JP5283167B2 - Polymer membrane with microphase separation structure - Google Patents

Description

  The present invention relates to a block copolymer film having a microphase separation structure oriented in a direction perpendicular to the film surface.

Technology that imparts a fine structure to materials and uses their unique functions and physical properties is generally called nanotechnology. In recent years, it is expected to be applied not only in the electronics field but also in a wide range of fields such as energy and environment. .
One such nanotechnology is the microphase separation structure of block copolymers. As materials that can form nanometer-order patterns on a substrate in a self-organized manner and can be applied to the manufacture of magnetic recording media, solar cells, light-emitting elements, precision filters, etc., aromatic ring-containing polymer chains and acrylic polymer chains A pattern material that contains a block copolymer or graft copolymer having a structure and forms a microphase-separated structure is known (Patent Documents 1 and 2).

On the other hand, it is generally known that in a membrane containing a block copolymer produced by a solvent casting method, the microphase separation structure tends to be oriented parallel to the membrane surface (Non-patent Document 1). Such a structure is disadvantageous in terms of performance when used for precision filter applications, for example. Therefore, means for orienting the microphase separation structure perpendicular to the film surface has been studied.
Patent Document 3 discloses a method of orienting the microphase separation structure of the block copolymer in a vertical direction and also in one direction in the substrate plane by combining stretching and heat treatment.
There is also known a method for producing a block copolymer film having a vertically aligned lamella structure by placing a block copolymer resin on a substrate having a predetermined characteristic surface roughness or more and heat-treating the resin (patent) Reference 4).

For example, when a polystyrene-polymethyl methacrylate diblock copolymer film is cast on an electrode plate and a DC voltage of 30 to 40 V / μm is applied at 165 ° C. for 14 hours, the cylinder structure composed of polymethyl methacrylate is vertical. Orientation has been reported (Non-patent Document 2).
It is also known that after grafting a random copolymer of styrene-methyl methacrylate, a polystyrene-polymethyl methacrylate diblock copolymer is cast to form a cylinder structure that stands perpendicular to the surface (non-patented). Reference 3)
However, such a method requires complicated treatments such as treatment of the substrate or stretching, electric field, or heat treatment of the film.

Patent Document 5 discloses a method for forming a vertically aligned microphase separation structure more easily. That is, by using a solvent selected as a casting solvent, a cast film having a spherical microphase separation structure that is inherently unstable as a first stage is prepared, and an annealing treatment is performed on the cast film on the film surface in a second stage. A method for obtaining a microphase separation structure of a vertically oriented cylinder structure is disclosed.
However, even in this method, a process of finally heat-treating the film is essential, and a post-process is necessary after cast film formation.
Therefore, as a result of intensive studies, the present inventors have overcome the above technical problems and succeeded in producing a microphase separation structure perpendicular to the membrane surface by an as-cast method.
Here, the as-casting method is a solution casting method, that is, a film forming method in which a solution is cast on a support, and then a solvent is evaporated from the cast film, followed by heat treatment and the like. is there.

The present invention is characterized in that the manufacturing process is extremely simple compared to the conventional techniques. On the other hand, the vertical orientation obtained by this method does not necessarily have a high degree of orientation as compared with that obtained in Patent Document 5 after annealing. When the degree of orientation is not large, as described in Patent Document 5, if the peak half-value width of the scattering primary peak intensity depending on the azimuth angle is used as an index of the degree of orientation, the degree of orientation can be reduced by, for example, drawing the background. The value greatly changes and it is extremely difficult to determine the value uniquely.
Therefore, in the present invention, a new orientation degree index is introduced. In the present invention, when X-rays are incident from the film cross-sectional direction and small-angle X-ray scattering measurement is performed, the scattered primary peak intensity observed in the film surface direction is the scattered primary peak intensity observed in the film normal direction. The value Q divided by was used as an index of the degree of orientation. When the Q value is 1.5 or more, it is determined that the microphase separation structure is strongly oriented perpendicular to the film surface.

In X-ray scattering, when a linear or planar structure is oriented in a certain direction, the scattering appears in the normal direction. The scattering intensity is proportional to the number of structures. Therefore, if the Q value shown above is larger than 1, it can be said that the microphase separation structure is oriented perpendicular to the film surface.
In fact, Patent Document 5 also evaluates orientation based on this principle. Patent Document 5 states that in the sample after annealing in Patent Document 5, the peak appears in a spot shape only in the meridian direction, and the cylindrical structure is oriented vertically. The fact that the peak appears only in the meridian direction is the same as the fact that the peak intensity in the meridian direction is stronger than other orientations, and the microphase-separated structure is oriented in the direction perpendicular to the orientation with the strong peak intensity. The principle that it is doing is used. In Patent Document 5, the meridian direction is the film surface direction.
Even when the microphase-separated structure forms a spherical structure, the orientation can be defined by considering the scattering from the surface formed by the array of the spheres as in the case of the crystal.
In Patent Document 5, it is described that the vertical alignment of the micro phase separation structure is realized by annealing after cast film formation. On the other hand, the orientation of the microphase separation structure of the film before annealing is only described as a two-dimensional SAXS pattern, and is not described in particular.

JP 2001-151834 A JP 2002-279616 A JP 2006-159815 A JP 2004-99667 A JP 2006-299106 A Structureand Properties of Taperd Block Polymer. 4. “Domain-BoundaryMixing” and “Mixing-in-Domain” Effects on Microdomain Morphology and Linear Dynamic Mechanical Response, T. Hashimoto, Y. Tsukahara, K. Tachi, H. Kawai, Macromolecules 1993, 16, 648 Ultrahigh-DensityNanowire Arrays Grown in Self-Assembled Diblock Copolymer Templates, T. Thurn-Albrecht, J. Schotter, GA Kaestle, N. Emley, T. Shibauchi, L. Krusin-Elbaum, K. Guarini, CTBlack, MT Tuominen, and TP Russell, Science Dec15 2000: 2126-2129 K. Shin, K. A. Leach, J. T. Goldbach, D. H. Kim, J. Y. Jho, M. Tuominen, C. J. Hawker, T. P. Russell, Nano Letters, 2, 933 (2002)

  An object of the present invention is to provide a block copolymer film in which the microphase-separated structure is oriented perpendicular to the film surface only by an as-cast method without solving the inconveniences in the above-described prior art and annealing treatment. .

As a result of intensive studies to solve the above problems, the inventors of the present invention controlled the molecular weight of the block copolymer so that the film surface of the block copolymer film can be formed only by the as-cast method without annealing. It has been found that the microphase separation structure can be oriented vertically.
That is, the present invention provides the following block copolymer film.
(1) It is composed of a block copolymer having a number average molecular weight of 500,000 to 2.5 million and has a film thickness of 5 μm to 1000 μm, and the microphase separation structure by the block copolymer is oriented in a direction perpendicular to the film surface. Block copolymer film having the above structure.
(2) The block copolymer is selected from styrene, α-methyl styrene, vinyl pyridine, methyl methacrylate, tert-butyl methacrylate, ethylene, propylene, isoprene, butadiene, isobutane and butane as monomers for forming block polymerization. The block copolymer film according to (1), containing at least any two of them.

(3) The block copolymer film according to (2), wherein the block copolymer contains styrene and methyl methacrylate as monomers that form block polymerization.
(4) The block copolymer film according to any one of (1) to (3), containing 10 to 99.99% by weight of a block copolymer.
(5) Block copolymer is methylene chloride, chloroform, tetrahydroxyfuran, methyl ethyl ketone, toluene, propylene glycol monomethyl ether acetate, ethyl lactate, o-dichlorobenzene, acetophenone, 1-methyl-2-pyrrolidone, γ-butyllactone The block copolymer film according to any one of (1) to (4), which is soluble in 1-methylnaphthalene or a mixture thereof.
(6) The block copolymer film according to any one of (1) to (5), wherein a Q value that is an index of the degree of orientation is 1.5 or more.

According to the present invention, it is possible to obtain a film including a microphase-separated structure that is oriented perpendicular to the film surface only by a casting process without annealing.
The micro phase separation structure formed by the block copolymer of the present invention forms an ordered structure of several to several hundreds of nanometer scale. For example, patterned media such as optical recording media and magnetic recording media, solar cells, optical switches, etc. High-performance optical materials such as photoelectric conversion elements, light modulation elements, optical phase difference films and polarization films, light emitting elements such as laser oscillation elements, display materials, organic FET elements, electrolyte films, nano-reaction field films, thermoelectric conversion elements, It can be used for printing screens, resist agents, precision filters, catalysts, fine molds, and the like. Furthermore, as a use of a nanoporous material obtained by decomposing or dissolving at least one component of a block copolymer forming a microphase-separated structure, a catalyst carrier, nanostamp, nanoporous hollow fiber, adsorbent, precision filter Such as separation membranes, fine molds, nanotemplates and the like.
In order to improve functionality in such applications, it is necessary to be able to control the orientation of the microphase separation structure. For example, in a separation membrane such as a precision filter, it is often advantageous that the microphase separation structure is oriented in a direction perpendicular to the membrane surface. As described in Non-Patent Document 1, in the film obtained by normal casting, the microphase separation structure is oriented in the direction parallel to the film surface. The membrane having the microphase separation structure can contribute to the improvement of the performance of the high-performance material in the above field.

Hereinafter, the best mode for carrying out the present invention will be described in detail.
The present invention relates to a block copolymer membrane having a microphase separation structure oriented in a direction perpendicular to the membrane surface. The orientation of the microphase-separated structure is confirmed by a small angle X-ray scattering (SAXS) method. Specifically, X-rays are incident from the film cross-sectional direction, and the scattered light that has been transmitted is detected by a two-dimensional detector. From the two-dimensional SAXS pattern, a one-dimensional scattering profile is obtained by taking a fan-like average in the azimuth angle range of plus or minus 15 degrees in the film surface direction and the film normal direction, respectively, and the scattering primary peak intensity in the film surface direction is determined by the film method. When the value Q divided by the scattering primary peak intensity in the linear direction is 1.5 or more, it can be determined that the microphase separation structure is strongly oriented in the direction perpendicular to the film surface.

  The reason why it is possible to form a microphase-separated structure having a different orientation direction according to the present invention is related to the fact that the microphase-separated structure is formed with the solvent remaining in the casting process and is further immobilized by gelation. It is estimated that Therefore, the block copolymer of the present invention needs to form a microphase separation structure in a relatively low concentration solution. Since the block copolymer forms microphase separation in a solution having a low concentration as the molecular weight increases, the block copolymer used in the present invention needs to have a molecular weight of a certain size or more. However, since the solution in which the block copolymer in the system is microphase-separated is very difficult to process due to its high viscosity, the block copolymer is in a disordered state (one-phase mixed state) in the solution before casting. It is desirable to take. If the molecular weight of the block copolymer is too large, the concentration at which a disordered state can be obtained becomes extremely low, which is problematic in terms of productivity.

From such a viewpoint, the number average molecular weight (Mn) of the block copolymer is preferably in the range of 500,000 to 2.5 million, more preferably in the range of 800,000 to 2.5 million, and 1.3 million to 2.5 million. More preferably, it is the range.
The block copolymer of the present invention is composed of two or more, more preferably two types of repeating monomer units, and the block copolymer (polymer component) of block chains formed from at least one type of repeating monomer units A. The weight fraction in the coalescence is preferably between 10% and 50%, more preferably between 10% and 40%, and more preferably between 15% and 35%.

Specific examples of monomers forming the block polymerization used in the block copolymer of the present invention include styrene, α-methylstyrene, vinylpyridine, methyl methacrylate, tert-butyl methacrylate, ethylene, propylene, isoprene, and butadiene. , Isobutane, butane and the like, and a combination that forms microphase separation is selected. Among them, styrene, α-methylstyrene, vinyl pyridine, methyl methacrylate, and tert-butyl methacrylate are preferably selected, and styrene and methyl methacrylate are more preferable.
The block copolymer film of the present invention may contain other components in addition to the block copolymer. Other components include high-boiling low-molecular compounds such as homopolymers and plasticizers. The ratio of the block copolymer in the block copolymer film is preferably 10 to 99.99% by weight, more preferably 30 to 99.99% by weight, and 50 to 99.99% by weight. More preferably.

The membrane of the present invention is produced by a solvent casting method. If the film thickness is too thin, the orientation of the microphase separation structure itself cannot be defined, and if it is too thick, it takes too much time to evaporate the solvent. Therefore, the film thickness is preferably 1 μm to 1000 μm, more preferably 5 μm to 500 μm, and even more preferably 10 μm to 200 μm.
As the solvent used in the solvent casting method of the membrane of the present invention, methylene chloride, chloroform, tetrahydroxyfuran, methyl ethyl ketone, toluene, propylene glycol monomethyl ether acetate, ethyl lactate, o-dichlorobenzene, acetophenone, 1-methyl-2 -Pyrrolidone (NMP), γ-butyl lactone, 1-methylnaphthalene, or mixtures thereof are preferred.

Among these, chloroform, tetrahydroxyfuran, methyl ethyl ketone, propylene glycol monomethyl ether acetate, o-dichlorobenzene, acetophenone, 1-methyl-2-pyrrolidone, γ-butyllactone, 1-methylnaphthalene, or a mixture thereof is more desirable. More preferred are chloroform, tetrahydroxyfuran, methyl ethyl ketone, acetophenone, 1-methylnaphthalene, or mixtures thereof.
In order to prepare a block copolymer by the solvent casting method, it is necessary that the block copolymer is soluble in these solvents.

The film of the present invention can be produced as follows.
The block copolymer and other components are dissolved in a soluble solvent to prepare a cast solution.
Specifically, methylene chloride, chloroform, tetrahydroxyfuran, methyl ethyl ketone, toluene, propylene glycol monomethyl ether acetate, ethyl lactate, o-dichlorobenzene, acetophenone, 1-methyl-2-pyrrolidone, γ-butyllactone, 1-methyl Using naphthalene or a mixture thereof as a solvent, a solution containing a block copolymer is prepared.

A film is formed from the cast solution thus prepared by a casting method. As a film forming method, there is a method in which a cast solution is developed in a container such as a petri dish, and most of the solvent is distilled off and then peeled off from the container to obtain a film-like body. Alternatively, the film can be cast on a glass plate or film using a device such as a blade coater, gravure coater or comma coater having a mechanism such as a blade, an air knife or a reverse roll so that the thickness of the solution becomes uniform. It can also be formed by spin casting.
It is desirable to perform the casting process by the as-cast method because there are few manufacturing processes and it is simple.

Hereinafter, the present embodiment will be described more specifically by way of examples. However, the present embodiment is not limited to only these examples.
(Small angle X-ray scattering measurement)
In the present invention, the degree of orientation of the microphase-separated structure is determined by a Q value that is an index of the degree of orientation obtained by small angle X-ray scattering (SAXS) measurement. If the Q value is greater than 1.5, it is determined that the degree of orientation is high. The measurement was performed as follows in the beam line 08B2 of the large synchrotron radiation facility SPring8. The positional relationship between the sample and X-ray incidence is shown in FIG.
(1) A large number of samples were cut out from a cast film in a 2 mm × 4 mm strip shape, and a laminated film (stack) in which these samples were stacked was prepared. The laminated film was impregnated with silicon oil to prevent total reflection from the film surface.
(2) Point focus X-rays were incident on the laminated film from a direction perpendicular to the film surface and the long axis of the strip. An X-ray wavelength of 0.15 nm was used.

(3) Scattering measurement was performed with a CCD camera with an image intensifier set at a position of a camera length of 6 m.
(4) The background and empty cell scattering correction is applied to the obtained two-dimensional SAXS pattern, and a one-dimensional scattering profile is obtained by taking a fan average in the azimuth angle range of plus or minus 15 degrees for the film surface direction and the film normal direction. Asked. A schematic diagram of this procedure is shown in FIG.
(5) The primary peak intensity of the scattering derived from the microphase separation structure is calculated from the obtained film surface and one-dimensional scattering profile in the film normal direction, and the scattering primary peak intensity in the film surface direction is determined as the film normal direction scattering. The value Q divided by the primary peak intensity was calculated.

(Number average molecular weight (Mn), polydispersity index (Mw / Mn) measurement of molecular weight distribution)
Two columns (TSKgel GMHXL, 35 ° C.) were connected to HLC-8020 manufactured by Tosoh Corporation, and measurement was performed with a GPC apparatus equipped with a UV / RI detector. Tetrahydrofuran was used as the mobile phase. The molecular weight was calculated in terms of polystyrene by creating a calibration curve using polystyrene standard (manufactured by Tosoh Corporation).

(Composition measurement of block copolymer)
The composition of the block copolymer was calculated by H-NMR. The apparatus used was AVANCE400 (BRUKER), and CDC13 was used as the solvent. The number average molecular weight of polystyrene (PS) and polymethyl methacrylate (PMMA) in the block copolymer was calculated from the composition obtained by this measurement and the result of molecular weight measurement by GPC.

[Example 1]
As the block copolymer, polystyrene-polymethacrylic acid diblock copolymer (PS-b-PMMA) was used. The Mn of PS, which is a constituent component of the block copolymer, is 240,000, the Mn of PMMA is 1.14 million, the Mn of the block copolymer is 1.38 million, and the Mw / Mn is 1.34.
This block copolymer was dissolved in 1-methylnaphthalene using a shaker to obtain a cast solution having a solid content of 3% by weight.
The cast solution thus obtained was dropped onto a watch glass, and when it was dried, dripping was repeated three times to obtain a film having a thickness of 163 μm. Casting was performed at room temperature. The membrane was dried at room temperature and atmospheric pressure for 2 days, and then dried in vacuum at room temperature for 3 hours.
This sample was subjected to SAXS measurement at the beam line 08B2 of the large synchrotron radiation facility SPring8.
Table 1 shows the Q value calculated from the two-dimensional scattering pattern thus obtained. The Q value is greater than 1.5, and the microphase separation structure is oriented perpendicular to the film surface.

[Example 2]
Table 1 shows the Q value obtained for Example 1 in which the solvent was changed to acetophenone. The film thickness obtained was 127 μm.

[Example 3]
Table 1 shows the Q values obtained for Example 1 in which the solvent was changed to MEK. The film thickness of the obtained film was 81 μm.

[Example 4]
Table 1 shows the Q value obtained for Example 1 in which the solvent was changed to THF. The film thickness of the obtained film was 131 μm.

[Example 5]
Table 1 shows the Q values obtained for Example 1 in which the solvent was changed to chloroform. The film thickness of the obtained film was 99 μm.

[Example 6]
In Example 3, the block copolymer has a Mn of PS of 500,000, a Mn of PMMA of 15.4 million, a Mn of the block copolymer of 2.04 million, and a polydispersity index (Mw / Mn) of the molecular weight distribution of 1.4. Table 1 shows the Q values obtained for some PS-b-PMMA. The film thickness of the obtained film was 91 μm.

[Example 7]
Table 1 shows the Q values obtained in Example 6 in which the solvent was changed to chloroform. The film thickness of the obtained film was 120 μm.

[Example 8]
Table 1 shows the Q value of the block copolymer film obtained by adding 23% by weight of homopolystyrene having an Mn of 240,000 to 100% by weight of the block copolymer in Example 3. The film thickness of the obtained film was 95 μm.

[Example 9]
Table 1 shows the Q values obtained in Example 8 in which the solvent was changed to THF. The film thickness of the obtained film was 101 μm.

[Example 10]
Table 1 shows the Q values obtained in Example 8 in which the solvent was changed to chloroform. The film thickness of the obtained film was 113 μm.

[Example 11]
Table 1 shows the Q value of Example 1 in which the solvent was changed to 1-methyl-2-pyrrolidone (NMP) and the casting method was changed to spin casting. Spin casting was performed as follows. First, the block copolymer was dissolved in a solvent to prepare a 5 wt% solution. This was spin-cast on a 6-inch diameter silicon substrate. The spin coater was 1M-360S manufactured by Mikasa Co., Ltd., and the above solution was spin coated at 500 rpm for 30 seconds. Next, the substrate was dried on a hot plate at 100 ° C. for 10 minutes, and after cooling, spin coating and drying were performed under the same conditions. Repeated 4 times. The obtained film was vacuum dried at 50 ° C. for 16 hours together with the substrate. The film thickness was 10 μm.

[Comparative Example 1]
In Example 1, the block copolymer has a Mn of PS of 60,000, a Mn of PMMA of 190,000, a Mn of the block copolymer of 250,000, and a polydispersity index (Mw / Mn) of molecular weight distribution of 1.48. Table 1 shows the Q values of those obtained by changing to some PS-b-PMMA and further changing the solvent to THF. The film thickness of the obtained film was 121 μm. The Q value is smaller than 1, indicating that the microphase separation structure is oriented parallel to the film surface.

[Comparative Example 2]
Table 1 shows the Q value of Comparative Example 1 except that the solvent was changed to chloroform. The film thickness of the obtained film was 105 μm.

[Comparative Example 3]
PS-b-PMMA with PS Mn of 30,000, PMMA Mn of 120,000, block copolymer Mn of 150,000 and molecular weight distribution polydispersity index (Mw / Mn) of 1.31 is dissolved in THF. A 5 wt% solution was prepared. Thereafter, this solution was developed on a glass petri dish, and THF was evaporated at room temperature to obtain an as-cast film. The film thickness of the obtained film was 25 μm. The Q value of this film is shown in Table 1.

[Comparative Example 4]
The volume fraction of PS is 0.16, Mn is 66,000, the polydispersity index (Mw / Mn) of the molecular weight distribution is 1.03, and the mole fraction of butylene chains in the polyethylene butylene chain is 0.41. Polystyrene-polyethylene butylene-polystyrene triblock copolymer (SEBS) (Tuftec (registered trademark) H1062 manufactured by Asahi Kasei Chemicals Co., Ltd.) is dissolved in a mixed solvent of heptane and methylene chloride in a volume ratio of 1: 1, and a 5 wt% solution Got. This cast solution was put in a petri dish and the solvent was evaporated at 23 ° C. to prepare a block copolymer film (as cast film). The film thickness of the obtained film was 300 μm.

  As a result of Table 1, in all of Examples 1 to 11, the Q value is 1.5 or more, and the microphase separation structure is oriented perpendicular to the film surface, whereas in the comparative example, the Q value is 1 It can be seen that the vertical alignment is not more than 1.

  According to the present invention, a microphase separation structure oriented in a direction perpendicular to the film surface can be manufactured very simply. According to the present invention, high-functional material design in a wide range of fields is possible. Examples of such highly functional materials include patterned media such as optical recording media and magnetic recording media, photoelectric conversion elements such as solar cells and optical switches, optical modulation elements, optical functional films such as optical phase difference films, and polarization films, Examples of the light emitting element such as a laser oscillation element, a display material, an organic FET element, an electrolyte film, a nanoreaction field film, a thermoelectric conversion element, a printing screen, a resist agent, a precision filter, a catalyst, and a fine mold. Furthermore, as a use of the nanoporous material obtained by decomposing or dissolving at least one component of the as-cast membrane in the present invention, a catalyst carrier, a nano stamp, a nanoporous hollow fiber, an adsorbent, a separation membrane such as a precision filter, Examples include molds and nano templates.

FIG. 1 shows the positional relationship between the sample and X-ray incidence in the SAXS measurement of the example. FIG. 2 shows a schematic diagram of a method for obtaining a one-dimensional scattering profile in the film surface direction and the film normal direction from a two-dimensional scattering pattern obtained by SAXS measurement.

Claims (6)

A structure comprising a block copolymer having a number average molecular weight of 500,000 to 2.5 million, a film thickness of 5 μm to 1000 μm, and a microphase separation structure by the block copolymer oriented in a direction perpendicular to the film surface. A block copolymer film. The block copolymer is at least one selected from styrene, α-methylstyrene, vinylpyridine, methyl methacrylate, tert-butyl methacrylate, ethylene, propylene, isoprene, butadiene, isobutane and butane as a monomer for forming block polymerization. The block copolymer film according to claim 1 containing two. The block copolymer film according to claim 2, wherein the block copolymer contains styrene and methyl methacrylate as monomers forming the block polymerization. The block copolymer film according to any one of claims 1 to 3, comprising 10 to 99.99% by weight of a block copolymer. The block copolymer is methylene chloride, chloroform, tetrahydroxyfuran, methyl ethyl ketone, toluene, propylene glycol monomethyl ether acetate, ethyl lactate, o-dichlorobenzene, acetophenone, 1-methyl-2-pyrrolidone, γ-butyllactone, 1- The block copolymer film according to any one of claims 1 to 4, which is soluble in methylnaphthalene or a mixture thereof. The block copolymer film according to claim 1, wherein a Q value that is an index of the degree of orientation is 1.5 or more.

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