CN108659055B - Iron complex based on flexible framework, preparation method thereof and application thereof in isoprene polymerization - Google Patents

Iron complex based on flexible framework, preparation method thereof and application thereof in isoprene polymerization Download PDF

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CN108659055B
CN108659055B CN201810400796.8A CN201810400796A CN108659055B CN 108659055 B CN108659055 B CN 108659055B CN 201810400796 A CN201810400796 A CN 201810400796A CN 108659055 B CN108659055 B CN 108659055B
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王庆刚
赵梦梦
王晓武
王亮
咸漠
张献辉
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Qingdao Institute of Bioenergy and Bioprocess Technology of CAS
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Abstract

The invention discloses an iron complex based on a flexible framework, a preparation method thereof and application thereof in isoprene polymerization. The method comprises the following steps: adding a main catalyst, a solvent and a cocatalyst, and then adding an isoprene monomer for polymerization reaction to obtain polyisoprene. The proportion range of the cis-1,4 structure in the obtained isoprene rubber is 29-48%, and the proportion range of the 3,4 structure is 52-71%. And the polymer has high molecular weight and narrow molecular weight distribution. The preparation method of isoprene rubber provided by the invention can effectively improve the use efficiency and industrial application value of the iron catalyst.

Description

Iron complex based on flexible framework, preparation method thereof and application thereof in isoprene polymerization
Technical Field
The present invention relates to the field of chemical synthesis.
Background
Isoprene rubber, one of synthetic rubber varieties with superior comprehensive properties, has not only certain similar characteristics to natural rubber, but also the advantages of wide sources of synthetic raw materials, good processability and the like, and plays an increasingly important role in the synthetic rubber industry. Since 1860 Williams separated isoprene from natural rubber decomposition products, more and more scientists have devoted themselves to the study of isoprene to synthesize natural rubber. There are four different microstructures for polyisoprene: cis-1, 4-polyisoprene; trans-1, 4-polyisoprene; 3, 4-polyisoprene and 1, 2-polyisoprene. Because different structural units and the connection mode of the structural units exist in the polyisoprene, different polyisoprenes have larger performance difference. For example, cis-1, 4-polyisoprene has the same microstructure as natural rubber and can be used as a substitute for natural rubber; the 3, 4-polyisoprene has larger side group and is generally used for tire wet skid resistance improving agents, anti-vibration damping materials and the like.
Iron catalysts have been used in the 60 s of the 20 th century for the catalytic polymerization of conjugated dienes to produce dimers, trimers and small amounts of high polymers, but these have not been studied in depth. In 1970, the Swift topic group reported that three-component catalytic systems catalyze the polymerization of isoprene: by applying a magnetic field in Fe (acac)3/AlEt3Adding a nitrogen-containing ligand to catalyze and synthesize polyisoprene with the same cis-1,4 and 3,4 structures. However, the catalytic polymerization is carried out at-23 ℃ to have high activity, and an increase in polymerization temperature results in a significant decrease in polymer yield, probably because the active sites of the resulting catalyst are unstable at high temperatures or the iron catalyst is excessively reduced to be deactivated. In 2004, Zhang Chun full topic team studied Fe (acac)3/Al(i-Bu)3The ternary system of diethyl phosphite is used for catalyzing isoprene polymerization. On the basis, the subject group studied to replace Al (i-Bu) with MMAO3Iron as a cocatalyst catalyzes isoprene polymerization, and 3, 4-structure polyisoprene can be prepared with higher activity. In 2012, an iron/pyridine imine complex is combined by the Ritter topic, a ternary system consisting of alkyl aluminum and boron salt is combined to catalyze isoprene polymerization, and the catalyst has high activity and regioselectivity. Unlike the prior iron-catalyzed polymerization, the polyisoprene structure obtained by the catalytic system is mainly 1,4 structure and can be adjusted by the change of a ligand structure: the polyisoprene prepared by the complex containing alkyl substituent is mainly of trans-1,4 structure, while the polyisoprene prepared by the complex containing aryl substituent is mainly of cis-1,4 structure. On the basis, the Chengyngle task group designs and synthesizes a series of iron/pyridine alkyl imine and iron/pyridine aryl imine complexes. The influence of ligands containing different substituents on reactivity and stereoselectivity was investigated with MAO as a cocatalyst. Unlike the ternary catalyst system reported by Ritter, the 1, 4-structured polyisoprene obtained by the binary catalyst system has only medium yield (62-78%), and the aryl substituted and alkyl substituted complexes have little influence on the catalytic selectivity.
The activity and selectivity of the iron-based catalyst for catalyzing isoprene polymerization reported at present are not high, and the gap from industrial application is large. Therefore, the design and synthesis of a novel catalyst for realizing the controllable polymerization of iron-catalyzed isoprene with high activity and high stereoselectivity still has very important research significance and practical value.
Disclosure of Invention
In order to solve the problems that the molecular weight distribution of a polymer is wide, the polymerization cost is high, the controllable polymerization of a catalytic microstructure cannot be carried out and the like in the existing isoprene polymerization technology, the application provides a novel iron catalyst. The pyridine benzyl imine/iron complex with a more flexible structure is used as a main catalyst to catalyze isoprene to polymerize under the action of an industrialized cocatalyst MAO, the polymerization activity is higher, the obtained molecular weight is higher, the molecular weight distribution is narrower, and the control of the polyisoprene structure is realized by regulating the main catalyst structure and the reaction conditions.
The invention also provides a preparation method of the pyridine imine/iron catalyst.
The preparation method of the iron complex comprises the following steps: reacting imine pyridine ligand with ferrous chloride in equimolar ratio in dichloromethane at room temperature, and carrying out post-treatment to obtain the iron complex. The post-treatment operation was vacuum drying of dichloromethane, three washes with n-hexane, vacuum drying to constant weight.
The invention also provides application of the iron catalyst in isoprene polymerization.
The invention is realized by the following technical scheme:
an iron complex based on a flexible framework has a structure shown in a formula I,
Figure BDA0001645665880000021
wherein R is one or more of 4-fluoro group, 2, 6-difluoro group, 4-trifluoromethyl group, 2-methyl group, 2,4, 6-trimethyl group or 4-methoxy group, preferably R is 2, 6-difluoro group, and the structural formula is formula III:
Figure BDA0001645665880000022
the preparation method of the iron complex based on the flexible framework comprises the steps of reacting a pyridine imine ligand with ferrous chloride in an equimolar ratio in tetrahydrofuran or dichloromethane at the temperature of 25-60 ℃, and carrying out aftertreatment to obtain the iron complex.
The pyridine imine ligand has a structural general formula as follows:
Figure BDA0001645665880000023
the specific structural formula is one or more than two of the following structural formulas:
Figure BDA0001645665880000024
the invention also provides the application of the iron complex based on the flexible framework in isoprene polymerization, wherein the iron complex based on the flexible framework is used as a main catalyst, and a cocatalyst is trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, methylaluminoxane or modified methylaluminoxane; the structural general formula of the Methylaluminoxane (MAO) is
Figure BDA0001645665880000031
Wherein n is a natural number of 4 to 40; the molar ratio of the aluminum element in the cocatalyst to the iron element in the main catalyst is (10-500): 1.
The method comprises the following steps: adding a main catalyst, a solvent and a cocatalyst, and then adding an isoprene monomer for polymerization reaction to obtain polyisoprene.
The polymerization solvent is toluene, p-xylene, n-hexane, cyclohexane, pentane, dichloromethane and tetrahydrofuran, and toluene is preferred; the amount of the solvent is as follows: the volume ratio of the solvent to the isoprene monomer is (1-10): 1.
The polymerization reaction temperature is-30-50 ℃, and preferably 25 ℃;
the polymerization reaction time is 10min-1h, preferably 10 min.
The molar ratio of the isoprene monomer to the main catalyst is (200) -10000) to 1, preferably 2000: 1;
the molar ratio of the aluminum element in the cocatalyst to the iron element in the main catalyst is (10-500):1, preferably 100: 1;
the preferable feeding sequence of the polymerization reaction comprises a main catalyst, a solvent, a cocatalyst and an isoprene monomer;
the number average molecular weight of the polyisoprene prepared is 23.2 × 104-37.5×104The molecular weight distribution is 1.8-3.6.
The proportion range of the cis-1,4 structure of the prepared polyisoprene is 29-48%, and the proportion range of the 3,4 structure of the polyisoprene is 52-71%.
Advantageous effects
(1) The main catalyst in the iron catalyst is an iron/benzyl imine pyridine complex, and the synthesis method is simple and low in cost; the cocatalyst is MAO, so that the price is lower than that of the boron salt of the three components in the background introduction;
(2) the iron-based catalyst can realize the controllable polymerization of isoprene with high activity and high selectivity, and the polymerization activity can reach as high as 107The obtained polyisoprene had a number average molecular weight of 23.2 × 104-37.5×104The molecular weight distribution is 1.8-3.6.
Drawings
FIG. 1 is a nuclear magnetic hydrogen spectrum of a ligand obtained in preparation example 1;
FIG. 2 is a nuclear magnetic carbon spectrum of the ligand obtained in preparation example 1;
FIG. 3 is a nuclear magnetic hydrogen spectrum of polyisoprene obtained in example 3;
FIG. 4 is a nuclear magnetic carbon spectrum of the polyisoprene obtained in example 3.
Example of the implementation
Preparation example 1
This example prepares an iron pyridinimine complex of formula II:
a100 mL dry reaction flask was charged with 4A molecular sieves and baked for 30 minutes. Under an argon atmosphere, dry dichloromethane (40mL), 4-fluorobenzylamine (1.2g, 9.3mmol), and pyridine-2-carbaldehyde (1.0g, 9.3mmol) were added in this order. The reaction was carried out overnight at room temperature and the aldehyde substrate was completely reacted as detected by TLC plate. Filtration, spin-drying, and vacuum suction-drying gave a yellow liquid (1.9g, yield): 93%) of structural formula
Figure BDA0001645665880000041
25mL of dry reaction tube, and 15mL of redistilled dichloromethane and anhydrous FeCl with equal molar ratio are sequentially added into a glove box2(100.0mg, 0.8mmol) and the above prepared pyridimine ligand (169.0mg, 0.8mmol) were stirred at room temperature for 15 h. After the reaction was completed, methylene chloride was vacuum-dried, and washed 3 times with 10mL of dry n-hexane, and vacuum-dried to a constant weight to obtain 246mg of a purple solid (yield: 83%).
Mass spectrometry analysis: c13H11ClFFeN2[M-Cl]+Theoretical value: 304.9944, respectively; measured value: 304.9911.
elemental analysis: c13H11Cl2FFeN2: theoretical value: c, 45.79%; h, 3.25%; n, 8.22%; measured value: c, 45.63%; h, 3.19%; n,8.11 percent.
Preparation example 2
This example prepares an iron pyridinimine complex of formula III:
a100 mL dry reaction flask was charged with 4A molecular sieves and baked for 30 minutes. Under an argon atmosphere, dry dichloromethane (40mL), 2, 6-difluorobenzylamine (1.34g, 9.34mmol), and 2-pyridinecarboxaldehyde (1.0g, 9.34mmol) were added in this order. The reaction was carried out overnight at room temperature and the aldehyde substrate was completely reacted as detected by TLC plate. Filtration, spin-drying, and vacuum suction-drying gave a yellow solid (1.7g, yield: 79%) of formula
Figure BDA0001645665880000042
25mL of dry reaction tube, and 15mL of redistilled dichloromethane and anhydrous FeCl with equal molar ratio are sequentially added into a glove box2(100.0mg, 0.8mmol) and the above-prepared pyridimine ligand (183.0mg, 0.8mmol) were stirred at room temperature for 15 h. After the reaction was completed, dichloromethane was vacuum-dried, 10mL of dry n-hexane was added and washed 3 times, and vacuum-dried to a constant weight to obtain 241mg of a purple solid (yield: 85%).
Mass spectrometry analysis: c13H10ClF2FeN2[M-Cl]+Theoretical value: 322.9850, respectively; measured value: 322.9813.
elemental analysis: c13H10Cl2F2FeN2: theoretical value: c, 43.50%; h, 2.81%; n, 7.80%; measured value: c, 43.41%; h, 2.84%; and N,2.48 percent.
Preparation example 3
This example prepares an iron pyridinimine complex of formula IV:
a100 mL dry reaction flask was charged with 4A molecular sieves and baked for 30 minutes. Under an argon atmosphere, dry dichloromethane (60mL), 4-trifluoromethylbenzylamine (2.5g, 14.0mmol), and pyridine-2-carbaldehyde (1.5g, 14.0mmol) were added in that order. The reaction was carried out overnight at room temperature and the aldehyde substrate was completely reacted as detected by TLC plate. Filtered, spin-dried, and vacuum-dried to give a yellow liquid (3.3g, yield: 90%) of the formula
Figure BDA0001645665880000051
25mL of dry reaction tube, and 15mL of redistilled dichloromethane and anhydrous FeCl with equal molar ratio are sequentially added into a glove box2(100.0mg, 0.8mmol) and the above prepared pyridimine ligand (208.5mg, 0.8mmol) were stirred at room temperature for 15 h. After the reaction was completed, methylene chloride was vacuum-dried, and then 10mL of dry n-hexane was added and washed 3 times, and vacuum-dried to a constant weight to obtain 240mg of a purple solid (yield: 78%).
Mass spectrometry analysis: c14H11ClF3FeN2[M-Cl]+Theoretical value: 354.9912, respectively; measured value: 354.9933.
elemental analysis: c14H11Cl2F3FeN2: theoretical value: c, 43.01%; h, 2.84%; n, 7.16%; measured value: c, 42.92%; h, 2.91%; and N,7.22 percent.
Preparation example 4
This example prepares an iron pyridinimine complex of formula V:
a100 mL dry reaction flask was charged with 4A molecular sieves and baked for 30 minutes. Under an argon atmosphere, dry dichloromethane (60mL), 2-methylbenzylamine (1.1g, 9.3mmol) andpyridine-2-carbaldehyde (1.0g, 9.3 mmol). The reaction was carried out overnight at room temperature and the aldehyde substrate was completely reacted as detected by TLC plate. Filtration, spin-drying, and vacuum-pumping to give a pale yellow liquid (3.3g, yield: 90%) of the formula
Figure BDA0001645665880000052
25mL of dry reaction tube, and 15mL of redistilled dichloromethane and anhydrous FeCl with equal molar ratio are sequentially added into a glove box2(100.0mg, 0.8mmol) and the above prepared pyridimine ligand (165.9mg, 0.8mmol) were stirred at room temperature for 15 h. After the reaction was completed, methylene chloride was vacuum-dried, and then 10mL of dry n-hexane was added and washed 3 times, and vacuum-dried to a constant weight to obtain 160mg of a purple solid (yield: 60%).
Mass spectrometry analysis: c14H14Cl2FeN2[M-Cl]+Theoretical value: 301.0195, respectively; measured value: 301.0178.
elemental analysis: c14H14Cl2FeN2: theoretical value: c, 49.89%; h, 4.19%; n, 8.31%; measured value: c, 49.72%; h, 3.83%; and 7.20 percent of N.
Preparation example 5
This example prepares an iron pyridinimine complex of formula VI:
a100 mL dry reaction flask was charged with 4A molecular sieves and baked for 30 minutes. Under an argon atmosphere, dry dichloromethane (60mL), 2,4, 6-trimethylbenzylamine (1.4g, 9.4mmol) and pyridine-2-carbaldehyde (1.0g, 9.3mmol) were added in this order. The reaction was carried out overnight at room temperature and the aldehyde substrate was completely reacted as detected by TLC plate. Filtered, spin-dried, and vacuum-dried to give a yellow solid (1.9g, yield: 85%) of formula
Figure BDA0001645665880000061
25mL of dry reaction tube, and 15mL of redistilled dichloromethane and anhydrous FeCl with equal molar ratio are sequentially added into a glove box2(50.0mg, 0.4mmol) and the above prepared pyridimine ligand (94.0mg, 0.4mmol) were stirred at room temperature for 12 h. After the reaction, the dichloromethane was vacuum-dried and 10mL of dry n-hexane was addedThe column was washed 3 times with hexane and vacuum-dried to constant weight to give 128mg of a purple solid (yield: 89%).
Mass spectrometry analysis: c16H18ClFeN2[M-Cl]+Theoretical value: 329.0508, respectively; measured value: 329.0527.
elemental analysis: c16H18Cl2FeN2: theoretical value: c, 52.64%; h, 4.97%; n, 7.67%; measured value: c, 52.49%; h, 5.06%; and N,7.85 percent.
Preparation example 6
This example prepares an iron pyridinimine complex of formula VII:
a100 mL dry reaction flask was charged with 4A molecular sieves and baked for 30 minutes. Under an argon atmosphere, dry dichloromethane (60mL), 2,4, 6-trimethylbenzylamine (1.3g, 9.4mmol) and pyridine-2-carbaldehyde (1.0g, 9.3mmol) were added in this order. The reaction was carried out overnight at room temperature and the aldehyde substrate was completely reacted as detected by TLC plate. Filtered, spin-dried, and vacuum-dried to give a yellow liquid (2.0g, yield: 93%) of the formula
Figure BDA0001645665880000062
25mL of dry reaction tube, and 15mL of redistilled dichloromethane and anhydrous FeCl with equal molar ratio are sequentially added into a glove box2(100mg, 0.79mmol) and the above prepared pyridimine ligand (178.5mg, 0.8mmol) were stirred at room temperature for 24 h. After the reaction was completed, methylene chloride was vacuum-dried, and then 10mL of dry n-hexane was added and washed 3 times, and vacuum-dried to a constant weight to obtain 220mg of a purple solid (yield: 79%).
Mass spectrometry analysis: c14H14ClFeN2O[M-Cl]+Theoretical value: 317.0144, respectively; measured value: 317.0123.
elemental analysis: c14H14Cl2FeN2O: theoretical value: c, 47.63%; h, 4.00%; n, 7.94%; measured value: c, 47.59%; h, 3.85%; and N, 7.89%.
Example 1
25mL of a dry reaction tube is transferred to a glove box, 3.4mg (10 mu mol) of a weighed main catalyst shown in formula II is added, the mixture is transferred to the outside of the glove box, 5mL of anhydrous toluene and 3.33mL (1.5M) of methylaluminoxane are added under the argon atmosphere, 2mL (20mmol) of isoprene monomer is added, the mixture reacts for 10min at room temperature, 20mL of methanol dilute hydrochloric acid (1:50, V/V) solution is used for terminating the reaction, the mixture is filtered, a large amount of ethanol is used for washing, the mixture is vacuum-pumped to constant weight at room temperature, the yield is 100%, the number average molecular weight is 243715, the molecular weight distribution is 2.5, the cis-1,4 structure content is 48%, and the 3,4 structure content is 52%.
Example 2
25mL of a dry reaction tube is transferred to a glove box, 3.6mg (10 mu mol) of a weighed main catalyst shown in formula III is added, the mixture is transferred to the outside of the glove box, 5mL of anhydrous toluene and 3.33mL (1.5M) of methylaluminoxane are added under the argon atmosphere, 2mL (20mmol) of isoprene monomer is added, the mixture reacts for 10min at room temperature, 20mL of methanol dilute hydrochloric acid (1:50, V/V) solution is used for terminating the reaction, the mixture is filtered, a large amount of ethanol is used for washing, the mixture is vacuum-pumped to constant weight at room temperature, the yield is 100%, the number average molecular weight is 375197, the molecular weight distribution is 1.8, the cis-1,4 structure content is 44%, and the 3,4 structure content is 56%.
Example 3
25mL of a dry reaction tube is transferred to a glove box, 3.9mg (10 mu mol) of a weighed main catalyst shown in formula IV is added, the mixture is transferred to the outside of the glove box, 5mL of anhydrous toluene and 3.33mL (1.5M) of methylaluminoxane are added under the argon atmosphere, 2mL (20mmol) of isoprene monomer is added, the mixture reacts for 10min at room temperature, 20mL of methanol dilute hydrochloric acid (1:50, V/V) solution is used for terminating the reaction, the mixture is filtered, a large amount of ethanol is used for washing, the mixture is vacuum-pumped to constant weight at room temperature, the yield is 100%, the number average molecular weight is 281684, the molecular weight distribution is 3.6, the cis-1,4 structure content is 43%, and the 3,4 structure content is 57%.
Example 4
25mL of a dry reaction tube is transferred to a glove box, 3.4mg (10 mu mol) of a weighed main catalyst shown as a formula V is added, the dry reaction tube is transferred to the outside of the glove box, 5mL of anhydrous toluene and 3.33mL (1.5M) of methylaluminoxane are added under the argon atmosphere, 2mL (20mmol) of isoprene monomer is added, the reaction is carried out for 10min at room temperature, 20mL of methanol dilute hydrochloric acid (1:50, V/V) solution is used for terminating the reaction, the filtration is carried out, a large amount of ethanol is used for washing, the vacuum pumping is carried out at room temperature until the weight is constant, the yield is 100%, the number average molecular weight is 329983, the molecular weight distribution is 2.0, the cis-1,4 structure content is 33%, and the 3,4 structure.
Example 5
25mL of a dry reaction tube is transferred to a glove box, 3.6mg (10 mu mol) of a weighed main catalyst shown in formula VI is added, the mixture is transferred to the outside of the glove box, 5mL of anhydrous toluene and 3.33mL (1.5M) of methylaluminoxane are added under the argon atmosphere, 2mL (20mmol) of isoprene monomer is added, the mixture reacts for 10min at room temperature, 20mL of methanol dilute hydrochloric acid (1:50, V/V) solution is used for terminating the reaction, the mixture is filtered, a large amount of ethanol is used for washing, the mixture is vacuum-pumped to constant weight at room temperature, the yield is 100%, the number average molecular weight is 351581, the molecular weight distribution is 2.4, the cis-1,4 structure content is 29%, and the 3,4 structure content is 71%.
Example 6
25mL of a dry reaction tube is transferred to a glove box, 3.5mg (10 mu mol) of a weighed main catalyst shown as a formula VII is added, the mixture is transferred to the outside of the glove box, 2mL of anhydrous toluene and 3.33mL (1.5M) of methylaluminoxane are added under the argon atmosphere, 2mL (20mmol) of isoprene monomer is added, the mixture reacts for 10min at room temperature, 20mL of methanol dilute hydrochloric acid (1:50, V/V) solution is used for terminating the reaction, the mixture is filtered, a large amount of ethanol is used for washing, the mixture is vacuum-pumped to constant weight at room temperature, the yield is 100%, the number average molecular weight is 256870, the molecular weight distribution is 2.0, the cis-1,4 structure content is 46%, and the 3,4 structure content is 54%.
Example 7
Isoprene polymerization was carried out by the method of example 2, except that 5.0mL of triethylaluminum (1.0M) was used as a co-catalyst and reacted for 1h, and no solid was precipitated after quenching.
Example 8
Isoprene was polymerized by the method of example 2, except that 5.0mL of triisobutylaluminum (1.0M) was used as a co-catalyst and reacted for 1 hour, and no solid was precipitated after quenching.
Example 9
Isoprene was polymerized by the method of example 2, except that 5.0mL of diethylaluminum monochloride (1.0M) was used as a cocatalyst and reacted for 1h, and no solid was precipitated after quenching.
Example 10
Isoprene was polymerized by the method of example 2, except that 5.0mL of ethyl aluminum dichloride (1.0M) was used as a co-catalyst and reacted for 1h, and a large amount of white solid was precipitated as a cross-linking by-product after quenching.
Example 11
Isoprene polymerization was carried out by the method of example 2, except that 0.67mL of methylaluminoxane (1.5M) was used as a cocatalyst, reacted for 10min, and quenched to precipitate a large amount of white solid, yield was 100%, number average molecular weight was 331563, molecular weight distribution was 1.9, cis-1,4 structure content was 45%, and 3,4 structure content was 55%.
Example 12
Isoprene was polymerized by the method of example 2, except that 0.33mL of methylaluminoxane (1.5M) was used as a cocatalyst and reacted for 10min, and a large amount of white solid was precipitated after quenching, with a yield of 99%, a number average molecular weight of 236954, a molecular weight distribution of 2.0, a cis-1,4 structure content of 44%, and a 3,4 structure content of 56%.
Example 13
Isoprene polymerization was carried out by the method of example 2, except that 0.067mL of methylaluminoxane (1.5M) was used as a cocatalyst, reacted for 10min, and quenched to precipitate a large amount of white solid, yield 80%, number average molecular weight 267520, molecular weight distribution 2.0, cis-1,4 structure content 44%, and 3,4 structure content 56%.
Example 14
Isoprene was polymerized by the method of example 2, except that 0.033mL of methylaluminoxane (1.5M) was used as a cocatalyst and reacted for 10min, and no solid was precipitated after quenching.
Example 15
Isoprene was polymerized by the method of example 13, except that polymerization was catalyzed for 30min, and a large amount of white solid was precipitated after quenching, with a yield of 91%, a number average molecular weight of 199631, a molecular weight distribution of 2.2, a cis-1,4 structure content of 44%, and a 3,4 structure content of 56%.
Example 16
Isoprene was polymerized by the method of example 13, except that polymerization was catalyzed for 1 hour, and a large amount of white solid was precipitated after quenching, the yield was 100%, the number average molecular weight was 115862, the molecular weight distribution was 2.3, the cis-1,4 structure content was 45%, and the 3,4 structure content was 55%.
Example 17
Isoprene was polymerized by the method of example 11, except that the order of addition was changed: a25 mL dry reaction tube was transferred to a glove box, and 3.4mg (10. mu. mol) of the weighed main catalyst represented by formula II was added thereto, and then transferred to the outside of the glove box, and 5mL of anhydrous toluene and 2mL (20mmol) of an isoprene monomer were added thereto under an argon atmosphere, and then 0.67mL (1.5M) of methylaluminoxane was added thereto. After quenching, a large amount of white solid was precipitated, the yield was 100%, the number average molecular weight was 95411, the molecular weight distribution was 5.6, the cis-1,4 structure content was 38%, and the 3,4 structure content was 62%.
Example 18
Isoprene was polymerized by the method of example 11, except that the order of addition was changed: a25 mL dry reaction tube was charged under argon with 5mL of dry toluene, 2mL (20mmol) of isoprene, 0.67mL (1.5M) of methylaluminoxane and finally a solution of 3.4mg (10. mu. mol) of catalyst (R is 4-fluoro) in dichloromethane (1 mL). After quenching, a large amount of white solid was precipitated, the yield was 100%, the number average molecular weight was 256430, the molecular weight distribution was 2.6, the cis-1,4 structure content was 48%, and the 3,4 structure content was 52%.
Example 19
Isoprene was polymerized by the method of example 11, except that the order of addition was changed and polyisoprene was prepared by the "one-pot" method: a25 mL dry reaction tube is added with ferrous chloride, ligand and 5mL of anhydrous toluene under argon atmosphere, reacted for 30min at room temperature, and then added with 0.67mL (1.5M) of methylaluminoxane and 2mL (20mmol) of isoprene in sequence, and reacted for 10 min. After quenching, a large amount of white solid was precipitated, the yield was 100%, the number average molecular weight was 314498, the molecular weight distribution was 2.0, the cis-1,4 structure content was 43%, and the 3,4 structure content was 57%.
Example 20
250mL of a dry reaction tube is transferred to a glove box, 14.4mg (40 mu mol) of a weighed main catalyst shown in formula III is added, the mixture is transferred to the outside of the glove box, 50mL of anhydrous toluene and 13.3mL (1.5M) of methylaluminoxane are added under the argon atmosphere, 20mL (200mmol) of isoprene is added, the mixture reacts for 10min at room temperature, 200mL of methanol dilute hydrochloric acid (50:1) solution is used for terminating the reaction, the mixture is filtered, a large amount of ethanol is used for washing, the mixture is vacuum-pumped to constant weight at room temperature, the yield is 90%, the number average molecular weight is 321660, the molecular weight distribution is 2.0, the cis-1 and 4 structure content is 45%, and the 3 and 4 structure content is 55%.

Claims (5)

1. An application of an iron complex based on a flexible skeleton in isoprene polymerization is characterized by comprising the following steps: adding a main catalyst, a solvent and a cocatalyst, and then adding an isoprene monomer for polymerization reaction to obtain polyisoprene; the main catalyst is an iron complex based on a flexible framework and has the structure as follows;
Figure FDA0002264347410000011
Figure FDA0002264347410000012
one or more than two of them;
the preparation method of the iron complex based on the flexible framework comprises the steps of reacting a pyridine imine ligand with ferrous chloride in an equimolar ratio in tetrahydrofuran or dichloromethane at the temperature of 25-60 ℃, and carrying out aftertreatment to obtain the iron complex; the structural formula of the pyridine imine ligand is one or more than two of the following structural formulas:
Figure FDA0002264347410000013
the iron complex based on the flexible framework is used as a main catalyst, and the cocatalyst is methylaluminoxane; the structural general formula of the Methylaluminoxane (MAO) is
Figure FDA0002264347410000014
Wherein n is a natural number of 4 to 40; the molar ratio of the aluminum element in the cocatalyst to the iron element in the main catalyst is (10-500): 1.
2. The use according to claim 1, wherein the solvent is one or more of toluene, p-xylene, n-hexane, cyclohexane, pentane, dichloromethane and tetrahydrofuran; the molar ratio of the monomer isoprene to the iron element in the main catalyst is (200) -10000) to 1.
3. Use according to claim 1, wherein the polymerization temperature is-30 to 50 ℃.
4. Use according to claim 1, wherein the polymerization time is from 10min to 1 h.
5. Use according to any one of claims 1 to 3, characterized in that the polyisoprene obtained has a number-average molecular weight of 23.2 × 104-37.5×104The molecular weight distribution is 1.8-3.6; the proportion range of the obtained polyisoprene cis-1,4 structure is 29-48%, and the proportion range of the 3,4 structure is 52-71%.
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