JP2021054904A - Copolymer, rubber composition, and tire - Google Patents

Abstract

To provide a copolymer excellent in the effect of reducing rolling resistance of a tire, and to provide a rubber composition and a tire containing the copolymer.SOLUTION: The copolymer of the present invention has, in the molecule, a polymer A containing at least butadiene as a constituent unit and a polymer B of a monomer b containing N-vinyl-2-pyrrolidone. The polymer A preferably contains polybutadiene or a modified polybutadiene. Since the copolymer of the present invention is excellent in the effect of reducing rolling resistance of a tire, the copolymer can be suitably used, for example, as an additive for rubber.SELECTED DRAWING: None

Description

The present invention relates to copolymers and rubber compositions and tires.

In recent years when the problem of global warming has been raised, the industrial world is actively making efforts to suppress the release of carbon dioxide into the atmosphere. For example, in the automobile industry, it is effective to improve the fuel efficiency of automobiles in order to reduce the amount of carbon dioxide emitted, and technological development for that purpose is being promoted all over the world. In particular, in automobiles, the rolling resistance of tires has a large effect on fuel efficiency. For example, it is said that improving the rolling resistance by 20% improves fuel efficiency by about 5%. Therefore, improving the performance of automobile tires is extremely important from the viewpoint of improving the fuel efficiency of automobiles.

From this point of view, in recent years, there has been an increasing demand for fuel-efficient tires, so-called eco-tires, in which the rolling resistance of the tire is reduced as compared with the conventional one. In general, eco-tires use silica together with carbon black as a reinforcing material to reduce rolling resistance. Recently, eco-tires have been proposed in which 100% silica is used instead of carbon material.

In a tire containing these silicas, it is important to disperse a reinforcing material such as silica more uniformly in the tire. In this regard, although it is common to improve the dispersibility of silica in a tire by using a silane coupling agent or the like, the dispersibility is often not sufficient yet. Therefore, for example, silica and carbon are uniformly dispersed by using an activator or the like in combination. In addition, various additives for improving the dispersibility of silica have also been studied. For example, in Patent Document 1, by adding an amino compound having a specific structure to a rubber composition, the dispersibility of silica in a tire is improved and the rolling resistance of the tire is reduced.

Japanese Unexamined Patent Publication No. 2013-87185

However, from the viewpoint of further improving fuel efficiency in recent years, it has been desired to further reduce the rolling resistance of the tire, and it has been difficult for the above-mentioned conventional rubber compositions and the like to meet the high demand.

For example, it is conceivable to use polyvinylpyrrolidone (PVP) having excellent silica dispersibility as a means for improving the dispersibility of silica, carbon and the like and improving the rolling resistance of the tire. However, since PVP has poor compatibility with rubber, it is not possible to exert a sufficient dispersion force of PVP in rubber, and on the contrary, the rolling resistance of the tire is deteriorated.

The present invention has been made in view of the above, and an object of the present invention is to provide a copolymer having an excellent effect of reducing rolling resistance of a tire, a rubber composition containing the copolymer, and a tire.

As a result of intensive research to achieve the above object, the present inventors have used a copolymer containing a polymer containing butadiene as a constituent unit and a poly (N-vinyl-2-pyrrolidone). It was found that the above object can be achieved, and the present invention has been completed.

That is, the present invention includes, for example, the subjects described in the following sections.
Item 1
A copolymer having at least a polymer A containing butadiene as a constituent unit and a polymer B of a monomer b containing N-vinyl-2-pyrrolidone in the molecule.
Item 2
Item 2. The copolymer according to Item 1, wherein the polymer A contains polybutadiene or modified polybutadiene.
Item 3
Item 3. The copolymer according to Item 1 or 2, which is a graft polymer in which the polymer A is a stem polymer and the polymer B is a branch polymer.
Item 4
Item 2. The copolymer according to any one of Items 1 to 3, which is used as an additive for rubber.
Item 5
A rubber composition containing at least the copolymer according to Item 4 and a diene-based rubber.
Item 6
A tire containing the rubber composition according to Item 5.

According to the copolymer of the present invention, the effect of reducing the rolling resistance of the tire is excellent, and therefore, for example, it can be suitably used as an additive for rubber.

Hereinafter, embodiments of the present invention will be described in detail. In addition, in this specification, the expressions "contains" and "includes" include the concepts of "contains", "includes", "substantially consists" and "consists of only".

1. 1. Copolymer The copolymer of the present invention has at least a polymer A containing butadiene as a constituent unit and a polymer B of a monomer b containing N-vinyl-2-pyrrolidone in its molecule. More specifically, the copolymer of the present invention is a copolymer of a moiety having polymer A as a unit and a moiety having polymer B as a unit. Hereinafter, the copolymer of the present invention will be referred to as "copolymer C" in the present specification. When the copolymer C is applied to a tire as an additive for rubber, for example, the rolling resistance of the tire can be reduced.

(Polymer A)
The copolymer C has the polymer A in the molecule. The polymer A is a polymer containing butadiene as a constituent unit.

The polymer A is not particularly limited as long as it contains butadiene as a constituent unit. For example, the polymer A can be a homopolymer of butadiene (ie, polybutadiene) or a modified polybutadiene. The modified polybutadiene is a polymer in which some butadiene units of the butadiene units are modified (modified) with a functional group or the like, or a structural unit in which some butadiene units contain a functional group (other than the butadiene structural unit). It means that it is a polymer replaced with (constituent unit of). Therefore, copolymers of butadiene and monomers other than butadiene are also included in the modified polybutadiene. A structural unit in which the butadiene unit is modified with a functional group or the like, or a structural unit containing a functional group (a structural unit other than the butadiene structural unit) may be referred to as a “modified butadiene unit”.

When the polymer A is modified polybutadiene, the type thereof is not particularly limited, and for example, known modified polybutadiene can be widely applied.

Specific examples of the modified polybutadiene include carboxy group-modified polybutadiene, epoxy-modified polybutadiene, hydroxyl group-modified polybutadiene, acrylic-modified polybutadiene, amino group-modified polybutadiene, and isocyanate group-modified polybutadiene. Examples of the carboxy group-modified polybutadiene include maleic acid-modified polybutadiene. Examples of the hydroxyl group-modified polybutadiene include polybutadiene glycol and polybutadiene having a hydroxyl group at the terminal. Examples of the acrylic-modified polybutadiene include polybutadiene glycol acrylate. Examples of the isocyanate group-modified polybutadiene include polybutadiene having an isocyanate group at the terminal.

As the polymer A, a copolymer having a butadiene skeleton such as a styrene-butadiene random copolymer can also be exemplified.

The polymer A preferably contains polybutadiene or modified polybutadiene, and particularly preferably contains modified polybutadiene. When the polymer A contains modified polybutadiene, for example, when the copolymer C is used as an additive for rubber, it has excellent affinity with the rubber component, so that it is easy to disperse when silica or the like is present in the rubber. , It is easy to increase the effect of reducing the rolling resistance of tires. Further, when the polymer A contains modified polybutadiene, it becomes easy to introduce the polymer B described later into the copolymer C, and it becomes easy to produce the copolymer C.

Among them, the modified polybutadiene is preferably a carboxy group-modified polybutadiene, and particularly preferably a maleic acid-modified polybutadiene. Among these, maleic acid-modified polybutadiene is, for example, a polymer composed of butadiene units and maleic acid units.

In the modified polybutadiene, the introduction ratio of the modified butadiene unit is not particularly limited. For example, from the viewpoint that the compatibility with rubber is not easily impaired, the introduction ratio of the modified butadiene unit is preferably 0.1 to 80% by weight, preferably 0.5 to 80% by weight, based on all the constituent units of the modified polybutadiene. More preferably, it is 70% by weight. In particular, when the modified polybutadiene is maleic acid-modified polybutadiene, the introduction ratio of the maleic acid unit is preferably 1 to 50% by weight, preferably 2 to 40% by weight, based on all the constituent units of the maleic acid-modified polybutadiene. More preferably, it is particularly preferably 3 to 30% by weight. The modified polybutadiene is not limited to a random polymer, a block polymer, etc., but is usually a random polymer.

The number average molecular weight of the polymer A is preferably 500,000 to 100,000, more preferably 1,000 to 50,000, and even more preferably 1,500 to 10,000, from the viewpoint of easily reducing rolling resistance. , 2000-8000 is particularly preferable. In the present specification, the number average molecular weight of the polymer A means a value measured by gel permeation chromatography (GPC). However, when the polymer A is a commercially available product or the like, the catalog value, the product guarantee value, or the like may be adopted as the number average molecular weight of the polymer A.

The polymer A may have other structural units in addition to the butadiene unit and the modified butadiene unit as long as the effect of the present invention is not impaired, or may be formed of only the butadiene unit and the modified butadiene unit. When the polymer A has other structural units, the content ratio of the other structural units is 5 mol% or less, preferably 1 mol% or less, more preferably 0.1, based on all the structural units of the polymer A. It can be less than or equal to mol%, particularly preferably not more than 0.05 mol%.

(Polymer B)
The copolymer C has the polymer B in the molecule. The polymer B is a polymer of the monomer b containing N-vinyl-2-pyrrolidone. N-vinyl-2-pyrrolidone is hereinafter abbreviated as "NVP".

The monomer b may be NVP alone, or may contain NVP and other polymerizable monomers. When the monomer b contains another polymerizable monomer, the content ratio of the other polymerizable monomer is 5% by mass or less, preferably 1% by mass or less, based on the total mass of the monomer b. More preferably, it can be 0.1% by mass or less, and particularly preferably 0.05% by mass or less.

When the monomer b is NVP only, the polymer B is a homopolymer of polyvinylpyrrolidone. On the other hand, when the monomer b contains a polymerizable monomer other than NVP, the polymer B is a copolymer of NVP and another polymerizable monomer, and in this case, usually, It is a random copolymer.

The number average molecular weight of the polymer B is preferably 10 to 1.5 million, more preferably 3000 to 800,000, and even more preferably 5000 to 500,000 from the viewpoint of easily reducing rolling resistance. It is particularly preferably 10,000 to 100,000. In the copolymer C, the above-mentioned range of the preferable number average molecular weight of the polymer A and the range of the preferable number average molecular weight of the polymer B can be arbitrarily combined.

(Copolymer C)
The copolymer C has a polymer A and a polymer B in the molecule. Specifically, in the copolymer C, the polymer A and the polymer B are bonded by a chemical bond (particularly a covalent bond) to form one molecule. Therefore, the copolymer C is a polymer compound having a block of the polymer A and a block of the polymer B. In this case, the block of the polymer A and the block of the polymer B can be directly chemically bonded, or another functional group can be interposed between the polymer A and the polymer B.

As a further specific example of the copolymer C, a graft polymer in which the polymer A is a stem polymer and the polymer B is a branch polymer can be mentioned. When the copolymer C forms such a graft polymer, the copolymer C has a particularly excellent affinity with the rubber component, and when silica or the like is present in the rubber, it is easier to disperse the silica, resulting in As a result, the effect of reducing the rolling resistance of the tire is particularly enhanced. Further, when the copolymer C is the graft polymer, the production of the copolymer C becomes easy. Above all, when the polymer A is modified polybutadiene, it is easy to produce the copolymer C which is a graft polymer.

When the copolymer C is a graft polymer, the polymer B, which is a branch polymer, may be grafted from any part of the polymer A, and its position is not limited. In particular, when the polymer A is modified polybutadiene, the polymer B is likely to be grafted from the main chain portion of the modified butadiene unit described above. Specifically, when the modified polybutadiene which is the polymer A has a maleic anhydride unit, the copolymer C has a structure in which the hydrogen of the carbon atom to which the carboxy group of the maleic anhydride is bonded is substituted with the polymer B. Can have.

Whether or not the copolymer C is a graft polymer ^{can be determined from, for example, 13} C-NMR measurement.

In the copolymer C, the content ratio of the polymer A and the polymer B is not particularly limited. For example, in the copolymer C, the content ratio of the polymer B can be 3 to 95% by mass with respect to the total mass of the polymer A and the polymer B. In this case, the affinity between the copolymer C and the rubber component is high, and when silica or the like is present in the rubber, the silica is easily dispersed, and the rolling resistance of the tire can be sufficiently reduced. it can. In the copolymer C, the content ratio of the polymer B is preferably 10% by mass or more, more preferably 20% by mass or more, and more preferably 30% by mass, based on the total mass of the polymer A and the polymer B. It is more preferably% or more, and particularly preferably 40% by mass or more. Further, in the copolymer C, the content ratio of the polymer B is preferably 90% by mass or less, more preferably 80% by mass or less, based on the total mass of the polymer A and the polymer B. It is more preferably 70% by mass or less, and particularly preferably 60% by mass or less.

When the copolymer C is used in a tire as an additive for rubber, the rolling resistance of the tire can be reduced, and the fuel efficiency of an automobile can be improved. In particular, since the copolymer C has a polymer A containing polybutadiene as a main component and a polymer B containing polyvinylpyrrolidone as a main component in the molecule, it is highly compatible with the rubber component and is silica. It also has excellent performance to disperse carbon and the like. Therefore, by using the copolymer C as an additive for tires and the like, the copolymer C can be uniformly present in the rubber, and the reinforcing material such as silica and carbon that may be contained in the tire is good. It is possible to further reduce the rolling resistance of the tire as compared with the conventional one.

2. Method for Producing Copolymer The method for producing the copolymer C is not particularly limited, and various production methods can be adopted. For example, the copolymer C can be obtained by a production method comprising a step of reacting the polymer A with a monomer b containing N-vinyl-2-pyrrolidone (NVP) in the presence of a polymerization initiator. Can be done. This step is abbreviated as "step 1" below.

The polymer A used in step 1 is the same as the polymer A. Therefore, the polymer A used in step 1 preferably contains modified polybutadiene, and more preferably contains maleic acid-modified polybutadiene. The polymer A can be used alone or in combination of two or more.

The polymer A used in step 1 can be obtained by a known method. Alternatively, the polymer A used in step 1 can also be obtained from a commercially available product or the like.

The monomer b used in step 1 is the same as the above-mentioned monomer b. Therefore, the monomer b may be NVP alone or may contain NVP and other polymerizable monomers. The method for producing the NVP contained in the monomer b is also not particularly limited, and for example, it can be obtained by a known method, or it can be obtained from a commercially available product or the like.

In step 1, the ratio of the polymer A and the NVP used is not particularly limited, and can be appropriately determined according to the chain lengths of the polymer A and the polymer B and the like. For example, the ratio of NVP used can be 3 to 95% by mass with respect to the total mass of the polymers A and NVP. In this case, the obtained copolymer C has a high affinity with the rubber component, and when silica or the like is present in the rubber, the silica is easily dispersed, and the effect of reducing the rolling resistance of the tire is sufficiently exhibited. be able to. The ratio of NVP used is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more, and more preferably 40% by mass, based on the total mass of the polymers A and NVP. It is particularly preferable that it is mass% or more. The proportion of NVP used is preferably 90% by mass or less, more preferably 80% by mass or less, and further preferably 70% by mass or less, based on the total mass of the polymers A and NVP. , 60% by mass or less is particularly preferable.

In step 1, the type of polymerization initiator is not particularly limited, and for example, known polymerization initiators can be widely used. Specific examples of the polymerization initiator include persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate; organic peroxides such as benzoyl peroxide and dicumyl peroxide lauroyl peroxide; 2'-azobis [2-( 2-Imidazolin-2-yl) Propane] Water-soluble azo compounds such as dihydrochloride, 2,2'-azobis (2-amidinopropane) dihydrochloride; 2,2'-azobis (2,4-dimethylbutyro) Nitrile), 2,2'-azobis (2-isopropylbutyronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile) and other water-insoluble azo compounds; Examples thereof include a redox initiator that uses hydrogen peroxide and the like. Among them, persulfate, organic peroxide and the like are preferable, and persulfate is particularly preferable, from the viewpoint that the polymer A has an excellent hydrogen abstraction ability and the polymerization reaction of the monomer b can easily proceed.

The amount of the polymerization initiator used is not particularly limited, and can be appropriately set according to the properties such as the half-life temperature of the polymerization initiator used. For example, the amount of the polymerization initiator used can be 0.01 to 15 parts by mass per 100 parts by mass of the total mass of the polymer A and the monomer b.

The reaction of step 1 can be carried out in a reaction solvent, if necessary. As the reaction solvent, water or various organic solvents can be used, for example, aliphatic hydrocarbons such as hexane and heptane; alicyclic hydrocarbons such as cyclohexane; ketone solvents such as acetone and methyl ethyl ketone; benzene and toluene. And aromatic hydrocarbons such as xylene; chlorine-based hydrocarbons such as chloroform and 1,2-dichloroethane; alcohols such as methanol, ethanol, isopropyl alcohol and t-butanol; nitrile compounds such as acetonitrile; and the like. The organic solvent can be used alone or as a mixture of two or more kinds.

In the reaction of step 1, the amount of the reaction solvent used is not particularly limited. For example, the amount of the reaction solvent used can be 50 to 800 parts by mass per 100 parts by mass of the total mass of the polymer A and the monomer b.

The reaction temperature in step 1 is not particularly limited, and can be appropriately set according to the properties such as the half-life temperature of the polymerization initiator used. For example, the reaction temperature in step 1 can be set to 40 to 230 ° C.

The method for reacting the polymer A with the monomer b containing N-vinyl-2-pyrrolidone (NVP) is not particularly limited, and a known method can be widely adopted. For example, a method of dropping a solution in which the polymerization initiator and the monomer b are dissolved in the solution of the polymer A can be adopted. In this case, the solvent type for preparing both solutions is not limited, and can be appropriately selected in consideration of solubility and the like. For example, it can be appropriately selected from the above-mentioned reaction solvents. The solvents of both solutions may be the same or different.

The reaction in step 1 may be carried out under atmospheric pressure, reduced pressure, or pressurized, and may be carried out in an atmosphere of an inert gas such as nitrogen, if necessary. There are no restrictions on the reaction vessel, reaction device, etc. used for the reaction.

By the reaction in step 1, for example, the polymerization of NVP proceeds starting from the polymer A, and a block polymer of the polymer A and polyvinylpyrrolidone (polymer B) can be produced. In particular, when the polymer A is a modified polybutadiene such as maleic acid-modified polybutadiene, polyvinylpyrrolidone (polymer B) easily grows from the main chain portion of the modified butadiene unit as described above, and as a result, the polymer A is produced. A graft polymer having a stem polymer and a polymer B as a branch polymer is likely to be formed. Therefore, when modified polybutadiene is used as the polymer A, the copolymer C having a graft structure can be easily obtained in step 1.

After the reaction in step 1 is completed, the desired copolymer C can be obtained by performing a purification treatment or the like by an appropriate means.

In addition, in step 1, not all polyvinylpyrrolidone (PVP) produced by polymerization is necessarily bonded (for example, grafted) to polymer A, and some of them may exist alone. The PVP produced as a by-product in this way may be removed by an appropriate method, or the copolymer C may be obtained in a state of being mixed in the target copolymer C.

3. 3. Rubber Composition The rubber composition of the present invention contains at least the above-mentioned copolymer C and a diene-based rubber. By containing the copolymer C, the rubber composition of the present invention can reduce the rolling resistance of the tire when the tire is formed.

The type of diene-based rubber is not particularly limited, and for example, known diene-based rubbers used for forming tires can be widely mentioned. For example, examples of the diene-based rubber include natural rubber and diene-based synthetic rubber. Examples of the diene-based synthetic rubber include polyisoprene rubber (IR), polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), butyl rubber (IIR), and ethylene-propylene copolymer. The diene-based rubber contained in the rubber composition may be one kind alone or two or more kinds.

The rubber composition can further contain silica as a reinforcing material. The type of silica is not particularly limited, and for example, silica used in known rubber compositions can be widely applied. For example, wet silica (hydrous silicic acid), dry silica (silicic anhydride), colloidal silica and the like can be mentioned, and wet silica is preferable.

The content of the copolymer C contained in the rubber composition is not particularly limited. For example, from the viewpoint that the effect of reducing the rolling resistance of the copolymer C is easily exhibited, the content of the copolymer C can be 0.1 to 30 parts by mass per 100 parts by mass of the diene rubber, and is 0.5. It is preferably ~ 20 parts by mass, more preferably 1 to 10 parts by mass, further preferably 2 to 8 parts by mass, and particularly preferably 3 to 6 parts by mass.

When the rubber composition contains silica, the content of the copolymer C contained in the rubber composition is 0.1 to 25 parts by mass, more preferably 0.5 to 25 parts by mass based on 100 parts by mass of silica. It is 20 parts by mass, more preferably 1 to 15 parts by mass, and particularly preferably 3 to 10 parts by mass.

Here, in the rubber composition, in addition to the copolymer C, polyvinylpyrrolidone (PVP) produced as a by-product during the production of the copolymer C, that is, exists alone without being bound to the polymer A. PVP may be included.

Further, when the rubber composition contains silica, the content of silica is not particularly limited. For example, from the viewpoint of improving low loss, the silica content is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, still more preferably 20 parts by mass or more, based on 100 parts by mass of the diene rubber. Particularly preferably, it can be 40 parts by mass or more. From the viewpoint of improving workability, the silica content is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, still more preferably 120 parts by mass or less, particularly preferably 120 parts by mass or less, based on 100 parts by mass of the diene rubber. It is preferably 100 parts by mass or less.

The rubber composition may contain various additives in addition to the copolymer C, the diene-based rubber and silica added as needed. Examples of the additive include reinforcing materials other than silica, silane coupling agents, lubricating oils, antioxidants, light stabilizers, antioxidants, preservatives, flame retardants, pigments, colorants, fungicides and the like. Examples of the reinforcing material include carbon black, talc, calcium carbonate, aluminum hydroxide, magnesium carbonate and the like. The content of these additives is not particularly limited, and for example, various additives can be contained in the same content as known rubber compositions. For example, the blending amount of the silane coupling agent can be, for example, 1 to 20 parts by mass, preferably 6 to 12 parts by mass with respect to 100 parts by mass of silica.

Using the rubber composition of the present invention, for example, a rubber molded product such as a tire can be manufactured. More specifically, a rubber molded product can be produced by a method including a first kneading step of preparing a rubber composition and a second kneading step of mixing the rubber composition and a vulcanizing agent.

In the first kneading step, the copolymer C, the diene rubber, silica added as needed, and the additive are kneaded in a predetermined blending amount to prepare a rubber composition. The kneading method in the first kneading step is not particularly limited, and for example, kneading can be performed by a known mixing means. The mixer or the like used in the first kneading step is not limited, and a known mixer can be widely adopted.

In the second kneading step, a vulcanizing agent or the like is added to the rubber composition prepared in the first kneading step. The type of vulcanizing agent is not particularly limited, and for example, known vulcanizing agents can be widely adopted.

Examples of the vulcanizing agent include sulfur-based vulcanizing agents. Examples of the sulfur-based sulfurizing agent include sulfur such as powdered sulfur and colloidal sulfur; and sulfur-containing compounds such as sulfur chloride and sulfur dichloride.

In the second kneading step, a vulcanization accelerator may be added in addition to the vulcanization agent. As the vulcanization accelerator, for example, a known vulcanization accelerator used for vulcanization of rubber can be widely adopted.

In the second kneading step, the blending amounts of the vulcanizing agent and the vulcanization accelerator are not particularly limited. For example, the total amount of the vulcanizing agent and the vulcanization accelerator can be 3 to 20 parts by mass, preferably 5 to 15 parts by mass, per 100 parts by mass of the diene rubber in the rubber composition.

A rubber molded product can be obtained by performing a vulcanization treatment after the second kneading step. The method of vulcanization treatment is not particularly limited, and for example, it can be the same as a known vulcanization method.

The shape of the rubber molded body is not particularly limited, and it can be molded into a desired shape according to various rubber products other than tires. In particular, the rubber molded body is preferably a tire. Since such a tire is formed by using the rubber composition of the present invention, it has low rolling resistance and can contribute to the improvement of fuel efficiency of automobiles.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the aspects of these Examples.

(Example 1)
A solution of polymer A was obtained by dissolving 80 g of maleic acid-modified polybutadiene (“Ricon 156MA17” manufactured by CRAY VALLY, number average molecular weight 2500) in 800 g of acetonitrile and mixing while deoxidizing by nitrogen purging. While maintaining this solution at 80 ° C., a monomer b in which 80 g of NVP and 6.4 g of ammonium persulfate were dissolved in 64 g of isopropyl alcohol was added dropwise over 1.5 hours to carry out a polymerization reaction (step 1). In this step 1, the compounding mass ratio of maleic acid-modified polybutadiene and NVP was 50:50 (Mn of the produced PVP was 51000). After completion of the reaction, the solvent was removed by vacuum drying to obtain a copolymer C.

(Example 2)
Copolymer C was obtained in the same manner as in Example 1 except that the compounding mass ratio of maleic acid-modified polybutadiene and NVP was changed to 70:30.

(Example 3)
Copolymer C was obtained in the same manner as in Example 1 except that the compounding mass ratio of maleic acid-modified polybutadiene and NVP was changed to 30:70.

(Example 4)
Copolymer C was obtained in the same manner as in Example 1 except that the maleic acid-modified polybutadiene was changed to a number average molecular weight of 9100.

(Example 5)
Copolymer C was obtained in the same manner as in Example 1 except that the maleic acid-modified polybutadiene was changed to a number average molecular weight of 5000.

(Example 6)
Copolymer C was obtained in the same manner as in Example 1 except that the amount of ammonium persulfate used was adjusted so that the number average molecular weight Mn of PVP was 650,000.

(Example 7)
Copolymer C was obtained in the same manner as in Example 1 except that the amount of ammonium persulfate used was adjusted so that the number average molecular weight Mn of PVP was 5000.

(Analysis of copolymer C)
When the structure of the graft copolymer obtained in each example was ^{confirmed by 13} C-NMR measurement, it was produced by grafting PVP to the tertiary carbon derived from maleic acid in the maleic acid-modified polybutadiene main chain. A peak derived from quaternary carbon was observed around 41 ppm. From this, it was confirmed that vinylpyrrolidone was graft-polymerized on maleic acid-modified polybutadiene. That is, the copolymers C obtained in Examples 1 to 7 were grafts in which the stem polymer was modified polybutadiene (polymer A) and the branch polymer was PVP (polymer B; polyvinylpyrrolidone).

Further, in the copolymer obtained in Example 1, the number average molecular weight of the PVP site was 51,000, and in the copolymer obtained in Example 2, the number average molecular weight of the PVP site was 50,000, which was obtained in Example 3. In the copolymer, the number average molecular weight of the PVP site was 52000. The number average molecular weight of the PVP site was measured by gel permeation chromatography (GPC) according to the following procedure.

<Measurement of number average degree of polymerization of PVP site (polymer B)>
The copolymer C obtained in Examples was added to diethyl ether, the insoluble matter was removed by filtration or the like, and then diethyl ether was distilled off to obtain a solid content. The obtained solid content was measured by gel permeation chromatography (GPC). The measurement conditions by GPC are as follows.
-GPC device: HLC-8020 RI detection (manufactured by TOSOH)
-Column: TSK guard volume PWXL, TSKgel G2500 PWXL, TSKgel G3000PWXL, TSKgel G4000 PWXL, TSKgel G6000 PWXL (manufactured by TOSOH)
-Eluent: 0.08 M aqueous sodium acetate solution / acetonitrile (50/50 vol%)
・ Flow velocity: 0.7 mL / min
・ Temperature: 40 ℃

Next, using the obtained copolymer C as an additive for rubber, a rubber composition is prepared by the methods described in the following preparation examples and comparative examples, and a rubber molded product is produced by vulcanization treatment. did.

(Preparation Example 1)
4 parts by mass of the copolymer C obtained in Example 1, 70 parts by mass of the styrene-butadiene copolymer rubber (SBR), 30 parts by mass of the polybutadiene rubber (BR), 60 parts by mass of silica, and silane coupling. A rubber composition was obtained by blending 4.9 parts by mass of an agent, 15 parts by mass of oil, 2 parts by mass of stearic acid, and 1 part by mass of an antioxidant and mixing them (first kneading step). 4 parts by mass of zinc oxide, 2 parts by mass of vulcanization accelerator DPG, 1.8 parts by mass of vulcanization accelerator CBS and 1.5 parts by mass of sulfur are mixed and mixed with the obtained rubber composition to obtain a raw material for molding. Obtained (second kneading step). By vulcanizing the obtained molding raw material, a 16 cm square (thickness about 2 mm) rubber molded product was obtained. The raw materials used in each preparation example were as follows.
SBR: JSR SL552
BR: BR54 manufactured by JSR Corporation
Silica: Nip Seal AQ manufactured by Tosoh Corporation
Silane coupling agent: Cabras-2 manufactured by Osaka Soda Co., Ltd.
Oil: Sunthene 415 manufactured by Nippon Sun Oil Co., Ltd.
Stealic acid: Anti-aging agent manufactured by Fuji Film Wako Pure Chemical Industries, Ltd .: N-phenyl-1-naphthylamine zinc oxide manufactured by Tokyo Chemical Industry Co., Ltd .: Zinc oxide vulcanization accelerator manufactured by Fuji Film Wako Pure Chemical Industries, Ltd. DPG: Fuji Film Wako Pure Chemical Industries, Ltd. N, N-diphenylguanidine vulcanization accelerator CBS: Tokyo Chemical Industry Co., Ltd. N-cyclohexyl-2-benzothiazolyl sulfenamide Sulfur: Fuji Film Wako Pure Chemical Industries, Ltd. Made

(Preparation Example 2)
A rubber molded product was obtained in the same manner as in Preparation Example 1 except that the copolymer C obtained in Example 1 was changed to 2 parts by mass.

(Preparation Example 3)
A rubber molded product was obtained in the same manner as in Preparation Example 1 except that the copolymer C obtained in Example 1 was changed to 8 parts by mass.

(Preparation Example 4)
A rubber molded product was obtained in the same manner as in Preparation Example 1 except that the copolymer C obtained in Example 1 was changed to the copolymer C obtained in Example 2.

(Preparation Example 5)
A rubber molded product was obtained in the same manner as in Preparation Example 1 except that the copolymer C obtained in Example 1 was changed to the copolymer C obtained in Example 3.

(Preparation Example 6)
A rubber molded product was obtained in the same manner as in Preparation Example 1 except that the copolymer C obtained in Example 1 was changed to the copolymer C obtained in Example 4.

(Preparation Example 7)
A rubber molded product was obtained in the same manner as in Preparation Example 1 except that the copolymer C obtained in Example 1 was changed to the copolymer C obtained in Example 5.

(Preparation Example 8)
A rubber molded product was obtained in the same manner as in Preparation Example 1 except that the copolymer C obtained in Example 1 was changed to the copolymer C obtained in Example 6.

(Preparation Example 9)
A rubber molded product was obtained in the same manner as in Preparation Example 1 except that the copolymer C obtained in Example 1 was changed to the copolymer C obtained in Example 7.

(Comparative Example 1)
The same method as in Preparation Example 1 except that the copolymer C obtained in Example 1 was changed to PVP homopolymer (“Pitzcol K-50, number average molecular weight 77000) manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.). A rubber molded body was obtained in.

(Comparative Example 2)
A rubber molded product was obtained in the same manner as in Preparation Example 1 except that the copolymer C obtained in Example 1 was changed to maleic acid-modified polybutadiene (“Ricon 156MA17” manufactured by CRAY VALLY, number average molecular weight 2500). It was.

(Rolling resistance evaluation)
The rolling resistance of the rubber molded product obtained in each preparation example and comparative example was evaluated using a viscoelasticity measuring device (“Rheogel-E4000” manufactured by UBM). Tan δ was measured at 5% and a frequency of 15 Hz. For comparison, a rubber molded product molded by the same method as in Preparation Example 1 except that the copolymer C obtained in Example 1 was not used. The inverse number of tan δ of this reference was set to 100, and the rolling resistance of the rubber molded product obtained in each preparation example was evaluated based on the relative value based on this as the reference. The larger the value, the lower the rolling resistance. Therefore, it can be said that A, B and C have a high effect of reducing the rolling resistance (particularly A is excellent), and D has a poor effect of reducing the rolling resistance.
<Criteria>
A: 110 or more and B: 105 or more and less than 110 C: 100 or more and less than 105 D: less than 100

Table 1 shows the compounding conditions and results of each preparation example.

From Table 1, it was found that the rubber molded product obtained by using the rubber composition containing the copolymer C obtained in the examples had a small rolling resistance.

Claims (6)

A copolymer having at least a polymer A containing butadiene as a constituent unit and a polymer B of a monomer b containing N-vinyl-2-pyrrolidone in the molecule. The copolymer according to claim 1, wherein the polymer A contains polybutadiene or modified polybutadiene. The copolymer according to claim 1 or 2, wherein the polymer A is a stem polymer and the polymer B is a branch polymer. The copolymer according to any one of claims 1 to 3, which is used as an additive for rubber. A rubber composition containing at least the copolymer according to claim 4 and a diene-based rubber. A tire comprising the rubber composition according to claim 5.