Preparation and application of temperature-sensitive poly (N-isopropylacrylamide / N-benzyl acrylamide) hydrogel suitable for cold chain temperature early warning in refrigeration

Abstract

The invention provides temperature-sensitive poly (N-isopropylacrylamide / N-benzyl acrylamide) hydrogel suitable for early warning of refrigeration cold chain temperature and a preparation method of the temperature-sensitive poly (N-isopropylacrylamide / N-benzyl acrylamide) hydrogel. N-isopropylacrylamide is used as a main raw material, and N-benzyl acrylamide is added to adjust the LCST of the composite acrylamide hydrogel. The LCST of the synthesized composite acrylamide hydrogel is 22 DEG C, changes invisible to naked eyes at 22 DEG C are changed into color changes which can be directly observed by naked eyes, and dependence on detection equipment is avoided. The method has the advantages of high sensitivity, high response speed, reusability, high portability, low cost and the like, and can monitor the storage temperature change of the microenvironment in which food or medicines are located in the cold-chain transportation process. The temperature monitoring process in the cold chain transportation process is greatly optimized, the detection time is shortened within 5 min, and monitoring which is not identified by detection instruments and professionals is achieved. The method has a wide application prospect in the storage and transportation temperature monitoring process of food or medicines in cold chain transportation.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials, and particularly relates to a preparation method of a temperature-sensitive poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel suitable for refrigerated cold chain temperature warning. Background Art

[0002] The cold chain is of great significance to the modern food and pharmaceutical industries and logistics. Cold chain transportation can guarantee the quality and safety of products. In the food field, it can inhibit the growth of microorganisms, maintain nutritional components, and reduce chemical pollution; in the pharmaceutical field, it can maintain the stability of drug efficacy, ensure that its active ingredients do not degrade, and avoid toxicity risks. In addition, it can extend the shelf life of food and drugs and reduce waste. The cold chain is the "lifeline" of the modern food and pharmaceutical industries and logistics. Its significance lies not only in temperature control at the technical level, but also in global food safety, public health safety, and economic sustainable development. The cold chain logistics industry is developing, and the original methods of monitoring the cold chain logistics temperature only by manual / electronic thermometers and sampling detection can no longer adapt to the development of the times. At present, the temperature monitoring means in cold chain transportation are not perfect, especially in that the difference between the macroscopic temperature record and the microenvironment temperature of the microscopic sample is large, and accurate monitoring cannot be carried out when the temperature fluctuates. Targeted broken-chain monitoring is the key to ensuring the effective operation of the cold chain, which helps to guarantee food and drug safety, reduce losses, maintain corporate reputation, and meet regulatory requirements. Therefore, there is an urgent need to develop monitoring technologies for temperature changes in cold chain transportation.

[0003] Temperature-responsive materials can change their physical form or chemical properties according to external temperature changes, so as to realize real-time monitoring of the temperature of the environment where food is located. According to their different phase transition temperatures, they are mainly divided into the following two categories: lower critical solution temperature (LCST) type materials and upper critical solution temperature (UCST) type materials. Temperature-responsive materials show great potential in the fields of food intelligent packaging, processing optimization, and storage management by precisely regulating the phase transition temperature. For example, by using the light transmittance or volume change of LCST materials, visual tags are designed to reflect in real time whether the cold chain is interrupted (such as color change caused by abnormal temperature). Precise monitoring of temperature anomalies through intelligent packaging can avoid unnecessary low-temperature maintenance.

[0004] Poly(N-isopropylacrylamide) is a hydrogel material that is temperature-sensitive and has high biosecurity. Generally, the LCST of poly(N-isopropylacrylamide) is 32 °C. When the temperature is below the LCST, the light transmittance is high. When the temperature is above the LCST, the isopropyl hydrophobic groups of poly(N-isopropylacrylamide) are exposed, resulting in the contraction of the molecular chain and a decrease in light transmittance. However, traditional poly(N-isopropylacrylamide) hydrogels have no obvious change in the low-temperature range (below 30 °C) and cannot be used for temperature monitoring during cold chain transportation. By increasing the types of acrylamide monomers and controlling the environmental temperature during the preparation stage, the polymer network structure can be changed, significantly affecting the temperature-responsive behavior of the hydrogel. In particular, modification can be carried out by inserting monomers with different hydrophilic and hydrophobic side chains into the main chain of N-isopropylacrylamide to adjust its LCST. Summary of the Invention

[0005] To solve the above technical problems in the background art, the purpose of this application is to develop an intelligent indicator that responds to environmental temperature, synthesize a new composite acrylamide hydrogel with an LCST as low as 22 °C, and monitor and warn of possible "broken chain" problems in the cold chain. The aim is to overcome the defect of the excessively high LCST (above 32 °C) of traditional hydrogels, and provide a poly(N-isopropylacrylamide / N-benzylacrylamide) thermochromic hydrogel. Compared with traditional poly(N-isopropylacrylamide), the LCST of the low-temperature-responsive composite acrylamide hydrogel prepared in this invention is reduced by 10 °C, which is suitable for cold chain temperature warning during refrigeration. Compared with other temperature-color-changing packaging materials, this invention solves the problem of the slow response speed of temperature-color-changing packaging materials when the temperature rises under refrigeration temperature, and realizes the control of the broken chain detection time within 5 minutes, and can quickly respond when the environmental temperature changes. This method can be conveniently used in the field of temperature monitoring.

[0006] This invention provides a method for a temperature-sensitive poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel that can be applied to cold chain temperature warning during refrigeration.

[0007] Among them, the preparation method of the new composite acrylamide hydrogel with an LCST as low as 22 °C is mainly achieved by adjusting the types and proportions of acrylamide polymerization monomers, mainly including N-isopropylacrylamide, N-benzylacrylamide, and methacrylamide.

[0008] By changing the molar ratio of N-benzylacrylamide to other monomers, a new composite acrylamide hydrogel with an LCST as low as 22 ± 3 °C is synthesized to meet the temperature requirements of cold chain transportation.

[0009] The present invention synthesizes a novel composite acrylamide hydrogel with a lower critical solution temperature (LCST) as low as 22 °C, which converts the temperature change invisible to the naked eye at room temperature into a color change that can be directly observed by the naked eye, avoiding the dependence on detection equipment. The method has the advantages of high sensitivity, fast response speed, reusability, high portability and low cost. This is mainly due to the addition of N-benzylacrylamide in the initial stage of the polymerization reaction, which enables the LCST to be adjusted to a lower value and can monitor the temperature change of food or medicine during cold chain transportation. The invention greatly optimizes the temperature monitoring process during cold chain transportation, shortens the cold chain "broken chain" warning time within 5 minutes, and can monitor the temperature of the local microenvironment without the need for detection instruments.

[0010] To achieve the above object, the present invention provides a method for preparing the above-mentioned poly(N-isopropylacrylamide / N-benzylacrylamide) thermochromic hydrogel. Among them, the polymerization monomers are N-isopropylacrylamide and N-benzylacrylamide, the cross-linking agent is N,N'-methylenebisacrylamide, the reaction initiator is ammonium persulfate, the reaction catalyst is tetramethylethylenediamine, and the reaction process is carried out in a low-temperature environment.

[0011] The first object of the present invention is to provide a method for preparing a temperature-sensitive poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel suitable for cold chain temperature warning during refrigeration, which specifically includes the following steps:

[0012] a. Prepare an aqueous solution containing N-isopropylacrylamide monomer and N-benzylacrylamide monomer, and mix the two in the same aqueous solution;

[0013] b. Add an aqueous solution of N,N'-methylenebisacrylamide to the solution prepared in step a and stir to dissolve;

[0014] c. Subsequently, add ammonium persulfate to the aqueous solution prepared in step b and continuously stir to initiate the emulsion polymerization reaction;

[0015] d. After stirring for a period of time, slowly drop tetramethylethylenediamine into the solution obtained in step c and stir rapidly to obtain a novel composite acrylamide hydrogel;

[0016] e. Subpackage the novel composite acrylamide hydrogel prepared in step d and let it stand to obtain a temperature-sensitive poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel suitable for cold chain temperature warning during refrigeration.

[0017] Further, the molar ratio of N-isopropylacrylamide to N-benzylacrylamide in step a is not higher than 15:1. Preferably, the molar ratio of N-isopropylacrylamide to N-benzylacrylamide in step a is 9:1 to 15:1.

[0018] Further, in the aqueous solution described in step a, the concentration of N-isopropylacrylamide is 0.001 - 0.002 mol / mL. Preferably, in the aqueous solution described in step a, the concentration of N-isopropylacrylamide is 0.0015 mol / mL.

[0019] Further, the stirring speed for preparing the aqueous solution in steps a and b is 200 - 500 r / min, and stirring is continued until dissolution; in a specific embodiment, the stirring time is 30 - 60 min.

[0020] Among them, the stirring and dissolution in step a are not necessary. After adding N,N'-methylenebisacrylamide in step b, the N-isopropylacrylamide monomer, N-benzylacrylamide monomer, and N,N'-methylenebisacrylamide can also be stirred and dissolved together.

[0021] Further, the molar ratio of N,N'-methylenebisacrylamide to N-isopropylacrylamide in step b is 1:250, and the stirring time is 30 - 60 min.

[0022] Further, the amount of ammonium persulfate added in step c is such that its concentration in the solution of step b is 30 - 50 mg / mL; the rotation speed of the magnetic stirrer is 200 - 500 r / min, and the stirring time is 10 - 40 min.

[0023] Further, the volume ratio of the added tetramethylethylenediamine to the solution obtained in step c in step d is 0.1% - 0.5%, the stirring speed is 1000 - 1300 r / min, the stirring time is 30 - 60 s, and the reaction ambient temperature in step d is 2 - 8°C.

[0024] Further, the ambient temperature for steps a - e is 2 - 8°C.

[0025] The second object of the present invention is to provide a temperature-sensitive poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel applicable to cold chain temperature warning for refrigeration, which is prepared by the aforementioned preparation method. The low-temperature responsive poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel can achieve a sensitive color change when the temperature changes from the cold chain temperature for refrigeration (2 - 8°C) to room temperature of 22 ± 3°C.

[0026] The third object of the present invention is to provide the application of the aforementioned temperature-sensitive poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel applicable to cold chain temperature warning for refrigeration in the preparation of visual temperature monitoring products. The visual temperature monitoring products are applicable to the cold chain transportation temperature indication of sample microenvironments, mainly related to food, medicine, etc.; preferably, the food includes pork, mutton, beef, chicken, fish, duck, fish, etc.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] The present invention prepares poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel by adding poly(N-isopropylacrylamide) and N-benzylacrylamide in different proportions. N-benzylacrylamide is a hydrophobic material. By adding different proportions of N-benzylacrylamide and polymerization monomers such as N-benzylacrylamide and methacrylamide, and combining with temperature control during the preparation process, the LCST of the new composite acrylamide hydrogel material is effectively reduced, and the change that is invisible to the naked eye at 22±3°C is transformed into a color change that can be directly observed with the naked eye, avoiding the dependence on detection instruments; by designing a hydrogel patch with a certain shape, it can be used in the packaging of food or medicine to achieve the function of color display. This preparation method effectively regulates the LCST of the new composite acrylamide hydrogel material, can monitor the breakage of food or medicine during cold chain transportation, is sensitive to temperature changes, shortens the detection time within 5 minutes, and realizes temperature monitoring without relying on experimental instruments and professional operators. Description of the Drawings

[0029] Figure 1 It is a scanning electron microscope test chart of poly(N-isopropylacrylamide) hydrogel (a) prepared in Comparative Example 1 and poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel (b) prepared in Example 1.

[0030] Figure 2 It is a variable-temperature ultraviolet transmittance test chart and actual color change pictures of poly(N-isopropylacrylamide) hydrogel (a) prepared in Comparative Example 1, poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel (b) prepared in Example 1, poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel (c) prepared in Example 2, poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel (d) prepared in Comparative Example 3, and poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel (e) prepared in Comparative Example 4.

[0031] Figure 3 It is the UV-Vis spectral characterization of poly(N-isopropylacrylamide) hydrogel (a) in Comparative Example 1 and poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel (b) prepared in Example 1.

[0032] Figure 4 It is the FTIR chart of poly(N-isopropylacrylamide) hydrogel (a) in Comparative Example 1 and poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel (b) in Example 1.

[0033] Figure 5It is a test chart completed for the poly(N-isopropylacrylamide) hydrogel of Comparative Example 1 and the poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel (b) of Example 1 under environments less than LCST (a) and greater than LCST (b).

[0034] Figure 6 It is a test chart of the variable-temperature linear transmittance for the poly(N-isopropylacrylamide) hydrogel of Comparative Example 1 and the poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel of Example 1. Detailed implementation manners

[0035] The present invention discloses a preparation method of a thermosensitive poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel applicable to cold-chain temperature warning for refrigeration. The present invention will be further described in detail below in conjunction with examples and drawings, but the implementation manners of the present invention are not limited thereto. Those skilled in the art can draw on the content of this article and appropriately modify the process parameters to achieve. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all regarded as included in the present invention. The following-described examples are only a part of the examples of the present invention, rather than all the examples. The methods and products of the present invention have been described through preferred examples, and those related can obviously make changes or appropriate modifications and combinations to the methods described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0036] In the examples of the present invention, those not specified under specific conditions are carried out according to conventional conditions or the conditions recommended by the manufacturer. The raw materials, reagents, etc. not specified by the manufacturer can all be obtained as conventional products through commercial purchase. Unless otherwise specified, the reagents involved in the examples of the present invention are all commercially available products and can be obtained through commercial channels.

[0037] Example 1

[0038] Preparation of poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel:

[0039] a. At 4°C, prepare 10 ml of an aqueous solution of 0.015 mol of N-isopropylacrylamide monomer and N-benzylacrylamide, and the molar ratio of the two substances is 9:1; stir at 400 r / min for 60 min.

[0040] b. At 4°C, add 0.00006 mol of N,N'-methylenebisacrylamide to the solution prepared in step a, and stir at 400 r / min for 60 min to dissolve it;

[0041] c. At 4°C, then add 40.5 mg of ammonium persulfate and continuously stir at 400 r / min for 20 min to initiate the emulsion polymerization reaction;

[0042] d. After stirring, at 4 °C, slowly add 20 μL of tetramethylethylenediamine, and rapidly stir at 1200 r / min for 60 s to obtain a novel composite acrylamide hydrogel;

[0043] e. Dispense the prepared novel composite acrylamide hydrogel, and let it stand for one day at 4 °C to obtain a poly(N-isopropylacrylamide / N-benzylacrylamide) thermochromic hydrogel.

[0044] Example 2

[0045] Preparation of poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel:

[0046] a. At 4 °C, prepare a 10 ml aqueous solution of 0.015 mol of N-isopropylacrylamide monomer and N-benzylacrylamide, and the molar ratio of the two substances is 15:1.

[0047] b. At 4 °C, add 0.00006 mol of N,N'-methylenebisacrylamide to the solution prepared in step a, and stir and dissolve at 400 r / min for 60 min;

[0048] c. At 4 °C, then add 40.5 mg of ammonium persulfate, and continuously stir at 400 r / min for 20 min to initiate the emulsion polymerization reaction;

[0049] d. After stirring, at 4 °C, slowly add 20 μL of tetramethylethylenediamine, and rapidly stir at 1200 r / min for 60 s to obtain a novel composite acrylamide hydrogel;

[0050] e. Dispense the prepared novel composite acrylamide hydrogel, and let it stand for one day at 4 °C to obtain a poly(N-isopropylacrylamide / N-benzylacrylamide) thermochromic hydrogel.

[0051] Comparative Example 1 Comparative example without adding N-benzylacrylamide monomer

[0052] Change in the reaction environment temperature of poly N-isopropylacrylamide hydrogel:

[0053] a. At 4 °C, prepare a 10 ml aqueous solution of 0.015 mol of N-isopropylacrylamide monomer

[0054] b. At 4 °C, add 0.00006 mol of N,N'-methylenebisacrylamide, and stir and dissolve at 400 r / min for 60 min;

[0055] c. Subsequently, at 4 °C, add 40.5 mg of ammonium persulfate, and continuously stir at 400 r / min for 20 min to initiate the emulsion polymerization reaction;

[0056] d. After stirring, slowly add 20 μL of tetramethylethylenediamine dropwise under the condition of 4 °C, and quickly stir at 1200 r / min for 60 s to obtain poly(N-isopropylacrylamide) hydrogel;

[0057] e. Subpackage the prepared novel composite acrylamide hydrogel, and let it stand for one day under the condition of 4 °C to obtain poly(N-isopropylacrylamide) thermochromic hydrogel.

[0058] Comparative Example 2: Comparative example of increasing the preparation temperature

[0059] Preparation of poly(N-isopropylacrylamide) hydrogel:

[0060] a. At room temperature, prepare 10 ml of 0.015 mol aqueous solution of N-isopropylacrylamide monomer

[0061] b. At room temperature, add 0.00006 mol of N,N'-methylenebisacrylamide, and stir and dissolve at 400 r / min for 60 min;

[0062] c. Subsequently, at room temperature, add 40.5 mg of ammonium persulfate, and continuously stir at 400 r / min for 20 min to initiate emulsion polymerization reaction;

[0063] d. After stirring, at room temperature, slowly add 20 μL of tetramethylethylenediamine dropwise, and quickly stir at 1200 r / min for 60 s to obtain poly(N-isopropylacrylamide) hydrogel;

[0064] e. Subpackage the prepared poly(N-isopropylacrylamide) hydrogel, and let it stand for one day at room temperature to obtain poly(N-isopropylacrylamide) thermochromic hydrogel.

[0065] Comparative Example 3: Comparative example of increasing the ratio of N-isopropylacrylamide monomer and N-benzylacrylamide Preparation of poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel:

[0066] a. At 4 °C, prepare 10 ml of aqueous solution of 0.015 mol N-isopropylacrylamide monomer and N-benzylacrylamide, and the molar ratio of the two substances is 25:1.

[0067] b. At 4 °C, add 0.00006 mol of N,N'-methylenebisacrylamide, and stir and dissolve at 400 r / min for 60 min;

[0068] c. At 4 °C, subsequently add 40.5 mg of ammonium persulfate, and continuously stir at 500 r / min for 20 min to initiate emulsion polymerization reaction;

[0069] d. After stirring, at 4 °C, slowly add 20 μL of tetramethylethylenediamine and quickly stir at 1200 r / min for 60 s to obtain a novel composite acrylamide hydrogel;

[0070] e. Dispense the prepared novel composite acrylamide hydrogel and let it stand for one day at 4 °C to obtain a poly(N-isopropylacrylamide / N-benzylacrylamide) thermochromic hydrogel.

[0071] Preparation of poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel in Comparative Example 4 with increased ratio of N-isopropylacrylamide monomer to N-benzylacrylamide:

[0072] a. At 4 °C, prepare a 10 ml aqueous solution of 0.015 mol of N-isopropylacrylamide monomer and N-benzylacrylamide, and the molar ratio of the two substances is 29:1.

[0073] b. At 4 °C, add 0.00006 mol of N,N'-methylenebisacrylamide and stir to dissolve at 400 r / min for 60 min;

[0074] c. At 4 °C, then add 40.5 mg of ammonium persulfate and continuously stir at 400 r / min for 20 min to initiate the emulsion polymerization reaction;

[0075] d. After stirring, at 4 °C, slowly add 20 μL of tetramethylethylenediamine and quickly stir at 1200 r / min for 60 s to obtain a novel composite acrylamide hydrogel;

[0076] e. Dispense the prepared novel composite acrylamide hydrogel and let it stand for one day at 4 °C to obtain a poly(N-isopropylacrylamide / N-benzylacrylamide) thermochromic hydrogel.

[0077] Preparation of poly(N-isopropylacrylamide / methacrylamide) hydrogel in Comparative Example 5 by replacing N-benzylacrylamide:

[0078] a. At 4 °C, prepare a 10 ml aqueous solution of 0.015 mol of N-isopropylacrylamide monomer and methacrylamide, and set the molar ratios of the two substances to 9:1 and 15:1 treatment groups.

[0079] b. At 4 °C, add 0.00006 mol of N,N'-methylenebisacrylamide and stir to dissolve at 400 r / min for 60 min;

[0080] c. At 4 °C, then add 40.5 mg of ammonium persulfate and continuously stir at 400 r / min for 20 min to initiate the emulsion polymerization reaction;

[0081] d. After stirring, at 4 °C, slowly add 20 μL of tetramethylethylenediamine, and quickly stir at 1200 r / min for 60 s to obtain a novel composite acrylamide hydrogel;

[0082] e. Subpackage the prepared novel composite acrylamide hydrogel, and let it stand for one day at 4 °C to obtain a poly(N-isopropylacrylamide / methacrylamide) thermochromic hydrogel.

[0083] Preparation of poly(N-isopropylacrylamide / N-tert-butylacrylamide) hydrogel as a comparative example by replacing N-benzylacrylamide in Comparative Example 6:

[0084] a. At 4 °C, prepare 10 ml of an aqueous solution of 0.015 mol of N-isopropylacrylamide monomer and N-tert-butylacrylamide, and set the molar ratios of the two substances as 9:1 and 15:1 treatment groups.

[0085] b. At 4 °C, add 0.00006 mol of N,N'-methylenebisacrylamide, and stir to dissolve at 400 r / min for 60 min;

[0086] c. At 4 °C, then add 40.5 mg of ammonium persulfate, and continuously stir at 400 r / min for 20 min to initiate the emulsion polymerization reaction;

[0087] d. After stirring, at 4 °C, slowly add 20 μL of tetramethylethylenediamine, and quickly stir at 1200 r / min for 60 s to obtain a novel composite acrylamide hydrogel;

[0088] e. Subpackage the prepared novel composite acrylamide hydrogel, and let it stand for one day at 4 °C to obtain a poly(N-isopropylacrylamide / N-tert-butylacrylamide) thermochromic hydrogel.

[0089] Figure 1 It is a scanning electron microscope test diagram of the poly(N-isopropylacrylamide) hydrogel prepared in Comparative Example 1 and the poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel prepared in Example 1.

[0090] It can be seen from the figure that the poly(N-isopropylacrylamide) hydrogel prepared in Comparative Example 1 presents a porous network structure, with a relatively uniform pore size distribution, smooth pore walls, and a three-dimensional morphological structure. The unmodified poly(N-isopropylacrylamide) shows a uniform porous structure, with a pore size of about 50 - 100 μm and smooth pore walls.

[0091] After benzyl modification in Example 1, the pore size is reduced to 20 - 50 μm, the pore walls are rough, and local hydrophobic micro-region aggregations appear. Benzyl enhances crosslinking through hydrophobic interactions, resulting in a decrease in pore size and surface roughening, which may improve the mechanical strength of the material.

[0092] Figure 2 It is the variable-temperature ultraviolet transmittance test chart (left figure) and the physical picture (right figure) of the poly(N-isopropylacrylamide) hydrogel prepared in Comparative Example 1 and the poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogels prepared in Examples 1 and 2 and Comparative Examples 3 and 4. (This part of the results was measured by a microplate reader. The 4°C test curve was obtained by quickly transferring the sample from a 4°C cold storage to the instrument for testing within 1 minute. The other temperature curves were the test curves after the microplate reader was set to the desired temperature and stabilized. The lowest temperature that the microplate reader can be set to is 25°C, which is the same as the room temperature.)

[0093] The results show that the light transmittance of the unmodified poly(N-isopropylacrylamide) hydrogel material prepared in Comparative Example 1 changes at an environmental temperature of 32°C, proving that its LCST is around 32°C. When the environmental temperature is lower than 32°C, the sample is transparent and has a high light transmittance; when the environmental temperature is higher than the LCST, the sample appears white and has a low light transmittance.

[0094] For the novel composite acrylamide hydrogel material modified with N-benzylacrylamide in Example 1, the light transmittance began to decrease at 25°C and had decreased to about 40% at 25°C. According to the physical picture, it can be seen that the light transmittance changed at 22°C, and the color of the sample changed from transparent at 4°C to white opaque at 22°C, indicating that its LCST is at 22 ± 2°C. When the environmental temperature continued to rise, its light transmittance also gradually decreased. This proves that the LCST of the modified novel composite acrylamide hydrogel has changed, and the addition of benzyl can lower the LCST of the novel composite acrylamide hydrogel.

[0095] For the novel composite acrylamide hydrogel material modified with N-benzylacrylamide in Example 2, the light transmittance began to decrease at 25°C and had decreased to about 40% at 27°C. According to the physical picture, it can be seen that the light transmittance changed at 26°C, and the color of the sample changed from transparent at 4°C to white opaque at 26°C. Its LCST is at 26 ± 2°C. When the environmental temperature continued to rise, its light transmittance also gradually decreased. This proves that the LCST of the modified novel composite acrylamide hydrogel has changed, and the addition of benzyl can lower the LCST of the novel composite acrylamide hydrogel.

[0096] However, for the novel composite acrylamide hydrogel material modified with N-benzylacrylamide in Comparative Example 3, the light transmittance began to decrease at 29 °C, and the light transmittance decreased to about 40% at 29 °C. It can be seen from the physical picture that the light transmittance changed at 29 °C, and the sample color changed from transparent at 4 °C to white opaque at 29 °C. Its LCST was at 29 ± 2 °C, and the light transmittance gradually decreased as the ambient temperature continued to rise. It was proved that the LCST of the modified novel composite acrylamide hydrogel changed. Adding benzyl could lower the LCST of the novel composite acrylamide hydrogel, but compared with the LCST of 32 °C of poly(N-isopropylacrylamide), the effect was not obvious, indicating that not any ratio of N-isopropylacrylamide monomer and N-benzylacrylamide monomer could achieve good results.

[0097] For the novel composite acrylamide hydrogel material modified with N-benzylacrylamide in Comparative Example 4, the light transmittance began to decrease at 30 °C, and the light transmittance decreased to about 40% at 30 °C. It can be seen from the physical picture that the light transmittance changed at 30 °C, and the sample color changed from transparent at 4 °C to white opaque at 30 °C. Its LCST was at 30 ± 2 °C, and the light transmittance gradually decreased as the ambient temperature continued to rise. It was proved that the LCST of the modified novel composite acrylamide hydrogel changed. Adding benzyl could lower the LCST of the novel composite acrylamide hydrogel, but similar to Comparative Example 3, compared with the LCST of 32 °C of poly(N-isopropylacrylamide), the effect was not obvious, indicating that not any ratio of N-isopropylacrylamide monomer and N-benzylacrylamide monomer could achieve good results.

[0098] Figure 3 It is the UV-Vis spectral characterization of the poly(N-isopropylacrylamide) hydrogel prepared in Comparative Example 1 and the poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel prepared in Example 1.

[0099] The unmodified poly(N-isopropylacrylamide) in Comparative Example 1 had a weak absorption peak at <250 nm.

[0100] For the novel composite acrylamide hydrogel modified with benzyl in Example 2, an obvious absorption peak appeared near 260 nm. The peak intensity increased with the increase of benzyl content, and the absorption peak became slightly wider. Benzyl was successfully introduced into N-isopropylacrylamide and produced a characteristic absorption peak near 260 nm. The broadening of the absorption peak indicated that there was a strong interaction between benzyl and the N-isopropylacrylamide chain.

[0101] Figure 4 It is the FTIR diagram of the poly(N-isopropylacrylamide) hydrogel prepared in Comparative Example 1 and the poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel prepared in Example 1.

[0102] Curve 5 shows the infrared spectrum of the poly(N-isopropylacrylamide) hydrogel prepared in Comparative Example 1. There is a broad absorption peak of -NH (N-H stretching vibration absorption peak) in the range of 3300 - 3500 cm -1 ; there appears a C-H vibration absorption peak of saturated carbon-hydrogen (methyl, methylene, and methine) in the polymer in the range of 2800 - 3000 cm -1 ; the amide II band absorption peak (N-H bending vibration) is at 1540 - 1560 cm-1; the amide I band absorption peak (C=O stretching vibration) is near 1600 cm-1.

[0103] In contrast, in the infrared spectrum of poly(N-isopropylacrylamide / N-benzylacrylamide) corresponding to Curve (1 - 4) of Example 1, multiple peaks appear in the range of 1450 - 1600 cm-1, which is the C=C stretching vibration of the benzene ring; the C-H stretching vibration of the benzyl group may overlap with the C-H peak of poly(N-isopropylacrylamide) in the range of 2800 - 3000 cm-1, and the intensity increases in Curve 1. This proves the successful introduction of N-benzylacrylamide.

[0104] Figure 5 It is the test environmental temperature graph of the poly(N-isopropylacrylamide) hydrogel prepared in Comparative Example 1 and the poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel prepared in Example 1 after preparation and placed in a centrifuge tube.

[0105] The modified poly(N-isopropylacrylamide) hydrogel material in Example 1 can have an obvious color change above and below the LCST. When the temperature is lower than the LCST, the sample color is transparent and the pattern can be seen through; when the temperature is higher than the LCST, the sample color is white and the pattern cannot be seen through. This proves that after adding benzyl, a sensitive color change can be achieved at 22°C, and a new composite acrylamide hydrogel poly(N-isopropylacrylamide) with an LCST of 22°C can be prepared by adding benzyl.

[0106] Figure 6 It is the variable-temperature linear transmittance test graph of the poly(N-isopropylacrylamide) hydrogel prepared in Comparative Example 1 and the poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel prepared in Example 1. It is measured by a color difference meter and calculated by measuring the L value. From this graph, it can be seen that the LCST of the poly(N-isopropylacrylamide) prepared in Comparative Example 1 is about 32°C. In Example 2, the LCST can be changed by changing the ratio of the two acrylamides. In Example 2, a new composite acrylamide hydrogel with an LCST of 22°C can be prepared, and adding an appropriate amount of benzyl makes the hydrogel meet the actual cold chain transportation requirements.

[0107] Compared with Example 1, in Comparative Example 2, the preparation ambient temperature was increased from 4°C to room temperature (25°C). The LCST of the prepared poly(N-isopropylacrylamide) hydrogel material was higher than that of the hydrogel prepared in Example 1 under the environmental condition of 4°C. The hydrogel material prepared in Comparative Example 2 did not meet the actual application requirements.

[0108] In Comparative Example 5, N-benzylacrylamide was replaced with methacrylamide. Methacrylamide is a hydrophilic material. The preparation result showed that the acrylamide copolymer added was transparent and did not change color when the temperature was raised to 40°C, indicating that its LCST was even higher than that of traditional poly(N-isopropylacrylamide) (32°C) and could not meet the actual application requirements.

[0109] In Comparative Example 6, N-benzylacrylamide was replaced with N-tert-butylacrylamide. N-tert-butylacrylamide is a hydrophobic material, but the preparation result was not ideal and could not achieve the expected effect. When the monomer was changed, it was found that the copolymer was white and did not change color when the environmental temperature was changed from 4°C to 32°C, unable to meet the actual application requirements. Finally, N-isopropylacrylamide and N-benzylacrylamide were combined to adjust the LCST of the polymer to meet the requirements of cold chain temperature warning for refrigeration.

[0110] The above examples are only for illustrating the technical concept and characteristics of the present invention, and the purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly, and it cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit and essence of the present invention should be covered by the protection scope of the present invention.

Claims

1. A preparation method of a temperature-sensitive poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel applicable to cold chain temperature warning for refrigeration, characterized in that, Specifically, it includes the following steps: a. Prepare an aqueous solution containing N-isopropylacrylamide monomer and N-benzylacrylamide monomer; b. Add N,N'-methylenebisacrylamide to the solution prepared in step a and stir to dissolve; c. Subsequently, add ammonium persulfate to the solution prepared in step b and continuously stir to initiate emulsion polymerization reaction; d. After stirring for a period of time, slowly drop tetramethylethylenediamine into the solution obtained in step c and stir rapidly to obtain a novel composite acrylamide hydrogel; e. Subpackage the novel composite acrylamide hydrogel prepared in step d and let it stand to obtain the thermosensitive poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel.

2. The preparation method according to claim 1, characterized in that, In step a, the molar ratio of N-isopropylacrylamide to N-benzylacrylamide is not higher than 15:

1. Preferably, in step a, the molar ratio of N-isopropylacrylamide to N-benzylacrylamide is 9:1 - 15:

1.

3. The preparation method according to claim 1, characterized in that, In the aqueous solution in step a, the concentration of N-isopropylacrylamide is 0.001 - 0.002 mol / mL. Preferably, in the aqueous solution in step a, the concentration of N-isopropylacrylamide is 0.0015 mol / mL.

4. The preparation method according to claim 1, characterized in that, In steps a and b, the stirring speed for preparing the aqueous solution is 200 - 500 r / min and stir until dissolved.

5. According to the preparation method described in claim 1, the molar ratio of N,N'-methylenebisacrylamide to N-isopropylacrylamide in step b is 1:

250.

6. According to the preparation method described in claim 1, the concentration of ammonium persulfate added in step c in the solution of step b is 3 - 5 mg / mL; the stirring speed is 200 - 500 r / min and the stirring time is 10 - 40 min.

7. The preparation method according to claim 1, characterized in that, In step d, the volume ratio of the added tetramethylethylenediamine to the solution obtained in step c is 0.1% - 0.5%, the stirring speed is 1000 - 1300 r / min, and the stirring time is 30 - 60 s.

8. The preparation method according to claim 1, characterized in that, The ambient temperature in steps a - e is 2 - 8°C.

9. A thermosensitive poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel applicable to temperature warning in cold chain refrigeration, characterized in that, Prepared by using the preparation method described in any one of claims 1 to 8, the thermosensitive poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel applicable to cold chain temperature warning for refrigeration can have a sensitive color change in an environment of 22 ± 3°C.

10. Use of the thermosensitive poly(N-isopropylacrylamide / N-benzylacrylamide) hydrogel according to claim 9 for refrigerated cold chain temperature warning in the preparation of a visual temperature monitoring product, characterized in that, The visual temperature monitoring product is applicable to the temperature indication of cold chain transportation of sample microenvironment.

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