Vanadium bipyridine complex and its preparation method and application

Abstract

The application discloses a vanadium bipyridine complex, and has a chemical formula of V(bipyalk)(CH3OH)Cl3, wherein bipyalk is 2,2'-([2,2'-bipyridine]-6,6'-dimethyl) bis(propan-2-ol), and comprises the following steps: (1) adding bipyalk and vanadium trichloride into a first solvent to react to obtain a mixture of a crude sample; and (2) concentrating the mixture of the crude sample, then diffusing a second solvent into the mixture of the concentrated crude sample, and obtaining the vanadium bipyridine complex after crystallization. The application can catalyze copolymerization of unpurified epoxide and cyclic anhydride to prepare a polyester under an atmospheric atmosphere, and can effectively reduce the commercial production cost of the polyester. The obtained polymer has high selectivity (polyester chain > 90%), appropriate molecular weight and narrow molecular weight distribution.

Description

Technical Field

[0001] This invention relates to the field of coordination compounds, and more specifically to a vanadium bipyridine complex, its preparation method, and its applications. Background Technology

[0002] Since current commercial polyesters are typically prepared by the condensation of diacids or diesters with diols (e.g., polyethylene terephthalate), this process requires the removal of small molecule byproducts such as water or alcohols. A major problem with this step-growth polymerization process is that it requires high temperatures and vacuum conditions (200-220°C, 0.1 mmHg). This method is very energy-intensive, cannot synthesize polyesters with easy heat recovery, and further complicates the application of volatile monomers.

[0003] Ring-opening polymerization (ROP) of cyclic esters is an atom-economical alternative to step-growth polymerization (e.g., polylactic acid). In ROP, a catalyst is used to open the ring of a cyclic monomer to create a reaction center. The reaction center coordinates with a new cyclic monomer, which inserts into the reaction center to form a longer chain. ROP of cyclic esters can proceed under mild conditions (room temperature, ambient pressure) with appropriate initiation / catalysis systems because the active center lowers the reaction energy barrier and the process does not require the removal of small molecule byproducts. However, ring-opening is driven by the enthalpy generated by ring stress release, which limits its monomer range (mainly 4, 6, and 7-membered rings; 5-membered rings are difficult to ring-open due to their smaller ring strain).

[0004] The ring-opening alternating copolymerization of cyclic anhydrides and epoxides (ROAC) is also an atom-economic reaction in the polyester chain growth pathway. Furthermore, the ΔH for each insertion of an epoxy-anhydride pair in ROAC is approximately -30 kcal / mol. This means that, like ROP, ROAC can be carried out under mild conditions (25-110℃) with highly efficient and selective catalysts. Compared to ROP with cyclic ester monomers, the ROAC process has another advantage: the structure and properties of the polymer can be adjusted by modifying the feedstock. Due to its significant economic and environmental benefits, ROAC has attracted considerable attention in the field of polyester synthesis.

[0005] Although many catalysts for ROACs using acid anhydrides and epoxides have been developed, most are sensitive to oxygen and proton impurities (water, acids, alcohols, amines). Trace amounts of water in the air, as well as in unpurified acid anhydrides, epoxides, and solvents, can react with the anhydride to produce acids during the reaction, causing the active intermediates of the catalyst to degrade into free ligands and metal ions, thus reducing or eliminating catalytic activity. Therefore, this reaction often requires nitrogen protection and meticulous purification and dehydration of the acid anhydride, epoxide, and solvent before the reaction. For example, most literature requires sublimation or multiple sublimations of the acid anhydride before experiments, and epoxides need to be stirred in calcium hydride for 1-3 days followed by distillation. Even small amounts of catalyst or co-catalyst require multiple recrystallizations or production and storage under a nitrogen-protected atmosphere. These operations increase production costs, making ROAC-produced polyesters difficult to commercialize due to the additional costs of raw material purification and nitrogen protection required to compete with commercially available polyesters. Summary of the Invention

[0006] To address the problem that existing epoxide and cyclic anhydride ring-opening copolymerization catalysts (ROAC) are deactivated in the presence of proton impurities and oxygen, making it difficult to reduce production costs, this invention provides a vanadium bipyridine complex, its preparation method, and its applications.

[0007] The technical solution adopted in this invention is:

[0008] A vanadium bipyridine complex with the chemical formula V(bipyalk)(CH3OH)Cl3, wherein bipyalk is 2,2'-([2,2'-bipyridine]-6,6'-dimethyl)bis(propane-2-ol), and its chemical structural formula is as follows:

[0009]

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

[0011] (1) Bipyalk and vanadium trichloride were added to the first solvent and reacted to obtain a mixture of crude samples;

[0012] (2) The mixture of the crude sample is concentrated, and then a second solvent is diffused into the concentrated mixture of the crude sample. After crystallization, a vanadium bipyridine complex is obtained.

[0013] Preferably, the above process is carried out in a light-protected environment, which can prevent trivalent vanadium from being oxidized by impurities in the solvent and further improve the reaction yield.

[0014] In step (2), the crude sample mixture can be concentrated by conventional vacuum distillation.

[0015] Preferably, the organic solvent is at least one of methanol and ethanol.

[0016] Preferably, in step (1), the molar ratio of vanadium trichloride to bipyalk is 1-4:1; more preferably 2-3:1. This improves reaction efficiency while ensuring the quality of the obtained product. Excess vanadium trichloride promotes complete bipyalk reaction, reduces bipyalk consumption, and lowers production costs.

[0017] Preferably, in step (1), the molar ratio of the first solvent to bipyalk is 250-1000:1; more preferably, the molar ratio is 7000-8000:1. An appropriate amount of the first solvent can completely dissolve vanadium trichloride, while reducing solvent usage and accelerating the reaction rate.

[0018] Preferably, the second solvent is anhydrous diethyl ether. Adding the less polar second solvent to the more polar first solvent can effectively precipitate single crystals. The molar ratio of anhydrous diethyl ether to bipyalk is 12.5-200:1. At this molar ratio, the concentration of the vanadium bipyridine complex is close to its saturated solution concentration, which can effectively reduce the difficulty of single crystal growth and improve production efficiency.

[0019] Preferably, in step (1), the reaction temperature is 25-80℃; in step (2), the crystallization temperature is -20-50℃. This can improve the reaction efficiency while ensuring the quality of the obtained product.

[0020] The present invention also provides the application of the above-mentioned vanadium bipyridine complex as a catalyst in the copolymerization reaction of epoxides and cyclic anhydrides.

[0021] Specific methods include: using epoxides and cyclic anhydrides as raw materials, vanadium bipyridine complexes as catalysts, and onium salts or heterocyclic nitrogen bases as co-catalysts, catalyzing the polymerization of cyclic anhydrides and propylene oxide in toluene to prepare polyesters.

[0022] Preferably, the cyclic anhydride is at least one selected from maleic anhydride, succinic anhydride, phthalic anhydride, and norbornene. This results in a narrower molecular weight distribution of the reaction product.

[0023] Preferably, the onium salt is selected from bis(triphenylphosphine)ammonium chloride (PPNCl); the heterocyclic nitrogen base is selected from 4-dimethylaminopyridine (DMAP). This results in a faster reaction rate and a narrower molecular weight distribution of the reaction products.

[0024] Preferably, the polymerization temperature is 80-100℃. Within this temperature range, the catalyst exhibits higher activity while reducing transesterification side reactions and maintaining a narrow molecular weight distribution.

[0025] The beneficial effects of this invention are:

[0026] 1. When the vanadium bipyridine complex of the present invention is used as a catalyst, its bipyridine moiety is more stable than that of traditional salon ligands, and the branched dimethyl group effectively prevents the oxidation of the catalyst central ion. This allows for the catalytic copolymerization of unpurified epoxides and cyclic anhydrides to produce polyesters under atmospheric conditions, effectively reducing the commercial production cost of polyesters. Furthermore, the resulting polyester has a molecular weight of 1-6 kDa and a molecular weight distribution of 1.04-1.3. The present invention features high selectivity (polyester chain length >90%), appropriate molecular weight, and a narrow molecular weight distribution.

[0027] 2. The preparation method of the vanadium bipyridine complex of the present invention is simple and has a high yield. Attached Figure Description

[0028] Figure 1 This is a single-crystal test image of the vanadium bipyridine complex of the present invention.

[0029] Figure 2 The polyester obtained in Example 7 1 H NMR spectrum.

[0030] Figure 3 The polyester obtained in Example 10 1 H NMR spectrum.

[0031] Figure 4 The polyester obtained in Example 11 1 H NMR spectrum.

[0032] Figure 5 The polyester obtained in Example 12 1 H NMR spectrum.

[0033] Figure 6 The GPC curve of the polyester in Example 11 is shown (35°C, THF as the mobile phase). Detailed Implementation

[0034] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] The instrument used for single-crystal testing of vanadium bipyridine complexes was a Bruker D8 Venture.

[0036] polymer products 1 The HNMR testing instrument used was a Bruker Avance NEO 500MHz from Germany.

[0037] Gel permeation chromatography (GPC) was performed using a Malvern Viscotek GPC / SEC workstation. The method was as follows: sample concentration 2 mg / mL, injection volume 100 μL, column temperature 35 °C, and THF mobile phase. Polystyrene (PSt) was used as the sample characterization agent, and the flow rate was set to 1.0 mL / min. After sample dissolution, transition metal ions were adsorbed using neutral alumina, followed by filtration through a 0.22 μm filter membrane.

[0038] Example 1

[0039] 2 mmol (315 mg) of vanadium trichloride and 1 mmol (273 mg) of bipyalk were dissolved separately in 20 mL of methanol. The resulting methanol solution of vanadium trichloride was slowly added dropwise to the methanol solution of the resulting ligand. The system was stirred and heated to 50 °C in a closed system and maintained for 5-6 h. After the reaction was complete, the liquid was concentrated to 2-4 mL using a rotary evaporator. 0.1 mol (10 mL) of anhydrous diethyl ether was diffused into the concentrated liquid. Recrystallization was carried out at 25 °C in the dark. The recrystallized solid was dried under vacuum to obtain approximately 308 mg of vanadium bipyridine complex. The yield was approximately 71%. Single crystal test results are shown in […]. Figure 1 .

[0040] Example 2

[0041] 1 mmol (157 mg) of vanadium trichloride and 1 mmol (273 mg) of bipyalk were dissolved separately in 20 mL of methanol. The resulting methanol solution of vanadium trichloride was slowly added dropwise to the methanol solution of the resulting ligand. The system was stirred and heated to 50 °C in a closed system and maintained for 5-6 h. After the reaction was complete, the liquid was concentrated to 2-4 mL using a rotary evaporator. 0.2 mol (20 mL) of anhydrous diethyl ether was diffused into the concentrated liquid. Recrystallization was carried out at 25 °C in the dark. The recrystallized solid was dried under vacuum to obtain approximately 201 mg of vanadium bipyridine complex. The yield was approximately 47%. Single crystal test results are shown in […]. Figure 1 .

[0042] Example 3

[0043] 4 mmol (629 mg) of vanadium trichloride and 1 mmol (273 mg) of bipyalk were dissolved separately in 20 mL of methanol. The resulting methanol solution of vanadium trichloride was slowly added dropwise to the methanol solution of the resulting ligand. The system was stirred and heated to 50 °C in a closed system for 5-6 h. After the reaction was complete, the liquid was concentrated to 2-4 mL using a rotary evaporator. 0.05 mol (5 mL) of anhydrous diethyl ether was diffused into the concentrated liquid, and recrystallization was carried out under light at 25 °C. The recrystallized solid was dried under vacuum to obtain approximately 189 mg of vanadium bipyridine complex. The yield was approximately 44%. Single crystal test results are shown in […]. Figure 1 .

[0044] Example 4

[0045] 2 mmol (315 mg) of vanadium trichloride and 1 mmol (273 mg) of bipyalk were dissolved separately in 40 mL of methanol. The resulting methanol solution of vanadium trichloride was slowly added dropwise to the methanol solution of the resulting ligand. The system was stirred and heated to 50 °C in a closed system and maintained for 5-6 h. After the reaction was complete, the liquid was concentrated to 2-4 mL using a rotary evaporator. 0.1 mol (10 mL) of anhydrous diethyl ether was diffused into the concentrated liquid, and recrystallization was carried out at 25 °C in the dark. The recrystallized solid was dried under vacuum to obtain approximately 230 mg of vanadium bipyridine complex. The yield was approximately 53%. Single crystal test results are shown in […]. Figure 1 .

[0046] Example 5

[0047] 2 mmol (315 mg) of vanadium trichloride and 1 mmol (273 mg) of bipyalk were dissolved separately in 20 mL of methanol. The resulting methanol solution of vanadium trichloride was slowly added dropwise to the methanol solution of the resulting ligand. The system was stirred and heated to 80 °C in a closed system for 5-6 h. After the reaction was complete, the liquid was concentrated to 2-4 mL using a rotary evaporator. 0.1 mol (10 mL) of anhydrous diethyl ether was diffused into the concentrated liquid. Recrystallization was carried out under light at 50 °C. The recrystallized solid was dried under vacuum to obtain approximately 129 mg of vanadium bipyridine complex. The yield was approximately 30%. Single crystal test results are shown in […]. Figure 1 .

[0048] Example 6

[0049] 2 mmol (315 mg) of vanadium trichloride and 1 mmol (273 mg) of bipyalk were dissolved separately in 20 mL of methanol. The resulting methanol solution of vanadium trichloride was slowly added dropwise to the methanol solution of the resulting ligand. The system was stirred and heated to 25 °C in a closed system for 5-6 h. After the reaction was complete, the liquid was concentrated to 2-4 mL using a rotary evaporator. 0.1 mol (10 mL) of anhydrous diethyl ether was diffused into the concentrated liquid. Recrystallization was carried out at -20 °C in the dark. The recrystallized solid was dried under vacuum to obtain approximately 140 mg of vanadium bipyridine complex. The yield was approximately 35%. Single crystal test results are shown in […]. Figure 1 .

[0050] Example 7

[0051] In an air atmosphere, 8 μmol of the vanadium bipyridine complex prepared in Example 1, 8 μmol of DMAP, 1.44 mmol of succinic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added sequentially to the test bottle. The bottle was sealed with a polytetrafluoroethylene-lined cap, heated to 80°C, and reacted for 16 h. After the reaction product was concentrated, the crude product was subjected to... 1 The yield and polyether fragment content of the polyester were determined by ¹H NMR characterization. The concentrated crude product was dissolved in 2 mL of dichloromethane, and precipitated by adding 20 mL of ethanol. The supernatant was discarded, and the process of dissolution, precipitation, and washing was repeated three times. The product was then vacuum dried to obtain pure polyester. The pure polyester was analyzed by GPC (gel permeation chromatography), and the results are shown in the figure. Figure 2 The molecular weight and molecular weight distribution of the product were obtained, and the results are shown in Table 1.

[0052] Example 8

[0053] In an air atmosphere, 8 μmol of the vanadium bipyridine complex prepared in Example 2, 8 μmol of PPNCl, 1.44 mmol of succinic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added sequentially to the test bottle. The bottle was sealed with a polytetrafluoroethylene-lined cap, heated to 80°C, and reacted for 16 h. After the reaction product was concentrated, the crude product was subjected to... 1 The yield of polyester and the content of polyether fragments were characterized by H NMR. The concentrated crude product was dissolved in 2 mL of dichloromethane, and 20 mL of ethanol was added for precipitation. The supernatant was poured off, and the dissolution, precipitation, and washing were repeated three times. The product was then dried under vacuum to obtain pure polyester. The pure polyester was tested by GPC (gel permeation chromatography) to obtain the molecular weight and molecular weight distribution of the product. The test results are shown in Table 1.

[0054] Example 9

[0055] In an air atmosphere, 8 μmol of the vanadium bipyridine complex prepared in Example 3, 8 μmol of PPNCl, 1.44 mmol of succinic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added sequentially to the test bottle. The bottle was sealed with a polytetrafluoroethylene-lined cap, heated to 100°C, and reacted for 16 h. After the reaction product was concentrated, the crude product was subjected to... 1 The yield of polyester and the content of polyether fragments were characterized by H NMR. The concentrated crude product was dissolved in 2-4 mL of dichloromethane, and 20 mL of ethanol was added for precipitation. The supernatant was poured off, and the dissolution, precipitation, and washing were repeated three times. The product was then dried under vacuum to obtain pure polyester. The pure polyester was tested by GPC (gel permeation chromatography) to obtain the molecular weight and molecular weight distribution of the product. The test results are shown in Table 1.

[0056] Example 10

[0057] In an air atmosphere, 8 μmol of the vanadium bipyridine complex prepared in Example 4, 1.44 mmol of maleic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added sequentially to the test flask. The flask was sealed with a polytetrafluoroethylene-lined cap, heated to 100°C, and reacted for 16 h. After the reaction product was concentrated, the crude product was subjected to... 1 The yield and polyether fragment content of the polyester were determined by ¹H NMR characterization. The concentrated crude product was dissolved in 2 mL of dichloromethane, and precipitated by adding 20 mL of ethanol. The supernatant was discarded, and the process of dissolution, precipitation, and washing was repeated three times. The product was then vacuum dried to obtain pure polyester. The pure polyester was analyzed by GPC (gel permeation chromatography), and the results are shown in the figure. Figure 3 The molecular weight and molecular weight distribution of the product were obtained, and the results are shown in Table 1.

[0058] Example 11

[0059] In an air atmosphere, 8 μmol of the vanadium bipyridine complex prepared in Example 5, 8 μmol of PPNCl, 1.44 mmol of norbornene olefinic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added sequentially to the test flask. The flask was sealed with a polytetrafluoroethylene-lined cap, heated to 100°C, and reacted for 16 h. After the reaction product was concentrated, the crude product was subjected to... 1 The yield and polyether fragment content of the polyester were determined by ¹H NMR characterization. The concentrated crude product was dissolved in 2 mL of dichloromethane, and precipitated by adding 20 mL of ethanol. The supernatant was discarded, and the process of dissolution, precipitation, and washing was repeated three times. The product was then vacuum dried to obtain pure polyester. The pure polyester was subjected to GPC (gel permeation chromatography) testing and GPC curve analysis. The results are shown in the figure. Figure 4 and Figure 6 The molecular weight and molecular weight distribution of the product were obtained, and the results are shown in Table 1.

[0060] Example 12

[0061] In an air atmosphere, 4 μmol of the vanadium bipyridine complex prepared in Example 6 and 4 μmol of the vanadium bipyridine complex prepared in Example 7, 8 μmol of PPNCl, 1.44 mmol of phthalic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added sequentially to the test bottle. The bottle was sealed with a polytetrafluoroethylene-lined cap, heated to 100°C, and reacted for 16 h. After the reaction product was concentrated, the crude product was subjected to... 1 The yield and polyether fragment content of the polyester were determined by ¹H NMR characterization. The concentrated crude product was dissolved in 2 mL of dichloromethane, and precipitated by adding 20 mL of ethanol. The supernatant was discarded, and the process of dissolution, precipitation, and washing was repeated three times. The product was then vacuum dried to obtain pure polyester. The pure polyester was analyzed by GPC (gel permeation chromatography), and the results are shown in the figure. Figure 5 The molecular weight and molecular weight distribution of the product were obtained, and the results are shown in Table 1.

[0062] Comparative Example 1

[0063] According to the literature Alkali Metal Carboxylates: Simple and Versatile Initiators for Ring-Opening Alternating Copolymerization of Cyclic Anhydrides / Epoxides; Chong-Min Chen, Xiaowei Xu, He-Yuan Ji, Bin Wang, Li Pan, Yi Luo, and Yue-Sheng Li; Macromolecules 2021 54(2), 713-724; DOI:10.1021 / acs.macromol.0c02389, potassium acetate can be used to catalyze the copolymerization of epoxides and cyclic anhydrides.

[0064] In an air atmosphere, 8 μmol potassium acetate, 1.44 mmol succinic anhydride, 320 mmol toluene, and 2.88 mmol propylene oxide were added sequentially to the test bottle. The bottle was sealed with a polytetrafluoroethylene-lined cap and heated to 100°C for 16 h. If the product was completely dissolved in ethanol after the reaction, it indicates that there was no product or that the product was an oligomer.

[0065] Comparative Example 1 illustrates that although alkali metal carboxylates can catalyze the polymerization of propylene oxide and cyclic anhydrides, the polymerization results in an air atmosphere are unsatisfactory.

[0066] Comparative Example 2

[0067] In an air atmosphere, 8 μmol potassium acetate, 8 μmol PPNCl, 1.44 mmol succinic anhydride, 320 mmol toluene, and 2.88 mmol propylene oxide were added sequentially to a test flask. The flask was sealed with a polytetrafluoroethylene-lined cap, heated to 100°C, and reacted for 16 hours. After concentrating the reaction product, the crude product was subjected to... 1 The yield of polyester and the content of polyether fragments were obtained by H NMR characterization. The concentrated crude product was dissolved in 2 mL of dichloromethane, and 20 mL of ethanol was added for precipitation. The supernatant was poured off, and the dissolution, precipitation, and washing were repeated three times. The product was then dried under vacuum to obtain pure polyester.

[0068] The obtained pure polyester was subjected to GPC (gel permeation chromatography) to obtain the product molecular weight and molecular weight distribution. The conversion rate was only 25%, and the product was an oligomer. No peaks with molecular weights higher than 500 were observed in the GPC test. Comparative Example 2 shows that even with the addition of an additional co-catalyst, alkali metal carboxylates did not perform well.

[0069] Comparative Example 3

[0070] (1) Chromium complexes were prepared according to the literature Ring-Opening Copolymerization of Maleic Anhydride with Epoxides: A Chain-Growth Approach to Unsaturated Polyesters; Angela M. DiCiccio and Geoffrey W. Coates; Journal of the American Chemical Society 2011 133(28), 10724-10727; DOI:10.1021 / ja203520p.

[0071] (2) In an air atmosphere, 8 μmol of the chromium complex obtained in step (1), 8 μmol of PPNCl, 1.44 mmol of succinic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added sequentially to the test bottle. The bottle was sealed with a polytetrafluoroethylene-lined cap and heated to 100°C for 16 h. The complex quickly lost its activity, and the anhydride conversion rate was only 15%. Furthermore, the conversion rate was too low to purify the catalyst for molecular weight testing. Comparative Example 3 illustrates that although these catalysts exhibit good performance under nitrogen protection, they perform poorly in the presence of oxygen and protonated compounds.

[0072] Comparative Example 4

[0073] (1) According to the literature Development of Highly Active and Regioselective Catalysts for the Copolymerization of Epoxides with Cyclic Anhydrides: An Unanticipated Effect of Electronic Variation; Angela M. DiCiccio, Julie M. Longo, Gabriel G. Rodríguez-Calero, and Geoffrey W. Coates; Journal of the American Chemical Society 2016 138(22),7107-7113; DOI:10.1021 / jacs.6b03113 Preparation of aluminum complexes.

[0074] (2) In an air atmosphere, 8 μmol of the aluminum complex prepared in step (1), 8 μmol of PPNCl, 1.44 mmol of succinic anhydride, 320 mmol of toluene, and 2.88 mmol of propylene oxide were added sequentially to the test bottle. The bottle was sealed with a polytetrafluoroethylene-lined cap and heated to 100°C for 16 h. The complex quickly lost its activity, and the anhydride conversion rate was only 11%. Furthermore, the conversion rate was too low to purify the catalyst for molecular weight testing. Comparative Example 4 shows that although these catalysts exhibit good performance under nitrogen protection, they perform poorly in the presence of oxygen and protonated compounds.

[0075] Table 1. Reaction conditions and results of Examples 7-12

[0076]

[0077] In Table 1, SA stands for succinic anhydride, MA for maleic anhydride, CPMA for norbornyl phthalic anhydride, and PA for phthalic anhydride. The abbreviations for co-catalysts are: DMAP for 4-dimethylaminopyridine and PPNCl for bis(triphenylphosphine)ammonium chloride. The conversion rate and polyether ratio are determined by… 1 The polyether content could not be determined by ¹H NMR analysis because the norbornene adiene anhydride exhibited a raw material / product peak at a chemical shift of approximately 3.5 ppm. The number-average molecular weight, weight-average molecular weight, and molecular weight distribution index were determined by GPC.

[0078] Table 1 shows that the vanadium bipyridine catalyst of this invention exhibits good catalytic effects on the polymerization of various acid anhydrides with propylene oxide, indicating that the catalyst of this invention has good catalytic activity and high versatility. Even when using excess propylene oxide, there is no significant homopolymerization of propylene oxide, demonstrating high catalyst selectivity.

[0079] Examples 7-12 and Comparative Examples 1-4 demonstrate that the vanadium bipyridine catalyst prepared in this invention possesses resistance to proton impurities and oxygen, a property not found in other propylene oxide and cyclic anhydride copolymerization catalysts.

[0080] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that specific embodiments of the present invention can still be modified or some technical features can be equivalently replaced. Without departing from the spirit of the technical solutions of the present invention, all such modifications and substitutions should be included within the scope of the technical solutions claimed in the present invention.

Claims

1. A vanadium bipyridine complex characterized by: The chemical formula is V(bipyalk)(CH3OH)Cl3, wherein bipyalk is 2,2'-([2,2'-bipyridine]-6,6'-dimethyl)bis(propan-2-ol), and the chemical structural formula is:

2. The process for the production of the vanadium bipyridine complex as claimed in claim 1, characterized in that, The method comprises the following steps: (1) adding bipyalk and vanadium trichloride into a first solvent to obtain a mixture of a crude sample; (2) concentrating the mixture of the crude sample, then diffusing a second solvent into the concentrated mixture of the crude sample, and crystallizing to obtain a vanadium bipyridine complex.

3. The production method according to claim 2, characterized by, The first solvent is at least one of methanol and ethanol.

4. The production method according to claim 2, characterized by, In step (1), the molar ratio of vanadium trichloride to bipyalk is 1-4:1, and the molar ratio of the first solvent to vanadium trichloride is 250-1000:

1.

5. The preparation method according to claim 2, characterized in that, The second solvent is anhydrous ether, and the molar ratio of anhydrous ether to vanadium trichloride is 12.5-200:

1.

6. The preparation method according to claim 2, characterized in that, In step (1), the reaction temperature is 25-80°C, and in step (2), the crystallization temperature is -20-50°C.

7. The vanadium bipyridine complex of claim 1 as a catalyst in the copolymerization of an epoxide and a cyclic anhydride.

8. Use according to claim 7, characterized in that, The method comprises: Using an epoxide and a cyclic anhydride as raw materials, a vanadium bipyridine complex as a catalyst, and an onium salt or a heterocyclic nitrogen base as a cocatalyst, a polyester is prepared by catalyzing the polymerization of the cyclic anhydride and propylene oxide in toluene.

9. Use according to claim 8, characterized in that, The cyclic anhydride is at least one of maleic anhydride, succinic anhydride, phthalic anhydride, and norbornene diacid anhydride.

10. Use according to claim 8, characterized in that, The onium salt is selected from bis(triphenylphosphine)ammonium chloride, and the heterocyclic nitrogen base is selected from 4-dimethylaminopyridine.

11. Use according to claim 8, characterized in that, The polymerization temperature is 80-100°C.

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