CN112430306B - Self-reinforcing photochromic material and preparation method thereof - Google Patents

Abstract

The invention discloses a self-enhancing mechanochromic material and a preparation method thereof. The preparation method comprises the following steps: adding a dihalogenated three-membered cyclopropane structural unit, a spiro ring mechanochromic structural unit, a catalyst and other multifunctional monomers into a The polycondensation reaction is carried out in a solvent at 50-85 °C; the prepared polymer solution is precipitated in an alcohol solvent and then dried to obtain a sample; the sample and the small molecule cross-linking agent are uniformly mixed and then molded to obtain self-reinforcing Mechanochromic materials. The preparation method is simple and low in cost; the prepared self-enhancing mechanochromic material contains a force-sensitive dihalogenated three-membered cyclopropane structure and a spiro ring mechanochromic structure. When the matrix material is stressed, the spiro ring mechanochromic structure The unit gives early warning of its destructive damage, and the dihalogenated three-membered cyclopropane structural unit cross-links the damaged part to play a self-reinforcing role. sensing and engineering materials.

Description

A kind of self-enhancing mechanochromic material and preparation method thereof

technical field

The invention belongs to the technical field of organic intelligent polymer materials, in particular to a self-enhancing force-induced color change material and a preparation method thereof.

Background technique

The development and wide application of smart materials make people's demand for functional polymer materials increasingly urgent. The use of external stimuli can effectively control various performance indicators of such materials, so as to achieve various functions. There have been many reports on smart responsive fluorescent materials with stimulation sources such as pH, chemistry, electricity and temperature, while the research on mechanochromic materials with force as the external stimulation source is still in the developing stage. The existence of mechanical force is very extensive, and it has many unique advantages in regulating the properties of materials, such as easy application, convenient regulation, and simple operation. Therefore, mechanochromic materials have great application value in biomimetic materials, optical storage, display, mechanical sensing, and even in the field of life sciences.

At present, the design and development of mechanochromic materials mainly focus on the problem of how to realize the color change of materials under force. The most representative work is the spiropyran-based mechanochromic polymer material reported by the Sottos group in 2009 (Nature, 2009, 459, 68-72). Spiropyran is a non-conjugated molecule, because Among them, the spiro ring C-O bond has a weaker bond energy and will be interrupted by external force to form a merocyanidin structure. At this time, the conjugated chain of the molecule is reformed and emits red fluorescence. In addition to spiropyran, other mechanochromic groups have been reported as spirothiopyran (Angewandte Chemie International Edition, 2016, 55, 3040-3044), cyclobutane peroxide (Macromolecules, 2014, 47, 3797-3805), reversible Free radical system (Angew. Chem. Int. Ed., 2015, 54, 6168-6172) and the like. However, these technical routes developed above can only provide early warning of discoloration of the destructive stress of the material, but cannot self-enhance the mechanical properties of the material in time. Therefore, it still lacks certain practical applicability. Craig et al. developed a polybutadiene-based self-reinforcing polymer (Nature Chemistry, 2013, 5, 757-761), the dihalocyclopropane structure introduced on the main chain of the polymer is subjected to force ring-opening and will interact with small molecules. The cross-linking agent reacts and cross-links, so as to play a self-enhancing role. Before this, the cross-linking agent molecule does not react with any structure in the polymer main chain, but this technical route cannot affect the system. Discoloration warning for stress. Therefore, it is of great significance to design a self-enhancing mechanochromic material that can not only provide early warning of destructive stress, but also enhance the mechanical properties of the material itself.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to aim at the deficiencies of the above-mentioned prior art, and to provide a self-enhancing force-induced color changing material and a preparation method thereof. The preparation method is simple and efficient, and the prepared self-enhancing force-induced color changing material receives stress damage when It has both discoloration warning and self-enhancing performance.

In order to achieve the above-mentioned technical purpose, the technical solution adopted in the present invention is: a preparation method of a self-enhancing force-induced color changing material, comprising the following steps:

S1. Add the dihalogenated three-membered cyclopropane structural unit, the spiro ring mechanochromic structural unit, the catalyst and other multifunctional monomers into the solvent, and carry out the polycondensation reaction at 50-85 °C;

S2. The polymer solution obtained in step S1 is precipitated in an alcohol solvent and then dried to obtain a sample;

S3. The sample prepared in step S2 and the small molecule cross-linking agent are uniformly mixed and then molded to obtain a self-reinforcing force-induced color change material.

Further, the chemical structural formula of the dihalogenated three-membered cyclopropane structural unit is:

Wherein, R ₁ group is one of -Br, -I; R ₂ group is -OH, -SH, -COOH, -F, -Cl, -Br, -I, -CHO, -NH ₂ A type of; m ranges from 0-12.

Further, in step S1, the molar content of the dihalogenated three-membered cyclopropane structural unit is 10% to 30%.

Further, the mechanochromic structural unit is one of the following substances:

wherein R ₁ , R ₂ , R ₃ and R ₄ are all selected from one of the following structures: -OH, -SH, -COOH, -F, -Cl, -Br, -I, -CHO, -NH ₂ .

Further, in step S1, the molar content of the spiro ring mechanochromic structural unit is 0.5% to 5%.

Further, the other polyfunctional monomers are one or more of polyvalent hydroxy compounds, polyvalent amine-based compounds, and polyvalent isocyanates.

Further, in step S1, the dihalogenated three-membered cyclopropane structural unit, the spiro ring mechanochromic structural unit, the catalyst and other multifunctional monomers are all dried before use.

Further, the catalyst is a tin-based or amine-based catalyst.

Further, in step S3, the cross-linking agent molecule is used after reacting with an organic base to form a salt, the small-molecule cross-linking agent is one of polycarboxylic acids, and the organic base is tetramethylguanidine, 1 , One or more of 8-diazabicycloundec-7-ene, triethylamine, diethylamine, ammonia water and diisopropylamine.

Further, the small molecule cross-linking agent is one of adipic acid, glutaric acid, succinic acid, malonic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid.

The present invention also provides the self-enhancing mechanochromic material prepared by the above preparation method.

Compared with the prior art, the present invention has the following technical effects:

1) In the self-enhancing mechanochromic material designed by the present invention, a dihalogenated three-membered cyclopropane structural unit (a self-enhancing structure) and a mechanochromic structural unit are simultaneously connected in series in the polymer main chain structure, and the dihalogenated three-membered cyclopropane structural unit is connected in series. The cyclopropane structural unit is prone to ring-opening isomerization when it is disturbed by mechanical force, and the halogen atoms in the structure before and after isomerization show significantly different chemical reactivity to nucleophiles. It has no reactivity to nucleophiles before ring-opening, but after ring-opening, the reactivity is greatly enhanced, and it reacts with the cross-linking agent molecules in the matrix material and the cross-linking plays a self-enhancing role, and the mechanochromic structural unit changes to cause fluorescence Therefore, when the material is subjected to destructive stress, the dihalogenated three-membered cyclopropane structural unit and the mechanochromic structural unit can be stressed at the same time. The combined reaction enhances the mechanical properties of the damaged part, making the load-bearing polymer material more intelligent. In view of the fact that the damage and damage of the current engineering polymer material cannot be determined on the spot, the self-enhancing mechanochromic material provided by the present invention can be used for real-time display of engineering heights. The load-bearing situation of molecular materials has very important application prospects in this field;

2) In the preparation process of self-enhancing mechanochromic materials, when the content of dihalogenated three-membered cyclopropane structural unit is too low, the enhancement of mechanical properties is not obvious when the material is subjected to stress, while when the content of dihalogenated three-membered cyclopropane structural unit is too high, the mechanical properties of the material are not significantly enhanced. When the material is stressed, the degree of crosslinking of the system is too large, which will further lead to the brittleness of the final material. Therefore, the present invention determines that the molar content of the dihalogenated three-membered cyclopropane structural unit in the raw material needs to be controlled within 10%~ Within the range of 30%; when the content of the mechanochromic structural unit is low, the mechanochromic phenomenon is not obvious for the self-enhancing mechanochromic material, and when the molar content of the mechanochromic structural unit is too high, the mechanochromic phenomenon is not obvious. The change of the discoloration phenomenon also gradually slows down, so the present invention determines that the molar content of the mechanochromic structural unit needs to be controlled within the range of 0.5% to 5% through a large number of technical optimizations, so as to ensure that the final prepared self-enhancing mechanochromic material is damaged by stress. On the one hand, the destructive damage can be warned of discoloration, and on the other hand, the damaged part can be cross-linked to play a self-reinforcing role to ensure mechanical strength. The preparation method is relatively simple, and the required cost is low, which is beneficial to its Practical applications in the fields of bionic materials, mechanical sensing and engineering materials.

Description of drawings

Fig. 1 is the preparation flow chart of the self-enhancing force-induced color changing material of the present invention;

2 is a flow chart of the preparation of the self-enhancing mechanochromic material SM-1 of Example 1 of the present invention;

3 is a flow chart of the preparation of the self-enhancing mechanochromic material SM-2 in Example 2 of the present invention;

4 is a flow chart of the preparation of the self-enhancing mechanochromic material SM-6 of Example 6 of the present invention;

5 is a flow chart of the preparation of the self-enhancing mechanochromic material SM-7 in Example 7 of the present invention;

6 is a flow chart of the preparation of the self-enhancing mechanochromic material SM-8 of Example 8 of the present invention;

Figure 7 shows the fluorescence spectra of the self-enhancing mechanochromic material SM-1 spline before and after stretching;

Figure 8 is the stress-strain curve of the self-enhancing mechanochromic material SM-1 during the first and second uniaxial stretching;

9 is a structural change diagram of the self-enhancing force-induced color changing material of the present invention before and after being subjected to force;

Figure 10 is the uniaxial tensile stress-strain curve of the self-enhancing mechanochromic material SM-2 and the self-enhancing mechanochromic material SM-3;

Figure 11 shows the fluorescence spectra of self-enhancing mechanochromic material SM-4 and self-enhancing mechanochromic material SM-5 after uniaxial stretching;

Figure 12 shows the stress-strain curves of the self-enhancing mechanochromic material SM-7 during the first and second uniaxial stretching processes.

Detailed ways

The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

The experimental methods used in the following examples, unless otherwise specified, are conventional methods, and the used reagents, methods and equipment, unless otherwise specified, are conventional reagents, methods and equipment in the technical field.

Referring to Fig. 1, the preparation method of the self-enhancing mechanochromic material of the present invention comprises the following steps:

S1. Add the dihalogenated three-membered cyclopropane structural unit, the spiro ring mechanochromic structural unit, the catalyst and other multifunctional monomers into the solvent, and carry out the polycondensation reaction at 50-85 °C;

Wherein the catalyst is tin or amine catalyst, preferably organotin; other multifunctional monomers are one or more of polyvalent hydroxy compounds, polyvalent amine-based compounds, and polyvalent isocyanates;

The molar content of the dihalogenated three-membered cyclopropane structural unit is 10% to 30%, preferably 20%;

The chemical structural formula of the dihalogenated three-membered cyclopropane structural unit is:

In the formula, R ₁ group is one of -Br, -I; R ₂ group is -OH, -SH, -COOH, -F, -Cl, -Br, -I, -CHO, -NH ₂ One of the; m is in the range 0-12;

The molar content of the spiro ring mechanochromic structural unit is 0.5% to 5%, preferably 3%, and the spiro ring mechanochromic structural unit is one of the following substances:

In the formula, R ₁ , R ₂ , R ₃ and R ₄ are all selected from one of the following structures: -OH, -SH, -COOH, -F, -Cl, -Br, -I, -CHO, -NH ₂ ;

S2. The polymer solution obtained in step S1 is precipitated in an alcohol solvent and then dried to obtain a sample;

S3, the sample obtained in step S2 and the small molecule cross-linking agent are uniformly mixed and then molded to obtain a self-reinforcing force-induced discoloration material;

Wherein, the crosslinking agent molecule is used after reacting with an organic base to form a salt, and the small molecular crosslinking agent is adipic acid, glutaric acid, succinic acid, malonic acid, pimelic acid, suberic acid, azelaic acid A kind of polycarboxylic acid such as acid, sebacic acid, the organic base is tetramethylguanidine, 1,8-diazabicycloundec-7-ene, triethylamine, diethylamine, ammonia water , one or more of diisopropylamine.

It should be noted that, in step S1, the dihalogenated three-membered cyclopropane structural unit, the spiro mechanochromic structural unit, the catalyst and other multifunctional monomers are all dried before use to avoid deterioration of the raw materials.

Preferably, in step S2, the polymer solution is precipitated in methanol three times and then dried in a vacuum oven overnight.

Preferably, in step S3, the sample and the small molecule cross-linking agent are uniformly mixed and then molded in a dumbbell-shaped mold to obtain a self-reinforcing mechanochromic material.

Example 1: Self-Enhancing Mechanochromic Material SM-1

Referring to Figure 2, the preparation method of the self-enhancing mechanochromic material SM-1 includes the following steps:

a. Add 2g 3-hexene-1,6-diol (1eq.), 20mL tribromomethane (6eq.) and 1.35g cetyltrimethylammonium bromide (0.1eq.) to 300mL dichloromethane In methane, deoxygenate by nitrogen bubbling for 1 h, then add 12 g (8 eq.) aqueous NaOH solution dropwise, then stir the system at room temperature for 30 h and wash three times with 500 mL of deionized water; the organic phase is concentrated and purified by column chromatography The oily product M1 (dibromo three-membered cyclopropane structural unit) was obtained, and the yield was 85%;

b. Monohydroxyrhodamine 6G (4.0 g, 8.7 mmol) and potassium carbonate (9.6 g, 69.8 mmol) were added to 40 mL of chloroethanol, and the reaction system was reacted at 100 ° C for 24 hours; The excess chloroethanol was distilled off under pressure; the residue was poured into water and extracted three times with dichloromethane; the organic phase was separated, dried with anhydrous sodium sulfate, and the solvent was distilled off under reduced pressure; the crude product was purified by silica gel chromatography (eluting The agent is dichloromethane/ethanol=35/1) to obtain the target product M2 (spiro-ring mechanochromic structural unit), and the yield is 70%;

c. Compound M1 (molar content is 20%), compound M2 (molar content is 3%), PEG1000 (molar content is 27%) and hexamethylene diisocyanate (molar content is 50%) is added to 1,4 -In the dioxane solvent, then add dibutyltin dilaurate with a total molar content of 0.1% of monomers (compound M1, compound M2, PEG1000, hexamethylene diisocyanate) to the above system, and react at 70°C for 24h;

d. The polymer solution obtained in step c is precipitated three times in methanol and then dried in a vacuum oven overnight;

e. The sample obtained in step d is uniformly mixed with the small molecular salt cross-linking agent (obtained by the reaction of adipic acid and tetramethylguanidine), and then molded in a dumbbell-shaped mold to obtain the final self-enhancing force-induced color change material SM- 1.

Example 2: Self-enhancing Mechanochromic Material SM-2

Referring to Figure 3, the preparation method of the self-enhancing mechanochromic material SM-3, the difference between this example and Example 1 is that the molar percentages of compounds M1, M2 and PEG1000 used in step c are 10% and 3%, respectively. , 37%.

Example 3: Self-Enhancing Mechanochromic Material SM-3

The preparation method of self-enhancing mechanochromic material SM-3, the difference between this example and Example 1 is that the mole percentages of compounds M1, M2 and PEG1000 used in step c are 30%, 3%, and 17%, respectively.

Example 4: Self-Enhancing Mechanochromic Material SM-4

The preparation method of the self-enhancing mechanochromic material SM-4 is different from Example 1 in that the mole percentages of compounds M1, M2 and PEG1000 used in step c are 20%, 0.5% and 29.5%, respectively.

Example 5: Self-Enhancing Mechanochromic Material SM-5

The preparation method of the self-enhancing mechanochromic material SM-5 is different from Example 1 in that the molar percentages of the compounds M1, M2 and PEG1000 used in step c are 20%, 5% and 25%, respectively.

Example 6: Self-Enhancing Mechanochromic Material SM-6

Referring to FIG. 4 , the preparation method of the self-enhancing mechanochromic material SM-6, the difference between this example and Example 1 is that in step c, other multifunctional monomers are selected from diphenylmethane diisocyanate (MDI).

Example 7: Self-Enhancing Mechanochromic Material SM-7

Referring to Figure 5, the preparation method of the self-enhancing mechanochromic material SM-7, the difference between this example and Example 1 is that step a: 2g 3-hexene-1,6-diol (1eq.), 20mL Trichloromethane (6eq.) and 1.35g cetyltrimethylammonium bromide (0.1eq.) were added to 300mL dichloromethane; deoxygenated by nitrogen bubbling for 1h, and then 12g (8eq.) NaOH was added dropwise aqueous solution; then the system was stirred at room temperature for 30 h and washed with 500 mL of deionized water for 3 times; the organic phase was concentrated and purified by column chromatography to obtain oily product M1 (dichloro three-membered cyclopropane structural unit) with a yield of 85 %.

Example 8: Self-Enhancing Mechanochromic Material SM-8

Referring to FIG. 6 , the preparation method of the self-enhancing mechanochromic material SM-8, the difference between this example and Example 1 is that step c: compound M1 (molar content is 20%), compound M2 (molar content is 3%) ), butanediol (27% by mole) and hexamethylene diisocyanate (50%) were added to 1,4-dioxane solvent, followed by adding dilauric acid with a total mole content of 0.1% of the above monomers Dibutyltin was added to the above system and reacted at 70°C for 24h.

Example 9

The self-enhancing force-induced discoloration material prepared by the present invention is tested according to the following instruments and methods:

Fluorescence spectrum was measured with Shimadzu RF-5301PC fluorescence spectrophotometer; UV absorption spectrum was measured with PgeneralUV-Vis TU-1901 UV-Vis spectrophotometer; uniaxial tensile test was measured with universal tensile testing machine.

9.1. Discoloration warning and force-induced self-enhancement performance test of self-enhancing force-induced color materials

9.1.1 Test method

The self-enhancing mechanochromic material SM-1 was subjected to uniaxial tensile test using a universal tensile testing machine, and the self-enhancing mechanochromic material SM-1 before and after stretching was subjected to a fluorescence spectrum test using a Shimadzu RF-5301PC fluorescence spectrophotometer. , the test results are shown in Figure 7 and Figure 8;

9.1.2 Results and Analysis

It can be seen from the fluorescence spectra of the self-enhancing mechanochromic material SM-1 before and after stretching shown in Fig. 7 that the self-enhancing mechanochromic material SM-1 exhibits obvious blue fluorescence before stretching, and the fluorescence emission peak is located at 420 nm. , while no obvious fluorescence emission was found in other bands; when the self-enhancing mechanochromic material SM-1 spline was unidirectionally stretched, the fluorescence color of the self-enhancing mechanochromic material SM-1 spline changed significantly, Specifically, a distinct fluorescence emission peak appeared at 600 nm after stretching. It can be seen that the self-enhancing mechanochromic material SM-1 spline can provide early warning of discoloration of external stress.

It can be seen from the stress-strain curves of the self-enhancing mechanochromic material SM-1 in the first and second uniaxial stretching process shown in Figure 8, the stress-strain curve of the second stretching process is compared with the first time The slope of the curve increases significantly, indicating that the strength of the self-enhancing mechanochromic material SM-1 spline is not reduced after the first stretching, but has a certain degree of enhancement. This phenomenon confirms that the self-enhancing mechanochromic material SM-1 spline After the first uniaxial stretching, the dihalocyclopropane structure in the strip structure undergoes isomerization reaction and reacts with the small molecule crosslinking agent in the matrix material to crosslink, thus showing force-induced self-enhancement phenomenon; Figure 9 shows the structural changes before and after the reinforced mechanochromic material is stressed.

9.2. The molar content of the dihalogenated three-membered cyclopropane structural unit in the molecular backbone of the self-enhancing mechanochromic material needs to be controlled between 10% and 30%

The self-reinforcing force-induced color material SM-2 and the self-reinforcing force-induced color material SM-3 were subjected to uniaxial tensile test using a universal tensile testing machine; the test results are shown in Figure 10;

From the uniaxial tensile stress-strain curves of the self-enhancing mechanochromic material SM-2 and the self-enhancing mechanochromic material SM-3 shown in Fig. 10, it can be seen that the self-enhancing The self-enhancing phenomenon of the reinforced mechanochromic material SM-2 spline is not obvious in repeated tensile experiments, while the self-enhancing mechanochromic material SM-3 spline with a high content of dihalogenated three-membered cyclopropane structural units shows A very obvious self-reinforcing phenomenon was observed, but the elongation at break of the splines was reduced to 118% due to the magnitude of the force-induced cross-linking reaction. The above results show that when the content of dihalogenated three-membered cyclopropane structural unit is too low, the mechanical properties of the material are not significantly enhanced when subjected to stress; while when the content of dihalogenated three-membered cyclopropane structural unit is too high, the degree of crosslinking of the system when the material is stressed Too large will further cause the final material to become brittle. Therefore, in the actual preparation of the self-enhancing mechanochromic material, the molar content of the dihalogenated three-membered cyclopropane structural unit needs to be controlled within the range of 10% to 30%.

9.3. The molar content of the spiro ring mechanochromic structural unit in the molecular backbone of the self-enhancing mechanochromic material needs to be controlled between 0.5% and 5%

The self-enhancing mechanochromic material SM-4 and the self-enhancing mechanochromic material SM-5 were uniaxially stretched to the same degree by a universal tensile testing machine, and then the tensile strength was measured by a Shimadzu RF-5301PC fluorescence spectrophotometer. The resulting self-enhancing mechanochromic material SM-4 and self-enhancing mechanochromic material SM-5 were tested by fluorescence spectrum, and the test results are shown in Figure 11;

From the fluorescence spectra of the self-enhancing mechanochromic material SM-4 and the self-enhancing mechanochromic material SM-5 after uniaxial stretching shown in Figure 11, it can be seen that when the content of the mechanochromic structural unit is low, the For the reinforced mechanochromic material SM-4 spline, the mechanochromic phenomenon is not obvious, and the fluorescence intensity at 600 nm after stretching is only slightly enhanced. When the molar content of the mechanochromic structural unit is higher than 5% , the change of the mechanochromic phenomenon gradually slowed down. Therefore, in the actual preparation of the self-enhancing mechanochromic material, the molar content of the mechanochromic structural unit needs to be controlled within the range of 0.5% to 5%.

9.4. Influence of the R ₁ group in the dihalogenated three-membered cyclopropane structural unit on the self-enhancement effect

The self-reinforcing force-induced color change material SM-7 was subjected to a uniaxial tensile test using a universal tensile testing machine, and the test results are shown in Figure 12;

Due to the large atomic radius of the iodine atom formed after ring opening, the diiodocyclopropane structural unit is easily attacked and left by nucleophiles, and its reactivity is higher than that of chlorinated and bromoalkanes.

It can be seen from the stress-strain curves of the self-enhancing mechanochromic material SM-7 in the first and second uniaxial tensile processes shown in Fig. No obvious self-enhancement phenomenon was found. The main reason for this phenomenon is that the reactivity of the chlorine atom and the nucleophile formed after the dichlorocyclopropane is opened by force is not as good as that of the bromine atom, so the subsequent cross-linking reaction cannot occur.

In summary, it can be seen that the self-enhancing mechanochromic material provided by the present invention can, on the one hand, carry out early warning of discoloration when subjected to destructive stress, and on the other hand, can enhance the mechanical properties of the material through subsequent cross-linking reaction. The technical route is relatively simple and the required cost is low, which is beneficial to its practical application in the fields of biomimetic materials, mechanical sensing and engineering materials.

The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions that belong to the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims (4)

1. a preparation method of self-enhancing force-induced color change material, is characterized in that, comprises the following steps: S1. Add the dihalogenated three-membered cyclopropane structural unit, the spiro ring mechanochromic structural unit, the catalyst and other multifunctional monomers into the solvent, and carry out the polycondensation reaction at 50-85 °C; S2. The polymer solution obtained in step S1 is precipitated in an alcohol solvent and then dried to obtain a sample; S3, the sample obtained in step S2 and the small molecule cross-linking agent are uniformly mixed and then molded to obtain a self-reinforcing force-induced discoloration material; in, The chemical structural formula of the dihalogenated three-membered cyclopropane structural unit is:

In the formula, the R ₁ group is one of -Br and -I; the R ₂ group is one of -OH, -SH, -COOH, and -NH ₂ ; the range of m is 0-12; The spiro ring mechanochromic structural unit is one of the following substances:

In the formula, R ₁ , R ₂ , R ₃ and R ₄ are all selected from one of the following structures: -OH, -SH, -COOH, -NH ₂ ; The other polyfunctional monomers are one or more of polyvalent hydroxyl compounds, polyvalent amine-based compounds, and polyvalent isocyanates; In step S1, the molar content of the dihalogenated three-membered cyclopropane structural unit is 10% to 30%; the molar content of the spiro ring mechanochromic structural unit is 0.5% to 5%; In step S3, the small-molecule cross-linking agent is used after reacting with an organic base to form a salt, the small-molecule cross-linking agent is one of polycarboxylic acids, and the organic base is tetramethylguanidine, 1,8 -One or more of diazabicycloundec-7-ene, triethylamine, diethylamine and diisopropylamine. 2. preparation method according to claim 1, is characterized in that: in step S1, before using, the dihalogenated three-membered cyclopropane structural unit, the spiro ring mechanochromic structural unit, the catalyst and other polyfunctional monomers are all dried before use . 3. The preparation method according to claim 1, wherein the catalyst is a tin or amine catalyst. 4. The self-enhancing mechanochromic material prepared by the preparation method according to any one of claims 1-3.

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