Method for breaking coordination bonds of complex polymers

Abstract

The problem to be solved by the present invention is to provide a method by which crosslinking of a polymer can be easily eliminated. The solution to the problem is a method for breaking coordination bonds of a complex polymer, the complex polymer comprising at least one polymer chain and a plurality of nitrogen- and / or phosphorus-containing functional groups capable of forming coordination bonds and bonded to the polymer chain, and wherein the nitrogen- and / or phosphorus-containing functional groups capable of forming coordination bonds are bound to each other via metal ions by coordination bonds, the method being characterized in that the complex polymer is dissolved in a solvent comprising free ligands, thereby breaking the coordination bonds.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for breaking coordination bonds of complex polymers. BACKGROUND

[0002] In the past, most of the used vulcanized rubber products such as old tires have been disposed of as waste without being recycled. However, from the viewpoint of solving environmental problems, promoting resource saving, and the like, recycling of vulcanized rubber waste such as old tires is a pressing matter.

[0003] As a method for regenerating vulcanized rubber, for example, there is a conventionally known method of regenerating vulcanized rubber by applying heat and shear force to the vulcanized rubber using a twin-screw extruder.

[0004] Further, PTL 1 proposes a technology of devulcanizing vulcanized rubber and regenerating the rubber as unvulcanized rubber.

[0005] LIST OF CITATIONS

[0006] PATENT LITERATURE

[0007] PTL 1: JP 2005-023225 A SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] However, in the related art, a crosslinked product of a polymer such as vulcanized rubber is inevitably deteriorated by regeneration because the crosslinked product is regenerated by treatment under severe conditions. For example, a rubber product using regenerated rubber has a problem that the rubber product exhibits poor performance in physical properties such as breaking strength, compared to a rubber product not using the regenerated rubber. Therefore, there is still room for improvement in recycling a crosslinked product of a polymer such as vulcanized rubber, and further studies are required.

[0010] In view of this, an object of the present application is to solve the above-described problems of the related art, and to provide a method capable of easily breaking crosslinking of a polymer such as rubber.

[0011] SOLUTION TO PROBLEM

[0012] As a result of intensive studies made in order to solve the above-described problems, the inventors of the present application found that, for a specific complex polymer which forms a coordination bond via a metal ion, crosslinking therein can be easily broken by dissolving the complex polymer in a solvent containing a free ligand. The present application was completed based on this finding. Specifically, the main features of the present application for achieving the above-described object are as follows.

[0013] The method for breaking coordinate bonds of a complex polymer according to the present application is a method for breaking coordinate bonds of a complex polymer, the complex polymer comprising at least one polymer chain and a plurality of nitrogen- and / or phosphorus-containing functional groups which are bonded to the polymer chain and which are capable of forming coordinate bonds, wherein the coordinately bondable nitrogen- and / or phosphorus-containing functional groups form coordinate bonds via metal ions, characterized in that the method comprises dissolving the complex polymer in a solvent comprising free ligands to break the coordinate bonds.

[0014] Effects of the Invention

[0015] According to the present application, it is possible to provide a method capable of easily breaking crosslinking of a polymer. DETAILED DESCRIPTION

[0016] Hereinafter, the method for breaking coordinate bonds of a complex polymer according to the present application will be described in detail by embodiments of the present application.

[0017] <Method for breaking coordinate bonds of a complex polymer>

[0018] The method for breaking coordinate bonds of a complex polymer according to the present application is a method for breaking coordinate bonds of a complex polymer, the complex polymer comprising at least one polymer chain and a plurality of nitrogen- and / or phosphorus-containing functional groups which are bonded to the polymer chain and which are capable of forming coordinate bonds, wherein the coordinately bondable nitrogen- and / or phosphorus-containing functional groups form coordinate bonds via metal ions, characterized in that the method comprises dissolving the complex polymer in a solvent comprising free ligands to break the coordinate bonds.

[0019] The complex polymer subjected to the method according to the present application has at least one polymer chain and a plurality of nitrogen- and / or phosphorus-containing functional groups which are bonded to the polymer chain and which are capable of forming coordinate bonds, wherein the coordinately bondable nitrogen- and / or phosphorus-containing functional groups form coordinate bonds via metal ions therebetween. Since the nitrogen- and / or phosphorus-containing functional groups form coordinate bonds via metal ions therebetween, the complex polymer has a crosslinked structure. When the complex polymer is dissolved in a solvent comprising free ligands, a ligand exchange reaction occurs, and the free ligands form coordinate bonds with the metal ions, whereby the coordinate bonds of the complex polymer (more specifically, the coordinate bonds between the metal ions and the nitrogen- and / or phosphorus-containing functional groups bonded to the polymer chain) can be easily broken, and thus the crosslinking between the polymer chains can be easily broken. Therefore, the complex polymer is a polymer having a crosslinked form in which sulfur crosslinking is replaced, which is recyclable.

[0020] Conventional sulfur-vulcanized rubbers have main chains connected by strong covalent bonds, and thus it is difficult to break the crosslinks and recover the original raw material therefrom. Regenerated rubbers such as reclaimed rubber are known, but in the regenerated rubbers, significant deterioration of the main chains occurs. On the other hand, when the above complex polymer (i.e., a polymer in which nitrogen- and / or phosphorus-containing functional groups bonded to the polymer chain are crosslinked by metal ions) is dissolved in a solvent containing free ligands, a ligand exchange reaction occurs, so that the crosslinks are destroyed and the polymer chains are dissolved. When a typical vulcanized rubber is subjected to the same conditions as described above, only the solvent is absorbed to swell, so that de-crosslinking cannot be performed.

[0021] Thus, with the method of the present application, the crosslinks of the polymer can be easily destroyed without the need for treatment under harsh conditions, whereby deterioration of the properties of the polymer chains can be well inhibited.

[0022] (polymer chain)

[0023] The complex polymer contains at least one polymer chain. In the case where the complex polymer has one polymer chain, the complex polymer forms coordinate bonding by metal ions, and thus is crosslinked within its molecule. In the case where the complex polymer has two or more polymer chains, the complex polymer can form coordinate bonding by metal ions, and thus is crosslinked not only within its molecule but also between molecules (between its polymer chains). The complex polymer contains a plurality of nitrogen- and / or phosphorus-containing functional groups capable of forming coordinate bonding. The plurality of nitrogen- and / or phosphorus-containing functional groups can be bonded to a single polymer chain or two or more polymer chains, respectively. The plurality of nitrogen- and / or phosphorus-containing functional groups can be the same kind or different kinds.

[0024] The polymer chain preferably contains a conjugated diene unit and / or an olefin unit. That is, the polymer chain preferably contains a conjugated diene unit or an olefin unit, or both a conjugated diene unit and an olefin unit.

[0025] The conjugated diene unit represents a monomer unit derived from a conjugated diene compound. The conjugated diene compound as a monomer preferably has 4 to 8 carbon atoms. Specific examples of the conjugated diene compound include 1,3-butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-l,3-butadiene, and the like. From the viewpoint of satisfactory elastomeric properties, the conjugated diene compound as a monomer preferably includes 1,3-butadiene and / or isoprene.

[0026] The content of the conjugated diene unit in the polymer chain is not particularly limited, and can be 0 mol%, preferably > 0.1 mol%, more preferably > 1 mol%, and can be 100 mol%. When the above content is > 1 mol%, a complex polymer having excellent elastomeric properties can be obtained.

[0027] The olefin unit represents a monomer unit derived from an olefin compound. The olefin compound as a monomer preferably has 2 to 10 carbon atoms. Specific examples of the olefin compound include α-olefins such as ethylene, propylene, 1-pentene, 1-hexene, 1-heptene, and 1-octene, and the like; heteroatom-substituted olefin compounds such as vinyl pivalate, 1-phenylthioethylene, N-vinylpyrrolidone; and the like.

[0028] The content of the olefin unit in the polymer chain is not particularly limited, and can be 0 mol%, preferably > 1 mol%, and can be 100 mol%.

[0029] The polymer chain can further include a unit derived from another monomer copolymerizable with the above conjugated diene compound and / or olefin compound. Examples of the unit derived from another monomer include an aromatic vinyl unit and the like. The content of the unit derived from another monomer in the polymer main chain is not particularly limited, and can be 0 mol%, in one embodiment, preferably > 1 mol% and < 50 mol%.

[0030] The aromatic vinyl unit represents a monomer unit derived from an aromatic vinyl compound. The aromatic vinyl compound represents an aromatic compound substituted with at least a vinyl group. The aromatic vinyl compound as a monomer preferably has 8 to 10 carbon atoms. Specific examples of the aromatic vinyl compound include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene, and the like.

[0031] (Nitrogen- and / or phosphorus-containing functional group)

[0032] The complex polymer contains a plurality of nitrogen- and / or phosphorus-containing functional groups that are bonded to the polymer chain and are capable of forming coordinate bonding. The nitrogen- and / or phosphorus-containing functional groups that are capable of coordinate bonding form coordinate bonding therebetween via a metal ion. By the coordinate bonding, the bond between the metal ion and the nitrogen- and / or phosphorus-containing functional group can be sufficiently imparted with reversibility. Furthermore, the coordinate bonding between the nitrogen- and / or phosphorus-containing functional group and the metal ion is sufficiently strong, whereby a crosslinking of a strength equivalent to that of sulfur crosslinking can be formed, and thus the complex polymer has satisfactorily high durability. Preferred examples of the nitrogen-containing functional group include groups having a nitrogen-containing heterocycle such as a 4,5-dihydro pyridazine ring, a pyridine ring, a pyrimidine ring, a triazine ring, or a tetrazine ring. Examples of the phosphorus-containing functional group include groups obtained by replacing each nitrogen atom of the nitrogen-containing heterocycle of the above-described nitrogen-containing functional group with a phosphorus atom.

[0033] In the present application, it is preferred that the nitrogen- and / or phosphorus-containing functional group does not contain a sulfur atom. In the case where the nitrogen- and / or phosphorus-containing functional group does not contain a sulfur atom, crosslinking between polymer chains due to a sulfur atom can be prevented, and thus the recyclability of the complex polymer is improved.

[0034] In the complex polymer of the present application, the dissociation energy of the dissociable bond between the metal ion and the nitrogen- and / or phosphorus-containing functional group is preferably ≥ 200 kJ / mol, and more preferably ≥ 250 kJ / mol, and preferably ≤ 500 kJ / mol. When the above-described bond dissociation energy is ≥ 200 kJ / mol, a crosslinking structure having a high strength equivalent to that of sulfur crosslinking can be formed, and thus the durability of the complex polymer is satisfactorily high. When the bond dissociation energy is ≥ 250 kJ / mol, the durability of the complex polymer is further improved. When the bond dissociation energy is ≤ 500 kJ / mol, the coordinate bond between the metal ion and the nitrogen-containing functional group can be more easily broken, and thus the complex polymer can be more easily recycled than otherwise.

[0035] In the present application, the dissociation energy of the dissociable bond between the metal ion and the nitrogen-containing functional group represents a value measured in vacuo at a structure optimization level of M06 / 6-31G(d,p) / / B3PW91-D3 / 6-31G(d,p) or M06 / 6-31G(d,p). It is assumed that the metal ion and the nitrogen- and / or phosphorus-containing functional group form an ionic aggregate. Gaussian09 or GRRM14 can be used for the calculation of the bond dissociation energy.

[0036] The nitrogen- and / or phosphorus-containing functional group is preferably derived from a compound containing a triazine ring or a tetrazine ring. The compound containing a triazine ring or a tetrazine ring that reacts with the polymer chain easily forms a functionalized polymer due to its reactivity with the polymer chain. Further, the nitrogen-containing functional group derived from the compound containing a triazine ring or a tetrazine ring easily forms crosslinking with the metal ion, thereby successfully forming a crosslinking structure having a high strength equivalent to that of sulfur crosslinking.

[0037] In the present application, in the case where the nitrogen- and / or phosphorus-containing functional group is derived from a compound containing a triazine ring or a tetrazine ring, it is preferable that a pyridyl group / pyrimidyl group be bonded to the triazine / tetrazine ring of the compound. In this regard, it is more preferable that two pyridyl groups / pyrimidyl groups be bonded to the triazine / tetrazine ring. In the case where a pyridyl group / pyrimidyl group is bonded to the triazine / tetrazine ring, the nitrogen-containing functional group is more easily complexed with a metal ion, whereby the bond dissociation energy relating thereto is more easily high, and thus a crosslinked structure having a higher strength than in other cases can be formed. Further, in the case where two pyridyl groups / pyrimidyl groups are bonded to the triazine / tetrazine ring, the nitrogen-containing functional group is even more easily complexed with a metal ion, whereby the bond dissociation energy relating thereto is even more easily high, and thus a crosslinked structure having an even higher strength than in other cases can be formed.

[0038] The pyridyl group can be any one of a 2-pyridyl group, a 3-pyridyl group, and a 4-pyridyl group, and is preferably a 2-pyridyl group. The pyrimidyl group can be any one of a 2-pyrimidyl group, a 4-pyrimidyl group, and a 5-pyrimidyl group.

[0039] The nitrogen- and / or phosphorus-containing functional group is preferably derived from a compound represented by General Formula (1) shown below.

[0040]

[0041] In General Formula (1), X 1 and X 2 each independently represent a pyridyl group / pyrimidyl group, and Y 1 and Y 2 each independently represent a single bond or a divalent hydrocarbon group.

[0042] The compound represented by General Formula (1) is easily subjected to a Diels-Alder reaction with a polymer chain, and thus a functionalized polymer is easily formed. Further, in the case where the nitrogen- and / or phosphorus-containing functional group is derived from a compound represented by General Formula (1), the nitrogen-containing functional group is particularly easily complexed with a metal ion, whereby the bond dissociation energy relating thereto is even more easily high, and thus a crosslinked structure having a particularly high strength can be formed.

[0043] In General Formula (1), X 1 and X 2 each independently represent a pyridyl group / pyrimidyl group. From the viewpoint of ease of synthesis, X 1 and X 2 each are preferably a pyridyl group. The pyridyl group can be any one of a 2-pyridyl group, a 3-pyridyl group, and a 4-pyridyl group, and is preferably a 2-pyridyl group. The pyrimidyl group can be any one of a 2-pyrimidyl group, a 4-pyrimidyl group, and a 5-pyrimidyl group.

[0044] In General Formula (1), Y1 and Y 2 each independently represents a single bond or a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include alkylene, alkenylene, and arylene groups, etc. Specifically, examples of the alkylene group include methylene, ethylene, trimethylene, and tetramethylene groups, etc. Examples of the alkenylene group include ethenylene, propenylene, and butenylene groups, etc. Examples of the arylene group include phenylene, tolylene, and naphthylene groups, etc. From the viewpoint of ease of synthesis, Y 1 and Y 2 each is preferably a single bond (i.e., it is preferred that X 1 and X 2 each is directly bonded to the triazine ring).

[0045] In the present application, in General Formula (1), it is preferred that X 1 and X 2 each is a pyridyl group, and Y 1 and Y 2 each is a single bond. In this case, the compound of General Formula (1) is not only easy to obtain, but also the functional group is particularly easy to complex with a metal ion, whereby the relevant bond dissociation energy is even more easily high, and thus a crosslinked structure having particularly high strength can be formed.

[0046] Examples of the compound represented by General Formula (1) include 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine, 3,6-bis(3-pyridyl)-1,2,4,5-tetrazine, 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine, 3,6-bis(2-pyridylmethyl)-1,2,4,5-tetrazine, 3,6-bis(2-pyridylethyl)-1,2,4,5-tetrazine, 3-(2-pyridylmethyl)-6-(2-pyridylethyl)-1,2,4,5-tetrazine, 3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine, 3,6-bis(4-pyrimidyl)-1,2,4,5-tetrazine, and 3,6-bis(5-pyrimidyl)-1,2,4,5-tetrazine, etc. Among these examples, 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine is preferred.

[0047] In the complex polymer of the present application, the nitrogen- and / or phosphorus-containing functional group is bonded to the polymer chain in an amount preferably in the range of 0.1 to 10 mol%, more preferably in the range of 0.3 to 8 mol%, even more preferably in the range of 0.4 to 5 mol%, and particularly preferably in the range of 0.5 to 3 mol% relative to the monomer units of the polymer chain. In the case where the nitrogen- and / or phosphorus-containing functional group is bonded to the polymer chain in an amount of > 0.1 mol% relative to the monomer units of the polymer chain, a crosslinked structure having a high strength comparable to sulfur crosslinking can be formed, and thus a complex polymer having a satisfactorily high durability is obtained. In the case where the nitrogen- and / or phosphorus-containing functional group is bonded to the polymer chain in an amount of < 10 mol% relative to the monomer units of the polymer chain, a complex polymer having a satisfactorily high elastomeric property can be easily obtained.

[0048] (metal ion)

[0049] In the complex polymer, the nitrogen- and / or phosphorus-containing functional group that can be coordinately bonded forms a coordinate bond together with the metal ion. Any metal ion that can be coordinately bonded with the nitrogen- and / or phosphorus-containing functional group can be used as the metal ion in the complex polymer.

[0050] From the viewpoint of the ability to form a coordinate bond with the nitrogen- and / or phosphorus-containing functional group, the metal ion is preferably a metal ion of an element of Groups 7 to 10 in the periodic table, and more preferably a metal ion of an element of Group 8 in the periodic table.

[0051] Specifically, examples of the element of Group 7 include manganese, rhenium, and the like.

[0052] Examples of the element of Group 8 include iron, ruthenium, and osmium, and the like.

[0053] Examples of the element of Group 9 include cobalt, rhodium, and iridium, and the like.

[0054] Examples of the element of Group 10 include nickel, palladium, and platinum, and the like.

[0055] The metal ion of the element of Groups 7 to 10 in the periodic table easily forms a strong bond with the nitrogen- and / or phosphorus-containing functional group, thereby successfully forming a crosslinked structure having a high strength comparable to sulfur crosslinking. Further, in the case where the metal ion is a metal ion of an element of Group 8 in the periodic table, the coordinate bond between the metal ion and the nitrogen- and / or phosphorus-containing functional group is easily stronger than in other cases, and thus ensures the formation of a crosslinked structure having a higher strength than in other cases.

[0056] The valence number of the metal ion is not particularly limited, and it can be set to any valence number that the element can take.

[0057] Iron ions are particularly preferable as the above metal ions. Iron ions easily form particularly strong bonds with nitrogen- and / or phosphorus-containing functional groups, thereby making it possible to form crosslinked structures having particularly high strength. The valence of iron ions is preferably divalent (Fe 2+ ) or trivalent (Fe 3+ ).

[0058] The metal ions can form coordinate bonds with the nitrogen- and / or phosphorus-containing functional groups, for example, by adding a relevant metal salt to a polymer chain to which the nitrogen- and / or phosphorus-containing functional groups are bonded. In this case, a complex polymer can be easily obtained, and thus crosslinked structures having high strength comparable to sulfur crosslinking can be easily formed. The form of the metal salt to be added is not particularly limited, and can be, for example, a metal salt hydrate. The amount of the metal salt to be added is preferably in the range of 1 to 30 parts by mass, more preferably in the range of 1 to 15 parts by mass, even more preferably in the range of 1 to 10 parts by mass, and particularly preferably in the range of 1 to 5 parts by mass, relative to 100 parts by mass of the polymer chain.

[0059] Examples of the metal salt include metal halides, metal sulfates, and metal nitrates, and the like. Among these examples, metal halides are preferable. Metal halides are easy to handle, and are capable of forming crosslinked structures having high strength comparable to sulfur crosslinking.

[0060] Examples of the metal halide include metal fluorides, metal chlorides, metal bromides, and metal iodides, and the like. Among these examples, metal chlorides are preferable. Metal chlorides are easy to handle, and are capable of forming crosslinked structures having high strength comparable to sulfur crosslinking.

[0061] Specific examples of the metal salt include FeCl2, FeCl2·4H2O, FeCl3, and FeCl3·6H2O, and the like. One of these embodiments alone or a combination of two or more of these embodiments can be used as the metal salt.

[0062] (Method for producing complex polymer)

[0063] The complexation polymer can be synthesized, for example, by reacting a compound having a nitrogen- and / or phosphorus-containing functional group with a polymer chain, thereby forming a functionalized polymer in which the nitrogen- and / or phosphorus-containing functional group is bonded to the polymer chain, and complexing the functionalized polymer with a metal ion. In the present application, the compound having a nitrogen- and / or phosphorus-containing functional group is preferably a compound including a triazine ring or a tetrazine ring as described above, and more preferably a compound represented by General Formula (1). In the reaction between the polymer chain and the compound having a nitrogen- and / or phosphorus-containing functional group, it is preferable that the reaction conditions such as temperature, pressure, and reaction time, etc. are appropriately selected according to the kind and reactivity of the polymer chain and / or the compound having a nitrogen- and / or phosphorus-containing functional group used for the reaction. Further, in the reaction of complexing the functionalized polymer with a metal ion, it is preferable that the reaction conditions such as temperature, pressure, and reaction time, etc. are appropriately selected according to the kind and reactivity of the functionalized polymer and the metal ion used for the reaction.

[0064] When 3,6-bis(2-pyridyl)-l,2,4,5-tetrazine is used as the compound having a nitrogen-containing functional group and ferrous chloride (FeCl2) is used as the metal ion, a reaction scheme for functionalizing a polymer chain and complexing the resulting functionalized polymer with a metal ion, as one example of a method for producing a complexation polymer, is shown below.

[0065]

[0066] As shown in the upper half of the reaction scheme, the functionalized polymer can be produced by a Diels-Alder reaction between a polymer chain having an unsaturated bond and a compound having a nitrogen-containing functional group. Although nitrogen is released in the Diels-Alder reaction in the example shown above, any other optional reaction can be utilized to perform the functionalization reaction of the polymer chain.

[0067] Further, as shown in the lower half of the reaction scheme, the functionalized polymer is complexed with ferrous chloride and crosslinked, thereby producing a complexation polymer. Although the reaction scheme shows a reaction in which a nitrogen atom in the tetrazine residue, a nitrogen atom in the pyridyl group bonded to the tetrazine residue, and an iron ion form a coordinate bond (i.e., these nitrogen atoms are complexed with the iron ion and crosslinked), the complexation polymer of the present application can take various complexation forms.

[0068] The complexation polymer can further include other functional groups that are not coordinate-bonded to the metal ion. The kind of such other functional groups as described above is not particularly limited, and can be appropriately selected according to the physical properties, etc. of the desired complexation polymer.

[0069] The complexation polymer can be prepared in advance by being synthesized as described above. Alternatively, the complexation polymer can be synthesized in situ during the production of the rubber composition.

[0070] For example, the complexed polymer can be generated by mixing a polymer chain and a compound having a nitrogen- and / or phosphorus-containing functional group, thereby forming a functionalized polymer as a polymer main chain having a nitrogen- and / or phosphorus-containing functional group bonded thereto at a first stage of mixing in the manufacturing process of the rubber composition; and adding metal salts to the functionalized polymer and mixing them at a second stage of mixing or a stage after the second stage, thereby complexing the functionalized polymer with the metal ions to form the complexed polymer. In this case, the synthesis of the complexed polymer and the manufacturing of the rubber composition can be performed simultaneously.

[0071] Alternatively, the complexed polymer can be generated by preparing a functionalized polymer in advance as a polymer chain having a nitrogen- and / or phosphorus-containing functional group bonded thereto; mixing the functionalized polymer and any optional compounding agent at a first stage of mixing in the manufacturing process of the rubber composition; and adding metal salts to the functionalized polymer or the like and mixing them at a second stage of mixing or a stage after the second stage, thereby complexing the functionalized polymer with the metal ions to form the complexed polymer. In this case, the synthesis of the complexed polymer and the manufacturing of the rubber composition can also be performed simultaneously.

[0072] (free ligand)

[0073] The method for breaking the coordination bond of the complexed polymer according to the present application is characterized by including dissolving the complexed polymer in a solvent containing a free ligand to break the coordination bond.

[0074] When the complexed polymer is dissolved in a solvent containing a free ligand, a ligand exchange reaction occurs between the complexed polymer and the free ligand, so that the free ligand forms a coordination bond with the metal ion. As a result, the crosslinking between the polymer chains of the complexed polymer can be easily broken.

[0075] In the present application, the term "ligand" refers to a compound that is coordinated to a metal. Typically, the ligand contains a group having a lone pair of electrons, whereby the group can be coordinated to a metal to form a complex. The term "free ligand" refers to a ligand that is in a state not coordinated to a metal or a polymer chain.

[0076] The free ligand is preferably a nitrogen- and / or phosphorus-containing compound. In the case where the free ligand is a nitrogen- and / or phosphorus-containing compound, a ligand exchange reaction easily occurs between the complexed polymer and the free ligand, whereby the free ligand easily forms a coordination bond with the metal ion, so that the original coordination bond of the complexed polymer can be more easily broken, and the crosslinking between the polymer chains can be more easily broken than in other cases.

[0077] As the nitrogen- and / or phosphorus-containing compound, a nitrogen-containing aromatic compound is preferable. In the case where the free ligand is a nitrogen-containing aromatic compound, ligand exchange reaction between the complex polymer and the free ligand occurs more easily, whereby the free ligand more easily forms a coordinate bond with the metal ion, so that the original coordinate bond of the complex polymer can be broken even more easily, and the crosslinking between the polymer chains can be broken even more easily than in other cases.

[0078] As the nitrogen-containing aromatic compound, a nitrogen-containing aromatic heterocyclic compound is preferable. Examples of the nitrogen-containing aromatic heterocyclic compound include pyridine, pyrimidine, pyrazine, and pyridazine, etc. Among these examples, from the viewpoint of easily forming a coordinate bond with the metal ion, pyridine and pyrimidine are preferable. In the case where the free ligand is selected from pyridine and pyrimidine, the crosslinking between the polymer chains can be broken particularly easily.

[0079] As the nitrogen- and / or phosphorus-containing compound, an amine compound is also preferable. The amine compound also easily undergoes ligand exchange reaction with the complex polymer, and easily forms a coordinate bond with the metal ion, so that the original coordinate bond of the complex polymer can be broken more easily, and the crosslinking between the polymer chains can be broken more easily than in other cases.

[0080] Examples of the amine compound include tetramethylethylenediamine (TMEDA), hexylamine, heptylamine, octylamine, aniline, and dimethylaniline.

[0081] One alone or a combination of two or more of the above examples can be used as the free ligand. The amount of the free ligand is preferably in the range of 1 part by mass to 2,000 parts by mass, more preferably in the range of 20 parts by mass to 1,500 parts by mass, even more preferably in the range of 30 parts by mass to 1,300 parts by mass, and particularly preferably in the range of 50 parts by mass to 1,100 parts by mass, with respect to 100 parts by mass of the complex polymer. When the amount of the free ligand is set in the above range, ligand exchange reaction between the complex polymer and the free ligand occurs easily.

[0082] From the viewpoint of easily breaking the crosslinking between the polymer chains, it is preferable that the content of the free ligand is greater than the content of the metal salt blended therewith (i.e., greater than the content of the metal contained in the complex polymer). In this regard, specifically, with respect to 1 equivalent of the metal salt, it is more preferable to use ≥ 2 equivalents, even more preferable to use ≥ 4 equivalents, and particularly preferable to use ≥ 6 equivalents of the free ligand. Since the ligand exchange reaction between the complex polymer and the free ligand is an equilibrium reaction, when the content of the free ligand is relatively large, the exchange reaction is advantageously promoted.

[0083] (Solvent)

[0084] As the solvent, any solvent can be used. The solvent is preferably capable of at least partially dissolving the free ligand. One kind alone or a combination of two or more kinds can be used as the solvent. The volume ratio of the free ligand with respect to the solvent (free ligand: solvent) is preferably in the range of 1:50 to 1:1. When the volume ratio is set in the above range, the free ligand is easily dissolved in the solvent.

[0085] The amount of the solvent is preferably in the range of 500 parts by mass to 10,000 parts by mass with respect to 100 parts by mass of the complex polymer. When the amount of the solvent is set in the above range, the de-crosslinked polymer chain is easily dissolved in the solvent.

[0086] The solvent is preferably an organic solvent. The ligand exchange reaction between the complex polymer and the free ligand is an equilibrium reaction. By using an organic solvent as the solvent, the equilibrium reaction can be easily controlled. Further, in the case where an organic solvent is used as the solvent, both the free ligand and the resulting de-crosslinked polymer chain are easily dissolved in the solvent.

[0087] Examples of the organic solvent include tetrahydrofuran (THF), hexane, cyclohexane, pentane, cyclopentane, toluene, and xylene, and the like. Among these examples, from the viewpoint of easy control of the equilibrium reaction, tetrahydrofuran, hexane, and cyclohexane are preferred. In the case where the organic solvent is selected from tetrahydrofuran, hexane, and cyclohexane, the equilibrium reaction (ligand exchange reaction) between the complex polymer and the free ligand can be more easily controlled than in other cases.

[0088] The temperature at which the complex polymer is dissolved in the solvent containing the free ligand is preferably equal to or lower than the boiling point of the free ligand and the solvent. The temperature can be room temperature, but is preferably in the range of 40°C to 65°C. When the temperature is set in the above range, the ligand exchange reaction is likely to occur between the complex polymer and the free ligand. The ligand exchange reaction is likely to occur between the complex polymer and the free ligand

[0089] It is preferred that the time at which the complex polymer is dissolved in the solvent containing the free ligand is appropriately selected depending on the kind of the free ligand and the solvent, the molar ratio between the complex polymer and the free ligand, and the temperature, and the like. In one example, the time is preferably 3 hours to 48 hours.

[0090] As one example of the reaction scheme of the cleavage of the coordination bond, the reaction scheme of the cleavage of the coordination bond of the complex polymer synthesized according to the above reaction scheme by using pyridine (Py) as the free ligand is shown below.

[0091]

[0092] As shown in the upper half of the reaction scheme, the metal ion in the complex polymer is coordinately bonded with the free ligand, so that the metal ion can be dissociated from the nitrogen-containing functional group of the polymer chain. The dissociation of the metal ion from the nitrogen-containing functional group of the polymer chain breaks the coordination bond of the complex polymer, thereby destroying the crosslinking between the polymer chains. Although in the example of the upper half of the reaction scheme, the metal ion is completely dissociated from the nitrogen-containing functional group of the polymer chain, it is also acceptable that the metal ion is not completely dissociated from the nitrogen-containing functional group of the polymer chain, as shown in the lower half of the reaction scheme.

[0093] In the lower half of the reaction scheme, one of the two polymer chains is dissociated because some of the free ligand, instead of one polymer chain, is coordinately bonded with the metal ion in the complex polymer. The crosslinking between the polymer chains is successfully destroyed because one of the two polymer chains has been dissociated. It should be noted that in this case, the coordination bonding of the metal ion with the nitrogen-containing functional group of the polymer chain still partially exists.

[0094] In one embodiment of the method according to the present application, it is acceptable that only one of the above two schemes occurs or both of the schemes occur simultaneously. The above two reactions (reaction schemes) are generally in an equilibrium relationship, and the equilibrium state can be appropriately adjusted by changing the kind of the free ligand and the solvent, the molar ratio between the complex polymer and the free ligand, and the temperature, etc.

[0095] (Use of the present application)

[0096] The method according to the present application is applicable to various rubber products and resin products containing the above-mentioned complex polymer. Examples of the rubber products include tires, anti-vibration rubbers, shock insulation rubbers, belts (conveyor belts), rubber tracks, and various hoses, etc. By applying the method according to the present application to these rubber products, the coordination bond of the complex polymer in the rubber products can be broken, thereby successfully recovering the functionalized polymer and thus recycling the complex polymer.

[0097] (Use of the regenerated polymer (de-crosslinked polymer))

[0098] The functionalized polymer obtained by breaking the coordination bond of the complex polymer by the above-mentioned method can be regenerated to the complex polymer by complexing the functionalized polymer with the metal ion. Alternatively, the functionalized polymer can be used for other purposes without being complexed.

[0099] The functionalized polymer obtained by breaking the coordination bond of the complex polymer and the complex polymer regenerated therefrom are applicable to various rubber products and resin products. Examples of the rubber products include tires, anti-vibration rubbers, shock insulation rubbers, belts (conveyor belts), rubber tracks, and various hoses, etc.

[0100] Examples

[0101] The present application will be described in further detail below by way of examples. The present application is not limited in any way by these examples.

[0102] <Method for producing functional polymer A>

[0103] A functional polymer sample (functional polymer A) was prepared by the following.

[0104] In a glass bottle, 50 g of "TUFDENE 2000R" (styrene-butadiene rubber (SBR) as a polymer chain containing a conjugated diene unit) manufactured by Asahi Kasei Corporation was dissolved in 600 mL of THF; TM 2000R" (styrene-butadiene rubber (SBR) as a polymer chain containing a conjugated diene unit) manufactured by Asahi Kasei Corporation was dissolved in 600 mL of THF;

[0105] 2.4 g (10 mmol) of 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine manufactured by Tokyo Chemical Industry Co., Ltd. was added to the glass bottle, and the reaction mixture was heated to reflux for 3 hours; and

[0106] The resulting solution was vacuum-dried at 60°C for 7 hours, thereby obtaining 50 g of functional polymer A.

[0107] In the functional polymer A thus obtained, the content of the nitrogen-containing functional group was 1.2 mol% with respect to the monomer units of the polymer chain.

[0108] <Production of complex polymer>

[0109] A rubber composition or a complex polymer sample was prepared by using a conventional Banbury mixer according to the blending formulation shown in Table 1. The first stage and the second stage of the mixing process were performed in this order, and in each example, so that ferric (II) chloride tetrahydrate was added to the mixture in the second stage of the mixing process to form a complex polymer. The first stage of the mixing process was performed at 140°C for 3 minutes, and the second stage of the mixing process was performed at 80°C for 1 minute.

[0110] For the rubber composition sample prepared in Example 1 and each complex polymer sample prepared in Examples 2 to 5, the bond dissociation energy of the dissociation of the iron ion and the nitrogen-containing functional group was 249.7 kJ / mol.

[0111] <Decrosslinking of vulcanized rubber or complex polymer>

[0112] The rubber composition samples of Comparative Example 1 and Example 1, and the complex polymer samples of Examples 2 to 5 were each immersed in a relevant solvent containing a relevant free ligand shown in Table 1 at 65°C for 12 hours to perform a de-crosslinking reaction. Pyridine or tetramethylethylenediamine (TMEDA) was used as the free ligand. Tetrahydrofuran (THF) or cyclohexane was used as the solvent, so that the volume ratio of the free ligand to the solvent (free ligand:solvent) was 1:9.

[0113] As for the amount of the free ligand, 1 mL (980 phr) of pyridine was used with respect to 100 mg of the rubber in Comparative Example 1 and Examples 1 to 3, and 1 mL (780 phr) of TMEDA was used with respect to 100 mg of the rubber in Examples 4 and 5. The amount of the solvent (THF or cyclohexane) was 10 mL in each of the comparative and exemplary examples.

[0114] The state of each of the rubber composition samples or the complex polymer samples after the de-crosslinking reaction is shown in Table 1. In Table 1, “swelling” indicates that the rubber composition sample absorbed the solvent and swelled, and “dissolution” indicates that the rubber composition sample or the complex polymer sample was dissolved in the solvent.

[0115] Further, the rubber composition sample or the complex polymer sample after the de-crosslinking reaction was passed through a mesh having a mesh pitch of 1 mm, and the proportion of the rubber composition sample or the complex polymer sample that successfully passed through the mesh was determined. The results are shown in Table 1.

[0116] Table 1

[0117]

[0118] *1 Polymer: “TUFDENE 2000R” manufactured by Asahi Kasei Corporation, styrene-butadiene rubber (SBR)

[0119] *2 Functionalized polymer A: synthesized by the above-described method

[0120] *3 Carbon black: “N234” manufactured by Tokai Carbon Co., Ltd.

[0121] *4 Oil: “JOMO PROCESS NC300BN” manufactured by JX Nippon Oil & Energy Corporation

[0122] *5 Wax: “SUNTIGHT A” manufactured by Seiko-Chemical Co., Ltd.

[0123] *6 Antioxidant: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.

[0124] *7 Vulcanization accelerator A: Bis(2-benzothiazyl) disulfide

[0125] *8 Vulcanization accelerator B: N-tert-butyl-2-benzothiazyl sulfenamide

[0126] As can be understood from Table 1, with the method according to the embodiment of the present application, by dissolving the complex polymer in a solvent containing a free ligand, it is possible to easily break the crosslinked structure of the complex polymer having coordination bonds formed by metal ions.

[0127] Industrial applicability

[0128] The method for breaking the coordination bonds of the complex polymer according to the present application can be used for recycling the polymer.

Claims

1. A method for breaking coordination bonds in a complex polymer, said complex polymer comprising at least one polymer chain and a plurality of nitrogen- and / or phosphorus-containing functional groups bonded to said polymer chain and capable of forming coordination bonds, wherein the coordinate-bonded nitrogen- and / or phosphorus-containing functional groups form coordination bonds via metal ions, characterized in that, The method includes: The complex polymer is dissolved in a solvent containing free ligands to break the coordination bonds of the complex polymer. The polymer chain comprises conjugated diene units and / or olefin units. The plurality of nitrogen- and / or phosphorus-containing functional groups, which are bonded to the polymer chains and capable of forming coordination bonds, form coordination bonds via metal ions, thereby crosslinking the polymer chains intramolecularly and intermolecularly. The coordination bonds of the complex polymer are broken through a ligand exchange reaction between the free ligand and the complex polymer, thereby causing the metal ions to completely or partially dissociate from the nitrogen- and / or phosphorus-containing functional groups, thus disrupting the crosslinking between the polymer chains.

2. The method for breaking coordination bonds in a complex polymer according to claim 1, wherein the nitrogen- and / or phosphorus-containing functional groups do not contain sulfur atoms.

3. The method for breaking coordination bonds in a complex polymer according to claim 1 or 2, wherein the nitrogen- and / or phosphorus-containing functional groups are derived from compounds containing triazine or tetraazine rings.

4. The method for breaking coordination bonds in the complex polymer according to claim 3, wherein the pyridinyl or pyrimidinyl group is bonded to the triazine ring or the tetraazine ring.

5. The method for breaking coordination bonds in a complex polymer according to claim 4, wherein two pyridinyl or pyrimidinyl groups are bonded to the triazine ring or the tetraazine ring.

6. The method for cleaving coordination bonds in a complex polymer according to claim 3, wherein the nitrogen- and / or phosphorus-containing functional groups are derived from compounds represented by the following general formula (1): In general formula (1), X 1 and X 2 Each independently represents a pyridinyl / pyrimidinyl group, and Y 1 and Y 2 Each can independently represent a single bond or a divalent hydrocarbon group.

7. The method for breaking coordination bonds in a complex polymer according to claim 6, wherein in general formula (1), X 1 and X 2 Each is pyridyl, and Y 1 and Y 2 Each is a single key.

8. The method for breaking coordination bonds in a complex polymer according to claim 1 or 2, wherein the metal ion is selected from metal ions of elements in groups 7 to 10 of the periodic table.

9. The method for breaking the coordination bonds of a complex polymer according to claim 8, wherein the metal ion is a metal ion of a group 8 element in the periodic table.

10. The method for breaking coordination bonds in a complex polymer according to claim 9, wherein the metal ion is an iron ion.

11. The method for breaking coordination bonds in a complex polymer according to claim 1 or 2, wherein the nitrogen- and / or phosphorus-containing functional groups are bonded to the polymer chain in an amount ranging from 0.1 mol% to 10 mol% relative to the monomer units in the polymer chain.

12. The method for breaking coordination bonds in a complex polymer according to claim 1 or 2, wherein the bond dissociation energy of the metal ion and the nitrogen- and / or phosphorus-containing functional groups is 200 kJ / mol or higher.

13. The method for breaking coordination bonds in a complex polymer according to claim 1 or 2, wherein the free ligand is a nitrogen- and / or phosphorus-containing compound.

14. The method for breaking coordination bonds in a complex polymer according to claim 13, wherein the nitrogen- and / or phosphorus-containing compound is a nitrogen-containing aromatic compound.

15. The method for breaking coordination bonds in a complex polymer according to claim 14, wherein the nitrogen-containing aromatic compound is selected from pyridine and pyrimidine.

16. The method for breaking coordination bonds in a complex polymer according to claim 13, wherein the nitrogen- and / or phosphorus-containing compound is an amine compound.

17. The method for breaking coordination bonds in a complex polymer according to claim 1 or 2, wherein the solvent is an organic solvent.

18. The method for breaking coordination bonds in a complex polymer according to claim 17, wherein the organic solvent is selected from tetrahydrofuran, hexane, and cyclohexane.

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