Polymer, polymer manufacturing method, lubricating oil additive, and lubricating oil

Abstract

To provide a polymer that has a high thickening effect in a high temperature range above a practical temperature range and a low thickening effect near the practical temperature range.SOLUTION: A polymer has a weight average molecular weight of 1,600,000 or more and a molar branching degree of 2 or more to 150 or less, the polymer preferably contains at least two (meth)acrylate monomer units as a structural unit, and has a total proportion of (meth)acrylate monomer units of 20 pts.mass or more. The polymer is used as a lubricant additive.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polymer, a method for producing a polymer, a lubricating oil additive, and a lubricating oil. [Background technology]

[0002] It is desirable for lubricating oils and hydraulic oils used in automobiles to maintain a constant viscosity within the operating range. While lubricating oils and hydraulic oils need a certain viscosity to protect components, if the viscosity is too high, problems arise such as reduced operability due to friction and reduced fuel economy.

[0003] In recent years, there has been an increasing demand for improved fuel efficiency in automobiles, and the viscosity of lubricating oils and other products is becoming lower. Since the viscosity of low-viscosity lubricating oils decreases further as the temperature increases, viscosity index improvers are added to them to maintain the required viscosity at high temperatures.

[0004] For this reason, for example, Patent Documents 1 and 2 describe viscosity index improvers made of (meth)acrylate polymers having long-chain alkyl groups. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-203913 [Patent Document 2] Japanese Patent Application Publication No. 10-298576 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to improve fuel economy, it is important to reduce the viscosity as much as possible at low temperatures and maintain the viscosity necessary to protect components at high temperatures. Therefore, an additive that has a low thickening effect at low temperatures and a high thickening effect at high temperatures is required. However, according to the studies of the present inventors, it has been found that the viscosity index improvers described in Patent Documents 1 and 2 may not have a sufficient viscosity index improving effect at high temperatures.

[0007] Therefore, an object of the present invention is to provide a polymer that has a high thickening effect in a high temperature range equal to or higher than the practical temperature range, but has a low thickening effect around the practical temperature range, a method for producing the polymer, a lubricating oil additive, and a lubricating oil. [Means for solving the problem]

[0008] That is, the present invention is summarized as follows. [1] The mass average molecular weight is 1,600,000 or more, A polymer having a molar branching degree (B3w) of 2 or more and 150 or less. [2] The polymer according to [1], having a mass average molecular weight of 8,000,000 or less. [3] The polymer according to [1] or [2], which contains a (meth)acrylate monomer unit as a constituent unit. [4] The polymer according to any one of [1] to [3], which contains at least two or more types of (meth)acrylate monomer units as constituent units. [5] The polymer according to [3] or [4], wherein the total proportion of the (meth)acrylate monomer units per 100 parts by mass of the structural units constituting the polymer is 20 parts by mass or more. [6] A lubricating oil additive, which is the polymer according to any one of [1] to [5]. [7] A lubricating oil comprising the lubricating oil additive according to [6]. [8] A method for producing the polymer according to any one of [1] to [5], A method for producing a polymer by radical polymerization. [Effects of the Invention]

[0009] The polymer of the present invention has a high thickening effect in a high temperature range above the practical temperature range, but a low thickening effect around the practical temperature range. The method for producing a polymer of the present invention can provide the above-mentioned polymer. The lubricating oil additive and lubricating oil of the present invention have a high thickening effect in a high temperature range above the practical temperature range, but a low thickening effect around the practical temperature range.

[0010] According to the polymers of the present invention, they have a high thickening effect at high temperatures and can be used as viscosity index improvers that exhibit good viscosity behavior. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following description, and modifications other than those exemplified below may be made as appropriate within the scope of the present invention.

[0012] In the present invention, the term "monomer" means a compound having a polymerizable carbon-carbon double bond. The term "monomer unit" refers to a constituent unit based on a monomer that is formed by polymerizing one molecule of the monomer. "(Meth)acrylate" shall mean acrylate or methacrylate. Furthermore, "to" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0013] The polymer of the present invention has a mass average molecular weight (Mw) of 1,600,000 or more and a molar branching degree (B3w) of 2 or more and 150 or less. In the present invention, the molar branching degree (B3w) can be measured by a static light scattering method, and specifically, can be measured by the method described in <Molar branching degree (B3w)> in the Examples below.

[0014] When the polymer satisfies the above-mentioned constitution, it is possible to provide a polymer that, when used as a lubricating oil additive, has a high thickening effect at high temperatures above the practical temperature range, but has a low thickening effect at 40°C or around the practical temperature. The mechanism behind this is not clear, but the following reasons are thought to be the cause.

[0015] When a polymer has an appropriate branching structure, molecular chains (backbones) that are insoluble in the lubricating oil solvent at operating temperatures can be dispersed with molecular chains (branches) that dissolve in the lubricating oil even at operating temperatures. The molecular chains (backbones) of the dispersed polymer will dissolve at temperatures above the operating temperature. When the polymer dissolves, entanglement of the molecular chains occurs in the solution, and the higher the molecular weight of the polymer, the more likely it is that entanglement of the molecular chains will occur in the solution. When entanglement of the molecular chains occurs in the solution, the viscosity of the solution increases. Therefore, when a polymer satisfies this structure, the thickening effect is high at high temperatures above the operating temperature, but is low near the operating temperature.

[0016] Among the above, the mass average molecular weight (Mw) of the polymer is preferably 2,000,000 or more, and particularly preferably 3,000,000 or more, because this allows for better viscosity behavior at high temperatures. On the other hand, the mass average molecular weight (Mw) of the polymer is preferably 8,000,000 or less, more preferably 7,000,000 or less, even more preferably 6,000,000 or less, and particularly preferably 5,000,000 or less, because this allows for better solubility in base oil and viscosity index. The mass average molecular weight (Mw) of the polymer can be measured by the method described in the Examples below.

[0017] Among the above, the degree of branching (Bn) of the polymer is more preferably 8 or more, even more preferably 10 or more, and particularly preferably 30 or more, in order to ensure good viscosity behavior at high temperatures. On the other hand, from the viewpoint of solubility in base oil, the degree of branching Bn is more preferably 130 or less, even more preferably 100 or less, and particularly preferably 80 or less.

[0018] The distribution of the mass average molecular weight (Mw) of the polymer is not particularly limited, but in the differential molecular weight distribution curve of the polymer composition measured by gel permeation chromatography (GPC) using a "TSK-GEL GMH HR-H(20)" (7.8 mmΦ×300 mm) column and polymethyl methacrylate as a standard substance, the peak area attributable to polymers with molecular weights of 1,600,000 or more is preferably 10% or more of the peak area attributable to the entire polymer, more preferably 12% or more, and particularly preferably 14% or more.

[0019] On the other hand, the peak area derived from polymers having a mass average molecular weight (Mw) of 2,000,000 or more is preferably 80% or less of the peak area derived from the entire polymer, more preferably 70% or less, and particularly preferably 60% or less.

[0020] The Z-average molecular weight (Mz) of the polymer is not particularly limited, but is preferably 3,000,000 or more, more preferably 5,000,000 or more, and even more preferably 8,000,000 or more, in order to improve viscosity behavior at high temperatures. On the other hand, the Z-average molecular weight (Mz) of the polymer is preferably less than 100,000,000, more preferably 800,000,000 or less, and even more preferably 700,000,000 or less, in order to improve solubility in base oil and viscosity index. The Z-average molecular weight (Mz) of the polymer can be measured by the method described in the Examples below.

[0021] The monomer units constituting the polymer are not particularly limited as long as they have a specific mass average molecular weight and a specific degree of branching (Bn), and examples thereof include (meth)acrylic monomer units, carboxyl group-containing vinyl monomer units, acid anhydride group-containing vinyl monomers, unsaturated dicarboxylic acid diester monomer units, amino group-containing vinyl monomer units, amide group-containing vinyl monomer units, aromatic vinyl monomer units, and olefin monomer units.

[0022] Among these, the polymer is preferably a copolymer, and more preferably a (meth)acrylic polymer containing at least a (meth)acrylate monomer unit.

[0023] The (meth)acrylate monomer refers to a monomer having a (meth)acryloyl group. Examples of the (meth)acrylate monomer include (meth)acrylic acid and (meth)acrylic acid esters.

[0024] The (meth)acrylic copolymer may be configured to contain two or more kinds of (meth)acrylate monomers. The (meth)acrylic copolymer may also be configured to further contain a monomer other than the (meth)acrylate monomer. Preferred examples of the (meth)acrylic polymer will be described below.

[0025] In particular, the ratio of (meth)acrylate monomer units to 100 parts by mass of the structural units constituting the polymer is preferably 20 parts by mass or more, more preferably 35 parts by mass or more, even more preferably 50 parts by mass or more, particularly preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, and particularly preferably 90 parts by mass or more, with the upper limit being 100 parts by mass.

[0026] The (meth)acrylate is not particularly limited, but examples thereof include hydrocarbon group-containing (meth)acrylic acid esters, hydroxyl group-containing (meth)acrylic acid esters, epoxy group-containing (meth)acrylic acid esters, amino group-containing (meth)acrylic acid esters, and amide group-containing (meth)acrylic acid esters.

[0027] The hydrocarbon-containing (meth)acrylic acid ester is not particularly limited, and examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, hexa (meth)acrylate, and the like. Examples of the acrylate include decyl, nonyl (meth)acrylate, isononyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, 3,5,5-trimethylcyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, terpene acrylate and derivatives thereof, hydrogenated rosin acrylate and derivatives thereof, and docosyl (meth)acrylate.

[0028] The hydroxyl group-containing (meth)acrylic acid ester is not particularly limited, and examples thereof include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and glycerol (meth)acrylate.

[0029] The epoxy group-containing (meth)acrylic acid ester is not particularly limited, and examples thereof include glycidyl (meth)acrylate, glycidyl α-ethylacrylate, and 3,4-epoxybutyl (meth)acrylate.

[0030] The amino group-containing (meth)acrylic acid ester is not particularly limited, and examples thereof include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, and the like.

[0031] The amide group-containing (meth)acrylic acid ester is not particularly limited, and examples thereof include (meth)acrylamide, Nt-butyl(meth)acrylamide, N-methylol(meth)acrylamide, N-isopropylacrylamide, hydroxyethylacrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, and diacetone acrylamide.

[0032] Among the above, the polymer is preferably a copolymer containing, as monomer units, an alkyl methacrylate a1 having 5 to 14 carbon atoms in the alkyl group (hereinafter sometimes simply referred to as alkyl methacrylate a1), an alkyl acrylate a2 having 5 to 14 carbon atoms in the alkyl group (hereinafter sometimes simply referred to as alkyl acrylate a2), and an alkyl acrylate a3 having 1 to 4 carbon atoms in the alkyl group (hereinafter sometimes simply referred to as alkyl acrylate a3).

[0033] Examples of the alkyl methacrylate a1 include methacrylates having a linear alkyl group such as n-pentyl methacrylate, n-hexyl methacrylate, n-heptyl methacrylate, n-octyl methacrylate, n-nonyl methacrylate, n-decyl methacrylate, n-undecyl methacrylate, n-dodecyl methacrylate, n-tridecyl methacrylate, and n-tetradecyl methacrylate; isoamyl methacrylate, 2-ethylhexyl methacrylate, i-nonyl methacrylate, i-decyl methacrylate, 3-i-propylheptyl methacrylate, and the like. methacrylates having a branched alkyl group such as butyl methacrylate, i-undecyl methacrylate, 2-t-butylheptyl methacrylate, i-dodecyl methacrylate, i-tridecyl methacrylate, and i-tetradecyl methacrylate; and methacrylates having a cyclic alkyl group such as cyclopentyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate, dicyclopentenyl methacrylate, dicyclopentenoxyethyl methacrylate, dicyclopentanyl methacrylate, and adamantyl methacrylate. Two or more of these may be used in combination.

[0034] Among these, alkyl methacrylate a1 is preferably a linear or branched alkyl methacrylate having an alkyl group with 8 or more carbon atoms, more preferably a linear or branched alkyl methacrylate having an alkyl group with 10 or more carbon atoms, and even more preferably a linear or branched alkyl methacrylate having an alkyl group with 12 or more carbon atoms, because it has an excellent effect of improving the viscosity index. On the other hand, alkyl methacrylate a1 is preferably a linear or branched alkyl methacrylate having an alkyl group with 18 or less carbon atoms, more preferably a linear or branched alkyl methacrylate having an alkyl group with 16 or less carbon atoms, and even more preferably a linear or branched alkyl methacrylate having an alkyl group with 14 or less carbon atoms, from the viewpoint of solubility.

[0035] In addition, in order to improve the viscosity index of the base oil, the proportion of alkyl methacrylate a1 relative to the total mass of the polymer is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more; on the other hand, in order to improve solubility in the base oil, it is preferably 50 parts by mass or less, more preferably 45 parts by mass or less, and even more preferably 40 parts by mass or less.

[0036] Examples of the alkyl acrylate a2 include acrylates having a linear alkyl group, such as n-pentyl acrylate, n-hexyl acrylate, n-heptyl acrylate, n-octyl acrylate, n-nonyl acrylate, n-decyl acrylate, n-undecyl acrylate, n-dodecyl acrylate, n-tridecyl acrylate, and n-tetradecyl acrylate; i-amyl acrylate, 2-ethylhexyl acrylate, i-nonyl acrylate, i-decyl acrylate, and 3-i-propylheptyl acrylate. acrylate, i-undecyl acrylate, 2-t-butylheptyl acrylate, i-dodecyl acrylate, i-tridecyl acrylate, i-tetradecyl methacrylate, and other methacrylates having a branched alkyl group; cyclopentyl methacrylate, cyclohexyl acrylate, isobornyl acrylate, dicyclopentenyl acrylate, dicyclopentenoxyethyl acrylate, dicyclopentanyl acrylate, adamantyl acrylate, and other acrylates having a cyclic alkyl group. Two or more of these may be used in combination.

[0037] Among these, the alkyl acrylate a2 is preferably a linear or branched alkyl acrylate having an alkyl group with 8 or more carbon atoms, more preferably a linear or branched alkyl acrylate having an alkyl group with 10 or more carbon atoms, and even more preferably a linear or branched alkyl acrylate having an alkyl group with 12 or more carbon atoms, because it has an excellent effect of improving the viscosity index. On the other hand, from the viewpoint of solubility, the alkyl acrylate a2 is preferably a linear or branched alkyl acrylate having an alkyl group with 18 or less carbon atoms, more preferably a linear or branched alkyl acrylate having an alkyl group with 16 or less carbon atoms, and even more preferably a linear or branched alkyl acrylate having an alkyl group with 14 or less carbon atoms.

[0038] In addition, in order to improve the viscosity index of the base oil, the proportion of alkyl acrylate a2 relative to the total mass of the polymer is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more; on the other hand, in order to improve the solubility in the base oil, it is preferably 50 parts by mass or less, more preferably 45 parts by mass or less, and even more preferably 40 parts by mass or less.

[0039] Examples of the alkyl acrylate a3 include acrylates having a linear alkyl group such as methyl acrylate, ethyl acrylate, n-propyl acrylate, and n-butyl acrylate; and acrylates having a branched alkyl group such as i-propyl acrylate, i-butyl acrylate, t-butyl acrylate, and s-butyl acrylate. Two or more of these may be used in combination.

[0040] Among these, alkyl acrylates in which the alkyl group has two or more carbon atoms are preferred, alkyl acrylates in which the alkyl group has three or more carbon atoms are more preferred, and alkyl acrylates in which the alkyl group has four carbon atoms are even more preferred, because they have an excellent effect of improving the viscosity index.

[0041] Furthermore, in order to improve the viscosity index of the base oil, the proportion of alkyl acrylate a3 relative to the total mass of the polymer is preferably 30 parts by mass or more, more preferably 35 parts by mass or more, and even more preferably 40 parts by mass or more; on the other hand, in order to improve the solubility in the base oil, it is preferably 80 parts by mass or less, more preferably 75 parts by mass or less, and even more preferably 70 parts by mass or less.

[0042] As described above, the (meth)acrylic polymer may contain other monomer units in addition to the (meth)acrylate units.

[0043] The vinyl monomer of the other monomer unit is not particularly limited, but examples thereof include a carboxyl group-containing vinyl monomer, an acid anhydride group-containing vinyl monomer, an unsaturated dicarboxylic acid diester monomer, an amino group-containing vinyl monomer, an aromatic vinyl monomer, and an olefin monomer.

[0044] The carboxyl group-containing vinyl monomer is not particularly limited, and examples thereof include 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxypropyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, 2-(meth)acryloyloxypropyl phthalic acid, 2-(meth)acryloyloxyethyl maleic acid, 2-(meth)acryloyloxypropyl maleic acid, 2-(meth)acryloyloxyethyl maleic acid, 2-(meth)acryloyloxypropyl maleic acid, 2-(meth)acryloyloxy Examples of the acrylate copolymer include diethylsuccinic acid, 2-(meth)acryloyloxypropylsuccinic acid, crotonic acid, fumaric acid, maleic acid, itaconic acid, citraconic acid, monomethyl maleate, monoethyl maleate, monooctyl maleate, monomethyl itaconate, monoethyl itaconate, monobutyl itaconate, monooctyl itaconate, monomethyl fumarate, monoethyl fumarate, monobutyl fumarate, monooctyl fumarate, and monoethyl citraconic acid.

[0045] The acid anhydride group-containing vinyl monomer is not particularly limited, and examples thereof include maleic anhydride and itaconic anhydride.

[0046] The unsaturated dicarboxylic acid diester monomer is not particularly limited, and examples thereof include dimethyl maleate, dibutyl maleate, dimethyl fumarate, dibutyl fumarate, dibutyl itaconate, and diperfluorocyclohexyl fumarate.

[0047] The amino group-containing vinyl monomer is not particularly limited, and examples thereof include 4-vinylpyridine, 2-vinylpyridine, N-vinylpyrrole, N-vinylpyrrolidone, and N,N-dimethylaminostyrene.

[0048] The amide group-containing vinyl monomer is not particularly limited, and examples thereof include maleic acid amide, maleimide, N-vinylformamide, N-vinylacetamide, isopropionylamide, and N-vinylhydroxyacetamide.

[0049] The aromatic vinyl monomer is not particularly limited, and examples thereof include styrene, α-methylstyrene, α-ethylstyrene, vinyltoluene, 2,4-dimethylstyrene, 4-ethylstyrene, 4-isopropylstyrene, 4-butylstyrene, 4-phenylstyrene, 4-cyclohexylstyrene, 4-benzylstyrene, p-methylstyrene, monochlorostyrene, dichlorostyrene, tribromostyrene, tetrabromostyrene, 4-crotylbenzene, indene, and 2-vinylnaphthalene.

[0050] The olefin monomer is not particularly limited, and examples thereof include ethylene, propylene, n-butene, isobutene, norbornene, butadiene, and isoprene. These may be used in combination of two or more kinds.

[0051] In order to achieve both improved solubility in the base oil and an improved viscosity index, the proportion of other monomers other than the (meth)acrylic monomer relative to the total mass of the polymer is preferably 80 parts by mass or less, more preferably 65 parts by mass or less, even more preferably 50 parts by mass or less, particularly preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 10 parts by mass or less, with the lower limit being 0 parts by mass.

[0052] As the polymer, a copolymer is preferable as described above, but a graft copolymer is particularly preferable because it contains multiple structural units with different solubilities in the base oil, which makes it easier to achieve a good viscosity index.

[0053] When the polymer is a graft copolymer, the polymer preferably contains a constituent unit derived from a vinyl-based radically polymerizable monomer m1 and a constituent unit derived from a macromonomer M different from m1. In the present invention, macromonomer M refers to a compound containing two or more constituent units derived from a monomer m2 having a vinyl-based radically polymerizable group and having a radically polymerizable group at its terminal, and two or more types of macromonomer M may be used in combination.

[0054] The monomers m1 and m2 may be the (meth)acrylic monomers, carboxyl group-containing vinyl monomers, acid anhydride group-containing vinyl monomers, unsaturated dicarboxylic acid diester monomers, amino group-containing vinyl monomers, amide group-containing vinyl monomers, aromatic vinyl monomers, and olefin monomers, respectively, as described above.

[0055] The graft copolymer preferably contains alkyl methacrylate a1, alkyl acrylate a2, and alkyl acrylate a3. The alkyl methacrylate a1, alkyl acrylate a2, and alkyl acrylate a3 may be contained in either the monomer m1 or the macromonomer M, or may be contained in both. However, it is preferable that the vinyl radical polymerizable monomer m1 contains alkyl acrylate a2 and alkyl acrylate a3, as this makes it easier to adjust the solubility in the base oil.

[0056] Furthermore, among the above, the monomer m2 preferably contains an alkyl methacrylate having an alkyl group with 5 or more carbon atoms, as this has an excellent effect of improving the viscosity index, and it is even more preferable that the monomer m2 contains alkyl methacrylate a1, as this has excellent solubility in the base oil.

[0057] Furthermore, the macromonomer M preferably has a structure represented by the following formula (1) in terms of radical polymerizability with the monomer m1.

[0058] [ka]

[0059] In formula (1), X 1 ~X n-1 each independently represents a hydrogen atom, a methyl group, or CHOH. 1 ~Y n is a substituent bonded to the vinyl group of the component (m2) which is a monomer structural unit, and for example, OR 1 , halogen atoms, COR 2 , COOR 3 ,CN,CONR 4 R 5 , NHCOR 6 , or R 7 indicates R 1 ~R 7each independently represents a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, etc. Z represents a terminal group, and n represents an integer of 2 to 10,000. The terminal group Z may be a hydrogen atom or a group derived from a radical polymerization initiator, similar to terminal groups of polymers obtained by known radical polymerization.

[0060] The number average molecular weight of the macromonomer M measured by gel permeation chromatography is preferably 500 or more, more preferably 1000 or more, and particularly preferably 2000 or more, because this allows for good solubility in base oils and a good viscosity index. On the other hand, the number average molecular weight of the macromonomer M measured by gel permeation chromatography is preferably 30000 or less, more preferably 25000 or less, and particularly preferably 20000 or less.

[0061] The macromonomer M may be one produced by a known method or a commercially available product. Examples of methods for producing the macromonomer M include a method using a cobalt chain transfer agent (U.S. Patent No. 4,680,352), a method using an α-substituted unsaturated compound such as α-bromomethylstyrene as a chain transfer agent (WO 88 / 04304), a method of chemically bonding a polymerizable group (JP-A No. 60-133007 and U.S. Patent No. 5,147,952), and a method using thermal decomposition (JP-A No. 11-240854).

[0062] The method using a cobalt chain transfer agent is preferred in terms of the number of production steps and the use of a catalyst with a high chain transfer constant. Because the cobalt chain transfer agent has a high chain transfer constant, a macromonomer with a controlled molecular weight can be obtained by adding a small amount. As the cobalt chain transfer agent, a known cobalt complex can be used. The amount of the cobalt chain transfer agent is preferably 0.00001 to 0.1 parts by mass, more preferably 0.00001 to 0.05 parts by mass, and particularly preferably 0.0001 to 0.02 parts by mass, relative to 100 parts by mass of the vinyl radical polymerizable monomer m2.

[0063] Next, an example of a method for producing a polymer will be described. The polymer can be produced by polymerizing a monomer mixture containing a macromonomer and a vinyl radical-polymerizable monomer other than the macromonomer in a base oil by a known method. Examples of the base oil include API Group III oils such as YUBASE3 manufactured by SK Corporation, and API Group III plus oils such as YUBASE4.

[0064] The macromonomer is a macromonomer obtained by polymerizing a monomer mixture containing a vinyl radical-polymerizable monomer in a base oil using a cobalt chain transfer agent. Because the cobalt chain transfer agent has a high chain transfer constant, a macromonomer with a controlled molecular weight can be obtained by adding a small amount. Furthermore, the macromonomer preferably contains alkyl methacrylate a1 as a structural unit. The vinyl radical polymerizable monomer may be a polymerizable monomer m1, which preferably includes an alkyl acrylate a2 and an alkyl acrylate a3.

[0065] In the present invention, a monomer mixture containing a macromonomer and a vinyl radical-polymerizable monomer other than the macromonomer is polymerized to obtain the polymer composition of the present invention, which is a mixture of polymers with different structures such as diblock copolymers and graft copolymers.

[0066] The polymerization may be carried out under known conditions, but it is preferable to use α-methylstyrene dimer as a chain transfer agent because it is particularly effective in suppressing heat generation during polymerization.

[0067] The polymer according to this embodiment can be used as a lubricating oil additive to be added to lubricating oils such as engine oils, gear oils, and hydraulic oils used in industrial machinery, robots, automobiles, and other mobility applications. Examples of base oils for engine oils, gear oils, hydraulic oils, and the like include mineral base oils refined from crude oil and chemically synthesized synthetic oils, such as API Group III base oils such as YUBASE3 manufactured by SK Corporation, and API Group III plus base oils such as YUBASE4 manufactured by SK Corporation.

[0068] Furthermore, the lubricating oil additive can be suitably used as a viscosity index improver for lubricating oil. The degree of viscosity increase due to the addition of a viscosity index improver is preferably large at high temperatures and small at low temperatures. For example, when used in an engine, the viscosity at a temperature higher than the operating temperature (150°C), the operating temperature (e.g., 100°C), and the temperature at engine start (e.g., 40°C) are used as indicators of the degree of viscosity increase due to the addition.

[0069] The degree of increase in viscosity due to the addition of a viscosity index improver is greatest at 150°C, and is better at temperatures lower than 150°C. Therefore, when comparing the viscosity at 100°C of samples with the same viscosity at 150°C, the smaller the difference between the viscosity at 100°C, the better the viscosity behavior. The difference in viscosity between 150°C and 100°C (viscosity difference) is 24 x 10 -4 Pa·s or less is preferable, and 21×10 -4 Pa·s or less is more preferable, and 18×10 -4 It is more preferably Pa·s.

[0070] The lubricating oil composition containing the polymer according to this embodiment may contain other additives, such as antioxidants, viscosity index improvers, pour point depressants, detergents and dispersants, corrosion inhibitors, rust inhibitors, extreme pressure agents, oiliness improvers, antifoaming agents, emulsifiers, wear modifiers, fungicides, and demulsifiers.

[0071] The content of the polymer according to this embodiment contained in the lubricating oil composition is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and particularly preferably 0.1 parts by mass or more, when the total mass of the lubricating oil composition is 100 parts by mass, while it is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and particularly preferably 20 parts by mass or less. By making the content of the lubricating oil additive 0.01 parts by mass or more, the viscosity index of the lubricating oil composition is improved, and by making it 30 parts by mass or less, the kinematic viscosity of the lubricating oil composition at low temperatures is suppressed, improving fuel economy. The lubricating oil composition may further contain a polymer other than the polymer according to this embodiment. [Example]

[0072] The present invention will be described in more detail below with reference to examples and comparative examples. In the examples, "parts" means "parts by mass." Evaluations were performed by the following methods.

[0073] <Molecular weight of macromonomer M> Measurement was performed using gel permeation chromatography (GPC) (HLC-8320, manufactured by Tosoh Corporation). After preparing a 0.2% by mass solution of macromonomer M in tetrahydrofuran, 10 μL of the solution was injected into an apparatus equipped with a Tosoh Corporation column (TSK GUARD COLUMN SUPER HZ-L (inner diameter 4.6 mm, length 35 mm) and two TSK-GEL SUPER HZM-N (inner diameter 6.0 mm, length 150 mm) connected in series). Measurement was performed under conditions of a flow rate of 0.35 mL / min, eluent: tetrahydrofuran, and column temperature: 40°C, and the mass average molecular weight (Mw) and number average molecular weight (Mn) were calculated in terms of standard PMMA.

[0074] <Molecular weight of polymer> Measurement was performed using gel permeation chromatography (GPC) (HLC-8220, manufactured by Tosoh Corporation). After preparing a 0.2% by mass solution of the polymer composition in tetrahydrofuran, 10 μL of the solution was injected into an apparatus equipped with a Tosoh Corporation column "TSK-GEL GMH HR-H(20)" (inner diameter 7.8 mm, length 300 mm) and a TSKguard column SuperHZ-H (inner diameter 4.6 mm, length 3.5 cm), and measurement was performed under the following conditions: flow rate 0.6 mL / min, eluent: tetrahydrofuran, column temperature: 40°C. Polymethyl methacrylate (10 types: Mp (peak molecular weight) = 2,100,000, 1,100,000, 600,000, 300,000, 122,300, 51,000, 35,000, 11,800, 4,900, 1,950; manufactured by American Polymer Standard) was used as a standard substance to calculate the Z-average molecular weight (Mz), mass-average molecular weight (Mw), number-average molecular weight (Mn), and peak top molecular weight (Mp).

[0075] <Solution viscosity> Measurements were performed using a rotational rheometer (manufactured by Thermo, trade name: HAAKE MARS 60). A cone plate with a radius of 50 mm and a tilt angle of 1° was used for the measurements. The concentration of the polymer composition obtained in this example was adjusted with base oil so that the viscosity at 150°C was 0.0037 Pa s, and measurements were performed at a gap of 0.098 mm, a shear rate of 200 / s, a heating rate of 10°C / min, and a temperature range of 25°C to 150°C.

[0076] <Molar branching index (B3w)> A stock solution of the polymer composition with a concentration of 5 mg / mL was prepared using tetrahydrofuran (THF; Fujifilm Wako Pure Chemical Industries, Ltd., special-grade reagent, containing 300 ppm BHT) as a solvent. This stock solution was diluted with THF to prepare five measurement solutions with concentrations ranging from approximately 0.1 to 0.5 mg / mL. The measurement solutions were repeatedly filtered three times through a 0.5 μm pore size PTFE membrane filter (ADVANTEC, DISMIC-25JP). Static light scattering (SLS) measurements were performed using an Otsuka Electronics SLS-6500 static light scattering photometer to determine the weight-average molecular weight Mw, the Z-average squared radius of inertia Rg2, and the second virial coefficient A2. The scattering angle θ was measured at 25°C, ranging from 20° to 150° in 10° intervals. Toluene (Tokyo Chemical Industry Co., Ltd., spectrophotometer grade) was used to calibrate the instrument. The refractive index concentration increment dn / dc was measured using the same measurement solution with a differential refractometer DRM-3000 manufactured by Otsuka Electronics Co., Ltd. Measurements were performed at 25°C. The molar branching degree B3w was calculated from the Zimm-Stockmayer random trifunctional branching equation using the shrinkage factor g calculated by comparing with the Z-average squared radius of linear polymer Rg2L.

[0077] The compounds used in the examples are as follows: SLMA: A mixture of alkyl methacrylate with 12 carbon atoms and alkyl methacrylate with 13 carbon atoms (manufactured by Mitsubishi Chemical Corporation, trade name: Acryester SL) Co catalyst: Cobalt chain transfer agent obtained in Production Example 1 below α-Methylstyrene dimer: α-Methylstyrene dimer (NOF Corporation, product name: Nofumer MSD) ·LA: Dodecyl acrylate BA: n-butyl acrylate LMA: Dodecyl methacrylate BMA: n-butyl methacrylate MMA: Methyl methacrylate Base oil A: Product name YUBASE4 (SK Corporation) Base oil B: Product name YUBASE3 (SK Corporation) Base oil C: Product name YUBASE4+ (SK Corporation)

[0078] [Manufacturing Example 1] (Synthesis of Co complex (cobalt chain transfer agent)) In a synthesis apparatus equipped with a stirrer, 2.00 g (8.03 mmol) of cobalt (II) acetate tetrahydrate (Wako Pure Chemical Industries, Ltd., Wako Special Grade), 3.86 g (16.1 mmol) of diphenylglyoxime (Tokyo Chemical Industry Co., Ltd., EP Grade), and 100 ml of diethyl ether that had been deoxygenated in advance by nitrogen bubbling were placed under a nitrogen atmosphere, and the mixture was stirred at 25°C for 2 hours.

[0079] Next, 20 ml of boron trifluoride diethyl ether complex (Tokyo Chemical Industry Co., Ltd., EP grade) was added, and the mixture was stirred for another 6 hours. The obtained mixture was filtered, and the solid was washed with diethyl ether and dried at 100 MPa or less at 20°C for 12 hours to obtain 5.02 g (7.93 mmol, yield 99% by mass) of Co complex (1) as a brown solid.

[0080] [Manufacturing Example 2] A reaction vessel equipped with a stirrer, condenser, and thermometer was charged with 50 parts of base oil A, 50 parts of Acrylate SL, and 0.0025 parts of the Co complex prepared in Production Example 1. While stirring, nitrogen was bubbled through to remove dissolved oxygen. After the liquid temperature was raised to 85°C, a mixture consisting of 50 parts of Acrylate SL and 0.5 parts of polymerization initiator 1,1,3,3-tetramethylbutylperoxy 2-ethylhexanoate (NOF Corporation, trade name: Perocta O) was added dropwise over 4 hours. After maintaining the temperature at 85°C for 1 hour, a mixture consisting of 35 parts of base oil A and 0.4 parts of Perocta O was added, and the temperature was raised to 95°C. The liquid temperature was maintained at 95°C for 4 hours, followed by cooling, yielding a solution containing 54% by mass of macromonomer M1. The results of GPC analysis of the resulting macromonomer M1 are shown in Table 1.

[0081] [Manufacturing Example 3] A reaction vessel equipped with a stirrer, condenser, and thermometer was charged with 100 parts of toluene, 2 parts of methyl methacrylate, and 0.0004 parts of the Co complex prepared in Production Example 1, and the mixture was stirred. 100 parts of Acrylate SL was added, and nitrogen was bubbled through the mixture while stirring to remove dissolved oxygen. After raising the liquid temperature to 80°C, 0.5 parts of 2,2'-azobis(isobutyronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: 2,2'-azobis(isobutyronitrile)) was added as a polymerization initiator. The mixture was then maintained for 5 hours and cooled to obtain a solution containing 50% by mass of macromonomer M2. 800 parts of tetrahydrofuran was added, and the resulting solution was added dropwise to 10,000 parts of methanol with stirring. The resulting mixture was decanted to obtain a solid macromonomer M2. The GPC results for the resulting macromonomer M2 are shown in Table 1.

[0082] [Manufacturing Example 4] Macromonomer M3 was obtained in the same manner as in Production Example 2, except that the amount of Co complex was changed to the amount shown in Table 1. The results of GPC of the obtained macromonomer M3 are shown in Table 1.

[0083] [Table 1]

[0084] Example 1 A reaction vessel equipped with a stirrer, condenser, and thermometer was charged with 6.9 parts of base oil A, 47.6 parts of the base oil A solution of macromonomer M1 obtained in Production Example 2, 60 parts of n-butyl acrylate, 15 parts of dodecyl acrylate, 0.015 parts of t-butylperoxy-2-ethylhexanoate (NOF Corporation, trade name: Perbutyl O) as a polymerization initiator, and 0.01 parts of α-methylstyrene dimer (NOF Corporation, trade name: Nofmer MSD) as a chain transfer agent. The mixture was stirred and bubbled with nitrogen to remove dissolved oxygen. The liquid temperature was raised to 85°C and maintained at 85°C for 2 hours, after which a mixture of base oil A (40 parts) and Perbutyl O (0.015 parts) was added dropwise over 2 hours. After further maintaining the temperature at 85°C for 1 hour, a mixture of base oil A (67.5 parts) and Perocta O (0.5 parts) was added, the temperature was raised to 95°C, and the liquid temperature was maintained at 95°C for 1 hour. After adding base oil A (46.7 parts), the mixture was cooled to obtain a base oil A solution containing 35% by mass of the lubricating oil additive. The evaluation results of the obtained lubricating oil additive are shown in Table 2.

[0085] <Example 2> A reaction vessel equipped with a stirrer, condenser, and thermometer was charged with 25 parts of toluene, 35 parts of the solid macromonomer M2 obtained in Production Example 3, 41 parts of n-butyl acrylate, 17.5 parts of dodecyl acrylate, 4.5 parts of n-butyl methacrylate, 2 parts of dodecyl methacrylate, and 0.225 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator. Dissolved oxygen was removed by bubbling nitrogen through the mixture while stirring. The liquid temperature was raised to 55°C and maintained at 55°C for 7 hours. After cooling, 1250 parts of tetrahydrofuran was added, and the resulting solution was added dropwise to 15,000 parts of methanol while stirring. The resulting mixture was decanted to obtain a solid lubricating oil additive. The evaluation results of the resulting lubricating oil additive and the estimated molar branching degree B3w are shown in Table 2.

[0086] Example 3 A lubricating oil additive was obtained in the same manner as in Example 2, except that the amounts of the vinyl radical polymerizable monomer and macromonomer were changed to the amounts shown in Table 2. The evaluation results of the obtained lubricating oil additive and the estimated value of the molar branching degree B3w are shown in Table 2.

[0087] <Comparative Example 1> A reaction vessel equipped with a stirrer, condenser, and thermometer was charged with 78.7 parts of base oil A, 25 parts of Acryester SL, 52 parts of n-butyl acrylate, 23 parts of dodecyl acrylate, 0.03 parts of Perbutyl O as a polymerization initiator, and 0.02 parts of Nofumer MSD as a chain transfer agent. Dissolved oxygen was removed by bubbling nitrogen through the mixture while stirring. The liquid temperature was raised to 85°C and held at 85°C for 2 hours. A mixture of 40 parts of base oil A and 0.015 parts of Perbutyl O was then added dropwise over 2 hours. After further holding at 85°C for 1 hour, a mixture of 67 parts of base oil A and 0.5 parts of Perocta O was added, and the mixture was heated to 95°C. The liquid temperature was held at 95°C for 1 hour, followed by cooling to obtain a solution containing 35% by mass of a (meth)acrylic polymer. The evaluation results of the resulting lubricating oil additive are shown in Table 2.

[0088] <Comparative Examples 2 and 3> A polymer was obtained in the same manner as in Example 1, except that the amounts of the vinyl radical polymerizable monomer and α-methylstyrene dimer were changed to the amounts shown in Table 2. The evaluation results of the obtained polymer are shown in Table 2.

[0089] [Table 2]

[0090] As shown in Table 2, Examples 1 to 3 have a mass average molecular weight (Mw) of 1,600,000 or more as determined by PMMA-equivalent GPC, and a molar branching degree (B3w) of 2 or more and 150 or less as measured by static light scattering. Therefore, they have excellent solubility in base oil C, and the difference in viscosity of the base oil C solution at 100 to 150°C is 24 × 10 -4 Because the value is small, at less than Pa·s, it was confirmed that this is suitable as a viscosity index improver for lubricating oils at high temperatures. [Industrial Applicability]

[0091] The polymer according to this embodiment can be used as a lubricating oil additive, and can be used as a drive system lubricant, hydraulic oil, engine oil, traction oil, and the like.

Claims

1. A polymer containing a (meth)acrylate monomer unit as a constituent unit, a graft copolymer comprising a constituent unit derived from a vinyl radical polymerizable monomer m1 and a constituent unit derived from a macromonomer M, the macromonomer M contains two or more structural units derived from a monomer m2 having a vinyl radical polymerizable group, As the (meth)acrylate monomer unit, the monomer m2 includes an alkyl methacrylate a1 having an alkyl group with 5 to 14 carbon atoms, and the vinyl radical polymerizable monomer m1 includes an alkyl acrylate a2 having an alkyl group with 5 to 14 carbon atoms and an alkyl acrylate a3 having an alkyl group with 1 to 4 carbon atoms, a proportion of alkyl methacrylate a1 units having 5 to 14 carbon atoms in the alkyl group is 1 part by mass or more and 50 parts by mass or less, a proportion of alkyl acrylate a2 units having 5 to 14 carbon atoms in the alkyl group is 1 part by mass or more and 50 parts by mass or less, and a proportion of alkyl acrylate a3 units having 1 to 4 carbon atoms in the alkyl group is 30 parts by mass or more and 80 parts by mass or less, relative to the total mass of the polymer; The mass average molecular weight is 1,600,000 or more, A polymer having a molar branching degree (B3w) of 2 or more and 150 or less.

2. The polymer according to claim 1, having a weight average molecular weight of 8,000,000 or less.

3. A lubricating oil additive which is the polymer of claim 1 or 2.

4. A lubricating oil comprising the lubricating oil additive of claim 3.

5. A method for producing the polymer according to claim 1 or 2, A method for producing a polymer by radical polymerization.

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