JP3855060B2 - Thermal sensor and pH sensor - Google Patents

Description

The present invention relates to a thermal sensor (thermal responsive sensor) and a pH sensor (pH responsive sensor) containing a crosslinked polymer having an amino acid residue in the side chain.

  Conventionally, as an electrolyte polymer, anionic polymer electrolytes such as polyacrylic acid and polymethacrylic acid, and cationic polymers such as poly (N, N-dimethylaminopropylacrylamide) and poly (N, N-dimethylaminoethyl acrylate) Electrolytes are well known.

In these polymers, the electrolyte site undergoes dissociation-non-dissociation change due to changes in pH and ionic strength, and various properties such as viscosity and electrical properties change.
In addition, monomers such as acrylic acid, methacrylic acid, N, N-dimethylaminopropyl acrylamide, N, N-dimethylaminoethyl acrylate, N-substituted acrylamides such as N-isopropyl acrylamide and N-isopropyl methacrylamide, and N-substituted Copolymers with monomers such as methacrylamide show thermal sensitivity, and the solubility in water changes at a certain temperature, dissolves below that temperature, becomes insoluble above that temperature, and dissolves at a pH of pH. It has also been reported that it can be controlled by ionic strength.

Furthermore, it is also known that the cross-linked gelled products of these polymer electrolytes and polymers reversibly change the gel volume with changes in pH and temperature.
However, these polymers and their gelled products have a drawback that dissociation occurs at a certain pH in an acidic or alkaline region, but no dissociation is observed in both acidic and alkaline regions.

  In order to solve such problems, the present inventors have proposed an acrylamide derivative in which the amino group and carboxyl group at the α-position of an amino acid such as L-lysine are protected and the side chain amino group is acrylamideated, and N -A copolymer with isopropylacrylamide was proposed (Japanese Patent No. 3434299).

  By performing a deprotecting group reaction, this copolymer becomes free of the amino group and the carboxyl group at the α-position of an amino acid group such as an L-lysine group, and exhibits the properties of an ampholyte. The solubility changes, and below that temperature (phase transition temperature) it dissolves and becomes transparent, above the phase transition temperature it becomes insoluble and white turbid, and this phase transition phenomenon appears in both acidic and alkaline regions. It can be used as a responsive polymer material and a pH responsive polymer material.

  However, according to the studies by the present inventors after that, this copolymer has a relatively high phase transition temperature, has some problems in low-temperature responsiveness, and has a phase transition over both acidic and alkaline regions. However, the pH range for the transparent state is relatively narrow, and further, the boundary between the pH range for the transparent state and the pH range for the white turbid state is not always clear, and the sensitivity of the thermal response and the pH response is not necessarily limited. I was not satisfied.

  The present invention has been made under such circumstances, and has a low phase transition temperature, a relatively wide pH range that is transparent, and a pH range that is transparent and a pH range that is cloudy. It is an object of the present invention to provide a polymer material that has a clear boundary and exhibits sharp thermal response and pH response.

（式中、Ｒは水素原子又はメチル基、ｎは１から４の整数であり、Ｑ_１は、水素原子又は低級アルキル基を、Ｑ_２は低級アルキル基を示す。ｘ及びｙは共重合体中の各構成成分のモル分率を示す。）
第二に、上記一般式（Ｉ）で表される繰り返し単位からなる共重合体の架橋体を含有するｐＨセンサーが提供される。
As a result of intensive studies to achieve the above object, the present inventors have used as a repeating unit a monomer in which the amino group in the side chain of the amino acid is protected and the α-position amino group is amidated or methacrylamided. The present inventors have found that the crosslinked polymer containing the polymer exhibits sharp thermal response and pH response, and has completed the present invention.
That is, according to the present invention,
First, there is provided a thermal sensor containing a crosslinked product of a copolymer composed of repeating units represented by the following general formula (I).

Wherein R is a hydrogen atom or a methyl group, n is an integer of 1 to 4, Q ₁ is a hydrogen atom or a lower alkyl group, Q ₂ is a lower alkyl group, and x and y are copolymers. (The mole fraction of each constituent component is shown.)
Secondly, there is provided a pH sensor containing a crosslinked product of a copolymer comprising the repeating unit represented by the general formula (I).

(1) The aqueous solution of the copolymer consisting of the repeating unit represented by the general formula (I) dissolves in water at a transition temperature or lower and becomes transparent, but at a transition temperature or higher, causes phase separation and insolubilizes in water. However, since the solution becomes cloudy, it can be used as a thermoresponsive polymer. Furthermore, since this copolymer contains a specific amino acid group, the phase separation behavior changes depending on the pH, and the aqueous solution does not cause phase separation in the range of pH 4 to 10 in both acidic and alkaline regions. It retains transparency and exhibits a unique behavior that causes phase separation in the vicinity of an acidity of pH 4 or less and an alkali pH of 10 or more, resulting in white turbidity. Further, this copolymer has a relatively low phase transition temperature, a phase transition over both acidic and alkaline regions, a relatively wide transparent pH region, and a pH region and a cloudy state in which the transparent state is obtained. Since the boundary of the pH range is clear, it shows sharp thermal response and pH response. And since the unique crosslinked amino acid group (gelation product) of the copolymer which consists of a repeating unit represented by general formula (I) of this invention contains a specific amino acid group, a phase transition behavior changes with pH, pH4 Although it is in a contracted state in the vicinity of -10, the gel swells rapidly and greatly at a pH lower than that.
(2) Therefore, the crosslinked product of the present invention is effective as a thermoresponsive polymer material and a pH-responsive polymer material that recognize temperature, pH, etc., and includes sensors, actuators, and column packing materials. It can also be used as a separation material.

一般式（Ｉ）において、Ｒは水素、メチル基であり、ｎは１から４の整数である。Ｑ１、Ｑ２は、水素原子又はｎ−プロピル基、イソプロピル基、ｎ−ブチル基、ｓｅｃ−ブチル基、ｔｅｒｔ−ブチル基などの低級アルキル基を示す。この中でもＱ１が水素原子、Ｑ２が低級アルキル基の組み合わせ、及びＱ１がエチル基、Ｑ２がエチル基の組み合わせのものが好ましい。ｘ及びｙは共重合体中の各構成成分のモル分率を示し、一般にｘは０．５〜０．９５、好ましくは０．８〜０．９５であり、ｙは０．０５〜０．５、好ましくは０．０５〜０．２である。
この共重合体の分子量は一般に１０，０００〜２，０００，０００、好ましくは２０，０００〜１，０００，０００である。 The copolymer crosslinked in the present invention comprises a repeating unit represented by the following general formula (I).

In the general formula (I), R is hydrogen or a methyl group, and n is an integer of 1 to 4. Q1 and Q2 each represent a hydrogen atom or a lower alkyl group such as an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, or a tert-butyl group. Among these, a combination in which Q1 is a hydrogen atom, Q2 is a combination of a lower alkyl group, Q1 is an ethyl group, and Q2 is an ethyl group is preferable. x and y represent the mole fraction of each constituent component in the copolymer, generally x is 0.5 to 0.95, preferably 0.8 to 0.95, and y is 0.05 to 0.00. 5, preferably 0.05 to 0.2.
The molecular weight of this copolymer is generally 10,000 to 2,000,000, preferably 20,000 to 1,000,000.

Such a copolymer is obtained by polymerizing a monomer represented by the general formula (II) and an N-substituted acrylamide or N-substituted methacrylamide monomer represented by the general formula (III), and then forming a protective group Z. It can be manufactured by deprotection.
This synthetic reaction is represented in Scheme 1.
In the general formula (II), R represents hydrogen or a methyl group, n represents an integer of 1 to 4, and Z represents an amino-protecting group. In this case, the amino-protecting group Z includes all conventionally known protecting groups, and examples thereof include benzyloxycarbonyl, m-chlorobenzyloxycarbonyl, p-nitrobenzyloxycarbonyl, t-butoxycarbonyl and the like. It is done. Of these, protecting groups such as benzyloxycarbonyl and m-chlorobenzyloxycarbonyl are preferably used. In general formula (III), R represents hydrogen or a methyl group, and Q1 and Q2 represent the same groups as described above.
The monomer represented by the general formula (II) is a novel substance. For example, an amino acid whose side chain amino group is protected is reacted with an alkali salt such as sodium hydroxide to convert the amino acid salt. First, it is synthesized, and then this product is reacted with an acrylic acid derivative such as acrylic acid chloride in a solvent to form an amide bond with the amino group at the α-position.

The copolymer can be made into a crosslinked body (gel product) by a crosslinking method such as γ-ray crosslinking, chemical crosslinking, or copolymerization with a crosslinking monomer.
Hereinafter, the crosslinking method will be described in detail.

(1) γ-ray crosslinking When the copolymer of the present invention, particularly R in the structural formula is a hydrogen atom, a gelled product is obtained by dissolving these polymers in water and irradiating γ-rays. In this case, the aqueous solution concentration is 10 to 20 wt. %, And the amount of γ-ray irradiation is preferably about 70 to 150 kGy.

(2) Copolymerization with a crosslinkable monomer As described above, the copolymer of the present invention gives a gelled product by radiation crosslinking or chemical crosslinking. In the polymerization, a production method in which a small amount of a divinyl compound is added to synthesize a gelled product and then the protective group is removed is preferable.

Further, the monomer represented by the general formula (II), the acrylic monomer such as N-substituted acrylamide or N-substituted methacrylamide represented by the general formula (III), and N, N ′ When a divinyl compound such as methylenebisacrylamide or N, N ′-(1,2-dihydroxyethylene) -bisacrylamide is dissolved in an organic solvent such as dimethylsulfoxide and copolymerized, a gelled product having a protecting group Z is obtained. .
In this case, the total concentration of the monomer represented by the general formula (II) and the acrylic monomer such as N-substituted acrylamide or N-substituted methacrylamide represented by the general formula (III) is: 10-20 wt. %, And the crosslinking agent concentration is preferably 0.5 to 3 mol% with respect to the total amount of monomers.
After the gelled product having the protective group Z obtained is swollen in a solvent such as acetic acid, a deprotecting base such as a 25% hydrogen bromide / acetic acid solution is added to remove the protective group (Z). A crosslinked product (gel product) obtained by crosslinking the copolymer having the repeating unit represented by (I) is obtained.

In addition, the aqueous solution of the copolymer dissolves in water at a transition temperature or lower and becomes transparent, but at a transition temperature or higher, it causes phase separation and becomes insoluble in water, and the solution becomes cloudy. Can be used.
Furthermore, since this copolymer contains a specific amino acid group, the phase separation behavior changes depending on the pH, and the aqueous solution does not cause phase separation in the range of pH 4 to 10 in both acidic and alkaline regions. It retains transparency and exhibits a unique behavior that causes phase separation in the vicinity of an acidity of pH 4 or less and an alkali pH of 10 or more, resulting in white turbidity. Further, this copolymer has a relatively low phase transition temperature, a phase transition over both acidic and alkaline regions, a relatively wide transparent pH region, and a pH region and a cloudy state in which the transparent state is obtained. Since the boundary of the pH range is clear, it shows sharp thermal response and pH response.

  Furthermore, since the cross-linked copolymer (gelated product) of the present invention contains a unique amino acid group, the phase transition behavior changes depending on the pH, and it is in a contracted state around pH 4-10. As described above, at pH lower than that, the gel swells rapidly and greatly.

  Therefore, such copolymers and their crosslinked products (gelated products) can also be used as separation materials such as sensors and actuators for recognizing temperature, pH, etc., or column fillers.

Next, the present invention will be described in more detail based on reference examples and examples.
Reference example 1
[Acrylamide monomer containing lysine residue (synthesis of compound (4)]
Compound (4) was synthesized according to Scheme 2 below.

Compound (1) (3.0 g, 10.7 mmol) was dissolved in 0.1N sodium hydroxide aqueous solution (108 ml, 10.8 mmol) to obtain an aqueous solution of compound (2). Dioxane 53.5 ml, 1N-sodium hydroxide aqueous solution (10.7 ml, 10.7 mmol) was added and stirred vigorously. This solution was designated as solution A. A liquid B was prepared by dissolving acryloyl chloride (compound (3)) (1.21 g, 13.4 mmol) in 12 ml of dioxane. 1N-aqueous sodium hydroxide solution (12.3 ml, 12.3 mmol) was prepared, and this was designated as solution C. In an ice bath, the B liquid and the C liquid were divided into 4 times, added to the A liquid every 10 minutes, and stirred for 7 hours. After completion of the reaction, the reaction solution was adjusted to pH 5 using 1N hydrochloric acid aqueous solution. Dioxane was distilled off under reduced pressure and the product was dissolved in methylene chloride. The organic phase was washed with 100 ml of water. Anhydrous magnesium sulfate was added for dehydration, the filtrate was concentrated under reduced pressure, and crystals were precipitated in a hexane-chloroform mixed solution (180 ml: 20 ml (= 9: 1)). After leaving still at low temperature, it was decanted and dried under reduced pressure to obtain a white compound (4).
Yield: 1.8 g, Yield: 50.3%
1H-NMR (DMSO, room temperature, δ): 1.2-1.8 (m, (CH ₂ ) ₄ , 8H), 4.2-4.3 (m, CH, 1H), 5.0 (s _{,) 5.0 (s, CH 2} , 1H), 5.6 (d, CH 2 = CH, 1H), 6.0-6.4 (m, CH 2 = CH, 2H), 7.3-7. 4 (m, benzene, 5H), elemental analysis: calculated value (%): C, 61.1; H, 6.63; N, 8.38, measured value (%): C, 60.2; H, 6.74; N, 8.14

Reference Example 2 (Scheme 3)
[Synthesis of Polymer (6)]
According to the following scheme 3, a polymer (6) (m = 1,500) was synthesized.

1) Polymerization of acrylamide monomer containing lysine residue (compound (4)) Compound (4) (4.7 g, 14 mmol) was dissolved in 20 ml of dimethyl sulfoxide. Α, α′-Azobisisobutyronitrile (23.3 mg, 0.14 mmol) was added as a polymerization initiator and reacted at 60 ° C. for 24 hours in a nitrogen atmosphere. After returning to room temperature, the mixture was precipitated with water and freeze-dried to obtain a white polymer (5).
Yield: 4.11 g, Yield: 87.4%

2) Synthesis of Polymer (6) (m = 1,500) by Removal of Protecting Group Polymer (5) (2.5 g) was dissolved in 25 ml of acetic acid, and 25% hydrogen bromide / acetic acid solution (25 ml) Was added. After stirring at room temperature for 3 hours, the mixture was concentrated under reduced pressure. The product was dissolved in water and dialyzed. By lyophilization, a white cotton-like polymer (6) (m = 1,500) was obtained.
Yield: 1.20 g, Yield: 80.7%

Reference Example 3 (Scheme 4)
[Synthesis of Copolymer (9) (Copolymer of Compound (7) and Compound (4); x = 0.9, y = 0.1)
A copolymer (9) was synthesized according to the following scheme 4.

1) Copolymerization of acrylamide monomer containing lysine residue (compound (4)) and N-isopropylacrylamide (compound (7)) Compound (7) (1.45 g, 12.8 mmol) and compound (4) (0 .47 g, 1.42 mmol) (molar ratio; compound (7): compound (4) = 9: 1) was dissolved in 20 ml of dimethyl sulfoxide. Α, α′-Azobisisobutyronitrile (23.3 mg, 0.14 mmol) was added as a polymerization initiator and reacted at 60 ° C. for 24 hours in a nitrogen atmosphere. After returning to room temperature, the mixture was precipitated with water and freeze-dried to obtain a white polymer (8).
Yield: 1.71 g, Yield: 89.2%

2) Synthesis of copolymer (9) by removal of protecting group Polymer (8) (0.8 g) was dissolved in 25% hydrogen bromide / acetic acid solution (25.6 ml) and allowed to stand at room temperature for 3 hours. Then, it concentrated under reduced pressure. The product was dissolved in water and dialyzed. The white cotton-like copolymer (9) (x = 0.9, y = 0.1; molecular weight 350,000) was obtained by freeze-drying.
Yield: 0.64 g, Yield: 85.2%
Reference Example 5

The phase separation behavior of the copolymer (9) obtained in Reference Example 1 was examined with a light transmittance of 500 nm using hydrochloric acid and sodium hydroxide aqueous solution adjusted to 0.01 with sodium chloride as the solvent. The measurement results are shown in FIG. At pH 4-10, phase separation occurred around 48-50 ° C., and the solution became cloudy, so the transmittance decreased.
At pH 3.5 and 10.6, the phase separation temperature increased, and at pH 2 and pH 12, no phase separation was observed and the solution remained clear. The point at which the transmittance of light at 500 nm is 50% is defined as the phase separation temperature, and the results of examining the pH response of the copolymer (9) are shown in FIG.
For comparison, the relationship between the phase transition temperature and the pH of the copolymer (A) having a repeating unit represented by the following general formula (IV) synthesized in Example 1 of Japanese Patent No. 3304299 was similarly measured. This is illustrated.

As can be seen from FIG. 2, the aqueous solution of the copolymer (9) used in the present invention has an almost constant transition temperature of 48 to 50 ° C. at a pH of 4 to 10, and below that at a pH higher than that. Since the amino group or carboxyl group is dissociated and the hydrophilicity is increased, the transition temperature is rapidly increased.
On the other hand, the aqueous solution of the polymer (A) has a pH of 4 to 8 and a transition temperature of 54 to 57 ° C., and below that, the amino group or the carboxyl group is dissociated at a pH higher than that. However, since the hydrophilicity increased, the transition temperature was abrupt, but no sudden rise in transition temperature as in the copolymer (9) was observed.
Therefore, it was found that the copolymer (9) of the present invention showed a pH response more sensitive than that of the copolymer (A) described in Japanese Patent No. 3434299.
Example 1

[Synthesis of Crosslinked Copolymer (Gered Product) (11) (Gerylated Product of Copolymer (9))]
1) Synthesis of copolymer gelled product (10) of acrylamide monomer (compound (4)) containing lysine residue and N-isopropylacrylamide (compound 7) NIPAAm (compound (7)) (0.73 g, 6. 42 mmol) and compound (4) (0.24 g, 0.71 mmol) (NIPAAm: compound (4) = 9: 1) were dissolved in 6.2 ml of dimethyl sulfoxide. As a polymerization initiator, α, α′-azobisisobutyronitrile (11.8 mg, 0.07 mmol) was added as a crosslinking agent, and N, N′-methylenebisacrylamide (11.0 mg, 0.07 mmol) was added to perform nitrogen substitution. The mixture was reacted in a glass tube at 60 ° C. for 24 hours. After returning to room temperature, the gel was repeatedly washed with water to obtain a copolymer gel product (10).

2) Synthesis of crosslinked copolymer (gelated product) (11) of the copolymer of the present invention by removal of protecting group The washed copolymer gelled product (10) was immersed in 100 ml of acetic acid and a 25% hydrogen bromide / acetic acid solution. 30 ml was added and left at room temperature for 5 hours. After completion of the reaction, the gel was repeatedly washed with water to obtain a copolymer gel product (11).
Example 2

Using a hydrochloric acid adjusted with ionic strength to 0.01 with sodium chloride and a sodium hydroxide aqueous solution as a solvent, the change in the degree of swelling of the crosslinked product (gelated product) (11) of the copolymer obtained in Example 3 at room temperature investigated. The measurement results are shown in FIG. The degree of swelling d / do was determined from the diameter d of the gel at 25 ° C. and the inner diameter do of the glass tube synthesized with the gel at each pH. For comparison, the same measurement was performed on the gelled product of the copolymer (A) having a repeating unit represented by the above general formula, which was synthesized in Example 1 of Japanese Patent No. 3044299, and the results are shown in FIG. This is also shown in 3.
From FIG. 3, the crosslinked product (gelled product) (11) of the copolymer of the present invention exhibits a substantially constant swelling degree at pH 4 to 9, and below that, the amino group or the carboxyl group is at a higher pH. The degree of swelling of the gel increases rapidly due to dissociation and increased hydrophilicity.
In contrast, the polymer (A) cross-linked product was in a contracted state in the pH range of 4 to 8, but had a minimum value near pH 6, and the degree of swelling slightly increased at pH lower than that. did. At pH 4 or lower and pH 9 or higher, the amino group or carboxyl group was dissociated and the hydrophilicity increased, so the rate of increase in the degree of swelling of the gel increased. However, the rate of increase was lower than that of the crosslinked copolymer (11). It was.
Therefore, it was found that the crosslinked product of the copolymer (11) of the present invention showed a sharper pH responsiveness than that of the copolymer (A) described in Japanese Patent No. 3044299.

  Next, the volume change of the crosslinked body (gel product) (11) of the copolymer accompanying the temperature change in each pH solution was examined. The results are shown in FIG. It was found that the gel shrinks continuously in the pH 2, 6, 12 solution as the temperature increases. Therefore, it was found that the copolymer gel (11) changes in volume not only with pH change but also with temperature change.

The graph which shows the pH dependence of the transmittance | permeability of the copolymer aqueous solution of the reference example 1. FIG. 3 is a graph showing the relationship between the phase transition temperature of the aqueous copolymer solution of Reference Example 1 and pH. The graph which shows the relationship between the swelling degree and pH of the copolymer gelled material which concerns on this invention. The graph which shows the swelling degree change accompanying the temperature change in each pH of the crosslinked body (gelled material) of the copolymer which concerns on this invention.

Claims (2)

A heat sensor comprising a crosslinked product of a copolymer comprising a repeating unit represented by the following general formula (I).

Wherein R is a hydrogen atom or a methyl group, n is an integer of 1 to 4, Q ₁ is a hydrogen atom or a lower alkyl group, Q ₂ is a lower alkyl group, and x and y are copolymers. (The mole fraction of each constituent component is shown.) A pH sensor comprising a crosslinked product of a copolymer comprising the repeating unit represented by the general formula (I).

Images