Method for cleaving coordinate bond of complexation polymer

Abstract

The present invention addresses the problem of providing a method for cleaving a coordinate bond of a complexation polymer, the method being capable of stably providing a non-crosslinked rubber that may not generate an odor when reused. The solution is a method for cleaving a coordinate bond of a complexation polymer that has at least one polymer chain and a plurality of nitrogen-containing functional groups capable of forming coordinate bonds and bonded to the polymer chain, the nitrogen-containing functional groups capable of forming coordinate bonds forming therebetween a coordinate bond via at least one metal ion selected from the group consisting of metal ions of the D block elements, the method being characterized by comprising a step for cleaving the coordinate bond between the metal ion and the nitrogen-containing functional group using a mixed solvent containing hydrogen peroxide solution and a water-soluble ether.

Description

Method for breaking the coordination bonds of complexed polymers

[0001] The present invention relates to a method for breaking the coordination bonds of complexed polymers.

[0002] Conventionally, most cross-linked rubber products such as used tires have been disposed of without being reused. However, from the viewpoints of environmental issues and resource conservation, there is an urgent need to recycle rubber waste.

[0003] In contrast, Patent Document 1 below discloses, as thermally recyclable crosslinked rubber, a complexed polymer that includes a polymer main chain containing conjugated diene units and / or olefin units and a functional group bonded to the polymer main chain, the functional group containing a nitrogen atom and / or a phosphorus atom and complexed with a metal ion of an element in Groups 7 to 10 of the periodic table, as well as a rubber composition and a rubber product (crosslinked rubber) that include the complexed polymer.The document also discloses that crosslinked rubber containing the complexed polymer can be crushed, remolded, and subjected to heat and pressure to cause crosslink exchange (recombination), and that even the crosslinked rubber can be remolded and reused like a thermoplastic elastomer.

[0004] However, once a thermally recyclable crosslinked rubber such as that described in Patent Document 1 is crosslinked, it cannot be returned to an uncrosslinked state that is free to deform (at room temperature), and therefore the molding process used in normal tire manufacturing cannot be utilized. Therefore, in order to reuse and remanufacture tires as tire materials, it is necessary to return the tires to an uncrosslinked rubber.

[0005] In contrast to this, as a method for returning crosslinked rubber to an uncrosslinked rubber, Patent Document 2 listed below discloses a method for releasing the coordinate bonds of a complexed polymer, which comprises a polymer chain and a plurality of nitrogen- and / or phosphorus-containing functional groups capable of forming coordinate bonds bonded to the polymer chain, wherein the nitrogen- and / or phosphorus-containing functional groups capable of forming coordinate bonds form coordinate bonds with each other via metal ions, and the complexed polymer is dissolved in a solvent containing a free ligand to release the coordinate bonds.

[0006] International Publication No. WO 2022 / 049961 International Publication No. WO 2022 / 049962

[0007] However, in the method described in the above-mentioned Patent Document 2, although the solvent and free ligands coordinate to metal ions instead of the functional groups of the complexed polymer, thereby achieving a decrosslinked state, the present inventors have found that, upon removal of the solvent and free ligands and leaving the mixture to stand, the functional groups bonded to the polymer chains return to a crosslinked state in which they form coordinate bonds via metal ions, making it difficult to stably obtain decrosslinked rubber. Furthermore, upon further investigation by the present inventors, it has been found that although pyridine used as the free ligand in the above-mentioned Patent Document 2 is capable of decrosslinking, it has a high boiling point and is therefore difficult to completely remove from the rubber, which raises concerns about the generation of a specific odor during the recrosslinking and kneading processes, and the remaining pyridine acts as a free ligand (decrosslinking agent), thereby hindering recrosslinking, etc.

[0008] Therefore, an object of the present invention is to provide a method for breaking the coordinate bond of a complexed polymer, which solves the above-mentioned problems of the conventional technology and makes it possible to stably obtain uncrosslinked rubber that does not generate odors when reused.

[0009] The method for releasing the coordinate bond of a complex polymer of the present invention, which solves the above-mentioned problems, is outlined as follows.

[0010] [1] A method for releasing a coordinate bond of a complexed polymer having at least one polymer chain and a plurality of nitrogen-containing functional groups capable of forming coordinate bonds bonded to the polymer chain, wherein the nitrogen-containing functional groups capable of forming coordinate bonds form coordinate bonds with each other via at least one metal ion selected from the group consisting of metal ions of D-block elements, the method comprising the step of releasing the coordinate bond between the metal ion and the nitrogen-containing functional group using a mixed solvent containing hydrogen peroxide and a water-soluble ether.

[0011] [2] The method for releasing the coordinate bond of a complex polymer according to [1], wherein the water-soluble ether is tetrahydrofuran.

[0012] [3] The method for releasing the coordinate bond of the complex polymer according to [1] or [2], wherein the nitrogen-containing functional group is derived from a compound containing a triazine ring or a tetrazine ring.

[0013] [4] The method for breaking the coordinate bond of a complex polymer according to any one of [1] to [3], wherein the nitrogen-containing functional group does not contain a sulfur atom.

[0014] [5] The method for releasing the coordinate bond of the complex polymer according to [3] or [4], wherein two pyridyl groups or two pyrimidyl groups are bonded to the triazine ring or the tetrazine ring.

[0015] [6] The nitrogen-containing functional group is represented by the following general formula (1): [In the formula, X １ and X ２ are each independently a pyridyl group or a pyrimidinyl group, and Y １ and Y ２ are each independently a single bond or a divalent hydrocarbon group.].

[0016] [7] The method for breaking the coordinate bond of a complex polymer according to any one of [1] to [6], wherein the metal ion is selected from the group consisting of an iron ion, a zinc ion, a cobalt ion, and a nickel ion.

[0017] [8] The method for breaking the coordinate bond of a complex polymer according to any one of [1] to [7], wherein the metal ion is an iron ion.

[0018] [9] The method for releasing the coordinate bond of a complexed polymer according to any one of [1] to [8], wherein the polymer chain contains a conjugated diene unit.

[0019] According to the present invention, it is possible to provide a method for breaking the coordinate bond of a complexed polymer, which makes it possible to stably obtain a decrosslinked rubber that does not generate odors when reused.

[0020] The method for releasing the coordinate bond of the complex polymer of the present invention will be described in detail below by way of example based on the embodiments.

[0021] <Definitions> The compounds described herein may be derived in whole or in part from fossil resources, from biological resources such as plant resources, from recycled resources such as used tires, or from a mixture of two or more of fossil resources, biological resources, and recycled resources.

[0022] <Method for Dissociating Coordination Bonds of Complexed Polymers> The method for dissociating coordination bonds of a complexed polymer of this embodiment is a method for dissociating coordination bonds of a complexed polymer having at least one polymer chain and a plurality of nitrogen-containing functional groups capable of forming coordination bonds attached to the polymer chain, wherein the nitrogen-containing functional groups capable of forming coordination bonds form coordination bonds with each other via at least one metal ion selected from the group consisting of metal ions of D-block elements. The method for dissociating coordination bonds of a complexed polymer of this embodiment is characterized by including a step of dissociating the coordination bonds between the metal ions and the nitrogen-containing functional groups in a mixed solvent containing hydrogen peroxide and a water-soluble ether.

[0023] In the method for breaking the coordinate bond of a complexed polymer according to the present embodiment, a method for breaking the coordinate bond of a complexed polymer (crosslinked rubber) in which nitrogen-containing functional groups form coordinate bonds via metal ions is performed by reacting the complexed polymer with hydrogen peroxide to convert the metal ions into hydroxides or oxides, thereby deactivating the nitrogen-coordinating ability of the metal ions. Furthermore, by deactivating the nitrogen-coordinating ability of the metal ions, the coordinate bond (metal coordinate bond) of the complexed polymer can be easily broken (broken), and the crosslinks between polymer chains can be more easily eliminated, resulting in the production of a functionalized polymer as an uncrosslinked rubber. Furthermore, according to the method for breaking the coordinate bond of a complexed polymer according to the present embodiment, since the nitrogen-coordinating ability of the metal ions is deactivated, a decrosslinked rubber can be stably obtained. Furthermore, in the method according to the present embodiment, a water-soluble ether is used in combination to allow hydrogen peroxide to penetrate deep into the complexed polymer (crosslinked rubber) as a condition for easily breaking the coordinate bond of a complexed polymer using aqueous hydrogen peroxide. By using a water-soluble ether and aqueous hydrogen peroxide in combination, when the water-soluble ether penetrates (swells) into the interior of the complexed polymer (crosslinked rubber), the aqueous hydrogen peroxide also penetrates into the interior of the complexed polymer (crosslinked rubber) and severs the coordinate bonds. This makes it possible to easily dissociate the coordinate bonds under mild conditions of room temperature and normal pressure without using special pressurizing or heating equipment. The method of this embodiment can also be combined with pressurization and heating, which makes it possible to easily dissociate the coordinate bonds in a shorter time. Furthermore, by using aqueous hydrogen peroxide in combination with a water-soluble ether, decrosslinking can be achieved even when the rubber and the solution form a heterogeneous state. This makes it easy to separate (extract) the decrosslinked rubber, eliminating the need for a subsequent process of extracting (separating) the decrosslinked rubber, as in the alcohol reprecipitation method. Therefore, the method of dissociating the coordinate bonds of a complexed polymer of this embodiment also has the advantage of being able to dissociate the coordinate bonds with fewer processes and using a smaller amount of solvent. Furthermore, the hydrogen peroxide solution and the water-soluble ether used in the mixed solvent can be easily and completely removed from the uncrosslinked rubber by washing with water, and there is no concern that they will generate an odor when reused in re-crosslinking or kneading steps, etc., and there is also no problem of interfering with re-crosslinking.Therefore, according to the method of the present embodiment for breaking the coordinate bond of the complex polymer, it is possible to stably obtain rubber in a decrosslinked state, and there is no concern that the obtained rubber in a decrosslinked state will generate an odor when it is reused.

[0024] (Complexed Polymer) The complexed polymer that is the target of the method for breaking the coordinate bond of a complexed polymer of this embodiment has at least one polymer chain and a plurality of nitrogen-containing functional groups capable of forming coordinate bonds bonded to the polymer chain, wherein the nitrogen-containing functional groups capable of forming coordinate bonds form coordinate bonds with each other via at least one metal ion selected from the group consisting of metal ions of D-block elements. The complexed polymer is crosslinked by the formation of coordinate bonds between the nitrogen-containing functional groups via the metal ions. However, by treating the complexed polymer with a mixed solvent containing hydrogen peroxide and a water-soluble ether, the crosslinks between the polymer chains can be easily broken down, and a functionalized polymer can be obtained as an uncrosslinked rubber.

[0025] -Polymer Chain- The complexed polymer has at least one polymer chain. When there is one polymer chain, the complexed polymer forms a coordinate bond via a metal ion within the molecule, resulting in crosslinking. When there are two or more polymer chains, in addition to intramolecularly, coordinate bonds can also be formed between molecules (between polymer chains) via a metal ion, resulting in crosslinking. The complexed polymer has a plurality of nitrogen-containing functional groups capable of forming coordinate bonds, and the plurality of nitrogen-containing functional groups may be bonded to a single polymer chain, or may be bonded separately to two or more polymer chains. The plurality of nitrogen-containing functional groups may be the same or different.

[0026] The polymer chain preferably contains conjugated diene units and / or olefin units, i.e., the polymer chain preferably contains conjugated diene units or olefin units, and more preferably contains both conjugated diene units and olefin units.

[0027] It is more preferable that the polymer chain contains a conjugated diene unit. When the polymer chain of the complexed polymer contains a conjugated diene unit, the complexed polymer has elastomeric properties useful for various rubber articles. Furthermore, by treating such a complexed polymer with excellent elastomeric properties with the above-mentioned mixed solvent containing hydrogen peroxide and a water-soluble ether, a functionalized polymer that can be used as a raw material for complexed polymers useful for various rubber articles can be recovered.

[0028] The conjugated diene unit is a monomer unit derived from a conjugated diene compound. The conjugated diene compound used as a monomer preferably has 4 to 8 carbon atoms. Specific examples of such conjugated diene compounds include 1,3-butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. From the viewpoint of good elastomeric properties, the conjugated diene compound used as a monomer preferably contains 1,3-butadiene and / or isoprene. The proportion of the conjugated diene unit in the polymer chain is not particularly limited and may be 0 mol %, but is preferably 0.1 mol % or more, more preferably 1 mol % or more, and may even be 100 mol %. When the proportion is 1 mol % or more, a complexed polymer with excellent elastomeric properties is obtained.

[0029] The olefin unit is a monomer unit derived from an olefin compound. The olefin compound as a monomer preferably has 2 to 10 carbon atoms. Specific examples of such olefin compounds include α-olefins such as ethylene, propylene, 1-pentene, 1-hexene, 1-heptene, and 1-octene, and heteroatom-substituted alkene compounds such as vinyl pivalate, 1-phenylthioethene, and N-vinylpyrrolidone. The proportion of the olefin unit in the polymer chain is not particularly limited and may be 0 mol %, but is preferably 1 mol % or more, and may also be 100 mol %.

[0030] The polymer chain may contain units derived from other monomers copolymerizable with the conjugated diene compound and / or the olefin compound. Examples of such units derived from other monomers include aromatic vinyl units. The proportion of units derived from other monomers in the polymer chain is not particularly limited and may be 0 mol %, but in one embodiment, it is preferably 1 mol % or more and 50 mol % or less. The aromatic vinyl units are monomer units derived from aromatic vinyl compounds. The aromatic vinyl compounds refer to aromatic compounds substituted with at least a vinyl group. The aromatic vinyl compounds used as monomers preferably have 8 to 10 carbon atoms. Specific examples of such aromatic vinyl compounds include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene.

[0031] Nitrogen-Containing Functional Group The complex polymer has a plurality of nitrogen-containing functional groups capable of forming coordinate bonds attached to the polymer chain. The nitrogen-containing functional groups capable of forming coordinate bonds form coordinate bonds with each other via metal ions. Because of the coordinate bonds, sufficient reversibility can be imparted to the bond between the metal ion and the nitrogen-containing functional group. Furthermore, the coordinate bond between the nitrogen-containing functional group and the metal ion is sufficiently strong, and can form a crosslink with a strength equivalent to that of sulfur crosslinking, so the complex polymer has sufficient durability. As the nitrogen-containing functional group, a group containing a nitrogen-containing heterocycle such as a 4,5-dihydropyridazine ring, a pyridine ring, a pyrimidine ring, a triazine ring, or a tetrazine ring is preferred.

[0032] Here, the nitrogen-containing functional group preferably does not contain a sulfur atom, which can suppress crosslinking between polymer chains due to sulfur atoms, thereby improving the recyclability of the complex polymer.

[0033] In the complex polymer, the bond dissociation energy between the metal ion and the nitrogen-containing functional group is preferably 200 kJ / mol or more, more preferably 250 kJ / mol or more, and preferably 500 kJ / mol or less. A bond dissociation energy of 200 kJ / mol or more allows a stronger crosslinked structure to be formed, further improving the durability of the complex polymer. A bond dissociation energy of 250 kJ / mol or more further improves the durability of the complex polymer. A bond dissociation energy of 500 kJ / mol or less allows the coordinate bond between the metal ion and the nitrogen-containing functional group to be more easily dissolved, making the complex polymer more easily recyclable.

[0034] Here, in this specification, the bond dissociation energy between a metal ion and a nitrogen-containing functional group is a value calculated at the M06 / 6-31G(d,p) / / B3PW91-D3 / 6-31G(d,p) level or the M06 / 6-31G(d,p) level in a vacuum. It is considered that the metal ion and the nitrogen-containing functional group form ionic aggregates. Gaussian09 or GRRM14 can be used to calculate the bond dissociation energy.

[0035] The nitrogen-containing functional group is preferably derived from a compound having a triazine ring or a tetrazine ring. Compounds containing a triazine ring or a tetrazine ring have high reactivity with polymer chains and easily form functionalized polymers by reacting with the polymer chains. Furthermore, nitrogen-containing functional groups derived from compounds containing a triazine ring or a tetrazine ring are easily complexed with metal ions to form crosslinks, and can form stronger crosslinked structures. Note that when the nitrogen-containing functional group is derived from a compound having a triazine ring or a tetrazine ring, the complexed polymer forms stronger coordinate bond crosslinks, but even such strong coordinate bond crosslinks can be dissolved by using the mixed solvent containing the above-mentioned hydrogen peroxide solution and water-soluble ether.

[0036] Here, it is preferable that a pyridyl group or a pyrimidinyl group is bonded to the triazine ring or the tetrazine ring of the compound having a triazine ring or a tetrazine ring, and it is even more preferable that two pyridyl groups or two pyrimidinyl groups are bonded to the triazine ring or the tetrazine ring. When the nitrogen-containing functional group is derived from a compound having a triazine ring or a tetrazine ring and a pyridyl group or a pyrimidinyl group is bonded to the triazine ring or the tetrazine ring, the nitrogen-containing functional group and the metal ion are more easily complexed, the bond dissociation energy is more easily increased, and a crosslinked structure with higher strength can be formed. Furthermore, when two pyridyl groups or two pyrimidinyl groups are bonded to the triazine ring or the tetrazine ring, the nitrogen-containing functional group and the metal ion are more easily complexed, the bond dissociation energy is more easily increased, and a crosslinked structure with higher strength can be formed. In addition, when the nitrogen-containing functional group is derived from a compound having a triazine ring or a tetrazine ring and two pyridyl groups or pyrimidinyl groups are bonded to the triazine ring or the tetrazine ring, the complexed polymer forms a coordinate bond crosslink with even greater strength, but even such a strong coordinate bond crosslink can be dissolved by using the mixed solvent containing the above-mentioned hydrogen peroxide solution and a water-soluble ether. Here, the pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, with the 2-pyridyl group being preferred. Furthermore, the pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

[0037] The nitrogen-containing functional group is represented by the following general formula (1): [In the formula, X １ and X ２ are each independently a pyridyl group or a pyrimidinyl group, and Y １ and Y ２are each independently a single bond or a divalent hydrocarbon group. The compound represented by general formula (1) is preferably derived from a compound represented by the formula:

[0023] . The compound represented by general formula (1) easily undergoes a Diels-Alder reaction with a polymer chain, and easily forms a functionalized polymer. Furthermore, when the nitrogen-containing functional group is derived from a compound represented by general formula (1), the nitrogen-containing functional group and a metal ion are particularly likely to complex, and the bond dissociation energy is particularly likely to be high, resulting in the formation of a crosslinked structure with even greater strength. Note that when the nitrogen-containing functional group is derived from a compound represented by general formula (1), the complexed polymer forms a coordinate bond crosslink with even greater strength, but even such a strong coordinate bond crosslink can be dissolved by the mixed solvent containing the above-mentioned hydrogen peroxide solution and water-soluble ether.

[0038] In the above general formula (1), X １ and X ２ are each independently a pyridyl group or a pyrimidinyl group. １ and X ２ is preferably a pyridyl group. The pyridyl group may be a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, with a 2-pyridyl group being preferred. The pyrimidinyl group may be a 2-pyrimidinyl group, a 4-pyrimidinyl group, or a 5-pyrimidinyl group.

[0039] In the above general formula (1), Y １ and Y ２ are each independently a single bond or a divalent hydrocarbon group. Here, examples of the divalent hydrocarbon group include an alkylene group, an alkenylene group, and an arylene group. More specifically, examples of the alkylene group include a methylene group, an ethylene group, a trimethylene group, and a tetramethylene group. Examples of the alkenylene group include a vinylene group, a propenylene group, and a butenylene group. Examples of the arylene group include a phenylene group, a tolylene group, and a naphthylene group. From the viewpoint of ease of synthesis, Y １ and Y ２ is preferably a single bond (i.e., X is not attached to the tetrazine ring). １ and X ２ is preferably directly bonded).

[0040] Here, X in the general formula (1) １ and X ２ is a pyridyl group, and Y １ and Y ２ is preferably a single bond. In this case, the compound of formula (1) is easily available, and is particularly likely to form a complex with a metal ion, and the bond dissociation energy is particularly likely to be high, making it possible to form a crosslinked structure with even higher strength.

[0041] The compounds represented by the general formula (1) include 3,6-di(2-pyridyl)-1,2,4,5-tetrazine, 3,6-di(3-pyridyl)-1,2,4,5-tetrazine, 3,6-di(4-pyridyl)-1,2,4,5-tetrazine, 3,6-di(2-pyridylmethyl)-1,2,4,5-tetrazine, 3,6-di(2-pyridylethyl)-1,2,4,5-tetrazine, 3-(2-pyridyl)-1,2,4,5-tetrazine, lysylmethyl)-6-(2-pyridylethyl)-1,2,4,5-tetrazine, 3,6-di(2-pyrimidinyl)-1,2,4,5-tetrazine, 3,6-di(4-pyrimidinyl)-1,2,4,5-tetrazine, 3,6-di(5-pyrimidinyl)-1,2,4,5-tetrazine, and the like. Among these, 3,6-di(2-pyridyl)-1,2,4,5-tetrazine is preferred.

[0042] In the complex polymer, the nitrogen-containing functional group is preferably bonded in an amount of 0.1 to 10 mol %, more preferably 0.3 to 8 mol %, even more preferably 0.4 to 5 mol %, and particularly preferably 0.5 to 3 mol %, relative to the monomer units in the polymer chain. When the nitrogen-containing functional group is bonded in an amount of 0.1 mol % or more relative to the monomer units in the polymer chain, a stronger crosslinked structure can be formed, resulting in a complex polymer with sufficient durability. Furthermore, when the nitrogen-containing functional group is bonded in an amount of 10 mol % or less relative to the monomer units in the polymer chain, a complex polymer with sufficient elastomeric properties is likely to be obtained.

[0043] The complex polymer may further have another functional group that does not form a coordinate bond with the metal ion. The other functional group is not particularly limited and can be appropriately selected depending on the physical properties of the target complex polymer.

[0044] In the complex polymer, the nitrogen-containing functional groups capable of forming a coordinate bond form a coordinate bond with each other via at least one metal ion selected from the group consisting of metal ions of D block elements. The metal ions of D block elements have a high ability to form coordinate bonds with the nitrogen-containing functional groups, and can form a strong crosslinked structure.

[0045] From the viewpoint of the ability to form a coordinate bond with the nitrogen-containing functional group, the metal ion of the D block element is preferably a metal ion of an element in Groups 3 to 12 of the periodic table, more preferably a metal ion of an element in Groups 7 to 10 of the periodic table, and even more preferably a metal ion of an element in Group 8 of the periodic table. Specific examples of elements in Group 3 of the periodic table include scandium and yttrium. Examples of elements in Group 4 of the periodic table include titanium and zirconium. Examples of elements in Group 5 of the periodic table include vanadium and niobium. Examples of elements in Group 6 of the periodic table include chromium and molybdenum. Examples of elements in Group 7 of the periodic table include manganese and rhenium. Examples of elements in Group 8 of the periodic table include iron, ruthenium, and osmium. Examples of elements in Group 9 of the periodic table include cobalt, rhodium, and iridium. Examples of elements in Group 10 of the periodic table include nickel, palladium, and platinum. Examples of elements in Group 11 of the periodic table include copper, silver, and gold. Examples of elements in Group 12 of the periodic table include zinc. Metal ions of elements in Groups 3 to 12 of the periodic table have the ability to form coordinate bonds with nitrogen-containing functional groups. Metal ions of elements in Groups 7 to 10 of the periodic table have even stronger coordinate bond abilities with nitrogen-containing functional groups, allowing for the formation of stronger crosslinked structures. When the metal ions are metal ions of elements in Group 8 of the periodic table, they tend to form even stronger coordinate bonds with nitrogen-containing functional groups, allowing for the formation of even stronger crosslinked structures. Note that the valence of the metal ions is not particularly limited, and each element can have any possible valence.

[0046] The metal ions are preferably selected from the group consisting of iron ions, zinc ions, cobalt ions, and nickel ions. Iron ions, zinc ions, cobalt ions, and nickel ions are more likely to form stronger coordinate bonds with nitrogen-containing functional groups, allowing for the formation of stronger crosslinked structures. When the metal ions are iron ions, zinc ions, cobalt ions, or nickel ions, the complex polymer forms stronger coordinate bond crosslinks. However, even such strong coordinate bond crosslinks can be dissolved by using the mixed solvent containing the hydrogen peroxide solution and the water-soluble ether.

[0047] As the metal ion, iron ions are particularly preferred. Iron ions are likely to form particularly strong bonds with nitrogen-containing functional groups, and can form a crosslinked structure with even greater strength. When the metal ion is an iron ion, the complex polymer forms even stronger coordinate bond crosslinks, but even such strong coordinate bond crosslinks can be dissolved by using the mixed solvent containing the above-mentioned hydrogen peroxide solution and water-soluble ether. Here, the valence of the iron ion is divalent (Fe ２＋ ) or trivalent (Fe ３＋ ) is preferred.

[0048] For example, by adding a metal salt to a polymer chain to which the nitrogen-containing functional group is bonded, the metal ion can form a coordinate bond with the nitrogen-containing functional group of the polymer chain. In this case, a complex polymer can be easily obtained, and a crosslinked structure with high strength can be formed. The form of the metal salt to be added is not particularly limited, and may be, for example, a hydrate. The amount of metal salt (metal ion) added is preferably in the range of 1 to 30 parts by mass, more preferably 1 to 15 parts by mass, even more preferably 1 to 10 parts by mass, and particularly preferably 1 to 5 parts by mass, per 100 parts by mass of the polymer chain.

[0049] Examples of the metal salt include metal halides, metal sulfates, and metal nitrates, and among these, metal halides are preferred. Metal halides are easy to handle and can form a crosslinked structure with high strength.

[0050] Examples of the metal halide include metal fluorides, metal chlorides, metal bromides, and metal iodides, and among these, metal chlorides are preferred. Metal chlorides are easier to handle and can form a crosslinked structure with high strength.

[0051] Specific examples of the metal salt include FeCl ２ , FeCl ２ ・4H ２ O, FeCl ３ , FeCl ３ ・6H ２ O. The metal salt may be a single type or a combination of two or more types.

[0052] -Method for Producing Complexed Polymer- The complexed polymer can be synthesized, for example, by reacting a polymer chain with a compound having a nitrogen-containing functional group to form a functionalized polymer in which the nitrogen-containing functional group is bonded to the polymer chain, and then complexing the functionalized polymer with a metal ion. Here, the compound having the nitrogen-containing functional group is preferably a compound having a triazine ring or tetrazine ring as described above, and more preferably a compound represented by general formula (1). Furthermore, in the reaction between the polymer chain and the compound having the nitrogen-containing functional group, the reaction conditions such as temperature, pressure, and time are preferably selected appropriately depending on the type and reactivity of the polymer chain and the compound having the nitrogen-containing functional group used. Furthermore, in the complexation reaction between the functionalized polymer and the metal ion, the reaction conditions such as temperature, pressure, and time are preferably selected appropriately depending on the type and reactivity of the functionalized polymer and the metal ion used.

[0053] As an example, 3,6-di(2-pyridyl)-1,2,4,5-tetrazine is used as a compound having a nitrogen-containing functional group, and iron chloride (FeCl) is used as a source of metal ions. ２ The reaction scheme for functionalization of the polymer chain and complexation of the functionalized polymer using .

[0054] As shown in the upper part of the reaction scheme above, a functionalized polymer can be produced by the Diels-Alder reaction of a polymer chain having an unsaturated bond with a compound having a nitrogen-containing functional group. In this example, nitrogen is eliminated during the Diels-Alder reaction, but any other reaction may be used for the functionalization reaction.

[0055] As shown in the lower part of the above reaction scheme, the functionalized polymer and iron chloride are complexed and crosslinked to form a complexed polymer. While the above reaction scheme shows a coordinate bond between the nitrogen atom in the tetrazine residue, the nitrogen atom of the pyridyl group bonded to the tetrazine residue, and the iron ion (complexation and crosslinking), the complexed polymer can take various complexation forms.

[0056] The complexing polymer may be prepared in advance by synthesis or the like as described above, but may also be generated in situ during the production process of the rubber composition, for example.

[0057] For example, in the first stage of kneading in the production process of the rubber composition, a polymer chain and a compound having a nitrogen-containing functional group are kneaded together to form a functionalized polymer in which the nitrogen-containing functional group is bonded to the polymer chain, and in the second or subsequent stages of kneading, a metal salt is added and kneaded to complex the functionalized polymer to form a complex polymer. In this case, the production of the rubber composition and the synthesis of the complex polymer can be carried out simultaneously.

[0058] Alternatively, for example, a functionalized polymer having a nitrogen-containing functional group bonded to a polymer chain may be prepared in advance, and the functionalized polymer may be kneaded with any compounding ingredients in the first stage of kneading in the production process of the rubber composition. In the second or subsequent stage of kneading, a metal salt may be added and kneaded to complex the functionalized polymer to form a complex polymer. In this case, the production of the rubber composition and the synthesis of the complex polymer can be carried out simultaneously.

[0059] - Rubber Composition - The complex polymer may be contained in a rubber composition, which may contain, in addition to the complex polymer, compounding agents commonly used in the rubber industry, such as fillers (carbon black, silica, etc.), antioxidants, softeners, stearic acid, silane coupling agents, etc.

[0060] (Mixed Solvent Containing Hydrogen Peroxide and Water-Soluble Ether) The method for breaking the coordinate bond of a complexed polymer according to the present embodiment is characterized by comprising a step of breaking the coordinate bond between the metal ion and the nitrogen-containing functional group of the complexed polymer using a mixed solvent containing hydrogen peroxide and a water-soluble ether. The complexed polymer is crosslinked by forming coordinate bonds between the nitrogen-containing functional groups via the metal ion. By treating the complexed polymer with a mixed solvent containing hydrogen peroxide and a water-soluble ether, the crosslinks between the polymer chains are broken, and a functionalized polymer can be obtained as an uncrosslinked rubber.

[0061] The concentration of hydrogen peroxide in the hydrogen peroxide solution is not particularly limited. The concentration of hydrogen peroxide in the hydrogen peroxide solution is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and preferably 50% by mass or less, even more preferably 40% by mass or less. The amount of hydrogen peroxide used is not particularly limited, but is preferably in the range of 2 to 50 mol, more preferably 5 to 20 mol, per mol of metal ion in the complex polymer. If the amount of hydrogen peroxide used is within this range, it is easier to further convert the metal ions into hydroxides or oxides, and it is easier to further deactivate the nitrogen-coordinating ability of the metal ions. The concentration of hydrogen peroxide in the mixed solution is preferably in the range of 0.01 to 5 mol / L, more preferably 0.1 to 3 mol / L.

[0062] The water-soluble ether has an ether bond (—O—) and is soluble in water. The water-soluble ether preferably dissolves in an amount of 1 g or more, and more preferably 5 g or more, per 100 g of water at room temperature (25° C.). Examples of such water-soluble ethers include tetrahydrofuran (THF), diethyl ether, dioxane, trioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, and diethylene glycol diethyl ether. Among these, tetrahydrofuran is preferred as the water-soluble ether. The combined use of hydrogen peroxide and tetrahydrofuran facilitates penetration of the hydrogen peroxide into the interior of the complexed polymer, and also facilitates the dissociation of the complexed polymer and the elimination of crosslinks between polymer chains.

[0063] In the mixed solvent, the volume ratio of the hydrogen peroxide solution to the water-soluble ether (hydrogen peroxide solution / water-soluble ether) is preferably in the range of 1 / 99 to 50 / 50, more preferably in the range of 5 / 95 to 40 / 60, and even more preferably in the range of 10 / 90 to 30 / 70. When the volume ratio of the hydrogen peroxide solution to the water-soluble ether is within these ranges, the hydrogen peroxide solution can more easily penetrate into the interior of the complex polymer.

[0064] The mixed solvent may contain a solvent other than the hydrogen peroxide solution and the water-soluble ether, such as alcohols such as methanol and ethanol.

[0065] The amount of the mixed solvent used is preferably in the range of 500 to 10,000 parts by mass per 100 parts by mass of the complex polymer. When the amount of the mixed solvent used is within this range, the hydrogen peroxide solution can more easily penetrate into the interior of the complex polymer.

[0066] The temperature at which the complexed polymer is treated with the mixed solvent may be room temperature, but is preferably in the range of 5°C to 80°C. If the treatment temperature is in this range, the hydrogen peroxide solution can more easily penetrate into the interior of the complexed polymer. Furthermore, the pressure at which the complexed polymer is treated with the mixed solvent may be normal pressure, reduced pressure, or increased pressure. Performing the treatment at normal pressure simplifies the overall process. Performing the treatment under increased pressure also makes it possible to easily dissolve the coordinate bonds in a shorter time. Furthermore, the time for which the complexed polymer is treated with the mixed solvent is preferably selected appropriately depending on the treatment temperature and the like, and is preferably 1 to 100 hours, for example.

[0067] As an example, the reaction scheme for breaking the coordinate bond of the complex polymer synthesized according to the above-mentioned reaction scheme using a mixed solvent containing hydrogen peroxide and a water-soluble ether is shown below.

[0068] As shown in the reaction scheme above, the complexed polymer is treated with hydrogen peroxide (H ２ O ２ ) to convert the metal ions into hydroxides or oxides, deactivating the nitrogen-coordinating ability of the metal ions, and thereby removing the metal ions from the nitrogen-containing functional groups of the polymer chain. Also, removing the metal ions from the nitrogen-containing functional groups of the polymer chains releases the coordination bonds of the complexed polymer, eliminating the crosslinks between the polymer chains, and thus obtaining a functionalized polymer.

[0069] (Applications) The method for breaking the coordinate bond of a complexed polymer according to this embodiment can be applied to various rubber products and resin products. Examples of such rubber products include tires, rubber vibration absorbers, rubber seismic isolation devices, conveyor belts, rubber crawlers, and various hoses. By applying the method for breaking the coordinate bond of a complexed polymer according to this embodiment to these rubber products, the coordinate bond of the complexed polymer in the rubber product can be broken, and the functionalized polymer can be recovered, allowing the complexed polymer to be recycled.

[0070] (Uses of Recycled Polymers (Decrosslinked Polymers)) The functionalized polymer obtained by breaking the coordination bonds of the complexed polymer using the method described above can be recycled as a complexed polymer by complexing it with a metal ion, or it can be used for other purposes without being complexed. The functionalized polymer obtained by breaking the coordination bonds of the complexed polymer and the complexed polymer can be used in various rubber products and resin products. Examples of such rubber products include tires, seismic isolation rubber, rubber crawlers, and various hoses.

[0071] The complex polymer described above can be used in a rubber composition, which may contain, in addition to the complex polymer described above, compounding agents commonly used in the rubber industry, such as fillers (carbon black, silica, etc.), antioxidants, softeners, stearic acid, silane coupling agents, etc.

[0072] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples in any way.

[0073] <Method for producing complexed polymer A> Using a conventional laboratory mixer, styrene-butadiene rubber (SBR) and 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (manufactured by Tokyo Chemical Industry Co., Ltd.) were added to the compounding formulation shown in Table 1, and the mixture was kneaded at 140°C for 3 minutes to prepare functionalized polymer A.

[0074] Next, iron (II) chloride tetrahydrate was added to functionalized polymer A according to the formulation shown in Table 1, and the mixture was kneaded at 60°C for 1 minute, and then pressed in a mold at 160°C for 60 minutes to prepare complexed polymer A.

[0075]

[0076] *1 SBR: Styrene-butadiene rubber, manufactured by Asahi Kasei Corporation, product name "Tufden 2000R"

[0077] <Decrosslinking using hydrogen peroxide / water-soluble ether solution> (Example 1) Complexed polymer A was cut into pieces of approximately 2 to 3 mm on a side to prepare granular rubber, which was then immersed in a mixed solution of hydrogen peroxide and tetrahydrofuran (THF) in the mixing ratio shown in Table 2 to carry out a decrosslinking reaction. The state of the solution after a predetermined temperature and a predetermined time is shown in Table 2.

[0078] Next, the solution in which the granular rubber had been decrosslinked and became uniform was added to a large amount of methanol to precipitate the rubber, and the resulting precipitated rubber was redissolved in the same amount of THF solvent as the amount used in the mixed solution. Redissolution indicates that the decrosslinked state was maintained even after the decrosslinking agent species was removed. The results are shown in Table 3.

[0079] (Example 2) Complex polymer A was cut into pieces approximately 2 to 3 mm on a side to prepare granular rubber, which was then immersed in a mixed solution of hydrogen peroxide and tetrahydrofuran (THF) in the mixing ratio shown in Table 2 to carry out a decrosslinking reaction. The state of the solution after a predetermined temperature and a predetermined time is shown in Table 2.

[0080] The solvent was then removed by decantation, and the rubber precipitate was redissolved in the same amount of THF as the mixed solution. Redissolution indicates that the decrosslinked state was maintained even in a heterogeneous state. The results are shown in Table 3.

[0081] (Examples 3 and 4) The decrosslinking reaction was carried out in the same manner as in Example 1. Table 2 shows the state of the solution after a predetermined temperature and a predetermined time, and Table 3 shows the results of redissolving the solution in THF solvent.

[0082] Comparative Example 1 Similar to Example 1, complexed polymer A was cut into pieces of approximately 2 to 3 mm on a side to prepare granular rubber, which was then immersed in a solution of only hydrogen peroxide without using water-soluble ether to carry out a decrosslinking reaction. As shown in Table 2, the rubber was not decrosslinked even after a predetermined temperature and time, and remained in the form of granular rubber.

[0083] Comparative Example 2 In the same manner as in Example 1, the complexed polymer A was cut into pieces of approximately 2 to 3 mm on a side to prepare granular rubber, which was then immersed in a mixed solution of pyridine and tetrahydrofuran (THF) in the mixing ratio shown in Table 2 at 65°C for 12 hours to carry out a decrosslinking reaction.

[0084] Next, the solution in which the granular rubber had been decrosslinked and became uniform was added to a large amount of methanol to precipitate the rubber, and the resulting precipitated rubber was redissolved in THF solvent in an amount equal to the amount used in the mixed solution. The results are shown in Table 3. As shown in Table 3, some of the rubber was insoluble in THF, and it is thought that removing the pyridine, the decrosslinking agent, caused the rubber to return to its original crosslinked state.

[0085] Comparative Example 3 In the same manner as in Example 1, complexed polymer A was cut into pieces approximately 2 to 3 mm on a side to prepare granular rubber, which was then immersed at 20°C for 72 hours in a mixed solution of pyridine and tetrahydrofuran (THF) in the mixing ratio shown in Table 2 to carry out a decrosslinking reaction. As shown in Table 2, the decrosslinking of the rubber was insufficient and not uniform at room temperature, and as shown in Table 3, the rubber was insoluble in THF solvent.

[0086]

[0087]

[0088] The results of the Examples in Tables 2 and 3 show that treatment with a mixed solvent containing aqueous hydrogen peroxide and a water-soluble ether can break the coordinate bonds of the complexed polymer, enabling good de-crosslinking, and that the de-crosslinked state can be well maintained even after the de-crosslinking agent species (aqueous hydrogen peroxide) is removed.

[0089] On the other hand, the results of Comparative Example 1 show that the complexed polymer cannot be decrosslinked when treated with hydrogen peroxide alone. Furthermore, the results of Comparative Example 2 show that, although decrosslinking is possible when pyridine is used as a decrosslinking agent and treated at high temperatures, removing the pyridine decrosslinking agent returns the polymer to its original crosslinked state, making it impossible to stably maintain the decrosslinked state. Furthermore, the results of Comparative Example 3 show that when pyridine is used as a decrosslinking agent, decrosslinking does not proceed sufficiently at room temperature.

[0090] <Method for producing complexed polymer B> Using a conventional laboratory mixer, styrene-butadiene rubber (SBR), 3,6-di(2-pyridyl)-1,2,4,5-tetrazine (manufactured by Tokyo Chemical Industry Co., Ltd.), and carbon black (HAF grade) were added to the formulation shown in Table 4, and the mixture was kneaded at 110°C for 3 minutes to prepare functionalized polymer B (a mixture of functionalized polymer and carbon black).

[0091] Next, iron (II) chloride tetrahydrate and antioxidant (6C) were added to functionalized polymer B according to the formulation shown in Table 5, and the mixture was kneaded at 60°C for 1 minute, and then pressed in a mold at 160°C for 60 minutes to prepare complexed polymer B.

[0092] <Method for producing sulfur-crosslinked rubber> Using a conventional laboratory mixer according to the formulation shown in Table 4, 50 parts by mass of carbon black (HAF grade) was added to 100 parts by mass of styrene-butadiene rubber (SBR), and the mixture was kneaded at 110°C for 3 minutes to prepare an unfunctionalized polymer (a mixture of an unfunctionalized polymer and carbon black).

[0093] Next, zinc oxide, an antioxidant, a vulcanization accelerator, and sulfur were added to the unfunctionalized polymer according to the compounding recipe shown in Table 5, and the mixture was kneaded at 80°C for 1 minute, and then pressed in a mold at 160°C for 20 minutes to prepare a sulfur-crosslinked rubber.

[0094]

[0095] *1 SBR: Styrene-butadiene rubber, manufactured by Asahi Kasei Corporation, product name "Tufden 2000R"

[0096]

[0097] * 3 Antioxidant 6C: N-(1,3-dimethylbutyl)-N'-p-phenylenediamine, manufactured by Ouchi Shinko Chemical Co., Ltd., trade name "Knocklac 6C" * 4 Vulcanization accelerator DM: Dibenzothiazyl disulfide, manufactured by Ouchi Shinko Chemical Co., Ltd., trade name "Noccela DM-P" * 5 Vulcanization accelerator CZ: N-cyclohexyl-2-benzothiazolyl sulfenamide, manufactured by Ouchi Shinko Chemical Co., Ltd., trade name "Noccela CZ-G"

[0098] (Example 5) Complex polymer B was cut into pieces approximately 2 to 3 mm on a side to prepare granular rubber, which was then immersed in a mixed solution of hydrogen peroxide and tetrahydrofuran (THF) in the mixing ratio shown in Table 6 to carry out a decrosslinking reaction. The state of the solution after a predetermined temperature and a predetermined time is shown in Table 6.

[0099] Next, the suspension was precipitated in a large amount of methanol, and the precipitated rubber was air-dried at room temperature for one day, after which the roll processability and odor during roll work were evaluated by the following methods.

[0100] [Evaluation of Roll Processability, Odor During Rolling] Roll processability was evaluated at 65°C using a twin-screw roll. The evaluation criteria are as follows: A: Good remolding (wrapped around roll sheet, smooth surface, controllable sheet thickness) B: Unable to wrap around roll sheet, could be made into a sheet but had surface irregularities and edge cuts C: Unable to wrap around roll sheet, rubber granules remained In addition, the odor generated during this process was compared with that of Comparative Example 4 (sulfur-crosslinked rubber). The results are shown in Table 7.

[0101] (Examples 6 and 7) As in Example 5, complexed polymer B was cut into pieces approximately 2 to 3 mm on a side to prepare granular rubber, which was then immersed for a predetermined time in a mixed solution of hydrogen peroxide and tetrahydrofuran (THF) in the mixing ratio shown in Table 6 to carry out a decrosslinking reaction. The state of the solution after a predetermined time at a predetermined temperature is shown in Table 6.

[0102] The solvent was then removed by decantation, and the resulting precipitated rubber was air-dried at room temperature for one day. Similar to Example 5, roll processability was evaluated using a twin-roll mill, and the odor generated was compared. The results are shown in Table 7.

[0103] Comparative Example 4 In the same manner as in Example 5, the sulfur-crosslinked rubber was cut into pieces of approximately 2 to 3 mm on a side to prepare granular rubber, which was then immersed for a predetermined time in a mixed solution of hydrogen peroxide and tetrahydrofuran (THF) in the mixing ratio shown in Table 6 to carry out a decrosslinking reaction. The state of the solution after a predetermined time at a predetermined temperature is shown in Table 6.

[0104] The solvent was then removed by decantation, and the resulting precipitated rubber was air-dried at room temperature for one day. Similar to Example 5, roll processability was evaluated using a twin-roll mill, and the odor generated was compared. The results are shown in Table 7.

[0105] Comparative Example 5 Similar to Example 5, complexed polymer B was cut into pieces approximately 2 to 3 mm on a side to prepare granular rubber, which was then immersed for a predetermined time in a mixed solution of pyridine and tetrahydrofuran (THF) in the mixing ratio shown in Table 6 to carry out a decrosslinking reaction. The state of the solution after a predetermined time at a predetermined temperature is shown in Table 6.

[0106] Next, the suspension was precipitated in a large amount of methanol, and the precipitated rubber was air-dried at room temperature for one day. As in Example 5, roll processability was evaluated using a twin-roll mill and the odor was compared. The results are shown in Table 7.

[0107]

[0108]

[0109] From Table 6, it can be seen that the coordinate bond of the complex polymer can be broken by using a mixed solvent containing hydrogen peroxide and a water-soluble ether, and the crosslinking can be successfully removed.

[0110] Furthermore, Table 7 shows that the decrosslinked rubber (functionalized polymer) obtained by decrosslinking has good remoldability and does not emit any odor.

[0111] The method of the present invention for breaking the coordinate bond of a complexed polymer can be used for recycling the polymer.

Claims

1. A method for breaking the coordination bond of a complex polymer having at least one polymer chain and a plurality of nitrogen-containing functional groups capable of forming coordination bonds attached to the polymer chain, wherein the nitrogen-containing functional groups capable of forming coordination bonds form coordination bonds with each other via at least one metal ion selected from the group consisting of metal ions of D-block elements, the method comprising the step of breaking the coordination bond between the metal ion and the nitrogen-containing functional group using a mixed solvent containing hydrogen peroxide and a water-soluble ether.

2. The method for releasing the coordinate bonds of a complexed polymer according to claim 1, wherein the water-soluble ether is tetrahydrofuran.

3. A method for releasing the coordinate bond of a complexed polymer according to claim 1, wherein the nitrogen-containing functional group is derived from a compound containing a triazine ring or a tetrazine ring.

4. The method for breaking the coordinate bond of a complexed polymer according to claim 1, wherein the nitrogen-containing functional group does not contain a sulfur atom.

5. A method for releasing the coordinate bond of a complex polymer according to claim 3, wherein two pyridyl groups or two pyrimidyl groups are bonded to the triazine ring or the tetrazine ring.

6. The nitrogen-containing functional group is represented by the following general formula (1): [In the formula, X １ and X ２ are each independently a pyridyl group or a pyrimidinyl group, and Y １ and Y ２ and each independently represent a single bond or a divalent hydrocarbon group.

7. The method for breaking the coordination bonds of a complexed polymer according to claim 1, wherein said metal ions are selected from the group consisting of iron ions, zinc ions, cobalt ions and nickel ions.

8. The method for breaking the coordination bond of a complexed polymer according to claim 1, wherein the metal ion is an iron ion.

9. A method for breaking the coordinate bonds of a complexed polymer according to claim 1, wherein said polymer chains contain conjugated diene units.

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