JP6504628B2 - Nanofibers, assembly of nanofibers, mixed product for electrospinning, method of manufacturing nanofibers, and method of manufacturing aggregate of nanofibers. - Google Patents

Description

The present invention relates to a method for simply imparting functionality to vinyl alcohol resins, which are usually difficult to impart functionality due to high stability, as well as the materials used for this functionalization.
Priority is claimed on Japanese Patent Application No. 2015-198316, filed October 6, 2015, the content of which is incorporated herein by reference. In addition, the present application relates to the contents of the non-patent documents "Yohei Kotsuchibashi and Mitsuhiro Ebara: Polymers 2016, 8 (2), 41, p1 to 11; doi: 10.3390 / polym8020041" and their "Supplementary Materials S1 to S3". Incorporated here (incorporated by reference).

  Ethylene-vinyl alcohol copolymer (poly (ethylene-co-vinylalcohol), for example, Eval (registered trademark) sold by Kuraray Co., Ltd., hereinafter abbreviated as EVOH) is a polymer having high gas barrier properties and It is widely used in packaging films and fuel tanks. EVOH also exhibits high biocompatibility, and is also put to practical use as a hollow fiber (dilatizer) for artificial dialysis.

However, EVOH is difficult to newly add functionality due to its high stability. Although it is possible to change the surface properties by, for example, oxidation of the OH group of EVOH or UV treatment to add functionality, in this case many operation steps are required and it takes time to generate. There is also a problem. In addition to this, performing such processing changes the structure of the EVOH itself, which may cause adverse effects on the characteristics thereof.
As another method, it is also possible to form a composite material by mixing EVOH with a hydrophobic polymer. However, depending on the conditions, a polymer mixed from a film, a fiber or the like formed using this composite material may leak out, which causes a problem in practical use.
On the other hand, it is known that the benzoxaborole group has stronger bondability with diol than phenylboronic acid (Non-patent Document 1). In addition, the inventors of the present application have published the preparation of a gel with a sugar polymer using the benzooxaborole polymer having this benzooxaborole group (Non-Patent Documents 2 and 3).

M. Dowlut and D. G. Hall, J. Am. Chem. Soc. 2006, 128, 4226-4227. Y. Kotsuchibashi et al. , ACS Macro Lett. 2013, 2, 260-264. Y. Kotsuchibashi et al. , J. Phys. Chem. B 2015, 119, 2323-2329.

  An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for easily imparting various functions to EVOH and a substance used in the method. In addition, EVOH can change the ratio of ethylene and vinyl alcohol as its monomers in a wide range, and the present invention can be applied particularly when ethylene is not contained (that is, in the case of polyvinyl alcohol). Used in the sense of a polymer containing up to polyvinyl alcohol. The "vinyl alcohol resin" of the present invention is also used in the meaning of "ethylene-vinyl alcohol copolymer or polyvinyl alcohol".

According to one aspect of the present invention, there is provided a vinyl alcohol resin functionalization method in which a benzooxaborole polymer having a benzooxaborole structure and a vinyl alcohol resin are mixed and reversibly bonded to each other.
Here, the desired functionality may be selected from the group consisting of temperature response, viscosity, electrospinning and staining.
In addition, the desired functionality may be the functionality possessed by the benzoxaborole polymer.
Also, the benzoxaborole polymer may be a copolymer comprising a monomer having a benzoxaborole structure and a monomer providing the functionality.
Also, the benzooxaborole polymer may be a benzooxaborole polymer having a (meth) acrylamide type and a (meth) acrylate type as a basic skeleton.
According to another aspect of the present invention, there is provided a vinyl alcohol resin functionalizing agent comprising a benzooxaborole polymer comprising a benzooxaborole structure.
Here, the desired functionality may be selected from the group consisting of temperature response, viscosity, electrospinning and staining.
In addition, the desired functionality may be the functionality possessed by the benzoxaborole polymer.
Also, the benzoxaborole polymer may be a copolymer comprising a monomer having a benzoxaborole structure and a monomer providing the functionality.
Also, the benzooxaborole polymer may be a benzooxaborole polymer having a (meth) acrylamide type and a (meth) acrylate type as a basic skeleton.
According to another aspect of the present invention, there is provided a benzooxaborole polymer comprising a monomer-derived structure giving functionality and a benzooxaborole structure, and a vinyl alcohol resin having a diol structure, the benzooxaborole structure and the diol. The present invention provides a mixed product of a benzooxaborole polymer and a vinyl alcohol resin, which is characterized by being reversibly bonded by bonding with a structure.
The benzooxaborole polymer may be a copolymer of a monomer having the benzooxaborole structure and a monomer providing the functionality.
Also, the benzooxaborole polymer may be a benzooxaborole polymer having a (meth) acrylamide type and a (meth) acrylate type as a basic skeleton.

  According to the present invention, functionality can be imparted to EVOH by a very simple process of adding and mixing a functionalizing agent with ordinary EVOH.

The figure explaining the coupling | bonding with benzo oxaborole and a diol. EVOH and _{P (MEO 2 MA-co-} OEGMA-co-MAAmBO) and obtained by mixing the gel photo. EVOH and _P shows a (MEO 2 MA-co-OEGMA -co-MAAmBO) results and comparative example in which the mixed product was electrospun with the results obtained by electrospinning a. (A) Photograph of an aggregate obtained by electrospinning a mixed product of EVOH and a benzooxaborole polymer modified with a carboxyl group. (B) A photograph of an aggregate obtained by electrospinning a mixed product of EVOH and a benzooxaborole polymer not modified with a carboxyl group as a comparative example. (A) A photograph showing the result of staining the accumulation shown in FIG. 4 (a) with methylene blue. (B) A photograph showing the result of staining the accumulation shown in FIG. 4 (b) with methylene blue.

  In order to solve the above-mentioned problems of the prior art, in one aspect of the present invention, EVOH represented by the formula (1)

And benzoxaborole (benzoxaborole; also called boroxole) represented by the formula (2) capable of reversibly binding to

A polymer having the structure of (hereinafter referred to as benzoxaborole polymer) was synthesized. Benzoxaborole polymers can be synthesized by radical polymerization commonly used with benzoxaborole monomers, and their structure and composition can be precisely controlled by using living radical polymerization. . Copolymers can also be synthesized with other monomers. Thus, the molecular weight, molecular weight distribution, structure, etc. of the polymer can be controlled. Since various types of functionality (for example, stimulus reactivity, biocompatibility, conductivity, fire resistance, etc.) can be imparted to the benzoxaborole polymer, no special functionalization treatment is performed on the EVOH side. Also, the capacity of EVOH products can be improved. In addition, the present invention is very simple and inexpensive because it can be realized extremely simply by mixing the benzooxaborole polymer having the desired functionality with EVOH in a solvent. In addition, as the benzooxaborole polymer having a desired functionality, a benzooxaborole polymer modified with a functional group as necessary to express a desired functionality, and a monomer having a benzooxaborole structure are desired. Various embodiments are possible, such as copolymers with other monomers to provide the functionality of

  The interaction between the benzooxaborole structure and the hydroxyl group possessed by EVOH, as shown in FIG. 1, was utilized for the reversible binding of the benzooxaborole polymer to the EVOH. The reversible reaction shown in FIG. 1 proceeds to the right (in the direction in which the benzoxaborole group and the diol are bonded) in neutral to alkaline, and to the left (in the direction in which the benzoxaborole group and the diol are dissociated) in the acidity. . In addition, although the interaction of benzooxaborole itself and diol is shown in FIG. 1, this is an exemplary description, and the interaction is expressed with any compound having a benzooxaborole structure. Examples of the compound having such a benzooxaborole structure include, but not limited to, benzooxaborole polymers having a (meth) acrylamide type and a (meth) acrylate type as a basic skeleton. It should be noted that even if the polymer is highly stereoregular, if it has the structure of benzoxaborole, the equilibrium reaction of bonding with the diol shown in FIG. 1 proceeds to some extent. Even if it gets harder, it does not change what happens.

  Incidentally, although the reaction as shown in FIG. 1 occurs by mixing the benzooxaborole polymer and EVOH, the process is merely mixing the two, so in the following, the two are mixed as shown in FIG. The product in the state where the reaction as shown has occurred may be referred to as "mixed product".

  In addition, when the benzo oxaborole group and phenylboronic acid are compared, it is proved that the benzoxaborole group has stronger bondability with the diol (Non-patent Document 1). Therefore, gelation and the like can be more efficiently caused when using a benzooxaborole polymer.

  In the following examples, it is shown that EVOH can be made to have the functionality by combining EVOH with a benzooxaborole polymer having temperature response and staining properties. By giving temperature responsiveness, even a polymer that is easily dissolved at room temperature can be processed to be able to be adsorbed by the material. Also, when EVOH and the benzooxaborole polymer are combined as shown in FIG. 1, the viscosity generally increases. This viscosity is also one of the functions. For example, fibers of the mixed product can be obtained by electrospinning these mixed products with appropriate viscosity. Of course, the functionality that can be imparted to EVOH is not limited to temperature responsiveness, viscosity, dyeability, etc., and may be any functionality that can be imparted by the method described herein.

  Hereinafter, the present invention will be described in more detail based on examples. In the following, Eval (ethylene copolymerization ratio (molar ratio) 44%) manufactured by Kuraray Co., Ltd. was used as the EVOH, but it is obvious that, of course, generality is not lost.

Example 1
<Functionalized benzoxaborole polymer>
Below, the example which gives functionality, such as temperature responsiveness, gelatinization, electrospinning property, to EVOH is shown. The temperature response in this case means that the surface properties of the mixed product of gel and fiber consisting of EVOH and benzooxaborole polymer can be controlled to be hydrophilic / hydrophobic by temperature. The structural formula of P (MEO ₂ MA-co-OEGMA-co-MAAmBO), which is an example of a benzooxaborole polymer that can be used for that purpose, is shown in Formula (3). 5-methacrylamido-1,2-benzoxaborole (MAAmBO) is 2- (2-methoxyethoxy) ethyl methacrylate (MEO ₂ MA) and oligo (ethylene glycol) methacrylate (OEGMA) because of the addition of the benzoxaborole structure It was chosen to control the temperature which shows temperature responsiveness. The benzooxaborole polymer is obtained by copolymerizing a monomer having a functionality to be added based on these monomers and further mixing. Since the copolymerization method itself used here is a known item, the specific description is omitted, but if necessary, refer to Non-Patent Documents 2 and 3 which are the papers of the present inventor.

  Units other than the benzooxaborole structure in the benzoxaborole polymer shown above have a temperature response of ethylene glycol type. Since the phase transition temperature of this polymer changes depending on the molecular weight and structure of these temperature responsive units, it is possible to obtain an appropriate polymer by appropriately selecting and copolymerizing these monomers.

<Mixed product of EVOH and benzooxaborole polymer 1: gelation>
Figure 2 shows a photograph of a gel obtained by mixing the EVOH and _{P (MEO 2 MA-co-} OEGMA-co-MAAmBO). As a method of preparing the gel, HFIP (1, 1, 1, 3, 3, 3-, 70 mg / mL and 70 mg / mL of EVOH and P (MEO ₂ MA-co-OEGMA-co-MAAmBO), respectively. It was dissolved in hexafluoroisopropanol at room temperature. The same volume of solution was mixed at room temperature to obtain a gel-like mixed product in a few minutes. It is possible to prepare a gel structure because a three-dimensional crosslinked structure is constructed by the interaction of the two as shown in FIG. The strength of the gel can be controlled by the ratio of polymers mixed. Further, the viscosity in the sol state can be similarly controlled.

  The mixed product of EVOH and the benzoxaborole polymer can be handled as either a sol or a gel depending on the concentration and the mixing ratio in the solution, and thus the molding process is easy. From the bulk state, it can be processed into film-like thin films, capsules or nanofibers.

Example 2
<Mixed Product of EVOH and Benzoxaborol Polymer 2: Nanofiber>
The benzooxaborole polymer P (MEO ₂ MA-co-OEGMA-co-MAAmBO) represented by the formula (3) obtained in Example 1 was used. FIG. 3 (B) shows the result of electrospinning of a solution of EVOH (concentration: 3.5 wt%) and P (MEO ₂ MA-co-OEGMA-co-MAAmBO) (concentration: 2.5 wt%) mixed in HFIP. The SEM image of a result is shown.
As can be seen from FIG. 3 (B), an aggregate of nanofibers can be obtained by electrospinning the mixed product 2 of EVOH and P (MEO ₂ MA-co-OEGMA-co-MAAmBO). In this aggregate, the sizes of the gaps between the fibers are relatively uniform. The size of the gap can be controlled by adjusting the conditions of electrospinning, the concentration of the mixed product, and the like.

[Example 3]
<Mixed product of EVOH and benzooxaborole polymer 3: nanofibers>
The benzooxaborole polymer P (MEO ₂ MA-co-OEGMA-co-MAAmBO) represented by the formula (3) obtained in Example 1 was used. FIG. 3 (C) shows the result of electrospinning a mixed solution of EVOH (concentration: 3.5 wt%) and P (MEO ₂ MA-co-OEGMA-co-MAAmBO) (concentration: 0.5 wt%) in HFIP. The SEM image of a result is shown.
In FIG. 3 (C), although nanofibers are not formed despite electrospinning of the mixed product 3 of EVOH and P (MEO ₂ MA-co-OEGMA-co-MAAmBO), this is not P (MEO). _{Since the amount of 2} MA-co-OEGMA-co-MAAmBO is as small as 0.5 wt% as compared with 2.5 wt% in FIG. 3 (B) of Example 2, the viscosity of the mixed product 3 is as shown in FIG. It is because it fell compared with the case of B).

Comparative Example 1
<EVOH alone HFIP solution>
FIG. 3 (A) shows a SEM image of the result of electrospinning an HFIP solution of EVOH (concentration: 3.5 wt%) alone.
Comparative Example 2
<Mixture of copolymer not having EVOH and benzooxaborole structure>
In FIG. 3 (D), EVOH (concentration: 3.5 wt%) and P (MEO ₂ MA-co-OEGMA) (concentration: 2.5 wt%) (ie, a copolymer having no benzooxaborole structure) The SEM image of the result of electrospinning of the solution which mixed and in HFIP was shown.
With respect to the results of Examples 2 and 3, the EVOH of Comparative Example 1 alone (FIG. 3A) and the polymer mixed with the EVOH of Comparative Example 2 do not contain a benzooxaborole structure (FIG. 3). In (D)), although the amount of EVOH was 3.5 wt% as in the case of FIG. 3 (B), no nanofibers were formed. This is because the viscosity remains low because the interaction as shown in FIG. 1 does not occur.

Example 4
<Mixed Product of EVOH and Benzoxaborole Polymer Having Carboxyl Group 4: Addition of Dyeing Function>
Benzoxaborole polymer having a skeleton modified with a carboxyl group, having a structure generally represented by the following formula (4)

The dyeability of EVOH to the cationic dye can be improved by mixing E. and EVOH. The specific structure of the benzooxaborole polymer used in this example is as shown in the following formula (5).

An aggregate (FIG. 4 (a)) obtained by electrospinning a mixed product of EVOH and this benzoxaborole polymer was prepared as a target of the staining experiment.
Methylene blue represented by the formula (6)

The results of staining with are shown in FIG. 5 (a).
[ Example 5 ]
<Mixed product of EVOH and benzooxaborole polymer containing no carboxyl group>
A benzooxaborole polymer represented by the formula (7) which has substantially the same structure as that of the benzooxaborole polymer represented by the formula (5) of Example 4 except that the carboxyl group is not modified ; In Comparative Example 3, it is assumed that the example 5 is read.

A comparative accumulation (FIG. 4 (b)) was prepared by electrospinning the mixture product with
Similar to Example 4, the result of staining this accumulated product with methylene blue represented by the formula (6) is shown in FIG. 5 (b).
In addition, when these two types of benzoxaborole polymers represented by the said Formula (5) and (7) are compared, the benzo oxaborole polymer represented by Formula (5) of Example 4 is Formula (7) of Comparative Example 3, It can be seen that a structure derived from a relatively small monomer having a carboxyl group is further added to the benzooxaborole polymer represented by
As can be seen from FIG. 5, the aggregate prepared from the mixed product 4 of EVOH and a carboxyl group-modified benzoxaborole polymer, which is Example 4 of the present invention, is a carboxyl group-unmodified benzo compound. It can be seen that the dye is strongly stained as compared to the accumulation using the oxaborole polymer. Since FIG. 5 is a black-and-white photograph, the (a) side only looks slightly black compared to the (b) side, but in fact the (b) side is blue while the (b) side is blue. The side was dyed dark blue, and the difference in dyeability could be clearly seen. The reason why the aggregate prepared by mixing EVOH and the carboxyl group-modified benzooxaborol polymer has higher dyeability is that it is ionized in the aggregate and exists in the form of -COO- It is because the carboxyl group and the cationic dye methylene blue cause electrostatic interaction. In this example, methylene blue was used as the dye, and the benzooxaborole polymer was modified with a carboxyl group, but the present invention is not limited to this combination, and any functional that negatively ionizes with any cationic dye. An improvement in dyeability can be achieved by combination with a group-modified benzoxaborole polymer. Conversely, the dyeability can be improved by combining any anionic dye with any positively ionizable benzooxaborole polymer modified with any functional group.

  As described above in detail, in the present invention, EVOH uses existing materials which are easily available, and the characteristics of EVOH can be obtained simply by mixing the benzooxaborole polymer having the desired functionality thereto. The present invention is expected to be widely used for expanding the application of EVOH and the like because desired functionality can be provided while maintaining it.

Claims (8)

A nanofiber comprising a mixed product obtained by mixing a benzooxaborole polymer having a benzooxaborole structure and a vinyl alcohol resin and reversibly bonding the two . The benzoxaborole polymer as a basic skeleton a (meth) acrylamide and (meth) acrylate type, nanofibers according to 請 Motomeko 1.   The nanofiber according to claim 1 or 2, wherein the bond is a bond between the benzooxaborole structure and a diol structure possessed by the vinyl alcohol resin.   The nanofiber according to any one of claims 1 to 3, wherein the benzoxaborole polymer further has a repeating unit having an oxyethylene group.   An aggregate of nanofibers comprising the nanofiber according to any one of claims 1 to 4.   A mixed product for electrospinning comprising a benzooxaborole polymer containing a benzooxaborole structure and a vinyl alcohol resin mixed and reversibly bonded to each other.   A mixed product is obtained by mixing a benzooxaborole polymer having a benzooxaborole structure and a vinyl alcohol resin, and the mixed product is electrospun to obtain any one of claims 1 to 4. A method of producing nanofibers, wherein the nanofibers are obtained.   A method for producing an assembly of nanofibers, wherein nanofibers obtained by the method for producing nanofibers according to claim 7 are integrated to obtain an assembly of nanofibers.