A medium-low temperature shape memory polyurethane flexible conductive elastomer and its preparation method

Abstract

The present invention discloses a medium and low temperature shape memory polyurethane flexible conductive elastomer and a preparation method thereof. First, a polyurethane prepolymer is formed by a bis-NCO-functionalized ureidopyrimidinone (UPy) derivative (UPy-2NCO) and an -OH-terminated flexible chain molecule, and then reacted with a diamine to obtain a polyurethane elastomer. Subsequently, using the polyurethane elastomer as a substrate, silver nanoparticles are directly deposited onto the polyurethane elastomer film by hydrazine hydrate reduction of silver trifluoroacetate to prepare a high tensile strength and medium and low temperature shape memory function polyurethane-based composite flexible conductive elastomer. Compared with the prior art, the flexible conductive elastomer has ultra-high tensile strength and deformation behavior, excellent electrical conductivity, good shape memory behavior, outstanding medium and low temperature resistance performance, stable sensing performance and good electrical conductivity repair performance, and can be used as a flexible sensor and a temperature control element, and can be applied to fields such as electronic circuits and aerospace.

Description

Technical Field

[0001] The present invention relates to a flexible conductive elastomer of a polyurethane-based composite material with high tensile strength and medium-low temperature shape memory function and a preparation method thereof, belonging to the technical field of functional high-performance polymer materials and composite materials. Background Art

[0002] Based on flexible elastomers and conductive particles is one of the common methods for preparing flexible conductive composites. Polyurethane elastomers, due to their light weight, good mechanical properties, reversible elastic response, cost-effectiveness, and high processing performance, have significant application value in flexible conductive materials. With the expansion of the application fields of flexible conductive materials such as flexible sensors and wearable devices, higher requirements are imposed on their reliability and conductivity. Among many conductive materials, nano-silver has outstanding stable conductivity and low price, so it is widely used in the preparation of conductive composites. Research shows that directly forming a blended conductive composite material of nano-silver and an elastomer will significantly reduce the mechanical properties and mechanical stability of the material. The reason is the poor interfacial interaction force between the nano-particles and the substrate and the easy agglomeration of the nano-particles. When preparing conductive composites by spraying and solution impregnation methods, problems such as poor interfacial adhesion often exist, which is likely to cause particle detachment, thus affecting the stability of the conductive performance. Therefore, preparing flexible conductive composites with excellent mechanical and conductive properties has positive significance for expanding their applications. In addition, traditional flexible elastomers often have a single low-temperature glass transition temperature (T g ), which is generally applicable to low-temperature and normal-temperature environments. With the strictness of the material usage environment, the development of flexible conductive materials with excellent heat resistance is required, and traditional flexible conductive composites can no longer meet the development needs. It can be seen that constructing flexible conductive composites with high and low-temperature usage performance has obvious application value. Summary of the Invention

[0003] Aiming at the application bottleneck problem of existing flexible conductive composites, the present invention provides a flexible conductive elastomer of a polyurethane-based composite material with high tensile strength and medium-low temperature shape memory function and a preparation method thereof; the prepared conductive elastomer not only has excellent mechanical properties and conductive properties, but also has high and low-temperature usage performance, shape memory behavior, and good self-healing electrical properties.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] A preparation method of a medium-low temperature shape memory polyurethane flexible conductive elastomer, comprising the following steps:

[0006] (1) React a bis-NCO-functionalized ureidopyrimidinone derivative (UPy-2NCO) with an -OH-terminated flexible chain molecule to obtain a polyurethane prepolymer, and then add a diamine and continue the reaction to obtain a polyurethane elastomer;

[0007] (2) Immerse the polyurethane elastomer in a silver compound solution, take it out and perform reduction treatment to obtain a medium-low temperature shape memory polyurethane flexible conductive elastomer.

[0008] In the above technical solution, the reaction between the bis-NCO-functionalized ureidopyrimidinone derivative and the -OH-terminated flexible chain molecule is carried out in the presence of a catalyst and under an inert gas, the reaction temperature is 60-80 °C, and the reaction time is 1-4 hours; the process of the subsequent reaction is to react at 20-60 °C for 12-24 h, and then react at 60-180 °C for 2-24 h. Preferably, the inert gas includes nitrogen.

[0009] In the above technical solution, the silver compound solution includes a silver trifluoroacetate alcohol solution; the reduction treatment is a chemical reduction treatment, and the reducing agent used includes hydrazine hydrate; the number of times of immersing the polyurethane elastomer in the silver compound solution, taking it out and performing reduction treatment is 1-10 times, preferably 1-5 times; the time for the polyurethane elastomer to be immersed in the silver solution is 20-30 minutes, and the time for the reduction treatment is 3-10 minutes. Here, the time refers to the time for single immersion and reduction treatment.

[0010] In the above technical solution, the molar ratio of the bis-NCO-functionalized ureidopyrimidinone derivative, the -OH-terminated flexible chain molecule, the catalyst, and the diamine is (5-60):(1-10):(0-0.1):(1-10); preferably, the molar ratio of the bis-NCO-functionalized ureidopyrimidinone derivative, the -OH-terminated flexible chain molecule, the catalyst, and the diamine is (5-20):(2.5-10):(0.01-0.08):(2-10).

[0011] In the above technical solution, the bis-NCO-functionalized ureidopyrimidinone derivative is a diisocyanate-modified ureidopyrimidinone derivative; the -OH-terminated flexible chain molecule includes polytetrahydrofuran and / or polyether polyol; the diamine includes polyetheramine and aromatic diamine.

[0012] Preferably, the diisocyanate includes one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate; the ureidopyrimidinone derivative includes 5-(2-hydroxyethyl)-6-methyl-2-aminouracil.

[0013] The present invention discloses a medium-low temperature shape memory polyurethane flexible conductive elastomer prepared according to the preparation method of the above medium-low temperature shape memory polyurethane flexible conductive elastomer. Among them, the temperature range of the medium-low temperature is -74 °C to 136 °C.

[0014] The present invention discloses the application of the above-mentioned medium and low temperature shape memory polyurethane flexible conductive elastomer in the preparation of functional materials; the functional materials include one or several of elastic materials, shape memory materials, self-healing materials, and conductive materials.

[0015] The present invention discloses the application of the above-mentioned medium and low temperature shape memory polyurethane flexible conductive elastomer in the preparation of functional devices; for example, the elastomer can be used for the preparation of flexible sensors and temperature control elements.

[0016] As an embodiment of the present invention, the preparation process of the medium and low temperature shape memory polyurethane flexible conductive elastomer is as follows:

[0017] (1) Under a nitrogen atmosphere and in the presence of a catalyst, react a bis-NCO-functionalized ureidopyrimidinone derivative (UPy-2NCO) and an -OH-terminated flexible chain molecule at 60 - 80 °C for 1 - 4 h, then cool to 25 - 45 °C to obtain a polyurethane prepolymer; then add a diamine and continue to react at 30 - 60 °C for 12 - 24 h, and then react at 60 - 180 °C for 2 - 24 h to obtain a polyurethane elastomer;

[0018] (2) Immerse the prepared elastomer in a silver trifluoroacetate ethanol solution for 20 - 30 min, take it out and dry it, then immerse it in a hydrazine hydrate / ethanol solution for reduction for 3 - 10 min, take it out, rinse and dry it. The above operations are continuously carried out 1 - 10 times, preferably 1 - 5 times, to obtain a medium and low temperature shape memory functional polyurethane-based flexible conductive elastomer.

[0019] In the above technical solution, the bis-NCO-functionalized ureidopyrimidinone derivative (UPy-2NCO) is a diisocyanate-modified ureidopyrimidinone derivative, specifically a diisocyanate-modified 5-(2-hydroxyethyl)-6-methyl-2-aminouracil product. The modification process is as follows: Under a nitrogen atmosphere, mix one or more diisocyanate mixtures with 5-(2-hydroxyethyl)-6-methyl-2-aminouracil (UPy-P), add pyridine, and react at 80 - 120 °C for 1 - 4 h. After precipitation with an organic solvent and then drying, the modified product can be obtained, where: -NCO∶UPy-P∶pyridine (molar ratio) = (190 - 200)∶5∶20.

[0020] Preferably, the diamine is a polyetheramine (such as polyetheramines D230, D400, and D2000 with different molecular weights), an aromatic diamine (diaminodiphenyl ether, diaminodiphenyl sulfone), or a mixture of the above diamines. When adding the diamine, it can be formulated into a solution (the solution mass is 0 - 5 times that of the diamine) with a solvent and added together; the above solvent is N,N-dimethylformamide, N,N-dimethylacetamide, ethanol, and acetone.

[0021] In the above technical solution, the catalyst is organotin (such as dibutyltin dilaurate, stannous octoate), organolead (such as tetraethyllead and triethyllead), or organic amine catalyst (such as amino acid, triethylamine, diethylenetriamine, 1-methyl-4-(2-dimethylaminoethyl)piperazine, N,N-dimethylbenzylamine, piperazine, triethanolamine, polyethyleneimine, etc.).

[0022] In the above technical solution, the mass ratio of silver trifluoroacetate to ethanol is 1:(2 - 6); the volume ratio of hydrazine hydrate to ethanol is 1:(1 - 5).

[0023] The elastomer prepared by the above technical solution has ultra-high tensile properties, high deformation, and has double T g (ultra-low temperature T g and high temperature T g ), excellent electrical conductivity, good self-healing and shape memory properties. Among them, the tensile strength of the flexible conductive elastomer can reach 83 MPa, the elongation at break can reach 1200%, the low temperature T g can be -74 °C, the high temperature T g can be 136 °C, the self-healing efficiency can reach 100%, and the conductivity can reach 4.3 S·cm -1 .

[0024] Compared with the prior art, the beneficial effects obtained by the present invention are: the flexible conductive elastomer of the composite material of the present invention can have outstanding high tensile strength and strain, high electrical conductivity, excellent high and low temperature resistance, medium temperature shape memory effect and self-healing performance. Description of the Drawings

[0025] Figure 1 For the 1 1H NMR spectrum (a) and high-resolution mass spectrum (b) of UPy-P in Example 1, the FTIR spectrum (c) of the HDI-functionalized ureidopyrimidinone derivative (UPy-2NCO), 1 1H NMR (d) and 13 13C NMR (e) spectrum.

[0026] Figure 2 For the FTIR spectra of the polyurethane elastomer, PTHF, UPy-2NCO and D230 prepared in Example 1.

[0027] Figure 3 For the C=O fitting deconvolution of the elastomer in Example 1 in the range of 1750 - 1600 cm -1 .

[0028] Figure 4Microscopic cross-section photos, surface SEM photos and SEM photos of the interface layer of the polyurethane-based flexible conductive elastomer films in Example 1 (a, b), Comparative Example 1-2 (c, d), Comparative Example 1-3 (e), and Comparative Example 1-5 (f).

[0029] Figure 5 Stress-strain curves of the polyurethane-based flexible conductive elastomer in Example 1, the polyurethane elastomer in Comparative Example 1-1, the composite elastomers in Comparative Example 1-2 and Comparative Example 1-3, the polyurethane elastomer in Comparative Example 1-4, and the flexible conductive elastomer in Comparative Example 1-5.

[0030] Figure 6 Graphs of the storage modulus (a) and loss factor (c) of the elastomer in Example 1.

[0031] Figure 7 Pictures of the conductive behavior of the polyurethane-based flexible conductive elastomer in Example 1 in series with an LED lamp under a constant voltage of 0.346 V.

[0032] Figure 8 Values of the relative resistance change (R / R0) of the polyurethane-based flexible conductive elastomer sample in Example 1 during cyclic processes in the strain ranges of 0.05 - 10% (a), 20 - 100% (b), and 120 - 200% (c).

[0033] Figure 9 Relationship between ΔR / R0 and GF of the polyurethane-based flexible conductive elastomer sample in Example 1 with respect to strain.

[0034] Figure 10 Response time and recovery time of the polyurethane-based flexible conductive elastomer sample in Example 1 under a 0.5% tensile strain.

[0035] Figure 11 ΔR / R0 (a) of the flexible polyurethane-based flexible conductive elastomer sample in Example 1 at different tensile frequencies (0.1 - 1 Hz) and ΔR / R0 (b) after 2000 cyclic cycles at a fixed 20% strain.

[0036] Figure 12 Values of ΔR / R0 of the polyurethane-based flexible conductive elastomer sample in Example 1 under slow or fast index finger bending (a and b), wrist bending (c), and eyebrow raising (d).

[0037] Figure 13 Pictures of the surface of the polyurethane-based flexible conductive elastomer sample in Example 1 without treatment and after treatment at 90 °C for 1 h (a), 2 h (b), and 3 h (c).

[0038] Figure 14Photographs of the conductive behavior of the polyurethane-based flexible conductive elastomer sample in Example 1 before and after being treated at 100 °C for 3 h (a), and the ΔR / R0 value of the healed flexible conductive elastomer sample in Example 1 under a 20% tensile strain (b).

[0039] Figure 15 Photographs of the torsional shape memory behavior of the polyurethane-based flexible conductive elastomer sample in Example 1 (a) and photographs of four bending-recovery tests (b).

[0040] Figure 16 A picture of the polyurethane-based flexible conductive elastomer sample in Example 1 as a temperature control switch. Detailed implementation manners

[0041] The present invention discloses a preparation method of a medium and low temperature shape memory functional polyurethane-based flexible conductive elastomer, comprising the following steps:

[0042] (1) Under a nitrogen atmosphere, reacting a bis-NCO-functionalized 5-(2-hydroxyethyl)-6-methyl-2-aminouracil (UPy) derivative (UPy-2NCO), an -OH-terminated flexible chain molecule and a catalyst at 60-80 °C for 1-4 h, cooling to 25-45 °C to obtain a polyurethane prepolymer, then adding a diamine, reacting at 30-60 °C for 12-24 h, and further reacting at 60-180 °C for 2-24 h to obtain a double-T g ultra-high tensile strength polyurethane elastomer; a conventional mold can be used to form the required shapes such as a polyurethane elastomer film;

[0043] (2) Immersing the elastomer prepared above in a silver trifluoroacetate ethanol solution for 20-30 min, taking it out and drying it, then immersing it in a hydrazine hydrate / ethanol solution for reduction for 3-10 min, taking it out, rinsing it with water, and drying it. The above operations are continuously carried out 1-10 times to obtain a composite flexible conductive elastomer; wherein: the molar ratio of UPy-2NCO: -OH-terminated flexible chain molecule: catalyst: diamine = (5-60):(1-10):(0-0.1):(1-10); the mass ratio of silver trifluoroacetate to ethanol is 1:(2-6); the volume ratio of hydrazine hydrate to ethanol is 1:(1-5).

[0044] Among them, the double-NCO functionalized UPy derivative (UPy-2NCO) is a product of modifying 5-(2-hydroxyethyl)-6-methyl-2-semicarbazide pyrimidine with diisocyanate. Preferably, the diisocyanate includes toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), hexamethylene diisocyanate (HDI), lysine diisocyanate (LDI), and mixtures thereof. The modification process is as follows: Mix one or more diisocyanate mixtures with 5-(2-hydroxyethyl)-6-methyl-2-semicarbazide pyrimidine (UPy-P), add pyridine, react at 80-120 °C for 1-4 h, precipitate with petroleum ether, and dry at 60-80 °C for 4-10 h to obtain the modified product UPy-2NCO, where: -NCO / UPy-P / pyridine (molar ratio) = (190-200):5:20.

[0045] Among them, the flexible chain molecule of -OH is: polytetrahydrofuran, polyether polyol, or a mixture thereof; the diamine is: polyetheramine (such as D230, D400, and D2000, etc.), aromatic diamine (diaminodiphenyl ether, diaminodiphenyl sulfone), or a mixture of the above diamines; the catalyst is organotin (such as dibutyltin dilaurate (DBTDL), stannous octoate, etc.), organolead (such as tetraethyllead and triethyllead), organic amine catalyst (such as amino acid, triethylamine, diethylenetriamine, 1-methyl-4-(2-dimethylaminoethyl)piperazine, N,N-dimethylbenzylamine, piperazine, triethanolamine, polyethyleneimine, etc.).

[0046] In the present invention, the reaction between UPy-2NCO and the flexible chain molecule capped with -OH is carried out in a solvent, and the amount of the solvent is 5-10 times the sum of the masses of the raw material components; when adding diamine, it can be formulated into a solution with the solvent (the mass concentration of diamine is 0-100%) and added together; the above solvent is N,N-dimethylformamide, N,N-dimethylacetamide, ethanol, and acetone.

[0047] In the present invention, diamine is added to the polyurethane prepolymer, and the initial reaction temperature is 30-60 °C, and then the reaction is carried out at a high temperature of 60-180 °C for 2-24 h; this process promotes the formation of hydrogen bond interactions between the polyurethane prepolymer molecular chains based on the hydrogen bond sites to fix and arrange the molecular chains and promotes the further chain extension of the prepolymer and diamine. At the same time, the possibly remaining solvent is volatilized; it also promotes the chemical cross-linking reaction of the remaining -NCO groups and amino derivatives, improving the cross-linking density of the elastomer and ensuring that the elastomer has a high temperature T g .

[0048] The polyurethane flexible conductive elastomer prepared by the present invention has ultra-high tensile properties, high deformation, double T g (ultra-low temperature T g and high temperature Tg ), excellent electrical conductivity, good self-healing and shape memory properties. Among them, the tensile strength of the conductive elastomer can reach 83 MPa, the elongation at break can reach 1200%, the low temperature T g is -74 °C, the high temperature T g is 136 °C, the self-healing efficiency can reach 100% and the conductivity can reach 4.3 S·cm -1 ; The flexible conductive elastomer prepared by the present invention can be used for flexible sensors and temperature control elements.

[0049] The technical solution of the present invention will be further described below with reference to the drawings and embodiments. The raw materials used in the present invention are existing products, and the specific preparation operations and performance tests are conventional technologies.

[0050] Synthesis Example

[0051] The synthesis process of 5-(2-hydroxyethyl)-6-methyl-2-aminouracil (UPy-P) is as follows: 2-acetylbutyrolactone (40 mmol), guanidine carbonate (40 mmol), catalyst triethylamine Et3N (80 mmol) and solvent absolute ethanol (40 mL, 70 mmol) are placed in a round-bottom flask equipped with a stirrer and a reflux condenser; under nitrogen protection, the above mixture is stirred at 90 °C for 3 h and then precipitated and filtered to obtain a pale yellow solid, which is then washed with ethanol 3 times and dried at 60 °C for 6 h to obtain a white powder solid 5-(2-hydroxyethyl)-6-methyl-2-aminouracil; where: the molar ratio of 2-acetylbutyrolactone, guanidine carbonate, catalyst triethylamine Et3N, and ethanol = 40∶40∶80∶70.

[0052] The synthesis process of UPy-2NCO is as follows: Under a nitrogen atmosphere, UPy-P (0.85 g, 5.0 mmol) is dissolved in a mixture of HDI (17.1 mL, 98 mmol) and pyridine (1.6 mL, 20 mmol); after the above mixture is stirred and reacted at 100 °C for 2 h, it is precipitated with petroleum ether, and the obtained solid is dried at 60 °C for 6 h to obtain a white powder, which is UPy-2NCO (a hexamethylene diisocyanate (HDI)-functionalized 5-(2-hydroxyethyl)-6-methyl-2-aminouracil derivative).

[0053] Adopt 1 1H NMR, 13 13C NMR, high-resolution mass spectrometry (HRMS), and FTIR were used to characterize the chemical structures of UPy-P and UPy-P modified with hexamethylene diisocyanate (UPy-2NCO), as Figure 1 shown. For UPy-P, its 1The chemical shift signals at δ = 10.98, 6.43, 4.52, 3.36, 2.44, and 2.07 ppm in the 1H NMR spectrum correspond to the protons on -NH-, -NH2, -OH, -CH3, and -CH2-, respectively ( Figure 1 a) in. The HRMS spectrum of UPy-P confirmed that its molecular weight was 170.1 g·mol -1 ( Figure 1 b) in, which was basically consistent with the theoretical molecular weight of 170 g·mol -1 , indicating the successful synthesis of UPy-P. For UPy-2NCO, its FTIR spectrum showed that the N-H stretching vibration band of -NH appeared at 3318 cm -1 , and the C-H stretching vibration bands of -CH2- and -CH3 appeared at 2853 - 2927 cm -1 . The characteristic absorption band of -NCO appeared at 2263 cm -1 , and the stretching vibration band of C=O appeared at 1690 cm -1 ( Figure 1 c) in. The 1H-NMR spectrum of UPy-2NCO showed chemical shift signals at δ = 12.86 - 4.61, 4.10 - 2.20, and 1.47 - 1.19 ppm ( 1 d) in, corresponding to the protons in -NHCO- / -NHC=N-, -CH2-, and -CH2, respectively. Figure 1 The chemical shifts of the carbon atoms in the 13C NMR spectrum also perfectly matched the carbon positions in UPy-2NCO ( 13 e) in. The above FTIR, Figure 1 1H NMR, and 1 13C NMR analyses of UPy-2NCO confirmed the successful synthesis of UPy-2NCO. 13

[0054] Referring to the above method, hexamethylene diisocyanate (HDI) was replaced with isophorone diisocyanate (IPDI) or diphenylmethane diisocyanate (MDI) to obtain isophorone diisocyanate (IPDI)-functionalized 5-(2-hydroxyethyl)-6-methyl-2-aminouracil derivative or diphenylmethane diisocyanate (MDI)-functionalized 5-(2-hydroxyethyl)-6-methyl-2-aminouracil derivative.

[0055] Performance test method:

[0056] The initial thermal decomposition temperature T di is the temperature at which the polyurethane loses 5 wt% of its weight, determined by the TGA method, in a nitrogen atmosphere with a heating rate of 10 °C / min.

[0057] The glass transition temperature T​g Determined by dynamic mechanical analysis (DMA) method, with a heating rate of 3 °C / min and a frequency of 1 Hz.

[0058] For the mechanical property test, dumbbell-shaped samples (12 mm × 2 mm × 0.9 mm) were used, and the loading rate was 50 mm / min.

[0059] The resistance value of the sample was measured by a digital multimeter (DMM6500) from Tektronix, USA, and the conductivity (σ) was calculated, which is defined as the current flowing through 1 cm of the material under a unit potential, as shown in formula (1). 3 of the material, as shown in formula (1).

[0060] (1)

[0061] L is the sample length, S is the cross-sectional area of the sample, ρ is the resistivity (Ω·cm), R is the resistance value, σ is the conductivity (S·cm -1 ).

[0062] The change in the resistance signal of the flexible conductive elastomer film under different tensile strains was collected using a digital multimeter (DMM6500). In a resistive strain sensor, the conductive network sensitive to the external force behavior is defined as the sensitivity, also known as the gauge factor (GF). Usually, GF is used to quantitatively characterize the relationship between the relative resistance change (ΔR / R0) and the applied strain behavior, as shown in formula (2).

[0063] (2)

[0064] where ΔR = R - R0, ε = ΔL / L 0 . R0 is the initial resistance (Ω) when the sensor is not applied, R is the resistance during the stretching process (Ω), ε is the applied strain, which is the ratio of the deformed length (ΔL) to the original length (L0).

[0065] The stability of the electrical signal response was characterized by studying ΔR / R0 within 2000 cycle periods under a 20% tensile strain. The polyurethane flexible conductive elastomer film was attached to positions such as the finger, wrist, and eyebrow tip, and the change in the film resistance during finger, wrist, and eyebrow movements was collected. Example 1

[0066] Under a nitrogen atmosphere, 5-(2-hydroxyethyl)-6-methyl-2-semicarbazide pyrimidine derivative functionalized with hexamethylene diisocyanate (HDI) (5.05 g, 10 mmol), dry -OH terminated flexible chain molecule polytetrahydrofuran (5 g, 2.5 mmol, PTFH), catalyst dibutyltin dilaurate (0.02 g, 0.032 mmol, DBTDL) and N,N-dimethylformamide DMF (80 mL, 75.84 g) were reacted in a reactor at 80 °C for 3 h, then cooled to 40 °C to obtain a polyurethane prepolymer. Then, diamine D230 (0.575 g, 2.5 mmol) was added and reacted at 30 °C for 12 h. Then, it was cast in a mold (conventional film-forming mold) and placed at 80 °C for 24 h, and naturally cooled to room temperature to obtain a polyurethane elastomer film;

[0067] The prepared elastomer film was immersed in a 20% silver trifluoroacetate ethanol solution for 30 min, taken out and dried at 25 °C. Subsequently, it was immersed in a hydrazine hydrate / ethanol solution (volume ratio 1:3) for reduction for 5 min, taken out, rinsed with deionized water, and dried at 25 °C; The above operations were continuously carried out 3 times to obtain a flexible conductive elastomer. The mass fraction of Ag particles in the flexible conductive elastomer was calculated to be 10.5% by the change in the mass of the sample before and after.

[0068] Among them: the molar ratio of UPy-2NCO, -OH terminated flexible chain molecule, catalyst, and diamine is = 10: 2.5:0.032:2.5.

[0069] Comparative Example 1-1

[0070] A polyurethane elastomer film obtained by referring to the method of Example 1.

[0071] Comparative Example 1-2

[0072] At room temperature, 1.1 g of silver particles with an average particle size of 50 nm (equivalent to 10.5% of the mass of the polyurethane elastomer film) were dispersed in 27.5 g of DMF, and then the solution was evenly drop-coated on the surface of the polyurethane elastomer film (prepared by referring to the method of Example 1), and left for 48 h until the solvent had completely evaporated to obtain a flexible conductive elastomer with a silver particle coating.

[0073] Comparative Example 1-3

[0074] Under a nitrogen atmosphere, 5-(2-hydroxyethyl)-6-methyl-2-aminouracil derivative functionalized with hexamethylene diisocyanate (HDI) (5.05 g, 10 mmol), dry -OH terminated flexible chain molecule polytetrahydrofuran (5 g, 2.5 mmol, PTFH), catalyst dibutyltin dilaurate (0.02 g, 0.032 mmol, DBTDL), and N,N-dimethylformamide DMF (80 mL, 75.84 g) were reacted in a reactor at 80 °C for 3 h, then cooled to 40 °C to obtain a polyurethane prepolymer. Then, 1.1 g of silver nanoparticles (average particle size 50 nm) and diamine D230 (0.575 g, 2.5 mmol) were added, and the reaction was carried out at 30 °C for 12 h. Then, it was cast in a mold (conventional film-forming mold), and then placed at 80 °C for 24 h, and naturally cooled to room temperature to obtain a flexible composite elastomer film containing silver particles.

[0075] Comparative Examples 1-4

[0076] Under a nitrogen atmosphere, hexamethylene diisocyanate (HDI) (1.68 g, 10 mmol), dry -OH terminated flexible chain molecule polytetrahydrofuran (5 g, 2.5 mmol, PTFH), catalyst dibutyltin dilaurate (0.02 g, 0.032 mmol, DBTDL), and N,N-dimethylformamide DMF (80 mL, 75.84 g) were reacted in a reactor at 80 °C for 3 h, then cooled to 40 °C to obtain a polyurethane prepolymer, reacted at 30 °C for 12 h, then poured into a mold (conventional film-forming mold), and then placed at 80 °C for 24 h, and naturally cooled to room temperature to obtain a polyurethane elastomer film.

[0077] Comparative Examples 1-5

[0078] The polyurethane elastomer film (prepared by referring to the method of Comparative Examples 1-4) was immersed in a 20% silver trifluoroacetate ethanol solution for 30 min, taken out and dried at 25 °C, then immersed in a hydrazine hydrate / ethanol solution (volume ratio 1:3) for reduction for 5 min, taken out and rinsed with deionized water, and dried at 25 °C; the above operations were continuously carried out 3 times to obtain a flexible conductive elastomer.

[0079] Table 1 shows the performance test results of the polyurethane-based flexible conductive elastomer films and polyurethane elastomer films prepared in Example 1 and Comparative Examples 1-1 to 5; Table 2 shows the R of the polyurethane-based flexible conductive elastomer film sample in Example 1 for four bending-recovery tests f and R r .

[0080] Figure 2FTIR spectra of the polyurethane elastomer, PTHF, UPy-2NCO, and D230 prepared in Example 1. By comparing the FTIR spectra of PTHF, UPy-2NCO, and D230, it can be seen that in the FTIR spectrum of the polyurethane elastomer, the absorption peaks at 3531 and 3327 cm -1 correspond to the stretching vibration peaks of free N-H and hydrogen-bonded N-H, the weak peak at 3059 cm -1 is the C-H stretching vibration peak in the UPy ring, the absorption peaks at 2937 - 2795 cm -1 are the C-H stretching vibration peaks of CH2 in PTHF, the absorption peaks at 1750 - 1600 cm -1 are the stretching vibration peaks of C=O in the urethane group (-NHCOO-) and urea group (-NHCONH-), the absorption peaks at 1257 cm -1 and 1018 cm -1 are the stretching vibration peaks of C-O and C-O-C respectively, and the absorption peak at 1581 cm -1 is the stretching vibration peak of the C=N bond in UPy. In addition, no characteristic peak of -NCO appears at 2263 cm -1 in the polyurethane elastomer, indicating that -NCO has completely reacted. In the FTIR spectrum of the polyurethane elastomer, the C=O peaks at 1696, 1661, 1637, and 1621 cm -1 and the N-H peak at 3531 cm -1 also indicate the existence of rich multiple hydrogen bond interactions between the urethane, urea, and UPy units in the polyurethane elastomer.

[0081] Figure 3 is the fitting deconvolution of C=O in the range of 1750 - 1600 cm -1 for the polyurethane elastomer film in Example 1. The C=O absorption band of the elastomer sample can be deconvoluted into 6 sub-peaks, namely I, II, III, IV, V, and VI, corresponding to the free C=O of urethane, the hydrogen-bonded (ordered) C=O in urethane, the free C=O in urea, the hydrogen-bonded (disordered) C=O in urea, the hydrogen-bonded (ordered) C=O in urea, and the hydrogen-bonded (ordered) C=O in amide respectively. Based on the area ratio of hydrogen-bonded C=O to all C=O absorption peaks in the range of 1750 - 1600 cm -1 , the hydrogen bond content of the elastomer can be calculated to be 82% (Table 1). It can be seen that the polyurethane elastomer prepared in Example 1 has rich hydrogen bonds.

[0082] Figure 4Pictures of the surface, cross-section and interfacial layer of the polyurethane-based flexible conductive elastomer film in Example 1, Comparative Example 1-2, Comparative Example 1-3 and 1-5. The size of the Ag particles deposited on the surface of the polyurethane-based flexible conductive elastomer sample in Example 1 is about 50-100 nm, and the silver particle layer is dense ( Figure 3 upper right picture in a), and the deposition thickness of the Ag particles on the substrate is uniform ( Figure 3 a in). The interfacial adhesion between the polyurethane and the Ag particles is good and there is no obvious particle shedding phenomenon ( Figure 3 b in), and the deposition inside the Ag particle layer is dense. It can be seen that the Ag particles form a good conductive path on the surface of the polyurethane film and can have excellent conductivity. The surface of the Ag particle layer on the surface of the polyurethane-based flexible conductive elastomer sample in Comparative Example 1-2 is relatively rough and the pores between the particles are larger ( Figure 3 c in), and the cross-section of the polyurethane-based flexible conductive elastomer sample shows that the structure of the silver particle layer is relatively loose ( Figure 3 d in), which indicates that it is not easy to form a dense silver particle layer by depositing Ag particles using a silver particle-containing solution, and the conductive network is reduced. The cross-section of the polyurethane-based flexible conductive elastomer sample in Comparative Example 1-3 shows that the Ag particles and their aggregates are dispersed in the polyurethane matrix, and the distance between the particles is relatively large ( Figure 3 e in), which indicates that it is difficult to form a conductive path in the polyurethane by adding about 10.5% of silver particles, and the silver particles are prone to agglomeration. For Comparative Example 1-5, although the same process as in Example 1 is used to deposit silver particles, the cross-sectional photo of the elastomer shows that the interfacial layer between the polyurethane and the silver particles is narrower than that of the sample in Example 1, and exfoliated silver particles can be found, which indicates that the conductive layer structure of the flexible conductive elastomer is unstable, and the interface damaged by the solvent cannot be completely restored due to the appearance of silver particles.

[0083] Figure 5Typical stress-strain curves of the polyurethane-based flexible conductive elastomer films and substrates in Example 1 and Comparative Examples 1-1 to 1-5. The tensile strength of the polyurethane-based flexible conductive elastomer film in Example 1 can reach 81 MPa, and the elongation at break can reach 1008% (Table 1). Compared with the polyurethane elastomer film without a silver layer deposited in Comparative Example 1-1, the mechanical properties of the elastomer are comparable after the silver layer is deposited (Table 1), indicating that the polyurethane elastomer maintains the surface structure of the polyurethane and can effectively improve the adhesion between the polyurethane and Ag particles, thereby maintaining the mechanical properties of the elastomer and enhancing the electrical conductivity of the elastomer. The mechanical properties and conductivity of the polyurethane-based flexible conductive elastomer film in Comparative Example 1-2 are significantly lower than those of the flexible conductive elastomer in Example 1, which indicates that the electrical properties of the flexible conductive elastomer prepared by depositing a silver layer using a silver particle-containing solution are poor and are not conducive to maintaining the mechanical properties of the elastomer. After silver particles are deposited on the polyurethane elastomer in Comparative Example 1-4, that is, the mechanical properties of the flexible conductive elastomer in Comparative Example 1-5 are significantly weakened, and the conductivity is also significantly lower than that of the flexible conductive elastomer in Example 1, indicating that the technology in Comparative Example 1-5 is not conducive to the restoration of the polyurethane surface structure and the improvement of the interface interaction between silver particles and polyurethane. In addition, the mechanical properties of the sample in Example 1 are significantly higher than those of the sample in Comparative Example 1-5, mainly because a large number of hydrogen bonds can increase the mechanical loss.

[0084] Based on Figure 4 and the mechanical and electrical property data analysis in Table 1, it can be speculated that the flexible conductive elastomer prepared by the method of the present invention has outstanding mechanical properties and conductive behavior.

[0085] Figure 6 Graphs of the storage modulus (a) and loss factor (b) of the elastomer in Example 1. The storage modulus of the elastomer at 25 °C is 216 MPa. The elastomer has both a low T g and a high T g , where the low T g value is -64 °C and the high T g value is 91 °C. Most of the reported T g of polyurethane elastomers are single low T g or high T g , and there is no report on those with both an extremely low low Tg and a high Tg. Based on the storage modulus data at T g +50 °C and viscoelastic theory, the crosslinking density v e of the elastomer is calculated to be 1182 mol / m 3 , which means that the elastomer has a high crosslinking density. Obviously, the elastomer in Example 1 has a significantly higher crosslinking density than the sample in Comparative Example 1-5 and has an additional high-temperature T g . The high-temperature T gAnd a relatively high crosslinking density means that the heat resistance of the elastomer and its high-temperature use environment are improved, and it also implies the high-temperature shape memory function of the elastomer.

[0086] In Example 1, the conductivity of the polyurethane-based flexible conductive elastomer was 3.7 S·cm -1 , and the conductivity of the highly elastic conductive materials reported in the literature is mostly 1.1×10 -4 ~1.48 S·cm -1 , and compared with the samples of Comparative Examples 1-2, 1-3 and 1-5, the polyurethane-based flexible conductive elastomer in Example 1 showed more excellent conductive behavior. Figure 7 Figure 11 is a photograph of the electrical behavior of the polyurethane-based flexible conductive elastomer in Example 1 in series with two LED lights in a circuit under a constant voltage of 0.346 V. When the polyurethane-based flexible conductive elastomer sample in Example 1 was connected in series to the circuit, both LED lights could emit light, proving that the composite material has excellent conductive performance.

[0087] Figure 8 Figure 15 shows the relative resistance change (ΔR / R0) values of the polyurethane-based flexible conductive elastomer in Example 1 during the tensile cycle in the strain ranges of 0.05~10% (a), 20~100% (b) and 120~200 % (c). In the strain ranges of 0.05~10%, 20~100% and 120~200 %, that is, in the small strain and large strain ranges, the elastomer sample can obtain a stable ΔR / R0. The reason is that under the action of mechanical external force, the abundant hydrogen bonds in the polyurethane elastomer are easily dissociated and relatively slip occurs, and at the same time, the hydrogen bond action will be re-established to play a role in adjusting between molecular chains, thus effectively avoiding the damage of the composite material interface layer and maintaining the conductive performance of the material.

[0088] In order to quantitatively characterize the relationship between ΔR / R0 and the applied strain behavior, based on the relationship between ΔR / R0 and the applied strain behavior, that is, the sensitivity (also called the measurement factor, GF) is used to evaluate the sensor strain sensitivity. By linearly fitting the relationship between ΔR / R0 and strain, the slope of the straight line can be obtained, which is the GF. Figure 9 Figure 20 is a graph showing the relationship between the GF of the polyurethane-based flexible conductive elastomer in Example 1 and the strain change of ΔR / R0. In the strain range of 0.05~80%, the GF value of the sample is 87, and the GF in the strain range of 80-200% is 1714. Compared with the GF values (0.9~549) of most reported similar products, the polyurethane-based flexible conductive elastomer in Example 1 has a larger GF value and a wider GF value range, which further shows that the polyurethane-based flexible conductive elastomer in the present invention has outstanding signal sensitivity and a wide application range.

[0089] To further characterize the sensitivity of the sample, the ΔR / R0 value of the polyurethane-based flexible conductive elastomer in Example 1 at a tensile strain of 0.5% was tested. Refer to Figure 10 , the signal response time of the sample was 80 ms, and the recovery time was 140 ms. The sample in Example 1 had a fast signal response and recovery time, which further indicated that the sample in Example 1 had outstanding strain sensitivity.

[0090] Figure 11 shows the ΔR / R0 values of the polyurethane-based flexible conductive elastomer in Example 1 at different tensile frequencies (0.1 - 1 Hz) and the ΔR / R0 values after 2000 tensile cycles under a fixed strain of 20%. Under a fixed strain of 20%, the sample was stretched at different tensile rates (0.1 Hz, 0.25 Hz, 0.5 Hz, 0.75 Hz, and 1 Hz). It was found that the ΔR / R0 values were similar at different tensile frequencies, but the signal duration periods were different. Obviously, as the tensile frequency increased, the signal duration period became shorter, which meant it was suitable for recording signals at different time intervals. In addition, under a fixed strain of 20%, the ΔR / R0 values were collected for 2000 tensile cycles, and it was found that ΔR / R0 could basically remain constant during 2000 tensile deformation cycles, indicating that the electrical signal response of the sensor prepared with this polyurethane-based flexible conductive elastomer was very stable.

[0091] Due to the high strain sensitivity and response stability of the polyurethane-based flexible conductive elastomer in Example 1, it can be used as a strain sensor. Figure 12 shows the ΔR / R0 values of the polyurethane-based flexible conductive elastomer in Example 1 under slow or fast index finger bending, wrist bending, and eyebrow raising. It can be found that when the polyurethane-based flexible conductive elastomer sample in Example 1 was attached to the finger and wrist joints, ΔR / R0 was stable when the finger and wrist joints moved. When the polyurethane-based flexible conductive elastomer sample in Example 1 was attached to the side of the eyebrow, the slight movement of the eyebrow caused regular changes in ΔR / R0. The above experimental phenomena confirmed that the polyurethane-based flexible conductive elastomer in Example 1 could be used to detect small and large deformation movements of the human body.

[0092] Figure 13 shows pictures of the polyurethane-based flexible conductive elastomer in Example 1 with untreated surface scratches and treated at 90 °C for 1 h (a), 2 h (b), and 3 h (c). At 90 °C, the width of the surface scratches of the sample significantly narrowed with the extension of the heat treatment time. When the heat treatment time was 3 h, the scratches completely healed, and the self-healing efficiency was close to 100%.

[0093] Figure 14These are the photos of the conductive behavior of the polyurethane-based flexible conductive elastomer in Example 1 before and after being treated at 100 °C for 3 h, and the ΔR / R0 value of the healed polyurethane-based flexible conductive elastomer in Example 1 under 20% tensile strain. The cut sample was connected in series with an LED lamp in the circuit. It was found that the sample could be welded together by heating at 100 °C for 3 h, and the LED lamp could emit light again, indicating that the sample still had good conductive performance after self-healing. Through the analysis of ΔR / R0 of the repaired sample under 20% strain, it was found that the change of ΔR / R0 before and after sample repair was basically the same, confirming that the polyurethane-based flexible conductive elastomer in Example 1 had excellent conductive self-healing ability.

[0094] The polyurethane-based flexible conductive elastomer in Example 1 has good shape memory behavior. As Figure 15 shown in (a) below, the polyurethane-based flexible conductive elastomer in Example 1 was heated to 120 °C (about T g +30 °C), and an external force was applied to deform it into a spiral shape. When cooled to 25 °C, the shape was fixed. When the sample was heated to 120 °C again, the deformed specimen restored to its initial shape within 1 min. A bending-recovery test was carried out on the sample. As Figure 15 shown in (b) below, when the sample was heated to 120 °C, a certain external force was applied to bend it to 90°, and it was cooled to 25 °C under the external force, and the temporary angle θ1 was recorded. The deformed sample was heated to 120 °C again, and when it restored to its initial shape, the angle was recorded as θ2. The shape fixation rate (R f , ) and shape recovery rate (R r , ) of the sample were calculated (Table 2). The R f of the sample in four bending-recovery tests was between 92.3 - 99.0%, and Rr was between 99.6 - 99.9%, indicating that the polyurethane-based flexible conductive elastomer in Example 1 had good shape memory performance.

[0095] Based on the good shape memory performance and electrical properties of the polyurethane-based flexible conductive elastomer in Example 1, it can be used as a temperature control switch. As Figure 16 shown, two LED lamps were connected in parallel in the circuit. The deformed polyurethane-based flexible conductive elastomer sample in Example 1 was used to connect the first circuit to make the yellow LED lamp light up. At a temperature of 120 °C, the polyurethane-based flexible conductive elastomer sample in Example 1 gradually restored to its initial shape, and at this time the yellow LED lamp went out. When the polyurethane-based flexible conductive elastomer sample in Example 1 restored to its initial shape, it automatically connected the second circuit, and at this time the red LED lamp lit up. It can be seen that the polyurethane-based flexible conductive elastomer in Example 1 can be used as a shape memory switch.

[0096] Table 1 Mechanical properties, thermal properties, electrical conductivity, hydrogen bond content and crosslinking density of the elastomer in Example 1

[0097]

[0098] Table 2 R of the polyurethane-based flexible conductive elastomer in Example 1 for four bending-recovery tests f and R r

[0099] Example 2

[0100] Under a nitrogen atmosphere, 5-(2-hydroxyethyl)-6-methyl-2-aminouracil derivative functionalized with hexamethylene diisocyanate (HDI) (5.05 g, 10 mmol), dry -OH terminated flexible chain molecule polytetrahydrofuran (5 g, 2.5 mmol, PTFH), catalyst dibutyltin dilaurate (0.02 g, 0.032 mmol, DBTDL) and N,N-dimethylformamide DMF (80 mL, 75.84 g) were reacted in a reactor at 80 °C for 3 h, then cooled to 40 °C to obtain a polyurethane prepolymer. Then, diamine D230 (0.575 g, 2.5 mmol) was added and reacted at 30 °C for 12 h. Then, it was cast in a mold (conventional film-forming mold) and placed at 80 °C for 24 h, and naturally cooled to room temperature to obtain a polyurethane elastomer film. Then, the prepared elastomer film was immersed in a 20% silver trifluoroacetate ethanol solution for 30 min, taken out and dried at 25 °C. Subsequently, it was immersed in a hydrazine hydrate / ethanol solution (volume ratio 1:3) for reduction for 5 min, taken out, rinsed with deionized water, and dried at 25 °C to obtain a flexible conductive elastomer.

[0101] Table 3 shows the mechanical properties, thermal properties, electrical conductivity, hydrogen bond content and crosslinking density of the polyurethane-based flexible conductive elastomer in Example 2. The tensile strength of the flexible conductive elastomer is 83 MPa, the elongation at break can reach 1122%, and the conductivity is 0.3 S·cm -1 , and its mechanical properties are better than those of the flexible conductive elastomer in Example 1. It can be seen that for the products of the present invention, even with one silver deposition, the flexible conductive elastomer has good electrical conductivity on the premise of maintaining excellent mechanical properties and heat resistance, which is mainly attributed to the rich hydrogen bonds and high crosslinking density of the polyurethane matrix. The rich hydrogen bonds are beneficial to maintaining the stability of the interface, and the high crosslinking density is beneficial to improving the solvent resistance of the matrix.

[0102] Table 3 Performance characterization of the conductive elastomer in Example 2

[0103] Example 3

[0104] Under a nitrogen atmosphere, 5-(2-hydroxyethyl)-6-methyl-2-semicarbazide pyrimidine derivative functionalized with isophorone diisocyanate (IPDI) (6.4 g, 10 mmol), dry -OH terminated flexible chain molecular polyether polyol (14 g, 5 mmol, average molecular weight 2800), catalyst dibutyltin dilaurate (0.025 g, 0.04 mmol, DBTDL), and N,N-dimethylformamide DMF (100 mL, 94.8 g, 1.1 mol) were reacted in a reactor at 80 °C for 3 h, cooled to 40 °C to obtain a polyurethane prepolymer, then diamine D2000 (4 g, 2 mmol) was added, and the reaction was continued at 30 °C for 12 h. Then it was cast into a mold, and placed at 80 °C and 100 °C for 20 h and 4 h respectively, and then naturally cooled to room temperature to obtain a polyurethane elastomer film; the prepared elastomer film was soaked in a 20% silver trifluoroacetate ethanol solution for 30 min, taken out and dried at 25 °C, and then soaked in a hydrazine hydrate / ethanol solution (volume ratio 1:3) for reduction for 5 min, taken out, rinsed with deionized water, and dried at 25 °C to obtain a flexible conductive elastomer film. Among them: the molar ratio of IPDI, -OH terminated flexible chain molecule, catalyst, and diamine is = 10:5:0.04:2.

[0105] Table 4 shows the mechanical properties, thermal properties, electrical conductivity, hydrogen bond content, and crosslinking density of the polyurethane-based film in Example 3. The tensile strength of the flexible conductive elastomer can reach 46 MPa, and the elongation at break can reach 1200%. The low / high T g is -41 / 46 °C, and the conductivity is 0.6 S·cm -1 . The above data show that the polyurethane-based flexible conductive elastomer in Example 3 has both outstanding mechanical strength, large deformation, low / high double T g , and good electrical conductivity. The relatively high hydrogen bond content can endow the elastomer with excellent electrical conductivity repair performance; the low / high T g indicates that the elastomer has a wide temperature resistance performance, and also indicates that the elastomer has a medium and low temperature shape memory function.

[0106] Table 4 Mechanical properties, thermal properties, electrical conductivity, hydrogen bond content, and crosslinking density of the elastomer in Example 3

[0107] Example 4

[0108] Under a nitrogen atmosphere, 5-(2-hydroxyethyl)-6-methyl-2-aminouracil derivative functionalized with diphenylmethane diisocyanate (MDI) (6.7 g, 10 mmol), dry -OH terminated flexible chain molecule polytetrahydrofuran (4 g, 2 mmol, PTFH), a small amount of catalyst dibutyltin dilaurate (0.01 g, 0.016 mmol, DBTDL), and N,N-dimethylformamide DMF (100 ml, 94.8 g, 1.1 mol) were reacted in a reactor at 80 °C for 3 h, cooled to 40 °C to obtain a polyurethane prepolymer, then a DMF solution (1.24 g) containing 4,4'-diaminodiphenylsulfone (0.248 g, 1 mmol) was added, and the reaction continued at 60 °C for 12 h, then cast in a mold, and placed at 80 °C and 180 °C for 20 h and 4 h respectively, and then naturally cooled to room temperature to obtain a polyurethane elastomer film; the prepared elastomer film was soaked in a 20% silver trifluoroacetate ethanol solution for 30 min, taken out and dried at 25 °C, then soaked in a hydrazine hydrate / ethanol solution (volume ratio 1:3) for reduction for 10 min, taken out, rinsed with deionized water, and dried at 25 °C. The above operations were continuously carried out 4 times to obtain a flexible conductive elastomer. Among them: the molar ratio of UPy-2NCO, -OH terminated flexible chain molecule, catalyst, and diamine is = 10: 2: 0.016: 1.

[0109] Table 5 shows the mechanical properties, thermal properties, electrical conductivity, hydrogen bond content, and crosslinking density of the polyurethane-based film in Example 4. The tensile strength of the polyurethane-based flexible conductive elastomer in Example 4 can reach 61 MPa, and the elongation at break can reach 623%. The low / high T g is -21 / 136 °C, and the conductivity is 4.3 S·cm -1 . The above data show that the polyurethane-based flexible conductive elastomer in Example 4 has both outstanding mechanical strength, large deformation, low / high double T g , and excellent electrical conductivity. The high hydrogen bond content can endow the elastomer with excellent electrical conductivity repair performance; the low / high Tg indicates that the elastomer has good low and high temperature resistance, and also indicates that the elastomer has medium and low temperature shape memory function.

[0110] Table 5 Mechanical properties, thermal properties, electrical conductivity, hydrogen bond content, and crosslinking density of the elastomer in Example 4

[0111] Example 5

[0112] Under a nitrogen atmosphere, 5-(2-hydroxyethyl)-6-methyl-2-aminouracil derivative functionalized with hexamethylene diisocyanate (HDI) (12.625 g, 25 mmol), dry -OH terminated flexible chain molecule polytetrahydrofuran (10 g, 5 mmol, PTFH), catalyst dibutyltin dilaurate (0.06 g, 0.1 mmol, DBTDL), and N,N-dimethylformamide DMF (80 mL, 75.84 g) were reacted in a reactor at 80 °C for 3 h, then cooled to 40 °C to obtain a polyurethane prepolymer. Then, diamine D230 (1.15 g, 5 mmol) was added and reacted at 30 °C for 12 h. Then, it was cast in a mold (conventional film-forming mold) and placed at 80 °C for 24 h, and naturally cooled to room temperature to obtain a polyurethane elastomer film;

[0113] The prepared elastomer film was immersed in a 20% silver trifluoroacetate ethanol solution for 30 min, taken out and dried at 25 °C, then immersed in a hydrazine hydrate / ethanol solution (volume ratio 1:3) for reduction for 5 min, taken out and rinsed with deionized water, and dried at 25 °C; The above operations were continuously carried out 2 times to obtain a flexible conductive elastomer.

[0114] Among them: the molar ratio of UPy-2NCO, -OH terminated flexible chain molecule, catalyst, and diamine is = 25: 5: 0.1:5.

[0115] Table 6 shows the mechanical properties, thermal properties, electrical conductivity, hydrogen bond content, and crosslinking density of the polyurethane-based film in Example 5. The tensile strength of the flexible conductive elastomer can reach 72 MPa, and the elongation at break can reach 763%. The low / high T g is -68 / 113 °C, and the conductivity is 2.5 S·cm -1 . The above data show that the polyurethane-based flexible conductive elastomer in Example 5 not only has outstanding mechanical strength, large deformation, low / high double T g , but also has excellent electrical conductivity. The high hydrogen bond content can endow the elastomer with excellent electrical conductivity repair performance; the low / high T g indicates that the elastomer has good low and high temperature resistance, and also indicates that the composite material has medium and low temperature shape memory function.

[0116] Table 6 Mechanical properties, thermal properties, electrical conductivity, hydrogen bond content, and crosslinking density of the elastomer in Example 5

[0117]

[0118] Based on the above-mentioned defects in the preparation and use of current flexible conductive elastomers. The present invention prepares a flexible conductive polyurethane composite material with high mechanical properties for use at high and low temperatures. In the polyurethane matrix, the conductive elastomer matrix and the conductive particles have good adhesion and increase the energy consumption behavior of the material during use; the template with microscopically ordered molecular chains improves the heat resistance and thermal stability of the material, and by constructing a certain chemical cross-linked network structure between the molecular chains, the heat resistance of the material is improved. In the present invention, the polyurethane-based flexible conductive elastomer not only facilitates the adhesion between the conductive particles and the matrix, but also effectively improves the use stability of the material, prevents the damage of the interface layer of the composite material and repairs the interface layer in a timely manner, thereby improving the stability of the use performance of the material. In particular, this elastomer has excellent performance recoverability.

Claims

1. A method for preparing a medium- and low-temperature shape memory polyurethane flexible conductive elastomer, characterized in that: The following steps are involved: (1) reacting a di-NCO functionalized ureidopyrimidone derivative with a -OH terminated flexible chain molecule to obtain a polyurethane prepolymer, and then adding a diamine and continuing the reaction to obtain a polyurethane elastomer; the di-NCO functionalized ureidopyrimidone derivative is a diisocyanate modified ureidopyrimidone derivative; the -OH terminated flexible chain molecule includes a polyether polyol; the diamine includes a polyether amine and an aromatic diamine; (2) immersing the polyurethane elastomer in a silver compound solution, taking it out and performing a reduction treatment to obtain a medium-low temperature shape memory polyurethane flexible conductive elastomer, wherein the silver compound solution includes a trifluoroacetic acid silver alcohol solution; The medium and low temperature range is -74°C to 136°C; The molar ratio of the di-NCO functionalized ureido pyrimidone derivative, -OH terminated flexible chain molecule, catalyst and diamine is (5-60): (1-10): (0-0.1): (1-10).

2. The method for preparing the medium- and low-temperature shape memory polyurethane flexible conductive elastomer according to claim 1, characterized in that: The reaction of the di-NCO functionalized ureidopyrimidone derivative and the -OH terminated flexible chain molecule is carried out in the presence of a catalyst and under an inert gas, with a reaction temperature of 60 to 80°C and a reaction time of 1 to 4 hours; the continued reaction process is to react at 20 to 60°C for 12 to 24 hours, and then react at 60 to 180°C for 2 to 24 hours.

3. The method for preparing the medium- and low-temperature shape memory polyurethane flexible conductive elastomer according to claim 1, characterized in that: The reduction treatment is a chemical reduction treatment; the polyurethane elastomer is immersed in a silver compound solution, taken out and subjected to reduction treatment 1 to 10 times; the polyurethane elastomer is immersed in the silver compound solution for 20 to 30 minutes, and the reduction treatment time is 3 to 10 minutes.

4. The method for preparing the medium- and low-temperature shape memory polyurethane flexible conductive elastomer according to claim 1, characterized in that: The diisocyanate includes one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate; the ureidopyrimidone derivative includes 5-(2-hydroxyethyl)-6-methyl-2-aminouracil.

5. A medium-low temperature shape memory polyurethane flexible conductive elastomer prepared according to the method for preparing a medium-low temperature shape memory polyurethane flexible conductive elastomer according to claim 1.

6. Use of the medium- and low-temperature shape memory polyurethane flexible conductive elastomer according to claim 5 in the preparation of functional materials.

7. The use according to claim 6, characterized in that: The functional material includes one or more of elastic materials, shape memory materials, self-repairing materials, and conductive materials.

8. Use of the medium- and low-temperature shape memory polyurethane flexible conductive elastomer according to claim 5 in the preparation of functional devices.

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