A polyurethane material and polyurethane film having a mechanochromic property and a method for preparing the same

Abstract

The application discloses a polyurethane material with a force-induced color change performance and a polyurethane film and a preparation method thereof, and belongs to the technical field of polyurethane materials. The polyurethane material with the force-induced color change performance contains a mechanical response group, a hydrogen bond and a metal coordination bond, wherein a molecular structural formula of the polyurethane material with the force-induced color change performance is shown as follows: wherein x and y are positive integers, x>1 and y>1; a structural formula of R is shown as follows: The polyurethane material with the force-induced color change performance can generate a detectable optical signal change under the action of external force.

Description

Technical Field

[0001] This invention relates to the field of polyurethane materials technology, and in particular to a polyurethane material and a polyurethane film with mechanochromic properties, and a method for preparing the same. Background Technology

[0002] In recent years, functional polymer materials with responsiveness to external stimuli have attracted widespread attention. Among them, mechanochromic materials can produce color or fluorescence changes under external forces such as stretching, compression, or bending, thereby enabling visualization of stress or deformation processes. They have promising applications in stress sensing, information display, and anti-counterfeiting identification. These materials are typically achieved by introducing mechanoresponsive groups. When the material is subjected to external forces, the mechanoresponsive groups undergo structural changes under stress, thereby generating changes in optical signals.

[0003] However, existing mechanochromic polymer materials mostly employ softer matrices or less cross-linked network structures to reduce the difficulty of activating mechanoresponsive groups. While these materials readily produce a color-changing response, their mechanical strength and structural stability are relatively limited, making it difficult to meet the application requirements under high-strength or long-term use conditions. Furthermore, in polymer systems with high mechanical properties, external stress is easily dissipated by chain segment movement and intermolecular interactions during internal material transmission, leading to a reduction in the effective stress transmitted to the mechanoresponsive groups, thus affecting the generation of the mechanochromic response. Therefore, achieving a stable mechanochromic response while ensuring the material's mechanical properties remains a significant challenge. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a polyurethane material with mechanochromic properties and its preparation method. The mechanochromic polyurethane material of this invention can produce detectable changes in optical signals under external force.

[0005] A further technical problem to be solved by the present invention is to provide a polyurethane film with mechanochromic properties.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A mechanochromic polyurethane material, characterized in that the mechanochromic polyurethane material contains mechanoresponsive groups, hydrogen bonds, and metal coordination bonds, wherein the molecular structural formula of the mechanochromic polyurethane material is as follows:

[0008] Where x and y are positive integers, and x > 1, y > 1; the structure of R is as follows:

[0009] .

[0010] Preferably, the coordination structure in the mechanochromic polyurethane material is as follows:

[0011] .

[0012] The preparation method of the above-mentioned polyurethane material with mechanochromic properties includes the following steps:

[0013] (1) A polyurethane prepolymer, a first chain extender and an organic solvent are mixed to carry out a first chain extension reaction to obtain a first chain extended product; wherein the molar ratio of the polyol in the polyurethane prepolymer to the first chain extender is 1:1 to 3.33:1;

[0014] (2) The first chain extender, the second chain extender and the organic solvent are mixed to carry out a second chain extension reaction to obtain the second chain extender; wherein the molar ratio of the polyol and the second chain extender in the polyurethane prepolymer is 1:1 to 3.33:1;

[0015] (3) The second chain extender, crosslinking agent and organic solvent are mixed to carry out a crosslinking reaction to obtain a crosslinked product; wherein the molar ratio of polyol to crosslinking agent is 3.75:1~15:1;

[0016] (4) The crosslinking product, the metal ion compound and the organic solvent are mixed and a coordination reaction is carried out to obtain the polyurethane material; wherein the molar ratio of the metal ion compound to the second chain extender is 1:2.

[0017] The first chain extender is one or more of 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dimethyl oxime, polyethylene glycol, 4,4'-diaminodicyclohexylmethane, 1,4-phenylenediamine, 2,6-diaminopyridine, succinic acid dihydrazide, and adipic acid dihydrazide.

[0018] The second chain extender is one or more of 4,4′-diaminobibenzyl, 5,5′-dihydroxy-2,2′-bipyridine, 4,4′-diaminobenzophenone, 5,5′-diamino-2,2′-bipyridine, and benzidine;

[0019] The cross-linking agent is a trihydroxyrhodamine derivative;

[0020] The metal ion compound is one or more of zinc chloride, copper chloride, ferric nitrate, europium trifluoromethanesulfonate, and aluminum chloride.

[0021] The first chain extension reaction is carried out at a temperature of 60℃~100℃ for 1h~3h; the second chain extension reaction is carried out at a temperature of 60℃~100℃ for 1h~3h; the crosslinking reaction is carried out at a temperature of 60℃~100℃ for 5h~8h; and the coordination reaction is carried out at a temperature of 20℃~50℃ for 5h~12h.

[0022] The polyurethane prepolymer is prepared using the following steps:

[0023] A polyol and an organic solvent are mixed to obtain a mixture; the mixture, diisocyanate, organometallic catalyst and organic solvent are mixed to carry out a prepolymerization reaction to obtain a polyurethane prepolymer; the temperature of the prepolymerization reaction is 60℃~100℃ and the reaction time is 2h~5h.

[0024] Among them, the polyol is one or more of polyether or polyester polyol;

[0025] The diisocyanate is one or more of isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (HMDI), diphenylmethane diisocyanate (MDI), toluene-2,4-diisocyanate (2,4-TDI), and hexamethylene diisocyanate (HDI);

[0026] The organometallic catalyst is one or more of triethylamine, dibutyltin dilaurate, N,N-dimethylbenzylamine, stannous isooctanoate, and zinc isooctanoate;

[0027] The molar ratio of polyol to diisocyanate is 1:2 to 1:2.4; the amount of organometallic catalyst added is 0.02g.

[0028] The prepolymerization reaction, the first chain extension reaction, the second chain extension reaction, the crosslinking reaction, and the coordination reaction are all carried out in a protective atmosphere.

[0029] The organic solvent is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), and N-methylpyrrolidone (NMP).

[0030] A polyurethane film with mechanochromic properties is obtained by performing a film-forming treatment on the aforementioned polyurethane material with mechanochromic properties.

[0031] The beneficial effects of this invention are as follows:

[0032] (1) The mechanochromic polyurethane material of the present invention can generate detectable changes in optical signals under external force. When the material is subjected to force, the mechanically responsive groups undergo structural changes and cause changes in spectral characteristics. These changes can be characterized by fluorescence spectroscopy, manifested as changes in fluorescence emission peaks. By covalently introducing mechanically responsive groups containing multiple hydroxyl groups into the polyurethane network, the present invention effectively avoids the problem of easy migration or precipitation of functional molecules in traditional physical doping methods, thereby improving the stability of the material response and its reusability.

[0033] (2) The mechanochromic polyurethane material of the present invention exhibits good mechanical properties and structural stability. The polyurethane material of the present invention contains both hydrogen bonds and metal coordination bonds. Hydrogen bonds influence chain segment movement and material deformation behavior, while metal coordination bonds enhance the interaction strength within the network, thereby improving the material's rigidity and structural stability. By regulating the composition of the polyurethane network and intermolecular interactions, the stress transmission efficiency within the material is improved to a certain extent, enabling external stress to be more effectively transmitted along the polymer chain to the mechanically responsive groups. This achieves a stable mechanochromic response while maintaining good mechanical properties, thus balancing the relationship between structural strength and functional response.

[0034] (3) The preparation method of the polyurethane material with mechanochromic properties of the present invention has the characteristics of relatively simple process and applicable to the preparation of film or elastomer. It has certain application value for expanding the application of mechanochromic materials in stress visualization, information display, anti-counterfeiting identification and related functional materials. At the same time, it provides a feasible technical path for developing polyurethane materials with both excellent mechanical properties and functional response characteristics. Attached Figure Description

[0035] Figure 1 The infrared spectra of the polyurethane materials with mechanochromic properties prepared in Examples 1 to 4 and Comparative Example 3 of this invention, as well as the polyurethane materials prepared in Comparative Examples 1 and 2.

[0036] Figure 2 An atomic force microscope image of the mechanochromic polyurethane material prepared in Example 1 of the present invention, wherein... Figure 2 (a) in the diagram is a phase diagram. Figure 2 (b) in the figure is a height map.

[0037] Figure 3 An atomic force microscope image of the mechanochromic polyurethane material prepared in Example 2 of the present invention, wherein... Figure 3 (a) in the diagram is a phase diagram. Figure 3 (b) in the figure is a height map.

[0038] Figure 4 An atomic force microscope image of the mechanochromic polyurethane material prepared in Example 3 of the present invention, wherein... Figure 4 (a) in the diagram is a phase diagram. Figure 4 (b) in the figure is a height map.

[0039] Figure 5 An atomic force microscope image of the mechanochromic polyurethane material prepared in Example 4 of this invention, wherein... Figure 5 (a) in the diagram is a phase diagram. Figure 5 (b) in the figure is a height map.

[0040] Figure 6 Here is an atomic force microscope image of the polyurethane material prepared in Comparative Example 1 of the present invention, wherein... Figure 6 (a) in the diagram is a phase diagram. Figure 6 (b) in the figure is a height map.

[0041] Figure 7 Here is an atomic force microscope image of the polyurethane material prepared in Comparative Example 2 of the present invention, wherein... Figure 7 (a) in the diagram is a phase diagram. Figure 7 (b) in the figure is a height map.

[0042] Figure 8 Here is an atomic force microscope image of the mechanochromic polyurethane material prepared in Comparative Example 3 of the present invention, wherein... Figure 8 (a) in the diagram is a phase diagram. Figure 8 (b) in the figure is a height map.

[0043] Figure 9 Thermogravimetric analysis curve of the polyurethane material with mechanochromic properties prepared in Example 2 of the present invention.

[0044] Figure 10 This is a summary diagram of the stress-strain curves of the polyurethane materials with mechanochromic properties prepared in Examples 1 to 4 of the present invention.

[0045] Figure 11 This is a summary diagram of the stress-strain curves of the polyurethane materials prepared in Comparative Examples 1 and 2, and the polyurethane material with mechanochromic properties prepared in Comparative Example 3, according to the present invention.

[0046] Figure 12 This is a normalized fluorescence intensity diagram of the polyurethane material prepared in Comparative Example 1 of the present invention during the stretching process.

[0047] Figure 13 This is a normalized fluorescence intensity diagram of the polyurethane material prepared in Comparative Example 2 of the present invention during the stretching process.

[0048] Figure 14 This is a normalized fluorescence intensity diagram of the polyurethane material with mechanochromic properties prepared in Comparative Example 3 of the present invention during the stretching process.

[0049] Figure 15 Normalized fluorescence intensity diagram of the polyurethane material with mechanochromic properties prepared in Example 2 of the present invention during the stretching process. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0051] Polyurethane materials possess a tunable network structure. By adjusting the soft segments, hard segments, and intermolecular interactions, the mechanical properties and deformation behavior of the material can be controlled within a certain range. Furthermore, supramolecular interactions (hydrogen bonds, metal coordination bonds, π-π stacking, etc.) within the polyurethane network help regulate chain segment movement and structural stability, thereby influencing the stress transmission process within the material. Based on this, this invention provides a polyurethane material with mechanochromic properties. By covalently introducing mechanoresponsive groups into the polyurethane network and combining hydrogen bonding and metal coordination interactions to regulate the network structure, the efficiency of stress transmission within the polymer chain is improved, allowing external stress to act more effectively on the mechanoresponsive groups, thus achieving a mechanochromic response in the material.

[0052] The method for preparing the mechanochromic polyurethane material of the present invention includes the following steps:

[0053] Part 1: Preparation of polyurethane prepolymer.

[0054] (1) Select appropriate polyether or polyester polyol (molecular weight range: 1000~3000) and organic solvent to mix to obtain a mixture. Specifically, the polyol and organic solvent are mixed and placed in a three-necked flask. Under the oil bath conditions of 100℃~150℃, nitrogen gas is introduced and stirred (30min~120min) to fully remove water and other impurities.

[0055] (2) Prepolymerization reaction: After the temperature of the mixed solution is cooled to 60℃~100℃, add an equivalent amount of diisocyanate (the diisocyanate is one or more of toluene-2,4-diisocyanate (2,4-TDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (HMDI), diphenylmethane diisocyanate (MDI), and hexamethylene diisocyanate (HDI), and measure a certain amount of organic solvent. Mix the two and add them dropwise to the reaction flask. Add a small amount of metal-organic catalyst to carry out the prepolymerization reaction to obtain polyurethane prepolymer. The metal-organic catalyst is one or more of triethylamine, N,N-dimethylcyclohexylamine, N,N-dimethylbenzylamine, dibutyltin dilaurate, stannous isooctanoate, and zinc isooctanoate. The prepolymerization reaction is carried out in a N2 atmosphere for 2h~5h.

[0056] Part 2: Preparation of polyurethane materials with mechanochromic properties.

[0057] (1) First chain extension reaction: A first chain extender is added to the polyurethane prepolymer prepared in the first part, and a certain amount of the same organic solvent is added to the reaction flask to carry out the first chain extension reaction to obtain the first chain extension product. The first chain extension reaction is carried out under N2 atmosphere, the reaction temperature is 60℃~100℃, and the reaction time is 1h~3h. The first chain extender is one or more of 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dimethyl oxime, polyethylene glycol, 4,4'-diaminodicyclohexylmethane, 1,4-phenylenediamine, 2,6-diaminopyridine, succinic acid dihydrazide, and adipate dihydrazide.

[0058] (2) Second chain extension reaction: A second chain extender is added to the first chain extension product to carry out a second chain extension reaction to obtain a second chain extension product. The second chain extension reaction is carried out at 60℃~100℃ and under a N2 atmosphere for 1h~3h. The second chain extender is one or more of 4,4′-diaminobibenzyl, 5,5′-dihydroxy-2,2′-bipyridine, 4,4′-diaminobenzophenone, 5,5′-diamino-2,2′-bipyridine, and benzidine. If the chain extender is a solid, it needs to be dissolved in an organic solvent, sonicated to make it completely dissolved, and then added dropwise to the reaction flask.

[0059] (3) Crosslinking reaction: After the chain extension reaction is completed, a certain amount of crosslinking agent is weighed and dissolved in an organic solvent. After ultrasonic treatment until completely dissolved, it is added dropwise to the reaction flask to carry out the crosslinking reaction. The crosslinking reaction is carried out at 60℃~100℃ and under N2 atmosphere for 5h~8h. The crosslinking agent is a trihydroxyrhodamine derivative.

[0060] (4) Coordination reaction: A certain amount of metal ion compound is weighed and dissolved in an organic solvent. After ultrasonic treatment until completely dissolved, it is added dropwise to a reaction flask to carry out the coordination reaction. The coordination reaction is carried out at 20℃~50℃ under a N2 atmosphere for 5h~12h. The metal ion compound is one or more of zinc chloride, copper chloride, ferric nitrate, europium trifluoromethanesulfonate, and aluminum chloride.

[0061] Part 3: Preparation of polyurethane films with mechanochromic properties.

[0062] After the reaction is complete, the solution obtained in the second part is poured into a polytetrafluoroethylene mold and vacuum dried at 60℃~120℃ for 24h~72h to remove residual solvent, thereby obtaining a polyurethane film with mechanochromic properties.

[0063] The organic solvent used in the above preparation is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), and N-methylpyrrolidone (NMP).

[0064] Example 1:

[0065] Example 1 includes a prepolymerization reaction, a first chain extension reaction, a second chain extension reaction, a crosslinking reaction, and a coordination reaction.

[0066] Part 1: Preparation of polyurethane prepolymer.

[0067] (1) Weigh 12 mmol, 24.0 g of polytetramethylene ether glycol (PTMEG-2000) with a molecular weight of 2000 g / mol and 25 mL of N,N-dimethylformamide (DMF) and mix them in a three-necked flask. Stir for 60 min in an oil bath at 120 °C under N2 atmosphere to remove moisture and other impurities.

[0068] (2) Next, after the temperature of the above mixture is cooled to 80°C, 24 mmol and 5.35 g of IPDI (molecular weight 222.29 g / mol) are weighed, and 25 mL of N,N-dimethylformamide (DMF) is measured as an organic solvent. After mixing, the mixture is added to a three-necked flask, and 0.02 g of dibutyltin dilaurate (DBTDL) is added as a metal-organic catalyst. The prepolymerization reaction is carried out under oil bath conditions at 80°C and N2 atmosphere for 3 h to obtain isocyanate-terminated polyurethane prepolymer.

[0069] Part 2: Preparation of polyurethane materials with mechanochromic properties.

[0070] (1) After the prepolymerization reaction is completed, weigh 5.4 mmol and 1.14 g of 4,4'-diaminodicyclohexylmethane (DDM) and measure 30 mL of DMF solvent. Mix the two and sonicate until completely dissolved. Add the mixture to a three-necked flask for the first chain extension reaction. The first chain extension reaction is carried out under oil bath conditions at 80 °C and N2 atmosphere with stirring for 60 min.

[0071] (2) After the first chain extension reaction is completed, weigh 5.4 mmol and 1.01 g of solid chain extender: 5,5'-diamino-2,2'-bipyridine (BPY), and measure 30 mL of DMF solvent. Mix the two, sonicate until completely dissolved, and add to a three-necked flask for the second chain extension reaction. The second chain extension reaction is carried out under oil bath conditions at 80 °C and N2 atmosphere with stirring for 60 min.

[0072] (3) After the second chain extension reaction is completed, weigh 0.8 mmol and 0.44 g of trihydroxyrhodamine derivative (THR), measure 25 mL of DMF solvent, mix the two and add them to the reaction flask to carry out the cross-linking reaction. The cross-linking reaction is carried out at 80 °C and under N2 atmosphere for 5 h.

[0073] (4) After the cross-linking reaction is completed, weigh 2.7 mmol and 0.37 g of zinc chloride, measure 25 mL of DMF solvent, mix the two and add them to the reaction flask, and carry out the reaction at 30 °C under N2 atmosphere for 10 h.

[0074] The coordination reaction process is as follows:

[0075] Where x and y are positive integers, and x > 1, y > 1; the structure of R is as follows:

[0076] ;

[0077] The coordination structure in zinc ion-coordinated polyurethane is as follows:

[0078] .

[0079] Part 3: Preparation of polyurethane films with mechanochromic properties.

[0080] After the reaction was completed, the solution obtained in the second part was poured into a polytetrafluoroethylene mold and dried under vacuum at 80°C for 48 hours to remove residual solvent. This solution was named Example 1.

[0081] Example 2:

[0082] The specific steps were the same as in Example 1, except that the amount of the first chain extender, 4,4'-diaminodicyclohexylmethane (DDM), was 4.8 mmol; the amount of the second chain extender, 5,5'-diamino-2,2'-bipyridine (BPY), was 4.8 mmol; the amount of trihydroxyrhodamine derivative (THR) was 1.6 mmol; and the amount of zinc chloride was 2.4 mmol. The sample was named Example 2.

[0083] Example 3:

[0084] The specific steps were the same as in Example 1, except that the amount of the first chain extender, 4,4'-diaminodicyclohexylmethane (DDM), was 4.2 mmol; the amount of the second chain extender, 5,5'-diamino-2,2'-bipyridine (BPY), was 4.2 mmol; the amount of trihydroxyrhodamine derivative (THR) was 2.4 mmol; and the amount of zinc chloride was 2.1 mmol. The sample was named Example 3.

[0085] Example 4:

[0086] The specific steps were the same as in Example 1, except that the amount of the first chain extender, 4,4'-diaminodicyclohexylmethane (DDM), was 3.6 mmol; the amount of the second chain extender, 5,5'-diamino-2,2'-bipyridine (BPY), was 3.6 mmol; the amount of trihydroxyrhodamine derivative (THR) was 3.2 mmol; and the amount of zinc chloride was 1.8 mmol. The sample was named Example 4.

[0087] Comparative Example 1:

[0088] Comparative Example 1 only includes the prepolymerization reaction and the first chain extension reaction.

[0089] The first part is the same as in Example 1.

[0090] Part Two: Preparation of Polyurethane Materials

[0091] After the prepolymerization reaction was completed, 12 mmol and 2.52 g of 4,4'-diaminodicyclohexylmethane (DDM) were weighed out, and 50 mL of DMF solvent was measured out. The two were mixed and sonicated until completely dissolved. The mixture was then added to a three-necked flask and stirred in an oil bath at 80 °C under a N2 atmosphere for 60 min.

[0092] Part 3: Preparation of polyurethane films.

[0093] After the reaction was completed, the solution obtained in the second part was poured into a polytetrafluoroethylene mold and dried under vacuum at 80°C for 48 hours to remove residual solvent. This solution was named Comparative Example 1.

[0094] Comparative Example 2:

[0095] Comparative Example 2 includes a prepolymerization reaction, a second chain extension reaction, and a coordination reaction.

[0096] The first part is the same as in Example 1.

[0097] Part Two: Preparation of Polyurethane Materials

[0098] (1) After the prepolymerization reaction is completed, weigh 12 mmol and 2.22 g of solid chain extender 5,5'-diamino-2,2'-bipyridine (BPY) and measure 50 mL of DMF solvent. Mix the two and sonicate until completely dissolved. Add the mixture to a three-necked flask for reaction (second chain extension reaction). The reaction is carried out under oil bath conditions at 80 °C and N2 atmosphere with stirring for 60 min.

[0099] (2) Next, weigh 6 mmol and 0.82 g of zinc chloride and measure 30 mL of DMF solvent. Mix the two and add them to the reaction flask to carry out the coordination reaction. The coordination reaction was carried out at 30 °C under N2 atmosphere for 10 h.

[0100] Part 3: Preparation of polyurethane films.

[0101] After the reaction was completed, the solution obtained in the second part was poured into a polytetrafluoroethylene mold and dried under vacuum at 80°C for 48 hours to remove residual solvent. This solution was named Comparative Example 2.

[0102] Comparative Example 3:

[0103] The specific steps are the same as in Example 2, except that zinc chloride is not added for coordination in this comparative example. The sample was named Comparative Example 3.

[0104] Experimental Results and Analysis:

[0105] I. Characterization Analysis.

[0106] Figure 1 Infrared spectra of the polyurethane materials with mechanochromic properties prepared in Examples 1 to 4 and Comparative Example 3 of this invention, and the polyurethane materials prepared in Comparative Examples 1 and 2. Figure 1 The results show that 3330cm in the figure -1 The characteristic peak at 1750-1600 cm⁻¹ is attributed to the stretching vibration of the N–H group. -1 The peaks observed within the range are attributed to the stretching vibrations of C=O in the urethane and urea groups. Meanwhile, at approximately 1100 cm⁻¹... -1 The absorption band at 2260–2280 cm⁻¹ corresponds to the C–O stretching vibration of the polyurethane group (NHCOO–). Furthermore, the absorption band at 2260–2280 cm⁻¹... -1 No characteristic absorption peak of the –NCO group was detected within the range, confirming that the isocyanate group was completely consumed. These results indicate that polyurethane materials with mechanochromic properties were successfully prepared in Examples 1 to 4 and Comparative Example 3.

[0107] II. To further analyze the distribution of soft and hard segments in the mechanochromic polyurethane materials, the microstructure and surface morphology of Examples 1-4 and Comparative Examples 1-3 were characterized using atomic force microscopy (AFM). The tests were conducted in tapping mode, with a scanning area of ​​2 μm × 2 μm.

[0108] Figure 2 This is an atomic force microscope (AFM) image of Example 1, in which... Figure 2 (a) in the diagram is a phase diagram. Figure 2 (b) in the figure is a height map. Figure 3 This is an atomic force microscope (AFM) image of Example 2, in which... Figure 3 (a) in the diagram is a phase diagram. Figure 3 (b) in the figure is a height map. Figure 4This is an atomic force microscope (AFM) image of Example 3, in which... Figure 4 (a) in the diagram is a phase diagram. Figure 4 (b) in the figure is a height map. Figure 5 This is an atomic force microscope (AFM) image of Example 4, in which... Figure 5 (a) in the diagram is a phase diagram. Figure 5 (b) in the figure is a height map. Figure 6 This is an atomic force microscope (AFM) image of Comparative Example 1, in which... Figure 6 (a) in the diagram is a phase diagram. Figure 6 (b) in the figure is a height map. Figure 7 This is an atomic force microscope (AFM) image from Comparative Example 2, in which... Figure 7 (a) in the diagram is a phase diagram. Figure 7 (b) in the figure is a height map. Figure 8 This is an atomic force microscope (AFM) image of Comparative Example 3, in which... Figure 8 (a) in the diagram is a phase diagram. Figure 8 (b) in the figure is a height map.

[0109] Depend on Figures 2 to 8 The results show that the AFM phase diagrams of all embodiments exhibit distinct light and dark contrast regions, indicating the presence of microphase separation structures in the system. The dark regions mainly correspond to the soft segment regions formed by polyether diols, while the bright regions originate from the aggregation of hard segments. This microphase separation behavior is significant for the mechanical properties of the material. Further comparison of different embodiments reveals that the interface between the light and dark regions is clearest in Example 2, indicating the highest degree of microphase separation. Combined with the mechanical property test results, it can be seen that adjusting the composition and interaction of soft and hard segments in the polyurethane system helps to regulate the microphase structure of the material, thereby affecting its overall mechanical properties.

[0110] III. To effectively evaluate the thermal properties of the prepared optimal material, thermogravimetric analysis was performed on the polyurethane material with mechanochromic properties from Example 2. The test atmosphere was nitrogen, and the test temperature range was 50°C to 750°C.

[0111] Figure 9 Thermogravimetric analysis curve of the polyurethane material with mechanochromic properties prepared in Example 2 of the present invention. Figure 9 The thermogravimetric analysis curves show that the polyurethane material with mechanochromic properties prepared in Example 2 exhibits high thermal stability, with an initial thermal decomposition temperature (Td, the temperature corresponding to 5% weight loss of the sample) of 304.1℃, which is better than most polyurethane elastomers, demonstrating good heat resistance and meeting the requirements of various practical applications.

[0112] IV. To accurately evaluate the mechanical properties of the prepared polyurethane materials, stress-strain tests were conducted on film samples of seven formulations (Examples 1-4 and Comparative Examples 1-3) using a tensile testing machine. The tests were performed according to GB / T 1040-2006 standard at an ambient temperature of 25℃ and a tensile speed of 100 mm / min. Tensile strength, elongation at break, and toughness (i.e., the area under the stress-strain curve) were compared, and the results are as follows: Figure 10 and Figure 11 As shown, the relevant data is summarized in Table 1. Figure 10 This is a summary diagram of the stress-strain curves of the polyurethane materials with mechanochromic properties prepared in Examples 1 to 4 of the present invention.

[0113] Figure 11 This is a summary diagram of the stress-strain curves of the polyurethane materials prepared in Comparative Examples 1 and 2, and the polyurethane material with mechanochromic properties prepared in Comparative Example 3, according to the present invention.

[0114] Table 1. Mechanical performance test results of Examples 1 to 4 and Comparative Examples 1 to 3

[0115]

[0116] Depend on Figure 10 , Figure 11 As shown in Table 1, its tensile behavior is strongly dependent on the network composition. Among the samples with different THR contents, Example 2 exhibited the highest tensile strength of 56 MPa, while maintaining an elongation at break of 1513.6% and 217.3 MJ / m. 3 The high toughness of the material was demonstrated. Although Example 1 exhibited considerable toughness, and Examples 3 and 4 showed greater elongation at break, their tensile strength was significantly reduced, indicating that excessive chain segment movement or excessive crosslinking could not provide an optimized load-bearing network. Comparative Examples 1 and 2 showed poor tensile properties, indicating that a single chain extender was insufficient to optimize the network structure. Furthermore, Example 2 exhibited higher mechanical properties than Comparative Example 3, demonstrating the reinforcing effect of zinc ion coordination. These results indicate that by adjusting the polyurethane network composition and crosslinking structure, the mechanical properties of the material can be effectively controlled, achieving combinations of strength, ductility, and toughness in different samples to meet the mechanical property requirements under different application conditions.

[0117] V. Optical Response Analysis.

[0118] Changes in fluorescence spectral intensity provide important clues for understanding the force response behavior of materials. Figure 12 This is a normalized fluorescence intensity diagram of the polyurethane material prepared in Comparative Example 1 of the present invention during the stretching process. Figure 13This is a normalized fluorescence intensity diagram of the polyurethane material prepared in Comparative Example 2 of the present invention during the stretching process. Figure 14 This is a normalized fluorescence intensity diagram of the polyurethane material with mechanochromic properties prepared in Comparative Example 3 of the present invention during the stretching process. Figure 15 Normalized fluorescence intensity diagram of the polyurethane material with mechanochromic properties prepared in Example 2 of the present invention during the stretching process.

[0119] from Figures 12 to 15 As can be seen, no significant changes were observed in this region in the polyurethane materials prepared in Comparative Examples 1 and 2, indicating that the polymer network lacks the ability to convert mechanical stimuli into optical signals without the introduction of mechanoresponsive groups. In contrast, the polyurethane material prepared in Comparative Example 3 showed a identifiable enhancement in the emission peak near 560 nm under applied stress, indicating that the mechanoresponsive groups were partially activated through force-induced structural transformation. However, compared with the mechanochromic polyurethane material of Example 2, the response of the polyurethane material prepared in Comparative Example 3 was still relatively limited, while the mechanochromic polyurethane material of Example 2 showed a more significant enhancement in the same fluorescence band. This gradual difference indicates that the force transfer efficiency and the subsequent degree of activation of the mechanoresponsive groups strongly depend on the network structure and intermolecular interactions within the material.

[0120] The more pronounced response observed in the fluorescence intensity plot of the mechanochromic polyurethane material of Example 2 is likely attributable to a more efficient stress transfer pathway, allowing a higher proportion of the mechanoresponsive functional groups to undergo a ring-opening transition from the spironolactone form, forming an emissive open structure. Force-induced bond breaking leads to enhanced fluorescence output. Furthermore, the superior mechanical properties of Example 2 indicate the formation of a more robust and highly integrated network structure, which contributes to a more uniform stress distribution and reduces energy dissipation through inefficient pathways. This combination of enhanced mechanical properties and enhanced optical response highlights the importance of synergistically optimizing the network architecture and intermolecular interactions.

[0121] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention. The above embodiments are provided only for the purpose of describing the present invention and are not intended to limit the present invention. Parts not described in detail in this specification are well-known in the art and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. All equivalent substitutions and modifications made without departing from the spirit and principle of the present invention should be covered within the scope of the present invention.

Claims

1. A polyurethane material with mechanochromic properties, characterized in that, The mechanochromic polyurethane material contains mechanoresponsive groups, hydrogen bonds, and metal coordination bonds. The molecular structure of the mechanochromic polyurethane material is as follows: Where x and y are positive integers, and x > 1, y > 1; the structure of R is as follows: 。 2. The polyurethane material with mechanochromic properties according to claim 1, characterized in that, The coordination structure of the polyurethane material with mechanochromic properties is as follows: 。 3. The method for preparing the polyurethane material with mechanochromic properties as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: (1) A polyurethane prepolymer, a first chain extender and an organic solvent are mixed to carry out a first chain extension reaction to obtain a first chain extended product; wherein the molar ratio of the polyol in the polyurethane prepolymer to the first chain extender is 1:1 to 3.33:1; (2) The first chain extender, the second chain extender and the organic solvent are mixed to carry out a second chain extension reaction to obtain the second chain extender; wherein the molar ratio of the polyol and the second chain extender in the polyurethane prepolymer is 1:1 to 3.33:1; (3) The second chain extender, crosslinking agent and organic solvent are mixed to carry out a crosslinking reaction to obtain a crosslinked product; The molar ratio of polyol to crosslinking agent is 3.75:1 to 15:1; (4) The crosslinking product, the metal ion compound and the organic solvent are mixed and a coordination reaction is carried out to obtain the polyurethane material; wherein the molar ratio of the metal ion compound to the second chain extender is 1:

2.

4. The method for preparing the polyurethane material with mechanochromic properties according to claim 3, characterized in that, The first chain extender is one or more of 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dimethyl oxime, polyethylene glycol, 4,4'-diaminodicyclohexylmethane, 1,4-phenylenediamine, 2,6-diaminopyridine, succinic acid dihydrazide, and adipic acid dihydrazide. The second chain extender is one or more of 4,4′-diaminobibenzyl, 5,5′-dihydroxy-2,2′-bipyridine, 4,4′-diaminobenzophenone, 5,5′-diamino-2,2′-bipyridine, and benzidine; The cross-linking agent is a trihydroxyrhodamine derivative; The metal ion compound is one or more of zinc chloride, copper chloride, ferric nitrate, europium trifluoromethanesulfonate, and aluminum chloride.

5. The method for preparing the polyurethane material with mechanochromic properties according to claim 3, characterized in that, The temperature for the first chain extension reaction is 60℃~100℃, and the time is 1h~3h; the temperature for the second chain extension reaction is 60℃~100℃, and the time is 1h~3h; the temperature for the crosslinking reaction is 60℃~100℃, and the time is 5h~8h; the temperature for the coordination reaction is 20℃~50℃, and the time is 5h~12h.

6. The method for preparing the polyurethane material with mechanochromic properties according to claim 3, characterized in that, The polyurethane prepolymer was prepared using the following steps: A polyol and an organic solvent are mixed to obtain a mixture; the mixture, diisocyanate, organometallic catalyst and organic solvent are mixed to carry out a prepolymerization reaction to obtain a polyurethane prepolymer; the temperature of the prepolymerization reaction is 60℃~100℃ and the reaction time is 2h~5h.

7. The method for preparing the polyurethane material with mechanochromic properties according to claim 6, characterized in that, The polyol is one or more of polyether or polyester polyol; The diisocyanate is one or more of isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (HMDI), diphenylmethane diisocyanate (MDI), toluene-2,4-diisocyanate (2,4-TDI), and hexamethylene diisocyanate (HDI); The organometallic catalyst is one or more of triethylamine, dibutyltin dilaurate, N,N-dimethylbenzylamine, stannous isooctanoate, and zinc isooctanoate; The molar ratio of polyol to diisocyanate is 1:2 to 1:2.

4.

8. The method for preparing the polyurethane material with mechanochromic properties according to claim 6, characterized in that, The prepolymerization reaction, the first chain extension reaction, the second chain extension reaction, the crosslinking reaction, and the coordination reaction are all carried out in a protective atmosphere.

9. The method for preparing the polyurethane material with mechanochromic properties according to claim 6, characterized in that, The organic solvent is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), and N-methylpyrrolidone (NMP).

10. A polyurethane film with mechanochromic properties, characterized in that, The mechanochromic polyurethane film is obtained by film-forming the mechanochromic polyurethane material as described in claim 1 or 2.

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