Polymethacrylate viscosity index improver and preparation method thereof

Abstract

The invention relates to a polymethacrylate viscosity index improver and a preparation method thereof. The viscosity index improver comprises polyalkyl methacrylate; the polyalkyl methacrylate contains 50-70 parts by mass of a monomer unit derived from an alkyl methacrylate having 12-14 carbon atoms in an alkyl group, 20-40 parts by mass of a monomer unit derived from an alkyl methacrylate having 8-10 carbon atoms in an alkyl group, and 1-18 monomer units derived from an alkyl methacrylate having 16-18 carbon atoms in an alkyl group. And 0.014 to 0.075 parts by mass of a unit derived from a functional crosslinking monomer. The viscosity index improver provided by the invention has excellent anti-shearing stability and low-temperature performance by performing a semi-continuous bulk polymerization process on a mixed monomer, using an industrial-grade mixed methacrylate monomer, taking base oil as a reaction medium and introducing a small amount of functional monomer to perform cross-linking modification.

Description

Technical Field

[0001] This invention relates to lubricating oil additives, and in particular to additives (polyalkyl methacrylate viscosity index improvers) for improving viscosity index and methods for manufacturing the same. Background Technology

[0002] Viscosity index improvers are key components in lubricant additives. Their main function is to optimize the viscosity-temperature characteristics of lubricants, ensuring that the lubricant is not too viscous at low temperatures and not too viscous at high temperatures, thus providing excellent lubrication performance under various temperature conditions. Currently, polymethyl methacrylate (PMA) viscosity index improvers are widely used in the lubricant industry due to their excellent thickening properties, shear stability, and low-temperature fluidity.

[0003] The molecular structure of polymethacrylate viscosity index improvers has a significant impact on their performance. Patent document 1 (CN104178253B) discloses a polymethacrylate viscosity index improver, which is copolymerized from C2-C6 alkyl methacrylates, C7-C10 alkyl methacrylates, C11-C12 alkyl methacrylates, and C13-C16 alkyl methacrylates, exhibiting excellent shear stability, low-temperature performance, and thickening properties. However, this technical solution uses a large number of monomers, increasing production costs and process complexity.

[0004] Patent document 2 (CN119431673A) discloses a method for preparing viscosity index improvers for extremely cold specialty oils using atom transfer radical polymerization. This method has the advantages of a wide range of applicable monomers, easy modification of polymer end groups, strong molecular design capabilities, and controllable structure. However, this method requires the use of special catalysts and reducing agents, is complex to operate, and is not conducive to large-scale industrial production.

[0005] To improve the performance of viscosity index improvers, researchers have explored different molecular structure designs. Patent document 3 (CN103443258B) discloses a viscosity index improver containing a star-shaped polymer, which is obtained by reacting divinylbenzene with an alkyl methacrylate containing stearyl methacrylate. This star-shaped polymer has a core derived from divinylbenzene and arms representing the polymeric chain of the alkyl methacrylate. While this structural design improves the performance of the viscosity index improver to some extent, its preparation process is complex and mainly relies on the high-priced stearyl methacrylate monomer.

[0006] In addition, patent document 4 (CN113150857A) discloses the application of polymethacrylate with a molecular weight distribution index of 1.0 to 1.5 as a viscosity index improver for energy-saving hydraulic oil. This viscosity index improver can enable energy-saving hydraulic oil to have good energy-saving effects. However, to obtain such a narrow molecular weight distribution, special polymerization techniques such as living polymerization or controlled free radical polymerization are usually required, which increases the difficulty and cost of production.

[0007] Furthermore, Patent Document 5 (CN112876626A) discloses a poly(meth)acrylate block polymer, its preparation method, and its applications. This polymer is synthesized via RAFT reversible addition-fragmentation chain transfer radical polymerization and contains fluorinated alkyl ester units, which can reduce the friction coefficient of lubricating oils. However, this technology uses fluorinated monomers, which is not only costly but also has potential environmental impacts.

[0008] Despite some progress in the field of viscosity index improvers, existing technologies still face several challenges: First, current polymethyl methacrylate (PMMA) viscosity index improvers typically rely on high-purity single long-chain alkyl ester monomers (such as C18 alkyl esters). The synthesis of these monomers requires high-priced higher alcohols (such as octadecyl alcohol), and the purification process is complex, leading to high production costs. Second, while some research has addressed the preparation of ultra-high molecular weight poly(methyl)acrylate polymers, their applications and performance advantages in the field of lubricant additives have not been fully explored. Finally, current technologies lack a PMMA viscosity index improver that can significantly increase the viscosity of base oils at relatively low dosages, failing to meet the demands of high-efficiency and energy-saving lubricants. Therefore, developing a viscosity index improver that is readily available, easy to prepare, and exhibits excellent performance is of significant practical importance. Summary of the Invention

[0009] This invention aims to address several technical problems faced by existing polymethyl methacrylate viscosity index improvers, including high raw material costs, complex production processes, a lack of application performance research in the field of lubricant additives, and insignificant viscosity improvement effects at low dosages. Therefore, this invention provides a low-cost, simplified, and high-performance polymethyl methacrylate viscosity index improver and its manufacturing method.

[0010] To address the aforementioned technical problems, the present invention provides a viscosity index improver comprising polyalkyl methacrylate, wherein the polyalkyl methacrylate is composed of monomer units of alkyl methacrylate with 12 to 14 carbon atoms derived from alkyl groups, monomer units of alkyl methacrylate with 8 to 10 carbon atoms derived from alkyl groups, monomer units of alkyl methacrylate with 16 to 18 carbon atoms derived from alkyl groups, and monomer units derived from functional crosslinking monomers.

[0011] Preferably, relative to 100 parts by mass of the polyalkyl methacrylate, the alkyl methacrylate having 12 to 14 carbon atoms comprises 50 to 70 parts by mass, the alkyl methacrylate having 8 to 10 carbon atoms comprises 20 to 40 parts by mass, and the alkyl methacrylate having 16 to 18 carbon atoms comprises 1 to 20 parts by mass.

[0012] Further, relative to 100 parts by weight of the polyalkyl methacrylate, the functional crosslinking monomer is 0.014 to 0.075 parts by weight.

[0013] Furthermore, the functional crosslinking monomer is selected from one or more of the group consisting of divinylbenzene (DVB), diacrylate / dimethacrylate, glycidyl methacrylate (GMA), and trimethylolpropane trimethacrylate (TMPTMA).

[0014] Preferably, the polymethacrylate has a weight-average molecular weight of 1 million or more, and more preferably 3 million or more.

[0015] The present invention also provides a method for manufacturing a viscosity index improver, wherein the manufacturing method includes the following steps:

[0016] Raw material pretreatment process: Mix the mixed methacrylate monomers, functional crosslinking monomers, and initiators in a ratio of (70-90):(0.01-0.05):(0.1-1.0), stir evenly, and obtain the raw material mixture;

[0017] Semi-continuous bulk polymerization process: Add base oil to the reactor, heat to 70-100°C, purge with nitrogen for protection, then add the raw material mixture dropwise over 2-3 hours, keep the reaction at the temperature for 2-5 hours to obtain a polymethyl methacrylate mixture;

[0018] Post-processing step: After the reaction is completed, the polymethyl methacrylate mixture is cooled to 40-70°C, and 0.05-0.20 parts of antioxidant are added relative to 100 parts by weight of polymethyl methacrylate. The mixture is stirred for 1-3 hours to obtain a polymethyl methacrylate viscosity index improver with a solid content of 20%-40%.

[0019] Preferably, the mixed methacrylate monomers are composed of 50-70 parts by mass of alkyl methacrylates with 12-14 carbon atoms, 20-40 parts by mass of alkyl methacrylates with 8-10 carbon atoms, and 1-20 parts by mass of alkyl methacrylates with 16-18 carbon atoms.

[0020] Furthermore, the functional crosslinking monomer is selected from one or more of the group consisting of divinylbenzene (DVB), diacrylate / dimethacrylate, glycidyl methacrylate (GMA), and trimethylolpropane trimethacrylate (TMPTMA).

[0021] Furthermore, the antioxidant is one or more selected from the group consisting of benzoyl peroxide (BPO), tert-butyl peroxide, and tert-butyl peroxide-2-ethylhexanoate.

[0022] In addition, the base oil is a Group II base oil, and the base oil accounts for 15% to 35% by mass in the entire polymerization system.

[0023] This invention uses industrial-grade mixed high-carbon alcohols to replace high-purity single long-chain alkyl ester monomers, eliminating the need for expensive higher alcohols (such as octadecyl alcohol), significantly reducing raw material costs, and eliminating the need for complex purification processes.

[0024] The viscosity index improver of the present invention has excellent low-temperature performance. At an addition of 10% by mass, the pour point can reach below -40°C, and especially below -45°C, indicating that the product of the present invention has better flow properties in low-temperature environments and significantly improved thickening effect.

[0025] This invention, through the design of mixed monomers and a semi-continuous bulk polymerization process, prepares a polymethacrylate viscosity index improver with a molecular weight of over 1 million, or even over 3 million, which is far higher than existing technologies. Thus, it can significantly improve the viscosity of base oils with a relatively low dosage.

[0026] This invention employs a semi-continuous bulk polymerization process, using base oil as the reaction medium and also as the carrier for the final product, eliminating the solvent recovery step and simplifying the process flow.

[0027] This invention improves the shear stability of the product by introducing a small amount of functional crosslinking monomers to crosslink the polymer, thus enabling it to maintain long-term stable performance in practical applications. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, those skilled in the art can make appropriate adjustments and implementations, and these also fall within the scope of protection of this invention.

[0029] Preparation Example 1

[0030] Preparation of mixed methacrylate monomers

[0031] Mix 300g of higher alcohols (C8-C) 18 alcohols, of which C 12 -C 14 60% by mass, C8-C 10 30% by mass, C 16 -C 18 The content is 10% by mass, and the purity is ≥95%. The quality indicators refer to GB / T16451-2008. Natural fatty alcohols) are mixed with 150g of methacrylic acid, and esterified at 120℃ for 4 hours using 9.0g of p-toluenesulfonic acid as a catalyst. After filtration, no purification is required to obtain 418.45g of liquid mixed alkyl methacrylate monomers, of which C... 12 ~C 14 Alkyl ester is 60% by mass, C8-C 10 Alkyl ester is 30% by mass, C 16 ~C 18 The alkyl ester is 10% by mass.

[0032] Preparation Example 2

[0033] Preparation of mixed methacrylate monomers

[0034] Mix 350g of higher alcohols (C8-C) 18 alcohols, of which C 12 -C 14 70% by mass, C8-C 10 10% by mass, C 16 -C 18 The content is 20% by mass, and the purity is ≥95%. The quality indicators refer to GB / T16451-2008. Natural fatty alcohols are mixed with 175g of methacrylic acid, and esterified at 120℃ for 4 hours using 11.25g of p-toluenesulfonic acid as a catalyst. After filtration, no purification is required, yielding 420.69g of liquid mixed alkyl ester monomers, of which C... 12 ~C 14 Alkyl ester is 70% by mass, C8-C 10 Alkyl ester is 10% by mass, C 16 ~C 18 The alkyl ester is 20% by mass.

[0035] Preparation Example 3

[0036] Preparation of mixed linear (meth)acrylate monomers

[0037] Mix 320g of higher alcohols (C8-C) 18 alcohols, of which C 12 -C 14 60% by mass, C8-C 10 20% by mass, C16 -C 18 The content is 20% by mass, and the purity is ≥95%. The quality indicators refer to GB / T16451-2008. Natural fatty alcohols are mixed with 160g of methacrylic acid, and esterified at 120℃ for 4 hours using 9.0g of p-toluenesulfonic acid as a catalyst. After filtration, no purification is required to obtain 415.27g of liquid mixed alkyl ester monomers, of which C... 12 ~C 14 Alkyl ester is 60% by mass, C8-C 10 Alkyl ester is 20% by mass, C 16 ~C 18 The alkyl ester is 20% by mass.

[0038] Preparation Example 4

[0039] Preparation of mixed methacrylate monomers

[0040] Mix 350g of higher alcohols (C8-C) 18 alcohols, of which C 12 -C 14 50% by mass, C8-C 10 20% by mass, C 16 -C 18 The content is 30% by mass, and the purity is ≥95%. The quality indicators refer to GB / T16451-2008. Natural fatty alcohols are mixed with 175g of methacrylic acid, and esterified at 120℃ for 4 hours using 11.25g of p-toluenesulfonic acid as a catalyst. After filtration, no purification is required to obtain 410.50g of liquid mixed alkyl ester monomers, of which C... 12 ~C 14 Alkyl ester is 50% by mass, C8-C 10 Alkyl ester is 20% by mass, C 16 ~C 18 The alkyl ester is 30% by mass.

[0041] Preparation Example 5

[0042] Preparation of mixed branched (meth)acrylate monomers

[0043] Mix 350g of higher alcohols (C8-C) 18 alcohols, of which C 12 -C 14 50% by mass, C8-C 10 30% by mass, C 16 -C 18The content is 20% by mass, and the purity is ≥95%. The quality indicators refer to GB / T16451-2008. Natural fatty alcohols) are mixed with 175g of methacrylic acid, and esterified at 120℃ for 4 hours using 11.25g of p-toluenesulfonic acid as a catalyst. After filtration, no purification is required, yielding 408.53g of liquid mixed alkyl ester monomers, of which C... 12 ~C 14 Alkyl ester is 50% by mass, C8-C 10 Alkyl ester is 30% by mass, C 16 ~C 18 The alkyl ester is 20% by mass.

[0044] Example 1: Preparation of a polymethacrylate viscosity index improver

[0045] In a 1000 mL four-necked glass bottle, 100 g of the mixed alkyl methacrylate monomer obtained in Preparation Example 1, 0.15 g of the functional crosslinking monomer (GMA), and 2.0 g of benzoyl oxide (BPO) were added and mixed thoroughly to obtain a mixed solution (120.18 mL).

[0046] Add 400g of base oil to the reactor, heat to 90℃, and purge with nitrogen for protection. Then, over 2.5 hours, add 120.18mL of the mixture of the above-mentioned mixed alkyl methacrylate monomer and initiator dropwise, and maintain the reaction temperature for 3 hours. After the reaction is complete, cool to 60℃, add 0.5g of 2,6-di-tert-butyl-p-cresol as an antioxidant, and stir for 2 hours to obtain the finished polymethyl methacrylate adhesive indexer. The obtained polymethyl methacrylate adhesive indexer has a solid content of 20% by mass and a weight-average molecular weight of 3.02 million.

[0047] Example 2: Preparation of a polymethacrylate viscosity index improver

[0048] In a 1000 mL four-necked glass bottle, 125 g of the mixed alkyl methacrylate monomer obtained in Preparation Example 1, 0.1 g of the functional crosslinking monomer (GMA), and 0.6 g of benzoyl dioxide (BPO) were added and mixed thoroughly to obtain a mixture of 147.88 mL.

[0049] Add 375g of base oil to the reactor, heat to 90℃, and purge with nitrogen for protection. Then, over 2.5 hours, add 147.88mL of the mixture of the above-mentioned mixed alkyl methacrylate monomer and initiator dropwise, and maintain the reaction temperature for 3 hours. After the reaction is complete, cool to 60℃, add 0.5g of 2,6-di-tert-butyl-p-cresol as an antioxidant, and stir for 2 hours to obtain the finished polymethyl methacrylate adhesive indexer. The obtained polymethyl methacrylate adhesive indexer has a solid content of 25% by mass and a weight-average molecular weight of 3.39 million.

[0050] Example 3: Preparation of a polymethacrylate viscosity index improver

[0051] In a 1000 mL four-necked glass bottle, 150 g of the mixed alkyl methacrylate monomer obtained in Preparation Example 1, 0.05 g of the functional crosslinking monomer (GMA), and 1.0 g of benzoyl oxide (BPO) were added and mixed thoroughly to obtain a mixed solution (177.71 mL).

[0052] Add 350g of base oil to the reactor, heat to 90℃, and purge with nitrogen for protection. Then, over 2.5 hours, add 177.71mL of the mixture of the above-mentioned mixed alkyl methacrylate monomer and initiator dropwise, and maintain the reaction temperature for 3 hours. After the reaction is complete, cool to 60℃, add 0.5g of 2,6-di-tert-butyl-p-cresol as an antioxidant, and stir for 2 hours to obtain the finished polymethyl methacrylate adhesive indexer. The obtained polymethyl methacrylate adhesive indexer has a solid content of 30% by mass and a weight-average molecular weight of 3.55 million.

[0053] Example 4: Preparation of a polymethacrylate viscosity index improver

[0054] In a 1000 mL four-necked glass bottle, 150 g of the mixed alkyl methacrylate monomer obtained in Preparation Example 2, 0.1 g of the functional crosslinking monomer (GMA), and 0.1 g of benzoyl oxide (BPO) were added and mixed thoroughly to obtain a mixed solution (176.71 mL).

[0055] Add 350g of base oil to the reactor, heat to 90℃, and purge with nitrogen for protection. Then, over 2.5 hours, add 176.71mL of the mixture of the above-mentioned mixed alkyl methacrylate monomer and initiator dropwise, and maintain the reaction temperature for 3 hours. After the reaction is complete, cool to 60℃, add 0.5g of 2,6-di-tert-butyl-p-cresol as an antioxidant, and stir for 2 hours to obtain the finished polymethyl methacrylate adhesive indexer. The obtained polymethyl methacrylate adhesive indexer has a solid content of 30% by mass and a weight-average molecular weight of 3.73 million.

[0056] Comparative Example 1:

[0057] In a 1000mL four-necked glass bottle, 83.33g of linear (meth)acrylate prepared in Preparation Example 3, 33.33g of (meth)acrylate prepared in Preparation Example 4, 8.34g of branched (meth)acrylate prepared in Preparation Example 5, and 375g of base oil were added respectively. Nitrogen gas was introduced for protection, and the mixture was stirred evenly. The temperature was raised to 90°C, and 1.0g of benzoyl dioxide (BPO) was added. The copolymerization reaction was maintained at this temperature for 5 hours, and then the reaction was stopped.

[0058] Comparative Example 2:

[0059] In a 1000mL four-necked glass bottle, 59.12g of linear (meth)acrylate prepared in Preparation Example 3, 8.82g of (meth)acrylate prepared in Preparation Example 4, 7.06g of branched (meth)acrylate prepared in Preparation Example 5, and 425g of base oil were added respectively. Nitrogen gas was introduced for protection, and the mixture was stirred evenly. The temperature was raised to 90°C, and 1.0g of benzoyl diphosphate (BPO) was added. The copolymerization reaction was maintained at this temperature for 5 hours, and then the reaction was stopped.

[0060] The molecular weight and properties of the polymethacrylates prepared in Examples 1-4 and Comparative Examples 1 and 2 were determined.

[0061] The molecular weight and distribution of polymethacrylates prepared in Examples 1-4 and Comparative Examples 1 and 2 were determined by GPC (gel permeation chromatography), and the results are shown in Table 1 below.

[0062] Table 1. Comparison of the molecular weight of polymethacrylates in the Examples and Comparative Examples

[0063]

[0064] The results show that, using the method of the present invention, the examples can obtain polymethacrylates with a weight-average molecular weight of 3 million or more, which is higher than the weight-average molecular weight of the polymethacrylates obtained in the comparative example (less than 1 million). Furthermore, using the method of the present invention, the examples can obtain polymethacrylates with a molecular weight distribution (PD) as high as 30 or more, compared to the comparative example polymethacrylates with a molecular weight distribution of only 20 or less.

[0065] For the polymethyl methacrylate viscosity index improvers prepared in Examples 1-4 and Comparative Examples 1 and 2, the oils were blended with 10% by mass of the polymethyl methacrylate viscosity index improver and 90% by mass of Group II base oil. Then, the viscosity index was measured using an automatic viscometer (model: U-Visc 220) based on ASTM D445. The results are shown in Table 2 below.

[0066] For the polymethyl methacrylate viscosity index improvers prepared in Examples 1-4 and Comparative Examples 1 and 2, the oil was blended with 10% by mass of the polymethyl methacrylate viscosity index improver and 90% by mass of Group II base oil, and then the viscosity index was measured using an automatic pour point instrument (model: OptiMPP) based on ASTM D7346. The results are shown in Table 2 below.

[0067] Table 2 Comparison of thickening ability and pour point of the adhesive indexing agent in the examples and comparative examples with the same dosage.

[0068]

[0069] The results above show that, according to the viscosity index improver of the present invention, only 10% by mass is needed to increase the thickening of the base oil to 20 mm. 2 / s or more, in contrast, the viscosity index improver in the comparative example only thickened the base oil by less than 20 mm. 2 / s. Furthermore, the viscosity index improver of this embodiment can reduce the pour point (PP) of the base oil to below -40°C, while the viscosity index improver of the comparative example can only reduce the pour point (PP) of the base oil to above -40°C. Therefore, the viscosity index improver of this invention can significantly increase the viscosity of the base oil with a lower dosage, exhibiting excellent thickening effect, and its low-temperature performance is superior to that of the comparative example.

[0070] Industrial availability

[0071] This invention employs a mixed monomer design and a semi-continuous bulk polymerization process to prepare a viscosity index improver for polymethyl methacrylate. Through technological innovation and process optimization, the molecular weight of this viscosity index improver reaches over 3 million. In terms of performance, it can significantly improve the viscosity of base oil with a relatively low dosage, exhibits excellent thickening and low-temperature performance, and has significant economic advantages.

Claims

1. A viscosity index improver, wherein, The viscosity index improver comprises polyalkyl methacrylate, which comprises monomer units of alkyl methacrylate with 12 to 14 carbon atoms derived from alkyl groups, monomer units of alkyl methacrylate with 8 to 10 carbon atoms derived from alkyl groups, monomer units of alkyl methacrylate with 16 to 18 carbon atoms derived from alkyl groups, and units derived from functional crosslinking monomers.

2. The viscosity index improver according to claim 1, wherein, Of the 100 parts by weight of the polyalkyl methacrylate, 50 to 70 parts by weight of the alkyl methacrylate having 12 to 14 carbon atoms, 20 to 40 parts by weight of the alkyl methacrylate having 8 to 10 carbon atoms, and 1 to 20 parts by weight of the alkyl methacrylate having 16 to 18 carbon atoms.

3. The viscosity index improver according to claim 1 or 2, wherein, The functional crosslinking monomer is 0.014 to 0.075 parts by weight relative to 100 parts by weight of the polyalkyl methacrylate.

4. The viscosity index improver according to claim 1 or 2, wherein, The functional crosslinking monomer is selected from one or more of the group consisting of divinylbenzene (DVB), diacrylate / dimethacrylate, glycidyl methacrylate (GMA), and trimethylolpropane trimethacrylate (TMPTMA).

5. The viscosity index improver according to claim 1 or 2, wherein, The polymethacrylate has a weight-average molecular weight of over 1 million.

6. A method for manufacturing a viscosity index improver, wherein, The manufacturing method includes: Raw material pretreatment process: Mix the mixed methacrylate monomers, functional crosslinking monomers, and initiators in a ratio of (70-90):(0.01-0.05):(0.1-1.0), stir evenly, and obtain the raw material mixture; Semi-continuous bulk polymerization process: Add base oil to the reactor, heat to 70-100°C, purge with nitrogen for protection, then add the mixture dropwise over 2-3 hours, keep the reaction at the temperature for 2-5 hours to obtain polymethyl methacrylate mixture; Post-processing step: After the reaction is completed, the polymethyl methacrylate mixture is cooled to 40-70°C, and 0.05-0.20 parts of antioxidant are added relative to 100 parts by weight of polymethyl methacrylate. The mixture is stirred for 1-3 hours to obtain a polymethyl methacrylate viscosity index improver with a solid content of 20%-40% by weight.

7. The method for manufacturing the viscosity index improver according to claim 6, wherein, The mixed methacrylate monomers consist of 50-70 parts by mass of alkyl methacrylates with 12-14 carbon atoms, 20-40 parts by mass of alkyl methacrylates with 8-10 carbon atoms, and 1-20 parts by mass of alkyl methacrylates with 16-18 carbon atoms.

8. The method for manufacturing the viscosity index improver according to claim 5 or 6, wherein, The functional crosslinking monomer is selected from one or more of the group consisting of divinylbenzene (DVB), diacrylate / dimethacrylate, glycidyl methacrylate (GMA), and trimethylolpropane trimethacrylate (TMPTMA).

9. The method for manufacturing the viscosity index improver according to claim 5 or 6, wherein, The antioxidant is selected from one or more of the group consisting of benzoyl peroxide (BPO), tert-butyl peroxide, and tert-butyl peroxide-2-ethylhexanoate.

10. The method for manufacturing the viscosity index improver according to claim 5 or 6, wherein, The base oil is a Group II base oil, and the base oil accounts for 15% to 35% by mass in the entire polymerization system.

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