JP4831606B2 - Copolymers, organic-inorganic composite materials and methods for synthesizing them - Google Patents

Description

  The present invention relates to a copolymer having a heterocyclic ring in a part of a side chain group and a composite material of this and calcium carbonate. The present invention also relates to a method for synthesizing these copolymers and organic-inorganic composite materials.

Sea creatures that perform calcification may have enzymes that have sites that promote the carbon dioxide hydration reaction as well as sites that capture calcium. Conventionally, for example, as a method for artificial calcification, calcification using a saturated aqueous solution of calcium carbonate on a polymer film having a function of capturing calcium ions (Non-patent Document 1), a copolymer or silanolate is dissolved. An attempt has been made to calcify (Non-Patent Documents 2 and 3) in which concentrated aqueous solutions of carbonate and calcium salt are added to an aqueous solution to be produced. As a polymer having only a site for capturing calcium ions, there is a polymer made of polyacrylic acid, polymethacrylic acid, or polyethylene glycol. In the presence of a zinc array substrate having a function of promoting hydration of carbon dioxide and a polymer film having a function of capturing calcium, a calcium carbonate multiphase form was formed on the film from an aqueous calcium salt solution that absorbed carbon dioxide in the atmosphere (Non-patent Document 4). ).
T. Kato et al., Chem. Mater, 2001, Vol. 13, p. 688-693 H. Colfen et al., Langmuir, 1998, Vol. 14, p. 582-589 Y. Chugo et al., J. Materials Chemistry, 2002, Vol. 12, p. 2449-2452 K. Ichikawa et al., Chemistry Europe J. 2003, Vol. 9, p. 3235-3241

  However, in the case of the conventional methods including the method described in Non-Patent Document 1-3, calcium carbonate is not generated from carbon dioxide although it has a function of capturing calcium. Although the method described in Non-Patent Document 4 produced a calcium carbonate multiphase form from carbon dioxide, it was not sufficiently efficient.

  Therefore, the present invention provides a biomimetic polymer that has not only a site for capturing calcium ions but also a site for capturing zinc ions, which can be suitably used for the synthesis of calcium carbonate. Objective.

  The present invention also provides a novel organic-inorganic composite material formed by combining this biomimetic polymer and calcium carbonate.

  The copolymer according to the present invention has a molecular chain composed of a structural unit A represented by the following structural formula (A) and a structural unit B represented by the following structural formula (B).

In the formulas (A) and (B), R ₁ represents a hydrogen atom or an alkyl group, and R ₂ represents a group consisting of a heterocyclic ring having at least one of a nitrogen atom and a sulfur atom.

  This copolymer can capture Zn ions by complex formation of a heterocyclic ring present in its side chain. The carboxyl group in the copolymer has a function of capturing calcium. That is, this copolymer has not only a site for capturing calcium but also a site for capturing zinc. This copolymer can be suitably used for the synthesis of an organic-inorganic composite material described later.

  In the copolymer of the present invention according to claim 2, when the ratio of the structural unit B to the total amount of the structural unit A and the structural unit B is the esterification rate, the esterification rate is 0.3 to 0.6. is there. By setting the esterification rate within such a specific range, the calcium carbonate multiphase form of the organic-inorganic composite material in which the copolymer is combined with calcium carbonate can be controlled.

R ₂ in formula (B) is preferably a heterocyclic group selected from the group consisting of imidazole, imidazoline, pyrazole, pyridine, pyrimidine, pyrazine, thiophene and thiazole.

  The method for producing a copolymer according to the present invention has at least one of a nitrogen atom and a sulfur atom as a part of a carboxyl group in a polymer having a molecular chain composed of the structural unit A represented by the structural formula (A). A step of producing a copolymer having a molecular chain composed of the structural unit B represented by the structural formula (B) and the structural unit A not subjected to the esterification by esterification by a reaction with a heterocyclic ring-containing compound. Is provided.

  By this production method, it is possible to synthesize the copolymer of the present invention.

  The organic-inorganic composite material according to the present invention is a material containing the copolymer of the present invention, zinc ions captured by the copolymer, and calcium carbonate complexed with the copolymer.

  The present invention also produces calcium carbonate from calcium ions and hydrogen carbonate ions in an aqueous solution containing the copolymer of the present invention and zinc ions, and the copolymer, zinc ions entrapped in the copolymer, and a composite of the copolymer. A method for synthesizing an organic-inorganic composite material comprising a step of generating an organic-inorganic composite material containing calcium carbonate.

  The copolymer of the present invention has not only a site for capturing calcium ions but also a site for capturing zinc ions. For synthesis of calcium carbonate and synthesis of an organic-inorganic composite material in which the copolymer and calcium carbonate are combined. It can be used suitably. By using this copolymer, a novel organic-inorganic composite material can be obtained by a bio-mimetic energy-saving clean green synthesis method.

  Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

  The copolymer of the present invention has a molecular chain composed of the structural unit A represented by the structural formula (A) and the structural unit B represented by the structural formula (B). The structural unit A has a carboxyl group, and it is considered that the copolymer can capture calcium ions by the action of the carboxyl group. In addition, the structural unit B has a heterocyclic ring that forms a complex with a zinc ion, and it is considered that the copolymer can capture the zinc ion by the action of the heterocyclic ring.

In the formulas (A) and (B), R ₁ represents a hydrogen atom or an alkyl group. R ₁ is preferably a hydrogen atom.

In the formula (B), R ₂ represents a group consisting of a heterocyclic ring having at least one of a nitrogen atom and a sulfur atom. The heterocyclic ring as R ₂ is not particularly limited as long as it can form a zinc complex with a zinc ion, but at least one selected from the group consisting of imidazole, imidazoline, pyrazole, pyridine, pyrimidine, pyrazine, thiophene and thiazole. It is preferable that Among these, imidazole is particularly preferable. That is, it is particularly preferable that the structural unit B is represented by the following chemical formula (B-1).

In the molecular chain in the copolymer, when the ratio of the structural unit B to the total amount of the structural unit A and the structural unit B is the esterification rate x, the copolymer can also be represented by the following structural formula (1). Wherein _(1), R 1, _{R 2} have the same meanings as _R 1, _{R 2} in formula (A) and (B). In the molecular chain, the order of binding of the structural unit A and the structural unit B is not particularly limited, and each of them may be bonded at random. The esterification rate x in this embodiment is 0.3 to 0.6.

  The copolymer of the present invention includes, for example, a functional group that forms an ester bond by reacting a part of a carboxyl group in a polymer (preferably polyacrylic acid) having a molecular chain composed of the structural unit A with a carboxyl group and nitrogen. The structural unit A represented by the structural formula (A) and the structural formula shown above are esterified by reaction with a heterocyclic-containing compound having a monovalent group consisting of a heterocyclic ring having at least one of an atom and a sulfur atom. It can be obtained from a production method comprising a step of producing a copolymer having a molecular chain composed of the structural unit B represented by (B).

As the heterocycle-containing compound used in this method, a compound having a halogen group as a functional group that reacts with a carboxyl group to form an ester bond is suitably used. In this case, the heterocyclic ring-containing compound is represented by the following structural formula (2). X in formula (2) represents a halogen atom, _{R 2} has the same meaning as _{R 2} in the formula (B).

  The esterification reaction can be carried out under ordinary esterification conditions, as will be understood by those skilled in the art. For example, esterification can be promoted by heating polyacrylic acid and the heterocycle-containing compound of formula (2) in a solvent such as DMSO in the presence of a catalyst. The catalyst used at this time is preferably a tertiary amine compound, more specifically diisopropylethylamine (DIPEA).

  The esterification rate x of the obtained copolymer can be controlled by appropriately adjusting the molar ratio of the polymer, the heterocyclic compound and the catalyst used as starting materials in the esterification reaction. For example, when a copolymer is synthesized from polyacrylic acid in the presence of DIPEA, x = 0 when polyacrylic acid: heterocyclic ring-containing compound: DIPEA = 1: 4: 2 or 1: 4: 4 (molar ratio). About 6 copolymers can be obtained. Further, when polyacrylic acid: heterocycle-containing compound: DIPEA = 1: 1: 1 (molar ratio), a copolymer having x = 0.3 to 0.4 can be obtained. In these molar ratios, the number of moles of polyacrylic acid is the number of moles of polyacrylic acid monomer units contained in the polymer.

  The organic-inorganic composite material of the present invention is a composite material containing the copolymer, zinc ions trapped in the copolymer, and calcium carbonate complexed with the copolymer.

  This organic-inorganic composite material includes, for example, a copolymer and zinc ions entrapped in the copolymer by generating calcium carbonate from calcium ions and bicarbonate ions in an aqueous solution containing the copolymer of the present invention and zinc ions. And an organic-inorganic composite material containing calcium carbonate complexed with the copolymer.

  According to this method, the copolymer is increased in quantity through zinc ions, and at the same time as the formation of the zinc complex, the formation of calcium carbonate (calcification reaction) proceeds. Then, the produced calcium carbonate forms a material integrated with the copolymer, that is, is combined, and a nanoparticulate organic-inorganic composite material is deposited. This organic-inorganic composite material can be grown from nanoscale to micron scale by calcium carbonate crystal growth.

  For example, calcium ions are supplied as an aqueous solution of calcium salt (nitrate or the like), and hydrogen carbonate ions are supplied as an aqueous solution of hydrogen carbonate (sodium hydrogen carbonate or the like). Alternatively, hydrogen carbonate ions may be generated in the solution by a carbon dioxide hydration reaction.

  In this method, it is possible to control the multiphase form of calcium carbonate produced by appropriately adjusting the esterification rate and concentration of the copolymer used. In addition, calcite is generated at room temperature and atmospheric pressure. However, aragonite can be selectively produced in the presence of the copolymer.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

1. Synthesis of Poly (acrylic acid-co- (imidazolylmethyl) acrylate (MPAA) As a monomer for obtaining the copolymer MPAA, 4-Chloromthylimidazole (ClIm) was synthesized from 4- (Hydroxymethyl) imidazole hydrochloride (HOIm) by the reaction of the following formula. First, 1.05 g (7.4 mmol) of HOIm hydrochloride was suspended in 3 mL of benzene, and 4.0 mL of 4.5 M SOCl ₂ in benzene was added thereto, and the reaction solution was stirred. The mixture was heated to 70 ° C. and refluxed for about 7 hours, and further stirred at room temperature for 15 hours, and then the suspension was filtered and dried for 1 hour in Divac, then poured into benzene and stirred overnight at room temperature. Finally, the filtered suspension was dried with Divac for 1 hour and with a rotary pump for 2-3 hours to obtain a white solid ClIm (0.98 g, 82% yield).
¹ H NMR for CIIm ((CD ₃ ) ₂ SO) δ (ppm): 4.9 (s, 2H, -CH ₂ -Cl), 7.7 (s, 1H, Im H-5), 9.1 (s, 1H, Im H -2)

  0.10 g (MV = about 450,000) of polyacrylic acid was added to a solution obtained by dissolving 0.86 g (5.6 mmol) of ClIm obtained above in 1/3 mL of anhydrous DMSO, and heated to 80 ° C. with stirring. Thereto, 0.5 mL (2.8 mmol) of Diisopropylethylamine (DIPEA) was added dropwise as a catalyst for esterification every two minutes using a 2 mL syringe. And stirring was continued at 80 ° C. for 17 hours. The reaction solution was a yellow paste.

The paste was mixed with ethanol at 1:20 (volume ratio), and the precipitated white precipitate was removed by centrifugation. This was dried with Divac for 1 hour and with a rotary pump for 2 to 3 hours, and dissolved in about 0.5 mL of DMSO to obtain a paste. This paste was mixed with ethanol at 1:20 (volume ratio) and stirred overnight, and then the precipitated white precipitate was removed by centrifugation, dried with Divac for 1 hour and with a rotary pump for 2-3 hours, A light yellow solid MPAA was obtained.
¹ H NMR for MPAA ((CD ₃ ) ₂ SO) δ (ppm): 1.2-2.0 (br, CH ₂ in the main chain), 2.2 (br, CHin the main chain), 5.5-6.3 (br, Im CH ₂ ), 7.5-8.5 (br, Im)

When the esterification rate x of the obtained MPAA was determined by the following procedure, it was about 0.6.
1) From the ¹ H NMR measurement, it was confirmed that the starting material (ClIm, HOIm) was not contained in the product.
2) The total weight W _{T, N} of nitrogen atoms in MPAA was determined by elemental analysis of nitrogen atoms.
3) 7M _{m, C} : 2M _{m, N} which is the weight ratio of carbon atom to nitrogen atom in the esterified structural unit (where M _{m, C} and M _{m, N} are the atomic weights of carbon atom and nitrogen atom, respectively) ) And W _{T, N} values, the weight W _{e, C} of the carbon atom in the constituent unit is determined.
4) The total weight W _{T, C} of carbon atoms in MPAA was determined by elemental analysis of carbon atoms.
5) The above _{W e,} and _C, and the weight _W ne carbon atoms in the structural unit unesterified in _{MPAA, C (= W T,} C -W e, C) , the carbon contained in the respective structural units Considering the number of atoms, the following formula:
We _{, C} : Wne _{, C} = 7xMm _{, c} : 3 (1-x) Mm _{, C}
Meet. The esterification rate x was calculated from this formula.

  In addition, MPAA having an esterification rate of 0.3 to 0.6 was synthesized by appropriately adjusting the molar ratio of polyacrylic acid (PAA), ClIm, and DIPEA when synthesizing MPAA.

2. Synthesis of Organic-Inorganic Composite Material An organic-inorganic composite material containing calcium carbonate was synthesized by calcification using MPAA having an esterification rate x of about 0.4, about 0.6, or about 0.3.

For example, MPAA (x = 0.40: 9.6 × 10 ⁻⁵ mol or 9.6 × 10 ⁻⁶ mol); the equimolar number is the arithmetic average weight of the weight of each constituent unit of MPAA and the total weight of MPAA Is dissolved in 30 mL of a mixed solvent (DMSO / H ₂ O = 1/1 (v / v)), and the molar ratio of imidazole group to zinc ion in MPAA is 3: 1. (NO ₃ ) ₂ was added (the amount of imidazole groups in MPAA was calculated from the above x = 0.40). This solution (about pH 6) was adjusted to pH 8 by adding aqueous NaOH solution and kept under stirring in a constant temperature room at 25 ° C. Next, 50 μL each of 0.5 M Ca (NO ₃ ) ₂ aqueous solution (pH 8) and 0.5 M NaHCO ₃ aqueous solution (pH 8) were dropped 8 times in total every 2 minutes (total dropping amount was 2.0 × 10 ⁻⁴ mol each). ). At this time, the solution became cloudy. Then, the solution was stirred at 25 ° C. for 24 hours while appropriately adding an aqueous NaOH solution and maintaining the pH at 8. Thereafter, white precipitates were taken out by centrifugation (28 mg and 17 mg, respectively). In addition to the organic-inorganic composite material obtained after 24 hours, samples collected every 1 hour and 6 hours were characterized.

3. Composition analysis of organic-inorganic composite material For the organic-inorganic composite material synthesized from the calcification reaction using MPAA, the nitrogen atom content and the carbon atom content were determined from elemental analysis of nitrogen atoms and carbon atoms. Further, the content of carbon atoms of MPAA in the organic-inorganic composite material is determined from the ratio of the number of nitrogen atoms to carbon atoms in the esterified structural unit of 2: 7 and the above nitrogen content. Calculated. The amount obtained by removing the carbon atom content of MPAA from the carbon atom content of the organic-inorganic composite material is the content of carbon atoms contained in the generated calcium carbonate, and based on this, the composite material The content of calcium carbonate in was determined. On the other hand, the calcium carbonate content was determined from the atomic absorption analysis of calcium, and the error of the previously obtained content was examined. As a result, it was revealed that the organic-inorganic composite material taken out after 24 hours contained about 10% by weight of MPAA.

  From the elemental analysis spectrum determined by EDAX-SEM measurement of the synthesized organic-inorganic composite material, it was confirmed that the organic-inorganic composite material contained zinc (FIG. 1).

4). Calcium carbonate multiphase control The multiphase form of calcium carbonate in the organic-inorganic composite material prepared above was analyzed. When the esterification rate is about 0.6, calcium carbonate was mainly composed of bundled aragonite when the MPAA concentration was high (FIG. 2). When the esterification rate was about 0.4, when the MPAA concentration was low, calcium carbonate was mainly composed of circular vaterite (FIG. 3). When the esterification rate is 0.3 or less, or when zinc is not present regardless of the esterification rate, calcium carbonate is mainly composed of calcite. However, it is considered that the multiphase form and form of calcium carbonate are also affected by the pH and temperature of the aqueous solution during calcification (in this calcification experiment, about pH 8,25 ° C. as described above). In addition, identification and relative ratio determination of the produced | generated calcium carbonate multiphase form were performed by collating the powder method X-ray-diffraction measurement data and the diffraction pattern standard data of each multiphase form.

5). Aragonite Formation Mechanism FIGS. 4 and 5 are SEM images of the organic-inorganic composite material taken out after 24 hours. FIG. 4 is an image obtained when MPAA having an esterification rate of 0.4 and FIG. 5 is used with an esterification rate of 0.6. As shown in FIGS. 4 and 5, calcification occurs simultaneously with the zinc-assisted self-assembly of the copolymer fine particles, and a cylindrical organic-inorganic composite material having an average diameter of about 30 × 60 nm ² is formed. It was. FIG. 6 shows a TEM image of the organic-inorganic composite material. In the diffraction pattern, in addition to imperfect diffraction spots, a blurred circular pattern peculiar to amorphous is seen, so the calcium carbonate in the organic-inorganic composite material is an aragonite type that has not grown to a perfect crystal. It was confirmed that there was.

Furthermore, starting from the columnar organic-inorganic composite material, the state of growth into bundled aragonite (FIG. 2) was confirmed from the SEM image (FIG. 7) and the TEM image (FIG. 8). This bundle-shaped aragonite is composed of rectangles (200 × 1000 nm ² ) and oriented so that they overlap each other, and it is confirmed that the rectangles are formed by overlapping the cylindrical composite materials. It was. Moreover, the electron beam diffraction image (FIG. 9) in the area | region S of FIG. 8 showed that each rectangle was an aragonite crystal.

  From the above, it is considered that MPAA was taken into calcium carbonate in the process of forming the organic-inorganic composite material. Aragonite grown as a crystal is composed of two components, calcium carbonate and MPAA (about 10% by weight as described above). By clarifying the growth process of each multiphase crystal of calcium carbonate, it is judged that a technical process capable of controlling the formation of aragonite or vaterite will be established.

  The present invention can generate a micron-scale organic-inorganic composite material from a nanoscale-sized copolymer and ions in a biomimetic, energy-saving, clean green process, with an initial stage sub-nanoscale composite material. It is a seeds technology that makes it possible to grow a bundle of micron-scale aragonite crystals. This organic-inorganic composite material can be said to be a biomimetic material from the viewpoint of components, growth mechanism, and multiphase control.

  Furthermore, this technology is expected to become a key technology for bottom-up production technology that synthesizes materials of larger scales via nano-sized materials. If nano-micron and micron-to-millimeter hierarchical structure control becomes possible, it is expected that it will open the way to the creation of structural materials that have contradictory physical properties, such as rigidity and toughness, plasticity and elasticity, beyond conventional common sense. .

  In addition, the organic-inorganic composite material of the present invention is expected to be applied to products of electric shock / antistatic coating materials and tablet coating materials.

It is an elemental analysis spectrum of an organic-inorganic composite material. It is a SEM image of an organic-inorganic composite material. It is a SEM image of an organic-inorganic composite material. It is a SEM image of an organic-inorganic composite material. It is a SEM image of an organic-inorganic composite material. It is a TEM image of an organic-inorganic composite material. It is a SEM image of an organic-inorganic composite material. It is a TEM image of an organic-inorganic composite material. 9 is an electron diffraction pattern in a region S of FIG.

Claims (5)

A copolymer having a molecular chain composed of a structural unit A represented by the following structural formula (A) and a structural unit B represented by the following structural formula (B).

[In the formulas (A) and (B),
R ₁ represents a hydrogen atom or an alkyl group,
R ₂ represents a group consisting of imidazole . ]   The copolymer according to claim 1, wherein the esterification rate is 0.3 to 0.6 when the ratio of the structural unit B to the total amount of the structural unit A and the structural unit B is an esterification rate. A part of the carboxyl group in the polymer having a molecular chain composed of the structural unit A represented by the following structural formula (A) is esterified by reaction with a heterocyclic-containing compound having imidazole , and the following structural formula (B) A process for producing a copolymer, comprising the step of producing a copolymer having a molecular chain consisting of the structural unit B represented by formula (I) and the structural unit A that has not undergone esterification.

[In the formulas (A) and (B),
R ₁ represents a hydrogen atom or an alkyl group,
R ₂ represents a group consisting of imidazole . ] A copolymer according to claim 1 or 2 , and
Zinc ions entrapped in the copolymer;
An organic-inorganic composite material comprising calcium carbonate complexed with the copolymer. By generating calcium carbonate from calcium ions and hydrogen carbonate ions in an aqueous solution containing the copolymer of claim 1 or 2 and zinc ions,
A method for synthesizing an organic-inorganic composite material, comprising the step of producing an organic-inorganic composite material containing the copolymer, zinc ions captured by the copolymer, and calcium carbonate complexed with the copolymer.

Images