JPH07216244A - Polymer gel and its production - Google Patents

Abstract

PURPOSE:To obtain a polymer gel having asymmetric change to external stimulation irrespective of the kind and the shape of a polymer constituting a polymer gel and the kind of a solvent. CONSTITUTION:The polymer gel comprises a three-dimensional cross-linked polymer and a solvent. The three-dimensional cross-linked polymer has low cross-linked point density parts and high cross-linked point density parts and the high cross-linked point density parts have a given shape. The main chain of the polymer is cross-linked to form the solvent-insoluble low cross-linked point density parts, which are irradiated with an active light rays, the high cross-linked point density parts are formed in a given shape to give the three- dimensional cross-linked polymer, which is swollen in a solvent to provide a method for producing the polymer gel.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to polymer gels.
More specifically, the present invention relates to a polymer gel that can be used as a chemo-mechanical material used for artificial muscles and the like, a drug delivery system (DDS), a recording material and the like.

[0002]

2. Description of the Related Art A polymer gel consisting of a crosslinked product obtained by crosslinking a polymer main chain into a three-dimensional network structure and a solvent is exposed to external stimuli such as temperature change, solvent exchange and pH change. , And is known to cause a swelling or contraction volume change in response to these stimuli. Utilizing the response of polymer gel to such external stimuli, the actuator,
Applications in a wide range of fields such as DDS and chemical valves are being researched. In these applications, the strength and strength of the polymer gel are important as well as the rate and amount of change that the polymer gel exhibits in response to external stimuli. is there. Of these required characteristics,
Regarding the rate of change, for example, when the gel is spherical, its diameter is improved, and when it is fibrous, the diameter of the fiber is reduced, and the size of the gel is improved. It is possible to shorten the time required for the volume change of the polymer gel to several tens of millimeters / second, which is equivalent to the response time of the muscle to external stimuli. Further, as a means for increasing the amount of change, it has been proposed to impart anisotropy to the shape of the gel. For example, by making the shape of the polymer gel fibrous, it is possible to increase the absolute change amount in the fiber axis direction when the gel undergoes a volume change. In addition, the fiber is stretched (Makoto Suzuki, Kobunshi Shinbun, Vol. 46, pp. 603-611, 1989), and liquid crystal polymer is used as the main chain polymer (Ryoichi Kishi et al., POLYMER PRE.
PRINTS, JAPAN Vol. 40, p. 4135, 1
(991) and other measures for improving strength have also been proposed. However, the gels obtained by these methods are isotropic in their changes to external stimuli macroscopically,
Therefore, it is still insufficient to be applied to the practical use as described above.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polymer gel which is anisotropically changed by an external stimulus irrespective of the kind, shape and solvent of the polymer constituting the polymer gel. It is to be.

[0004]

Thus, according to the present invention, there is provided a polymer gel comprising a three-dimensional cross-linked polymer and a solvent, wherein the three-dimensional cross-linked polymer comprises a low cross-linking point density portion and a high cross-linking point density portion. And a high cross-linking point density portion having a predetermined shape. Further, the main chain of the polymer is cross-linked to form a solvent-insoluble low cross-linking point density portion, and then the actinic ray is irradiated to form the high cross-linking point density portion into a predetermined shape to obtain a three-dimensional cross-linked polymer. There is provided a method for producing a polymer gel, which comprises swelling a crosslinked polymer in a solvent.

The three-dimensional crosslinked polymer used in the present invention has a low crosslinking point density portion and a high crosslinking point density portion. The crosslinking point density in the present invention refers to the number of crosslinking points per unit volume of the polymer gel. The three-dimensional crosslinked polymer used in the present invention is one in which the main chains of the polymer are crosslinked with each other. Here, the cross-link is a covalent bond, an ionic bond,
It may be by any of chemical cross-linking such as van der Waals bond or physical method such as partially crystallizing, but the bond cannot be broken due to response to external stimuli such as swelling-contraction. is necessary. Such a three-dimensional crosslinked polymer can be obtained by crosslinking the main chain of the polymer to form a solvent-insoluble low-crosslinking point density portion, and then irradiating with actinic rays to form the high-crosslinking point density portion into a predetermined shape.

The polymer is not particularly limited as long as it is swellable with a solvent, and vinyl alcohol and its derivatives; homopolymers and copolymers of monomers selected from acrylic acid, acrylamide, vinyl methyl ether and the like. And derivatives thereof can be exemplified. These polymers may be used alone or in combination of two or more. Among these polymers, polyvinyl alcohol,
Polyacrylamide and derivatives thereof are preferable from the viewpoint of easy formation of crosslinks.

Examples of the method for crosslinking the main chain of the polymer include the conventionally known methods for crosslinking the water-soluble polymer. For example, in the case of polyvinyl alcohol, a method of gelling with a sulfate or chromate, a method of gelling by freeze-drying; a method of gelling by hydrolysis in the case of starch-acrylonitrile graft copolymer, a case of polyacrylamide Is a method of cross-linking using methylenebisacrylamide; in the case of polyacrylic acid, a method of cross-linking with spirobenzopyran, and other methods applicable to general polymers. By such cross-linking, a solvent-insoluble low cross-linking point density portion can be formed in the polymer.

Then, the polymer in which the solvent-insoluble low-crosslinking point density portion has been formed is irradiated with actinic rays to form the high-crosslinking point density portion in a predetermined shape. The actinic ray in the present invention is an electron beam or light, preferably an electron beam. When irradiating an actinic ray to form a high cross-linking point density portion, it is preferable to irradiate the actinic ray after coating and impregnating a polymer with a photosensitive cross-linking agent that is activated by irradiating the actinic ray. Examples of the photosensitive crosslinking agent include dichromates such as potassium dichromate, sodium dichromate and ammonium dichromate; chromates such as potassium chromate, sodium chromate and ammonium chromate; tetrabi ( Examples thereof include diazo compounds such as bisdiazo) nium salts. When such a photosensitive cross-linking agent is used in the step of forming the low cross-linking point density portion in the polymer, it may not be used again. The intensity of the actinic ray, the irradiation time, etc. differ depending on the type of polymer, the predetermined shape, etc., and are accordingly set.

By the above operation, the high cross-linking point density portion can be formed into a predetermined shape. The predetermined shape here depends on the application of the polymer gel and the like. For example, as will be described later, when used as an information recording medium, the high cross-linking point density portion is formed in a shape such as a character or a symbol which is an object of information. Further, in order to give strength to the fibrous gel, the high cross-linking point density portion and the low cross-linking point density portion are alternately provided in a disk shape in the radial direction.

The three-dimensional crosslinked polymer of the present invention is obtained by molding the polymer into a desired shape such as a film, fiber, column, rod or sphere, and then uniformly crosslinking the entire polymer main chain. It can be obtained by a method in which only desired sites are additionally cross-linked, a method in which each site of the polymer main chain is sequentially cross-linked so as to have a desired cross-linking point density, etc., but is not limited to these methods.

In the present invention, in order to sufficiently manifest the anisotropy of change due to external stimulus, the difference in volume change rate between the portions of the polymer gel having different cross-linking point densities is relatively 0.0.
It is preferably 1 or more. More preferably, the difference is 0.1-5. Here, the volume change rate means the ratio of the volume change caused by the polymer gel to an external stimulus to the volume before the change.

The polymer gel of the present invention can be obtained by swelling the three-dimensional crosslinked polymer obtained by the above operation in a solvent. As the solvent used in the present invention, a polar solvent such as water, alcohol or acetone; a non-polar solvent such as toluene or hexane may be appropriately selected according to the type of polymer used. When a water-soluble polymer such as polyvinyl alcohol or polyacrylamide is used as the polymer, water, methanol, acetone or the like is used, and when a water-insoluble polymer such as styrene-maleic anhydride copolymer or polystyrene is used. Examples include dimethylformamide.

[0013]

The polymer gel of the present invention thus obtained has the anisotropy of change in that the response behavior to external stimuli differs depending on the site. For example, when a site having a cross-linking density higher than other sites is formed in a flat polymer gel in the shape of letters or figures, the volume change rates of both sites are different, and thus the polymer gel was swollen with a solvent. At times, it becomes possible to develop characters and figures that did not appear when dried or shrunk, so that it can be expected to be applied as an information recording medium. Further, for the fibrous gel, by alternately providing a portion having a high density of cross-linking points and a portion having a low density in a disc shape in the radial direction, the swelling in the radial direction is suppressed, and the swelling is performed only in the axial direction. It is possible to prevent the strength of the gel from decreasing. In the case of a columnar polymer gel, the strength of the polymer gel can be increased by increasing the density of cross-linking points in the portion perpendicular to the direction in which force is applied to increase the density of polymer chains per unit cross-sectional area. Can be improved. When mechanically holding the polymer gel with a clamp or a chuck, the mechanical holding of the polymer gel can be facilitated by increasing the strength of only the portion that mechanically contacts.

The preferred embodiments of the polymer gel of the present invention and the method for producing the same are shown below. (1) The polymer gel of the present invention, wherein the polymer of the three-dimensional crosslinked polymer is polyvinyl alcohol, polyacrylamide and derivatives thereof. (2) The polymer gel of the present invention in which the difference in volume change rate between the portions of the polymer gel having different cross-linking densities is 0.01 or more. (3) A three-dimensional crosslinked polymer obtained by forming a solvent-insoluble low-crosslinking point density portion by crosslinking and then forming a high-crosslinking point density portion having a predetermined shape by electron beam irradiation is swollen in a solvent of the present invention. Polymer gel manufacturing method. (4) Polymer of the present invention in which a three-dimensional crosslinked polymer obtained by crosslinking polyvinyl alcohol with a sulfate and then immersing it in a chromate and irradiating it with an electron beam to crosslink it into a predetermined shape is swollen in a solvent Gel manufacturing method.

[0015]

EXAMPLES The present invention will be described in more detail with reference to the following examples. The parts and% in the examples and comparative examples are based on weight unless otherwise specified. Example 1 A 15% aqueous solution of polyvinyl alcohol was cast on a glass substrate and immersed in a saturated aqueous solution of sodium sulfate to form a gel film. After drying it under vacuum,
It was immersed in a 100 mmol aqueous solution of potassium chromate.
After drying this, an electron beam (20 nm) was applied to a predetermined place using an electron beam drawing device (ELS3300 manufactured by Elionix Co., Ltd.).
KV, 100 μC / cm ⁻² ) was irradiated to form crosslinks. The width of the bridging site is 10 μm, the spacing between the bridging parts is 40 μm
The electron beam was irradiated so that The state of the crosslinked film is shown in FIG. FIG. 2 shows a state in which the crosslinked film was dipped in water to swell, and then FIG. 3 shows a state in which it was dipped in acetone to shrink. Further, the dimensional change of each site at the time of swelling and shrinking was measured from the micrograph, and the rate of change (dimension at swelling / dimension at shrinking × 100) was calculated.
It shows in Table 1. From FIGS. 1 to 3 and Table 1, in the high cross-linking point density portion (3 and 4 in FIGS. 1 and 2), swelling / shrinking in the vertical and horizontal directions is unlikely to occur, while in the low cross-linking point density portion (FIG. 1).
Also, it can be seen from FIGS. 2 and 5) that swelling / contraction in the vertical and horizontal directions easily occurs. The vertical change rate of the low cross-linking point density portion is 1.3% (5 in FIGS. 1 and 2), while the horizontal change rate is 1.1% (FIGS. 1 and 2). 6), and it can be seen that the behavior of swelling / contraction is different between the two, that is, the volume change has anisotropy.

[0016]

[Table 1]

[Brief description of drawings]

FIG. 1 is a traced electron micrograph of a crosslinked film.

FIG. 2 is a diagram in which an electron micrograph of a crosslinked film at the time of swelling is traced.

FIG. 3 is a diagram tracing an electron micrograph of the crosslinked film when it contracts.

[Explanation of symbols]

 1 High cross-linking point density part 2 Low cross-linking point density part 3 Longitudinal dimension of high cross-linking point density part 4 Horizontal dimension of high cross-linking point density part 5 Longitudinal dimension of low cross-linking point density part 6 Side of low cross-linking point density part Dimension in direction

Claims (2)

[Claims] 1. A polymer gel comprising a three-dimensional crosslinked polymer and a solvent, wherein the three-dimensional crosslinked polymer has a low crosslink point density portion and a high crosslink point density portion, and the high crosslink point density portion has a predetermined density. A polymer gel having a shape. 2. A three-dimensional crosslinked polymer is obtained by crosslinking a main chain of a polymer to form a solvent-insoluble low crosslinking point density portion and then irradiating with actinic rays to form a high crosslinking point density portion into a predetermined shape. The method for producing a polymer gel according to claim 1, wherein the crosslinked polymer is then swollen in a solvent.