Acid-binding agent for initiating ring-opening polymerization reaction of cyclic ester compound, method for carrying out ring-opening polymerization reaction of cyclic ester compound and application of epoxy compound

Abstract

The invention relates to an acid-binding agent for initiating a ring-opening polymerization reaction of a cyclic ester compound, and the acid-binding agent comprises an epoxy compound, and the epoxy compound comprises an epoxy small molecule compound, an epoxy polymer or a combination of the epoxy small molecule compound and the epoxy polymer. The invention also relates to a method for carrying out ring-opening polymerization on the cyclic ester compound and application of the epoxy compound. In the ring-opening polymerization process of the cyclic ester compound, the acid-binding agent provided by the invention can reduce the content of unexpected acid in a reaction system, and has certain capability of initiating ring-opening polymerization. Specifically, when the acid-binding agent disclosed by the invention is applied to the ring-opening polymerization reaction of lactide, the melt index of the obtained polylactic acid is reduced, the hydrolysis resistance and the heat resistance are improved, and the polymerization reaction speed can be effectively controlled, so that the polymerization quality and the performance of a polymerization product are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and specifically relates to an acid binding agent for initiating a ring-opening polymerization reaction of a cyclic ester compound, a method for carrying out the ring-opening polymerization of the cyclic ester compound, and the use of an epoxy compound. Background Art

[0002] Polylactic acid (PLA) has good biocompatibility and degradability, and the raw materials for preparing PLA come from renewable resources. These characteristics make PLA an environmentally friendly material with extremely broad application prospects. In recent years, with the gradual deepening of the concept of green development, degradable materials have received more and more attention, so the demand for PLA has further expanded, and production capacity has gradually increased. However, although PLA material has excellent processing performance and environmental protection characteristics, it still has some shortcomings, such as poor hydrolysis resistance and poor heat resistance, which limit the application of PLA in some fields.

[0003] Increasing the molecular weight of polylactic acid is beneficial to improving the performance of polylactic acid materials, and the lactide ring-opening polymerization method is one of the effective ways to prepare high molecular weight polylactic acid. In the ring-opening polymerization process of lactide, the purity and quality of lactide in the reaction system have an important influence on the preparation of high molecular weight polylactic acid. For example, CN112142968A discloses a process for preparing polylactic acid by ring-opening polymerization of lactide, which purifies crude lactide by multiple methods, including crystallization, recrystallization and dynamic crystallization, thereby obtaining high-purity lactide, so that the final synthesized polylactic acid has high purity and high molecular weight.

[0004] During the ring-opening polymerization process, the presence of carboxyl-containing impurities such as lactic acid in the reaction system will have a negative impact on the polymerization quality and the hydrolysis resistance of the polymerization product. Therefore, it is necessary to select suitable additives with acid-binding function and apply them to lactide polymerization to improve the polymerization quality and product performance. Summary of the invention

[0005] The inventor of the present application has found that in the ring-opening polymerization of cyclic ester compounds, the performance of the product obtained by using conventional acid binding agents is not enough. For example, when conventional acid binding agents (such as organic bases such as triethylamine, pyridine) are used in the ring-opening polymerization of lactide, the problems such as yellowing, increase of melt index, poor heat resistance, etc. of the color of the polylactic acid product often occur. In addition, the polylactic acid molecular chain contains a large amount of ester bonds and terminal carboxyl groups. In the environment of high temperature and high humidity, the ester bonds are more susceptible to the corrosion of water or moisture to break the molecular chain, which easily causes the service life of the polylactic acid product to be greatly reduced and the comprehensive performance of the product to be greatly reduced. Thereby it is necessary to develop a new suitable auxiliary agent with acid binding effect to be applied to the ring-opening polymerization of cyclic ester compounds, to avoid the above-mentioned defects.

[0006] In order to optimize the polymerization quality and product performance of the ring-opening polymerization of cyclic ester compounds, on one hand, the present invention provides an acid binding agent for initiating the ring-opening polymerization reaction of cyclic ester compounds, which comprises: an epoxy compound, wherein the epoxy compound includes: an epoxy small molecule compound, an epoxy polymer or a combination thereof.

[0007] On the other hand, the present application provides a method for ring-opening polymerization of a cyclic ester compound, comprising: subjecting the cyclic ester compound to a ring-opening polymerization reaction in the presence of the acid binding agent of the present application.

[0008] In yet another aspect, the present application provides use of the epoxy compound herein for binding acid and / or initiating ring-opening polymerization in the ring-opening polymerization of cyclic ester compounds. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] For a more complete understanding of the present invention, reference should now be made to the embodiments shown in more detail in the accompanying drawings and described below by way of example of the invention, in which:

[0010] Figure 1 : Schematic diagram of the ring-opening polymerization reaction of lactide, in which the epoxy compound is used as an acid binding agent to initiate the ring-opening polymerization of lactide.

[0011] Figure 2 : Appearance photos of sample 1 and sample 2.

[0012] Figure 3 : Appearance photo of the polylactic acid sample of Example 2.

[0013] Figure 4 : Thermogravimetric analysis curves of the polylactic acid sample of Example 1 (red curve) and the polylactic acid sample of Comparative Example 1 (black curve).

[0014] Figure 5 : Thermogravimetric analysis curves of the polylactic acid sample of Example 2 (red curve) and the polylactic acid sample of Comparative Example 2 (black curve).

[0015] Figure 6 : Thermogravimetric analysis curves of the polylactic acid sample of Example 3 (red curve) and the polylactic acid sample of Comparative Example 3 (black curve).

[0016] Figure 7 : Thermogravimetric analysis curves of the polylactic acid sample of Example 4 (red curve) and the polylactic acid sample of Comparative Example 4 (black curve).

[0017] Figure 8 : Thermogravimetric analysis curves of the polylactic acid sample of Example 5 (red curve) and the polylactic acid sample of Comparative Example 5 (black curve). DETAILED DESCRIPTION

[0018] General Definitions and Terminology

[0019] Unless otherwise indicated, all publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the event of a conflict, the definitions provided herein shall prevail.

[0021] Unless otherwise indicated, all percentages, parts, ratios, etc. are by weight.

[0022] When quantity, concentration or other value or parameter is given as range, preferred range or preferred upper limit and lower limit or specific value, it should be understood as specifically disclosing all ranges formed by paired values ​​from any upper limit range or preferred value and any lower limit range or preferred value, regardless of whether the range is disclosed separately. Unless otherwise stated, when numerical range is quoted herein, the range refers to including its endpoints and integers and fractions within all such ranges. The scope of the present invention is not limited to the specific numerical value quoted when defining the range. For example, "1-8" covers 1, 2, 3, 4, 5, 6, 7, 8 and any sub-range consisting of any two values ​​therein, such as 2-6, 3-5.

[0023] The terms "about" and "approximately" when used with a numerical variable generally refer to the value of that variable and all values ​​of that variable are within experimental error (e.g., within a 95% confidence interval for the mean) or within ±10% of the specified value, or a wider range.

[0024] The terms "comprises", "includes", "has", "contains" or "involves" and other variations thereof herein are inclusive or open-ended and do not exclude other unlisted elements or method steps. It will be understood by those skilled in the art that the above terms such as "comprising" encompass the meaning of "consisting of". The expression "consisting of" excludes any element, step or ingredient not specified. The expression "consisting essentially of" means that the scope is limited to the specified elements, steps or ingredients, plus the optional presence of elements, steps or ingredients that do not substantially affect the basic and novel features of the claimed subject matter. It will be understood that the expression "comprising" encompasses the expressions "consisting essentially of" and "consisting of".

[0025] The term "selected from..." means that one or more elements in the group listed later are independently selected and may include combinations of two or more elements.

[0026] When values ​​or end-points of a range are described herein, it should be understood that the disclosure includes the specific value or end-point cited.

[0027] As used herein, the terms "one or more" or "at least one" refer to one, two, three, four, five, six, seven, eight, nine or more.

[0028] Unless otherwise specified, the terms "combination thereof" and "mixture thereof" refer to a multi-component mixture of the elements, such as a two-component mixture, a three-component mixture, a four-component mixture and the maximum possible multi-component mixture.

[0029] In addition, if the number of parts or components of the present invention is not indicated before, it means that there is no limit to the number of occurrences (or existence) of the parts or components. Therefore, it should be interpreted as including one or at least one, and the singular form of the parts or components also includes the plural form, unless the numerical value obviously represents the singular.

[0030] As used herein, the term "optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes both occurring and not occurring of said event or circumstance.

[0031] When describing methods, components or steps, the use of letters or numbers is only for the purpose of distinction, and does not limit these methods, components or steps to be performed in the order or sequence of the identification. Those skilled in the art can make reasonable adjustments.

[0032] When the lower and upper limits of a numerical range are disclosed, any numerical value and any included range falling within the range are specifically disclosed. In particular, each range of values ​​disclosed herein (in the form of "about a to b", or equivalently, "approximately a to b", or equivalently, "about ab"), should be understood to represent each numerical value and range encompassed within the broader range.

[0033] The term "weight average molecular weight" as used herein or weight average molar mass can be measured by light scattering, gel chromatography, ultracentrifugal sedimentation velocity method, etc. The weight average molecular weight of the present invention can be measured, for example, using gel permeation chromatography (GPC).

[0034] The term "room temperature" (RT) as used herein refers to about 20 to 35°C, preferably about 25°C.

[0035] Acid Binding Agent

[0036] In one aspect, the present application relates to an acid-binding agent for initiating a ring-opening polymerization reaction of a cyclic ester compound, which comprises an epoxy compound, and the epoxy compound may include: an epoxy small molecule compound, an epoxy polymer or a combination thereof.

[0037] Cyclic ester compounds refer to compounds containing a cyclic structure and having an ester group (-COO-) in the ring. The cyclic ester compounds of the present application may include, but are not limited to, lactones, lactides, etc. The ring-opening polymerization process of cyclic ester compounds may be as conventionally understood in the art. For the purpose of illustration and not limitation, the ring-opening polymerization process of cyclic ester compounds may refer to: under certain conditions, after the ester bond in the cyclic structure within the cyclic ester compound molecule is opened, the generated active end group reacts with other cyclic ester molecules, causing the molecular chain to grow continuously, thereby connecting to form a polymer process.

[0038] In the process of ring-opening polymerization, carboxylic acid impurities present in the cyclic ester compounds have an adverse effect on the polymerization quality and product performance. The sources of these carboxylic acid impurities include, but are not limited to: existing as impurities in the provided cyclic ester compound raw materials, or being produced by the self-decomposition of the cyclic ester compounds during the ring-opening polymerization process.

[0039] The inventors of the present application have found that conventional acid-binding agents (such as triethylamine, pyridine and other organic bases) may cause the performance of the polymer product to fail to reach the expected level, resulting in problems such as yellowing of the product color, increased melt index, poor heat resistance, etc. The acid-binding agent of the present application comprises an epoxy compound, which can improve the above problems and help obtain a ring-opening polymer product with excellent performance.

[0040] Herein, "acid binding agent" may also be referred to as "acid absorber", "acid trapping agent", etc., which refers to a substance that can remove acid from a system or inactivate it, and the process can be carried out, for example, by physical adsorption or chemical reaction. It should be understood that "removing acid from the reaction or inactivating it" as described herein means that the content of the acidic substance that is not expected to exist in the system is reduced to below a certain level. When the acidic substance is at this content level, the target reaction can proceed smoothly, and it does not require that the content of the acidic substance must be zero.

[0041] Epoxides

[0042] Herein, epoxy compound has the meaning understood by those skilled in the art, that is, refers to a compound containing epoxy group. It is a three-membered ring structure composed of one oxygen atom and two carbon atoms. The epoxy compound of the present application includes: epoxy small molecule compounds, epoxy polymers or a combination thereof.

[0043] Not bound by theory, reference Figure 1 Taking the ring-opening polymerization of lactide to generate polylactic acid as an example, the role of epoxy compounds is explained: in the reaction system, the carboxyl group of a small amount of acidic impurities (such as lactic acid, etc.) contained in lactide will attack the epoxy group of the epoxy compound, causing the epoxy group to open the ring and generate a product containing an ester group and a hydroxyl group (such as Figure 1The product containing ester group and hydroxyl group generated by the ring-opening of epoxy group can be used as an initiator for the subsequent ring-opening polymerization of lactide. The hydroxyl group contained in it can initiate the ring-opening polymerization of lactide (such as Figure 1 It is worth noting that although the epoxy group can react with the hydroxyl group in theory, the electrophilicity of the hydroxyl group is weaker than that of the carboxyl group. Therefore, in fact, the reaction between the epoxy group and the hydroxyl group is weak and can be ignored, so no small molecule byproducts are generated in the reaction.

[0044] Suitable epoxy compounds can fully play the role described above in the ring-opening polymerization reaction of cyclic ester compounds, and can also achieve beneficial effects such as more controllable polymerization rate, molecular weight and distribution of polymerization products.

[0045] The epoxy compound of the application can have a suitable epoxide equivalent range to provide desired reactivity. Epoxide equivalent refers to the mass of the epoxy compound containing 1mol epoxy groups herein, and the unit is represented by g / mol. In one embodiment, the epoxide equivalent of the epoxy compound of the application can be less than 400g / mol, preferably less than 350g / mol, such as 400g / mol, 380g / mol, 350g / mol, 320g / mol, 300g / mol, 280g / mol, 250g / mol, 220g / mol, 200g / mol, 180g / mol, 150g / mol, 120g / mol, 100g / mol, 80g / mol or 60g / mol etc. Epoxide equivalent is too high, and the reactivity of epoxy compound is too low, which is unfavorable for it and carboxyl reaction. In another embodiment, the epoxy equivalent of the epoxy compound can be 60 g / mol or more, such as 60 g / mol or more, 80 g / mol or more, 100 g / mol or more, 150 g / mol or more, or 200 g / mol or more. Such epoxy equivalent setting helps to further reduce the reaction of epoxy groups with hydroxyl groups as much as possible, avoid the generation of undesirable small molecule by-products, and thus improve the quality of the product.

[0046] Herein, epoxy small molecule compounds refer to non-polymeric compounds containing epoxy groups, and their molecular weight is usually small, for example, it can be below 1000g / mol. In one embodiment, the boiling point of the epoxy small molecule compounds of the present application at a standard atmospheric pressure can be above 60°C, for example, above 60°C, above 70°C, above 80°C, above 100°C, above 110°C, above 120°C, etc. The ring-opening polymerization reaction of cyclic ester compounds usually involves heating, so that the boiling point characteristics of epoxy small molecule compounds enable them to remain in the reaction system when heated and avoid escape, which is beneficial for them to play a role in the reaction and ensure the smooth progress of the reaction.

[0047] For the ring-opening polymerization of cyclic ester compounds, the following types of epoxy small molecules are preferred: glycidyl compounds, epoxycyclohexyl compounds or a combination thereof.

[0048] Glycidyl compounds refer to compounds containing glycidyl groups (i.e. The glycidyl compounds of the present application may include glycidyl esters and glycidyl ethers, preferably glycidyl methacrylate (CAS No.: 106-91-2), diglycidyl tetrahydrophthalate (CAS No.: 21544-03-6), glycidyl acrylate (CAS No.: 106-90-1), glycidyl acetate (CAS No.: 5031-95-0), glycidyl butyrate (CAS No.: 60456-26-0), glycidyl benzoate, glycidyl palmitate (CAS No.: 7501-44-2), glycidyl stearate (CAS No.: 1346598-19-3), glycidyl oleate (CAS No.: 5431-33-4), glycidyl linoleate (CAS No.: 5431-33-4), glycidyl linoleate (CAS No.: 5431-33-4), glycidyl methacrylate (CAS No.: 106-91-2), diglycidyl tetrahydrophthalate (CAS No.: 21544-03-6), glycidyl acrylate (CAS No.: 106-90-1), glycidyl acetate (CAS No.: 5031-95-0), glycidyl butyrate (CAS No.: 60456-26-0), glycidyl benzoate, glycidyl palmitate (CAS No.: 7501-44-2), glycidyl stearate (CAS No.: 1346598-19-3), glycidyl oleate (CAS No.: 5431-33-4), glycidyl linoleate (CAS No.: 5431-33-4), glycidyl linoleate (CAS No.: 5431-33- Oil esters (CAS No.: 24305-63-3), 4,5-epoxytetrahydrophthalic acid diglycidyl ester (CAS No.: 25293-64-5), 1,2-cyclohexanedicarboxylic acid diglycidyl ester (CAS No.: 5493-45-8), 4-tert-butylbenzoic acid glycidyl ester (CAS No.: 59313-58-5), adipic acid diglycidyl ester (CAS No.: 754-17-8), pentaerythritol tetraglycidyl ether (CAS No.: 3126-63-4), trimethylolpropane triglycidyl ether (CAS No.: 30499-70-8), neopentyl glycol diglycidyl ether (CAS No.: 17557-23-2), resorcinol diglycidyl ether (CAS No.: 101-90-6). In a more preferred embodiment, the glycidyl compound of the present application may be glycidyl methacrylate, diglycidyl tetrahydrophthalate or a combination thereof.

[0049] Epoxycyclohexyl compounds refer to compounds containing epoxycyclohexyl groups. The epoxycyclohexyl compounds of the present application may include epoxycyclohexane carboxylates, preferably including: 3,4-epoxycyclohexane carboxylic acid methyl ester (CAS No.: 41088-52-2), 3,4-epoxycyclohexyl methyl-3,4-epoxycyclohexyl carboxylate (CAS No.: 2386-87-0), bis((3,4-epoxycyclohexyl)methyl)adipate (CAS No.: 3130-19-6) or a combination thereof. In a more preferred embodiment, the glycidyl compounds of the present application may be 3,4-epoxycyclohexyl methyl-3,4-epoxycyclohexyl carboxylate.

[0050] Herein, epoxy polymer refers to a polymer containing epoxy groups in the structure. In one embodiment, the weight average molecular weight of epoxy polymer can be 200-10000Da, such as 200Da, 500Da, 1000Da, 2000Da, 5000Da, 8000Da, 10000Da etc. The epoxy polymer of suitable molecular weight contributes to the formation of homogeneous system in the polymerization process, which is conducive to the reaction. The epoxy polymer of the present application can include: epoxy functionalized styrene-acrylate oligomer, epoxy resin or its combination.

[0051] Epoxy functionalized styrene-acrylate oligomer refers to an oligomeric copolymer of styrene and acrylate containing epoxy groups. In a preferred embodiment, the epoxy functionalized styrene-acrylate oligomer includes: ADR-4370S, ADR-4380, KL-E4370 or a combination thereof. Among them, the supplier of ADR-4370S and ADR-4380 is BASF, and the supplier of KL-E4370 is Shanxi Chemical Research Institute.

[0052] Epoxy resin has the meaning commonly understood in the art, that is, refers to a high molecular oligomer with an organic compound as a skeleton, containing two or more epoxy groups and capable of undergoing a curing reaction through the ring opening of the epoxy groups. The epoxy resin of the present application may include: glycidyl ester epoxy resin, bisphenol A epoxy resin, bisphenol F epoxy resin, polyphenol glycidyl ether epoxy resin, aliphatic glycidyl ether epoxy resin, alicyclic epoxy resin or a combination thereof.

[0053] In one embodiment, the acid binding agent of the present application is composed of epoxy compounds as described above. The acid binding agent can only be composed of a single type of epoxy compounds, or can include two or more epoxy compounds. Under the premise that the ring-opening polymerization can not bring obvious negative effects, the acid binding agent of the present application can also include a certain amount of other compounds with acid binding effect.

[0054] The acid binding agent of the present application, especially the preferred one, has advantageous effects when used to initiate the ring-opening polymerization of cyclic ester compounds: it can avoid the problems of yellowing, increased melt index, poor heat resistance, etc. during the polymerization application process, and can also effectively control the reaction speed and improve the polymerization quality. The obtained polymer product has a high molecular weight and excellent hydrolysis resistance and heat resistance.

[0055] In one embodiment, the cyclic ester compound may include: lactide, glycolide, ε-caprolactone, δ-valerolactone, β-butyrolactone, γ-butyrolactone, β-propiolactone, trimethylene carbonate, hydroxytrimethylene carbonate, chlorotrimethylene carbonate or a combination thereof. In a preferred embodiment, the cyclic ester compound of the present application is lactide. Lactide may include L-lactide, D-lactide, Meso-lactide, racemic lactide or any combination thereof.

[0056] Accordingly, in another aspect, the present application also relates to the use of the epoxy compound as described above in the ring-opening polymerization of cyclic ester compounds to bind acid and / or initiate ring-opening polymerization.

[0057] Herein, "acid binding" may also be referred to as "acid absorption", "acid capture", etc., which refers to the process of removing the acid from the reaction system or making it inactive, which can be carried out by physical adsorption or chemical reaction. For example, Figure 1 Process (1) shows a process in which lactic acid reacts chemically with an epoxy compound to remove lactic acid that is undesirably present in the system.

[0058] Herein, "initiated ring-opening polymerization" refers to a polymerization reaction in which the ring structures in the cyclic monomer molecules are opened, thereby starting and connecting to each other to form a long polymer chain. Figure 1 Process (2) shows that the reaction product of an epoxy compound and lactic acid is used as an initiator to initiate the ring-opening polymerization of lactide.

[0059] Method for ring-opening polymerization of cyclic ester compounds

[0060] On the other hand, the present application provides a method for ring-opening polymerization of a cyclic ester compound, comprising: subjecting the cyclic ester compound to a ring-opening polymerization reaction in the presence of an acid binding agent.

[0061] The acid binding agent may be as defined above.

[0062] The ring-opening polymerization process of cyclic ester compounds can be as conventionally understood in the art, see above, and will not be repeated here. In one embodiment, the cyclic ester compounds may include: lactide, glycolide, ε-caprolactone, δ-valerolactone, β-butyrolactone, γ-butyrolactone, β-propiolactone, trimethylene carbonate, hydroxytrimethylene carbonate, chlorotrimethylene carbonate or a combination thereof. In a preferred embodiment, the cyclic ester compound of the present application is lactide. Lactide may include L-lactide, D-lactide, Meso-lactide, racemic lactide or any combination thereof.

[0063] In one embodiment, the cyclic ester compound and the acid binding agent are mixed, and then the reaction system is heated to a molten state; and then the temperature of the reaction system is further increased to allow the cyclic ester compound to undergo ring-opening polymerization.

[0064] In the molten state, the acidic impurities in the cyclic ester compound can react with the acid binding agent, thereby facilitating the subsequent ring-opening polymerization. The reaction system can be kept in the molten state for a period of time to allow the acidic impurities in the cyclic ester compound to fully react with the acid binding agent.

[0065] Before further increasing the temperature of the reaction system to carry out the polymerization reaction, other additives may be added to the system, including but not limited to: catalysts, antioxidants, etc. Those skilled in the art may select the appropriate type of additive according to the specific raw material type. The catalyst can effectively increase the reaction rate, avoid side reactions, and thus increase the concentration of the target product. The oxidation process of organic compounds belongs to a series of free radical chain reactions. Under the action of heat, light or oxygen, the chemical bonds of organic molecules break, generating active free radicals and hydroperoxides, and the hydroperoxides undergo decomposition reactions, also generating hydrocarbon oxygen free radicals and hydroxyl free radicals. These free radicals can trigger a series of free radical chain reactions, resulting in undesirable changes in the product structure and properties. The role of the antioxidant is to eliminate the newly generated free radicals, or to promote the decomposition of the hydroperoxide, thereby preventing the chain reaction from proceeding, promoting the reaction process to develop in an expected manner, and finally obtaining the target product.

[0066] Before further increasing the temperature of the reaction system to carry out the polymerization reaction, the system may be stirred. Stirring is conducive to a more uniform reaction system. The stirring speed may be, for example, 5-200 r / min, and the stirring time may be, for example, 0.01-6 h.

[0067] Further increasing the temperature of the reaction system to allow the ring-opening polymerization reaction to proceed can be carried out in a gradient heating manner. This is beneficial to polymerization efficiency and product performance. In one embodiment, the gradient heating is carried out in a manner of heating 10° C. every 20-120 minutes.

[0068] The reaction process of ring-opening polymerization can be carried out under an inert atmosphere, for example, under a nitrogen environment or an argon environment. An inert gas environment is conducive to reducing side reactions and maintaining catalyst activity. If under vacuum conditions, the raw materials will be carried out, resulting in a decrease in the yield of the target product. Preferably, the system pressure during the reaction can be 0.05-0.4MPa.

[0069] The ring-opening polymerization reaction process does not require stirring, which is beneficial to the polymerization process and optimizes product performance.

[0070] For the ring-opening polymerization of lactide, the weight ratio of lactide to the acid binding agent can be 100:(0.01-2.0), for example, 100:0.01, 100:0.05, 100:0.1, 100:0.2, 100:0.5, 100:0.8, 100:1.0, 100:1.5, 100:2.0, etc. Such a ratio can give full play to the acid binding effect of the acid binding agent and avoid the adverse effect of excessive amount of the acid binding agent on the product, thereby helping to obtain polylactic acid with high molecular weight and excellent performance.

[0071] In one embodiment, after the lactide and the acid binding agent are mixed, the system is heated to a molten state, and the heating temperature can be 100-200°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, etc.

[0072] In one embodiment, the reaction system after the lactide and the acid binding agent are mixed can be maintained in a molten state for 0.01-6 hours, for example, 0.01 hours, 0.1 hours, 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, etc.

[0073] Catalysts suitable for the ring-opening polymerization of lactide include, but are not limited to, tin catalysts, zinc catalysts, and combinations thereof. Tin catalysts refer to compounds containing elemental tin, which may be organic tin compounds or inorganic tin compounds. Zinc catalysts refer to compounds containing elemental zinc, which may be organic zinc compounds or inorganic zinc compounds. For example, zinc oxide, stannous chloride, stannous octoate, zinc lactate, etc. The content of the catalyst will affect the efficiency of the polymerization reaction, and on the other hand, it will also affect the cost. Based on the weight of lactide, the amount of the catalyst used in the present invention may be 0.01-2.0% by weight.

[0074] The antioxidants suitable for the ring-opening polymerization of lactide include, but are not limited to, hindered phenol compounds and their derivatives, phosphorus-containing and sulfur-containing organic compounds, etc. For example, it can be one of antioxidant 1010, antioxidant 1076, antioxidant 1035, antioxidant 168, antioxidant 3010, antioxidant 2010, etc., or a mixture thereof in any proportion. Based on the weight of lactide, the amount of the antioxidant used in the present invention can be 0.01-2.0% by weight.

[0075] In one embodiment, the reaction temperature of the ring-opening polymerization of lactide can be 100-250° C. A reaction temperature that is too high will increase the energy consumption during the reaction and will also cause the decomposition of the reactants, resulting in a decrease in the yield of the target product; a reaction temperature that is too low is not conducive to the occurrence of the reaction, resulting in a decrease in the reaction rate and a decrease in the yield of the target product.

[0076] In one embodiment, for the ring-opening polymerization process of lactide, the temperature of the molten reaction system can be raised to the reaction temperature of the ring-opening polymerization by a gradient temperature increase. The gradient temperature increase can be performed by increasing the temperature by 10° C. every 20-120 minutes. This is beneficial to the reaction efficiency.

[0077] In one embodiment, the reaction time of the ring-opening polymerization of lactide can be 0.5-10 hours. If the reaction time is too short, the polymerization reaction will be incomplete, the molecular weight of the target product will be too low, and it will not be conducive to obtaining polylactic acid with high molecular weight and excellent performance; if the reaction time is too long, the energy consumption in the reaction process will be increased and thermal degradation will be easily caused.

[0078] In one embodiment, the ring-opening polymerization of lactide is carried out under a nitrogen atmosphere. Preferably, the system pressure during the reaction is 0.05-0.4 MPa.

[0079] Beneficial Effects

[0080] The acid binding agent comprising epoxy compounds of the present application, compared to conventional acid binding agents such as triethylamine and pyridine, shows a more outstanding effect in the ring-opening polymerization process of cyclic ester compounds (such as lactide). The acid binding agent of the present application will not have problems such as yellowing, increased melt index, poor heat resistance, etc., and a polymer product with excellent performance can be obtained. The product generated by the acid binding agent of the present application and the acid reaction, the hydroxyl group contained in it can play an initiation role in the subsequent ring-opening polymerization process, which helps to control the reaction speed and improve the polymerization quality. The polylactic acid of the present application performs well in the water bath aging test, has excellent hydrolysis resistance, and has good comprehensive performance and service life. In addition, the polylactic acid of the present application has the characteristics of high molecular weight, high monomer conversion, and the semi-decomposition temperature is higher, showing good heat resistance.

[0081] Example

[0082] The solution of the present invention is further described in detail below in conjunction with specific embodiments.

[0083] It should be noted that the following examples are merely examples for clearly illustrating the technical solutions of the present invention, and are not intended to limit the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description, and it is not necessary and impossible to exhaustively list all the embodiments here, and the obvious changes or modifications derived therefrom are still within the scope of protection of the present invention. Unless otherwise specified, the instruments, equipment, and reagents used herein are all commercially available.

[0084] preparation

[0085] Small-scale experiments

[0086] Sample 1: 200g of lactide (Zhejiang Haizheng Biomaterial Co., Ltd., purity 99.1%) was added to a flask, the reaction system was kept at a slightly positive pressure with nitrogen, and the reaction system was heated to 150°C. After 20 minutes, 0.4g of an antioxidant compounded from antioxidant 1010 and antioxidant 1035 (supplier: Shanghai MacLean Biochemical Technology Co., Ltd.) and 0.3g of stannous chloride were added to the system, and the reaction system was mixed evenly. Thereafter, the system temperature was maintained at 150-200°C for 6h to obtain a polylactic acid sample of sample 1.

[0087] Sample 2: 200g of lactide (purchased from Zhejiang Haizheng Biomaterial Co., Ltd., purity 99.1%) and 0.2g of pyridine were added to the flask, the reaction system was kept at a slightly positive pressure with nitrogen, and the reaction system was heated to 150°C. After 20 minutes, 0.4g of antioxidant compounded by antioxidant 1010 and antioxidant 1035 (supplier: Shanghai MacLean Biochemical Technology Co., Ltd.) and 0.3g of stannous chloride were added to the system, and the reaction system was mixed evenly. Thereafter, the system temperature was maintained at 150-200°C for 6h to obtain a polylactic acid sample of sample 2.

[0088] Sample 3: 200g of lactide (purchased from Zhejiang Haizheng Biomaterial Co., Ltd., purity 99.1%) and 0.2g of triethylamine were added to the flask, the reaction system was kept at a slightly positive pressure with nitrogen, and the reaction system was heated to 150°C. After 20 minutes, 0.4g of antioxidant compounded by antioxidant 1010 and antioxidant 1035 (supplier: Shanghai MacLean Biochemical Technology Co., Ltd.) and 0.3g of stannous chloride were added to the system, and the reaction system was mixed evenly. Thereafter, the system temperature was maintained at 150-200°C for 6h to obtain a polylactic acid sample of sample 3.

[0089] Experimental Results

[0090] Sample 1 is a blank control without adding an acid binding agent, and samples 2-3 use pyridine and triethylamine as acid binding agents, respectively. The experimental results show that compared with sample 1, samples 2-3 have obvious yellowing in the system during the reaction process of preparing polylactic acid, and the obtained product has an unfavorable appearance of yellow-brown. In addition, the melt index of the product of samples 2-3 is significantly higher than that of sample 1, which is not conducive to practical use.

[0091] Figure 2 The photographs of the reaction systems of Sample 1 and Sample 2 are shown. The reaction system of Sample 2 (flask on the left) is yellow-brown, and the system of Sample 1 (flask on the right) is colorless and transparent.

[0092] Scaling up experiments

[0093] Example 1

[0094] 1000 g of L-lactide (supplier: Zhejiang Haizheng Biomaterial Co., Ltd., purity 98.8%) and 0.8 g of diglycidyl tetrahydrophthalate were added to the reactor, and then nitrogen was introduced into the reactor for replacement until the pressure reached 0.15 MPa. The reactor was then heated to 150° C. and the system was mechanically stirred at the same time, with the stirring speed set at 100 r / min.

[0095] After 30 minutes, 1.5 g of an antioxidant compounded from antioxidant 2010 and antioxidant 1010 (supplier: Shanghai MacLean Biochemical Technology Co., Ltd.) and 1 g of stannous octoate were added to the reactor, and the system was purged with nitrogen again until the pressure reached 0.15 MPa, and then stirring was continued for 20 minutes before stopping stirring. Thereafter, the system temperature was maintained at 150-200° C. for 6 hours to obtain the polylactic acid sample of Example 1.

[0096] Example 2

[0097] 1000 g of L-lactide (supplier: Zhejiang Hisun Biomaterials Co., Ltd., purity 99.1%) and 1 g of ADR-4370S (supplier: BASF) were added to the reactor, and then nitrogen was introduced into the reactor for replacement until the pressure reached 0.2 MPa. Subsequently, the reactor was heated to 150° C. and the system was mechanically stirred at the same time, with the stirring speed set to 70 r / min.

[0098] After 30 minutes, 2 g of an antioxidant compounded from antioxidant 1010 and antioxidant 1035 (supplier: Shanghai MacLean Biochemical Technology Co., Ltd.) and 1 g of stannous octoate were added to the reactor, and the system was purged with nitrogen again until the pressure reached 0.2 MPa, and then stirring was continued for 25 minutes before stopping stirring. Thereafter, the system temperature was maintained at 150-200° C. for 6 hours to obtain the polylactic acid sample of Example 2.

[0099] Example 3

[0100] 1000 g of L-lactide (supplier: Zhejiang Haizheng Biomaterial Co., Ltd., purity 98.9%) and 1 g of KL-E4370 (supplier: Shanxi Chemical Research Institute) were added to the reactor, and then nitrogen was introduced into the reactor for replacement until the pressure reached 0.15 MPa. Subsequently, the reactor was heated to 140° C. and the system was mechanically stirred at the same time, with the stirring speed set to 100 r / min.

[0101] After 30 minutes, 2 g of an antioxidant compounded from antioxidant 1076 and antioxidant 3010 (supplier: BASF) and 1.5 g of stannous octoate were added to the reactor, and the system was purged with nitrogen again until the pressure reached 0.15 MPa, and then stirring was continued for 20 minutes before stopping. Thereafter, the system temperature was maintained at 140-190° C. for 6 hours to obtain the polylactic acid sample of Example 3.

[0102] Example 4

[0103] 1000g of L-lactide (supplier: Zhejiang Hisun Biomaterials Co., Ltd., purity 99.2%) and 1.2g of methyl 3,4-epoxycyclohexanecarboxylate (supplier: Shanghai MacLean Biochemical Technology Co., Ltd.) were added to the reactor, and then nitrogen was introduced into the reactor for replacement until the pressure reached 0.18MPa. Subsequently, the reactor was heated to 150°C and the system was mechanically stirred at the same time, with the stirring speed set to 90r / min.

[0104] After 30 minutes, 1.8 g of antioxidant prepared by combining antioxidant 2010 and antioxidant 1010 (supplier: Shanghai MacLean Biochemical Technology Co., Ltd.) and 1.5 g of stannous chloride were added to the reactor, and the system was purged with nitrogen again until the pressure reached 0.18 MPa, and then stirring was continued for 20 minutes before stopping stirring. Thereafter, the system temperature was maintained at 150-200° C. for 6 hours to obtain the polylactic acid sample of Example 4.

[0105] Example 5

[0106] 1000 g of L-lactide (supplier: Zhejiang Haizheng Biomaterial Co., Ltd., purity 99.0%) and 0.6 g of epoxy resin DER732 (supplier: Shanghai Kaiyin Chemical Co., Ltd.) were added to the reactor, and then nitrogen was introduced into the reactor for replacement until the pressure reached 0.2 MPa. Subsequently, the reactor was heated to 140° C. and the system was mechanically stirred at the same time, with the stirring speed set to 80 r / min.

[0107] After 30 minutes, 2 g of an antioxidant compounded from antioxidant 1010 and antioxidant 1035 (supplier: Shanghai MacLean Biochemical Technology Co., Ltd.) and 1 g of stannous chloride were added to the reactor, and the system was purged with nitrogen again until the pressure reached 0.2 MPa, and then stirring was continued for 20 minutes before stopping. Thereafter, the system temperature was maintained at 140-190° C. for 6 hours to obtain the polylactic acid sample of Example 5.

[0108] Comparative Example 1

[0109] 1000 g of L-lactide (supplier: Zhejiang Hisun Biomaterials Co., Ltd., purity 98.8%) was added to the reactor, and then nitrogen was introduced into the reactor for replacement until the pressure reached 0.15 MPa. The reactor was then heated to 150° C. and the system was mechanically stirred at the same time, with the stirring speed set at 100 r / min.

[0110] After 20 minutes, 1.5 g of an antioxidant compounded from antioxidant 2010 and antioxidant 1010 (supplier: Shanghai MacLean Biochemical Technology Co., Ltd.) and 1 g of stannous octoate were added to the reactor, and the system was purged with nitrogen again until the pressure reached 0.15 MPa, and then stirring was continued for 20 minutes before stopping stirring. Thereafter, the system temperature was maintained at 150-200° C. for 6 hours to obtain a polylactic acid sample of Comparative Example 1.

[0111] Comparative Example 2

[0112] 1000 g of L-lactide (supplier: Zhejiang Hisun Biomaterials Co., Ltd., purity 99.1%) was added to the reactor, and then nitrogen was introduced into the reactor for replacement until the pressure reached 0.2 MPa. Subsequently, the reactor was heated to 150° C. and the system was mechanically stirred at the same time, with the stirring speed set to 70 r / min.

[0113] After 20 minutes, 2 g of an antioxidant compounded from antioxidant 1010 and antioxidant 1035 (supplier: Shanghai MacLean Biochemical Technology Co., Ltd.) and 1 g of stannous octoate were added to the reactor, and the system was purged with nitrogen again until the pressure reached 0.2 MPa, and then stirring was continued for 25 minutes before stopping stirring. Thereafter, the system temperature was maintained at 150-200° C. for 6 hours to obtain a polylactic acid sample of Comparative Example 2.

[0114] Comparative Example 3

[0115] 1000 g of L-lactide (supplier: Zhejiang Hisun Biomaterials Co., Ltd., purity 98.9%) was added to the reactor, and then nitrogen was introduced into the reactor for replacement until the pressure reached 0.15 MPa. Subsequently, the reactor was heated to 140° C. and the system was mechanically stirred at the same time, with the stirring speed set to 100 r / min.

[0116] After 20 minutes, 2 g of an antioxidant compounded from antioxidant 1076 and antioxidant 3010 (supplier: BASF) and 1.5 g of stannous octoate were added to the reactor, and the system was purged with nitrogen again until the pressure reached 0.15 MPa, and then stirring was continued for 20 minutes before stopping. Thereafter, the system temperature was maintained at 140-190° C. for 6 hours to obtain a polylactic acid sample of Comparative Example 3.

[0117] Comparative Example 4

[0118] 1000 g of L-lactide (supplier: Zhejiang Hisun Biomaterials Co., Ltd., purity 99.2%) was added to the reactor, and then nitrogen was introduced into the reactor for replacement until the pressure reached 0.18 MPa. Subsequently, the reactor was heated to 150° C. and the system was mechanically stirred at the same time, with the stirring speed set to 90 r / min.

[0119] After 20 minutes, 1.8 g of antioxidant prepared by combining antioxidant 2010 and antioxidant 1010 (supplier: Shanghai MacLean Biochemical Technology Co., Ltd.) and 1.5 g of stannous chloride were added to the reactor, and the system was replaced with nitrogen again until the pressure reached 0.18 MPa, and then stirring was continued for 20 minutes and then stopped. Thereafter, the system temperature was maintained at 150-200° C. for 6 hours to obtain the polylactic acid sample of Comparative Example 4.

[0120] Comparative Example 5

[0121] 1000 g of L-lactide (supplier: Zhejiang Hisun Biomaterials Co., Ltd., purity 99.0%) was added to the reactor, and then nitrogen was introduced into the reactor for replacement until the pressure reached 0.2 MPa. Subsequently, the reactor was heated to 140° C. and the system was mechanically stirred at the same time, with the stirring speed set to 80 r / min.

[0122] After 20 minutes, 2 g of an antioxidant prepared by mixing antioxidant 1010 and antioxidant 1035 (supplier: Shanghai MacLean Biochemical Technology Co., Ltd.) and 1 g of stannous chloride were added to the reactor, and the system was replaced with nitrogen again until the pressure reached 0.2 MPa, and then stirring was continued for 20 minutes and then stopped. Thereafter, the system temperature was maintained at 140-190° C. for 6 hours to obtain a polylactic acid sample of Comparative Example 5.

[0123] Performance Testing

[0124] Product appearance: The polylactic acid samples of the examples of the present application exhibit excellent appearance, with no yellowing visible to the naked eye. Figure 3 The appearance photo of the polylactic acid sample of Example 2 is shown. Figure 3 As shown, the sample is basically colorless and transparent.

[0125] Quantitative test: According to the following test method, the samples of the embodiments and comparative examples were tested, and the test data are shown in the following Table 1-2.

[0126] Melt flow rate (MFR): The samples of the examples and comparative examples were measured at 190° C. and a load of 2.16 kg; instrument: melt index tester (MFI-1211).

[0127] Number average molecular weight (Mn): measured by gel permeation chromatography (GPC).

[0128] Acid value: tested by Swiss Metrohm 905 potentiometric titrator.

[0129] Thermogravimetric analysis: The test was carried out using a thermogravimetric instrument.

[0130] Table 1

[0131]

[0132] Note*: Water bath aging is carried out in the following manner: water bath aging test is carried out on the material through a constant temperature water bath, vacuum oven, and melt index. The water bath thermostat is set at 70°C. After the water bath temperature stabilizes, a beaker with distilled water is placed in it. After 20 minutes, the sample is added to the beaker, the beaker is covered with plastic wrap, and placed in a constant temperature water bath. After the sample is in a constant temperature water bath at 70°C for 6 hours, it is taken out and drained, and dried in a vacuum oven at 90°C for 16 hours, and the MFR is measured. Compare the initial MFR of the sample to evaluate the change.

[0133] According to Table 1, compared with Comparative Examples 1-5, the polylactic acid samples of Examples 1-5 have lower melt flow rates before and after water bath aging. And after water bath aging, the increase in melt flow rate of the polylactic acid samples of the embodiments is lower than that of the corresponding comparative examples, which shows that the degree of change in performance before and after water bath aging is smaller, and has better hydrolysis resistance. In addition, compared with the comparative examples, the polylactic acid samples of the embodiments of the present application also have the significant advantages of higher molecular weight and lower acid value.

[0134] Figure 2-4 The thermogravimetric curves of the embodiments and comparative examples are shown. The relevant data are summarized in Table 2 below.

[0135] Table 2

[0136]

[0137] The first stage thermal weight loss ratio refers to the ratio of the weight lost by the sample when the temperature rises from 100°C to 250°C to the initial weight of the sample. The second stage thermal weight loss ratio refers to the ratio of the weight lost by the sample when the temperature rises from 250°C to 300°C to the initial weight of the sample.

[0138] The weight loss of unpolymerized monomers is concentrated in the first stage of thermal weight loss. When entering the second stage of thermal weight loss, the weight change of the sample is mainly due to the weight loss of oligomers and the weight loss caused by the decomposition of polymers under high temperature.

[0139] According to Table 2 and Figure 2 From the comparison between Comparative Example 1 and Example 1, it can be seen that the first stage thermal weight loss ratio of Example 1 is lower, which shows that the monomer conversion rate of its polymerization process is higher. In addition, for the second stage thermal weight loss, the second stage thermal weight loss ratio of Example 1 is also lower than that of Comparative Example 1. Comparative Example 2 and Example 2, Comparative Example 3 and Example 3, Comparative Example 4 and Example 4, and Comparative Example 5 and Example 5 also have similar situations.

[0140] Half-Decomposition Temperature refers to the temperature at which the mass loss of a sample reaches 50% of its initial mass in a thermogravimetric analysis experiment. It can be used to evaluate the thermal stability of a material. The higher the half-decomposition temperature, the better the thermal stability of the material.

[0141] It can be seen from Table 2 that the samples of the present application examples have higher half-decomposition temperatures and better heat resistance. In addition, the half-decomposition temperatures of the polylactic acid samples of Examples 1-5 are all higher than those of the corresponding comparative examples, indicating that their heat resistance is improved compared to the comparative examples.

[0142] The above embodiments are only intended to introduce preferred embodiments of the present invention. For those skilled in the art, any obvious changes and improvements made without departing from the spirit of the present invention should be regarded as part of the present invention.

Claims

1. An acid binding agent for initiating a ring-opening polymerization reaction of a cyclic ester compound, comprising: Epoxides, The epoxy compounds include: Epoxy small molecule compounds, epoxy polymers or combinations thereof.

2. The acid binding agent according to claim 1, wherein The epoxy equivalent of the epoxy compound is 400 g / mol or less, preferably 350 g / mol or less; and / or The epoxy equivalent of the epoxy compound is 60 g / mol or more, preferably 80 g / mol or more.

3. The acid binding agent according to claim 1 or 2, wherein The boiling point of the epoxy small molecule compound under a standard atmospheric pressure is above 60° C., preferably above 80° C.

4. The acid binding agent according to any one of claims 1 to 3, wherein The epoxy small molecule compound includes: a glycidyl compound, an epoxycyclohexyl compound or a combination thereof; Preferably, The glycidyl compounds include glycidyl esters, glycidyl ethers or combinations thereof, preferably glycidyl methacrylate, diglycidyl tetrahydrophthalate, glycidyl acrylate, glycidyl acetate, glycidyl butyrate, glycidyl benzoate, glycidyl palmitate, glycidyl stearate, glycidyl oleate, glycidyl linoleate, diglycidyl 4,5-epoxytetrahydrophthalate, diglycidyl 1,2-cyclohexanedicarboxylate, glycidyl 4-tert-butylbenzoate, diglycidyl adipic acid, pentaerythritol tetraglycidyl ether, trimethylolpropane triglycidyl ether, neopentyl glycol diglycidyl ether, resorcinol diglycidyl ether or combinations thereof; and / or The epoxycyclohexyl compounds include epoxycyclohexane carboxylates, preferably 3,4-epoxycyclohexane carboxylic acid methyl ester, 3,4-epoxycyclohexyl methyl-3,4-epoxycyclohexyl carboxylate, bis((3,4-epoxycyclohexyl)methyl)adipate or a combination thereof.

5. The acid binding agent according to any one of claims 1 to 4, wherein The weight average molecular weight of the epoxy polymer is 200-10000 Da.

6. The acid binding agent according to any one of claims 1 to 5, wherein The epoxy polymer includes: epoxy-functionalized styrene-acrylate oligomer, epoxy resin or a combination thereof; Preferably, The epoxy functionalized styrene-acrylate oligomer comprises: ADR-4370S, ADR-4380, KL-E4370 or a combination thereof; and / or The epoxy resin includes: glycidyl ester epoxy resin, bisphenol A epoxy resin, bisphenol F epoxy resin, polyphenol glycidyl ether epoxy resin, aliphatic glycidyl ether epoxy resin, alicyclic epoxy resin or a combination thereof.

7. The acid binding agent according to any one of claims 1 to 6, wherein The cyclic ester compounds include: lactide, glycolide, ε-caprolactone, δ-valerolactone, β-butyrolactone, γ-butyrolactone, β-propiolactone, trimethylene carbonate, hydroxytrimethylene carbonate, chlorotrimethylene carbonate or a combination thereof, preferably lactide.

8. A method for ring-opening polymerization of a cyclic ester compound, comprising: In the presence of the acid binding agent according to any one of claims 1 to 7, the cyclic ester compound is subjected to a ring-opening polymerization reaction.

9. The method of claim 8, comprising: After mixing the cyclic ester compound and the acid binding agent, heating the reaction system to a molten state; Further increasing the temperature of the reaction system to allow the cyclic ester compound to undergo ring-opening polymerization; in, Before further increasing the temperature of the reaction system, a catalyst and / or an antioxidant may be optionally added into the system.

10. The method according to claim 8 or 9, wherein The cyclic ester compounds include: lactide, glycolide, ε-caprolactone, δ-valerolactone, β-butyrolactone, γ-butyrolactone, β-propiolactone, trimethylene carbonate, hydroxytrimethylene carbonate, chlorotrimethylene carbonate or a combination thereof, preferably lactide.

11. The method of claim 9, wherein: The cyclic ester compound is lactide, and the ring-opening polymerization reaction is carried out under one or more of the following conditions: (1) The weight ratio of the lactide to the acid binding agent is 100:(0.01-2.0); (2) The heating temperature for melting the reaction system is 100-200° C.; (3) The reaction system is maintained in a molten state for 0.01 to 6 hours; (4) the temperature of the reaction system is further increased by a gradient temperature increase, preferably, the gradient temperature increase is performed by increasing the temperature by 10° C. every 20-120 minutes; (5) The reaction temperature of the ring-opening polymerization of lactide is 100-250°C; (6) The reaction time of the ring-opening polymerization of lactide is 0.5-10 hours.

12. Use of the epoxy compound defined in any one of claims 1 to 6 for binding acid and / or initiating ring-opening polymerization of cyclic ester compounds.

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