Star-shaped multi-arm HSD viscosity index improver with core-shell structure and preparation method of star-shaped multi-arm HSD viscosity index improver

Abstract

The invention discloses a preparation method of a star-shaped multi-arm HSD viscosity index improver with a core-shell structure, and the preparation method comprises the following steps: uniformly mixing a non-polar hydrocarbon solvent, isoprene and butadiene, adding a polarity regulator, heating, adding an alkyl lithium initiator, and reacting to obtain a polymer shell; then adding a mixed solution of styrene, a coupling agent and a solvent at one time, and continuously reacting to obtain a star-shaped multi-arm polymer with a core-shell structure; the star-shaped multi-arm polymer with the core-shell structure is directly transferred to a hydrogenation kettle, alcohol termination is not needed, then a hydrogenation catalyst is added, heating is performed, hydrogen is introduced for a hydrogenation reaction, catalyst metal ions are removed, a solution is flocculated and dried, and the star-shaped multi-arm HSD viscosity index improver with the core-shell structure is obtained. According to the star-shaped multi-arm HSD viscosity index improver with the core-shell structure, on the premise that the shearing stability of an oil product is kept, the oil product has higher thickening capacity, and the development requirements of high-end oil products and long-life oil products are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical engineering, and relates to a star-shaped multi-arm hydrogenated styrene-diene (HSD) viscosity index improver (VII) with a core-shell structure and a preparation method thereof. Background Art

[0002] Common lubricating oils we usually see are generally composed of 75% - 85% base oil and 15% - 25% additives, and the range of additive usage is very large. Viscosity is one of the key parameters for measuring the performance of lubricating oils, and the viscosity index is used to characterize the viscosity-temperature property. Since viscosity is significantly affected by conditions such as pressure and temperature, when the temperature drops, the viscosity of the base oil increases, and even solidification occurs, making it unable to be used normally; when the temperature rises, the viscosity of the base oil decreases, and it cannot play an effective role in reducing friction and wear, resulting in limited use temperature of the base oil.

[0003] In order to meet the high-temperature lubricity and low-temperature fluidity of the base oil, a viscosity index improver (Viscosity Index Improver, VII) needs to be added. Currently, the widely used viscosity index improvers include four categories: polymethacrylic acid (PMA), polyisobutene (PIB), ethylene-propylene copolymer (OCP), and hydrogenated styrene-diene copolymer (HSD). The advantages, defects, and development trends of various commonly used viscosity index improvers at home and abroad are as follows: Polyisobutene (PIB) - type viscosity index improvers, molecular weight: 9,000 - 40,000, are suitable for hydraulic oils and gear oils. The viscosity increases rapidly at low temperatures, and there are limitations in the production of multi-grade lubricating oils. Polymethacrylate (PMA) - type, molecular weight: 10,000 - 200,000, are used in hydraulic oils, gear oils, and internal combustion engine oils, and have excellent viscosity-increasing effects; poor shear stability, high unit price, and the development direction is the dispersed type and comb-shaped PMA, mainly in Japan and South Korea. Ethylene-propylene copolymer (OCP) - type, molecular weight: 60,000 - 300,000, are suitable for internal combustion engine oils, and the thickening performance and shear performance are relatively balanced; general low-temperature performance, poor solubility in type III and type IV oils, and the development direction is anti-oxidation, wear resistance, and soot dispersion, mainly in China. Hydrogenated styrene-diene (HSD) - type, molecular weight: 50,000 - 500,000, are suitable for internal combustion engine oils, and have balanced thickening performance and shear performance, and good low-temperature performance; high unit price, and the development direction is star-shaped multi-arm copolymers, mainly in Europe, America, and China.

[0004] Shear stability and thickening ability are the two most important and fundamental performance indicators of VII. However, they are often contradictory to each other, and a balance between them needs to be sought. Therefore, on the premise of meeting the requirements of shear stability, it is necessary to select a viscosity index improver with a large thickening ability as much as possible. This raises a question: Can the thickening ability of the viscosity index improver be improved under the condition of ensuring a high level of anti-shear stability? In order to obtain a viscosity index improver with high thickening ability, a long main chain is required in its structure. At the same time, in order to obtain good anti-shear stability, a short main chain structure is required. Most of the polymers in the main chain are non-crystalline polymers, which are most suitable for providing high thickening ability.

[0005] Compared with linear VII, star-shaped VII has higher thickening ability on the premise of maintaining similar shear stability. It is difficult to prepare star-shaped ethylene-propylene copolymers by catalytic polymerization methods. However, star-shaped styrene-based diene polymers can be prepared by living anionic polymerization and further hydrogenated, which can easily realize the synthesis of star-shaped ethylene-propylene copolymers. At the same time, this type of hydrogenated ethylene-propylene copolymer has unique strictly alternating ethylene-propylene units (which can be obtained by hydrogenating isoprene units), as well as controllable molecular weight, composition, microstructure (the content of saturated side chains of the hydrogenated product can be controlled by regulating the vinyl content of the base polymer), and topological structure. It can formulate high-grade lubricating oils with a large span and has become the most widely used HSD type viscosity index improver, with rich product grades and wide application fields.

[0006] Chinese Patent CN201410766239.X discloses an SBS containing a uniformly distributed 1,2-structured butadiene block, its hydride, and preparation and application methods, including: adding isoprene and butadiene to a non-polar hydrocarbon solvent in a reactor, and then adding a polar regulator and an alkyllithium initiator; adding styrene to the reactor and reacting until the styrene is exhausted to obtain a diblock copolymer; adding a coupling agent to the reactor and reacting until the coupling reaction ends, and then adding isopropyl alcohol to terminate the polymerization reaction; adding a hydrogenation catalyst to the obtained polymer solution and introducing hydrogen for hydrogenation reaction; removing the catalyst from the hydrogenated solution, and subjecting the solution to flocculation drying to obtain a star-shaped hydrogenated styrene diene copolymer. Although the viscosity index of the star-shaped hydrogenated styrene diene copolymer obtained by this preparation method is slightly increased, its long-term shear stability is poor.

[0007] Chinese Patent CN201410783659.9 discloses a star-shaped hydrogenated styrene-diene copolymer and its preparation method. The arms of the star-shaped hydrogenated styrene-diene copolymer are diblock copolymers. Block one is hydrogenated polyisoprene (EP), and block two is hydrogenated styrene-butadiene copolymer (SEB). Its structural formula is (EP-SEB)n-C, where C is the core of the coupling agent and n is the number of polymer arms, and n is greater than or equal to 3. The star-shaped hydrogenated styrene-diene copolymer is finally prepared through processes such as polymerization, coupling, and hydrogenation. This preparation method obtains a brand-new copolymer by adjusting the quantity, proportion, addition sequence, and microstructure of the monomers in the copolymer shell.

[0008] Chinese Patent CN201210490529.7 discloses a star-shaped isoprene-styrene block copolymer and its preparation method. The structure of the star-shaped isoprene-styrene block copolymer is: (PI-S)n-C, where: PI is a polyisoprene block, S is a polystyrene block, C is the residue of the star-shaped coupling agent, the coupling efficiency is greater than 80%, n is the average number of arms, n is greater than or equal to 3, and the number-average molecular weight of the star copolymer (PI-S)n-C is 5×10 4 ~5×10 5 , and the number-average molecular weight of the polymer arm PI-S is 1×10 3 ~1×10 5 , and by mass percentage, the content of S in the copolymer is 5-80%, and the content of PI is 20-95%; the preparation method of this copolymer is realized by adding the coupling agent dropwise in batches.

[0009] Chinese Patent CN201310680584.7 discloses a hydrogenated star polymer, its preparation method, a lubricating oil composition, and a lubricating oil masterbatch. The hydrogenated star polymer contains four types of block copolymer arm structures. The first type of arm is a polybutadiene block, the second type of arm is a polyisoprene block, the third type of arm is a polystyrene-polybutadiene diblock copolymer, and the fourth type of arm is a polystyrene-polybutadiene-polyisoprene triblock copolymer. At least part of the polyisoprene block and polybutadiene block in the hydrogenated star polymer are hydrogenated.

[0010] The above-mentioned relatively close patents are all for the preparation of star-structured HSD polymers. Usually, the core is a coupling agent, and the arms are one or two block copolymers composed of copolymers of styrene, isoprene, and butadiene. Since the viscosity index improver needs to meet the viscosity increasing requirements, the polymer molecular weight is relatively large. Taking CN201410766239.X (see Comparative Example 1 of the present invention for details) as an example, in step one, a copolymer of butadiene and isoprene is first synthesized, in step two, styrene is added and the reaction continues to form a block, and in step three, a coupling agent is added and the reaction continues to form a star-shaped multi-arm structure. The structure of this star-shaped viscosity index improver is asFigure 1 As shown. The main disadvantage is that the viscosity of the polymer solution is relatively high after the end of Step 1. It is difficult to graft after adding styrene in Step 2. Especially in Step 3 when adding a coupling agent for coupling, the increase in system viscosity and the rapid increase in temperature, as well as the fact that the molecular chains of the core part of the star polymer are difficult for the catalytic center to meet due to steric hindrance, the hydrogenation reaction is hindered, which will seriously affect the coupling efficiency, the number of coupling arms and the degree of hydrogenation. It not only affects the structural stability of the product and the resulting changes in the performance of the viscosity index improver, but also in order to improve the coupling efficiency and the number of coupling arms to achieve the purpose of high molecular weight, measures such as increasing the dosage of the coupling agent are taken, resulting in an increase in the polymerization cost, which is not conducive to the popularization and use of the viscosity index improver in high-end oils. Summary of the Invention

[0011] The object of the present invention is to provide a simple and feasible method for preparing a star-shaped multi-arm hydrogenated styrene-diene polymer with a core-shell structure. The obtained product can be used as a viscosity index improver (VII) in lubricating oils, so that the oil has higher thickening ability while maintaining shear stability, meeting the development requirements of high-end oils and long-life oils.

[0012] To achieve the above object, the present invention provides a method for preparing a star-shaped multi-arm HSD type viscosity index improver with a core-shell structure, which preparation method includes the following steps:

[0013] (1) Mix a non-polar hydrocarbon solvent, isoprene and butadiene evenly, then add a polar regulator, heat, and then add an alkyllithium initiator to react to obtain a polymer shell. Then, a mixed solution of styrene, a coupling agent and a solvent is added at one time and the reaction is continued to obtain a star-shaped multi-arm polymer with a core-shell structure;

[0014] (2) Directly transfer the star-shaped multi-arm polymer with a core-shell structure obtained in step (1) to a hydrogenation autoclave, without terminating with alcohol. Subsequently, add a hydrogenation catalyst, heat, and introduce hydrogen for hydrogenation reaction. Remove the catalyst metal ions from the hydrogenated solution, and flocculate and dry the solution to obtain a star-shaped multi-arm HSD type viscosity index improver with a core-shell structure.

[0015] In the method for preparing a star-shaped multi-arm HSD type viscosity index improver with a core-shell structure of the present invention, the mass ratio of isoprene:butadiene:styrene is 30-70:10-50:0-20. It is preferred that the content of isoprene is higher than that of butadiene, and the content of styrene is the least among the three.

[0016] The preparation method of the star-shaped multi-arm HSD type viscosity index improver with a core-shell structure of the present invention. The core-shell polymerization reaction in step (1) is carried out in an oxygen-free and water-free environment, belonging to solution polymerization. The polymerization process requires the participation of a non-polar hydrocarbon solvent. The non-polar hydrocarbon solvent includes aromatic hydrocarbons, straight-chain alkanes, cycloalkanes or a mixture of any two of them. The aromatic hydrocarbon is selected from at least one of benzene, toluene, and ethylbenzene. The straight-chain alkane is selected from at least one of pentane, hexane, heptane, and octane. The cycloalkane is selected from at least one of cyclopentane and cyclohexane, preferably cyclopentane and cyclohexane. The addition amount of the non-polar hydrocarbon solvent is 300wt% - 1000wt% of the total weight of the monomers of styrene, isoprene, and butadiene.

[0017] The preparation method of the star-shaped multi-arm HSD type viscosity index improver with a core-shell structure of the present invention. The alkyl lithium initiator is at least one of n-butyl lithium, sec-butyl lithium, tert-butyl lithium, and hexyl lithium. The most commonly used is n-butyl lithium. The dosage of the alkyl lithium initiator is 0.2 - 3 mmol per 100 grams of the total monomers, and the total monomers refer to the total weight of the monomers of styrene, isoprene, and butadiene.

[0018] The preparation method of the star-shaped multi-arm HSD type viscosity index improver with a core-shell structure of the present invention. The polar regulator is a heterocyclic organic compound containing nitrogen, oxygen, etc. with a certain polarity, selected from at least one of tetrahydrofuran, ethyl tetrahydrofurfuryl ether, tetramethyldivinyldiamine, tetrahydrofurfuryl alcohol, and diethylene glycol dimethyl ether (2G). The addition amount of the polar regulator is 20wt% - 2000wt% of the alkyl lithium initiator. The polar regulator can adjust the vinyl content of butadiene between 0 - 80%, and at the same time can cause a polarization or solvation effect on the alkyl lithium initiator, reduce its degree of association, and increase the initiation reaction rate of the alkyl lithium initiator such as n-butyl lithium.

[0019] The preparation method of the star-shaped multi-arm HSD type viscosity index improver with a core-shell structure of the present invention. The coupling agent is at least one of polyvinyl compounds, halides, ethers, aldehydes, ketones, and esters, preferably selected from at least one of divinylbenzene, tetravinylsilane, carbon tetrachloride, silicon tetrachloride, tin tetrachloride, and dimethyl terephthalate. Better coupling agents are divinylbenzene, silicon tetrachloride, or tin tetrachloride, etc. The molar ratio of the dosage of the coupling agent to the alkyl lithium initiator is 0.1 - 2.

[0020] The preparation method of the star-shaped multi-arm HSD type viscosity index improver with a core-shell structure of the present invention. After the hydrogenation reaction in step (2) is completed and transferred to a chemical treatment kettle, an antioxidant needs to be added, such as one or more of antioxidant 1520L, antioxidant 1076, antioxidant 1010, antioxidant 264, TNPP, and triisopropanolamine for compounding. The addition amount is 0.5-5 wt%, preferably 0.5-2 wt%. The separation of the polymer from the solution can be carried out by traditional stripping and coagulation methods or by a devolatilization type screw extruder.

[0021] The preparation method of the star-shaped multi-arm HSD type viscosity index improver with a core-shell structure of the present invention. In step (1), the temperature of the reaction is 40°C to 60°C, and the time is 30 min to 90 min.

[0022] The preparation method of the star-shaped multi-arm HSD type viscosity index improver with a core-shell structure of the present invention. In step (1), the temperature of the continued reaction is 50°C to 70°C, and the time is 20 min to 80 min.

[0023] The preparation method of the star-shaped multi-arm HSD type viscosity index improver with a core-shell structure of the present invention. In step (2), the hydrogenation catalyst is a homogeneous nickel-based hydrogenation catalyst; the temperature of the hydrogenation reaction is 50°C to 80°C, the pressure is 2.5 - 4.5 MPa, and the time is 60 min to 180 min.

[0024] The preparation method of the star-shaped multi-arm HSD type viscosity index improver with a core-shell structure of the present invention can be described in detail as follows:

[0025] (1) The preparation method of the viscosity index improver base rubber is as follows: In a 5L reaction kettle evacuated and replaced with argon, non-polar hydrocarbon solvents, isoprene, and butadiene are added to the reaction kettle. After stirring and mixing evenly, a polar regulator and an alkyllithium initiator are added. The initiation temperature is 40°C to 60°C, and the reaction time is 30 min to 90 min to obtain a polymer shell; a mixed solution of styrene, a coupling agent, and a solvent that has been premixed is added to the reactor all at once, and the reaction continues at 50°C to 70°C for 20 min to 80 min until the conversion rate reaches 100%, obtaining a polymer core, that is, a star-shaped multi-arm polymer with a core-shell structure is obtained.

[0026] (2) The method for preparing the viscosity index improver by hydrogenating the base rubber: The obtained base rubber polymer is directly transferred to a hydrogenation kettle without terminating with alcohols. Subsequently, a homogeneous nickel-based hydrogenation catalyst is added, and the hydrogenation reaction is carried out at 50°C to 80°C. The hydrogenation pressure is 2.5 - 4.5 MPa, and the hydrogenation time is 60 min to 180 min. The catalyst metal ions are removed from the hydrogenated solution, and the solution is flocculated and dried to obtain a star-shaped multi-arm hydrogenated styrene diene copolymer with a core-shell structure.

[0027] The idea of the present invention is to prepare a core-shell structured star multi-arm HSD polymer by changing the nucleation process, using polystyrene as the core and the copolymer of butadiene and isoprene as the shell, and then hydrogenating the polymer for application as a viscosity index improver VII product. The process flow of the present invention is simpler, eliminating the cumbersome process of adding materials in multiple batches step by step. It also makes the product structure and molecular weight stable, with high coupling efficiency, reduces costs, and improves the product quality, facilitating its application in high-end and long-life oils.

[0028] The preparation idea of the star multi-arm structure of the present invention minimizes the difficulty of styrene grafting and coupling, improves the coupling efficiency and the number of arms, and significantly enhances the thickening performance and shear stability of the core-shell structured star multi-arm HSD as a viscosity index improver. At the same time, the method of simultaneously adding styrene, coupling agent, and solvent in a blend also reduces the exothermic effect of the grafting and coupling reactions, reduces the energy consumption for cooling the system, and avoids the reduction of coupling efficiency at high temperatures, making the product molecular structure stable and controllable.

[0029] The present invention improves the shear stability and low-temperature performance of the core-shell structured star multi-arm HSD as a viscosity index improver by introducing an EP / EB block (obtained after hydrogenation of isoprene and butadiene) far from the polymer core; by introducing polystyrene and a coupling agent as the core to form a high-molecular-weight core-shell structured star multi-arm polymer, it improves the processing performance, thickening ability, and high-temperature high-shear viscosity of the core-shell structured star multi-arm HSD as a viscosity index improver. The core-shell structured star multi-arm HSD type viscosity index improver of the present invention can enable the oil to have a higher thickening ability while maintaining shear stability, meeting the development requirements of high-end oils and long-life oils. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic structural diagram of the star structure viscosity index improver of Comparative Example 1.

[0031] Figure 2 It is a schematic structural diagram of the core-shell structured star multi-arm HSD type viscosity index improver of Examples 1-6. DETAILED DESCRIPTION OF THE INVENTION

[0032] The following examples are selected to further illustrate the method of the present invention, but should not be limited thereto in practical applications.

[0033] The following instruments were used for polymer characterization in the examples: US Varian INOVA400 NMR nuclear magnetic resonance 11H-NMR was used for qualitative and quantitative analysis of the copolymer composition sequence distribution, microstructure, and hydrogenation degree. A TDA302 gel permeation chromatograph (GPC) from Viscotek Corporation, USA, was used to analyze the molecular weight and molecular weight distribution of the copolymer. A Varian Vista MPX was used for testing the metal ion content. The test methods for the performance of the lubricating oil composition included: the viscosity index (VI) was determined according to the method specified in GB / T - 1995 - 1998, the thickening ability (EP) was determined according to the method specified in SH / T0566 - 93, the shear stability index (SSI) was determined according to the method specified in SH / T0103 - 92, and the low-temperature cold start performance (CCS) was determined according to the method specified in GB / T6538 - 00.

[0034] Example 1

[0035] (1) In a 5L jacketed polymerization kettle, argon was introduced to replace the system three times. After adding 1700 g of hexane, 180 g of isoprene, and 90 g of butadiene to the polymerization kettle and stirring them evenly, 10 mL of tetrahydrofuran (20 vt%) was added. The temperature was raised to 50 °C, and then 5.5 mmol of n-butyllithium was added. The temperature was naturally raised to 70 °C, and after polymerization for 1 hour, a polymer shell was obtained. Subsequently, the mixed solution (30 g of styrene, 300 g of cyclopentane, and 5 g of divinylbenzene (10%)) was added all at once to the polymerization kettle, and the reaction continued for 0.5 hour to obtain a star-shaped multi-arm polymer L1 with a core-shell structure having polystyrene as the core.

[0036] (2) The star-shaped multi-arm polymer obtained in step (1) was directly transferred to a hydrogenation kettle. Hydrogen was introduced at low pressure to replace the system three times. Subsequently, a homogeneous nickel-based hydrogenation catalyst was added, and the hydrogenation reaction was carried out at 60 °C with a hydrogenation pressure of 3.0 MPa and a hydrogenation time of 120 min. The catalyst metal ions were removed from the hydrogenated solution, and the solution was subjected to flocculation drying to obtain a star-shaped multi-arm HSD type viscosity index improver VII-1 with a core-shell structure.

[0037] The properties of the star-shaped multi-arm HSD type viscosity index improver VII-1 with a core-shell structure and its performance test results in the oil are shown in Table 1.

[0038] Comparative Example 1

[0039] (1) In a 5L polymerization kettle with a jacket, the system was purged with argon three times. After adding 2000 g of hexane, 180 g of isoprene, and 90 g of butadiene into the polymerization kettle and stirring them evenly, 10 mL of tetrahydrofuran (20 vt%) was added. The temperature was raised to 50 °C by heating, and then 5.5 mmol of n-butyllithium was added. The temperature rose to 70 °C naturally. After polymerization for 1 hour, a polymer arm was obtained; then 30 g of styrene was added and reacted for 30 min; then 5 g of divinylbenzene (10%) was added, and after continuing to react for 0.5 hour, a polymer "core" was formed, and a star-shaped multi-arm polymer LC with divinylbenzene as the core and butadiene-styrene as the shell was obtained.

[0040] (2) The same as Example 1, the hydrogenated polymer VII-C was obtained.

[0041] The properties of the hydrogenated polymer VII-C and its performance test results in oil are shown in Table 1.

[0042] Example 2

[0043] According to the method of Example 1, the difference is that in step (1), "6 mL of tetrahydrofuran (20 vt%)" was used to replace "10 mL of tetrahydrofuran (20 vt%)", and a star-shaped multi-arm HSD type viscosity index improver VII-2 with a core-shell structure was obtained.

[0044] The properties of the star-shaped multi-arm HSD type viscosity index improver VII-2 with a core-shell structure and its performance test results in oil are shown in Table 1.

[0045] Example 3

[0046] According to the method of Example 1, the difference is that in step (1), "165 g of isoprene and 75 g of butadiene" was used to replace "180 g of isoprene and 90 g of butadiene", and "60 g of styrene" was used to replace "30 g of styrene", and a star-shaped multi-arm HSD type viscosity index improver VII-3 with a core-shell structure was obtained.

[0047] The properties of the star-shaped multi-arm HSD type viscosity index improver VII-3 with a core-shell structure and its performance test results in oil are shown in Table 1.

[0048] Example 4

[0049] According to the method of Example 2, the difference is that in step (1), "6.5 mmol of n-butyllithium" was used to replace "5.5 mmol of n-butyllithium", and a star-shaped multi-arm HSD type viscosity index improver VII-4 with a core-shell structure was obtained.

[0050] The properties of the star-shaped multi-arm HSD type viscosity index improver VII-4 with a core-shell structure and its performance test results in oil are shown in Table 1.

[0051] Example 5

[0052] According to the method of Example 2, the difference is that in step (1), “subsequently add 4.2 g of divinylbenzene (10%)” is used to replace “subsequently add 5 g of divinylbenzene (10%)”, and the star-shaped multi-arm HSD type viscosity index improver VII-5 with a core-shell structure is obtained.

[0053] The properties of the star-shaped multi-arm HSD type viscosity index improver VII-5 with a core-shell structure and its performance test results in oil are shown in Table 1.

[0054] Example 6

[0055] According to the method of Example 2, the difference is that in step (1), “150 g of isoprene and 120 g of butadiene” is used to replace “165 g of isoprene and 75 g of butadiene”, and the star-shaped multi-arm HSD type viscosity index improver VII-6 with a core-shell structure is obtained.

[0056] The properties of the star-shaped multi-arm HSD type viscosity index improver VII-6 with a core-shell structure and its performance test results in oil are shown in Table 1.

[0057] Example 7

[0058] According to the method of Example 2, the difference is that in step (1), “add 1700 g of cyclopentane to the polymerization kettle” is used to replace “add 1700 g of hexane to the polymerization kettle”, and the star-shaped multi-arm HSD type viscosity index improver VII-7 with a core-shell structure is obtained.

[0059] The properties of the star-shaped multi-arm HSD type viscosity index improver VII-6 with a core-shell structure and its performance test results in oil are shown in Table 1.

[0060] Example 8

[0061] According to the method of Example 2, the difference is that in step (1), “add 0.7 mL of ethyl tetrahydrofurfuryl ether (10 vt%)” is used to replace “add 10 mL of tetrahydrofuran (20 vt%)”, and the star-shaped multi-arm HSD type viscosity index improver VII-8 with a core-shell structure is obtained.

[0062] The properties of the star-shaped multi-arm HSD type viscosity index improver VII-8 with a core-shell structure and its performance test results in oil are shown in Table 1.

[0063] Example 9

[0064] According to the method of Example 2, the difference is that in step (1), “add 5.5 mmol of sec-butyl lithium” is used to replace “add 5.5 mmol of n-butyl lithium”, and the star-shaped multi-arm HSD type viscosity index improver VII-9 with a core-shell structure is obtained.

[0065] The properties of the core-shell star-shaped multi-arm HSD type viscosity index improver VII-9 and the test results of its performance in oil are shown in Table 1.

[0066] The testing process of the viscosity index improver in oil:

[0067] Preheat the Group III base oil Abu Dhabi 6 to 100 °C, add 1 wt% of the core-shell star-shaped multi-arm HSD type viscosity index improver of Examples 1-6 or the hydrogenated polymer of Comparative Example 1 and 0.8 wt% of the antioxidant respectively, heat up to 130 °C, and stir and dissolve for 4 h. Then measure the kinematic viscosity of the above oils at 100 °C and 40 °C respectively, and calculate the viscosity index, thickening ability and shear stability index.

[0068] Table 1 The properties of the viscosity index improver and the test results of its performance in oil

[0069]

[0070]

[0071] From the test results of VII-C and VII-1 in Table 1, it can be seen that compared with the traditional "three-step" feeding method, the coupling efficiency of the core-shell star-shaped multi-arm HSD type viscosity index improver of the present invention has been greatly improved, and the molecular weight of the obtained star-shaped polymer is relatively high, which is reflected in the shear stability, viscosity index and thickening ability in the final oil are all greatly improved. From VII-2 and VII-3, it can also be seen that with the increase of the styrene content, the thickening ability decreases significantly, and with the decrease of the side group content, the thickening ability increases, and other properties will also change accordingly, but the influence of the side group content on the thickening ability is slightly weaker than that of the styrene content. From VII-4 and VII-5, it can be seen that the thickening ability is positively correlated with both the arm molecular weight and the average number of arms, and the arm molecular weight has a greater influence on the thickening ability than the average number of arms, because the arm molecular weight has the greatest influence on the hydrodynamic volume of the core-shell star-shaped multi-arm HSD type viscosity index improver in oil. From VII-2 and VII-6, it can also be seen that increasing the butadiene content is beneficial to improving the thickening ability, but its shear stability and low-temperature performance decrease. Therefore, generally, the butadiene content is required not to be higher than 40%. From VII-7 to VII-9, it can be seen that there are some differences in the C5 and C6 solvents, different polar regulators and alkyl lithium initiators on the microstructure and polymerization activity of the polymer, but there is no difference in the molecular structure and performance of the polymer itself.

[0072] The above description of the embodiments is provided to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention according to the disclosure of the present invention.

Claims

1. Preparation method of star-shaped multi-arm HSD viscosity index improver with core-shell structure, characterized in that, it includes the following steps: (1) Mix non-polar hydrocarbon solvent, isoprene and butadiene evenly, then add polar regulator, heat, then add alkyllithium initiator, react to obtain polymer shell, and then add the mixed solution of styrene, coupling agent and solvent at one time, and continue to react to obtain star-shaped multi-arm polymer with core-shell structure; (2) Directly transfer the star-shaped multi-arm polymer with core-shell structure obtained in step (1) to a hydrogenation kettle without terminating with alcohol, then add a hydrogenation catalyst, heat, introduce hydrogen for hydrogenation reaction, remove the catalyst metal ions from the hydrogenated solution, and carry out flocculation drying on the solution to obtain star-shaped multi-arm HSD viscosity index improver with core-shell structure.

2. The preparation method according to claim 1, characterized in that, the mass ratio of isoprene: butadiene: styrene is 30-70: 10-50: 0-20.

3. The preparation method according to claim 1, characterized in that, in step (1), the non-polar hydrocarbon solvent includes aromatic hydrocarbon, straight-chain alkane, cycloalkane or a mixture of any two of them; the aromatic hydrocarbon is selected from at least one of benzene, toluene, and ethylbenzene, the straight-chain alkane is selected from at least one of pentane, hexane, heptane, and octane, the cycloalkane is selected from at least one of cyclopentane and cyclohexane, and the addition amount of the non-polar hydrocarbon solvent is 300wt%-1000wt% of the total monomer weight of styrene, isoprene and butadiene.

4. The preparation method according to claim 1, characterized in that, the alkyllithium initiator is at least one of n-butyllithium, sec-butyllithium, tert-butyllithium, and hexyllithium, and the dosage of the alkyllithium initiator is 0.2-3 mmol per 100 grams of total monomer.

5. The preparation method according to claim 1, characterized in that, the polar regulator is selected from at least one of tetrahydrofuran, ethyltetrahydrofurfuryl ether, tetramethyldivinyldiamine, tetrahydrofurfuryl alcohol, and diethylene glycol dimethyl ether (2G), and the addition amount of the polar regulator is 20wt%-2000wt% of the alkyllithium initiator.

6. The preparation method according to claim 1, characterized in that, the coupling agent is at least one of polyvinyl compounds, halides, ethers, aldehydes, ketones, and esters, and the molar ratio of the dosage of the coupling agent to the alkyllithium initiator is 0.1-2.

7. The preparation method according to claim 1, characterized in that, in step (2), an antioxidant is also added; the antioxidant is selected from one or more of antioxidant 1520L, antioxidant 1076, antioxidant 1010, antioxidant 264, TNPP, and triisopropanolamine for compounding, and the addition amount is 0.5-5wt%.

8. The preparation method according to claim 1, characterized in that, in step (1), the reaction temperature is 40°C-60°C and the time is 30min-90min.

9. The preparation method according to claim 1, characterized in that, In step (1), the temperature for the continued reaction is 50°C to 70°C, and the time is 20 min to 80 min.

10. According to the preparation method described in claim 1, characterized in that in step (2), the hydrogenation catalyst is a homogeneous nickel-based hydrogenation catalyst; the temperature of the hydrogenation reaction is 50°C to 80°C, the pressure is 2.5 - 4.5 MPa, and the time is 60 min to 180 min.

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