Force-induced discoloration polythionocarbamate material and preparation method thereof

Abstract

The invention relates to the technical field of preparation of mechanochromic materials, in particular to a mechanochromic polythionocarbamate material and a preparation method thereof. The preparation method comprises the following steps: mixing a mechanochromic element, a diisocyanate group raw material, a sulfydryl raw material and a catalyst, degassing, heating, carrying out a curing reaction, and annealing after the reaction is finished, so as to obtain the mechanochromic polythionocarbamate material. Compared with the prior art, the mechanochromic polythionocarbamate material is prepared by adopting a simple and efficient'one-step method ', so that the prepared mechanochromic polythionocarbamate material has a remarkable mechanical discoloration effect, is good in stability and high in response speed, and can realize stress monitoring in a large stress state range.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of mechanochromic materials, and particularly to a mechanochromic polyurethane material and a preparation method thereof. Background Art

[0002] With the development of science and technology, color-changing display materials based on light, electricity, and heat induction have been developed, and the research and development of mechanochromic materials based on mechanical stress and strain (tensile, compressive, shear) induction are becoming a research hotspot. Mechanochromic materials can achieve fluorescence switching and color transformation under the induction of external mechanical force, and have important application spaces in anti-counterfeiting and encryption, stress monitoring, flexible display, and basic research on microscopic stress conduction.

[0003] At present, intrinsic mechanochromic materials are a research hotspot in mechanochromic materials. Intrinsic mechanochromic materials often achieve color transformation through changes in the inherent structure (physical color / structural color) or chemical properties (chemical color) of the material itself. The preparation technologies of "structural color" materials include atomic layer deposition method, magnetic sputtering method, template method, self-assembly method, and phase separation method, etc. Based on the bionic strategy, mechanochromic liquid crystal elastomer materials represented by the "cholesteric phase" structural color have achieved a wide range of color transformation and high mechanical response sensitivity. They mainly promote the change of the color of an object under the observation angle of the human eye through the selective absorption and reflection of visible light. However, the preparation process of "cholesteric phase" mechanochromic materials is relatively complex, with high technical difficulty and high equipment requirements, and the introduced "nano-dot array" structure has poor stability, which increases the production cost of mechanochromic materials. Limited by the technical limitations of the preparation method, it is not suitable for the large-scale preparation of such materials, and the "cholesteric phase" often uses low molecular chain segments as raw materials, and the mechanical and physical properties of the material itself are poor, making it difficult to meet the application of color-changing materials in high-stress environments.

[0004] "Chemochromic" materials often have special mechanochromic units (mechanical carriers / force-sensitive groups / force-sensitive units) as the main body, which are introduced into the macroscopic matrix material by covalent bonding. Under the stimulation of external force, the weak chemical bonds on the microscopic mechanochromic group molecules are broken and the spatial conjugation property is destroyed, realizing fluorescence switching and color transformation. The advantage of this method is that the mechanochromic units are introduced by covalent means, the amount of mechanochromic units used is small, the amount of mechanical carriers can be adjusted, the content of the introduced mechanochromic units can be changed, the color change contrast of the material can be improved, and the stability of the color-changing material can be improved. At the same time, the performance of the mechanochromic material also mainly depends on the performance of the matrix material itself. The matrix material components are widely selected, so its application range and the material taking space are large, and the application prospect is great. However, the existing materials have poor stability and cannot meet the mechanical stress monitoring in high-stress environments. Moreover, during the preparation of the mechanochromic material using mechanochromic units as raw materials, the use of solvents will change the isomerization process of the mechanochromic units and affect the mechanochromic effect of the material.

[0005] Patent Publication No. CN116375937A discloses a doped nanomaterial liquid crystal elastomer mechanochromic nanocomposite material and a preparation method thereof. A liquid crystal elastomer containing a spiropyran derivative molecule is used as the matrix, and a nanocomposite material doped with nanomaterials. Utilizing the reversible force-isomerization characteristic of the spiropyran derivative, the color change of the material can occur under pressure, and it returns to the initial colorless state after the pressure is removed. However, the stability of this color-changing nanocomposite material is relatively poor, the sensitivity is relatively low, and the use of a solvent system will change the isomerization process of the mechanochromic units, affect the mechanochromic effect of the material, and the volatilization of organic solvents is easy to pollute the environment. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned existing technologies and provide a kind of mechanochromic polythiourethane material and its preparation method. The mechanochromic polythiourethane material is prepared by a simple and efficient "one-step method", so that the prepared mechanochromic polythiourethane material has a significant mechanochromic effect, good stability, fast response speed, and can meet the stress monitoring in high-stress environments.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] On the one hand, the present invention provides a preparation method of a mechanochromic polythiourethane material. The steps of the preparation method are: mixing a mechanochromic unit, a diisocyanate group raw material, a mercapto raw material and a catalyst, degassing, then heating up for curing reaction, and annealing after the reaction ends to obtain the mechanochromic polythiourethane material.

[0009] Furthermore, the force-responsive chromogenic unit includes one or more active functional groups such as hydroxyl group, amino group, acrylate group, and methacrylate group.

[0010] By the click reaction of "mercapto group" with "isocyanate group" and "mercapto group" with "double bond", and the nucleophilic addition reaction of "hydroxyl group" with "isocyanate group" and "amino group" with "isocyanate group", the force-responsive chromogenic polyurethane material is prepared by the "one-step method", which is simple and efficient and can be prepared in large quantities.

[0011] Furthermore, the force-responsive chromogenic unit includes spiropyran derivatives, spirooxazine derivatives, and rhodamine derivatives, preferably spiropyran derivatives. The structural formula of the spiropyran derivative is shown in Formula (1) or Formula (2), the structural formula of the spirooxazine derivative is shown in Formula (3) or Formula (4), and the structural formula of the rhodamine derivative is shown in Formula (5).

[0012]

[0013] Among them, represents the "spacer group", that is, the chemical structure of the intermediate part between the main structure of the force-responsive chromogenic unit and X, including where n≥1.

[0014] Furthermore, the raw material of the diisocyanate group includes hexamethylene diisocyanate (HDI), which has a bifunctional group.

[0015] The catalyst includes dibutyltin dilaurate (DBTDL).

[0016] Furthermore, the raw material of the mercapto group includes 3,6-dioxa-1,8-dimercaptooctane (EDDET).

[0017] Furthermore, the raw material of the mercapto group includes a mixture of EDDET and pentaerythritol tetra(3-mercaptopropionate) (PETMP).

[0018] Furthermore, in the mixture of EDDET and PETMP, the molar ratio of the two is 1:(0.0001 - 0.5), preferably 1:0.0001 - 0.1, and further preferably 1:0.0001 - 0.0002.

[0019] Furthermore, the molar ratio of the "mercapto group" content in the raw material of the mercapto group to the "isocyanate group" in the raw material of the diisocyanate group is 1:0.8 - 1.2, preferably 1:1.

[0020] The mass percentage of the mechanochromic unit in the total mass of the overall material preparation is 0.01 wt% to 0.1 wt%, preferably 0.01 wt% to 0.05 wt%; the catalyst accounts for 0.5 wt% to 5 wt% of the total mass of the overall material preparation, preferably 0.5 wt% to 2 wt%.

[0021] Since the content of the mechanochromic unit used in the system is extremely small, the consumption of the "isocyanate group" in the isocyanate group raw material by active functional groups such as hydroxyl groups, amino groups, acrylate groups, and methacrylate groups during the preparation process can be ignored.

[0022] Furthermore, the temperature of the curing reaction is 80 to 120 °C, and the time is 2 to 12 h; the annealing temperature is 60 to 70 °C, and the time is 2 to 12 h.

[0023] Furthermore, the degassing time is 5 to 60 min.

[0024] Furthermore, no solvent is added during the preparation process, and it is a solvent-free system. There is no need to introduce an external solvent during the material preparation process, avoiding the use of volatile organic solvents. While reducing environmental pollution, the isomerization effect of organic solvents on the mechanochromic unit is avoided.

[0025] On the other hand, the present invention also provides a mechanochromic polythiourethane material prepared by using the described preparation method.

[0026] Furthermore, the mechanochromic polythiourethane structure contains a wide range of "thiocarbamate bonds" formed by the reaction of "mercapto groups" and "isocyanate groups", which have dynamic reversible exchange properties, achieving a hot pressing reshaping effect and improving the processing performance of the material. In addition, the thiocarbamate bond has a good adhesion effect with metals, glass, etc. and can be used as an adhesive.

[0027] Furthermore, when the mechanochromic polythiourethane material is used as a stress monitoring material, its elongation at break is 300% to 600%, and the breaking strength is 30 to 60 MPa, greatly meeting the usage scenarios of stress monitoring materials.

[0028] Furthermore, when the mechanochromic polythiourethane material is irradiated with white light (30 to 100 W) for 5 to 30 s, it can be restored to a colorless state.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) In the present invention, a force-induced chromogenic element, a diisocyanate group raw material, a mercapto raw material, and a catalyst are mixed. After degassing, the temperature is raised for curing reaction. After the reaction is completed, annealing is carried out to obtain a force-induced chromogenic polyurethane material. The preparation process involves click reactions of "mercapto" with double bonds (acrylate, methacrylate), "mercapto" with "isocyanate", and nucleophilic addition reaction of "isocyanate" with "hydroxyl". The "one-step method" is used to prepare the force-induced chromogenic polyurethane material, which is simple and efficient, can be prepared in large quantities, and has low requirements for reaction conditions and process environment.

[0031] (2) The present invention is a solvent-free system, which avoids the introduction of highly polar solvents, reduces the damage of solvents to the stable structure of mechanical carriers, and avoids the emission and pollution of volatile organic solvents (VOCs).

[0032] (3) In the force-induced chromogenic polyurethane material of the present invention, there are common hydrogen bond action sites inside the network. The commonly existing physical cross-linking sites endow it with good mechanical and physical properties, which can meet the requirements of high-mechanical-performance materials and can meet the use space of force-induced chromogenic materials in the high-stress monitoring range.

[0033] (4) In the present invention, the amount of the force-induced chromogenic element used is small. The force-induced chromogenic element is sensitive to externally applied stress and strain, has a high sensitivity to strain-induced color change, and is low in cost.

[0034] (5) In the present invention, the polyurethane of the force-induced chromogenic polyurethane material acts as a reversible dynamic covalent bond, which can meet the effect of hot processing of the material.

[0035] (6) The force-induced chromogenic element used in the present invention also has effects such as light and heat-induced color change, unifying various stimulus-responsive color change effects, and broadening the application scenarios of the force-induced chromogenic polyurethane material, such as temperature monitoring, fire warning, and anti-counterfeiting encryption. Description of the Drawings

[0036] Figure 1 Structural formula of SP-1 shown in Example 1;

[0037] Figure 2 Synthesis route diagram of SP-1 shown in Example 1;

[0038] Figure 3 For SP-1 shown in Example 1 1 1H NMR spectrum;

[0039] Figure 4 Structural formula of SP-2 shown in Example 2;

[0040] Figure 5 Synthesis route diagram of SP-2 shown in Example 2;

[0041] Figure 6It is the structural formula of SP-3 shown in Example 3;

[0042] Figure 7 It is the synthetic route diagram of SP-3 shown in Example 3;

[0043] Figure 8 It is the stress-strain curve of the PTU-1 spline shown in Example 1;

[0044] Figure 9 It is the mechanical stress discoloration diagram of PTU-1 before and after stretching shown in Example 1, (a) before stretching, (b) after stretching;

[0045] Figure 10 It is the thermochromic effect diagram of PTU-1 and PTU-0 shown in Example 1, (a1) photo of PTU-1 at room temperature before heating, (b1) photo of PTU-1 after heating at 100 °C for 3 min, (c1) photo of PTU-1 at room temperature after natural cooling from 100 °C, (a2) photo of PTU-0 at room temperature before heating, (b2) photo of PTU-0 after heating at 100 °C for 3 min, (c2) photo of PTU-1 at room temperature after natural cooling from 100 °C;

[0046] Figure 11 It is the sample picture of PTU-2 shown in Comparative Example 2;

[0047] Figure 12 It is the influence of different solvents on the appearance color of the materials described in Comparative Example 3 and Comparative Example 4, (a) color behavior of the SP-1 mechanical carrier described in Comparative Example 3 and Comparative Example 4 in THF and DMF, (b) appearance photos of the materials in Comparative Example 3 and Comparative Example 4. Detailed implementation manners

[0048] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0049] Based on the given embodiments, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this application.

[0050] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art.

[0051] Among them, the raw materials EDDET (CAS No. 14970-87-7, purity ≥ 97%) and PETMP (CAS No. 7575-23-7) are all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0052] HDI (CAS No. 822-06-0, purity ≥ 99%) was purchased from Shanghai Macklin Biochemical Co., Ltd.

[0053] DBTDL (CAS No. 77-58-7, purity ≥ 98%) was purchased from Tokyo Chemical Industry Co., Ltd.

[0054] The raw materials part is not used to limit the scope, and other commercially available raw materials can also be used to prepare the mechanochromic polyurethane material.

[0055] A preparation method of a mechanochromic polyurethane material, the steps of the preparation method are as follows: mix a mechanochromic unit, a diisocyanate group raw material, a mercapto raw material and a catalyst, degas and then raise the temperature for curing reaction, and anneal after the reaction ends to obtain the mechanochromic polyurethane material.

[0056] In some specific embodiments, the mechanochromic unit includes one or more active functional groups such as hydroxyl group, amino group, acrylate group, and methacrylate group.

[0057] The mechanochromic polyurethane material is prepared by the "one-step method" through the click reactions of "mercapto" with "isocyanate" and "mercapto" with "double bond", and the nucleophilic addition reactions of "hydroxyl" with "isocyanate" and "amino" with "isocyanate", which is simple and efficient and can be prepared in large quantities.

[0058] In some specific embodiments, the mechanochromic unit includes spiropyran derivatives, spirooxazine derivatives, and rhodamine derivatives, preferably spiropyran derivatives, wherein the structural formula of the spiropyran derivative is shown in Formula (1) or Formula (2), the structural formula of the spirooxazine derivative is shown in Formula (3) or Formula (4), and the structural formula of the rhodamine derivative is shown in Formula (5).

[0059]

[0060] Among them, represents a "spacer group", that is, the chemical structure of the intermediate part between the main structure of the mechanochromic unit and X, including where n ≥ 1.

[0061] In some specific embodiments, the diisocyanate group raw material includes HDI, which has a bifunctional group;

[0062] The catalyst includes DBTDL.

[0063] In some specific embodiments, the mercapto raw material includes EDDET.

[0064] In some specific embodiments, the mercapto raw material includes a mixture of EDDET and PETMP.

[0065] In some specific embodiments, in the mixture of EDDET and PETMP, the molar ratio of the two is 1:(0.0001 - 0.5), preferably 1:0.0001 - 0.1, and more preferably 1:0.0001 - 0.0002.

[0066] In some specific embodiments, the molar ratio of the "mercapto" content in the mercapto raw material to the "isocyanate group" in the diisocyanate group raw material is 1:0.8 - 1.2, preferably 1:1;

[0067] The force - induced chromogenic element accounts for 0.01 wt% - 0.1 wt% of the total mass of the overall material preparation, preferably 0.01 wt% - 0.05 wt%; the catalyst accounts for 0.5 wt% - 5 wt% of the total mass of the overall material preparation, preferably 0.5 wt% - 2 wt%.

[0068] Due to the extremely low content of the force - induced chromogenic element in the system, the consumption of the "isocyanate group" in the isocyanate group raw material by active functional groups such as hydroxyl, amino, acrylate, and methacrylate groups during the preparation process can be ignored.

[0069] In some specific embodiments, the temperature of the curing reaction is 80 - 120 °C and the time is 2 - 12 h; the annealing temperature is 60 - 70 °C and the time is 2 - 12 h.

[0070] In some specific embodiments, the time for degassing is 5 - 60 min.

[0071] In some specific embodiments, no solvent is added during the preparation process, which is a solvent - free system. There is no need to introduce an external solvent during the material preparation process, avoiding the use of volatile organic solvents. While reducing environmental pollution, the isomerization effect of organic solvents on the force - induced chromogenic element is avoided.

[0072] A force - induced chromogenic polyurethane material is prepared by using the described preparation method.

[0073] In some specific embodiments, the force - induced chromogenic polyurethane structure contains a wide range of "thiocarbamate bonds" formed by the reaction of "mercapto" and "isocyanate group", which have dynamic reversible exchange properties, achieving a hot - pressing reshaping effect and improving the processing performance of the material. In addition, the thiocarbamate bond has good adhesion effects with metals, glass, etc., and can be used as an adhesive.

[0074] In some specific embodiments, when the force-induced color change polyurethane material is used as a stress monitoring material, its elongation at break is 300% - 600%, and its breaking strength is 30 - 60 MPa, which largely meets the usage scenarios of stress monitoring materials.

[0075] In some specific embodiments, when the force-induced color change polyurethane material is irradiated with white light (30 - 100 W) for 5 - 30 s, it can be restored to a colorless state.

[0076] Each of the above embodiments can be implemented alone, or in any combination of two or more.

[0077] The following will be described in conjunction with specific embodiments.

[0078] Example 1

[0079] A preparation method of a force-induced color change polyurethane material. Before preparation, the required raw materials and reaction vessels are dried. First, weigh 1.5 mg of the force-induced color change chromophore spiropyran derivative (named SP-1 here, with the structural formula as Figure 1 described), 1.0 g of HDI, 1.0839 g of EDDET, and 20.85 mg of DBTDL in a glass dish. After mixing, shake the mixed sample well. Then put the well-mixed sample into a vacuum oven for degassing for 10 minutes, raise the temperature to 100 °C for curing reaction for 30 minutes, and anneal at 70 °C for 2 hours to obtain the force-induced color change polyurethane material, named PTU-1.

[0080] Among them, the preparation process of SP-1 is as follows:

[0081] (1) Synthesis of 5-methoxy-2,3,3-trimethyl-3H-indole

[0082] Weigh 4-methoxyphenylhydrazine hydrochloride (14.63 g, 1 eq.) and methyl isopropyl ketone (7.21 g, 1 eq.), dissolve them in 200 mL of glacial acetic acid, and react at room temperature overnight. Detect whether the reaction is complete through a TLC plate. Concentrate the reaction solution by a rotary evaporator, mix the concentrated product with silica gel powder, and prepare a sample by dry method. Purify by column chromatography with a mixed solvent of n-hexane (Hexane):ethyl acetate (EtOAc) = 4:1 (v:v) to obtain an orange-red solid (13.86 g, yield: 94.7%).

[0083] (2) Synthesis of 2,3,3-trimethyl-3H-indol-5-ol

[0084] Weigh 5-methoxy-2,3,3-trimethyl-3H-indole (13.86 g, 1 eq.) and put it into a round-bottom flask. Measure 48% HBr (250 mL, 30 eq.) and add it thereto. Heat under reflux at 140 °C overnight, and detect the reaction situation by TLC plate. Add 120 mL of ice water to the hot solution after the reaction, and slowly add solid NaHCO₃ while stirring under ice bath conditions until the mixture is alkaline (pH = 2 - 4). Filter to collect the precipitate to obtain the desired product, which is a black-brown solid. To obtain a higher yield, the tarry substance remaining on the bottle wall can be dissolved with a small amount of methanol (MeOH), extracted with dichloromethane (DCM), dried over anhydrous Na₂SO₄, and the solvent is rotary evaporated and concentrated to obtain a black-brown asphalt-like solid. After purification by column chromatography with a eluent of dichloromethane (DCM):methanol (MeOH) = 20:1 (v:v), concentrate to obtain a black-brown solid (11.98 g, yield: 93.3%).

[0085] (3) Synthesis of 5-hydroxy-1,2,3,3-tetramethyl-3H-indol-1-ium iodide

[0086] Weigh 2,3,3-trimethyl-3H-indol-5-ol (10.05 g, 1 eq.) and place it in a two-necked flask. Add 60 mL of acetonitrile (MeCN) to disperse the black-brown solid, put in a magnetic stir bar, and displace nitrogen under vacuum. Slowly inject methyl iodide (CH₃I, 12.2 g, 1.5 eq.) through a rubber stopper under N₂ protection, and react overnight from 0 °C to room temperature. It is observed that the dispersed black-brown solid substance turns into a brown solid powder. Distill off the solvent under reduced pressure to obtain the target product, which is a brown powdery solid and does not require further purification (16.4 g, yield: 90%).

[0087] (4) Synthesis of 2,3-dihydroxy-5-nitrobenzaldehyde

[0088] Weigh the brown 2-hydroxy-3-methoxy-5-nitrobenzaldehyde powder (5 g, 1 eq.), measure 48% HBr (10 mL, 3 eq.) and add it thereto. Heat under reflux at 140 °C overnight, and detect the reaction situation by TLC plate. After the reaction is completed, distill off HBr under reduced pressure, concentrate to obtain a black-brown solid powder, and store it in the shade after air drying for later use (11.98 g, yield: 93.3%).

[0089] (5) Synthesis of 4-((6-hydroxyhexyl)oxy)benzoic acid

[0090] 4-Hydroxybenzoic acid (13.8 g, 1 eq.), 6-chloro-1-hexanol (14 g, 1.02 eq.) and sodium hydroxide (12 g, 3 eq.) were dissolved in a mixed solvent of 150 mL of anhydrous ethanol (EtOH) and 50 mL of H2O, and a reflux condenser was set up. The reaction mixture was refluxed at 80 - 90 °C for 15 hours, and then most of the ethanol was evaporated under reduced pressure. Concentrated hydrochloric acid was added to the mixture to adjust the pH value of the mixture solution to 2 - 3, and the formed precipitate was filtered to obtain a white solid. After purification by column chromatography with n-hexane:ethyl acetate (EtOAc) = 4:1 (v:v), it was concentrated to obtain a white solid powder (14.5 g, yield: 61%).

[0091] (6) Synthesis of 4-((6-(acryloyloxy)hexyl)oxy)benzoic acid

[0092] 4-((6-Hydroxyhexyl)oxy)benzoic acid (4 g, 1 eq.) was weighed and dissolved in 16 mL of DMAc. Acryloyl chloride (1.52 g, 1 eq.) was added dropwise to the above stirring solution through a rubber stopper. During the dropping, the temperature of the reaction mixture was kept at the ice-water bath temperature. After the dropping was completed, the reaction was stirred at room temperature, and the reaction progress was detected by TLC plate. After the reaction was completed, ice water was added dropwise to the reaction mixture until no more solid precipitated, and the formed precipitate was filtered to obtain the target product, which was a white solid (3.8 g, yield: 77.5%).

[0093] (7) Synthesis of SP-1 (1',3',3'-trimethyl-6-nitrospiro[chromene-2,2'-indoline]-5',8-diyl bis(4-((6-(acryloyloxy)hexyl)oxy)benzoate))

[0094] Weigh 5-hydroxy-1,2,3,3-tetramethyl-3H-indolium iodide (0.2 g, 1 eq.) and 2,3-dihydroxy-5-nitrobenzaldehyde (0.12 g, 1 eq.), disperse them in 5 mL of anhydrous ethanol, add piperidine (53.69 mg, 1 eq.) at room temperature, and catalyze the reaction overnight. After the reaction is completed, a dark green powder precipitate is obtained, filtered and dried for later use. Weigh the dried powder (0.2 g, 0.023 eq.), 4-((6-(acryloyloxy)hexyl)oxy)benzoic acid (0.33 g, 0.045 eq.), 4-dimethylaminopyridine (DMAP, 4.7 mg, 0.0016 eq.), and 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC, 175 mg, 0.046 eq.), dissolve them in 10 mL of reflux-dried tetrahydrofuran (THF), and react at room temperature for 7 hours. After the reaction is completed, remove the excess solvent by distillation under reduced pressure, purify by column chromatography with pure DCM, and concentrate to obtain a purple solid. The synthesis steps are as Figure 2 shown.

[0095] Figure 3 The 1 1H NMR spectrum of SP-1 is used to supplement and illustrate the structural characteristics of the preferred mechanochromic moiety, where "X" is The "spacer" is n = 6.

[0096] Example 2

[0097] Compared with Example 1, most of them are the same, except that "X" in SP in Example 1 is replaced with The structural formula is as Figure 4 shown, and it is named SP-2 here. The preparation process is as follows:

[0098] Steps (1)-(5) are the same as in Example 1.

[0099] (6) Synthesis of SP-2 (1',3',3'-trimethyl-6-nitrospiro[chromene-2,2'-indoline]-5',8-diyl bis(4-((6-hydroxyhexyl)oxy)benzoate))

[0100] Weigh 5-hydroxy-1,2,3,3-tetramethyl-3H-indolium iodide (0.2 g, 1 eq.) and 2,3-dihydroxy-5-nitrobenzaldehyde (0.12 g, 1 eq.), disperse them in 5 mL of anhydrous ethanol, add piperidine (53.69 mg, 1 eq.) at room temperature, and catalyze the reaction overnight. After the reaction is completed, a dark green powder precipitate is obtained, filtered and dried for later use. Weigh the dried powder (0.2 g, 0.023 eq.), 4-((6-hydroxyhexyl)oxy)benzoic acid (0.26 g, 0.045 eq.), 4-dimethylaminopyridine (DMAP, 4.7 mg, 0.0016 eq.) and 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC, 175 mg, 0.046 eq.), dissolve them in 10 mL of reflux-dried tetrahydrofuran (THF), and react at room temperature for 7 hours. After the reaction is completed, remove the excess solvent by distillation under reduced pressure, purify by column chromatography, and concentrate to obtain a purple solid. The synthesis steps are as Figure 5 shown.

[0101] Example 3

[0102] Compared with Example 1, most of them are the same, except that "X" in SP in Example 1 is replaced with The structural formula is as Figure 6 shown, and it is named SP-3 here. The preparation process is as follows:

[0103] Steps (1)-(5) are the same as those in Example 1.

[0104] (6) Synthesis of 4-(6-(methacryloyloxy)hexyl)oxy)benzoic acid (4-((6-(acryloyloxy)hexyl)oxy)benzoic acid)

[0105] Weigh 4-((6-hydroxyhexyl)oxy)benzoic acid (4 g, 1 eq.), dissolve it in 16 mL of DMAc, weigh methacryloyl chloride (1.76 g, 1 eq.), and add it dropwise to the above stirring solution via a rubber stopper. During the dropping, keep the temperature of the reaction mixture at the ice-water bath temperature. After the dropping is completed, stir the reaction at room temperature and detect the reaction progress by TLC plate. After the reaction is completed, add ice water dropwise to the reaction mixture until no more solid precipitates, filter the formed precipitate to obtain the target product, which is a white solid.

[0106] (7) Synthesis of SP-3 (1',3',3'-trimethyl-6-nitrospiro[chromene-2,2'-indoline]-5',8-diyl bis(4-((6-(methacryloyloxy)hexyl)oxy)benzoate))

[0107] Weigh 5-hydroxy-1,2,3,3-tetramethyl-3H-indolium iodide (0.2 g, 1 eq.) and 2,3-dihydroxy-5-nitrobenzaldehyde (0.12 g, 1 eq.), disperse them in 5 mL of anhydrous ethanol, add piperidine (53.69 mg, 1 eq.) at room temperature, and catalyze the reaction overnight. After the reaction is completed, a dark green powder precipitate is obtained, which is filtered and dried for later use. Weigh the dried powder (0.2 g, 0.023 eq.), 4-(6-(methacryloyloxy)hexyl)oxy)benzoic acid (0.35 g, 0.045 eq.), 4-dimethylaminopyridine (DMAP, 4.7 mg, 0.0016 eq.), and 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC, 175 mg, 0.046 eq.), dissolve them in 10 mL of reflux-dried tetrahydrofuran (THF), and react at room temperature for 7 hours. After the reaction is completed, remove the excess solvent by distillation under reduced pressure, purify by column chromatography, and concentrate to obtain the desired product. The synthesis steps are as Figure 7 shown.

[0108] Comparative Example 1

[0109] Compared with Example 1, most of them are the same, except that the mechanochromic motif SP-1 is not added. The specific steps are as follows:

[0110] All the raw materials and reaction vessels required before preparation are dried. First, weigh HDI (1 equivalent, 1.0 g), EDDET (1 equivalent, 1.0839 g), and DBTDL (1 wt%, 20.85 mg) calculated by weight or equivalent ratio into a glass dish. After mixing, shake the mixed sample well, put the well-mixed sample into a vacuum oven for degassing for 10 minutes, heat it to 100 °C for curing reaction for 30 minutes, and anneal at 70 °C for 2 hours to obtain a mechanochromic polyurethane material, named PTU-0.

[0111] Comparative Example 2

[0112] Compared with Example 1, most of them are the same, except that 1.0839 g of EDDET is replaced by 1.453 g of PETMP. The specific steps are as follows:

[0113] All the raw materials and reaction vessels required before preparation are dried. First, weigh SP-1 (1.5 mg, dosage accounts for 0.07 wt%), HDI (1 equivalent, 1.0 g), PETMP (0.5 equivalent, 1.453 g), and DBTDL (1 wt%, 20.85 mg) calculated by weight or equivalent ratio into a glass dish. After mixing, shake the mixed sample well, put the well-mixed sample into a vacuum oven for degassing for 10 minutes, heat it to 100 °C for curing reaction for 30 minutes, and anneal at 70 °C for 2 hours to obtain a mechanochromic polyurethane material, named PTU-2.

[0114] Comparative Example 3

[0115] Compared with Example 1, most of them are the same, except that a small amount of tetrahydrofuran (THF) is added as a solvent during the preparation process. The specific steps are as follows:

[0116] First, weigh 1.5 mg of the force-responsive chromogenic unit spiropyran derivative (named SP-1 here, with the structural formula as Figure 1 described), 1.0 g of HDI, 1.0839 g of EDDET, 0.85 mg of DBTDL, and 1 mL of tetrahydrofuran in a glass dish. After mixing, shake the mixed sample well. Then, put the well-mixed sample into a vacuum oven to degas for 10 minutes, heat it to 100 °C for curing reaction for 30 minutes, and anneal at 70 °C for 2 hours to obtain the force-responsive polyurethane material, named PTU-1-THF.

[0117] Comparative Example 4

[0118] Compared with Example 1, most of them are the same, except that a small amount of N,N-dimethylformamide (DMF) is added as a solvent during the preparation process. The specific steps are as follows:

[0119] First, weigh 1.5 mg of the force-responsive chromogenic unit spiropyran derivative (named SP-1 here, with the structural formula as Figure 1 described), 1.0 g of HDI, 1.0839 g of EDDET, 0.85 mg of DBTDL, and 1 mL of DMF in a glass dish. After mixing, shake the mixed sample well. Then, put the well-mixed sample into a vacuum oven to degas for 10 minutes, heat it to 100 °C for curing reaction for 30 minutes, and anneal at 70 °C for 2 hours to obtain the force-responsive polyurethane material, named PTU-1-DMF.

[0120] Table 1 shows the raw material preparation formulas of PTU-1, PTU-0, PTU-2, PTU-1-THF, and PTU-1-DMF.

[0121] Table 1 Raw material preparation formulas of PTU-1, PTU-0, PTU-2, PTU-1, PTU-1-THF, and PTU-1-DMF

[0122]

[0123] Table 2 shows the mechanical and physical properties of PTU-1, PTU-0, PTU-2, PTU-1, PTU-1-THF, and PTU-1-DMF.

[0124] Table 2 Mechanical and physical properties of PTU-1, PTU-0, PTU-2, PTU-1, PTU-1-THF, and PTU-1-DMF

[0125]

[0126] The stress-strain test was carried out on the force-induced color-changing polythiourethane material prepared in Example 1. The prepared force-induced color-changing polythiourethane material was cut into "dumbbell-shaped" splines, and it was stretched at a constant rate (3 mm / min) by a universal testing tensile machine until it was broken, and the photos of the splines before and after stretching were recorded. As Figure 8 shown, it indicates that the force-induced color-changing polythiourethane material prepared in Example 1 has excellent mechanical properties compared with the force-induced color-changing liquid crystal elastomer represented by the "cholesteric phase" structural color, and can meet the use effect of the material under large stress conditions.

[0127] The force-induced color-changing polythiourethane material prepared in Example 1 was colorless after being treated by white light irradiation, and then the mechanical color-changing effect before and after its stretching was tested by a universal testing tensile machine. As Figure 9 shown, it shows excellent mechanical and physical properties and excellent mechanical color-developing effects.

[0128] The thermochromic effect test was carried out on PTU-1 of Example 1 and PTU-0 of Comparative Example 1. The prepared PTU-1 and PTU-0 splines were put into a constant-temperature hot oven at 100 °C and heated for 3 min, and the photos before heating, after heating, and after the PTU-1 and PTU-0 splines were taken out of the constant-temperature hot oven and cooled were recorded. As Figure 10 shown, PTU-1 realizes the thermally induced color change of the material by heating, while PTU-0 shows the performance of ordinary polythiourethane without the introduction of SP-1 and has no thermochromic effect, indicating that the color change of the material is inseparable from the force-induced color-changing motif spiropyran derivative.

[0129] From the comparison between Example 1 and Comparative Example 2, Figure 11 is the sample diagram of PTU-2. The obtained material showed a purplish red color after heating. Because it is a cross-linked network structure, the "crowding effect" of the internal network of the material makes the material change color under conventional light, heat, and force induction, indicating that without the addition of EDDET, the addition of a higher content of PETMP increases the "crowding effect" inside the material, which is not conducive to the color-changing effect of the material and makes the mechanical force, thermal, and photo-induced color-changing effects of the material lost.

[0130] From the comparative analysis of Example 1 and Comparative Example 3, the addition of a small amount of THF has little effect on the force-induced color-changing effect of the prepared material. As Figure 12 shown, this is because the color-changing performance of the mechanical carrier in THF is not great. Although it does not affect the normal use of the material, in this process, the addition of THF increases the use of volatile organic solvents and pollutes the environment.

[0131] From the comparative analysis of Example 1 and Comparative Example 4, the addition of a small amount of DMF changes the appearance of the mechanochromic polyurethane, making the initial color of the material darker, which is not conducive to the display of the mechanochromic effect of the material. For example, Figure 12 after the preparation of PTU-1-DMF is completed, the initial appearance color is darker, which not only affects the contrast effect before and after the color change of the material, weakens the color change sensitivity, but also emits volatile organic solvents that are not environmentally friendly into the air.

[0132] In summary, in the present invention, a mechanochromic element, a diisocyanate group raw material, a mercapto raw material, and a catalyst are mixed, degassed, and then heated to carry out a curing reaction. After the reaction is completed, annealing is performed to obtain a mechanochromic polyurethane material. The preparation process involves click reactions of "mercapto" with double bonds (acrylate, methacrylate), "mercapto" with "isocyanate", and nucleophilic addition reaction of "isocyanate" with "hydroxyl". The "one-step method" is used to prepare the mechanochromic polyurethane material, which is simple and efficient, can be prepared in large quantities, and has low requirements for reaction conditions and process environment. Moreover, the present invention is a solvent-free system, which avoids the introduction of high-polarity solvents, reduces the damage of solvents to the stable structure of mechanical carriers, and avoids the emission and pollution of volatile organic solvents VOCs. In the mechanochromic polyurethane material network of the present invention, there are generally hydrogen bond interaction sites, and the generally existing physical cross-linking sites endow it with good mechanical and physical properties, which can meet the requirements of high-mechanical-performance materials and can meet the use space of mechanochromic materials in a high-stress monitoring range.

[0133] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. Obviously, those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A preparation method of a force-induced color change polythiourethane material, characterized in that, The steps of the preparation method are as follows: Mix a force-induced color change element, a diisocyanate group raw material, a mercapto group raw material, and a catalyst, degas, then raise the temperature for a curing reaction, and after the reaction is completed, anneal to obtain a force-induced color change polyurethane material.

2. The preparation method of a force-induced color-changing polythiourethane material according to claim 1, characterized in that The force-induced color change element includes one or more active functional groups among hydroxyl group, amino group, acrylate group, and methacrylate group.

3. The preparation method of a force-induced color-changing polythiourethane material according to claim 2, characterized in that, The force-induced color change element includes spiropyran derivatives, spirooxazine derivatives, and rhodamine derivatives. The structural formula of the spiropyran derivative is shown as formula (1) or formula (2), the structural formula of the spirooxazine derivative is shown as formula (3) or formula (4), and the structural formula of the rhodamine derivative is shown as formula (5). Among them, denotes "spacer group", i.e., the chemical structure of the intermediate spacer between the main structure of the mechanochromic moiety and X, including where n≥1.

4. The preparation method of a force-induced color-changing polythiourethane material according to claim 1, characterized in that, The diisocyanate group raw material includes hexamethylene diisocyanate. The catalyst includes dibutyltin dilaurate.

5. The preparation method of a force-induced color-changing polythiourethane material according to claim 1, characterized in that, The mercapto group raw material includes 3,6-dioxa-1,8-dimercaptooctane.

6. The preparation method of a force-induced color-changing polythiourethane material according to claim 1, characterized in that, The mercapto group raw material includes a mixture of 3,6-dioxa-1,8-dimercaptooctane and pentaerythritol tetra(3-mercaptopropionate).

7. The preparation method of a force-induced color-changing polythiourethane material according to claim 6, characterized in that, In the mixture of 3,6-dioxa-1,8-dimercaptooctane and pentaerythritol tetra(3-mercaptopropionate), the molar ratio of the two is 1:(0.0001 - 0.5).

8. The preparation method of a force-induced color change polythiourethane material according to claim 1, characterized in that, The molar ratio of the "mercapto group" content in the mercapto group raw material to the "isocyanate group" in the diisocyanate group raw material is 1:0.8 - 1.

2. The force-induced color change element accounts for 0.01wt% - 0.1wt% of the total mass of the overall material preparation, and the catalyst accounts for 0.5wt% - 5wt% of the total mass of the overall material preparation.

9. The preparation method of a force-induced color-changing polythiourethane material according to claim 1, characterized in that, The temperature of the curing reaction is 80 - 120°C, and the annealing temperature is 60 - 70°C.

10. A force-induced color change polyurethane material prepared by using the preparation method according to any one of claims 1 - 9.

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