Method for producing polyindigo

Abstract

To provide a method for producing that enables formation of polyindigo exhibiting excellent mechanical characteristics without molecular structural bending.SOLUTION: The method for producing polyindigo comprises removing an acetyl group from a polyindigo monomer represented by the following chemical formula (1) under an inert gas atmosphere, oxidatively polymerizing the polyindigo monomer from which the acetyl group has been removed under neutral conditions, thereby producing polyindigo, where Ar represents an aryl group and Ac represents an acetyl group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing polyindigo that can produce high strength polyindigo fibers. [Background technology]

[0002] Carbon fiber reinforced plastics (CFRP) are lightweight and extremely strong, making them widely used in aircraft, automobiles, industrial equipment, sporting goods, and more. However, carbon fiber is difficult to burn and cannot be burned in a normal incinerator, and CFRP, the reinforced plastic made from carbon fiber, cannot be incinerated either. Furthermore, because of its extreme strength, it is difficult to shred, and it is often disposed of in landfills in its original form, meaning that CFRP products place a high burden on the environment. For this reason, there has been active research into ways to recycle CFRP.

[0003] There has been active research into recovering and reusing plastic products after use, and methods that have been put into practical use include thermal recycling, in which plastic is burned and used as fuel, material recycling, in which plastic is remelted and reprocessed into sheets or fibers, and chemical recycling, in which plastic is chemically treated to break it down into monomers and then polymerized again for reuse.Polyethylene terephthalate (PET), which is widely used in everyday society as PET bottles and fibers, has a high recycling rate, and research is underway into chemical recycling, which does not deteriorate its physical properties during recycling.

[0004] On the other hand, polyindigo is expected to have high strength and a high modulus of elasticity, and if used in fiber-reinforced plastics (FRP), although its compressive performance falls short of that of CFRP, it could potentially be a material with tensile strength equivalent to that of CFRP and with impact resistance exceeding that of CFRP. Despite possessing such excellent physical properties, it is easily water-soluble as disclosed in Patent Document 1, making it possible to recover polyindigo from discarded FRP that uses polyindigo by adding water, and the recovered aqueous solution can be used as is as a spinning solution to regenerate polyindigo fiber.

[0005] Patent Document 2 discloses two methods for synthesizing polyindigo: one using paraphenylenediamine as a starting material, and the other using 2,5-dichloroterephthalic acid as a starting material. The synthetic route using paraphenylenediamine as a starting material is shown in the following chemical reaction formula (A), and the synthetic route using 2,5-dichloroterephthalic acid as a starting material is shown in the following chemical reaction formula (B).

[0006] [ka]

[0007] [ka]

[0008] Patent Document 3 discloses a method for producing a diglycyl terephthalic acid compound, which is a synthetic intermediate for polyindigo, using a cyclohexanediene compound as a starting material. The synthetic route disclosed in Patent Document 3 is shown in the following chemical reaction formula (C).

[0009] [ka]

[0010] Furthermore, Patent Document 4 discloses a method for synthesizing polyindigo by polymerizing a specific monomer in an acidic solvent. In addition, Non-Patent Documents 1 and 2 describe the production of indigo from indoxyl acetate, stating that when indigo is produced from indoxyl acetate, if oxygen is allowed to act on indoxyl from which the acetyl group has been removed in a basic or acidic environment, an isomer, isatin, is produced. Furthermore, they describe that a side reaction occurs in which indirubin is produced when this isatin combines with indoxyl. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-162193 [Patent Document 2] U.S. Patent No. 3,414,545 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-127321 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-56818 [Non-patent literature]

[0012] [Non-Patent Document 1] Satoshi Ushida, Yuka Taniyama, Masaaki Ota, 'Conditions for indirubin formation during indigo dyeing', Journal of the Japan Society of Home Economics, Vol. 49, No.4, 1998. [Non-patent document 2] Hiroki Furuhama, Satoshi Ushida, Toshika Ueno, Kaori Tanimitsu, 'Indirubin formation under acidic conditions in dyeing with fresh indigo leaves and its dyeing process', Journal of the Japan Society of Home Economics, Vol. 56, No. 12, 2005. Summary of the Invention [Problem to be solved by the invention]

[0013] The polyindigo monomer in the synthesis method described in Patent Document 3 (chemical reaction formula (C) above) is tetraacetylbenzodiketobispyrrole, but there is a problem that the acetyl group protecting the secondary amine is not removed under basic conditions during hydrolysis of tetraacetylbenzodiketobispyrrole. There is also a problem that a ring-opening reaction of the five-membered ring occurs. In the method disclosed in Patent Document 4, the acetyl group is removed by hydrolysis under sulfuric acid acidity, but there is a problem that sulfonation occurs as a side reaction.

[0014] When polyindigo is produced by polymerizing polyindigo monomers, if monomer isomers are produced as described in Non-Patent Documents 1 and 2, there is a risk of producing bent polyindigo isomers. The bent polyindigo isomers have impaired mechanical properties compared to linear polyindigo.

[0015] In view of the above circumstances, an object of the present invention is to provide a method for producing polyindigo that is free from bending of the molecular structure and that is capable of producing polyindigo that has excellent mechanical properties. [Means for solving the problem]

[0016] A method for producing polyindigo according to one embodiment of the present invention includes the steps of: The acetyl group is eliminated from a polyindigo monomer represented by the following chemical formula (1): The polyindigo monomer from which the acetyl group has been removed is polymerized under neutral conditions to produce polyindigo.

[0017] [ka] [In the formula, Ar represents an aryl group, and Ac represents an acetyl group]

[0018] The neutral conditions may be pH 5.0 or higher and 8.0 or lower.

[0019] The neutral conditions may be pH 6.0 or higher and 7.5 or lower.

[0020] The step of eliminating the acetyl group may be carried out by hydrolyzing the polyindigo monomer under weakly basic conditions in an inert gas atmosphere.

[0021] In the step of polymerizing the polyindigo monomer from which the acetyl group has been eliminated, a solution in which the polyindigo monomer from which the acetyl group has been eliminated is dissolved may be neutralized, and oxygen or air may be blown into the solution to oxidatively polymerize the polyindigo monomer. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a method for producing polyindigo that is free from bending of the molecular structure and that is capable of producing polyindigo that has excellent mechanical properties. DETAILED DESCRIPTION OF THE INVENTION

[0023] A method for producing polyindigo according to an embodiment of the present invention will be described. In the method for producing polyindigo according to this embodiment, polyindigo is produced by polymerizing the polyindigo monomers shown below.

[0024] [Polyindigo Monomer Structure] The polyindigo monomer according to this embodiment is a substance represented by the following chemical formula (1). [ka]

[0025] In the formula, Ar represents an aryl group, and Ac represents an acetyl group. The aryl group is any one of a phenyl group, a biphenyl group, a naphthyl group, a phenyl group modified with a substituent, a biphenyl group modified with a substituent, and a naphthyl group modified with a substituent. The substituent is at least one of a halogeno group and an alkyl group. This also applies to the following chemical formulas.

[0026] The substance represented by chemical formula (1) may have a trans isomer or a cis isomer depending on the structure of the aryl group (Ar). In this case, the polyindigo monomer according to this embodiment may be either or both of the trans isomer and the cis isomer.

[0027] In other words, the polyindigo monomer according to this embodiment has two pyrrole rings bonded to an aryl group (Ar), and an acetoxy group (-OAc) is bonded to the carbon atom at the third position of each pyrrole ring. The aryl group is, as described above, any of a phenyl group and the like.

[0028] Specifically, the polyindigo monomer according to this embodiment can be any of the substances represented by the following chemical formulas (2) to (5).

[0029] [ka]

[0030] [ka] In addition, in chemical formulas (2) and (3), R 1 , R 2 , R 3 , R 4 , R 5 and R 6 represents hydrogen, a halogeno group, an alkyl group, a phenyl group, or a benzyl group. The alkyl group is any of a methyl group, an ethyl group, a propyl group, an isopropyl group, and a tert-butyl group. This is the same in each of the following chemical formulas.

[0031] [ka]

[0032] [ka] In addition, in chemical formulas (4) and (5), R 1 and R 2represents hydrogen, a halogeno group, an alkyl group, a phenyl group, or a benzyl group. The alkyl group is any of a methyl group, an ethyl group, a propyl group, an isopropyl group, and a tert-butyl group. This is the same in each of the following chemical formulas. In chemical formula (4), R 1 and R 2 When R is hydrogen, the substance is called 3,7-diacetoxybenzo[1,2-b:4,5-b]dipyrrole. 1 and R 2 When is hydrogen, the substance is called 3,5-diacetoxybenzo[1,2-b:5,4-b]dipyrrole.

[0033] As shown in chemical formulas (1) to (5), the polyindigo monomer according to this embodiment has two pyrrole rings, each of which has an acetoxy group (-OAc) bonded to the carbon atom at the 3-position, while the nitrogen atom (N) of each pyrrole ring does not have an acetyl group (-Ac) bonded to it.

[0034] By adopting such a structure, it becomes possible to easily remove the acetyl group in the acetoxy group when polymerizing the polyindigo monomer, as described below. If an acetyl group is bonded to the nitrogen atom of the pyrrole ring, the bond is an amide bond, which cannot be easily removed, and treatment with a strong base or strong acid is required. In this case, a ring-opening reaction or sulfonation of the pyrrole ring may occur, which may result in a decrease in yield or the inclusion of by-products. The polyindigo monomer according to this embodiment does not require such treatment because an acetyl group is not bonded to the nitrogen atom of each pyrrole ring.

[0035] [Polyindigo manufacturing method] A method for producing polyindigo according to this embodiment will now be described. Polyindigo according to this embodiment can be produced by polymerizing polyindigo monomers represented by chemical formulas (1) to (5). The following chemical reaction formula (6) shows the method for producing polyindigo according to this embodiment.

[0036] [ka]

[0037] In the formula, M + is a cation in a base, e.g., sodium ion (Na + ). As shown in chemical reaction formula (6), when the polyindigo monomer is subjected to weakly basic conditions, the acetyl group (-Ac) in the acetoxy group (-OAc) is eliminated by hydrolysis. As described above, in the polyindigo monomer according to this embodiment, an acetoxy group (-OAc) is bonded to the carbon atom at the 3-position of each pyrrole ring, but an acetyl group (-Ac) is not bonded to the nitrogen atom (N) of each pyrrole ring. Therefore, by using weakly basic conditions, the acetyl group in the acetoxy group can be easily eliminated.

[0038] If an acetyl group is bonded to the nitrogen atom of the pyrrole ring, the bond is an amide bond, which cannot be easily removed, and treatment with a strong base or strong acid is required. In this case, a ring-opening reaction or sulfonation of the pyrrole ring may occur, which may result in a decrease in yield or the inclusion of by-products. In contrast, in the polyindigo monomer according to this embodiment, an acetyl group is not bonded to the nitrogen atom of the pyrrole ring, and therefore such treatment with a strong base or strong acid is not required.

[0039] After the acetyl group in the acetoxy group is removed, this substance is oxidized with air to polymerize and produce polyindigo. Specifically, the polymerization can be carried out by adjusting the solution in which this substance dissolves to a neutral pH and then blowing air or oxygen into the solution.

[0040] As described above, the oxidation step is carried out under neutral conditions, with the pH preferably being between 5.0 and 8.0, more preferably between 6.0 and 7.5, and most preferably 7.0. The following chemical reaction formula (7) shows the reaction for producing polyindigo when the acidity during the oxidation step is less than 5.0 or more than 8.0, i.e., when the oxidation step is carried out under basic or acidic conditions.

[0041] [ka]

[0042] After hydrolysis of polyindigo monomer, oxidation under basic or acidic conditions produces polyindigo, as shown by arrow α in chemical reaction equation (7). At the same time, isomers of the polyindigo monomer are produced, as shown by arrow β. A small percentage of the polyindigo monomer becomes an isomer. This isomer bonds with the parent material, as shown by arrow γ, to produce a bent polyindigo isomer. The mechanical properties of the bent polyindigo isomer are significantly impaired.

[0043] In contrast, by carrying out the oxidation process under neutral conditions as described above (see chemical reaction formula (6)), isomers of the polyindigo monomer are not generated. This results in the formation of linear polyindigo, which has no bending in the molecular structure and has excellent mechanical properties.

[0044] The following chemical reaction formulas (8) to (11) show specific polymerization reactions of polyindigo monomers according to this embodiment.

[0045] [ka]

[0046] [ka]

[0047] [ka]

[0048] [ka]

[0049] The polyindigo according to this embodiment may be produced by polymerizing multiple types of polyindigo monomers according to this embodiment. Alternatively, the polyindigo according to this embodiment may be produced by polymerizing one or more types of polyindigo monomers according to this embodiment with a polyindigo monomer that does not have the structure according to this embodiment.

[0050] Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and various modifications can be made, as a matter of course.

Claims

1. By eliminating the acetyl group from a polyindigo monomer represented by the following chemical formula (1), The polyindigo monomer from which the acetyl group has been removed is polymerized under neutral conditions to produce polyindigo. How to make polyindigo. 【Chemistry 1】 [wherein Ar represents an aryl group, and Ac represents an acetyl group]

2. 2. The method for producing polyindigo according to claim 1, The neutral condition is a pH of 5.0 or higher and 8.0 or lower. How to make polyindigo.

3. 2. The method for producing polyindigo according to claim 1, The neutral condition is a pH of 6.0 or higher and 7.5 or lower. How to make polyindigo.

4. 2. The method for producing polyindigo according to claim 1, The step of eliminating the acetyl group is carried out by hydrolyzing the polyindigo monomer under weakly basic conditions in an inert gas atmosphere. How to make polyindigo.

5. 2. The method for producing polyindigo according to claim 1, In the step of polymerizing the polyindigo monomer from which the acetyl group has been eliminated, a solution in which the polyindigo monomer from which the acetyl group has been eliminated is dissolved is neutralized, and oxygen or air is blown into the solution to oxidatively polymerize the polyindigo monomer. How to make polyindigo.

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