Spiropyran-modified sis dynamic cross-linked network with force-induced color change, preparation method and application thereof

Abstract

This invention provides a spiropyran-modified SIS dynamic crosslinked network with mechanochromic properties, its preparation method, and its applications. The method uses styrene-isoprene-styrene triblock copolymers (SIS) of different molecular weights and feed ratios as the main chain. The double bonds of the polyisoprene blocks (PI) in the SIS are functionalized as active sites. The SIS is converted to SIS-OH through epoxidation and hydroxylation. Then, a quantitative amount of covalent crosslinking agent SP-NCO and dynamic hydrogen-bonding crosslinking agent UPy-NCO are introduced via esterification of isocyanate (NCO) and hydroxyl groups (OH). This yields a SP-modified SIS dynamic crosslinked polymer network, SIS-SP-UPy, with both covalent and dynamic hydrogen-bonding properties. The SIS-SP-UPy prepared by this invention exhibits excellent mechanochromic properties, mechanical properties, and reprocessability, enabling the application of SIS thermoplastic elastomers in fields such as intelligent sensing and material flaw detection.

Description

Technical Field

[0001] This invention belongs to the field of polymer material modification technology, specifically relating to a spiropyran group modified polymer and its preparation method, and particularly to a spiropyran group modified SIS dynamically crosslinked polymer network with mechanochromic properties, its preparation method and its application. Background Technology

[0002] Thermoplastic elastomers, also known as thermoplastic rubbers, are hailed as the "third generation of rubber" after natural and synthetic rubbers due to their dual characteristics of highly elastic rubber and malleable plastics. Styrene-based thermoplastic elastomers are the most produced and fastest-growing type of thermoplastic elastomer material in recent years. Styrene-isoprene-styrene (SIS), developed in the 1970s, is a styrene-based thermoplastic elastomer produced by stepwise polymerization of styrene and isoprene. Its molecules consist of polystyrene (PS) as hard segments (plastic segments) at both ends and polyisoprene (PI) as soft segments (rubber segments) in the middle. At room temperature, the PS hard segments lose fluidity, associate or "crosslink" and solidify, forming physically crosslinked regions that act as reinforcing agents. At high temperatures, it exhibits plastic flow. SIS possesses excellent mechanical properties, cohesive strength, adhesive properties, and superior compatibility, and is widely used in hot melt pressure-sensitive adhesives, inks, coatings, plastics, and asphalt modification. Compared to other thermoplastic elastomers, SIS exhibits superior mechanical properties, particularly in elongation at break and tensile strength. In recent years, the demand for multifunctional and intelligent technologies has driven the continuous expansion of the application fields of smart polymers, bringing more innovation and convenience to human life and industrial development. However, research on the intelligentization and application of SIS, despite its excellent mechanical properties, is relatively limited, restricting its application scope.

[0003] Smart polymer materials refer to a class of polymer materials capable of sensing the external environment, responding to external stimuli, and possessing self-adaptive capabilities. The demand for multifunctional and intelligent materials is driving the continuous expansion of their application fields, bringing more innovation and convenience to human life and industrial development. Spiropyrans (SP) and their derivatives, as a class of multi-stimulus responsive compounds, are characterized by rapid and reversible transitions between closed-ring (SP) and open-ring (MC) structures under external stimuli such as light, heat, solvents, acids, alkalis, electricity, and stress, accompanied by changes in properties such as color, fluorescence, hydrophilicity, and aggregation morphology. They are typical research objects in the field of smart polymer materials. Among various external stimulus responses, mechanical force has advantages such as convenience and ease of implementation, providing convenience for the use of mechanosensitive smart materials. Optical signals are one of the most important means of information transmission, and color changes can intuitively reflect changes in material properties, showing potential application prospects in stress sensing, information storage, and material damage detection. Therefore, developing SIS modified with spiropyran groups and possessing mechanosensitive color-changing properties, utilizing the excellent mechanical properties of SIS and the typical mechanochromic characteristics of SP, has significant research and application value.

[0004] Modification of polymer synthesizers (SIS) mainly includes the introduction of polar monomer copolymerization and post-polymerization modification. The former involves introducing monomers with specific functions during SIS preparation to achieve modification; the latter is mainly described from physical and chemical perspectives. Physical modification primarily employs mechanical blending, mixing materials with corresponding functions according to the modification requirements to complete the modification. Chemical modification methods mainly include photochemical reactions, hydroxylation, epoxidation, sulfonation, and free radical grafting modification. Among these, post-polymerization modification aims to efficiently modify reactive polymer precursors with mild reaction conditions, avoiding the interaction between functional groups and the polymerization process, thus providing significant convenience for the preparation of multifunctional smart polymers.

[0005] In practical applications, the elasticity, mechanical properties, and recyclability of rubber materials are closely related to their covalent crosslinking, reinforcement, and extensibility. Covalently crosslinked rubber, due to its high elasticity, plays an indispensable role in practical applications. The self-healing and extensibility of rubber materials are also crucial, as they can repair damage and be reprocessed to extend lifespan and reduce environmental pollution. Therefore, this invention, based on anionic copolymerization, designs and synthesizes a styrene-isoprene-styrene triblock copolymer (SIS) with controllable molecular weight and tunable structure through a stepwise feeding method. Using the double bonds of PI as functionalized active sites, hydroxyl groups are converted through functional group modification. Furthermore, bi-terminated isocyanate (NCO)-functionalized SP is designed and synthesized as a functional monomer and covalent crosslinking agent, while NCO-terminated UPy serves as a dynamic hydrogen-bonding crosslinking agent. 5-20 mol% of permanent covalent crosslinking agent and dynamic hydrogen-bonding crosslinking agent are quantitatively introduced via the esterification reaction of NCO and hydroxyl groups to prepare a dynamic polymer network of SP-modified SIS with multiple stimulus responses. This material possesses excellent mechanical properties and mechanochromic characteristics, making it applicable to intelligent sensing and material flaw detection. Summary of the Invention

[0006] To broaden the application of SIS thermoplastic elastomers in intelligent sensing and material flaw detection, this invention designs and synthesizes styrene-isoprene-styrene triblock copolymers (SIS) based on active anionic solution polymerization technology. Using the double bonds of the PI blocks as functionalized active sites, and modifying double-terminal NCO-functionalized SP as a covalent crosslinking agent and single-terminal NCO-functionalized UPy as a dynamic hydrogen-bonding crosslinking agent via functional group transformation reactions, a SP-modified SIS with both covalent and dynamic hydrogen-bonding crosslinking is prepared. Through structural control, the SP-modified SIS dynamic crosslinking network can achieve good elasticity, excellent mechanochromic properties, and reprocessable performance.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a dynamic crosslinking network (SIS-SP-UPy) of spiropyran-modified SIS with mechanochromic properties. The spiropyran (SP)-modified SIS dynamic crosslinking polymer network SIS-SP-UPy uses styrene-isoprene-styrene (SIS) with different molecular weights and styrene / isoprene ratios as the main chain. The network is converted to SIS-OH by epoxidation-hydroxylation of the double bonds in the polyisoprene (PI) blocks of SIS, utilizing isocyanate (NCO) and... The esterification reaction of OH uses bivalent NCO-functionalized SP (SP-NCO) as a covalent crosslinking agent and NCO-functionalized ureidopyrimidinone (UPy-NCO) as a dynamic hydrogen crosslinking agent. SP-NCO and UPy-NCO are grafted onto the PI block side chain of SIS. The resulting SP-modified SIS dynamic crosslinking network SIS-SP-UPy with covalent crosslinking and dynamic hydrogen crosslinking exhibits mechanochromic properties under ultrasonication, that is, it can undergo a transformation from a closed-ring SP form to an open-ring MC structure.

[0009] Furthermore, the SIS-SP-UPy is designed with different crosslinking densities and introduces different molar contents of covalent crosslinking agent SP-NCO and dynamic hydrogen crosslinking agent UPy-NCO, which can effectively improve the mechanical properties of the material. That is, the SIS-SP-UPy has excellent mechanical properties and reprocessability: the initial SIS-SP-UPy film has an elongation at break of 1200%-1600% and a tensile strength of 0.2-3.5 MPa. The second-generation film after cutting the initial film into pieces and re-laying it has an elongation at break of 1000%-1600% and a tensile strength of 0.2-3.3 MPa, showing good reprocessability.

[0010] Furthermore, the main chain of the SIS is a styrene-butadiene-styrene triblock copolymer initiated by alkyllithium; the number-average molecular weight (M) of the SIS is... n The value ranges from 5.0 to 500.0 kg·mol⁻¹. -1 The molecular weight distribution index (PDI) is 1.03-1.5; based on the mass of styrene and isoprene as 100%, the mass fraction of styrene polymer units in the SIS is 10-50 wt%, and the mass fraction of isoprene polymer units is 50-90 wt%; based on the total number of diblock and triblock blocks as 100%, the content of diblock SI is 0-80 mol%, and the remainder is a SIS triblock copolymer; based on the total number of double bonds in the isoprene polymer units as 100%, the content of 1,4-structures in the isoprene polymer units is 80-90 mol%, and the remainder is a 3,4-structure. The SIS is, in sequence, a polystyrene block PS, a polyisoprene block PI, and a polystyrene block PS copolymer, with the following structural formula:

[0011]

[0012] Furthermore, based on the total number of double bonds in the SIS main chain being 100%, the epoxy degree of the epoxy-functionalized SIS (ESIS) is 5%-50%, the elongation at break of the ESIS film is 1400%-1600%, and the tensile strength is 2.2-3.2 MPa; based on the total number of epoxy groups being 100%, the hydroxyl degree of the hydroxyl-functionalized SIS (SIS-OH) is 5%-100%, the elongation at break of the SIS-OH film is 1200%-1400%, and the tensile strength is 1.5-2.5 MPa.

[0013] Furthermore, the grafting density of the covalent crosslinking agent SP-NCO is 5-20 mol%, and its structural formula is as follows:

[0014]

[0015] Furthermore, the grafting density of the hydrogen-bonded crosslinking agent UPy-NCO is 5-20 mol%, and its structural formula is as follows:

[0016]

[0017] The second aspect is the application of a dynamic crosslinking network of spiropyran-modified SIS with mechanochromic properties. The SIS-SP-UPy solution exhibits mechanochromic properties (SP-MC) under ultrasonic irradiation, possesses excellent mechanical properties and reproducible processing performance, and can be applied to fields such as stress-strain sensing visualization and damage detection.

[0018] Thirdly, a method for preparing a dynamic crosslinking network SIS-SP-UPy of spiropyran (SP) group-modified SIS with mechanochromic properties mainly includes the following steps:

[0019] S1, Synthesis of SIS-OH

[0020] (1) Synthesis of the styrene-isoprene-styrene copolymer backbone (SIS): In a glove box, using a nonpolar hydrocarbon solvent as the solvent, monofunctional alkyl lithium (RLi) as the initiator, and tetrahydrofuran as the polar modifier, the polymerization process was carried out in three additions. First, styrene monomer was added, and the reaction was carried out at 10-90℃ for 1-5 h to form polystyrene lithium (PS-Li) active species. Then, isoprene monomer was added, and PS-Li initiated the polymerization of isoprene to generate active SI diblock active species PS-PI-Li. Finally, styrene monomer was added, and the reaction was carried out for 1-24 h. The reaction was terminated by adding purified isopropanol. The reaction solution was precipitated in a large amount of methanol, and the resulting viscous liquid was dried under vacuum to constant weight to obtain styrene-isoprene-styrene triblock polymers (SIS) of different molecular weights.

[0021] (2) First, dissolve SIS in cyclohexane, then add m-CPBA dissolved in tetrahydrofuran, and react at 25-60℃ for 1-10 h. After the reaction is complete, remove the solvent under reduced pressure, dissolve the reactants in a small amount of tetrahydrofuran, add ethanol dropwise to the solution and a viscous solid precipitates out. After centrifugation and discarding the supernatant, repeat the above operation to remove m-chloroperoxybenzoic acid and m-chlorobenzoic acid from the system to obtain pure ESIS.

[0022] (3) Dissolve ESIS in tetrahydrofuran, then add deionized water ZrCl4 (molar ratio of feed [Epo:H2O:ZrCl4]=1:15:0.5), react at 25-40℃ for 1-8h. After the reaction is complete, add ethanol dropwise to the solution and a viscous solid will precipitate. Centrifuge and repeat the above operation to remove ZrCl4 from the obtained solid to obtain pure SIS-OH.

[0023] S2, Synthetic covalent crosslinking agent SP-NCO

[0024] (4) Synthesis of the first intermediate product

[0025] Under inert gas protection, 2,3,3-trimethylindole, 2-iodoethanol, and toluene were added sequentially to a flask and reacted at 60-110°C for 8-24 h. The reaction solution was extracted three times with ethyl acetate, and the organic phase was evaporated under reduced pressure to remove the solvent. The solution was dried to constant weight in a vacuum drying oven to obtain the first intermediate product. The molar ratio of 2,3,3-trimethyl-3H-indole to 2-iodoethanol was 1:1 to 2.

[0026] (5) Synthesis of the second intermediate product

[0027] o-vanillin, glacial acetic acid, and deionized water were added sequentially to a flask. After the o-vanillin was completely dissolved, nitric acid was slowly added dropwise to the flask through a constant pressure dropping funnel. The reaction was carried out in an ice-water bath for 1-5 hours. The crude product obtained from the reaction was washed three times with deionized water and dried to constant weight in a vacuum drying oven to obtain the second intermediate product.

[0028] (6) Synthesis of the third intermediate product

[0029] The second intermediate and hydrobromic acid aqueous solution were added to a flask and reacted at 80-120℃ for 4-12 h. The reaction solution was diluted with deionized water and filtered. The crude product was dissolved in ethyl acetate, decolorized with activated carbon, and filtered. The obtained solid was recrystallized with hot ethanol and finally dried in a vacuum drying oven to constant weight to obtain the third intermediate.

[0030] (7) Synthesis of monomer SP

[0031] Under inert gas protection, the first intermediate, the third intermediate, and anhydrous ethanol were added to a flask, followed by the addition of triethylamine. The reaction was carried out at 40-70°C for 4-24 hours. The crude product obtained by filtration of the reaction solution was washed with cold ethanol and then dried in a vacuum drying oven to constant weight to obtain a dark green solid SP.

[0032] (8) Synthesis of covalent crosslinking agent SP-NCO

[0033] Under inert gas protection, monomer SP and excess hexamethylene diisocyanate (HDI) are added to a flask, followed by the catalyst n-butyltin dilaurate (DBTDL). The reaction is carried out at 25-40°C for 1-5 hours to obtain NCO-terminated covalent crosslinking agent (SP-NCO).

[0034] The synthetic route of the covalent crosslinking agent SP-NCO is as follows:

[0035]

[0036] S3, Synthesis of hydrogen-bonding crosslinking agent UPy-NCO

[0037] Under argon protection, 2-amino-4-hydroxy-6-methylpyrimidine was added to a round-bottom flask, along with hexamethylene diisocyanate (HDI) and pyridine. The mixture was stirred at 60-100°C for 12-24 hours. After the reaction was complete, an alkane hydrocarbon solution (n-hexane, n-pentane, etc.) was added to the reaction solution. The mixture was filtered, and the resulting solid powder was washed with acetone to remove unreacted HMDI. The powder was then dried to constant weight in a vacuum drying oven to obtain the hydrogen-bonded crosslinking agent UPy-NCO. The molar ratio of 2-amino-4-hydroxy-6-methylpyrimidine to HDI was 1:(5-8).

[0038] The synthetic route for the hydrogen-bonding crosslinking agent UPy-NCO is as follows:

[0039]

[0040] S4, Synthetic SP-group modified SIS dynamic crosslinked polymer network SIS-SP-UPy

[0041] Under inert gas (nitrogen, argon) protection, SIS-OH, covalent crosslinking agent SP-NCO, and hydrogen crosslinking agent UPy-NCO are dissolved in a polar solvent (such as chloroform, DMF, etc.), and then the catalyst n-butyltin dilaurate is added. The reaction is carried out at 40-60℃ for 12-24 hours. The reaction solution is allowed to settle in an alkane hydrocarbon solution (n-hexane, n-pentane, etc.) and dried to constant weight in a vacuum drying oven to obtain the SP-group modified SIS dynamic crosslinked polymer network SIS-SP-UPy.

[0042] Furthermore, the total mass concentration of all monomers added in step S1 is 5%-25%, preferably 8-12%.

[0043] Furthermore, the nonpolar hydrocarbon solvent used in step S1 is selected from at least one of nonpolar aromatic hydrocarbons and nonpolar aliphatic hydrocarbons, generally selected from: benzene, toluene, ethylbenzene, xylene, pentane, hexane, heptane, octane, cyclohexane, mixed aromatic hydrocarbons (e.g., mixed xylene), mixed aliphatic hydrocarbons (e.g., raffinate), preferably from: benzene, toluene, pentane, hexane, cyclohexane.

[0044] Further, in step S1, the alkyl lithium initiator is selected from one or a mixture of several monofunctional alkyl lithium RLi initiators that can be used for the anionic polymerization of isoprene and styrene, where R is a hydrocarbon group with 2-20 carbon atoms, which can be an alkane group or an aromatic group, preferably n-butyllithium, sec-butyllithium and tert-butyllithium.

[0045] Experimental tests of this invention:

[0046] (1) Tensile test: Instron 5567A universal tensile testing machine, tensile test at room temperature at a rate of 10 mm / min, each sample was repeated at least three times.

[0047] (2) Mechanochromic property analysis: Ultrasonic instruments and UV-Vis absorption spectroscopy were used for observation. A DMF solution of SIS-SP-UPy (0.6 mg / mL) was prepared and ultrasonicated. The color change of the solution at different time points was observed and detected by UV-Vis absorption spectroscopy. The SP-group modified SIS dynamic cross-linked polymer network SIS-SP-UPy exhibits mechanochromic properties in DMF solution under ultrasonication, i.e., it can undergo a closed-ring-opening (SP-MC) structure transition, and the solution color changes from pink to yellow-green.

[0048] The beneficial effects of this invention are as follows: Based on a living anionic polymerization method, this invention designs and synthesizes a styrene-isoprene-styrene triblock copolymer (SIS) through a stepwise feeding method. This SIS features controllable molecular weight and tunable structure. Using the double bonds of PI in SIS as functionalized active sites, it transforms them into hydroxyl groups through functional group modification. Then, utilizing the esterification reaction of NCO and OH, and by introducing covalent crosslinking agent SP-NCO and dynamic hydrogen crosslinking agent UPy-NCO, different crosslinking densities are designed to ultimately achieve the preparation of a structurally controllable copolymer with covalent crosslinking and... The dynamic polymer network of SIS modified with SP groups through dynamic hydrogen bonding exhibits mechanochromic properties (SP-MC) under ultrasonic irradiation, along with excellent mechanical properties (elongation at break of 1200%-1600% and tensile strength of 0.2-3.5 MPa for the initial film) and reprocessability (elongation at break of 1000%-1600% and tensile strength of 0.2-3.3 MPa for the second-generation film). This can broaden the application of SIS thermoplastic elastomers in fields such as stress-strain sensing visualization and material flaw detection. Attached Figure Description

[0049] Figure 1 NMR contrast images of SIS-SP-UPy, a dynamically cross-linked polymer network of SIS modified with spiropyran monomers, SIS and SP groups.

[0050] Figure 2 Stress-strain curves of SIS-SP-UPy

[0051] Figure 3 The UV-Vis spectrum of SIS-SP-UPy under ultrasonic treatment in DMF solution. Detailed Implementation

[0052] The present invention will be further described below with reference to specific embodiments.

[0053] Example 1

[0054] S1, Synthesis of SIS-OH

[0055] (1) Synthesis of the styrene-isoprene-styrene copolymer backbone (SIS): In a glove box, using 40 mL of cyclohexane as solvent, n-butyllithium (1.6 mol / L, 0.50 mL) as initiator, and tetrahydrofuran as polar modifier, the polymerization process was carried out in three additions. First, styrene monomer (0.2 g, 1.9 mmol) was added, and the reaction was carried out at 10 °C for 5 h to form polystyrene lithium (PS-Li) active species. Then, isoprene monomer (Ip, 3.6 g, 52.9 mmol) was added, and PS-Li initiated the polymerization of isoprene to generate the active SI diblock active species PS-PI-Li. Finally, styrene monomer (0.2 g, 1.9 mmol) was added, and the reaction was carried out for 24 h. The reaction was terminated by adding purified isopropanol. The reaction solution was precipitated in a large amount of methanol, and the resulting viscous liquid was dried under vacuum to constant weight to obtain the styrene-isoprene-styrene triblock polymer (SIS). The number average molecular weight M of the polymer was... n 5.0 kg·mol -1 The molecular weight distribution index is 1.5. The mass fraction of styrene units is 10 wt%, the mass fraction of isoprene polymer units is 90 wt%, the diblock SI content is 0 mol%, and the 1,4-structure content in the isoprene polymer units is 80 mol%.

[0056] (2) First, dissolve SIS5.0k (10g) in 100mL of cyclohexane, then add tetrahydrofuran-dissolved m-chloroperoxybenzoic acid (m-CPBA, controlling the molar ratio [m-CPBA:C=C]=0.25), and react at 25℃ for 10h. After the reaction is complete, remove the solvent under reduced pressure, dissolve the reactants in a small amount of tetrahydrofuran, and add ethanol dropwise to the solution. A viscous solid precipitates out. After centrifugation and discarding the supernatant, repeat the above operation to remove m-chloroperoxybenzoic acid and m-chlorobenzoic acid from the system to obtain pure ESIS5.0k.

[0057] (3) Dissolve 5.0k (5g) of ESIS in 100mL of tetrahydrofuran, and then add deionized water ZrCl4 (molar ratio of feed [Epo:H2O:ZrCl4]=1:15:0.5). React at 25℃ for 8h. After the reaction is complete, add ethanol dropwise to the solution and a viscous solid will precipitate. Centrifuge and repeat the above operation to remove ZrCl4 from the obtained solid to obtain pure SIS-OH5.0k.

[0058] S2, synthesized monomer SP

[0059] (4) Synthesis of the first intermediate product

[0060] Under argon protection, 2,3,3-trimethylindole (2.5 g, 0.016 mol), 2-iodoethanol (1.84 mL, 0.024 mol), and 30 mL of toluene were added sequentially to a 250 mL flask and reacted at 60 °C for 24 h. The reaction solution was extracted three times with ethyl acetate, and the organic phase was evaporated under reduced pressure to remove the solvent. The solution was dried in a vacuum drying oven to constant weight to obtain the first intermediate product.

[0061] (5) Synthesis of the second intermediate product

[0062] 5.0 g (0.03 mol) of o-vanillin, 32 mL of glacial acetic acid, and 1.5 mL of deionized water were added sequentially to a 250 mL flask. After the o-vanillin was completely dissolved, 2.30 mL (0.038 mol) of nitric acid was slowly added dropwise to the flask through a constant pressure dropping funnel. The reaction was carried out in an ice-water bath for 1 hour. The crude product obtained from the reaction was washed three times with 40 mL of deionized water and dried to constant weight in a vacuum drying oven to obtain the second intermediate product.

[0063] (6) Synthesis of the third intermediate product

[0064] The second intermediate (6 g, 0.03 mol) and 100 mL of hydrobromic acid aqueous solution were added to a 250 mL flask and reacted at 80 °C for 12 h. The reaction solution was diluted with 110 mL of deionized water and filtered. The crude product was dissolved in ethyl acetate, decolorized with activated carbon, and filtered. The obtained solid was recrystallized with hot ethanol and finally dried in a vacuum drying oven to constant weight to obtain the third intermediate.

[0065] (7) Synthesis of monomer SP

[0066] Under argon protection, the first intermediate (1.29 g, 0.004 mol), the third intermediate (0.72 g, 0.004 mol), and 40 mL of anhydrous ethanol were added to a 250 mL flask, followed by the addition of triethylamine (1.09 mL, 0.0078 mol). The reaction was carried out at 40 °C for 24 h. The crude product obtained by filtration of the reaction solution was washed with cold ethanol and then dried in a vacuum drying oven to constant weight to obtain a dark green solid SP.

[0067] (8) Synthesis of covalent crosslinking agent SP-NCO

[0068] Under argon protection, monomer SP (5 g, 13.6 mmol) and hexamethylene diisocyanate (HDI, 20 mL, 136 mmol) were added to a round-bottom flask, and 2 drops of catalyst n-butyltin dilaurate (DBTDL) were added. The reaction was carried out at 25 °C for 5 h to obtain NCO-terminated covalent crosslinking agent (SP-NCO).

[0069] S3, Synthesis of hydrogen-bonding crosslinking agent UPy-NCO

[0070] Under argon protection, 2-amino-4-hydroxy-6-methylpyrimidine (5 g, 40 mmol) was added to a round-bottom flask, along with hexamethylene diisocyanate (HDI, 50 mL, 312 mmol) and 4 mL of pyridine. The mixture was refluxed at 60 °C with stirring overnight for 24 h. After the reaction was complete, 15 mL of n-hexane was added to the reaction solution, and the mixture was filtered. The resulting solid powder was washed with acetone to remove unreacted HDI, and then dried in a vacuum drying oven to constant weight to obtain the hydrogen-bonded crosslinking agent UPy-NCO.

[0071] S4, Synthetic SP-group modified SIS dynamic crosslinked polymer network SIS-SP-UPy

[0072] Under nitrogen protection, 5.0 kJ of SIS-OH, 5 mol% of covalent crosslinking agent SP-NCO, and 5 mol% of hydrogen crosslinking agent UPy-NCO were dissolved in chloroform. Two drops of catalyst n-butyltin dilaurate were then added to the solution. The reaction was carried out at 40 °C for 24 h. The reaction solution was allowed to settle in n-hexane and dried to constant weight in a vacuum drying oven to obtain the SP-group modified SIS dynamic crosslinked polymer network SIS-SP-UPy.

[0073] Depend on Figure 1 Spiropyran monomers, SIS and SP groups modified SIS dynamic crosslinked polymer network SIS-SP-UPy 1 The comparison of HNMR spectra shows that the SP-group modified SIS dynamic cross-linked polymer network SIS-SP-UPy was successfully synthesized.

[0074] Depend on Figure 2 The stress-strain curves show that appropriately increasing the crosslinking density can effectively improve the mechanical properties of the material.

[0075] Depend on Figure 3 The UV-Vis spectrum shows that the synthesized SP-group modified SIS dynamic cross-linked polymer network SIS-SP-UPy exhibits mechanochromic properties (SP-MC).

[0076] Example 2

[0077] S1, Synthesis of SIS-OH

[0078] (1) Synthesis of the styrene-isoprene-styrene copolymer backbone (SIS): In a glove box, using 40 mL benzene as solvent, sec-butyllithium (0.23 mol / L, 0.087 mL) as initiator, and tetrahydrofuran as polar modifier, the polymerization process was carried out in three additions. First, styrene monomer (0.6 g, 5.8 mmol) was added, and the reaction was carried out at 50 °C for 3 h to form polystyrene lithium (PS-Li) active species. Then, isoprene monomer (Ip, 2.8 g, 41.1 mmol) was added, and PS-Li initiated the polymerization of isoprene to generate the active SI diblock active species PS-PI-Li. Finally, styrene monomer (0.6 g, 5.8 mmol) was added, and the reaction was carried out for 12 h. The reaction was terminated by adding purified isopropanol. The reaction solution was precipitated in a large amount of methanol, and the resulting viscous liquid was dried under vacuum to constant weight to obtain the styrene-isoprene-styrene triblock polymer (SIS). The number average molecular weight M of the polymer was... n 200.0 kg·mol -1 The molecular weight distribution index is 1.2. The mass fraction of styrene units is 30 wt%, the mass fraction of isoprene polymer units is 70 wt%, the diblock SI content is 40 mol%, and the 1,4-structure content in the isoprene polymer units is 85 mol%.

[0079] (2) First, dissolve SIS200.0k (20g) in 200mL of cyclohexane, then add tetrahydrofuran-dissolved m-chloroperoxybenzoic acid (m-CPBA, controlling the molar ratio [m-CPBA:C=C]=0.25), and react at 40℃ for 6h. After the reaction is complete, remove the solvent under reduced pressure, dissolve the reactants in a small amount of tetrahydrofuran, and add ethanol dropwise to the solution. A viscous solid precipitates out. After centrifugation and discarding the supernatant, repeat the above operation to remove m-chloroperoxybenzoic acid and m-chlorobenzoic acid from the system to obtain pure ESIS200.0k.

[0080] (3) Dissolve 10 g of ESIS200.0 kJ in 200 mL of tetrahydrofuran, then add deionized water ZrCl4 (molar ratio of feed [Epo:H2O:ZrCl4] = 1:15:0.5), and react at 30 °C for 5 h. After the reaction is complete, add ethanol dropwise to the solution and a viscous solid will precipitate. Centrifuge and repeat the above operation to remove ZrCl4 from the obtained solid to obtain pure SIS-OH200.0 kJ.

[0081] S2, Synthetic covalent crosslinking agent SP-NCO

[0082] (4) Synthesis of the first intermediate product

[0083] Under argon protection, 2,3,3-trimethylindole (5 g, 0.032 mol), 2-iodoethanol (3.67 mL, 0.047 mol), and 50 mL of toluene were added sequentially to a 250 mL flask. The reaction mixture was reacted at 90 °C for 12 h. The reaction solution was extracted three times with ethyl acetate. The organic phase was removed by rotary evaporation under reduced pressure. The solution was dried to constant weight in a vacuum drying oven to obtain the first intermediate product.

[0084] (5) Synthesis of the second intermediate product

[0085] 10.0 g (0.065 mol) of o-vanillin, 63 mL of glacial acetic acid, and 3 mL of deionized water were added sequentially to a 250 mL flask. After the o-vanillin was completely dissolved, 4.61 mL (0.075 mol) of nitric acid was slowly added dropwise to the flask through a constant pressure dropping funnel. The reaction was carried out in an ice-water bath for 3 hours. The crude product obtained from the reaction was washed three times with 75 mL of deionized water and dried to constant weight in a vacuum drying oven to obtain the second intermediate product.

[0086] (6) Synthesis of the third intermediate product

[0087] The second intermediate (12 g, 0.06 mol) and 200 mL of hydrobromic acid aqueous solution were added to a 500 mL flask and reacted at 100 °C for 8 h. The reaction solution was diluted with 225 mL of deionized water and filtered. The crude product was dissolved in ethyl acetate, decolorized with activated carbon, and filtered. The obtained solid was recrystallized with hot ethanol and finally dried in a vacuum drying oven to constant weight to obtain the third intermediate.

[0088] (7) Synthesis of monomer SP

[0089] Under argon protection, the first intermediate (2.59 g, 0.008 mol), the third intermediate (1.43 g, 0.008 mol), and 75 mL of anhydrous ethanol were added to a 250 mL flask, followed by the addition of triethylamine (2.19 mL, 0.015 mol). The reaction was carried out at 50 °C for 12 h. The crude product obtained by filtration of the reaction solution was washed with cold ethanol and then dried in a vacuum drying oven to constant weight to obtain a dark green solid SP.

[0090] (8) Synthesis of covalent crosslinking agent SP-NCO

[0091] Under argon protection, monomer SP (5 g, 13.6 mmol) and hexamethylene diisocyanate (HDI, 20 mL, 136 mmol) were added to a round-bottom flask, and 2 drops of catalyst n-butyltin dilaurate (DBTDL) were added. The reaction was carried out at 30 °C for 3 h to obtain NCO-terminated covalent crosslinking agent (SP-NCO).

[0092] S3, Synthesis of hydrogen-bonding crosslinking agent UPy-NCO

[0093] Under argon protection, 2-amino-4-hydroxy-6-methylpyrimidine (5 g, 40 mmol) was added to a round-bottom flask, along with hexamethylene diisocyanate (HDI, 50 mL, 312 mmol) and 4 mL of pyridine. The mixture was refluxed at 80 °C with stirring overnight for 18 h. After the reaction was complete, 15 mL of n-hexane was added to the reaction solution, and the mixture was filtered. The resulting solid powder was washed with acetone to remove unreacted HDI, and then dried in a vacuum drying oven to constant weight to obtain the hydrogen-bonded crosslinking agent UPy-NCO.

[0094] S4, Synthetic SP-group modified SIS dynamic crosslinked polymer network SIS-SP-UPy

[0095] Under nitrogen protection, SIS-OH200.0k, 10 mol% covalent crosslinking agent SP-NCO and 10 mol% hydrogen crosslinking agent UPy-NCO were dissolved in chloroform, and then 2 drops of catalyst n-butyltin dilaurate were added. The reaction was carried out at 50°C for 18 h. The reaction solution was allowed to settle in n-hexane and dried in a vacuum drying oven to constant weight to obtain the SP-group modified SIS dynamic crosslinked polymer network SIS-SP-UPy.

[0096] Under ultrasonic treatment, SIS-SP-UPy exhibits mechanochromic properties (SP-MC). The initial membrane has a breaking elongation of 1300% and a breaking strength of 1.7 MPa, while the second-generation membrane has a breaking elongation of 1100% and a breaking strength of 1.5 MPa.

[0097] Example 3

[0098] S1, Synthesis of SIS-OH

[0099] (1) Synthesis of the styrene-isoprene-styrene copolymer backbone (SIS): In a glove box, using 40 mL toluene as solvent, tert-butyllithium (0.16 mol / L, 0.05 mL) as initiator, and tetrahydrofuran as polar modifier, the polymerization process was carried out in three additions. First, styrene monomer (1 g, 9.6 mmol) was added, and the reaction was carried out at 90 °C for 1 h to form polystyrene lithium (PS-Li) active species. Then, isoprene monomer (Ip, 2 g, 29.4 mmol) was added, and PS-Li initiated the polymerization of isoprene to generate the active SI diblock active species PS-PI-Li. Finally, styrene monomer (1 g, 9.6 mmol) was added, and the reaction was carried out for 1 h. The reaction was terminated by adding purified isopropanol. The reaction solution was precipitated in a large amount of methanol, and the resulting viscous liquid was dried under vacuum to constant weight to obtain the styrene-isoprene-styrene triblock polymer (SIS). The number average molecular weight M of the polymer was... n 500.0 kg·mol -1The molecular weight distribution index is 1.03. The mass fraction of styrene units is 50 wt%, the mass fraction of isoprene polymer units is 50 wt%, the diblock SI content is 80 mol%, and the 1,4-structure content in the isoprene polymer units is 90 mol%.

[0100] (2) First, dissolve 5 g of SIS500.0 k in 50 mL of cyclohexane, then add tetrahydrofuran-dissolved m-chloroperoxybenzoic acid (m-CPBA, controlling the molar ratio [m-CPBA:C=C]=0.25), and react at 60 °C for 1 h. After the reaction is complete, remove the solvent under reduced pressure, dissolve the reactants in a small amount of tetrahydrofuran, and add ethanol dropwise to the solution. A viscous solid precipitates out. After centrifugation and discarding the supernatant, repeat the above operation to remove m-chloroperoxybenzoic acid and m-chlorobenzoic acid from the system to obtain pure SIS500.0 k.

[0101] (3) Dissolve ESIS500.0k (2.5g) in 50mL of tetrahydrofuran, then add deionized water ZrCl4 (molar ratio of feed [Epo:H2O:ZrCl4]=1:15:0.5), react at 40℃ for 1h. After the reaction is complete, add ethanol dropwise to the solution and a viscous solid precipitates out. Centrifuge and repeat the above operation to remove ZrCl4 from the obtained solid to obtain pure SIS-OH500.0k.

[0102] S2, Synthetic covalent crosslinking agent SP-NCO

[0103] (4) Synthesis of the first intermediate product

[0104] Under argon protection, 10 g of 2,3,3-trimethylindole (0.063 mol), 7.34 mL of 2-iodoethanol (0.094 mol), and 105 mL of toluene were added sequentially to a 250 mL flask. The reaction mixture was reacted at 110 °C for 8 h. The reaction solution was extracted three times with ethyl acetate. The organic phase was removed by rotary evaporation under reduced pressure. The solution was dried to constant weight in a vacuum drying oven to obtain the first intermediate product.

[0105] (5) Synthesis of the second intermediate product

[0106] 20.0 g (0.13 mol) of o-vanillin, 126 mL of glacial acetic acid, and 6 mL of deionized water were added sequentially to a 250 mL flask. After the o-vanillin was completely dissolved, 9.21 mL (0.15 mol) of nitric acid was slowly added dropwise to the flask through a constant pressure dropping funnel. The reaction was carried out in an ice-water bath for 5 h. The crude product obtained from the reaction was washed three times with 150 mL of deionized water and dried to constant weight in a vacuum drying oven to obtain the second intermediate product.

[0107] (6) Synthesis of the third intermediate product

[0108] The second intermediate (24 g, 0.12 mol) and 400 mL of hydrobromic acid aqueous solution were added to a 500 mL flask and reacted at 120 °C for 4 h. The reaction solution was diluted with 450 mL of deionized water and filtered. The crude product was dissolved in ethyl acetate, decolorized with activated carbon, and filtered. The obtained solid was recrystallized with hot ethanol and finally dried in a vacuum drying oven to constant weight to obtain the third intermediate.

[0109] (7) Synthesis of monomer SP

[0110] Under argon protection, the first intermediate (5.17 g, 0.016 mol), the third intermediate (2.86 g, 0.016 mol), and 150 mL of anhydrous ethanol were added to a 250 mL flask, followed by the addition of triethylamine (4.37 mL, 0.031 mol). The reaction was carried out at 70 °C for 4 h. The crude product obtained by filtration of the reaction solution was washed with cold ethanol and then dried in a vacuum drying oven to constant weight to obtain a dark green solid SP.

[0111] (8) Synthesis of covalent crosslinking agent SP-NCO

[0112] Under argon protection, monomer SP (5 g, 13.6 mmol) and hexamethylene diisocyanate (HDI, 20 mL, 136 mmol) were added to a round-bottom flask, and 2 drops of catalyst n-butyltin dilaurate (DBTDL) were added. The reaction was carried out at 40 °C for 1 h to obtain NCO-terminated covalent crosslinking agent (SP-NCO).

[0113] S3, Synthesis of hydrogen-bonding crosslinking agent UPy-NCO

[0114] Under argon protection, 2-amino-4-hydroxy-6-methylpyrimidine (5 g, 40 mmol) was added to a round-bottom flask, along with hexamethylene diisocyanate (HDI, 50 mL, 312 mmol) and 4 mL of pyridine. The mixture was refluxed at 100 °C with stirring overnight for 12 h. After the reaction was complete, 15 mL of n-pentane was added to the reaction solution, and the mixture was filtered. The resulting solid powder was washed with acetone to remove unreacted HDI, and then dried in a vacuum drying oven to constant weight to obtain the hydrogen-bonded crosslinking agent UPy-NCO.

[0115] S4, Synthetic SP-group modified SIS dynamic crosslinked polymer network SIS-SP-UPy

[0116] Under nitrogen protection, SIS-OH 500.0k, 20 mol% covalent crosslinking agent SP-NCO and 20 mol% hydrogen crosslinking agent UPy-NCO were dissolved in DMF, and then 2 drops of catalyst n-butyltin dilaurate were added. The reaction was carried out at 60℃ for 12 h. The reaction solution was allowed to settle in n-pentane and dried to constant weight in a vacuum drying oven to obtain the SP-group modified SIS dynamic crosslinked polymer network SIS-SP-UPy.

[0117] Under ultrasonic treatment, SIS-SP-UPy exhibits mechanochromic properties (SP-MC). The initial membrane has a breaking elongation of 1600% and a breaking strength of 3.5 MPa, while the second-generation membrane has a breaking elongation of 1600% and a breaking strength of 3.3 MPa.

[0118] The embodiments described above are merely illustrative of specific implementations of the present invention, enabling those skilled in the art to understand or implement the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A spiropyran-modified SIS dynamic crosslinking network with mechanochromic properties, characterized in that, The dynamic crosslinking network SIS-SP-UPy of the spiropyran-modified SIS with mechanochromic properties is based on styrene-isoprene-styrene SIS as the main chain, with a total number of diblock and triblock blocks of 100% and a diblock SI content of 0-80%. mol%, the remainder is SIS triblock copolymer; by epoxy functionalizing the double bonds of polyisoprene PI blocks in SIS to ESIS and hydroxyl functionalizing SIS-OH, using the reaction of isocyanate NCO and OH, spiropyran SP with double-ended NCO functionalization is used as covalent crosslinking agent SP-NCO and NCO functionalized 2-ureido-4[1H]-pyrimidinone as dynamic hydrogen crosslinking agent UPy-NCO, and SP-NCO and UPy-NCO are grafted onto the side chain of SIS-OH to obtain the dynamic crosslinking network SIS-SP-UPy of SP group modified SIS with covalent crosslinking and dynamic hydrogen crosslinking. Under ultrasonic action, it can undergo the transformation from closed-ring SP form to open-ring MC structure, showing the mechanochromic properties; The structural formula of the covalent crosslinking agent SP-NCO is as follows: 。 2. The spiropyran-modified SIS dynamic crosslinking network with mechanochromic properties according to claim 1, characterized in that, The main chain of the SIS is a styrene-isoprene-styrene triblock copolymer initiated by alkyllithium; the number-average molecular weight of the SIS is... M n The concentration ranges from 5.0 to 500.0 kg∙mol. -1 The molecular weight distribution index (PDI) is 1.03-1.5; based on the mass of styrene and isoprene as 100%, the mass fraction of styrene polymer units in the SIS is 10-50 wt%, and the mass fraction of isoprene polymer units is 50-90 wt%; based on the total number of double bonds in the isoprene polymer units as 100%, the content of 1,4-structure in the isoprene polymer units is 80-90 mol%, and the remainder is 3,4-structure.

3. The spiropyran-modified SIS dynamic crosslinking network with mechanochromic properties according to claim 1, characterized in that, Based on the total number of double bonds in the PI main chain of SIS being 100%, the epoxy degree of ESIS is 5%-50%, and the rest is SIS; based on the total number of epoxy groups being 100%, the hydroxyl degree of SIS-OH is 5%-100%, and the rest is ESIS.

4. The spiropyran-modified SIS dynamic crosslinking network with mechanochromic properties according to claim 1, characterized in that, With the total number of hydroxyl groups (OH) in SIS-OH being 100%, the grafting density of the covalent crosslinking agent SP-NCO is 5-20 mol, and the grafting density of the hydrogen crosslinking agent UPy-NCO is 5-20 mol.

5. The dynamic crosslinking network of spiropyran-modified SIS with mechanochromic properties according to claim 1, characterized in that, The initial SIS-SP-UPy membrane has an elongation at break of 1200%-1600% and a tensile strength of 0.2-3.5 MPa. The second-generation membrane, after being cut into pieces and re-laid, has an elongation at break of 1000%-1600% and a tensile strength of 0.2-3.3 MPa, exhibiting reprocessable properties.

6. A method for preparing a dynamic crosslinking network of spiropyran-modified SIS with mechanochromic properties as described in any one of claims 1-5, characterized in that, Includes the following steps: S1, Synthesis of SIS-OH A metered polar modifier is added to a reactor under anhydrous, oxygen-free, and inert gas protection in a nonpolar hydrocarbon solvent. A metered alkyl lithium initiator and styrene monomer are added according to the monomer ratio. The reaction is carried out at 10-90 °C for 1-5 h to form polystyrene lithium PS-Li active species. Then, isoprene monomer is added, and PS-Li initiates the polymerization of isoprene to generate active SI diblock active species PS-PI-Li. Finally, styrene monomer is added, and the reaction time is 1-24 h. A terminator is added to obtain styrene-isoprene-styrene triblock polymers SIS with different molecular weights and compositions. SIS is dissolved in an organic solvent and stirred until homogeneous. Then, m-chloroperoxybenzoic acid (m-CPBA) dissolved in the solvent is added according to the metered feed ratio. The reaction is carried out at 25-60 °C for 1-10 h. h, let the reaction solution stand in anhydrous ethanol to settle, and obtain ESIS; dissolve ESIS in an organic solvent, add deionized water and zirconium chloride ZrCl4 according to the measured feed ratio, react at 25-40 ℃ for 1-8 h, let the reaction solution stand in anhydrous ethanol to settle, and obtain SIS-OH. S2, Synthetic covalent crosslinking agent SP-NCO Under an inert gas atmosphere, 2,3,3-trimethylindole and 2-iodoethanol were dissolved in an organic solvent according to a predetermined feed ratio. The reaction was carried out at 60-110 °C for 8-24 h to obtain the first intermediate product, wherein the molar ratio of 2,3,3-trimethyl-3H-indole to 2-iodoethanol was 1:1~2. o-Vanillin and glacial acetic acid were added to deionized water according to a predetermined feed ratio. After o-Vanillin was completely dissolved, nitric acid was slowly added dropwise to the flask, and the reaction was carried out in an ice-water bath for 1-5 h to obtain the second intermediate product. The second intermediate product was added to an aqueous solution of hydrobromic acid according to a predetermined feed ratio, and the reaction was carried out at 80-120 °C for 4-12 h to obtain the third intermediate product. Under an inert gas atmosphere, the first and third intermediate products were added to anhydrous ethanol, followed by triethylamine, and the reaction was carried out at 40-70 °C for 4-24 h. h, a dark green solid SP was obtained; under inert gas protection, the monomer SP and excess hexamethylene diisocyanate HDI were added to a flask, and the catalyst n-butyltin dilaurate DBTDL was added. The reaction was carried out at 25-40 °C for 1-5 h to obtain the NCO-terminated covalent crosslinking agent SP-NCO. S3, Synthesis of hydrogen-bonding crosslinking agent UPy-NCO Under inert gas protection, 2-amino-4-hydroxy-6-methylpyrimidine was added to a round-bottom flask according to the metered feeding ratio, and hexamethylene diisocyanate (HDI) and pyridine were added. The mixture was stirred at 60-100 °C and reacted for 12-24 h. After the reaction was completed, hexane or pentane was added to the reaction solution, and the mixture was filtered. The resulting solid powder was washed with acetone to remove unreacted HDI and dried in a vacuum drying oven to constant weight to obtain the hydrogen-bonded crosslinking agent Upy-NCO, wherein the molar ratio of 2-amino-4-hydroxy-6-methylpyrimidine to HDI was 1:(5-8). S4, Synthetic SP-group modified SIS dynamic crosslinked polymer network SIS-SP-UPy Under inert gas protection, SIS-OH, SP-NCO and UPy-NCO were dissolved in a polar solvent according to a metered feeding ratio. Then, dilauric acid n-butyltin catalyst was added to the solvent, and the mixture was stirred evenly at 40-60 °C for 12-24 h to obtain SP-group modified SIS dynamic crosslinked polymer networks SIS-SP-UPy with different molecular weights and degrees of crosslinking.

7. The method for preparing a dynamic crosslinking network of spiropyran-modified SIS with mechanochromic properties according to claim 6, characterized in that, The total mass concentration of all monomers added in step S1 is 5%-25%.

8. The method for preparing a dynamic crosslinking network of spiropyran-modified SIS with mechanochromic properties according to claim 6, characterized in that, The nonpolar hydrocarbon solvent used in step S1 is selected from at least one of nonpolar aromatic hydrocarbons and nonpolar aliphatic hydrocarbons.

9. The method for preparing a dynamic crosslinking network of spiropyran-modified SIS with mechanochromic properties according to claim 6, characterized in that, In step S1, the alkyl lithium initiator is selected from n-butyllithium, sec-butyllithium, or tert-butyllithium.

10. The application of a dynamic crosslinking network of a spiropyran-modified SIS with mechanochromic properties as described in any one of claims 1-5, characterized in that, The SIS-SP-UPy solution can undergo a closed-loop SP-MC structure transformation under ultrasonic irradiation, exhibiting mechanochromic properties and possessing excellent mechanical properties and reprocessable performance, enabling the application of SIS thermoplastic elastomers in the fields of intelligent sensing and material flaw detection.

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