Polyhydroxyalkanoate and preparation method thereof

Abstract

The invention relates to the field of high polymer materials, in particular to polyhydroxyalkanoate and a preparation method thereof. The preparation method of the polyhydroxyalkanoate comprises the following steps: in the presence of a solvent, catalyzing ring opening polymerization of a lactone monomer by adopting a zinc-based catalyst to prepare the polyhydroxyalkanoate, the zinc-based catalyst is prepared by carrying out coordination reaction on diethyl zinc and micromolecular dihydric alcohol in an inert atmosphere; the micromolecular dihydric alcohol comprises at least one of C2-C10 dihydric alcohol. According to the invention, the zinc catalyst composed of diethyl zinc and micromolecular dihydric alcohol is adopted to catalyze ring opening polymerization of lactone in the presence of the solvent to prepare polyhydroxyalkanoate, so that the molecular weight is increased, the polyhydroxyalkanoate with narrower molecular weight distribution is obtained, and the use performance of the polyhydroxyalkanoate is further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high molecular materials, in particular to a polyhydroxyalkanoate and a preparation method thereof. BACKGROUND

[0002] Polyhydroxyalkanoate (PHA) has excellent biocompatibility, degradability and mechanical properties, and can be used as a medical material and a biodegradable material, and has a very wide application field. It is one of the most promising polymeric materials at present. Commercial PHA mainly includes poly-3-hydroxybutyrate (PHB), poly-3-hydroxybutyrate-3-hydroxyvalerate (PHBV), poly-3-hydroxybutyrate-3-hydroxyhexanoate (PHBH), poly-3-hydroxybutyrate-4-hydroxybutyrate (P34HB), etc., which are mainly produced by fermentation. The PHA produced by fermentation has a high molecular weight, which is beneficial to improve the stability and mechanical strength, but the reaction efficiency is low and the cost is high due to the limitations of substrate utilization rate, fermentation period and strain synthesis capacity. At the same time, the metabolic pathway of microorganisms and the activity of enzymes will affect the polymerization degree of PHA, and the PHA prepared by fermentation contains a large number of small molecular segments, and the molecular weight distribution is wide, which will lead to uneven degradation rate and reduced thermal stability, and also affect the mechanical strength of the material. SUMMARY

[0003] Therefore, the main purpose of the present application is to provide a preparation method of polyhydroxyalkanoate with high molecular weight and narrow molecular weight distribution.

[0004] In a first aspect, the present application provides a preparation method of polyhydroxyalkanoate, comprising the following steps:

[0005] The polyhydroxyalkanoate is prepared by ring-opening polymerization of lactone monomers catalyzed by a zinc-based catalyst in the presence of a solvent;

[0006] The zinc-based catalyst is prepared by coordination reaction of diethyl zinc and a small molecular diol under an inert atmosphere;

[0007] The small molecular diol includes at least one of C2-C10 diols.

[0008] In some embodiments, the small molecular diol includes at least one of the compounds shown in formula I;

[0009] (Formula I);

[0010] Wherein, R is selected from carbon-carbon single bond, C1-C6 alkylene or phenyl;

[0011] R1, R2 are each independently selected from H or C1-C2 alkyl;

[0012] Optionally, the small molecule diol includes one or more of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 2,3-butanediol, 1,3-butanediol and 1,4-phenylenediol.

[0013] In some embodiments, the lactone monomer includes one or more of β-butyrolactone, γ-butyrolactone, β-valerolactone, and β-caprolactone.

[0014] In some embodiments, the solvent includes one or more of dichloromethane, chloroform, toluene, tetrahydrofuran, and dioxane.

[0015] In some embodiments, the ring-opening polymerization conditions include: reacting at -50°C to 100°C for 30 minutes to 8 hours.

[0016] In some embodiments, in the mixture of the lactone monomer and the solvent, the molar concentration of the lactone monomer is 2M to 8M;

[0017] And / or, the mass ratio of the lactone monomer to the zinc-based catalyst is (1000-5000):1.

[0018] In some embodiments, the molar ratio of the diethyl zinc to the small molecule diol is 1:(1-2).

[0019] In some embodiments, the reaction conditions of diethyl zinc and small molecule diol under an inert atmosphere include: reaction temperature of -10°C to 40°C, and reaction time of 5 min to 1 h.

[0020] In a second aspect, the present application provides polyhydroxyalkanoate prepared by the preparation method described in the first aspect.

[0021] In some embodiments, the polyhydroxyalkanoate has a number average molecular weight of 1000 g / mol to 500000 g / mol;

[0022] and / or, the polydispersity index of the polyhydroxyalkanoate is 1.10-1.25;

[0023] And / or, the polyhydroxyalkanoate P3HB has a Pm>0.90.

[0024] Research has found that PHA produced by fermentation has a higher molecular weight, which is beneficial for improving stability and mechanical strength. However, due to factors such as substrate utilization, fermentation cycle, and strain synthesis capacity, the reaction efficiency is low and the cost is high. Furthermore, because microbial metabolic pathways and enzyme activity can affect the degree of PHA polymerization, PHA produced by fermentation contains more small molecular segments and a wider molecular weight distribution. This wide molecular weight distribution can lead to uneven degradation rates and reduced thermal stability, which can also affect the material's mechanical properties.

[0025] Based on this, the present application provides a method for preparing polyhydroxyalkanoates, which uses a zinc-based catalyst composed of diethylzinc and a small molecule diol to catalyze the ring-opening polymerization of lactones in the presence of a solvent to prepare polyhydroxyalkanoates. This method can efficiently, environmentally and economically prepare polyhydroxyalkanoates with high molecular weight and narrow molecular weight distribution. In the defined system, the use of the zinc-based catalyst greatly improves the reaction efficiency, while the introduction of the solvent prevents the precipitation of the polyhydroxyalkanoates, allowing for smooth mass transfer in the system and lowering the reaction temperature, thereby improving the reaction efficiency and degree of polymerization, which is beneficial for increasing the molecular weight and obtaining polyhydroxyalkanoates with a narrow molecular weight distribution, thereby improving the performance of the polyhydroxyalkanoates.

[0026] Furthermore, the preparation method of the polyhydroxyalkanoate of the present application has the following advantages:

[0027] The preparation process is simple, does not introduce heavy metal impurities, is environmentally friendly and economical, and is conducive to industrial production; it can meet the ring-opening polymerization of different types of lactone monomers, has few raw material restrictions, and has a wide range of applications. DETAILED DESCRIPTION

[0028] The polyhydroxyalkanoates and their preparation methods of the present application are further described in detail below with reference to specific examples. The present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the present disclosure.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0030] As used herein, "one or more" refers to any one, any two, or any two or more of the listed items.

[0031] In this application, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or quantity, nor as implicitly indicating the importance or quantity of the technical features indicated. Furthermore, terms such as "first," "second," "third," and "fourth" serve only as non-exhaustive enumeration and description, and should not constitute a closed-ended limitation on quantity.

[0032] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0033] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0034] Unless otherwise specified, the percentage contents mentioned in this application refer to mass percentage for solid-liquid mixture and solid-solid mixture, and refer to volume percentage for liquid-liquid mixture.

[0035] The percentage concentrations mentioned in this application, unless otherwise specified, refer to the final concentration, which refers to the percentage of the added component in the system after the addition of the component.

[0036] The temperature parameters in this application, unless otherwise specified, allow for both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows for temperature fluctuations within the precision range of instrument control.

[0037] In the present application, the lactone monomer conversion rate refers to the percentage of the amount of lactone monomer converted into polymer to the total amount of the lactone monomer fed, as measured by a Bruker 400 nuclear magnetic resonance spectrometer. A high lactone monomer conversion rate indicates a high degree of reaction. The catalyst yield refers to the percentage of the actual mass of the catalyst collected to the total mass of the raw materials (the total mass of diethylzinc and small molecule diol, excluding solvent), and is calculated as follows: yield (%) = actual mass of catalyst collected / (mass of diethylzinc + mass of alcohol) × 100%; molecular weight refers to the average molecular weight, measured by GPC, in g / mol; PDI is the polydispersity index, measured by GPC, and a larger PDI indicates a wider molecular weight distribution; and the tacticity Pm is measured by a Bruker 400 nuclear magnetic resonance spectrometer.

[0038] In this application, when describing the number of carbon atoms, i.e., the number following the capital letter "C", such as "C2-C10", "C1-C6", etc., the number following "C", such as "1", "2", "6", or "10", represents the number of carbon atoms in a specific functional group. That is, "C2-C10" means that the functional group can include any integer between 2 and 10 carbon atoms, or any integer range, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. For example, "C1-C6 alkyl" refers to an alkyl group having 1, 2, 3, 4, 5 or 6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl; "C1-C6 alkylene" refers to an alkylene group having 1, 2, 3, 4, 5 or 6 carbon atoms, such as methylene, ethylene, propylene, butylene, cyclobutylene, pentylene, hexylene, cyclohexylene, etc.

[0039] In some embodiments of the present application, a polyhydroxyalkanoate and a preparation method thereof are provided, comprising the following steps:

[0040] The steps include:

[0041] In the presence of a solvent, a zinc-based catalyst is used to catalyze the ring-opening polymerization of a lactone monomer to prepare the polyhydroxyalkanoate;

[0042] The zinc-based catalyst is prepared by a coordination reaction between diethyl zinc and a small molecule diol under an inert atmosphere;

[0043] The small molecule diol includes at least one of C2-C10 diols.

[0044] The present application provides a method for preparing polyhydroxyalkanoates, which utilizes a zinc-based catalyst composed of diethylzinc and a small molecule diol to catalyze the ring-opening polymerization of lactones in the presence of a solvent to prepare polyhydroxyalkanoates. This method allows for the efficient, environmentally friendly, and economical preparation of polyhydroxyalkanoates with high molecular weight and a narrow molecular weight distribution. In the defined system, the use of the zinc-based catalyst greatly improves reaction efficiency, while the introduction of the solvent prevents polyhydroxyalkanoate precipitation, facilitating smooth mass transfer in the system and reducing the reaction temperature, thereby improving reaction efficiency and the degree of polymerization. This contributes to increasing the molecular weight and obtaining polyhydroxyalkanoates with a narrow molecular weight distribution, thereby enhancing the performance of the polyhydroxyalkanoates.

[0045] Among them, the zinc-based catalyst is prepared by the coordination reaction of diethylzinc and a small molecule diol under an inert atmosphere, which can avoid the production of by-products caused by the presence of oxygen or water and is conducive to obtaining the expected zinc-based catalyst.

[0046] In some embodiments, the C2-C10 diol can specifically be C1 diol, C2 diol, C3 diol, C4 diol, C5 diol, C6 diol, C7 diol, C8 diol, C9 diol, or C10 diol. It is understood that the C2-C10 diol can be either an alkyl group or an aralkyl group, and can be either a linear alkyl group or a branched alkyl group.

[0047] In some embodiments, the small molecule diol includes at least one of the compounds shown in the structure of Formula I;

[0048] (Formula I);

[0049] Wherein, R is selected from a carbon-carbon single bond, a C1-C6 alkylene group or a phenyl group;

[0050] R1 and R2 are each independently selected from H or C1-C2 alkyl;

[0051] Optionally, the small molecule diol includes one or more of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 2,3-butanediol, 1,3-butanediol and 1,4-phenylenediol.

[0052] As can be understood, small molecule diols have a small molecular weight, low steric hindrance, and contain two hydroxyl groups, which are conducive to the coordination reaction with diethylzinc to prepare the desired zinc-based catalyst. As can be understood, small molecule diols can use chiral or achiral raw materials.

[0053] In some embodiments, the lactone monomer includes one or more of β-butyrolactone, γ-butyrolactone, β-valerolactone, and β-caprolactone. It is understood that the lactone monomer can be selected based on the target polyhydroxyalkanoate structure; optionally, the molar proportion of β-butyrolactone in the lactone monomer is 50%-100%, for example, 50%, 60%, 70%, 80%, 90%, 100%, etc. Depending on the composition of the lactone monomer, the corresponding polyhydroxyalkanoate includes at least one of P3HB, PHBV, PHBH, and P34HB. It is understood that the lactone monomer can be a chiral monomer and / or a racemic monomer.

[0054] In some embodiments, the solvent includes one or more of dichloromethane, chloroform, toluene, tetrahydrofuran, and dioxane. These solvents have good solubility for polyhydroxyalkanoates, facilitate smooth mass transfer in the reaction system, reduce reaction temperature, and improve reaction efficiency.

[0055] In some embodiments, the open ring polymerization conditions include a reaction temperature of -50°C to 100°C and a reaction time of 30 min to 8 h. The above reaction temperature and time are conducive to regulating the reaction progress and preparing polyhydroxyalkanoate with desired performance. Further, the reaction temperature can be -50°C, -40°C, -30°C, -20°C, -10°C, 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C; and the reaction time can be 30 min, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, or 8 h.

[0056] In some embodiments, the molar concentration of the lactone monomer in the mixture of the lactone monomer and the solvent is 2M to 8M, such as 2M, 3M, 4M, 5M, 6M, 7M, or 8M. Controlling the molar concentration of the lactone monomer in the mixture of the lactone monomer and the solvent in the above range is conducive to balancing the reaction efficiency and process cost.

[0057] In some embodiments, the mass ratio of the lactone monomer to the zinc-based catalyst is (1000-5000):1, such as 1000:1, 2000:1, 3000:1, 4000:1, or 5000:1. Controlling the molar ratio of the lactone monomer to the zinc-based catalyst in the above range is conducive to balancing the reaction stability and reaction efficiency.

[0058] In some embodiments, the molar ratio of the diethyl zinc to the small molecular diol is 1:(1-2), such as 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, or 1:2.

[0059] In some embodiments, the reaction conditions of the diethyl zinc and the small molecular diol in an inert atmosphere include a reaction temperature of -10°C to 40°C and a reaction time of 5 min to 1 h. Specifically, the reaction temperature can be -10°C, 0°C, 10°C, 20°C, 30°C, or 40°C; and the reaction time can be 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, or 1 h. The above reaction temperature and time are conducive to preparing the expected zinc-based catalyst with high efficiency and avoiding the generation of by-products. Understandably, the inert atmosphere includes a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, or a neon atmosphere.

[0060] In some embodiments, the diethyl zinc is in a toluene solution of diethyl zinc; and the molar content of the diethyl zinc in the toluene solution of diethyl zinc is 1M to 10M, such as 1M, 2M, 4M, 6M, 8M, or 10M.

[0061] In some embodiments, the process for preparing a zinc-based catalyst by a coordination reaction of diethylzinc with a small molecule diol under an inert atmosphere further includes a purification and drying step after the reaction is completed. The purification and drying process includes the steps of a first vacuum drying step, re-dissolution with a solvent, filtration, cryopreservation, and a second vacuum drying step. The conditions for the first vacuum drying step and the second vacuum drying step include drying at 30°C to 50°C and 1mbar to 10mbar for 4 to 12 hours. The conditions for cryopreservation include storage at -30°C to -10°C for 0.5 to 3 hours.

[0062] In some embodiments of the present application, a polyhydroxyalkanoate prepared by the preparation method described in the first aspect is provided.

[0063] In some embodiments, the polyhydroxyalkanoate has a number average molecular weight of 1000 g / mol to 500,000 g / mol, for example, 1000 g / mol, 5000 g / mol, 10,000 g / mol, 50,000 g / mol, 100,000 g / mol, 200,000 g / mol, 300,000 g / mol, 400,000 g / mol, and 500,000 g / mol.

[0064] In some embodiments, the polydispersity index of the polyhydroxyalkanoate is 1.10-1.25, for example, 1.10, 1.12, 1.14, 1.16, 1.18, 1.2, 1.22, 1.24, 1.25, etc.

[0065] In some embodiments, the polyhydroxyalkanoate has a Pm>0.90. When a single lactone raw material is used, the zinc-based catalyst used in this application has good stereoselectivity, so a polyhydroxyalkanoate with high regularity can be obtained.

[0066] For experimental parameters not specified in the following specific examples, reference is made to the guidance given in this application document, and reference may also be made to experimental manuals in the art or other experimental methods known in the art, or to the experimental conditions recommended by the manufacturer.

[0067] Unless otherwise specified, the raw materials and reagents in this application can be purchased from commercial sources. The following is an exemplary description.

[0068] γ-Butyrolactone, from Aladdin;

[0069] Chiral and racemic monomers: β-butyrolactone, β-valerolactone, and β-caprolactone were synthesized in the laboratory according to the routes reported in the literature or self-developed technology;

[0070] Diethylzinc solution in toluene (2M), small molecule diols (ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 1,3-butanediol, 1,4-p-xylenediol) from Inokem; PEG400 is common commercially available.

[0071] The chiral monomers used in the embodiments of the present application are all labeled or described, such as (R) β-butyrolactone, and if no special description is given, the racemic monomer is used by default.

[0072] In the present application, the alcohol ligand used by the zinc catalyst and the abbreviation are as shown in Table 1:

[0073] Table 1 Corresponding table of alcohol ligand used by zinc catalyst and abbreviation

[0074]

[0075] Preparation Example 1

[0076] Synthesis of catalyst Zn-1

[0077] In a glove box under nitrogen atmosphere, 5 mL of diethylzinc solution in toluene (2M) was added dropwise into 0.62 g (10 mmol) of ethylene glycol at 25°C, and after 5 min of reaction, the toluene solvent and unreacted ethylene glycol were removed by drying at 40°C under 5 mbar vacuum for 8 h to obtain a yellowish solid. 5 mL of anhydrous tetrahydrofuran was added to the yellowish solid, which was heated and stirred at 50°C for 1 h, and then filtered to remove the insoluble matter while hot. After cooling, the filtrate was added dropwise into 30 mL of anhydrous n-hexane, and then placed in a refrigerator at -20°C for 1 h before being filtered to obtain a white powder. The white powder was dried at 40°C under 5 mbar vacuum for 8 h to obtain a white powder (i.e., catalyst Zn-1, 1.41 g, yield 76.2%).

[0078] Preparation Example 2

[0079] Synthesis of catalyst Zn-2

[0080] In a glove box under nitrogen atmosphere, 5 mL of diethylzinc solution in toluene (2M) was added dropwise into 0.76 g (10 mmol) of 1,2-propanediol at -10°C, and after 1 h of reaction, the remaining steps were the same as in Preparation Example 1 to obtain a yellowish crystal (i.e., catalyst Zn-2, 1.85 g, yield 92.9%).

[0081] Preparation Example 3

[0082] Synthesis of catalyst Zn-3

[0083] In a nitrogen atmosphere glove box, 5 mL of a 2 M toluene solution of diethylzinc was added dropwise to 1.52 g (20 mmol) of 1,3-propylene glycol at 0°C and reacted for 20 min. The remaining steps were the same as those in Preparation Example 1 to obtain a white powder (i.e., catalyst Zn-3, 1.61 g, yield 80.9%).

[0084] Preparation Example 4

[0085] Synthesis of Catalyst Zn-4

[0086] The same steps as those in Preparation Example 1 were followed, except that 5 mL of a 2M toluene solution of diethylzinc and 0.90 g (10 mmol) of 1,4-butanediol were used as raw materials to obtain a white powder (i.e., catalyst Zn-4, 1.50 g, yield 70.4%).

[0087] Preparation Example 5

[0088] Synthesis of Catalyst Zn-5

[0089] The same steps as those in Preparation Example 1 were followed, except that 5 mL of a 2 M toluene solution of diethylzinc and 0.90 g (10 mmol) of 1,3-butanediol were used as raw materials to obtain a white powder (catalyst Zn-5, 1.45 g, yield 68.1%).

[0090] Preparation Example 6

[0091] Synthesis of Zn-6 Catalyst

[0092] The same operating steps as those in Preparation Example 1 were followed, except that 5 mL of a 2M toluene solution of diethylzinc and 0.90 g (10 mmol) of 2,3-butanediol were used as raw materials to obtain a white powder (i.e., catalyst Zn-6, 1.21 g, yield 56.8%).

[0093] Preparation Example 7

[0094] Synthesis of Catalyst Zn-7

[0095] The same operating steps were followed as in Preparation Example 1, except that 5 mL of a 2M toluene solution of diethylzinc and 0.90 g (10 mmol) of (2S,3S)-2,3-butanediol were used as raw materials to obtain a white powder (i.e., catalyst Zn-7, 1.21 g, yield 56.8%).

[0096] Preparation Example 8

[0097] Synthesis of Catalyst Zn-8

[0098] The procedure was the same as Preparation Example 1 except that diethyl zinc in toluene (2M) 5 mL and 1.38 g (10 mmol) 1,4-benzenedimethanol were used as raw materials, and a white powder was obtained (i.e., catalyst Zn-8, 1.01 g, yield 38.7%).

[0099] Preparation Example 9

[0100] Synthesis of catalyst Zn-9

[0101] The procedure was the same as Preparation Example 1 except that diethyl zinc in toluene (2M) 5 mL and 4.0 g (10 mmol) PEG400 were used as raw materials, and a white powder was obtained (i.e., catalyst Zn-9, 2.6 g, yield 49.7%).

[0102] Preparation Example 10

[0103] Synthesis of catalyst Zn-10

[0104] The procedure was the same as Preparation Example 1 except that diethyl zinc in toluene (2M) 5 mL and 0.92 g (20 mmol) ethanol were used as raw materials, and a white powder was obtained (i.e., catalyst Zn-10, 1.4 g, yield 64.1%).

[0105] Example 1

[0106] Synthesis of P3HB

[0107] (R)-β-butyrolactone (100 mmol, 8.6 g, 8.2 mL) was added to a reaction bottle under nitrogen protection, and tetrahydrofuran 41.8 mL and catalyst Zn-2 (1.7 mg) were added as solvents. The molar concentration of the lactone monomer in the mixture of lactone monomer and solvent was 2M, and the amount of Zn-2 was 1 / 5000 of the mass of the lactone monomer. The reaction was carried out at 60°C for 8 h. After the reaction was completed, the solvent was removed by drying, dichloromethane was added to dissolve the product, methanol was added dropwise to precipitate the polymer, and the polymer was dried in a vacuum at 50°C for 12 h to obtain a white polyester. The conversion rate of the lactone monomer was 99.3%, the molecular weight of the product was 2.1 x 10 5 g / mol, the molecular weight distribution PDI was 1.15, and P m = 0.98.

[0108] Example 2

[0109] Synthesis of P3HB

[0110] Under nitrogen protection, (Rac) β-butyrolactone (100 mmol, 8.6 g, 8.2 mL), 8.5 mL of toluene solvent, and 4.3 mg of Zn-7 catalyst were added to the reaction flask. The molar concentration of the lactone monomer in the mixture of lactone monomer and solvent was 6 M, and the amount of Zn-7 was 1 / 2000 of the lactone monomer mass. The reaction was carried out at 30°C for 8 h. After the reaction, the solvent was drained, dichloromethane was added to dissolve the product, and methanol was added dropwise to precipitate the polymer. The product was dried under vacuum at 50°C for 12 h to obtain a white polyester. The lactone monomer conversion rate was 99.5%, and the product molecular weight was 1.9×10 5 g / mol, molecular weight distribution PDI=1.15, P m =0.93. It can be seen that even when a racemic lactone monomer is used, the zinc-based catalyst of the present application still has high stereoselectivity.

[0111] Example 3

[0112] PHBV synthesis

[0113] Under nitrogen protection, (R) β-butyrolactone (90 mmol, 7.7 g, 7.4 mL) and β-valerolactone (10 mmol, 1.0 g, 1.0 mL), 33.1 mL of dioxane solvent, and 8.7 mg of Zn-2 catalyst were added to the reaction flask. The molar concentration of the lactone monomer in the mixture of lactone monomer and solvent was 2 M, and the amount of Zn-2 was 1 / 1000 of the lactone monomer mass. The reaction was carried out at 80°C for 4 h. After the reaction, the solvent was drained, dichloromethane was added to dissolve the product, and methanol was added dropwise to precipitate the polymer. The product was dried under vacuum at 50°C for 12 h to obtain a white polyester. The conversion rate of (R) β-butyrolactone monomer was 99.2%, and the conversion rate of β-valerolactone monomer was 99.1%. The product molecular weight was 7.4×10 4 g / mol, molecular weight distribution PDI=1.12.

[0114] Example 4

[0115] PHBH Synthesis

[0116] Under nitrogen protection, (R) β-butyrolactone (90 mmol, 7.7 g, 7.4 mL) and β-caprolactone (10 mmol, 1.1 g, 1.0 mL), 8.3 mL of toluene solvent, and catalyst Zn-1 (2.9 mg) were added to the reaction flask. In the mixture of lactone monomer and solvent, the molar concentration of lactone monomer was 4 M, and the amount of Zn-1 was 1 / 3000 of the mass of lactone monomer. The reaction was carried out at 80°C for 2 h. After the reaction, the solvent was drained, dichloromethane was added to dissolve the product, and methanol was added dropwise to precipitate the polymer. The product was vacuum dried at 50°C for 12 h to obtain white polyester. The conversion rate was 99.8%, and the conversion rate of β-caprolactone monomer was 99.5%. The product molecular weight was 2.1×10 5g / mol, molecular weight distribution PDI=1.23.

[0117] Example 5

[0118] P34HB synthesis

[0119] Under nitrogen, (R)β-butyrolactone (90 mmol, 7.7 g, 7.4 mL) and γ-butyrolactone (10 mmol, 0.9 g, 0.9 mL), 8.4 mL of toluene solvent, and 2.9 mg of Zn-5 catalyst were added to a reaction flask. The molar concentration of the lactone monomer in the mixture of lactone monomer and solvent was 6 M, and the amount of Zn-5 was 1 / 3000 of the lactone monomer mass. The reaction was carried out at 100°C for 8 h. After the reaction, the solvent was drained, dichloromethane was added to dissolve the product, and methanol was added dropwise to precipitate the polymer. The product was dried under vacuum at 50°C for 12 h to obtain a white polyester. The (R)β-butyrolactone monomer conversion rate was 99.4%, and the γ-butyrolactone monomer conversion rate was 30.1%. The product molecular weight was 1.6×10 5 g / mol, molecular weight distribution PDI=1.20.

[0120] Example 6

[0121] P34HB synthesis

[0122] Under nitrogen, (R)β-butyrolactone (90 mmol, 7.7 g, 7.4 mL) and γ-butyrolactone (10 mmol, 0.9 g, 0.9 mL), 8.4 mL of tetrahydrofuran (THF), and 2.9 mg of Zn-3 (catalyst) were added to the reaction flask. The molar concentration of the lactone monomer in the mixture of lactone monomer and solvent was 6 M, and the amount of Zn-3 was 1 / 2000 of the lactone monomer mass. The reaction was carried out at -50°C for 8 h. After the reaction, the solvent was drained, dichloromethane was added to dissolve the product, and methanol was added dropwise to precipitate the polymer. Vacuum drying at 50°C for 12 h yielded a white polyester. The (R)β-butyrolactone monomer conversion was 5.2%, and the γ-butyrolactone monomer conversion was 90.1%. The molecular weight was 2.0×10 4 g / mol, molecular weight distribution PDI=1.12.

[0123] Example 7

[0124] P34HB synthesis

[0125] Under nitrogen, a reaction flask was charged with (R)β-butyrolactone (90 mmol, 7.7 g, 7.4 mL) and γ-butyrolactone (10 mmol, 0.9 g, 0.9 mL), along with 8.4 mL of tetrahydrofuran (THF), and 4.2 mg of Zn-6 (catalyst). The lactone monomer and solvent mixture had a molar concentration of 6 M, and the amount of Zn-6 was 1 / 2000 of the lactone monomer mass. The reaction was continued at -50°C for 2 h, then the temperature was raised to 40°C for 2 h. Upon completion of the reaction, the solvent was drained, dichloromethane was added to dissolve the product, and methanol was added dropwise to precipitate the polymer. The product was dried under vacuum at 50°C for 12 h to yield a white polyester. The conversion of the (R)β-butyrolactone monomer was 98.7%, and the conversion of the γ-butyrolactone monomer was 82.5%. The product had a molecular weight of 1.8 × 10 5 g / mol, molecular weight distribution PDI=1.24.

[0126] Example 8

[0127] P3HB synthesis

[0128] Under nitrogen protection, (R) β-butyrolactone (100 mmol, 8.6 g, 8.2 mL), 41.8 mL of tetrahydrofuran solvent, and catalyst Zn-4 (4.3 mg) were added to the reaction flask. In the mixture of lactone monomer and solvent, the molar concentration of lactone monomer was 2 M, and the amount of Zn-4 was 1 / 2000 of the mass of lactone monomer. The reaction was carried out at 60°C for 8 h. After the reaction, the solvent was drained, dichloromethane was added to dissolve the product, and methanol was added dropwise to precipitate the polymer. The product was dried under vacuum at 50°C for 12 h to obtain a white polyester. The lactone monomer conversion rate was 98.1%, and the product molecular weight was 2.0×10 5 g / mol, molecular weight distribution PDI=1.18, P m =0.94.

[0129] Example 9

[0130] P3HB synthesis

[0131] Under nitrogen protection, (R) β-butyrolactone (100 mmol, 8.6 g, 8.2 mL), 41.8 mL of tetrahydrofuran solvent, and catalyst Zn-8 (4.3 mg) were added to the reaction flask. In the mixture of lactone monomer and solvent, the molar concentration of lactone monomer was 2 M, and the amount of Zn-8 was 1 / 2000 of the mass of lactone monomer. The reaction was carried out at 60°C for 8 h. After the reaction, the solvent was drained, dichloromethane was added to dissolve the product, and methanol was added dropwise to precipitate the polymer. The product was dried under vacuum at 50°C for 12 h to obtain a white polyester. The lactone monomer conversion rate was 95.8%, and the product molecular weight was 1.7×10 5 g / mol, molecular weight distribution PDI=1.21, P m =0.91.

[0132] Comparative Example 1

[0133] P3HB synthesis

[0134] Under nitrogen, (R)β-butyrolactone (100 mmol, 8.6 g, 8.2 mL) and catalyst Zn-2 (1.7 mg) were added to the reaction flask. The Zn-2 dosage was 1 / 5000 of the lactone monomer mass. The reaction was carried out at 60°C for 8 h. Upon completion of the reaction, dichloromethane was added to dissolve the product, which was then added dropwise to methanol to precipitate the polymer. The product was dried under vacuum at 50°C for 12 h to obtain a white polyester. The lactone monomer conversion was 64.3%, and the product molecular weight was 8.7 × 10 4 g / mol, molecular weight distribution PDI=1.41, P m =0.93.

[0135] Compared with Example 1, this comparative example adopts the bulk method without using a solvent. During the reaction, P3HB will gradually precipitate from the system and eventually form a whole hard white block in the reaction bottle, making it impossible to stir. The final monomer conversion rate is only 64.3%, and the monomer fails to react completely.

[0136] The melting point of P3HB is between 140-150°C. If a bulk method is used, the reaction temperature must be around 150°C to achieve a molten state in the middle and late stages of the reaction, allowing for effective stirring. However, both the (R)β-butyrolactone monomer and P3HB have poor heat resistance. Above 100°C, both P3HB and (R)β-butyrolactone easily form crotonic acid byproducts, leading to polymer chain termination or catalyst deactivation, preventing the production of high-molecular-weight products. Above 120°C, (R)β-butyrolactone will also thermally degrade into propylene and carbon monoxide. Therefore, a solvent method can effectively lower the reaction temperature, enabling efficient mass transfer in the system, increasing the conversion of the (R)β-butyrolactone monomer, and yielding high-molecular-weight products.

[0137] Comparative Example 2

[0138] P3HB synthesis

[0139] Under nitrogen, a reaction flask was charged with (R)β-butyrolactone (100 mmol, 8.6 g, 8.2 mL), 25 µL of a 2M toluene solution of diethylzinc (0.05 mmol of diethylzinc), 3.8 mg (0.05 mmol) of 1,2-propylene glycol, and 41.8 mL of tetrahydrofuran. The lactone monomer and solvent mixture had a molar concentration of 2 M. The reaction was carried out at 60°C for 24 h. After the reaction, the solvent was drained, dichloromethane was added to dissolve the product, and methanol was added dropwise to precipitate the polymer. The product was dried under vacuum at 50°C for 12 h to obtain a white polyester. The lactone monomer conversion rate was 12.7%, and the product molecular weight was 2.1 × 10 4 g / mol, molecular weight distribution PDI=8.53, P m =0.73.

[0140] Compared with Example 1, this comparative example uses a direct mixture of diethyl zinc and 1,2-propylene glycol to catalyze the lactone ring-opening. After 24 hours of reaction, the lactone monomer conversion rate is only 12.7%, and the obtained product has a low molecular weight and a molecular weight distribution of 8.53, indicating that the direct mixture of diethyl zinc and 1,2-propylene glycol has low catalytic activity and poor controllability.

[0141] Comparative Example 3

[0142] Under nitrogen protection, (R) β-butyrolactone (100 mmol, 8.6 g, 8.2 mL), 41.8 mL of tetrahydrofuran solvent, and 1.7 mg of Zn-9 catalyst were added to the reaction flask. In the mixture of lactone monomer and solvent, the molar concentration of lactone monomer was 2 M, and the amount of Zn-9 was 1 / 5000 of the lactone monomer mass. The reaction was carried out at 60°C for 8 h. After the reaction, the solvent was drained, dichloromethane was added to dissolve the product, and methanol was added dropwise to precipitate the polymer. The product was dried under vacuum at 50°C for 12 h to obtain a white polyester. The lactone monomer conversion rate was 4.3%, and the product molecular weight was 5.6×10 3 g / mol, molecular weight distribution PDI=1.31.

[0143] Compared with Example 1, only a low molecular weight product with a molecular weight of about 5,000 was obtained using Zn-9 as a catalyst, indicating that Zn-9 using PEG400 as a ligand has very poor catalytic activity for (R) β-butyrolactone under this condition.

[0144] Comparative Example 4

[0145] Under nitrogen, a reaction flask was charged with (R)β-butyrolactone (100 mmol, 8.6 g, 8.2 mL), 41.8 mL of tetrahydrofuran (THF), and 1.7 mg of Zn-10 catalyst. The lactone monomer and solvent mixture had a molar concentration of 2 M, and the Zn-10 dosage was 1 / 5000 of the lactone monomer mass. The reaction was carried out at 60°C for 8 h. Upon completion of the reaction, the solvent was drained, and dichloromethane was added to dissolve the product. No polymer precipitated upon addition of methanol.

[0146] Compared with Example 8, no obvious product was obtained when Zn-10 was used as the catalyst, indicating that Zn-10 using ethanol as the ligand had no catalytic activity towards (R)β-butyrolactone under these conditions.

[0147] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0148] The embodiments described above only express several implementation methods of the present application, which are convenient for understanding the technical solutions of the present application in a specific and detailed manner, but they cannot be understood as limiting the scope of protection of the patent application. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all fall within the scope of protection of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the scope of protection of the claims attached to the present application. Therefore, the scope of protection of the patent application of this application shall be based on the content of the attached claims, and the description can be used to interpret the content of the claims.

Claims

1. A method for preparing polyhydroxyalkanoate, characterized in that: The steps include: In the presence of a solvent, a zinc-based catalyst is used to catalyze the ring-opening polymerization of a lactone monomer to prepare the polyhydroxyalkanoate; The zinc-based catalyst is prepared by a coordination reaction between diethyl zinc and a small molecule diol under an inert atmosphere; The small molecule diol includes at least one of C2-C10 diols.

2. The preparation method according to claim 1, wherein The small molecule diol includes at least one of the compounds shown in the structure of formula I; (Formula I); Wherein, R is selected from a carbon-carbon single bond, a C1-C6 alkylene group or a phenyl group; R1 and R2 are each independently selected from H or C1-C2 alkyl; Optionally, the small molecule diol includes one or more of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 2,3-butanediol, 1,3-butanediol and 1,4-phenylenediol.

3. The preparation method according to claim 1, wherein The lactone monomer includes one or more of β-butyrolactone, γ-butyrolactone, β-valerolactone and β-caprolactone.

4. The preparation method according to any one of claims 1 to 3, wherein The solvent includes one or more of dichloromethane, chloroform, toluene, tetrahydrofuran and dioxane.

5. The preparation method according to any one of claims 1 to 3, wherein The conditions for the ring-opening polymerization include: reacting at -50°C to 100°C for 30 minutes to 8 hours.

6. The preparation method according to any one of claims 1 to 3, wherein In the mixture of the lactone monomer and the solvent, the molar concentration of the lactone monomer is 2M to 8M; And / or, the mass ratio of the lactone monomer to the zinc-based catalyst is (1000-5000):

1.

7. The preparation method according to any one of claims 1 to 3, characterized in that The molar ratio of the diethyl zinc to the small molecule diol is 1:(1-2).

8. The preparation method according to any one of claims 1 to 3, wherein The reaction conditions of diethyl zinc and small molecule diol under an inert atmosphere include: reaction temperature of -10°C to 40°C, and reaction time of 5 minutes to 1 hour.

9. The polyhydroxyalkanoate prepared by the preparation method according to any one of claims 1 to 8.

10. The polyhydroxyalkanoate according to claim 9, wherein The number average molecular weight of the polyhydroxyalkanoate is 1000 g / mol to 500000 g / mol; And / or, the polyhydroxyalkanoate has a polydispersity index of 1.10-1.25.

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