JP2010143951A - Ester-crosslinked rubber and method for producing the same, curable rubber composition and hydroxy-modified copolymer for production of the same, and molded article including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crosslinked rubber excellent in crosslinkability and heat resistance, which is obtained from a curable rubber composition excellent in moldability. <P>SOLUTION: The crosslinked rubber includes an ester-crosslinked rubber wherein a rubbery copolymer, obtained by copolymerization of an isomonoolefin and an aliphatic diene, is crosslinked through an ester linkage. The rubbery copolymer is dissolved in a solvent, hydroborated, then oxidized and hydrolyzed to give a hydroxy-modified copolymer having a hydroxy group added to a C-C double bond of the rubbery copolymer, which copolymer is mixed with a crosslinking agent having at least two functional groups which can form an ester linkage by reaction between the hydroxy-modified copolymer and a hydroxy group to give a curable rubber composition. A hydroxy group of the hydroxy-modified copolymer in the curable rubber composition is subjected to an esterification reaction with the functional group of the crosslinking agent to give the crosslinked rubber. The ester-crosslinked rubber is stable at the temperature of 150°C. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a rubbery copolymer obtained by copolymerizing at least one isomonoolefin having 4 to 7 carbon atoms and at least one aliphatic diene having 4 to 14 carbon atoms. The present invention relates to an ester crosslinked rubber crosslinked through a bond and a method for producing the same. The present invention further relates to a curable rubber composition and a hydroxyl-modified copolymer that can be used for producing the ester-crosslinked rubber, and further to a molded article containing the ester-crosslinked rubber.

  A rubbery copolymer obtained by copolymerizing an isomonoolefin having 4 to 7 carbon atoms such as isobutene or isopentene and a small amount of an aliphatic diene having 4 to 14 carbon atoms such as isoprene or butadiene Is simply referred to as “rubber-like copolymer”), and is also referred to as “butyl rubbers”, and its crosslinked rubber has high impact absorption capacity, extremely low gas permeability, and is stable to acids, alkalis, ozone, etc. Therefore, they are used in a wide range of applications such as vibration-proof materials, automobile tire tubes, pharmaceutical rubber products, capacitor and battery sealing bodies, belts, hoses and the like.

  Conventionally, sulfur crosslinking, quinoid crosslinking, and resin crosslinking are known as methods for crosslinking the rubbery copolymer.

  Sulfur crosslinking is performed by using sulfur or a sulfur donor in combination with a crosslinking accelerator such as thiazoles, dithiocarbamates, or thiurams. However, since heating at a high temperature for a long time is necessary, it is not preferable from the viewpoint of production efficiency, and there is a problem that bleed and bloom are likely to occur. In quinoid crosslinking using quinonedioximes such as p-quinonedioxime and p, p′-dibenzoylquinonedioxime, lead tan or lead dioxide is used as an oxidizing agent for activating the quinoid. Since these lead compounds are harmful to the human body, they have environmental health problems. Moreover, the crosslinked rubber obtained by quinoid crosslinking does not have sufficient heat resistance. Furthermore, resin crosslinking using halogenated alkylphenol-formaldehyde resins, or phenol-formaldehyde resins and inorganic halides such as tin dichloride, or halogen-containing elastomers such as chloroprene, has a significantly slow crosslinking rate and is long at high temperatures. Since heating of time is required, it is not preferable from the viewpoint of production efficiency. Moreover, since the rubber product obtained by resin crosslinking is commercialized in a state where the crosslinking is not completed, there is a problem that the physical properties of the rubber product change greatly due to the progress of the crosslinking reaction during the use of the rubber product.

  On the other hand, crosslinking using an organic peroxide such as benzoyl peroxide or dicumyl peroxide, which is suitable as a crosslinking method for diene rubbers, is not usually used for crosslinking rubbery copolymers. This is because a dehydrogenation reaction caused by the carbon-carbon double bond of the rubber-like copolymer occurs, so that the copolymer is decomposed and reduced in molecular weight and crosslinking does not proceed. However, crosslinking with an organic peroxide is advantageous in that the crosslinking speed is very fast and the resulting crosslinked rubber does not contain impurities such as sulfur. Rubbery copolymers have been investigated.

  For example, US Pat. No. 3,584,080 describes an isomonoolefin having 4 to 7 carbon atoms such as isobutene and an aliphatic diene having 4 to 14 carbon atoms such as isoprene. And a partially crosslinked rubber obtained by copolymerizing an aromatic divinyl compound such as divinylbenzene and capable of crosslinking with an organic peroxide alone. Further, as such partially crosslinked rubber, a partially crosslinked rubber of 97 mol% of isobutene-1.7 mol% of isoprene-1.3 mol% of divinylbenzene is commercially available from Bayer under the name “XL-10000”. . The vinyl groups in these partially crosslinked rubbers are crosslinked with an organic peroxide.

  Crosslinking of this partially crosslinked rubber with an organic peroxide proceeds rapidly, and the obtained crosslinked rubber is superior to the above-described crosslinked rubber by sulfur crosslinking in terms of heat resistance. For example, Patent Document 2 (Japanese Patent Laid-Open No. 2003-109880) discloses a curable rubber composition obtained by adding dicumyl peroxide, a filler, a processing aid, an antiaging agent, and a crosslinking aid to XL-10000 in an electrolytic capacitor. By using a crosslinked rubber obtained by curing a product as a sealing body, and further using an electrolyte containing sulfolane, γ-butyllactone, and 1-ethyl-2,3-dimethylimidazolinium phthalate as a driving electrolyte. Further, it is disclosed that the deterioration of the sealing body is suppressed even at the use temperature of 150 ° C. of the electrolytic capacitor.

U.S. Pat. No. 3,584,080 JP 2003-109880 A

  However, the partially crosslinked butyl rubber described above has a high Mooney viscosity and a very high gel content, so that the processability is extremely poor. Moreover, it cannot be said that the hardness and tear strength of the crosslinked rubber obtained by the organic peroxide crosslinking are sufficient, and the crosslinked rubber product may be deformed or cracked.

  Moreover, recently, higher heat resistance has been required for crosslinked rubber used in the fields of automobile parts, electrical parts and the like. Therefore, it is desired to develop a crosslinked rubber having heat resistance exceeding the crosslinked rubber obtained by organic peroxide crosslinking of the above partially crosslinked rubber.

  Accordingly, an object of the present invention is to provide a crosslinked rubber which can be obtained from a curable rubber composition excellent in processability, has excellent crosslinkability and also has excellent heat resistance, and a method for producing the same.

  The above-mentioned problems are addressed by 90 to 99.5 mol% of at least one isomonoolefin having 4 to 7 carbon atoms and at least one aliphatic diene having 4 to 14 carbon atoms 0.5 to 10 A hydroxyl-modified copolymer in which a hydroxyl group is added to a carbon-carbon double bond of a rubber-like copolymer copolymerized with a mol% has at least 2 functional groups capable of forming an ester bond by reaction with the hydroxyl group. This is achieved by an ester cross-linked rubber cross-linked through an ester bond cross-linked by an esterification reaction with individual cross-linking agents.

  The hydroxyl-modified copolymer in which a hydroxyl group is added to the carbon-carbon double bond of the rubber-like copolymer has a hydroxyl group that becomes a functional group for the esterification reaction, and the carbon-carbon double bond is saturated. Excellent heat resistance. An ester-crosslinked rubber crosslinked through an ester bond is obtained by an esterification reaction between the hydroxyl group of the hydroxyl-modified copolymer and the functional group of the crosslinking agent, and the hydroxyl-modified copolymer before crosslinking and The mixture with the crosslinking agent is excellent in processability, and the crosslinked ester-crosslinked rubber is superior in crosslinkability and heat resistance as compared with a rubber obtained by crosslinking a conventional partially crosslinked rubber.

  In the ester crosslinked rubber of the present invention, the amount of bonded aliphatic diene in the rubbery copolymer is generally in the range of 0.5 to 10.0 mol%. When the amount of the bonded aliphatic diene is more than 10.0 mol%, the rubber elasticity of the ester-crosslinked rubber is lowered, and when it is less than 0.5 mol%, sufficient effects of the present invention are hardly obtained. The amount of bonded aliphatic diene in the rubbery copolymer is particularly preferably in the range of 0.6 to 2.5 mol%.

  A desirable crosslinked rubber having extremely low gas permeability and excellent chemical resistance is butyl rubber, that is, a crosslinked rubber obtained by crosslinking an isobutene-isoprene copolymer. Also in the present invention, by using isobutene as the isomonoolefin in the rubbery copolymer and isoprene as the aliphatic diene, it is possible to obtain a desirable ester-crosslinked rubber having extremely low gas permeability and excellent chemical resistance. Can do.

  When a hydroxyl-modified copolymer substantially free of carbon-carbon double bonds is cross-linked, there is no carbon-carbon double bond in the main chain of the resulting ester-crosslinked rubber, and heat resistance is excellent. preferable. However, even if some carbon-carbon double bonds remain in the hydroxyl-modified copolymer, the effects of the present invention can be obtained.

Note that “substantially no carbon-carbon double bond” means that the signal derived from the carbon-carbon double bond disappears in ¹ H-NMR measurement of the hydroxyl-modified copolymer.

で表されるイソブテン−イソプレン共重合体(未架橋ブチルゴム)の炭素炭素二重結合にヒドロキシル基を導入すると、有利には、以下の式（ＩＩ）

で表される反マルコフニコフ水和化物がヒドロキシル変性共重合体として得られるが、この場合には、式（Ｉ）のＨ^ａで示す水素の^１Ｈ−ＮＭＲのシグナルが消失しているかどうかにより、炭素炭素二重結合が実質的に存在しないかどうかを判断することができる（図１参照）。 For example, the following formula (I)

When a hydroxyl group is introduced into the carbon-carbon double bond of the isobutene-isoprene copolymer (uncrosslinked butyl rubber) represented by the following formula (II),

While in anti-Markovnikov hydration product represented is obtained as hydroxyl modified copolymer, in this case, depending on whether the ^{1 H-NMR} signal of the hydrogen indicated by H ^a of formula (I) is lost It can be determined whether substantially no carbon-carbon double bond is present (see FIG. 1).

  The ester-crosslinked rubber of the present invention comprises 90 to 99.5 mol% of at least one isomonoolefin having 4 to 7 carbon atoms and at least one aliphatic diene having 4 to 14 carbon atoms. A rubbery copolymer copolymerized with 5 to 10 mol% is dissolved in a solvent, hydroborated, further oxidized and hydrolyzed, whereby a hydroxyl group is bonded to the carbon-carbon double bond of the rubbery copolymer. A modification step for obtaining a hydroxyl-modified copolymer to which is added, by mixing the hydroxyl-modified copolymer with a crosslinking agent having at least two functional groups capable of forming an ester bond by reaction with a hydroxyl group, The preparation step for obtaining the curable rubber composition, and the hydroxyl group of the hydroxyl-modified copolymer in the curable rubber composition and the functional group of the cross-linking agent By etherification reaction can be by a production method of an ester cross-linked rubber, characterized in that it comprises a cross-linking step to give the ester crosslinked rubber crosslinked via an ester bond, obtained suitably. Accordingly, the present invention also relates to a method for producing this ester-crosslinked rubber.

  By adding a hydroxyl group to the carbon-carbon double bond of the rubber-like copolymer, the carbon-carbon double bond is saturated and a functional group for esterification reaction is introduced. Since the carbon-carbon double bond is saturated, the heat resistance is improved. In addition, since this hydroxyl-modified copolymer does not have a crosslinked structure, this hydroxyl-modified copolymer is mixed with a crosslinking agent having at least two functional groups capable of reacting with hydroxyl groups to form ester bonds. Good processability is also exhibited when the functional rubber composition is molded into a desired shape. An ester crosslinked rubber crosslinked through an ester bond is obtained by an esterification reaction between a hydroxyl group as a functional group of the hydroxyl-modified copolymer and a functional group of the crosslinking agent. Further, it is superior in crosslinkability and heat resistance as compared with a rubber obtained by crosslinking a conventional partially crosslinked rubber.

  In the method for producing an ester-crosslinked rubber according to the present invention, the amount of bonded aliphatic diene in the rubbery copolymer is particularly preferably 0.6 to 2.5 mol%. The isomonoolefin is preferably isobutene and the aliphatic diene is preferably isoprene.

  In the hydroxyl-modified copolymer, when hydroxyl groups are added to all of the carbon-carbon double bonds of the rubber-like copolymer, carbon-carbon double bonds are present in the main chain of the ester-crosslinked rubber finally obtained. It is preferable because an ester cross-linked rubber that does not exist and has excellent heat resistance can be obtained. However, even if some carbon-carbon double bonds remain in the hydroxyl-modified copolymer, the effects of the present invention can be obtained. A hydroxyl-modified copolymer substantially free of carbon-carbon double bonds is obtained by performing hydroboration in the above modification step using 3 to 15 equivalents of a hydroborating agent per equivalent of bonded aliphatic diene. It is done. Here, the case where one BH group reacts with one carbon-carbon double bond in the bonded aliphatic diene is defined as one equivalent. If the amount of hydroborating agent is less than 3 equivalents, hydroboration does not proceed sufficiently, and if it exceeds 15 equivalents, post-treatment such as washing when recovering the hydroxyl-modified copolymer becomes troublesome and economical. Disadvantageous.

  When using a hydroborating agent having two or more B—H groups in the modification step, rather than using a hydroborating agent having only one B—H group of the same equivalent. Hydroboration is likely to proceed, but at the same time, gelation of the solution is likely to occur due to the crosslinking reaction, and the hydroboration reaction is suppressed, and as a result, the addition of hydroxyl groups is suppressed. Therefore, when a hydroborating agent having two or more B—H bonds is used in the modification step, the rubber is obtained in order to obtain a hydroxyl-modified copolymer substantially free of carbon-carbon double bonds. The hydroboration is preferably carried out in a solution having a concentration of a state copolymer of 1 w / v% or less.

  The crosslinking agent used in the ester crosslinked rubber of the present invention can be used without particular limitation as long as it is a compound having at least two functional groups capable of reacting with a hydroxyl group to form an ester bond. It is preferable to select a cross-linking agent from among dicarboxylic acid anhydrides, dicarboxylic acid halides and dicarboxylic acid esters because the cross-linking proceeds efficiently. Such crosslinkers are used in amounts of 1-3 equivalents per equivalent of bound aliphatic diene in the rubbery copolymer (and thus per equivalent of hydroxyl group), and most hydroxyl groups of the hydroxyl-modified copolymer. Is preferable because it forms an ester bond.

  The curable rubber composition that can be obtained in the preparation step in the method for producing the ester-crosslinked rubber of the present invention does not contain a copolymer having a crosslinked structure in advance. When molding, a cross-linked rubber that exhibits good processability and excellent tear strength can be provided. Accordingly, the present invention further relates to 90-99.5 mol% of at least one isomonoolefin having 4 to 7 carbon atoms and at least one aliphatic diene having 4 to 14 carbon atoms. A hydroxyl-modified copolymer in which a hydroxyl group is added to a carbon-carbon double bond of a rubbery copolymer copolymerized with 10 mol%, and a functional group capable of forming an ester bond by reaction with the hydroxyl group. The present invention relates to a curable rubber composition containing at least two crosslinking agents.

  The hydroxyl-modified copolymer substantially free of carbon-carbon double bonds that can be obtained in the modification step in the method for producing the ester-crosslinked rubber of the present invention described above has high heat resistance, and a hydroxyl group as a functional group is introduced. Therefore, it is particularly suitable for producing ester-crosslinked rubber having heat resistance. Accordingly, the present invention further relates to 90-99.5 mol% of at least one isomonoolefin having 4 to 7 carbon atoms and at least one aliphatic diene having 4 to 14 carbon atoms. The present invention relates to a hydroxyl-modified copolymer in which a hydroxyl group is added to a carbon-carbon double bond of a rubbery copolymer copolymerized with 10 mol%, and the carbon-carbon double bond is substantially absent.

  The ester-crosslinked rubber is excellent in crosslinkability and heat resistance. Since the composition for producing the ester-crosslinked rubber is excellent in processability, the ester-crosslinked rubber of the present invention is molded in various shapes and uses. It can be suitably used to obtain a molded body, particularly a molded body that is required to have heat aging resistance and long life. Therefore, the present invention further relates to a molded article containing the ester crosslinked rubber.

  According to the method for producing an ester-crosslinked rubber of the present invention, the carbon-carbon double bond is saturated and a hydroxyl group is introduced in the modification step. Since the carbon-carbon double bond is saturated, the heat resistance is improved, and the hydroxyl group becomes a functional group for the esterification reaction. Further, since this hydroxyl-modified copolymer does not have a cross-linked structure, good processability is obtained when a curable rubber composition obtained by mixing the hydroxyl-modified copolymer with the cross-linking agent is molded into a desired shape. Indicates. Then, an ester-crosslinked rubber crosslinked through an ester bond can be obtained by an esterification reaction between a hydroxyl group as a functional group of the hydroxyl-modified copolymer and a functional group of the crosslinking agent. This ester-crosslinked rubber is superior in crosslinkability and heat resistance to a rubber obtained by crosslinking a conventional partially crosslinked rubber. Therefore, it is possible to easily obtain a very stable molded body having a desired shape.

  The crosslinked rubber of the present invention comprises 90-99.5 mol% of at least one isomonoolefin having 4-7 carbon atoms and at least one aliphatic diene having 4-14 carbon atoms. To the carbon-carbon double bond of a rubbery copolymer copolymerized with 10 mol% (the total amount of isomonoolefin and aliphatic diene in the rubbery copolymer is 100 mol%). The hydroxyl-modified copolymer to which a group is added is crosslinked by an esterification reaction with a crosslinking agent having at least two functional groups capable of forming an ester bond by reaction with the hydroxyl group. This is an ester crosslinked rubber crosslinked via This ester-crosslinked rubber is obtained by dissolving the rubber-like copolymer in a solvent, hydroborating it, and further oxidizing and hydrolyzing it, thereby adding a hydroxyl group to the carbon-carbon double bond of the rubber-like copolymer. A curable rubber composition is obtained by mixing a modification step for obtaining a modified copolymer, the hydroxyl-modified copolymer and a crosslinking agent having at least two functional groups capable of forming an ester bond by reaction with a hydroxyl group. And a crosslinked ester ester rubber crosslinked via an ester bond by esterifying the hydroxyl group of the hydroxyl-modified copolymer in the curable rubber composition and the functional group of the crosslinking agent. It can obtain suitably by the bridge | crosslinking process of obtaining. Hereinafter, each step will be described in detail.

(A) Modification step In the production method of the present invention, at least one isomonoolefin having 4 to 7 carbon atoms and at least one aliphatic diene having 4 to 14 carbon atoms are copolymerized. A rubbery copolymer is used as a starting material.

  Examples of isomonoolefins having 4 to 7 carbon atoms include isobutene, 2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene, 4-methyl-1-pentene And mixtures thereof. As the isomonoolefin, isobutene is preferable.

  Examples of aliphatic dienes having 4 to 14 carbon atoms include isoprene, butadiene, 1,3-pentadiene, 3-methyl-1,3-pentadiene, 2,4-hexadiene, and 2-neopentylbutadiene. Conjugated dienes, 1,4-pentadiene, 2-methyl-1,4-pentadiene, 1,5-hexadiene, 2-methyl-1,5-hexadiene, 1,6-heptadiene, 2-methyl-1,6- Non-conjugated dienes such as heptadiene are mentioned. Two or more of these may be used. As the aliphatic diene, isoprene is preferred.

  These rubbery copolymers can be produced by known solution polymerization and suspension polymerization. A monomer mixture in an inert solvent can be produced by polymerizing at a low temperature in the presence of a Friedel-Crafts catalyst, for example, a suitable isobutene-isoprene copolymer (uncrosslinked butyl rubber) is obtained in methyl chloride, It can be obtained by polymerizing the monomer mixture at a low temperature of about −100 ° C. in the presence of an anhydrous aluminum chloride catalyst. Commercially available rubbery copolymers such as commercially available uncrosslinked butyl rubber can also be used. Although the degree of polymerization of these rubbery copolymers is not strictly limited, the molecular weight is preferably in the range of 50,000 to 1,000,000.

  The amount of bonded aliphatic diene in the rubbery copolymer used in the present invention is generally in the range of 0.5 to 10.0 mol%. When the amount of bonded aliphatic diene is more than 10.0 mol%, the rubber elasticity of the finally obtained ester-crosslinked rubber is lowered, and when it is less than 0.5 mol%, sufficient effects of the present invention are hardly obtained. The amount of bonded aliphatic diene in the rubbery copolymer is preferably in the range of 0.5 to 4.0 mol%, particularly preferably in the range of 0.6 to 2.5 mol%.

  In the present invention, the rubbery copolymer as a starting material is dissolved in a solvent while being heated, if necessary, and then hydroborated, followed by oxidation and hydrolysis to form a hydroxyl group on a carbon-carbon double bond. Add a group. The reaction itself for introducing a hydroxyl group into a carbon-carbon double bond by hydroboration and subsequent oxidation and hydrolysis is known.

  The solvent that can be used for dissolving the rubbery copolymer is not particularly limited as long as it is an inert solvent that does not impair the reaction. For example, aromatic hydrocarbons such as benzene and toluene, hexane, heptane, and the like Aliphatic hydrocarbons such as diethyl ether, diisopropyl ether, methyl-t-butyl ether, dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetrahydrofuran, dioxane and other ethers, halogenated hydrocarbons such as chlorobenzene and chloroform, or these The mixed solvent is mentioned. In particular, tetrahydrofuran or a mixed solvent containing tetrahydrofuran is preferable because it promotes hydroboration.

  Hydroboration is performed by allowing a hydroborating agent to act on the resulting rubbery copolymer solution. Examples of hydroborating agents that can be used include borane and its oligomers, methylborane, dimethylborane, ethylborane, diethylborane, dicyamylborane, texylborane, catecholborane, dicyclohexylborane, 9-borabicyclo [3,3,1] -nonane, Diisopinocan phenylborane, phenylborane, borane chloride, borane bromide, methoxyborane, ethoxyborane, phenoxyborane, borane / tetrahydrofuran complex, borane / diethyl ether complex, borane / dimethyl sulfide complex, borane / triethylamine complex . When tetrahydrofuran or a tetrahydrofuran mixed solvent is used as the solvent, it is preferable to use borane-tetrahydrofuran complex. The hydroboration reaction is generally performed at a temperature of 0 to 100 ° C. The reaction time is usually 1 hour or longer, preferably 5 hours or longer.

で表されるブチルゴムを出発材料とし、ボラン・テトラヒドロフラン錯体をヒドロホウ素化剤とした場合には、有利には炭素炭素二重結合に対する反マルコフニコフ付加により、以下の式（ＩＶ）

で表されるヒドロホウ素化物が得られるが、マルコフニコフ付加によるヒドロホウ素化部分も混在する。 For example, the following formula (III)

Is used as a starting material, and borane / tetrahydrofuran complex is used as a hydroborating agent, preferably by anti-Markovnikov addition to a carbon-carbon double bond, the following formula (IV)

Is obtained, but a hydroboration portion by Markovnikov addition is also mixed.

  The amount of the hydroborating agent added is basically selected so that all the carbon-carbon double bonds in the rubbery copolymer are hydroborated. If all the carbon-carbon double bonds are hydroborated, hydroxyl groups are introduced into all the carbon-carbon double bonds in the subsequent oxidation and hydrolysis. However, the amount of hydroborating agent may be selected so that carbon-carbon double bonds remain in the hydroxyl-modified copolymer. In particular, when the amount of bonded aliphatic diene in the rubbery copolymer is relatively large, when a hydroxyl group is introduced into all of the carbon-carbon double bonds, the rubber elasticity of the finally obtained ester-crosslinked rubber is lowered. Although there is a tendency, the amount of the hydroborating agent may be selected so that a carbon-carbon double bond remains, although it is slightly disadvantageous in terms of heat resistance. The amount of residual carbon-carbon double bonds in the hydroxyl-modified copolymer is generally 80% or less, preferably 70% or less, of the amount of carbon-carbon double bonds in the rubbery copolymer. In order to obtain a hydroxyl-modified copolymer substantially free of carbon-carbon double bonds, 3 to 15 equivalents of a hydroborating agent is used per equivalent of the bonded aliphatic diene of the rubbery copolymer. Is preferred. If the amount of hydroborating agent is less than 3 equivalents, hydroboration does not proceed sufficiently, and if it exceeds 15 equivalents, post-treatment such as washing when recovering the hydroxyl-modified copolymer becomes troublesome, It is economically disadvantageous.

  When using a hydroborating agent having two or more B—H bonds, a hydroboron having only one B—H bond, such as the same equivalent of 9-borabicyclo [3,3,1] -nonane. Hydroboration is more likely to proceed than using an agent, but at the same time gelation of the solution is likely to occur due to a crosslinking reaction. Since this gel tends to dissolve in the process of the next oxidation and hydrolysis reaction, the gelation may proceed to some extent, but if the gelation proceeds too rapidly, the hydroboration reaction is suppressed, As a result, the introduction of hydroxyl groups is suppressed, and part of the gel may remain even after the subsequent oxidation or hydrolysis reaction, which is not preferable. When the concentration of the rubber-like copolymer solution is high, gelation proceeds rapidly. Therefore, when a hydroborating agent having two or more B—H bonds is used, the concentration of the rubber-like copolymer is reduced. The carbon-carbon double bond is 2 w / v% (weight% of the rubbery copolymer with respect to the volume of the solvent) or less, preferably 1.5 w / v% or less, particularly preferably 1.0 w / v% or less. Is preferable for obtaining a hydroxyl-modified copolymer substantially free of. No gelation of the solution was observed at a rubbery copolymer solution concentration of 1.0 w / v% or less.

  Next, the solution after hydroboration is oxidized and hydrolyzed with alkaline hydrogen peroxide to obtain a hydroxyl-modified copolymer. As the peroxide, in addition to hydrogen peroxide, perbenzoic acid, benzoyl peroxide and the like can be used, but it is preferable to use hydrogen peroxide. This oxidation and hydrolysis reaction is usually performed at a temperature of 0 to 60 ° C. The reaction time is usually 1 hour or longer, preferably 5 hours or longer.

で表される反マルコフニコフ水和化物に変化するが、マルコフニコフ水和部分も混在する。 By this oxidation and hydrolysis reaction, the advantageously formed hydroborated product represented by the above formula (IV) is represented by the following formula (V):

It changes to the anti-Markovnikov hydrate represented by the formula, but the Markovnikov hydrate part is also mixed.

The obtained hydroxyl-modified copolymer is easily recovered by adding the solution after oxidation and hydrolysis to a poor solvent such as methanol to precipitate the hydroxyl-modified copolymer, washing it thoroughly, and then filtering it. be able to. After drying and removing the solvent, it is used in the preparation process shown below. The hydroxyl group introduction degree (and hence the carbon-carbon double bond residual degree) of the hydroxyl-modified copolymer can be confirmed by ¹ H-NMR.

  The hydroxyl-modified copolymer substantially free of carbon-carbon double bonds of the present invention that can be obtained in this step is extremely heat stable because all of the double bonds are substantially saturated. And is extremely suitable as a material for producing ester-crosslinked rubber.

(B) Preparation Step Next, a crosslinking agent having at least two functional groups capable of forming an ester bond by reaction with a hydroxyl group and the hydroxyl-modified copolymer are mixed to obtain a curable rubber composition.

  In the present invention, any crosslinking agent having at least two functional groups capable of forming an ester bond by reaction with a hydroxyl group can be used without particular limitation. Crosslinkers capable of reacting with hydroxyl groups to form carboxylic acid esters, such as dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, Maleic acid, fumaric acid, itaconic acid, citraconic acid, cyclohex-4-ene-1,2-dicarboxylic acid, bicyclo [2,2,1] hept-5-ene-2,3-dicarboxylic acid, phthalic acid, isophthalic acid Acid, terephthalic acid, 5-methylisophthalic acid, 4,5-methoxyphthalic acid, biphenyl-2,2'-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid; tricarboxylic acid such as ethane-1,1,2, -Tricarboxylic acid, butane-1,2,4-tricarboxylic acid, hexane-2,3,5-tricarboxylic acid, benzene-1,2,3- Recarboxylic acid, benzene-1,2,4-tricarboxylic acid, benzene-1,3,5-tricarboxylic acid, naphthalene-1,2,4-tricarboxylic acid; tetracarboxylic acid such as 1,2,3,4- Butanetetracarboxylic acid, cyclohexane-1,2,4,5-tetracarboxylic acid, benzene-1,2,3,4-tetracarboxylic acid, benzene-1,2,3,5-tetracarboxylic acid, benzene-1 , 2,4,5-tetracarboxylic acid, naphthalene-1,4,5,8-tetracarboxylic acid; pentacarboxylic acid, such as benzenepentacarboxylic acid; hexacarboxylic acid, such as benzenehexacarboxylic acid, and these Derivatives such as these acid halides, acid anhydrides and esters can be used. The derivative may have two or more different types of functional groups such as a carboxyl group and an acid anhydride group in one molecule. These crosslinking agents may be used alone or as a mixture of two or more crosslinking agents. It is preferable to use a crosslinking agent selected from dicarboxylic acids and derivatives thereof because crosslinking proceeds efficiently. Moreover, when using aliphatic carboxylic acid, it is preferable to use what does not contain a carbon-carbon double bond.

  Also use crosslinkers that can react with hydroxyl groups to form phosphate esters, such as phosphorus oxychloride, phosphorus pentoxide, phosphorus trichloride, phosphorus pentachloride, orthophosphoric acid, phosphate esters, and mixtures thereof. be able to.

  Since the crosslinking agent esterifies most hydroxyl groups of the hydroxyl-modified copolymer, an amount of 1-3 equivalents per equivalent of bound aliphatic diene (and thus one equivalent of hydroxyl group) in the starting rubbery copolymer. Used in.

  The curable rubber composition may be a liquid composition by adding a solvent, or may be a solid phase composition without using a solvent. The composition for producing a molded body is preferably a solid phase composition.

  The solvent that can be used in the liquid composition is not particularly limited as long as it is an inert solvent that does not impair the reaction. For example, aromatic hydrocarbons such as benzene and toluene, aliphatic hydrocarbons such as hexane and heptane, diethyl Examples include ether, diisopropyl ether, methyl-t-butyl ether, dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ethers such as tetrahydrofuran and dioxane, halogenated hydrocarbons such as chlorobenzene and chloroform, and mixed solvents thereof.

  The curable rubber composition further includes a protonic acid catalyst such as hydrochloric acid, toluenesulfonic acid, silica, alumina, zeolite, heteropolyacid or sodium hydroxide, potassium hydroxide, pyridine, piperidine for accelerating the esterification reaction. , Bases such as trimethylamine and tributylamine, adsorbents such as silicate compounds, fillers such as carbon black, talc, clay and mica, antioxidants, anti-aging agents, heat stabilizers, light stabilizers Conventional additives such as ozone stabilizers, processing aids, dyes and pigments may be added as necessary.

  In addition to the hydroxyl-modified copolymer and the crosslinking agent obtained in the modification step, if necessary, a solvent, a proton acid catalyst or base, and a conventional additive are mixed by using a suitable mixing means to cure. A rubber composition can be obtained. When obtaining a solid phase composition, a closed mixer, an open roll mill or the like can be suitably used as a mixing means.

  Since the curable rubber composition of the present invention that can be obtained in this step does not contain a copolymer having a crosslinked structure in advance, it has excellent processability when processed into a predetermined shape and has good tear strength. It can be suitably used to obtain an ester crosslinked rubber.

(C) Crosslinking process The curable rubber composition obtained in the above preparation process is heated to react the hydroxyl-modified copolymer with the crosslinking agent to crosslink via an ester bond. Get.

For example, when a curable rubber composition containing an advantageously generated hydroxyl-modified copolymer represented by the above formula (V) and isophthalic acid or a derivative thereof as a crosslinking agent is used, An ester-crosslinked rubber represented by the formula (VI) is obtained.

  When the curable rubber composition is a liquid composition, it is heated as it is or after coating on a predetermined substrate, and the esterification reaction proceeds. In the case of a composition having a large amount of solvent, the esterification reaction is generally carried out under reflux. The reaction time is generally 1 hour, preferably 5 hours or longer. The ester-crosslinked rubber can be easily obtained by adding the composition after the reaction to a poor solvent such as methanol to precipitate the ester-crosslinked rubber, washing it thoroughly, and filtering.

  The solid phase composition is formed into a desired shape by an extrusion method, a molding method, or the like, and then the esterification reaction proceeds by heating while applying pressure as necessary. The temperature, pressure, and reaction time vary depending on the type of crosslinking agent used, the shape of the molded body, the mold used, and the like, and are not strictly limited, but the temperature is generally 50 to 200 ° C., preferably 150 to 200. The pressure is generally in the range of 0.1 to 30 Mpa, preferably 3 to 20 Mpa, and the reaction time is generally 5 minutes to 10 hours, preferably 5 minutes to 1 hour. Range. The obtained ester crosslinked rubber can be subjected to secondary vulcanization as necessary. Further, the obtained ester-crosslinked rubber can be post-processed as necessary to obtain a molded article having a predetermined shape.

  The ester-crosslinked rubber of the present invention that can be produced by the above-mentioned ester-crosslinked rubber is more excellent in crosslinkability than a rubber obtained by crosslinking a partially crosslinked rubber such as conventional XL-10000, exhibits high hardness, and heat resistance. Is also excellent. Moreover, since the butyl rubber which has low gas permeability is used as a starting material, low gas permeability is shown similarly. Furthermore, since the curable rubber composition does not contain a copolymer having a crosslinked structure in advance, a crosslinked rubber having excellent processability when processed into a predetermined shape and having good tear strength can be obtained. Therefore, products for a wide range of applications such as automobile and bicycle tire tubes, automobile parts, curing bags, pharmaceutical rubber products, electrical parts, sealing bodies such as capacitors and batteries, wire coverings, belts, hoses, vibration damping materials, etc. It can be suitably used to obtain In particular, the ester-crosslinked rubber of the present invention is required to have a molded product requiring gas barrier properties, or a molded product required to have heat aging resistance and long life, particularly heat aging resistance at a high temperature of about 150 ° C. It is very suitable for products for various applications.

  Examples of the present invention are shown below, but the present invention is not limited to the following examples.

1. Production of hydroxyl-modified copolymer Example 1
Uncrosslinked butyl rubber (bound isoprene content; 2 mol%, molecular weight; about 400,000) was cut into small pieces, and 3 g thereof was introduced into a 1000 mL three-necked flask with a stirrer. Next, 400 mL of tetrahydrofuran was introduced into the flask, and the atmosphere in the flask was replaced with nitrogen. Then, the uncrosslinked butyl rubber was dissolved in tetrahydrofuran while stirring.

  Next, 7.2 mL of borane / tetrahydrofuran complex (Kanto Chemical) (6.7 equivalents of B—H groups per equivalent of bound isoprene) was added to the flask. The hydroboration reaction was carried out under reflux for 5 hours while heating in an oil bath at a temperature of 90 ° C. The solution did not gel.

  Next, the flask was cooled in an ice bath, and 11.8 mL of a solution obtained by dissolving 3.93 g of sodium hydroxide in methanol was added dropwise with stirring. Further, 9.12 mL of hydrogen peroxide solution (hydrogen peroxide 31%, Kanto Chemical) was added dropwise. After completion of the dropping, the mixture was heated in an oil bath at a temperature of 60 ° C. and subjected to oxidation and hydrolysis reaction for 15 hours while stirring.

  The obtained reaction solution was added dropwise to methanol with stirring. The precipitate was collected and dried to remove the solvent to obtain a hydroxyl-modified copolymer.

Example 2
3 g of uncrosslinked butyl rubber used in Example 1 was dissolved in a flask in which 450 mL of tetrahydrofuran was introduced, 12 mL of borane / tetrahydrofuran complex (11 equivalents of B—H group per equivalent of bound isoprene), 3.93 g of sodium hydroxide The procedure of Example 1 was repeated using 20 mL of a solution in which methanol was dissolved in methanol and 15.2 mL of hydrogen peroxide. The solution did not gel after hydroboration.

Example 3
3 g of uncrosslinked butyl rubber used in Example 1 was dissolved in a flask into which 400 mL of tetrahydrofuran was introduced, 3.6 mL of borane / tetrahydrofuran complex (3.3 equivalents of B—H groups per equivalent of bound isoprene), hydroxylated The procedure of Example 1 was repeated using 5.8 mL of a solution obtained by dissolving 3.93 g of sodium in methanol and 4.56 mL of hydrogen peroxide. The solution did not gel after hydroboration.

Example 4
6 g of uncrosslinked butyl rubber used in Example 1 was dissolved in a flask into which 450 mL of tetrahydrofuran was introduced, 12 mL of borane / tetrahydrofuran complex (5.5 equivalents of B—H group per equivalent of bound isoprene), sodium hydroxide 3 The procedure of Example 1 was repeated using 20 mL of a solution obtained by dissolving .93 g in methanol and 15.2 mL of aqueous hydrogen peroxide. The solution gelled after hydroboration, but dissolved in the course of the next oxidation and hydrolysis reaction, and a viscous reaction solution was obtained after the reaction.

Example 5
6 g of uncrosslinked butyl rubber used in Example 1 was dissolved in a flask introduced with 450 mL of tetrahydrofuran, and 9-borabicyclo [3,3,1] -nonane (Kanto Chemical) was dissolved in 24 mL (B-per equivalent of bound isoprene). The procedure of Example 1 was repeated using 20 mL of a solution of 11 equivalents of H groups), 3.93 g of sodium hydroxide in methanol, and 15.5 mL of hydrogen peroxide. The solution did not gel after hydroboration.

Comparative Example 1
3 g of the uncrosslinked butyl rubber used in Example 1 was dissolved in a flask in which 400 mL of tetrahydrofuran was introduced, and 2.5 mL of borane / tetrahydrofuran complex (2.3 equivalents of B—H groups per equivalent of bound isoprene) was hydroxylated. The procedure of Example 1 was repeated using 4.0 mL of a solution prepared by dissolving 3.93 g of sodium in methanol and 3.18 mL of hydrogen peroxide. The solution did not gel after hydroboration.

FIG. 1 shows ¹ H-NMR data of the hydroxyl-modified copolymer obtained in Example 1 and the starting material, uncrosslinked butyl rubber. Using an AL-400 MHz-NMR spectrometer manufactured by JEOL Ltd., 10 to 50 mg of the hydroxyl-modified copolymer or starting material was dissolved in 1 mL of deuterated chloroform as a solvent and measured at 24 ° C. Signal chemical shift δ5.05ppm corresponds to the signal of the ^{H a} in uncrosslinked butyl rubber of the formula (I), signal δ3.30ppm corresponds to the signal of the ^{H b} at the anti-Markovnikov hydration product of formula (II) . The signal of the Markovnikov hydration part overlapped with other signals and could not be recognized.

  As is clear from FIG. 1, in the hydroxyl-modified copolymer of Example 1, the signal of chemical shift δ5.05 ppm disappeared, and the hydroxyl-modified copolymer substantially has a carbon-carbon double bond. I understand that it is not.

The following table summarizes the presence or absence of a signal with a chemical shift of δ5.05 ppm and a signal of δ3.30 ppm in each of Examples 1 to 5 and Comparative Example 1.

  From the above results, the borane-tetrahydrofuran complex is more suitable for hydroboration of uncrosslinked butyl rubber than 9-borabicyclo [3,3,1] -nonane if the number of equivalents is the same. It can be seen that the hydroboration hardly proceeds when the tetrahydrofuran complex is 2.3 equivalents.

  FIG. 2 shows thermogravimetric analysis data of the hydroxyl-modified copolymer obtained in Example 1 and the starting material uncrosslinked butyl rubber. A TG / DTA6200 thermogravimetric analyzer manufactured by Seiko Denshi Kogyo Co., Ltd. was used, and measurement was performed in a nitrogen stream (100 mL / min) at a temperature rising rate of 10 ° C./min. The thermal decomposition starting temperature of the hydroxyl-modified copolymer is about 360 ° C., and the thermal decomposition starting temperature of the uncrosslinked butyl rubber is about 280 ° C. It can be seen that the heat resistance is improved by saturation of the carbon-carbon double bond.

2. Preparation and crosslinking of curable rubber composition Example 6
The hydroxyl-modified copolymer obtained in Example 1, the isophthalic acid chloride as a crosslinking agent, and tributylamine were kneaded by a two-roll mill to obtain a solid phase composition. One equivalent of isophthalic acid chloride and one equivalent of tributylamine were used per equivalent of hydroxyl group in the hydroxyl-modified copolymer.

  About the obtained solid-phase composition, rheometer curve (time-torque, time-tan-delta) was measured on condition of 195 degreeC and measurement pressure 0.35MPa using ALPHA TECHNOLOGIES Rheometer MDR2000.

  Furthermore, about the ester crosslinked rubber molding after rheometer curve measurement, the FT-IR spectrum was measured by the film method using Perkin-Elmer 1600-FT-IR infrared spectrometer. Moreover, the molded object was hold | maintained at 150 degreeC and the change of the Shore A hardness (peak hardness) and the weight loss were measured.

Comparative Example 2
To 100 g of Bayer's partially crosslinked rubber XL-10000, 2 g of dicumyl peroxide (40% diluted product) was added and kneaded to obtain a solid phase composition. In the same manner as in Example 1, a rheometer MDR2000 manufactured by ALPHA TECHNOLOGIES was used, and the obtained solid phase composition was subjected to a rheometer curve (time-torque, time-tan δ) under the conditions of 170 ° C. and measurement pressure 0.35 MPa. Measurements were made. Further, in the same manner as in Example 6, the crosslinked rubber molded body after the rheometer curve measurement was held at 150 ° C., and the change in Shore A hardness (peak hardness) and the weight loss were measured.

FIG. 3 shows FT-IR spectrum data of the ester crosslinked rubber of Example 6 and the uncrosslinked butyl rubber starting material. In the spectrum of the ester-crosslinked rubber, a C═O stretching vibration band of isophthalic acid ester-bonded at 1720 ± 10 cm ⁻¹ is observed. Although the C═O stretching vibration bands in isophthalic acid chlorides are observed at 1710 ± 10 cm ⁻¹ and 1765 ± 5 cm ⁻¹ , these bands are not observed in the FT-IR spectrum of the ester-crosslinked rubber. It can be seen that all of the objects have reacted substantially.

  FIG. 4 shows rheometer curves in Example 6 and Comparative Example 2. As the crosslinking proceeds, the torque value increases and the tan δ value decreases. At the start of crosslinking, the torque value in Example 6 is smaller than the torque value in Comparative Example 2, and the processability of the curable rubber composition of the present invention is better than the curable rubber composition using the conventional partially crosslinked rubber. I understand. On the other hand, in Comparative Example 2, the Max torque value is 3.0 dNm, whereas in Example 6, although it takes about 5 minutes to complete the crosslinking, the Max torque value reaches 4.3 dNm. It can be seen that the ester-crosslinked rubber of the invention is superior in crosslinkability to a rubber obtained by crosslinking a conventional partially crosslinked rubber. The tan δ value was 0.1 or less in both Example 6 and Comparative Example 2, and both were good values.

  FIG. 5 is a graph showing changes in hardness in an aging test in an atmosphere of 150 ° C. of the ester crosslinked rubber of the present invention of Example 6 and the conventional crosslinked rubber of Comparative Example 2. The initial Shore A hardness was 30 Hs in Example 6 and 25 Hs in Comparative Example 2, and the ester crosslinked rubber of the present invention of Example 6 showed a larger value than the conventional crosslinked rubber of Comparative Example 2. As can be understood from FIG. 4, this result is considered to reflect that the ester crosslinked rubber of the present invention is superior in crosslinkability than the conventional crosslinked rubber.

  The ester-crosslinked rubber of the invention of Example 6 did not decrease Shore A hardness and maintained about 33 Hs even after 24 hours at 150 ° C. On the other hand, the conventional crosslinked rubber of Comparative Example 2 had a Shore A hardness greatly reduced only after 1 hour at 150 ° C., and was not measurable thereafter.

  6 is a graph showing changes in weight in an aging test in an atmosphere of 150 ° C. of the ester crosslinked rubber of the present invention of Example 6 and the conventional crosslinked rubber of Comparative Example 2. FIG. After 24 hours at 150 ° C., the conventional crosslinked rubber of Comparative Example 2 showed about twice the weight loss of the inventive ester crosslinked rubber of Example 6.

  As understood from FIGS. 5 and 6, the ester crosslinked rubber of the present invention is superior in heat resistance and hardness to a crosslinked rubber obtained by crosslinking a conventional partially crosslinked rubber with an organic peroxide.

It is a diagram showing ^{1 H-NMR} data of the hydroxyl modified copolymer uncrosslinked butyl rubber of the starting materials. It is a figure which shows the thermogravimetric analysis curve of the hydroxyl-modified copolymer and the uncrosslinked butyl rubber of a starting material. It is a figure which shows the FT-IR spectrum data of the ester crosslinked rubber of this invention, and the uncrosslinked butyl rubber of a starting material. It is a figure which shows the rheometer curve of the ester crosslinked rubber of this invention, and the conventional partial crosslinked rubber. It is a figure which shows the hardness change in the aging test in 150 degreeC atmosphere of the ester crosslinked rubber of this invention, and the conventional partial crosslinked rubber. It is a figure which shows the weight loss in the aging test in 150 degreeC atmosphere of the ester crosslinked rubber of this invention, and the conventional partial crosslinked rubber.

Claims (14)

  90 to 99.5 mol% of at least one isomonoolefin having 4 to 7 carbon atoms and 0.5 to 10 mol% of at least one aliphatic diene having 4 to 14 carbon atoms A hydroxyl-modified copolymer in which a hydroxyl group is added to a carbon-carbon double bond of a polymerized rubber-like copolymer, a crosslinking agent having at least two functional groups capable of forming an ester bond by reaction with the hydroxyl group; An ester-crosslinked rubber crosslinked through an ester bond, crosslinked by an esterification reaction.   The ester-crosslinked rubber according to claim 1, wherein the amount of bonded aliphatic diene in the rubbery copolymer is 0.6 to 2.5 mol%.   The ester-crosslinked rubber according to claim 1 or 2, wherein the isomonoolefin is isobutene and the aliphatic diene is isoprene.   The ester-crosslinked rubber according to any one of claims 1 to 3, wherein a hydroxyl-modified copolymer substantially free of carbon-carbon double bonds is crosslinked. 90 to 99.5 mol% of at least one isomonoolefin having 4 to 7 carbon atoms and 0.5 to 10 mol% of at least one aliphatic diene having 4 to 14 carbon atoms A hydroxyl-modified copolymer in which a hydroxyl group is added to the carbon-carbon double bond of the rubber-like copolymer by dissolving the polymerized rubber-like copolymer in a solvent, hydroborating, further oxidizing and hydrolyzing. A denaturing step to obtain a coalescence,
A preparation step of obtaining a curable rubber composition by mixing the hydroxyl-modified copolymer and a crosslinking agent having at least two functional groups capable of forming an ester bond by reaction with a hydroxyl group; and
A cross-linking step of obtaining an ester cross-linked rubber cross-linked via an ester bond by esterifying the hydroxyl group of the hydroxyl-modified copolymer in the curable rubber composition and the functional group of the cross-linking agent. A method for producing an ester-crosslinked rubber characterized by the above.   The method for producing an ester-crosslinked rubber according to claim 5, wherein the amount of bonded aliphatic diene in the rubbery copolymer is 0.6 to 2.5 mol%.   The method for producing an ester-crosslinked rubber according to claim 5 or 6, wherein the isomonoolefin is isobutene and the aliphatic diene is isoprene.   In the modification step, hydroboration is performed using 3 to 15 equivalents of a hydroborating agent per equivalent of bonded aliphatic diene in the rubbery copolymer, so that the hydroxyl modification is substantially free of carbon-carbon double bonds. The method for producing an ester-crosslinked rubber according to any one of claims 5 to 7, wherein a copolymer is obtained.   The hydroboration is performed in a solution having a concentration of the rubbery copolymer of 1 w / v% or less using a hydroborating agent having two or more B—H bonds in the modification step. The manufacturing method of ester crosslinked rubber as described in any one of Claims 1-3.   In the said preparation process, at least 1 sort (s) of compound selected from dicarboxylic acid, dicarboxylic anhydride, dicarboxylic acid halide, and dicarboxylic acid ester is used as said crosslinking agent. The manufacturing method of ester crosslinked rubber as described in claim | item.   The method for producing an ester-crosslinked rubber according to claim 10, wherein in the preparation step, 1 to 3 equivalents of the crosslinking agent is used per equivalent of bonded aliphatic diene in the rubbery copolymer.   90 to 99.5 mol% of at least one isomonoolefin having 4 to 7 carbon atoms and 0.5 to 10 mol% of at least one aliphatic diene having 4 to 14 carbon atoms A hydroxyl-modified copolymer in which a hydroxyl group is added to a carbon-carbon double bond of a polymerized rubber-like copolymer, and a crosslinking agent having at least two functional groups capable of forming an ester bond by reaction with the hydroxyl group; A curable rubber composition containing   90 to 99.5 mol% of at least one isomonoolefin having 4 to 7 carbon atoms and 0.5 to 10 mol% of at least one aliphatic diene having 4 to 14 carbon atoms A hydroxyl-modified copolymer in which a hydroxyl group is added to a carbon-carbon double bond of a polymerized rubbery copolymer, and the carbon-carbon double bond is substantially absent.   The molded object containing the ester crosslinked rubber of any one of Claims 1-4.

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