JP2002145971A - Nano structural functional material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise two- and three-dimensional structural functions of a surface grafted polymer to a higher level. SOLUTION: This nano structure functional material is obtained by converting a chemical composition of a graft polymer chain constituting a graft polymer layer arranged on the substrate surface by graft polymerization in the film thickness direction into a multilayered structure with a copolymer with a monomer or an oligomer of a different kind.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The invention of this application relates to a nanostructure functional body. More specifically, the invention of this application relates to a novel nanostructured functional body having a surface polymer film controlled on a nanoscale, which is useful as an external stimulus-responsive composite particle, a multifunctional sensor, or the like.

[0002]

2. Description of the Related Art Surfaces and interfaces play an extremely important role in expressing the functions of substances, and it is undeniable that precise control of the structure leads to higher functions. For example, in a biological system with high efficiency and high selectivity, a sophisticated membrane structure in which functional groups are effectively arranged and oriented in a three-dimensional space in the membrane and on the membrane surface expresses its functions. Various attempts have been made to achieve this. However, at present, sufficient control of the structure cannot be achieved in the artificial membrane. Unlike the surface of an inorganic or metal material, the surface of an organic material such as a polymer film forms a wide interface layer ranging from several nm to several hundred nm. For this reason, control of the structure not only in the film surface direction but also in the film thickness direction at the nanoscale is indispensable for achieving high functions.

For example, surface graft polymerization is widely performed because it is possible to form a graft layer on the order of nm to μm, and various surface properties can be imparted by changing the type of monomer to be polymerized. This is one of the surface modification methods. In particular, when a polymerization initiating group introduced on the surface of a material is used, grafting at a high density can be expected. However, in this surface graft polymerization, it has been conventionally difficult to control the molecular weight, molecular weight distribution, and graft density (graft chain surface density) of the graft chain, which are deeply related to the surface characteristics.

[0004] Under such circumstances, the inventors of the present application quickly found the possibility of application to surface graft polymerization due to the simplicity and theoretical simplicity of living radical polymerization. The study has begun. Living radical polymerization is a polymerization method that has recently attracted worldwide attention as a method for easily synthesizing a polymer having a narrow molecular weight distribution and a clear structure by radical polymerization. This is because it has advantages such as simplicity, which are not found in other living polymerization systems. By applying this polymerization method, the present inventors succeeded in grafting a polymer chain having a controlled chain length and chain length distribution at a higher density than ever before, and furthermore, by steric repulsion between adjacent graft chains, The graft chains were almost fully extended, revealing that they formed literally polymer brushes. As a result, this method is expected as a new surface modification method capable of producing an ultrathin film having high anisotropy and excellent uniformity.

[0005] The above-mentioned findings are epoch-making which have not been known so far, and make it possible to develop a new technology of a nano-polymer structure. Based on technology, the structure is controlled on a nano-scale in two-dimensional (film direction) or three-dimensional (film thickness direction), and it is thermally and mechanically stable and has excellent uniformity. It has been a problem to be able to form a thin film, thereby enabling application as, for example, composite particles or composite elements responsive to external stimuli, multifunctional centers, and the like.

[0006]

Means for Solving the Problems The present invention solves the above-mentioned problems. First, a graft polymer chain constituting a graft polymer layer disposed on the surface of a substrate by graft polymerization is formed of another kind. The present invention provides a nanostructure functional body characterized in that a chemical composition has a multilayered structure in a film thickness direction by copolymerization with a monomer or an oligomer, and secondly, a chemical composition having a gradient structure. A feature of the nanostructure functional body is provided. Thirdly, in the above invention, in the graft polymer layer disposed on the substrate surface by the graft polymerization, the polymerization initiation portion of the graft polymer chain constituting the same is inactivated in a predetermined pattern in the film surface direction. Fourth, the present invention provides a nanostructure functional body characterized in that the graft polymer chain to be inactivated has a pattern in the film surface direction such that the graft density is different in the film thickness direction in advance. To provide a nanostructured functional body characterized in that:

Fifth, the invention of this application is based on the fact that the graft polymer chain constituting the graft polymer layer disposed on the surface of the substrate by graft polymerization has a functional group formed by modifying or chemically modifying the reactive group of the side chain. Is provided.

Further, the invention of the present application is directed to a sixth aspect of the present invention, in which after a polymerization initiation portion of a molecule disposed on the surface of a substrate is deactivated in a predetermined pattern in a film surface direction, the polymerization is not deactivated. The nanostructured functional body is provided in which the start portion is graft-polymerized and the graft polymer layer is disposed in a predetermined pattern. Seventh, the graft polymerization has a different graft density in the film thickness direction. Provided is a nanostructure functional body characterized by being controlled as a film surface direction pattern.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The invention of this application has the features as described above, and embodiments thereof will be described below.

[0010] In any of the first to fifth inventions of this application, a nanostructure having a graft polymer layer disposed on the surface of a substrate by graft polymerization is premised. For this nanostructure, a surface graft polymerization method by living radical polymerization, which has been technically established by the inventors, is employed. By this method, it is possible to grow a polymer chain having a regulated length and length distribution on a substrate surface with an unprecedentedly high surface density.Because of its high graft density, it can be expanded by swelling with a solvent. The film thickness is comparable to the length of the cut chain, and the true “polymer brush” state is realized for the first time. The control of the chain length and the chain length distribution and the control of the graft density are illustratively described as follows. <Control of chain length and chain length distribution> The initiator 1 or 2 of the following formula is immobilized on the surface of, for example, a silicon substrate or silica fine particles (average particle size of about 12 nm) by a Langmuir-Blodgett (LB) method or a chemisorption method. For example, a substrate surface having the following CTS partial structure is formed.

[0011]

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[0012]

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Next, the surface of the substrate is placed in a solvent,
For example, in the presence of TsCl or the like, copper halide (Cu
Let ¹ X / ligand (L) atom transfer radical polymerization, such as methyl methacrylate (MMA) or styrene (St) with a complex (ATRP). The ATRP method is one of the living radical polymerization methods, and the polymer terminal halogen (P-
A monomer is added to a growing radical (P) reversibly generated by the extraction of X) by the Cu ¹ X / L complex to proceed, and the molecular weight distribution is regulated by a sufficient frequency of reversible activation and inactivation. Is done.

Here, the free (unfixed) T
Addition of a polymerization initiator such as sCl is important for precisely controlling the graft polymerization.

When MMA was graft-polymerized with initiator 1 immobilized on the surface of a silicon substrate or silica fine particles in the presence of a free initiator, the number average molecular weight _Mn of the free polymer maintained a narrow molecular weight distribution. As it is, it increases in proportion to the polymerization rate. FIG. 1 shows the relationship between the graft amount and the _Mn of the free polymer determined by ellipsometry and infrared absorption spectroscopy. Even if the graft polymerization rate is changed (● and ● in the figure), the graft amount increases in proportion to _Mn . this is,
The activation frequencies are comparable at the graft chain ends and the free polymer ends, suggesting that both have approximately equal molecular weights. To directly confirm this, the H
The graft chain was cut out by the F hydrolysis treatment and its molecular weight and molecular weight distribution were measured. As shown in FIG. 2, the graft chain had a narrow molecular weight distribution (M _w / M _n <1.
In addition to having 3), its _Mn is approximately equal to the value of the free polymer, revealing that the free polymer is a good indicator of the graft chains, as expected. Therefore, the horizontal axis in FIG. 1 can be read as _Mn of the graft chain. That is, the graft amount is determined by the M of the graft chain.
_It can be concluded that it increases in proportion to _n . This means that the graft polymerization is proceeding while keeping the graft density constant, that is, the graft polymerization is regulated and proceeds in a living manner. By the inclination of the straight line in FIG.
The graft density is estimated to be approximately 0.4 chains / nm ² . This value is an extremely high graft density which is only about three times the monomer cross-sectional area in terms of the occupied area per graft chain. In the conventional radical polymerization based on surface initiation, once generated radicals grow until they stop irreversibly, and successively form graft chains. Therefore, steric hindrance of the previously grown graft chains hinders grafting in the vicinity thereof. On the other hand, in this system, polymerization proceeds in a living manner, that is, all graft chains grow almost evenly, so that steric hindrance between adjacent graft chains was reduced, and a high graft density was obtained. It is considered a factor. <Control of Graft Density> As described above, high-density grafting is realized by living radical polymerization, but control of the graft density, for example, reduction in density, is also possible.

For example, it can be considered as the photodegradability of the polymerization initiating group. In practice, for example, the substrate on which the above-mentioned initiator 1 is immobilized is irradiated with ultraviolet rays, the surface density (σ _i ) of the initiator is determined by high-sensitivity reflection infrared spectroscopy, and then the grafting of MMA on this substrate is performed. When the polymerization is performed and the graft density (σ) is estimated from the graft amount, FIG.
From the figure showing the dependence of σ _i and σ on the dose (time), σ _i monotonically decreases with increasing dose, whereas σ is initially approximately constant and σ _i is approximately It can be seen that it begins to decrease after becoming equal. In other words, it indicates that there is a threshold value for σ, and it cannot be increased any more. Assuming that PMMA grows from all starting groups in the unirradiated sample, its density is PMMA
This value is much larger than the density of pulp.
The threshold value of σ is considered to be the maximum value of the graft density that can be achieved due to steric hindrance between adjacent graft chains and the like. Below this threshold value, the starting efficiency σ / σ _i = 1, ie, ATRP
It is believed that the high initiation efficiency characteristic of the polymerization system is achieved. As described above, although the threshold value exists in the graft density, the graft density can be controlled by the irradiation amount. <Structure and physical properties of high-density polymer brush layer> The graft chain, in which one end of the polymer is immobilized on the solid surface, becomes higher than the substrate surface due to the interaction (steric repulsion) between adjacent graft chains as the graft density increases. To take the conformation stretched in the vertical direction to form a so-called polymer brush layer. The degree of stretching strongly depends on the graft density,
It greatly affects the physical properties of the brush surface. As mentioned above, the polymer graft (brush) surface prepared by living radical surface graft polymerization has an unprecedentedly high graft density, so it is not possible to clarify its structure and physical properties from the viewpoint of surface design. is important. According to the force measurement in liquid by an atomic force microscope (AFM) (FIG. 4),
It can be seen that the structure and interaction between the surfaces of this high-density polymer brush are characteristic.

FIG. 5 shows an example of a force curve (distance dependence of inter-surface force) when a PMMA brush layer is compressed with a diameter of 10 μm in a toluene (good solvent) and fixed to the tip of a cantilever. It is a thing.
Force (repulsive force) due to steric repulsion of the swollen PMMA graft chains is observed, and increases sharply with compression. Here, L _e is the distance begins to be observed steric repulsion, corresponds to the equilibrium swelled film thickness brush layer. Steric repulsion, dry film thickness (L _d) of the brush layer than has risen sharply in the large distance (D _o) much, in the cantilever used can not be compressed further. Usually AF
Distance obtained by force measurement by M, rather than the distance (D) from the substrate surface, the film thickness can not be compressed samples more, i.e., a relative distance from D _o, the maximum which force measurement by AFM Was a drawback. On the other hand, the inventor has succeeded in actually measuring D _o by observing an AFM image of the boundary region only by scratching the polymer brush layer and accurately estimating D.

The equilibrium swollen film thickness _{L e} increases as the increase of _{M n} and sigma. FIG. 6 shows P swollen in toluene.
MMA brush _{L e} and weight average Nobikiri (all-t
(r conform) chain length (L _ew ) is plotted on a double logarithmic scale against the graft density. The results of the “semidilute” polymer brush which has been conventionally studied are also shown by hollow symbols. In order to compare the results of polymer brushes with different types of polymer chains (chain cross-sectional areas), the graft density uses a dimensionless value σ ^* converted per cross-sectional area of a monomer unit. It can be seen that the graft density (in the figure, ● and black square) of the polymer brush covers an area much higher than the conventional one. In the material with the highest graft density, _Le
Was found to reach about 90% of the extended chain length.
Also, as shown in FIG. 6, it is worth noting that the results of the polymer brushes having different types, chain lengths, and graft densities of the polymers draw one curve (master curve).

It can be seen that the characteristic of the high-density polymer brush is a strong repulsion (resistance) force against compression. This is _Do
It can be evaluated by the / _Le ratio (an index of how much the brush layer can be compressed compared to the time of equilibrium swelling). As shown in FIG. 7, _Do / L as M _n and σ increase.
_It can be seen that the _e ratio increases and the brush layer is less likely to be compressed. In a large article M _n and sigma, 20 to 30% of the swollen film thickness, can only compressed to about three times the _{L d.}
This large steric repulsion is expected to provide high dispersion stability when grafted to the surface of colloid particles.

In the invention of this application, for example, the graft polymer layer disposed on the substrate surface by the characteristic graft polymerization as exemplified above is used. In this case, the present invention is not limited to the above example. An initiator that enables graft polymerization by surface-initiated living polymerization and a monomer that constitutes the graft polymer are appropriately selected. The same applies to the substrate. For example, the monomer is not limited to MMA,
Similarly, various kinds of unsaturated vinyl monomers such as styrene, acrylonitrile, and acrylate may be selected.

In the first invention of the present application, a three-dimensional (thickness direction) functional enhancement is realized by using a different kind of a graft polymer chain constituting the above graft polymer layer. That is, it is characterized in that a monomer different from the monomer forming the polymer chain or an oligomer thereof is block-copolymerized to form a multilayered chemical composition in the film thickness direction.

In the graft polymer layer as described above, since grafting at an extremely high density is possible, in a brush formed by block copolymerization, the end blocks are unevenly distributed near the surface of the brush layer, and the length is long. Even with a short block, the performance of the brush layer surface can be effectively changed.

The multi-layer structure formation of the chemical composition by the block copolymerization is performed, for example, by using a silicon substrate on which the initiator 1 is immobilized, using MMA, and then 4-vinyl.
The structure obtained by carrying out the sequential ATRP polymerization of lpyridine (4VP) by chemical formula is as follows.

[0024]

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The block copolymerization reaction in this reaction can be carried out, for example, in the presence of free PMMA-Cl and a reaction with a PMMA brush body under the following conditions, for example, at 0 ° C. for 0.5 hour. .

[0026]

[Table 1]

The results of UV-visible absorption spectrum measurement of the graft layer and GPC analysis of the free polymer are shown in FIGS. 8 and 9. Precursor PMMA brush (M _n = 57
000) at the end of the P4VP block (M _n = 3000)
It was found that a high density block copolymer brush introduced with high block efficiency was formed. As a result of evaluating the surface characteristics in a good solvent and when dried by AFM force measurement and contact angle measurement, respectively, it was found that the P4VP block had a very short length compared to the PMMA block, but the graft layer surface was as expected. Was effectively covered with the P4VP block.

The multilayer structure of this PMMP-P4VP has a graft density of 0.1 chains / nm.
It has been confirmed that it is feasible with ^two or more, and difficult with less than 0.1. 8 and 9 have a graft density of 0.7.

It is needless to say that the monomer for blocking is not limited to 4-VP in the multilayer structure of the chemical composition by block copolymerization. For example, any radical polymerizable monomer such as styrene and acrylonitrile as various vinyl monomers may be used. In addition to the two-layer structure of the chemical composition obtained by the block copolymerization of the PMMA brush and 4-VP, the monomer having a chemical composition of three or more layers is obtained by further block copolymerizing a different monomer with 4-VP. Will be realized.

Then, as in the second invention of this application,
By performing random copolymerization while sequentially changing the composition, it becomes possible to introduce a gradient structure of the chemical composition in the film thickness direction. For example, a combination of MMA and St (styrene), St (styrene) and AN (acrylonitrile), or the like is used.

Further, in this application, as in the fifth invention, the graft polymer chain constituting the graft polymer layer disposed on the surface of the substrate by graft polymerization as a nanostructured functional body has the reactivity of the side chain. Also provided are those into which functional groups have been introduced by group modification or chemical modification.

The inventors have already made it possible to form a graft polymer layer using an MMA derivative monomer having a sugar chain in the side chain, but without being limited to such a sugar chain, for example, The purpose is to have a reactive side chain such as an epoxy group in the graft polymer chain and to introduce various functional groups into this reactive side group.

For example, various functional groups can be introduced on the surface on which GMA: glycidyl methacrylate is graft-polymerized by utilizing the high reactivity of the side chain epoxy group.
For example, a GMA-grafted substrate is treated with sodium sulfite /
Isopropyl alcohol / water (10/15/75 by
(Wright) The polymer electrolyte brush can be constructed by immersing in a solution and performing a sulfonation reaction. The reaction is schematically shown as follows.

[0034]

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As a result of the infrared absorption spectrum measurement shown before (a) and after (b) sulfonation in FIG. 10, the disappearance of the epoxy group and the formation of the sodium salt type sulfonic acid group,
It is also confirmed that almost no side reactions such as elimination or decomposition of the graft chain occurred during the sulfonation reaction. For example, as shown in the results of the AFM force measurement in FIG. 11, the regulated polymer electrolyte brush having such a structure not only stabilizes the colloidal dispersion system but also models the interaction on the cell surface and the drug delivery. Attention as a system.

In FIG. 11, NaC of pH = 5.9 was used.
1 shows a force curve in a forward mode of a p (3MA-SA) brush measured in an aqueous solution. Under the measurement conditions, the p (GMA-SA) brush layer is negatively charged due to dissociation of the sulfonic acid group, and the surface of the silica particles is also negatively charged.
Repulsion has been observed. The distance at which repulsion is observed is NaC
1 decreased with increasing concentration. This is thought to be because the electrostatic interaction is more effectively shielded by the increase in the salt concentration.

Further, in this application, as in the third to fourth and sixth and seventh aspects of the present invention, there is provided a nanostructure function body in which the structure in the film surface direction is controlled by patterning.

That is, in the graft polymer layer disposed on the substrate surface by the graft polymerization, the polymerization initiation portion of the graft polymer chain constituting the graft polymer layer is inactivated in a predetermined pattern in the film surface direction. The graft polymer chain to be inactivated,
A nanostructured functional body characterized in that it has a pattern in the film surface direction so as to have a different graft density in the film thickness direction in advance.

Further, after the polymerization initiation portion of the molecules disposed on the substrate surface is deactivated in a predetermined pattern in the film surface direction, the non-inactivation polymerization initiation portion is graft-polymerized to form a graft polymer. A nanostructured functional body characterized in that the layers are arranged in a predetermined pattern, wherein the graft polymerization is controlled as a pattern in the film surface direction so as to have different graft densities in the film thickness direction. It is a nanostructure functional body.

For example, a fine image of a polymer ultrathin film can be formed by patterning (inactivation of the initiator by exposure) onto the polymerization initiator fixed on the substrate surface and graft polymerization (phenomenon). Since the initiator monomolecular film is irradiated with light (exposure to an ultra-thin film), high resolution of the pattern is expected. As a patterning technique, not only light irradiation, but also ion beam or electron beam irradiation, and the use of a scanning probe microscope, a nano-scale image can be formed.

The film is uniform and has a thickness (several nm to several hundreds).
nm) is easy to control. If necessary, a gradient structure can be introduced into the film thickness, for example, by gradient exposure.

FIGS. 12 and 13 show the patterned PMMA graft polymerization by UV irradiation, and FIG. 13 is an optical micrograph after the graft polymerization. This is an example in which a photomask (grid for electron microscope) is used.

FIGS. 14 and 15 show controlled graft polymerization by electron beam lithography and AFM images of the graft surface.

[0044]

As described in detail above, according to the invention of this application, in addition to controlling the chain length, chain length distribution, and graft density of the graft chain, various copolymerizations such as surface patterning, random block, composition gradient type, etc. More precise surface design is possible by expanding the system and introducing functional groups by (co) polymerization of functional monomers and post-treatment. The technology for controlling the two-dimensional and three-dimensional structures in the film surface direction and the film thickness direction on a nano-scale is based on the design of immobilization initiators and immobilization methods (light irradiation, plasma treatment, chemical treatment, etc.) Various materials (metals,
Inorganic and organic materials), it is useful as a new surface design technique for the development of new functional materials, such as high-performance nanostructure blocking, which has never existed before.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a relationship between a graft amount and _Mn of a free polymer.

FIG. 2 is a diagram illustrating the molecular weight and molecular weight distribution of a graft polymer and a free polymer.

FIG. 3 is a diagram exemplifying a relationship between UV irradiation time, surface density (σ _i ) of an initiating group, and graft density (σ).

FIG. 4 is a schematic diagram showing a measurement of a force in liquid by AFM.

FIG. 5 is a diagram illustrating an example of an AFM force curve.

FIG. 6 is a diagram illustrating the ratio between the equilibrium swollen film thickness and the weight-average extended chain length of a PMMA brush, plotted on a logarithmic scale with respect to the graft density.

The 7 _D o / _{L e,} is a diagram illustrating a relationship between _{M n} and sigma.

FIG. 8 is a diagram exemplifying a UV spectrum of a two-layer structure of PMMA-P4VP.

FIG. 9: GPC before and after the two-layer structure of PMMA-P4VP
It is the figure which illustrated the curve.

FIG. 10 is a diagram illustrating IR spectra before and after sulfonation.

FIG. 11 is a diagram exemplifying a result of AFM force measurement after sulfonation.

FIG. 12 is a schematic diagram showing patterning by UV irradiation and controlled graft polymerization.

FIG. 13 is an optical micrograph illustrating the result of the method of FIG.

FIG. 14 is a schematic diagram showing patterning by electron beam writing and controlled graft polymerization.

FIG. 15 is an AFM image illustrating the result of the method of FIG. 14;

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J026 AA17 AA45 AC00 AC15 BA05 BA27 BA31 BA40 CA07 CA09 DA05 DA20 DB40 EA08 FA05 FA08 GA01 GA02 HA11 HA35 HA39 HA42 HB17 HB35 HB39 HB42 HE01

Claims (7)

[Claims] The present invention is characterized in that a graft polymer chain constituting a graft polymer layer disposed on the surface of a substrate by graft polymerization has a multi-layered chemical composition in a film thickness direction by copolymerization with another kind of monomer or oligomer. The nanostructure functional body. 2. The nanostructure functional body according to claim 1, wherein the chemical composition has a gradient structure. 3. A graft polymer layer disposed on a substrate surface by graft polymerization, wherein a polymerization initiation portion of a graft polymer chain constituting the graft polymer layer is inactivated in a predetermined pattern in a film surface direction. The nanostructured functional body according to claim 1 or 2, wherein: 4. The graft polymer chain to be inactivated has a pattern in a film surface direction such that the graft density differs in a film thickness direction in advance.
Nanostructured functional body. 5. A nano-particle characterized in that a functional group is introduced into a graft polymer chain constituting a graft polymer layer disposed on the surface of a substrate by graft polymerization, by modification or chemical modification of a reactive group in a side chain thereof. Structural function body. 6. The polymerization initiator of molecules disposed on the surface of the substrate is inactivated in a predetermined pattern in the direction of the film surface, and then the uninactivated polymerization initiator is graft-polymerized to form a graft polymer layer. Are arranged in a predetermined pattern. 7. The nanostructured functional body according to claim 6, wherein the graft polymerization is controlled as a pattern in a film surface direction so as to have a different graft density in a film thickness direction.