Crosslinking method for elastomers

Abstract

To provide a crosslinking method of an elastomer using an elastomer which can easily be crosslinked and decrosslinked.SOLUTION: Provided is a crosslinking method of an elastomer, where the elastomer has a monoboronic acid ester-containing functional group represented by a predetermined general formula (4) and the crosslinking method includes a step of contacting the elastomer with a diboronic acid compound in the presence of a solvent, where the solvent has an SP value of 10 (cal / cm3)1 / 2 to 13 (cal / cm3)1 / 2 and contains at least a single solvent having an SP value of 8 (cal / cm3)1 / 2 to 10 (cal / cm3)1 / 2.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for crosslinking elastomers. [Background technology]

[0002] Recently, from the viewpoints of environmental issues and resource conservation, recycling of vulcanized rubber (crosslinked rubber) used in tires, etc. after use has been promoted. As a recycling technology for vulcanized rubber, a method of devulcanizing vulcanized rubber has been known, but the devulcanization reaction requires very high temperatures, which has the drawback of being energy inefficient.

[0003] Therefore, techniques for decomposing vulcanized rubber by methods other than devulcanization have also been investigated. For example, Patent Document 1 discloses a method for decomposing and recovering vulcanized rubber, in which vulcanized rubber is decomposed by a lipid peroxidation reaction, and the lipids are removed in alcohol to which an alkali has been added to recover the rubber component. This method is disclosed to have a low decomposition reaction temperature, excellent energy efficiency, a fast decomposition rate, and to produce decomposition products that are easy to recycle and recover. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-153272 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology of Patent Document 1 above targets vulcanized rubber in general as the decomposition target, and does not consider at all rubber (crosslinked elastomer) crosslinked by a method other than vulcanization (sulfur crosslinking).

[0006] Furthermore, focusing on the crosslinked elastomer itself, the development of a crosslinked elastomer that can be easily decrosslinked and subsequently recrosslinked (having so-called reversible crosslinking properties) would be extremely useful from the viewpoint of further effective utilization and versatility of materials.

[0007] Therefore, an object of the present invention is to provide a method for crosslinking an elastomer using an elastomer that can be easily crosslinked and decrosslinked. [Means for solving the problem]

[0008] As a result of intensive research to solve the above problems, the present inventors have found that by using an elastomer having a specific functional group at a site to be crosslinked, crosslinking and subsequent de-crosslinking can be easily carried out starting from the site under predetermined conditions, and have thus completed the present invention. That is, the gist of the present invention that solves the above problems is as follows.

[0009] The present invention provides a method for crosslinking an elastomer, comprising the steps of: The elastomer has the following general formula (4): [ka] [where, X 2 is hydrogen or any monovalent group; contacting the elastomer with a diboronic acid compound in the presence of a solvent; The solvent has an SP value of 10 (cal / cm 3 ) 1 / 2 More than 13(cal / cm 3 ) 1 / 2 The SP value is 8 (cal / cm 3 ) 1 / 2 More than 10(cal / cm 3 ) 1 / 2 The composition is characterized by containing at least one single solvent, which is: The method for crosslinking an elastomer uses an elastomer that can be easily crosslinked and decrosslinked.

[0010] In the crosslinking method of the present invention, the amount of the diboronic acid compound in the contacting step is preferably 20 parts by mass or less relative to 100 parts by mass of the elastomer, which allows the elastomer to sufficiently maintain its elastomeric properties after crosslinking.

[0011] In the crosslinking method of the present invention, the elastomer is preferably derived from a diene-based elastomer having a vinyl bond content of 30% by mass or less and a weight-average molecular weight of 1000 or more. In this case, gelation can be effectively suppressed when the elastomer is heated and molded, and sufficient entanglement occurs in the elastomer after crosslinking, allowing the elastomer to exhibit sufficient mechanical strength when used in rubber articles such as tires. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a method for crosslinking an elastomer using an elastomer that can be easily crosslinked and decrosslinked. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described. However, these descriptions are for the purpose of illustrating the present invention and are not intended to limit the present invention in any way.

[0014] (Method of crosslinking elastomer) A method for crosslinking an elastomer according to one embodiment of the present invention (hereinafter sometimes referred to as the "crosslinking method of the present embodiment") comprises crosslinking an elastomer containing a compound represented by the following general formula (4): [ka] [where, X 2 is hydrogen or any monovalent group], a step of contacting the elastomer with a diboronic acid compound in the presence of a solvent (diboronic acid contacting step), The solvent has an SP value of 10 (cal / cm 3 ) 1 / 2 More than 13(cal / cm 3 ) 1 / 2 The SP value is 8 (cal / cm 3 ) 1 / 2 More than 10(cal / cm 3 ) 1 / 2 The composition is characterized by containing at least one single solvent, which is:

[0015] In this specification, the term "diboronic acid compound" refers to a compound having two boronic acids (-B(OH)2) in one molecule.

[0016] When the elastomer described above is contacted with a diboronic acid compound in the presence of a specific solvent, an exchange reaction occurs at the monoboronic acid ester-containing functional group in the elastomer, and the monoboronic acid ester is replaced with the ester derived from the diboronic acid compound. In this regard, since the diboronic acid compound has two boronic acids that function as bonding bonds to the elastomer, linking (crosslinking) elastomers together is achieved. Therefore, crosslinking can be easily achieved using the crosslinking method of this embodiment. Furthermore, when the crosslinked elastomer (crosslinked elastomer) is brought into contact with a monoboronic acid compound under certain conditions, an exchange reaction occurs at the crosslinking sites of the crosslinked elastomer, and crosslinks via the diboronic acid ester skeleton unit replace the bonds of the monoboronic acid compound. In this regard, since the monoboronic acid compound has only one boronic acid that functions as a bond to the elastomer, the bonds between the elastomers are eliminated (in other words, decrosslinked). Therefore, the elastomer used in the crosslinking method of this embodiment can be easily crosslinked and decrosslinked. Furthermore, the elastomer after decrosslinking has a structure substantially equivalent to that of the elastomer used in the crosslinking method of the present embodiment. Therefore, by using the crosslinking method of the present embodiment, it is expected that the elastomer can be easily decrosslinked and recrosslinked repeatedly.

[0017] <Elastomer> The elastomer used in the crosslinking method of the present embodiment is represented by the following general formula (4): [ka] [where, X 2 is hydrogen or any monovalent group. 2 Examples of the monovalent group that can be mentioned include hydrocarbon groups, and specific examples include linear or branched aliphatic groups having 1 to 10 carbon atoms (alkyl groups, alkenyl groups, alkynyl groups); aromatic-containing groups having 6 to 20 carbon atoms (phenyl groups, naphthyl groups, biphenyl groups, etc.); heteroaromatic groups (2-furyl groups, etc.). The aliphatic groups and aromatic-containing groups include -O-, -S-, -OC(=O)-, -C(=O)-O-, -OC(=O)-O-, -NR 2 -C(=O)-, -C(=O)-NR 2 -, -NR 2 - or -C(=O)- may be present. 2 represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

[0018] The elastomer used in the crosslinking method of this embodiment is preferably derived from a diene-based elastomer. In other words, the elastomer used in the crosslinking method of this embodiment is preferably a diene-based elastomer to which a monoboronic acid ester-containing functional group has been added. Here, the diene-based elastomer refers to an elastomer containing at least a diene unit, and examples thereof include natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), and chloroprene rubber (CR). The diene-based elastomer may be used alone or in combination of two or more. Among these, butadiene rubber (BR) and styrene-butadiene rubber (SBR) are preferred as the diene-based elastomer from the viewpoint of ensuring sufficient mechanical strength of rubber articles such as tires.

[0019] The diene elastomer preferably has a vinyl bond content of 30% by mass or less and a weight-average molecular weight (Mw) of 1,000 or more. In other words, the elastomer used in the crosslinking method of this embodiment is preferably derived from a diene elastomer having a vinyl bond content of 30% by mass or less and a weight-average molecular weight of 1,000 or more. When the vinyl bond content of the diene elastomer is 30% by mass or less, gelation can be effectively suppressed when the elastomer is heated and molded. When the weight-average molecular weight (Mw) of the diene elastomer is 1,000 or more, sufficient entanglement occurs in the elastomer after crosslinking, allowing the elastomer to exhibit sufficient mechanical strength when used in rubber articles such as tires. From the same viewpoint, the vinyl bond content of the diene elastomer is preferably 28% by mass or less, and more preferably 26% by mass or less. On the other hand, the lower limit of the vinyl bond content of the diene elastomer is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, and particularly preferably 10% by mass or more. In this specification, the vinyl bond content of a diene elastomer refers to the mass proportion of diene units that are vinyl-bonded to the entire diene elastomer, not the proportion of vinyl-bonded units to the diene units. The weight average molecular weight (Mw) can be determined by gel permeation chromatography (GPC) using polystyrene as a standard substance.

[0020] When the elastomer is derived from a diene-based elastomer, the monoboronic acid ester-containing functional group in the elastomer is preferably bonded to a carbon atom constituting a vinyl group remaining in a vinyl-bonded diene unit in the diene-based elastomer. The bond between the monoboronic acid ester-containing functional group and the diene-based elastomer may be a direct bond or a bond via an arbitrary group (e.g., an alkylene group having 1 to 3 carbon atoms).

[0021] The elastomer used in the crosslinking method of this embodiment may have a filler such as carbon black dispersed therein by blending it during the production of the elastomer. When the filler is dispersed in the elastomer, the blending amount of the filler per 100 parts by mass of the elastomer may be 10 parts by mass or more and 100 parts by mass or less.

[0022] The elastomer used in the crosslinking method of the present embodiment is not particularly limited and can be prepared by various methods. For example, the elastomer used in the crosslinking method of the present embodiment can be obtained by crosslinking a diene-based elastomer in the following step A to obtain a crosslinked elastomer, and then returning the crosslinked sites of the crosslinked elastomer to an uncrosslinked state in the following step B.

[0023] <Step A for obtaining elastomer> In step A, a diene-based elastomer (a diene-based elastomer having no monoboronic acid ester-containing functional group) is reacted with a compound represented by the following general formula (2) in the presence of a radical initiator: [ka] [where, X 1 is a single bond or any divalent group, and Y 1 and Y 2 and each independently represent a single bond or a divalent hydrocarbon group, thereby forming a diboronic acid ester compound represented by the following general formula (1): [ka] [where, X 1 is a single bond or any divalent group], thereby obtaining a crosslinked elastomer having a diboronic acid ester skeleton unit represented by the formula:

[0024] Specifically, in the above-mentioned step A, a radical initiator and a diboronic acid ester compound are blended with the above-mentioned diene-based elastomer, mixed in a mixer or the like, and the mixture is heated to obtain a crosslinked elastomer. The heating temperature and time are preferably adjusted appropriately taking into consideration the vinyl bond content of the diene-based elastomer used, the type and amount of the radical initiator used, etc.

[0025] In addition to the diene elastomer, radical initiator, and diboronic acid ester compound, an appropriate amount of other components may be added in step A. Examples of other components include fillers such as carbon black.

[0026] <Step B for obtaining elastomer> In step B, the crosslinked elastomer obtained in step A is reacted with a compound represented by the following general formula (3): [ka] [In the formula, X 2 is hydrogen or any monovalent group]. In this step B, an exchange reaction occurs at the crosslinking site of the crosslinked elastomer, and the crosslinking via the diboronic acid ester skeleton unit replaces the bond of the monoboronic acid compound. In this step, typically, the crosslinking sites of the two linked elastomers are bonded to a monoboronic acid compound represented by the following general formula (4): [ka] In this way, the elastomer used in the crosslinking method of the present embodiment can be obtained. In step B, at the same time as capping the functional groups, typically, a functional group represented by the following formula (9): derived from the diboronic acid ester skeleton unit at the crosslinking site is capped. [ka] This results in the production of a diboronic acid compound represented by the following formula: Such a diboronic acid compound can be used as the diboronic acid compound essential for the crosslinking method of this embodiment.

[0027] The organic solvent used in step B has an SP value of 7 (cal / cm 3 ) 1 / 2 More than 10(cal / cm 3 ) 1 / 2 In this case, the compatibility with the crosslinked elastomer is increased, and the exchange reaction can be more reliably caused. The SP value can be calculated according to the Hansen method. The organic solvent may be a single solvent or a mixed solvent.

[0028] In the above step B, the molar abundance ratio of the monoboronic acid compound to the diboronic acid ester skeleton unit (monoboronic acid compound / diboronic acid ester skeleton unit) is preferably more than 2 and not more than 5. In this case, the linkage between the elastomers can be effectively eliminated, and the subsequent crosslinking (i.e., crosslinking by the crosslinking method of the present embodiment) can also be more easily carried out.

[0029] The elastomer obtained through the above-mentioned steps A and B is, in short, a decrosslinked elastomer. Furthermore, when the crosslinking method of the present embodiment is carried out using such a decrosslinked elastomer, the resulting crosslinked elastomer has substantially the same structure as the crosslinked elastomer obtained in step A. In other words, in this case, decrosslinking and recrosslinking can be easily repeated.

[0030] <Solvent> The solvent used in the crosslinking method of this embodiment has an SP value of 10 (cal / cm 3 ) 1 / 2 More than 13(cal / cm 3 ) 1 / 2 The SP value is 8 (cal / cm 3 ) 1 / 2 More than 10(cal / cm 3 ) 1 / 2It is necessary to include at least a single solvent whose SP value as a whole is 10 (cal / cm 3 ) 1 / 2 More than 13(cal / cm 3 ) 1 / 2 If the value is outside the range below, the compatibility with the elastomer may be reduced, and the exchange reaction in the monoboronic acid ester-containing functional group may not occur sufficiently. 3 ) 1 / 2 More than 10(cal / cm 3 ) 1 / 2 If the solvent does not contain a single solvent having a viscosity of 100 MPa or less, the compatibility with the elastomer will be low, and there is a risk that the exchange reaction at the monoboronic acid ester-containing functional group will not occur sufficiently. Furthermore, when a filler is dispersed in the elastomer, the SP value of the solvent as a whole should be 11 (cal / cm) or less, from the viewpoint of more reliably causing the exchange reaction. 3 ) 1 / 2 The above is preferable. The SP value can be calculated according to the Hansen method.

[0031] In addition, the SP value is 8 (cal / cm 3 ) 1 / 2 More than 10(cal / cm 3 ) 1 / 2 Examples of the following single solvents include, but are not limited to, toluene, tetrahydrofuran (THF), and the like.

[0032] <Diboronic acid compounds> The diboronic acid compound used in the crosslinking method of the present embodiment is, for example, a compound represented by the following general formula (9): [ka] [In the formula, X 1 is a single bond or any divalent group. 1Examples of divalent groups that may be mentioned include hydrocarbon groups, and specific examples include linear or branched aliphatic groups having 1 to 10 carbon atoms (alkylene groups, alkenylene groups, alkynylene groups); aromatic-containing groups having 6 to 20 carbon atoms (1,2-phenylene groups, 1,3-phenylene groups, 1,4-phenylene groups, 1,4-naphthylene groups, 1,5-naphthylene groups, 2,6-naphthylene groups, 4,4'-biphenylene groups, etc.). In addition, the aliphatic groups and aromatic-containing groups include -O-, -S-, -OC(=O)-, -C(=O)-O-, -OC(=O)-O-, -NR 2 -C(=O)-, -C(=O)-NR 2 -, -NR 2 - or -C(=O)- may be present. 2 represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

[0033] X in general formula (9) 1 The divalent group which can be represented by X in the above general formula (4) 2 It is preferable that the X in the general formula (4) is the same as the monovalent group obtained by removing hydrogen from the group 2 If an elastomer in which X is a phenyl group is used, 1 It is preferable to use a diboronic acid compound in which is a phenylene group, in which case the exchange reaction can be more effectively carried out.

[0034] <Diboronic acid contact step> In the diboronic acid contacting step, the elastomer is contacted with the diboronic acid compound in the presence of the above-mentioned predetermined solvent. This contact causes an exchange reaction at the monoboronic acid ester-containing functional group in the elastomer. In this case, for example, when the diboronic acid compound represented by the above general formula (9) is used, the two elastomers are typically converted into the diboronic acid compound represented by the following general formula (1): [ka] At the same time, crosslinking is typically achieved via a moiety having a diboronic acid ester skeleton unit represented by the following general formula (3): [ka] Thus, a monoboronic acid compound represented by the following formula is produced.

[0035] In the diboronic acid contacting step, the amount of the diboronic acid compound is preferably 20 parts by mass or less per 100 parts by mass of the elastomer. In this case, the elastomeric properties can be sufficiently maintained after crosslinking. From the same viewpoint, the amount of the diboronic acid compound per 100 parts by mass of the elastomer is more preferably 16 parts by mass or less, and even more preferably 11 parts by mass or less. On the other hand, the lower limit of the amount of the diboronic acid compound per 100 parts by mass of the elastomer is not particularly limited as long as it is more than 0 parts by mass, but from the viewpoint of increasing the strength of the resulting crosslinked elastomer to the same level as that of sulfur crosslinking, it is preferably 1 part by mass or more, and more preferably 2 parts by mass or more.

[0036] In the diboronic acid contact step, the elastomer concentration (the mass ratio of the elastomer to the total mass of the elastomer and the solvent) is preferably 5% by mass or more and 65% by mass or less. If the elastomer concentration is within the above range, crosslinking can be achieved more sufficiently and effectively. From the same viewpoint, the elastomer concentration is more preferably 10% by mass or more. In particular, when a filler is dispersed in the elastomer, the elastomer concentration is more preferably 20% by mass or more. The lower the concentration of the elastomer, the more the elastomer is immersed in the solvent, whereas the higher the concentration of the elastomer, the more the elastomer is swollen with the solvent.

[0037] The specific conditions (temperature, time, etc.) for the diboronic acid contact step are not particularly limited. However, to increase the frequency of contact with the diboronic acid compound, it is preferable to finely pulverize the elastomer in advance. Furthermore, after the diboronic acid contact step, a solid-liquid separation treatment may be performed using a known method. [Example]

[0038] The present invention will be described in more detail below with reference to examples. However, these examples are intended to illustrate the present invention and are not intended to limit the present invention in any way.

[0039] In the following, in addition to the method for crosslinking the elastomer of the present invention, examples of the pre-processing steps A and B for obtaining the elastomer will also be shown in series.

[0040] (Preparation of Crosslinked Elastomer) Elastomer compositions were prepared according to the formulations shown in Table 1. Next, these elastomer compositions were heated under the conditions shown in Table 1 using a rubber processability analyzer (manufactured by Alpha Technologies), and the storage modulus G' was measured. The results are shown in Table 1. In all examples, the storage modulus G' was approximately the desired value, and therefore it was determined that crosslinking had occurred. Reference Example 1 is an example of sulfur crosslinking (vulcanization) without using carbon black as a filler, while Examples 1-1 to 1-4 are examples in which the carbon black was not used and the conditions were appropriately adjusted so that the storage modulus G' approximated that of Reference Example 1. Similarly, Reference Example 2 is an example of sulfur crosslinking (vulcanization) with carbon black as a filler, while Example 1-5 is an example in which the carbon black was used and the conditions were appropriately adjusted so that the storage modulus G' approximated that of Reference Example 2.

[0041] [Table 1]

[0042] *1 Diene elastomer: Asahi Kasei Corporation, "Tufden (registered trademark) 2000R", styrene-butadiene rubber, vinyl bond content: 10 to 26% by mass, weight average molecular weight: 373,000 (3 significant digits) *2 BDB: Diboronic acid ester compound (synthetic product) represented by the following formula (5) [ka] *3 CB: HAF grade carbon black *4 Radical initiator: azobisisobutyronitrile (AIBN) *5 Vulcanization accelerator DPG: 1,3-diphenylguanidine *6 Vulcanization accelerator MBTS: Di-2-benzothiazolyl disulfide *7 Vulcanization accelerator TBBS: N-(tert-butyl)-2-benzothiazole sulfenamide

[0043] The crosslinked elastomers obtained in Examples 1-1 to 1-5 were found to be a compound of the following formula (6) by appropriate use of solution NMR: [ka] Furthermore, in these crosslinked elastomers, the diboronic acid ester skeleton unit is directly bonded to the carbon atom constituting the vinyl group remaining in the vinyl-bonded butadiene unit in the diene-based elastomer, thereby forming a crosslink.

[0044] (Decrosslinking treatment of crosslinked elastomer) Here, the crosslinked elastomer obtained in Example 1-4 was selected as an elastomer not mixed with carbon black, and the crosslinked elastomer obtained in Example 1-5 was selected as an elastomer mixed with carbon black. This crosslinked elastomer was finely crushed and then dissolved in tetrahydrofuran (THF, SP value: 8.95 (cal / cm 3 ) 1 / 2), and then phenylboronic acid (PhB(OH)2) as the monoboronic acid compound (BA) was added and mixed thoroughly, and the mixture was left to stand at room temperature (approximately 25°C) for one day. At this time, the concentration of the crosslinked elastomer (mass ratio of the crosslinked elastomer to the total of the crosslinked elastomer and organic solvent) and the molar abundance ratio of the monoboronic acid compound to the diboronic acid ester skeleton unit in the crosslinked elastomer (BA / BDB skeleton unit) were adjusted to be as shown in Table 2. After standing, the mixture was cast and the solvent was evaporated to obtain a treated elastomer.

[0045] <Evaluation of decrosslinking> The resulting treated elastomer was subjected to roll molding. If roll molding was possible, it was evaluated as having been decrosslinked (the crosslinked sites had returned to an uncrosslinked state), thereby imparting softness. The results are shown in Table 2.

[0046] [Table 2]

[0047] As shown in Table 2, the evaluation results for decrosslinking were good in all of Examples 2-1 to 2-7. That is, the crosslinked elastomers obtained in Examples 1-4 and 1-5 could be easily decrosslinked by contacting them with a monoboronic acid compound in the presence of a predetermined organic solvent.

[0048] In the treated elastomers (decrosslinked elastomers) obtained in Examples 2-1 to 2-7, solution NMR was appropriately used to confirm that the bonding site of the skeleton represented by the above formula (6) in the crosslinked elastomer before treatment was replaced by the bonding site of the skeleton represented by the following formula (7): [ka] It was confirmed that the crosslinking was eliminated (the crosslinked site returned to an uncrosslinked state). At the same time, by appropriately using solution NMR, it was possible to identify the functional group represented by the following formula (8): [ka] It was confirmed that a diboronic acid compound ((1,4-phenylene)diboronic acid) represented by the formula:

[0049] Furthermore, since the crosslinked elastomers obtained in Examples 1-1 to 1-3 also have the above-mentioned diboronic acid ester skeleton unit, it is believed that they can be easily decrosslinked by the same treatment as above.

[0050] (Recrosslinking of decrosslinked elastomer) Here, the decrosslinked elastomer (treated elastomer) obtained in Example 2-2 or Example 2-3 was selected as an elastomer not containing carbon black, and the decrosslinked elastomer (treated elastomer) obtained in Example 2-5 was selected as an elastomer containing carbon black. This decrosslinked elastomer was placed in a solvent shown in Table 3 together with the diboronic acid compound produced during the decrosslinking treatment, and a radical initiator was then added in the formulation shown in Table 3, followed by standing overnight at room temperature (approximately 25°C). At this time, the concentration of the decrosslinked elastomer (the mass proportion of the decrosslinked elastomer in the total of the decrosslinked elastomer and the solvent) was adjusted to be as shown in Table 3. After standing, the mixture was cast and the solvent was evaporated to obtain a treated elastomer.

[0051] <Evaluation of crosslinking (recrosslinking)> The resulting treated elastomer was heated at 120°C for 10 to 30 minutes (until the storage modulus G' value stabilized) using a rubber processability analyzer (Alpha Technologies), and the storage modulus G' was measured. In all cases, the measured storage modulus G' was 20% or more compared to the storage modulus G' of the crosslinked elastomer before the addition of the monoboronic acid compound, indicating that crosslinking had occurred. More specifically, if the measured storage modulus G' was 50% or more compared to the storage modulus G' of the crosslinked elastomer before the addition of the phenylboronic acid, the crosslinking was evaluated as having a sufficient amount of crosslinking, and was evaluated as "Good." On the other hand, if the measured storage modulus G' was less than 50%, the crosslinking was evaluated as "Fair." The results are shown in Table 3.

[0052] [Table 3]

[0053] As shown in Table 3, the uncrosslinked elastomers obtained in Examples 2-2, 2-3, and 2-5 could be easily crosslinked (recrosslinked) by contacting them with a diboronic acid compound in the presence of a specific solvent.

[0054] The treated elastomers (re-crosslinked elastomers) obtained in Examples 3-1 to 3-7 were analyzed by solution NMR as follows: [ka] It was confirmed that each of the treated elastomers (re-crosslinked elastomers) obtained in Examples 3-1 to 3-7 had a structure substantially equivalent to that of the crosslinked elastomers obtained in Examples 1-1 to 1-5. [Industrial Applicability]

[0055] According to the present invention, it is possible to provide a method for crosslinking an elastomer using an elastomer that can be easily crosslinked and decrosslinked.

Claims

1. 1. A method for crosslinking an elastomer, comprising: The elastomer has the following general formula (4): 【Chemistry 1】 [In the formula, X ２ is hydrogen or any monovalent group; the elastomer is derived from a diene-based elastomer having a vinyl bond content of 30% by mass or less and a weight-average molecular weight of 1,000 or more, contacting the elastomer with a diboronic acid compound in the presence of a solvent; The solvent has an SP value of 10 (cal / cm ３ ) １／２ Above 13 (cal / cm ３ ) １／２ The SP value is 8 (cal / cm ３ ) １／２ More than 10 (cal / cm ３ ) １／２ A method for crosslinking an elastomer, comprising at least one solvent selected from the group consisting of:

2. The crosslinking method according to claim 1 , wherein the amount of the diboronic acid compound in the contacting step is 20 parts by mass or less relative to 100 parts by mass of the elastomer.

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