A catalyst for preparing polyester by ring-opening polymerization and a method for preparing polyester

Abstract

The invention discloses a catalyst for preparing polyester by ring-opening polymerization and a method for preparing polyester, belonging to the technical field of organic catalysis and polymer materials. In the presence of an initiator alcohol, a cyclic ester monomer is ring-opened and polymerized under the catalysis of an organic bifunctional phosphine salt to obtain polyester. The catalyst used in the method does not contain metal, is cheap and easy to obtain, and has the characteristics of high temperature resistance, and may be applied in bulk polymerization under industrial conditions. The method is simple in process, low in cost, high in reaction activity, and the prepared polyester has the advantages of accurate molecular weight and low molecular weight distribution.

Description

Technical Field

[0001] The invention belongs to the technical field of organic catalysis and polymer materials, and in particular relates to a catalyst for preparing polyester through ring-opening polymerization and a method for preparing polyester. Background Art

[0002] Among many synthetic polymer materials, aliphatic polyesters occupy an important position due to their excellent biodegradability, bioabsorbability and biocompatibility. As a new environmentally friendly material, this type of polyester material has attracted much research attention in the field of polymer chemistry and has been gradually applied to the biomedical and microelectronic fields.

[0003] The traditional method for preparing polyester is mainly the condensation method, which usually requires high temperature and high energy consumption. In addition, the product obtained has a low molecular weight and a wide molecular weight distribution. The reaction process is uncontrollable and most of the time there are side reactions.

[0004] The preparation of aliphatic polyesters by ring-opening polymerization of cyclic monomers is one of the active and controllable methods. The polyester prepared by ring-opening polymerization has the characteristics of high molecular weight and narrow molecular weight distribution. It can not only accurately control the chemical composition of the polymerization product, but also improve the stability of material performance, make the properties and uses of the material more mild, and broaden the application field of aliphatic polyesters. In the past decade, the research on the preparation of polyesters using metal complexes has been relatively extensive, but the polylactic acid prepared by this method cannot be used in fields such as biomedicine and microelectronics because it is extremely difficult to remove metal residues.

[0005] Ring-opening polymerization catalyzed by organic catalysts is mild, efficient, and free of transesterification reactions. It also avoids the problem of metal residues in the product, and the resulting polyester has a clear structure and low molecular weight distribution. It is precisely because of the excellent properties of organic catalysis that finding an organic catalyst that is more suitable for ring-opening polymerization has great commercial application value.

[0006] The industrial production of polyesters, polycarbonates and other related polymers generally adopts bulk polymerization, which has a high polymerization temperature. Many excellent organic catalysts have low thermal stability and are deactivated or degraded at industrial production temperatures, limiting their application. Summary of the invention

[0007] The object of the present invention is to provide a method for preparing polyester by ring-opening polymerization of cyclic monomers catalyzed by organic bifunctional phosphonium salts. The catalyst used in the method does not contain metal, is cheap and readily available, and has the characteristics of high temperature resistance, and may be applied in bulk polymerization under industrial conditions. The method has the advantages of simple process, low cost, high reaction activity, and the prepared polyester does not contain metal residues, has accurate molecular weight and low molecular weight distribution.

[0008] The idea of ​​the present invention is as follows:

[0009] (1) Under the reaction conditions, the organic bifunctional phosphonate activates both the cyclic monomer and the initiator.

[0010] (2) In the presence of an alcohol initiator, an organic bifunctional phosphine salt catalyzes the ring-opening polymerization of cyclic monomers to obtain polyester.

[0011] The present invention has found that different organic bifunctional phosphonate substituents will affect the catalytic efficiency. The ring-opening polymerization reaction needs to determine the appropriate temperature and temperature range according to the property requirements of the polymerization product and the process conditions of the polymerization reaction device to ensure that the polymerization reaction is effectively carried out within a certain temperature range.

[0012] The controllable distribution of the terminal structure and molecular weight of the polylactone, such as the narrow molecular weight distribution, can be solved by adding a compound containing active hydrogen (ROH) as an initiator in the ring-opening polymerization reaction. The terminal structures of the initiated monomers are RO- and -OH, respectively, and the ratio of the lactone monomer to the initiator determines the target molecular weight of the obtained polylactone. In the presence of an initiator, the ring-opening polymerization catalyzed by an organic bifunctional phosphine salt is active, and the molecular weight and terminal structure of the obtained polymer are controllable and the molecular weight distribution is narrow.

[0013] The technical solution of the present invention is as follows:

[0014] The invention provides a method for preparing polyester by using an organic difunctional phosphonium salt as a catalyst to catalyze the ring-opening polymerization of cyclic monomers. The method uses cyclic monomers as reaction monomers, an organic difunctional phosphonium salt as a catalyst, and an alcohol compound as an initiator. The ring-opening polymerization reaction is carried out under bulk conditions, and the polyester is obtained through separation and purification.

[0015] The structure of the organic bifunctional phosphine salt catalyst described in the above preparation method is shown in formula (I):

[0016]

[0017] in

[0018] R1, R2, and R3 are selected from straight-chain or branched alkyl groups having 1 to 8 carbon atoms, cycloalkyl groups having 5 or 6 carbon atoms, and substituted or unsubstituted phenyl groups; R1, R2, and R3 may be from the same group or may not be from the same group, and the "substituted" substituents are straight-chain or branched alkyl groups having 1 to 4 carbon atoms, methoxy groups, and halogen groups.

[0019] Preferred are methyl, ethyl, propyl, butyl, hexyl, octyl, 1-methylpentyl, 2-methylpentyl, 5-methylhexyl, isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, isohexyl, cyclobutyl, cyclopentyl, cyclohexyl, phenyl, benzyl, o-methylphenyl, p-methylphenyl, m-methylphenyl, p-methoxyphenyl, 4-fluorophenyl and the like.

[0020] Typically, formula (I) may have structures as shown in numbers 1 to 20:

[0021]

[0022]

[0023] A method for preparing polyester by ring-opening polymerization, in the presence of an initiator, using an organic bifunctional phosphonium salt to catalyze the ring-opening polymerization of cyclic monomers to obtain polyester compounds, wherein the organic bifunctional phosphonium salt is a catalyst for the organic bifunctional phosphonium salt described above.

[0024] The cyclic monomers used in the above method for preparing polyester by ring-opening polymerization are selected from one or more of the following:

[0025] (1) The monomer has a structure as shown in formula (II):

[0026]

[0027] Where A is [—(CR 1 R 2 )—] n , n is an integer from 2 to 10; R 1 , R 2 The same or different groups selected from H, an alkyl group having 1 to 5 carbon atoms and an alkyl group having 1 to 5 carbon atoms and substituted by a halogen atom or a hydroxyl group, such as β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, macrocyclic decalactone, chlorocaprolactone;

[0028] (2) The monomer has a structure as shown in formula (III):

[0029]

[0030] Among them, A and B are [—(CR 1 R 2 )—] n , n is an integer from 0 to 10, A and B are the same or different; R 1 , R 2 The same or different groups selected from H, an alkyl group having 1 to 5 carbon atoms and substituted by a halogen atom or a hydroxyl group, such as glycolide, lactide, bromoglycolide, butyride, decide, macrocyclic dodecanide, O-carboxylic acid anhydride;

[0031] (3) The monomer has a structure as shown in formula (IV):

[0032]

[0033] Among them, R 1 , R2 The same or different groups selected from H, alkyl groups having 1 to 5 carbon atoms and substituted by halogen atoms or hydroxyl groups, such as trimethylene carbonate, hydroxytrimethylene carbonate, chlorotrimethylene carbonate.

[0034] Preferably, the cyclic monomer is selected from one or more of the following: β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, macrocyclic decalactone, chlorocaprolactone, glycolide, lactide, bromoglycolide, butyride, decide, macrocyclic dodecanide, O-carboxylic acid anhydride, trimethylene carbonate, hydroxytrimethylene carbonate, chlorotrimethylene carbonate.

[0035] The initiator preferably used is an alcohol compound, including methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, benzyl alcohol, phenylethyl alcohol, phenylpropanol, ethylene glycol, ethylene glycol acetal or pentaerythritol.

[0036] The bulk conditions described in the above preparation method refer to reaction conditions without using a reaction solvent, the reaction temperature is 40 to 200 degrees Celsius, preferably 60 to 140 degrees Celsius; the reaction time is 0.2 to 90 hours, preferably 0.5 to 48 hours; the molar ratio of the cyclic monomer to the initiator is 5 to 500:1, preferably 25 to 200:1; the molar ratio of the cyclic monomer to the catalyst is 5 to 500:1, preferably 25 to 250:1.

[0037] The separation and purification described in the above preparation method refers to dissolving the reaction product with a good solvent and then precipitating it with a precipitation solvent. The good solvent used is dichloromethane, chloroform, toluene, benzene, acetone or tetrahydrofuran, preferably dichloromethane, chloroform or tetrahydrofuran, and the precipitation solvent used is methanol, ethanol or water.

[0038] Beneficial Effects

[0039] In this patent, an organic bifunctional phosphonium salt is used as a catalyst to catalyze the ring-opening polymerization of cyclic monomers to prepare polyester. This method adopts a bulk polymerization method, and there is no need to introduce additional reaction solvents into the reaction system, which is conducive to industrial production. Moreover, in a bulk polymerization system, the reaction temperature is generally high, which greatly reduces the sensitivity of the reaction system to air and water, and facilitates industrial operation. This process can controllably synthesize a product polyester with a target molecular weight according to demand, with a high product yield, no monomer residue, and a clean and white product appearance. In summary, the present invention has obvious advantages such as high efficiency, simple operation, and a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The embodiments of the present invention are described in detail with reference to the accompanying drawings, wherein

[0041] Figure 1 Example 1 prepared poly L-lactide 1H NMR spectrum;

[0042] Figure 2 . Spectrum of poly-L-lactide prepared in Example 1 in size exclusion chromatography analysis;

[0043] Figure 3 Example 7 Preparation of polytrimethylene carbonate 1 H NMR spectrum;

[0044] Figure 4 . Spectrum of polytrimethylene carbonate prepared in Example 7 in size exclusion chromatography analysis;

[0045] Figure 5 Example 10 Preparation of polyvalerolactone 1 H NMR spectrum;

[0046] Figure 6 .The spectrum of the size exclusion chromatography analysis of polyvalerolactone prepared in Example 10.

[0047] Figure 7-9 . The catalyst (8) prepared in Example 1 1 H NMR, 13 C NMR, 31 P NMR spectrum.

[0048] Figure 10-12 . Catalyst (2) prepared in Example 2 1 H NMR, 13 C NMR, 31 P NMR spectrum.

[0049] Figure 13-16 . The catalyst (13) prepared in Example 5 1 H NMR, 13 C NMR, 31 P NMR, 19 F NMR spectrum.

[0050] Figure 17-19 . Catalyst (12) prepared in Example 7 1 H NMR, 13 C NMR, 31 P NMR spectrum.

[0051] Figure 20-22 . The catalyst (9) prepared in Example 8 1 H NMR, 13 C NMR, 31 P NMR spectrum.

[0052] Figure 23-25. Catalyst (7) prepared in Example 9 1 H NMR, 13 C NMR, 31 P NMR spectrum. DETAILED DESCRIPTION

[0053] The present invention can be further described by the following examples, which are intended to illustrate but not to limit the present invention. Any person skilled in the art will appreciate that these examples do not limit the present invention in any way and that appropriate modifications and data conversions may be made thereto without violating the spirit of the present invention and departing from the scope of the present invention.

[0054] The organic bifunctional phosphine salt catalyst used in the examples has the following structure:

[0055]

[0056] Example 1

[0057] In a 10 mL polymerization tube, L-lactide (0.36 g, 2.5 mmol), catalyst (8) (0.033 g, 0.1 mmol), and phenylpropanol (13.5 μL, 0.1 mmol) were added. The mixture was stirred under magnetic stirring at 140° C. for 0.5 h. The reaction was stopped. A small amount of dichloromethane was added dropwise to the obtained mixture to dissolve it. The obtained solution was then slowly added dropwise to cold methanol. A white polymer was precipitated. After centrifugation and vacuum drying, 0.21 g of the product was obtained. The conversion rate was 96%. The number average molecular weight of the poly (L-lactide) was M n The molecular weight distribution PDI is 1.08. Figure 1 , 2 )

[0058] The preparation method of catalyst (8) is as follows: add a rotor to a 50mL round-bottom flask and perform a schlenk operation. Add triphenylphosphine (2.62g, 10mmol, 1.0eq) and chloroform (10mL) under an inert atmosphere. In a closed system, slowly add acrylic acid (0.84mL, 12mmol, 1.2eq) with a syringe while stirring at room temperature, and the solution gradually turns light yellow. Stir at room temperature for 24 hours, concentrate the reaction solution in vacuo, and precipitate in ether as a white slurry. Wash the ether precipitate three times, purify by column chromatography (DCM:MeOH=1:1), and vacuum dry to constant weight to obtain catalyst (8) as a white solid (2.71g, 81%). (Attached Figure 7-9 )

[0059] Example 2

[0060] In a 10 mL polymerization tube, D-lactide (0.36 g, 2.5 mmol), catalyst (2) (0.027 g, 0.1 mmol), and pentaerythritol (9.7 μL, 0.1 mmol) were added. The mixture was stirred under magnetic stirring at 140° C. for 2 hours. The reaction was stopped. A small amount of dichloromethane was added dropwise to the obtained mixture to dissolve it. The obtained solution was then slowly added dropwise to cold methanol. A white polymer precipitated. After centrifugation and vacuum drying, 0.19 g of the product was obtained. The conversion rate was 93%. The number average molecular weight of poly D-lactide M n It is 3320 g / mol and the molecular weight distribution PDI is 1.15.

[0061] The preparation method of catalyst (2) is as follows: add a rotor to a 50mL round-bottom flask and perform a schlenk operation. Add tributylphosphine (2.50mL, 10mmol, 1.0eq) and chloroform (10mL) under an inert atmosphere. In a closed system, slowly add acrylic acid (0.84mL, 12mmol, 1.2eq) with a syringe while stirring at room temperature, and the solution gradually turns light yellow. Stir at room temperature for 24 hours, concentrate the reaction solution in a vacuum, and precipitate in ether as a yellow viscous liquid. Wash the ether precipitate three times, and vacuum dry to constant weight to obtain catalyst (2) as a yellow viscous liquid (2.32g, 84%). (Attached Figure 10-12 )

[0062] Example 3

[0063] In a 10 mL polymerization tube, L-lactide (0.36 g, 2.5 mmol), catalyst (3) (0.027 g, 0.1 mmol), and benzyl alcohol (10.0 μL, 0.1 mmol) were added. The mixture was stirred under magnetic stirring at 140° C. for 2 hours. The reaction was stopped. A small amount of dichloromethane was added dropwise to the obtained mixture to dissolve it. The obtained solution was then slowly added dropwise to cold methanol. A white polymer precipitated. After centrifugation and vacuum drying, 0.22 g of the product was obtained. The conversion rate was 95%. The number average molecular weight of the poly (L-lactide) was M n It is 3370 g / mol and the molecular weight distribution PDI is 1.14.

[0064] Example 4

[0065] In a 10 mL polymerization tube, glycolide (0.348 g, 3 mmol), catalyst (15) (0.035 g, 0.1 mmol), and phenylpropanol (13.5 μL, 0.1 mmol) were added. The mixture was stirred magnetically at 130° C. for 4 hours. The reaction was stopped. A small amount of tetrahydrofuran was added dropwise to the obtained mixture to dissolve it. The obtained solution was then slowly added dropwise to cold methanol. A white polymer was precipitated. After centrifugation and vacuum drying, 0.28 g of the product was obtained. The conversion rate was 96%. The number average molecular weight of polyglycolide M nThe molecular weight distribution PDI is 1.17.

[0066] Example 5

[0067] In a 10 mL polymerization tube, L-butyrolactide (1.512 g, 9 mmol), catalyst (13) (0.039 g, 0.1 mmol), and benzyl alcohol (10.0 μL, 0.1 mmol) were added, and magnetic stirring was performed at 140° C. for 8 hours. The reaction was stopped, and a small amount of tetrahydrofuran was added dropwise to the obtained mixture to dissolve it. The obtained solution was then slowly dropped into cold methanol, and a white polymer was precipitated. After centrifugation and vacuum drying, 1.02 g of the product was obtained, with a conversion rate of 95%. The number average molecular weight of poly L-butyrolactide M n The molecular weight is 14300 g / mol and the molecular weight distribution PDI is 1.24.

[0068] The preparation method of catalyst (13) is as follows: add a rotor to a 50mL round-bottom flask and perform a schlenk operation. Add tri(4-fluorophenyl)phosphine (3.16g, 10mmol, 1.0eq) and chloroform (10mL) under an inert atmosphere. In a closed system, slowly add acrylic acid (0.84mL, 12mmol, 1.2eq) with a syringe while stirring at room temperature, and the solution gradually turns light yellow. Stir at room temperature for 24 hours, concentrate the reaction solution in vacuo, and precipitate in ether as a white slurry. Wash the ether precipitate three times, purify by column chromatography (DCM:MeOH=1:1), and vacuum dry to constant weight to obtain catalyst (13) as a white solid (2.79g, 72%). (Attached Figure 13-16 )

[0069] Example 6

[0070] In a 10 mL polymerization tube, L-lactide (1.728 g, 12 mmol), catalyst (8) (0.033 g, 0.1 mmol), and isopropanol (7.6 μL, 0.1 mmol) were added. The mixture was stirred under magnetic stirring at 140° C. for 3 hours. The reaction was stopped. A small amount of tetrahydrofuran was added dropwise to the obtained mixture to dissolve it. The obtained solution was then slowly added dropwise to cold methanol. A white polymer precipitated. After centrifugation and vacuum drying, 1.34 g of the product was obtained. The conversion rate was 94%. The number average molecular weight of the poly (L-lactide) was M . n The molecular weight is 16500 g / mol and the molecular weight distribution PDI is 1.19.

[0071] Example 7

[0072] In a 10 mL polymerization tube, trimethylene carbonate (0.306 g, 3 mmol), catalyst (12) (0.042 g, 0.1 mmol), and phenylpropanol (13.5 μL, 0.1 mmol) were added, and magnetic stirring was performed at 60° C. for 48 hours. The reaction was stopped, and a small amount of chloroform was added dropwise to the obtained mixture to dissolve it. The obtained solution was then slowly added dropwise to cold ethanol, and a white polymer was precipitated. After centrifugation and vacuum drying, 0.18 g of the product was obtained, and the conversion rate was 96%. The number average molecular weight of polytrimethylene carbonate M n It is 3510 g / mol and the molecular weight distribution PDI is 1.15.

[0073] (Attached Figure 3 , 4 )

[0074] The preparation method of catalyst (12) is as follows: add a rotor to a 50mL round-bottom flask and perform a schlenk operation. Add tri(4-methoxyphenyl)phosphine (3.52g, 10mmol, 1.0eq) and chloroform (10mL) under an inert atmosphere. In a closed system, slowly add acrylic acid (0.84mL, 12mmol, 1.2eq) with a syringe while stirring at room temperature, and the solution gradually turns light yellow. Stir at room temperature for 24 hours, concentrate the reaction solution in vacuo, and precipitate in ether as a white slurry. Wash the ether precipitate three times, purify by column chromatography (DCM:MeOH=1:1), and vacuum dry to constant weight to obtain catalyst (12) as a white solid (3.94g, 93%). (Attached Figure 17-19 )

[0075] Example 8

[0076] In a 10 mL polymerization tube, hydroxytrimethylene carbonate (0.714 g, 6 mmol), catalyst (9) (0.038 g, 0.1 mmol), and isopropanol (7.6 μL, 0.1 mmol) were added. The mixture was stirred under magnetic stirring at 60° C. for 48 hours. The reaction was stopped. A small amount of chloroform was added dropwise to the obtained mixture to dissolve it. The obtained solution was then slowly added dropwise to cold ethanol. A white polymer was precipitated. After centrifugation and vacuum drying, 0.42 g of the product was obtained. The conversion rate was 93%. The number average molecular weight M of polyhydroxytrimethylene carbonate was 0. n It is 6180 g / mol and the molecular weight distribution PDI is 1.22.

[0077] The preparation method of catalyst (9) is as follows: add a rotor to a 50mL round-bottom flask and perform a schlenk operation. Add tri(4-methylphenyl)phosphine (3.04g, 10mmol, 1.0eq) and chloroform (10mL) under an inert atmosphere. In a closed system, slowly add acrylic acid (0.84mL, 12mmol, 1.2eq) with a syringe while stirring at room temperature, and the solution gradually turns light yellow. Stir at room temperature for 24 hours, concentrate the reaction solution in vacuo, and precipitate in ether as a white slurry. Wash the ether precipitate three times, purify by column chromatography (DCM:MeOH=1:1), and vacuum dry to constant weight to obtain catalyst (9) as a white solid (3.42g, 91%). (Attached Figure 20-22 )

[0078] Example 9

[0079] In a 10 mL polymerization tube, chlorotrimethylene carbonate (0.825 g, 6 mmol), catalyst (7) (0.035 g, 0.1 mmol), and n-butanol (9.1 μL, 0.1 mmol) were added. The mixture was stirred under magnetic stirring at 60° C. for 48 hours. The reaction was stopped. A small amount of chloroform was added dropwise to the obtained mixture to dissolve it. The obtained solution was then slowly added dropwise to cold ethanol. A white polymer was precipitated. After centrifugation and vacuum drying, 0.47 g of the product was obtained. The conversion rate was 94%. The number average molecular weight of polychlorotrimethylene carbonate was M n The molecular weight distribution PDI is 1.22.

[0080] The preparation method of catalyst (7) is as follows: add a rotor to a 50mL round-bottom flask and perform a schlenk operation. Add tricyclohexylphosphine (2.80g, 10mmol, 1.0eq) and chloroform (10mL) under an inert atmosphere. In a closed system, slowly add acrylic acid (0.84mL, 12mmol, 1.2eq) with a syringe while stirring at room temperature, and the solution gradually turns light yellow. Stir at room temperature for 24 hours, concentrate the reaction solution in vacuo, and precipitate in ether as a white slurry. Wash the ether precipitate three times, and vacuum dry to constant weight to obtain catalyst (7) as a white solid (3.31g, 94%). (Attached Figure 23-25 )

[0081] Example 10

[0082] In a 10 mL polymerization tube, δ-valerolactone (1.65 mL, 6 mmol), catalyst (4) (0.036 g, 0.1 mmol), and benzyl alcohol (10.0 μL, 0.1 mmol) were added. The mixture was stirred under magnetic stirring at 90° C. for 48 hours. The reaction was stopped. A small amount of dichloromethane was added dropwise to the obtained mixture to dissolve it. The obtained solution was then slowly added dropwise to cold ethanol. A white polymer was precipitated. After centrifugation and vacuum drying, 1.3 g of the product was obtained. The conversion rate was 91%. The number average molecular weight of polyvalerolactone was M n The molecular weight distribution PDI is 1.25. Figure 5 , 6 )

[0083] Embodiment 11

[0084] In a 10 mL polymerization tube, ε-caprolactone (0.36 mL, 3 mmol), catalyst (8) (0.033 g, 0.1 mmol), and phenylpropanol (13.5 μL, 0.1 mmol) were added. The mixture was stirred under magnetic stirring at 90° C. for 18 hours. The reaction was stopped. A small amount of dichloromethane was added dropwise to the obtained mixture to dissolve it. The obtained solution was then slowly added dropwise to cold ethanol. A white polymer was precipitated. After centrifugation and vacuum drying, 0.25 g of the product was obtained. The conversion rate was 96%. The number average molecular weight of polycaprolactone was M n It is 3360 g / mol and the molecular weight distribution PDI is 1.21.

Claims

1. A method for preparing polyester by ring-opening polymerization, characterized in that: In the presence of an initiator, an organic bifunctional phosphonate is used to catalyze the ring-opening polymerization of a cyclic monomer to obtain a polyester compound, wherein the organic bifunctional phosphonate has a structure as shown in formula (I): Wherein, R1, R2, and R3 are selected from a straight chain or branched alkyl group having 1 to 8 carbon atoms, a cycloalkyl group having 5 or 6 carbon atoms, and a substituted or unsubstituted phenyl group; R1, R2, and R3 may be the same or different, and the "substituted" substituent is a straight chain or branched alkyl group having 1 to 4 carbon atoms, a methoxy group, or a halogen.

2. The method according to claim 1, characterized in that R1, R2, and R3 in the organic bifunctional phosphine salt may be the same or different and are selected from methyl, ethyl, propyl, butyl, hexyl, octyl, 1-methylpentyl, 2-methylpentyl, 5-methylhexyl, isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, isohexyl, cyclobutyl, cyclopentyl, cyclohexyl, phenyl, benzyl, o-methylphenyl, p-methylphenyl, m-methylphenyl, p-methoxyphenyl, and 4-fluorophenyl.

3. The method according to claim 1, characterized in that The organic bifunctional phosphonic acid salt is selected from the structures shown in numbers 1 to 20:

4. The method according to claim 1, characterized in that: The cyclic monomer used is selected from one or more of the following: (1) The monomer has a structure as shown in formula (II): Where A is [—(CR 1 R 2 )—] n , n is an integer from 2 to 10; R 1 , R 2 independently selected from H, substituted or unsubstituted alkyl groups having 1 to 5 carbon atoms, the substituent being a halogen atom or a hydroxyl group; (2) The monomer has a structure as shown in formula (III): Among them, A and B are [—(CR 1 R 2 )—] n , n is an integer from 0 to 10, A and B are the same or different; R 1 , R 2 independently selected from H, substituted or unsubstituted alkyl groups having 1 to 5 carbon atoms, the substituent being a halogen atom or a hydroxyl group; (3) The monomer has a structure as shown in formula (IV): Among them, R 1 , R 2 Independently selected from H, substituted or unsubstituted alkanes having 1 to 5 carbon atoms, the substituent is a halogen atom or a hydroxyl group.

5. The method according to claim 4, characterized in that The cyclic monomer is selected from one or more of the following: β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, macrocyclic decalactone, chlorocaprolactone, glycolide, lactide, bromoglycolide, butyrolactide, decanoide, macrocyclic dodecanide, O-carboxylic acid anhydride, trimethylene carbonate, hydroxytrimethylene carbonate, and chlorotrimethylene carbonate.

6. The method according to claim 1, characterized in that The initiator is methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, benzyl alcohol, phenylethyl alcohol, phenylpropanol, ethylene glycol, ethylene glycol condensate or pentaerythritol.

7. The method according to claim 1, characterized in that The molar ratio of the cyclic monomer to the initiator is 5-500:1; the molar ratio of the cyclic monomer to the catalyst is 5-500:1; the reaction temperature of the method for preparing polyester is 40-200°C and the reaction time is 0.2-90 hours.

8. The method according to claim 7, characterized in that The molar ratio of the cyclic monomer to the initiator is 25 to 250:1; the molar ratio of the cyclic monomer to the catalyst is 25 to 250:1; the reaction temperature of the method for preparing polyester is 60 to 140°C, and the reaction time is 0.5 to 48 hours.

9. The method according to claim 1, characterized in that: The method further comprises dissolving the reaction product with a good solvent and then precipitating it with a precipitation solvent, wherein the good solvent is dichloromethane, chloroform, toluene, benzene, acetone or tetrahydrofuran, and the precipitation solvent is methanol, ethanol or water.

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