Isoprene elastomer with bond-exchanging dynamic covalent bonds and process for the preparation thereof

Abstract

To obtain an isoprene elastomer having characteristics of a crosslinked rubber and remoldability and to provide a method for producing the same.SOLUTION: The isoprene elastomer having bond-exchange-type dynamic covalent bonds is composed of a crosslinked product of an isoprene polymer composition containing (A) a carboxyl group-modified isoprene polymer, (B1) a compound having two or more epoxy groups, and (C) an ester exchange catalyst. The method for producing an isoprene elastomer includes an isoprene polymer composition preparation step of preparing an isoprene polymer composition by combining and stirring (A), (B1), and (C), and a crosslinking step of heating the isoprene polymer composition to allow a crosslinking reaction to proceed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to remoldable elastomers and methods for making the same. [Background technology]

[0002] Crosslinked rubber has a three-dimensional network structure in which polymer chains are connected, giving it the excellent properties unique to rubber, including elasticity. For example, natural rubber and isoprene rubber, which has a similar chemical structure, have high tensile strength, excellent abrasion resistance, and excellent vibration absorption properties, and are therefore used in a variety of rubber products such as vibration-proof rubber, tires, hoses, and belts.

[0003] In recent years, there has been a demand for the reuse of used materials from the perspectives of environmental protection and resource conservation. However, the network structure of crosslinked rubber is formed by strong covalent bonds, and the crosslinking points are irreversible. For this reason, crosslinked rubber is poorly remoldable and recyclable. Furthermore, while extending the life of materials is also desirable, crosslinked rubber does not have the self-repairing ability, and therefore cannot exhibit its intended properties if it is damaged or broken.

[0004] Patent Document 1, for example, describes a polymer with remoldability and scratch repair properties: a crosslinked polyester resin obtained by mixing a polyester resin raw material containing multiple ester bonds and carboxylic acid groups, a diepoxy crosslinking agent, and a transesterification catalyst, and then heating the mixture to crosslink. This crosslinked polyester resin contains a polyester resin containing a polymer main chain containing multiple ester bonds, multiple covalent crosslinking moieties containing ester bonds and free OH groups, and a transesterification catalyst. When this crosslinked polyester resin is heated, the transesterification catalyst causes a free OH group to attack the C-0 bond of a nearby ester bond, resulting in a transesterification reaction and the formation of a new bond by swapping the main chains. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 045439 Summary of the Invention [Problem to be solved by the invention]

[0006] Materials using para-bond dynamic covalent bonds, which simultaneously dissociate and recombine, as crosslinking points, such as the crosslinked polyester resin described in Patent Document 1, are sometimes called "vitrimers." In "vitrimers," bond exchange occurs upon heating, but the connectivity of the polymer chains forming the network structure is not lost even at high temperatures, and the crosslinking points do not disappear. Therefore, unlike thermoplastic resins, they can be deformed without melting, resulting in excellent remoldability. However, the material described in the same document is a resin. Therefore, it is difficult to achieve the properties of crosslinked rubber, limiting its applications. Furthermore, because resins are synthesized by polycondensation reactions, it is difficult to increase the degree of polymerization, limiting the improvement of physical properties.

[0007] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide an isoprene elastomer having the properties of a crosslinked rubber and remoldability, and a method for producing the same. [Means for solving the problem]

[0008] (1) The isoprene elastomer having a bond-exchange type dynamic covalent bond according to the first aspect of the present disclosure is characterized by comprising a crosslinked product of an isoprene polymer composition having the following (A), (B1), and (C): (A) Carboxyl group-modified isoprene polymer. (B1) A compound having two or more epoxy groups. (C) Transesterification catalyst.

[0009] The phrase "having a bond-exchange dynamic covalent bond" means that a normal dynamic covalent bond is used in the crosslinking chains that form the network structure of the isoprene elastomer. In the isoprene elastomer having a bond-exchange dynamic covalent bond according to the first aspect of the present disclosure (hereinafter, regardless of whether it is the first or second aspect, it may be simply referred to as the "isoprene elastomer of the present disclosure"), a carboxyl group-modified isoprene polymer (A) is reacted with a compound (B1) having two or more epoxy groups to crosslink the polymer through a reaction between the carboxyl groups and the epoxy groups (epoxy ring-opening reaction). Ester bonds and hydroxyl (OH) groups are generated in the crosslinked chains of the resulting crosslinked product. Because the crosslinked product contains a transesterification catalyst (C), when heated to a predetermined temperature, a transesterification reaction occurs between the OH group of one crosslinked chain and the ester bond of another crosslinked chain, resulting in the main chains being swapped and new bonds being generated.

[0010] In this way, new bonds can be generated without losing the connectivity of the polymer chains, and the isoprene elastomer of the present disclosure achieves both the rubber elasticity and remoldability of a crosslinked rubber. Because the isoprene elastomer of the present disclosure can be deformed by applying heat, it may be possible to apply blow molding, which has traditionally been used to mold thermoplastic resins, expanding the range of uses for the material. It also improves recyclability. Furthermore, even if the material is damaged, it can be expected to have an additional effect of extending its lifespan by utilizing its self-repairing function, which involves heating to promote a transesterification reaction and reconstruct the network structure.

[0011] (2) The isoprene elastomer having a bond-exchange type dynamic covalent bond according to the second aspect of the present disclosure is characterized by comprising a crosslinked product of an isoprene polymer composition having the following (A) and (B2): (A) Carboxyl group-modified isoprene polymer. (B2) A compound having two or more epoxy groups and a tertiary amine structure.

[0012] This embodiment differs from the first embodiment (configuration (1) above) in that the compound (B1) having two or more epoxy groups, which acts as a crosslinking agent for the carboxyl group-modified isoprene polymer (A), has a tertiary amine structure, and the transesterification catalyst (C) is not an essential component of the isoprene polymer composition. In this embodiment, the tertiary amine structure in the compound (B2) acting as a crosslinking agent acts as a base. This allows the aforementioned transesterification reaction to proceed in the crosslinked product (isoprene elastomer) and generate new bonds, without the need for a separate transesterification catalyst. As a result, the isoprene elastomer having bond-exchange dynamic covalent bonds according to this embodiment also achieves both rubber elasticity and remoldability, as in the first embodiment.

[0013] (3) In any of the above configurations, the carboxyl group-modified isoprene polymer (A) may be a liquid polymer. Liquid polymers have appropriate fluidity at room temperature and can be mixed with other components as is to crosslink. This has the advantage that the crosslinked product can be easily produced and requires less energy for production. The isoprene elastomer obtained by this configuration is suitable for use in sealing materials, adhesives, pressure-sensitive adhesives, paints, etc.

[0014] (4) In any of the above configurations, the number-average molecular weight of the carboxyl group-modified isoprene polymer (A) may be 2,000 or more and 500,000 or less, and the carboxyl group equivalent may be 700 or more and 40,000 or less. When the number-average molecular weight of the carboxyl group-modified isoprene polymer falls within this range, an isoprene elastomer can be obtained that is excellent in moldability and workability, as well as being relatively flexible. The carboxyl group equivalent refers to the molecular weight of the isoprene polymer per carboxyl group. When the carboxyl group equivalent falls within this range, the crosslinking reaction with the compound (B1) or (B2) is facilitated.

[0015] (5) In the above structure (1), or in the structure (3) or (4) that cites the above structure (1), the compound (B1) may be one or more selected from 1,4-butanediol diglycidyl ether, 1,2,7,8-diepoxyoctane, and neopentyl glycol diglycidyl ether. These compounds have excellent compatibility with the carboxyl group-modified isoprene polymer (A).

[0016] (6) In the above structure (2), or in the structures (3) or (4) that cite the above structure (2), the compound (B2) may be one or more selected from 4,4'-methylenebis(N,N-diglycidylaniline), N,N'-[1,3-phenylenebis(methylene)]bis[bis(oxiran-2-ylmethyl)amine], 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, and N-[2-methyl-4-(oxiranylmethoxy)phenyl]-N-(oxiranylmethoxy)oxiranimethaneamine. According to this structure, these compounds have excellent compatibility with the carboxyl group-modified isoprene polymer (A).

[0017] (7) In the above-mentioned (1) configuration or any of the configurations (3) to (5) which cite the above-mentioned (1), the transesterification catalyst (C) may be one or more selected from zinc acetate, zinc acetylacetonate (II) salt, triphenylphosphine, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

[0018] (8) In any of the above configurations, the isoprene polymer composition may further contain (D) a crosslinking reaction catalyst, which can accelerate the crosslinking reaction between the carboxyl group-modified isoprene polymer (A) and the compound (B1) or (B2), thereby shortening the time required for production.

[0019] (9) The method for producing an isoprene elastomer having a bond-exchange type dynamic covalent bond according to the third aspect of the present disclosure is one form of the method for producing an isoprene elastomer having a bond-exchange type dynamic covalent bond having the configuration described in (1) above, and is characterized by comprising: an isoprene polymer composition preparation step of mixing and stirring the (A) carboxyl group-modified isoprene polymer, the (B1) compound having two or more epoxy groups, and the (C) transesterification catalyst to prepare the isoprene polymer composition; and a crosslinking step of heating the isoprene polymer composition to cause a crosslinking reaction to proceed.

[0020] (10) The method for producing an isoprene elastomer having a bond-exchange type dynamic covalent bond according to the fourth aspect of the present disclosure is one form of the method for producing an isoprene elastomer having a bond-exchange type dynamic covalent bond having the configuration described in (2) above, and is characterized by comprising: an isoprene polymer composition preparation step of mixing and stirring the (A) carboxyl group-modified isoprene polymer and the (B2) compound having two or more epoxy groups and a tertiary amine structure to prepare the isoprene polymer composition; and a crosslinking step of heating the isoprene polymer composition to cause a crosslinking reaction to proceed.

[0021] According to the methods for producing an isoprene elastomer having a bond-exchange-type dynamic covalent bond according to the third and fourth aspects of the present disclosure (hereinafter, regardless of whether it is the third or fourth aspect, it may be simply referred to as the "production method of the present disclosure"), the isoprene elastomer of the present disclosure can be produced by the relatively simple process of preparing and heating a predetermined isoprene polymer composition. [Effects of the Invention]

[0022] The isoprene elastomer of the present disclosure has the properties of a crosslinked rubber and is remoldable due to bond-exchange dynamic covalent bonds. The isoprene elastomer of the present disclosure can be easily produced by the production method of the present disclosure. [Brief explanation of the drawings]

[0023] [Figure 1]1 is a reaction formula showing an example of a crosslinking reaction of an isoprene polymer composition. [Figure 2] 1 is a reaction formula showing an example of a transesterification reaction of an isoprene elastomer. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the isoprene elastomer having a bond-exchange type dynamic covalent bond and the method for producing the same according to the present disclosure will be described. Note that the embodiments are not limited to the following embodiments, and various modifications and improvements that can be made by those skilled in the art can be made.

[0025] <Isoprene elastomer with bond-exchange dynamic covalent bonds> The isoprene elastomer of the present disclosure comprises a crosslinked product of an isoprene polymer composition having a material appropriately selected from the following (A), (B1), (B2), and (C):

[0026] (A) Carboxyl group-modified isoprene polymer The carboxyl group-modified isoprene polymer is not particularly limited, but preferably has a plurality of carboxyl groups. It may also have a substituent or functional group other than the carboxyl group. The carboxyl group-modified isoprene polymer may be a single type or a mixture of two or more types. From the viewpoint of facilitating the production of the isoprene polymer composition, it is desirable that the carboxyl group-modified isoprene polymer be a liquid polymer that is liquid at room temperature.

[0027] The number average molecular weight of the carboxyl group-modified isoprene polymer is desirably 2,000 or more, preferably 3,000 or more, and even more desirably 5,000 or more, taking into consideration the viscosity and moldability of the resulting isoprene elastomer. On the other hand, taking into consideration the flexibility of the resulting isoprene elastomer and the workability in preparing the isoprene polymer composition, the number average molecular weight is desirably 500,000 or less, preferably 200,000 or less, and even more desirably 70,000 or less. In this specification, the number average molecular weight is the polystyrene-equivalent number average molecular weight determined by gel permeation chromatography (GPC).

[0028] Considering the crosslinking reaction with the compound (B1) or (B2) described below, the molecular weight of the isoprene polymer per carboxyl group (carboxyl group equivalent) is desirably 700 or more, more desirably 1,000 or more, and 40,000 or less, more desirably 30,000 or less.

[0029] (B1) Compound having two or more epoxy groups A compound having two or more epoxy groups acts as a crosslinking agent for the carboxyl-modified isoprene polymer. Considering ease of mixing with the carboxyl-modified isoprene polymer, the compound is preferably lipophilic. The epoxy groups may be located at multiple locations, such as the terminals and side chains of the compound. The (B1) compound may be used alone or in combination. For example, 1,4-butanediol diglycidyl ether, 1,2,7,8-diepoxyoctane, and neopentyl glycol diglycidyl ether are preferred from the viewpoint of excellent compatibility with the carboxyl-modified isoprene polymer. The amount of the (B1) compound to be added is preferably adjusted so that the equivalent ratio of the carboxyl groups to the epoxy groups between the carboxyl-modified isoprene polymer and the compound is 1.0:0.5 to 1.0:2.0, preferably 1.0:0.5 to 1.0:1.5. In this specification, a numerical range indicated using "to" is a range that includes the lower limit value written before "to" and the upper limit value written after "to".

[0030] (B2) Compounds having two or more epoxy groups and a tertiary amine structure The compound (B2) is selected from the compounds (B1) described above, and is a compound having a tertiary amine structure. When this compound is used, the transesterification catalyst (C) described below may not be used, but the use of this catalyst is not excluded. That is, the isoprene polymer composition may contain the transesterification catalyst (C) in addition to (A) and (B2). When this compound is used and a transesterification catalyst is also present, the crosslinking reaction (ester bond formation by epoxy ring-opening reaction) is thought to be promoted.

[0031] The compound (B2) may be used alone or in combination with two or more. This compound may also be used in combination with the compound (B1). As the compound (B2), from the viewpoint of excellent compatibility with the carboxyl group-modified isoprene polymer, 4,4'-methylenebis(N,N-diglycidylaniline), N,N'-[1,3-phenylenebis(methylene)]bis[bis(oxiran-2-ylmethyl)amine], 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N-[2-methyl-4-(oxiranylmethoxy)phenyl]-N-(oxiranylmethoxy)oxiranimethaneamine), etc. are suitable. As with the compound (B1), the amount of the compound (B2) added is preferably adjusted so that the equivalent ratio of the carboxyl group to the epoxy group between the carboxyl group-modified isoprene polymer and this compound is 1.0:0.5 to 1.0:2.0, in terms of sufficient crosslinking reaction. The ratio is preferably 1.0:0.5 to 1.0:1.5.

[0032] (C) Transesterification catalyst The transesterification catalyst may be a known acid catalyst, metal salt, or the like used in transesterification, such as zinc acetate, zinc(II) acetylacetonate, triphenylphosphine, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, etc. These may be used alone or in combination of two or more.

[0033] The amount of the transesterification catalyst to be added is preferably 0.01 parts by mass or more, 0.1 parts by mass or more, or even 1 part by mass or more per 100 parts by mass of the carboxyl group-modified isoprene polymer from the viewpoint of exerting its catalytic function, while being 20 parts by mass or less, or even 10 parts by mass or less, is preferable in consideration of the effect on the properties of the isoprene elastomer.

[0034] The isoprene polymer composition may contain additional components other than the aforementioned (A), (B1), (B2), and (C). Examples of such additional components include (D) a crosslinking catalyst, which promotes the crosslinking reaction. Additionally, examples of such additional components include (E) a reinforcing material, which improves the hardness, tensile strength, elongation, and other properties of the isoprene elastomer.

[0035] The crosslinking catalyst may be appropriately selected depending on the materials of (A) and the crosslinking agents (B1) and (B2). Examples include tertiary amines and imidazoles. These may be used alone or in combination. The amount of the crosslinking catalyst may be appropriately selected depending on the materials used, crosslinking conditions, etc. For example, it may be 0.1 to 5 parts by mass per 100 parts by mass of the carboxyl group-modified isoprene polymer. Preferably, it is 1 part by mass or less.

[0036] Suitable reinforcing materials include silica, carbon, and the like, which are typically compounded in crosslinked rubber. These materials may be used alone or in combination. From the viewpoint of improving dispersibility in the carboxyl-modified isoprene polymer, hydrophobic silica, the surface of which is hydrophobized, is preferred. The amount of reinforcing material to be added may be determined appropriately so that the isoprene elastomer has the desired properties. For example, the amount of reinforcing material may be 5 to 30 parts by mass per 100 parts by mass of the carboxyl-modified isoprene polymer.

[0037] As an example of a crosslinking reaction of an isoprene polymer composition according to the present disclosure, the reaction scheme is shown in Figure 1, where a side-chain carboxyl group-modified liquid polyisoprene is used as (A) and 4,4'-methylenebis(N,N-diglycidylaniline) is used as (B2). As shown in Figure 1, in the crosslinking reaction, the carboxyl groups of (A) react with the four epoxy groups of (B2) to form bonds. The crosslinked chains of the resulting crosslinked product (isoprene elastomer) contain ester bonds derived from the carboxyl groups and OH groups derived from the epoxy groups.

[0038] Figure 2 shows the reaction scheme for the transesterification reaction in the isoprene elastomer obtained in Figure 1. In Figure 2, the right half of the isoprene elastomer shown in Figure 1 is omitted, and the transesterification reaction area is enclosed by a dotted line. As shown in Figure 2, when the isoprene elastomer is heated to a certain temperature, a transesterification reaction occurs between the ester bond of one polymer chain and the OH group of another polymer chain, even in the absence of a transesterification catalyst. This results in an exchange of the isoprene moiety (i) with the isoprene moiety (ii) in the two polymer chains. In this way, the exchange reaction of the polymer chain bonds is repeated while maintaining the network structure.

[0039] <Manufacturing method> One embodiment of the method for producing an isoprene elastomer according to the present disclosure includes an isoprene polymer composition preparation step and a crosslinking step. Each step will be described below.

[0040] [Isoprene polymer composition preparation process] This step is a step of preparing an isoprene polymer composition by mixing together materials appropriately selected from the aforementioned (A), (B1), (B2), and (C). For example, when producing an isoprene elastomer having bond-exchange type dynamic covalent bonds according to the first embodiment, materials selected from (A), (B1), and (C) may be selected. When producing an isoprene elastomer having bond-exchange type dynamic covalent bonds according to the second embodiment, materials selected from (A) and (B2) may be selected.

[0041] Stirring can be performed using a stirrer such as a blade stirrer, or active shear force can be applied. When the isoprene polymer composition contains additional components such as (D) and (E), the additional components can be added to materials appropriately selected from (A), (B1), (B2), and (C) and stirred. When using a transesterification catalyst (C), the catalyst can be dissolved in a solvent in advance to prepare a catalyst solution, which can then be combined with other materials. Examples of solvents that can be used include chloroform, methanol, and ethanol, and these can be mixed appropriately. When using a solvent, it is desirable to remove the solvent from the prepared isoprene polymer composition before the next crosslinking step. Removing the solvent in advance can improve heating efficiency in the next crosslinking step, facilitating the crosslinking reaction.

[0042] [Crosslinking process] This step is a step in which the isoprene polymer composition produced in the previous step is heated to promote the crosslinking reaction. The heating temperature may be appropriately determined taking into consideration the progress of the crosslinking reaction, productivity, etc. For example, the heating temperature may be 120°C or higher and 150°C or lower. Furthermore, from the viewpoint of accelerating the crosslinking reaction and shortening the crosslinking time, this step may be carried out under reduced pressure. [Example]

[0043] Next, the present disclosure will be described more specifically with reference to examples.

[0044] <Production of isoprene elastomer samples> [Sample 1] First, (A) side-chain carboxyl group-modified liquid polyisoprene ("LIR-410" manufactured by Kuraray Co., Ltd., carboxyl group equivalent: 3000), (B1) 1,4-butanediol diglycidyl ether (hydroxyl group equivalent: 101), and (C) zinc acetate were added to a planetary mixer and stirred for 15 minutes to prepare an isoprene polymer composition. Next, the prepared isoprene polymer composition was removed and crosslinked at a temperature of 150°C for 1 hour. In this way, isoprene elastomer Sample 1 was produced. The blending amounts of each material are summarized in Table 1 below. The blending amounts of (A) side-chain carboxyl group-modified liquid polyisoprene and (B1) 1,4-butanediol diglycidyl ether were adjusted so that the equivalent ratio of carboxyl groups to epoxy groups was 1.0:1.5.

[0045] [Sample 2] Sample 2 was produced in the same manner as Sample 1, except that the compound having two or more epoxy groups was replaced with (B2) 4,4'-methylenebis(N,N-diglycidylaniline) (hydroxyl group equivalent: 105.5) having a tertiary amine structure, and (C) zinc acetate was not added. The amounts of (A) side-chain carboxyl group-modified liquid polyisoprene and (B2) 4,4'-methylenebis(N,N-diglycidylaniline) added were adjusted so that the equivalent ratio of carboxyl groups to epoxy groups was 1.0:1.5.

[0046] [Sample 3] (D) Sample 3 was produced in the same manner as Sample 1, except that 1,8-diazabicyclo[5.4.0]-7-undecene was additionally blended as a crosslinking reaction catalyst.

[0047] [Sample 4] (C) Sample 4 was produced in the same manner as Sample 1, except that zinc acetate was not added.

[0048] <Evaluation method> [Remoldability] First, a square sheet-shaped test piece measuring 50 mm in length, 50 mm in width, and 2 mm in thickness was cut from the manufactured sample. Next, the vertical and horizontal sides of the test piece were each cut in half to create four equal pieces. Next, the four pieces were placed in a mold to return to their original square shape and held at a temperature of 160°C for two hours. After that, the sample was allowed to cool to room temperature (20°C ± 5°C). If the four pieces were bonded together, they were evaluated as having remoldability (indicated by a circle in Table 1 below), and if they were not bonded, they were evaluated as not having remoldability (indicated by an x ​​in the same table).

[0049] [Adhesiveness] (1) Self-adhesive First, two test pieces with the same shape and dimensions were cut from the manufactured sample. The two test pieces (2 mm thick) were prepared according to JIS K 6854-3:1999. Next, the two test pieces were stacked together to form a laminate. This laminate was placed in a mold and compressed at 160°C and 10 kPa for 2 hours. After the laminate was returned to room temperature and the two test pieces were confirmed to be bonded, it was attached to a testing machine and subjected to a T-peel test according to JIS K 6854-3:1999. The gripper movement speed was 200 mm / min. If one of the test pieces broke (material failure), the self-adhesion was evaluated as good (indicated by a circle in Table 1 below). If the test pieces did not bond together even after being heated and pressurized in the mold, the self-adhesion was evaluated as poor (indicated by an x ​​in the same table).

[0050] (2) Adhesion to glass First, a glass substrate (soda-lime glass plate) was prepared as the adherend. Furthermore, strip-shaped test pieces measuring 25 mm wide, 50 mm long, and 2 mm thick were cut from the manufactured sample. Next, the test pieces were laminated onto the glass substrate, and this laminate was placed in a mold and compressed at 160°C and 10 kPa for 2 hours. After the laminate was returned to room temperature and the test pieces were confirmed to be adhered to the glass substrate, the laminate was attached to a testing machine and a peel test was performed according to "Method 1" of "10.3 Test Method" specified in "10 Adhesion Strength" of JIS Z 0237:2022. If the test pieces were destroyed (material destruction), the adhesion to glass was evaluated as good (indicated by a circle in Table 1 below). In addition, if the test piece did not adhere to the glass substrate even after being heated and pressurized in the mold, or if it did adhere but the peel test showed interfacial failure rather than material failure, it was evaluated as having no adhesion to glass (indicated by an x ​​in the table).

[0051] (3) Adhesion to iron First, an iron substrate (steel plate) was prepared as the adherend. Furthermore, strip-shaped test pieces measuring 25 mm wide, 50 mm long, and 2 mm thick were cut from the manufactured samples. Next, the test pieces were layered on the iron substrate to form a laminate. This laminate was placed in a mold and compressed at 160 °C and 10 kPa for 2 hours. After the laminate was returned to room temperature and the adhesion of the test pieces to the iron substrate was confirmed, the laminate was attached to the testing machine and a peel test was performed as described in (2) above. If the test pieces broke (material failure), the adhesion to iron was evaluated as good (indicated by a circle in Table 1 below). If the test pieces did not adhere to the iron substrate even after being heated and pressurized in the mold, or if the adhesion was confirmed but the peel test showed interfacial failure rather than material failure, the adhesion to iron was evaluated as poor (indicated by an x ​​in the same table).

[0052] [Static characteristics] (1) Tensile strength at break (T b ) and elongation at break (E b ) The tensile strength and elongation at break of the produced samples were measured in accordance with JIS K 6251: 2017. Test specimens used were dumbbell No. 3 (thickness of the parallel part: 2.0 mm), and the tensile speed was 200 mm / min.

[0053] (2)Hardness The Type A durometer hardness of the produced samples was measured using a hardness tester (ASKER P1-A type manufactured by Kobunshi Keiki Co., Ltd.) conforming to JIS K 6253-3: 2012. The measurement was carried out by stacking three test pieces with a thickness of 1 mm cut out from the sample, and the value measured 15 seconds after the indenter came into contact with the test pieces was used.

[0054] <Evaluation results> The amounts of materials used in each sample and the evaluation results are summarized in Table 1. The isoprene elastomers in Samples 1, 2, and 3 fall within the concept of isoprene elastomers of the present disclosure. [Table 1]

[0055] As shown in Table 1, Samples 1, 2, and 3, which are examples of the isoprene elastomer of the present disclosure, were confirmed to be remoldable and adhesive not only to each other but also to glass and steel members. Furthermore, the tensile strength at break, elongation at break, and hardness values ​​confirmed that these samples possessed the properties of crosslinked rubber. Of these, Sample 2 did not contain a transesterification catalyst, but because it used a compound with a tertiary amine structure as a crosslinker, it exhibited remoldability and adhesiveness similar to Samples 1 and 3. In contrast, Sample 4, which also did not contain a transesterification catalyst, did not have remoldability or adhesiveness because the crosslinker compound did not have a tertiary amine structure.

[0056] As shown in the examples, when two isoprene elastomers of the present disclosure are brought into contact with each other and heated, a transesterification reaction occurs at the contact surface, forming new bonds, allowing for adhesion. Furthermore, the isoprene elastomers of the present disclosure may also be able to adhere to dissimilar materials if the mating component has an ester bond or a hydroxyl group. It is believed that heating after adhesion makes it possible to separate the materials. [Industrial Applicability]

[0057] The isoprene elastomer having a bond-exchange type dynamic covalent bond of the present disclosure is useful for sealing materials, adhesives, pressure-sensitive adhesives, coating materials, and the like.

Claims

1. 1. An isoprene elastomer having a bond-exchange type dynamic covalent bond, comprising a crosslinked product of an isoprene polymer composition having the following (A), (B1), and (C): (A) Carboxyl group-modified isoprene polymer. (B1) A compound having two or more epoxy groups. (C) a transesterification catalyst.

2. An isoprene elastomer having a bond-exchange type dynamic covalent bond, characterized by comprising a crosslinked product of an isoprene polymer composition having the following (A) and (B2): (A) Carboxyl group-modified isoprene polymer. (B2) A compound having two or more epoxy groups and a tertiary amine structure.

3. 3. The isoprene elastomer having a bond-exchange type dynamic covalent bond according to claim 1 or 2, wherein the carboxyl group-modified isoprene polymer (A) is a liquid polymer.

4. 3. The isoprene elastomer having a bond-exchange type dynamic covalent bond according to claim 1 or 2, wherein the carboxyl group-modified isoprene polymer (A) has a number average molecular weight of 2,000 or more and 500,000 or less, and a carboxyl group equivalent weight of 700 or more and 40,000 or less.

5. 2. The isoprene elastomer having a bond-exchange type dynamic covalent bond according to claim 1, wherein the compound (B1) is at least one selected from the group consisting of 1,4-butanediol diglycidyl ether, 1,2,7,8-diepoxyoctane, and neopentyl glycol diglycidyl ether.

6. The isoprene elastomer having a bond-exchange type dynamic covalent bond according to claim 2, wherein the compound (B2) is at least one selected from the group consisting of 4,4'-methylenebis(N,N-diglycidylaniline), N,N'-[1,3-phenylenebis(methylene)]bis[bis(oxiran-2-ylmethyl)amine], 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, and N-[2-methyl-4-(oxiranylmethoxy)phenyl]-N-(oxiranylmethoxy)oxiranimethaneamine.

7. 2. The isoprene elastomer having a bond-exchange type dynamic covalent bond according to claim 1, wherein the transesterification catalyst (C) is at least one selected from the group consisting of zinc acetate, zinc acetylacetonate (II) salt, triphenylphosphine, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

8. The isoprene elastomer having a bond-exchange type dynamic covalent bond according to claim 1 or 2, wherein the isoprene polymer composition further comprises (D) a crosslinking reaction catalyst.

9. A method for producing an isoprene elastomer having bond exchange type dynamic covalent bonds according to claim 1, comprising: an isoprene polymer composition preparation step of mixing and stirring the (A) carboxyl group-modified isoprene polymer, the (B1) compound having two or more epoxy groups, and the (C) transesterification catalyst to prepare the isoprene polymer composition; a crosslinking step of heating the isoprene polymer composition to promote a crosslinking reaction; A method for producing an isoprene elastomer having a bond-exchange type dynamic covalent bond, comprising:

10. A method for producing an isoprene elastomer having bond exchange type dynamic covalent bonds according to claim 2, comprising: an isoprene polymer composition preparation step of mixing and stirring the (A) carboxyl group-modified isoprene polymer and the (B2) compound having two or more epoxy groups and a tertiary amine structure to prepare the isoprene polymer composition; a crosslinking step of heating the isoprene polymer composition to promote a crosslinking reaction; A method for producing an isoprene elastomer having a bond-exchange type dynamic covalent bond, comprising:

Images