JP2006316169A - Solid lubricating material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid lubricating material having a sliding part such as an artificial joint and giving sufficient lubricity even in an environment in the living body. <P>SOLUTION: A polymer chain of methyl methacrylate, etc., is grafted in high density to the surface of a substrate such as a silicon wafer constituting a lubricating part by living polymerization to improve friction properties. The surface treatment of the substrate is carried out by forming a Langmuir-Blodgett film with 2-(4-chlorosulfonylphenyl)ethyl trimethoxysilane, etc., to form a polymerization starting group. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lubricant comprising a surface grafted with polymer chains.

With the progress of precision and integration of processing technology, small and precise equipment such as so-called micromachines has attracted attention. In lubrication of sliding parts such as such micromachines, smoothness of sub-micron or nano-order is required. In addition, in a micromachine that has a manipulation function at the tip of a catheter used at the time of surgery, lubricity in an in vivo environment is also required.
Further, in lubrication of sliding portions of devices such as artificial joints used in the living body, biocompatibility is required in addition to lubricity in the in vivo environment.

  On the other hand, it is reported that a so-called polymer brush obtained by grafting an electrolyte polymer chain on a solid surface at a relatively low density reduces friction in an aqueous solvent having a very low salt concentration (Non-patent Document 1: Nature, 425, 163-165 (2003)).

Nature, 425, 163-165 (2003)

However, since such a polymer brush reduces friction due to the electric field effect of the electrolyte polymer chain, sufficient lubrication cannot be obtained in an environment where the electric field effect is inhibited, such as a salt concentration in an in vivo environment. There was a problem.
Therefore, there is a strong demand for a lubricant that can provide sufficient lubricity even in an environment where the electric field effect is inhibited, such as an in vivo environment.

  As a result of intensive studies to solve the above problems, the present inventors have found that a surface grafted with a polymer chain at a high graft density exhibits high lubricity even in an environment where the electric field effect is inhibited, and the present invention. Was completed.

That is, the present invention
(1) A lubricant comprising a surface on which polymer chains are grafted at a graft density of 0.1 chain / nm ² or more;
(2) The lubricant according to the above (1), wherein the graft density is 0.15 chain / nm ² or more;
(3) The lubricant according to (2), wherein the graft density is 0.2 to 2 chains / nm ² ;
(4) The lubricant according to any one of the above (1) to (3), wherein the polymer chain graft is a polymer chain graft by a graft-from method or a graft-on-to method;
(5) The lubricant according to (4) above, wherein the polymer chain graft is a polymer chain graft by a graft-from method;
(6) The lubricant according to any one of (1) to (5), wherein the polymer chain graft is a polymer chain graft by radical polymerization;
(7) The lubricant according to (6), wherein the radical polymerization is living radical polymerization;
(8) The lubricant according to (7), wherein the living radical polymerization is atom transfer radical polymerization;
(9) The lubricant according to any one of the above (5) to (8), wherein the polymerization is started from a polymerization initiating group immobilized on the surface of the substrate by the Langmuir-Blodgett method or the chemical adsorption method. ;
(10) The lubricant according to (9) above, wherein the polymerization is initiated from a polymerization initiating group immobilized on the surface of the substrate by the Langmuir-Blodgett method;
(11) The lubricant according to any one of (5) to (10) above, wherein the polymerization initiating group is a halogenated alkyl group or a halogenated sulfonyl group;
(12) The lubricant according to the above (11), wherein the polymerization initiating group is a chlorosulfonyl group;
(13) The lubricant according to any one of (1) to (12), wherein the polymer chain is a homopolymerized polymer chain;
(14) The lubricant according to (13), wherein the homopolymerized polymer chain is poly (methyl methacrylate) or poly (2-hydroxyethyl methacrylate);
(15) Graft density is 0.2-2 chains / nm ² , polymer chain grafting is polymer chain grafting by radical polymerization, and polymerization is immobilized on the surface of the substrate by Langmuir-Blodgett method A lubricant comprising a surface on which a polymer chain is grafted, wherein the polymerization start group is a chlorosulfonyl group, the polymer chain is a homopolymerized polymer chain,
(16) An article containing the lubricant according to any one of (1) to (15) above;
(17) The article according to the above (16), wherein the surface on which the polymer chain is grafted is formed on the surface of a member of the article;
(18) The article according to (16) or (17), which is a medical article;
(19) The article according to (18) above, wherein the medical article is an artificial joint.

  According to a preferred aspect of the present invention, it is possible to provide a lubricant that exhibits high lubricity even in an environment where the electric field effect is inhibited. Further, it is possible to provide a lubricant that is less deformed by weight. Furthermore, a lubricant having biocompatibility can also be provided.

1. Lubricant having surface grafted with polymer chains The lubricant of the present invention can be obtained by grafting polymer chains onto a substrate to form a surface grafted with polymer chains.
Hereinafter, the lubricant including the surface grafted with the polymer chain of the present invention will be described in detail.

(1) Polymer that forms a polymer chain The polymer that forms a polymer chain used in the present invention is not particularly limited, and may be a non-electrolyte polymer or an electrolyte polymer. . Further, it may be a hydrophobic polymer or a hydrophilic polymer. Examples of the non-electrolytic polymer include poly (methyl methacrylate) (PMMA). Examples of the electrolyte polymer include PSGMA (poly (sodium sulphonated glycidyl methacrylate), for example, see Nature, 425, 163-165 (2003), etc.). Examples of the hydrophobic polymer include poly (methyl methacrylate) (PMMA). Examples of the hydrophilic polymer include poly (2-hydroxyethyl methacrylate) (PHEMA). The hydrophilic polymer may be prepared using a hydrophilic monomer, or may be prepared by preparing a polymer using a hydrophobic monomer and then introducing a hydrophilic group into the polymer ( For example, refer to JP2003-327638A).
Further, the polymer chain used in the present invention may be one obtained by homopolymerization of one kind of monomer, or may be one obtained by copolymerization of two or more kinds of monomers. The copolymerization may be random copolymerization, block copolymerization, or gradient copolymerization.
The monomer used for forming the polymer chain of the present invention is not particularly limited as long as it can form a polymer chain grafted on the surface of the substrate. Examples thereof include monomers having at least one addition polymerizable double bond such as a monofunctional monomer having one addition polymerizable double bond. Examples of the monofunctional monomer having one addition polymerizable double bond include (meth) acrylic acid monomers and styrene monomers.
Moreover, both a hydrophobic monomer and a hydrophilic monomer can be used suitably.

  Examples of the (meth) acrylic acid monomer include (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl ( (Meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, Nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, phenyl (meth) acrylate, toluyl (meth) acrylate, benzyl (meth) acrylate, 2-methoxy Ethyl (meth) acrylate, 3-methoxypropyl (meth) acrylate, 3-methoxybutyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, stearyl (meth) acrylate, glycidyl ( (Meth) acrylate, 3-ethyl-3- (meth) acryloyloxymethyloxetane, 2- (meth) acryloyloxyethyl isocyanate, (meth) acrylate-2-aminoethyl, 2- (2-bromopropionyloxy) ethyl (meth) ) Acrylate, 2- (2-bromoisobutyryloxy) ethyl (meth) acrylate, 1- (meth) acryloxy-2-phenyl-2- (2,2,6,6-tetramethyl-1-piperidinyl) Oxy) ethane, 1- (4-((4 (Meth) acryloxy) ethoxyethyl) phenylethoxy) piperidine, γ- (methacryloyloxypropyl) trimethoxysilane, 3- (3,5,7,9,11,13,15-heptaethylpentacyclo [9.5. 1.13, 9.15, 15.17, 13] octasiloxane-1-yl) propyl (meth) acrylate, 3- (3,5,7,9,11,13,15-heptaisobutyl-pentacyclo [9] 5.1.13, 9.15, 15.17, 13] octasiloxane-1-yl) propyl (meth) acrylate, 3- (3,5,7,9,11,13,15-heptaisooctyl Pentacyclo [9.5.1.13,9.15,15.17,13] octasiloxane-1-yl) propyl (meth) acrylate, 3- (3,5,7,9 11,13,15-heptacyclopentylpentacyclo [9.5.1.13, 9.15,15.17,13] octasiloxane-1-yl) propyl (meth) acrylate, 3- (3,5,7 , 9,11,13,15-heptaphenylpentacyclo [9.5.1.13, 9.15,15.17,13] octasiloxane-1-yl) propyl (meth) acrylate, 3-[(3 5,7,9,11,13,15-heptaethylpentacyclo [9.5.1.13, 9.15, 15.17,13] octasiloxane-1-yloxy) dimethylsilyl] propyl (meth) Acrylate, 3-[(3,5,7,9,11,13,15-heptaisobutylpentacyclo [9.5.1.13, 9.15,15.17,13] octasiloxane-1-i Oxy) dimethylsilyl] propyl (meth) acrylate, 3-[(3,5,7,9,11,13,15-heptaisooctylpentacyclo [9.5.1.13, 9.15, 15.17 , 13] octasiloxane-1-yloxy) dimethylsilyl] propyl (meth) acrylate, 3-[(3,5,7,9,11,13,15-heptacyclopentylpentacyclo [9.5.1.13]. 9.15, 15.17, 13] Octasiloxane-1-yloxy) dimethylsilyl] propyl (meth) acrylate, 3-[(3,5,7,9,11,13,15-heptaphenylpentacyclo [9] 5.1.13, 9.15, 15.17, 13] octasiloxane-1-yloxy) dimethylsilyl] propyl (meth) acrylate, (meth) acrylic Ethylene oxide adduct of phosphoric acid, trifluoromethylmethyl (meth) acrylate, 2-trifluoromethylethyl (meth) acrylate, 2-perfluoroethylethyl (meth) acrylate, 2-perfluoroethyl-2-perfluorobutylethyl (meth) ) Acrylate, 2-perfluoroethyl (meth) acrylate, trifluoromethyl (meth) acrylate, diperfluoromethylmethyl (meth) acrylate, 2-perfluoromethyl-2-perfluoroethylethyl (meth) acrylate, 2-perfluorohexylethyl ( Examples include meth) acrylate, 2-perfluorodecylethyl (meth) acrylate, and 2-perfluorohexadecylethyl (meth) acrylate.

  Examples of the styrene monomer include styrene, vinyl toluene, α-methyl styrene, p-chlorostyrene, p-chloromethyl styrene, m-chloromethyl styrene, o-aminostyrene, p-styrene chlorosulfonic acid, and styrene sulfonic acid. And salts thereof, vinylphenylmethyldithiocarbamate, 2- (2-bromopropionyloxy) styrene, 2- (2-bromoisobutyryloxy) styrene, 1- (2-((4-vinylphenyl) methoxy) -1 -Phenylethoxy) -2,2,6,6-tetramethylpiperidine, 1- (4-vinylphenyl) -3,5,7,9,11,13,15-heptaethylpentacyclo [9.5. .13, 9.15, 15.17, 13] octasiloxane, 1- (4-vinylphenyl) -3,5,7,9,1 , 13,15-heptaisobutylpentacyclo [9.5.1.13, 9.15, 15.17,13] octasiloxane, 1- (4-vinylphenyl) -3,5,7,9,11, 13,15-heptaisooctylpentacyclo [9.5.1.13, 9.15, 15.17,13] octasiloxane, 1- (4-vinylphenyl) -3,5,7,9,11, 13,15-heptacyclopentylpentacyclo [9.5.1.13, 9.15, 15.17,13] octasiloxane, 1- (4-vinylphenyl) -3,5,7,9,11,13 , 15-heptaphenylpentacyclo [9.5.1.13, 9.15,15.17,13] octasiloxane, 3- (3,5,7,9,11,13,15-heptaethylpentacyclo [9.5.1.13 .15,15.17,13] octasiloxane-1-yl) ethylstyrene, 3- (3,5,7,9,11,13,15-heptaisobutylpentacyclo [9.5.1.13,9 .15,15.17,13] octasiloxane-1-yl) ethylstyrene, 3- (3,5,7,9,11,13,15-heptaisooctylpentacyclo [9.5.1.13. 9.15,15.17,13] octasiloxane-1-yl) ethylstyrene, 3- (3,5,7,9,11,13,15-heptacyclopentylpentacyclo [9.5.1.13. 9.15, 15.17,13] octasiloxane-1-yl) ethylstyrene, 3- (3,5,7,9,11,13,15-heptaphenylpentacyclo [9.5.1.13 9.15, 15.17, 1 3] Octasiloxane-1-yl) ethylstyrene, 3-((3,5,7,9,11,13,15-heptaethylpentacyclo [9.5.1.13, 9.15, 15.17). , 13] octasiloxane-1-yloxy) dimethylsilyl) ethylstyrene, 3-((3,5,7,9,11,13,15-heptaisobutylpentacyclo [9.5.1.13, 9.15). , 15.17,13] octasiloxane-1-yloxy) dimethylsilyl) ethylstyrene, 3-((3,5,7,9,11,13,15-heptaisooctylpentacyclo [9.5.1. 13,9.15,15.17,13] octasiloxane-1-yloxy) dimethylsilyl) ethylstyrene, 3-((3,5,7,9,11,13,15-heptacyclopentylpenta) Chro [9.5.1.13, 9.15, 15.17,13] octasiloxane-1-yloxy) dimethylsilyl) ethylstyrene and 3-((3,5,7,9,11,13,15) -Heptaphenylpentacyclo [9.5.1.13, 9.15, 15.17,13] octasiloxane-1-yloxy) dimethylsilyl) ethylstyrene and the like.

  Furthermore, examples of the monofunctional monomer having one addition polymerizable double bond include fluorine-containing vinyl monomers (perfluoroethylene, perfluoropropylene, vinylidene fluoride, etc.), silicon-containing vinyl monomers (vinyltrimethoxysilane). , Vinyltriethoxysilane, etc.), maleic anhydride, maleic acid, monoalkyl and dialkyl esters of maleic acid, fumaric acid, monoalkyl and dialkyl esters of fumaric acid, maleimide monomers (maleimide, methylmaleimide, ethylmaleimide, Propylmaleimide, butylmaleimide, hexylmaleimide, octylmaleimide, dodecylmaleimide, stearylmaleimide, phenylmaleimide, cyclohexylmaleimide), nitrile group-containing Nomers (such as acrylonitrile and methacrylonitrile), amide group-containing monomers (such as acrylamide and methacrylamide), vinyl ester monomers (such as vinyl acetate, vinyl propionate, vinyl pivalate, vinyl benzoate, and vinyl cinnamate), olefins (Ethylene, propylene, etc.), conjugated diene monomers (butadiene, isoprene, etc.), vinyl halides (vinyl chloride, etc.), vinylidene halides (vinylidene chloride, etc.), allyl halides (eg, allyl chloride), allyl alcohol, vinylpyrrolidone Vinyl pyridine, N-vinyl carbazole, methyl vinyl ketone and vinyl isocyanate. Furthermore, a macromonomer having one polymerizable double bond in one molecule and having a main chain derived from styrene, (meth) acrylic acid ester, siloxane or the like can be mentioned.

Examples of the hydrophobic monomer include acrylic acid esters (eg, alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, cyclohexyl acrylate, and hexafluoroisopropyl acrylate); aryl acrylates such as phenyl acrylate; benzyl acrylate Arylalkyl acrylates such as; alkoxyalkyl acrylates such as methoxymethyl acrylate), methacrylic acid esters (eg, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, alkyl esters of methacrylic acid such as hexafluoroisopropyl methacrylate; Such as phenyl methacrylate Reel methacrylate; arylalkyl methacrylate such as benzyl methacrylate; alkoxyalkyl methacrylate such as methoxymethyl methacrylate), fumaric acid ester (eg, alkyl ester of fumaric acid such as dimethyl fumarate, diethyl fumarate, diallyl fumarate, etc.), malee Acid esters (eg, alkyl esters of maleic acid such as dimethyl maleate, diethyl maleate, diallyl maleate), itaconic acid esters (eg, alkyl esters of itaconic acid), crotonic acid esters (eg, alkyl of crotonic acid) Esters), methyl vinyl ether, ethoxyethyl vinyl ether, vinyl acetate, vinyl propionate, vinyl benzoate, styrene, alkyl styrene, vinyl chloride Vinyl methyl ketone, vinyl stearate, vinyl alkyl ethers, and mixtures thereof, and the like.
Examples of hydrophilic monomers include hydroxy-substituted alkyl acrylates (eg, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl acrylate, 2,3-dihydroxypropyl acrylate, polyethoxyethyl acrylate, polyethoxypropyl acrylate). Etc.), hydroxy-substituted alkyl methacrylates (eg 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxypropyl methacrylate, 2,3-dihydroxypropyl methacrylate, polyethoxyethyl methacrylate, polyethoxypropyl methacrylate, etc.), acrylamide, N-alkyl acrylamide (eg, N-methyl acrylamide, N, N-dimethyl acryl N-alkyl methacrylamide (eg, N-methyl methacrylamide), polyethylene glycol monoacrylate, polyethylene glycol monomethacrylate, alkoxy polyethylene glycol acrylate, alkoxy polyethylene glycol methacrylate, phenoxy polyethylene glycol acrylate, phenoxy polyethylene glycol methacrylate, 2-glucosyloxyethyl methacrylate, acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, crotonic acid, methacrylamide, allyl alcohol, N-vinylpyrrolidone and N, N-dimethylaminoethyl acrylate, and mixtures thereof can give.

  In addition, monomers having a specific group in the side chain as described in, for example, JP-A No. 2003-327638 can be suitably used. For example, a monomer having a group easily convertible to a carboxyl group or a carboxyl base in the side chain can be rendered hydrophilic by converting the side chain of the polymer to a carboxyl group or a carboxyl base after the polymer has been prepared. It is preferable in that it can be performed (see, for example, JP-A-2003-327638). Examples of the monomer having a carboxyl group or a group that can be easily converted into a carboxyl base in the side chain include 1-methoxyethyl acrylate, 1-ethoxyethyl acrylate, 1-propoxyethyl acrylate, 1- (1-methylethoxy) ethyl acrylate. 1-butoxyethyl acrylate, 1- (2-methylpropoxy) ethyl acrylate, 1- (2-ethylhexoxy) ethyl acrylate, pyranyl acrylate, 1-methoxyethyl methacrylate, 1-ethoxyethyl methacrylate, 1-propoxyethyl Methotrete, 1- (1-methylethoxy) ethyl methacrylate, 1-butoxyethyl methacrylate, 1- (2-methylpropoxy) ethyl methacrylate, 1- (2-ethylhexoxy) ethyl methacrylate, Ranyl methacrylate, di-1-methoxyethyl maleate, di-1-ethoxyethyl maleate, di-1-propoxyethyl maleate, di-1- (1-methylethoxy) ethyl maleate, di-1-butoxyethyl Examples thereof include malate, di-1- (2-methylpropoxy) ethyl malate, and dipyranyl malate.

The lubricant of the present invention can achieve high lubricity without using the electric field effect by using a surface grafted with polymer chains at a high graft density. For example, poly (methyl methacrylate) ( Non-electrolyte polymers such as PMMA) can also be suitably used.
When the lubricant of the present invention is used for lubrication of articles used in vivo, for example, micromachines or artificial joints having a manipulating function at the tip of a catheter used during surgery, nonspecific adsorption of proteins and the like is suppressed. Therefore, it is preferably a hydrophilic polymer.

(2) Polymer chain grafting method The polymer chain grafting method is not particularly limited as long as the polymer chain can be grafted at a desired graft density. For example, a grafting-from method, a grafting-onto method, or the like can be used, but a grafting-from method is preferable. In addition, the hydrophobic part of a polymer chain (for example, PMMA-b-PSGMA) which is a hydrophobic-hydrophilic diblock copolymer is adhered to the surface of a hydrophobic or hydrophobicized substrate. (See, for example, Nature, 425, 163-165 (2003)).
The polymer chain polymerization method is not particularly limited as long as the polymer chain can be polymerized at a desired graft density, and a radical polymerization method is preferable. For radical polymerization, various copolymers (eg, random copolymers, block copolymers, composition gradient copolymers, etc.) that are easy to control the molecular weight and molecular weight distribution of the polymer chains to be grafted can be used. Further, a living radical polymerization (LRP) method is preferred in that it is easy to graft. As the living radical polymerization method, an atom transfer radical polymerization (ATRP) method is more preferable (for example, J. Am. Chem. Soc., 117, 5614 (1995), Macromolecules, 28, 7901 (1995), Science, 272, 866 (1996), Macromolecules, 31, 5934-5936 (1998)).
As the polymer chain grafting method, a grafting method using living radical polymerization (for example, see JP-A Nos. 11-263819 and 2002-145971) is preferable.

The catalyst used for radical polymerization is not particularly limited as long as it can catalyze radical polymerization, but a transition metal complex is preferable. Preferable examples of the transition metal complex are metal complexes having a group metal of Group 7, 8, 9, 9, 10, or 11 of the periodic table as a central metal. Further preferred catalysts are zero-valent copper, monovalent copper, divalent ruthenium, divalent iron or divalent nickel complex. Of these, a copper complex is preferable. Examples of the monovalent copper compound are cuprous chloride, cuprous bromide, cuprous iodide, cuprous cyanide, cuprous oxide, and cuprous perchlorate.
When using a copper compound, it is preferable to add a ligand in order to increase the catalytic activity. Examples of the ligand include 2,2′-bipyridyl or a derivative thereof, 1,10-phenanthroline or a derivative thereof, polyamine (tetramethylethylenediamine, pentamethyldiethylenetriamine, hexamethyltris (2-aminoethyl) amine, etc.), And polycyclic alkaloids such as L-(−)-spartein.
A tristriphenylphosphine complex of divalent ruthenium chloride (RuCl ₂ (PPh ₃ ) ₃ ) is also suitable as a catalyst. When a ruthenium compound is used as a catalyst, it is preferable to add an aluminum alkoxide as an activator.
Furthermore, a divalent iron bistriphenylphosphine complex (FeCl ₂ (PPh ₃ ) ₂ ), a divalent nickel bistriphenylphosphine complex (NiCl ₂ (PPh ₃ ) ₂ ), a divalent nickel bistributylphosphine complex ( NiBr ₂ (PBu ₃ ) ₂ ) and the like are also suitable as the catalyst.
A solvent may be used for the polymerization reaction. Examples of solvents used include hydrocarbon solvents (benzene, toluene, etc.), ether solvents (diethyl ether, tetrahydrofuran, diphenyl ether, anisole, dimethoxybenzene, etc.), halogenated hydrocarbon solvents (methylene chloride, chloroform, chlorobenzene, etc.) ), Ketone solvents (acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.), alcohol solvents (methanol, ethanol, propanol, isopropanol, butyl alcohol, t-butyl alcohol, etc.), nitrile solvents (acetonitrile, propionitrile, benzonitrile) Etc.), ester solvents (ethyl acetate, butyl acetate, etc.), carbonate solvents (ethylene carbonate, propylene carbonate, etc.), amide solvents (N, N-dimethyl) Lumamide, N, N-dimethylacetamide), hydrochlorofluorocarbon solvents (HCFC-141b, HCFC-225), hydrofluorocarbon (HFCs) solvents (HFCs having 2 to 4, 5 and 6 or more carbon atoms), perfluorocarbons Solvents (perfluoropentane, perfluorohexane), alicyclic hydrofluorocarbon solvents (fluorocyclopentane, fluorocyclobutane), oxygen-containing fluorine solvents (fluoroether, fluoropolyether, fluoroketone, fluoroalcohol), water and the like. These may be used alone or in combination of two or more. Polymerization can also be performed in an emulsion system or a system using supercritical fluid CO ₂ as a medium. In addition, the solvent which can be used is not restrict | limited to these examples.

When using a graft from method as a polymer chain grafting method, a polymerization initiating group must be present on the surface of the substrate. The polymerization initiating group is not particularly limited as long as it can initiate polymerization, but is preferably a halogenated alkyl group, a halogenated sulfonyl group, more preferably a halogenated sulfonyl group, and even more preferably a chlorosulfonyl group. The polymerization initiating group is physically or chemically bonded to the substrate surface in terms of controllability of the graft density and the primary structure of the grafted polymer chain (molecular weight, molecular weight distribution, monomer arrangement pattern). preferable. The method for introducing (bonding) the polymerization initiating group to the substrate surface is not particularly limited, and can be performed by a chemical adsorption method, a Langmuir-Blodget (LB) method, or the like. For example, immobilization of a chlorosulfonyl group (polymerization initiating group) on the surface of a silicon wafer (base material) by chemical bonding is performed by 2- (4-chlorosulfonylphenyl) ethyltrimethoxysilane or 2- (4-chlorosulfonylphenyl) This can be performed by reacting ethyltrichlorosilane or the like with an oxide layer on the surface of the silicon wafer. Specifically, the introduction of the polymerization initiating group onto the surface of the substrate can be carried out according to the methods described in, for example, JP-A Nos. 11-263819 and 2002-145971. The introduction of the polymerization initiating group on the surface of the base material is based on the Langmuir-Blodget (LB) method in terms of uniformity of the introduced polymerization initiating group and controllability of the graft density of the polymerization initiating group. Is preferred.
In the LB method, first, the film forming material is dissolved in an appropriate solvent (eg, chloroform, benzene, etc.). Next, after a small amount of this solution is developed on a clean liquid surface, preferably on the surface of pure water, the solvent is evaporated or diffused into the adjacent aqueous phase to form a low-density film-forming molecule on the water surface. A film is formed. Subsequently, usually the partition plate is mechanically swept over the water surface, and the membrane is compressed by increasing the density by reducing the surface area of the water surface on which the film-forming molecules are deployed. Get. Next, under appropriate conditions, the substrate on which the monomolecular layer is deposited is immersed or pulled in a direction crossing the monomolecular film on the water surface while keeping the surface density of the molecules constituting the monomolecular film on the water surface constant. Thus, the monomolecular film on the water surface is transferred onto the substrate, and a monomolecular layer is deposited on the substrate. Details and specific examples of the LB method are as follows: “Fukuda Kiyonari et al., New Experimental Chemistry Lecture Volume 18 (Interface and Colloid) Chapter 6, (1977) Maruzen”, “Fukuda Kiyonari, Sugi Michio, Sparrow Section Hiroyuki, LB Membrane and Electronics, (1986) CMC "or" Ishii Ikuo, Practical Techniques for Making Good LB Films, (1989) Kyoritsu Shuppan ".

(3) Graft density of polymer chain The graft density of the polymer chain may be a graft density that exhibits high lubricity even in an environment where the electric field effect is inhibited, and is appropriately determined depending on the type of polymer or solvent used. Although it may be set, it is usually 0.1 chain / nm ² or more. Preferably, 0.15 chain / nm ² or more, more preferably 0.2 chain / nm ² or more, more preferably 0.3 chain / nm ² or more, particularly preferably 0.4 chain / nm ² or more, most preferably Is 0.45 chain / nm ² or more.
In view of ease of grafting of polymer chains, etc., preferably 5 chains / nm ² or less, more preferably 2 chains / nm ² or less, further preferably 1.5 chains / nm ² or less, particularly preferably. 1 chain / nm ² or less, most preferably 0.8 chain / nm ² or less.

The graft density of the polymer chain can be measured according to a known method. For example, Macromolecules, 31, 5934-5936 (1998), Macromolecules, 33, 5608-5612 (2000), Macromolecules, 38, 2137-2142 (2005 ) And the like.
Specifically, the graft density (chain / nm ² ) is determined by measuring the graft amount (W) and the number average molecular weight (M _n ) of the graft chain, using the following formula:
Graft density (chain / nm ² ) = W (g / nm ² ) / M _n × (Avocado number)
(Wherein, W represents the graft amount, and M _n represents the number average molecular weight.)
Can be obtained.
When the base material is a flat substrate such as a silicon wafer, the graft amount (W) is measured by measuring the film thickness in the dry state by the ellipsometry method, that is, the thickness of the grafted polymer chain layer in the dry state. It can be determined by calculating the graft amount per unit area using the density of the film. When the substrate is silica particles or the like, it can be measured by infrared absorption spectroscopy (IR), thermogravimetric loss measurement (TG), elemental analysis measurement, or the like.
The number average molecular weight (M _n), since the M _n of free polymer produced in the solution at the time of polymerization is approximately equal to the M _n of the graft chain may be used M _n of free polymer produced in solution during polymerization. Further, when the substrate is silica, _Mn and _Mw / _Mn can be determined by gel permeation chromatography (GPC) method after cutting the graft chain from the graft point using a hydrofluoric acid solution. . In addition, it has confirmed that these values are substantially equal to the value of the free polymer produced | generated in a solution.
Moreover, it can measure according to the method of Unexamined-Japanese-Patent No. 11-263819, the method of Unexamined-Japanese-Patent No. 2002-145971, the method of Nature, 425, 163 (2003) etc., for example. Specifically, the slope of a graph plotting the thickness of the grafted polymer chain layer in the dry state and the number average molecular weight of the polymer chain (see, for example, JP-A-11-263819), the grafted polymer The graft density of the polymer chain can be determined from the slope of the graph plotting the graft amount of the chain and the number average molecular weight of the polymer chain (for example, see JP-A-2002-145971).

(4) Molecular Weight and Molecular Weight Distribution of Polymer Chain The number average molecular weight (M _n ) of the polymer chain of the present invention may be any molecular weight that exhibits the desired lubricity, but is preferably about 500 to 1,000,000. 000, more preferably about 1000 to 100,000. The molecular weight distribution index (M _w / M _n ) may be any molecular weight distribution index exhibiting desired lubricity, but is preferably about 1.01 to 2.0, more preferably about 1.01 to 1.01. 1.5.

(5) Base material used in the present invention The base material used in the present invention may be any base material that can be used for polymer chain grafting by the above-described graft-from method, graft-on-to method, etc. , Organic material, inorganic material, metal material and the like can be appropriately selected, and there is no particular limitation. Either a hydrophobic substrate or a hydrophilic substrate can be suitably used.
The substrate is preferably a solid, but a substrate such as a cross-linked hydrogel can also be suitably used. Solids used as the substrate include polyurethane materials, polyvinyl chloride materials, polystyrene materials, polyolefin materials, PMMA, PET, cellulose acetate, silica, inorganic glass, paper, plastic laminate films, ceramics (eg, alumina) Ceramics, bioceramics, composite ceramics such as zirconia-alumina composite ceramics, etc.), metal (eg, aluminum, zinc, copper, titanium, etc.), metal-deposited paper, silicon, silicon oxide, silicon nitride, polycrystalline silicon, And composite materials thereof. In addition, materials used for artificial joints can also be suitably used.

Examples of the hydrophobic organic material used as the base material include polyolefins (eg, polyethylene, polypropylene, polyisobutylene, ethylene alpha olefin copolymer), silicon polymers, acrylic polymers (eg, polyacrylonitrile, Polymethyl methacrylate, polyethylene methacrylate, polyethyl acrylate, polyester acrylate, polyester methacrylate, etc.) and copolymers, fluoropolymers (eg, polytetrafluoroethylene, chlorotrifluoroethylene, fluorinated ethylene-propylene, polyvinyl fluoride, etc.), vinyl Polymer (eg, polyvinyl chloride, polyvinyl methyl ether, polystyrene, polyvinyl acetate, polyvinyl ketone, etc.), vinyl monomer-containing copolymer (eg, ABS, etc.), natural and synthetic rubber (eg, latex rubber, butadiene-styrene copolymer, polyisoprene, polybutadiene, butadiene-acrylonitrile copolymer, polychloroprene polymer, polyisobutylene rubber, ethylene-propylene diene copolymer, Polyisobutylene-isoprene, etc.), polyurethane (eg, polyether urethane, polyester urethane, polycarbonate urethane, polysiloxane urethane, etc.), polyamide (eg, nylon 6, nylon 66, nylon 10, nylon 11, etc.), polyester, epoxy Examples thereof include a polymer, cellulose, and modified cellulose.
Further, hydrophilic organic materials used as the substrate include hydrophilic acrylic polymers (eg, polyacrylamide, poly-2-hydroxyethyl acrylate, poly-N, N′-dimethylacrylamide, polyacrylic acid, polymethacrylic acid). Acid), hydrophilic vinyl polymers (eg, poly-N-vinyl pyrrolidone, polyvinyl pyridine, etc.), polymaleic acid, poly-2-hydroxyethyl fumarate, maleic anhydride, polyvinyl alcohol and the like.

  The substrate may be in any form or shape, such as a tube, sheet, fiber, strip, film, plate, foil, membrane, pellet, powder, molded product (eg, extrusion molded product, cast molded product, etc.) Also good. Examples of the material include polyurethane, polyvinyl chloride, polystyrene, polycarbonate, PMMA, PET, cellulose acetate, silica, inorganic glass, aluminum, copper, silicon, and silicon oxide.

(6) Production of Lubricant Having Surface Grafted with Polymer Chain The lubricant of the present invention can be produced, for example, by grafting a polymer chain onto the surface of a sheet-like substrate. The obtained sheet-like lubricant is a known method such as adhesion or welding to a place where lubrication is required (for example, a sliding part) such as an article (for example, a micromachine or an artificial joint) that requires lubrication. It can be fixed and used.
Further, the lubricant of the present invention requires lubrication by grafting a polymer chain on the surface of a member where lubrication is required, such as an article requiring lubrication, on the surface thereof. You may produce on the surface of a place. In this way, it is preferable to produce the lubricant on the surface where lubrication is required because the step of fixing the lubricant is unnecessary.
The surface on which the polymer chain used in the lubricant of the present invention is grafted is, for example, JP-A Nos. 11-263819, 2002-145971, 2003-327638, and 2003-2003. It can also be produced according to the method described in Japanese Patent No. 327641.

(7) Friction coefficient (μ) of the lubricant of the present invention
The friction coefficient (μ) of the lubricant of the present invention can be measured using an atomic force microscope (AFM) as described in the examples described later.
Specifically, the lubricant of the present invention was formed on the surface of a probe such as a silicon wafer and silica particles (radius R), the probe was adhered to the cantilever, and the polymer chain was swollen with a good solvent. Measure in state. From the cantilever shear coefficient (G), the cantilever width (W), the cantilever thickness (T), and the cantilever length (L), the following formula:
k _L = GWT ³ / 3L
Thus, the torsion spring constant k _L of the cantilever is calculated (see Adv Colloid Interface Sci, 27, 189 (1987)).
The vertical force (F _N , normal force) is:
F _N = k _N Δz
(Where Δz represents the vertical displacement of the cantilever).
The cantilever angle (twist) displacement (θ _L ) is calculated by reciprocating the probe (silica particles) at a constant speed in the y direction with a load applied on the sample substrate (silicon wafer) with a constant vertical force. Then, it can be measured by sliding.
And the horizontal force (F _L , lateral force), that is, the frictional force, using these measured values, the following formula:
F _L = k _L θ _L / R
The friction coefficient (μ) can be obtained from the relationship between the obtained vertical force (F _N ) and horizontal force (F _L , lateral force).
The friction coefficient (μ) of the lubricant of the present invention is preferably less than 0.05, more preferably less than 10 ⁻² , and even more preferably less than 10 ⁻³ .

2. Articles comprising a lubricant having a surface grafted with polymer chains The present invention also relates to articles comprising a lubricant having a surface grafted with polymer chains.
The article containing a lubricant having a surface grafted with a polymer chain is not particularly limited as long as it contains the lubricant of the present invention. For example, a micromachine (eg, a manipulating function at the tip of a catheter used during surgery) Etc.), medical articles (eg, artificial joints, vials and stoppers thereof, syringes, etc.).
An article including a lubricant having a surface grafted with a polymer chain of the present invention has the lubricant of the present invention on both sliding surfaces where lubrication is required (for example, a sliding portion). Is preferred.
The article including the lubricant having the surface grafted with the polymer chain of the present invention needs to lubricate, for example, a sheet-like lubricant of the present invention, and an article requiring lubrication (for example, a micromachine, an artificial joint, etc.). It can be manufactured by fixing to a place (for example, a sliding part) by a known method such as adhesion or welding. Further, the material of the place where lubrication is required is used as a base material, a polymer chain is grafted on the surface thereof, and the lubricant of the present invention is formed on the surface where lubrication is required. Can also be manufactured. Thus, it is preferable to produce a lubricant on the surface of a place where lubrication is required for an article that requires lubrication because a step of fixing the lubricant is unnecessary.

The lubricant of the present invention exhibits good lubricity by swelling the polymer chain grafted with a solvent. In the lubricant of the present invention, since the polymer chains are grafted at a high graft density, the polymer chains are stretched by swelling with a solvent, and preferably are highly stretched to be comparable to a stretched chain. . When the polymer chain of the present invention is swollen with a solvent, it is considered that a large load can be supported by a large osmotic pressure effect due to the concentrated solution system of the swollen polymer chain layer. Also, in the contact area, the grafted polymer chains do not interpenetrate and suppress entanglement by eliminating the increase in local concentration and the large entropy gain (obtained due to the high stretch state). It is considered that low friction characteristics are developed.
The lubricant of the present invention is preferably used in a solvent that can swell or extend the polymer chain because the low-friction characteristic is exhibited by the extension of the polymer chain in the solvent. As the solvent capable of swelling or extending the polymer chain, a good solvent is preferable.
The good solvent varies depending on the grafted polymer chain, and may be appropriately selected according to the polymer chain. For example, when a polymer chain of PMMA is grafted, examples of the good solvent include nonpolar solvents such as toluene. When a PHEMA polymer chain is grafted, examples of the good solvent include polar solvents such as methanol. In general, when the hydrophilic polymer chain is grafted, the good solvent includes an aqueous solvent containing water. Examples of the aqueous solvent include body fluids of animals including humans. That is, when a hydrophilic polymer chain is grafted, it is preferable to use a body fluid of an animal including a human as a good solvent, so that low friction characteristics can be expressed. It can be suitably used for lubrication of micromachines and artificial joints used in vivo.
In the lubricant of the present invention, since the polymer chains are grafted at a high graft density, low friction characteristics are exhibited without using the side chain electric field effect. Therefore, either a solvent that inhibits the side chain field effect or a solvent that does not inhibit the side chain field effect may be used.

  As described above, since the lubricant of the present invention exhibits low friction characteristics in a good solvent, the lubricant of the present invention is fixed or produced on both the sliding surface where lubrication is required, and the lubricant The sliding surface or the like can be lubricated by swelling or stretching the polymer chain grafted on the surface with a good solvent.

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto.
Example 1
Grafting of poly (methyl methacrylate) (PMMA) chain onto a silicon wafer and probe silica particles (radius R = 5 μm) 2- (4-chlorosulfonylphenyl) ethyltrimethoxysilane (CETS) on the water surface using chloroform solvent Developed on (pH 5-6). Thereafter, the mixture was kept for 30 minutes to evaporate the chloroform solvent and hydrolyze the methoxysilyl group. Subsequently, one layer was accumulated on the silicon wafer by a vertical pulling method at a surface pressure of 10 mN / m. After accumulation, it was fixed on the substrate by heat treatment at 110 ° C. for 10 minutes.
Polymerization of methyl methacrylate (MMA) was performed using the obtained single molecule-immobilized silicon wafer. The polymerization of MMA was performed by a grafting-from method using an atom transfer radical polymerization (ATRP) method which is a kind of a living radical polymerization (LRP) method. ATRP polymerization is performed by adding 4-toluenesulfonyl chloride (TsCl) and MMA to diphenyl ether (DPE) containing CuBr and 4,4′-di-heptyl-2,2′-bipyridine (dHbipy) under vacuum deaeration ([[ CuBr] = 0.010M, [dHbipy] = 0.020M, [TsCl] = 0.024M, [MMA] = 4.7M), and the substrate was immersed in this at 90 ° C. for a predetermined time.
The molecular characteristics of the graft chain (PMMA chain) are considered to be in good agreement with the molecular characteristics of the PMMA homopolymer formed simultaneously from the free (unbound) polymerization initiator added in the polymerization solution. Therefore, the measured value of the PMMA homopolymer simultaneously generated in the polymerization solution was used as the molecular weight of the graft chain (number average molecular weight (Mn) and weight average molecular weight (Mw)). The molecular weight and molecular weight distribution of the polymethyl methacrylate (PMMA) homopolymer produced in the polymerization solution were determined by a gel permeation chromatograph (GPC) method calibrated with PMMA. The dry thickness (Ld) of the PMMA chain layer grafted on the silicon wafer was determined by spectroscopic ellipsometry (M-2000U, JA Woollam, USA). The graft density (σ) was determined from the thickness (Ld) and the number average molecular weight (Mn) of the graft chain layer.
Table 1 shows the molecular characteristics of the obtained graft chains. As shown in Table 1, the graft density was 0.53 chain / nm ² .
Grafting of PMMA chains onto probe silica particles (radius R = 5 μm) was performed in the same manner as the above silicon wafer.

Comparative Example 1
Grafting with low graft density of poly (methyl methacrylate) chains on silicon wafer and probe silica particles (radius R = 5 μm) Grafting with low graft density of PMMA chains on silicon wafer and probe silica particles is (2 -Bromo-2-methyl) propionyloxypropyltriethoxysilane (BPE) was used as a free initiator to synthesize poly (methyl methacrylate) (PMMA) having a terminal alkoxysilyl group from MMA by ATRP method, This was done by the grafting-to method of reacting with the wafer and probe silica particles.
Table 1 shows the molecular characteristics of the obtained graft chains. As shown in Table 1, the graft density was 0.024 chain / nm ² .

Example 2
Measurement of frictional properties of a lubricant having a surface grafted with a polymer chain by an atomic force microscope (AFM) between a silicon wafer having a surface grafted with a polymer chain obtained in Example 1 and probe silica particles The interaction force was measured using an atomic force microscope (AFM) (FIG. 1). The measurement was performed in toluene. The probe silica particles were used by adhering to a silicon nitride cantilever (Olympus, OMCL-RC800, flexible spring constant K _N = 0.1 N / m). The torsion spring constant k _L is:
k _L = GWT ³ / 3L
(In the formula, G represents the shear coefficient of the cantilever, W represents the width of the cantilever, T represents the thickness of the cantilever, and L represents the length of the cantilever.)
Calculated as 20 N / m (see Adv Colloid Interface Sci, 27, 189 (1987)).
The vertical force (F _N , normal force) is:
F _N = k _N Δz
(Where Δz represents the vertical displacement of the cantilever). The vertical force profile was determined by measuring the vertical force (F _N , normal force) as a function of separation. The measured normal force (F _N ) can be reduced to the free energy of interaction (G _f ) between two parallel planes according to the Derjaguin approximation (F / R = 2πG _f ).
The horizontal (friction) force (F _L , lateral force) is:
F _L = k _L θ _L / R
(In the formula, θ _L represents the angular (twist) displacement of the cantilever). θ _L was measured by sliding the probe silica particles back and forth at 20 μm / s in the y direction in a state where a load was applied with a constant vertical force on the sample substrate (silicon wafer).
For comparison, the friction characteristics of a lubricant having a surface grafted with the polymer chain obtained in Comparative Example 1 at a low graft density were also measured in the same manner as described above.
FIG. 2 shows the relationship between the horizontal (friction) force (F _L ) and the vertical force (F _N ) (load). In a wide load load (F _N ) range, the lubricant having the surface grafted with the polymer chain of the present invention is compared with the lubricant having the surface grafted with the polymer chain of Comparative Example 1 at a low graft density. The frictional force (F _L ) was overwhelmingly small. The coefficient of friction (μ) was almost constant within the range of experimental error, irrespective of the applied load, and was estimated to be less than 10 ⁻³ .

Example 3
Measurement of rebound characteristics of a lubricant having a surface grafted with a polymer chain by an atomic force microscope (AFM) The silicon wafer grafted with the polymer chain obtained in Example 1 was grafted with the polymer chain. The vertical force (with no horizontal displacement applied) when compressed with no probe silica particles (radius R = 5 μm) was measured. Similarly, measurement was also performed on a silicon wafer in which the polymer chain obtained in Comparative Example 1 was grafted at a low graft density. The measurement results are shown in FIG. Although it is usually difficult to measure the true distance between the substrate surface and the silica probe, in this example, the portion of the sample surface where the polymer chains were scraped and the portion that was not scraped off. The true distance is accurately measured by AFM-imaging across the boundary. The equilibrium swelling thickness (L _e ) of the polymer chain layer was determined from the limit distance at which repulsive force was observed.
Lubricant having a surface on which the polymer chains of the first embodiment is grafted, is also resistant to compression in the F / R> 1mN / m or more, was only compressed to D / L _e is approximately 0.7. In contrast, the lubricant having a surface grafted with the polymer chain of Comparative Example 1 with a low graft density was compressed to D / L _e <0.2 at F / R> 1 mN / m or more.
Such a strong resistance to compression of the lubricant having the surface grafted with the polymer chain of the present invention is an important property as a lubricant used under a large load.

Example 4
Grafting of poly (2-hydroxyethyl methacrylate) (PHEMA) chains onto silicon wafers and probe silica particles (radius R = 5 μm) and measurement of friction properties In the same manner as in Example 1, poly (2-hydroxy methacrylate) An ethyl) (PHEMA) chain grafted silicon wafer and probe silica particles were prepared.
When the graft density was measured, it was 0.6 chain / nm ² .
When the friction characteristics in methanol (good solvent) between the obtained silicon wafer having the surface grafted with the polymer chain and the probe silica particles were measured, the silicon wafer and probe silica obtained in Example 1 were measured. It was confirmed to show the same low friction characteristics as the particles.

  Since the lubricant of the present invention has a surface in which polymer chains are grafted at a high graft density, it can be used as a lubricant exhibiting high lubricity even in an environment where the electric field effect is inhibited. In addition, since the surface on which polymer chains are grafted with a high graft density shows high load resistance, it is possible to provide a lubricant with less deformation due to load, and it can be used as a lubricant for micromachines that require high precision. can do. In addition, the lubricant of the present invention exhibits low friction characteristics when the thickness of the polymer chain layer is on the order of 10 to 100 nm, and is less deformed by load. It is also effective as a lubricant for moving parts. Furthermore, since a lubricant having a surface grafted with a hydrophilic polymer chain or the like is expected to have biocompatibility, it can be used as a lubricant lubricant for devices used in vivo such as artificial joints. .

It is the figure illustrated about the measurement of the friction characteristic by an atomic force microscope (AFM). It is a figure which shows the measurement result of a friction characteristic. It is a figure which shows the measurement result of a resilience characteristic.

Claims (19)

A lubricant comprising a surface grafted with polymer chains at a graft density of 0.1 chain / nm ² or more. The lubricant according to claim 1, wherein the graft density is 0.15 chain / nm ² or more. The lubricant according to claim ² , wherein the graft density is 0.2 to 2 chains / nm ² . The lubricant according to any one of claims 1 to 3, wherein the polymer chain graft is a polymer chain graft by a graft-from method or a graft-on-to method. The lubricant according to claim 4, wherein the polymer chain graft is a polymer chain graft by a graft-from method. The lubricant according to any one of claims 1 to 5, wherein the polymer chain graft is a polymer chain graft by radical polymerization. The lubricant according to claim 6, wherein the radical polymerization is living radical polymerization. The lubricant according to claim 7, wherein the living radical polymerization is atom transfer radical polymerization. The lubricant according to any one of claims 5 to 8, wherein the polymerization is initiated from a polymerization initiating group immobilized on the surface of the substrate by a Langmuir-Blodgett method or a chemical adsorption method. The lubricant according to claim 9, wherein the polymerization is initiated from a polymerization initiating group immobilized on the surface of the substrate by the Langmuir-Blodgett method. The lubricant according to any one of claims 5 to 10, wherein the polymerization initiating group is a halogenated alkyl group or a halogenated sulfonyl group. The lubricant according to claim 11, wherein the polymerization initiating group is a chlorosulfonyl group. The lubricant according to any one of claims 1 to 12, wherein the polymer chain is a homopolymerized polymer chain. The lubricant according to claim 13, wherein the homopolymerized polymer chain is poly (methyl methacrylate) or poly (2-hydroxyethyl methacrylate). Polymerization in which the graft density is 0.2-2 chains / nm ² , the polymer chain grafting is a polymer chain grafting by radical polymerization, and the polymerization is immobilized on the surface of the substrate by the Langmuir-Blodgett method A lubricant comprising a surface on which a polymer chain is grafted, wherein the polymer chain is a polymer chain that is initiated from an initiation group, the polymerization initiation group is a chlorosulfonyl group, and the polymer chain is homopolymerized. An article comprising the lubricant according to any one of claims 1 to 15. The article according to claim 16, wherein the surface on which the polymer chains are grafted is formed on the surface of a member of the article. The article according to claim 16 or 17, which is a medical article. The article according to claim 18, wherein the medical article is an artificial joint.

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