediate 6-1 was added, resulting in a white precipitate. The precipitate was stirred for 2 h, washed, filtered, and the filter cake was collected. This process was repeated 5 times. The filter cake was collected and dried to obtain binuclear magnesium catalyst 1-1 (2.32 g, 3.00 mmol, crude product yield 92%). 1 H NMR (Acetone- d 6, 400 MHz): δ0.01-0.05 (m, 4H), 1.21-1.23 (m,10H), 1.26 (s, 18H), 1.31-1.35 (m, 4H), 1.40 (s, 18H), 2.29 (s, 6H), 2.63-2.71(m, 4H), 3.62 (m, 4H), 3.64-3.68(m, 4H), 3.69-3.74(s, 4H), 6.80-6.86(m, 2H),7.12-7.18(m, 2H).

[0042] Example 2 The synthesis reaction equation for binuclear magnesium catalyst 1-2 is as follows: The operation method of binuclear magnesium catalyst 1-2 is similar to that of binuclear magnesium catalyst 1-1, except that the raw material ethylene glycol in Example 1 is replaced with propylene glycol. Binuclear magnesium catalyst 1-2 is obtained by drying, with a yield of 89%. 1H NMR (Acetone-d6,400 MHz): δ0.01-0.05 (m, 4H), 1.21-1.23 (m, 10H), 1.26 (s, 18H),1.31-1.35 (m,4H), 1.40 (s, 18H),1.75-1.83 (m, 2H), 2.29 (s, 6H), 2.63-2.71 (m, 4H), 3.62(m, 4H), 3.64-3.68 (m, 4H), 3.69-3.74 (s, 4H), 6.80-6.86 (m, 2H), 7.12-7.18(m, 2H).

[0043] Example 3 The synthesis reaction equations for binuclear magnesium catalysts 1-3 are as follows: The operation method of binuclear magnesium catalyst 1-3 is similar to that of binuclear magnesium catalyst 1-1, except that the raw material ethylene glycol in Example 1 is replaced with 1,4-butanediol. After drying, binuclear magnesium catalyst 1-3 is obtained with a yield of 94%. 1 H NMR (Acetone- d 6, 400 MHz): δ0.01-0.05 (m, 4H), 1.21-1.23 (m, 10H), 1.26 (s, 18H), 1.31-1.35 (m, 4H), 1.40 (s, 18H), 1.65-1.69 (m, 4H), 2.29 (s, 6H), 2.63-2.71 (m, 4H), 3.62 (m, 4H), 3.64-3.68(m, 4H), 3.69-3.74(s, 4H), 6.80-6.86(m, 2H), 7.12-7.18(m, 2H).

[0044] Example 4 The synthesis reaction equation for mononuclear magnesium catalyst 3 is as follows: The specific preparation steps of mononuclear magnesium catalyst 3 are as follows: Under nitrogen protection, 2,4-di-tert-butylphenol (12.66 g, 61.35 mmol) and 2-methoxy- N 2-Methylethylamine (5.47 g, 61.35 mmol) and paraformaldehyde (2.76 g, 92.03 mmol) were mixed, dissolved in methanol (47.95 g), and the mixture was stirred at 60 °C for 12 h. After cooling to room temperature, a mixture containing 2-methoxy- NA 3-methylethylamine molar ratio of 1.2:1 was dissolved in hydrochloric acid-ethanol solution (30% by mass, 8.96 g, 73.62 mmol), yielding a white precipitate. The precipitate was filtered, the filter cake was collected, and washed three times with methanol. After drying, the precipitate was dissolved in water at a mass ratio of 3:1. The pH of the solution was adjusted to 6-7 with a saturated aqueous solution of NaHCO3. The precipitate was extracted three times with dichloromethane at a mass ratio of 5:1. The organic phase was collected, and after removing water with a drying agent, the dichloromethane was removed under reduced pressure to obtain the 3-ligand (18.11 g, 58.90 mmol), with a yield of 96%. Under nitrogen protection, the 3-ligand (2.00 g, 6.50 mmol) was dissolved in n-hexane (10.00 g) at a mass ratio of 5:1. Di-n-butylmagnesium (1 M, 6.50 mL, 6.50 mmol) at a molar ratio of 1:1 was added dropwise at 0 °C for 3 h. After the addition was complete, the reaction was maintained at this temperature for 2 h, and a white precipitate formed. The precipitate was filtered, collected, and washed three times with n-hexane. After vacuum drying, mononuclear magnesium 3 (2.30 g, 5.92 mmol) was obtained, with a yield of 91%. 1 H NMR (CDCl3, 400 MHz): d 0.01-0.05 (m, 2H),1.21-1.23 (m, 5H), 1.28 (s, 9H),1.31-1.35 (m, 2H),δ 1.42 (s, 9H), 2.34 (s,3H), 2.63-2.68 (m, 2H),3.31 (s, 3H), 3.49-3.54 (m, 2H), 3.70 (s, 2H), 6.82 (m, 1H), 7.20 (m, 1H).

[0045] Example 5 The synthesis reaction equation for binuclear magnesium catalyst 2-1 is as follows: The specific preparation steps of the dual-nuclear magnesium catalyst 2 are as follows: Under nitrogen protection, potassium phthalimide (18.52 g, 100 mmol) was mixed with DMF (74.08 g) at a mass ratio of 4:1, heated to reflux, and stirred to dissolve. Intermediate 4-1 (7.48 g, 40 mmol) at a molar ratio of 1:2.5 with potassium phthalimide was dissolved in DMF (29.92 g), with the amount of DMF being 4 times the mass of intermediate 4-1. The solution was added to the reaction system at a uniform rate over 2 h, and the reaction was refluxed for 15 h. After the reaction was completed, the mixture was cooled to room temperature, and deionized water at a mass ratio of 3:1 with DMF was added. The mixture was stirred for 2 h, filtered, the filter cake was collected, and dried to obtain crude intermediate 7-1.

[0046] Potassium hydroxide (16 g, 400 mmol) with a molar ratio of 10:1 to intermediate 4-1 was added, and a small amount of deionized water was added to dissolve the potassium hydroxide. The reaction was carried out at 80 °C for 12 h, and then at room temperature until the solution changed from a suspension to a clear and transparent solution. Water was removed under normal pressure, methyl tert-butyl ether was added, and the mixture was stirred and washed. The mixture was filtered, and the filtrate was collected. The solvent was removed by rotary evaporation to obtain crude intermediate 8-1. Crude intermediate 8-1 was obtained by vacuum distillation (4.33 g, 29.20 mmol, yield 73%).

[0047] Intermediate 8-1 (4.33 g, 29.20 mmol) and 3,5-di-tert-butylsalicylaldehyde (13.68 g, 58.40 mmol) in a molar ratio of 1:2 were added to anhydrous ethanol (21.65 g). The mass ratio of anhydrous ethanol to intermediate 8-1 was 5:1. The mixture was heated to reflux and reacted for 5 h. The mixture was then slowly cooled to 40 °C. The mixture was filtered at this temperature, and the filter cake was collected and dried to obtain intermediate 9-1 (15.77 g, 27.16 mmol, yield 93%).

[0048] Under nitrogen protection, intermediate 9-1 (2 g, 3.44 mmol) was dissolved in anhydrous tetrahydrofuran (8 g) at a mass ratio of 4:1. The solution was then added dropwise over 2 h at a constant rate to di-n-butylmagnesium (17.2 mL, 17.2 mmol, 1 M in n-hexane) at a molar ratio of 5:1 to intermediate 9-1. After the addition was complete, the mixture was brought to room temperature and the reaction was maintained for 20 h. Once the reaction was complete, the solvent was removed under reduced pressure, and then n-hexane at a mass ratio of 5:1 to intermediate 9-1 was added. A white precipitate formed. The mixture was stirred for 1 h, washed, filtered, and the filter cake was collected. This process was repeated three times. The filter cake was collected and dried to obtain binuclear magnesium catalyst 2-1 (1.99 g, 2.68 mmol, yield 78%). 1 HNMR (CDCl3, 400 MHz): d 0.01-0.03 (m, 4H), 1.19-1.22 (m, 10H), 1.30 (s, 18H), 1.31-1.35 (m, 4H), 1.44 (s, 18H), 3.62 (s, 4H), 3.71 (m, 8H), 7.08 (d, 2H),7.37 (t, 2H), 8.35 (s, 2H).

[0049] Example 6 The synthesis reaction equation for binuclear magnesium catalyst 2-2 is as follows: The operation method of the binuclear magnesium catalyst 2-2 is similar to that of the binuclear magnesium catalyst 2-1, except that intermediate 4-1 in Example 4 is replaced with intermediate 4-2. The binuclear magnesium catalyst 2-2 is obtained by drying, with a yield of 74%. 1 H NMR (CDCl3, 400 MHz): d 0.01-0.03 (m, 4H), 1.19-1.22 (m, 10H), 1.30 (s, 18H), 1.31-1.35 (m,4H), 1.44 (s, 18H), 1.81 (m, 2H), 3.62 (s, 4H), 3.71 (m, 8H),7.08 (d, 2H),7.37 (t, 2H), 8.35 (s, 2H).

[0050] Example 7 The synthesis reaction equation for binuclear magnesium catalyst 2-3 is as follows: The operation method of the binuclear magnesium catalyst 2-2 is similar to that of the binuclear magnesium catalyst 2-1, except that intermediate 4-1 in Example 4 is replaced with intermediate 4-2. The binuclear magnesium catalyst 2-2 is obtained by drying, with a yield of 74%. 1 H NMR (CDCl3, 400 MHz): d 0.01-0.03 (m, 4H), 1.19-1.22 (m, 10H), 1.30 (s, 18H), 1.31-1.35 (m,4H), 1.44 (s, 18H), 1.68-1.73 (m, 4H),3.62 (s, 4H),3.71 (m, 8H), 7.08 (d, 2H), 7.37 (t, 2H), 8.35 (s, 2H).

[0051] Example 8 The synthesis reaction equation for mononuclear magnesium catalyst 4 is as follows: The specific preparation steps of mononuclear magnesium catalyst 4 are as follows: Under nitrogen protection, 2-methoxyethylamine (7.51 g, 100 mmol) and 3,5-di-tert-butylsalicylaldehyde (23.43 g, 100 mmol) in a molar ratio of 1:1 were mixed, dissolved in ethanol (50 g), and the mixture was stirred at 80 °C for 4 h. After cooling to room temperature, the mixture was filtered, the filter cake was collected, washed three times with ethanol, and dried to obtain the 4-ligand (26.81 g, 92 mmol), with a yield of 92%. Under nitrogen protection, 4-ligand (2 g, 6.86 mmol) was dissolved in n-hexane (10 g) at a mass ratio of 5:1, and di-n-butylmagnesium (1 M, 6.86 mL, 6.86 mmol) at a molar ratio of 1:1 was added dropwise at -5 °C for 2 h. After the addition was complete, the reaction was maintained at this temperature for 2 h, and a precipitate was formed. The precipitate was filtered, collected, and washed three times with n-hexane. After vacuum drying, 4-ligand (2.17 g, 5.83 mmol) was obtained, with a yield of 85%. 1 H NMR (CDCl3, 400 MHz): d 0.01-0.03 (m, 2H), 1.19-1.22 (m, 5H), 1.30 (s, 9H), 1.31-1.35 (m, 2H), 1.44 (s, 9H), 2.82 (m, 2H), 3.62 (s, 3H), 3.71 (m, 2H), 7.08 (d, 1H), 7.37 (t, 1H), 8.35 (s, 1H).

[0052] Example 9 100 mL reaction flasks equipped with magnetic induction at 120°C o Dry at C for more than 12 hours, then evacuate and allow to cool to room temperature before purging with nitrogen for use. Under nitrogen protection, weigh a certain amount of binuclear magnesium catalyst 1-1 (38.69 mg, 0.05 mmol) at room temperature and add it to a solution with a molar ratio of 2000:1 to the binuclear magnesium catalyst 1-1. e ε-caprolactone (11.41 g, 100.00 mmol) was added to ethanol (9.2 mg, 0.20 mmol) at a molar ratio of 1:500 to ε-caprolactone. e1,4-Dioxane (22.82 g) with a caprolactone mass ratio of 2:1 was reacted at 25°C for 45 min. After stirring was stopped, a very small amount of the reaction mixture was collected for 1H NMR and GPC analysis. 1H NMR showed a monomer conversion rate of 99.3%, and GPC analysis showed a polymer molecular weight of 57.0 kg / mol and a molecular weight distribution of 1.02. The remaining polymer was purified by dissolving the crude product in a small amount of dichloromethane, then adding a large amount of methanol and stirring vigorously to precipitate the polymer. This process was repeated, and the product was dried under vacuum to obtain the polyester.

[0053] The experimental procedures for Examples 9-1 to 9-5 and Comparative Examples 9-6 and 9-7 in Table 1 are the same as those for Example 9, and the raw materials used are all the same. e -Caprolactone, reaction temperature 25 ℃, reaction time 45 min, ethanol was used as the chain transfer agent, ethanol and... e The molar ratio of caprolactone to 1:500, and the solvent used in both cases was 1,4-dioxane, and was compatible with... e The mass ratio of caprolactone was 2:1, but the catalyst was different, resulting in different monomer conversion rates and corresponding polymer molecular weights and molecular weight distributions at the end of the reaction. Details are as follows: Table 1 e Test results of polyester preparation by self-polymerization of caprolactone

[0054] Example 10 100 mL reaction flasks equipped with magnetic induction at 120°C o Dry at C for more than 12 h, evacuate and allow to cool to room temperature, then purge with nitrogen for use. Under nitrogen protection, weigh a certain amount of binuclear magnesium catalyst 2-1 (7.72 mg, 0.01 mmol) at room temperature, add lactide (144.13 g, 100.00 mmol) at a molar ratio of 10000:1 to binuclear magnesium catalyst 2-1, and add terephthalic acid (2.76 mg, 0.02 mmol) at a molar ratio of 1:5000 to lactide. Set the temperature to 150 °C and react for 6 h. Stop stirring and take out a very small amount of the reaction mixture for 1H NMR and GPC analysis. 1H NMR showed a monomer conversion rate of 99.7%, and GPC analysis showed a polymer molecular weight of 705.8 kg / mol and a molecular weight distribution of 1.82. The remaining reacted polymer is purified by dissolving the crude product in a small amount of dichloromethane, then adding a large amount of methanol and stirring vigorously to precipitate the polymer. This process is repeated, and the polyester is obtained by vacuum drying.

[0055] The experimental procedures for Examples 10-1 to 10-5 and Comparative Examples 10-6 to 10-7 in Table 1 are the same as those for Example 10. All examples use lactide as the raw material, the reaction temperature is 150 °C, the reaction time is 6 h, and the chain transfer agent is terephthalic acid (TPA), with a molar ratio of TPA to lactide of 1:5000. The differences lie in the catalyst, the monomer conversion rate at the end of the reaction, and the molecular weight and molecular weight distribution of the corresponding polymers. Details are as follows: Table 2 Test results of polyester preparation by self-polymerization of lactide

[0056] Example 11 100 mL reaction flasks equipped with magnetic induction at 120°C o Dry at C for more than 12 hours, then evacuate and allow to cool to room temperature before purging with nitrogen. Under nitrogen protection, weigh a certain amount of binuclear magnesium catalyst 1-3 (40.09 mg, 0.05 mmol) at room temperature and add it to a 1:1 molar ratio of [missing information - likely a specific ingredient or product]. d -Velolactone (10.00 g, 100.00 mmol) and e -Caprolactone (11.40 g, 100.00 mmol), added with d Glycerol (9.21 mg, 0.1 mmol) with a valproic acid molar ratio of 1:1000 was added to tetrahydrofuran with a mass ratio of 3:1 to the monomer. The reaction was carried out at 90 °C for 8 h. After stirring, a very small amount of the reaction mixture was taken out for 1H NMR and GPC analysis. The 1H NMR spectrum showed... d -Velolactone conversion rate was 99.8%. e The conversion rate of caprolactone was 99.5%, and GPC testing showed that the polymer molecular weight was 234.5 kg / mol with a molecular weight distribution of 1.32. The remaining reactant polymer was purified by dissolving the crude product in a small amount of dichloromethane, then adding a large amount of methanol and stirring vigorously to precipitate the polymer. This process was repeated, and the polyester was obtained by vacuum drying.

[0057] The experimental procedures for Examples 11-1 to 11-5 and Comparative Examples 11-6 and 11-7 in Table 3 are the same as those for Example 11, and the raw materials are all used in a molar ratio of 1:1. d -valerol and e β-caprolactone was reacted at 90 °C for 8 hours, with glycerol used as the chain transfer agent. Glycerol and... d The molar ratio of valproic acid to monomer was 1:1000, and the solvent was tetrahydrofuran. The ratio of solvent to monomer mass was 3:1. The differences lay in the catalyst, the monomer conversion rate at the end of the reaction, and the molecular weight and molecular weight distribution of the corresponding polymers. Details are as follows: Table 3 d -Velolactone and e Test results of polyester preparation by copolymerization of caprolactone

[0058] Example 12 100 mL reaction flasks equipped with magnetic induction at 120°C o Dry at C for more than 12 hours, then evacuate and allow to cool to room temperature before purging with nitrogen. Under nitrogen protection, weigh a certain amount of binuclear magnesium catalyst 2-3 (30.79 mg, 0.04 mmol) at room temperature and add... e - Decanolide (17.25 g, 100.00 mmol), added with e Ethylene glycol with a molar ratio of 1:1250 to decanolide was added to... e Toluene with a mass ratio of 5:1 to decanolide was added, the reaction was carried out at 120°C for 5 h, and then... e L-lactide in a 1:1 mass ratio with decanolide was reacted for another 5 h. Stirring was then stopped, and a very small amount of the reaction mixture was collected for 1H NMR and GPC analysis. The 1H NMR spectrum showed... e The conversion rate of decyl lactone was 99.8%, and the conversion rate of L-lactide was 99.9%. GPC testing showed that the polymer molecular weight was 438.6 kg / mol, and the molecular weight distribution was 1.55. The remaining reactant polymer was purified by dissolving the crude product in a small amount of dichloromethane, then adding a large amount of methanol and stirring vigorously to precipitate the polymer. This process was repeated, and the polyester was obtained by vacuum drying.

[0059] The experimental procedures for Examples 12-1 to 12-5 and Comparative Examples 12-6 and 12-7 in Table 4 are the same as those for Example 12, and the raw materials used are all in a mass ratio of 1:1. e - Decanolactone and L-lactide, both reacted at 120 °C, with the addition of... e The reaction with decanolide was completed after 5 hours, followed by the addition of L-lactide and another 5 hours of reaction. Ethylene glycol was used as the chain transfer agent. e The molar ratio of 1:1250 for decanolide was used, and toluene was used as the solvent in both cases. e The mass ratio of -decanolide to decanolide is 5:1, but the catalyst, monomer conversion rate at the end of the reaction, and the molecular weight and molecular weight distribution of the corresponding polymers differ. Details are as follows: Table 4 e Test results of polyester preparation by copolymerization of decanolactone and levolic lactone

Claims

1. A type of bimetallic magnesium catalyst, characterized in that, The bimetallic magnesium catalyst has a general structural formula of 1 or 2; In the formula: R is .

2. The bimetallic magnesium catalyst according to claim 1, characterized in that, The synthesis reaction equation for binuclear magnesium catalyst 1 is as follows: The specific preparation steps of the dual-nuclear magnesium catalyst 1 are as follows: Under inert gas protection, a mixture of diol and potassium tert-butoxide in a molar ratio of 1:5 to 5.5 was prepared. A first portion of tetrahydrofuran was added, with a tetrahydrofuran to diol mass ratio of 40 to 50:

1. Chloroacetic acid was then dissolved in a second portion of tetrahydrofuran, with a chloroacetic acid to diol molar ratio of 2.3 to 2.5:

1. The system was heated to reflux, and the tetrahydrofuran solution of chloroacetic acid was added to the reaction system at a uniform rate over 1 to 5 hours. After the addition was complete, the reaction was maintained at this temperature for 8 to 12 hours. The tetrahydrofuran was removed by vacuum distillation to obtain crude intermediate 1, which was not purified and proceeded directly to the next reaction step. Add methanol (40-50:1 by mass ratio to diol) and concentrated sulfuric acid (2-3:1 by mass ratio to diol) to the crude intermediate 1. Heat to reflux and react for 10-15 h. After the reaction is complete, cool to room temperature, filter, collect the filtrate, and rotary evaporate. First, extract with ethyl acetate and deionized water (1:1 by volume) and collect the organic phase. Then, extract with ethyl acetate and saturated sodium carbonate solution (1:1 by volume) and collect the organic phase. Dry, filter, collect the filtrate, remove the solvent under reduced pressure, and obtain a dark brown liquid, which is the crude intermediate 2. Under inert gas protection, crude intermediate 2 was dissolved in anhydrous tetrahydrofuran at a mass ratio of 2.5-3:

1. Lithium aluminum hydride at a molar ratio of 2-3:1 to crude intermediate 2 was added slowly over 1-4 hours at -5 to 0 °C, while controlling the system temperature to not exceed 0 °C. After the addition was complete, the temperature was raised to 20-30 °C and the reaction was maintained for 12-15 hours. The reaction was then quenched with water. The mixture was filtered multiple times, the filtrate was collected, dried, filtered again, and the filtrate was collected. The solvent was removed under reduced pressure to obtain crude intermediate 3. The crude intermediate 3 was then obtained by vacuum distillation. Under an inert gas atmosphere, pyridine at a molar ratio of 2-3:1 to intermediate 3 was added, followed by 1,4-dioxane at a mass ratio of 1.5-2.5:1 to intermediate 3. The mixture was heated to 80-90 °C, and thionyl chloride at a molar ratio of 2.5:1 to intermediate 3 was added uniformly over 2-5 h through a constant pressure funnel. The reaction was maintained at this temperature for 10-14 h. After the reaction was completed, excess pyridine and thionyl chloride were removed by rotary evaporation. Methyl tert-butyl ether was added, and the mixture was stirred, washed, filtered, and the filtrate was collected. This process was repeated several times, and the filtrate was concentrated and purified by vacuum distillation to obtain intermediate 4. Intermediate 4 was added to an aqueous methylamine solution, with a molar ratio of methylamine to intermediate 4 of 3-10:

1. The temperature was raised to 70-90 °C and the reaction was carried out for 10-12 h. After the reaction was completed, the temperature was lowered to room temperature, and sodium hydroxide was slowly added until the system no longer showed obvious exothermic reaction or bubble generation, and obvious stratification occurred. The upper layer was collected and distilled under reduced pressure to obtain intermediate 5. Intermediate 5, 2,4-di-tert-butylphenol, and paraformaldehyde were mixed in a molar ratio of 1:2.1~2.5:2.5~3 under an inert gas atmosphere and dissolved in ethanol at a mass ratio of 7~10:1 to intermediate 5. The mixture was then stirred at 90~120℃ for 12~16 h. After the reaction was complete, ethyl hydrochloric acid solution at a molar ratio of 2.3~2.5:1 to intermediate 5 was added to obtain a white precipitate. The precipitate was filtered, the filter cake was collected, and washed with ethanol. The dried filter cake was dissolved in water at a mass ratio of 3~5:1 to the filter cake. NaHCO3 was added to adjust the pH of the solution to 6~7. Dichloromethane at a mass ratio of 3~5:1 to the filter cake was added for extraction. The organic phase was collected, and after adding a desiccant to remove water, the solvent was removed under reduced pressure to obtain intermediate 6. Under inert gas protection, intermediate 6 was dissolved in anhydrous tetrahydrofuran at a mass ratio of 2-5:

1. The solution was then added dropwise at a uniform rate to di-n-butylmagnesium at a molar ratio of 5-10:1 to intermediate 6 over 1-3 h at -15 to -10 °C. After the addition was complete, the mixture was brought to room temperature and the reaction was maintained for 20-24 h. Once the reaction was complete, the solvent was removed under reduced pressure, and then n-hexane at a mass ratio of 3-5:1 to intermediate 6 was added. A white precipitate formed. The mixture was stirred for 1-2 h, washed, filtered, and the filter cake was collected. This process was repeated 3-5 times. The filter cake was collected and dried to obtain binuclear magnesium catalyst 1.

3. The bimetallic magnesium catalyst according to claim 2, characterized in that, The intermediate 4 was used to synthesize a binuclear magnesium catalyst 2. The synthesis reaction equation for the binuclear magnesium catalyst 2 is as follows: The specific preparation steps of the dual-nuclear magnesium catalyst 2 are as follows: Under inert gas protection, potassium phthalimide was mixed with DMF at a mass ratio of 3-4:1, heated to reflux, and stirred to dissolve. Intermediate 4, with a molar ratio of 1:2.5-3 to potassium phthalimide, was dissolved in DMF, with the amount of DMF being 4-5 times the mass of intermediate 4. The solution was added to the reaction system at a uniform rate over 1-4 h, and the reaction was refluxed for 12-15 h. After the reaction was completed, the mixture was cooled to room temperature, and deionized water at a mass ratio of 2-3:1 to DMF was added. The mixture was stirred for 1-2 h, filtered, the filter cake was collected, and dried to obtain crude intermediate 7. Potassium hydroxide was added at a molar ratio of 8-12:1 to intermediate 4, and deionized water was added to dissolve the potassium hydroxide. The reaction was carried out at 70-90 °C for 10-12 h, and then at room temperature until the solution changed from a suspension to a clear and transparent solution. Water was removed under normal pressure, methyl tert-butyl ether was added, and the mixture was stirred and washed. The solution was filtered, the filtrate was collected, and the solvent was removed by rotary evaporation to obtain crude intermediate 8. Intermediate 8 was obtained by vacuum distillation. Intermediate 8 with a molar ratio of 1:2 to 2.5 and 3,5-di-tert-butylsalicylaldehyde were added to anhydrous ethanol. The mass ratio of anhydrous ethanol to intermediate 8 was 3 to 5:

1. The mixture was heated to reflux and reacted for 3 to 5 h. The mixture was then slowly cooled to 40 to 45 °C. The mixture was filtered at this temperature, the filter cake was collected, and dried to obtain intermediate 9. Under inert gas protection, intermediate 9 was dissolved in anhydrous tetrahydrofuran at a mass ratio of 2-5:

1. The tetrahydrofuran solution of intermediate 9 was added dropwise over 1-4 h at a uniform rate to di-n-butylmagnesium at a molar ratio of 5-10:1 to intermediate 9. After the addition was complete, the temperature was raised to room temperature and the reaction was maintained for 20-24 h. After the reaction was completed, the solvent was removed under reduced pressure, and then n-hexane at a mass ratio of 3-5:1 to intermediate 9 was added, resulting in the precipitation of a white precipitate. The precipitate was stirred for 1-2 h, washed, filtered, and the filter cake was collected. This process was repeated 3-5 times. The filter cake was collected and dried to obtain binuclear magnesium catalyst 2.

4. A method for preparing lactones, lactide self-polymers, or copolymers using any one of the bimetallic magnesium catalysts according to claims 1 to 3, characterized in that, The specific reaction process is as follows: a bimetallic magnesium catalyst, lactone and / or lactone are added to the reactor, a chain transfer agent is selectively added, and an organic solvent is selectively added. The mixture is stirred for a certain time at a certain reaction temperature, and then the reaction is stopped. A large amount of methanol or ethanol is added to the crude product and stirred vigorously to precipitate the polymer. The precipitation process is repeated to obtain polyester. The lactone is ε -caprolactone, ε - Decaprolactone, butylcaprolactone δ -A mixture of one or more of valproic acid lactones, wherein the lactide is one or two of lactide or glycolide, with the specific structure as follows: ； The chain transfer agent is one of methanol, ethanol, ethylene glycol, terephthalic acid, glycerol, and pentaerythritol.

5. The method according to claim 4, characterized in that, When only one of lactone or lactide is added, the molar ratio of the bimetallic magnesium catalyst to lactone or lactide is 1:500 to 10000; the molar ratio of the chain transfer agent to lactone or lactide is 1:30 to 5000. When only both lactone and lactide are added, the molar ratio of the bimetallic magnesium catalyst to the sum of the molar amounts of lactone and lactide is 1:500 to 10000; the molar ratio of the chain transfer agent to the sum of the molar amounts of lactone and lactide is 1:30 to 5000.

6. The method according to claim 4, characterized in that, The reaction temperature is 0~150 ℃; the reaction time is 0.1~10.0 h.

7. The method according to claim 4, characterized in that, The organic solvent is one of dichloromethane, dichloroethane, tetrahydrofuran, 1,4-dioxane, toluene, or n-hexane.

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