A zinc complex containing nitrogen-phosphorus double bond, a preparation method and application thereof in catalytic synthesis of polylactide

Abstract

The application provides a zinc complex containing a nitrogen-phosphorus double bond, which catalyzes ring-opening polymerization of propylene lactone as a catalyst, has high catalytic activity, short polymerization time and green polymerization. In an actual production process, the purposes of saving energy, shortening a production cycle and reducing production cost can be achieved. The method can realize controllable polymerization, has mild polymerization reaction conditions, simple operation, is expected to realize batch industrial production, has good biological safety and is expected to realize its application in the fields of biomedicine and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of polymerization, especially relates to the polymerization of lactide, in particular, relates to a zinc complex containing nitrogen-phosphorus double bond and a preparation method thereof, and application of the zinc complex as a catalyst in ring-opening polymerization of lactide. BACKGROUND

[0002] In 1920, Hermann Staudinger published the first article introducing the concept of polymerization. Over the past one hundred years, with the development of petrochemical industry, polymer materials have gradually become the cornerstone of modern life and are widely used in various fields. However, from the environmental point of view, most polymers are derivatives of petrochemical products, so there are corresponding defects in sustainability. Although only a small part of oil and natural gas is used to manufacture polymer materials, since fossil fuels are a non-renewable resource, it is crucial to find a renewable raw material substitute. On the other hand, in the post-processing of waste polymers, only a part enters the landfill, while a considerable amount of plastic fragments enter the ocean circulation, causing harmful effects on marine organisms and potentially human life. The emergence of biodegradable polymer materials provides a more convenient way of polymer processing, which can effectively avoid the problem of landfill accumulation; similarly, the source of biodegradable polymer materials is renewable, for example, the commercially available polylactic acid (PLA) is derived from starch-rich plants: sugar beets, corn and potatoes, etc.

[0003] Among the many synthetic biodegradable materials, the most studied are linear aliphatic polyesters, especially homopolymerization and copolymerization of poly(lactide) (PLA), poly(caprolactone) (PCL), poly(glycolide) (PGA), etc. These polymers are metabolized in the body and are excreted in the form of water and carbon dioxide, so they not only have biodegradability, but also have certain biocompatibility. In addition, lactide can be obtained from crops and cash crops, and the raw materials are inexhaustible. Therefore, it is possible to realize large-tonnage production of these polymers, and even replace petroleum-based materials. These environmentally friendly polymer materials can be rapidly degraded without harming natural organisms and the environment, and aliphatic polyesters such as PLA have a prominent role in various fields as one of the most potential alternative materials. With the development of technology, people expect to use efficient metal catalysts to catalyze the ROP of cyclic esters with high catalytic activity and stereoselectivity.

[0004] In recent years, the Williams group found that the introduction of phosphorus atoms to replace carbon atoms in the Salen structure to prepare a series of metal complexes containing phosphorus imine structures not only has high catalytic efficiency, but also maintains good stereoselectivity for racemic lactide. Therefore, metal complexes containing phosphorus-nitrogen double bonds have attracted attention. Further studies have shown that, compared with the C=N bond in the Salen ligand structure, the P=N double bond structure has a significantly different electronic distribution due to the large difference in electronegativity between phosphorus and nitrogen atoms, thereby making P=N have high ionic bond properties. The nitrogen atom has strong σ and π electron-donating ability due to two lone electron pairs, which improves the Lewis acidity of the coordinated metal center and makes the metal-oxygen bond more loose, which is beneficial to the insertion of monomers and thus improves the activity of ring-opening polymerization. At the same time, in terms of geometric configuration, the phosphorus in the phosphorus imine (P=N) is a pyramid with two substituents, which is different from the sp 2 hybridized C=N, and the imine carbon is a triangular planar structure with only one substituent, so their bond lengths are obviously different vs ). Therefore, the P=N double bond in the phosphorus imine has a highly polarized characteristic, and it mainly forms a stable complex with a transition metal through the nitrogen atom with approximate sp 2 hybridization, thereby exhibiting unique catalytic properties.

[0005] Zinc is one of the elements involved in human metabolism, and it is a common metal in nature, with low acquisition cost and low price. In recent years, there have been many studies on the catalysis of ring-opening polymerization of lactide by zinc complexes. However, the catalytic activity of the new catalysts is weak, and the stability in air is poor, which makes storage and transportation difficult. In order to meet the large-scale production of polymer materials and to prepare biodegradable materials with high biological safety, high molecular weight and narrow molecular weight distribution, it is urgent to develop a polyester polymerization method with simple process and industrialization production, and to prepare biodegradable polyesters with high biological safety and good performance. SUMMARY

[0006] In order to overcome the above problems, the present application provides a zinc complex containing a nitrogen-phosphorus double bond, and uses the zinc complex and a co-initiator as a catalyst composition to catalyze the ring-opening polymerization of lactide, thereby achieving efficient polymerization of lactide under mild conditions, and thus completing the present application.

[0007] The first aspect of the present application aims to provide a zinc complex containing a nitrogen-phosphorus double bond, wherein zinc forms a bicoordination with phosphorus imine and amine or imine groups in the ligand, and the ligand comprises a diphenyl phosphine group and a substituted or unsubstituted phenylenediamine group, which are connected by a nitrogen-phosphorus double bond.

[0008] Preferably, the zinc complex containing nitrogen-phosphorus double bond is a complex having the structure as shown in formula (1):

[0009]

[0010] wherein Ph is a phenyl group,

[0011] R is selected from hydrogen, alkyl, halogenated group or aromatic group, preferably selected from hydrogen, C1-C5 alkyl, fluorine-substituted group, chlorine-substituted group, bromine-substituted group, phenyl group, alkylphenyl group, alkoxyphenyl group, more preferably hydrogen, methyl, chlorine-substituted group or fluorine-substituted group;

[0012] R0 is selected from hydrogen, alkyl or aromatic group, preferably selected from hydrogen, C1-C5 alkyl, phenyl group, more preferably hydrogen or phenyl group;

[0013] X is an anion that makes the zinc complex containing nitrogen-phosphorus double bond electrically neutral, such as chloride ion, bromide ion, nitrate ion, acetate ion, etc., preferably chloride ion.

[0014] The second aspect of the present application also aims to provide a preparation method of the zinc complex containing nitrogen-phosphorus double bond, which specifically comprises the following steps:

[0015] Step 1, bromine is added to a solution of diphenylphosphoromethane to obtain reaction solution I;

[0016] Step 2, a solution of phenylenediamine compound is added to the reaction solution I, and the reaction is stirred to obtain reaction solution II;

[0017] Step 3, the reaction solution II is post-treated to obtain a ligand containing nitrogen-phosphorus double bond;

[0018] Step 4, a solution of zinc salt is added to a solution of the ligand containing nitrogen-phosphorus double bond, and the reaction is stirred, and the reaction solution is post-treated to obtain the zinc complex containing nitrogen-phosphorus double bond.

[0019] The third aspect of the present application aims to provide a catalyst composition for catalyzing ring-opening polymerization of lactide, which comprises the zinc complex containing nitrogen-phosphorus double bond.

[0020] The catalyst composition further comprises an organosilicon amine metal compound and an organic alcohol.

[0021] The fourth aspect of the present application aims to provide a preparation method of polylactide, which adds lactide into a solution containing the catalyst composition for polymerization.

[0022] The method specifically comprises the following steps:

[0023] Step a, the catalyst composition is added to a reaction solvent, and is aged to obtain a mixed solution;

[0024] Step b, adding lactide monomer to the mixed solution, heating and reacting to obtain a reaction solution;

[0025] Step c, post-treating the reaction solution to obtain polylactide.

[0026] The preparation method of the zinc complex containing nitrogen-phosphorus double bonds and polylactide provided by the application has the following beneficial effects:

[0027] (1) The zinc complex containing nitrogen-phosphorus double bonds in the application has low toxicity, and the preparation method is simple, easy to synthesize, and can effectively control the high conversion rate of reactants by controlling the reaction conditions. The activity of the obtained complex is uniform, and the stability is good in air or humid environment, facilitating storage, transportation and subsequent catalytic application.

[0028] (2) The zinc complex containing nitrogen-phosphorus double bonds in the application is used as a catalyst in a small amount, can realize large-scale polymerization, and meets the needs of industrial production. Moreover, the polymerization process is simple and easy to control, and the requirement for equipment is low, which can effectively reduce the production cost.

[0029] (3) The polyester preparation method in the application uses the zinc complex containing nitrogen-phosphorus double bonds as a catalyst, has high activity, can catalyze the ring-opening polymerization of lactide in batches, has low toxicity, good biological safety, and does not affect the subsequent application of polyester in the biomedical field. DETAILED DESCRIPTION

[0030] The application will be described in detail below through specific embodiments, and the characteristics and advantages of the application will become more clear and explicit with these descriptions.

[0031] The first aspect of the application is to provide a zinc complex containing nitrogen-phosphorus double bonds, wherein the zinc in the zinc complex containing nitrogen-phosphorus double bonds is two-coordinated with phosphorus imine groups and amine groups or imine groups in the ligand, the ligand comprises a diphenyl phosphine group and a substituted or unsubstituted phenylenediamine group, and the two are connected through nitrogen-phosphorus double bonds.

[0032] Preferably, the zinc complex containing nitrogen-phosphorus double bonds is a complex having a structure as shown in formula (1):

[0033]

[0034] wherein Ph is a phenyl group,

[0035] R is selected from hydrogen, an alkyl group, a halogenated group or an aromatic group, preferably selected from hydrogen, a C1-C5 alkyl group, a fluorine substituted group, a chlorine substituted group, a bromine substituted group, a phenyl group, an alkyl phenyl group, an alkoxy phenyl group, more preferably hydrogen, a methyl group, a chlorine substituted group or a fluorine substituted group;

[0036] R0 is selected from hydrogen, an alkyl group or an aromatic group, preferably selected from hydrogen, a C1-C5 alkyl group, a phenyl group, more preferably hydrogen or a phenyl group;

[0037] X is an anion that makes the nitrogen-containing phosphorus double bond zinc complex electrically neutral, such as chloride ion, bromide ion, nitrate ion, acetate ion, etc., preferably chloride ion.

[0038] Preferably, the ligand is selected from L1-L5:

[0039]

[0040] wherein, -Ph is a phenyl group.

[0041] Preferably, the nitrogen-containing phosphorus double bond zinc complex is selected from C1-C5:

[0042] C1: R is hydrogen (H), R0 is hydrogen (H), X is chloride ion;

[0043] C2: R is methyl (Me), R0 is hydrogen (H), X is chloride ion;

[0044] C3: R is a chlorine substituent (-Cl), R0 is hydrogen (H), X is chloride ion;

[0045] C4: R is a fluorine substituent (-F), R0 is hydrogen (H), X is chloride ion; C5: R is a hydrogen substituent (-H), R0 is a phenyl group (Ph), X is chloride ion.

[0046]

[0047] The present application also provides a preparation method of the nitrogen-containing phosphorus double bond zinc complex, which specifically comprises the following steps:

[0048] Step 1, bromine is added to a diphenyl phosphoromethane solution to obtain reaction solution I;

[0049] The solvent is selected from one or more of alcohol, ether and ketone solvents, preferably selected from tetrahydrofuran and / or dichloromethane, more preferably dichloromethane.

[0050] The diphenyl phosphoromethane is selected from diphenyl phosphor-substituted methane, preferably bis(diphenyl phosphor)methane.

[0051] In the diphenyl phosphoromethane solution, the molar volume ratio of diphenyl phosphoromethane to solvent is 10 mmol:(20-80) mL, preferably 10 mmol:(30-70) mL, more preferably 10 mmol:(40-60) mL.

[0052] The reaction temperature is -94 to 0°C, preferably -94 to -75°C, more preferably -78°C. The reaction time is 2-30 h, preferably 3-15 h, more preferably 8-12 h.

[0053] In step 1, the reaction is carried out in a protective gas under stirring. The protective gas is nitrogen or argon, preferably nitrogen.

[0054] Step 2, adding a solution of phenylenediamine compound to reaction solution I, and stirring to obtain reaction solution II;

[0055] The phenylenediamine compound is:

[0056] wherein,

[0057] R is selected from hydrogen, alkyl, halogenated group or aromatic group, preferably selected from hydrogen, C1-C5 alkyl, fluorine substituted group, chlorine substituted group, bromine substituted group, phenyl, alkylphenyl, alkoxyphenyl, more preferably hydrogen, methyl, chlorine substituted group or fluorine substituted group;

[0058] R0 is selected from hydrogen, alkyl or aromatic group, preferably selected from hydrogen, C1-C5 alkyl, phenyl, more preferably hydrogen or phenyl.

[0059] The molar ratio of the phenylenediamine compound to diphenylphosphoromethane is (0.2-2.8):1, preferably (0.3-2.5):1, more preferably (0.4-2.2):1.

[0060] Preferably, a bromine transfer agent is added to the solution of phenylenediamine compound, and the bromine transfer agent is one or more of primary amine and tertiary amine, preferably one or more of phenylenediamine, triethylamine, tributylamine and triethylenediamine, more preferably triethylenediamine.

[0061] The molar ratio of the bromine transfer agent to diphenylphosphoromethane is (0.2-1.8):1, preferably (0.3-1.5):1, more preferably (0.4-1.2):1.

[0062] The reaction temperature is -94-0℃, preferably -94--75℃, more preferably -78℃. The reaction time is 2-30h, preferably 3-15h, more preferably 8-12h.

[0063] In step 2, the reaction is carried out in a protective gas under stirring. The protective gas is nitrogen or argon, preferably nitrogen.

[0064] Step 3, post-treating reaction solution II to obtain a ligand containing nitrogen-phosphorus double bond;

[0065] The post-treatment includes washing, drying and column chromatography.

[0066] The washing is adding washing liquid to reaction liquid II. The washing agent is selected from aqueous ammonium salt or water, preferably aqueous ammonium chloride, aqueous sodium chloride, aqueous potassium chloride or deionized water, more preferably aqueous ammonium chloride or deionized water.

[0067] The drying is preferably vacuum drying, and the ligand solid powder is obtained after drying.

[0068] The column chromatography stationary phase is selected from silica gel or alumina, preferably alumina, more preferably basic alumina.

[0069] Step 4, adding zinc salt solution to the ligand solution containing nitrogen-phosphorus double bond, stirring the reaction, and treating the reaction liquid to obtain zinc complex containing nitrogen-phosphorus double bond.

[0070] In the method, the zinc salt solution is slowly added to the ligand solution containing nitrogen-phosphorus double bond, preferably dropwise.

[0071] The molar ratio of the ligand containing nitrogen-phosphorus double bond to zinc salt is 1:(0.3-1.6), preferably 1:(0.5-1.4), more preferably 1:(0.7-1.2), such as 1:1, wherein the molar amount of zinc salt is calculated based on the molar amount of zinc therein. In the reaction process, the zinc salt solution is slowly added to the ligand solution containing nitrogen-phosphorus double bond, so that the zinc salt and the ligand containing nitrogen-phosphorus double bond are fully reacted. In the present application, the zinc salt and the ligand containing nitrogen-phosphorus double bond are preferably reacted in equimolar amount, so as to avoid excessive ligand or zinc salt after the reaction ends, which affects the subsequent reaction.

[0072] The reaction temperature is 15-38℃, preferably 20-30℃; the reaction time is 6-18h, preferably 10-14h.

[0073] After the reaction is completed, the reaction liquid is filtered, preferably at a temperature lower than 20℃, the obtained precipitate is washed, the washing liquid is cold solvent, and the precipitate is dried to obtain the zinc complex containing nitrogen-phosphorus double bond.

[0074] The present application also provides a catalyst composition for catalyzing the polymerization of lactide, and the zinc complex containing nitrogen-phosphorus double bond is used as a component of the catalyst composition to catalyze the polymerization of lactide, so that the polymerization conditions of lactide are more mild and the activity is higher than the existing process.

[0075] The catalyst composition comprises the zinc complex containing nitrogen-phosphorus double bond. Preferably, the zinc complex containing nitrogen-phosphorus double bond is selected from C1-C5.

[0076] Preferably, the catalyst composition further comprises organosilicon amine metal compound. The organosilicon amine metal compound is selected from one or more of organosilicon amine lithium and organosilicon amine zinc, preferably one or more of organosilicon amine lithium, more preferably bis-trimethylsilyl amine lithium.

[0077] Preferably, the catalyst composition further comprises an organic alcohol. The organic alcohol is selected from one or more of methanol, ethanol, isopropanol, n-butanol and benzyl alcohol, preferably one or more of isopropanol, n-butanol and benzyl alcohol, more preferably benzyl alcohol.

[0078] The molar ratio of the organosilane amine metal compound to the zinc complex containing nitrogen-phosphorus double bond is (1-10):1, preferably (2-5):1, more preferably 4:1.

[0079] The molar ratio of the zinc complex containing nitrogen-phosphorus double bond to the organic alcohol is 1:(1-11), preferably 1:(1-8), more preferably 1:(1-5).

[0080] The present application also provides a method for preparing polylactide, which comprises adding lactide into a solution containing the catalyst composition for polymerization. The method specifically comprises the following steps:

[0081] Step a, adding the catalyst composition into a reaction solvent for aging to obtain a mixed solution;

[0082] The reaction solvent is selected from one or more of aromatic hydrocarbons such as toluene, xylene, chlorobenzene, halogenated alkane solvents such as dichloromethane, ethers such as tetrahydrofuran, preferably selected from toluene and / or dichloromethane, more preferably toluene.

[0083] The aging is the aging of the zinc complex containing nitrogen-phosphorus double bond and the organosilane amine metal compound in the reaction solvent, so as to effectively activate the zinc complex containing nitrogen-phosphorus double bond. The aging temperature is 15-35℃, preferably 20-30℃; the aging time is 0.1-2h, preferably 0.5-1h, such as 0.5h.

[0084] In the present application, step a is carried out under anhydrous and anaerobic conditions, preferably in the environment of dry nitrogen, for example in a glove box filled with dry nitrogen.

[0085] Step b, adding lactide monomer into the mixed solution for heating reaction to obtain a reaction solution;

[0086] The molar ratio of the lactide monomer to the zinc complex containing nitrogen-phosphorus double bond is (100-5000):1, preferably (200-2500):1, more preferably (250-2000):1.

[0087] The molar volume ratio of the lactide monomer to the solvent is (1-100)mmol:(0.4-5)mL, preferably (1.5-50)mmol:(0.6-3)mL, more preferably (2.5-20)mmol:(0.8-2)mL.

[0088] The reaction temperature is 15-100℃, preferably 40-90℃, such as 80℃; the reaction time is 2-30min, preferably 8-16min, such as 10min.

[0089] Step c, post-treatment of the reaction solution to obtain polylactide.

[0090] After the reaction is completed, a cold precipitating solvent is added to precipitate the product, and polylactide is obtained after filtration and drying. The precipitating solvent is selected from alcohol solvents, preferably one or more of methanol, ethanol and propanol, and more preferably methanol.

[0091] The zinc complex containing a nitrogen-phosphorus double bond provided in the present application can be used as a catalyst to catalyze the ring-opening polymerization of lactide to prepare polylactide. The catalyst has very high catalytic activity, and compared with the existing process, the catalyst in the present application has higher catalytic activity, the polymerization time is shortened, and the synthesis process of polylactide is optimized, thereby achieving the purpose of reducing production cost.

[0092] Examples

[0093] Example 1

[0094] At -78℃, 0.159g of liquid bromine was slowly added to a 50mL dichloromethane solution of 3.84g (about 0.01mol) of bis-diphenylphosphine methane. As the reaction proceeded, the solution quickly became turbid and then became a clear transparent yellow solution, and then was stirred at room temperature for 2 hours. After being cooled to -78℃ again, 2.16g (about 0.02mol) of 1,2-phenylenediamine in 20mL dichloromethane was slowly added, wherein 1,2-phenylenediamine is both a reactant and a bromine transfer agent. The solution immediately became turbid. After stirring at -78℃ for 1 hour, the cold bath was removed, and stirring was carried out at room temperature for 12h, during which a light yellow suspension was formed. The suspension was washed with water twice, the organic layer was dried with anhydrous MgSO4, the solvent was removed under vacuum, and a light yellow solid was obtained. The light yellow solid was purified by column chromatography (petroleum ether and ethyl acetate in a volume ratio of 1:1) with basic alumina as the stationary phase, and the separated ligand L1 was a light yellow powder with a molar yield of 24%.

[0095] In a 50mL Schlenk tube, 0.5g (about 0.001mol) of ligand L1 was added, 10mL of ethanol was added, and stirring was carried out at room temperature until L1 was completely dissolved. 0.14g (about 0.001mol) of zinc chloride was dissolved in 5mL of ethanol, and the zinc chloride ethanol solution was added dropwise into the L1 ethanol solution, and then stirring was carried out at room temperature for 12 hours, during which white solid was generated. After the reaction was completed, the white solid was filtered, washed with ethanol three times, and naturally air-dried to obtain the zinc complex C1 containing a nitrogen-phosphorus double bond, which was a white solid with a molar yield of 85%.

[0096] The ligand L1 and zinc complex C1 containing nitrogen-phosphorus double bond were characterized by nuclear magnetic resonance, and the nuclear magnetic resonance data are as follows:

[0097] Ligand L1:

[0098] 1 H NMR (400 MHz, CDCl3, ppm): δ 7.78-7.74 (m, 4H, PPh2), 7.50-7.21 (m, 16H, PPh2), 6.64-6.62 (d, 1H, Ph), 6.53-6.50 (t, 1, Ph), 6.31-6.27 (t, 1H, Ph), 6.21-6.20 (d, 1, Ph), 3,25 (d, 2H, PCH2P).

[0099] 13 C NMR (100 MHz, CDCl3, ppm): δ 141.88, 141.67, 138.39, 138.32, 138.17, 138.03, 132.86, 132.65, 132.04, 132.02, 131.95, 131.93, 131.79, 131.66, 131.64, 130.90, 128.76, 128.69, 128.57, 128.48, 128.41, 119.85, 119.75, 118.15, 117.82, 113.92, 30.62, 30.27, 29.83, 29.51.

[0100] 31 P NMR (162 MHz, CDCl3, ppm): δ 5.76 (d, 1P), -27.77 (d, 1P).

[0101] Zinc complex C1 containing nitrogen-phosphorus double bond:

[0102] 1 H NMR (400 MHz, CDCl3, ppm): δ 7.93-7.88 (m, 4H, PPh2), 7.52-7.45 (m, 2H, PPh2), 7.39-7.36 (m, 8H, PPh2), 7.21-7.17 (m, 6H, PPh2), 7.14-7.11 (d, 1H, Ph), 6.64-6.63 (m, 2, Ph), 6.26-6.24 (m, 2, Ph), 4.23 (s, 2H, NH2), 3.97-3.93 (d, 2H, PCH2P).

[0103] 13C NMR (100 MHz, CDC13, ppm): 144.02, 135.07, 134.99, 133.28, 133.25, 133.11, 133.08, 133.02, 132.98, 132.82, 129.42, 129.18, 129.06, 128.76, 128.68, 127.38, 124.65, 122.76, 120.13, 119.63.

[0104] 31 P NMR (162 MHz, CDC13, ppm, ppm): -33.31 (d, 1P), 27.64 (d, 1P). Example 2

[0105] At -78 °C, under nitrogen atmosphere, 0.159 g of liquid bromine was slowly added to a solution of 3.84 g of bisdiphenylphosphoromethane in 50 mL of dichloromethane. As the reaction proceeded, the solution quickly became turbid and then a clear transparent yellow solution, then, it was raised to room temperature and stirred for 2 hours. After cooling again to -78 °C, a solution of 0.56 g (about 0.005 mol) of triethylenediamine and 1.22 g (about 0.01 mol) of 2,3-diaminotoluene in dichloromethane was slowly added, the solution immediately became turbid. After stirring at -78 °C for 1 hour, the cold bath was removed, and it was stirred at room temperature for 12 h, during which a brown suspension was formed. The suspension was washed twice with water, the organic layer was dried with anhydrous MgS04, and the solvent was removed under vacuum to obtain a light brown solid. The light brown solid was purified by column chromatography (petroleum ether and ethyl acetate in a volume ratio of 4:1), and the ligand L2 isolated was a light yellow powder, with a molar yield of 17%.

[0106] In a 50 mL Schlenk tube, 0.5 g of ligand L2 was added and 10 mL of ethanol solution was added, and it was stirred at room temperature until L2 was completely dissolved. 0.135 g of zinc chloride was dissolved in 5 mL of ethanol solution, and the zinc chloride ethanol solution was added dropwise to the L2 ethanol solution, and then it was stirred at room temperature for 12 hours, and white solid was generated, after the reaction was completed, the white solid was filtered, and washed with ethanol three times, and naturally air-dried to obtain a zinc complex C2 containing a nitrogen-phosphorus double bond, with a molar yield of 85%.

[0107] The ligand L2 and the zinc complex C2 containing a nitrogen-phosphorus double bond were characterized by nuclear magnetic resonance, and the nuclear magnetic resonance data were as follows:

[0108] Ligand L2:

[0109] 1H NMR (400 MHz, CDC13, ppm): δ 7.78-7.66 (m, 4H, PPh2), 7.46-7.13 (m, 16H, PPh2, NPh), 6.34-6.32 (d, 1H, Ph), 6.16-6.13 (t, 1H, Ph), 6.03-6.01 (d, 1H, Ph), 3,15 (d, 2H, PCH2P), 2.05 (s, 1H, Me).

[0110] 13 C NMR (100 MHz, CDC13, ppm): δ, 138.40, 138.32, 138.25, 137.71, 132.86, 132.65, 132.05, 132.03, 131.98, 131.95, 131.93, 131.60, 131.58, 131.09, 128.74, 128.67, 128.56, 128.46, 128.39, 121.27, 119.70, 117.43, 117.33, 116.94, 30.65, 30.33, 17.99, 17.94

[0111] 31 P NMR (162 MHz, CDC13, ppm): δ 5.78 (d, 1P), -27.72 (d, 1P).

[0112] Zinc complex C2 containing nitrogen-phosphorus double bond:

[0113] 1 H NMR (400 MHz, CDC13, ppm): δ 7.91-7.88 (m, 4H, PPh2), 7.51-7.15 (m, 16H, PPh2, NPh), 6.54-6.53 (m, 1H, Ph), 6.12-6.10 (t, 1H, Ph), 4.31 (s, 2H, NH2), 3,98 (d, 2H, PCH2P), 2.31 (s, 1H, Me).

[0114] 13 C NMR (100 MHz, CDC13, ppm): δ 143.96, 135.46, 135.38, 135.33, 135.29, 133.16, 133.10, 133.02, 132.82, 129.33, 129.13, 129.01, 128.70, 128.67, 128.63, 128.49, 126.45, 123.69, 122.81, 121.34, 117.88, 117.77.

[0115] 31P NMR (162 MHz, CDC13, ppm): δ -33.31 (d, 1P), 27.66 (d, 1P).

[0116] Example 3

[0117] Prepared according to the method in Example 2, except that 1.42 g (about 0.01 mol) of 3-chloro-1,2-phenylenediamine was added instead of 2,3-diaminotoluene, to obtain 1.31 g of ligand L3 as a light yellow solid, with a molar yield of 25%. Coordination was carried out by adding a zinc chloride ethanol solution containing 0.129 g of zinc chloride to 0.5 g of L3 to obtain 0.52 g of nitrogen-phosphorus double bond-containing zinc complex C3 as a white solid, with a molar yield of 83%.

[0118] The ligand L3 and the nitrogen-phosphorus double bond-containing zinc complex C3 were subjected to nuclear magnetic characterization, and the nuclear magnetic data are as follows:

[0119] Ligand L3:

[0120] 1 H NMR (400 MHz, CDC13, ppm): δ 7.78-7.66 (m, 4H, PPh2), 7.46-7.13 (m, 16H, PPh2, NPh), 6.34-6.32 (d, 1H, Ph), 6.16-6.13 (t, 1H, Ph), 6.03-6.01 (d, 1H, Ph), 3.86 (s, 2H, NH2), 3.21 (d, 2H, PCH2P).

[0121] 13 C NMR (100 MHz, CDC13, ppm): δ 139.22, 138.70, 138.13, 138.06, 137.98, 137.91, 132.82, 132.61, 131.95, 131.86, 131.84, 131.42, 131.26, 131.16, 130.51, 128.96, 128.88, 128.81, 128.69, 128.51, 128.44, 118.06, 117.29, 117.19, 116.91, 30.42, 30.09, 29.33.

[0122] 31 P NMR (162 MHz, CDC13, ppm): δ 5.96 (d, 1P), -27.72 (d, 1P).

[0123] Nitrogen-phosphorus double bond-containing zinc complex C3:

[0124] 1H NMR (400 MHz, CDCI3, ppm): δ 7.90-7.88 (m, 4H, PPh2), 7.52-7.16 (m, 16H, PPh2, NPh), 6.54-6.52 (d, 1H, Ph), 6.12-6.10 (t, 1H, Ph), 4.32 (s, 2H, NH2), 4.03 (d, 2H, PCH2P).

[0125] 13 C NMR (100 MHz, CDCI3, ppm): δ 139.22, 139.70, 139.13, 138.06, 134.78, 134.71, 133.82, 133.61, 132.97, 132.84, 132.76, 130.42, 130.26, 130.16, 129.51, 127.96, 127.87, 127.81, 126.69, 126.51, 126.34, 119.06, 118.29, 116.33, 115.89, 32.36, 32.25, 29.77.

[0126] 31 P NMR (162 MHz, CDCI3, ppm): δ -33.44 (d, 1P), -27.88 (d, 1P). Example 4

[0127] Prepared according to the method in Example 2, except that 0.63 g (about 0.005 mol) of 2,3-diaminofluorobenzene was added instead of 2,3-diaminotoluene to obtain 0.33 g of ligand L4 as a light yellow solid with a molar yield of 13%, and the above process was repeated to prepare L4 for standby. 0.129 g of zinc chloride was coordinated with 0.5 g of L4 to obtain 0.52 g of nitrogen-phosphorus double bond-containing zinc complex C4 as a white solid with a molar yield of 83%.

[0128] The ligand L4 and the nitrogen-phosphorus double bond-containing zinc complex C4 were characterized by nuclear magnetic resonance, and the nuclear magnetic resonance data are as follows:

[0129] Ligand L4:

[0130] 1 H NMR (400 MHz, CDCI3, ppm): δ 7.78-7.66 (m, 4H, PPh2), 7.46-7.13 (m, 16H, PPh2, NPh), 6.34-6.32 (d, 1H, Ph), 6.16-6.13 (t, 1H, Ph), 6.03-6.01 (d, 1H, Ph), 3.86 (s, 2H, NH2), 3,21 (d, 2H, PCH2P).

[0131] 13 C NMR (100 MHz, CDC13): δ 139.56, 138.70, 138.13, 138.06, 137.98, 137.91, 132.82, 132.61, 131.95, 131.89, 131.78, 131.56, 131.26, 131.16, 130.51, 128.96, 128.88, 128.81, 128.69, 128.51, 128.44, 118.06, 117.29, 117.19, 116.91, 30.58, 30.56, 29.45.

[0132] 31 P NMR (162 MHz, CDC13, ppm): δ 5.72 (d, 1P), -27.62 (d, 1P).

[0133] Zinc complex C4 containing nitrogen-phosphorus double bond:

[0134] 1 H NMR (400 MHz, CDC13, ppm): δ 7.93-7.88 (m, 4H, PPh2), 7.53-7.17 (m, 16H, PPh2, NPh), 6.54-6.52 (d, 1H, Ph), 6.12-6.10 (t, 1H, Ph), 4.32 (s, 2H, NH2), 3.99 (d, 2H, PCH2P).

[0135] 13 C NMR (100 MHz, CDC13, ppm): δ 145.56, 139.28, 136.55, 134.18, 133.92, 133.41, 133.34, 133.19, 132.89, 132.76, 129.54, 129.43, 129.78, 128.98, 128.58, 127.48, 124.76, 122.54, 120.25, 119.16, 30.42, 30.09, 29.33.

[0136] 31 P NMR (162 MHz, CDC13, ppm): δ -33.44 (d, 1P), 27.88 (d, 1P). Example 5

[0137] Prepared according to the procedure described in Example 2, except that 0.92 g (about 0.005 mol) of o-aminodiphenylamine was added instead of 2,3-diaminotoluene to give 0.59 g of ligand L5 as a light yellow solid with a molar yield of 21%. 0.12 g of zinc chloride was coordinated with 0.5 g of L5 to give 0.53 g of the nitrogen-containing phosphorus double bond-containing zinc complex C5 as a white solid with a molar yield of 85%.

[0138] The ligand L5 and the nitrogen-containing phosphorus double bond-containing zinc complex C5 were characterized by nuclear magnetic resonance, and the nuclear magnetic resonance data are as follows:

[0139] Ligand L5:

[0140] 1 1H NMR (400 MHz, CDCl3, ppm): δ 7.87-7.62 (m, 4H, PPh2), 7.46-7.03 (m, 19H, PPh2, NPh), 6.78-6.74 (t, 1H, Ph), 6.53-6.50 (t, 1, Ph), 6.31-6.27 (t, 1H, Ph), 6.21-6.20 (d, 1, Ph), 3,15 (d, 2H, PCH2P).

[0141] 13 13C NMR (100 MHz, CDCl3): δ 132.81, 132.60, 131.95, 131.93, 131.86, 131.84, 131.79, 131.76, 128.84, 128.76, 128.5, 128.49, 128.42, 116.05, 115.95, 115.23, 115.11, 104.83, 104.64.

[0142] 31 31P NMR (162 MHz, CDCl3, ppm): δ 6.50 (d, 1P), -27.77 (d, 1P).

[0143] Nitrogen-containing phosphorus double bond-containing zinc complex C5:

[0144] 1H NMR (400 MHz, CDCl3, ppm): δ 7.78-7.66 (m, 4H, PPh2), 7.46-7.13 (m, 19H, PPh2, NPh), 6.34-6.32 (d, 1H, Ph), 6.16-6.13 (t, 1H, Ph), 6.03-6.01 (d, 1H, Ph), 4.06 (s, 2H, NH2), 3,98 (d, 2H, PCH2P).

[0145] 13C NMR (100 MHz, CDC13, ppm): δ 133.46, 133.43, 133.06, 133.02, 132.96, 132.93, 132.86, 129.57, 129.28, 129.15, 128.79, 128.71, 123.35, 122.45, 106.49, 106.29.

[0146] 31 P NMR (162 MHz, CDC13, ppm): δ -34.44 (d, IP), 28.83 (d, IP)

[0147] Example 6

[0148] In a glove box under nitrogen atmosphere, 10 μmol of C2 and 1 ml of toluene were added into a 100 ml Schlenk flask, shaken for a while, then 1 M of lithium bis(trimethylsilyl)amide tetrahydrofuran solution (lithium bis(trimethylsilyl)amide content was 40 μmol) was added, and the catalyst mixture was stirred at room temperature for 30 min for aging.

[0149] Under nitrogen atmosphere, 0.36 g (about 2.5 mmol) of L-lactide was added into the catalyst mixture, and the reaction was carried out at 20 °C for 10 min. After the reaction, the L-lactide monomer conversion rate was directly detected, then cold methanol was added into the reaction vessel for stirring to obtain white solid, which was filtered and dried in a vacuum drying oven for 24 hours to collect the product polylactide. 1 The L-lactide monomer conversion rate was 33% detected by HNMR, and the number average molecular weight of the polylactide was 1.17 x 10 4 g / mol, and the molecular weight distribution index was 1.61 detected by GPC (gel permeation chromatography).

[0150] Example 7

[0151] The polylactide was prepared according to the preparation method in Example 6, except that the reaction temperature was 40 °C. The number average molecular weight of the polylactide was 1.48 x 10 4 g / mol, and the molecular weight distribution index was 1.37. The monomer conversion rate was 90%.

[0152] Example 8

[0153] The polylactide was prepared according to the preparation method in Example 6, except that the reaction temperature was 60 °C. The number average molecular weight of the polylactide was 1.30 x 10 4 g / mol, and the molecular weight distribution index was 1.77. The monomer conversion rate was 98%.

[0154] Example 9

[0155] The poly-L-lactide was prepared according to the preparation method of Example 6, except that the amount of L-lactide added was 0.72 g (about 5 mmol) and the reaction temperature was 60 °C and the reaction time was 5 minutes. The number average molecular weight of the poly-L-lactide was 1.53 x 10 4 g / mol and the molecular weight distribution index was 1.91. The monomer conversion was 83%.

[0156] Example 10

[0157] The poly-L-lactide was prepared according to the preparation method of Example 9, except that the reaction time was 10 minutes. The number average molecular weight of the poly-L-lactide was 1.28 x 10 4 g / mol and the molecular weight distribution index was 1.80. The monomer conversion was 97%.

[0158] Example 11

[0159] The poly-L-lactide was prepared according to the preparation method of Example 9, except that the amount of L-lactide added was 1.44 g (about 10 mmol) and the reaction time was 10 minutes. The number average molecular weight of the poly-L-lactide was 1.40 x 10 4 g / mol and the molecular weight distribution index was 1.89. The monomer conversion was 73%.

[0160] Example 12

[0161] The poly-L-lactide was prepared according to the preparation method of Example 11, except that the reaction temperature was 70 °C. The number average molecular weight of the poly-L-lactide was 1.39 x 10 4 g / mol and the molecular weight distribution index was 1.63. The monomer conversion was 79%.

[0162] Example 13

[0163] The poly-L-lactide was prepared according to the preparation method of Example 11, except that the reaction temperature was 80 °C. The number average molecular weight of the poly-L-lactide was 1.43 x 10 4 g / mol and the molecular weight distribution index was 1.65. The monomer conversion was 94%.

[0164] Example 14

[0165] The poly-L-lactide was prepared according to the preparation method of Example 11, except that the reaction temperature was 90 °C. The number average molecular weight of the poly-L-lactide was 1.36 x 10 4 g / mol and the molecular weight distribution index was 1.92. The monomer conversion was 95%.

[0166] Example 15

[0167] Polylactide was prepared according to the method described in Example 13, except that 1 mL of n-hexane was used instead of toluene as the reaction solvent. The number-average molecular weight of the polylactide was 1.73 × 10⁻⁶. 4 g / mol and 0.26×10 4 The molecular weight distribution (MHD) is g / mol, exhibiting a bimodal distribution with molecular weight distribution indices of 1.15 and 1.00. The monomer conversion rate is 15%.

[0168] Example 16

[0169] Polylactide was prepared according to the method described in Example 13, except that 1 mL of tetrahydrofuran was used instead of toluene as the reaction solvent. The number-average molecular weight of the polylactide was 1.36 × 10⁻⁶. 4 The monomer concentration is g / mol, and the molecular weight distribution index is 1.62. The monomer conversion rate is 95%.

[0170] Example 17

[0171] Polylactide was prepared according to the method described in Example 13, except that the reaction solvent was 1 mL of dichloromethane. The number-average molecular weight of the polylactide was 2.12 × 10⁻⁶. 4 The monomer concentration is g / mol, and the molecular weight distribution index is 1.89. The monomer conversion rate is 88%.

[0172] Example 18

[0173] Polylactide was prepared according to the preparation method in Example 13, except that the amount of L-lactide added was 1.80 g (approximately 15 mmol). The number-average molecular weight of the polylactide was 1.37 × 10⁻⁶. 4 The monomer concentration is g / mol, and the molecular weight distribution index is 1.96. The monomer conversion rate is 89%.

[0174] Example 19

[0175] Polylactide was prepared according to the preparation method in Example 13, except that the amount of L-lactide added was 2.16 g (approximately 20 mmol). The number-average molecular weight of the polylactide was 2.40 × 10⁻⁶. 4 The monomer concentration is g / mol, and the molecular weight distribution index is 1.84. The monomer conversion rate is 66%.

[0176] Example 20

[0177] The polylactide was prepared according to the preparation method in Example 19, except that 0.1 mL of a toluene solution of benzyl alcohol (0.1 mmol / mL) was added additionally. The number average molecular weight of the polylactide was 2.23 x 10 4 g / mol and the molecular weight distribution index was 1.80. The monomer conversion was 83%.

[0178] Example 21

[0179] The polylactide was prepared according to the preparation method in Example 19, except that 0.5 mL of a toluene solution of benzyl alcohol (0.1 mmol / mL) was added additionally. The number average molecular weight of the polylactide was 1.23 x 10 4 g / mol and 0.48 x 10 4 g / mol and the molecular weight distribution index was 1.18 and 1.04. The monomer conversion was 88%.

[0180] Example 22

[0181] The polylactide was prepared according to the preparation method in Example 13, except that catalyst C2 was replaced by catalyst C1. The number average molecular weight of the polylactide was 1.61 x 10 4 g / mol and the molecular weight distribution index was 1.78. The monomer conversion was 92%.

[0182] Example 23

[0183] The polylactide was prepared according to the preparation method in Example 13, except that catalyst C2 was replaced by catalyst C3. The number average molecular weight of the polylactide was 1.41 x 10 4 g / mol and the molecular weight distribution index was 1.47. The monomer conversion was 94%.

[0184] Example 24

[0185] The polylactide was prepared according to the preparation method in Example 13, except that catalyst C2 was replaced by catalyst C4. The number average molecular weight of the polylactide was 2.07 x 10 4 g / mol and the molecular weight distribution index was 1.85. The monomer conversion was 95%.

[0186] Example 25

[0187] The polylactide was prepared according to the preparation method in Example 13, except that catalyst C2 was replaced by catalyst C5. The number average molecular weight of the polylactide was 2.19 x 10 4 g / mol and the molecular weight distribution index was 1.84. The monomer conversion was 95%.

[0188] Example 26

[0189] The poly-L-lactide was prepared according to the preparation method in Example 19, except that catalyst C2 was replaced by catalyst C1. The number average molecular weight of the poly-L-lactide was 2.13 x 10 4 g / mol and the molecular weight distribution index was 1.76. The monomer conversion was 70%.

[0190] Example 27

[0191] The poly-L-lactide was prepared according to the preparation method in Example 19, except that catalyst C2 was replaced by catalyst C3. The number average molecular weight of the poly-L-lactide was 2.56 x 10 4 g / mol and the molecular weight distribution index was 1.82. The monomer conversion was 79%.

[0192] Example 28

[0193] The poly-L-lactide was prepared according to the preparation method in Example 19, except that catalyst C2 was replaced by catalyst C4. The number average molecular weight of the poly-L-lactide was 2.87 x 10 4 g / mol and the molecular weight distribution index was 1.86. The monomer conversion was 89%.

[0194] Example 29

[0195] The poly-L-lactide was prepared according to the preparation method in Example 19, except that catalyst C2 was replaced by catalyst C5. The number average molecular weight of the poly-L-lactide was 2.93 x 10 4 g / mol and the molecular weight distribution index was 1.79. The monomer conversion was 45%.

[0196] Comparative Example

[0197] Comparative Example 1

[0198] The poly-L-lactide was prepared according to the preparation method in Example 13, except that the reaction solvent was 1 mL of n-hexane. The number average molecular weight of the poly-L-lactide was 1.73 x 10 4 g / mol and 0.26 x 10 4 g / mol and the molecular weight distribution index was 1.15 and 1.00. The monomer conversion was 15%.

[0199] Comparative Example 2

[0200] The poly-L-lactide was prepared according to the preparation method in Example 13, except that the reaction solvent was 1 mL of tetrahydrofuran. The number average molecular weight of the poly-L-lactide was 1.36 x 10 4 g / mol, and the molecular weight distribution index was 1.62. The monomer conversion was 95%.

[0201] Comparative Example 3

[0202] The poly-L-lactide was prepared according to the preparation method in Example 13, except that the reaction solvent was 1 mL of tetrahydrofuran. The number average molecular weight of the poly-L-lactide was 1.36 x 10 4 g / mol, and the molecular weight distribution index was 1.62. The monomer conversion was 95%.

[0203] As can be seen from the comparative examples, the conversion in the polymerization system using n-hexane as the solvent was the lowest, only 15%, and there was a significant bimodal distribution of molecular weight, which can be due to the low polarity of the solvent resulting in a decrease in activity, and can also be due to the presence of two active centers resulting in a significant bimodal distribution. When the solvent was dichloromethane and tetrahydrofuran, the polymerization activity was slightly decreased, and the monomer conversion was much higher than when n-hexane was used as the solvent, which can be due to the difference in solubility in different solvents.

[0204] The above detailed description of the application in conjunction with the specific embodiments and / or exemplary examples should not be construed as limiting the application. Those skilled in the art understand that various equivalent substitutions, modifications or improvements can be made to the technical solutions and embodiments of the application without departing from the spirit and scope of the application, and these all fall within the scope of the application. The scope of protection of the application is defined by the appended claims.

Claims

1. A zinc complex containing nitrogen-phosphorus double bonds, characterized in that, It is a complex having a structure as shown in formula (1): Where Ph is phenyl, R is selected from hydrogen, alkyl, halogroup or aromatic group; R0 is selected from hydrogen, alkyl, or aromatic groups; X is an anion that makes zinc complexes containing nitrogen and phosphorus double bonds electrically neutral.

2. The zinc complex containing nitrogen-phosphorus double bonds according to claim 1, characterized in that, R is selected from hydrogen, C1-C5 alkyl, fluorine substituent, chlorine substituent, bromine substituent, phenyl, alkylphenyl, alkoxyphenyl; R0 is selected from hydrogen, C1-C5 alkyl groups, and phenyl groups.

3. The zinc complex containing nitrogen-phosphorus double bonds according to claim 1, characterized in that, R is selected from hydrogen, methyl, chlorine substituent or fluorine substituent; R0 is selected from hydrogen or phenyl.

4. The zinc complex containing nitrogen-phosphorus double bonds according to claim 1, characterized in that, The zinc complex containing nitrogen-phosphorus double bonds is selected from C1-C5: C1: R is hydrogen (H), R0 is hydrogen (H), X is chloride ion; C2: R is methyl (Me), R0 is hydrogen (H), and X is chloride ion; C3: R is a chloride substituent (-Cl), R0 is hydrogen (H), and X is a chloride ion; C4: R is a fluorine substituent (-F), R0 is hydrogen (H), and X is a chloride ion; C5: R is a hydrogen substituent (-H), R0 is a phenyl group (Ph), and X is a chloride ion.

5. A method for preparing a zinc complex containing a nitrogen-phosphorus double bond according to claim 1, characterized in that, The method specifically includes the following steps: Step 1: Add bromine to a diphenylphosphine methane solution to obtain reaction solution I; Step 2: Add a phenylenediamine compound solution to reaction solution I and stir the reaction to obtain reaction solution II; Step 3: Post-process reaction solution II to obtain ligands containing nitrogen and phosphorus double bonds; Step 4: Add the zinc salt solution to the ligand solution containing nitrogen and phosphorus double bonds, stir the reaction, and then process the reaction solution to obtain the zinc complex containing nitrogen and phosphorus double bonds.

6. The method according to claim 5, characterized in that, In step 2, the phenylenediamine compound is: in, R is selected from hydrogen, alkyl, halogroup or aromatic group; R0 is selected from hydrogen, alkyl, or aromatic groups.

7. The method according to claim 6, characterized in that, R is selected from hydrogen, C1-C5 alkyl, fluorine substituent, chlorine substituent, bromine substituent, phenyl, alkylphenyl, alkoxyphenyl; R0 is selected from hydrogen, C1-C5 alkyl groups, and phenyl groups.

8. The method according to claim 6, characterized in that, R is selected from hydrogen, methyl, chlorine substituent or fluorine substituent; R0 is selected from hydrogen or phenyl.

9. A catalyst composition for catalyzing the polymerization of lactide, characterized in that, The catalyst composition comprises a zinc complex containing a nitrogen-phosphorus double bond according to any one of claims 1-4. The catalyst composition also includes organosilicon amine metal compounds and organic alcohols.

10. The catalyst composition according to claim 9, characterized in that, The zinc complex containing nitrogen-phosphorus double bonds is selected from C1-C5. The organosilicone amine-based metal compound is selected from one or more of organosilicone amine-lithium and organosilicone amine-zinc. The organic alcohol is selected from one or more of methanol, ethanol, isopropanol, n-butanol and benzyl alcohol.

11. The catalyst composition according to claim 10, characterized in that, The organosilicone amine-based metal compound is selected from one or more organosilicone amine-based lithium compounds. The organic alcohol is selected from one or more of isopropanol, n-butanol, and benzyl alcohol.

12. The catalyst complex according to claim 10, characterized in that, The organosilicon amine-metal compound is bis(trimethylsilylamine)lithium. The organic alcohol is benzyl alcohol.

13. A method for preparing polylactide, characterized in that, The method involves adding lactide to a solution containing the catalyst composition according to any one of claims 9-12, and then polymerizing it.

14. The preparation method according to claim 13, characterized in that, The method specifically includes the following steps: Step a: Add the catalyst composition to the reaction solvent and age it to obtain a mixture; Step b: Add lactide monomer to the mixture, heat to react, and obtain the reaction solution; Step c: Post-process the reaction solution to obtain polylactide.

15. The preparation method according to claim 14, characterized in that, In step a, the reaction solvent is selected from aromatic hydrocarbons, haloalkanes, and ethers.

16. The preparation method according to claim 14, characterized in that, In step a, the reaction solvent is selected from one or more of toluene, xylene, chlorobenzene, dichloromethane, and tetrahydrofuran.

17. As described in claim 14, characterized in that, In step a, the reaction solvent is selected from toluene and / or dichloromethane.

18. The preparation method according to claim 14, characterized in that, In step b, The molar ratio of the lactide monomer to the zinc complex containing nitrogen and phosphorus double bonds is (100-5000):1; The molar volume ratio of the lactide monomer to the solvent is (1-100) mol:(0.4-5) mL; The reaction temperature is 15-100℃; the reaction time is 2-30 min.

19. The preparation method according to claim 18, characterized in that, In step b, The molar ratio of the lactide monomer to the zinc complex containing nitrogen and phosphorus double bonds is (200-2500):1; The molar volume ratio of the lactide monomer to the solvent is (1.5-50) mol:(0.6-3) mL; The reaction temperature is 40-90℃; the reaction time is 8-16 min.

20. The preparation method according to claim 18, characterized in that, In step b, The molar ratio of the lactide monomer to the zinc complex containing nitrogen and phosphorus double bonds is (250-2000):1; The molar volume ratio of the lactide monomer to the solvent is (2.5-20) mol:(0.8-2) mL.

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