JP2006273890A - Anisotropic ion conductive polymer membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an anisotropic ion conductive material characterized by substance dispersion characteristics depending on the orientation of a phase separation structure in a membrane by utilizing an orientation type extremely finely patterned flat membrane (patent reference 1) by a polymer thin membrane showing the phase separation in a nano meter zone. <P>SOLUTION: This anisotropic ion conductive polymer membrane consisting of an amphiphilic polymer with proton or a metallic anion is provided with that the amphiphilic polymer is a block copolymer obtained by bonding a hydrophilic polymer component with a hydrophobic polymer component by a covalent bond and having ≤1.3 molecular weight distribution (Mw/Mn) and a cylinder consisting of the hydrophilic polymer component orienting in a definite direction in the membrane and localizing the proton or metallic anion at the cylinder part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ion conductive polymer film having anisotropy in ion conductivity, and more particularly to an anisotropic ion conductive polymer film useful as an electrolyte film or the like.

  In the field of ionics, liquid electrolytes are still used, and there are many unsolved issues in realizing all-solid-state devices. Solid fuel cells using ion-conductive materials that have been developed so far include solid oxide fuel cells using oxides or sulfides such as zirconium, yttrium, bismuth and vanadium, and solid fuel cells using molten carbonate and phosphoric acid. And solid fuel cells using fluorine-based polymer electrolyte membranes represented by Nafion (registered trademark) and Dow (registered trademark). A layered porous flat membrane made of polyethylene or polypropylene, a polyolefin-based resin, or the like has been put into practical use as a solid electrolyte for conducting lithium ions because it can be thinned and has a high porosity. More recently, crown ethers with functional functional groups, ionic liquids that are organic molten salts with an organic cation structure, and polymer ions such as polymethacrylates, polyethylene, and polystyrene with oligoethylene oxide moieties in the side chain. Conductivity has been reported (Non-Patent Documents 1 and 2).

In order to mass-produce such ionic conductors at low cost, it is required to refine the pore structure and control the shape of the pores and to control the orientation in the film, but there are few examples achieved by existing technologies ( Non-patent documents 3, 4).
Attention is also focused on organic compounds and polymer materials that allow the design of materials that have both a soft part that can move ions faster and a hard part that maintains the shape of the solid. An ion conduction mechanism has been developed that uses a cross-linked polymer gel network structure, a layered structure in a film surface formed by blends of different types of polymers, ionic liquids, liquid crystals, etc. (Non-patent Document 3, 5, 6) The orientation control is difficult due to the chemical structure of the raw material used, and the ion transport anisotropy has not been exhibited with respect to the electrode substrate.

JP2004-124088 K. Kimura, et al., Macromolecules, 37, 1871 (2004). C. T. Imrie, et al., Adv. Mater., 11, 832 (1999). T. Kato, et al., JACS, 126, 994 (2004). C. Tschierske, J. Mater. Chem., 11, 2647 (2001). Adam. Z. Weber, et al., J. Electrochem. Soc., 150 (7), A1008 (2003). T. Kato, et al., JACS, 125, 3196 (2003).

  The present invention utilizes an oriented ultrafine patterned flat film (Patent Document 1) with a polymer thin film exhibiting phase separation in the nanometer region, and material diffusion characteristics depending on the orientation of the phase separation structure in the film. A method for producing an anisotropic ion conductive material is provided.

In the present invention, a highly oriented nano-cylinder structure (Patent Document 1) having a thin film obtained by depositing an amphiphilic polymer is used. By using this amphiphilic polymer, it becomes possible to control the orientation of the nanocylinder structure relative to the electrode substrate and the synthetic chemical cylinder diameter, and form a complex between the mobile polymer and the hydrophilic polymer chain that forms the cylinder. This makes it possible to conduct selective ion conduction, and has the advantage that the valence of mobile ions is not limited.
That is, the present invention is an anisotropic ion conductive polymer membrane comprising an amphiphilic polymer and a proton or metal anion, and the amphiphilic polymer shares a hydrophilic polymer component and a hydrophobic polymer component. A block copolymer having a molecular weight distribution (Mw / Mn) of 1.3 or less, bonded by bonding, having a cylinder made of the hydrophilic polymer component oriented in a certain direction in the film, and the proton or metal It is an anisotropic ion conductive polymer membrane in which anions are localized in the cylinder portion.

  The anisotropic ion-conducting polymer membrane of the present invention has an anisotropic ion-conducting property based on the orientation of the phase-separated structure, with a nanometer-order phase-separated structure formed by an amphiphilic polymer. It is provided as a new solid electrolyte material to make the ionics element all solid.

The anisotropic ion conductive polymer membrane of the present invention is mainly composed of an amphiphilic block copolymer (Patent Document 1), and the structure thereof is a hydrophilic nanocylinder and a hydrophobic property serving as a matrix thereof. It consists of a liquid crystal domain and contains a proton or metal cation complexed in the hydrophilic nanocylinder portion.
The cylinder diameter and distance between cylinders of this hydrophilic nanocylinder can be precisely determined by the structure of this polymer, and the in-film orientation of this hydrophilic nanocylinder can be controlled by heat treatment or electric field application. .
Since the anisotropic ion conductive polymer film of the present invention uses complex formation with a hydrophilic site as a driving force, it is possible to introduce not only monovalent ions but also divalent and trivalent mobile ions.

The amphiphilic block copolymer of the present invention is a block copolymer in which a hydrophilic polymer component (A) and a hydrophobic polymer component (B) that are incompatible with each other are covalently linked. Has conflicting chemical and physical properties. Moreover, the molecular weight distribution is 1.3 or less, and the order of the constituent polymer chains A and B does not matter.
Examples of the hydrophilic polymer chain A include poly (ethylene oxide), poly (propylene oxide), poly (vinyl alcohol), poly (acrylic acid), poly (methacrylic acid), poly (acrylamide), oligo (ethylene oxide), and crown. Poly (methacrylate) or poly (acrylate) having a hydrophilic side chain such as ether, cryptand or sugar chain, preferably poly (ethylene oxide) methyl ether.
Examples of the hydrophobic polymer chain B include poly (methacrylate) or poly (acrylate), poly (styrene), and vinyl polymer having a mesogen side chain, a long alkyl side chain, or a hydrophobic side chain.

The mesogenic side chain is, for example, the following general formula E- (Y1-F) n-Y2-G
The thing which has one or more structural units represented by these is mentioned.
In the formula, E, F and G may be the same or different and are respectively 1,4-phenylene, 1,4-cyclohexylene, 1,4-cyclohexenylene, naphthalene-2,6- Diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, 1,4-bicyclo [2.2.2] octylene, 1,3-dioxane-2 , 5-diyl, pyridine-2,5-diyl, pyrazine-2,5-diyl, pyridazine-3,6-diyl, pyrimidine-2,5-diyl, and Y1 and Y2 are the same Or may be different, a single bond, —CH ₂ CH ₂ —, —CH ₂ O—, —OCH ₂ —, —C (═O) O—, —OC (═O) —, —C≡C -, - CH = CH -, - CF = CF -, - (CH 2) 4 -, _{CH 2 CH 2 CH 2 O -} , - OCH 2 CH 2 CH 2 -, - CH = CH-CH 2 CH 2 -, - CH 2 CH 2 -CH = CH -, - N = N -, - CH = CH -C (= O) O- or -OC (= O) -CH = CH- is represented, and n represents an integer of 0 to 3.
The long-chain alkyl side chain means an alkyl side chain having preferably 6 to 22 carbon atoms.
Examples of the hydrophobic side chain include an aliphatic side chain.
The molecular weight of this block copolymer is preferably 5,000 to 100,000, more preferably 10,000 to 50,000.

As this block copolymer, the following general formula (Formula 2)
(In the formula, m and n each represent an integer of 5 to 500, a represents an integer of 1 to 22, X represents a halogen atom, and R represents a hydrogen atom or an alkyl group having 1 to 22 carbon atoms. .) Is preferred.

The thickness of the anisotropic ion conductive polymer film of the present invention is preferably about 30 nm to about 10 μm.
There is no particular limitation on the method for forming an anisotropic ion conductive polymer film from an amphiphilic block copolymer, and it is usually performed by applying a polymer dissolved in a solvent on a substrate and drying the solvent. .
As the solvent, organic solvents such as toluene, tetrahydrofuran, xylene, chloroform and pyridine are usually used. Further, a doped silicon wafer, ITO, a titanium plate, a copper plate, an electrode substrate such as platinum, or the like can be used as the substrate.
As film formation methods, spin coating method (film thickness 80-200 nm), water surface development method (film thickness 50-100 nm), bar coating method (film thickness 500 nm-2 μm), microgravure method (film thickness 50 ~ 200 nm) is used (in parentheses indicate the film thickness normally obtained).

There is no particular limitation on the method for forming an oriented cylinder structure in such an anisotropic ion conductive polymer film, but (1) heat treatment and (2) electric field application are preferable.
(1) The heat treatment is usually performed according to the following procedure.
When this polymer thin film is heated at a temperature equal to or higher than the melting point, a large number of cylinders made of a hydrophilic polymer are oriented in a direction substantially perpendicular to the film surface.
The melting point can be measured by DSC (differential scanning calorimetry), and the melting point of the amphiphilic block copolymer of the present invention is usually 120 to 140 ° C.
(2) Electric field application is usually performed according to the following procedure.
During film formation, or the formed film is placed on a substrate and heated at a temperature 10 to 100 ° C. lower than the melting point of the amphiphilic block copolymer, for example 50 to 80 ° C. By applying an electric field of 10 ^{5 to} 3 × 10 ⁷ V / m, the cylinder can be oriented in the electric field direction.

The anisotropic polymer film thus obtained forms a hexagonal close-packed cylinder structure that is a periodic phase separation structure in the nanometer region. The cylinder structure formed by the domains of the hydrophilic polymer chain is further stabilized by the liquid crystal alignment in the hydrophobic matrix.
The cylinder diameter is usually about 0.003 to 0.020 μm, and the distance between the cylinders is usually about 0.010 to 0.060 μm. These can be measured by a small angle X-ray scattering measurement, a transmission electron microscope, or an atomic force microscope.
The cylinder diameter depends on the size of the hydrophilic polymer portion of the amphiphilic block copolymer (for example, m in the above general formula (Formula 2)), and the distance between the cylinders is the hydrophobicity of the amphiphilic block copolymer. By designing an amphiphilic block copolymer having an appropriate size, the desired cylinder structure can be obtained, depending on the size of the functional polymer portion (for example, n in the above general formula (Chemical Formula 2)). It is possible to produce an anisotropic ion conductive polymer film having the same.
This cylinder part can be oriented in the desired direction by the above-mentioned means for orientation, but it is extremely useful in view of its use when oriented in a direction perpendicular to the surface of the polymer film. It is thought that.

Next, a method for imparting ion conductivity to the hydrophilic polymer portion of the anisotropic polymer film obtained above will be described.
The ion conduction source contained in the hydrophilic nanocylinder part includes protons, monovalent metals such as Na, Li, and K, and divalent metals such as Mg, Ca, Ni, Cu, Zn, Co, Pb, Cd, and Hg. A metal cation is mentioned.
In order to introduce protons, an acid such as phosphoric acid or an alcohol, preferably an acid, is usually used.
In order to introduce metal cations, these metal salts are usually used. For example, the above metals and CF ₃ SO ₃ , Br, Cl, F, I, ClO ₄ , BF ₄ , PF ₆ , SO ₃ , OH, NO ₃ , CH ₃ SO ₃ , CH ₃ COO, AlCl ₄ , AlO ₂ , Salts with SO ₄ , S, CO ₃ , PO ₄ , SO ₃ and the like can be used.

There is no particular limitation on the method of introducing mobile ions, and it may be any of during or after film formation, or before or after alignment treatment. Examples of the introduction method include (1) a method in which the acid or metal salt is dissolved in a solution in which the amphiphilic block copolymer is dissolved, and (2) the amphiphilic block copolymer. A method of immersing a film formed after forming the film in a solution in which the acid or metal salt is dissolved, or (3) forming a film formed after forming the amphiphilic block copolymer, And a method in which an electric field is applied thereto.
Of these, (1) is particularly convenient and preferred. In this case, a thin film is produced using a polymer solution mixed with an electrolyte (proton or metal cation) that becomes mobile ions. In the heat-dried thin film, mobile ions selectively form a complex with the hydrophilic cylinder portion, and the cylinder is oriented in a direction perpendicular to the substrate. This polymer thin film exhibits an ionic conductivity in the direction parallel to the nanocylinder orientation and an anisotropic ionic conductivity that does not show in the vertical direction.
In addition to electrolyte ions, bio-related molecules such as DNA, metals (including metal oxides), or polydispersed fine powders made of general-purpose polymers are included in the cylinder part, so that a wide range of target substances can be obtained. Based on chemical properties, it is also possible to have the feature of specific mass transport at the hydrophilic nanocylinder site.

The anisotropic ion conductive polymer film thus obtained exhibits anisotropic ion conductivity and can be used appropriately depending on the application. For example, a portion in which the orientation is changed in one anisotropic ion conductive polymer film may be provided. Further, a plurality of anisotropic ion conductive polymer films which may be the same or different may be laminated and used at a desired film thickness.
Further, such an anisotropic ion conductive polymer film may be used as an ion conductive film, and the anisotropic ion conductive polymer film may be sandwiched between two electrodes to form an element. Any electrode may be used as such an electrode (anode and cathode), but a metal plate such as platinum or nickel, a porous carbon or fluorine-based polymer material carrying a noble metal catalyst such as platinum or gold, platinum or the like An insulating plate (polymer or the like) covered with a metal thin film such as gold can be used. The above-mentioned ion conductive film can be sandwiched between these two electrodes to form an element.

The following examples illustrate the invention but are not intended to limit the invention.
Production Example 1
A block copolymer was synthesized comprising poly (ethylene oxide) methyl ether (molecular weight 5000) as a hydrophilic polymer chain and azobenzene-containing liquid crystalline side chains having a polymerization degree of 114 and a polymethacrylate as a hydrophobic polymer chain. The synthesis was performed by an atom transfer radical polymerization method using a copper complex as a catalyst.
The obtained block copolymer has the following general formula (Formula 3)
The number average molecular weight was 28100, Mw / Mn = 1.08, the polymethacrylate (MA) content was 82% by weight, and the melting point was 120 ° C.

The block copolymer (pEO-b-pMA (Az)) obtained in Production Example 1 and lithium triflate (LiCF ₃ SO ₃ ) were dissolved in purified tetrahydrofuran. Three types of mixing ratios were prepared: [EO]: [Li ⁺ ], which is a lithium ion concentration [Li ⁺ ] with respect to the ethylene oxide monomer unit [EO], of 120: 1, 20: 1, and 4: 1. The mixture was stirred at room temperature for 6 hours to promote complex formation between polyethylene oxide sites and Li ions. Thereafter, using this solution, a film was formed on a quartz substrate or a conductive silicon wafer by spin coating (film thickness: about 0.3 μm). The thin film made of the obtained lithium ion-polymer complex was heat-treated at 140 ° C. for 10 hours under vacuum.

An atomic force microscope (AFM) photograph of the obtained film is shown in FIG.
On the surface of the thin film with lithium ions [EO]: [Li ⁺ ] = 120: 1, 20: 1 after heat treatment, a dot pattern consisting of a hexagonal close packed pEO domain was observed. From the cross-sectional image, a pEO cylinder structure oriented perpendicular to the substrate was observed (FIG. 1). In the thin film satisfying the film formation condition of [EO]: [Li ⁺ ] = 4: 1 containing more Li ions, a phase separation structure with low regularity and orientation was observed.

  The DSC curve of the obtained film is shown in FIG. The two liquid crystal phase transition temperatures (68 ° C. and 100 ° C.), the melting point (138 ° C.) and the kind of azobenzene liquid crystal phase can be seen. When the phase separation structure is measured by small-angle X-ray scattering, this structure depends on temperature, and forms a cylindrical type below the melting point and a spherical phase separation structure above the melting point.

Next, the ion conductivity of the obtained membrane was measured by impedance analysis in two directions shown in FIG. The temperature dependence of the ionic conductivity is shown in Table 1 and FIG. Ion conduction properties with large anisotropy (450) were observed in the thin films using the mixing ratio of [EO]: [Li ⁺ ] = 20: 1. The anisotropy of the thin film using a mixing ratio of [EO]: [Li ⁺ ] = 4: 1 was 40. When considered together with the AFM surface observation of FIG. 1, this thin film, which is a lithium ion-polymer complex, is an anisotropic ionic conductor that exhibits higher ionic conductivity with respect to the orientation direction of the cylinder in the film. I can say that.

  Since the anisotropic ion conductive polymer membrane of the present invention can be oriented out of plane, selective permeation (transport) such as a polymer electrolyte fuel cell can be used as a highly selective, high density, high energy type ion conductive material. ) Can be applied to membranes, separation membranes, solid absorbent materials (separated absorbent materials), high energy absorbent materials (vibration absorbent materials), etc.

It is a figure which shows the atomic force microscope photograph of an anisotropic ion conductive polymer film. A and B are [EO]: [Li ⁺ ] = 120: 1, C and D are [EO]: [Li ⁺ ] = 20: 1, and E and F are [EO]: [Li ⁺ ] = These were prepared at a mixing ratio of 4: 1, A, C, and E are surface photographs, and B, D, and F are cross-sectional photographs. The scale bar in the figure indicates 200 nm. It is a figure which shows the DSC curve of an anisotropic ion conductive polymer film. It is a figure which shows the measurement direction of the ion conductivity of an anisotropic ion conductive polymer film. It is a figure which shows the ionic conductivity of an anisotropic ion conductive polymer film.

Claims (6)

An anisotropic ion conductive polymer membrane comprising an amphiphilic polymer and a proton or metal anion, wherein the amphiphilic polymer has a hydrophilic polymer component and a hydrophobic polymer component bonded by a covalent bond. A block copolymer having a distribution (Mw / Mn) of 1.3 or less, having a cylinder made of the hydrophilic polymer component oriented in a certain direction in the membrane, and the proton or metal anion is in the cylinder part Localized anisotropic ion conductive polymer membrane. The hydrophilic polymer chain is poly (ethylene oxide), poly (propylene oxide), poly (vinyl alcohol), poly (acrylic acid), poly (methacrylic acid), poly (acrylamide), or poly having hydrophilic side chains (Methacrylate) or poly (acrylate), wherein the hydrophobic polymer chain has a mesogenic side chain, a long alkyl side chain or a hydrophobic side chain, poly (methacrylate) or poly (acrylate), poly (styrene), The anisotropic ion conductive polymer film according to claim 1, which is a vinyl polymer. The block copolymer has the following general formula (Formula 1)
(In the formula, m and n each represent an integer of 5 to 500, a represents an integer of 1 to 22, X represents a halogen atom, and R represents a hydrogen atom or an alkyl group having 1 to 22 carbon atoms. The anisotropic ion conductive polymer film according to claim 1, represented by: The anisotropic ion conductive polymer film according to any one of claims 1 to 3, wherein the cylinder is oriented in a direction substantially perpendicular to the surface of the film. An anisotropic ion conductive polymer film formed by laminating a plurality of anisotropic ion conductive polymer films according to any one of claims 1 to 4. An element comprising the anisotropic ion conductive polymer film according to any one of claims 1 to 5 sandwiched between two electrodes.