JP6594280B2 - Copolymer for pH indication in wide range and synthesis method thereof - Google Patents

Description

  The present invention relates to a wide-range pH indicating copolymer and a synthesis method thereof, and more particularly to a wide-range pH indicating copolymer capable of measuring pH over a wide range.

  In environmental monitoring of rivers / lakes, air / air, geology, etc., for example, it may be required to continuously monitor pH at a predetermined point over a long period of time (pH monitoring). Conventionally, a general pH measurement method is a colorimetric analysis in which a color change of a pH indicator brought into contact with a liquid (aqueous solution or the like) is observed, and an electrochemical analysis in which an electromotive force of an electrode immersed in the liquid is measured. However, the conventional colorimetric analysis uses a low molecular pH indicator (such as litmus paper) impregnated in paper or the like, and there is a problem in that the pH indicator is eluted if it is immersed in a liquid for a long period of time. . Electrochemical analysis requires frequent maintenance of the electrode. If the electrode is immersed in a liquid for a long period of time, foreign matter may be deposited on the surface. It is difficult to apply to long-term pH monitoring.

In contrast, a monomer component having a pH indicating site and a polymerizable site (pH indicating monomer) is copolymerized with a monomer component having an electrically neutral site and a polymerizable site (nonionic monomer). It has been proposed to use a color change type polymer material for pH monitoring (see Patent Documents 1 and 2). For example, in Patent Document 1, as shown in the formula (2), dimethylaminoazobenzene acrylate (AABAA) obtained by reacting methyl yellow and methacrylic acid is used as a pH-indicating monomer, and N— which is a nonionic monomer. A color change copolymer copolymerized with isopropylacrylamide (NIPAAm) is disclosed.

  (2) In the color tone changing copolymer as shown in the formula, the pH indicator is supported on the polymer chain by a strong covalent bond, and there is no possibility that the pH indicator will be eluted even if immersed in a liquid for a long period of time. . Further, if necessary, copolymerization is carried out including a monomer component (ionic monomer) having an ionic part and a polymerizable part as shown in the formula (2), and the pH region in which the pH indicator monomer changes color tone is changed to a base. By shifting to the acid side or the acid side, the color tone change region of the copolymer can be moved from the color change region specific to the pH indicating monomer, and the color tone change region can be controlled.

  Furthermore, in order to apply the color tone changing copolymer represented by the formula (2) to pH monitoring, a method of measuring the pH value with accuracy from the color development of the pH indicating monomer has been proposed (see Patent Document 3). For example, in Patent Document 3, the color development of the pH indicating monomer is plotted on a chromaticity diagram M (see FIG. 6A) in which the white point O is arranged at the center, and the color development on the polar coordinate centered on the white point O The deviation angle D of point C is detected, and the deviation angles D1, D2,... Of the color development points C1, C2,. A relational expression F1 (see FIGS. 6B and 6C) is set in advance, and the deviation angle D of the color development point C is detected from the color development of the copolymer immersed in the liquid to be measured. A method for obtaining the pH value of the liquid to be measured from the deviation angle D of C and the relational expression F1 is disclosed.

FIG. 6A shows a CIExy chromaticity diagram M1, which is an example of the chromaticity diagram M. In this chromaticity diagram M1, all colors are represented by two numerical values (x, y) = (X / (X + Y + Z), Y / (X + Y + Z) based on the stimulus values (X, Y, Z) of the three primary colors on the color. )), And the color development of the pH indicating monomer can be plotted as the two color development points C (x, y). In addition, a white point O is arranged almost at the center, and by assuming a polar coordinate system centered on the white point O, numerical values (x, y) of all colors are converted into a radius vector r and a declination angle D. can do. FIG. 6 (B) shows that the color development points C1, C2,... Of the color change type copolymers brought into contact with a plurality of specimens having different pH values are arranged in an arc with the white point O as the center. FIG. 6C shows an example of a relational expression F1 between the pH value of each of the coloring points C1, C2,. Patent Document 3 discloses that it is effective to use the relational expression F1 approximated by a logistic model (logistic curve) such as the expression (A) in order to accurately estimate the pH value from the declination angle D. .
D = α / (1 + β · exp (−γ · pH)) ……………………… (A)

JP 2012-163484 A JP 2014-142220 A Japanese Patent Laying-Open No. 2015-081806

  By using a color tone change type copolymer like the above-mentioned (2) formula, and applying the measuring method as shown in FIG. 6 for obtaining the pH value from the color development through the deviation angle D on the chromaticity diagram M1. , It can be expected to realize continuous pH monitoring in the environment over a long period of time. However, the copolymer having AABAA as a pH indicating monomer disclosed in Patent Document 1 exhibits a change in color tone in a relatively narrow acidic range (about pH 1.0 to 4.0, see FIG. 6C). ), It is possible to slightly shift the color change region by copolymerization including the ionic monomer, but the measurable pH range is limited. In environmental monitoring, etc., it may be required to continuously measure pH over a wide range from acidic to basic, and color tone change can be measured based on v over a wide pH range, showing color change over a wide pH range. Development of coalescence is required.

  Accordingly, an object of the present invention is to provide a pH indicating copolymer exhibiting a color change in a wide pH range.

  The inventor has focused on copolymerizing a plurality of types of pH indicating monomers that change color tone in different pH ranges. Even if the pH range that can be measured with a single pH indicator monomer such as AABAA described above is limited, by combining a plurality of types of pH indicator monomers that change color tone in different pH ranges, the color change copolymerization is obtained. It can be expected to widen the measurable pH range. However, in order to obtain the pH value from the color tone change of the copolymer, it is necessary to avoid the copolymer from having the same color at different pH values. For example, as shown in FIG. 6C, in order to obtain the pH value from the color development of the copolymer via the deviation angle D on the chromaticity diagram, the deviation angle D increases as the pH value increases. It is necessary to change the color of the polymer. The inventor has the idea that it is effective to change the color tone of the copolymer in two stages like thymol blue in order to change the color tone so that the declination angle D increases as the pH value increases. As a result of research and development of a copolymer that changes its color tone in two stages, the present invention has been completed.

  The wide-range pH indicating copolymer according to the present invention includes a first pH indicating moiety that changes color tone in the first pH range and a first pH indicating monomer that includes a polymerizable group, and a second pH that changes color tone in a second pH range different from the first pH range. In the middle region of the first and second pH ranges, the second pH indicating monomer containing an indicator moiety and a polymerizable group and a nonionic monomer containing an electrically neutral moiety and a polymerizable group are copolymerized. Both pH indicating monomers are approximate colors or at least one is colorless, and both pH indicating monomers are different colors at both ends of the first and second pH ranges.

  In a preferred embodiment, the copolymerization further includes an ionic monomer containing an ionic moiety and a polymerizable group. For example, the first pH indicating monomer can be changed in color in the acidic range, and the second pH indicating monomer can be changed in color in the basic range.

  In a preferred embodiment, the mixing ratio of the first and second pH indicating monomers is the color of the pH indicating copolymer at a plurality of different pH values spanning the first and second pH ranges. When the deviation angle D of the coloring point on the polar coordinate centered on the white point is detected by plotting on the degree diagram, adjustment is performed so that the deviation angle D of each coloring point increases as the pH value increases.

  Alternatively, when copolymerizing including ionic monomers, the mixing ratio of the ionic monomers is such that the color of the pH indicating copolymer at a plurality of different pH values spanning the first and second pH ranges is centered on the white point. When the deviation angle D of the color development point on the polar coordinates centered on the white point is detected by plotting on the arranged chromaticity diagram, the deviation angle D of each color development point increases as the pH value increases. It is also possible to adjust to.

  The wide-range pH indicating copolymer according to the present invention is a copolymer of a first pH indicating monomer that changes color tone in the first pH range and a second pH indicating monomer that changes color tone in a second pH range different from the first pH range, Since both pH indicating monomers are approximate colors in the middle range of the first and second pH ranges, or at least one is colorless and different colors at both ends of the first and second pH ranges, the pH value increases. The color tone can be changed in two stages, and the pH over a wide range can be measured from the color tone change. Further, when the color development at a plurality of different pH values is plotted on a chromaticity diagram in which the white point is arranged at the center, and the deviation angle D of the color development point on the polar coordinate centered on the white point is detected, each pH value Can be arranged on the chromaticity diagram M1 so as to draw an arc centering on the white point O, that is, the declination D increases as the pH value increases. The pH value can be measured.

  If the declination angle D of the color development point on the chromaticity diagram M1 of the pH indicating copolymer is generated as the pH value increases, the mixing ratio of the first and second pH indicating monomers is adjusted. Thus, a decrease in the deflection angle D can be avoided, and a pH indicating copolymer can be obtained in which the deflection angle D of each color development point on the chromaticity diagram M1 increases as the pH value increases. In addition, by copolymerization including an ionic monomer having an ionic part and a polymerizable part, it is possible to control the color change region of the first pH indicating monomer and the second pH indicating monomer. If the declination angle D of the coloring point on the chromaticity diagram M1 of the pH indicating copolymer increases with the increase, the declination angle D can be reduced by adjusting the mixing ratio of the ionic monomers. It is also possible to avoid it.

Hereinafter, embodiments and examples for carrying out the present invention will be described with reference to the accompanying drawings.
Is the relational expression F1 between the deviation angle D and the pH value on the chromaticity diagram M indicated by the first pH indicating monomer (AABAA), and the chromaticity diagram M indicated by the second pH indicating monomer (6 vinyl-αNP). It is an example of the graph which shows the difference with the relational expression F2 of the deflection angle D and pH value. Is an explanatory diagram of a chromaticity diagram M1 in which the color development points C obtained by coloring the copolymer of the first pH indicating monomer (AABAA) and the second pH indicating monomer (6 vinyl-αNP) at different pH values are plotted. is there. These are the graphs of the relational expression F3 of the deviation angle D and pH value on the chromaticity diagram M of each coloring point C shown in FIG. Is a description of the chromaticity diagram M1 in which the color development points C obtained by coloring other copolymers of the first pH indicating monomer (AABAA) and the second pH indicating monomer (6 vinyl-αNP) at different pH values are plotted. FIG. These are the graphs of the relational expression F4 of the deflection angle D and pH value on the chromaticity diagram M of each coloring point C shown in FIG. These are explanatory drawing of the pH measuring method using the conventional chromaticity diagram M. FIG.

  In the present invention, a first pH indicating monomer and a second pH indicating monomer that change color tone in different pH ranges are copolymerized to obtain a wide pH indicating copolymer that changes color tone in two stages. One example of such first and second pH indicating monomers was synthesized by using a conventional low molecular weight pH indicator showing a color change in a specific pH region as a pH indicating site and introducing a polymerizable group into the specific site. Monomer. Many of the conventional representative low molecular pH indicators show a yellow color. For example, as shown in Table 1, a group A showing a yellow color on the low pH side (acid side) of the pH range showing a color tone change, a color tone change. It can be classified into Group B showing yellow on the high pH side (basic side) of the pH range shown, and Group C showing a color change but not showing yellow.

  Further, the present invention provides both pH indicating monomers in an intermediate range (including a region where both pH ranges overlap) between a first pH range in which the first pH indicating monomer changes its color tone and a second pH range in which the second pH indicating monomer changes its color tone. Is a color obtained by copolymerizing a plurality of types of pH indicating monomers such that both pH indicating monomers are different colors at both ends of the first pH range and the second pH range. For example, in Table 1, the first pH indicating monomer having methyl yellow of group B (color tone change pH range is acidic) and the bromothymol blue (color change pH range neutral) of group A as pH indicating sites. When the second pH indicating monomer is synthesized, both monomers are approximate colors (yellow) in the middle of the color change pH range. Also, methyl yellow is red on the low pH side (acid side) at one end of the color change pH range, whereas bromothymol blue is blue on the high pH side (basic side) at the other end of the color change pH range. Therefore, both monomers have different colors at both ends of the color change pH range. Therefore, the first pH indicating monomer having such a methyl yellow as the pH indicating site and the second pH indicating monomer having the bromothymol blue as the pH indicating site are copolymerized to produce the broad pH indicating copolymer of the present invention. Can be combined.

  Further, in Table 1, the first pH indicating monomer having the group C methyl orange (color change pH range is acidic) as the pH indicating site and the group A cresol red (color change pH range being basic) are indicated as the pH indicating site. When the second pH indicating monomer is synthesized, both monomers are approximate colors (yellow and orange) in the middle of the color change pH range. Also, methyl orange is red on the low pH side (acidic side) at one end of the color change pH range, whereas cresol red is reddish purple on the high pH side (basic side) at the other end of the color change pH range. Therefore, both monomers have different colors at both ends of the color change pH range. Therefore, the first pH indicating monomer having the methyl orange as the pH indicating site and the second pH indicating monomer having the cresol red as the pH indicating site are copolymerized to obtain the wide range pH indicating copolymer of the present invention. It can be.

  The polymerizable group introduced to make the pH indicator shown in Table 1 into a pH indicator monomer can be addition-polymerized with an unsaturated bond such as a (meth) acryloyl group, a (meth) acryloyloxy group, or a vinyl group. A polymerizable group such as an amino group, a carboxyl group, an aldehyde group, or a cyclic ether group can be used as the polymerizable group. Further, the pH indicator and the polymerizable group can be directly bonded, but can also be bonded via at least one of an alkylene group, an ether bond, a carbonyl group, and an amide bond (—CO—NH—). .

  However, in general, a low molecular pH indicator exhibiting a color tone change may not exhibit a similar color tone change when a polymerizable group is introduced, and the color tone change indicated by the low molecular pH indicator shown in Table 1 is not necessarily the pH value. It does not indicate a change in color tone of a pH indicator monomer synthesized using an indicator as a pH indicator site. It is necessary to use in the present invention after confirming the color change of the synthesized pH indicating monomer. In the following description, two kinds of pH indicators that have been confirmed to exhibit a similar color change as a pH-indicating monomer by introducing a polymerizable group in Table 1, that is, group B methyl yellow (with acidic pH range). Dimethylaminoazobenzene acrylate (AABAA) synthesized using pH change site as the pH indicator site is used as the first pH indicator monomer, and α-naphtholphthalein (α-NP, color tone change in basic pH range) of Group A is used as the pH indicator site. An example using 6 vinyl naphtholphthalein (6 vinyl-αNP) synthesized as a second pH indicating monomer will be described. However, the present invention is not limited to the use of a pH indicator monomer synthesized from the pH indicator shown in Table 1, and it is also possible to use other pH indicator monomers that change color tone within a predetermined pH range. .

(1) Preparation of first pH indicating monomer and confirmation of change in color tone As the first pH indicating monomer, dimethylamino introduced with a polymerizable group by reacting with methacrylic acid using methyl yellow of group B in Table 1 as a pH indicating site. Azobenzene acrylate (AABAA) was prepared (see formula (2)). Then, the prepared AABAA was copolymerized with N-isopropylacrylamide (NIPAAm) as a nonionic monomer and N, N-methylenebisacrylamide (MBAAm) as a crosslinking agent under the polymerization conditions shown in Table 2. A polymer (NIPAAm-ABAAA) was produced.

  A plurality of test pieces (1 × 1 cm) are formed using the prepared pH indicating copolymer (NIPAAm-ABAAA), and each test piece is immersed in an aqueous solution having different pH values of 0 to 8 prepared at pH 1 intervals. As in the case of Patent Document 3 described above, the color of each test piece is plotted on the chromaticity diagram M1 in FIG. 6A in which the white point O is arranged at the center. The deviation angle D of the coloring point C on the central polar coordinates was detected, and a relational expression F1 that approximated the relationship between the deviation angle D of the coloring point C and the pH value of each test piece with a logistic model (logistic curve) was obtained. The obtained relational expression F1 is shown in FIG.

  The relational expression F1 in FIG. 1 shows that the color-changing pH indicating copolymer using AABAA changes from red to yellow in the acidic region of pH 2 to 7, and the declination angle D increases as the pH increases. However, the curve changes from a concave state to a convex state, indicating that the pH (= pKa) at the inflection point is about 3.3. In addition, by co-polymerizing with AABAA and NIPAAm including an ionic monomer having an ionic part and a polymerizable part, the pH range where the color tone of the relational formula F1 changes can be shifted to the basic side or the acidic side. .

(2) Preparation of second pH indicating monomer and confirmation of change in color tone As the second pH monomer, as shown in the formula (6), α-naphtholphthalein (α-NP) of Group A in Table 1 is used as the pH indicating site, 6 vinyl naphtholphthalein (6 vinyl-αNP) in which a vinyl group was introduced as a polymerizable group at the 6-position of the isobenzofuran condensed ring was produced. Then, the produced 6 vinyl-αNP was copolymerized with NIPAAm, which is a nonionic monomer, and MBAAm, which is a crosslinking agent, under the polymerization conditions shown in Table 3 to produce a pH indicating copolymer (NIPAAm-6 vinyl αNP). .

  Next, a plurality of test pieces (1 × 1 cm) were formed using the prepared pH indicating copolymer (NIPAAm-6 vinyl αNP), and aqueous solutions having different pH values of 6 to 12 were prepared at pH 1 intervals. In the same way as in the case of the first pH indicating monomer described above, the color development of each test piece is plotted on the chromaticity diagram M1 in FIG. 6A and the white point O is the central polar coordinate. The deviation angle D of the upper coloring point C was detected, and a relational expression F2 that approximated the relationship between the deviation angle D of the coloring point C and the pH value of each test piece with a logistic model (logistic curve) was obtained. The obtained relational expression F2 is shown in FIG. 1 together with the relational expression F1.

  The relational expression F2 in FIG. 1 shows that the color changing pH-indicating copolymer using 6 vinyl-αNP changes in color from yellow to blue (light blue) in the basic region of pH 6-12. As the declination D increases, the curve changes from a concave state to a convex state while increasing, indicating that the pH (= pKa) at the inflection point is about 9.9. By co-polymerizing with 6 vinyl-αNP and NIPAAm including an ionic monomer having a ionic site and a polymerizable site, the pH range where the color tone of relational formula F2 changes is shifted to the basic side or acidic side. Can be made.

(3) Production of pH-indicating copolymer obtained by copolymerizing first pH-indicating monomer and second pH-indicating monomer What are the first pH-indicating monomer (AABAA) and the second pH-indicating monomer (6 vinyl-αNP)? The color change of each monomer is an approximate color (yellow) in the middle range of the pH range, that is, in the neutral range. The first pH indicating monomer (AABAA) is red on the low pH side (acid side) at one end of the color change pH range, whereas it is on the high pH side (basic side) at the other end of the color change pH range. Since the second pH indicating monomer (6 vinyl-αNP) is blue (light blue), both monomers have different colors at both ends of the color change pH range. Therefore, the first pH indicating monomer and the second pH indicating monomer satisfy the copolymerization conditions of the present invention.

Also, the relational expressions F1 and F2 in FIG. 1 are curves that change from a concave state to a convex state while the declination angle D increases as the pH increases, and the pKa of the first pH indicating monomer is about This indicates that the pKa of the second pH indicating monomer is about 9.9, while it is 3.3, so if both are copolymerized into the same polymer chain, two inflection points will be obtained. This suggests that a color-change-type pH indicating copolymer such as that possessed can be synthesized. Therefore, the pH indicating copolymer (8) is obtained by copolymerizing the first pH indicating monomer and the second pH indicating monomer, which change color tone in different pH ranges, with NIPAAm which is a nonionic monomer under the conditions shown in Table 4. Produced.

(4) Confirmation of change in color tone of pH indicating copolymer Different pH values obtained by molding a plurality of test pieces (2 × 2 cm) using the prepared pH indicating copolymer, and preparing each test piece at pH 1 intervals. As shown in FIG. 2A, the white point O is arranged at the center in the same manner as in the case of the first and second pH indicating monomers described above. Plotting on the chromaticity diagram M1, the deviation angle D of the coloring point C on the polar coordinates centered on the white point O was detected. The chromaticity diagram M1 in FIG. 2A is the same as the chromaticity diagram in FIG. And the relational expression F3 which approximated the relationship between the deflection angle D of the coloring point C of each test piece plotted as shown in FIG. 2A and the pH value by a logistic model (logistic curve) was obtained. The obtained relational expression F3 is shown in FIG.

  The relational expression F3 in FIG. 6 shows that the pH indicating copolymer obtained by copolymerizing the first pH indicating monomer using 6 vinyl-αNP and the second pH indicating monomer using AABAA has an acidic region of pH 2 to 7. The color tone changes from red to yellow at pH 2, and the first inflection point is present at pH 2 to 3. Further, the color changes from yellow to blue in the basic region of pH 7 to 12, indicating that the second inflection point exists at pH 9 to 10. That is, by copolymerizing the first pH indicating monomer (AABAA) and the second pH indicating monomer (6 vinyl-αNP), pH 2 to 3 and pH 7 to 12 have two color change points. It was possible to obtain a pH-indicating copolymer showing a two-stage color change that turns blue, and it was confirmed that a single copolymer could realize pH monitoring in a wide pH range from acidic to basic. .

(5) Adjustment of color tone change of pH indicating copolymer The copolymer of the first pH indicating monomer (AABAA) and the second pH indicating monomer (6 vinyl-αNP) is red, neutral in the acidic range. It shows a two-stage color change, yellow in the region and blue in the basic region. For example, by visually observing such a color change, it can be used for pH measurement over a wide range of pH 2-12. However, as can be seen from the relational expression F3 in FIG. 3, in the neutral region to the basic region of pH 5 to 8, the declination angle D on the chromaticity diagram M1 of the color development point of the copolymer depends on the increase of the pH value. There was a tendency to decrease. As shown in the enlarged view of the chromaticity diagram M1 in FIG. 2 (B), the cause of the decrease in the deviation angle D is from red to dark yellow (similar to orange) to light yellow from acid to neutral. Change from light yellow to dark yellow (similar to orange) again to blue from neutral to basic, and the color change between light yellow and dark yellow reciprocates. It is thought that there is in doing.

  The reason why the color tone changes to light yellow in the neutral range of FIG. 2B is that the light yellow color in the neutral range of the second pH indicating monomer (6 vinyl-αNP) is shown in the relational expression F2 in FIG. The result is strongly reflected. Therefore, in order to reduce the color tone change to light yellow in the neutral range, the first pH indicating monomer (AABAA), the second pH indicating monomer (6 vinyl-αNP), and the nonionic monomer NIPAAm are used under the conditions shown in Table 5. And a pH indicating copolymer (8) was prepared. In Table 5, the mixing ratio of the first pH indicating monomer and the second pH indicating monomer is changed as compared with Table 4, the mixing ratio of the first pH indicating monomer is increased, and the mixing ratio of the second pH indicating monomer is increased. Was lowered.

  A plurality of test pieces (2 × 2 cm) were molded using the pH indicating copolymer prepared under the conditions shown in Table 5, and each test piece was immersed in an aqueous solution having a pH value of 0 to 12 to develop a color. As shown in Fig. 4, the color development of each test piece is plotted on a chromaticity diagram M1 in which the white point O is arranged at the center to detect the polar angle D of each color development point C (see plot F4 in Fig. 4). . The chromaticity diagram M1 of FIG. 4 is the same as the chromaticity diagram of FIG. 2 (A), and the coloring point (plot F3) of the pH indicating copolymer prepared under the conditions of Table 4 is also shown for comparison. It is shown. And the relational expression F4 which approximated the relationship between the deviation angle D of the coloring point C and pH value of each plotted test piece with a logistic model (logistic curve) was obtained. The obtained relational expression F4 is shown in FIG. FIG. 5 also shows the relational expression F3 of FIG. 3 for comparison.

  As can be seen from FIG. 5, in the neutral region to the basic region of pH 5 to 8, in the relational expression F3, the deviation angle D on the chromaticity diagram M1 of the color development point of the copolymer decreases as the pH value increases. Although a tendency was observed, in the relational expression F4, the declination angle D on the chromaticity diagram M1 of the color development point of the copolymer is almost constant, and no tendency to decrease is observed. The reason why the tendency to decrease is not seen is that the mixing ratio of the first pH indicating monomer (AABAA) is relatively high and the mixing ratio of the second pH indicating monomer (6 vinyl-αNP) is relatively low. , The reflection of the color tone (light yellow) in the neutral range of the second pH indicating monomer was kept low, and it was thought that it was possible to avoid reciprocal unstable color change between light yellow and dark yellow. It is done.

  That is, in the present invention in which the first pH indicating monomer and the second pH indicating monomer are copolymerized, it is possible to control the change in the deviation angle D with respect to the pH value by adjusting the mixing ratio of the first and second pH indicating monomers. Thus, it was confirmed that a pH indicating copolymer can be synthesized such that the deviation angle D of each color development point on the chromaticity diagram M1 increases as the pH value increases. Note that the relational expression F4 in FIG. 5 has a smaller change in color tone (difference between the maximum value and the minimum value of the deflection angle D) than the relational expression F3, and the mixing ratio of the first and second pH indicating monomers. It can be seen that not only the change of the deflection angle D with respect to the pH value but also the difference between the maximum value and the minimum value of the deflection angle D can be controlled by adjusting the above. Therefore, it is important to design the mixing ratio of the first and second pH indicating monomers by taking into consideration both the optimization of the change of the deviation angle D with respect to the pH value and the optimization of the width of the color tone change.

  The wide-range pH indicating copolymer according to the present invention can change color tone in two steps according to an increase in pH value, and can measure pH over a wide range from the color tone change. Further, when the color development at a plurality of different pH values is plotted on a chromaticity diagram in which the white point is arranged at the center, and the deviation angle D of the color development point on the polar coordinate centered on the white point is detected, each pH value Can be arranged on the chromaticity diagram M1 so as to draw an arc centering on the white point O, that is, the declination D increases as the pH value increases. The pH value can be measured.

  Thus, the provision of “a pH indicating copolymer exhibiting a color change in a wide pH range”, which is an object of the present invention, can be achieved.

  In the above description, when both pH indicating monomers are approximate colors in the intermediate range between the first pH range in which the color tone of the first pH indicating monomer is changed and the second pH range in which the color tone of the second pH indicating monomer is changed. Although the invention can be applied, the present invention can also be applied when at least one of the pH indicating monomers is colorless in the intermediate range between the first pH range and the second pH range. By copolymerizing the monomer for use, it is possible to produce a copolymer for indicating a wide range of pH that changes its color tone in two steps as the pH value increases. In the intermediate range, the color development of one of the pH indicating monomers and the color development of the other pH indicating monomer do not interfere with each other, so that a smooth color change (smooth declination D of smooth declination D) occurs as the pH value increases. Increase).

  For example, in Table 1, the first pH indicating monomer having methyl yellow of group B (the color change pH range is acidic) and the thymolphthalein of group C (basic change pH range is basic) as the pH indicating site When the second pH indicating monomer is synthesized, one of the second pH indicating monomers is colorless in the middle range of the color change pH range, that is, in the neutral range. In addition, methyl yellow is red on the low pH side (acid side) at one end of the color change pH range, whereas thymolphthalein is blue on the high pH side (basic side) at the other end of the color change pH range. Therefore, both monomers have different colors at both ends of the color change pH range. Therefore, by copolymerizing the first pH indicator monomer having methyl yellow as the pH indicator site and the second pH indicator monomer having thymolphthalein as the pH indicator site, the color tone is increased in two stages according to the increase in pH value. The wide range pH indicating copolymer of the present invention can be changed.

  In the present invention, a first pH indicating monomer and a second pH indicating monomer that change color tone in different pH ranges are copolymerized to obtain a wide pH indicating copolymer that changes color tone in two stages. By changing the ion concentration around the main chain of the polymer by copolymerization including an ionic monomer having a neutral site, the color change region of the copolymer can be shifted to the basic side or the acidic side.

The ionic site can be an anionic site or a cationic site, and any one of the anions represented by the following formulas (I) to (VI) can be a cation and a salt. It is desirable that it is a forming group. Here, R ₁ in formula (II) is either an alkyl group or a hydrogen atom, any one of R _{2 to} R _{4 in} formula (IV) is a single bond, and the other two are the same or It is a different alkyl group, and R _{5 in} formula (V) is an alkyl group.

When the ionic moiety is a cationic moiety, a group in which —NR _n H _(3-n) ⁺ (R is an alkyl group, n is an integer of 0 to 3) forms a salt with an anion, or It is desirable that the cationized heterocycle and an anion form a salt.

  Further, when copolymerizing including an ionic monomer, instead of adjusting the mixing ratio of the first pH indicating monomer and the second pH indicating monomer described above, or the first pH indicating monomer and the second pH indicating monomer, In addition to the adjustment of the mixing ratio, it is also expected to control the color tone change with respect to the pH value by adjusting the mixing ratio of the ionic monomer. That is, as shown by the relational expression F3 in FIG. 3, for example, an undesired color tone change of the color development point of the copolymer in a specific color tone change region (the declination angle D on the chromaticity diagram M1 corresponds to an increase in pH value). A first pH range in which the color tone of the first pH indicating monomer is changed and a second pH range in which the color tone of the second pH indicating monomer is changed by adjusting the mixing ratio of the ionic monomer when a tendency to decrease is observed. It is possible to control the color tone change (change in the declination angle D with respect to the pH value) in the middle range of the image, and by improving the undesired color tone change, the declination angle D on the chromaticity diagram M1 increases the pH value. It can be expected to be a pH indicating copolymer that increases accordingly.

C ... Color development point D ... Deflection angle F ... Relational expression M ... Chromaticity diagram O ... White point

Claims (7)

A first pH indicator monomer containing a first pH indicator site and a polymerizable group that changes color in the first pH range, and a second pH indicator containing a second pH indicator site and a polymerizable group that changes color in a second pH range different from the first pH range And a nonionic monomer containing an electrically neutral site and a polymerizable group, and both pH indicating monomers are approximate colors in the intermediate range of the first and second pH ranges. A wide-range pH-indicating copolymer that is or at least one of which is colorless and the two pH-indicating monomers have different colors in both end regions of the first and second pH ranges. 2. The copolymer for pH indication according to claim 1, wherein the copolymer further comprises an ionic monomer containing an ionic moiety and a polymerizable group. The copolymer according to claim 1 or 2, wherein the first pH indicating monomer changes color in an acidic range, and the second pH indicating monomer changes color in a basic range. Coalescence. 4. The pH indicating copolymer according to claim 1, wherein the mixing ratio of the first and second pH indicating monomers is a plurality of different pH values spanning the first and second pH ranges. When the color development of the copolymer is plotted on a chromaticity diagram in which the white point is arranged at the center and the deviation angle D of the color development point on the polar coordinates of the white point is detected, the pH value increases. A wide-range pH indicating copolymer that is adjusted so that the deviation angle D of each color development point increases. The pH indicating copolymer according to claim 2 or claim 3 subordinate to claim 2, wherein the mixing ratio of the ionic monomer is the pH indicating at a plurality of different pH values spanning the first and second pH ranges. When the color development of the copolymer is plotted on a chromaticity diagram in which the white point is arranged at the center and the deviation angle D of the color development point on the polar coordinates of the white point is detected, the pH value increases. A wide-range pH indicating copolymer that is adjusted so that the deviation angle D of each color development point increases. The method for synthesizing a pH indicating copolymer according to any one of claims 1 to 3, wherein the white point indicates the color development of the pH indicating copolymer at a plurality of different pH values over the first and second pH ranges. When the deviation angle D of the color development point on the polar coordinates centered on the white point is detected by plotting on the arranged chromaticity diagram, the deviation angle D of each color development point increases as the pH value increases. And a method for synthesizing a wide-range pH indicating copolymer obtained by adjusting the mixing ratio of the first and second pH indicating monomers. The method for synthesizing a pH indicating copolymer according to claim 2 or claim 3 dependent on claim 2, wherein the pH indicating copolymer is colored at a plurality of different pH values over the first and second pH ranges. When the white point is plotted on the chromaticity diagram arranged at the center and the deviation point D of the coloring point on the polar coordinates of the white point is detected, the deviation angle of each coloring point according to the increase of the pH value A method for synthesizing a wide-range pH indicating copolymer obtained by adjusting the mixing ratio of the ionic monomer so that D increases.