阅读说明：本技术 一种热致物理交联的彩色水凝胶及其制备方法 (Thermotropic physical crosslinked colored hydrogel and preparation method thereof ) 是由 鲁希华 李雪婷 李晓晓 于 2021-02-09 设计创作，主要内容包括：本发明具体涉及一种热致物理交联的彩色水凝胶及其制备方法。首先以N-异丙基丙烯酰胺(NIPAm)为聚合物提供温敏性的功能单体,N-叔丁基丙烯酰胺(TBA)为疏水性单体,L-N-丙酰基苯丙氨酸(Aphe)为亲水性单体,通过控制调整Aphe的引入量,共聚得到具有温度响应性的P(NIPAm-TBA-Aphe)三元共聚纳米水凝胶。然后采用温度触发原位实现溶胶-凝胶化过程并保持其亮丽的结构色：将纳米水凝胶在一定温度范围内升温,调节其浓度范围,其由可流动的溶液状态转为不可流动的宏观果冻状水凝胶状态,同时该水凝胶具有亮丽的结构色,且该原位溶胶-凝胶化转变具有可逆性。(The invention particularly relates to a thermotropic physical crosslinked colored hydrogel and a preparation method thereof. Firstly, N-isopropyl acrylamide (NIPAm) is used as a functional monomer for providing temperature sensitivity for a polymer, N-tert-butyl acrylamide (TBA) is used as a hydrophobic monomer, L-N-propionyl phenylalanine (Aphe) is used as a hydrophilic monomer, and P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel with temperature responsiveness is obtained through copolymerization by controlling and adjusting the introduction amount of Aphe. Then, the sol-gelation process is realized in situ by adopting temperature triggering, and the bright structural color is kept: the nano hydrogel is heated within a certain temperature range, the concentration range of the nano hydrogel is adjusted, the nano hydrogel is converted into a non-flowable macroscopic jelly-shaped hydrogel state from a flowable solution state, meanwhile, the nano hydrogel has a bright structural color, and the in-situ sol-gel conversion is reversible.)

1. The thermotropic physical crosslinked colored hydrogel and the preparation method thereof are characterized by comprising the following steps:

(1) preparing P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel: dissolving monomers of N-isopropylacrylamide, N-tert-butylacrylamide (TBA), L-N-propionyl phenylalanine (Aphe), a crosslinking agent of N, N' -methylene bisacrylamide and an emulsifier of sodium dodecyl sulfate in deionized water, heating to 60-80 ℃ in a nitrogen atmosphere, preserving heat for 20-40 min, adding an initiator of ammonium persulfate to react for 4 hours, and dialyzing after the reaction to obtain P (NIPAm-TBA-Aphe) ternary copolymerization nano hydrogel;

(2) formation of colored hydrogels by thermal physical crosslinking: placing the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel after dialysis and purification in a 50 ℃ oven, concentrating to a specific concentration range, then placing the nano hydrogel in a thermostat, heating at a specific temperature range and a specific heating rate, and keeping the temperature for 5min at intervals of 1 temperature point to enable the nano hydrogel to generate thermal sol-gelation transformation under the condition of no salt ions, thereby obtaining the jelly-like thermal physical crosslinking colored hydrogel.

2. The thermophysically crosslinked colored hydrogel according to claim 1, wherein the monomer for providing temperature sensitivity to the polymer in step (1) is N-isopropylacrylamide, and the amount added is 68 to 84% of the total molar amount of the four reactants, N-isopropylacrylamide, N-tert-butylacrylamide, L-N-propionylphenylalanine, and N, N' -methylenebisacrylamide.

3. The thermophysically crosslinked colored hydrogel according to claim 1, wherein the hydrophobic monomer in step (1) is N-t-butylacrylamide, and is added in an amount of 12-20% of the total molar amount of the four reactive species N-isopropylacrylamide, N-t-butylacrylamide, L-propionylphenylalanine, and N, N' -methylenebisacrylamide.

4. The thermophysically crosslinked colored hydrogel according to claim 1, wherein the hydrophilic monomer in step (1) is L-N-propionylphenylalanine, and the amount added is 2 to 10% of the total molar amount of the four reactive species of N-isopropylacrylamide, N-t-butylacrylamide, L-N-propionylphenylalanine, and N, N' -methylenebisacrylamide.

5. The thermotropic physically crosslinked colored hydrogel according to claim 1, wherein the crosslinking agent in step (1) is N, N '-methylenebisacrylamide, and is added in an amount of 1 to 3% of the total molar amount of the four reactive materials of N-isopropylacrylamide, N-t-butylacrylamide, L-N-propionylphenylalanine, and N, N' -methylenebisacrylamide.

6. The thermophysically crosslinked colored hydrogel according to claim 1, wherein the emulsifier in step (1) is sodium dodecyl sulfate, and is added in an amount of 3 to 6% by mass based on the total amount of the four reactive materials, i.e., N-isopropylacrylamide, N-t-butylacrylamide, L-propionylphenylalanine, and N, N' -methylenebisacrylamide.

7. The thermophysically crosslinked colored hydrogel according to claim 1, wherein the initiator in step (1) is ammonium persulfate, and the amount added is 5-8% of the total mass of the four reactive species of N-isopropylacrylamide, N-tert-butylacrylamide, L-propionyl-phenylalanine, and N, N' -methylenebisacrylamide.

8. The thermophysically crosslinked colored hydrogel according to claim 1, wherein the specific conditions of dialysis in step (1) are soaking in ultrapure water for 3-7 days, water is changed 3 times per day, and the cut-off molecular weight of a dialysis bag used in dialysis is 8000-14000.

9. The thermophysically crosslinked color hydrogel according to claim 1, wherein the P (NIPAm-TBA-Aphe) ternary copolymer nano hydrogel purified by dialysis in step (2) is evaporated and concentrated in an oven at 50 ℃ to a concentration range of 1.6-6% by mass concentration.

10. The sol-gel method of the thermophysically crosslinked color hydrogel according to claim 9, wherein the concentrated nano-hydrogel is placed in a thermostat to undergo a thermal sol-gel transition, wherein the thermostat has a temperature ranging from 25 ℃ to 40 ℃ and a heating rate of 1 ℃/min.

Technical Field

The invention belongs to the field of nano hydrogel and preparation thereof, and particularly relates to a thermotropic physical crosslinked colored hydrogel and a preparation method thereof.

Background

Currently, temperature-triggered thermotropic physically crosslinked hydrogels are mostly based on the preparation of poly (N-isopropylacrylamide) (PNIPAm) hydrogels. The hydrogel dispersion liquid can form a physical crosslinking site by mutually intertwining hydrophobic groups of PNIPAm above the phase transition temperature to generate in-situ sol-gel transformation, thereby obtaining the thermotropic physical crosslinking jelly-like hydrogel.

However, the severe shrinkage of the PNIPAm component above the phase transition temperature results in an increase in the haze of the hydrogel, and the resulting physically crosslinked hydrogel changes color to a milky white color. For example, PNIPAm-based nanohydrogels prepared by Hu et al can undergo a thermotropic sol-gel transition above the phase transition temperature, but the resulting thermotropic physically crosslinked hydrogels appear milky (Langmuir, Vol. 20, number 6, 2004).

At present, the preparation of colored macroscopic hydrogels based on in situ formation is generally based on organic hydrogels with supramolecular structures or hydrogels of ionic liquid type. For example, Li et al prepared supramolecular hydrogels based on 2, 6-pyridinedicarboxylic acid functionalized dextran (PDA), which hydrogel dispersions undergo a sol-gel transition upon photo-induction, resulting in crosslinked colored hydrogels. However, this type of crosslinking is chemical crosslinking and is not reversible. In addition, the hydrogel generally has the defects of complicated preparation process, easy introduction of toxic reagents, irreversible sol-gelation process and the like.

Therefore, the method for developing the PNIPAm-based thermotropic physical crosslinking colored hydrogel which is simple, convenient and feasible and is easy to produce in a large scale has certain significance for widening the research direction of the PNIPAm-type hydrogel.

Disclosure of Invention

The invention provides a thermotropic physical crosslinked colored hydrogel and a preparation method thereof, the synthesis process adopted by the invention is simple and easy to implement, green and environment-friendly, the in-situ sol-gelation conversion is realized only by temperature triggering, and simultaneously the formed jelly-like macroscopic hydrogel has bright structural color and reversibility.

In order to achieve the purpose, the invention is realized by the following technical scheme:

a thermotropic physical crosslinked colored hydrogel and a preparation method thereof, comprising the following steps:

(1) preparing P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel: dissolving monomers of N-isopropylacrylamide, N-tert-butylacrylamide (TBA), L-N-propionyl phenylalanine (Aphe), a crosslinking agent of N, N' -methylene bisacrylamide and an emulsifier of sodium dodecyl sulfate in deionized water, heating to 60-80 ℃ in a nitrogen atmosphere, preserving heat for 20-40 min, adding an initiator of ammonium persulfate to react for 4 hours, and dialyzing after the reaction to obtain P (NIPAm-TBA-Aphe) ternary copolymerization nano hydrogel;

(2) formation of colored hydrogels by thermal physical crosslinking: placing the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel after dialysis and purification in a 50 ℃ oven, concentrating to a specific concentration range, then placing the nano hydrogel in a thermostat, heating at a specific temperature range and a specific heating rate, and keeping the temperature for 5min at intervals of 1 temperature point to enable the nano hydrogel to generate thermal sol-gelation transformation under the condition of no salt ions, thereby obtaining the jelly-like thermal physical crosslinking colored hydrogel.

Furthermore, the monomer providing temperature sensitivity for the polymer in the step (1) is N-isopropylacrylamide, and the adding amount is 68-84% of the total mol amount of the four reaction substances of N-isopropylacrylamide, N-tert-butylacrylamide, L-propionyl phenylalanine and N, N' -methylene bisacrylamide.

Furthermore, the hydrophobic monomer in the step (1) is N-tertiary butyl acrylamide, and the adding amount of the hydrophobic monomer is 12-20% of the total mol amount of four reaction substances of N-isopropyl acrylamide, N-tertiary butyl acrylamide, L-N-propionyl phenylalanine and N, N' -methylene bisacrylamide.

Furthermore, the hydrophilic monomer in the step (1) is L-N-propionyl phenylalanine, and the adding amount of the hydrophilic monomer is 2 to 10 percent of the total mole amount of four reaction substances of N-isopropyl acrylamide, N-tert-butyl acrylamide, L-N-propionyl phenylalanine and N, N' -methylene bisacrylamide.

Furthermore, the cross-linking agent in the step (1) is N, N '-methylene bisacrylamide, and the adding amount is 1 to 3 percent of the total mole amount of the four reaction substances of N-isopropylacrylamide, N-tert-butylacrylamide, L-N-propionyl phenylalanine and N, N' -methylene bisacrylamide.

Furthermore, the emulsifier in the step (1) is sodium dodecyl sulfate, and the adding amount of the emulsifier is 3-6% of the total mass of four reaction substances of N-isopropylacrylamide, N-tert-butylacrylamide, L-N-propionyl phenylalanine and N, N' -methylene bisacrylamide.

Further, the initiator in the step (1) is ammonium persulfate, and the adding amount of the initiator is 5-8% of the total mass of four reaction substances of N-isopropylacrylamide, N-tert-butylacrylamide, L-N-propionyl phenylalanine and N, N' -methylene bisacrylamide.

Further, in the step (1), the specific conditions of dialysis are soaking for 3-7 days by adopting ultrapure water, water is changed for 3 times every day, and the cut-off molecular weight of a dialysis bag used for dialysis is 8000-14000.

Further, in the step (2), the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel after dialysis and purification is placed in an oven at 50 ℃ for evaporation and concentration, and the concentration range is 1.6-6% by mass concentration.

Further, in the step (2), the concentrated nano hydrogel is placed in a thermostat to generate thermal sol-gelation transformation, the temperature range of the thermostat is 25-40 ℃, and the heating rate is 1 ℃/min.

The principle of the invention is as follows:

the invention utilizes N-isopropyl acrylamide (NIPAm) as a temperature-sensitive functional monomer, N-tert-butyl acrylamide (TBA) as a hydrophobic monomer and L-N-propionyl phenylalanine (Aphe) as a hydrophilic monomer to carry out ternary polymerization to obtain the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel with temperature responsiveness (figure 1). By adjusting the introduction amount of the hydrophilic monomer Aphe, under certain conditions of concentration and temperature, the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel can generate thermally-induced in-situ sol-gel transformation under the condition of no salt ions, so that the thermally-induced physically-crosslinked colored jelly-like hydrogel is obtained.

Compared with the prior art, the invention has the beneficial effects that:

the method has simple process and is environment-friendly, and the ternary copolymerized nano hydrogel dispersion liquid can generate sol-gelation phase transformation to form the colorful jelly-shaped macroscopic hydrogel. And maintains beautiful color without any pigment incorporation during the thermal gelation process, and the in-situ sol-gel transition is reversible.

Drawings

FIG. 1 is a schematic diagram of the synthesis of P (NIPAm-TBA-Aphe) copolymerized nano-hydrogel;

FIG. 2 is an optical photograph of P (NIPAm-TBA-Aphe) copolymerized nanohydrogel of examples 1 to 3 and comparative example 1 during sol-gel transition (dark blue, cyan, light blue in order from left to right nanohydrogel color at 37 ℃ and white turbid color, blue, cyan, light blue in order from left to right color at 37 ℃);

FIG. 3 is a phase transition curve of particle size of P (NIPAm-TBA-Aphe) copolymerized nanohydrogel according to example 1 with temperature;

FIG. 4 is an optical photograph of P (NIPAm-TBA-Aphe) copolymerized nanohydrogel in example 1 and comparative examples 2-3 during sol-gel transition (red, cyan, yellow-green, blue, bluish-purple, in order from left to right at 25 ℃ and white-turbid, cyan, yellow-green, blue, bluish-purple, in order from left to right at 37 ℃);

FIG. 5 is a graph showing the change of viscosity with temperature during thermal sol-gelation process of P (NIPAm-TBA-Aphe) copolymerized nanohydrogel of examples 1 to 3;

FIG. 6 is a color reflectance spectrum of one-to-one structural color during sol-gel transition of the P (NIPAm-TBA-Aphe) copolymerized nanohydrogel of example 1 and comparative examples 2-3 of FIG. 4.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

Examples 1-9 are examples of the preparation of P (NIPAm-TBA-Aphe) copolymerized nanohydrogel of the present invention, which was obtained by thermal physical crosslinking and had reversibility in a macroscopic jelly-like color hydrogel.

Comparative example 1 is a preparation example of P (NIPAm-TBA-Aphe) copolymerized nano hydrogel introduced with very low content of hydrophilic monomer L-N-propionyl phenylalanine, and in case that the introduced amount of L-N-propionyl phenylalanine is insufficient, the nano hydrogel of comparative example 1 is gelled to form a macroscopic jelly-like hydrogel but loses its beautiful structural color even though the concentration and temperature of the nano hydrogel are adjusted.

Comparative example 2 is that when the nano hydrogel concentration was too low, even though the hydrophilic monomer L-N-propionyl phenylalanine was introduced in a sufficient amount, not only the brilliant structural color thereof was lost, but also the thermal sol-gel transition could not occur due to small intermolecular force at a low concentration, and a macroscopic hydrogel could not be formed.

Comparative example 3 is a case where the concentration of the nano-hydrogel was too low, and even though the hydrophilic monomer L-N-propionylphenylalanine was introduced in a sufficient amount, the color of the blue-green structure was maintained, but the thermal sol-gel transition did not occur due to the small intermolecular force at a low concentration, and the macroscopic hydrogel could not be formed.

Comparative example 1:

approximately 0.9551g of monomeric N-isopropylacrylamide (NIPAm), 0.1521g of monomeric N-tert-butylacrylamide, 0.0341g of monomeric L-propionylphenylalanine (Aphe), 0.0302g of crosslinker N, N' -methylenebisacrylamide and 0.0412g of emulsifier sodium dodecyl sulfate were dissolved in 95 ml of deionized water and bubbled with N at room temperature₂Deoxidizing and magnetically stirring for 30 minutes;

the reaction temperature was raised to 70 ℃ and maintained at N₂Preserving the heat for 30 minutes under protection;

about 0.0612 g of initiator ammonium persulfate was then dissolved in 5 ml of deionized water and added as described aboveIn solution, maintain N₂Continuing the reaction for 4 hours under the atmosphere;

then soaking the obtained reactant in deionized water for dialysis for 7 days, changing water three times a day, and removing residual reaction raw materials and electrolyte in the reaction system. The cut-off molecular weight of the dialysis bag is 8000-14000. Thus obtaining the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel.

Placing the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel after dialysis and purification in a 50 ℃ oven, and concentrating to a mass concentration of 2.5 wt%. Then the mixture is put into a thermostat at 25 ℃ and is kept at the temperature rising rate of 1 ℃/min for 5min at intervals and is heated to 37 ℃. Due to too small amount of Aphe, the copolymerized nano hydrogel of the comparative example forms the thermophysically crosslinked hydrogel, but has a white turbid color and loses structural color (as shown in FIG. 2), i.e., the thermophysically crosslinked colored jelly-like hydrogel cannot be obtained.

Comparative example 2:

approximately 0.9231g of monomeric N-isopropylacrylamide (NIPAm), 0.1526g of monomeric N-tert-butylacrylamide, 0.0962g of monomeric L-N-propionylphenylalanine (Aphe), 0.0295g of crosslinker N, N' -methylenebisacrylamide and 0.0408g of emulsifier sodium dodecyl sulfate were dissolved in 95 ml of deionized water, and N was bubbled at room temperature₂Deoxidizing and magnetically stirring for 30 minutes;

the reaction temperature was raised to 70 ℃ and maintained at N₂Preserving the heat for 30 minutes under protection;

about 0.0679 g of initiator ammonium persulfate was then dissolved in 5 ml of deionized water and added to the above solution, maintaining N₂Continuing the reaction for 4 hours under the atmosphere;

then soaking the obtained reactant in deionized water for dialysis for 7 days, changing water three times a day, and removing residual reaction raw materials and electrolyte in the reaction system. The cut-off molecular weight of the dialysis bag is 8000-14000. Thus obtaining the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel.

Placing the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel after dialysis and purification in a 50 ℃ oven, and concentrating to the mass concentration of 1.0 wt%. Then the mixture is put into a thermostat at 25 ℃ and is kept at the temperature rising rate of 1 ℃/min for 5min at intervals and is heated to 34 ℃. Because the concentration of the comparative example copolymerized nano hydrogel is too low, the copolymerized nano hydrogel not only has a white turbid color and loses structural color (the color reflection spectrum is obviously weakened as shown in figure 6, namely the structural color is destroyed), but also cannot become a macroscopic jelly-shaped hydrogel (as shown in figure 4) because the intermolecular force is small at low concentration, namely the thermotropic physically crosslinked colored jelly-shaped hydrogel cannot be obtained.

Comparative example 3:

approximately 0.9231g of monomeric N-isopropylacrylamide (NIPAm), 0.1526g of monomeric N-tert-butylacrylamide, 0.0962g of monomeric L-N-propionylphenylalanine (Aphe), 0.0295g of crosslinker N, N' -methylenebisacrylamide and 0.0408g of emulsifier sodium dodecyl sulfate were dissolved in 95 ml of deionized water, and N was bubbled at room temperature₂Deoxidizing and magnetically stirring for 30 minutes;

the reaction temperature was raised to 70 ℃ and maintained at N₂Preserving the heat for 30 minutes under protection;

about 0.0679 g of initiator ammonium persulfate was then dissolved in 5 ml of deionized water and added to the above solution, maintaining N₂Continuing the reaction for 4 hours under the atmosphere;

then soaking the obtained reactant in deionized water for dialysis for 7 days, changing water three times a day, and removing residual reaction raw materials and electrolyte in the reaction system. The cut-off molecular weight of the dialysis bag is 8000-14000. Thus obtaining the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel.

Placing the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel after dialysis and purification in a 50 ℃ oven, and concentrating to the mass concentration of 1.5 wt%. Then the mixture is put into a thermostat at 25 ℃ and is kept at the temperature rising rate of 1 ℃/min for 5min at intervals and is heated to 34 ℃. Although the comparative example copolymerized nano hydrogel still maintains a brilliant blue-green structural color (as shown in fig. 6) due to a too low concentration, it cannot become a macroscopic jelly-like hydrogel (as shown in fig. 4) due to a small intermolecular force at a low concentration, i.e., a thermophysically crosslinked colored jelly-like hydrogel cannot be obtained.

Example 1:

about 0.9231g of monomeric N-isopropylacrylamide (NIPAm) and 0.1526g of monomeric N-tert-butylpropanol were takenEnamide, 0.0962g of monomeric L-N-propionylphenylalanine (Aphe), 0.0295g of crosslinker N, N' -methylenebisacrylamide, 0.0408g of emulsifier sodium dodecyl sulfate were dissolved in 95 ml of deionized water, and N was bubbled in at room temperature₂Deoxidizing and magnetically stirring for 30 minutes;

the reaction temperature was raised to 70 ℃ and maintained at N₂Preserving the heat for 30 minutes under protection;

about 0.0679 g of initiator ammonium persulfate was then dissolved in 5 ml of deionized water and added to the above solution, maintaining N₂Continuing the reaction for 4 hours under the atmosphere;

then soaking the obtained reactant in deionized water for dialysis for 7 days, changing water three times a day, and removing residual reaction raw materials and electrolyte in the reaction system. The cut-off molecular weight of the dialysis bag is 8000-14000. Thus obtaining the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel.

Placing the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel after dialysis and purification in a 50 ℃ oven, and concentrating to a mass concentration of 2.5 wt%. Then the mixture is put into a thermostat at 25 ℃ and is kept at the temperature rising rate of 1 ℃/min for 5min at intervals and is heated to 37 ℃. The concentration of the copolymerized nano hydrogel in the example is kept unchanged (as shown in fig. 2) while the sol-gel transformation is completed, namely, the thermotropic physical crosslinked colored jelly-like hydrogel is formed.

As can be seen from the phase transition curve of the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel in FIG. 3, the particle size of the nano hydrogel of the sample in example 1 decreases with the temperature increase from 20 ℃ to 45 ℃ at the pH value of 5.5, and the observation shows that the particle size of the nano hydrogel changes significantly at the temperature point of 32 ℃, which indicates that the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel has temperature responsiveness.

As can be seen from the optical picture of the reversible sol-gelation process of the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel in FIG. 4 under different concentrations and the corresponding color reflection spectrum of FIG. 6, when the concentration is 2.0wt%, the temperature is raised from 25 ℃ to 34 ℃, and the thermotropic physical crosslinked brilliant yellow-green jelly-like hydrogel is obtained. When the concentration is 2.5wt%, the temperature is raised from 25 ℃ to 34 ℃, and the thermal physical crosslinked brilliant blue jelly hydrogel is obtained. When the concentration is 3.0wt%, the temperature is raised from 25 ℃ to 34 ℃, and then the thermal physical crosslinking brilliant blue-violet jelly hydrogel is obtained, wherein the viscosity curve along with the temperature change in fig. 5 shows that if the nano hydrogel generates temperature-triggered sol-gel transition, the viscosity of the nano hydrogel is obviously increased along with the temperature increase, and further shows that the nano hydrogel generates temperature-triggered sol-gel transition.

In summary, it is shown that the temperature-induced sol-gelation process is completed only when the nano-hydrogel in this example is at a concentration of 2.0wt% or more. When the temperature returns to room temperature of 25 ℃, it may undergo a gel-lyotropic transition. Thus indicating that the gelation process of the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel has reversibility.

Example 2:

about 0.9062g of monomeric N-isopropylacrylamide (NIPAm), 0.1512g of monomeric N-tert-butylacrylamide, 0.1298g of monomeric L-propionyl phenylalanine (Aphe), 0.0306g of crosslinker N, N' -methylenebisacrylamide, 0.0398g of emulsifier sodium dodecyl sulfate were dissolved in 95 ml of deionized water, and N was bubbled at room temperature₂Deoxidizing and magnetically stirring for 30 minutes;

the reaction temperature was raised to 70 ℃ and maintained at N₂Preserving the heat for 30 minutes under protection;

about 0.0615 g of initiator ammonium persulfate was then dissolved in 5 ml of deionized water and added to the above solution, maintaining the N₂Continuing the reaction for 4 hours under the atmosphere;

then soaking the obtained reactant in deionized water for dialysis for 7 days, changing water three times a day, and removing residual reaction raw materials and electrolyte in the reaction system. The cut-off molecular weight of the dialysis bag is 8000-14000. Thus obtaining the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel.

Placing the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel after dialysis and purification in a 50 ℃ oven, and concentrating to a mass concentration of 2.5 wt%. Then the mixture is put into a thermostat at 25 ℃ and is kept at the temperature rising rate of 1 ℃/min for 5min at intervals and is heated to 37 ℃. In this example, the concentration of the copolymerized nano hydrogel is maintained to be unchanged (as shown in fig. 2) while the sol-gel transformation is completed (as shown in fig. 5), i.e., the thermotropic physical crosslinked colored jelly-like hydrogel is formed.

Example 3:

approximately 0.8761g of monomeric N-isopropylacrylamide (NIPAm), 0.1518g of monomeric N-tert-butylacrylamide, 0.1881g of monomeric L-N-propionylphenylalanine (Aphe), 0.0297g of crosslinker N, N' -methylenebisacrylamide and 0.0401g of emulsifier sodium dodecyl sulfate were dissolved in 95 ml of deionized water and bubbled with N at room temperature₂Deoxidizing and magnetically stirring for 30 minutes;

the reaction temperature was raised to 70 ℃ and maintained at N₂Preserving the heat for 30 minutes under protection;

about 0.0625 g of initiator ammonium persulfate was then dissolved in 5 ml of deionized water and added to the above solution, maintaining N₂Continuing the reaction for 4 hours under the atmosphere;

then soaking the obtained reactant in deionized water for dialysis for 7 days, changing water three times a day, and removing residual reaction raw materials and electrolyte in the reaction system. The cut-off molecular weight of the dialysis bag is 8000-14000. Thus obtaining the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel.

Placing the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel after dialysis and purification in a 50 ℃ oven, and concentrating to a mass concentration of 2.5 wt%. Then the mixture is put into a thermostat at 25 ℃ and is kept at the temperature rising rate of 1 ℃/min for 5min at intervals and is heated to 37 ℃. The concentration of the copolymerized nano hydrogel in this example is kept unchanged (as shown in fig. 2) while the sol-gel transformation is completed (as shown in fig. 5), i.e., the thermotropic physical crosslinked colored jelly-like hydrogel is formed.

Example 4:

approximately 0.9298g of monomeric N-isopropylacrylamide (NIPAm), 0.1526g of monomeric N-tert-butylacrylamide, 0.0821g of monomeric L-N-propionylphenylalanine (Aphe), 0.0303g of crosslinker N, N' -methylenebisacrylamide, 0.0403g of emulsifier sodium dodecyl sulfate were dissolved in 95 ml of deionized water, and N was bubbled at room temperature₂Deoxidizing and magnetically stirring for 30 minutes;

the reaction temperature is raised to 70 DEG CAnd is in N₂Preserving the heat for 30 minutes under protection;

about 0.0623g of initiator ammonium persulfate was then dissolved in 5 ml of deionized water and added to the above solution, maintaining N₂Continuing the reaction for 4 hours under the atmosphere;

then soaking the obtained reactant in deionized water for dialysis for 7 days, changing water three times a day, and removing residual reaction raw materials and electrolyte in the reaction system. The cut-off molecular weight of the dialysis bag is 8000-14000. Thus obtaining the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel.

Placing the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel after dialysis and purification in a 50 ℃ oven, and concentrating until the mass concentration is 3.5 wt%. Then the mixture is put into a thermostat at 25 ℃ and is kept at the temperature rising rate of 1 ℃/min for 5min at intervals and is heated to 37 ℃. The concentration of the copolymerization nano hydrogel in the embodiment can keep the original bright bluish purple structure color unchanged while finishing the sol-gel transformation, namely the thermotropic physical crosslinking color jelly-shaped hydrogel is formed.

Example 5:

approximately 0.9104g of monomeric N-isopropylacrylamide (NIPAm), 0.1519g of monomeric N-tert-butylacrylamide, 0.1205g of monomeric L-propionylphenylalanine (Aphe), 0.0304g of crosslinker N, N' -methylenebisacrylamide and 0.0405g of emulsifier sodium dodecyl sulfate were dissolved in 95 ml of deionized water and bubbled with N at room temperature₂Deoxidizing and magnetically stirring for 30 minutes;

the reaction temperature was raised to 70 ℃ and maintained at N₂Preserving the heat for 30 minutes under protection;

about 0.0623g of initiator ammonium persulfate was then dissolved in 5 ml of deionized water and added to the above solution, maintaining N₂Continuing the reaction for 4 hours under the atmosphere;

then soaking the obtained reactant in deionized water for dialysis for 7 days, changing water three times a day, and removing residual reaction raw materials and electrolyte in the reaction system. The cut-off molecular weight of the dialysis bag is 8000-14000. Thus obtaining the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel.

Placing the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel after dialysis and purification in a 50 ℃ oven, and concentrating until the mass concentration is 3.0 wt%. Then the mixture is put into a thermostat at 25 ℃ and is kept at the temperature rising rate of 1 ℃/min for 5min at intervals and is heated to 37 ℃. In the embodiment, the concentration of the copolymerized nano hydrogel is kept unchanged when the sol-gel transformation is completed, namely the thermotropic physical crosslinked colorful jelly-shaped hydrogel is formed.

Example 6:

about 0.9020g of monomeric N-isopropylacrylamide (NIPAm), 0.1512g of monomeric N-tert-butylacrylamide, 0.1380g of monomeric L-propionyl phenylalanine (Aphe), 0.0303g of crosslinker N, N' -methylenebisacrylamide, 0.0402g of emulsifier sodium dodecyl sulfate were dissolved in 95 ml of deionized water, and N was bubbled at room temperature₂Deoxidizing and magnetically stirring for 30 minutes;

the reaction temperature was raised to 70 ℃ and maintained at N₂Preserving the heat for 30 minutes under protection;

about 0.0689g of initiator ammonium persulfate was then dissolved in 5 ml of deionized water and added to the above solution, maintaining N₂Continuing the reaction for 4 hours under the atmosphere;

then soaking the obtained reactant in deionized water for dialysis for 7 days, changing water three times a day, and removing residual reaction raw materials and electrolyte in the reaction system. The cut-off molecular weight of the dialysis bag is 8000-14000. Thus obtaining the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel.

Placing the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel after dialysis and purification in a 50 ℃ oven, and concentrating to a mass concentration of 2.2 wt%. Then the mixture is put into a thermostat at 25 ℃ and is kept at the temperature rising rate of 1 ℃/min for 5min at intervals and is heated to 37 ℃. The concentration of the copolymerization nano hydrogel in the embodiment can keep the original bright yellow-green structure color unchanged while finishing the sol-gel transformation, namely the thermotropic physical crosslinking colored jelly-like hydrogel is formed.

Example 7:

about 0.8870g of monomeric N-isopropylacrylamide (NIPAm), 0.1521g of monomeric N-tert-butylacrylamide, 0.1649g of monomeric L-N-propionylphenylalanine (Aphe), 0.0307g of crosslinker N, N' -methylenebisacrylamide, and,0.0399g of the emulsifier sodium lauryl sulfate are dissolved in 95 ml of deionized water and N is bubbled at room temperature₂Deoxidizing and magnetically stirring for 30 minutes;

the reaction temperature was raised to 70 ℃ and maintained at N₂Preserving the heat for 30 minutes under protection;

about 0.0713g of initiator ammonium persulfate was then dissolved in 5 ml of deionized water and added to the above solution, maintaining N₂Continuing the reaction for 4 hours under the atmosphere;

then soaking the obtained reactant in deionized water for dialysis for 7 days, changing water three times a day, and removing residual reaction raw materials and electrolyte in the reaction system. The cut-off molecular weight of the dialysis bag is 8000-14000. Thus obtaining the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel.

Placing the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel after dialysis and purification in a 50 ℃ oven, and concentrating to a mass concentration of 2.5 wt%. Then the mixture is put into a thermostat at 25 ℃ and is kept at the temperature rising rate of 1 ℃/min for 5min at intervals and is heated to 37 ℃. The concentration of the copolymerization nano hydrogel in the embodiment can keep the original bright blue-green structure color unchanged while finishing the sol-gel transformation, namely the thermotropic physical crosslinking color jelly hydrogel is formed.

Example 8:

approximately 0.8723g of monomeric N-isopropylacrylamide (NIPAm), 0.1518g of monomeric N-tert-butylacrylamide, 0.1939g of monomeric L-N-propionylphenylalanine (Aphe), 0.0308g of crosslinker N, N' -methylenebisacrylamide, 0.0397g of emulsifier sodium dodecyl sulfate were dissolved in 95 ml of deionized water, and N was bubbled at room temperature₂Deoxidizing and magnetically stirring for 30 minutes;

the reaction temperature was raised to 70 ℃ and maintained at N₂Preserving the heat for 30 minutes under protection;

about 0.0702g of initiator ammonium persulfate was then dissolved in 5 ml of deionized water and added to the above solution, maintaining N₂Continuing the reaction for 4 hours under the atmosphere;

then soaking the obtained reactant in deionized water for dialysis for 7 days, changing water three times a day, and removing residual reaction raw materials and electrolyte in the reaction system. The cut-off molecular weight of the dialysis bag is 8000-14000. Thus obtaining the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel.

Placing the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel after dialysis and purification in a 50 ℃ oven, and concentrating to a mass concentration of 2.5 wt%. Then the mixture is put into a thermostat at 25 ℃ and is kept at the temperature rising rate of 1 ℃/min for 5min at intervals and is heated to 37 ℃. In the embodiment, the concentration of the copolymerized nano hydrogel is kept unchanged when the sol-gel transformation is completed, namely the thermotropic physical crosslinked colorful jelly-shaped hydrogel is formed.

Example 9:

about 0.8647g of monomeric N-isopropylacrylamide (NIPAm), 0.1523g of monomeric N-tert-butylacrylamide, 0.2087g of monomeric L-propionylphenylalanine (Aphe), 0.0302g of crosslinker N, N' -methylenebisacrylamide and 0.0401g of emulsifier sodium dodecyl sulfate were dissolved in 95 ml of deionized water, and N was bubbled at room temperature₂Deoxidizing and magnetically stirring for 30 minutes;

the reaction temperature was raised to 70 ℃ and maintained at N₂Preserving the heat for 30 minutes under protection;

about 0.0692g of initiator ammonium persulfate was then dissolved in 5 ml of deionized water and added to the above solution, maintaining N₂Continuing the reaction for 4 hours under the atmosphere;

then soaking the obtained reactant in deionized water for dialysis for 7 days, changing water three times a day, and removing residual reaction raw materials and electrolyte in the reaction system. The cut-off molecular weight of the dialysis bag is 8000-14000. Thus obtaining the P (NIPAm-TBA-Aphe) ternary polymerization nano hydrogel.

Placing the P (NIPAm-TBA-Aphe) copolymerized nano hydrogel after dialysis and purification in a 50 ℃ oven, and concentrating until the mass concentration is 3.8 wt%. Then the mixture is put into a thermostat at 25 ℃ and is kept at the temperature rising rate of 1 ℃/min for 5min at intervals and is heated to 37 ℃. The concentration of the copolymerization nano hydrogel in the embodiment can keep the original bright bluish purple structure color unchanged while finishing the sol-gel transformation, namely the thermotropic physical crosslinking color jelly-shaped hydrogel is formed.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.