Rare earth catalyst for preparing trans-1, 4-polyisoprene as well as preparation method and application of rare earth catalyst

Abstract

The invention relates to the field of olefin polymerization, in particular to a rare earth catalyst for preparing trans-1, 4-polyisoprene as well as a preparation method and application of the rare earth catalyst. The rare earth catalyst is selected from a compound with a structure as shown in a formula I. According to the rare earth catalyst, a large-steric-hindrance substituent is introduced to a cyclopentadienyl skeleton, and when isoprene is catalyzed to be subjected to solution polymerization to prepare trans-1, 4-polyisoprene, the rare earth catalyst can form a cation active center after being activated by an organic boride, so that the trans-1, 4-polyisoprene is prepared. A large steric hindrance ligand in the rare earth catalyst can compress the space environment of an active center; therefore, a larger space required by cis-insertion of the isoprene monomer is effectively inhibited by ligand resistance, and the isoprene monomer can only be inserted into the growth chain in a trans-configuration; meanwhile, cyclopentadienyl in the rare earth catalyst is a strong electron donor, so that the electron cloud density of a metal center can be improved, and the catalytic activity is enhanced.

Description

Technical Field

[0001] This application relates to the field of olefin polymerization, and in particular to a rare earth catalyst for the preparation of trans-1,4-polyisoprene, its preparation method, and its application. Background Technology

[0002] Trans-1,4-polyisoprene (TPI), a stereoregular polymer isomer of natural rubber (cis-1,4-polyisoprene), exhibits irreplaceable application value in high-performance tires, medical rehabilitation devices, and intelligent flexible materials due to its low dynamic heat generation, low rolling resistance, wear and fatigue resistance, and unique shape memory properties. The performance regulation and industrialization of TPI are highly dependent on catalytic synthesis technology; the stereoselectivity, catalytic efficiency, and cost of the catalyst directly determine the microstructure, product quality, and market competitiveness of TPI.

[0003] In existing technologies, the synthesis of TPI mainly relies on vanadium-based and titanium-based catalyst systems. However, these catalysts have significant limitations: First, vanadium-based catalysts are highly toxic, requiring an additional vanadium removal process in post-processing. Heavy metal residues are easily generated during production, increasing processing costs and limiting the application of TPI in food contact and medical fields. Second, the trans-1,4-selectivity of titanium-based catalysts is difficult to control, making it difficult to maintain the trans-1,4-structure content in the product at a stable level above 95%, and the catalytic activity is low, requiring a large investment to ensure polymerization efficiency. Third, traditional catalysts are mostly heterogeneous systems, and subsequent separation and recovery processes are complex, further restricting the high-end application of TPI. Summary of the Invention

[0004] Based on this, the purpose of this application is to overcome the shortcomings of the prior art and provide a rare earth catalyst for the preparation of trans-1,4-polyisoprene, its preparation method and application, so as to solve the technical problems of difficult control of trans-1,4-selectivity and low activity of traditional catalysts.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] First, this application provides a rare earth catalyst for preparing trans-1,4-polyisoprene, wherein the rare earth catalyst is selected from compounds having the structure shown in Formula I.

[0007]

[0008] Wherein, Ln is selected from rare earth metals; R1 is selected from hydrogen or alkyl groups having 1 to 6 carbon atoms; R2 is selected from hydrogen, alkylsilyl groups having 1 to 6 carbon atoms, alkenylsilyl groups having 1 to 6 carbon atoms, or bromine-containing alkylsilyl groups having 1 to 6 carbon atoms; X is selected from hydrogen, alkyl-substituted aryl groups having 6 to 13 carbon atoms, alkenyl-substituted aryl groups having 6 to 13 carbon atoms, or alkoxy-substituted aryl groups having 6 to 13 carbon atoms.

[0009] Preferably, Ln is selected from any one of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

[0010] Preferably, R1 is selected from hydrogen, methyl, ethyl, propyl, isopropyl, tert-butyl, or isopentyl.

[0011] Preferably, R2 is selected from trimethylsilyl, triethylsilyl, tri-n-propylsilyl, triisopropylsilyl, tri-tert-butylsilyl, tri-n-hexylsilyl, trivinylsilyl, tripropylenesilyl, tri(bromomethyl)silyl, or tri(2-bromoethyl)silyl.

[0012] Preferably, the rare earth catalyst is selected from at least one of compounds having a structure as shown in Formulas I1 to I7.

[0013]

[0014]

[0015] .

[0016] Based on a general inventive concept, this application also provides a method for preparing a rare earth catalyst, comprising the following steps:

[0017] S1. Provide intermediates having the structure shown in Formula II and intermediates having the structure shown in Formula III, respectively;

[0018] S2. The intermediate having the structure shown in Formula II is mixed with an alkyllithium reagent and subjected to a deprotonation lithiation reaction to obtain lithiation intermediate 1.

[0019] S3. The lithiation intermediate 1 is mixed with an intermediate having the structure shown in Formula III and a nucleophilic substitution reaction is carried out to obtain a compound with the structure shown in Formula I.

[0020] ,

[0021] R3 is selected from halogens.

[0022] Preferably, R3 is selected from Cl, Br or I.

[0023] Preferably, when adding an alkyllithium reagent for deprotonation lithiation, the alkyllithium reagent is first added dropwise to the reaction system at -80℃ to -70℃. After the addition is complete, the temperature is raised to room temperature and the reaction continues for 1 to 3 hours. In the preparation method of this application, the temperature and time conditions for adding the alkyllithium reagent for deprotonation lithiation in each step are the same as those described herein, and will not be repeated below.

[0024] Preferably, the alkyllithium reagent is selected from at least one of n-butyllithium, tert-butyllithium, and diisopropylaminolithium.

[0025] Preferably, the deprotonation lithiation reaction is carried out under anhydrous and oxygen-free conditions.

[0026] Preferably, the deprotonation lithiation reaction is carried out in anhydrous tetrahydrofuran, diethyl ether, or toluene solvent.

[0027] Preferably, the molar ratio of the intermediate having the structure shown in Formula II to the alkyl lithium reagent is 1:(1~1.1).

[0028] Preferably, the molar ratio of the intermediate having the structure shown in Formula II to the intermediate having the structure shown in Formula III is 1:(1.5~2.5).

[0029] Preferably, the preparation steps of the intermediate having the structure shown in Formula II include:

[0030] S11. Cyclopentadiene is deprotonated and lithiated with an alkyl lithiation reagent, and then a C1-C6 haloalkane is added for nucleophilic substitution to obtain an intermediate with the structure shown in Formula IV.

[0031] S12. The intermediate having the structure shown in Formula IV is subjected to a deprotonation lithiation reaction with an alkyl lithiation reagent, and then a silane shown in Formula V is added to carry out a nucleophilic substitution reaction to obtain the intermediate having the structure shown in Formula II.

[0032]

[0033] R4 is selected from C1-C6 alkyl, C2-C6 alkenyl, or C1-C6 brominated alkyl; R5 is halogen or hydrogen.

[0034] Preferably, the molar ratio of cyclopentadiene to alkyllithium reagent is 1:(3~5).

[0035] Preferably, the molar ratio of cyclopentadiene to C1-C6 haloalkanes is 1:(4-5).

[0036] Preferably, the haloalkane added in step S11 is selected from isopropyl bromide, iodomethane, bromoethane, or bromomethane.

[0037] Preferably, the silane represented by Formula V is selected from trimethylchlorosilane, trivinylsilane, triethylchlorosilane, or triisopropylchlorosilane.

[0038] Preferably, in step S12, the molar ratio of the intermediate having the structure shown in Formula IV to the alkyl lithium reagent is 1:(1~1.1).

[0039] Preferably, in step S12, the molar ratio of the intermediate having the structure shown in Formula IV to the silane shown in Formula V is 1:(1~1.1).

[0040] Preferably, the preparation steps of the intermediate having the structure shown in Formula III include:

[0041] S14. Lithification reaction of Br-X bromoalkane with metallic lithium to obtain Li-X intermediate;

[0042] S15. The complex of Ln(R3)3 and tetrahydrofuran is added to the Li-X intermediate for a substitution reaction to obtain the intermediate with the structure shown in Formula III.

[0043] Preferably, the bromoalkane of formula Br-X is bromobenzene, 2-bromonaphthalene, diphenylchloromethane, cinnamyl bromide, 2-bromo-1,3-diisopropylbenzene, or 4-bromoanisole.

[0044] Preferably, the complex of Ln(R3)3 with tetrahydrofuran is selected from YCl3·3THF, GdCl3·3THF, GdCl3·3THF or SmCl3·3THF.

[0045] Preferably, the lithiation reaction is carried out under organic solvent conditions. This organic solvent can be diethyl ether.

[0046] Preferably, in step S14, the molar ratio of Br-X bromoalkane to lithium metal is 1:(2~2.5).

[0047] Preferably, in step S14, the molar ratio of the complex of Ln(R3)3 and tetrahydrofuran to the Li-X intermediate is 1:(1.5~2.5).

[0048] Based on a general inventive concept, this application also provides an application of the above-mentioned rare earth catalyst in catalyzing the solution polymerization of isoprene to prepare trans-1,4-polyisoprene.

[0049] Preferably, catalysts for the solution polymerization of isoprene to prepare trans-1,4-polyisoprene also include organoboron and alkylaluminum.

[0050] Preferably, the molar ratio of rare earth catalyst, organoboron and alkylaluminum is 1:1:(1~5000).

[0051] Preferably, the organoboron is selected from at least one of triphenylcarbazo-tetra(pentafluorophenyl)borate, N,N-dimethylphenylammonium tetra(pentafluorophenyl)borate, and tri(pentafluorophenyl)borane.

[0052] Preferably, the alkylaluminum is selected from at least one of trimethylaluminum, triethylaluminum, triisobutylaluminum, tripentylaluminum, trioctylaluminum, and diethylaluminum chloride.

[0053] Preferably, when isoprene is solution polymerized to prepare trans-1,4-polyisoprene, the molar ratio of rare earth catalyst to isoprene monomer is 1:(5000~10000); more preferably, it is 1:1:(1~2000). By further controlling the molar ratio of rare earth catalyst to isoprene monomer, catalytic activity and cost can be balanced. Furthermore, excess alkyl aluminum leads to a broadening of the molecular weight distribution.

[0054] Preferably, the reaction temperature for solution polymerization is -50℃ to 45℃, and the reaction time is 4h to 24h. More preferably, the reaction temperature is -40℃ to 20℃, and the reaction time is 4h to 5h.

[0055] Preferably, the solution polymerization is carried out sequentially under a five-stage gradient temperature condition, the five stages of which are as follows:

[0056] First stage: React at -50℃ to -35℃ for 0.8h to 1.2h;

[0057] Second stage: Heat to -30℃ to -25℃, react for 0.8h to 1.2h;

[0058] Third stage: Heat to -15℃ to -10℃ and react for 0.8h to 1.2h;

[0059] Fourth stage: Increase the temperature to 5℃~10℃ and react for 0.8h~1.2h;

[0060] Fifth stage: Increase the temperature to 15℃~20℃ and react for 0.8h~1.2h.

[0061] Preferably, the heating rate between adjacent temperature ranges is 5℃ / min to 6℃ / min.

[0062] Solution polymerization under the aforementioned five-stage gradient temperature conditions is beneficial for the conversion of isoprene and the selective formation of trans-1,4-polyisoprene. Specifically, in the first stage, the initial polymerization is carried out under the aforementioned low-temperature conditions, which can enhance steric inhibition and lock the initial chain segment with a high trans structure. Then, polymerization is carried out under the second stage temperature condition, where the temperature difference between the second and first stages is relatively small, and the gentle temperature increase can promote monomer diffusion and match high catalytic activity. Then, polymerization is carried out under the third stage temperature condition, which is conducive to balancing the activity of the polymerization reaction and the selectivity of trans-1,4-polyisoprene, and avoiding deactivation of active centers. The temperature continues to rise to the fourth stage to improve the conversion efficiency of the remaining monomers. Then, the temperature is raised to the fifth stage, where the dormant active centers of the catalyst can be activated under this temperature adjustment, and highly active species can be formed by promoting ligand dissociation and alkyl aluminum reduction, thereby promoting complete monomer conversion.

[0063] Preferably, the solvent in the solution polymerization is selected from two or more mixtures of toluene, xylene, benzene, n-hexane, n-heptane, cyclohexane, chlorobenzene, and dichlorobenzene.

[0064] Preferably, the solvent in solution polymerization is a mixed solvent obtained by mixing toluene and n-hexane in a 1:1 volume ratio.

[0065] Preferably, after polymerization under five gradient temperature conditions is completed, anhydrous ethanol acidified with hydrochloric acid is added to the reaction system to terminate the polymerization, and then the polymer is precipitated with ethanol and dried under vacuum at 60°C to constant weight.

[0066] Preferably, the volume ratio of hydrochloric acid to anhydrous ethanol in hydrochloric acid-acidified anhydrous ethanol is 1:10.

[0067] Preferably, the drying time is 8h to 12h to ensure that the residual solvent content in the polymer is <0.1%.

[0068] Preferably, in the polymer obtained by solution polymerization of isoprene, the molar content of trans-1,4-polyisoprene is 91%~94%; and the molecular weight distribution of trans-1,4-polyisoprene is 2.0~2.3.

[0069] Compared with existing technologies, the catalyst of this application has the following beneficial effects:

[0070] Regarding the catalyst composition, the catalyst in this application includes a rare earth catalyst having the structure shown in Formula I, an organoboron, and an alkylaluminum. The rare earth catalyst having the structure shown in Formula I introduces a sterically hindered substituent onto the cyclopentadienyl framework. After activation by organoboronides, this rare earth catalyst can form a cationic active center. The sterically hindered ligands in the rare earth catalyst can compress the spatial environment of the active center. Thus, the larger space required for the cis insertion of the isoprene monomer is effectively suppressed by the steric hindrance of the ligands, and the isoprene monomer can only insert into the growing chain in a trans configuration. Simultaneously, the cyclopentadienyl group in the rare earth catalyst is a strong electron donor, which can increase the electron cloud density of the metal center and enhance catalytic activity.

[0071] In addition, rare earth elements, with their unique electronic configuration and coordination chemistry, can form stable complexes with ligands to construct precise active centers and achieve efficient control of monomer insertion direction. On the other hand, rare earth elements are far less toxic than heavy metals such as vanadium and titanium, and their complexes can be easily homogenized or loaded through ligand modification, simplifying subsequent separation processes.

[0072] In the catalytic polymerization process, the above-mentioned catalyst works synergistically with a gradient temperature control strategy within the range of -50℃ to 20℃: at the low temperature in the initial stage of polymerization, the steric inhibition effect of the sterically hindered ligands in the rare earth catalyst is maximized, preferentially locking the initial chain segment of trans-1,4-intercalation (trans selectivity > 94%); as the reaction is gradually heated to -30℃ to -25℃ and -15℃ to -10℃, the gradient heating conditions are mild, which can avoid the weakening of the steric hindrance effect of the ligands and accelerate the diffusion of monomers in the homogeneous system, matching the chain growth requirements brought about by the high electron cloud density of the active center; finally, when the temperature is raised to 15℃ to 20℃, under the premise that the ligands can still effectively inhibit cis-intercalation, a small number of active centers that have been "dormant" due to the decrease in monomer concentration are activated, driving the conversion rate of isoprene to exceed 90%.

[0073] The synergistic mechanism in the solution polymerization reaction of this application not only retains the core advantages of "high selectivity (trans-1,4->91%) + high activity" conferred by the ligand structure, but also optimizes the living polymerization characteristics through dynamic matching of temperature gradient and active center state, ultimately achieving a triple synergistic improvement of "selectivity-activity-efficiency". Attached Figure Description

[0074] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0075] Figure 1The high-temperature GPC spectrum of trans-1,4-polyisoprene prepared in Example 1 is shown.

[0076] Figure 2 The high-temperature GPC spectrum of trans-1,4-polyisoprene prepared in Example 2 is shown.

[0077] Figure 3 The high-temperature GPC spectrum of trans-1,4-polyisoprene prepared in Example 3 is shown.

[0078] Figure 4 The high-temperature GPC spectrum of trans-1,4-polyisoprene prepared in Example 4 is shown.

[0079] Figure 5 The high-temperature GPC spectrum of trans-1,4-polyisoprene prepared in Example 5 is shown.

[0080] Figure 6 The high-temperature GPC spectrum of trans-1,4-polyisoprene prepared in Example 6 is shown.

[0081] Figure 7 The high-temperature GPC spectrum of trans-1,4-polyisoprene prepared in Example 7 is shown.

[0082] Figure 8 The high-temperature GPC spectrum of trans-1,4-polyisoprene prepared in Example 8 is shown.

[0083] Figure 9 The high-temperature GPC spectrum of trans-1,4-polyisoprene prepared in Comparative Example 1 is shown. Detailed Implementation

[0084] The embodiments described in this specification are merely for explaining this application and are not intended to limit this application.

[0085] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0086] Those skilled in the art will understand that the order in which the steps are written in the various embodiments or examples does not imply a strict execution order and does not limit the implementation process in any way. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but sequentially is preferred.

[0087] The following abbreviations may be used in this document: Me is methyl, Et is ethyl, Bu is butyl, nBu is n-butyl, iBu is isobutyl, sBu is sec-butyl, tBu is tert-butyl, Oct is octyl, Ph is phenyl, Bn is benzyl, MAO is methylaluminoxane, Ind is indyl, Cp is cyclopentadienyl, Flu is fluorenyl, OTf is trifluoromethanesulfonate / ester, PhB(OH)2 is phenylboronic acid, tetrakis(triphenylphosphine)palladium, LiAlH4 is lithium aluminum hydride, THF is tetrahydrofuran, TsOH is p-toluenesulfonic acid, Tol is toluene, Pr i and i Pr represents isopropyl, aryl represents hydrogen on the aromatic ring, including benzene ring, naphthalene ring and indene ring, etc.; Cp-H represents hydrogen in bis(cyclopentadienyl).

[0088] All operations involving water and oxygen-sensitive reagents in this application use standard Schlenk techniques and a glove box (nitrogen atmosphere, water and oxygen content <0.1ppm); solvents such as toluene and n-hexane are distilled after being refluxed with sodium wire / benzophenone until they turn blue, and then soaked in 4Å molecular sieves in the glove box for later use; isoprene is dried with calcium hydride and then distilled under reduced pressure, and stored in the glove box for later use.

[0089] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0090] In this application, room temperature refers to 20℃~30℃.

[0091] In this application, "eq" represents equivalent amount. For example, in the case of 4.0 eq, the amount of n-butyllithium added is 4.0, which means 4.0 equivalent amount.

[0092] Preparation of rare earth catalysts:

[0093] Preparation Example 1: Preparation of Rare Earth Catalyst 1 – Bis(1,2,3,4-tetraisopropyl-5-trimethylsilylcyclopentadienyl)phenylyttrium

[0094] (1) Preparation of 1,2,3,4-tetraisopropylcyclopentadiene: A dry Schlenk flask was used to add 2.0 g (30.2 mmol) of cyclopentadiene and anhydrous tetrahydrofuran, and stirred until completely dissolved. The mixture was cooled to -78 °C, and 48.3 mL (120.8 mmol, 4.0 eq) of 2.5 M n-butyllithium solution was slowly added dropwise. After the addition was complete, the mixture was slowly heated to room temperature and stirred for 2 hours, gradually turning into a pale yellow suspension. The reaction flask was cooled to -78 °C again, and 13.0 mL (138.9 mmol, 4.6 eq) of isopropyl bromide was added dropwise. After the addition was complete, the mixture was heated to room temperature and refluxed at 70 °C for 12 hours. After the reaction was complete, the mixture was cooled to room temperature, the reaction was quenched with saturated ammonium chloride aqueous solution, the organic phase was extracted with diethyl ether, dried over magnesium sulfate, filtered, concentrated under reduced pressure, and recrystallized in petroleum ether at -20 °C. Filtering yielded 6.4 g of white crystals, with a yield of 81%.

[0095]

[0096] (2) Preparation of 1,2,3,4-tetraisopropyl-5-trimethylsilylcyclopentadiene: In a dry Schlenk flask, 5.0 g (18.7 mmol) of the 1,2,3,4-tetraisopropylcyclopentadiene prepared in step 1 was dissolved in anhydrous tetrahydrofuran by stirring. The solution was cooled to -78 °C, and 7.8 mL (19.6 mmol, 1.05 eq) of 2.5 M n-butyllithium solution was slowly added dropwise, stirring for 1 hour to deprotonate the 5-position of the cyclopentadiene. At -78 °C, 2.5 mL (19.8 mmol, 1.06 eq) of trimethylchlorosilane was added dropwise. After the addition was complete, the temperature was slowly raised to room temperature, and stirring continued for 8 hours. The tetrahydrofuran was removed by vacuum concentration. The residue was dissolved in petroleum ether, and the lithium chloride precipitate was removed by filtration. The filtrate was concentrated again under vacuum, placed at -20 °C for recrystallization, and 5.8 g of white crystals were collected by filtration, yielding 90%.

[0097]

[0098] (3) Preparation of phenyllithium: A dry three-necked flask was purged with nitrogen to maintain a slight positive pressure. 1.54 g (0.22 mol) of lithium particles was quickly weighed and added to the flask. 40 mL of anhydrous diethyl ether was added, and nitrogen protection was maintained continuously. 15.7 g (0.1 mol) of bromobenzene was mixed with 30 mL of anhydrous diethyl ether, and the bromobenzene-diethyl ether solution was slowly added dropwise at low temperature. After the addition was complete, the mixture was brought to room temperature and stirred for 1-2 h until most of the lithium particles disappeared and the system became a dark red, clear solution. The reaction was complete. The product was an anhydrous diethyl ether solution of phenyllithium, which should be prepared and used immediately.

[0099]

[0100] (4) Synthesis of bis(1,2,3,4-tetraisopropyl-5-trimethylsilylcyclopentadienyl)phenylyttrium: 5.0 g (14.4 mmol) of the product from step two was dissolved in THF by stirring. The solution was cooled to -78 °C, and 6.0 mL (15.0 mmol, 1.04 eq) of n-BuLi solution was added dropwise. After the addition was complete, the solution was heated to room temperature and stirred for 2 h. The THF was removed by concentration under reduced pressure. The residue was washed with pentane and dried to obtain a white solid cyclopentadienyllithium. A dry Schlenk flask was used to add 2.5 g of YCl3·3THF and anhydrous toluene, and the solution was stirred to suspend it. The solution was cooled to -78 °C, and 7.0 mL (12.6 mmol, 2.0 equivalence) of phenyllithium diethyl ether solution was added dropwise. The solution was then slowly heated to room temperature and reacted for 2 h. The solution was cooled to -78 °C again, and a toluene solution of cyclopentadienyllithium was slowly added dropwise. The solution was then slowly heated to room temperature and reacted overnight. After the reaction was complete, lithium chloride was removed by filtration, the mixture was concentrated under reduced pressure, washed with anhydrous pentane, and allowed to recrystallize, resulting in bright yellow crystals. The crystals were collected by filtration, yielding 6.8 g of the target catalyst, with a yield of 73%.

[0101]

[0102] The NMR data for rare earth catalyst 1 are as follows:

[0103] 1 H NMR (C6D6, 400MHz, 25℃): 0.23(s, 18H, Si(CH3)3), 1.08(m, 24H, CH(CH3)2), 1.25(m, 24H, CH(CH3)2), 3.34(m, 8H, CH(CH3)2), 7.25(m, 5H, aryl).

[0104] Preparation Examples 2-7

[0105] Preparation Example 2

[0106] Preparation Example 2 prepared rare earth catalyst 2, and its preparation method was basically the same as that of Preparation Example 1. The main difference was that the ligand substituents and auxiliary ligands were different. In the specific operation process, the raw material "isopropyl bromide" was replaced with "iodomethane", "trimethylchlorosilane" was replaced with "trivinylchlorosilane", and "bromobenzene" was replaced with "2-bromonaphthalene". Other steps and conditions were the same as in Preparation Example 1, and rare earth catalyst 2 with the structure shown in Formula I2 was obtained. Its NMR data are as follows:

[0107] ¹H NMR (C6D6, 400MHz, 25℃): 1.95 (s, 12H, CH3), 2.03 (s, 12H, CH3), 2.11 (m, 6H, (CHCH2)3), 3.20 (t, 12H, (CHCH2)3), 7.58 (m, 7H, aryl).

[0108] Preparation Example 3

[0109] Preparation Example 3 prepared rare earth catalyst 3. The preparation method was basically the same as in Preparation Example 1, with the main difference being the different ligand substituents and auxiliary ligands. Specifically, in the operation process, the raw material "isopropyl bromide" was replaced with "bromoethane," and "bromobenzene" was replaced with "diphenylchloromethane." Other steps and conditions were the same as in Preparation Example 1, yielding rare earth catalyst 3 with the structure shown in Formula I3. Its NMR data are as follows:

[0110] 1 H NMR (C6D6, 400MHz, 25℃): 0.23(s, 18H, Si(CH3)3), 0.64(q, 8H, CH2CH3), 0.68(q, 8H, CH2C H3), 1.15 (t, 12H, CH2CH3), 1.19 (t, 12H, CH2CH3), 4.65 (m, 1H, Cp-H), 7.33 (m, 10H, aryl).

[0111] Preparation Example 4

[0112] Preparation Example 4 prepared rare earth catalyst 4. The preparation method was basically the same as in Preparation Example 1, with the main difference being the central metal element and auxiliary ligand. Specifically, in the operation, the raw material "isopropyl bromide" was replaced with "bromomethane," "bromobenzene" was replaced with "cinnamyl bromide," and "YCl3·3THF" was replaced with "GdCl3·3THF." Other steps and conditions were the same as in Preparation Example 1, yielding rare earth catalyst 4 with the structure shown in Formula I4. Its NMR data are as follows:

[0113] 1 H NMR (C6D6, 400MHz, 25℃): 0.23(s, 18H, Si(CH3)3), 1.54(s, 12H, CH3), 1.57(s, 12H, CH3), 7.18(m, 5H, aryl).

[0114] Preparation Example 5

[0115] Preparation Example 5 prepared rare earth catalyst 5. The preparation method was basically the same as in Preparation Example 1, with the main difference being the central metal element and auxiliary ligand. Specifically, in the operation, "bromobenzene" was replaced with "2-bromo-1,3-diisopropylbenzene," and "YCl3·3THF" was replaced with "GdCl3·3THF." Other steps and conditions were the same as in Preparation Example 1, yielding rare earth catalyst 5 with the structure shown in Formula I5. Its NMR data are as follows:

[0116] 1H NMR (C6D6, 400MHz, 25℃): 0.23(s, 18H, Si(CH3)3), 1.15(m, 24H, CH(CH3)2), 1.23(m, 24H, CH(CH3)2 ), 1.40(d, 12H, GdCH(CH3)2), 3.28(d, 8H, CH(CH3)2), 3.58(m, 2H, GdCH(CH3)2), 7.34(m, 3H, aryl).

[0117] Preparation Example 6

[0118] Preparation Example 6 prepared rare earth catalyst 6. The preparation method was basically the same as that of Preparation Example 1, with the main difference being the different central metal element and auxiliary ligand. In the specific operation process, "isopropyl bromide" was replaced with "iodomethane", "trimethylchlorosilane" was replaced with "triethylchlorosilane", "bromobenzene" was replaced with "4-bromoanisole", and "YCl3·3THF" in step (4) was replaced with "SmCl3·3THF". Other steps and conditions were the same as in Preparation Example 1, and rare earth catalyst 6 with the structure shown in Formula I6 was obtained. Its NMR data are as follows:

[0119] 1 H NMR (C6D6, 400MHz, 25℃): 0.58(q, 12H, Si(CH2CH2)3), 1.09(t, 18H, Si(CH2CH2)3),

[0120] 1.54 (s, 12H, CH3), 1.58 (s, 12H, CH3), 3.65 (s, 3H, OCH3), 6.70 (m, 4H, aryl).

[0121] Preparation Example 7

[0122] Preparation Example 7 prepared rare earth catalyst 7. The preparation method was basically the same as that in Preparation Example 1, with the main difference being the different central metal element and auxiliary ligand. In the specific operation process, "isopropyl bromide" in step (1) was replaced with "iodomethane", "trimethylchlorosilane" in step (2) was replaced with "triisopropylchlorosilane", and "YCl3·3THF" in step (4) was replaced with "SmCl3·3THF". Other steps and conditions were the same as in Preparation Example 1, and rare earth catalyst 7 with the structure shown in Formula I7 was obtained. Its NMR data are as follows:

[0123] 1H NMR (C6D6, 400MHz, 25℃): 1.18(d, 18H, Si(CH(CH3)2), 1.22(d, 18H, Si(CH(CH3)2), 2 .36(m, 12H, CH3), 2.41(m, 12H, CH3), 3.32(m, 6H, Si(CH(CH3)2), 7.40(m, 5H, aryl).

[0124] Rare earth catalysts 1 to 7 are compounds having the structures shown in formulas I1 to I7.

[0125]

[0126]

[0127]

[0128] The following is an example of the preparation of trans-1,4-polyisoprene by homogeneous catalytic polymerization of isoprene using the above rare earth catalyst.

[0129] Example 1

[0130] A 100 mL polymerization flask was vacuum dried at 100 °C for 12 h. After cooling to room temperature in a glove box, the following materials were added sequentially: 10 mmol triisobutylaluminum, 20 mL toluene and n-hexane mixture, and 50 mmol isoprene (monomer:catalyst = 5000:1). The flask was pre-cooled in a -40 °C cryogenic bath for 30 min. Then, a mixture of 10 μmol rare earth catalyst 1 and 10 μmol triphenylcarbon-tetra(pentafluorophenyl)borate was added to start polymerization and the temperature was controlled in a five-stage gradient: first, the reaction was carried out at -40 °C for 1 h; then, the temperature was increased to -25 °C at a rate of 5 °C / min and the reaction was carried out for 1 h; then, the temperature was increased to -10 °C at a rate of 5 °C / min and the reaction was carried out for 1 h; then, the temperature was increased to 10 °C at a rate of 5 °C / min and the reaction was carried out for 1 h; finally, the temperature was increased to 20 °C at a rate of 5 °C / min and the reaction was carried out for 1 h.

[0131] After the reaction was completed, 20 mL of 10% hydrochloric acid was added to acidify the ethanol to terminate the reaction, precipitate the polymer, and dry it under vacuum at 60 °C for 12 h to obtain white polyisoprene powder.

[0132] Example 2

[0133] The preparation method of this embodiment is basically the same as that of Example 1, except that the rare earth catalyst added is different. In this embodiment, rare earth catalyst 2 is added.

[0134] Example 3

[0135] The preparation method of this embodiment is basically the same as that of Example 1, except that the rare earth catalyst added is different. In this embodiment, rare earth catalyst 3 is added.

[0136] Example 4

[0137] The preparation method of this embodiment is basically the same as that of Example 1, except that the rare earth catalyst added is different. In this embodiment, rare earth catalyst 4 is added.

[0138] Example 5

[0139] The preparation method of this embodiment is basically the same as that of Example 1, except that the rare earth catalyst added is different. In this embodiment, rare earth catalyst 5 is added.

[0140] Example 6

[0141] The preparation method of this embodiment is basically the same as that of Example 1, except that the rare earth catalyst added is different. In this embodiment, rare earth catalyst 6 is added.

[0142] Example 7

[0143] The preparation method of this embodiment is basically the same as that of Example 1, except that the rare earth catalyst added is different. In this embodiment, rare earth catalyst 7 is added.

[0144] Example 8

[0145] The preparation method in this embodiment is basically the same as that in Example 1, except that the temperature control during solution polymerization is different. Specifically, polymerization is started and the temperature is controlled in five stages: first, the reaction is carried out at -40℃ for 1 hour; then the temperature is increased to -10℃ at a rate of 5℃ / min and the reaction is carried out for 1 hour; then the temperature is increased to -20℃ at a rate of 5℃ / min and the reaction is carried out for 1 hour; then the temperature is increased to 35℃ at a rate of 5℃ / min and the reaction is carried out for 1 hour; finally, the temperature is increased to 45℃ at a rate of 5℃ / min and the reaction is carried out for 1 hour.

[0146] Comparative Example 1

[0147] The preparation method of this comparative example is basically the same as that of Example 1, except that the temperature control during solution polymerization is different. Specifically, after all raw materials are added, the temperature is kept constant at 25°C and the reaction is carried out for 2 hours.

[0148] Performance testing:

[0149] Monomer conversion rate: The monomer conversion rate is calculated according to the following formula: Monomer conversion rate = weight of monomer after polymerization / initial amount of monomer * 100%.

[0150] Number-average molecular weight (Mn) and weight-average molecular weight (Mw): The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of trans-1,4-polyisoprene prepared in each example and comparative example were tested according to the method specified in high-temperature gel permeation chromatography (ASTM D5296). Then, the molecular weight distribution width was calculated according to the formula: Molecular weight distribution width = Mn / Mw.

[0151] Trans-1,4-polyisoprene content: The trans-1,4-polyisoprene content in the reaction product was calculated by integrating the characteristic peaks in the proton NMR spectrum.

[0152] The results of preparing trans-1,4-polyisoprene in each embodiment and comparative example are shown in Table 1.

[0153] Table 1 Results of preparation of trans-1,4-polyisoprene in each example

[0154]

[0155] Figures 1-7 These are the high-temperature gel permeation chromatograms of trans-1,4-polyisoprene prepared in Examples 1-7. The blue curve represents the differential mass distribution curve plotted according to the logarithmic molecular weight range (corresponding to the left ordinate, where dW / dlogM represents the polymer mass percentage within the unit logarithmic molecular weight range), reflecting the relative content distribution of polymer components with different molecular weights in the sample. The red curve represents the cumulative mass distribution curve plotted according to molecular weight (corresponding to the right ordinate, where %Ht represents the cumulative mass percentage), reflecting the proportion of polymer components with molecular weight ≤ the current value in the total sample mass. As can be seen from the spectra, the obtained polymers all exhibit a unimodal distribution characteristic, with a molecular weight distribution coefficient (PDI) between 2.01 and 2.35, indicating a narrow molecular weight distribution; the number-average molecular weight (Mn) is between 2.07 and 3.14 × 10⁻⁶. 5 Within the g / mol range, this indicates that the series of polymers has a relatively concentrated and uniform molecular weight level.

[0156] Based on the data in Table 1, it can be seen that this application suppresses steric interference from side reactions through the design of sterically hindered cyclopentadienyl ligands, while simultaneously enhancing the selectivity of the target reaction through "gradient heating." The synergistic optimization of these two methods achieves high trans-1,4-selectivity and high activity of rare earth catalysts in isoprene polymerization, solving the toxicity and selectivity issues of traditional catalysts. Example data demonstrate that this catalyst system can stably prepare TPI with a trans-1,4- content >91.1%, suitable for the high-end, green industrialization needs of TPI.

[0157] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A rare earth catalyst for preparing trans-1,4-polyisoprene, characterized in that, The rare earth catalyst is selected from compounds having the structure shown in Formula I; Wherein, Ln is selected from rare earth metals; R1 is selected from hydrogen or alkyl groups having 1 to 6 carbon atoms; R2 is selected from hydrogen, alkylsilyl groups having 1 to 6 carbon atoms, alkenylsilyl groups having 1 to 6 carbon atoms, or bromine-containing alkylsilyl groups having 1 to 6 carbon atoms; X is selected from hydrogen, alkyl-substituted aryl groups having 6 to 13 carbon atoms, alkenyl-substituted aryl groups having 6 to 13 carbon atoms, or alkoxy-substituted aryl groups having 6 to 13 carbon atoms.

2. The rare earth catalyst according to claim 1, characterized in that, Ln is selected from any one of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium; R1 is selected from hydrogen, methyl, ethyl, propyl, isopropyl, tert-butyl, or isopentyl; R2 is selected from trimethylsilyl, triethylsilyl, tri-n-propylsilyl, triisopropylsilyl, tri-tert-butylsilyl, tri-n-hexylsilyl, trivinylsilyl, tripropylsilyl, tri(bromomethyl)silyl, or tri(2-bromoethyl)silyl; X is selected from phenyl, naphthyl, diphenylmethyl, diisopropylbenzene, 4-methoxyphenyl or 3-phenyl-2-propenyl.

3. The rare earth catalyst according to claim 1, characterized in that, The rare earth catalyst is selected from at least one of compounds having the structure shown in Formulas I1 to I7; 。 4. The method for preparing the rare earth catalyst according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Provide intermediates having the structure shown in Formula II and intermediates having the structure shown in Formula III, respectively; S2. The intermediate having the structure shown in Formula II is mixed with an alkyllithium reagent and subjected to a deprotonation lithiation reaction to obtain lithiation intermediate 1. S3. The lithiation intermediate 1 is mixed with an intermediate having the structure shown in Formula III and a nucleophilic substitution reaction is carried out to obtain a compound with the structure shown in Formula I. ， R3 is selected from halogens.

5. The application of the rare earth catalyst according to any one of claims 1 to 3 or the rare earth catalyst obtained by the preparation method according to claim 4 in the solution polymerization of isoprene to prepare trans-1,4-polyisoprene.

6. The application according to claim 5, characterized in that, Catalysts for the solution polymerization of isoprene to prepare trans-1,4-polyisoprene also include organoboron and alkylaluminum.

7. The application according to claim 6, characterized in that, The application meets at least one of the following conditions: (1) When isoprene is subjected to solution polymerization to prepare trans-1,4-polyisoprene, the molar ratio of the rare earth catalyst to the isoprene monomer is 1:(5000~10000). (2) The molar ratio of the rare earth catalyst, the organoboron and the alkylaluminum is 1:1:(1~5000). (3) The organoboron is selected from at least one of triphenylcarbazo-tetra(pentafluorophenyl)borate, N,N-dimethylphenylammonium tetra(pentafluorophenyl)borate and tri(pentafluorophenyl)borane; (4) The alkyl aluminum is selected from at least one of trimethylaluminum, triethylaluminum, triisobutylaluminum, tripentylaluminum, trioctylaluminum and diethylaluminum chloride.

8. The application according to claim 6, characterized in that, The solution polymerization reaction is carried out at a temperature of -50℃ to 45℃ for a time of 4h to 24h.

9. The application according to claim 6, characterized in that, The solution polymerization was carried out sequentially under a five-stage gradient temperature condition, which was as follows: First stage: React at -50℃ to -35℃ for 0.8h to 1.2h; Second stage: Heat to -30℃ to -25℃, react for 0.8h to 1.2h; Third stage: Heat to -15℃ to -10℃ and react for 0.8h to 1.2h; Fourth stage: Increase the temperature to 5℃~10℃ and react for 0.8h~1.2h; Fifth stage: Increase the temperature to 15℃~20℃ and react for 0.8h~1.2h.

10. The application according to claim 6, characterized in that, The solvent used in the solution polymerization is selected from two or more of toluene, xylene, benzene, n-hexane, n-heptane, cyclohexane, chlorobenzene, and dichlorobenzene.

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