JPH07292040A - Heat-sensitive shape-memory gel - Google Patents

Abstract

PURPOSE:To obtain a heat-sensitive shape-memory hydrogel which reversibly changes its moldulus from high to low at a specified temp. by forming a high- molecular hydrogel contg. hydrophobic monomer units. CONSTITUTION:A heat-sensitive shape-memory hydrogel which reversibly changes its modulus from high to low at a specified temp. is obtd. by copolymerizing a hydrophilic monomer and a hydrophobic monomer. A gel which changes its modulus from 10<8>dyn/cm<2> or higher to 10<4>dyn/cm<2> or lower is obtd. by copolymerizing e.g. a hydrophilic acrylic monomer and a hydrophobic acrylic monomer in the presence of a cross-linker. An example of the hydrophobic monomer is a (meth)acrylate having a 5-30C alkyl or its deriv. group at the side chain. For instance, a 6-20C alkyl acrylate or its deriv. is copolymerized with (meth)acrylic acid under cross-linking reaction giving the gel.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Valves, cushioning materials, cushions, sustained-release carriers, DDS, switches, sensors, etc. that reversibly change to rigid-flexible bodies due to temperature changes and that utilize shape memory characteristics.

[0002]

2. Description of the Related Art A polymer gel is a substance in which a three-dimensional network polymer is swollen with a solvent. When this solvent is water, it is called hydrogel, and it is widely used as an absorbent material, a soil treatment material, and a single drug substance. (For details, see Nagata / Fushimi /
See "Gel" by Ogino and Yamauchi <Industrial Books>). Conventionally, polymethyl vinyl ether, poly N alkyl acrylamide, cellulose derivative and the like have been known as heat-sensitive polymer gels, but all of them have mechanical properties, especially those that undergo volume change such as swelling / shrinking at a specific temperature. It had a large elastic modulus and no function of reversibly changing it. Also, as the shape memory polymer, polynorbornadiene, stretched polyethylene, etc. are known.
These do not have the properties such as hydrophilicity, biocompatibility, and water absorption characteristic of hydrous gels. In this case, by synthesizing a polymer hydrogel containing a hydrophobic group as a component in the gel, it exhibits a rigid (high elastic modulus) -flexible (low elastic modulus) characteristic change reversibly at a specific temperature and has a shape. The present invention relates to a hydrogel having memory properties.

Conventionally known hydrogels have high water absorption because they are swollen with water, but they are generally amorphous and mechanically weak. So far, no gel has been known that has water absorbency and sufficient mechanical strength.

[0004]

The present invention is to swell with water and maintain a lamella-like array structure or crystal structure by polymerizing a hydrophilic monomer and a hydrophobic monomer in an appropriate ratio, It relates to the synthesis of gels that guarantee mechanical strength. The characteristics of this gel are that it has a large mechanical strength and a high elastic modulus shape memory at low temperature, which is derived from the arrangement structure of the hydrophobic monomer. It is to change to an amorphous flexible hydrogel and at the same time to recover the shape at the time of gel preparation.

[0005]

[Means for Solving the Problems] The hydrophobic group in the gel may be any aromatic compound such as a long-chain alkyl group, a phenyl group or a naphthyl group, or a cycloalkane having hydrophobicity in the molecule. . However, it is necessary to introduce an appropriate amount of a hydrophilic monomer unit having a hydrophilic group such as a carboxyl group, a hydroxyl group, an amino group, and a hydroxyl group in order to impart a water absorbing property as a hydrogel. The transition phenomenon is based on the arrangement structure of these hydrophobic groups or the crystal structure-amorphous structure transition, and generally exhibits high elastic modulus and devitrification in the crystalline state, and rubber elasticity and transparency in the low elastic modulus. The transition temperature can be freely controlled because it depends on the size and amount of the hydrophobic group. When a long-chain alkyl group is used, the longer the chain length and the higher the content, the higher the transition temperature and the elastic modulus. For example, when acrylic acid (AA) is used as a hydrophilic monomer and stearyl acrylate (SA) is used as a hydrophobic monomer and these are copolymerized with a suitable cross-linking agent at a molar ratio of 7.5 parts to 2.5 parts, The crystalline-amorphous temperature occurs at 48 ° C. However, when hexadecyl acrylate (HA) is used instead of SA, the temperature changes to 38 ° C. Also, AA and S
Even in the case of A, when the ratio is copolymerized at a ratio of 8.5 parts to 1.5 parts, it changes to 45 ° C. (Table 1). The change in mechanical strength due to the crystal-amorphous transition and the water content can also be controlled by the amount of the cross-linking agent. For example, if the cross-linking agent is added in an amount of 5 mol% with respect to the total amount of the monomer, the transition can occur without causing a large volume change. The amount of water increases and the mechanical strength of the gel also decreases significantly. The water content of the gel thus obtained is generally 10% to 500%, and the water content is lower in the crystalline state.

A hydrogel having such a structure has an array structure or a crystalline structure at a low temperature of 10 ⁸ to 10 10 at a low temperature.
^It exhibits a high elastic modulus of about ⁹ dyne / cm ^2, and exhibits mechanical properties as a plastic and a strong shape maintaining ability. However, when the temperature rises and the transition occurs, this gel softens significantly,
Its elastic modulus becomes 10 ⁴ dyne / cm ² or less, and it becomes freely deformable (FIG. 1). Therefore, at the time of polymerization, a suitable cross-linking agent is coexisted to form a specific shape, and after being softened at a transition temperature or higher, it is deformed by applying an appropriate stress, and if it is cooled below the transition point, it is in a deformed state. The shape can be fixed. When it is desired to restore the original shape upon polymerization, the gel is restored to the shape upon polymerization by heating again above the transition point and exhibits shape memory characteristics. The purpose of forming a gel having a three-dimensional network structure by a cross-linking agent is to impart shape maintenance of the gel and improve its crystallinity even after it is transformed and softened. For example, when compared to a linear polymer of the same chemical composition that was polymerized without a cross-linking agent, the crosslinked gel shows higher crystallinity and superior mechanical properties. The polymerization is not particularly limited to a radical polymerization method, an ionic polymerization method, a plasma polymerization method, and a radiation polymerization method, but it is convenient to carry out radical polymerization in a suitable solvent, particularly in a polar organic solvent such as ethanol or methanol. Further, in order to prevent phase separation, a redox method is used for polymerization at low temperature.

[0007]

[Function] Since it is a shape memory gel that behaves as a rigid body at low temperature and a flexible body that can be deformed at high temperature, it serves as a valve, cushion or sensor. In addition, since the substance has a large diffusion coefficient in a flexible state, it acts as a sustained release action, a sensor, or a switch.

[0008]

Example 1 Initiation of polymerization of azobisisobutyronitrile using 0.1 mol of stearyl acrylate and 0.4 mol of acrylic acid as a crosslinking agent of 300 ml of 0.004 mol of N, N ethylenebisacrylamide in ethyl alcohol. Radical polymerization was performed on the glass plate as an agent to obtain a thin plate-shaped white polymer having a thickness of 2 mm. When the elastic modulus of the hydrogel obtained by immersing this polymer in a large amount of water and substituting with water was measured, it was 5 × 10 ⁹ dyne / cm ² (or 5 × 10 ⁸ Pa).
Met. The gel contained 24% of its own weight of water.
Next, when the transition temperature of this gel was measured by DSC, it was 42 ° C.
It was found to melt at. Elastic modulus when melted is 10
^{It was 3} dyne / cm ² . Further, when a wide-angle X-ray diffraction image of the sample before melting was taken, a Laue pattern showing a crystal structure was observed. This hydrogel was cut into a disk shape having a diameter of 30 mm, and then divided into six equal parts to prepare a valve. After this was attached to one end of an iron pipe with a diameter of 30 mm, a 1% starch aqueous solution was put into this pipe and a permeation experiment was conducted.
At 5 ° C, the valve is closed and the solution does not permeate at all.
It was found that heating to 9 ° C softens the gel and causes the aqueous starch solution to flow down. When the valve cooled, it closed again by itself and was impermeable to the aqueous solution.

[0009]

Example 2 The same gel as in Example 1 was obtained by polymerizing stearyl acrylate at a ratio of 0.15 mol and acrylic acid at a ratio of 0.85 mol. This gel melts at 45 ° C., 8 × 10 ⁹ dyne / cm ² before melting and 1 after melting.
The elastic modulus was 0 ³ dyne / cm ² . The water content of the gel was 280% before melting and 540% after melting. or,
When a valve was made in the same manner as in Example 1, it was found that the valve similarly opened and closed by a temperature change to function as a temperature-sensitive shape memory gel.

[0010]

Example 3 A gel was synthesized using hexadecyl acrylate instead of stearyl acrylate under the same conditions as in Example 1, and a heat-sensitive polymer gel that transferred at 37 ° C. was obtained. Pilocarbine hydrochloride (Pil) heated to 40 ° C.
2g of this gel is added to 1 liter of 1M aqueous solution for 48 hours at 40 ° C.
Was dipped in to prepare a gel containing 0.02 mol of Pil.
Even if 1 g of this gel was immersed in 100 ml of water at 25 ° C for 48 hours, no Pil was released, but with warm water at 50 ° C, Pil was released into the water for a long time, and it had a sustained release property. I understood.

[0011]

[Example 4] Under the same conditions as in Example 1, naphthyl acrylate was used instead of stearyl acrylate, and styrene sulfonic acid was used instead of acrylic acid. Was obtained.

[0012]

Example 5 The thin plate polymer prepared in Example 1 has a width of 20 mm.
When it was cut into a rectangle with a length of 50 mm, heated and stretched in warm water at 60 ° C., it was stretched to a width of about 7 mm and a length of 16 mm, and when cooled as it was, the shape was maintained and fixed in that state. In this state, when a wide-angle X-ray diffraction photograph was taken, a strong diffraction image was obtained in the equatorial direction (top and bottom), from which the main chain was oriented in the stretching direction and the side chains were oriented in the direction perpendicular to it. all right. When the elastic modulus in this state was measured, the stretching direction was increased to 9 × 10 ⁹ dyne / cm ² . Next, when the thin film in the stretched state was placed in a warm bath at 60 ° C., the gel immediately showed its original size, width 20 mm, length 5
It returned to 0 mm. This can be repeated many times and was found to have shape memory.

[0013]

Example 6 In the same manner as in Example 1, a raw material having the same composition was polymerized in a casting mold having a length of 40 mm to obtain a fish-shaped hydrogel. After washing this with water, it was softened in a warm bath at 60 ° C. in the same manner as in Example 5, deformed by applying force to lose the shape of the fish, and allowed to cool, and then fixed in the deformed shape. The next day, when the deformed gel was put in a warm bath at 60 ° C., the gel immediately recovered to the original fish shape.

[0014]

【The invention's effect】 [Brief description of drawings]

FIG. 1 is the temperature dependence of the elastic modulus of a shape memory gel. 8 parts acrylic acid, 2 parts stearyl acrylate.

[Short description of table]

[Table 1] Crystal of hexadecyl acrylate (C ₁₆ ) or octadecyl acrylate (C ₁₈ ) and acrylic acid copolymer gel-
Amorphous transition temperature.

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[Procedure amendment]

[Submission date] October 10, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is the temperature dependence of the elastic modulus of a shape memory gel. 8 parts acrylic acid, 2 parts stearyl acrylate.

Claims (5)

[Claims] 1. A heat-sensitive shape memory hydrogel, which comprises a hydrophilic monomer as one component and a hydrophobic monomer as one component, and polymerizes these to change from a high elastic modulus to a low elastic modulus at a specific temperature. 2. An elastic modulus of 10 ⁸ dyne due to crystal-amorphous transition by heating in the presence of an appropriate bridging agent of 1.
/ Cm ² or more to 10 ⁴ dyne / cm ² or less, a thermosensitive shape memory gel. 3. A heat-sensitive shape memory gel obtained by copolymerizing an acrylic hydrophilic monomer and an acrylic hydrophobic monomer of the above 1. 4. A heat-sensitive shape-memory hydrogel containing acrylate or methacrylate containing a C _{5 to} C ₃₀ alkyl group or a derivative thereof as a hydrophobic group in 1 in a side chain. 5. A polymer obtained by polymerizing C ₆ -C ₂₀ alkyl acrylate or its derivative as a hydrophobic component and acrylic acid or methacrylic acid as a hydrophilic component in 1 and polymerizing them while carrying out an appropriate crosslinking reaction. Heat-sensitive shape memory hydrogel.