Catalyst composition, polylactide and preparation method and application thereof

Abstract

The invention relates to the technical field of polymers, and discloses a catalyst composition, polylactide and a preparation method and application thereof. The catalyst composition contains a rare earth metal complex with a structure as shown in a formula (I) and a hydroxyl-containing compound, in the formula (I), Ln is rare earth metal, and R1-R6 are respectively and independently selected from hydrogen or C1-C3 alkyl; r7 is selected from hydrogen or C1-C3 alkyl or halogen; and R8 is a silicon-containing group. When the catalyst composition provided by the invention is used for preparing polylactide through ring-opening polymerization of lactide, the catalytic activity is high, the molecular weight of the obtained polymer is relatively high, the molecular weight is adjustable, and the molecular weight distribution is narrow.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polymer technology, in particular, to a catalyst composition, polylactide and a preparation method and application thereof. BACKGROUND

[0002] Polylactic acid (PLA) is a kind of polyester biodegradable material, which has excellent biodegradation performance, and is widely used in the production of tableware, film, fiber, clothing, automobile parts and disposable containers, which is conducive to solving the environmental pollution problem caused by petrochemical resources. In addition, polylactic acid also has good biocompatibility, non-toxicity and adjustable degradation, which meets the requirements of medical polymer materials, and has wide application prospects in fracture internal and external fixation materials, surgical sutures, tissue engineering scaffold materials and drug release and controlled release carrier materials.

[0003] The early synthesis method of polyester mainly uses the condensation reaction of acid compounds and alcohol compounds, but the structure of the polymer synthesized by this reaction is uncontrollable, which can be linear, branched or cyclic structure, the molecular weight distribution is too wide, the molecular weight is low and difficult to control, and finally leads to poor mechanical properties of the polymer. In order to improve the comprehensive performance of the polymer, in recent years, the synthesis of polyester mainly focuses on the development of coordination polymerization reaction catalyst to initiate ring ester ring-opening polymerization to prepare polyester polymer. Compared with the above condensation reaction method, the method of preparing polyester by ring-opening polymerization has the following advantages: first, the molecular weight of polyester can be accurately controlled, and the molecular weight distribution is narrow; second, no water is generated in the process of ring-opening polymerization, and a polymer with high molecular weight can be obtained; third, through the selection of catalyst, the selective polymerization of chiral monomers can be realized in the process of ring-opening polymerization.

[0004] The catalyst system applied to lactone coordination ring-opening polymerization mainly includes stannous octoate, metal aluminum, calcium, magnesium, zinc, titanium complex and group IIIB metal complex. Stannous octoate is currently recognized as a better catalyst, which has high catalytic activity, requires less catalyst, and can prepare high molecular weight polymer. Its disadvantage is that it can only carry out high temperature bulk polymerization, and when the molecular weight reaches the highest, the conversion rate is only about 50%. If you want to improve the conversion rate, you must reduce the molecular weight. SUMMARY

[0005] The purpose of the present application is to overcome the problems of low catalytic activity and uncontrollable molecular weight in the prior art, and to provide a catalyst composition, polylactide and a preparation method and application thereof. The catalyst composition provided by the present application has high catalytic activity when used for preparing polylactide by ring-opening polymerization of lactide, and the molecular weight of the obtained polymer is high, the molecular weight is controllable and the molecular weight distribution is narrow.

[0006] The inventors of the present application have found, through in-depth research, that when a compound containing a hydroxyl group is added to the rare earth metal complex of the specific structure of the present application, the polymer chain growth can still be catalyzed normally without causing polymer termination; in the catalysis of lactide monomer polymerization, the rare earth metal complex plays a catalytic role in the polymerization of lactide monomers, and the compound containing a hydroxyl group plays the role of a chain transfer agent, i.e., the compound containing a hydroxyl group and the initiation center can initiate active chain transfer, thereby continuously growing the polymer chain, and the apparent effect is that one complex molecule can initiate a 1-1000-fold macromolecular chain growth, thus the catalytic efficiency is very high, the conversion rate of the polymerization reaction is high, and the "immortal" polymerization characteristics are exhibited; by using this point, the molecular weight of the polymer can be adjusted in a large range by controlling the addition amount of the compound containing a hydroxyl group, and the addition of the compound containing a hydroxyl group also makes the polymer have an ideal molecular weight distribution.

[0007] Therefore, the first aspect of the present application provides a catalyst composition, wherein the catalyst composition contains a rare earth metal complex of the structure shown in formula (I) and a compound containing a hydroxyl group,

[0008]

[0009] In formula (I), Ln is a rare earth metal, R1-R6 are independently selected from hydrogen or C1-C3 alkyl; R7 is selected from hydrogen or C1-C3 alkyl or halogen; and R8 is a silicon-containing group.

[0010] In formula (I), THF represents tetrahydrofuran.

[0011] Preferably, the Ln is selected from scandium, yttrium, a lanthanide series metal or an actinide series metal, preferably selected from scandium or yttrium; R1-R5 are hydrogen; R6 is methyl, ethyl or isopropyl; R7 is hydrogen or chlorine; and R8 is trimethylsilylmethylene or hexamethyldisilylamino.

[0012] Preferably, the rare earth metal complex of the structure shown in formula (I) is selected from at least one of the following complexes,

[0013] In formula (I), the complex in which Ln is scandium, R1-R5 are hydrogen, R6 is methyl, R7 is hydrogen, and R8 is trimethylsilylmethylene;

[0014] In formula (I), the complex in which Ln is scandium, R1-R5 are hydrogen, R6 is methyl, R7 is hydrogen, and R8 is trimethylsilylmethylene;

[0015] In formula (I), the complex in which Ln is yttrium, R1-R5 are hydrogen, R6 is isopropyl, R7 is hydrogen, and R8 is hexamethyldisilylamino;

[0016] In formula (I), Ln is yttrium, R1-R5 are hydrogen, R6 is methyl, R7 is chlorine, and R8 is hexamethyldisilylamido.

[0017] Preferably, the hydroxyl-containing compound is at least one of a straight-chain or branched aliphatic alcohol, an aromatic alcohol, an alcohol amine, and a phenol, each of which is substituted or unsubstituted.

[0018] Preferably, the hydroxyl-containing compound is at least one of a straight-chain or branched aliphatic alcohol, an aromatic alcohol, an alcohol amine, and a phenol, each of which is substituted or unsubstituted. 20 Preferably, the hydroxyl-containing compound is at least one of a straight-chain or branched aliphatic alcohol, an aromatic alcohol, an alcohol amine, and a phenol, each of which is substituted or unsubstituted. 10 Preferably, the hydroxyl-containing compound is at least one of a straight-chain or branched aliphatic alcohol, an aromatic alcohol, an alcohol amine, and a phenol, each of which is substituted or unsubstituted.

[0019] Preferably, the hydroxyl-containing compound is at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, ethylene glycol, triethanolamine, benzyl alcohol, tritolyl alcohol, benzyl alcohol, and phenol.

[0020] Preferably, the molar ratio of the rare earth metal complex to the hydroxyl-containing compound is 1:0.01-500, preferably 1:0.1-100, and more preferably 1:0.1-50.

[0021] According to a second aspect of the present application, there is provided a method for preparing polylactide, wherein the method comprises the step of subjecting lactide monomers to solution polymerization in the presence of a rare earth metal complex having a structure represented by formula (I) and a hydroxyl-containing compound,

[0022]

[0023] In formula (I), Ln is a rare earth metal, R1-R6 are each independently selected from hydrogen or C1-C3 alkyl, R7 is selected from hydrogen or C1-C3 alkyl or halogen, and R8 is a silicon-containing group.

[0024] Preferably, Ln is selected from scandium, yttrium, a lanthanide series metal, or an actinide series metal, and is preferably selected from scandium or yttrium; R1-R5 are hydrogen; R6 is methyl, ethyl, or isopropyl; R7 is hydrogen or chlorine; and R8 is trimethylsilylmethylene or hexamethyldisilylamido.

[0025] Preferably, the rare earth metal complex having a structure represented by formula (I) is at least one of the following complexes,

[0026] In formula (I), Ln is scandium, R1-R5 are hydrogen, R6 is methyl, R7 is hydrogen, and R8 is trimethylsilylmethylene.

[0027] In formula (I), Ln is scandium, R1-R5 are hydrogen, R6 is ethyl, R7 is hydrogen, and R8 is trimethylsilylmethylene.

[0028] In formula (I), Ln is yttrium, R1-R5 are hydrogen, R6 is isopropyl, R7 is hydrogen, and R8 is hexamethyldisilylamido.

[0029] In formula (I), Ln is yttrium, R1-R5 are hydrogen, R6 is methyl, R7 is chlorine, and R8 is hexamethyldisilylamido.

[0030] Preferably, the hydroxyl-containing compound is an alcohol compound and / or a phenol compound.

[0031] Preferably, the hydroxyl-containing compound is at least one of a substituted or unsubstituted C1-C5 linear or branched aliphatic alcohol, a C6-C10 aromatic alcohol, a C4-C6 alcohol amine, and a phenol, the substituent group being selected from a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C10 aryl group. 20 10

[0032] Preferably, the hydroxyl-containing compound is at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, ethylene glycol, triethanolamine, benzoin, triphenyl carbinol, benzyl alcohol, and phenol.

[0033] Preferably, the molar ratio of the rare earth metal complex to the hydroxyl-containing compound is 1:0.01-500, preferably 1:0.1-100, and more preferably 1:0.1-50.

[0034] Preferably, the molar ratio of the hydroxyl-containing compound to the lactide monomer is 1:1-10000, preferably 1:20-8000, more preferably 1:20-6000, more preferably 1:20-5000, and further preferably 1:500-5000.

[0035] Preferably, the molar ratio of the rare earth metal complex to the lactide monomer is 1:10-5000, preferably 1:50-3000, more preferably 1:100-2500, and further preferably 1:100-2000.

[0036] Preferably, the solution polymerization conditions include a reaction temperature of 10-160°C, preferably 25-100°C, and a reaction time of 0.02-24h, preferably 0.1-3h.

[0037] According to a third aspect of the present application, there is provided a poly-lactide prepared by the method of preparing a poly-lactide according to the first aspect of the present application.

[0038] According to a fourth aspect of the present application, there is provided a use of the catalyst composition according to the first aspect of the present application in preparing a poly-lactide.

[0039] ​​Through the above technical solutions, the catalyst composition and its application, as well as the polylactide and its preparation method provided by the present invention, achieve the following beneficial effects:

[0040] The catalyst composition comprising a rare earth metal complex with a specific structure and a hydroxyl-containing compound provided by this invention can efficiently catalyze the ring-opening polymerization of lactide at a low metal catalyst concentration, exhibiting high catalytic efficiency and high conversion rate of the polymerization reaction. Simultaneously, during the catalytic process, the hydroxyl-containing compound undergoes active chain transfer with the initiation center, thereby enabling the polylactide chain to continuously grow, exhibiting "undying" polymerization characteristics and a molecular weight distribution close to 1, and obtaining polylactide with controllable molecular weight. Detailed Implementation

[0041] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0042] According to a first aspect of the present invention, a catalyst composition is provided, wherein the catalyst composition comprises a rare earth metal complex with the structure shown in formula (I) and a hydroxyl-containing compound.

[0043]

[0044] In formula (I), Ln is a rare earth metal, R1-R6 are each independently selected from hydrogen or C1-C3 alkyl groups; R7 is selected from hydrogen or C1-C3 alkyl groups or halogens; and R8 is a silicon-containing group.

[0045] In this invention, the C1-C3 alkyl groups can be methyl, ethyl, propyl or isopropyl, among which methyl, ethyl or isopropyl are preferred.

[0046] According to the present invention, preferably, the halogen is fluorine, chlorine, bromine or iodine, more preferably chlorine or bromine, and even more preferably chlorine.

[0047] According to the present invention, R8 is a silicon group, preferably, R8 is a trimethylsilylmethylene or hexamethyldisilazine group.

[0048] As a rare earth metal complex with the structure shown in formula (I), it is preferably selected from at least one of the following complexes.

[0049] In formula (I), Ln is a complex of scandium, R1-R5 are hydrogen, R6 is methyl, R7 is hydrogen, and R8 is trimethylsilylmethylene.

[0050] a complex of formula (I) wherein Ln is scandium, R1-R5 are hydrogen, R6 is ethyl, R7 is hydrogen, and R8 is trimethylsilylmethylene;

[0051] a complex of formula (I) wherein Ln is yttrium, R1-R5 are hydrogen, R6 is isopropyl, R7 is hydrogen, and R8 is hexamethyldisilylamido;

[0052] a complex of formula (I) wherein Ln is yttrium, R1-R5 are hydrogen, R6 is methyl, R7 is chlorine, and R8 is hexamethyldisilylamido.

[0053] According to the present application, the hydroxyl-containing compound can be an alcohol compound and / or a phenol compound. Preferably, the hydroxyl-containing compound is at least one of a substituted or unsubstituted C1-C5 linear or branched aliphatic alcohol, a C6-C10 aromatic alcohol, a C4-C6 alcohol amine, and a phenol, the substituent being selected from C1-C6 alkyl, C1-C6 alkoxy, or C6-C10 aryl; more preferably, the hydroxyl-containing compound is at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, ethylene glycol, triethanolamine, benzyl alcohol, benzhydrol, benzyl alcohol, and phenol; particularly preferably, the hydroxyl-containing compound is at least one of isopropanol, benzyl alcohol, benzhydrol, benzhydrol, and triethanolamine. 20 10

[0054] According to the present application, the content of the rare earth metal complex and the hydroxyl-containing compound can vary in a wide range, for example, the molar ratio of the rare earth metal complex to the hydroxyl-containing compound can be 1:0.01-500, preferably 1:0.1-100, more preferably 1:0.1-50, and particularly preferably 1:1-10.

[0055] According to the present application, by means of the catalyst composition comprising the rare earth metal complex and the hydroxyl-containing compound of specific structure, the ring-opening polymerization of lactide can be efficiently catalyzed at a low concentration of metal catalyst, the catalytic efficiency is very high, and the conversion rate of the polymerization reaction is high; meanwhile, in the catalytic process, the hydroxyl-containing compound and the initiation center generate active chain transfer, so that the poly-lactide chain can be continuously grown, showing the "immortal" polymerization characteristics and the molecular weight distribution close to 1, and the poly-lactide with controllable molecular weight can be obtained.

[0056] In the present application, the rare earth metal complex can be synthesized according to the conventional method in the art, and in a preferred embodiment of the present application, the method comprises:

[0057] 1) in the presence of a solvent, a compound of formula (1) is subjected to a first contact reaction with a compound of formula (2) in the presence of Na2S2O2, to obtain a compound of formula (II) (hereinafter also referred to as ligand);​​

[0058] 2) subjecting the compound represented by formula (II) to a second contact reaction with an alkyl rare earth metal compound or an amine-based rare earth metal compound in an organic solvent to obtain a rare earth metal complex represented by formula (I),

[0059] wherein the alkyl rare earth metal compound is selected from Ln[CH2Si(CH3)3]3(THF)2, and the amine-based rare earth metal compound is selected from Ln{N[Si(CH3)3]2}3(THF)2.

[0060]

[0061] In formula (1), formula (2) and formula (II), for the R1, R2, R3, R4, R5, R6, R7and R8groups, as described above, in addition, the rare earth metal in the alkyl rare earth metal compound or the amine-based rare earth metal compound is as described above Ln, which will not be repeated here.

[0062] Step 1): subjecting the compound represented by formula (1) to a first contact reaction with the compound represented by formula (2) in the presence of a solvent in the presence of Na2S2O2to obtain the compound represented by formula (II).

[0063] As the solvent, it can be a solvent capable of dissolving the reaction raw materials and inert to the reaction raw materials, for example, a mixed solvent of N,N-dimethylformamide (DMF) and water can be used.

[0064] In a preferred embodiment of the present application, the solvent is a mixed solvent of N,N-dimethylformamide and water, and the volume ratio of N,N-dimethylformamide to water is 2-5:1, preferably 3-4:1.

[0065] The amount of the solvent is not particularly limited and can be a conventional amount in the art.

[0066] The amount of the compound represented by formula (2) can also be selected according to the amount of the compound represented by formula (1), for example, the molar ratio of the compound represented by formula (1) to the compound represented by formula (2) can be 1:1-2, preferably 1:1-1.5, more preferably 1:1-1.2, and further preferably 1:1-1.1.

[0067] The amount of Na2S2O2can also be selected according to the amount of the compound represented by formula (1), for example, the molar ratio of the compound represented by formula (1) to Na2S2O2can be 1:2-5, preferably 1:3-4.

[0068] The first contact reaction is preferably carried out at 80-100°C, for example, it can be carried out at 100°C.

[0069] The first contact reaction can be performed for 0.5 hours or more, preferably for 1 to 10 hours, more preferably for 3 to 8 hours, and further preferably for 4 to 6 hours.

[0070] After the first contact reaction is completed, the reaction product can be cooled to room temperature and neutralized with aqueous ammonia to obtain the ligand (compound of the structure represented by formula (II)).

[0071] Step 2: The compound of the structure represented by formula (II) is subjected to a second contact reaction with an alkyl rare earth metal compound or an amine-based rare earth metal compound in an organic solvent to obtain the rare earth metal complex of the structure represented by formula (I).

[0072] The alkyl rare earth metal compound or the amine-based rare earth metal compound can be prepared according to a conventional synthesis method in the art, for example, by using the method described in the Preparation Examples below.

[0073] As Ln[R8]3(THF)2, for example, R8Li can be subjected to a contact reaction with LnCl3(THF)2.

[0074] As for the conditions of the contact reaction described above, a conventional condition in the art can be used.

[0075] As the organic solvent, for example, n-hexane or the like can be used.

[0076] In a preferred embodiment of the present application, the alkyl rare earth metal compound or the amine-based rare earth metal compound is dissolved in the organic solvent, and then subjected to a second contact reaction with the compound of the structure represented by formula (II).

[0077] The second contact reaction is preferably performed at room temperature, and for example, can be performed at 10 to 40°C.

[0078] The second contact reaction can be performed for 0.5 hours or more, preferably for 1 to 24 hours, more preferably for 8 to 15 hours, and further preferably for 8 to 12 hours.

[0079] After the second contact reaction is completed, the reaction product can be suction-filtered, washed with chilled n-hexane 2 to 3 times, and vacuum-dried to obtain the rare earth metal complex A of the structure represented by formula (I).

[0080] According to the second aspect of the present application, there is provided a method for producing a polylactide, wherein the method for producing a polylactide includes a step of subjecting a lactide monomer to solution polymerization in the presence of the rare earth metal complex of the structure represented by formula (I) and a compound containing a hydroxyl group,

[0081]

[0082] In formula (I), Ln is a rare earth metal, R1-R6 are independently selected from hydrogen or C1-C3 alkyl; R7 is selected from hydrogen or C1-C3 alkyl or halogen; and R8 is a silicon-containing group.

[0083] In the present application, the use of the rare earth metal complex in combination with the hydroxyl-containing compound reduces the amount of the rare earth metal complex, and a small amount of the rare earth metal complex can catalyze the obtaining of high-molecular-weight polylactide, and the catalytic efficiency is very high; meanwhile, in the catalytic process, the hydroxyl-containing compound is activated with the initiation center to form a living active chain, so that the polylactide chain can be continuously grown, showing the "immortal" polymerization characteristics and the molecular weight distribution close to 1, and the molecular weight controllable polylactide can be obtained.

[0084] In the present application, "lactide monomer" refers to L-lactide, D-lactide, L,D-lactide.

[0085] In addition, for Ln and R1, R2, R3, R4, R5, R6, R7 and R8 groups, as described above, they will not be repeated here.

[0086] As the rare earth metal complex of formula (I), it is preferably at least one selected from the following complexes,

[0087] In formula (I), Ln is scandium, R1-R5 are hydrogen, R6 is methyl, R7 is hydrogen, and R8 is trimethylsilylmethylene;

[0088] In formula (I), Ln is scandium, R1-R5 are hydrogen, R6 is ethyl, R7 is hydrogen, and R8 is trimethylsilylmethylene;

[0089] In formula (I), Ln is yttrium, R1-R5 are hydrogen, R6 is isopropyl, R7 is hydrogen, and R8 is hexamethyldisilylamino;

[0090] In formula (I), Ln is yttrium, R1-R5 are hydrogen, R6 is methyl, R7 is chlorine, and R8 is hexamethyldisilylamino.

[0091] The following will describe in detail the preparation method of the polylactide of the present application using the rare earth metal complex and the hydroxyl-containing compound (i.e. the catalyst composition of the present application).

[0092] According to the present application, the amounts of the rare earth metal complex and the hydroxyl group-containing compound can be varied within a wide range, for example, the molar ratio of the rare earth metal complex to the hydroxyl group-containing compound can be 1 : 0.01-500. In order to further improve the catalytic efficiency, preferably, the molar ratio of the rare earth metal complex to the hydroxyl group-containing compound is 1 : 0.1-100; more preferably, the molar ratio of the rare earth metal complex to the hydroxyl group-containing compound is 1 : 0.1-50; further preferably, the molar ratio of the rare earth metal complex to the hydroxyl group-containing compound is 1 : 1-10.

[0093] In order to further improve the catalytic efficiency, preferably, the molar ratio of the hydroxyl group-containing compound to the lactide monomer is 1 : 1-10000, preferably 1 : 20-8000, more preferably 1 : 20-6000, more preferably 1 : 20-5000, further preferably 1 : 500-5000.

[0094] In order to further improve the catalytic efficiency, preferably, the molar ratio of the rare earth metal complex to the lactide monomer is 1 : 10-5000, preferably 1 : 50-3000, more preferably 1 : 100-2500, further preferably 1 : 100-2000.

[0095] In the present application, the rare earth metal complex and the hydroxyl group-containing compound can be added separately at the time of the reaction, can be added simultaneously, or can be prepared in advance according to the following method and then added simultaneously: under dry and rapid stirring conditions, an organic solvent containing the rare earth metal complex is slowly dropped into an organic solvent containing the hydroxyl group-containing compound, and the resulting mixture is vacuum-filtered to obtain a catalyst composition.

[0096] The organic solvent containing the rare earth metal complex and the organic solvent containing the hydroxyl group-containing compound can be the same or different, and preferably, both are the same. In addition, as the organic solvent, a solvent used in solution polymerization can be used.

[0097] According to the present application, the solvent used in the solution polymerization can be an organic solvent, and preferably, at least one of a substituted or unsubstituted alkane, a substituted or unsubstituted benzene, and a substituted or unsubstituted ether.

[0098] In a preferred embodiment of the present application, the solvent is at least one of pentane, hexane, benzene, chlorobenzene, toluene, tetrahydrofuran, diethyl ether, and dichloromethane; more preferably, the solvent is one or more of toluene, tetrahydrofuran, and dichloromethane.

[0099] According to the present application, preferably, the solution polymerization conditions include: reaction temperature is 10-160℃, reaction time is 0.02-24h; more preferably, the solution polymerization conditions include: reaction temperature is 25-100℃, reaction time is 0.1-3h. In addition, in order to avoid the influence of water and oxygen and the like on the catalytic activity of the catalyst, the reaction of the present application is preferably carried out under the condition of no water and no oxygen.

[0100] After the reaction is completed, the post-treatment is carried out to obtain the polylactide, which can include adding the reacted mixed liquid into the ethanol solution of hydrochloric acid with the volume concentration of 5-20v% (preferably 8-12v%) to terminate the reaction, then settling in ethanol, filtering to obtain white solid, and drying the white solid at 30-50℃ for 36-60h to obtain the polylactide.

[0101] According to the third aspect of the present application, the polylactide prepared by the preparation method of the second method of the present application is provided.

[0102] In the preparation method of the present application, the rare earth metal complex is used in combination with the hydroxyl-containing compound, which reduces the amount of the rare earth metal complex, and a small amount of the rare earth metal complex can catalyze to obtain the polylactide with high molecular weight, and the catalytic efficiency is very high; at the same time, in the catalytic process, the hydroxyl-containing compound and the initiation center generate active chain transfer, so that the polylactide chain can continuously grow, showing the "immortal" polymerization characteristics and the molecular weight distribution close to 1, and the polylactide with controllable molecular weight can be obtained.

[0103] Specifically, the number average molecular weight of the polylactide can be 0.1-200, preferably 0.35-170; the molecular weight distribution is 1-1.5, preferably 1-1.3.

[0104] According to the fourth aspect of the present application, the application of the catalyst composition of the first aspect of the present application in the preparation of polylactide is provided.

[0105] The present application will be described in detail by the following examples, but the present application is not limited to the following examples.

[0106] In the following examples, the room temperature is about "25℃";

[0107] (1) Conversion rate of the polymer: detected by the Swiss Bruker Avance 400 nuclear magnetic resonance instrument; test conditions are: solvent is deuterated chloroform, and the test temperature is room temperature.

[0108] (2) Molecular weight and distribution of the polymer: detected by the Japanese Shimadzu LC-20A type liquid phase gel permeation chromatograph (GPC); test conditions are: solvent is chloroform, test temperature is 25℃, and the flow rate is 1mL / min;

[0109] (3) Elemental analysis of the metal complex: measured by using Elementar Vario EL elemental analyzer;

[0110] The ligand structure used in the embodiments of the present application is shown in formula (II), and the preparation method is as follows:

[0111]

[0112] The compound shown in formula (1) and the compound shown in formula (2) are weighed in a molar ratio of 1:1, respectively dissolved in a DMF / H2O (volume ratio of 3:1) solution, 3 times the molar amount of Na2S2O2 is added, stirred at 100℃ for 5h, cooled and neutralized with ammonia water, to obtain the desired ligand (compound shown in formula (II)), filtered, vacuum dried and stored for use.

[0113] wherein,

[0114] The ligand A (in formula (II), R1-R5 are hydrogen, R6 is methyl, and R7 is hydrogen) has a molecular formula of C 17 H 13 N3O (found): C, 74.17 (74.16); H, 4.76 (4.78); N, 15.26 (15.25); O, 5.81 (5.81).

[0115] The ligand B (in formula (II), R1-R5 are hydrogen, R6 is ethyl, and R7 is hydrogen) has a molecular formula of C 18 H 15 N3O (found): C, 74.72 (74.71); H, 5.23 (5.25); N, 14.52 (14.52); O, 5.53 (5.52).

[0116] The ligand C (in formula (II), R1-R5 are hydrogen, R6 is isopropyl, and R7 is hydrogen) has a molecular formula of C 19 H 17 N3O (found): C, 75.23 (75.21); H, 5.65 (5.66); N, 13.85 (13.85); O, 5.27 (5.28).

[0117] The ligand D (in formula (II), R1-R5 are hydrogen, R6 is methyl, and R7 is chlorine) has a molecular formula of C 17 H 12 ClN3O (found): C, 65.92 (65.91); H, 3.90 (3.92); N, 13.57 (13.56); O, 5.17 (5.17).

[0118] Preparation of alkyl yttrium:

[0119] Li+(CH3)3SiCH2Cl→(CH3)3SiCH2Li

[0120] (CH3)3SiCH2Li+YCl3(THF)2→Y[CH2Si(CH3)3]3(THF)2

[0121] In a glove box, a 100 ml single-neck flask was charged with yttrium trichloride (1.0 g) and 40 ml of tetrahydrofuran (THF) and stirred at room temperature overnight. A 50 ml conical flask was charged with alkyl lithium (1.4 g) and 20 ml of tetrahydrofuran (THF) and stirred at room temperature. The tetrahydrofuran solution of alkyl lithium was slowly added to the tetrahydrofuran mixture of yttrium trichloride. After the addition was completed, the mixture was stirred at room temperature for 3 hours. After the reaction was completed, the tetrahydrofuran was removed by suction to obtain a grayish-white solid. The solid was washed with 10 ml x 8 n-hexane and transferred to a clean flask. About 1 / 3 of the solvent was removed by suction under vacuum, and the mixture was frozen at -30 °C. After 1 hour, the frozen mixture was removed, and the yellow oil adhered to the wall of the flask was transferred to a conical flask. The above operation was repeated until no more yellow oil was precipitated. The clear solution was removed by suction to obtain a white crystalline solid, which was alkyl yttrium, in a yield of 74%.

[0122] Preparation of alkyl scandium:

[0123] The preparation was carried out according to the above method for preparing alkyl yttrium, except that YCl3(THF)2was replaced by ScCl3(THF)2.

[0124] Preparation of amido yttrium:

[0125] [(CH3)3Si]2NLi+YCl3(THF)2→Y{N[Si(CH3)3]2}3(THF)2

[0126] In a glove box, a 50 ml single-neck flask was charged with yttrium trichloride (0.77 g) and 20 ml of tetrahydrofuran (THF) and stirred at room temperature overnight. Then, the tetrahydrofuran was removed by suction, 20 ml of n-hexane was added, and the mixture was stirred. The powder of lithium amide (1.6 g) was slowly added to the n-hexane mixture under stirring. After the addition was completed, the mixture was stirred at room temperature for 15 hours. After the reaction was completed, the mixture was filtered, and the filter cake was washed with a small amount of chilled n-hexane. The filter cake was frozen in a refrigerator to precipitate white crystals. The clear solution was removed by suction to obtain a white solid, which was amido yttrium, in a yield of 64%.

[0127] Preparation of amido scandium:

[0128] The preparation was carried out according to the above method for preparing amido yttrium, except that YCl3(THF)2was replaced by ScCl3(THF)2.

[0129] Preparation Example 1

[0130] Preparation of rare earth metal complex A (in formula (I), Ln is scandium, R1-R5 are hydrogen, R6 is methyl, R7 is hydrogen, and R8 is trimethylsilylmethylene)

[0131] The ligand A has a structure as shown in formula (II), wherein R1-R5 are hydrogen, R6 is methyl, and R7 is hydrogen. 1.0 mmol of alkyl scandium is weighed and dissolved in n-hexane. After being placed in a refrigerator for half an hour, the alkyl scandium is taken out and slowly added to a powder containing an equal amount of ligand A while stirring. After the addition is completed, the reaction is carried out at room temperature for 12 hours. The product is extracted by filtration and washed with frozen n-hexane 2-3 times. The rare earth metal complex A is obtained by vacuum drying, and the yield is 58%.

[0132] The elemental analysis data of the product are as follows: C 24 H 29 N3O2ScSi (actual value): C, 62.05 (62.04); H, 6.29 (6.30); N, 9.05 (9.04); O, 6.89 (6.89).

[0133] Preparation Example 2

[0134] Preparation of rare earth metal complex B (in formula (I), Ln is scandium, R1-R5 are hydrogen, R6 is ethyl, R7 is hydrogen, and R8 is trimethylsilylmethylene)

[0135] The ligand B has a structure as shown in formula (II), wherein R1-R5 are hydrogen, R6 is ethyl, and R7 is hydrogen. 1.0 mmol of alkyl scandium is weighed and dissolved in n-hexane. After being placed in a refrigerator for half an hour, the alkyl scandium is taken out and slowly added to a powder containing an equal amount of ligand A while stirring. After the addition is completed, the reaction is carried out at room temperature for 12 hours. The product is extracted by filtration and washed with frozen n-hexane 2-3 times. The rare earth metal complex A is obtained by vacuum drying, and the yield is 60%.

[0136] The elemental analysis data of the product are as follows: C 25 H 31 N3O2ScSi (actual value): C, 62.74 (62.75); H, 6.53 (6.55); N, 8.78 (8.76); O, 6.69 (6.70).

[0137] Preparation Example 3

[0138] Preparation of rare earth metal complex C (in formula (I), Ln is yttrium, R1-R5 are hydrogen, R6 is isopropyl, R7 is hydrogen, and R8 is hexamethyldisilylamino)

[0139] The ligand C having the structure as shown in formula (II) wherein R1-R5 are hydrogen, R6 is isopropyl and R7 is hydrogen. 1.0 mmol of amide yttrium was weighed and dissolved in n-hexane. After being kept in the refrigerator for half an hour, it was taken out and slowly added with equal amount of ligand A powder while stirring. After the addition was completed, the reaction was carried out at room temperature for 12 hours. The product was filtered and washed with frozen n-hexane for 2-3 times and dried in vacuum to obtain the rare earth metal complex A with a yield of 56%.

[0140] The elemental analysis data of the product are as follows: C 27 H 38 N4O2Si2Y (found): C, 54.44 (54.43); H, 6.43 (6.44); N, 9.41 (9.41); O, 5.37 (5.38).

[0141] Preparation Example 4

[0142] Preparation of the rare earth metal complex D (in formula (I), Ln is yttrium, R1-R5 are hydrogen, R6 is methyl, R7 is chlorine and R8 is hexamethyldisilylamido)

[0143] The ligand D having the structure as shown in formula (II) wherein R1-R5 are hydrogen, R6 is methyl and R7 is chlorine. 1.0 mmol of amide yttrium was weighed and dissolved in n-hexane. After being kept in the refrigerator for half an hour, it was taken out and slowly added with equal amount of ligand A powder while stirring. After the addition was completed, the reaction was carried out at room temperature for 12 hours. The product was filtered and washed with frozen n-hexane for 2-3 times and dried in vacuum to obtain the rare earth metal complex A with a yield of 54%.

[0144] The elemental analysis data of the product are as follows: C 25 H 33 ClN4O2Si2Y (found): C, 49.87 (49.87); H, 5.52 (5.53); N, 9.31 (9.31); O, 5.31 (5.32).

[0145] Example 1

[0146] At room temperature, 10 μmol of the rare earth metal complex A, 10 μmol of benzyl alcohol and 10 mL of toluene solvent were added into a 20 mL anhydrous and oxygen-free polymer bottle, 20 mmol of L,D-lactide monomer was added, and the reaction was carried out at room temperature for 1 hour. Then, the reaction was terminated by adding 10 v% hydrochloric acid in ethanol solution, and the reaction solution was poured into ethanol to precipitate and filter to obtain a white solid. The white solid was dried in a vacuum drying oven at 40°C for 48 hours to obtain a polylactide solid.

[0147] The conversion rate was 89% as determined by nuclear magnetic resonance test.

[0148] The number average molecular weight Mn was 12.1 million, and the molecular weight distribution was Mw / Mn= 1.38. w n was 1.38.

[0149] Example 2

[0150] At room temperature, 10 μmol of rare earth metal complex A, 10 μmol of benzyl alcohol, and 10 mL of dichloromethane solvent were added to a 20 mL anhydrous and anaerobic polymerization bottle, 20 mmol of L,D-lactide monomer was added, and the reaction was stirred at room temperature for 1 h. Then, the reaction was terminated by adding a 10 v% hydrochloric acid solution in ethanol, the reaction solution was poured into ethanol to precipitate, and a white solid was obtained by filtration. The white solid was dried in a vacuum drying oven at 40°C for 48 h to obtain a polylactide solid.

[0151] The conversion rate was 97% as tested by nuclear magnetic resonance.

[0152] The number average molecular weight Mnof the polylactide was 14.8 million as measured by GPC analysis, and the molecular weight distribution was Mw / Mn= 1.13. n w n was 1.13.

[0153] Example 3

[0154] At room temperature, 10 μmol of rare earth metal complex A, 10 μmol of benzyl alcohol, and 10 mL of tetrahydrofuran solvent were added to a 20 mL anhydrous and anaerobic polymerization bottle, 20 mmol of L,D-lactide monomer was added, and the reaction was stirred at room temperature for 1 h. Then, the reaction was terminated by adding a 10 v% hydrochloric acid solution in ethanol, the reaction solution was poured into ethanol to precipitate, and a white solid was obtained by filtration. The white solid was dried in a vacuum drying oven at 40°C for 48 h to obtain a polylactide solid.

[0155] The conversion rate was 98% as tested by nuclear magnetic resonance.

[0156] The number average molecular weight Mnof the polylactide was 16.1 million as measured by GPC analysis, and the molecular weight distribution was Mw / Mn= 1.14. n w n was 1.14.

[0157] Example 4

[0158] ​​​​​At room temperature, 10 μmol of rare earth metal complex B, 10 μmol of benzyl alcohol and 10 mL of tetrahydrofuran solvent were added into a 20 mL anhydrous and anaerobic polymerization bottle, 10 mmol of L,D-lactide monomer was added, and the reaction was stirred at room temperature for 1 h, then the reaction was terminated by adding 10 v% hydrochloric acid in ethanol solution, the reaction solution was poured into ethanol for precipitation and filtration to obtain white solid, and the white solid was dried in a vacuum drying oven at 40 °C for 48 h to obtain polylactide solid.

[0159] The conversion rate was 95% tested by nuclear magnetic resonance.

[0160] The number average molecular weight M n of polylactide was 128,000 measured by GPC analysis, and the molecular weight distribution was M w / M n 1.15.

[0161] Example 5

[0162] At room temperature, 10 μmol of rare earth metal complex C, 100 μmol of benzyl alcohol and 10 mL of tetrahydrofuran solvent were added into a 20 mL anhydrous and anaerobic polymerization bottle, 10 mmol of L,D-lactide monomer was added, and the reaction was stirred at room temperature for 1 h, then the reaction was terminated by adding 10 v% hydrochloric acid in ethanol solution, the reaction solution was poured into ethanol for precipitation and filtration to obtain white solid, and the white solid was dried in a vacuum drying oven at 40 °C for 48 h to obtain polylactide solid.

[0163] The conversion rate was 95% tested by nuclear magnetic resonance.

[0164] The number average molecular weight M n of polylactide was 82,000 measured by GPC analysis, and the molecular weight distribution was M w / M n 1.21.

[0165] Example 6

[0166] At room temperature, 10 μmol of rare earth metal complex D, 10 μmol of benzyl alcohol and 10 mL of tetrahydrofuran solvent were added into a 20 mL anhydrous and anaerobic polymerization bottle, 5 mmol of L,D-lactide monomer was added, and the reaction was stirred at room temperature for 1 h, then the reaction was terminated by adding 10 v% hydrochloric acid in ethanol solution, the reaction solution was poured into ethanol for precipitation and filtration to obtain white solid, and the white solid was dried in a vacuum drying oven at 40 °C for 48 h to obtain polylactide solid.

[0167] The conversion rate was 95% tested by nuclear magnetic resonance.

[0168] The number average molecular weight M n of polylactide was 92,000 measured by GPC analysis, and the molecular weight distribution was Mw / M n was 1.23.

[0169] Example 7

[0170] At room temperature, 10 μmol of rare earth metal complex C, 200 μmol of benzyl alcohol and 10 mL of tetrahydrofuran solvent were added into a 20 mL anhydrous and anaerobic polymerization bottle, 10 mmol of L,D-lactide monomer was added, the reaction was stirred at room temperature for 1 h, then the reaction was terminated by adding 10 v% hydrochloric acid in ethanol solution, the reaction solution was poured into ethanol for precipitation and filtration to obtain white solid, and the white solid was dried in a vacuum drying oven at 40 °C for 48 h to obtain polylactide solid.

[0171] The conversion rate was 93% by nuclear magnetic resonance test.

[0172] The number average molecular weight M n of polylactide was 28,000, and the molecular weight distribution was M w / M n was 1.14.

[0173] Example 8

[0174] At room temperature, 10 μmol of rare earth metal complex A, 500 μmol of benzyl alcohol and 10 mL of tetrahydrofuran solvent were added into a 20 mL anhydrous and anaerobic polymerization bottle, 10 mmol of L,D-lactide monomer was added, the reaction was stirred at room temperature for 1 h, then the reaction was terminated by adding 10 v% hydrochloric acid in ethanol solution, the reaction solution was poured into ethanol for precipitation and filtration to obtain white solid, and the white solid was dried in a vacuum drying oven at 40 °C for 48 h to obtain polylactide solid.

[0175] The conversion rate was 88% by nuclear magnetic resonance test.

[0176] The number average molecular weight M n of polylactide was 83,000, and the molecular weight distribution was M w / M n was 1.13.

[0177] Example 9

[0178] At room temperature, 10 μmol of rare earth metal complex C, 10 μmol of benzyl alcohol and 10 mL of tetrahydrofuran solvent were added into a 20 mL anhydrous and anaerobic polymerization bottle, 1 mmol of L,D-lactide monomer was added, the reaction was stirred at room temperature for 1 h, then the reaction was terminated by adding 10 v% hydrochloric acid in ethanol solution, the reaction solution was poured into ethanol for precipitation and filtration to obtain white solid, and the white solid was dried in a vacuum drying oven at 40 °C for 48 h to obtain polylactide solid.

[0179] NMR test conversion rate was 92%.

[0180] GPC analysis showed that the number average molecular weight M n was 7.42 million, and the molecular weight distribution M w / n was 1.22.

[0181] Example 10

[0182] At room temperature, 10 μmol of rare earth metal complex A, 10 μmol of isopropyl alcohol and 10 mL of tetrahydrofuran solvent were added to a 20 mL anhydrous and anaerobic polymerization bottle, 10 mmol of L,D-lactide monomer was added, and the reaction was stirred at room temperature for 1 h, then the reaction was terminated by adding 10 v% hydrochloric acid in ethanol solution, the reaction liquid was poured into ethanol for sedimentation and filtration to obtain white solid, and the white solid was dried in a vacuum drying oven at 40°C for 48 h to obtain polylactide solid.

[0183] NMR test conversion rate was 95%.

[0184] GPC analysis showed that the number average molecular weight M n was 14.1 million, and the molecular weight distribution M w / n was 1.18.

[0185] Example 11

[0186] At room temperature, 10 μmol of rare earth metal complex B, 0.5 μmol of benzyl alcohol, 0.5 μmol of benzhydrol and 10 mL of tetrahydrofuran solvent were added to a 20 mL anhydrous and anaerobic polymerization bottle, 5 mmol of L,D-lactide monomer was added, and the reaction was stirred at room temperature for 48 h, then the reaction was terminated by adding 10 v% hydrochloric acid in ethanol solution, the reaction liquid was poured into ethanol for sedimentation and filtration to obtain white solid, and the white solid was dried in a vacuum drying oven at 40°C for 48 h to obtain polylactide solid.

[0187] NMR test conversion rate was 91%.

[0188] GPC analysis showed that the number average molecular weight M n was 6.8 million, and the molecular weight distribution M w / n was 1.23.

[0189] Example 12

[0190] At room temperature, 10 μmol of rare earth metal complex A, 10 μmol of benzyl alcohol and 10 mL of tetrahydrofuran solvent were added into a 20 mL anhydrous and anaerobic polymerization bottle, 1 mmol of L,D-lactide monomer was added, and the reaction was stirred at room temperature for 1 h, then the reaction was terminated by adding 10v% hydrochloric acid in ethanol solution, the reaction solution was poured into ethanol for precipitation and filtration to obtain white solid, and the white solid was dried in a vacuum drying oven at 40°C for 48 h to obtain polylactide solid.

[0191] The conversion rate was 85% tested by nuclear magnetic resonance.

[0192] The number average molecular weight M n of the polylactide was 32,000, and the molecular weight distribution M w / M n was 1.22.

[0193] Comparative Example 1

[0194] At room temperature, 10 μmol of rare earth metal complex A and 10 mL of tetrahydrofuran solvent were added into a 20 mL anhydrous and anaerobic polymerization bottle, 1 mmol of L,D-lactide monomer was added, and the reaction was stirred at room temperature for 1 h, then the reaction was terminated by adding 10v% hydrochloric acid in ethanol solution, the reaction solution was poured into ethanol for precipitation and filtration to obtain white solid, and the white solid was dried in a vacuum drying oven at 40°C for 48 h to obtain polylactide solid.

[0195] The conversion rate was 79% tested by nuclear magnetic resonance.

[0196] The number average molecular weight M n of the polylactide was 12,000, and the molecular weight distribution M w / M n was 1.35.

[0197] It can be known from the above examples that the catalyst composition provided by the application has high catalytic activity when used for preparing polylactide by ring-opening polymerization of lactide, the molecular weight of the obtained polymer is high, the molecular weight is controllable, and the molecular weight distribution is narrow.

[0198] It can be known by comparing Example 1 with Comparative Example 1 that the conversion rate is significantly improved (that is, the catalytic activity is significantly improved) and the number average molecular weight is significantly improved when the catalyst composition provided by the application is used for preparing polylactide by ring-opening polymerization of lactide.

[0199] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including that each technical feature is combined in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A catalyst composition characterized in that, The catalyst composition contains a rare earth metal complex having a structure represented by formula (I) and a hydroxyl group-containing compound, In formula (I), Ln is a rare earth metal, R1 to R6 are each independently selected from hydrogen or C1 to C3 alkyl, R7 is selected from hydrogen or C1 to C3 alkyl or halogen, and R8 is a silicon-containing group.

2. The catalyst composition of claim 1, wherein, The Ln is selected from scandium, yttrium, a lanthanide series metal, or an actinide series metal, and is preferably selected from scandium or yttrium; R1 to R5 are hydrogen; R6 is methyl, ethyl, or isopropyl; R7 is hydrogen or chlorine; and R8 is trimethylsilylmethylene or hexamethyldisilylamino.

3. The catalyst composition of claim 1 or 2, wherein, The rare earth metal complex having a structure represented by formula (I) is selected from at least one of the following complexes, In formula (I), Ln is scandium, R1 to R5 are hydrogen, R6 is methyl, R7 is hydrogen, and R8 is trimethylsilylmethylene. In formula (I), Ln is scandium, R1 to R5 are hydrogen, R6 is ethyl, R7 is hydrogen, and R8 is trimethylsilylmethylene. In formula (I), Ln is yttrium, R1 to R5 are hydrogen, R6 is isopropyl, R7 is hydrogen, and R8 is hexamethyldisilylamino. In formula (I), Ln is yttrium, R1 to R5 are hydrogen, R6 is methyl, R7 is chlorine, and R8 is hexamethyldisilylamino.

4. The catalyst composition of any of claims 1-3, wherein, The hydroxyl group-containing compound is an alcohol compound and / or a phenol compound.

5. The catalyst composition of any of claims 1-4, wherein, said hydroxyl-containing compound is at least one of a substituted or unsubstituted C1-C5 linear or branched aliphatic alcohol, a C6-C10 aromatic alcohol, a C4-C6 alcohol amine, and a phenol, the substituents being selected from a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C10 aryl group; 20 said hydroxyl-containing compound is at least one of a substituted or unsubstituted C1-C5 linear or branched aliphatic alcohol, a C6-C10 aromatic alcohol, a C4-C6 alcohol amine, and a phenol, the substituents being selected from a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C10 aryl group; 10 said hydroxyl-containing compound is at least one of a substituted or unsubstituted C1-C5 linear or branched al Preferably, the hydroxyl group-containing compound is at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, ethylene glycol, triethanolamine, benzhydrol, benzoin, benzyl alcohol, and phenol.

6. The catalyst composition of any of claims 1-5, wherein, The molar ratio of the rare earth metal complex to the hydroxyl group-containing compound is 1:0.01 to 500; Preferably, the molar ratio of the rare earth metal complex to the hydroxyl group-containing compound is 1:0.1 to 100; Preferably, the molar ratio of the rare earth metal complex to the hydroxyl group-containing compound is 1:0.1 to 50.

7. A process for the preparation of poly-L-lactide, characterized in that, The production method includes a step of subjecting lactide monomers to solution polymerization in the presence of a rare earth metal complex having a structure represented by formula (I) and a hydroxyl group-containing compound, In formula (I), Ln is a rare earth metal, R1 to R6 are each independently selected from hydrogen or C1 to C3 alkyl, R7 is selected from hydrogen or C1 to C3 alkyl or halogen, and R8 is a silicon-containing group.

8. The method of claim 7, wherein, The Ln is selected from scandium, yttrium, a lanthanide series metal, or an actinide series metal; Preferably, the Ln is selected from scandium or yttrium; R1 to R5 are hydrogen; R6 is methyl, ethyl, or isopropyl; R7 is hydrogen or chlorine; and R8 is trimethylsilylmethylene or hexamethyldisilylamino.

9. The method of claim 8, wherein, The rare earth metal complex having a structure represented by formula (I) is selected from at least one of the following complexes, In formula (I), Ln is scandium, R1 to R5 are hydrogen, R6 is methyl, R7 is hydrogen, and R8 is trimethylsilylmethylene. In formula (I), Ln is scandium, R1 to R5 are hydrogen, R6 is ethyl, R7 is hydrogen, and R8 is trimethylsilylmethylene. In formula (I), Ln is yttrium, R1 to R5 are hydrogen, R6 is isopropyl, R7 is hydrogen, and R8 is hexamethyldisilylamino. In formula (I), Ln is yttrium, R1 to R5 are hydrogen, R6 is methyl, R7 is chlorine, and R8 is hexamethyldisilylamino.

10. The method of any of claims 7-9, wherein, The hydroxyl-containing compound is an alcohol compound and / or a phenol compound.

11. The method of claim 10, wherein, said hydroxyl-containing compound is at least one of a substituted or unsubstituted C1-C5 linear or branched aliphatic alcohol, a C6-C10 aromatic alcohol, a C4-C6 alcohol amine, and a phenol, the substituents being selected from a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C10 aryl group; 20 10 said hydroxyl-containing compound is at least one of a substituted or unsubstituted C1-C5 linear or branched aliphatic alcohol, a C6-C10 aromatic alcohol, a C4-C6 alcohol amine, and a phenol, the substituents being selected from a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C10 aryl group;​ Alternatively, the hydroxyl-containing compound is at least one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, ethylene glycol, triethanolamine, benzhydrol, tritolyl alcohol, benzyl alcohol and phenol.

12. The method of any of claims 7-11, wherein, The solution polymerization conditions include a reaction temperature of 10-160°C, preferably 25-100°C; and a reaction time of 0.02-24h, preferably 0.1-3h.

13. The method of any of claims 7-12, wherein, The molar ratio of the rare earth metal complex to the hydroxyl-containing compound is 1:0.01-500, preferably 1:0.1-100, and more preferably 1:0.1-50; and / or, the molar ratio of the hydroxyl-containing compound to the lactide monomer is 1:1-10000, preferably 1:20-8000, more preferably 1:20-6000, more preferably 1:20-5000, and further preferably 1:500-5000; and / or, the molar ratio of the rare earth metal complex to the lactide monomer is 1:10-5000, preferably 1:50-3000, more preferably 1:100-2500, and further preferably 1:100-2000.

14. The polylactide prepared by the method of any one of claims 7-13.

15. Use of the catalyst composition of any one of claims 1-6 in the preparation of polylactide.

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