A polyurethane elastomer and a method for producing the same

Abstract

The application relates to a polyurethane elastomer and a preparation method thereof, a self-healing polyurethane containing a dynamic imidazole urea bond is synthesized by the reaction of 2,2-dimethyl methane and isoflurone diisocyanate, a physically cross-linked polyurethane elastomer containing a double dynamic bond of a copper ion coordination bond and an imidazole urea bond is prepared, and the application realizes efficient healing of the polymer under remote and infrared light.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of high polymer materials, and particularly relates to a polyurethane elastomer and a preparation method thereof. BACKGROUND

[0002] In recent years, with the development of dynamic covalent chemistry and supramolecular chemistry, more and more researchers have begun to pay attention to the field of constructing multifunctional polymer materials by dynamic bonds.

[0003] The flexible molecular structure of polyurethane materials can be adjusted to prepare materials with different properties to meet the needs of different application fields. However, in the long-term use of polyurethane materials, damage under external stress will reduce the mechanical properties of the materials, reduce the service life of the materials, and even cause safety hazards. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a polyurethane elastomer and a preparation method thereof.

[0005] The polyurethane elastomer of the present application has the following structure:

[0006]

[0007] In the formula, m is any integer between 1 and 30, n is any integer between 1 and 30, and x is any integer between 1 and 30.

[0008] The polyurethane elastomer based on the copper ion coordination of the present application has the following structure:

[0009]

[0010] In the formula, m is any integer between 1 and 30, n is any integer between 1 and 30, and x is any integer between 1 and 30. 10-40% of the 2,2-dimethyl imidazole ligand units in the polyurethane elastomer are coordinated with copper ions (i.e., the molar ratio of 2,2-dimethyl imidazole to copper salt in the polymer is 2:10%-2:40%).

[0011] The preparation method of the polyurethane elastomer of the present application comprises:

[0012] The raw materials containing polytetrahydrofuran diol PTMG, 2,2-dimethyl imidazole BIM and isofluroketone diisocyanate IPDI are reacted to obtain a polyurethane elastomer.

[0013] The preferred mode of the above preparation method is as follows:

[0014] The preparation method comprises:

[0015] polytetramethylene glycol PTMG, 2,2-dimethyl methane, a solvent are mixed, and then the mixture is heated and stirred under a protective gas, and then isophorone diisocyanate IPDI and a catalyst are added, and the mixture is reacted at 70-80 DEG C for 15-30 hours under a protective gas to obtain a polyurethane elastomer; the molar ratio of polytetramethylene glycol PTMG, 2,2-dimethyl methane, isophorone diisocyanate IPDI and the catalyst is 3.5-4.5:3.5-4.5:7.5-10.5:0.01-0.1;

[0016] or polytetramethylene glycol PTMG, 2,2-dimethyl methane, a first part of a catalyst, a solvent are mixed, and then the mixture is heated and stirred under a protective gas, and then isophorone diisocyanate IPDI is added, and the mixture is reacted at 70-80 DEG C for 15-30 hours under a protective gas, and then glycerol and a second part of a catalyst are added, and the mixture is further reacted for 4-30 hours to obtain a polyurethane elastomer; the molar ratio of polytetramethylene glycol PTMG, 2,2-dimethyl methane, the first part of the catalyst, isophorone diisocyanate IPDI, glycerol and the second part of the catalyst is 3.5-4.5:3.5-4.5:0.01-0.1:7.5-10.5:0-1.4:0.01-0.1.

[0017] Further preferably, the preparation reaction equation of the polyurethane elastomer is as follows:

[0018]

[0019] in the formula, m is any integer between 1 and 30, n is any integer between 1 and 30, and x is any integer between 1 and 30.

[0020] A preparation method of a polyurethane elastomer containing copper ion coordination according to the present application comprises:

[0021] The polyurethane elastomer solution is added with copper chloride, and then is left to stand to obtain a polyurethane elastomer containing copper ion coordination;

[0022] or polytetramethylene glycol PTMG, 2,2-dimethyl methane, a first part of a catalyst, a solvent are mixed, and then the mixture is heated and stirred under a protective gas, and then isophorone diisocyanate IPDI is added, and the mixture is reacted at 70-80 DEG C for 15-30 hours under a protective gas, and then glycerol and a second part of a catalyst are added, and the mixture is further reacted for 4-30 hours to obtain a polyurethane elastomer; the molar ratio of polytetramethylene glycol PTMG, 2,2-dimethyl methane, the first part of the catalyst, isophorone diisocyanate IPDI, glycerol and the second part of the catalyst is 3.5-4.5:3.5-4.5:0.01-0.1:7.5-10.5:0-1.4:0.01-0.1.

[0023] The solvent is N,N-dimethylformamide DMF, and the catalyst is dibutyltin dilaurate DBTDL; the protective gas is argon; and the heating and stirring of the mixture is heating to 70-80 DEG C and then stirring.

[0024] The molar ratio of the polytetrahydrofuran glycol PTMG, 2,2-dimethyl methane, the first part of the catalyst, isophorone diisocyanate IPDI, glycerol, the second part of the catalyst is 3.5-4.5:3.5-4.5:0.01-0.1:7.5-10.5:0-1.4:0.01-0.1; the molar ratio of the copper salt and 2,2-dimethyl methane is 0-0.5:2, and further, the molar ratio is 0.1-0.5:2.

[0025] Further preferably, the preparation reaction equation of the copper ion coordination containing polyurethane elastomer is as follows:

[0026]

[0027] In the formula, m is any integer between 1 and 30, n is any integer between 1 and 30, and x is any integer between 1 and 30. The polyurethane elastomer is applied to a light-controlled self-healing electronic device.

[0028] Advantages

[0029] The physical crosslinking polyurethane (Cu-BIMU-LPU) elastomer containing copper ion coordination bonds and imidazole urea double dynamic bonds in the application, the introduction of the double dynamic bonds ensures the efficient healing of the material, and the physical crosslinking network of the copper ion coordination significantly improves the mechanical properties of the material, and the prepared Cu-BIMU-LPU elastomer has efficient self-healing performance and good mechanical properties.

[0030] The application constructs BIMU-CPU and Cu-BIMU-CPU elastomers with three-dimensional covalent network structures. The coordination complex of copper ions and imidazole-urea bonds constructs a covalent crosslinking polyurethane elastomer with a triple synergistic effect of copper ions, called Cu-BIMU-CPU. First, the coordination of copper ions and imidazole-urea bonds enhances the dynamic exchange of imidazole-urea bonds and promotes the self-healing ability. Second, the physical crosslinking network provided by the coordination complex of copper ions improves the mechanical properties. More importantly, the special conjugated structure of imidazole-urea bonds endows the material with excellent near-infrared light triggered self-healing ability, and the coordination of copper ions significantly enhances the photothermal effect of the material. The triple synergistic effect of copper ions based on the coordination of copper ions and imidazole-urea bonds improves the service performance of the polymer material, while ensuring excellent mechanical strength and light triggered healing ability. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1(a) Local magnification of infrared absorption spectra of BIMU-LPU and Cu-BIMU-LPU; (b) Temperature-dependent infrared absorption spectra of Cu-BIMU-LPU; (c) Dynamic mechanical analysis curves of BIMU-LPU and (d) Cu-BIMU-LPU; (e) Thermogravimetric curves of BIMU-LPU and Cu-BIMU-LPU;

[0032] Figure 2 (a) Tensile stress-strain curves of BIMU-LPU and Cu-BIMU-LPU; (b) Continuous cyclic tensile curves of Cu-BIMU-LPU at different strains with strain increment; (c) Cyclic tensile curves of Cu-BIMU-LPU at 100% strain (continuous between 1st-10th cycle, 12 h waiting before 11th cycle); (d) Tensile stress-strain curves of BIMU-LPU samples before and after healing; (e) Tensile stress-strain curves of Cu-BIMU-LPU samples before and after healing;

[0033] Figure 3 Design of photo-thermal responsive self-healing Cu-BIMU-CPU elastomers;

[0034] Figure 4 (a) Photographs of BIMU-CPU and 10%, 20%, 40% Cu-BIMU-CPU before and after swelling in DMF; (b) Thermogravimetric curves of BIMU-CPU and 10%, 20%, 40% Cu-BIMU-CPU; (c) Dynamic mechanical analysis curves of BIMU-CPU and (d) 10%, (e) 20%, (f) 40% Cu-BIMU-CPU;

[0035] Figure 5 (a) Tensile stress-strain curves of BIMU-CPU and 10%, 20%, 40% Cu-BIMU-CPU samples; (b) Tensile strength and high-temperature healing rate of BIMU-CPU and 10%, 20%, 40% Cu-BIMU-CPU samples; (c) Tensile stress-strain curves of 20% Cu-BIMU-CPU sample before and after high-temperature healing;

[0036] Figure 6 (a) UV-Vis-NIR absorption spectra of Cu-BIMU and BIMU; (b) Fluorescence spectra of BIMU-CPU and 20% Cu-BIMU-CPU under excitation light of 365 nm; (c) Infrared thermal imaging camera measured BIMU-CPU and 10%, 20%, 40% Cu-BIMU-CPU under 808 nm laser irradiation with power density of 1.1 W / cm 2

[0037] ​(d) Surface temperature profile of 20%Cu-BIMU-CPU under 808 nm laser irradiation at power density of 0.6 W / cm 2 , 1.1 W / cm 2 , 1.6 W / cm 2 and 2.1 W / cm 2 ; (e) Surface temperature profile of 20%Cu-BIMU-CPU under 808 nm laser on / off irradiation at power density of 1.1 W / cm 2 ; (f) Tensile stress-strain curves of 20%Cu-BIMU-CPU sample before and after photothermal healing; (g) Thermal imaging pictures of 20%Cu-BIMU-CPU under 808 nm laser irradiation at power density of 1.1 W / cm 2 . DETAILED DESCRIPTION

[0038] The application is further described below in connection with specific embodiments. It will be understood, however, that these embodiments are set forth only for the purpose of illustration and are not intended to be limiting in any way. Furthermore, it will be understood that those skilled in the art can make various changes and modifications of the application without departing from its scope. It is therefore intended that the application be construed as including all such changes and modifications as fall within the scope of the appended claims.

[0039] Raw material sources:

[0040] 2,2-Diimidazole methane (97%) was purchased from Beijing Huaweiruike Chemical Co., Ltd.; Polytetrahydrofuran diol (Mn = 2000 g / mol) was purchased from Shanghai Macklin Biochemical Co., Ltd.; Isophorone diisocyanate (99%) and dibutyltin dilaurate (95%) were purchased from Aladdin Reagent (Shanghai) Co., Ltd.; Tetrahydrofuran (99.8%) and N,N-dimethylformamide (99.8%) were purchased from Biotang Co., Ltd.; Copper chloride (98%) was purchased from Adamas Beta (Shanghai) Co., Ltd.; Glycerol (99%) was purchased from Sigma-Aldrich Co.

[0041] Example related characterization and test

[0042] FTIR spectra were recorded on a Fourier transform infrared spectrometer (Nicolet iS50, Thermo Scientific). Spectra were collected by 32 scans with a spectral resolution of 4 cm -1 and a wavenumber range of 4000-500 cm -1Thermal stability was characterized by thermogravimetric analysis (Libra / 209F1, Netzsch) under nitrogen atmosphere at a heating rate of 10 °C / min. Dynamic mechanical analysis (DMA1, Mettler Toledo) was performed at a frequency of 1 Hz, a strain of 0.1%, and an instrument heating rate of 5 °C / min. Uniaxial tensile tests were performed using an electronic universal material testing machine (Exceed E42, MTS, 100 N) at a tensile rate of 50 mm / min. Cyclic tensile tests were performed at a tensile rate of 50 mm / min and an unloading rate of 10 mm / min. The sample was cut into two parts using a knife blade, and the two parts were then contacted and healed. The mechanical properties of the healed sample were then measured using an electronic universal material testing machine (Exceed E42, MTS, 100 N). UV-visible near-infrared absorption spectroscopy was performed using a UV-visible near-infrared absorption spectrometer (UV3600, Shimadzu, Japan) to characterize the two polymer solutions. Fluorescence emission intensity was characterized using a fluorescence spectrometer (QM / TM) with an excitation light of 365 nm. An 808 nm spatial output laser (DL-808-2000-T2, Shanghai Xilong) was placed 20 cm above the polymer material, and different samples were irradiated by adjusting the laser power. The real-time temperature of the sample surface was monitored using an infrared thermal imager (testo-885-2, Germany), and the temperature change of the sample over time under 808 nm near-infrared light irradiation was recorded

[0043] Example 1

[0044] Synthesis and preparation of BIMU-LPU:

[0045] Reaction equation:

[0046]

[0047] wherein m is any integer between 1 and 30, n is any integer between 1 and 30, and x is any integer between 1 and 30.

[0048] Polytetramethylene glycol (PTMG, 16 g, 8 mmol) was added to a reaction flask, and the reaction flask was warmed to 110 °C in a vacuum oven and vacuumed for 2 h to remove the bound water in the polytetramethylene glycol. After vacuuming at 110 °C for 2 h, the reaction flask was removed from the vacuum oven and sealed. After the reaction flask was cooled to room temperature, 2,2-bisimidazole methane (BIM, 1.1853 g, 8 mmol) and N,N-dimethylformamide (DMF, 36 mL) were added in sequence. An argon ball was inserted, and the reaction system was purged of air under the pressure of an argon atmosphere to ensure that the reaction was carried out under an argon atmosphere. The reaction flask was placed in an oil bath and warmed to 75 °C, and magnetic stirring (300 rpm) was started to mix the reaction materials. Isophorone diisocyanate (IPDI, 3.3565 g, 16 mmol) was added. Dibutyltin dilaurate (DBTDL, 0.0822 g) was dissolved in 4 mL of N,N-dimethylformamide (DMF) and added to the reaction flask. After all the materials were added, the entire reaction system was reacted under an argon atmosphere at 75 °C for 24 h. The polymer solution after the reaction was poured into a polytetrafluoroethylene mold, and the mold was placed in a vacuum oven at 80 °C and vacuumed to dry to obtain dark brown solid BIMU-LPU.

[0049] 3.2400 g of solid BIMU-LPU was dissolved in 30 mL of tetrahydrofuran (THF) solvent. After the material was dissolved, the solution was left to stand for several hours, and the solvent was evaporated at room temperature for 72 h in a fume hood. Then, the BIMU-LPU film with a thickness of about 0.7 mm was obtained by vacuuming at 50 °C for 12 h. The molar ratio of polytetramethylene glycol / isophorone diisocyanate / 2,2-bisimidazole methane was 1:2:1.

[0050] Preparation of Cu-BIMU-LPU

[0051] Reaction equation:

[0052]

[0053] In the formula, m is any integer between 1 and 30, n is any integer between 1 and 30, and x is any integer between 1 and 30.

[0054] Take 3.2400 g of solid BIMU-LPU, dissolve it in 30 mL of tetrahydrofuran (THF) solvent, after the material is fully dissolved, add copper chloride (CuCl2, 0.0170 g, 0.1262 mmol) to the solution, after the CuCl2 is fully mixed and uniform in the solution, stand for several hours, cast in a polytetrafluoroethylene mold and place in a fume hood at room temperature for 72 h to volatilize the solvent, then vacuumize in a vacuum oven at 50°C for 12 h to obtain a Cu-BIMU-LPU film with a thickness of about 0.7 mm.

[0055] As shown in Figure 1 (a), after the formation of copper ion coordination complex in the BIMU-LPU network, the characteristic peaks of C-H bond and C-N bond in the imidazole group are respectively blue-shifted from 997 cm -1 to 993 cm -1 , from 752 cm -1 to 748 cm -1 , which indicates that the copper ion in Cu-BIMU-LPU produces metal coordination with the imidazole group.

[0056] The high-temperature dissociation characteristics of the dynamic imidazole-urea bond in Cu-BIMU-LPU molecules were studied by temperature-increasing infrared spectroscopy. As shown in Figure 1 (b), in the temperature range of 25-120°C, there is no obvious characteristic peak of isocyanate group (N=C=O) around 2260 cm -1 in the infrared spectrum of Cu-BIMU-LPU. When the temperature rises to 140°C, the characteristic peak of isocyanate group begins to appear in the infrared spectrum. When the temperature rises to 180°C, the obvious characteristic peak of isocyanate group appears, at this time a large number of free isocyanate groups are produced by the dissociation of imidazole-urea bond in the polyurethane. With the increase of temperature, the dynamic cracking / recombination equilibrium of imidazole-urea bond begins to proceed in the direction of dissociating imidazole group and isocyanate group. The above results show that the imidazole-urea bond has high-temperature dissociation dynamics.

[0057] As shown in Figure 1 (e) are the thermal gravimetric curves of BIMU-LPU and Cu-BIMU-LPU, the temperature corresponding to the loss of 5% of the mass of the material is recorded as the thermal decomposition onset temperature (t 5％ ) of the material. As shown in the figure, the decomposition onset temperatures (t 5％ ) of BIMU-LPU and Cu-BIMU-LPU are 286°C and 274°C respectively, compared with BIMU-LPU, the t 5％decreased, mainly because copper ions as Lewis acid catalyzed the dissociation of dynamic imidazole-urea bond, promoted the thermal decomposition of the material under high temperature. Although the catalysis of copper ions reduced the thermal stability of Cu-BIMU-LPU, its thermal decomposition onset temperature (t 5％ ) was still much higher than the ambient temperature of normal use of polyurethane materials. Figure 1 (c) and (d) are the dynamic thermomechanical curves of BIMU-LPU and Cu-BIMU-LPU, respectively, as shown, BIMU-LPU and Cu-BIMU-LPU have similar trends of storage modulus, loss modulus and loss factor with temperature, the glass transition temperature (Tg) of BIMU-LPU and Cu-BIMU-LPU can be obtained from the maximum of the loss factor, which are -67°C and -65°C, respectively, and the coordination of copper ions has no obvious effect on the thermomechanical behavior and glass transition temperature of the elastomer. The low glass transition temperature of BIMU-LPU and Cu-BIMU-LPU indicates that the elastomer has a wide temperature range of use.

[0058] As shown in Figure 2 (a) is the stress-strain curve of BIMU-LPU and Cu-BIMU-LPU, after introducing copper ions into BIMU-LPU, the mechanical properties of the material are significantly improved. The tensile strength of Cu-BIMU-LPU (7.31±0.98 MPa) is 1.53 times that of BIMU-LPU before introducing copper ions (4.77±0.23 MPa), while the elongation at break of Cu-BIMU-LPU (1230±93%) is 1.22 times that of BIMU-LPU before introducing copper ions (1006±59%). The elastic modulus of Cu-BIMU-LPU (3.36±0.26 MPa) is also higher than that of BIMU-LPU before introducing copper ions (3.11±0.05 MPa). The coordination bond of copper ions forms physical crosslinking points between linear molecular chains, which restricts the slip of molecular chains under external force, and plays a reinforcing role on the elastomer. The fracture of metal coordination bond dissipates energy, further improving the mechanical properties of the material. At the same time, the coordination of copper ions promotes more flexible molecular chains to fold in the hard segment region, thereby forming longer hidden length, improving the elongation at break of the material.

[0059] The mechanical properties of the material are significantly improved after the formation of coordination bond, as shown in Figure 2(b) shows the stress-strain curves of Cu-BIMU-LPU in the strain-incremental continuous cyclic tensile test. In the strain-incremental continuous cyclic tensile test, the elastomer can almost recover to the original state after the first tensile cycle at a strain of 100%, indicating that the polymer network exhibits good elasticity at small strains. However, under the condition of gradually increasing strain in the subsequent cycles, part of the dynamic bonds dissociate and then reform at new positions with the deformation of the polymer network, resulting in an increasing hysteresis loop in the cyclic tensile test, showing more and more obvious residual strain. Figure 2 (c) shows the stress-strain curves of Cu-BIMU-LPU in the repeated cyclic tensile test with a maximum strain of 100%, the first tensile cycle dissipates the most energy, and in the subsequent increasing cycles, the hysteresis loop becomes smaller and smaller, because the reversible broken dynamic bonds are increasingly unable to recombine to dissipate enough energy. At the same time, the reversible broken dynamic bonds reform at new positions with the stretching of the material, which leads to the residual strain of the polymer network. After the material has experienced 10 cycles of tensile test, it is relaxed at room temperature for 12 h to fully recover the elastic properties, and the 11th cycle of tensile test is carried out.

[0060] The cyclic tensile test results show that the cyclic tensile curve after relaxation for 12 h has no obvious residual strain, and the hysteresis loop is slightly smaller than that of the first cycle tensile test, indicating that Cu-BIMU-LPU has excellent elasticity. The broken dynamic bonds during the first 10 cycles of tensile test also reversibly recombine at the original positions.

[0061] The self-healing properties of BIMU-LPU and Cu-BIMU-LPU were characterized, and the self-healing rate of the material was defined as the ratio of the tensile strength of the sample after healing to the original tensile strength of the sample. As shown in Figure 2 (d) shows the tensile stress-strain curves of BIMU-LPU sample before and after healing, after healing at 70°C for 2 h, the tensile strength of BIMU-LPU can recover to 4.51 ± 0.43 MPa, and the self-healing rate is 94.5% ± 9.1%. Figure 2(e) are the tensile stress-strain curves of Cu-BIMU-LPU before and after healing, and the tensile strength of Cu-BIMU-LPU can recover to 6.95 ± 0.21 MPa after healing for 2 h at 70 °C, and the self-healing rate is 95.1% ± 2.9%. Although the self-healing rates of BIMU-LPU and Cu-BIMU-LPU are very similar, and both reach a high self-healing rate of more than 90%, the recovered tensile strength of Cu-BIMU-LPU is significantly higher than that of BIMU-LPU under the same healing conditions, and the former is 1.54 times that of the latter. The recombination of dynamic imidazole-urea bonds and copper ion coordination bonds in the molecular network of Cu-BIMU-LPU simultaneously promotes the self-healing process of the material.

[0062] As shown in Figure 2 (e), further study the effect of different healing temperatures on the self-healing properties of Cu-BIMU-LPU samples within the same time. The tensile strength of Cu-BIMU-LPU samples only recovers to 1.17 ± 0.07 MPa after healing for 2 h at room temperature of 25 °C, and the self-healing rate is only 16.1% ± 0.9%. It can be seen that it is difficult to activate the chain rearrangement of Cu-BIMU-LPU molecular network and the recombination of dynamic covalent bonds and coordination bonds at room temperature, and the two material sections after cutting are only bonded together by weak hydrogen bonds, and effective healing is not achieved. When the healing temperature is increased to 50 °C, the tensile strength of Cu-BIMU-LPU samples also only recovers to 3.98 ± 0.48 MPa after healing for 2 h, and the self-healing rate is only 54.4% ± 6.6%. Compared with the healing condition when the healing temperature is 25 °C, after 2 h of healing at 50 °C, the Cu-BIMU-LPU molecular network is activated by the stimulation of higher temperature to activate the partial rearrangement of molecular chain segments and the partial recombination of dynamic bonds, so that the Cu-BIMU-LPU sample recovers certain mechanical properties. However, under the condition of 50 °C, it is difficult to achieve efficient chain rearrangement of Cu-BIMU-LPU molecular network within 2 h of healing time. When the healing temperature is further increased to 70 °C, the higher temperature stimulation further improves the chain segment migration ability of the polymer network, and promotes the dynamic dissociation / recombination of imidazole-urea bonds and metal coordination bonds, so that the Cu-BIMU-LPU sample basically recovers to the original mechanical strength level.

[0063] Example 2

[0064] Synthesis and preparation of BIMU-CPU:

[0065]

[0066] In the formula, m is any integer between 1 and 30, n is any integer between 1 and 30, and x is any integer between 1 and 30.

[0067] Polytetrahydrofuran diol (PTMG, 4.8 g, 2.4 mmol) was added to the reaction flask. The mixture was heated to 110 °C and evacuated for 2 hours in a vacuum oven to thoroughly remove bound water from the PTMG. After evacuation at 110 °C for 2 hours, the reaction flask was removed from the vacuum oven and sealed. Once the flask had cooled to room temperature, 2,2-diimidazolium methane (BIM, 0.3556 g, 2.4 mmol), dibutyltin dilaurate (DBTDL, 0.0163 g), and N,N-dimethylformamide (DMF, 4 mL) were added sequentially. An argon balloon was inserted to purge air from the reaction system under argon pressure, ensuring the reaction proceeded under an argon atmosphere. The reaction flask was placed in an oil bath and heated to 75°C. A magnetic stirrer (300 rpm) was used to thoroughly mix the reactants. Then, isoflurane diisocyanate (IPDI, 1.3070 g, 5.88 mmol) was added, and the reaction was continued at 75°C under an argon atmosphere for 20 h. A solution of glycerol (GLY, 0.0663 g, 0.72 mmol) dissolved in 2 mL of LDMF and 2 drops of DBTDL were added to the reaction flask, and the reaction was continued at 75°C under an argon atmosphere for 4 h. The resulting polymer solution was poured into a polytetrafluoroethylene mold and heated gradually from 60°C to 75°C over 24 h in a vacuum oven. Finally, the reaction system was thoroughly dried under vacuum at 75°C for 36 h to obtain a dark brown BIMU-CPU membrane.

[0068] Example 3

[0069] Synthesis and Preparation of Cu-BIMU-CPU

[0070]

[0071] In the formula, m = any integer between 1 and 30, n = any integer between 1 and 30, and x = any integer between 1 and 30.

[0072] Polytetrahydrofuran diol (PTMG, 4.8 g, 2.4 mmol) was added to the reaction flask, and the mixture was heated to 110 °C in a vacuum oven.

[0073] The reaction flask was evacuated for 2 hours to thoroughly remove bound water from the polytetrahydrofuran diol. After evacuating at 110°C for 2 hours, the reaction flask was removed from the vacuum oven and sealed. Once the flask had cooled to room temperature, 2,2-diimidazolium methane (BIM, 0.3556 g, 2.4 mmol), dibutyltin dilaurate (DBTDL, 0.0163 g), copper chloride (CuCl2, 8.1 mg, 16.1 mg, 32.3 mg, and 64.5 mg), and N,N-dimethylformamide (DMF, 4 mL) were added sequentially. An argon balloon was inserted to purge air from the reaction system under argon pressure, ensuring the reaction proceeded under an argon atmosphere. The reaction flask was placed in an oil bath and heated to 75°C. A magnetic stirrer (300 rpm) was turned on to ensure thorough mixing of the reactants. Then, isoflurane diisocyanate (IPDI, 1.3070 g, 5.88 mmol) was added, and the reaction was continued at 75°C under an argon atmosphere for 20 h. A solution of glycerol (GLY, 0.0663 g, 0.72 mmol) dissolved in 2 mL of LDMF and 2 drops of DBTDL were added to the reaction flask, and the reaction was continued at 75°C under an argon atmosphere for 4 h. The resulting polymer solution was poured into a polytetrafluoroethylene mold and heated in a vacuum oven, gradually increasing the temperature from 60°C to 75°C over 24 h. Finally, the reaction system was thoroughly dried in a vacuum oven at 75°C for 36 hours to obtain dark brown 10%, 20%, and 40% Cu-BIMU-CPU films (10%, 20%, and 40% represent the presence of 10%, 20%, and 40% molar ratios of 2,2-diimidazolium methane ligand units in the polymer that coordinate with copper ions, respectively) (10%, 20%, and 40% represent the molar ratios of 2,2-diimidazolium methane to copper salt in the polymer that are 2:10%, 2:20%, and 2:40%, respectively).

[0074] like Figure 3 As shown, glycerol with trihydroxy functionality was used as a crosslinking agent to form a three-dimensional covalent crosslinked network in the polymer network, which effectively improved the mechanical properties and chemical solvent stability of the polymer elastomer.

[0075] like Figure 4 As shown in (a), BIMU-CPU and 10%, 20%, and 40% Cu-BIMU-CPU elastomers were cut into rectangular strips and placed in sample vials containing 5 mL of LDM solvent. After 48 hours, obvious swelling was observed in all four materials. This indicates that the BIMU-CPU / Cu-BIMU-CPU material has a three-dimensional chemical cross-linked structure.

[0076] Thermogravimetric analysis (TGA) was used to characterize the thermal stability of BIMU-CPU and Cu-BIMU-CPU elastomers with different copper ion coordination contents. The temperature at which the elastomer material loses 5% of its mass is denoted as the thermal decomposition temperature (t). 5％ ).like Figure 4 (b) shows the thermal decomposition temperatures (t) of BIMU-CPU and 10%, 20%, and 40% Cu-BIMU-CPU. 5％ Within the range of 274-281℃, different types of elastomer materials have very similar thermal decomposition temperatures (t). 5％ This indicates that the introduction of copper ion coordination bonds did not affect the thermal stability of the covalently cross-linked network. The thermal decomposition temperature (t) of the above materials... 5％ The temperatures are all much higher than the temperatures required for subsequent self-healing of the material, which ensures the thermal stability of the material during subsequent self-healing and other research processes.

[0077] The thermomechanical properties of BIMU-CPU and Cu-BIMU-CPU elastomers with different copper ion coordination contents were characterized by thermomechanical analysis instruments, such as... Figure 4 As shown in (c, d, e, f), the storage modulus, loss modulus, and loss factor of the above materials all exhibit similar trends with temperature, indicating that the introduction of copper ion coordination complexes did not alter the thermomechanical behavior of the polymer molecular chains. The maximum loss factor yields glass transition temperatures of -61℃, -62℃, -59℃, and -57℃ for BIMU-CPU and 10%, 20%, and 40% Cu-BIMU-CPU elastomers, respectively. These similar glass transition temperatures indicate that copper ion coordination did not significantly affect the transition of the polymer network between the glassy and elastic states. The low glass transition temperatures of BIMU-CPU and 10%, 20%, and 40% Cu-BIMU-CPU elastomers suggest a wide operating temperature range. With increasing temperature, the relaxation of polymer chain segments accelerates, enhancing the migration ability of the polymer molecular chains. Unlike traditional thermosetting polyurethane materials where the storage modulus gradually stabilizes in the high-elasticity region, the storage modulus of BIMU-CPU and 10%, 20%, and 40% Cu-BIMU-CPU elastomers continuously decreases with increasing temperature. This indicates that the reversible dissociation of dynamic bonds at high temperatures alters the polymer's rheological behavior, further reducing its storage modulus. However, because the covalent crosslinked network does not dissociate with the reversible recombination of dynamic bonds, the polymer maintains a covalent crosslinked state with a storage modulus greater than its loss modulus throughout the process, ensuring good thermal stability of the material during use.

[0078] The mechanical properties of BIMU-CPU and Cu-BIMU-LPU elastomers with different copper ion coordination contents were characterized by single tensile tests using an electronic universal testing machine.Figure 5 (a) shown, the mechanical strength of BIMU-CPU and 10%, 20%, 40% Cu-BIMU-CPU elastomers were 14.06 ± 1.82 MPa, 24.66 ± 0.42 MPa, 27.56 ± 1.73 MPa, 35.63 ± 1.60 MPa, respectively; the elongation at break were 766.02% ± 23.85%, 941.75% ± 72.46%, 800.04% ± 58.57%, 793.99% ± 49.79%, respectively; the elastic modulus were 3.32 ± 0.20 MPa, 3.35 ± 0.27 MPa, 4.10 ± 0.40 MPa, 4.39 ± 0.36 MPa, respectively. Compared with BIMU-LPU and Cu-BIMU-LPU elastomers with linear structure, the mechanical strength of all the elastomers were significantly improved due to the construction of three-dimensional covalent crosslinking network of trihydroxy glycerol crosslinking. With the increase of copper ion content, the tensile strength of the elastomers gradually increased, and the tensile strength of 40% Cu-BIMU-CPU elastomer with the highest copper ion content (35.63 ± 1.60 MPa) was 2.53 times that of BIMU-CPU elastomer without copper ion coordination (14.06 ± 1.82 MPa). The coordination complex formed by copper ions and imidazole groups provided a second crosslinking network in addition to the covalent crosslinking network of the polymer network, and the force of the physical crosslinking points further strengthened the force between the molecular chains. The more the content of copper ion coordination bond, the higher the density of physical crosslinking formed in the polymer network, and the interaction force between the high molecular chains also increased, and the strong double crosslinking network further bound the chain segment sliding under external stress, which macroscopically manifested as the increase of tensile strength and elastic modulus of the material. With the increase of copper ion content, the elongation at break of the elastomers showed a trend of first increasing and then decreasing. This may be because the lower content of copper ion coordination complex made part of the polymer chains fold in the hard phase, and the hidden length was released after the phase separation in the hard phase; while the higher content of copper ion coordination complex formed a higher density of physical crosslinking points in the molecular network, which to some extent shortened the length between the soft segments.

[0079] The self-healing properties of BIMU-CPU and 10%, 20%, 40% Cu-BIMU-CPU elastomers were evaluated by the recovery of mechanical properties after the sample was completely cut. The sample was completely cut into two parts with a blade, and the fracture surfaces of the two parts were gently contacted. The non-covalent bond interaction in the material made the fracture surfaces of the two parts recombine into a whole after contact. After the healing conditions were set, the mechanical properties of the sample were tested by single tensile test using an electronic universal testing machine. The self-healing rate of the material was defined as the ratio of the tensile strength of the healed sample to the original tensile strength of the sample. For example, Figure 5(b) As shown, the tensile strength of BIMU-CPU and 10%, 20%, 40% Cu-BIMU-CPU elastomers after healing for 4 h at 100 °C was 10.53 ± 1.40 MPa, 22.08 ± 2.10 MPa, 26.34 ± 1.82 MPa and 6.44 ± 3.53 MPa, respectively, and the self-healing rate was 74.8% ± 10.0%, 89.6% ± 8.5%, 95.6% ± 6.6% and 18.1% ± 10.0%, respectively. The self-healing rate of BIMU-CPU elastomer was only 74.8% ± 10.0%, and the original mechanical strength was not recovered, because the trifunctional crosslinker was introduced into the molecular backbone to form a covalently bonded three-dimensional network. The crosslinking points restrict the chain segment movement, making it difficult for the polymer chain to rearrange and fully move at the cut surface, and cannot provide sufficient reaction sites for the reversible recombination of dynamic imidazole-urea bonds. With the introduction of copper ion coordination complexes into the polymer network, the catalytic effect of copper ions on the reversible cleavage of imidazole-urea bonds improves the self-healing performance of the material. When the coordination ratio of copper ions to imidazole groups increases to 10% and 20%, the self-healing rate of the material gradually increases with the increase of copper ion content. Especially, the self-healing rate of 20% Cu-BIMU-CPU elastomer is as high as 95.6% ± 6.6%, and its mechanical properties are basically restored to the original level, which is mainly because the copper ions catalyze the dynamic reaction of imidazole-urea bonds, and the molecular main chain is continuously cleaved into shorter molecular chains with the dissociation of imidazole-urea bonds, improving the movement ability of the chain segments. The polymer molecular network migrates enough molecular chain segments to the cut surface in the process of continuous rearrangement, providing sufficient reaction sites for the reversible recombination of dynamic imidazole-urea bonds. At the same time, the exchange rate of dynamic imidazole-urea bonds is improved under the catalysis of copper ions, and these two factors together provide the conditions for the high-efficiency self-healing of 20% Cu-BIMU-CPU elastomer. However, when the coordination ratio of copper ions to imidazole groups increases to 40%, the self-healing rate of 40% Cu-BIMU-CPU elastomer decreases sharply to 18.1% ± 10.0%, and the tensile strength is only restored to 6.44 ± 3.53 MPa, which is mainly because the introduction of a large amount of copper ion coordination complexes leads to the formation of more dense physical crosslinking points in the polymer network. The strong force between the molecular chains significantly improves the tensile resistance of the material, but on the other hand, it more tightly binds the movement of the chain segments, making it difficult for the molecular network to undergo sufficient thermal motion and chain rearrangement, and further reducing the reaction sites for the dynamic bond exchange at the cut surface. In addition, the tight entanglement between the molecular chains also limits the dissociation and recombination of the dynamic imidazole-urea bonds to some extent. The above research results show that the appropriate introduction of copper ion coordination complexes can effectively balance the contradiction between the mechanical properties and self-healing properties of covalently crosslinked polymer materials.The comprehensive mechanical properties and self-healing properties were evaluated for the four prepared samples, and it was considered that the 20% Cu-BIMU-CPU elastomer had the most excellent performance, which was a kind of elastomer material with excellent tensile resistance and self-healing performance.

[0080] As Figure 5 As shown in (c), further study was made on the influence of different time and different healing temperature conditions on the self-healing performance of the 20% Cu-BIMU-CPU elastomer. After the 20% Cu-BIMU-CPU sample was healed at 100°C for 2h, the tensile strength was only restored to 13.75±1.07MPa, and the self-healing rate was only 49.9%±3.9%. Even under the same temperature conditions, shorter healing time did not allow the molecular network of the 20% Cu-BIMU-CPU to undergo sufficient chain segment rearrangement and dynamic covalent bond and coordination bond exchange, and the molecular network on the material cut surface was only connected together through weak non-covalent interaction and partially completed covalent bond recombination, and effective healing was not achieved, indicating that polymer material healing often requires more sufficient time. Under the condition of maintaining the original healing for 4h, the healing temperature of the 20% Cu-BIMU-CPU sample was reduced to 80°C, and the result showed that the tensile strength of the material after healing was only 14.99±0.79MPa, and the self-healing rate was only 54.4%±2.9%. This is mainly because lower temperature is difficult to fully activate the movement ability of polymer molecular chain segments and the reversible exchange of dynamic bonds, so that the 20% Cu-BIMU-CPU sample cannot recover to the original mechanical strength level, which shows that polymer material healing also requires higher temperature stimulation. The above research results show that the healing of covalently crosslinked polymer materials can be achieved by increasing the healing temperature and prolonging the healing time to fully rearrange the molecular chains and recombine the dynamic bonds, so as to more efficiently realize the healing of the material and restore its original mechanical properties.

[0081] The special conjugated structure of imidazole-urea bond makes it have the potential to construct near-infrared light responsive materials. BIMU-LPU / Cu-BIMU-LPU has the same imidazole-urea bond structure and copper ion-imidazole group coordination ratio as BIMU-CPU / 20% Cu-BIMU-CPU. BIMU-LPU and Cu-BIMU-LPU were respectively matched into 10mg / mL DMF solution, and the ultraviolet visible near-infrared absorption spectrum test was carried out on the imidazole-urea bond (BIMU) group and the complex (Cu-BIMU) group formed by the coordination of copper ion and imidazole-urea bond. As Figure 6(a) shows that both BIMU and Cu-BIMU groups exhibit a wide absorption peak platform in the near-infrared region around 800 nm, indicating that BIMU and Cu-BIMU groups can absorb near-infrared light with a wavelength of 808 nm as a light-to-heat conversion group, which broadens the design idea for constructing near-infrared light-responsive self-healing polymer materials. More importantly, as a urea bond group and a urea bond metal coordination complex, BIMU and Cu-BIMU groups can be easily introduced into the main chain of the polymer by addition polymerization with isocyanate, avoiding the problems of difficult preparation of composite materials and poor comprehensive mechanical properties caused by external light-heat fillers. In addition, the absorption peak intensity of Cu-BIMU group with copper ion coordination complex is significantly greater than that of BIMU group before coordination around 800 nm, because the metal coordination bond also contributes to the absorption of near-infrared light to a certain extent, which macroscopically improves the light-to-heat conversion ability of the polymer.

[0082] In order to further study the enhancement of copper ion coordination on the light-heat effect of imidazole-urea bond group, the fluorescence spectrum was used to test the steady-state fluorescence emission scanning of BIMU-CPU and 20% Cu-BIMU-CPU materials with an excitation light of 365 nm. As shown in Figure 6 (b), BIMU-CPU exhibits strong fluorescence emission in the wavelength range of 400-700 nm, indicating that a large part of the absorbed light energy of the imidazole-urea bond group in BIMU-CPU material is released in the form of fluorescence emission. While 20% Cu-BIMU-CPU has very low fluorescence emission intensity in the wavelength range of 400-700 nm, which may be because the coordination of copper ion and imidazole group forms a ligand to metal ion charge transfer, which quenches the fluorescence emission of imidazole group and significantly reduces the fluorescence emission intensity of the coordination complex. The above results show that most of the light energy absorbed by the complex formed by the copper ion coordination bond and the imidazole-urea bond in the 20% Cu-BIMU-CPU material is converted into heat, and the synergistic effect of copper ion significantly enhances its light-to-heat conversion ability.

[0083] In order to further study the light-heat response of the polymer material under 808 nm near-infrared light irradiation, the infrared thermal imager was used to record the curve of the surface temperature of the material changing with time under the irradiation of 808 laser emitter. The 808 nm spatial output laser was placed 20 cm above the polymer material to keep the spot area (5x5 mm 2 ) fixed, and the power density of the relative near-infrared light was obtained by adjusting the emission power of the laser emitter. As shown in Figure 6 (c), the 808 nm near-infrared power density was adjusted to 1.1 W / cm 2The temperature of the surface of BIMU-CPU and 10%, 20%, 40% Cu-BIMU-CPU materials increased from room temperature to 42°C, 64°C, 73°C, 78°C respectively within 120s under the irradiation of near-infrared light at room temperature of 25°C. The above materials reached the balance of heat exchange with the outside air after 120s, and the temperature of the surface of the materials did not change significantly. The results of temperature rise showed that the increase of copper ion content effectively enhanced the light-heat conversion ability of the polymer material, which proved the synergistic enhancement effect of copper ion of metal coordination complex on the photo-thermal effect of polymer material. As shown in Figure 6 (d), the surface of 20% Cu-BIMU-CPU material was irradiated by near-infrared light with power density of 0.6 W / cm 2 , 1.1 W / cm 2 , 1.6 W / cm 2 , 2.1 W / cm 2 , respectively. The temperature of the surface of the material was 41°C, 72°C, 93°C, 115°C, respectively, after 120s. With the increase of the power density of near-infrared light, the material converted more heat after absorbing more light energy. As shown in Figure 6 (e), the surface of 20% Cu-BIMU-CPU material was irradiated by near-infrared light with power density of 1.1 W / cm 2 . After 30s of irradiation, the laser emitter was turned off to stop irradiation. After 30s of stopping irradiation, the laser emitter was turned on to start irradiation. The process of 60s was a cycle. The surface of the material was irradiated by laser for 5 cycles. The experimental results showed that during the 5 cycles of laser irradiation, the surface temperature of the material increased rapidly and stabilized at 62-65°C after 30s of irradiation, and the surface temperature of the material decreased rapidly and stabilized at 29-31°C after 30s of stopping irradiation, which proved the excellent photo-thermal stability of 20% Cu-BIMU-CPU material. As shown in Figure 6 (g), the surface of 20% Cu-BIMU-CPU material was irradiated by near-infrared light with power density of 1.1 W / cm 2 , and the temperature of the surface of the material was monitored and photographed in real time by an infrared thermal imager. The thermal imaging pictures showed that the temperature of 20% Cu-BIMU-CPU material increased from 26°C to 58°C after 20s of near-infrared light irradiation, the temperature was 67°C after 40s of irradiation, and the temperature was 70°C after 60s of irradiation. The fast temperature rise rate indicated that 20% Cu-BIMU-CPU material had excellent near-infrared light responsiveness.

[0084] It has been proved that 20% Cu-BIMU-CPU material has the photothermal effect of copper ion synergistic strengthening. In order to further study the photothermal self-healing ability of 20% Cu-BIMU-CPU material under near-infrared light irradiation, the sample of 20% Cu-BIMU-CPU was completely cut into two parts by a blade, and the two parts of the sample after cutting were contacted by manual butt joint. An 808 nm spatial output laser was placed 20 cm above the sample after splicing and recombination. After irradiation of near-infrared light with a power density of 1.1 W / cm 2 for a certain time, the mechanical properties of the sample were tested by a single tensile test using an electronic universal testing machine, and the mechanical properties of the sample after healing were obtained. The photothermal self-healing performance of the material was evaluated by comparing the mechanical properties of the material before and after healing. The photothermal self-healing rate of the material was defined as the ratio of the tensile strength of the sample after photothermal healing to the original tensile strength of the sample. As shown in Fig. Figure 6 (f), the tensile strength of the 20% Cu-BIMU-CPU sample after splicing and recombination was recovered to 21.31 ± 0.18 MPa and 26.99 ± 1.89 MPa after irradiation of near-infrared light with a power density of 1.1 W / cm 2 for 10 min and 20 min, respectively, and the self-healing rates were 77.3% ± 6.5% and 94.9% ± 9.4%, respectively. The photothermal self-healing induced by near-infrared light is essentially a way of triggering the reversible reaction of dynamic bonds with thermal stimulation. After irradiation of near-infrared light, the copper ion synergistic photothermal effect strengthens the compound formed by copper ion coordination bonds and imidazole-urea bonds, which releases the absorbed light energy in the form of heat, forming a high-efficiency heat accumulation in the irradiated area. This precise photo-heating process of the material damage site under near-infrared light irradiation can accurately concentrate heat in a specific area, thereby realizing the rapid thermal motion of molecular chains and the reversible recombination of dynamic bonds in the irradiated area, to achieve efficient photothermal healing. The experimental results show that increasing the irradiation time of near-infrared light from 10 min to 20 min can basically restore the tensile resistance of the material to the original level, which is mainly because sufficient light irradiation time allows the polymer chain segments to rearrange under concentrated thermal stimulation, providing a large number of reaction sites for the reversible exchange of dynamic bonds, and the dynamic bonds are rapidly and reversibly cleaved / recombined under the high-efficiency heat accumulation, thereby restoring the original mechanical properties. Compared with the high-temperature healing at 100°C, which requires 4 h to restore the original mechanical strength of the material, the photothermal self-healing response to near-infrared light reduces the healing time to 20 min under the action of copper ion synergistic photothermal effect, and basically restores the original mechanical properties.

[0085] The application designs and prepares polyurethane elastomer Cu-BIMU-LPU with excellent self-healing performance and mechanical properties by simultaneously introducing dynamic imidazole urea bond and copper ion coordination bond into polyurethane. The copper ion-imidazole group coordination complex is the key to molecular network design, and the copper ion coordination as a physical crosslinking point improves the mechanical properties of the material, and its dynamic nature promotes the reorganization of the polymer network, giving the material excellent self-healing properties.

[0086] The application also constructs BIMU-CPU and Cu-BIMU-CPU elastomers with covalent crosslinking network. The formation of the covalent crosslinking network significantly improves the mechanical properties of the material, and the 20% Cu-BIMU-CPU elastomer containing both covalent crosslinking and physical crosslinking has a double crosslinking network, which further improves the mechanical properties of the material, and also has high efficient high temperature self-healing rate. Through the test of photo-thermal conversion performance and photo-thermal self-healing performance, the synergistic enhancement effect of copper ions on the photo-thermal performance of 20% Cu-BIMU-CPU elastomer is studied. Based on the above research structure, it is proved that the copper ions have a triple synergistic enhancement effect on the mechanical, self-healing and photo-thermal properties of the 20% Cu-BIMU-CPU elastomer.

Claims

1. A copper ion-coordinated polyurethane elastomer, characterized by, The structural formula is shown as follows: In the formula, m is any integer between 1 and 30, n is any integer between 1 and 30, and x is any integer between 1 and 30; wherein the molar ratio of 2,2-dimethyl methane to copper salt in the polymer is 2:20%.

2. A method for preparing the copper ion-coordinated polyurethane elastomer according to claim 1, comprising: mixing polytetrahydrofuran glycol PTMG, 2,2-dimethyl methane, a catalyst, a copper salt, and a solvent, and then stirring and mixing under the protection of argon gas, and then adding isophorone diisocyanate IPDI, and then stirring and mixing under the protection of argon gas at 70-80°C for 15-30 hours, and then adding glycerol and a catalyst, and then continuing to react for 4-30 hours.

3. The preparation method according to claim 2, characterized in that, The solvent is N,N-dimethylformamide DMF, the catalyst is dibutyltin dilaurate DBTDL, and the copper salt includes one or more of hydrochloric acid copper, copper sulfate, copper bromide, copper acetate, copper nitrate, copper citrate, copper methane sulfonate, copper acetylpropionate, copper fluoroborate, copper difluoride, copper gluconate, basic copper carbonate, copper sulfide, copper thiocyanate, copper iodide, copper niobate, copper ethoxide, copper phosphate, copper oxalate, copper trifluoroacetate, tetraethylnitrile copper hexafluorophosphate, copper pyrophosphate, copper stearate, copper bis(trifluoromethanesulfonate) imide, and copper trifluoromethanesulfonate.

4. The preparation method according to claim 2, characterized in that, The molar ratio of the polytetrahydrofuran glycol PTMG, 2,2-dimethyl methane, isophorone diisocyanate IPDI, and glycerol is 3.5-4.5:3.5-4.5:7.5-10.5:0-1.

4.

5. The copper ion-coordinated polyurethane elastomer according to claim 1 is applied in light-controlled self-healing electronic devices.

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