Preparation method of a bio-based cyclic ester monomer and a corresponding bio-based polyester

Abstract

The present invention discloses a preparation method of a bio-based cyclic ester monomer and its corresponding bio-based polyester, comprising the following steps: esterifying a bio-based unsaturated fatty acid with a diol to obtain a corresponding unsaturated diester; preparing the bio-based unsaturated cyclic ester monomer and the saturated cyclic ester monomer from the bio-based unsaturated diester by combining the ring-closing depolymerization method and the catalytic hydrogenation method based on olefin metathesis. Specifically: preparing a bio-based unsaturated polyester precursor through a polymerization reaction based on olefin metathesis, and then preparing the bio-based unsaturated cyclic ester monomer by the ring-closing depolymerization method; subjecting the bio-based unsaturated polyester precursor to catalytic hydrogenation to prepare a bio-based saturated polyester precursor, and then preparing the bio-based saturated cyclic ester monomer by the ring-closing depolymerization method; the bio-based unsaturated cyclic ester monomer can be obtained as the bio-based saturated cyclic ester monomer through catalytic hydrogenation. The bio-based unsaturated cyclic ester monomer and the bio-based saturated cyclic ester monomer synthesized by the present invention can be polymerized to synthesize a bio-based polyester with good regularity, which is an environmentally friendly polymer material.

Description

Technical Field

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

[0002] Polyester is a general type of polymer material containing ester bonds in the main chain structure unit, and has good thermal properties and mechanical properties, and is widely used in films, bottle flakes 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, synthesizing polyester using renewable bio-based resources can replace or partially replace petroleum products and reduce the dependence on petroleum.

[0003] Among many biomass resources, vegetable oils and their derivatives are a green and pollution-free resource that is inexhaustible and also considered a good source for preparing aliphatic polyesters, and have advantages such as relatively low price, low toxicity and versatility. Most common vegetable oils contain unsaturated fatty acids, whose chain lengths range from 11 to 22 carbon atoms, and each chain has 0 to 3 double bonds. Therefore, vegetable oils are regarded as a very promising raw material for synthesizing monomers and polymers.

[0004] Olefin metathesis refers to the process of cleavage and reconnection of two carbon-carbon double bonds under the action of a metal catalyst. According to the change of 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 currently one of the important methods for synthesizing cyclic organic compounds. For example, it can be used to prepare muskone [Kamat, V. P.; 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 (the concentration of the linear diene substrate is about 1 gram per liter), and the amount of catalyst used is large and the cost is high.

[0006] ADMET polymerization can be used for the synthesis of unsaturated long-chain linear aliphatic polyesters. The key lies in the selection of catalysts. Currently, the most widely used catalyst is the Grubbs catalyst, that is, a catalyst with ruthenium as the metal center. The first-generation Grubbs catalyst has good water resistance and oxygen resistance, but poor thermal stability and low activity towards substituted olefins. The second-generation and third-generation Grubbs catalysts have high reaction activity, but are expensive and have problems such as olefin isomerization leading to olefin bond migration. Meier et al. [Fokou, P. A.; Meier, M. A. R. Journal of the American Chemical Society 2009, 131 , 1664–1665] studied the influencing factors of olefin bond migration during the polymerization of unsaturated diene ester monomers to synthesize unsaturated polyesters under Grubbs catalysts. It was found that the degree of olefin isomerization in the polyesters synthesized using the second-generation Grubbs catalyst was high, resulting in a lower melting point ( T m = 17 °C) of the synthesized polyesters than those synthesized using the first-generation Grubbs catalyst ( T m = 56 °C), that is, the side reaction of olefin isomerization would cause structural defects in the polyesters, leading to a decrease in the melting point.

[0007] Depolymerization to form a ring is a reaction for preparing cyclic oligomers from linear polymers based on the ring-chain equilibrium principle. The reaction can be controlled to shift towards the direction of generating cyclic oligomers by adjusting the equilibrium. The method of depolymerization to form a ring has advantages such as high yield and relatively high reaction concentration.

[0008] Based on the above analysis, the existing route of preparing the corresponding unsaturated diacid esters from unsaturated fatty acids and then carrying out olefin metathesis polymerization to prepare the corresponding polyesters has the problem of olefin isomerization, resulting in non-uniform methylene lengths in the synthesized polyesters, that is, inconsistent carbon chain lengths of the diacid units, causing structural defects and a 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 existing in olefin metathesis polymerization, thereby preparing bio-based polyesters with fewer structural defects and good properties and realizing the high-value utilization of vegetable oils. Summary of the Invention

[0009] To solve the above technical problems, the present invention provides a method for preparing a bio-based cyclic ester monomer and its corresponding bio-based polyester, that is, olefin metathesis polymerization reaction and depolymerization cyclization reaction are used in combination to prepare the bio-based cyclic ester monomer, which specifically includes 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 polymerized through a polymerization reaction based on olefin metathesis to prepare a bio-based unsaturated polyester precursor, and the bio-based unsaturated polyester precursor is then prepared into 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 prepared into a bio-based saturated cyclic ester monomer 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 bio-based saturated cyclic ester monomer can be polymerized to synthesize the corresponding bio-based polyester. In the present invention, the cyclic ester monomer prepared by depolymerization cyclization of the polyester precursor is easy to purify and can be used to synthesize polyester through a polymerization reaction related to cyclic esters, solving the problems of olefin isomerization and resulting in unclear structure, low melting point, etc. when directly preparing unsaturated polyester from unsaturated diester through ADMET polymerization.

[0010] The present invention is realized through the following technical solutions:

[0011] The first object of the present invention is to provide a method for preparing a bio-based cyclic ester monomer, including the following steps:

[0012] (1) Esterifying a bio-based unsaturated fatty acid with a diol to obtain a bio-based unsaturated diester;

[0013] (2) Polymerizing the obtained bio-based unsaturated diester through an olefin metathesis reaction to obtain a bio-based unsaturated polyester precursor;

[0014] (3) Preparing a bio-based cyclic ester monomer through depolymerization cyclization and / or catalytic hydrogenation of the obtained bio-based unsaturated polyester precursor; The bio-based cyclic ester monomer includes a bio-based unsaturated cyclic ester monomer (A) and a bio-based saturated cyclic ester monomer (B);

[0015] The structure of the bio-based unsaturated cyclic ester monomer is:

[0016] ;

[0017] The structure of the bio-based saturated cyclic ester monomer is:

[0018] ;

[0019] Among them, m is 7, 8 or 11; R 2 is selected from (CH 2 ) p , , and at least one of them; where p is any integer from 2 to 10.

[0020] The bio-based unsaturated cyclic ester monomer can be obtained as a bio-based saturated cyclic ester monomer through catalytic hydrogenation.

[0021] A bio-based unsaturated cyclic ester monomer and a bio-based saturated cyclic ester monomer are prepared by a method combining olefin metathesis reaction, a depolymerization cyclization method based on olefin metathesis and transesterification, and catalytic hydrogenation. The depolymerization cyclization method based on olefin metathesis has a simple reaction, one-pot depolymerization, short reaction time, and high yield; the depolymerization cyclization method based on transesterification uses a metal catalyst or an organic base catalyst, with lower cost, and also avoids the side reaction of olefin isomerization when using Grubbs catalyst.

[0022] The second object of the present invention is to provide a preparation method of a bio-based polyester. The bio-based cyclic ester monomer prepared by the preparation method is subjected to ring-opening polymerization or ring-opening-condensation cascade polymerization to prepare a bio-based polyester; the bio-based polyester includes a bio-based unsaturated polyester and a bio-based saturated polyester.

[0023] The bio-based unsaturated cyclic ester monomer can be polymerized by ring-opening polymerization or ring-opening-condensation cascade polymerization to synthesize the corresponding bio-based unsaturated polyester; the bio-based saturated cyclic ester monomer can be polymerized by ring-opening polymerization or ring-opening-condensation cascade polymerization to synthesize the corresponding bio-based saturated polyester. In the existing route of preparing the corresponding unsaturated diacid ester from unsaturated fatty acids and then performing acyclic diene metathesis polymerization (ADMET polymerization) to prepare the corresponding polyester, there is a problem of olefin isomerization, and there is also a problem of olefin isomerization in the process of preparing polyester by ring-opening metathesis polymerization (ROMP polymerization) of unsaturated cyclic ester monomers, resulting in non-uniform methylene length in the synthesized polyester. Such polymerization reactions of olefin bonds under the action of Grubbs catalyst will lead to inconsistent carbon chain lengths of diacid units in the polyester, causing structural defects and low melting points. However, the polymerization of unsaturated cyclic ester monomers or saturated cyclic ester monomers by ring-opening polymerization or ring-opening-condensation cascade polymerization of ester bonds can solve the problems of olefin isomerization occurring during polymerization and resulting in unclear structure, low melting point, etc.

[0024] In one embodiment of the present invention, the bio-based unsaturated fatty acid includes one or more of unsaturated fatty acids such as 10-undecenoic acid, oleic acid, and erucic acid;

[0025] and / or, the diol includes one or more of aliphatic or bio-based diols such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decanediol, 1,4-cyclohexanedimethanol, 2,5-furandimethanol, and neopentyl glycol.

[0026] In one embodiment of the present invention, the structural formula of the bio-based unsaturated diester is as follows:

[0027] ;

[0028] wherein, R 1 is selected from H or CH 3 (CH 2 ) 8 ; m is 7, 8 or 11, etc.; R 2 is selected from at least one of (CH 2 ) p , , and ; wherein, p is any integer from 2 to 10.

[0029] 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;

[0030] and / or, the catalyst used in the olefin metathesis reaction is a Grubbs catalyst, including but not limited to Grubbs first-generation catalyst, Grubbs second-generation catalyst, etc.; preferably, the Grubbs catalyst is Grubbs first-generation catalyst; the dosage of the catalyst is 0.5% - 5% of the molar amount of the bio-based unsaturated diester, preferably 1% - 2%;

[0031] and / or, the time of the olefin metathesis reaction is 1 h - 3 h, and the temperature is 26 °C - 80 °C.

[0032] In one embodiment of the present invention, in step (3), the bio-based unsaturated polyester precursor is depolymerized and cyclized in a dilute solution to synthesize an unsaturated cyclic ester monomer.

[0033] 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;

[0034] And / or, the catalyst used for the ring-opening depolymerization is one or more of Grubbs catalysts, metal catalysts, and organic base catalysts; 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.;

[0035] And / or, the reaction time for the ring-opening depolymerization is 1 h - 24 h, and the reaction temperature is 26°C - 140°C.

[0036] In one embodiment of the present invention, the addition amount of the catalyst in the present invention has a certain influence on the yield of the target product. When the catalyst used for the ring-opening depolymerization is a Grubbs catalyst based on olefin metathesis; after the synthesis of the bio-based unsaturated polyester precursor, no post-treatment is required, and the ring-opening depolymerization can be directly carried out in a dilute solution. The dosage of the catalyst added for the ring-opening depolymerization is 0 - 5% of the molar amount of the bio-based unsaturated diester, preferably 1% - 3%; the reaction time for the ring-opening depolymerization is 1 h - 9 h, and the reaction temperature is 26°C - 80°C.

[0037] In one embodiment of the present invention, the catalyst used for the ring-opening depolymerization can also be a metal catalyst or an organic base catalyst based on transesterification, including but not limited to metal catalysts and organic base catalysts such as dibutyltin oxide, zinc acetate, 4-dimethylaminopyridine (DMAP), 4-pyrrolidinopyridine (4-PPy), etc.; the dosage of the catalyst is 0.1% - 10% of the mass of the bio-based unsaturated diester, preferably 4 - 6%; for the ring-opening depolymerization reaction of the bio-based saturated polyester precursor, the addition amount of the metal catalyst or the organic base catalyst is 0.1% - 10% of the mass of the bio-based saturated polyester precursor, preferably 4 - 6%.

[0038] The reaction time is 1 h - 24 h, and the reaction temperature is 80°C - 140°C.

[0039] In one embodiment of the present invention, in step (3), the bio-based unsaturated polyester precursor is prepared into a bio-based saturated polyester precursor by catalytic hydrogenation, and the obtained bio-based saturated polyester precursor is prepared into a bio-based saturated cyclic ester monomer by ring-opening depolymerization.

[0040] In one embodiment of the present invention, the concentration of the bio-based unsaturated polyester precursor is 1 g / L - 400 g / L;

[0041] And / or, the catalyst for the catalytic hydrogenation is a palladium-carbon catalyst; the dosage of the catalyst is 0.5% - 10% of the mass of the bio-based unsaturated polyester.

[0042] In one embodiment of the present invention, the reaction concentration of the bio-based saturated polyester precursor is 2 g / L - 50 g / L;

[0043] and / or, the catalyst for depolymerization and cyclization is a metal catalyst or an organic base catalyst; the dosage of the catalyst is 0.1 - 10% of the mass of the bio-based saturated polyester precursor;

[0044] and / or, the reaction time for depolymerization and cyclization is 1 h - 24 h, and the reaction temperature is 80 °C - 200 °C.

[0045] In one embodiment of the present invention, the bio-based unsaturated cyclic ester monomer is used to prepare a bio-based saturated cyclic ester monomer through catalytic hydrogenation; 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 dosage of the catalyst is 0.5 - 10% of the mass of the bio-based unsaturated cyclic ester monomer.

[0046] In one embodiment of the present invention, the catalyst used for ring-opening polymerization is a metal-based catalyst, such as tetrabutyl titanate, stannous octanoate, etc.

[0047] The reaction temperature for the ring-opening polymerization is 150 °C - 240 °C; the reaction time is 4 h - 12 h;

[0048] In one embodiment of the present invention, the synthesized bio-based unsaturated cyclic ester monomer can undergo ring-opening polymerization or cascade polymerization to synthesize the corresponding bio-based unsaturated polyester; the bio-based saturated cyclic ester monomer can undergo ring-opening polymerization or cascade polymerization to synthesize the corresponding bio-based saturated polyester.

[0049] In the prior art, when directly synthesizing long-chain aliphatic polyesters from unsaturated diesters by the ADMET polymerization method, the degree of olefin isomerization is large, resulting in non-uniform methylene lengths in the synthesized polyesters, that is, the carbon chain lengths of the diacid units are inconsistent, causing structural defects and resulting in a low melting point, etc. However, the bio-based unsaturated cyclic ester monomer and bio-based saturated cyclic ester monomer synthesized in the present invention can be used to synthesize bio-based long-chain aliphatic polyesters with good regularity through ring-ester related polymerization reactions, such as ring-opening polymerization or cascade polymerization. Compared with similar structure polyesters reported in the literature, they have a higher melting point.

[0050] The above technical solutions of the present invention have the following advantages compared with the prior art:

[0051] 1. The present invention synthesizes a bio-based unsaturated fatty acid diol ester monomer. Through olefin metathesis polymerization combined with ring-opening depolymerization and catalytic hydrogenation, a series of bio-based unsaturated cyclic ester monomers and bio-based saturated cyclic ester monomers are obtained, 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. Such bio-based unsaturated fatty acids belong to renewable resources, have a wide range of sources and low prices, and conform to the concept of sustainable development.

[0052] 2. The bio-based unsaturated cyclic ester monomers and bio-based saturated cyclic ester monomers synthesized by the present invention can undergo ring-opening polymerization or ring-opening-condensation cascade polymerization reactions to synthesize bio-based long-chain aliphatic polyesters. The synthesized polyesters have high molecular weights, and there is no migration and isomerization of double bonds, solving the problem of olefin isomerization that occurs when directly preparing unsaturated polyesters through ADMET polymerization of unsaturated diesters, which leads to irregular structures. The melting point of the polyesters prepared by this method is higher than that of the polyesters synthesized through ADMET polymerization. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in combination with the drawings. Among them,

[0054] Figure 1 is the synthesis route diagram of the bio-based cyclic ester monomer in the present invention;

[0055] Figure 2 is the polymerization route diagram of the bio-based cyclic ester monomer in the present invention;

[0056] Figure 3 is the quantitative nuclear magnetic resonance hydrogen spectrum diagram of ethylene glycol 10-ene-eicosanedioate in Example 4 of the present invention (solvent: deuterated chloroform);

[0057] Figure 4 is the macromolecular mass spectrum diagram of ethylene glycol 10-ene-eicosanedioate in Example 4 of the present invention. The signal peak in the figure is the molecular ion peak of the cyclic monomer plus sodium;

[0058] Figure 5 is the quantitative nuclear magnetic resonance hydrogen spectrum diagram of ethylene glycol eicosanedioate in Example 12 of the present invention (solvent: deuterated chloroform);

[0059] Figure 6 is the macromolecular mass spectrum diagram of ethylene glycol eicosanedioate in Example 12 of the present invention. The signal peak in the figure is the molecular ion peak of the cyclic monomer plus sodium;

[0060] Figure 7 is the macromolecular mass spectrum diagram of butanediol 10-ene-eicosanedioate in Example 15 of the present invention. The signal peak in the figure is the molecular ion peak of the cyclic monomer plus sodium;

[0061] Figure 8 This is the macromolecular mass spectrum of the decanediol cycloester of 10-ene-eicosanedioic acid in Example 16 of the present invention. The signal peaks in the figure are the molecular ion peaks of the cyclic monomer plus sodium;

[0062] Figure 9 This is the macromolecular mass spectrum of the ethylene glycol cycloester of 9-ene-octadecanedioic acid in Example 17 of the present invention. The signal peaks in the figure are the molecular ion peaks of the cyclic monomer plus sodium;

[0063] Figure 10 This is the macromolecular mass spectrum of the 1,4-cyclohexanedimethanol cycloester of 10-ene-eicosanedioic acid in Example 18 of the present invention. The signal peaks in the figure are the molecular ion peaks of the cyclic monomer plus sodium;

[0064] Figure 11 This is the macromolecular mass spectrum of the 2,5-furandimethanol cycloester of 10-ene-eicosanedioic acid in Example 19 of the present invention. The signal peaks in the figure are the molecular ion peaks of the cyclic monomer plus sodium;

[0065] Figure 12 This is the macromolecular mass spectrum of the neopentyl glycol cycloester of 10-ene-eicosanedioic acid in Example 20 of the present invention. The signal peaks in the figure are the molecular ion peaks of the cyclic monomer plus sodium;

[0066] Figure 13 This is the size exclusion chromatogram of the biobased polyester polyethylene glycol dicarboxylate (P2E) in Example 22 of the present invention;

[0067] Figure 14 This is the DSC curve of the biobased polyester polyethylene glycol dicarboxylate (P2E) in Example 22 of the present invention;

[0068] Figure 15 This is the size exclusion chromatogram of the biobased polyester polybutylene glycol dicarboxylate (P4E) in Example 23 of the present invention;

[0069] Figure 16 This is the DSC curve of the biobased polyester polybutylene glycol dicarboxylate (P4E) in Example 23 of the present invention;

[0070] Figure 17 This is the size exclusion chromatogram of the biobased polyester polyethylene glycol 10-ene-eicosanedioate (P2UE) in Example 24 of the present invention;

[0071] Figure 18 This is the DSC curve of the biobased polyester polyethylene glycol 10-ene-eicosanedioate (P2UE) in Example 24 of the present invention. Detailed implementation manners

[0072] The present invention will be 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 be able to implement it, but the embodiments cited do not limit the present invention.

[0073] The present invention provides a method for preparing bio-based cyclic ester monomers and their corresponding bio-based polyesters, which is specifically as follows:

[0074] Esterify a bio-based unsaturated fatty acid with a diol to obtain a bio-based unsaturated diester; polymerize the obtained bio-based unsaturated diester through olefin metathesis reaction to obtain a bio-based unsaturated polyester precursor; prepare a bio-based cyclic ester monomer by depolymerization and cyclization and / or catalytic hydrogenation of the obtained bio-based unsaturated polyester precursor; the bio-based cyclic ester monomer includes a bio-based unsaturated cyclic ester monomer and a bio-based saturated cyclic ester monomer; prepare a bio-based polyester by ring-opening polymerization or ring-opening-condensation cascade polymerization reaction of the obtained bio-based cyclic ester monomer.

[0075] Further, 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 and cyclization is a Grubbs catalyst based on olefin metathesis, or a metal catalyst or an organic base catalyst based on transesterification, including but not limited to Grubbs first-generation catalyst, Grubbs second-generation catalyst, dibutyltin oxide, zinc acetate, 4-dimethylaminopyridine (DMAP), 4-pyrrolidinylpyridine (4-PPy), etc.

[0076] Further, the addition amount of the catalyst in the present invention has a certain influence on the yield of the target product. For the olefin metathesis polymerization reaction of bio-based unsaturated diester to prepare bio-based unsaturated polyester precursor, the addition amount of the catalyst is 0.5%-5% of the molar amount of bio-based unsaturated diester, preferably 1%-2%; for the depolymerization and cyclization reaction of bio-based unsaturated polyester precursor, the bio-based unsaturated polyester precursor can be directly depolymerized and cyclized in a dilute solution without post-treatment after synthesis. When using a Grubbs catalyst for depolymerization and cyclization, the supplementary addition amount of the catalyst is 0-5% of the molar amount of bio-based unsaturated diester, preferably 1-3%; when using a metal catalyst or an organic base catalyst for depolymerization and cyclization, the amount of the catalyst used is 0.1%-10% of the mass of bio-based unsaturated polyester precursor, preferably 4%-6%;

[0077] For the depolymerization and cyclization reaction of bio-based saturated polyester precursor, the addition amount of the metal catalyst or the organic base catalyst is 0.1%-10% of the mass of bio-based saturated polyester precursor, preferably 4%-6%.

[0078] 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.

[0079] Further, the reaction time has a certain influence on the yield of the target product. Within a certain range, as the reaction time prolongs, the yield also increases. For the olefin metathesis polymerization reaction of the bio - based unsaturated diester, the reaction time is 1 h - 3 h, preferably 1 h - 2 h; for the depolymerization and cyclization reaction of the bio - based unsaturated polyester precursor, the reaction time is 1 h - 24 h, preferably 3 h - 12 h; for the depolymerization and cyclization reaction of the bio - based saturated polyester precursor, the reaction time is 1 h - 24 h, preferably 12 h - 24 h.

[0080] Further, the reaction temperature has a certain influence on the yield of the target product. Within a certain range, as the reaction temperature increases, the yield also increases. In the present invention, the reaction temperature of 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 °C - 80 °C. Preferably, the reaction temperature is 40 °C - 80 °C; the reaction temperature of the depolymerization and cyclization of the bio - based unsaturated polyester precursor and the bio - based saturated polyester precursor using the metal catalyst and the organic base catalyst can be controlled at 80 °C - 200 °C, and the preferred reaction temperature is 110 °C - 140 °C.

[0081] Further, the bio - based unsaturated cyclic ester monomer and the bio - based saturated cyclic ester monomer obtained by depolymerization and cyclization can be used as monomers for polymerization to generate a bio - based aliphatic polyester with good regularity.

[0082] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods, and the materials, reagents, etc. used, unless otherwise specified, can all be obtained from commercial channels.

[0083] Table 1

[0084]

[0085] In the following embodiments of the present invention, a matrix-assisted laser desorption / ionization time-of-flight mass spectrometer (MALDI-TOF) of the Bruker Ultrafle Xtreme model was used for testing. The test was carried out in the reflectron mode. The matrix selected was trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene] malononitrile (DCTB), and the cationic salt was sodium trifluoroacetate (CF 3 COONa).

[0086] In the following embodiments of the present invention, a Waters size exclusion chromatograph was used for determination. The size exclusion chromatograph consisted of a 1515 pump, a 2707 autosampler, and an RI 2414 differential refractive index detector, and was equipped with three PL Mixed-C columns. The mobile phase was CHCl 3 , the flow rate was 1.0 mL / min, the test temperature was 35 °C, and the molecular weight was calibrated with a narrow-distribution polystyrene as the standard sample.

[0087] In the following embodiments of the present invention, a DSC of the TA Q2000 model was used for testing. The test atmosphere was a nitrogen atmosphere, the nitrogen flow rate was 25 mL / min, and the heating / cooling rate was set at 10 °C / min. Example 1

[0088] This example provides a method for preparing a bio-based unsaturated diester, which is specifically as follows:

[0089] 18.0 g of 10-undecenoic acid, 4.19 g of 1,4-butanediol, 20.6 g of the catalyst 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl), 1.79 g of the catalyst 4-dimethylaminopyridine (DMAP), and 200 mL of anhydrous dichloromethane were added to a reaction flask, nitrogen was passed through, and the mixture was stirred at room temperature overnight. After the reaction was completed, it was washed three times with water. The organic phase was taken and the solvent was removed by rotary evaporation. After column chromatography, a colorless oily liquid, butanediol bis(10-ene-undecanoate), was obtained with a yield of 87%.

[0090] Under the same reaction conditions (catalyst), using 10-undecenoic acid and ethylene glycol as raw materials, the product ethylene glycol bis(10-undecenoate) was synthesized with a yield of 90%; using 10-undecenoic acid and 1,3-propanediol as raw materials, the product propylene glycol bis(10-undecenoate) was synthesized with a yield of 89%; using 10-undecenoic acid and 1,10-decanediol as raw materials, the product decylene glycol bis(10-undecenoate) was synthesized with a yield of 84%; using 10-undecenoic acid and 1,4-cyclohexanedimethanol as raw materials, the product 1,4-cyclohexanedimethanol bis(10-undecenoate) was synthesized with a yield of 70%; using 10-undecenoic acid and furan dimethanol as raw materials, the product furan dimethanol bis(10-undecenoate) was synthesized with a yield of 90%; using 10-undecenoic acid and neopentyl glycol as raw materials, the product neopentyl glycol bis(10-undecenoate) was synthesized with a yield of 89%. Example 2

[0091] This example provides a method for preparing a bio-based unsaturated diester, which is as follows:

[0092] Nitrogen was passed through and the temperature was maintained at 30 °C. 9.55 g of triphenylphosphine oxide (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. After column chromatography, a colorless oily liquid, ethylene glycol bis(9-octadecenoate), was obtained with a yield of 79%. Example 3

[0093] This example provides a method for preparing a bio-based unsaturated diester, which is as follows:

[0094] 5.00 g of erucic acid, 1.29 g of 1,5-pentanediol, and 25.0 mg of p-toluenesulfonic acid as a catalyst were added to the reaction flask. Nitrogen was passed through and the mixture was heated to 130 °C and stirred for 5 h to terminate the reaction. After the reaction was completed, 100 mL of dichloromethane was added to the reaction flask. The solution was washed repeatedly with saturated sodium bicarbonate solution and water. The organic phase was taken and anhydrous sodium sulfate was added to remove water. After filtration and rotary evaporation to remove the solvent, a pale yellow oily liquid, pentylene glycol bis(13-docosenoate), was obtained with a yield of 81%. Example 4

[0095] This example provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows:

[0096] Add 0.21 g of ethylene glycol bis(10-undecenoate), 1 mL of dichloromethane, and 4.2 mg of Grubbs catalyst into a reaction flask. Purge with nitrogen and reflux for 1 h to carry out olefin metathesis polymerization. After the polymerization is completed, add 100 mL of dichloromethane and 4.18 mg of Grubbs catalyst, and carry out the depolymerization cyclization reaction at low concentration after dilution, refluxing for 3 h. The product ethylene glycol 10-ene-eicosanedioate cyclic ester is obtained by column separation with a yield of 86%.

[0097] Using deuterated chloroform as the solvent, the chemical structure of ethylene glycol 10-ene-eicosanedioate cyclic ester was characterized by quantitative nuclear magnetic resonance hydrogen spectrum. The nuclear magnetic resonance hydrogen spectrum is shown in Figure 3 .

[0098] The product was tested by matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF). The macromolecular mass spectrum is shown in Figure 4 . The results showed that a molecular ion peak appeared at 389.15 (m / z), which is the sodium ion addition peak of ethylene glycol 10-ene-eicosanedioate cyclic ester (the theoretical value of m / z is 389.27). It was proved that ethylene glycol 10-ene-eicosanedioate cyclic ester was synthesized. Example 5

[0099] This example provides a preparation method of a bio-based unsaturated cyclic ester monomer, which is as follows:

[0100] Add 2.01 g of ethylene glycol bis(10-undecenoate), 5 mL of anhydrous toluene, and 21.5 mg of Grubbs catalyst into a reaction flask. Purge with nitrogen and react at 80 °C for 3 h to carry out olefin metathesis polymerization. After the polymerization is completed, add 45 mL of dichloromethane and 0.215 g of Grubbs catalyst, and carry out the depolymerization cyclization reaction at low concentration after dilution, reacting at 80 °C for 3 h. The product ethylene glycol 10-ene-eicosanedioate cyclic ester is obtained with a yield of 13%. Example 6

[0101] This example provides a preparation method of a bio-based unsaturated cyclic ester monomer, which is as follows:

[0102] Add 0.410 g of ethylene glycol bis(10-undecenoate), 4 mL of dichloromethane, and 41.8 mg of Grubbs catalyst into a reaction flask. Purge with nitrogen and react at 26 °C for 1 h to carry out olefin metathesis polymerization. After the polymerization is completed, add 196 mL of dichloromethane, and carry out depolymerization cyclization at low concentration, reacting at 26 °C for 9 h. The product ethylene glycol 10-ene-eicosanedioate cyclic ester is obtained with a yield of 66%. Example 7

[0103] This embodiment provides a method for preparing a bio-based unsaturated polyester precursor, which is as follows:

[0104] Add 10.0 g of ethylene glycol bis(10-undecenoate), 20.8 mg of Grubbs catalyst, and 5 mL of dichloromethane into a reaction flask. Purge with nitrogen and reflux for 3 h. After the reaction, add 50 mL of chloroform into the reaction flask. The solution is precipitated in a large amount of anhydrous methanol, and the polymer is obtained by filtration. Dry under vacuum to obtain 9.17 g of polyethylene glycol 10-undecenedioate, with a yield of 92%. Example 8

[0105] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows:

[0106] Add 1.00 g of polyethylene glycol 10-undecenedioate, 100 mL of anhydrous p-xylene, and 40 mg of dibutyltin oxide into a reaction flask. Purge with nitrogen and reflux for 12 h. The product ethylene glycol 10-undecenedioate cyclic ester is obtained, with a yield of 43%. Example 9

[0107] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows:

[0108] Add 0.20 g of polyethylene glycol 10-undecenedioate, 100 mL of anhydrous p-xylene, and 20 mg of dibutyltin oxide into a reaction flask. Purge with nitrogen and reflux for 12 h. The product ethylene glycol 10-undecenedioate cyclic ester is obtained, with a yield of 36%. Example 10

[0109] This embodiment provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows:

[0110] Add 1.00 g of polyethylene glycol 10-undecenedioate, 100 mL of anhydrous N-methylpyrrolidone (NMP), and 50.0 mg of 4-dimethylaminopyridine (DMAP) into a reaction flask. Purge with nitrogen and react at 180 °C for 6 h. The product ethylene glycol 10-undecenedioate cyclic ester is obtained, with a yield of 33%. Example 11

[0111] This embodiment provides a method for preparing a bio-based saturated polyester precursor, which is as follows:

[0112] Add 10.0 g of polyethylene glycol 1,20 - eicosanedioate, 50 mL of anhydrous toluene, and 600 mg of palladium - carbon catalyst into a reaction flask. Pass hydrogen gas, and react at 60 °C for 12 h. After the reaction is completed, filter off the catalyst by suction filtration, remove the reaction solvent by rotary evaporation, and obtain 9.91 g of white solid product polyethylene glycol eicosanedioate after vacuum drying, with a yield of 99%. Example 12

[0113] This example provides a preparation method of a bio - based saturated cyclic ester monomer, which is as follows:

[0114] Add 1.00 g of polyethylene glycol eicosanedioate, 100 mL of anhydrous p - xylene, and 40.0 mg of dibutyltin oxide into a reaction flask. Pass nitrogen gas and reflux for 12 h. Obtain the product ethylene glycol eicosanedioic anhydride, with a yield of 21%.

[0115] Using deuterated chloroform as the solvent, the chemical structure of ethylene glycol eicosanedioic anhydride was characterized by quantitative nuclear magnetic resonance hydrogen spectrum. The nuclear magnetic resonance hydrogen spectrum is shown in Figure 5 .

[0116] The product was tested by matrix - assisted laser desorption / ionization time - of - flight mass spectrometry (MALDI - TOF). The macromolecular mass spectrum is shown in Figure 6 . The results show that a molecular ion peak appears at 391.35 (m / z), which is the sodium - adduct ion peak of ethylene glycol eicosanedioic anhydride (the theoretical value of m / z is 391.28). It is proved that ethylene glycol eicosanedioic anhydride was synthesized. Example 13

[0117] This example provides a preparation method of a bio - based saturated cyclic ester monomer, which is as follows:

[0118] Add 0.21 g of polyethylene glycol eicosanedioate, 100 mL of anhydrous p - xylene, and 20 mg of dibutyltin oxide into a reaction flask. Pass nitrogen gas and reflux for 24 h. Obtain the product ethylene glycol eicosanedioic anhydride, with a yield of 18%. Example 14

[0119] This example provides a preparation method of a bio - based saturated cyclic ester monomer, which is as follows:

[0120] Add 40.8 mg of polyethylene glycol eicosanedioate, 20 mL of anhydrous toluene, and 4.0 mg of 4 - pyrrolidinopyridine (4 - PPy) into a reaction flask. Pass nitrogen gas and react at 80 °C for 1 h. Obtain the product ethylene glycol eicosanedioic anhydride, with a yield of 10%. Example 15

[0121] This example provides a preparation method of a bio - based unsaturated cyclic ester monomer, which is as follows:

[0122] Add 0.2 g of butanediol bis(10-undecenoate), 5 mL of dichloromethane, and 4.0 mg of Grubbs catalyst into a reaction flask. Purge with nitrogen and reflux for 1 h to carry out olefin metathesis polymerization. After the polymerization is completed, add 95 mL of dichloromethane and 4.0 mg of Grubbs catalyst, and carry out a ring-opening depolymerization reaction at a low concentration after dilution, with reflux for 3 h. The product butanediol 10-undecenedioate cyclic ester is obtained with a yield of 72%.

[0123] The product was tested by matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF), and the macromolecular mass spectrum is shown in Figure 7 . The results show that a molecular ion peak appears at 417.38 (m / z), which is the sodium ion addition peak of butanediol 10-undecenedioate cyclic ester (theoretical value of m / z is 417.30), proving the synthesis of butanediol 10-undecenedioate cyclic ester. Example 16

[0124] This example provides a preparation method of a bio-based unsaturated cyclic ester monomer, which is as follows:

[0125] Add 1.00 g of decanediol bis(10-undecenoate), 5 mL of dichloromethane, and 16.3 mg of Grubbs catalyst into a reaction flask. Purge with nitrogen and reflux for 1 h to carry out olefin metathesis polymerization. After the polymerization is completed, add 95 mL of dichloromethane and 16.3 mg of Grubbs catalyst, and carry out a ring-opening depolymerization reaction at a low concentration after dilution, with reflux for 3 h. The product decanediol 10-undecenedioate cyclic ester is obtained with a yield of 37%.

[0126] The product was tested by matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF), and the macromolecular mass spectrum is shown in Figure 8 . The results show that a molecular ion peak appears at 501.39 (m / z), corresponding to the sodium ion addition peak of decanediol 10-undecenedioate cyclic ester (theoretical value of m / z is 501.39), proving the synthesis of decanediol 10-undecenedioate cyclic ester. Example 17

[0127] This example provides a preparation method of a bio-based unsaturated cyclic ester monomer, which is as follows:

[0128] Add 1.00 g of ethylene glycol bis(9-octadecenoate), 5 mL of anhydrous toluene, and 16.4 mg of Grubbs catalyst into a reaction flask. Purge with nitrogen and react at 80 °C for 1 h to carry out olefin metathesis polymerization. After the polymerization is completed, add 95 mL of anhydrous toluene and 16.4 mg of Grubbs catalyst, and carry out the depolymerization and cyclization reaction at low concentration after dilution. React at 80 °C for 3 h. The product ethylene glycol 9-octadecenedioate cyclic ester is obtained with a yield of 23%.

[0129] The product was tested by matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF), and the macromolecular mass spectrum is shown in Figure 9 . The results showed that a molecular ion peak appeared at 361.32 (m / z), which was the sodium ion addition peak of ethylene glycol 9-octadecenedioate cyclic ester (the theoretical value of m / z was 361.24), proving the synthesis of ethylene glycol 9-octadecenedioate cyclic ester. Example 18

[0130] This example provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows:

[0131] Add 1.00 g of 1,4-cyclohexanedimethanol bis(10-undecenoate), 5 mL of dichloromethane, and 17.3 mg of Grubbs catalyst into a reaction flask. Purge with nitrogen and reflux for 1 h to carry out olefin metathesis polymerization. After the polymerization is completed, add 95 mL of dichloromethane and 17.3 mg of Grubbs catalyst, and carry out the depolymerization and cyclization reaction at low concentration after dilution. Reflux for 3 h. The product 1,4-cyclohexanedimethanol 10-eicosenedioate cyclic ester is obtained with a yield of 43%.

[0132] The product was tested by matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF), and the macromolecular mass spectrum is shown in Figure 10 . The results showed that a molecular ion peak appeared at 471.37 (m / z), which was the sodium ion addition peak of 1,4-cyclohexanedimethanol 10-eicosenedioate cyclic ester (the theoretical value of m / z was 471.34), proving the synthesis of 1,4-cyclohexanedimethanol 10-eicosenedioate cyclic ester. Example 19

[0133] This example provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows:

[0134] Add 1.00 g of bis(10-ene-undecanoic acid)-2,5-furandimethanol ester, 5 mL of dichloromethane, and 17.9 mg of Grubbs catalyst into a reaction flask. Pass nitrogen gas, reflux for 1 h to carry out olefin metathesis polymerization reaction. After the polymerization is completed, add 95 mL of dichloromethane and 17.9 mg of Grubbs catalyst, and carry out depolymerization cyclization reaction at low concentration after dilution, reflux for 3 h. Obtain the product 10-ene-eicosanedioic acid-2,5-furandimethanol cyclic ester with a yield of 52%.

[0135] The product was tested by matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF), and the macromolecular mass spectrum is shown in Figure 11 . The results showed that a molecular ion peak appeared at 455.34 (m / z), which was the sodium ion addition peak of 10-ene-eicosanedioic acid-2,5-furandimethanol cyclic ester (theoretical value of m / z 455.27), proving the synthesis of 10-ene-eicosanedioic acid-2,5-furandimethanol cyclic ester. Example 20

[0136] This example provides a method for preparing a bio-based unsaturated cyclic ester monomer, which is as follows:

[0137] Add neopentyl glycol bis(10-ene-undecanoate), 5 mL of dichloromethane, and 18.9 mg of Grubbs catalyst into a reaction flask. Pass nitrogen gas, reflux for 1 h to carry out olefin metathesis polymerization reaction. After the polymerization is completed, add 95 mL of dichloromethane and 18.9 mg of Grubbs catalyst, and carry out depolymerization cyclization reaction at low concentration after dilution, reflux for 3 h. Obtain the product 10-ene-eicosanedioic acid neopentyl glycol cyclic ester with a yield of 21%.

[0138] The product was tested by matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF), and the macromolecular mass spectrum is shown in Figure 12 . The results showed that a molecular ion peak appeared at 431.42 (m / z), which was the sodium ion addition peak of 10-ene-eicosanedioic acid neopentyl glycol cyclic ester (theoretical value of m / z 431.42), proving the synthesis of 10-ene-eicosanedioic acid neopentyl glycol cyclic ester. Example 21

[0139] This example provides a method for preparing a bio-based saturated cyclic ester monomer from a bio-based unsaturated cyclic ester monomer, which is as follows:

[0140] Add 5.00 g of 10-ene-eicosanedioic acid ethylene glycol cyclic ester, 50 mL of absolute ethanol, and 200 mg of palladium-carbon catalyst into a reaction flask, pass hydrogen gas, and react at 40 °C for 12 h to obtain 4.95 g of the product ethylene glycol eicosanedioic acid cyclic ester with a yield of 99%.

[0141] Under the same reaction conditions, using 10-ene-docosanedioic acid butanediol cyclic ester as the raw material, after hydrogenation, the product butanediol docosanedioate cyclic ester was obtained with a yield of 99%. Example 22

[0142] This example provides a method for preparing a bio-based saturated polyester from a bio-based saturated cyclic ester monomer, as follows:

[0143] Add 5.00 g of ethylene glycol docosanedioate cyclic ester and 16.9 mg of ethylene glycol into the reaction flask, purge with nitrogen to remove air, add 2.5 μL of tetrabutyl titanate, stir mechanically, and heat to react at 210 - 220 °C for 4 h to obtain a white tough solid, polyethylene glycol docosanedioate P2E. Figure 13 This is the size exclusion chromatogram of P2E. The measured molecular weight of P2E is 30.6 kg / moL.

[0144] The DSC curve of P2E is shown in Figure 14 . The melting temperature of the polymer is 95 °C and the crystallization temperature is 78 °C. Example 23

[0145] This example provides a method for preparing a bio-based saturated polyester from a bio-based saturated cyclic ester monomer, as follows:

[0146] Add 5.00 g of butanediol docosanedioate cyclic ester and 22.8 mg of 1,4-butanediol into the reaction flask, purge with nitrogen to remove air, add 2.5 μL of tetrabutyl titanate, stir mechanically, and heat to react at 220 - 240 °C for 4 h to obtain a white tough solid P4E. Figure 15 This is the size exclusion chromatogram of P4E, and the measured molecular weight of P4E is 52.1 kg / moL.

[0147] The DSC curve of P4E is shown in Figure 16 . The measured melting temperature is 87 °C and the crystallization temperature is 78 °C. The melting point of the polybutylene docosanedioate synthesized in the present invention is 87 °C, which is significantly higher than the melting point of the P4E polyester synthesized by Nomura et al. through ADMET polymerization (68 °C) [Nomura, K.; Chaijaroen, P.; Abdellatif, M. M. ACS Omega 2020, 5 , 18301 - 18312], because there is obvious olefin isomerization during the ADMET polymerization process, the methylene length of the diacid unit in the polyester is non-uniform, resulting in a decrease in the regularity of the polyester and a corresponding decrease in its thermal properties, etc. Example 24

[0148] This embodiment provides a method for preparing a bio-based unsaturated polyester from a bio-based unsaturated cyclic ester monomer, which is as follows:

[0149] Add 9.80 g of ethylene glycol cycloester of 10-ene-eicosanedioic acid and 15.8 mg of 1,10-decanediol into a reaction flask. Purge the air with nitrogen, add 50 μL of stannous octoate, stir mechanically, and heat to 150 °C for reaction for 12 h to obtain a white tough solid poly(ethylene glycol 10-ene-eicosanedioate) P2UE. Figure 17 This is the size exclusion chromatogram of P2UE. The measured molecular weight of P2UE is 27.2 kg / mol.

[0150] The DSC curve of P2UE is shown in Figure 18 . The measured melting temperature is 67 °C and the crystallization temperature is 49 °C. The melting point is higher than the melting point (49 °C) of unsaturated polyesters synthesized by ADMET polymerization reported in the literature [Abdellatif, M. M.; Nomura, K. A CS Omega 2024, 9 , 9109-9122]. This shows that when directly synthesizing long-chain aliphatic polyesters by ADMET polymerization, the degree of olefin isomerization is large, resulting in uneven methylene lengths of the diacid units in the synthesized polyester, causing structural defects and a low melting point.

[0151] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill 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 manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for preparing bio-based polyester, characterized in that: The bio-based polyester is prepared by ring-opening polymerization or ring-opening-condensation cascade polymerization of the ester bond of the bio-based cyclic ester monomer; the bio-based polyester is selected from the group consisting of bio-based unsaturated polyester and bio-based saturated polyester; The above-mentioned preparation method also includes a preparation method of 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) preparing a bio-based cyclic ester monomer by depolymerizing the obtained bio-based unsaturated polyester precursor into a ring and / or catalytic hydrogenation; the bio-based cyclic ester monomer is selected from 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 ; Wherein, p is any integer between 2 and 10; 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; The catalyst used for the depolymerization and ring formation is one or more of dibutyltin oxide, 4-dimethylaminopyridine and 4-pyrrolidinopyridine.

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 and 1,10-decanediol.

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 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: 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.

6. The preparation method according to claim 1, characterized in that: The reaction concentration of the bio-based saturated polyester precursor is 2 g / L-50 g / L; and / or, 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.

7. 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.

8. The preparation method according to claim 1, 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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