Bio-based cyclic ester monomer and preparation method of corresponding bio-based polyester

Abstract

The invention discloses a bio-based cyclic ester monomer and a preparation method of corresponding bio-based polyester. The preparation method comprises the following steps: esterifying bio-based unsaturated fatty acid and diol to obtain corresponding unsaturated diester; the bio-based unsaturated diester is prepared into a bio-based unsaturated cyclic ester monomer and a saturated cyclic ester monomer through a reaction based on olefin metathesis in combination with a depolymerization cyclization method and a catalytic hydrogenation method. The method specifically comprises the following steps: preparing a bio-based unsaturated polyester precursor through a polymerization reaction based on olefin metathesis, and preparing a bio-based unsaturated cyclic ester monomer through a depolymerization cyclization method; carrying out catalytic hydrogenation on the bio-based unsaturated polyester precursor to prepare a bio-based saturated polyester precursor, and preparing a bio-based saturated cyclic ester monomer through a depolymerization cyclization method; the bio-based unsaturated cyclic ester monomer can be subjected to catalytic hydrogenation to obtain a bio-based saturated cyclic ester monomer. The bio-based unsaturated cyclic ester monomer and the bio-based saturated cyclic ester monomer synthesized by the invention can be polymerized to synthesize bio-based polyester with good regularity, and the bio-based polyester is an ecological environment-friendly high polymer material.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to a method for preparing a bio-based cyclic ester monomer and a corresponding bio-based polyester. Background Art

[0002] Polyester is a general-purpose polymer material with ester bonds in the main chain structural unit. It has good thermal and mechanical properties and is widely used in films, bottles and textile products. However, most polyesters are petroleum-based polyesters, but petroleum is a non-renewable resource. From the perspective of sustainable development, it is urgent to develop products based on renewable resources to replace non-renewable petroleum-based products. Therefore, the use of renewable bio-based resources to synthesize polyester can replace or partially replace petroleum products and reduce dependence on petroleum.

[0003] Among the numerous biomass resources, vegetable oil and its derivatives are an inexhaustible green and pollution-free resource. They are also considered to be a good source for the preparation of aliphatic polyesters, with advantages such as relatively low price, low toxicity and versatility. Most common vegetable oils contain unsaturated fatty acids with chain lengths ranging from 11 to 22 carbon atoms and 0 to 3 double bonds per chain. Therefore, vegetable oil is regarded as a promising raw material for the synthesis of monomers and polymers.

[0004] Olefin metathesis refers to the process of cutting and recombining two carbon-carbon double bonds under the action of metal catalysts. According to the changes in the molecular skeleton during the reaction, it can be divided into ring-closing metathesis (RCM), acyclic diene metathesis polymerization (ADMET), ring-opening metathesis polymerization (ROMP), etc.

[0005] Ring-closing metathesis (RCM) is one of the important methods currently used to synthesize cyclic organic compounds, for example, it can be used to prepare musk ketone [Kamat, VP; Hagiwara, H.; Katsumi, T.; Hoshi, T.; Suzuki, T.; Ando, ​​M. Tetrahedron 2000, 56 , 4397-4403]. However, RCM usually has to be carried out at extremely low concentrations (linear diene substrate concentration is about 1 gram per liter), and the amount of catalyst used is large, which is costly.

[0006] ADMET polymerization can be used to synthesize unsaturated long-chain linear aliphatic polyesters. The key lies in the choice of catalyst. The most widely used catalyst is Grubbs catalyst, which is a catalyst with ruthenium as the metal center. Grubbs' first-generation catalyst has good water resistance and oxygen resistance, but poor thermal stability and low activity for substituted olefins. Grubbs' second-generation catalyst and third-generation catalyst have high reaction activity, but are expensive and have the problem of olefin migration caused by olefin isomerization. Meier et al. [Fokou, PA; Meier, MAR Journal of the American Chemical Society 2009, 131 , 1664–1665] studied the factors affecting olefin migration in the process of synthesizing unsaturated polyesters by polymerization of unsaturated diene ester monomers with Grubbs catalyst. It was found that the degree of olefin isomerization in the polyester synthesized using Grubbs second-generation catalyst was high, resulting in a high melting point ( T m =17 ℃) is lower than the polyester synthesized by Grubbs' first generation catalyst ( T m =56 ℃), that is, the olefin isomerization side reaction will cause structural defects in the polyester, resulting in a decrease in the melting point.

[0007] Depolymerization and cyclization is a reaction to prepare cyclic oligomers from linear polymers based on the principle of ring-chain equilibrium. By adjusting the equilibrium, the reaction can be controlled to move in the direction of generating cyclic oligomers. The depolymerization and cyclization method has the advantages of high yield and relatively high reaction concentration.

[0008] Based on the above analysis, the existing route of preparing the corresponding unsaturated diacid from unsaturated fatty acid, and then preparing the corresponding polyester by olefin metathesis polymerization has the problem of olefin isomerization, which leads to uneven methylene length in the synthesized polyester, that is, the carbon chain length of the diacid unit is inconsistent, resulting in structural defects and low melting point. Therefore, it is necessary to study a method for converting bio-based unsaturated fatty acids into bio-based cyclic ester monomers. The ring-opening polymerization or ring-opening-condensation cascade polymerization of cyclic esters can eliminate the influence of olefin isomerization in olefin metathesis polymerization, thereby preparing bio-based polyesters with fewer structural defects and good performance, and realizing the high-value utilization of vegetable oils. Summary of the invention

[0009] In order to solve the above technical problems, the present invention provides a method for preparing a bio-based cyclic ester monomer and a corresponding bio-based polyester, that is, a bio-based cyclic ester monomer is prepared by combining an olefin metathesis polymerization reaction and a depolymerization cyclization reaction, specifically comprising the following steps: esterification of a bio-based unsaturated fatty acid with a diol to obtain a corresponding bio-based unsaturated diester; the bio-based unsaturated diester is used to prepare a bio-based unsaturated polyester precursor through an olefin metathesis-based polymerization reaction, and the bio-based unsaturated polyester precursor is then used to prepare a bio-based unsaturated cyclic ester monomer through a depolymerization cyclization method; the bio-based unsaturated polyester precursor can also be catalytically hydrogenated to prepare a bio-based saturated polyester precursor, and then a bio-based saturated cyclic ester monomer is prepared through a depolymerization cyclization method. The bio-based unsaturated cyclic ester monomer can be catalytically hydrogenated to obtain a bio-based saturated cyclic ester monomer. The synthesized bio-based unsaturated cyclic ester monomer and the bio-based saturated cyclic ester monomer can be polymerized to synthesize the corresponding bio-based polyester. The cyclic ester monomer prepared by depolymerizing a polyester precursor into a ring in the present invention is easy to purify and can be used to synthesize polyester through a cyclic ester-related polymerization reaction, thereby solving the problems of olefin isomerization occurring when unsaturated polyester is prepared directly from an unsaturated diester through ADMET polymerization, thereby causing unclear structure and low melting point.

[0010] The present invention is achieved through the following technical solutions: The first object of the present invention is to provide a method for preparing a bio-based cyclic ester monomer, comprising the following steps: (1) esterifying bio-based unsaturated fatty acids with diols to obtain bio-based unsaturated diesters; (2) polymerizing the obtained bio-based unsaturated diester through olefin metathesis reaction to obtain a bio-based unsaturated polyester precursor; (3) The obtained bio-based unsaturated polyester precursor is subjected to depolymerization and / or catalytic hydrogenation to prepare a bio-based cyclic ester monomer; the bio-based cyclic ester monomer includes a bio-based unsaturated cyclic ester monomer (A) and a bio-based saturated cyclic ester monomer (B); The structure of the bio-based unsaturated cyclic ester monomer is: ; The structure of the bio-based saturated cyclic ester monomer is: ; wherein m is 7, 8 or 11; R2 is selected from (CH2) p , , and At least one of; wherein p is any integer between 2 and 10.

[0011] The bio-based unsaturated cyclic ester monomer can be obtained by catalytic hydrogenation to obtain a bio-based saturated cyclic ester monomer.

[0012] Bio-based unsaturated cyclic ester monomers and bio-based saturated cyclic ester monomers are prepared by combining an olefin metathesis-based depolymerization and cyclization method based on olefin metathesis and ester exchange and a catalytic hydrogenation method. The olefin metathesis-based depolymerization and cyclization method has a simple reaction, one-pot depolymerization, short reaction time and high yield. The ester exchange-based depolymerization and cyclization method uses a metal catalyst or an organic base catalyst, has a low cost, and also avoids the side reaction of olefin isomerization that exists when using a Grubbs catalyst.

[0013] The second object of the present invention is to provide a method for preparing bio-based polyester, wherein the bio-based cyclic ester monomer prepared by the preparation method is subjected to ring-opening polymerization or ring-opening-condensation cascade polymerization reaction to prepare bio-based polyester; the bio-based polyester includes bio-based unsaturated polyester and bio-based saturated polyester.

[0014] Bio-based unsaturated cyclic ester monomers can be synthesized into corresponding bio-based unsaturated polyesters through ring-opening polymerization or ring-opening-condensation cascade polymerization; bio-based saturated cyclic ester monomers can be synthesized into corresponding bio-based saturated polyesters through ring-opening polymerization or ring-opening-condensation cascade polymerization. The existing route of preparing corresponding unsaturated diacids from unsaturated fatty acids and then preparing corresponding polyesters through acyclic diene metathesis polymerization (ADMET polymerization) has the problem of olefin isomerization, and the process of preparing polyesters from unsaturated cyclic ester monomers through ring-opening metathesis polymerization (ROMP polymerization) also has the problem of olefin isomerization, resulting in uneven methylene length in the synthesized polyester. This type of polymerization reaction through olefin bonds under the action of Grubbs catalyst will lead to inconsistent carbon chain lengths of diacid units in polyesters, resulting in structural defects and low melting points. The synthesis of polyesters through ring-opening polymerization or ring-opening-condensation cascade polymerization of ester bonds of unsaturated cyclic ester monomers or saturated cyclic ester monomers can solve the problems of olefin isomerization occurring during the polymerization process, which leads to unclear structures and low melting points.

[0015] In one embodiment of the present invention, the bio-based unsaturated fatty acid includes one or more unsaturated fatty acids such as 10-undecenoic acid, oleic acid and erucic acid; And / or, the diol includes one or more of aliphatic or bio-based diols such as ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, 1,4-cyclohexanedimethanol, 2,5-furan dimethanol and neopentyl glycol.

[0016] In one embodiment of the present invention, the structural formula of the bio-based unsaturated diester is as follows: ; Wherein, R1 is selected from H or CH3(CH2)8; m is 7, 8 or 11, etc.; R2 is selected from (CH2) p , , and At least one of; wherein p is any integer between 2 and 10.

[0017] In one embodiment of the present invention, in step (2), the concentration of the bio-based unsaturated diester is 100 g / L-400 g / L; And / or, the catalyst used in the olefin metathesis reaction is a Grubbs catalyst, including but not limited to a Grubbs first generation catalyst, a Grubbs second generation catalyst, etc.; preferably, the Grubbs catalyst is a Grubbs first generation catalyst; the amount of the catalyst is 0.5%-5% of the molar amount of the bio-based unsaturated diester, preferably 1%-2%;; And / or, the olefin metathesis reaction time is 1 h-3 h, and the temperature is 26° C.-80° C.

[0018] In one embodiment of the present invention, in step (3), the bio-based unsaturated polyester precursor is depolymerized into a ring in a dilute solution to synthesize an unsaturated cyclic ester monomer.

[0019] In one embodiment of the present invention, within a certain range, the lower the concentration of the reactants, the higher the yield, that is, the depolymerization and cyclization reaction in the present invention is more suitable for being carried out under dilute solution conditions. The concentration of the bio-based unsaturated polyester precursor is 2 g / L-50 g / L, preferably 2 g / L-20 g / L; for the depolymerization and cyclization reaction of the saturated polyester precursor, the concentration of the saturated polyester is 2 g / L-50 g / L, preferably 10 g / L-20 g / L; And / or, the catalyst used for the depolymerization and cyclization is one or more of a Grubbs catalyst, a metal catalyst and an organic base catalyst; including but not limited to a Grubbs first generation catalyst, a Grubbs second generation catalyst, dibutyltin oxide, zinc acetate, 4-dimethylaminopyridine (DMAP), 4-pyrrolidinylpyridine (4-PPy), etc.; And / or, the reaction time of the depolymerization into ring is 1 h-24 h, and the reaction temperature is 26° C.-140° C.

[0020] In one embodiment of the present invention, the amount of catalyst added in the present invention has a certain influence on the yield of the target product. When the catalyst used for the depolymerization and cyclization is a Grubbs catalyst based on olefin metathesis; the bio-based unsaturated polyester precursor can be directly depolymerized and cyclized in a dilute solution without post-treatment after synthesis. The amount of catalyst added for the depolymerization and cyclization is 0-5% of the molar amount of the bio-based unsaturated diester, preferably 1%-3%; the reaction time of the depolymerization and cyclization is 1 h-9 h, and the reaction temperature is 26°C-80°C.

[0021] In one embodiment of the present invention, the catalyst used for the depolymerization and cyclization may also be a metal catalyst or an organic base catalyst based on ester exchange, including but not limited to dibutyltin oxide, zinc acetate, 4-dimethylaminopyridine (DMAP), 4-pyrrolidinopyridine (4-PPy) and other metal catalysts and organic base catalysts; the amount of the catalyst used is 0.1%-10% of the mass of the bio-based unsaturated diester, preferably 4-6%; for the depolymerization and cyclization reaction of the bio-based saturated polyester precursor, the amount of the metal catalyst or organic base catalyst added is 0.1%-10% of the mass of the bio-based saturated polyester precursor, preferably 4-6%.

[0022] The reaction time is 1 h-24 h, and the reaction temperature is 80°C-140°C.

[0023] In one embodiment of the present invention, in step (3), the bio-based unsaturated polyester precursor is prepared by catalytic hydrogenation to obtain a bio-based saturated polyester precursor, and the obtained bio-based saturated polyester precursor is prepared by depolymerization to obtain a bio-based saturated cyclic ester monomer.

[0024] In one embodiment of the present invention, the concentration of the bio-based unsaturated polyester precursor is 1 g / L-400 g / L; And / or, the catalyst for catalytic hydrogenation is a palladium-carbon catalyst; the amount of the catalyst used is 0.5%-10% of the mass of the bio-based unsaturated polyester.

[0025] In one embodiment of the present invention, the reaction concentration of the bio-based saturated polyester precursor is 2 g / L-50 g / L; And / or, the catalyst for depolymerization into rings is a metal catalyst or an organic base catalyst; the amount of the catalyst is 0.1-10% of the mass of the bio-based saturated polyester precursor; And / or, the reaction time of the depolymerization into ring is 1 h-24 h, and the reaction temperature is 80°C-200°C.

[0026] In one embodiment of the present invention, the bio-based unsaturated cyclic ester monomer is prepared by catalytic hydrogenation to prepare a bio-based saturated cyclic ester monomer; the reaction concentration of the bio-based unsaturated cyclic ester monomer is 1 g / L-400 g / L; the catalyst used in the catalytic hydrogenation is a palladium-carbon catalyst; the amount of the catalyst is 0.5-10% of the mass of the bio-based unsaturated cyclic ester monomer.

[0027] In one embodiment of the present invention, the catalyst used in the ring-opening polymerization is a metal catalyst, such as tetrabutyl titanate, stannous octoate, etc.

[0028] The reaction temperature of the ring-opening polymerization is 150°C-240°C; the reaction time is 4 h-12 h; In one embodiment of the present invention, the synthesized bio-based unsaturated cyclic ester monomers can be subjected to ring-opening polymerization or cascade polymerization to synthesize the corresponding bio-based unsaturated polyesters; the bio-based saturated cyclic ester monomers can be subjected to ring-opening polymerization or cascade polymerization to synthesize the corresponding bio-based saturated polyesters.

[0029] In the prior art, when long-chain aliphatic polyesters are directly synthesized from unsaturated diesters by ADMET polymerization, the degree of olefin isomerization is large, resulting in uneven methylene lengths in the synthesized polyesters, that is, inconsistent carbon chain lengths of diacid units, causing structural defects, resulting in low melting points, etc. The bio-based unsaturated cyclic ester monomers and bio-based saturated cyclic ester monomers synthesized in the present invention can be synthesized into bio-based long-chain aliphatic polyesters with good regularity through cyclic ester-related polymerization reactions, such as ring-opening polymerization or cascade polymerization, and have a higher melting point than similar structure polyesters reported in the literature.

[0030] The above technical solution of the present invention has the following advantages compared with the prior art: 1. The present invention synthesizes a bio-based unsaturated fatty acid diol ester monomer, and obtains a series of bio-based unsaturated cyclic ester monomers and bio-based saturated cyclic ester monomers through olefin metathesis polymerization combined with depolymerization into rings and catalytic hydrogenation, which can be used to prepare bio-based polyesters. The raw materials used are bio-based unsaturated fatty acids, such as oleic acid, 10-undecenoic acid, etc. This type of bio-based unsaturated fatty acid belongs to renewable resources, has a wide range of sources, is low in price, and is in line with the concept of sustainable development.

[0031] 2. The bio-based unsaturated cyclic ester monomers and bio-based saturated cyclic ester monomers synthesized by the present invention can be subjected to ring-opening polymerization or ring-opening-condensation cascade polymerization to synthesize bio-based long-chain aliphatic polyesters. The synthesized polyester has a high molecular weight and does not have olefin migration and isomerization, which solves the problem of olefin isomerization and irregular structure when unsaturated diesters are directly polymerized by ADMET to prepare unsaturated polyesters. The melting point of the polyester prepared by this method is higher than that of the polyester synthesized by ADMET polymerization. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein: Figure 1 is a synthetic route diagram of the bio-based cyclic ester monomer in the present invention; Figure 2 is a polymerization route map of the bio-based cyclic ester monomer in the present invention; Figure 3 The quantitative H NMR spectrum of 10-ene-eicosanedioic acid ethylene glycol cyclic ester in Example 4 of the present invention (solvent: deuterated chloroform); Figure 4 This is a macromolecular mass spectrum of 10-ene-eicosanedioic acid ethylene glycol cyclic ester in Example 4 of the present invention, in which the signal peak is the molecular ion peak of the cyclic monomer plus sodium; Figure 5 The quantitative H NMR spectrum of eicosanedioic acid ethylene glycol cyclic ester in Example 12 of the present invention (solvent: deuterated chloroform); Figure 6 This is a macromolecular mass spectrum of eicosanedioic acid ethylene glycol cyclic ester in Example 12 of the present invention, in which the signal peak is the molecular ion peak of the cyclic monomer plus sodium; Figure 7 This is the macromolecular mass spectrum of 10-ene-eicosanedioic acid butanediol cyclic ester in Example 15 of the present invention, in which the signal peak is the molecular ion peak of the cyclic monomer plus sodium; Figure 8 This is the macromolecular mass spectrum of 10-ene-eicosanedioic acid decanedioic acid cyclic ester in Example 16 of the present invention, and the signal peak in the figure is the molecular ion peak of the cyclic monomer plus sodium; Fig. 9 This is the macromolecular mass spectrum of 9-ene-octadecane dioic acid ethylene glycol cyclic ester in Example 17 of the present invention, in which the signal peak is the molecular ion peak of the cyclic monomer plus sodium; Fig.10 This is the macromolecular mass spectrum of 10-ene-eicosanedioic acid-1,4-cyclohexanedimethanol cyclic ester in Example 18 of the present invention, and the signal peak in the figure is the molecular ion peak of the cyclic monomer plus sodium; Fig.11 This is a macromolecular mass spectrum of 10-ene-eicosanedioic acid-2,5-furan dimethanol cyclic ester in Example 19 of the present invention, in which the signal peak is the molecular ion peak of the cyclic monomer plus sodium; Fig.12 This is a macromolecular mass spectrum of 10-ene-eicosanedioic acid neopentyl glycol cyclic ester in Example 20 of the present invention, in which the signal peak is the molecular ion peak of the cyclic monomer plus sodium; Fig.13 is a size exclusion chromatogram of the bio-based polyester poly(ethylene glycol eicosanedioate) (P2E) in Example 22 of the present invention; Fig.14 is a DSC curve diagram of the bio-based polyester poly(ethylene glycol eicosanedioate) (P2E) in Example 22 of the present invention; Fig.15 is a size exclusion chromatogram of the bio-based polyester polybutylene eicosanoate (P4E) in Example 23 of the present invention; Fig.16 is a DSC curve diagram of the bio-based polyester polybutylene eicosanoate (P4E) in Example 23 of the present invention; Fig.17 is a size exclusion chromatogram of the bio-based polyester poly(10-ene-eicosanedioic acid) (P2UE) in Example 24 of the present invention; Fig.18 This is the DSC curve of the bio-based polyester poly (10-ene-eicosanedioic acid ethylene glycol ester) (P2UE) in Example 24 of the present invention. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0034] The present invention provides a method for preparing a bio-based cyclic ester monomer and a corresponding bio-based polyester, which is specifically as follows: Bio-based unsaturated fatty acids are esterified with diols to obtain bio-based unsaturated diesters; the obtained bio-based unsaturated diesters are polymerized through olefin metathesis reaction to obtain bio-based unsaturated polyester precursors; the obtained bio-based unsaturated polyester precursors are subjected to depolymerization into rings and / or catalytic hydrogenation to obtain bio-based cyclic ester monomers; the bio-based cyclic ester monomers include bio-based unsaturated cyclic ester monomers and bio-based saturated cyclic ester monomers; the obtained bio-based cyclic ester monomers are subjected to ring-opening polymerization or ring-opening-condensation cascade polymerization to obtain bio-based polyesters.

[0035] Furthermore, the catalyst for olefin metathesis is a Grubbs catalyst, including but not limited to Grubbs first-generation catalyst, Grubbs second-generation catalyst, etc.; the catalyst for depolymerization into rings is a Grubbs catalyst based on olefin metathesis, or a metal catalyst or an organic base catalyst based on ester exchange, including but not limited to Grubbs first-generation catalyst, Grubbs second-generation catalyst, dibutyltin oxide, zinc acetate, 4-dimethylaminopyridine (DMAP), 4-pyrrolidinopyridine (4-PPy), etc.

[0036] Furthermore, the amount of catalyst added in the present invention has a certain influence on the yield of the target product. For the preparation of bio-based unsaturated polyester precursors by olefin metathesis polymerization of bio-based unsaturated diesters, the amount of catalyst added is 0.5%-5% of the molar amount of the bio-based unsaturated diester, preferably 1%-2%; for the depolymerization and cyclization reaction of the bio-based unsaturated polyester precursor, the bio-based unsaturated polyester precursor does not need to be post-treated after synthesis, and can be directly depolymerized and cyclized in a dilute solution. When using Grubbs catalyst for depolymerization and cyclization, the amount of additional catalyst added is 0-5% of the molar amount of the bio-based unsaturated diester, preferably 1-3%; when using a metal catalyst or an organic base catalyst for depolymerization and cyclization, the amount of catalyst used is 0.1%-10% of the mass of the bio-based unsaturated polyester precursor, preferably 4%-6%; For the depolymerization and cyclization reaction of the bio-based saturated polyester precursor, the metal catalyst or organic base catalyst is added in an amount of 0.1%-10% by weight of the bio-based saturated polyester precursor, preferably 4%-6%.

[0037] Further, within a certain range, the lower the concentration of the reactants, the higher the yield, that is, the depolymerization and cyclization reaction in the present invention is more suitable for being carried out under dilute solution conditions. For the depolymerization and cyclization reaction of the unsaturated polyester precursor, the concentration of the unsaturated diester is 2 g / L-50 g / L, preferably 2 g / L-20 g / L; for the depolymerization and cyclization reaction of the saturated polyester precursor, the concentration of the saturated polyester is 2 g / L-50 g / L, preferably 10 g / L-20 g / L.

[0038] Furthermore, the reaction time has a certain influence on the yield of the target product. Within a certain range, as the reaction time increases, the yield increases. For the olefin metathesis polymerization reaction of bio-based unsaturated diesters, the reaction time is 1 h-3 h, preferably 1 h-2 h; for the depolymerization and cyclization reaction of bio-based unsaturated polyester precursors, the reaction time is 1 h-24 h, preferably 3 h-12 h; for the depolymerization and cyclization reaction of bio-based saturated polyester precursors, the reaction time is 1 h-24 h, preferably 12 h-24 h.

[0039] Furthermore, the temperature of the reaction has a certain influence on the yield of the target product. Within a certain range, as the reaction temperature increases, the yield becomes higher and higher. In the present invention, the olefin metathesis polymerization reaction of the bio-based unsaturated diester and the depolymerization and cyclization reaction using the Grubbs catalyst can be controlled at 26 ℃-80 ℃. Preferably, the reaction temperature is 40 ℃-80 ℃; the reaction temperature of the bio-based unsaturated polyester precursor and the bio-based saturated polyester precursor using a metal catalyst and an organic base catalyst for depolymerization and cyclization can be controlled at 80 ℃-200 ℃, and the preferred reaction temperature is 110 ℃-140 ℃.

[0040] Furthermore, the bio-based unsaturated cyclic ester monomers and bio-based saturated cyclic ester monomers obtained by depolymerization can be used as monomers for polymerization to generate bio-based aliphatic polyesters with good regularity.

[0041] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods, and the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0042] Table 1

[0043]

[0044] In the following embodiment of the present invention, the matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF) of Bruker Ultrafle Xtreme model is adopted to test.The test is carried out under reflection mode.The selected matrix is ​​trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenyl] malononitrile (DCTB), and the cationic salt is sodium trifluoroacetate (CF3COONa).

[0045] In the following examples of the present invention, a Waters size exclusion chromatograph was used for determination, which consisted of a 1515 pump, a 2707 autosampler, and an RI 2414 differential detector, and was equipped with three PL Mixed-C columns. The mobile phase was CHCl3, the flow rate was 1.0 mL / min, the test temperature was 35°C, and the molecular weight was calibrated using narrow distribution polystyrene as a standard.

[0046] In the following examples of the present invention, a TA Q2000 DSC was used for testing. The testing atmosphere was a nitrogen atmosphere, the nitrogen flow rate was 25 mL / min, and the temperature increase / decrease rate was set to 10°C / min. Example 1

[0047] This embodiment provides a method for preparing a bio-based unsaturated diester, which is as follows: Add 10-undecenoic acid 18.0 g, 1,4-butanediol 4.19 g, catalyst 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC·HCl) 20.6 g, catalyst 4-dimethylaminopyridine (DMAP) 1.79 g, anhydrous dichloromethane 200 mL into the reaction flask, pass nitrogen, stir at room temperature and react overnight. After the reaction, wash with water three times, take the organic phase and remove the solvent by rotary evaporation, and obtain colorless oily liquid di(10-ene-undecanoic acid) butanediol ester after column chromatography, with a yield of 87%.

[0048] Under the same reaction conditions (catalyst), 10-undecenoic acid and ethylene glycol were used as raw materials to synthesize di(10-ene-undecanoic acid) ethylene glycol ester with a yield of 90%; 10-undecenoic acid and 1,3-propylene glycol were used as raw materials to synthesize di(10-ene-undecanoic acid) propylene glycol ester with a yield of 89%; 10-undecenoic acid and 1,10-decanediol were used as raw materials to synthesize di(10-ene-undecanoic acid) decanediol ester with a yield of 84%. ; Using 10-undecenoic acid and 1,4-cyclohexanedimethanol as raw materials, the product di(10-ene-undecanoic acid)-1,4-cyclohexanedimethanol ester was synthesized with a yield of 70%; using 10-undecenoic acid and furandimethanol as raw materials, the product di(10-ene-undecanoic acid)-furan dimethanol ester was synthesized with a yield of 90%; using 10-undecenoic acid and neopentyl glycol as raw materials, the product di(10-ene-undecanoic acid)-neopentyl glycol ester was synthesized with a yield of 89%. Example 2

[0049] This embodiment provides a method for preparing a bio-based unsaturated diester, which is as follows: With nitrogen gas and the temperature maintained at 30 °C, 9.55 g of triphenylphosphoric acid (TPPO), 50 mL of dichloromethane, and 5.32 g of oxalyl chloride were added to the reaction flask. After stirring for 10 min, 9.55 g of oleic acid, 1.00 g of ethylene glycol, and 3.26 g of triethylamine were added. The reaction was terminated after stirring at room temperature for 1 h. After the reaction was completed, the solvent was removed by rotary evaporation, and colorless oily liquid di(9-ene-octadecanoic acid) ethylene glycol ester was obtained after column chromatography with a yield of 79%. Example 3

[0050] This embodiment provides a method for preparing a bio-based unsaturated diester, which is as follows: Add 5.00 g of erucic acid, 1.29 g of 1,5-pentanediol, and 25.0 mg of p-toluenesulfonic acid as catalyst to the reaction flask, pass nitrogen, heat to 130 °C, stir and react for 5 h, and then terminate the reaction. After the reaction, add 100 mL of dichloromethane to the reaction flask, wash the solution repeatedly with saturated sodium bicarbonate solution and water, and take the organic phase and add anhydrous sodium sulfate to remove water. Filter and remove the solvent by rotary evaporation to obtain a light yellow oily liquid di(13-ene-docosanoic acid) pentanediol ester with a yield of 81%. Example 4

[0051] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows: Add 0.21 g of di(10-ene-undecanoic acid) glycol ester, 1 mL of dichloromethane, and 4.2 mg of Grubbs catalyst to the reaction flask. Pass nitrogen and reflux for 1 h to carry out olefin metathesis polymerization. After the polymerization, add 100 mL of dichloromethane and 4.18 mg of Grubbs catalyst, dilute and carry out depolymerization and cyclization reaction at low concentration, and reflux for 3 h. After column separation, the product 10-ene-eicosandioic acid glycol cyclic ester was obtained with a yield of 86%.

[0052] Using deuterated chloroform as solvent, quantitative H-NMR spectrum was used to characterize the chemical structure of 10-ene-eicosanedioic acid ethylene glycol cyclic ester. The H-NMR spectrum is shown in Figure 3 .

[0053] The product was tested by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). The mass spectrum of the macromolecule is shown in Figure 4 The results showed that a molecular ion peak appeared at 389.15 (m / z), which was the sodium addition ion peak of 10-ene-eicosanedioic acid ethylene glycol cyclic ester (m / z theoretical value 389.27). This proved that 10-ene-eicosanedioic acid ethylene glycol cyclic ester was synthesized. Example 5

[0054] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows: Add 2.01 g of di(10-ene-undecanoic acid) glycol ester, 5 mL of anhydrous toluene, and 21.5 mg of Grubbs catalyst into the reaction flask. Pass nitrogen and react at 80 °C for 3 h to carry out olefin metathesis polymerization. After the polymerization, add 45 mL of dichloromethane and 0.215 g of Grubbs catalyst, dilute and carry out depolymerization and cyclization reaction at low concentration, and react at 80 °C for 3 h. The product 10-ene-eicosandioic acid glycol cyclic ester is obtained with a yield of 13%. Example 6

[0055] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows: Add 0.410 g of di(10-ene-undecanoic acid) glycol ester, 4 mL of dichloromethane, and 41.8 mg of Grubbs catalyst into the reaction flask. Pass nitrogen and react at 26 °C for 1 h to carry out olefin metathesis polymerization. After the polymerization, add 196 mL of dichloromethane, dilute and depolymerize at low concentration to form a ring, and react at 26 °C for 9 h. The product 10-ene-eicosandioic acid glycol cyclic ester is obtained with a yield of 66%. Example 7

[0056] This embodiment provides a method for preparing a bio-based unsaturated polyester precursor, which is as follows: Add 10.0 g of ethylene glycol di(10-ene-undecanoic acid), 20.8 mg of Grubbs catalyst, and 5 mL of dichloromethane to the reaction flask, pass nitrogen, and reflux for 3 h. After the reaction, add 50 mL of chloroform to the reaction flask, precipitate the solution in a large amount of anhydrous methanol, and filter to obtain the polymer. After vacuum drying, 9.17 g of poly(ethylene glycol 10-ene-eicosandioate) was obtained with a yield of 92%. Example 8

[0057] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows: Add 1.00 g of poly(10-ene-eicosanedioic acid) glycol ester, 100 mL of anhydrous p-xylene, and 40 mg of dibutyltin oxide to the reaction flask. Pass nitrogen and reflux for 12 h. The product 10-ene-eicosanedioic acid glycol cyclic ester is obtained with a yield of 43%. Example 9

[0058] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows: Add 0.20 g of poly(10-ene-eicosanedioic acid) glycol ester, 100 mL of anhydrous p-xylene, and 20 mg of dibutyltin oxide to the reaction flask. Pass nitrogen and reflux for 12 h to obtain the product 10-ene-eicosanedioic acid glycol cyclic ester with a yield of 36%. Example 10

[0059] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows: Add 1.00 g of poly(10-ene-eicosanedioic acid ethylene glycol) ester, 100 mL of anhydrous N-methylpyrrolidone (NMP), and 50.0 mg of 4-dimethylaminopyridine (DMAP) into the reaction flask. Pass nitrogen and react at 180 °C for 6 h. The product 10-ene-eicosanedioic acid ethylene glycol cyclic ester was obtained with a yield of 33%. Embodiment 11

[0060] This embodiment provides a method for preparing a bio-based saturated polyester precursor, which is as follows: 10.0 g of polyethylene 10-ene-eicosanedioate, 50 mL of anhydrous toluene, and 600 mg of palladium-carbon catalyst were added to a reaction flask, and hydrogen was passed through. The reaction was carried out at 60 °C for 12 h. After the reaction was completed, the catalyst was removed by suction filtration, and the reaction solvent was removed by rotary evaporation. After vacuum drying, 9.91 g of polyethylene 10-ene-eicosanedioate was obtained as a white solid product with a yield of 99%. Example 12

[0061] This embodiment provides a method for preparing a bio-based saturated cyclic ester monomer, which is as follows: Add 1.00 g of polyethylene glycol ester, 100 mL of anhydrous p-xylene, and 40.0 mg of dibutyltin oxide into the reaction flask. Pass nitrogen and reflux for 12 h. The product polyethylene glycol cyclic ester of eicosanedioic acid is obtained with a yield of 21%.

[0062] Using deuterated chloroform as solvent, quantitative H-NMR spectroscopy was used to characterize the chemical structure of ethylene glycol cyclic ester of eicosanedioic acid. The H-NMR spectrum is shown in Figure 5 .

[0063] The product was tested by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). The mass spectrum of the macromolecule is shown in Figure 6 The results showed that a molecular ion peak appeared at 391.35 (m / z), which was the sodium addition ion peak of ethylene glycol cyclic ester of eicosanedioic acid (theoretical value of m / z: 391.28). This proved that ethylene glycol cyclic ester of eicosanedioic acid was synthesized. Example 13

[0064] This embodiment provides a method for preparing a bio-based saturated cyclic ester monomer, which is as follows: Add 0.21 g of polyethylene glycol ester, 100 mL of anhydrous p-xylene, and 20 mg of dibutyltin oxide to the reaction flask. Pass nitrogen and reflux for 24 h. The product polyethylene glycol cyclic ester of eicosanedioic acid is obtained with a yield of 18%. Embodiment 14

[0065] This embodiment provides a method for preparing a bio-based saturated cyclic ester monomer, which is as follows: Add 40.8 mg of polyethylene glycol ester, 20 mL of anhydrous toluene, and 4.0 mg of 4-pyrrolidinylpyridine (4-PPy) into the reaction flask. Pass nitrogen and react at 80 °C for 1 h. The product, polyethylene glycol cyclic ester of eicosanedioic acid, is obtained with a yield of 10%. Embodiment 15

[0066] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows: Add 0.2 g of di(10-ene-undecanoic acid) butanediol ester, 5 mL of dichloromethane, and 4.0 mg of Grubbs catalyst to the reaction flask. Pass nitrogen and reflux for 1 h to carry out olefin metathesis polymerization. After the polymerization, add 95 mL of dichloromethane and 4.0 mg of Grubbs catalyst, dilute and carry out depolymerization and cyclization reaction at low concentration, and reflux for 3 h. The product 10-ene-eicosanediol cyclic ester was obtained with a yield of 72%.

[0067] The product was tested by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). The mass spectrum of the macromolecule is shown in Figure 7 The results showed that a molecular ion peak appeared at 417.38 (m / z), which was the sodium addition ion peak of 10-ene-eicosandioic acid butanediol cyclic ester (m / z theoretical value 417.30), proving that 10-ene-eicosandioic acid butanediol cyclic ester was synthesized. Example 16

[0068] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows: Add 1.00 g of di(10-ene-undecanoic acid) decanediol ester, 5 mL of dichloromethane, and 16.3 mg of Grubbs catalyst to the reaction flask. Pass nitrogen and reflux for 1 h to carry out olefin metathesis polymerization. After the polymerization, add 95 mL of dichloromethane and 16.3 mg of Grubbs catalyst, dilute and carry out depolymerization and cyclization reaction at low concentration, and reflux for 3 h. The product 10-ene-eicosandioic acid decanediol cyclic ester is obtained with a yield of 37%.

[0069] The product was tested by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). The mass spectrum of the macromolecule is shown in Figure 8 The results showed that a molecular ion peak appeared at 501.39 (m / z), corresponding to the sodium addition ion peak of 10-ene-eicosandioic acid decanedioic acid cyclic ester (m / z theoretical value 501.39), proving that 10-ene-eicosandioic acid decanedioic acid cyclic ester was synthesized. Embodiment 17

[0070] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows: Add 1.00 g of di(9-ene-octadecanoic acid) glycol ester, 5 mL of anhydrous toluene, and 16.4 mg of Grubbs catalyst to the reaction flask. Pass nitrogen and react at 80 °C for 1 h to carry out olefin metathesis polymerization. After the polymerization, add 95 mL of anhydrous toluene and 16.4 mg of Grubbs catalyst, dilute and carry out depolymerization and cyclization reaction at low concentration, and react at 80 °C for 3 h. The product 9-ene-octadecanoic acid glycol cyclic ester is obtained with a yield of 23%.

[0071] The product was tested by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). The mass spectrum of the macromolecule is shown in Fig. 9 The results showed that a molecular ion peak appeared at 361.32 (m / z), which was the sodium addition ion peak of 9-ene-octadecane dioic acid ethylene glycol cyclic ester (m / z theoretical value 361.24), proving that 9-ene-octadecane dioic acid ethylene glycol cyclic ester was synthesized. Embodiment 18

[0072] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows: Add 1.00 g of di(10-ene-undecanoic acid)-1,4-cyclohexanedimethanol ester, 5 mL of dichloromethane, and 17.3 mg of Grubbs catalyst to the reaction flask. Pass nitrogen and reflux for 1 h to carry out olefin metathesis polymerization. After the polymerization, add 95 mL of dichloromethane and 17.3 mg of Grubbs catalyst, dilute and carry out depolymerization and cyclization reaction at low concentration, and reflux for 3 h. The product 10-ene-eicosanedioic acid-1,4-cyclohexanedimethanol cyclic ester is obtained with a yield of 43%.

[0073] The product was tested by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). The mass spectrum of the macromolecule is shown in Fig.10 The results showed that a molecular ion peak appeared at 471.37 (m / z), which was the sodium addition ion peak of 10-ene-eicosanedioic acid-1,4-cyclohexanedimethanol cyclic ester (m / z theoretical value 471.34), proving that 10-ene-eicosanedioic acid-1,4-cyclohexanedimethanol cyclic ester was synthesized. Embodiment 19

[0074] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows: Add 1.00 g of di(10-ene-undecanoic acid)-2,5-furan dimethanol ester, 5 mL of dichloromethane, and 17.9 mg of Grubbs catalyst to the reaction flask. Pass nitrogen and reflux for 1 h to carry out olefin metathesis polymerization. After the polymerization, add 95 mL of dichloromethane and 17.9 mg of Grubbs catalyst, dilute and carry out depolymerization and cyclization reaction at low concentration, and reflux for 3 h. The product 10-ene-eicosane diacid-2,5-furan dimethanol cyclic ester is obtained with a yield of 52%.

[0075] The product was tested by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). The mass spectrum of the macromolecule is shown in Fig.11 The results showed that a molecular ion peak appeared at 455.34 (m / z), which was the sodium addition ion peak of 10-ene-eicosanedioic acid-2,5-furan dimethanol cyclic ester (m / z theoretical value 455.27), proving that 10-ene-eicosanedioic acid-2,5-furan dimethanol cyclic ester was synthesized. Embodiment 20

[0076] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows: Add di(10-ene-undecanoic acid) neopentyl glycol ester, 5 mL of dichloromethane, and 18.9 mg of Grubbs catalyst to the reaction flask. Pass nitrogen and reflux for 1 h to carry out olefin metathesis polymerization. After the polymerization, add 95 mL of dichloromethane and 18.9 mg of Grubbs catalyst, dilute and carry out depolymerization and cyclization reaction at low concentration, and reflux for 3 h. The product 10-ene-eicosane dioic acid neopentyl glycol cyclic ester is obtained with a yield of 21%.

[0077] The product was tested by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF). The mass spectrum of the macromolecule is shown in Fig.12 The results showed that a molecular ion peak appeared at 431.42 (m / z), which was the sodium addition ion peak of 10-ene-eicosanedioic acid neopentyl glycol cyclic ester (m / z theoretical value 431.42), proving that 10-ene-eicosanedioic acid neopentyl glycol cyclic ester was synthesized. Embodiment 21

[0078] This embodiment provides a method for preparing a bio-based saturated cyclic ester monomer from a bio-based unsaturated cyclic ester monomer, which is as follows: 5.00 g of 10-ene-eicosanedioic acid ethylene glycol cyclic ester, 50 mL of anhydrous ethanol, and 200 mg of palladium-carbon catalyst were added to the reaction flask, and hydrogen was passed through. The reaction was carried out at 40 °C for 12 h to obtain 4.95 g of the product eicosanedioic acid ethylene glycol cyclic ester with a yield of 99%.

[0079] Under the same reaction conditions, 10-ene-eicosanediol cyclic ester was used as the raw material, and the product eicosanediol cyclic ester was obtained after hydrogenation with a yield of 99%. Embodiment 22

[0080] This embodiment provides a method for preparing bio-based saturated polyester from bio-based saturated cyclic ester monomers, which is as follows: Add 5.00 g of ethylene glycol cyclic ester of eicosanedioic acid and 16.9 mg of ethylene glycol into the reaction bottle, remove the air with nitrogen, add 2.5 μL of tetrabutyl titanate, stir mechanically, heat to 210-220 °C and react for 4 h to obtain white tough solid polyeicosanedioic acid ethylene glycol ester P2E. Fig.13 This is the size exclusion chromatogram of P2E. The molecular weight of P2E was measured to be 30.6 kg / moL.

[0081] The DSC curve of P2E is shown in Fig.14 The melting temperature of the polymer is 95 °C and the crystallization temperature is 78 °C. Embodiment 23

[0082] This embodiment provides a method for preparing bio-based saturated polyester from bio-based saturated cyclic ester monomers, which is as follows: Add 5.00 g of butylene glycol cyclic ester of eicosandedioic acid and 22.8 mg of 1,4-butanediol to the reaction bottle, remove the air with nitrogen, add 2.5 μL of tetrabutyl titanate, stir mechanically, heat to 220-240 °C and react for 4 h to obtain a white tough solid P4E. Fig.15 This is the size exclusion chromatogram of P4E. The molecular weight of P4E was measured to be 52.1 kg / moL.

[0083] The DSC curve of P4E is shown in Fig.16 The melting temperature was measured to be 87 ºC and the crystallization temperature was 78 ºC. The melting point of the polybutylene glycol ester synthesized by the present invention is 87 ℃, which is significantly higher than the melting point (68 ℃) of the P4E polyester synthesized by ADMET polymerization by Nomura et al. [Nomura, K.; Chaijaroen, P.; Abdellatif, MM ACS Omega 2020, 5 , 18301-18312], because there is obvious olefin isomerization in its ADMET polymerization process, and the methylene length of the diacid unit in the polyester is not uniform, which makes the regularity of the polyester decrease, resulting in the decrease of the corresponding thermal properties. Embodiment 24

[0084] This embodiment provides a method for preparing bio-based unsaturated polyester from bio-based unsaturated cyclic ester monomers, which is as follows: Add 9.80 g of 10-ene-eicosanedioic acid ethylene glycol cyclic ester and 15.8 mg of 1,10-decanediol into the reaction bottle, remove the air with nitrogen, add 50 μL of stannous octoate, stir mechanically, heat to 150 °C and react for 12 h to obtain a white tough solid poly 10-ene-eicosanedioic acid ethylene glycol ester P2UE. Fig.17 This is the size exclusion chromatogram of P2UE. The molecular weight of P2UE was measured to be 27.2 kg / moL.

[0085] The DSC curve of P2UE is shown in Fig.18 The melting temperature was measured to be 67 ºC and the crystallization temperature was 49 ℃, which is higher than the melting point (49 ℃) of unsaturated polyester synthesized by ADMET polymerization reported in the literature [Abdellatif, MM; Nomura, K. A CS Omega 2024, 9 , 9109-9122], indicating that when long-chain aliphatic polyesters are directly synthesized by ADMET polymerization, the degree of olefin isomerization is large, resulting in uneven methylene lengths of the diacid units in the synthesized polyesters, causing structural defects and resulting in a low melting point.

[0086] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for preparing a bio-based cyclic ester monomer, characterized in that: The following steps are involved: (1) esterifying bio-based unsaturated fatty acids with diols to obtain bio-based unsaturated diesters; (2) polymerizing the obtained bio-based unsaturated diester through olefin metathesis reaction to obtain a bio-based unsaturated polyester precursor; (3) The obtained bio-based unsaturated polyester precursor is subjected to depolymerization and / or catalytic hydrogenation to prepare a bio-based cyclic ester monomer; the bio-based cyclic ester monomer includes a bio-based unsaturated cyclic ester monomer and a bio-based saturated cyclic ester monomer; The structure of the bio-based unsaturated cyclic ester monomer is: ； The structure of the bio-based saturated cyclic ester monomer is: ； wherein m is 7, 8 or 11; R2 is selected from (CH2) p , , and At least one of; wherein p is any integer between 2 and 10.

2. The preparation method according to claim 1, characterized in that: In step (1), the bio-based unsaturated fatty acid includes one or more of 10-undecenoic acid, oleic acid and erucic acid; And / or, the diol includes one or more of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, 1,4-cyclohexanedimethanol, 2,5-furandimethanol and neopentyl glycol.

3. The preparation method according to claim 1, characterized in that: In step (2), the concentration of the bio-based unsaturated diester is 100 g / L-400 g / L; And / or, the catalyst used in the olefin metathesis reaction is a Grubbs catalyst; the amount of the catalyst used is 0.5%-5% of the molar amount of the bio-based unsaturated diester; And / or, the olefin metathesis reaction time is 1 h-3 h, and the temperature is 26° C.-80° C.

4. The preparation method according to claim 1, characterized in that: In step (3), the bio-based unsaturated polyester precursor is depolymerized into a ring in a dilute solution to synthesize an unsaturated cyclic ester monomer; and / or, the concentration of the bio-based unsaturated polyester precursor is 2 g / L-50 g / L; And / or, the catalyst used for the depolymerization and cyclization is one or more of a Grubbs catalyst, a metal catalyst and an organic base catalyst; And / or, the reaction time of the depolymerization into ring is 1 h-24 h, and the reaction temperature is 26°C-140°C.

5. The preparation method according to claim 1, characterized in that: In step (3), the bio-based unsaturated polyester precursor is prepared by catalytic hydrogenation to obtain a bio-based saturated polyester precursor, and the obtained bio-based saturated polyester precursor is prepared by depolymerization to obtain a bio-based saturated cyclic ester monomer.

6. The preparation method according to claim 5, characterized in that: The concentration of the bio-based unsaturated polyester precursor is 1 g / L-400 g / L; And / or, the catalyst for catalytic hydrogenation is a palladium-carbon catalyst; the amount of the catalyst used is 0.5%-10% of the mass of the bio-based unsaturated polyester.

7. The preparation method according to claim 5, characterized in that: The reaction concentration of the bio-based saturated polyester precursor is 2 g / L-50 g / L; And / or, the catalyst for depolymerization into rings is a metal catalyst or an organic base catalyst; the amount of the catalyst is 0.1%-10% of the mass of the bio-based saturated polyester precursor; And / or, the reaction time of the depolymerization into ring is 1 h-24 h, and the reaction temperature is 80°C-200°C.

8. The preparation method according to claim 1, characterized in that: The bio-based unsaturated cyclic ester monomer is prepared by catalytic hydrogenation to prepare a bio-based saturated cyclic ester monomer; the reaction concentration of the bio-based unsaturated cyclic ester monomer is 1 g / L-400 g / L; the catalyst used in the catalytic hydrogenation is a palladium carbon catalyst; the amount of the catalyst is 0.5-10% of the mass of the bio-based unsaturated cyclic ester monomer.

9. A method for preparing bio-based polyester, characterized in that: The bio-based cyclic ester monomer prepared by the preparation method of claim 1 is subjected to ring-opening polymerization or ring-opening-condensation cascade polymerization to prepare bio-based polyester; the bio-based polyester includes bio-based unsaturated polyester and bio-based saturated polyester.

10. The preparation method according to claim 9, characterized in that: The catalyst used in the ring-opening polymerization is a metal catalyst; The reaction temperature of the ring-opening polymerization is 150°C-240°C; and the reaction time is 4 h-12 h.

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