Star-shaped multi-arm hsd viscosity index improver with core-shell structure and preparation method thereof

Abstract

The application 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 polar regulator, heating, adding an alkyl lithium initiator, and reacting 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; the star-shaped multi-arm polymer with a core-shell structure is directly transferred to a hydrogenation kettle, an alcohol is not needed for termination, a hydrogenation catalyst is then added, heating is performed, hydrogen is introduced for hydrogenation reaction, catalyst metal ions are removed, and the solution is flocculated and dried to obtain the star-shaped multi-arm HSD viscosity index improver with a core-shell structure. The star-shaped multi-arm HSD viscosity index improver with a core-shell structure can make oil products have higher thickening capacity under the premise of maintaining shear stability, and meets the development requirements of high-end oil products and long-life oil products.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology and relates to a core-shell structured star-shaped multi-arm hydrogenated styrene diene (HSD) viscosity index improver (VII) and its preparation method. Background Technology

[0002] Common lubricating oils are typically blended from 75% to 85% base oil and 15% to 25% additives, with a wide range of additive usage. Viscosity is one of the key parameters for evaluating lubricating oil performance, and the viscosity index is used to characterize viscosity-temperature properties. Because viscosity is significantly affected by conditions such as pressure and temperature, as temperature decreases, the viscosity of the base oil increases, and it may even solidify, rendering it unusable. Conversely, as temperature increases, the viscosity of the base oil decreases, failing to provide effective friction reduction and anti-wear properties, thus limiting the operating temperature of the base oil.

[0003] To meet the requirements of high-temperature lubricity and low-temperature fluidity of base oils, viscosity index improvers (VII) are needed. Currently, widely used viscosity index improvers fall into four main categories: polymethyl methacrylate (PMA), polyisobutylene (PIB), ethylene-propylene copolymer (OCP), and hydrogenated styrene-diene copolymer (HSD). The advantages, disadvantages, and development trends of commonly used viscosity index improvers both domestically and internationally are as follows: Polyisobutylene (PIB) viscosity index improvers, with a molecular weight of 9,000-40,000, are suitable for hydraulic oils and gear oils. Their viscosity increases rapidly at low temperatures, limiting their use in the production of multi-grade lubricants. Polymethyl methacrylate (PMA) viscosity index improvers, with a molecular weight of 10,000-200,000, are used in hydraulic oils, gear oils, and internal combustion engine oils. They have excellent viscosity index improving effects; however, they have poor shear stability and high unit price. Dispersed and comb-type PMA are the development directions, primarily used in Japan and South Korea. Ethylene-propylene copolymers (OCPs), with molecular weights of 60,000-300,000, are suitable for internal combustion engine oils, offering a relatively balanced thickening and shear properties. Their low-temperature performance is average, and they have poor solubility in Group III and IV oils. Antioxidant, wear-resistant, and soot-dispersing properties are the future development directions, primarily in the domestic market. Hydrogenated styrene-diolefins (HSDs), with molecular weights of 50,000-500,000, are also suitable for internal combustion engine oils, exhibiting balanced thickening and shear properties and good low-temperature performance. They are more expensive, and star-shaped multi-arm copolymers are the future development direction, primarily in Europe, America, and China.

[0004] Shear stability and thickening ability are the two most important and fundamental performance indicators for viscosity index improvers (VII), but they are often contradictory and a balance must be sought. Therefore, while meeting shear stability requirements, viscosity index improvers with high thickening ability should be selected as much as possible. This raises the question: can the thickening ability of the viscosity index improver be improved while ensuring a high level of shear stability? To obtain a viscosity index improver with high thickening ability, its structure needs a long main chain, while a short main chain structure is required to achieve good shear stability. Polymers with a predominantly non-crystalline main chain are most suitable for providing high thickening ability.

[0005] Compared to linear VII, star-shaped VII exhibits higher thickening capacity while maintaining similar shear stability. Star-shaped ethylene-propylene copolymers are difficult to prepare via catalytic polymerization, but star-shaped styrene diene polymers can be easily synthesized by using living anionic polymerization followed by hydrogenation. Furthermore, this type of hydrogenated ethylene-propylene copolymer possesses unique strictly alternating ethylene-propylene units (obtainable by hydrogenation of isoprene units) and controllable molecular weight, composition, microstructure (the content of saturated side groups in the hydrogenation product can be controlled by adjusting the vinyl content of the base polymer), and topology. It can be formulated into a wide range of high-grade lubricants and has become the most widely used HSD viscosity indexing agent, with a rich variety of product grades and broad applications.

[0006] Chinese patent CN201410766239.X discloses a diblock copolymer (SBS) containing uniformly distributed butadiene blocks with 1,2 structures, its hydrides, and methods for preparation and application. The method includes: adding isoprene and butadiene to a nonpolar hydrocarbon solvent in a reactor, followed by the addition of a polar modifier and an alkyllithium initiator; adding styrene to the reactor and reacting until the styrene is depleted to obtain a diblock copolymer; adding a coupling agent to the reactor and reacting until the coupling reaction is complete, then adding isopropanol to terminate the polymerization reaction; adding a hydrogenation catalyst to the obtained polymer solution and introducing hydrogen gas for hydrogenation; removing the catalyst from the hydrogenated solution and subjecting the solution to flocculation and drying to obtain a star-shaped hydrogenated styrene diene copolymer. While the viscosity index of the star-shaped hydrogenated styrene diene copolymer obtained by this preparation method is slightly improved, 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 star-shaped hydrogenated styrene diene copolymer has two arms that are diblock copolymers: block one is hydrogenated polyisoprene (EP), and block two is hydrogenated styrene-butadiene copolymer (SEB). Its structural formula is (EP-SEB)nC, where C is the core of the coupling agent, and n is the number of polymer arms, with n being greater than or equal to 3. This star-shaped hydrogenated styrene diene copolymer is ultimately obtained through polymerization, coupling, and hydrogenation processes. This preparation method, by adjusting the amount and ratio of monomers in the copolymer shell, the order of addition, and the microstructure, yields novel copolymers.

[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)nC, where: PI is a polyisoprene block, S is a polystyrene block, C is a star-shaped coupling agent residue with a coupling efficiency 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)nC is 5 × 10⁻⁶. 4 ~5×10 5 The number-average molecular weight of the polymer arm PI-S is 1×10⁻⁶. 3 ~1×10 5 The copolymer contains 5-80% sulfur and 20-95% polyimide by mass percentage. The copolymer is prepared by adding the coupling agent dropwise in stages.

[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 partially, the polyisoprene and polybutadiene blocks in the hydrogenated star polymer are hydrogenated.

[0010] The aforementioned patents, which are quite similar, all describe the preparation of star-shaped HSD polymers. Typically, the core is a coupling agent, and the arms are one or two blocks composed of copolymers of styrene, isoprene, and butadiene. Because the viscosity index agent needs to meet the thickening requirements, the polymer molecular weight is relatively large. Taking CN201410766239.X (see Comparative Example 1 of this invention) as an example, step one involves synthesizing a copolymer of butadiene and isoprene; step two involves adding styrene to continue the reaction and form blocks; and step three involves adding a coupling agent to continue the reaction and form a star-shaped multi-arm structure. The structure of this star-shaped viscosity index agent is as follows...Figure 1 As shown. The main drawbacks are that the viscosity of the polymer solution is relatively high after step one, grafting is difficult after adding styrene in step two, and especially in step three when coupling agent is added for coupling. The increase in system viscosity and rapid temperature increase, as well as the steric hindrance of the molecular chains in the core of the star polymer making it difficult for the catalytic center to meet, hinder the hydrogenation reaction. This seriously affects 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 viscosity index agent performance, but also leads to measures to increase the amount of coupling agent in order to improve the coupling efficiency and the number of coupling arms to achieve the goal of high molecular weight, thereby increasing the polymerization cost and hindering the promotion and use of viscosity index agents in high-end oil products. Summary of the Invention

[0011] The purpose of this invention is to provide a simple and easy method for preparing a core-shell structured star-shaped multi-arm hydrogenated styrene-diene polymer. The resulting product can be used as a viscosity index improver (VII) in lubricating oils, enabling the oil to have higher thickening capacity while maintaining shear stability, thus meeting the development requirements of high-end and long-life oils.

[0012] To achieve the above objectives, the present invention provides a method for preparing a core-shell structured star-shaped multi-arm HSD viscosity index improver, the method comprising the following steps:

[0013] (1) Mix non-polar hydrocarbon solvent, isoprene and butadiene evenly, add polar modifier, heat, add alkyl lithium initiator, react to obtain polymer shell, then add styrene, coupling agent and solvent mixed solution at one time, continue reaction to obtain core-shell structured star multi-arm polymer.

[0014] (2) The core-shell star-shaped multi-arm polymer obtained in step (1) is directly transferred to the hydrogenation reactor without the need for alcohol termination. Then, a hydrogenation catalyst is added, heated, and hydrogen is introduced to carry out the hydrogenation reaction. The catalyst metal ions are removed from the hydrogenated solution, and the solution is flocculated and dried to obtain a core-shell star-shaped multi-arm HSD viscosity index improver.

[0015] The method for preparing the core-shell structured star-shaped multi-arm HSD viscosity index improver of the present invention, wherein the mass ratio of isoprene:butadiene:styrene is 30-70:10-50:0-20, preferably the content of isoprene is higher than the content of butadiene, and the content of styrene is the lowest among the three.

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

[0017] The method for preparing a core-shell structured star-shaped multi-arm HSD viscosity index improver of the present invention, wherein the alkyl lithium initiator is at least one of n-butyllithium, sec-butyllithium, tert-butyllithium, and hexyllithium, with n-butyllithium being the most commonly used; the amount of the alkyl lithium initiator is 0.2 to 3 mmol per 100 grams of total monomers, wherein the total monomers refer to the total weight of styrene, isoprene, and butadiene monomers.

[0018] The present invention discloses a method for preparing a core-shell structured star-shaped multi-arm HSD viscosity index improver. The polarity modifier is a nitrogen- and oxygen-containing heterocyclic organic compound with a certain degree of polarity, selected from at least one of tetrahydrofuran, ethyl tetrahydrofurfuryl ether, tetramethyldivinyl diamine, tetrahydrofuran-methanol, and diethylene glycol dimethyl ether (2G). The amount of the polarity modifier added is 20 wt% to 2000 wt% of the alkyllithium initiator. The polarity modifier can adjust the vinyl content of butadiene between 0-80%, and simultaneously induce polarization or solvation effects in the alkyllithium initiator, reducing its association degree and increasing the initiation reaction rate of alkyllithium initiators such as n-butyllithium.

[0019] The present invention discloses a method for preparing a core-shell structured star-shaped multi-arm HSD viscosity index improver, wherein the coupling agent is at least one selected from polyvinyl compounds, halides, ethers, aldehydes, ketones, and esters, preferably at least one selected from divinylbenzene, tetravinylsilane, tetrachloromethane, silicon tetrachloride, tin tetrachloride, and dimethyl terephthalate. Preferred coupling agents include divinylbenzene, silicon tetrachloride, or tin tetrachloride. The molar ratio of the coupling agent to the alkyllithium initiator is 0.1-2.

[0020] In the preparation method of the core-shell structured star-shaped multi-arm HSD viscosity index improver of the present invention, in step (2), after the hydrogenation reaction is completed and the mixture is transferred to a chemical treatment vessel, an antioxidant is also required. This antioxidant may be one or more of the following: antioxidant 1520L, antioxidant 1076, antioxidant 1010, antioxidant 264, TNPP, and triisopropanolamine, and the amount added is 0.5–5 wt%, preferably 0.5–2 wt%. The polymer can be separated from the solution using a traditional stripping and condensation method, or a devolatilization screw extruder.

[0021] In the preparation method of the core-shell structured star-shaped multi-arm HSD viscosity index improver of the present invention, in step (1), the reaction temperature is 40℃~60℃ and the time is 30min~90min.

[0022] In the preparation method of the core-shell structured star-shaped multi-arm HSD viscosity index improver of the present invention, in step (1), the temperature of the continued reaction is 50℃~70℃ and the time is 20min~80min.

[0023] In the preparation method of the core-shell structured star-shaped multi-arm HSD viscosity index improver 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℃~80℃, the pressure is 2.5-4.5MPa, and the time is 60min~180min.

[0024] The preparation method of the core-shell structured star-shaped multi-arm HSD viscosity index improver of the present invention can be further described in detail below:

[0025] (1) The preparation method of the adhesive base is as follows: In a 5L reactor that is evacuated and replaced with argon, non-polar hydrocarbon solvent, isoprene and butadiene are added to the reactor and stirred and mixed evenly. Then, polar regulator and alkyl lithium initiator are added. The initiation temperature is 40℃~60℃ and the reaction time is 30min~90min to obtain the polymer shell. The pre-mixed styrene, coupling agent and solvent mixture is added to the reactor all at once. The reaction is continued at 50℃~70℃ for 20min~80min until the conversion rate reaches 100% to obtain the polymer core, thus obtaining the core-shell structured star-shaped multi-arm polymer.

[0026] (2) Method for preparing viscosity indexing agent by hydrogenation of base adhesive: The obtained base adhesive polymer is directly transferred to a hydrogenation reactor without the need for alcohol termination. Then, a homogeneous nickel-based hydrogenation catalyst is added, and the hydrogenation reaction is carried out at 50℃~80℃, with a hydrogenation pressure of 2.5-4.5MPa and a hydrogenation time of 60min~180min. The catalyst metal ions are removed from the hydrogenated solution, and the solution is flocculated and dried to obtain a core-shell structured star-shaped multi-arm hydrogenated styrene diene copolymer.

[0027] The present invention aims to prepare a core-shell structured star-shaped multi-arm HSD polymer by modifying the nucleation process. Using polystyrene as the core and a copolymer of butadiene and isoprene as the shell, the polymer is then hydrogenated to prepare a viscosity indexing agent VII product. The process of this invention is simpler, eliminating the cumbersome multi-step batch feeding process. It also ensures stable product structure and molecular weight, high coupling efficiency, reduced costs, and improved product quality, facilitating its application in high-end, long-life oil products.

[0028] The star-shaped multi-arm structure preparation method of this invention minimizes the difficulty of styrene grafting and coupling, improves coupling efficiency and arm number, and significantly enhances the thickening performance and shear stability of the core-shell star-shaped 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 grafting and coupling reaction, 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] This invention improves the shear stability and low-temperature performance of core-shell star-shaped multi-arm HSD as a viscosity index improver by introducing EP / EB blocks (obtained by hydrogenation of isoprene and butadiene) far from the polymer core. Furthermore, by introducing polystyrene and a coupling agent as the core, a high-molecular-weight core-shell star-shaped multi-arm polymer is formed, improving the processing performance, thickening ability, and high-temperature high-shear viscosity of core-shell star-shaped multi-arm HSD as a viscosity index improver. The core-shell star-shaped multi-arm HSD viscosity index improver of this invention enables oils to have higher thickening ability while maintaining shear stability, meeting the development requirements of high-end and long-life oils. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the star-shaped viscosity index improver of Comparative Example 1.

[0031] Figure 2 The diagram shows the structure of the core-shell star-shaped multi-arm HSD viscosity index improver in Examples 1-6. Detailed Implementation

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

[0033] The polymer characterization in this embodiment was performed using the following instrument: a US Varian INOVA 400 NMR nuclear magnetic resonance spectrometer. 1Qualitative and quantitative analysis of the copolymer composition, sequence distribution, microstructure, and degree of hydrogenation was performed using 1H-NMR. The molecular weight and molecular weight distribution of the copolymer were analyzed using a Viscotek TDA302 gel permeation chromatography (GPC) system. Metal ion content was tested using a Varian Vista MPX system. The test methods for the lubricating oil composition properties included: viscosity index (VI) determined according to GB / T-1995-1998; thickening capacity (EP) determined according to SH / T0566-93; shear stability index (SSI) determined according to SH / T0103-92; and low-temperature cold start performance (CCS) determined according to GB / T6538-00.

[0034] Example 1

[0035] (1) Argon gas was introduced into a 5L jacketed polymerization reactor to purge the system three times. 1700g of hexane, 180g of isoprene, and 90g of butadiene were added to the polymerization reactor and stirred until homogeneous. Then, 10mL of tetrahydrofuran (20vt%) was added, and the mixture was heated to 50°C. 5.5mmol of n-butyllithium was added, and the mixture was allowed to heat naturally to 70°C. After polymerization for 1 hour, a polymer shell was obtained. Subsequently, the entire mixture (30g of styrene, 300g of cyclopentane, and 5g of divinylbenzene (10%)) was added to the polymerization reactor at once, and the reaction was continued for 0.5 hours to obtain a star-shaped multi-arm polymer L1 with a core-shell structure of polystyrene.

[0036] (2) The star-shaped multi-arm polymer obtained in step (1) was directly transferred to a hydrogenation reactor, and hydrogen was introduced under low pressure for purging three times. Then, 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 flocculated and dried to obtain a core-shell structured star-shaped multi-arm HSD viscosity index improver VII-1.

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

[0038] Comparative Example 1

[0039] (1) Argon gas was introduced into a 5L jacketed polymerization reactor to purge the system three times. 2000g of hexane, 180g of isoprene, and 90g of butadiene were added to the polymerization reactor and stirred until homogeneous. Then, 10mL of tetrahydrofuran (20vt%) was added, and the mixture was heated to 50°C. 5.5mmol of n-butyllithium was then added, and the mixture was allowed to heat naturally to 70°C. After polymerization for 1 hour, polymer arms were obtained. Subsequently, 30g of styrene was added and reacted for 30min. Then, 5g of divinylbenzene (10%) was added, and the reaction was continued for 0.5 hours to form a polymer core, resulting in a star-shaped multi-arm polymer LC with divinylbenzene as the core and butyl-styrene as the shell.

[0040] (2) Same as in Example 1, hydrogenated polymer VII-C was obtained.

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

[0042] Example 2

[0043] The method of Example 1 is different except that in step (1), “10 mL of tetrahydrofuran (20 VT%)” is replaced with “6 mL of tetrahydrofuran (20 VT%)” to obtain core-shell structured star-shaped multi-arm HSD viscosity index improver VII-2.

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

[0045] Example 3

[0046] The method of Example 1 is different except that in step (1), "165g of isoprene and 75g of butadiene" are used instead of "180g of isoprene and 90g of butadiene", and "60g of styrene" is used instead of "30g of styrene", to obtain a core-shell structured star-shaped multi-arm HSD viscosity index improver VII-3.

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

[0048] Example 4

[0049] The method of Example 2 is different except that in step (1), "adding 6.5 mmol n-butyllithium" is used instead of "adding 5.5 mmol n-butyllithium" to obtain the core-shell structured star-shaped multi-arm HSD viscosity index improver VII-4.

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

[0051] Example 5

[0052] The method of Example 2 is different except that in step (1), "followingly add 4.2g of divinylbenzene (10%)" is replaced with "followingly add 5g of divinylbenzene (10%)", to obtain a core-shell structured star-shaped multi-arm HSD viscosity index improver VII-5.

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

[0054] Example 6

[0055] The method of Example 2 is different except that in step (1), "isoprene 150g, butadiene 120g" is used instead of "isoprene 165g, butadiene 75g" to obtain a core-shell structured star-shaped multi-arm HSD viscosity index improver VII-6.

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

[0057] Example 7

[0058] The method of Example 2 is different except that in step (1), "adding 1700g of cyclopentane to the polymerization reactor" is replaced with "adding 1700g of hexane to the polymerization reactor" to obtain the core-shell structured star-shaped multi-arm HSD viscosity index improver VII-7.

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

[0060] Example 8

[0061] The method of Example 2 is different except that in step (1), "adding 0.7 mL of ethyl tetrahydrofurfuryl ether (10 VT%)" is used instead of "adding 10 mL of tetrahydrofuran (20 VT%)" to obtain the core-shell structured star-shaped multi-arm HSD viscosity index improver VII-8.

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

[0063] Example 9

[0064] The method of Example 2 is different except that in step (1), "add 5.5 mmol of sec-butyllithium" is used instead of "add 5.5 mmol of n-butyllithium" to obtain the core-shell structured star-shaped multi-arm HSD viscosity index improver VII-9.

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

[0066] Testing process for viscosity index improvers in oils:

[0067] Group III base oil Abu Dhabi 6 was preheated to 100°C, and 1 wt% of the core-shell structured star-shaped multi-arm HSD viscosity index improver of Examples 1-6 or the hydrogenated polymer of Comparative Example 1 and 0.8 wt% of antioxidant were added respectively. The temperature was raised to 130°C and stirred for 4 hours to dissolve. Then, the kinematic viscosity of the above oil was tested at 100°C and 40°C respectively, and the viscosity index, thickening capacity and shear stability index were calculated.

[0068] Table 1. Properties of viscosity index improvers and their performance test results in oil products.

[0069]

[0070]

[0071] As can be seen from the test results of VII-C and VII-1 in Table 1, compared with the traditional "three-step" feeding method, the coupling efficiency of the core-shell structured star-shaped multi-arm HSD viscosity index improver of this invention is significantly improved. The resulting star polymer has a higher molecular weight, which is reflected in a significant improvement in the shear stability, viscosity index, and thickening ability of the final oil product. VII-2 and VII-3 also show that with the increase of styrene content, the thickening ability decreases significantly, while with the decrease of side group content, the thickening ability increases, and other properties also change accordingly. However, the effect of side group content on thickening ability is slightly weaker than that of styrene content. VII-4 and VII-5 show that the thickening ability is positively correlated with both arm molecular weight and the average number of arms. Among them, the arm molecular weight has a greater impact on the thickening ability than the average number of arms. This is because the arm molecular weight has the greatest impact on the hydrodynamic volume of the core-shell structured star-shaped multi-arm HSD viscosity index improver in the oil product. As can be seen from VII-2 and VII-6, increasing the butadiene content is beneficial to improving the thickening ability, but its shear stability and low-temperature performance decrease. Therefore, the butadiene content is generally required to be no higher than 40%. VII-7 to 9 show that C5 and C6 solvents, as well as different polarity modifiers and alkyl lithium initiators, have some differences in the polymer microstructure and polymerization activity, but have no difference in the molecular structure and properties of the polymer itself.

[0072] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a core-shell structured star-shaped multi-arm HSD-type viscosity index improver, characterized in that, Includes the following steps: (1) Mix non-polar hydrocarbon solvent, isoprene and butadiene evenly, add polarity regulator, heat, add alkyl lithium initiator, react to obtain polymer shell, then add styrene, coupling agent and solvent mixed solution at one time, continue reaction to obtain core-shell structured star multi-arm polymer. (2) The core-shell star-shaped multi-arm polymer obtained in step (1) is directly transferred to the hydrogenation reactor without the need for alcohol termination. Then, a hydrogenation catalyst is added, heated, and hydrogen is introduced to carry out the hydrogenation reaction. The catalyst metal ions are removed from the hydrogenated solution, and the solution is flocculated and dried to obtain a core-shell star-shaped multi-arm HSD viscosity index improver. The mass ratio of isoprene:butadiene:styrene is 30~70:10~50:0~20. The amount of the alkyllithium initiator is 0.2–3 mmol per 100 g of total monomer; The polarity modifier is selected from at least one of tetrahydrofuran, ethyl tetrahydrofurfural ether, tetramethyldivinyl diamine, tetrahydrofuran methanol, and diethylene glycol dimethyl ether, and the amount of the polarity modifier added is 20wt% to 2000wt% of the alkyllithium initiator; The molar ratio of the coupling agent to the alkyllithium initiator is 0.1-2; In step (1), the reaction temperature is 40℃~60℃ and the time is 30min~90min; In step (1), the temperature for the continued reaction is 50℃~70℃ and the time is 20min~80min.

2. The preparation method according to claim 1, characterized in that, In step (1), the nonpolar hydrocarbon solvent includes aromatic hydrocarbons, straight-chain alkanes, cycloalkanes, or a mixture of any two thereof; the aromatic hydrocarbons are selected from at least one of benzene, toluene, and ethylbenzene; the straight-chain alkanes are selected from at least one of pentane, hexane, heptane, and octane; the cycloalkanes are selected from at least one of cyclopentane and cyclohexane; and the amount of nonpolar hydrocarbon solvent added is 300wt% to 1000wt% of the total monomer weight of styrene, isoprene, and butadiene.

3. The preparation method according to claim 1, characterized in that, The alkyl lithium initiator is at least one of n-butyllithium, sec-butyllithium, tert-butyllithium, and hexyllithium.

4. 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.

5. 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, and the amount added is 0.5 to 5 wt%.

6. The preparation method according to 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℃~80℃, the pressure is 2.5-4.5MPa, and the time is 60min~180min.

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