Stress changing material and method for preparing the same
By introducing hydrophilic and hydrophobic segments into polyurethane or polyurea materials and using water as a plasticizer and hydrogen bonding crosslinking, the problem of high-temperature activation of segment movement is solved, achieving a balance between material size change and mechanical properties under water stimulation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUAZHONG UNIV OF SCI & TECH
- Filing Date
- 2024-12-12
- Publication Date
- 2026-06-05
AI Technical Summary
Existing thermotropic size change materials require high temperatures to activate chain segment movement, have poor mechanical properties, and their performance deteriorates when water is used as a plasticizer, limiting their applications.
By introducing hydrophilic and hydrophobic segments, using water as a plasticizer to promote segment movement, and maintaining mechanical strength through hydrogen bonding crosslinking, stress-sensitive materials are prepared.
It achieves volume expansion and shape recovery of materials under water stimulation, maintains excellent mechanical properties, and broadens the range of applications.
Smart Images
Figure CN119823344B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of polyurethane / polyurea technology, and more specifically, relates to a stress-reactive material and its preparation method. Background Technology
[0002] Smart polymer materials that can undergo size changes in response to external stimuli (such as heat and light) have important applications in biomedicine and aerospace, serving as vascular stents, surgical sutures, and shape-memory solar panel substrates. For example, shape-memory materials can be fabricated by utilizing the melting temperature of crystalline polymers or adjusting the glass transition temperature of amorphous polymers. Introducing molecular units with high coefficients of thermal expansion into polymer networks yields thermally responsive materials that expand in volume.
[0003] Common crystalline polymers include polyethylene, polypropylene, polyethylene oxide, and polycaprolactone. Introducing thermotropic shape memory materials into crystalline polymers often faces challenges such as excessively high response temperatures (>60℃) and poor mechanical properties, limiting their applications. The preparation of polymer materials with high coefficients of thermal expansion typically requires complex polymer design or the introduction of special chemical structural units (such as molecular cages), and the high cost limits their widespread application.
[0004] Whether it's volume expansion or shape memory materials, the microscopic essence of their dimensional changes lies in the movement of molecular chain segments. Given the unique time-temperature equivalence of polymers, heating is typically used to activate chain segment mobility, enabling controllable shape changes. Besides thermal stimulation, incorporating plasticizers can promote chain segment movement to achieve reversible dimensional changes in polymer materials. However, thermotropic dimensional change materials require high temperatures (>60℃) to activate chain segment movement, which is not conducive to practical applications. Furthermore, the deformation mechanism of thermotropic dimensional change materials is usually that of crystalline polymers, exhibiting the mechanical properties of plastic materials, thus limiting their application range. Water, as a natural and environmentally friendly solvent, can be used as a plasticizer to adjust chain segment mobility as needed. However, such polymer materials require complex structural designs, and their mechanical properties decrease significantly after absorbing water, thus lacking current application prospects. Summary of the Invention
[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, the present invention aims to provide a water-stimulated size-changing material (e.g., polyurethane or polyurea) and its preparation method. By adjusting the structure of the soft segments (i.e., hydrophobic or hydrophilic segments), the ratio of hydrophilic to hydrophobic segments, and the type of chain extender, a water-stimulated size-changing material that undergoes size changes under water stimulation can be obtained, while maintaining excellent mechanical properties. The synthesis of the water-stimulated material involves two steps: first, a soft segment raw material and a hard segment raw material (or diisocyanate) are mixed to obtain an isocyanate-terminated prepolymer; then, a chain extender is added, and the reaction proceeds to obtain the water-stimulated material.
[0006] Specifically, in this invention, hydrophilic segments are introduced into the stress-reducing material, and water, acting as a plasticizer, promotes the movement of polyurethane or polyurea segments within the material. By adjusting the structure of other components, the stress-reducing material prepared by this invention can expand in volume after absorbing water or recover its shape with the assistance of a small amount of water. After absorbing water, the hydrophilic segments rearrange, while the hydrophobic segments aggregate together, maintaining the material's mechanical strength through hydrogen bonding.
[0007] To achieve the above objectives, according to one aspect of the present invention, a stress-change material is provided, characterized in that the stress-change material comprises hydrophobic segments and hydrophilic segments.
[0008] Preferably, the raw materials constituting the hydrophobic segments are selected from hydrophobic polymeric polyols, and more preferably from at least one of polytetrahydrofuran diol, polycarbonate diol, polydimethylsiloxane diol, and polycaprolactone diol.
[0009] Preferably, the raw materials constituting the hydrophilic segments are selected from hydrophilic polymer polyols, and more preferably from one or two of polyethylene glycol and polypropylene glycol.
[0010] Preferably, the stress-reduction material further includes hard segments, the raw materials for preparing the hard segments being selected from diisocyanates. As a further preferred embodiment of the invention, the diisocyanate is selected from aliphatic diisocyanates and aromatic diisocyanates, preferably from one or more of isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and diphenylmethane diisocyanate.
[0011] Preferably, the stress-induced material further includes segments derived from a chain extender selected from at least one of cyclohexanediamine (e.g., 1,4-cyclohexanediamine), N,N-dihydroxyethyloxalamide, hexanediamine, and N,N-bis(3-aminopropyl)methylamine.
[0012] Preferably, the molar ratio of the hydrophilic polymer polyol to the hydrophobic polymer polyol is (0.5-4):1;
[0013] The molar ratio of the diisocyanate to the total amount of the polymer polyol (i.e., hydrophilic polymer polyol + hydrophobic polymer polyol) is (1.4~2.6):1;
[0014] The molar ratio of the chain extender dosage to the total amount of polymer polyols (i.e., hydrophilic polymer polyols + hydrophobic polymer polyols) is (0.4~1.6):1;
[0015] As a further preferred embodiment of the present invention, the number average molecular weight of both the hydrophilic polymer polyol and the hydrophobic polymer polyol is 600 to 4000, for example, 600, 800, 1000, 2000, 3000 or 4000.
[0016] According to another aspect of the present invention, the present invention provides a method for preparing the above-mentioned stress-reduction material, characterized by comprising the following steps:
[0017] (1) Using hydrophilic polymer polyol and hydrophobic polymer polyol as soft segment raw materials and diisocyanate as hard segment raw materials, the soft segment raw materials and the hard segment raw materials are subjected to polycondensation reaction in the presence of a catalyst to obtain an isocyanate-terminated prepolymer.
[0018] (2) The isocyanate-terminated prepolymer obtained in step (1) is mixed with a chain extender and subjected to a chain extension reaction under the action of a catalyst to obtain the stress-change material.
[0019] Preferably, in step (1), the reaction temperature of the polycondensation reaction is 30-70°C and the reaction time is 6-24h.
[0020] Preferably, in step (2), the reaction temperature of the chain extension reaction is 30-70°C and the reaction time is 6-24h.
[0021] Preferably, step (1) or step (2) is performed in an inert atmosphere.
[0022] Preferably, the reaction in step (1) is carried out in the presence of a solvent, preferably, the solvent is at least one of tetrahydrofuran, N,N'-dimethylformamide or N,N'-dimethylacetamide; preferably, step (1) is carried out under anhydrous conditions, for example, the solvent is an anhydrous solvent, such as at least one of anhydrous tetrahydrofuran, anhydrous N,N'-dimethylformamide or anhydrous N,N'-dimethylacetamide.
[0023] Preferably, in step (1) or step (2), the catalyst is selected from amine, tin, or bismuth catalysts. For example, the catalyst is selected from at least one of dibutyltin dilaurate, dimethylcyclohexylamine, and bismuth isooctanoate. The content of the catalyst is not particularly limited, as long as it enables the polycondensation reaction or chain extension reaction to occur.
[0024] The beneficial effects of this invention are:
[0025] 1. The water-stimulated size change stress change material provided by the present invention contains both hydrophilic polymer polyol and hydrophobic polymer polyol. Depending on the material composition, it can undergo two shape changes in an aquatic environment, namely water absorption and swelling, and water as a plasticizer to activate the movement of polymer chain segments to achieve shape recovery.
[0026] 2. In the stress-reactive material of this invention, the polarity difference between the hard segment urethane / urea groups and the soft segment polymer polyol promotes the formation of a microphase separation structure. The hard segment aggregates as the dispersed phase and their hydrogen bonding interactions endow the polyurethane / polyurea with excellent mechanical properties. In particular, when the material absorbs water, the hydrophobic segments (including urethane / urea groups) aggregate together, serving as physical crosslinking points to maintain the mechanical stability of the material.
[0027] 3. The stress-reduction material provided by this invention can be prepared on a large scale and has a linear structure, and can be processed by solution or thermal processing.
[0028] In summary, the stress-sensitive material prepared by this invention can undergo two types of size changes under water stimulation: first, by absorbing a large amount of water to induce hydrophilic segment rearrangement and achieve volume expansion; second, by absorbing a small amount of water as a plasticizer to promote segment movement and achieve shape recovery. At the same time, thanks to the introduction of hydrophobic segments, polyurethane / polyurea can maintain sufficient mechanical strength even in aquatic environments, thus broadening the application range of the material. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of the structure of the polyurethane prepared in Example 1.
[0030] Figure 2 The infrared spectrum of the polyurethane prepared in Example 1 is shown.
[0031] Figure 3 This is a schematic diagram of the stress-strain curves of the polyurethane prepared in Example 1 before and after water absorption.
[0032] Figure 4 The diagram shows the change in diameter of the polyurethane prepared in Example 1 before and after water absorption.
[0033] Figure 5 This is a shape memory effect diagram of the polyurethane prepared in Example 2 after being stimulated by water.
[0034] Figure 6 This is a schematic diagram of the stress-strain curves of the polyurethane prepared in Example 3 before and after water absorption.
[0035] Figure 7 The diagram shows the change in diameter of the polyurethane prepared in Example 3 before and after water absorption.
[0036] Figure 8 The image shows the diameter change of the polyurethane prepared in Example 4 before and after being stimulated by water to induce shape memory.
[0037] Figure 9 This is a schematic diagram of the force-strain curves of the polyurethane pipe prepared in Example 5 before and after water absorption.
[0038] Figure 10This is a schematic diagram of the stress-strain curves of the polyurethane prepared in Comparative Example 1 before and after water absorption.
[0039] Figure 11 The image shows the actual shape of the polyurethane prepared in Comparative Example 2 after it has absorbed water and dried.
[0040] Figure 12 This is a schematic diagram illustrating the dimensional changes of a material under stress when exposed to water. Detailed Implementation
[0041] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.
[0042] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.
[0043] Example 1
[0044] The polyurethane prepared in this embodiment has the following basic structure: Figure 1 As shown. Polyethylene glycol (4 mmol) with a number-average molecular weight of 1000 and polytetrahydrofuran (1 mmol) with a number-average molecular weight of 4000 were added to a round-bottom flask. The mixture was kept under vacuum at 100°C for 2 hours to remove trace amounts of water. Then, the temperature was lowered to 60°C, and anhydrous tetrahydrofuran was added and stirred to dissolve, resulting in a clear and homogeneous reaction solution. Dicyclohexylmethane diisocyanate (7 mmol) and 3 drops of dibutyltin dilaurate were added to the reaction solution. After reacting for 8 hours under an inert atmosphere, N,N-dihydroxyethyloxalamide (2 mmol) was added, and the reaction continued for 12 hours. The reaction solution was poured into a polytetrafluoroethylene mold, dried at room temperature for 24 hours, and then transferred to a vacuum oven and dried at 60°C for 24 hours to obtain a polyurethane film material.
[0045] The chemical structure of polyurethane was characterized using Fourier transform infrared spectroscopy, and the test results are as follows: Figure 2 As shown, wavenumbers are 3529-3316 cm⁻¹. -1 This is the peak of the NH stretching vibration in carbamates; wavenumber range: 2935–2864 cm⁻¹ -1 The peaks represent the stretching vibrations of -CH3 and -CH2-. Wavenumber 1703 cm⁻¹ -1 and 1677cm -1 The peaks represent the stretching vibrations of C=O in urethane and oxalamide, respectively. Infrared results indicate that polyurethane was successfully prepared.
[0046] The mechanical properties of polyurethane are tested using the following method: The polyurethane film material is cut into a standard shape and tested using a universal testing machine. For example... Figure 3 As shown, the polyurethane prepared in this embodiment has a tensile strength of 2.4 MPa and an elongation at break of 1600% before water absorption.
[0047] To further characterize the mechanical properties of polyurethane after water absorption, the prepared polyurethane was placed in room temperature water for 1 hour, and the test results were obtained. Figure 3 The results show that after water absorption, the tensile strength of polyurethane increases to 9.0 MPa, while the elongation at break decreases to 1200%. This is because water absorption promotes the formation of a microphase separation structure, with hydrophobic segments (including urethane esters) agglomerating together, which acts as physical crosslinking points to enhance the modulus of the material.
[0048] Further verification was conducted on the dimensional changes of polyurethane after exposure to water. Tubular polyurethane material was immersed in physiological saline solution. After 2.5 minutes, the weight of the polyurethane increased from 0.0576 g to 0.0836 g, with a water absorption rate of 45%. Figure 4 As shown, the diameter of the polyurethane pipe has increased from 7.30 mm to 9.74 mm, with a dimensional change rate (by diameter) of 35%.
[0049] Example 2
[0050] Polypropylene glycol (1 mmol) with a number-average molecular weight of 600 and polycarbonate (2 mmol) with a number-average molecular weight of 1000 were added to a round-bottom flask, and the mixture was kept under vacuum at 100°C for 2 hours to remove trace amounts of water. The temperature was then lowered to 60°C, and anhydrous tetrahydrofuran was added and stirred to dissolve, resulting in a clear and homogeneous reaction solution. Diphenylmethane diisocyanate (7.8 mmol) and 5 drops of dimethylcyclohexylamine were added to the reaction solution, and the mixture was reacted for 12 hours under an inert atmosphere. The temperature was then lowered to 30°C, and 1,4-cyclohexanediamine (4.8 mmol) was added. The reaction was continued for another 12 hours. The reaction solution was poured into a polytetrafluoroethylene mold, dried at room temperature for 24 hours, and then transferred to a vacuum oven and dried at 60°C for 24 hours to obtain a polyurethane membrane material.
[0051] This study verifies the shape memory function of polyurethane after water stimulation. The shape memory function exhibited by polymers stems from the stimulus-responsiveness of their molecular chains. Heating activates the mobility of polymer chain segments, allowing them to edit temporary shapes. Upon cooling, this mobility is frozen, and the material acquires a temporary shape. Upon external stimulation, the chain segment mobility is reactivated, and the material recovers its original shape under the action of a stationary phase. A polyurethane membrane material was heated to 60°C and a temporary shape was applied. The shape was then maintained and cooled to 10°C to fix the temporary shape. The polyurethane membrane with the fixed temporary shape was then immersed in water (25±5°C), and the degree of shape recovery was observed. Figure 5 As shown, the stress-induced material of this invention can recover to its original shape within 2 minutes. Water, as a plasticizer, can activate chain segment movement, while rigid polycarbonate and urethane groups act as a stationary phase, driving the material to recover to its original shape.
[0052] Example 3
[0053] Branched polyethylene glycol (1 mmol) with a number-average molecular weight of 1000 and polycaprolactone (1 mmol) with a number-average molecular weight of 2000 were added to a round-bottom flask, and the mixture was kept under vacuum at 100°C for 2 hours to remove trace amounts of water. The temperature was then lowered to 70°C, and anhydrous N,N'-dimethylformamide was added and stirred to dissolve, resulting in a clear and homogeneous reaction solution. Isophorone diisocyanate (4 mmol) and 4 drops of bismuth isooctanoate were added to the reaction solution, and the reaction was carried out under an inert atmosphere for 6 hours. The temperature was then lowered to 30°C, and hexamethylenediamine (2 mmol) was added. The reaction was continued for 12 hours. The reaction solution was poured into a polytetrafluoroethylene mold, dried at 80°C for 24 hours, and then transferred to a vacuum oven and dried at 60°C for 24 hours to obtain a polyurethane membrane material.
[0054] The mechanical properties of polyurethane were tested using the same test method as in Example 1, and the test results are as follows: Figure 6 As shown, the polyurethane prepared in this embodiment has a tensile strength of 6.8 MPa and an elongation at break of 410% before water absorption. After water absorption, the tensile strength of the polyurethane increases to 9.2 MPa, while the elongation at break decreases to 310%. This is because water absorption promotes the formation of a microphase separation structure, with hydrophobic segments (including urethane / urea groups) aggregating together, which acts as physical crosslinking points to enhance the modulus of the material.
[0055] To further verify the dimensional changes of polyurethane after exposure to water, tubular polyurethane materials were immersed in physiological saline for 3 minutes. Figure 7 As shown, the diameter of the polyurethane pipe has increased from 7.73 mm to 8.73 mm, with a dimensional change rate (by diameter) of 13%.
[0056] Example 4
[0057] Polyethylene glycol (2 mmol) with a number average molecular weight of 2000 and polydimethylsiloxane (1 mmol) with a number average molecular weight of 3000 were added to a round-bottom flask, and the mixture was kept under vacuum at 100°C for 2 hours to remove trace amounts of water. The mixture was then cooled to 70°C, and anhydrous N,N'-dimethylacetamide was added and stirred to dissolve, resulting in a clear and homogeneous reaction solution. Hexamethylene diisocyanate (6.6 mmol) and 3 drops of bismuth isooctanoate were added to the reaction solution, and the mixture was reacted under an inert atmosphere for 6 hours. The mixture was then cooled to 30°C, and N,N-bis(3-aminopropyl)methylamine (3.6 mmol) was added. The reaction was continued for 12 hours. The reaction solution was poured into a polytetrafluoroethylene mold, dried at 80°C for 24 hours, and then transferred to a vacuum oven and dried at 60°C for 24 hours to obtain a polyurethane film material.
[0058] The polyurethane pipe was heated to 60°C and flattened under pressure, maintaining its shape while cooling to 10°C to fix a temporary shape. The temporarily shaped pipe was then immersed in water (25±5°C), and the degree of shape recovery was observed. Figure 8 As shown, the pipe can recover within 2 minutes, and its diameter increases by 19% compared to its original shape. Water, acting as a plasticizer, activates chain segment movement, while rigid polycarbonate and urethane groups serve as a stationary phase, driving the pipe's recovery and further increasing its diameter.
[0059] Example 5
[0060] Polypropylene glycol (0.5 mol) and polycarbonate (0.25 mol) with a number average molecular weight of 2000 were dissolved in anhydrous N,N'-dimethylformamide after dehydration. Dicyclohexylmethane diisocyanate (1.5 mol) and 12 ml of dimethylcyclohexylamine were added to the reaction solution, and the mixture was heated to 70 °C and reacted for 8 h under an inert atmosphere. Then, the temperature was lowered to 30 °C and 1,4-cyclohexanediamine (0.75 mol) was added, and the reaction was continued for 12 h. The reaction solution was poured into a polytetrafluoroethylene mold, dried at room temperature for 24 h, and then transferred to a vacuum oven and dried at 60 °C for 24 h to obtain a polyurethane film material.
[0061] A universal testing machine was used to test the fracture force of polyurethane pipes before and after water absorption. Figure 9 The tensile curve of the polyurethane pipe shows that the breaking force of the pipe before water absorption is 16N, which increases to 19N after water absorption. Water can promote the formation of a microphase separation structure, thereby improving the strength of the material.
[0062] Comparative Example 1
[0063] Polytetrahydrofuran (2 mmol) with a number-average molecular weight of 4000 was added to a round-bottom flask and vacuumed at 100°C for 2 hours to remove trace amounts of water. The temperature was then lowered to 60°C, and anhydrous tetrahydrofuran was added and stirred to dissolve, resulting in a clear and homogeneous reaction solution. Dicyclohexylmethane diisocyanate (4 mmol) and 3 drops of dibutyltin dilaurate were added to the reaction solution, and the reaction was carried out under an inert atmosphere for 8 hours. Then, N,N-dihydroxyethyl oxalamide (2 mmol) was added, and the reaction continued for 12 hours. The reaction solution was poured into a polytetrafluoroethylene mold, dried at room temperature for 24 hours, and then transferred to a vacuum oven and dried at 60°C for 24 hours to obtain a polyurethane film material.
[0064] The mechanical properties of polyurethane were tested using the same test method as in Example 1, and the test results are as follows: Figure 10As shown, the polyurethane prepared in this comparative example had a tensile strength of 3.5 MPa and an elongation at break of 525% before water absorption. After water absorption, the tensile strength of the polyurethane decreased to 1.9 MPa and the elongation at break decreased to 170%. This is because the lack of hydrophilic soft segments resulted in an indistinct microphase separation structure after water absorption. Water molecules reduced the free space between molecular chains and broke some hydrogen bonds, leading to a decrease in both modulus and toughness.
[0065] Comparative Example 2
[0066] Polyethylene glycol (2 mmol) with a number average molecular weight of 1000 was added to a round-bottom flask, and the mixture was kept under vacuum at 100°C for 2 hours to remove trace amounts of water. The temperature was then lowered to 60°C, and anhydrous tetrahydrofuran was added and stirred to dissolve, resulting in a clear and homogeneous reaction solution. Dicyclohexylmethane diisocyanate (3 mmol) and 3 drops of dibutyltin dilaurate were added to the reaction solution, and the reaction was carried out under an inert atmosphere for 8 hours. Then, N,N-dihydroxyethyl oxalamide (1 mmol) was added, and the reaction was continued for 12 hours. The reaction solution was poured into a polytetrafluoroethylene mold, dried at room temperature for 24 hours, and then transferred to a vacuum oven and dried at 60°C for 24 hours to obtain a polyurethane film material.
[0067] This material has poor mechanical properties and cannot maintain its shape after absorbing water and drying. A picture of the actual product is shown below. Figure 11 As shown, this is because the large number of hydrophilic soft segments results in a low modulus of the material before water absorption.
[0068] The embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A stress-induced size change material responsive to water stimulation, characterized in that, The stress-induced size change material in this water-stimulated material includes hydrophobic and hydrophilic segments; The raw materials constituting the hydrophilic segments are selected from hydrophilic polymer polyols. The number-average molecular weights of the hydrophilic polymer polyols are all between 600 and 4000. The raw materials constituting the hydrophobic segments are selected from hydrophobic polymer polyols. The water-stimulated size change stress-reaction material also includes hard segments, the raw materials for which the hard segments are prepared are selected from diisocyanates; The water-stimulated size change stress-change material also includes a chain extender, which is selected from at least one of cyclohexanediamine, N,N-dihydroxyethyl oxalamide, hexanediamine and N,N-bis(3-aminopropyl)methylamine; The molar ratio of the hydrophilic polymer polyol to the hydrophobic polymer polyol is (0.5-4):1; The molar ratio of the diisocyanate to the total amount of the polymer polyol is (1.4–2.6):1; The molar ratio of the chain extender to the total amount of polymer polyol is (0.4–1.6):1; The raw materials constituting the hydrophobic segments are selected from at least one of polytetrahydrofuran diol, polycarbonate diol, polydimethylsiloxane diol, and polycaprolactone diol; The raw materials constituting the hydrophilic segments are selected from one or both of polyethylene glycol and polypropylene glycol.
2. The water-stimulated size change stress-response material according to claim 1, characterized in that, The diisocyanate is selected from aliphatic diisocyanates and aromatic diisocyanates.
3. The water-stimulated size change stress-response material according to claim 2, characterized in that, The diisocyanate is selected from one or more of isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and diphenylmethane diisocyanate.
4. The water-stimulated size change stress-response material according to claim 1, characterized in that, The number average molecular weight of the hydrophobic polymeric polyol is 600 to 4000.
5. A method for preparing the water-stimulated size change stress-reaction material according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Using hydrophilic polymer polyol and hydrophobic polymer polyol as soft segment raw materials and diisocyanate as hard segment raw materials, the soft segment raw materials and the hard segment raw materials are subjected to polycondensation reaction in the presence of a catalyst to obtain isocyanate-terminated prepolymer. (2) The isocyanate-terminated prepolymer obtained in step (1) is mixed with a chain extender and a chain extension reaction is carried out under the action of a catalyst to obtain the water-stimulated size change stress change material.
6. The preparation method according to claim 5, characterized in that, In step (1), the reaction temperature of the polycondensation reaction is 30-70 °C and the reaction time is 6-24 h.
7. The preparation method according to claim 5, characterized in that, In step (2), the reaction temperature of the chain extension reaction is 30-70 °C and the reaction time is 6-24 h.
8. The preparation method according to claim 5, characterized in that, Step (1) or step (2) is performed in an inert atmosphere.
9. The preparation method according to claim 5, characterized in that, The reaction in step (1) is carried out in the presence of a solvent, which is at least one of tetrahydrofuran, N,N'-dimethylformamide or N,N'-dimethylacetamide.
10. The preparation method according to claim 5, characterized in that, In step (1) or step (2), the catalyst is selected from amine, tin or bismuth catalysts.