Bimetal catalyst and method for preparing homopolymer or copolymer of lactone and lactide by using same

Abstract

The invention belongs to the field of polymer synthesis, and discloses a bimetallic catalyst and a method for preparing lactone and lactide homopolymer or copolymer by using the bimetallic catalyst, which comprises the following steps: adding the bimetallic catalyst, lactone and / or lactide, selectively adding a chain transfer agent and selectively adding an organic solvent into a reactor, and stirring for a certain time at a certain reaction temperature to obtain the bimetallic catalyst. Stopping the reaction time; and adding a large amount of methanol or ethanol into the crude product, violently stirring to precipitate the polymer, and repeating the precipitation process to obtain the polyester. The bimetallic catalyst is designed and synthesized, and autopolymerization and copolymerization of lactide or lactone can be synergistically catalyzed by bimetallic. Compared with a single-metal catalyst, the activity is greatly improved; according to the invention, magnesium, zinc and calcium necessary for human bodies are used as catalyst centers, so that potential dangers caused by toxic catalysts are avoided.

Description

Technical Field

[0001] This invention belongs to the field of polymer synthesis and relates to a novel type of bimetallic catalyst, which is used for the preparation of lactones, lactides, self-polymerization or copolymers. Background Technology

[0002] Polymers, as the most widely used synthetic materials of the 21st century, possess advantages such as corrosion resistance, light weight, and high strength, and have become necessities in people's daily lives. However, petroleum-based plastics, made from fossil fuels, are non-renewable resources and cannot be degraded in a short period, leading to a global plastic pollution crisis. Therefore, developing sustainable polymer materials is an important goal of polymer chemistry. Polyesters have degradable ester groups on their main chain, giving them a natural advantage in synthesizing sustainable polymers. Polyesters can be efficiently depolymerized into original monomers or other high-value chemicals through various chemical methods such as hydrolysis (back to acids and alcohols), alcoholysis (back to monomers or derivatives), ammonolysis, and glycolysis. Furthermore, ester bonds are widely existing chemical bonds in nature (such as in aliphatic and cellulose compounds), so polyesters generally have good biocompatibility and biodegradability. Nevertheless, designing effective catalysts for ester polymerization remains challenging. Stannous octoate is a mature industrial catalyst, but it typically exhibits low polymerization activity, requiring high catalyst dosages to achieve good activity. This leads to tin residues in the polyester, and separation processes are complex and costly. To address this issue, researchers have developed various highly efficient catalysts for the polymerization of lactones or lactides. For example, J. Polym. Sci. 2008, 46 (19), 6466-6476 describes a mononuclear zinc catalyst, as shown in Formula 1, which can achieve the polymerization of lactide. Chem. Eur. J. 2012, 18, 9360-9370 and CCS Chem, 2022, 4, 1263–1272 report a mononuclear magnesium catalyst, as shown in Formula 2, which can efficiently achieve the self-polymerization or copolymerization of cyclic carbonates and lactones under certain catalyst ratios. Compared with Formula 1, Formula 2 replaces the carbon-nitrogen double bonds in the catalyst ligands with carbon-nitrogen single bonds, resulting in better catalyst stability. The synthesis process can avoid deactivation caused by side reactions of the double bonds and effectively reduce the number of steps in catalyst synthesis.

[0003]

[0004] Formula 1 Formula 2

[0005] The development of novel catalysts for the polymerization of lactones or lactides is of great significance, as it can effectively reduce the amount of catalyst used. Compared with mononuclear metal complex catalysts, the bimetallic active centers of binuclear metal complex catalysts have a significant impact on the polymerization catalytic activity and the properties of the resulting polymers (including polymer microstructure, molecular weight, and molecular weight distribution). Therefore, developing suitable bimetallic catalysts to improve polymerization activity is urgently needed. Furthermore, divalent metals magnesium, zinc, and calcium are important elements for the body, and their residues in polymers, even when used as catalysts, do not pose a harm. Therefore, developing catalysts based on these three metals is also of great importance.

[0006] Based on the catalytic activity characteristics exhibited by the above catalysts, this application considers improving the catalyst activity through bimolecular synergistic effects. Based on this, this application designed and synthesized the catalyst of this invention, which connects two metal centers through biphenyl or naphthalene, and controls the distance between the two metal centers by changing the substituent groups, thereby obtaining a highly active catalyst. Summary of the Invention

[0007] The main content of this invention is to provide a class of bimetallic catalysts for the preparation of lactones, lactide homopolymers or copolymers.

[0008] The technical solution of this invention:

[0009] A type of bimetallic catalyst, wherein the bimetallic catalyst has the structural formula of Formula 3:

[0010]

[0011] Formula 3 Formula 4

[0012] In the formula, M 1 Zn 2+ Mg 2+ or Ca 2+ ;

[0013] X 1 It is a C1~C4 alkyl, C1~C7 alkoxy, or C1~C8 amino group;

[0014] R 1 It is a C1~C4 alkyl group;

[0015] R 4 for , , , , , or , Indicates the connection position;

[0016] R5 It can be a C1~C4 alkyl group, CH3O, CH3CH2O, F, Cl, Br, I, or NO2;

[0017] R 6 For H, or when R 5 When it is a C1~C4 alkyl group, R 6 With R 5 Formation of a benzene ring;

[0018] When A 1 When R is N or P: 2 It is a C1~C4 alkyl group or Ph, R 3 It is a C1~C4 alkyl group or Ph;

[0019] If A 1 When it is O or S: R 2 and R 3 Only one can exist, R 2 Or R 3 It is a C1~C4 alkyl group or Ph.

[0020] The ligand of formula 4 in the bimetallic catalyst shown in formula 3 is prepared by reacting 3,3'-dicarboxy-2,2'-hydroxy-1,1'-biphenyl containing substituted groups with an amine (a hydrocarbon-substituted diamine, a hydrocarbon-substituted hydroxylamine, a hydrocarbon-substituted thiolamine, or a hydrocarbon-substituted phosphinoamine); the resulting ligand is then reacted with alkyl, alkoxy, or amino compounds of magnesium, zinc, or calcium, as shown in the following general reaction formula:

[0021]

[0022] A method for preparing lactone, lactone and / or lactone self-polymers or copolymers using a bimetallic catalyst, the specific reaction process being as follows: adding a bimetallic 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, stopping the reaction time; 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 polyester;

[0023] Furthermore, the lactone is one or a mixture of two or more of δ-valerolactone, β-methyl-δ-valerolactone, δ-methyl-δ-valerolactone, ε-caprolactone, and ε-decanolactone, and the lactide is lactide and / or glycolide, with the specific structure as follows:

[0024]

[0025] δ-Volalactone, β-methyl-δ-Volalactone, δ-methyl-δ-Volalactone, glycolide, lactide, α-caprolactone, α-decanolactone

[0026] Furthermore, when only one of lactone or lactide is added, the molar ratio of the bimetallic catalyst to lactone or lactide is 1:100 to 10000; the molar ratio of the chain transfer agent to lactone or lactide is 1:30 to 5000.

[0027] When both lactone and lactide are added, the ratio of the bimetallic catalyst to the sum of the molar amounts of lactone and lactide is 1:100 to 10000; the ratio of the chain transfer agent to the sum of the molar amounts of lactone and lactide is 1:30 to 5000.

[0028] Furthermore, the reaction temperature is 0–150°C; the reaction time is 0.1–10.0 h.

[0029] Furthermore, the organic solvent is one of dichloromethane, dichloroethane, tetrahydrofuran, 1,4-dioxane, toluene, or n-hexane.

[0030] Furthermore, the chain initiator is one of methanol, ethanol, ethylene glycol, terephthalic acid, glycerol, and pentaerythritol.

[0031] The beneficial effects of this invention are:

[0032] (1) This invention designs and synthesizes a bimetallic 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;

[0033] (2) The present invention uses magnesium, zinc and calcium, which are essential for the human body, as catalyst centers to avoid the potential dangers of toxic catalysts. Attached Figure Description

[0034] Figure 1 This is the 1H NMR spectrum of the bimetallic magnesium catalyst synthesized in Example 1. Detailed Implementation

[0035] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0036] Example 1

[0037] The synthesis reaction equation for the dinuclear biphenyl magnesium catalyst is as follows:

[0038]

[0039] Under a nitrogen atmosphere, N,N,N'-trimethylethylenediamine (20 mmol, 2.04 g) was added to a solution of 3,3'-diformyl-2,2'-hydroxy-1,1'-biphenyl (10 mmol) in 1,2-dichloroethane. After reacting for 0.5 h, sodium triacetoxyborohydride (30 mmol, 3.40 g) was added, and the mixture was stirred overnight. The reaction was quenched with saturated sodium bicarbonate solution, and the mixture was extracted three times with 20 mL of dichloromethane. Hydrochloric acid solution was added to the extracted solution until the system turned orange-red. The aqueous phase was separated, and saturated sodium bicarbonate solution was added to the aqueous phase until the system turned pale yellow. The mixture was extracted three times with 20 mL of dichloromethane, and the organic phase was dried over anhydrous Na₂SO₄. After removing the solvent, the bitridentate ligand was recrystallized from ethanol. At -35°C, the above ligand (0.5 mmol, 0.21 g) was slowly added to 1.2 mmol (1 M, 1.2 mL) of di-n-butylmagnesium hexane solution in a glove box. The reaction was allowed to proceed for 10 h, followed by filtration and washing to obtain 0.21 g of a white solid, yielding 72%. HRMS (m / z): theoretical value 574.3948, measured value 574.3967.

[0040] Figure 1 The binuclear magnesium catalyst prepared in this embodiment is shown. 1 H NMR.

[0041] Example 2

[0042]

[0043] At -35°C, the ligand obtained in Example 1 (0.5 mmol, 0.21 g) was slowly added to 1.2 mmol (1 M, 1.2 mL) of diethylzinc hexane solution in a glove box. The reaction was carried out for 6 h, filtered, and washed to obtain 0.18 g of white solid, with a yield of 60%. HRMS (m / z): theoretical value 600.2173, measured value 600.2156.

[0044] Example 3

[0045]

[0046] At -35°C, the ligand obtained in Example 1 (0.5 mmol, 0.21 g) was dissolved in 10 mL of tetrahydrofuran in a glove box, and then slowly added to a tetrahydrofuran solution containing CaH2 (1.2 mmol, 50 mg). The reaction was allowed to proceed for 6 h, filtered, and washed to obtain 0.15 g of a white solid, yield 52%. HRMS (m / z): theoretical value 582.2771, measured value 582.2789.

[0047] Example 4

[0048] The synthesis reaction equation for the binuclear magnesium catalyst is as follows:

[0049]

[0050] Under a nitrogen atmosphere, N,N,N'-trimethylethylenediamine (20 mmol, 2.04 g) was added to a solution of 3,3'-diformyl-2,2'-hydroxy-1,1'-binaphthyl (10 mmol) in 1,2-dichloroethane. After reacting for 0.5 h, sodium triacetoxyborohydride (30 mmol, 3.40 g) was added, and the mixture was stirred overnight. The reaction was quenched with saturated sodium bicarbonate solution, and the mixture was extracted three times with 20 mL of dichloromethane. Hydrochloric acid solution was added to the extracted solution until the system turned brownish-red. The aqueous phase was separated, and saturated sodium bicarbonate solution was added to the aqueous phase until the system turned pale green. The mixture was extracted three times with 20 mL of dichloromethane, and the organic phase was dried over anhydrous Na₂SO₄. After removing the solvent, the mixture was recrystallized from ethanol to obtain the bitridentate ligand. At room temperature, the above ligand (0.5 mmol, 0.26 g) was slowly added to 1.2 mmol (1.0 M, 1.2 mL) of di-n-butylmagnesium hexane solution in a glove box. The reaction was allowed to proceed for 10 h, followed by heating to 60 °C for 4 h. After filtration and washing, 0.22 g of a white solid was obtained, yielding 59%. HRMS (m / z): theoretical value 674.4261, measured value 674.4267.

[0051] Example 5

[0052]

[0053] At room temperature, the above ligand (0.5 mmol, 0.26 g) was slowly added to 1.2 mmol (1.0 M, 1.2 mL) of a hexane solution of diethylzinc in a glove box. The reaction was allowed to proceed for 10 h, followed by filtration and washing to give 0.28 g of a white solid, yield 80%. HRMS (m / z): theoretical value 700.2486, measured value 700.2492.

[0054] The following describes in detail the specific polymerization embodiments of the present invention with reference to the technical solutions. Table 1 relates to the polymerization of lactones, lactides and their copolymerization catalyzed by biphenyl catalyst; Table 2 relates to the polymerization results of δ-valerolactone catalyzed by magnesium catalyst when catalyst A is O, S or P; Table 3 relates to the polymerization results of δ-valerolactone catalyzed by naphthalene catalyst.

[0055] In a 10 mL serum vial, at ambient temperature, the following steps were taken in sequence: a certain amount of catalyst (any metal complex described in claim 1), with or without chain transfer agent, with or without solvent, and then the lactone monomer. The mixture was stirred vigorously, and stirring was stopped after the specified reaction time. The polymer was washed three times with dichloromethane / methanol precipitation, dried under vacuum to constant weight, and the molecular weight and distribution of the polymer were determined by gel permeation chromatography.

[0056] Table 1. In the catalyst shown in Equation 3, M = Mg, X = Bu, A = N, R 6 = Results of the series of catalysts for the polymerization of lactones catalyzed by H a

[0057]

[0058]

[0059] Remark: a Temperature 25℃, solvent toluene, monomer concentration 1 mol / L, monomer is δ-valerolactone, and the molar ratio of catalyst to initiator to monomer is 1:1:1000; b The monomer is β-methyl-δ-valerolactone; c The monomer is δ-methyl-δ-valerolactone; d The monomer is glycolide; e The monomer is lactide; f The monomer is α-caprolactone; g The monomer is α-decanolide; h Temperature 50℃, monomer is lactide, no solvent; i d monomers are lactide and glycolide, solvent-free; j The temperature was 150℃, the monomer was lactide, and there was no solvent. k The molar ratio of catalyst to initiator and monomer is 1:1:10000; or the molar ratio of catalyst to initiator and monomer is 1:10:10000.

[0060] Table 2. R in the catalyst shown in Equation 3 1 = Me, R 5 = R 6 = H, X= n Results of the polymerization of δ-valerol catalyzed by a series of catalysts from Bu a

[0061]

[0062] Remark: a The reaction temperature was 25℃, the solvent was toluene, the monomer concentration was 1 mol / L, the monomer was δ-valerolactone, and the molar ratio of catalyst to initiator to monomer was 1:1:1000.

[0063] Table 3. In the catalyst shown in Equation 3, M = Mg, X = Bu, A = N, R 5 and R 6 Results of the polymerization of δ-valerol catalyzed by a series of catalysts forming benzene rings a

[0064]

[0065] Remark: a The reaction temperature was 25℃, the solvent was toluene, the monomer concentration was 1 mol / L, the monomer was δ-valerolactone, and the molar ratio of catalyst to initiator to monomer was 1:1:1000.

[0066] Example 6

[0067] The specific procedure for the polymerization experiment (serial number 1 in Table 1) was as follows: At 20°C, 10 μL of the 0.1 mol / L catalyst solution from Example 1 and 20 μL of 0.1 mol / L benzyl alcohol solution were added to a pre-dried 10 mL serum bottle. Then, 870 μL of toluene solution was added, followed by 0.1 g (1 mmol) of δ-valerolactone. The polymerization reaction was immediately quenched by adding 1 mL of benzoic acid / CH₂Cl₂ (10 mg / mL) after 1 min. Then, the polymerization was... 1 ¹H-NMR analysis revealed a monomer conversion rate of 95%. The quenched mixture was then precipitated in cold methanol, filtered, washed three times with cold methanol to remove any unreacted monomers, and dried overnight at room temperature in a vacuum oven to constant weight. A white solid was obtained, and the polymer's average molecular weight was determined to be 52.2 kg / mol with a molecular weight distribution of 2.0 by gel permeation chromatography.

[0068] Comparative Example 1

[0069] To compare the catalytic performance of the binuclear catalyst of this invention with that of a previously disclosed mononuclear catalyst with a similar structure, a mononuclear catalyst (Formula 2) was synthesized according to CCS Chem, 2022, 4, 1263–1272. Under the same experimental conditions, the catalytic activity of the binuclear magnesium catalyst synthesized in Example 1 and the mononuclear magnesium catalyst shown in Formula 2 in catalyzing the ring-opening polymerization of δ-valerolactone was compared.

[0070] Table 3. Comparison of polymerization results between Example 1 and Comparative Example 1

[0071]

[0072] The comparison of polymerization results shows that the binuclear magnesium catalyst in Example 1 reached polymerization equilibrium after 1 minute, with a monomer-to-polymer conversion rate of 95%. In contrast, the mononuclear magnesium catalyst with a similar structure in the comparative example only achieved a monomer-to-polymer conversion rate of 10% after 1 minute, requiring 15 minutes to reach polymerization equilibrium, with a conversion rate of only 90%. Therefore, the binuclear magnesium catalyst exhibits higher reactivity than the mononuclear magnesium catalyst, significantly saving reaction time.

[0073] The above-described embodiments are merely specific implementations of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A bimetallic catalyst characterized in that, The bimetallic catalyst has a structural formula as shown in Formula 3, and Formula 4 is a ligand thereof: ； Formula 3 Formula 4 In the formula, M 1 is Zn 2+ , Mg 2+ or Ca 2+ ; X 1 is C1-C4alkyl, C1-C7alkoxy or C1-C8amino; R 1 R is C1-C4alkyl; R 4 For , , , , , or , represents the point of attachment; R 5 is C1-C4alkyl, CH3O, CH3CH2O, F, CI, Br, I, or NO2; R 6 For H, or when R 5 When it is a C1~C4 alkyl group, R 6 With R 5 Formation of a benzene ring; When A 1 When R is N or P: 2 It is a C1~C4 alkyl group or Ph, R 3 It is a C1~C4 alkyl group or Ph; If A is O or S: R 1 and R 2 and R 3 only one can be present, R 2 or R 3 is C1-C4 alkyl or Ph.

2. A process for the preparation of a lactone, a lactide homopolymer or copolymer using the bimetallic catalyst of claim 1, characterized in that, The specific reaction process is as follows: the bimetallic catalyst, the lactone and / or the lactide, the chain transfer agent and the organic solvent are added into a reactor, and then the reaction is stirred at a certain temperature for a certain time, and then the reaction is stopped; the crude product is added into a large amount of methanol or ethanol, and then the polymer is precipitated by stirring; the precipitation process is repeated to obtain the polyester.

3. The method of claim 2, wherein, The lactone is one or a mixture of two or more of δ-valerolactone, β-methyl-δ-valerolactone, δ-methyl-δ-valerolactone, ε-caprolactone and ε-decalactone, and the lactide is lactide and / or glycolide, and the specific structures are as follows: ； δ-valerolactone β-methyl-δ-valerolactone δ-methyl-δ-valerolactone glycolide lactide ε-caprolactone ε-decalactone.

4. The method of claim 2, wherein, When only the lactone or the lactide is added, the molar ratio of the bimetallic catalyst to the lactone or the lactide is 1:100-10000, and the molar ratio of the chain transfer agent to the lactone or the lactide is 1:30-5000.

5. The method of claim 2, wherein, When both the lactone and the lactide are added, the molar ratio of the bimetallic catalyst to the sum of the molar amounts of the lactone and the lactide is 1:100-10000, and the molar ratio of the chain transfer agent to the sum of the molar amounts of the lactone and the lactide is 1:30-5000.

6. The method of claim 2, wherein, The reaction temperature is 0-150℃, and the reaction time is 0.1-10.0h.

7. The method of claim 2, wherein, The organic solvent is one of dichloromethane, dichloroethane, tetrahydrofuran, 1,4-dioxane, toluene or n-hexane.

8. The method of claim 2, wherein, The chain initiator is one of methanol, ethanol, ethylene glycol, p-xyleneglycol, glycerol and pentaerythritol.

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