Aliphatic polyester as well as preparation method and application thereof

Abstract

The invention provides aliphatic polyester as well as a preparation method and application thereof, and the preparation method comprises the following steps: carrying out esterification reaction on aliphatic dicarboxylic acid and aliphatic diol to obtain an ester; carrying out prepolymerization reaction on the ester in the presence of a catalyst and a branching agent to obtain a prepolymer; carrying out final polymerization reaction on the prepolymer to obtain a polymerization product; and sequentially carrying out first extraction and second extraction on the polymerization product to obtain the aliphatic polyester. A specific two-step extraction process is designed to purify a polymerization product, and low-molecular-weight substances in the product can be effectively removed, so that the obtained aliphatic polyester is high in molecular weight and narrow in molecular weight distribution, the mechanical and processing properties of the aliphatic polyester are improved, and particularly, the aliphatic polyester product has lower water vapor permeability and better water vapor permeability. And the risk of migration and precipitation of small molecular substances is reduced or avoided. The preparation method has the characteristics of safety, simplicity and high efficiency, and is suitable for industrial popularization.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to an aliphatic polyester, a preparation method thereof, and an application thereof. Background Art

[0002] A polymer is essentially a mixture, and its molecular weight is non-uniform. This non-uniformity of molecular weight is called polydispersity. The polymer dispersity index (PDI) of a polymer, also known as the molecular weight distribution coefficient, non-uniformity index, or dispersity, is used to represent the molecular weight distribution of the polymer and is the ratio of the weight-average molecular weight to the number-average molecular weight. PDI is an important measure of the quality of a polymer. Especially for polymers obtained by stepwise polymerization (such as polyesters), the larger the PDI, the wider the molecular weight distribution and the poorer the quality.

[0003] Aliphatic polyesters are a type of polymer with a linear structure, having good biocompatibility, being biodegradable and having non-toxic side effects for degradation products, and also having good mechanical and processing properties. They are widely used in the fields of biomedicine, agriculture, packaging, food, etc. The monomers of aliphatic polyesters are usually aliphatic dicarboxylic acids and aliphatic dihydroxy compounds. These two types of monomers are connected by ester groups formed by the reaction of their respective functional groups, carboxyl groups and hydroxyl groups, to form macromolecular polyesters. However, the preparation process of polyesters is usually accompanied by side reactions, generating a large amount of by-products with low molecular weights, resulting in a wide molecular weight distribution of the polymerization products and a decline in performance and quality. In particular, due to the head-to-tail connection of functional groups between aliphatic dicarboxylic acids and aliphatic dihydroxy compounds, a cyclization reaction occurs, producing low-molecular-weight cyclic oligomers. Such low-molecular-weight substances are extremely likely to migrate out of the material at high temperatures. Therefore, when aliphatic polyesters are applied to the field of food contact, there is a risk that low-molecular-weight substances in the material will precipitate out of the material or product, endangering human health.

[0004] In order to improve the properties of aliphatic polyesters, researchers have made improvements in aspects such as monomers, reaction additives, and process conditions. For example, CN102746493A discloses a method for preparing a fully bio-based poly(butylene succinate) (PBS). Using biomass dimethyl succinate and 1,4-butanediol as polymerization monomers, a fully bio-based PBS is prepared through a two-stage polymerization process route of transesterification and polycondensation. The product has a high molecular weight and good product color, but its PDI is 1.9 - 2.3, with a wide molecular weight distribution, which affects the application performance of the product, especially the excessively high water vapor transmission rate. CN112280011A discloses a method for preparing a low melt index poly(butylene succinate). Succinic acid, 1,4-butanediol, and a composite catalyst are added to the reaction kettle in one step, and then esterification reaction, pre-polycondensation reaction, and final polycondensation reaction are carried out in sequence to obtain a low melt index PBS. This method uses amino acids or amino acid esters, titanates, silicates, and metal acetates complexed with phosphoric acid compounds, and natural polyhydric alcohols are added to prepare a composite catalyst, enabling PBS to have a higher molecular weight. However, its PDI is above 1.92, there is a problem of too wide molecular weight distribution, and the cost of the composite catalyst is high, which is not suitable for large-scale application. CN105801818A discloses a method for preparing a high molecular weight poly(butylene succinate). Using succinic acid and butanediol as raw materials, a high molecular weight product PBS is formed through an oligomer formation stage, a polymer formation stage, and an extrusion chain extension reaction stage. Its number average molecular weight ≥ 100,000, and the molecular weight distribution range is 1.2 - 1.6. Although the molecular weight distribution is relatively narrow, the process is complex, the production efficiency is low, and the introduced chain extender succinyl chloride is toxic, which not only brings safety risks to operators but also limits the downstream application of PBS products.

[0005] Therefore, how to achieve the simple and safe preparation of aliphatic polyesters with a narrow molecular weight distribution is the research focus in this field. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide an aliphatic polyester, its preparation method and application. The preparation method uses aliphatic dicarboxylic acids and aliphatic diols as monomers, and through three-step reactions of esterification, prepolymerization, and final polymerization, a polymerization product is obtained, and combined with a specific two-step extraction process to purify the polymerization product, obtaining an aliphatic polyester with a high molecular weight, a low polydispersity index of molecular weight, and a narrow molecular weight distribution, making it have excellent mechanical and processing properties, especially reducing the water vapor transmission rate of the product and reducing or avoiding the risk of migration and precipitation of small molecule substances.

[0007] To achieve this purpose, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a method for preparing an aliphatic polyester, the preparation method comprising:

[0009] The aliphatic dicarboxylic acid and the aliphatic diol are subjected to an esterification reaction to obtain an esterified product;

[0010] The esterified product is subjected to a prepolymerization reaction in the presence of a catalyst and a branching agent to obtain a prepolymer;

[0011] The prepolymer is subjected to a final polymerization reaction to obtain a polymerization product;

[0012] The polymerization product is successively subjected to a first extraction and a second extraction to obtain the aliphatic polyester;

[0013] The first extractant used in the first extraction comprises a combination of a first cyclic ether solvent and water; the second extractant used in the second extraction comprises a second cyclic ether solvent.

[0014] In the present invention, an aliphatic dicarboxylic acid and an aliphatic diol are used as monomers, and a polymerization product is obtained through three-step reactions of esterification, prepolymerization and final polymerization. The polymerization product is purified by combining a specific two-step extraction process. The first extractant comprises a combination of a first cyclic ether solvent and water, and the second extractant comprises a second cyclic ether solvent. The cyclic ether solvent has a molecular structure similar to that of low-molecular-weight substances (especially cyclic oligomers) in the polymerization product, and can dissolve the low-molecular-weight substances as completely as possible in the extractant. At the same time, water is contained in the first extractant to avoid adverse effects of the cyclic ether solvent on the properties of the aliphatic polyester, so that the obtained aliphatic polyester has excellent processing properties and mechanical properties. The purification process combining the first extraction and the second extraction designed in the present invention can effectively remove low-molecular-weight substances such as oligomers in the polymerization product, so that the obtained aliphatic polyester has the characteristics of high molecular weight and narrow molecular weight distribution, thereby greatly improving the mechanical and processing properties of the aliphatic polyester. In particular, the aliphatic polyester product has a lower water vapor transmission rate, and the risk of migration and precipitation of small-molecular substances is reduced or avoided. The preparation method of the present invention does not need to use special / expensive catalysts, nor does it need to introduce reaction additives with toxicity risks, and has the characteristics of safety, simplicity and high efficiency, and is suitable for industrial promotion.

[0015] The following are the preferred technical solutions of the present invention, but do not limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the purpose and beneficial effects of the present invention can be better achieved and realized.

[0016] Preferably, the aliphatic dicarboxylic acid includes any one or a combination of at least two of succinic acid, glutaric acid and adipic acid.

[0017] Preferably, the aliphatic diol includes any one or a combination of at least two of ethylene glycol, 1,3-propanediol and 1,4-butanediol.

[0018] Preferably, the molar ratio of the aliphatic dicarboxylic acid to the aliphatic diol is 1:(1.2 - 1.6), for example, it can be 1:1.22, 1:1.25, 1:1.28, 1:1.3, 1:1.32, 1:1.35, 1:1.38, 1:1.4, 1:1.42, 1:1.45, 1:1.48, 1:1.5, 1:1.52, 1:1.55 or 1:1.58, etc.

[0019] Preferably, the temperature of the esterification reaction is 150 - 170°C, for example, it can be 152°C, 154°C, 155°C, 156°C, 158°C, 170°C, 172°C, 174°C, 175°C, 176°C or 178°C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0020] Preferably, the time of the esterification reaction is 2 - 4 h, for example, it can be 2.2 h, 2.5 h, 2.8 h, 3 h, 3.2 h, 3.5 h or 3.8 h, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0021] As a preferred technical solution of the present invention, in the esterification reaction stage, when the top temperature of the esterification condensation tower drops ≤ 85°C and the esterification water yield ≥ 95%, the esterification reaction is considered to be completed.

[0022] Preferably, the catalyst includes a titanate catalyst, preferably any one or a combination of at least two of tetramethyl titanate, tetraethyl titanate, tetra - isopropyl titanate, tetra - n - butyl titanate, and tetra - isooctyl titanate.

[0023] Preferably, based on the total mass of the aliphatic dicarboxylic acid and the aliphatic diol being 100%, the dosage of the catalyst is such that the mass of Ti element is 50 - 200 ppm, for example, it can be 60 ppm, 80 ppm, 100 ppm, 120 ppm, 140 ppm, 150 ppm, 160 ppm or 180 ppm, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0024] Preferably, the branching agent includes a polyol (other polyols different from aliphatic diols), and further preferably includes any one or a combination of at least two of glycerol, trimethylolpropane, pentaerythritol, dipentaerythritol, and 2,2 - dimethylolpropionic acid.

[0025] Preferably, based on the total mass of the aliphatic dicarboxylic acid and the aliphatic diol being 100%, the amount of the branching agent is such that the mass of the hydroxyl group is 200 - 1000 ppm. For example, it can be 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, 550 ppm, 600 ppm, 650 ppm, 700 ppm, 750 ppm, 800 ppm, 850 ppm, 900 ppm or 950 ppm, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0026] Preferably, the prepolymerization reaction is carried out in the presence of a heat stabilizer.

[0027] Preferably, the heat stabilizer includes phosphate ester compounds, and more preferably includes any one or a combination of at least two of trimethyl phosphate, triethyl phosphate, isopropyl phosphate, n-butyl phosphate, isooctyl phosphate, and triphenyl phosphate;

[0028] Preferably, based on the total mass of the aliphatic dicarboxylic acid and the aliphatic diol being 100%, the amount of the heat stabilizer is such that the mass of P element is 5 - 100 ppm. For example, it can be 10 ppm, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm, 80 ppm or 90 ppm, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0029] Preferably, the temperature of the prepolymerization reaction is 180 - 240 °C. For example, it can be 185 °C, 190 °C, 195 °C, 200 °C, 205 °C, 210 °C, 215 °C, 220 °C, 225 °C, 230 °C or 235 °C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0030] Preferably, the pressure of the prepolymerization reaction is 1 - 5 kPa. For example, it can be 1.5 kPa, 2 kPa, 2.5 kPa, 3 kPa, 3.5 kPa, 4 kPa or 4.5 kPa, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0031] Preferably, the time of the prepolymerization reaction is 0.5 - 3 h. For example, it can be 1 h, 1.2 h, 1.5 h, 1.8 h, 2 h, 2.2 h, 2.5 h or 2.8 h, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0032] Preferably, the temperature of the final polymerization reaction is 220 - 260°C, for example, it can be 222°C, 225°C, 228°C, 230°C, 232°C, 235°C, 238°C, 240°C, 242°C, 245°C, 248°C, 250°C, 252°C, 255°C or 258°C, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the said range.

[0033] Preferably, the pressure of the final polymerization reaction is 10 - 100 Pa, for example, it can be 20 Pa, 25 Pa, 30 Pa, 35 Pa, 40 Pa, 45 Pa, 50 Pa, 55 Pa, 60 Pa, 65 Pa, 70 Pa, 75 Pa, 80 Pa, 85 Pa, 90 Pa or 95 Pa, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the said range.

[0034] Preferably, the time of the final polymerization reaction is 1 - 6 h, for example, it can be 1.5 h, 2 h, 2.2 h, 2.5 h, 2.8 h, 3 h, 3.2 h, 3.5 h, 3.8 h, 4 h, 4.2 h, 4.5 h, 4.8 h, 5 h, 5.2 h, 5.5 h or 5.8 h, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the said range.

[0035] Preferably, the end point of the final polymerization reaction can be assisted in judgment according to the terminal carboxyl value of the product. When the terminal carboxyl value of the product ≤ 60 mol / t, it is regarded as the completion of the final polymerization reaction.

[0036] Exemplarily, the terminal carboxyl value can be obtained by testing through titration, for example, testing is carried out according to the method in standard FZ / T50012 - 2006.

[0037] Preferably, after the completion of the final polymerization reaction (before the first extraction), it further includes the steps of melt extrusion and granulation to obtain the granular polymerization product.

[0038] Preferably, the melt extrusion is carried out in a screw extruder.

[0039] Preferably, the screw speed of the screw extruder is 150 - 350 rpm, for example, it can be 180 rpm, 200 rpm, 220 rpm, 250 rpm, 280 rpm, 300 rpm, 320 rpm or 340 rpm, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the said range. Further preferably, it is 200 - 300 rpm.

[0040] Preferably, the temperature of the melt extrusion is 160 - 180°C, for example, it can be 162°C, 165°C, 168°C, 170°C, 172°C, 175°C or 178°C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0041] Preferably, the weight of 100 grains of the granular polymerization product is ≤1.31 g, for example, it can be 1.15 g, 1.18 g, 1.20 g, 1.22 g, 1.25 g, 1.28 g or 1.30 g, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range. Further preferably, it is 1.20 - 1.30 g.

[0042] In the present invention, the term "weight of 100 grains" represents the mass of 100 polymerization product particles, which can be obtained by weighing.

[0043] Preferably, each of the first cyclic ether solvent and the second cyclic ether solvent independently includes any one or a combination of at least two of tetrahydrofuran, 2 - methyltetrahydrofuran, and tetrahydropyran. Further preferably, it is tetrahydrofuran (THF) and / or 2 - methyltetrahydrofuran.

[0044] Preferably, the volume percentage content of the first cyclic ether solvent in the first extractant is 60% - 80%, for example, it can be 62%, 65%, 68%, 70%, 72%, 75% or 78%, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0045] As a preferred technical solution of the present invention, the volume percentage content of the first cyclic ether solvent in the first extractant is 60%-80%. The second extractant is a second cyclic ether solvent. The cyclic ether solvent has a similar molecular structure to low molecular weight substances such as cyclic oligomers. Due to the principle of similar solubility, it can extract low molecular weight substances from the polymerization product as completely as possible to obtain an aliphatic polyester with a narrow molecular weight distribution. At the same time, the second extractant (the second cyclic ether solvent) has a relatively low boiling point, which is easy to be removed by drying, and is beneficial to reducing the water content in the aliphatic polyester product. If the volume percentage content of the first cyclic ether solvent in the first extractant is too low, on the one hand, it will affect the extraction effect, resulting in an increase in the content of oligomers and affecting the molecular weight distribution of the aliphatic polyester; on the other hand, the first extractant contains more water, which will increase the subsequent drying difficulty and easily lead to a relatively high water content in the polyester product. If the volume percentage content of the first cyclic ether solvent in the first extractant is too high, it will affect the performance of the aliphatic polyester, resulting in cracks on the surface of the aliphatic polyester product, affecting the mechanical properties and appearance.

[0046] Preferably, the mass ratio of the polymerization product to the first extractant is 1:(1.3-2), for example, it can be 1:1.35, 1:1.4, 1:1.45, 1:1.5, 1:1.55, 1:1.6, 1:1.65, 1:1.7, 1:1.75, 1:1.8, 1:1.85, 1:1.9 or 1:1.95, etc.

[0047] Preferably, the solid obtained after the first extraction is subjected to a second extraction, and the mass ratio of the solid to the second extractant is 1:(1.3-2), for example, it can be 1:1.35, 1:1.4, 1:1.45, 1:1.5, 1:1.55, 1:1.6, 1:1.65, 1:1.7, 1:1.75, 1:1.8, 1:1.85, 1:1.9 or 1:1.95, etc.

[0048] Preferably, the first extraction and the second extraction are carried out under stirring conditions.

[0049] Preferably, the temperatures of the first extraction and the second extraction are independently 60-80°C, for example, it can be 62°C, 65°C, 68°C, 70°C, 72°C, 75°C or 78°C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range. Further preferably, it is 65-75°C.

[0050] Preferably, the time for the first extraction is 1 - 3.5 h, such as 1.2 h, 1.5 h, 1.8 h, 2 h, 2.2 h, 2.5 h, 2.8 h, 3 h, 3.2 h or 3.4 h, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range. Further preferably, it is 2 - 3 h.

[0051] Preferably, the time for the second extraction is 0.5 - 2 h, such as 0.8 h, 1 h, 1.2 h, 1.5 h or 1.8 h, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range. Further preferably, it is 1 - 1.5 h.

[0052] As a preferred technical solution of the present invention, the time for the first extraction ≥ the time for the second extraction. Further preferably, the time for the first extraction is 1 - 3.5 h. This process can extract most of the low - molecular - weight substances such as cyclic oligomers; the time for the second extraction is 0.5 - 2 h. This process uses a second cyclic ether solvent as the extractant, which can achieve deep extraction of low - molecular - weight substances such as oligomers to obtain an aliphatic polyester with a narrow molecular weight distribution. At the same time, the time for the second extraction is relatively short, which can avoid the adverse effects of the second cyclic ether solvent on the aliphatic polyester and prevent problems such as appearance defects (such as cracks) and a decrease in mechanical properties of the aliphatic polyester products.

[0053] Preferably, after the first extraction, solid - liquid separation and drying are carried out, and the obtained solid is subjected to the second extraction; after the second extraction, solid - liquid separation and drying are carried out again to obtain the aliphatic polyester.

[0054] Preferably, the temperature for drying is independently 70 - 80 °C, such as 71 °C, 72 °C, 73 °C, 74 °C, 75 °C, 76 °C, 77 °C, 78 °C or 79 °C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0055] Preferably, the preparation method includes the following steps:

[0056] (1) Mix an aliphatic dicarboxylic acid and an aliphatic diol in a molar ratio of 1:(1.2 - 1.6), and react at 150 - 170 °C for 2 - 4 h to obtain an esterified product;

[0057] (2) Place the esterified product obtained in step (1), a titanate catalyst, a polyol branching agent, and a phosphate heat stabilizer in a reaction device, and react at 180 - 240 °C and 1 - 5 kPa for 1 - 3 h to obtain a prepolymer;

[0058] Based on the total mass of the aliphatic dicarboxylic acid and the aliphatic diol being 100%, the amount of the titanate catalyst used is such that the mass of Ti element is 50 - 200 ppm, the amount of the polyol branching agent used is such that the mass of hydroxyl groups is 200 - 1000 ppm, and the amount of the phosphate heat stabilizer used is such that the mass of P element is 5 - 100 ppm;

[0059] (3) React the prepolymer obtained in step (2) at 220 - 260 °C and 20 - 100 Pa for 2 - 6 h to obtain a polycondensate; melt - extrude and pelletize the polycondensate in a screw extruder to obtain a granular polymerization product with a hundred - grain weight ≤ 1.31 g; the temperature of the melt - extrusion is 160 - 180 °C, and the screw speed is 150 - 350 rpm;

[0060] (4) Disperse the polymerization product obtained in step (3) in a first extraction agent, and perform the first extraction for 1.5 - 3.5 h at 60 - 80 °C under stirring conditions, then carry out solid - liquid separation and drying to obtain a solid;

[0061] The first extraction agent comprises a combination of a first cyclic ether solvent and water, wherein the volume percentage content of the first cyclic ether solvent is 60% - 80%, and the mass ratio of the first extraction agent to the polymerization product is (1.3 - 2):1;

[0062] Disperse the solid in a second extraction agent, perform the second extraction for 0.5 - 1.5 h at 60 - 80 °C under stirring conditions, and then carry out solid - liquid separation and drying to obtain the aliphatic polyester;

[0063] The second extraction agent comprises a second cyclic ether solvent, and the mass ratio of the second extraction agent to the solid is (1.3 - 2):1.

[0064] In a second aspect, the present invention provides an aliphatic polyester, which is prepared by the preparation method as described in the first aspect.

[0065] Preferably, the number - average molecular weight of the aliphatic polyester is 4×10 4 -9×10 4 , for example, it can be 4.5×10 4 , 5×10 4 , 5.2×10 4 , 5.5×10 4 , 5.8×10 4 , 6×10 4 , 6.2×10 4 , 6.4×10 4 , 6.5×10 4 , 6.6×10 4 , 6.8×10 4 , 7×104 and 7.2×10 4 and 7.4×10 4 and 7.5×10 4 and 7.8×10 4 and 8×10 4 or 8.5×10 4 , and the specific point values between the above point values. For the sake of brevity and limited space, the present invention does not exhaustively list the specific point values included in the above range. Further preferably, it is 5.5×10 4 -7.5×10 4 , and more preferably 5.8×10 4 -7×10 4 .

[0066] Preferably, the weight-average molecular weight of the aliphatic polyester is 5×10 4 -12×10 4 , for example, it can be 5.5×10 4 , 6×10 4 , 6.5×10 4 , 7×10 4 , 7.5×10 4 , 8×10 4 , 8.2×10 4 , 8.5×10 4 , 8.8×10 4 , 9×10 4 , 9.2×10 4 , 9.5×10 4 , 9.8×10 4 , 10×10 4 , 10.2×10 4 , 10.5×10 4 , 10.8×10 4 , 11×10 4 or 11.5×10 4 , and the specific point values between the above point values. For the sake of brevity and limited space, the present invention does not exhaustively list the specific point values included in the above range. Further preferably, it is 6.5×10 4 -10×10 4 .

[0067] Preferably, the Z-average molecular weight of the aliphatic polyester is 9×10 4 -18×10 4 , for example, it can be 9.5×10 4 , 10×10 4 , 10.5×10 4 , 11×10 4 , 11.5×10 4, 11.8×10 4 , 12×10 4 , 12.2×10 4 , 12.5×10 4 , 12.8×10 4 , 13×10 4 , 13.2×10 4 , 13.5×10 4 , 13.8×10 4 , 14×10 4 , 14.2×10 4 , 14.5×10 4 , 15×10 4 , 15.5×10 4 , 16×10 4 , 16.5×10 4 , 17×10 4 or 17.5×10 4 , and the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the said range. Further preferably, 11.5×10 4 -16.5×10 4 .

[0068] Preferably, the polydispersity index of the aliphatic polyester ≤ 1.6, for example, it can be 1.05, 1.08, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5, 1.55 or 1.58, and the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the said range. Further preferably, 1.1-1.4.

[0069] Preferably, the mass content of oligomers in the aliphatic polyester ≤ 5500 ppm, for example, it can be 500 ppm, 800 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, 5200 ppm or 5400 ppm, and the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the said range. Further preferably, 4500-5400 ppm.

[0070] In the present invention, the number-average molecular weight (M n ), weight-average molecular weight (M w ), Z-average molecular weight (M z) It can be obtained by gel permeation chromatography (GPC) test, and the molecular weight polydispersity index (PDI) is M w / M n . The mass content of oligomers in the aliphatic polyester is obtained by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS).

[0071] Exemplarily, in the GPC test, tetrahydrofuran is used as the eluent and polystyrene is used as the reference standard. In the MALDI-TOF MS test, 1,8,9-anthracenetriol is used as the matrix, nitrogen is used as the laser source, and the laser wavelength is 337 nm.

[0072] In the present invention, the term "oligomer" refers to a low molecular weight polymer with a number average molecular weight < 2000.

[0073] Exemplarily, the test method for oligomers in the aliphatic polyester includes: dissolving the sample to be tested with a mixed solvent of chloroform / trifluoroacetic acid TFA (the volume ratio of chloroform to TFA is 9:1), and then testing by high performance size exclusion chromatography-mass spectrometry (SEC-ESI-Q-TOF MS). In the obtained spectrum, the retention time of the aliphatic polyester < 10 min, and the retention time of the oligomer is 15 - 20 min. The quantitative test result of the oligomer is obtained according to the integral area of the chromatographic peak.

[0074] In the third aspect, the present invention provides an application of the aliphatic polyester as described in the second aspect in food contact materials or membrane bags.

[0075] In the fourth aspect, the present invention provides a polymer film, and the material of the polymer film includes the aliphatic polyester as described in the second aspect.

[0076] Optionally, the polymer film is prepared by a method of casting, extrusion and / or stretching.

[0077] Optionally, the thickness of the polymer film is 5 - 100 μm, for example, it can be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm or 90 μm, and specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the range.

[0078] Optionally, the thickness of the polymer film is 20 μm, and its water vapor transmission rate at 60 °C and 60% humidity ≤ 2500 g / d·m 2 , and it can be 2200 - 2500 g / d·m 2 .

[0079] Optionally, the thickness of the polymer film is 50 μm, and its water vapor transmission rate at 60 °C and 60% humidity ≤ 1000 g / d·m 2 , and it can be 800 - 950 g / d·m 2 .

[0080] Exemplarily, the test method for the water vapor transmission rate includes the following steps: Weigh the watch glass filled with water to obtain the mass m 1 (unit: g); Cover the polymer film to be tested on the watch glass filled with water, and after placing it for a preset time t (unit: d, days) at 60 °C and 60% humidity, remove the polymer film and weigh it again to obtain the mass m 2 (unit: g); Water vapor transmission rate = (m 1 - m 2 ) / (t·S), where S is the cross-sectional area of the watch glass (unit: m 2 ).

[0081] Compared with the prior art, the present invention has the following beneficial effects:

[0082] (1) In the preparation method provided by the present invention, aliphatic dicarboxylic acid and aliphatic diol are used as monomers, and a polymerization product is obtained through three-step reactions of esterification, prepolymerization and final polymerization. Combined with a specific two-step extraction process to purify the polymerization product, it can effectively remove low-molecular-weight substances such as cyclic oligomers in the product, and obtain an aliphatic polyester with high molecular weight and narrow molecular weight distribution. The preparation method does not need to use special expensive catalysts, nor does it need to introduce reaction additives with toxicity risks, and has the characteristics of safety, simplicity and high efficiency, and is suitable for industrial promotion.

[0083] (2) The aliphatic polyester provided by the present invention has the characteristics of high molecular weight and narrow molecular weight distribution, effectively improving the mechanical properties and processing properties of the aliphatic polyester. In particular, the aliphatic polyester products have a lower water vapor transmission rate, and reduce or avoid the risk of migration and precipitation of small molecule substances, expanding the application range of the aliphatic polyester. Specific Embodiments

[0084] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0085] As used herein, the terms "comprising", "including", "having", "containing" or any other variation thereof are intended to cover non-exclusive inclusion. For example, a composition, step, method, article or device containing the listed elements is not necessarily limited to those elements, but may also include other elements not explicitly listed or elements inherent to such composition, step, method, article or device.

[0086] In the present invention, features defined with "first" and "second" may explicitly or implicitly include one or more of such features, which are used to distinguish and describe features, without order or importance. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0087] In the following specific embodiments of the present invention, the test methods for various properties are as follows:

[0088] (1) Number-average molecular weight (M n ), weight-average molecular weight (M w ), Z-average molecular weight (M z ) and molecular weight polydispersity index (PDI): Gel permeation chromatography (GPC) is used to test each molecular weight, and PDI = M w / M n ; The specific test method of GPC is as follows: Using a chromatographic system at 35 °C, with a set of 2 tandem columns (particle diameter 5 μm), a refractive index detector, tetrahydrofuran as the eluent (flow rate 0.1 mL / min), and polystyrene as the reference standard.

[0089] (2) The test method for the content of oligomers is as follows:

[0090] High performance size exclusion chromatography-mass spectrometry (SEC-ESI-Q-TOF MS) is used for testing, including the following steps

[0091] I. Sample preparation

[0092] Weigh 5 mg of the aliphatic polyester sample to be tested, add 5 mL of preheated chloroform / trifluoroacetic acid (TFA) mixed solvent (chloroform:TFA = 9:1, volume ratio), and ultrasonically dissolve it in a 90 °C water bath for 30 min; then filter it using a 0.22 μm PTFE syringe filter to remove undissolved polyester macromolecules and impurities, and transfer the filtrate to a 2 mL brown injection vial for standby.

[0093] II. Instruments and analysis conditions

[0094] 2.1 Chromatographic system

[0095] Chromatographic column: TSKgel Super Multipore HZ-M (4.6×150 mm, particle size 3 μm);

[0096] Mobile phase: A mixed solution of chloroform + TFA (TFA content is 0.1 wt%, and the mixed solution is degassed using a 0.22 μm filter membrane);

[0097] Flow rate: 0.5 mL / min, column temperature: 40 °C, detection wavelength: 220 nm;

[0098] Sample volume: 20 μL, running time: 25 min.

[0099] 2.2 Mass spectrometry system (SEC-ESI-Q-TOF MS)

[0100] Ion source: electrospray ionization (ESI), negative ion mode (carboxyl groups are easily deprotonated);

[0101] Parameter settings: capillary voltage: -3.0 kV; cone voltage: -40 V; desolvation temperature: 300 °C; nebulizer gas flow rate: 8 L / min;

[0102] Mass scanning range: m / z 100 - 2000, resolution > 30000 (FWHM).

[0103] III. Separation and detection principle

[0104] Relationship between retention time and molecular weight:

[0105] Aliphatic polyesters (weight-average molecular weight M w > 10000): large hydrodynamic volume, retention time < 10 min;

[0106] Oligomers (number-average molecular weight M n < 2000): retention time 15 - 20 min;

[0107] Separate oligomers and aliphatic polyesters based on the difference in retention time.

[0108] IV. Data analysis and quantitative method

[0109] Chromatographic peak attribution and quantitative calculation:

[0110] Main peak of aliphatic polyester: retention time < 10 min;

[0111] Oligomer peak: Integrate the chromatographic peaks in the range of 15 - 20 min, quantify with a UV detector, and calculate the content of oligomers by peak area normalization method.

[0112] (3) 100-grain weight: Take 100 granular polymerization products, weigh them to obtain the 100-grain weight, with the unit of g.

[0113] (4) Water vapor transmission rate: Make the aliphatic polyester to be measured into a film with a thickness of 20 μm or 50 μm using a film blowing machine; Add deionized water to a clean empty surface dish, weigh it to obtain the mass m 1 (unit: g); Cover the film to be measured on the aforementioned surface dish containing water, place it for a preset time t (unit: d, days) at 60 °C and a humidity of 60%, then remove the film, and weigh the surface dish (with water) again to obtain the mass m 2(Unit: g); Water vapor transmission rate = (m 1 -m 2 ) / (t·S), where S is the cross-sectional area of the petri dish (unit: m 2 ).

[0114] (5) Tensile strength and elongation at break: Tested according to the method in Standard ISO 527-2-2012, and the test condition is 50 mm / min.

[0115] In the following specific embodiments of the present invention, the reagents whose preparation methods are not specified are all conventional commercially available chemicals. Tetrahydrofuran in the following specific embodiments is all of chemical pure grade or above, and its purity ≥ 99.9%.

[0116] Example 1

[0117] An aliphatic polyester (polybutylene succinate, PBS) and its preparation method, the preparation method comprising the following steps:

[0118] (1) Mix succinic acid and 1,4-butanediol in a molar ratio of 1:1.4, and carry out an esterification reaction at 155 °C for 2 h to obtain an esterified product;

[0119] (2) Place the esterified product obtained in step (1), a catalyst (tetra-n-butyl titanate), a branching agent (trimethylolpropane), and a heat stabilizer (trimethyl phosphate) in a prepolymerization reactor, and react at 210 °C and 5 kPa for 2 h to obtain a prepolymer;

[0120] Based on the total mass of the succinic acid and 1,4-butanediol being 100%, the dosage of the catalyst is such that the mass of Ti element is 88 ppm, the dosage of the branching agent is such that the mass of hydroxyl group is 880 ppm, and the dosage of the heat stabilizer is such that the mass of P element is 50 ppm;

[0121] (3) Transfer the prepolymer obtained in step (2) to a final polymerization reactor, and react at 245 °C and 30 Pa for 5 h to obtain a condensate;

[0122] Melt-extrude and granulate the condensate in a screw extruder, the temperature of melt-extrusion is 160 °C, and the screw speed is 200 rpm to obtain polymer particles with a hundred-grain weight of 1.22 g;

[0123] (4) Disperse the polymer particles obtained in step (3) in a first extractant (tetrahydrofuran THF aqueous solution, the volume percentage of THF is 70%), make the mass ratio of the polymer particles to the first extractant 1:1.5, extract at 65 °C for 3 h under stirring conditions, then carry out solid-liquid separation, and dry at 70 °C to obtain a solid;

[0124] Disperse the solid in a second extractant (THF) such that the mass ratio of the solid to the second extractant is 1:1.5, perform a second extraction at 65 °C for 1 h under stirring conditions, then perform solid-liquid separation, and dry at 70 °C to obtain the PBS, and its test data are shown in Table 1.

[0125] Example 2

[0126] An aliphatic polyester (polybutylene succinate, PBS) and a preparation method thereof, the preparation method comprising the following steps:

[0127] (1) Mix succinic acid and 1,4-butanediol in a molar ratio of 1:1.4, and perform an esterification reaction at 170 °C for 2 h to obtain an esterified product;

[0128] (2) Place the esterified product obtained in step (1), a catalyst (tetraisopropyl titanate), a branching agent (glycerol), and a heat stabilizer (triphenyl phosphate) in a prepolymerization reactor, and react at 210 °C and 4 kPa for 3 h to obtain a prepolymer;

[0129] Based on the total mass of the succinic acid and 1,4-butanediol being 100%, the amount of the catalyst is such that the mass of Ti element is 110 ppm, the amount of the branching agent is such that the mass of hydroxyl group is 900 ppm, and the amount of the heat stabilizer is such that the mass of P element is 80 ppm;

[0130] (3) Transfer the prepolymer obtained in step (2) to a final polymerization reactor, and react at 230 °C and 25 Pa for 4 h to obtain a condensate;

[0131] Melt-extrude and pelletize the condensate in a screw extruder, the temperature of the melt extrusion is 170 °C, and the screw speed is 300 rpm to obtain polymer particles with a hundred-grain weight of 1.25 g;

[0132] (4) Disperse the polymer particles obtained in step (3) in a first extractant (aqueous THF solution, the volume percentage content of THF is 75%) such that the mass ratio of the polymer particles to the first extractant is 1:2, perform a first extraction at 75 °C for 2 h under stirring conditions, then perform solid-liquid separation, and dry at 75 °C to obtain a solid;

[0133] Disperse the solid in a second extractant (THF) such that the mass ratio of the solid to the second extractant is 1:2, perform a second extraction at 75 °C for 1.5 h under stirring conditions, then perform solid-liquid separation, and dry at 75 °C to obtain the PBS, and its test data are shown in Table 1.

[0134] Example 3

[0135] An aliphatic polyester (polybutylene adipate, PBA) and a preparation method thereof, the preparation method comprising the following steps:

[0136] (1) Mix adipic acid and 1,4 - butanediol in a molar ratio of 1:1.3, and carry out an esterification reaction at 160 °C for 3 h to obtain an esterified product;

[0137] (2) Place the esterified product obtained in step (1), a catalyst (tetraisopropyl titanate), a branching agent (glycerol), and a heat stabilizer (triphenyl phosphate) in a prepolymerization reactor, and react at 220 °C and 3 kPa for 2 h to obtain a prepolymer;

[0138] Based on the total mass of the adipic acid and 1,4 - butanediol being 100%, the dosage of the catalyst is such that the mass of Ti element is 110 ppm, the dosage of the branching agent is such that the mass of hydroxyl group is 900 ppm, and the dosage of the heat stabilizer is such that the mass of P element is 80 ppm;

[0139] (3) Transfer the prepolymer obtained in step (2) to a final polymerization reactor, and react at 250 °C and 30 Pa for 2 h to obtain a condensate;

[0140] Melt - extrude and pelletize the condensate in a screw extruder. The temperature of melt - extrusion is 170 °C, and the screw speed is 300 rpm to obtain polymer particles with a hundred - grain weight of 1.25 g;

[0141] (4) Disperse the polymer particles obtained in step (3) in a first extractant (aqueous THF solution, the volume percentage of THF is 65%), such that the mass ratio of the polymer particles to the first extractant is 1:1.8, and carry out the first extraction at 70 °C for 2.5 h under stirring conditions, then carry out solid - liquid separation and drying at 72 °C to obtain a solid;

[0142] Disperse the solid in a second extractant (THF), such that the mass ratio of the solid to the second extractant is 1:1.8, and carry out the second extraction at 70 °C for 1 h under stirring conditions, then carry out solid - liquid separation and drying at 70 °C to obtain the PAB, and its test data is shown in Table 1.

[0143] Example 4

[0144] An aliphatic polyester (polyethylene succinate, PES) and its preparation method, the preparation method comprising the following steps:

[0145] (1) Mix succinic acid and ethylene glycol in a molar ratio of 1:1.4, and carry out an esterification reaction at 165 °C for 2 h to obtain an esterified product;

[0146] (2) Place the esterified product obtained in step (1), a catalyst (tetra - n - butyl titanate), a branching agent (trimethylolpropane), and a heat stabilizer (trimethyl phosphate) in a prepolymerization reactor, and react at 220 °C and 5 kPa for 1 h to obtain a prepolymer;

[0147] Based on the total mass of the succinic acid and ethylene glycol being 100%, the dosage of the catalyst is such that the mass of Ti element is 80 ppm, the dosage of the branching agent is such that the mass of hydroxyl group is 800 ppm, and the dosage of the heat stabilizer is such that the mass of P element is 40 ppm;

[0148] (3) Transfer the prepolymer obtained in step (2) to a final polymerization reactor and react at 220 °C and 40 Pa for 4 h to obtain a condensate;

[0149] Melt-extrude and pelletize the condensate in a screw extruder. The temperature of the melt extrusion is 170 °C and the screw speed is 220 rpm to obtain polymer particles with a 100-grain weight of 1.25 g;

[0150] (4) Disperse the polymer particles obtained in step (3) in a first extractant (aqueous THF solution, with the volume percentage of THF being 60%) such that the mass ratio of the polymer particles to the first extractant is 1:1.4, and extract at 60 °C for 3 h under stirring conditions. Then, perform solid-liquid separation and dry at 75 °C to obtain a solid;

[0151] Disperse the solid in a second extractant (THF) such that the mass ratio of the solid to the second extractant is 1:1.45, and extract at 70 °C for 1.5 h under stirring conditions. Then, perform solid-liquid separation and dry at 75 °C to obtain the PES, and its test data are shown in Table 1.

[0152] Example 5

[0153] An aliphatic polyester (polybutylene succinate, PBS) and its preparation method. The preparation method includes the following steps:

[0154] (1) Mix succinic acid and 1,4-butanediol in a molar ratio of 1:1.5 and perform an esterification reaction at 160 °C for 3 h to obtain an esterified product;

[0155] (2) Place the esterified product obtained in step (1), a catalyst (tetrabutyl titanate), a branching agent (trimethylolpropane), and a heat stabilizer (trimethyl phosphate) in a prepolymerization reactor and react at 230 °C and 3 kPa for 2 h to obtain a prepolymer;

[0156] Based on the total mass of the succinic acid and 1,4-butanediol being 100%, the dosage of the catalyst is such that the mass of Ti element is 180 ppm, the dosage of the branching agent is such that the mass of hydroxyl group is 900 ppm, and the dosage of the heat stabilizer is such that the mass of P element is 70 ppm;

[0157] (3) Transfer the prepolymer obtained in step (2) to a final polymerization reactor and react at 250 °C and 80 Pa for 4 h to obtain a condensate;

[0158] The polycondensate is melt-extruded and pelletized in a screw extruder at a melt-extrusion temperature of 160 °C and a screw rotation speed of 200 rpm to obtain polymer pellets with a 100-pellet weight of 1.22 g;

[0159] (4) The polymer pellets obtained in step (3) are dispersed in a first extractant (an aqueous solution of 2-methyltetrahydrofuran with a volume percentage of 2-methyltetrahydrofuran of 70%), such that the mass ratio of the polymer pellets to the first extractant is 1:2, and extracted at 65 °C for 3 h under stirring conditions, followed by solid-liquid separation and drying at 70 °C to obtain a solid;

[0160] The solid is dispersed in a second extractant (2-methyltetrahydrofuran), such that the mass ratio of the solid to the second extractant is 1:1.5, and extracted at 65 °C for 1 h under stirring conditions, followed by solid-liquid separation and drying at 70 °C to obtain the PBS, and its test data are shown in Table 1.

[0161] Example 6

[0162] A PBS and its preparation method, the difference between the preparation method and that of Example 1 is only that the first extractant is an aqueous solution of THF (the volume percentage of THF is 55%), and other materials, dosages, and processes are the same as those in Example 1, to obtain the PBS, and its test data are shown in Table 1.

[0163] Comparative Example 1

[0164] A PBS and its preparation method, the difference between the preparation method and that of Example 1 is only that the second extraction is not carried out, and the solid obtained after the first extraction, solid-liquid separation, and drying is the PBS end product, and its test data are shown in Table 1.

[0165] Comparative Example 2

[0166] A PBS and its preparation method, the difference between the preparation method and that of Example 1 is only that the first extraction is not carried out, that is, the polymer pellets obtained in step (3) are directly dispersed in a second extractant (THF), and extracted at 65 °C for 3 h under stirring conditions, followed by solid-liquid separation and drying at 70 °C to obtain the PBS, and its test data are shown in Table 1.

[0167] Comparative Example 3

[0168] A PBS and its preparation method, the difference between the preparation method and that of Example 1 is only that the first extractant is THF, and other materials, dosages, and processes are the same as those in Example 1, to obtain the PBS, and its test data are shown in Table 1.

[0169] Comparative Example 4

[0170] A PBS and its preparation method. The only difference between the preparation method and that of Example 1 is that the second extractant is an aqueous THF solution (the volume percentage content of THF is 70%), and other materials, dosages and processes are the same as those in Example 1, obtaining the PBS, and its test data are shown in Table 1.

[0171] Comparative Example 5

[0172] A PBS and its preparation method. The only difference between the preparation method and that of Example 1 is that both the first extractant and the second extractant are aqueous ethanol solutions (the volume percentage content of ethanol is 70%), and other materials, dosages and processes are the same as those in Example 1, obtaining the PBS, and its test data are shown in Table 1.

[0173] Table 1

[0174]

[0175] According to the data in Table 1, in the preparation method of the present invention, a specific two-step extraction process is used to purify the polymerization product. Through the design of the extractant and the combined action of two extractions, low-molecular-weight substances such as cyclic oligomers in the product are effectively removed, so that the mass content of oligomers in the obtained polyester product is ≤5500 ppm, PDI ≤1.4, having the characteristics of high molecular weight and narrow molecular weight distribution, thereby improving the mechanical properties and processing properties of the aliphatic polyester. Its tensile strength is 40.8 - 42 MPa, and the elongation at break is ≥255%, which can reach 255 - 280%. In particular, the water vapor transmission rate of the polyester film is reduced. The water vapor transmission rate of a 20-μm film is ≤2500 g / d·m 2 , and the water vapor transmission rate of a 50-μm film is ≤940 g / d·m 2 , reducing or avoiding the risk of migration and precipitation of small-molecule substances.

[0176] In the preparation methods of Comparative Examples 1-2, only one extraction was carried out, resulting in poor removal effect of low-molecular-weight substances, high content of oligomers, wide molecular weight distribution, insufficient mechanical properties, high water vapor transmission rate of the polyester film, and difficulty in meeting the actual application requirements. In Comparative Example 3, THF was used as the extraction agent for two extractions, and its removal of low-molecular-weight substances such as oligomers was relatively complete. However, due to the precipitation of a large amount of substances, obvious cracks appeared on the surface of the PBS products, and the elongation at break and tensile strength decreased. In Comparative Example 4, although two extractions were carried out, the same extraction agent was used in the second extraction as in the first extraction, resulting in insufficient extraction effect, still relatively high oligomer content, large PDI, wide molecular weight distribution, and reduced mechanical properties of the polyester products. In Comparative Example 5, ethanol aqueous solution was used for both extractions. Although the oligomer content was lower than that in Comparative Examples 1-2, it was still at a relatively high level. At the same time, the PDI was on the high side, the molecular weight distribution was relatively wide, the water vapor transmission rate of the film was high, the mechanical properties decreased, and there was a problem of migration and precipitation of small molecules.

[0177] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate the aliphatic polyester, its preparation method and application of the present invention. However, the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent substitution of each raw material of the products of the present invention, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing an aliphatic polyester, characterized in that: The preparation method comprises: Esterifying aliphatic dicarboxylic acid and aliphatic diol to obtain an esterified product; The esterified product is subjected to a prepolymerization reaction in the presence of a catalyst and a branching agent to obtain a prepolymer; The prepolymer is subjected to final polymerization to obtain a polymerization product; Performing a first extraction and a second extraction on the polymerization product in sequence to obtain the aliphatic polyester; The first extractant used in the first extraction includes a combination of a first cyclic ether solvent and water; the second extractant used in the second extraction includes a second cyclic ether solvent.

2. The preparation method according to claim 1, characterized in that: The aliphatic dicarboxylic acid includes any one of succinic acid, glutaric acid, and adipic acid, or a combination of at least two thereof; Preferably, the aliphatic diol includes any one of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, or a combination of at least two thereof; Preferably, the molar ratio of the aliphatic dicarboxylic acid to the aliphatic diol is 1:(1.2-1.6); Preferably, the temperature of the esterification reaction is 150-170°C; Preferably, the esterification reaction time is 2-4 hours.

3. The preparation method according to claim 1, characterized in that: The catalyst comprises a titanate catalyst, preferably any one of tetramethyl titanate, tetraethyl titanate, tetraisopropyl titanate, tetra-n-butyl titanate, and tetraisooctyl titanate, or a combination of at least two thereof; Preferably, based on 100% of the total mass of the aliphatic dicarboxylic acid and the aliphatic diol, the amount of the catalyst is such that the mass of the Ti element is 50-200 ppm; Preferably, the branching agent comprises a polyol, and more preferably comprises any one or a combination of at least two of glycerol, trimethylolpropane, pentaerythritol, dipentaerythritol, and 2,2-dimethylolpropionic acid; Preferably, based on the total mass of the aliphatic dicarboxylic acid and the aliphatic diol as 100%, the amount of the branching agent is such that the mass of the hydroxyl group is 200-1000 ppm; Preferably, the prepolymerization reaction is carried out in the presence of a thermal stabilizer; Preferably, the heat stabilizer comprises a phosphate compound, and further preferably comprises any one or a combination of at least two of trimethyl phosphate, triethyl phosphate, isopropyl phosphate, n-butyl phosphate, isooctyl phosphate, and triphenyl phosphate; Preferably, based on the total mass of the aliphatic dicarboxylic acid and the aliphatic diol being 100%, the amount of the heat stabilizer used is such that the mass of the P element is 5-100 ppm.

4. The preparation method according to claim 1, characterized in that: The temperature of the prepolymerization reaction is 180-240°C; Preferably, the prepolymerization pressure is 1-5 kPa; Preferably, the prepolymerization reaction time is 0.5-3h; Preferably, the temperature of the final polymerization reaction is 220-260°C; Preferably, the pressure of the final polymerization reaction is 10-100 Pa; Preferably, the final polymerization reaction time is 1-6 hours.

5. The preparation method according to claim 1, characterized in that: After the final polymerization reaction is completed, the steps of melt extrusion and granulation are further included to obtain the granular polymerization product; Preferably, the melt extrusion is carried out in a screw extruder; Preferably, the screw speed of the screw extruder is 150-350 rpm, more preferably 200-300 rpm; Preferably, the temperature of the melt extrusion is 160-180°C; Preferably, the 100-grain weight of the granular polymerization product is ≤1.31 g, more preferably 1.20-1.30 g.

6. The preparation method according to claim 1, characterized in that: The first cyclic ether solvent and the second cyclic ether solvent each independently include any one of tetrahydrofuran, 2-methyltetrahydrofuran, and tetrahydropyran, or a combination of at least two thereof; Preferably, the volume percentage of the first cyclic ether solvent in the first extractant is 60%-80%.

7. The preparation method according to claim 1, characterized in that: The mass ratio of the polymer product to the first extractant is 1:(1.3-2); Preferably, the solid obtained after the first extraction is subjected to a second extraction, and the mass ratio of the solid to the second extractant is 1:(1.3-2); Preferably, the first extraction and the second extraction are performed under stirring conditions; Preferably, the temperature of the first extraction and the second extraction is independently 60-80°C, more preferably 65-75°C; Preferably, the first extraction time is 1-3.5h, more preferably 2-3h; Preferably, the second extraction time is 0.5-2 h, more preferably 1-1.5 h.

8. An aliphatic polyester, characterized in that The aliphatic polyester is prepared by the preparation method according to any one of claims 1 to 7; Preferably, the number average molecular weight of the aliphatic polyester is 4×10 4 -9×10 4 , and more preferably 5.5×10 4 -7.5×10 4 ; Preferably, the weight average molecular weight of the aliphatic polyester is 5×10 4 -12×10 4 , and more preferably 6.5×10 4 -10×10 4 ; Preferably, the Z average molecular weight of the aliphatic polyester is 9×10 4 -18×10 4 , and more preferably 11.5×10 4 -16.5×10 4 ; Preferably, the molecular weight polydispersity index of the aliphatic polyester is ≤1.62, more preferably 1.1-1.6; Preferably, the mass content of oligomers in the aliphatic polyester is ≤5500 ppm.

9. Use of the aliphatic polyester according to claim 8 in food contact materials or film bags.

10. A polymer film, characterized in that: The material of the polymer film comprises the aliphatic polyester as claimed in claim 8.

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