Method for preparing polymerizable monomer, and polymerizable monomer

Abstract

A method for preparing a polymerizable monomer, and a polymerizable monomer, relating to the technical field of polymerizable monomer preparation. The method comprises the following step: under conditions for preparing a polymerizable monomer, reacting starting materials in the presence of a catalyst and a base solvent, wherein the temperature and pressure for preparing the polymerizable monomer are controlled such that the base solvent does not boil during reaction; at the temperature of 100°C, the solubility of the starting materials in the base solvent is not less than 10 g of starting materials per 100 g of solvent; and the boiling point of the base solvent is not less than 110°C. By means of the method, a solvent suitable for the reaction is selected, achieving good reaction continuity.

Description

Methods for preparing polymer monomers and polymer monomers

[0001] Cross-references to related applications

[0002] This application claims the benefit of Chinese patent applications 202510068780.1, 202510069020.2, and 202510068869.8, filed on January 16, 2025, the contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to the field of polymer monomer preparation technology, and specifically to a method for preparing polymer monomers and polymer monomers. Background Technology

[0004] Dimers such as polylactic acid (PLA) and polyglycolic acid (PGA) have excellent biodegradability and are environmentally friendly, capable of being completely degraded into CO2 and H2O by microorganisms in nature. Degradable materials such as PLA and PGA are widely used in packaging materials, industrial materials, medical materials, and agriculture.

[0005] Currently, in the preparation of products such as PLA and PGA, a large amount of water is generated directly from hydroxy acids, which inhibits the quality of the polymer products. Therefore, they are mainly prepared from dehydrated dimer lactone monomers, such as polylactic acid, which is prepared by the polymerization of lactide.

[0006] Currently, the main process for preparing lactide from lactic acid is a two-step method: lactic acid is polymerized to obtain oligolactic acid, which is then ring-opened to prepare lactide. This process is lengthy and requires high industrialization standards, resulting in high costs for monomeric lactide preparation and limiting the large-scale production and application of polylactic acid materials. In 2015, a one-step lactide preparation technique was reported in foreign literature. The reaction principle involves lactic acid and its dimer and trimer forms entering the pores of a catalyst such as a molecular sieve for selective catalysis, generating lactide. During the reaction, solvents such as toluene are used to remove water, thus achieving lactide preparation. This research is currently in the early stages of development, and there are no reports of industrial-scale applications.

[0007] The one-step lactic acid-to-lactide process currently faces several problems: First, water is generated during the lactic acid-to-lactide process, and lactide is highly susceptible to hydrolysis. If the water is not removed from the reaction system promptly, the reaction efficiency will drastically decrease. Current methods often employ azeotropic solvents to remove water. However, this approach is problematic because the boiling point and azeotropic temperature of the solvent are difficult to control. Furthermore, the azeotropic temperature between the solvent and water is fixed, thus limiting the reaction temperature, which is often difficult to adjust. This azeotropic temperature also tends to be difficult to align with the optimal reaction temperature of the catalyst. Second, due to the inherent acidity of lactic acid and the acidity of the catalyst, the one-step lactic acid-to-lactide process readily undergoes polymerization, generating a significant amount of polylactic acid (PLA). While PLA is difficult to convert into lactide, current methods often employ stirring in the reaction vessel to disperse lactic acid into the solvent system and reduce PLA generation. However, this method is difficult to implement for continuous production. Moreover, current methods cannot prevent the PLA generated from adhering to the catalyst surface, leading to catalyst carbon buildup and decreased reaction activity. Third, the one-step preparation of lactide from lactic acid mainly uses molecular sieve catalysts. The important active component in molecular sieves is aluminum. In the process of lactic acid reaction to produce lactide, there are acid, water, heat and other environments. Molecular sieves are prone to aluminum loss and deactivation under such environments, resulting in a decrease in catalyst life and activity.

[0008] In the article "Controlled Synthesis of L-Lactide Using Sn-Beta Zeolite Catalysts in a One-Step Route", Nanjing University used a one-step liquid-phase method to prepare lactide from lactic acid. The method uses a stirring reactor, which disperses lactic acid into the solvent system and reduces the amount of lactic acid polymers generated. However, this reaction process can only be carried out in batches and is difficult to achieve continuous production.

[0009] CN114853719A uses organic solvents as reaction solvents, such as ethers, ketones, hydrocarbons, and alcohols. It utilizes the azeotropic reaction of the organic solvent and water to remove the generated water from the reaction system. It also employs a packing material to achieve continuous operation. However, the boiling point and azeotropic temperature of the azeotropic solvent are difficult to control, making it difficult to maintain the overall reaction temperature and reach the optimal reaction temperature for the molecular sieve. Furthermore, the addition of a single azeotropic solvent results in insufficient solubility with lactic acid, making it impossible to prevent the formation of polylactic acid that adheres to the catalyst, causing a decrease in reaction efficiency. The addition of salts and physical dehydrators further complicates subsequent processing. Additionally, the catalyst-packing scheme cannot directly address the contact reaction between generated water and lactide within the reaction system.

[0010] CN112574165A discloses a one-step conversion method for producing lactide, which uses tin oxides and activated clay catalysts for the reaction. However, the one-step lactide preparation article "Shape-selective zeolite catalysis for bioplastics production" published in the journal Science in 2015 and subsequent studies by researchers have shown that efficient one-step lactide preparation requires the shape-selective effect of molecular sieves. Catalysts without shape-selective effect have poor reaction performance. Conventional two-step lactide preparation catalysts cannot achieve efficient one-step lactide production and continuous production. Summary of the Invention

[0011] To address the aforementioned shortcomings in the preparation of existing polymeric monomers, such as cyclic polymeric monomers, particularly lactide, this invention provides a method for preparing polymeric monomers and the polymeric monomers themselves. The method provided by this invention selects a suitable solvent for this reaction, achieving better continuous reaction performance.

[0012] Through research on methods for preparing polymerizable monomers, particularly the one-step preparation of lactide from lactic acid, the inventors discovered that if a solvent with a certain solubility in the raw materials and a high boiling point is used to provide a liquid reaction environment, the reaction will no longer be limited by the azeotropic temperature, and the raw materials can be highly dispersed, improving the reaction efficiency; and it will no longer be necessary to rely on stirring, which is conducive to achieving continuous reaction.

[0013] The first aspect of the present invention provides a method for preparing a polymeric monomer, the method comprising the following steps: reacting raw materials under conditions for preparing the polymeric monomer, in the presence of a catalyst and a base solvent, wherein the temperature and pressure for preparing the polymeric monomer are such that the base solvent does not boil during the reaction, and at a temperature of 100°C, the solubility of the raw material in the base solvent is not less than 10g of raw material / 100g of solvent; and the boiling point of the base solvent is not less than 110°C.

[0014] Preferably, the raw material contains hydroxyl and carboxyl groups; the reaction causes the hydroxyl and carboxyl groups in the raw material to undergo an esterification reaction.

[0015] Preferably, the base solvent contains at least one of oxygen, nitrogen, sulfur and chlorine.

[0016] Preferably, the base solvent is selected from at least one of benzophenone, dihydro-L-glucanone, N-methylpyrrolidone, trichloropropane, and sulfolane.

[0017] The method provided by this invention uses a base solvent with a high boiling point and high solubility for the raw materials, departing from the azeotropic reaction system of existing technologies. The selectable reaction temperature is no longer determined by the azeotropic temperature of the solvent and water. Therefore, the reaction temperature can be better matched with the selected catalyst, providing a technical basis for obtaining better reaction results in the preparation of polymerizable monomers. Simultaneously, the base solvent is a polar, inert, high-boiling-point solvent capable of dissolving lactic acid / polylactic acid, avoiding polylactic acid precipitation and adhesion, and slowing down catalyst deactivation. Furthermore, since the base solvent can dissolve the raw materials, the reaction can increase the raw material concentration, enhancing reaction efficiency while reducing subsequent separation costs. Detailed Implementation

[0018] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0019] The first aspect of the present invention provides a method for preparing a polymeric monomer, the method comprising the following steps: reacting raw materials under conditions for preparing the polymeric monomer, in the presence of a catalyst and a base solvent, wherein the temperature and pressure for preparing the polymeric monomer are such that the base solvent does not boil during the reaction, and at a temperature of 100°C, the solubility of the raw material in the base solvent is not less than 10g of raw material / 100g of solvent; and the boiling point of the base solvent is not less than 110°C.

[0020] In this invention, the temperature and pressure used to prepare the monomers so that the base solvent does not boil during the reaction means that, under the reaction conditions, the base solvent does not reach its boiling point. Those skilled in the art can achieve this control using conventional techniques, such as selecting a high-boiling-point solvent and choosing appropriate reaction temperatures and pressures.

[0021] The temperature and pressure used to prepare the monomer ensured that the base solvent did not boil during the reaction, which can be confirmed by nuclear magnetic resonance (NMR) monitoring. There was no solvent loss due to volatilization during the reaction.

[0022] In this invention, unless otherwise specified, the boiling point of various solvents refers to the boiling point at normal pressure (101.3 kPa); the boiling point is determined by the general method for determining the boiling point of chemical reagents in GB / T 616-2006.

[0023] According to a preferred embodiment of the present invention, at a temperature of 100°C, the solubility of the base solvent in the raw material is not less than 20g raw material / 100g solvent, preferably not less than 30g raw material / 100g solvent, for example, 30g raw material / 100g solvent, 40g raw material / 100g solvent, 50g raw material / 100g solvent, 60g raw material / 100g solvent, 70g raw material / 100g solvent, 80g raw material / 100g solvent, 90g raw material / 100g solvent, 100g raw material / 100g solvent, or 120g raw material / 100g solvent, etc.

[0024] In this invention, the solubility refers to the maximum amount of 100 wt% of the raw material (e.g., lactic acid or glycolic acid) that is miscible in the base solvent at 1 atmosphere and 100°C.

[0025] According to a preferred embodiment of the present invention, under the conditions for preparing the polymerizable monomer, the base solvent and the raw material do not undergo a chemical reaction. This preferred embodiment is more conducive to ensuring the stable performance of the solvent and enables the continuous execution of the method.

[0026] It should be noted that "no chemical reaction" as described in this invention does not mean that no reaction occurs at all, but rather that the base solvent is inert in the reaction system and no obvious chemical reaction occurs; it can also be understood as the reaction products having no or very small amounts of byproducts that affect the properties of the product due to the reaction of the base solvent.

[0027] The method provided by this invention is applicable to the preparation of different polymeric monomers. This invention does not specifically limit the polymeric monomers; they can be defined according to conventional definitions in the art. Specifically, the polymeric monomers described in this invention refer to small molecule compounds capable of polymerizing with the same or other molecules, serving as low-molecular-weight raw materials for polymer synthesis. For example, lactide is a polymeric monomer for producing polylactic acid, and glycolide is a polymeric monomer for producing polyglycolic acid. The polymeric monomers described in this invention can have linear or branched structures, or cyclic structures.

[0028] During the research process, the inventors of this invention discovered that the method provided by this invention is more suitable for the preparation of cyclic polymer monomers. Preferably, the polymer monomer is cyclic, more preferably glycolide and / or lactide, and most preferably lactide.

[0029] According to the present invention, preferably, the raw material contains hydroxyl and carboxyl groups; and / or, the reaction causes the hydroxyl and carboxyl groups in the raw material to undergo an esterification reaction.

[0030] According to the present invention, preferably, the reaction causes the raw material molecules to cyclize into a cyclic structure.

[0031] The method provided by this invention uses the above-mentioned preferred raw materials or performs the above-mentioned preferred reaction, and uses a base solvent with specific properties to provide a liquid environment that is completely miscible with the reactants, such as lactic acid. On the one hand, this increases the contact between the raw materials and the catalyst, making the reaction more complete, reducing the formation of by-product polymers such as polylactic acid, and increasing the selectivity of polymer monomers such as lactide. On the other hand, since the polymers such as polylactic acid are also soluble in the selected base solvent, the adhesion of the polymers such as polylactic acid to the catalyst can be reduced, the effect of catalyst deactivation caused by carbon deposition can be reduced, and the catalyst life can be improved.

[0032] According to a preferred embodiment of the present invention, the raw material is selected from at least one of glycolic acid, lactic acid and methyl glycolate, preferably glycolic acid and / or lactic acid, and more preferably lactic acid.

[0033] The method provided by this invention is particularly suitable for the one-step preparation of lactide from lactic acid. This invention does not particularly limit the type and source of lactic acid. Preferably, the lactic acid is selected from at least one of D-lactic acid and L-lactic acid. Depending on the source, the lactic acid raw material may also contain water, lactic acid dimers, or polymers.

[0034] Preferably, the lactic acid is lactic acid with a mass concentration of 30%-120%, and more preferably lactic acid with a mass concentration of 50%-100% as a reaction raw material. This preferred embodiment can balance the reaction effect and the high raw material throughput.

[0035] In this invention, unless otherwise specified, the definition of lactic acid concentration refers to the national standard GB / T 23877-2009, Determination of citric acid, fumaric acid and lactic acid in feed acidifiers by high performance liquid chromatography.

[0036] According to a preferred embodiment of the present invention, the boiling point of the base solvent is not lower than 120°C, preferably 140-400°C, for example 140°C, 160°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 320°C, 340°C, 360°C, 380°C, or 400°C.

[0037] According to a preferred embodiment of the present invention, the base solvent contains at least one of oxygen, nitrogen, sulfur, and chlorine. The presence of at least one of oxygen, nitrogen, sulfur, and chlorine is more conducive to ensuring a better solvation effect between the base solvent and the raw materials. Furthermore, in the preferred embodiment, when combined with the auxiliary solvent, it can achieve high raw material solubility and a high raw material reaction conversion rate while maintaining a low addition amount.

[0038] According to a preferred embodiment of the present invention, the base solvent is selected from at least one of benzophenone, dihydro-L-glucanone, N-methylpyrrolidone, trichloropropane, and sulfolane. The inventors of the present invention discovered during their research that the above-mentioned types of base solvents are more suitable for the preparation of polymeric monomers, particularly glycolide and / or lactide.

[0039] Benzophenone, dihydro-L-glucanone, N-methylpyrrolidone, trichloropropane, and sulfolane are miscible with 100 wt% lactic acid and glycolic acid at 100 °C.

[0040] Preferably, the amount of the base solvent relative to 1g of the raw material is 0.5-50mL, more preferably 1-30mL, for example 1mL, 5mL, 10mL, 15mL, 20mL, 25mL, or 30mL. The method provided by this invention has a good solvation effect between the base solvent and the raw material, achieving high raw material solubility with a low addition amount and a high reaction conversion rate.

[0041] During the research, the inventors further discovered that because some solvents containing soluble raw materials are highly polar, their interaction with the raw materials is too strong. Due to the strong solvation effect, the resistance to the raw materials entering the catalyst reaction channels is too high. Although continuous operation can be achieved, the desired reaction effect is not achieved to some extent, and the product yield needs further improvement. To address this problem, the inventors further analyzed and found that adding a certain amount of non-polar or weakly polar solvent with a lower boiling point than the base solvent to the base solvent can weaken the interaction between the raw materials and the main solvent. This can further improve the reaction conversion rate and product selectivity, and also achieve water removal, which is more conducive to the separation of subsequent products. According to a more preferred embodiment of the present invention, the reaction system further contains an auxiliary solvent, wherein the solubility of the raw material in the auxiliary solvent at 100°C is no greater than 5g of raw material / 100g of auxiliary solvent; the boiling point difference between the base solvent and the auxiliary solvent is 10°C or more, preferably 20°C or more, more preferably 30-250°C, for example 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C.

[0042] The method proposed in this invention, within its reaction system, preferably utilizes a specific combination of solvents to deviate from the azeotropic reaction system inherent in existing technologies for the preparation of polymeric monomers. This achieves high dispersion of raw materials, prevents polymer adhesion to the catalyst, and ensures appropriate interaction forces between the raw materials and the combined solvent, thereby improving the efficiency of the raw materials entering the catalyst channels for reaction, increasing conversion rate and monomer yield. Simultaneously, since the base solvent can dissolve both reactants and products, the reaction can increase the reactant concentration in the raw materials, enhancing reaction efficiency while reducing subsequent separation costs. Furthermore, the solvents selected in this invention can include water-repellent solvents and solvents with varying boiling points, which to some extent reduces the impact of water-induced aluminum loss on catalyst activity and allows for control of the reaction temperature. This enables one-step preparation of polymeric monomers, yielding high-yield products, and also allows for continuous production.

[0043] The present invention has a wide range of choices for the types of auxiliary solvents. Preferably, the auxiliary solvent is selected from at least one of substituted or unsubstituted C4-C12 alkanes and substituted or unsubstituted C6-C20 (preferably C6-C15) aromatics.

[0044] According to the present invention, "substituted" in "substituted or unsubstituted" means containing a substituent, which may be selected from halogen, hydroxyl, C1-C6 alkyl, halogenated C1-C6 alkyl, C1-C6 alkoxy or halogenated C1-C6 alkoxy.

[0045] In this invention, the alkyl group (such as C1-C6 alkyl) may be selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, isopentyl, n-hexyl, isohexyl or 3,3-dimethylbutyl.

[0046] In this invention, the alkoxy group (such as C1-C6 alkoxy) may be selected from methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, n-pentoxy, isopentoxy, n-hexyloxy, isohexyloxy, or 3,3-dimethylbutoxy.

[0047] In this invention, the halogen is selected from fluorine, chlorine, bromine or iodine.

[0048] According to the present invention, the alkane can be a chain alkane (straight chain or branched chain) or a cycloalkane.

[0049] In this invention, the C4-C12 alkane can be at least one of butane, pentane, hexane (n-hexane), heptane, octane, and cyclohexane.

[0050] In this invention, the aromatic hydrocarbon (such as C6-C20 aryl or C6-C15 aryl) may be selected from at least one of benzene, toluene, xylene and trimethylbenzene.

[0051] According to a preferred embodiment of the present invention, the auxiliary solvent is selected from at least one of benzene, toluene, cyclohexane, n-hexane, xylene, and trimethylbenzene.

[0052] Benzene, toluene, cyclohexane, n-hexane, xylene, and trimethylbenzene have a solubility of less than 5 g of raw material per 100 g of auxiliary solvent at 100 °C for 100% by weight of lactic acid.

[0053] The amount of the base solvent and the auxiliary solvent in this invention can be selected within a wide range and can be appropriately adjusted according to the raw material conditions, with the goal of achieving continuous reaction. Preferably, the volume ratio of the base solvent to the auxiliary solvent is 1:0.1-20, more preferably 1:0.5-5, for example 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, or any range between the two.

[0054] According to the present invention, the specific conditions for the reaction can be selected over a wide range, and can be appropriately matched according to the types of raw materials and solvents. Preferably, the reaction conditions include: a temperature of 80-200°C and a pressure of -0.1 to 6 MPa. More preferably, the temperature is 100-170°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C or 170°C, and the pressure is -0.01-1 MPa.

[0055] According to the present invention, preferably, the method further includes, during the reaction, introducing an inert gas and / or a low-boiling-point inert solvent into the reaction system to carry away the water generated in the reaction from the reaction system.

[0056] In this invention, the low-boiling-point inert solvent, also known as the aqueous solvent, rapidly removes water from the reaction system by azeotropically reacting with the water generated in the reaction, thus avoiding the hydrolysis of the generated product, such as lactide, and is more conducive to improving the yield of the product, such as lactide.

[0057] In this invention, preferably, the low-boiling-point inert solvent is a solvent that can vaporize after being introduced into the reaction system at the given temperature and pressure. More preferably, the low-boiling-point inert solvent is selected from at least one of benzene, toluene, methane, and butane.

[0058] In this invention, the types of low-boiling-point inert solvents (aqueous solvents) and auxiliary solvents partially overlap. It should be noted that in this invention, if no inert gas or vaporized benzene or toluene is introduced into the reaction system to remove the water generated during the reaction, then the benzene and toluene in the system are considered low-boiling-point inert solvents (aqueous solvents); if benzene and toluene are present in the solvent of the reaction system, and an inert gas or vaporized benzene or toluene is introduced, then the benzene and toluene present in the solvent are considered auxiliary solvents, and the benzene and toluene introduced after vaporization are considered low-boiling-point inert solvents (aqueous solvents).

[0059] Preferably, the inert gas is selected from at least one of nitrogen, argon, helium, neon, krypton, and xenon.

[0060] This invention does not impose any particular limitations on the amount or method of adding the inert gas or low-boiling-point inert solvent, as long as it can carry the water generated in the reaction out of the reaction system. Those skilled in the art can make adaptive choices based on the actual reaction conditions.

[0061] In this invention, the low-boiling-point inert solvent can be mixed with the base solvent and optional auxiliary solvent and then placed in the reaction system, or the low-boiling-point inert solvent can be vaporized first and then introduced into the reaction system. Preferably, the low-boiling-point inert solvent is vaporized first and then introduced into the reaction system.

[0062] This invention does not particularly limit the type of catalyst, and can be any catalyst conventionally used in the art capable of preparing polymer monomers. The catalyst is preferably a solid acid catalyst, such as a molecular sieve catalyst. The molecular sieve catalyst may contain all-silica molecular sieves or silica-alumina molecular sieves. Optionally, the molecular sieve catalyst may also contain a binder. There are no particular requirements regarding the type and content of the binder, which includes, but is not limited to, silica and alumina. Based on the total amount of the molecular sieve catalyst, the molecular sieve content is preferably 50-100% by mass, and the binder content is preferably 0-50% by mass; more preferably, the molecular sieve content is preferably 60-100% by mass, and the binder content is 0-40% by mass.

[0063] According to a preferred embodiment of the present invention, the silicon-aluminum molar ratio of the catalyst is 5-80, preferably 10-50, for example 10, 15, 20, 25, 30, 35, 40, 45 or 50.

[0064] According to a preferred embodiment of the present invention, the catalyst is at least one of a β-zeolite catalyst, a mesoporous zeolite catalyst, and a zeolite catalyst supported on a Sn metal component.

[0065] The present invention does not impose a particular limitation on the amount of catalyst used, and can use a conventional selection in the art. Those skilled in the art can make an adaptive selection based on the specific raw materials and the reactions involved.

[0066] The method can be carried out continuously (e.g., using a shaped catalyst, in a catalytic distillation reactor) or intermittently (e.g., in a reaction vessel).

[0067] Preferably, when the method is performed continuously, the mass hourly space velocity (MHSV) of the raw material is 0.1-2 h⁻¹. -1 .

[0068] Preferably, when the method is performed intermittently, the mass ratio of the raw material to the catalyst is 1:0.1-10.

[0069] According to the present invention, preferably, when the method is carried out continuously, the residence time of the reaction is 0.5-10 hours.

[0070] According to the present invention, preferably, when the method is performed intermittently, the reaction time is 0.1-10 hours.

[0071] According to a preferred embodiment of the present invention, a method for preparing lactide is provided, the method comprising: mixing lactic acid raw material with a solvent (i.e., the base solvent mentioned above) and contacting it with a catalyst, and reacting the lactic acid at 80-200°C and -0.1-6 MPa pressure to generate lactide, wherein the solvent comprises at least one selected from benzophenone, dihydro-L-glucanone, N-methylpyrrolidone, trichloropropane and sulfolane, and the reaction temperature and pressure are such that the solvent does not boil in the reaction system.

[0072] According to another preferred embodiment of the present invention, a method for preparing lactide from lactic acid in a one-step reaction is provided. Lactic acid raw material is mixed with a solvent and contacted with a catalyst. The lactic acid undergoes a dehydration reaction to generate lactide at 80-200°C and -0.1-6 MPa pressure. The solvent comprises solvent I and solvent II. Solvent I is selected from at least one of benzophenone, dihydro-L-glucanone, N-methylpyrrolidone, trichloropropane, and sulfolane. Solvent II is a C4-C12 alkane, substituted alkane, aromatic hydrocarbon, or substituted aromatic hydrocarbon. The solubility of lactic acid in solvent II at room temperature is not greater than 1 g lactic acid / 100 g solvent. Furthermore, the reaction temperature and pressure prevent solvent I from boiling in the reaction system.

[0073] According to another preferred embodiment of the present invention, a method for one-step preparation of lactide from liquid-phase lactic acid is provided. The method includes: mixing lactic acid raw material with at least one solvent selected from benzophenone and dihydro-L-glucanone (i.e., the base solvent mentioned above), contacting it with a catalyst, and reacting the lactic acid to generate lactide at 80-200°C and -0.1-6 MPa pressure, wherein the reaction temperature and pressure prevent the reaction system from boiling, and simultaneously introducing an inert gas or a low-boiling-point inert solvent into the reaction system to carry away the generated water from the reaction system.

[0074] According to another preferred embodiment of the present invention, a method for one-step preparation of lactide from liquid-phase lactic acid is provided. The method includes: mixing lactic acid raw material with at least one solvent selected from N-methylpyrrolidone and sulfolane (i.e., the base solvent mentioned above), contacting it with a catalyst, and reacting the lactic acid to generate lactide at 80-200°C and -0.1-6 MPa pressure, wherein the reaction temperature and pressure prevent the reaction system from boiling, and simultaneously introducing an inert gas or a low-boiling-point inert solvent into the reaction system to carry away the generated water from the reaction system.

[0075] Furthermore, in the preparation of lactide, the inventors discovered through screening conventional polar solvents that, to avoid reaction with lactic acid in the raw materials and lactide in the product, conventional alcohols and acids are not suitable for this reaction. Existing ethers and ketones, while generally weakly polar, allow the reaction to proceed smoothly, but their effectiveness has significant room for improvement. According to a preferred embodiment of the present invention, the solvent in the reaction system does not contain alcohols or acids.

[0076] A second aspect of the present invention provides a polymeric monomer prepared by the above method.

[0077] The following examples further illustrate the solution and effects of the present invention.

[0078] In the following examples and comparative examples, commercially available Beta molecular sieve powder with a silicon-to-aluminum molar ratio of 30 was used as the catalyst. The catalyst contained 70% by weight of molecular sieve and 30% by weight of alumina. The products after the reaction were analyzed by liquid chromatography to calculate the lactic acid conversion rate and lactide yield.

[0079] In Examples 1-17 and Comparative Example 1, intermittent reactions were carried out:

[0080] Example 1

[0081] A 100 mL mixed solvent, consisting of benzophenone and toluene in a 1:1 volume ratio, and a 100 wt% lactic acid solution were used. 5 g of lactic acid was added, and the mixture was placed in a 250 mL three-necked flask. 10 g of catalyst was added, and the system was heated in an external oil bath. A temperature measuring point was set inside the three-necked flask to determine the reaction temperature. A condenser and separator were installed at the top of the three-necked flask. After condensation, the toluene was separated from the water and then refluxed back into the reactor for further reaction. The reactor pressure was 0.1 MPa. At this reaction temperature and pressure, benzophenone did not boil.

[0082] Three hours later, the reaction product was sampled and mixed with acetonitrile at a mass ratio of 1:1 before being analyzed by liquid chromatography. The results of lactic acid conversion and lactide yield are shown in Table 1.

[0083] Example 2

[0084] Except for using an 88wt% lactic acid solution and adding 5g of lactic acid by weight, the rest is the same as in Example 1.

[0085] Example 3

[0086] Except for using an 88wt% lactic acid solution and adding 10g of lactic acid by weight, the rest is the same as in Example 1.

[0087] Example 4

[0088] Except for using an 88wt% lactic acid solution and adding 50g of lactic acid by weight, the rest is the same as in Example 1.

[0089] Example 5

[0090] Except for using a 50wt% lactic acid solution and adding 5g of lactic acid by weight, the rest is the same as in Example 1.

[0091] Example 6

[0092] A mixed solvent of 100 mL (1:1 volume ratio of benzophenone and toluene) was used. The lactic acid solution concentration was 88 wt%. 5 g of lactic acid was added by weight and placed in a 250 mL three-necked flask. 10 g of catalyst was added, and the system was heated in an external oil bath. A temperature measuring point was set inside the three-necked flask to determine the reaction temperature. A condenser and separator were installed at the top of the three-necked flask. After condensation, the toluene was separated from the water and then refluxed back into the reactor for further reaction. Nitrogen gas was introduced into the bottom of the flask at a flow rate of 20 mL / min, and the pressure inside the reactor was 0.1 MPa. After three hours, the reaction product was sampled and mixed with acetonitrile in a 1:1 ratio for liquid chromatography analysis. The lactic acid conversion rate and lactide yield are shown in Table 1.

[0093] Example 7

[0094] The method is the same as in Example 6, except that the nitrogen gas is replaced by toluene liquid vaporized at a rate of 1 mL / min.

[0095] Example 8

[0096] Lactic acid with a concentration of 88 wt% was used, with 5 g of lactic acid added based on the weight of lactic acid. The mixed solvent was a mixture of toluene and benzophenone in a volume ratio of 1:0.5. Other aspects were the same as in Example 1.

[0097] Example 9

[0098] Except for using lactic acid with a concentration of 88wt% and adding 50g of lactic acid by weight, everything else is the same as in Example 8.

[0099] Example 10-1

[0100] Except for the reaction temperature (see Table 1), everything else is the same as in Example 8.

[0101] Example 10-2

[0102] Except for the reaction temperature (see Table 1), everything else is the same as in Example 8.

[0103] Example 11

[0104] A 100 mL mixed solvent, consisting of benzophenone and toluene in a 1:3 volume ratio, and a glycolic acid solution with a concentration of 70 wt%, was used. 3 g of glycolic acid was added by weight and placed in a 250 mL three-necked flask. 10 g of catalyst was added, and the system was heated in an external oil bath. A temperature measuring point was set inside the three-necked flask to determine the reaction temperature. A condenser and separator were installed at the top of the three-necked flask. After condensation, the toluene was separated from the water and then refluxed back into the reactor for further reaction. Nitrogen gas was introduced at a flow rate of 20 mL / min through the bottom of the flask, and the pressure inside the reactor was 0.1 MPa. After three hours, the reaction product was sampled, and the sampled product was mixed with acetonitrile in a 1:1 ratio for liquid chromatography analysis. The glycolic acid conversion rate and glycolide yield are shown in Table 1.

[0105] Example 12

[0106] A mixed solvent of 100 mL sulfolane and toluene (volume ratio 1:1) was used. The lactic acid solution concentration was 100 wt%. 5 g of lactic acid was added by weight and placed in a 250 mL three-necked flask. 10 g of catalyst was added, and the system was heated in an external oil bath. A temperature measuring point was set inside the three-necked flask to determine the reaction temperature. A condenser and separator were installed at the top of the three-necked flask. After condensation, the toluene was separated from the water and then refluxed back into the reactor for further reaction. The pressure inside the reactor was 0.1 MPa. After three hours, the reaction product was sampled, and the sampled product was mixed with acetonitrile in a 1:1 ratio and analyzed by liquid chromatography. The lactic acid conversion rate and lactide yield are shown in Table 1.

[0107] Example 13

[0108] Lactic acid with a concentration of 88 wt% was used, with 5 g of lactic acid added based on the weight of lactic acid. The mixed solvent was a mixture of toluene and sulfolane in a volume ratio of 1:0.5. Other aspects were the same as in Example 12.

[0109] Example 14

[0110] The method used 50wt% lactic acid, with 5g of lactic acid added by weight. The mixed solvent was a mixture of toluene and sulfolane in a volume ratio of 1:0.5. Other aspects were the same as in Example 12.

[0111] Example 15

[0112] Lactic acid with a concentration of 88 wt% was used, and 50 g of lactic acid was added based on the weight of lactic acid. The mixed solvent was a mixture of toluene and sulfolane in a volume ratio of 1:0.5. Other aspects were the same as in Example 12.

[0113] Comparative Example 1

[0114] Except for using 100 mL toluene as the solvent, everything else is the same as in Example 1.

[0115] Example 16

[0116] Except for using 100 mL benzophenone as the solvent and passing nitrogen gas at a rate of 20 mL / min through the bottom of the flask as a dehydrating agent, everything else was the same as in Example 1.

[0117] Example 17

[0118] Except for using 100 mL sulfolane as the solvent and passing nitrogen gas at a rate of 20 mL / min through the bottom of the flask as a dehydrating agent, the process was the same as in Example 12.

[0119] Table 1

[0120] Continuous reaction tests were conducted in Examples 18-27 and Comparative Example 2:

[0121] The continuous reaction test was carried out in a catalytic distillation unit. The catalyst was loaded in the middle of the catalytic distillation unit with a loading amount of 200 mL. The feed was fed from the top of the catalyst bed and discharged from the bottom. The residence time in the reactor was 3 h. A water-carrying agent was introduced into the bottom of the reactor. If the water-carrying agent was in the liquid phase, it was vaporized by the vaporizer and then entered the reactor. The water-carrying agent and water were discharged from the top outlet of the reactor.

[0122] Example 18

[0123] The mixed solvent was a mixture of toluene and sulfolane in a volume ratio of 1:0.5. A lactic acid solution with a concentration of 88 wt% was used. The reaction feedstock was prepared at a ratio of 10 g lactic acid / 100 mL mixed solvent, based on the weight of the lactic acid. The reaction was carried out using the aforementioned continuous reaction apparatus. The space velocity of the lactic acid feed (based on 100 wt% lactic acid) relative to the catalyst was 0.3 h⁻¹. -1 Temperature measurement points were set inside the reactor to determine the reaction temperature of the system. The pressure was 0.1 MPa. Nitrogen gas was introduced into the bottom at a rate of 20 mL / min to carry water. Samples were taken at the 5th hour of the reaction. The sampled products were mixed with acetonitrile in a 1:1 ratio and analyzed by liquid chromatography. The lactic acid conversion rate and lactide yield at different reaction times are shown in Table 2.

[0124] Example 19

[0125] The mixed solvent is a mixture of cyclohexane and sulfolane in a volume ratio of 1:1. The dehydrating agent is cyclohexane heated to vapor. The liquid phase cyclohexane is introduced at a rate of 1 mL / min and enters the bottom of the reactor after vaporization. Other aspects are the same as in Example 18.

[0126] Example 20

[0127] The mixed solvent is a mixture of n-hexane and sulfolane in a volume ratio of 1:1. The dehydrating agent is n-hexane that is heated to vapor. The liquid phase n-hexane is introduced at a rate of 1 mL / min and enters the bottom of the reactor after vaporization. Other aspects are the same as in Example 18.

[0128] Example 21

[0129] The mixed solvent was a mixture of p-xylene and sulfolane in a volume ratio of 1:0.5. The reaction temperature is shown in Table 2, and other conditions are the same as in Example 18.

[0130] Example 22

[0131] The mixed solvent was a mixture of trimethylbenzene and sulfolane in a volume ratio of 1:0.5. The reaction temperature is shown in Table 2, and other conditions are the same as in Example 18.

[0132] Example 23

[0133] The mixed solvent was a mixture of toluene and dihydrolevulinolone in a volume ratio of 1:0.5. The reaction temperature is shown in Table 2, and other conditions are the same as in Example 18.

[0134] Example 24

[0135] The mixed solvent was a mixture of toluene and N-methylpyrrolidone in a volume ratio of 1:0.5. The reaction temperature is shown in Table 2, and other conditions are the same as in Example 18.

[0136] Example 25

[0137] The mixed solvent was a mixture of toluene and trichloropropane in a volume ratio of 1:0.5. The reaction temperature is shown in Table 2, and other conditions are the same as in Example 18.

[0138] Example 26

[0139] The mixed solvent is a 1:1 volume ratio mixture of benzophenone and toluene. A lactic acid solution with a concentration of 88 wt% was used. The reaction feedstock was prepared at a ratio of 10 g lactic acid per 100 mL of the mixed solvent, based on the weight of the lactic acid. The reaction was carried out using the aforementioned continuous reaction apparatus, with a feed space velocity relative to the catalyst of 0.3 h⁻¹. -1 Temperature measurement points were set inside the reactor to determine the reaction temperature of the system. The pressure was 0.1 MPa. Nitrogen gas carrying water was introduced into the bottom at a rate of 20 mL / min. Samples were taken at 5, 100 and 1000 hours of reaction. The sampled products were mixed with acetonitrile in a 1:1 ratio and analyzed by liquid chromatography. The lactic acid conversion rate and lactide yield at different reaction times are shown in Table 2.

[0140] Example 27

[0141] The mixed solvent is a mixture of sulfolane and p-xylene in a 1:1 volume ratio. A lactic acid solution with a concentration of 88 wt% was used. The reaction feedstock was prepared at a ratio of 10 g lactic acid / 100 mL mixed solvent, based on the weight of the lactic acid. The reaction was carried out using the aforementioned continuous reaction apparatus, with a feed space velocity relative to the catalyst of 0.3 h⁻¹. -1 Temperature measurement points were set inside the reactor to determine the reaction temperature of the system. The pressure was 0.1 MPa. Toluene with water was introduced into the bottom at a rate of 2 mL / min. Samples were taken at 5, 100 and 1000 hours of reaction. The sampled products were mixed with acetonitrile in a 1:1 ratio and analyzed by liquid chromatography. The lactic acid conversion rate and lactide yield at different reaction times are shown in Table 2.

[0142] Comparative Example 2

[0143] Unlike Example 24, the solvent was pure toluene, and the concentrations of the reactants and reaction conditions were the same as in Example 24. Because the external oil bath temperature was much higher than the boiling point of toluene, the reaction system was in a boiling state, and the toluene in the system could remove water; therefore, no other dehydrating agent was introduced. Samples were taken at 5 and 100 hours of reaction, and the samples were mixed with acetonitrile in a 1:1 ratio and analyzed by liquid chromatography. The lactic acid conversion rate and lactide yield at different reaction times are shown in Table 2.

[0144] Table 2

[0145] In Examples A1-A13, a single solvent was used, and the reaction was carried out in batches:

[0146] Example A1

[0147] Using 100 mL of benzophenone as solvent, the lactic acid solution concentration was 100 wt%. 5 g of lactic acid was added by weight and placed in a 250 mL three-necked flask. 10 g of catalyst was added, and a temperature measuring point was set inside the three-necked flask to determine the reaction temperature of the system. Nitrogen gas was introduced into the bottom of the three-necked flask at a rate of 20 mL / min, and the pressure inside the reactor was 0.1 MPa. After three hours, the reaction product was sampled, and the sampled product was mixed with acetonitrile in a 1:1 ratio and analyzed by liquid chromatography. The results of lactic acid conversion and lactide yield are shown in Table 3.

[0148] Example A2

[0149] Except that the concentration of lactic acid raw material is 88wt%, and 5g of lactic acid is added based on the weight of lactic acid, everything else is the same as in Example A1.

[0150] Example A3

[0151] Except that the concentration of lactic acid raw material is 50wt%, and 5g of lactic acid is added based on the weight of lactic acid, everything else is the same as in Example A1.

[0152] Example A4

[0153] Except for adding 10g of lactic acid by weight, the rest is the same as in Example A2.

[0154] Example A5

[0155] Except for adding 20g of lactic acid by weight, the rest is the same as in Example A2.

[0156] Example A6

[0157] Except for introducing 1 mL / min of n-hexane into the bottom of the Erlenmeyer flask instead of nitrogen as a dehydrating agent, everything else is the same as in Example A2.

[0158] Example A7

[0159] Except for adding 50g of lactic acid by weight, the rest is the same as in Example A2.

[0160] Example A8

[0161] The reaction temperature is shown in Table 3, and the other conditions are the same as in Example A2.

[0162] Example A9

[0163] The reaction temperature is shown in Table 3, and the other conditions are the same as in Example A2.

[0164] Example A10

[0165] Except for replacing the solvent with 100 mL of dihydro-L-glucosamine, everything else is the same as in Example A2.

[0166] Example A11

[0167] 100 mL of sulfolane was used as the solvent, and the lactic acid solution concentration was 100 wt%. 5 g of lactic acid was added by weight and placed in a 250 mL three-necked flask. 10 g of catalyst was added, and a temperature measuring point was set inside the three-necked flask to determine the reaction temperature of the system. Nitrogen gas was introduced into the bottom of the three-necked flask at a rate of 20 mL / min, and the pressure inside the reactor was 0.1 MPa. After three hours, the reaction product was sampled, and the sampled product was mixed with acetonitrile in a 1:1 ratio and analyzed by liquid chromatography. The results of lactic acid conversion and lactide yield are shown in Table 3.

[0168] Example A12

[0169] 100 mL of N-methylpyrrolidone was used as the solvent, and the lactic acid solution concentration was 50 wt%. 5 g of lactic acid was added by weight and placed in a 250 mL three-necked flask. 10 g of catalyst was added, and a temperature measuring point was set inside the three-necked flask to determine the reaction temperature of the system. Toluene was vaporized at a flow rate of 2 mL / min and then introduced into the reactor. The pressure inside the reactor was 0.1 MPa. After three hours, the reaction product was sampled, and the sampled products were mixed with acetonitrile in a 1:1 ratio and analyzed by liquid chromatography. The lactic acid conversion rate and lactide yield are shown in Table 3.

[0170] Example A13

[0171] 100 mL of sulfolane was used as the solvent, and the lactic acid solution concentration was 88 wt%. 5 g of lactic acid was added by weight and placed in a 250 mL three-necked flask. 10 g of catalyst was added, and a temperature measuring point was set inside the three-necked flask to determine the reaction temperature of the system. Nitrogen gas was introduced into the bottom of the three-necked flask at a rate of 20 mL / min, and the pressure inside the reactor was 0.1 MPa. After three hours, the reaction product was sampled, and the sampled products were mixed with acetonitrile in a 1:1 ratio and analyzed by liquid chromatography. The results of lactic acid conversion and lactide yield are shown in Table 3.

[0172] Table 3

[0173] Continuous reaction tests were conducted in Examples A14-18:

[0174] The continuous reaction experiment was carried out in a catalytic distillation unit. The catalyst was loaded in the middle of the catalytic distillation unit with a loading amount of 200 mL. The feed was fed from the top of the catalyst bed and discharged downwards. The residence time in the reactor was 3 h. A water-removing agent was introduced into the bottom of the reactor and discharged from the top outlet of the reactor.

[0175] Example A14

[0176] The solvent is benzophenone. A 100wt% lactic acid solution is used. The reaction feedstock is prepared at a ratio of 10g lactic acid / 100mL solvent, based on the weight of the lactic acid. The reaction is carried out using the aforementioned continuous reaction apparatus, with a feed space velocity relative to the catalyst of 0.3h⁻¹. -1 Temperature measurement points were set inside the reactor to determine the reaction temperature of the system. The pressure was 0.1 MPa. Nitrogen gas carrying water was introduced into the bottom at a rate of 20 mL / min. Samples were taken at the 5th and 100th hours of the reaction. The sampled products were mixed with acetonitrile in a 1:1 ratio and analyzed by liquid chromatography. The lactic acid conversion rate and lactide yield at different reaction times are shown in Table 4.

[0177] Example A15

[0178] The solvent is benzophenone. A lactic acid solution with a concentration of 88 wt% was prepared, and the reaction feedstock was prepared at a ratio of 10 g lactic acid / 100 mL solvent, based on the weight of the lactic acid. The reaction was carried out using the aforementioned continuous reaction apparatus, with a feed space velocity relative to the catalyst of 0.3 h⁻¹. -1 The reaction temperature was 140℃, the pressure was 0.1MPa, and nitrogen gas carrying water was introduced into the bottom at a rate of 20mL / min. Samples were taken at 5, 100 and 1000 hours of reaction. The sampled products were mixed with acetonitrile in a 1:1 ratio and analyzed by liquid chromatography. The lactic acid conversion rate and lactide yield at different reaction times are shown in Table 4.

[0179] Example A16

[0180] The solvent is sulfolane. A 100wt% lactic acid solution is used. The reaction feedstock is prepared at a ratio of 20g lactic acid / 100mL solvent, based on the weight of the lactic acid. The reaction is carried out using the aforementioned continuous reaction apparatus, with a feed space velocity relative to the catalyst of 0.3h. -1 Temperature measurement points were set inside the reactor to determine the reaction temperature of the system. The pressure was 0.1 MPa. Nitrogen gas carrying water was introduced into the bottom at a rate of 20 mL / min. Samples were taken at 5, 100 and 1000 hours of reaction. The sampled products were mixed with acetonitrile in a 1:1 ratio and analyzed by liquid chromatography. The lactic acid conversion rate and lactide yield at different reaction times are shown in Table 4.

[0181] Example A17

[0182] The solvent is sulfolane. A 50wt% lactic acid solution is used. The reaction feedstock is prepared at a ratio of 50g lactic acid / 100mL solvent, based on the weight of the lactic acid. The reaction is carried out using the aforementioned continuous reaction apparatus, with a feed space velocity relative to the catalyst of 0.2h. -1Temperature measurement points were set inside the reactor to determine the reaction temperature of the system. The pressure was 0.1 MPa. Nitrogen gas carrying water was introduced into the bottom at a rate of 20 mL / min. Samples were taken at 5, 100 and 1000 hours of reaction. The sampled products were mixed with acetonitrile in a 1:1 ratio and analyzed by liquid chromatography. The lactic acid conversion rate and lactide yield at different reaction times are shown in Table 4.

[0183] Example A18

[0184] The solvent is N-methylpyrrolidone. A 50wt% lactic acid solution was used. The reaction feedstock was prepared at a ratio of 20g lactic acid / 100mL solvent, based on the weight of the lactic acid. The reaction was carried out using the aforementioned continuous reaction apparatus, with a feed space velocity relative to the catalyst of 0.2h. -1 Temperature measurement points were set inside the reactor to determine the reaction temperature of the system. The pressure was 0.1 MPa. Vaporized toluene was introduced into the reactor at a flow rate of 3 mL / min from the bottom of the reactor. Samples were taken at 5, 100 and 200 hours of reaction. The sampled products were mixed with acetonitrile in a 1:1 ratio and then analyzed by liquid chromatography. The lactic acid conversion rate and lactide yield at different reaction times are shown in Table 4.

[0185] Table 4

[0186] The method provided by this invention eliminates the limitation of azeotropic temperature in the reaction, enabling continuous one-step polymerization of monomers such as lactide in a new solvent system.

[0187] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing polymeric monomers, characterized in that, The method includes the following steps: under the conditions for preparing the polymer monomer, in the presence of a catalyst and in the presence of a base solvent, reacting the raw materials, wherein the temperature and pressure for preparing the polymer monomer are such that the base solvent does not boil during the reaction, and at a temperature of 100°C, the solubility of the raw materials in the base solvent is not less than 10g of raw materials / 100g of solvent; and the boiling point of the base solvent is not less than 110°C.

2. The method according to claim 1, wherein, The reaction system also contains an auxiliary solvent, wherein the solubility of the raw material in the auxiliary solvent at 100°C is no greater than 5g of raw material / 100g of auxiliary solvent; the boiling point difference between the base solvent and the auxiliary solvent is 10°C or more, preferably 20°C or more. Preferably, the auxiliary solvent is selected from at least one of substituted or unsubstituted C4-C12 alkanes and substituted or unsubstituted C6-C20 (preferably C6-C15) aromatics; More preferably, the auxiliary solvent is selected from at least one of benzene, toluene, cyclohexane, n-hexane, xylene, and trimethylbenzene.

3. The method according to claim 2, wherein, The volume ratio of the base solvent to the auxiliary solvent is 1:0.1-20, preferably 1:0.5-5.

4. The method according to any one of claims 1-3, wherein, The solubility of the base solvent in the raw material is not less than 20g raw material / 100g solvent.

5. The method according to any one of claims 1-4, wherein, Under the conditions for preparing the polymerizable monomer, the base solvent does not chemically react with the raw material.

6. The method according to any one of claims 1-5, wherein, The raw material contains hydroxyl and carboxyl groups; and / or, the reaction causes the hydroxyl and carboxyl groups in the raw material to undergo an esterification reaction. And / or, the reaction causes the starting material molecules to cyclize into cyclic structures.

7. The method according to any one of claims 1-6, wherein, The raw material is selected from at least one of glycolic acid, lactic acid and methyl glycolate, preferably glycolic acid and / or lactic acid, and more preferably lactic acid.

8. The method according to any one of claims 1-7, wherein, The boiling point of the base solvent is not lower than 120°C, preferably 140-400°C; And / or, the base solvent contains at least one of oxygen, nitrogen, sulfur and chlorine; Preferably, the base solvent is selected from at least one of benzophenone, dihydro-L-glucanone, N-methylpyrrolidone, trichloropropane, and sulfolane; Preferably, the amount of the base solvent used is 0.5-50 mL relative to 1 g of the raw material, more preferably 1-30 mL.

9. The method according to any one of claims 1-8, wherein, The reaction conditions include a temperature of 80-200℃ and a pressure of -0.1 to 6 MPa, preferably a temperature of 100-170℃ and a pressure of -0.01-1 MPa.

10. The method according to any one of claims 1-9, wherein, The method further includes introducing an inert gas and / or a low-boiling-point inert solvent into the reaction system during the reaction to carry out the water generated in the reaction. Preferably, the inert gas is selected from at least one of nitrogen, argon, helium, neon, krypton, and xenon; Preferably, the low-boiling-point inert solvent is a solvent that can be vaporized after being introduced into the reaction system at the reaction temperature and pressure; more preferably, it is at least one of benzene, toluene, methane and butane.

11. The method according to any one of claims 1-10, wherein, The catalyst is a molecular sieve catalyst with a silicon-aluminum molar ratio of 5-80. Preferably, the catalyst is at least one of β-zeolite catalyst, mesoporous zeolite catalyst, and zeolite catalyst supported on Sn metal component; Preferably, the method is carried out continuously, and the mass hourly space velocity of the raw material is 0.1-2 h⁻¹. -1 ; Preferably, when the method is performed intermittently, the mass ratio of the raw material to the catalyst is 1:0.1-10.

12. The polymeric monomer prepared by the method according to any one of claims 1-11.

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