High-molecular polymer as well as preparation method and application thereof

Abstract

The invention provides a high-molecular polymer as well as a preparation method and application thereof, the preparation method of the high-molecular polymer comprises the following steps: S1, carrying out RAFT polymerization reaction on polycaprolactone and sodium 4-styrenesulfonate to obtain a PCL-b-PSSNa block copolymer; s2, the PCL-b-PSSNa block copolymer and a chain extender are subjected to a chain extension reaction, and the high-molecular polymer is obtained. According to the invention, crystalline polycaprolactone and sodium 4-styrenesulfonate are subjected to RAFT polymerization, a sodium polystyrenesulfonate block with higher glass transition temperature (higher modulus) can be introduced, and the sodium polystyrenesulfonate block can be used as a physical crosslinking point, so that the elastic modulus of the material can be remarkably improved; the material has high load capacity and a wide temperature window while having rapid thermal response, and overcomes the problem of easy instability.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and relates to a polymer, its preparation method and application. Background Technology

[0002] Compared to traditional mechanical systems, soft robots are typically made of relatively soft polymer materials, thus possessing better flexibility and environmental adaptability, and have significant application prospects in fields such as smart wearables, healthcare, and exploration and monitoring. With their exceptional adaptability, soft robots can easily integrate into diverse unstructured environments and exhibit unprecedented safety when interacting with humans. The design philosophy of soft robots is deeply inspired by biological models in nature, such as mimicking the peristaltic mechanism of earthworms, the flexible tentacles of octopuses, and the soft body of jellyfish, enabling them to deform in response to external stimuli and perform work.

[0003] Soft robots require rapid and coordinated deformation of their internal components to perform tasks. Current soft actuators used in soft robots are typically categorized into pH actuation, electro-actuation, fluid actuation, and thermal actuation, and are fabricated using materials such as crystalline polymers, polymer gels, and polymer dielectric elastomers. However, for these three types of materials, fabricating artificial muscle fibers capable of generating astonishing explosive force in a short time, comparable to real muscle tissue, remains a significant challenge in thermal actuation. The difficulty lies in the fact that artificial muscles fabricated based on traditional commercial polymer materials often struggle to achieve a balance between solid and fluid properties. Currently, soft actuators based on polymer materials often cannot simultaneously possess high load capacity and fast response time, making it difficult to rival real muscle tissue. While current crystalline polymer materials offer the advantage of fast response speeds, capable of responding on the order of seconds, their narrow temperature windows make them prone to instability. For electro-actuation, achieving good driving capability and cycle stability at low voltages is also a crucial challenge. Summary of the Invention

[0004] To address the issues in the prior art where soft actuators cannot simultaneously achieve high load and fast response time under thermal actuation, and where crystalline polymer materials have narrow temperature windows and are prone to instability, as well as the challenges of achieving good driving capability and cycle performance under electric actuation, this invention provides a polymer, its preparation method, and its applications.

[0005] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing a polymer, comprising: S1, polycaprolactone and sodium 4-styrenesulfonate were subjected to RAFT polymerization to obtain PCL-b-PSSNa block copolymer; S2, PCL-b-PSSNa block copolymer undergoes chain extension reaction with chain extender to obtain high molecular weight polymer.

[0006] Preferably, in S1, the preparation method of polycaprolactone is as follows: caprolactone, RAFT reagent and stannous octoate solution are mixed, toluene is added, and the reaction is carried out under heating conditions. After the reaction is completed, the resulting reaction solution is dissolved in a mixed solution of dichloromethane and n-hexane, methanol is added to precipitate, the precipitate is collected, dried, and polycaprolactone is obtained.

[0007] Preferably, in S1, the mass ratio of polycaprolactone to sodium 4-styrenesulfonate is 1:(0.5~1.5).

[0008] Preferably, S1 specifically includes: dissolving polycaprolactone, azodicyanovalerate and sodium 4-styrenesulfonate in a mixed solution of ethanol and water, reacting under inert gas protection by heating, and washing with a poor solvent after the reaction is completed to obtain PCL-b-PSSNa block copolymer.

[0009] Preferably, in S2, the chain extender is hexamethylene diisocyanate, 4,4-diisocyanate dicyclohexylmethane, isoflurone diisocyanate, or toluene diisocyanate.

[0010] Secondly, the present invention provides a polymer obtained by the preparation method described above.

[0011] Thirdly, the present invention provides a polymer electrolyte membrane comprising the aforementioned polymer and ionic liquid.

[0012] Preferably, the mass ratio of the polymer to the ionic liquid is 1:(1~4).

[0013] Fourthly, the present invention provides a method for preparing the polymer electrolyte membrane, wherein the polymer, ionic liquid and cellulose powder are dispersed in a solvent, heated and stirred, and dried to obtain the polymer electrolyte membrane.

[0014] Fifthly, the present invention provides a soft actuator, comprising the aforementioned polymer or the aforementioned polymer electrolyte membrane.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes RAFT polymerization of crystalline polycaprolactone (PCL) with sodium 4-styrene sulfonate to introduce sodium styrene sulfonate (PSSNa) blocks with high glass transition temperatures (high moduli). These PSSNa blocks act as physical crosslinking points, significantly enhancing the material's elastic modulus. This results in a material with rapid thermal response, high load-bearing capacity, and a wide temperature window, overcoming instability issues. However, the high glass transition temperature of the PSSNa blocks can increase brittleness. This invention employs a chain extension reaction of ABA-type triblock PCL-b-PSSNa with two terminal hydroxyl groups to further increase its molecular weight, thereby improving the polymer's toughness. This ensures that the final polymer will not suffer defects or damage due to excessive brittleness during future processing, molding, and actuation.

[0016] The polymer prepared by this invention has thermal actuation capability and fast response speed, and can be used in thermally driven soft actuators.

[0017] This invention utilizes a mixture of a polymer and an ionic liquid to form a polymer electrolyte membrane, which has the capability of electro-actuation and can be used in electrically driven soft actuators.

[0018] Both the thermally driven and electrically driven soft actuators based on the polymers described in this invention have high load capacity and wide temperature window. The electrically driven soft actuator prepared has a fast electrical response rate and a large electro-drive capability. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The NMR data are those of the PCL-b-PSSNa block copolymers obtained in Examples 1, 5-7 of this invention. Figure 2 Images showing the appearance of three different products obtained in Example 1 of this invention; Figure 3 The image shown is a DSC image of the PCL homopolymer obtained in Example 1 of this invention. Figure 4 The image shows a DSC image of the PCL-b-PSSNa block copolymer obtained in Example 1 of this invention. Figure 5The image shows a DSC image of the polymer obtained in Example 1 of this invention. Figure 6 The following figures illustrate the states of the polymer film formed by the polymer in Example 1 of this invention at different moments of deformation: (a) polymer film state at 0s; (b) polymer film state at 30s; (c) polymer film state at 60s; (d) polymer film state at 90s. Figure 7 The curve showing the change of the linear distance between the two ends of the polymer film formed by the polymer in Example 5 of the present invention over time; Figure 8 The conductivity test results of polymers doped with different amounts of ionic liquids obtained in Example 5 of this invention; Figure 9 The conductivity test results of polymers doped with different amounts of ionic liquids obtained in Example 6 of this invention; Figure 10 Before applying voltage to the soft actuator; Figure 11 After applying voltage to the soft actuator. Detailed Implementation

[0021] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0022] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.

[0023] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not intended to limit the order of the method steps or define the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0024] The method for preparing the polymer according to the present invention includes: S1, polycaprolactone and sodium 4-styrenesulfonate were subjected to RAFT polymerization to obtain PCL-b-PSSNa block copolymer; S2, PCL-b-PSSNa block copolymer undergoes chain extension reaction with chain extender to obtain high molecular weight polymer.

[0025] This invention involves RAFT polymerization of polycaprolactone and sodium 4-styrene sulfonate to introduce sodium styrene sulfonate blocks with high glass transition temperatures (high modulus). These sodium styrene sulfonate blocks act as physical crosslinking points, significantly improving the elastic modulus of the material. This results in a material with rapid thermal response, high load-bearing capacity, and a wide temperature window, overcoming the problem of instability. Simultaneously, the high glass transition temperature of the sodium styrene sulfonate blocks can increase the material's brittleness. This invention further increases the molecular weight of the ABA-type triblock PCL-b-PSSNa with two hydroxyl groups at the ends through chain extension, enhancing the polymer's toughness. This ensures that the final polymer will not suffer defects or damage due to excessive brittleness during future processing, molding, and actuation.

[0026] In some preferred embodiments of the present invention, in S1, the preparation method of polycaprolactone is as follows: caprolactone, RAFT reagent and stannous octoate solution are mixed, toluene is added, and the reaction is carried out under heating conditions. After the reaction is completed, the resulting reaction solution is dissolved in a mixed solution of dichloromethane and n-hexane, methanol is added to precipitate, the precipitate is collected, dried, and polycaprolactone is obtained.

[0027] This invention utilizes ring-opening polymerization to polymerize caprolactone, yielding crystalline polycaprolactone. The use of stannous octoate as a catalyst in the ring-opening polymerization of caprolactone maintains good polydispersity (typically less than 1.2) even at high conversion rates. Using toluene as the reaction solvent reduces the impact of any residual moisture on the polymerization, ensuring that the initiation centers originate from the hydroxyl groups on the difunctional small-molecule RAFT reagent.

[0028] In some preferred embodiments of the present invention, in S1, the mass ratio of polycaprolactone to sodium 4-styrenesulfonate is 1:(0.5~1.5).

[0029] In some preferred embodiments of the present invention, in S1, the reaction temperature of the RAFT polymerization reaction is 60~70°C and the reaction time is 10~14h.

[0030] In some preferred embodiments of the present invention, S1 specifically includes: dissolving polycaprolactone, azodicyanovalerate and sodium 4-styrenesulfonate in a mixed solution of ethanol and water, reacting under inert gas protection by heating, and washing with a poor solvent after the reaction is completed to obtain PCL-b-PSSNa block copolymer.

[0031] In this invention, during the RAFT polymerization reaction of polycaprolactone and sodium 4-styrenesulfonate, a reaction solvent (a mixture of water and methanol or a mixture of water and ethanol), a water-soluble initiator for sodium 4-styrenesulfonate monomer (azodicyanovalerate), and polycaprolactone are simultaneously added. An inert gas is continuously purged for 30 minutes to achieve an oxidation-free process. Controlling the feed ratio allows for control of the degree of polymerization and the total molecular weight of the final product. The resulting product requires repeated washing and precipitation with a poor solvent (a mixture of methanol and water). After repeating this process, vacuum drying yields the final powder sample, PCL-b-PSSNa block copolymer.

[0032] In some preferred embodiments of the present invention, in S2, the chain extender is a difunctional diisocyanate, such as hexamethylene diisocyanate, 4,4-diisocyanate dicyclohexylmethane, isoflurane diisocyanate, or toluene diisocyanate, more preferably hexamethylene diisocyanate. The solvent used in the chain extension process of the present invention can be DMF, because DMF has a high boiling point and strong polarity, which can swell the PCL homopolymer and PSSNa blocks to a certain extent.

[0033] In some preferred embodiments of the present invention, in S2, the molar ratio of the chain extender to the hydroxyl group in the PCL-b-PSSNa block copolymer is (1~1.2):1.

[0034] The polymer prepared by this invention has thermal actuation capability and fast response speed, and can be used for thermally driven soft actuators.

[0035] The present invention mixes the polymer and ionic liquid to prepare a polymer electrolyte membrane, which has the ability to be electrically actuated and can be used in electrically driven soft actuators.

[0036] The mass ratio of the polymer to the ionic liquid is 1:(1~4). The ionic liquid is 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (HMIMTFS) or 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIMTFO).

[0037] The method for preparing the polymer electrolyte membrane involves dispersing the polymer, ionic liquid, and cellulose powder in a solvent, heating and stirring, and drying to obtain the polymer electrolyte membrane.

[0038] This invention improves the film-forming properties of polymer electrolyte membranes and enhances their mechanical strength by introducing cellulose powder.

[0039] Example 1 The polymer material synthesis route in this embodiment is as follows: (1) Synthesis of RAFT reagent Carbon disulfide (9.130 g, or 0.12 mol), chloroform (35.830 g, or 0.30 mol), acetone (14.100 g, or 0.30 mol), tetrabutylammonium bisulfate (0.803 g, or 2.37 mmol), and 40 mL of paraffin oil were thoroughly mixed and then transferred to a 250 mL three-necked flask. To ensure the safety and stability of the reaction process, the following measures were taken: one port of the three-necked flask was connected to a nitrogen source for protection, ensuring that nitrogen gas was introduced below the liquid surface to achieve a liquid seal; another port was connected to a mechanical stirrer to ensure uniform mixing of the reactants; and the last port was connected to a constant-pressure dropping funnel. The entire reaction system was then placed in a low-temperature constant-temperature reaction bath, and the temperature was set to -10°C.

[0040] Subsequently, a 50% NaOH solution (67.2 g, or 0.84 mol) was gradually added through a constant-pressure dropping funnel. After the NaOH solution was completely added, the temperature of the reaction bath was gradually increased to 20°C, and nitrogen gas was continuously introduced while stirring to ensure that the reaction proceeded stably under nitrogen protection for 12 hours.

[0041] After the reaction was complete, the reaction solution in the three-necked flask was transferred to a beaker, and 300 mL of deionized water was added for rinsing. During rinsing, nitrogen gas was continuously introduced, and the mixture was stirred using a magnetic stirrer. Next, 40 mL of concentrated hydrochloric acid was slowly added in batches, and stirring continued for approximately 20 minutes until the pH of the solution dropped to around 2 (at which point pH paper would turn purple-red). After standing for about 15 minutes, the solution showed obvious stratification.

[0042] To separate the solid-liquid mixture, a Buchner funnel was used for vacuum filtration, and the filter cake was washed multiple times with deionized water. The resulting filter cake was broken up and transferred to a beaker, then placed in a vacuum chamber for drying for 4 hours. Subsequent steps involved dissolving the filter cake multiple times with acetone, followed by precipitation with toluene (acetone to toluene volume ratio 1:4). Finally, vacuum filtration was performed again using a sintered glass funnel, and the filter cake was broken up and placed in a vacuum chamber to dry at 40°C for 12 hours, yielding DMAT and completing the entire process.

[0043] DMAT (5.64 g, or 20 mmol) was added to a 250 mL three-necked flask. Then, under constant stirring and a nitrogen atmosphere, thionyl chloride (SOCl2, 60 mL total, corresponding to 800 mmol) was carefully and gradually introduced dropwise. During stirring, the temperature was gradually increased to 60 °C, and the mixture was thoroughly stirred with a magnetic stir bar for 4 h at this constant temperature. After stirring, rotary evaporation was used to remove excess solvent from the thionyl chloride. The resulting brown solid was then dissolved in 20 mL of dichloromethane to ensure complete dissolution, preparing for subsequent experimental steps.

[0044] In subsequent experiments, the reaction apparatus was carefully assembled following the instructions. First, the previously prepared solution was carefully loaded into a constant-pressure dropping funnel. Then, through precise control, the solution was gradually added dropwise into a pre-prepared three-necked flask. This flask already contained 20 g of ethylene glycol, 10 mL of dichloromethane, and 17 mL of triethylamine to ensure the reaction proceeded under suitable solvent and reactant concentrations. The entire operation was carried out under nitrogen atmosphere at 0°C with continuous stirring using a magnetic stirrer. After the addition was complete, nitrogen gas was continued to be introduced, and the mixture was allowed to return to room temperature, allowing the reaction to proceed overnight under nitrogen protection for 12 hours.

[0045] After the reaction, the system was first filtered, followed by extraction with deionized water (60 mL, 3 times), and the filtrate was collected after shaking. Dichloromethane was removed again by rotary evaporation, and the resulting product was dissolved in ethyl acetate and subjected to column chromatography on an alkaline alumina column. After column chromatography, the washed bands were rotary evaporated again to obtain DMAT-EG. Finally, this product was placed in an oven and dried at 60°C for 12 hours to obtain RAFT reagent.

[0046] (12) Synthesis of soft segments of block copolymers First, 5g of caprolactone, the purchased RAFT reagent prepared in step (1), and 115.4μL of stannous octoate solution (10wt%) were sequentially added to a 250mL Schlenk flask. Then, 11mL of toluene was injected via syringe, with 1mL of toluene removed under vacuum to ensure effective removal of impurities from the reaction system. Next, the treated Schlenk flask was heated in an oil bath at 100°C and stirred with a magnetic stirrer for 24 hours to promote thorough mixing and reaction of the reactants.

[0047] After the polymerization reaction was completed, the resulting product was dissolved in a mixed solution of dichloromethane and n-hexane. Then, methanol was added as a precipitant, and the precipitate was collected by centrifugation. Finally, the precipitate was dried in an oven at 60°C for 12 hours to obtain the pure polymerized product, polycaprolactone (PCL).

[0048] (23) Polymerization of hard segments of block copolymers First, a nitrogen-purged system was set up. 3g of anhydrous ethanol and 1g of ultrapure water were added to a 50mL flask. Nitrogen gas was then purged into the ethanol and ultrapure water mixture for 15 minutes. Next, the reaction system was set up. The mixture was transferred to a two-necked flask containing 1g of polycaprolactone, 40mg of azodicyanovalerate (ACVA), and 588mg of sodium 4-styrenesulfonate solid. Nitrogen gas was then purged for another 3 minutes. The two-necked flask was heated in a 70°C oil bath and stirred magnetically for 12 hours. The reaction solution was then washed with a poor solvent, namely a mixture of ethanol and deionized water in a 3:1 volume ratio. After washing, the supernatant became clear and was directly filtered. The resulting product was dried in an oven at 60°C for 12 hours. (PCL) 62 -b-PSSNa 10 Block copolymers. To verify the properties of the product, the dried solid was weighed and heated to 80 degrees Celsius in an oil bath. The product softened, indicating that the product properties met the standards.

[0049] (34) Chain extension of block copolymers First, the synthesized 1g PCL 62 -b-PSSNa 10 The block copolymer was dispersed in 3 g of anhydrous DMF solvent. Subsequently, 33 mg of hexamethylene diisocyanate (HDI) was dissolved in 0.2 g of anhydrous DMF solvent and then transferred to PCL. 62 -b-PSSNa 10 The block copolymer was dispersed in a reaction system. The resulting reaction system was then immersed in a 90°C oil bath and reacted for 3 hours. After the reaction was completed, the crude product was poured into 20g of a poor solvent (ethanol to deionized water volume ratio of 3:1) for washing, centrifugation, and drying to obtain the final chain-extended polymer.

[0050] Example 2 It is basically the same as Example 1, except that the hexamethylene diisocyanate in step (34) is replaced with 4,4-diisocyanate dicyclohexylmethane.

[0051] Example 3 It is basically the same as Example 1, except that the hexamethylene diisocyanate in step (34) is replaced with isoflurane diisocyanate (IPDI).

[0052] Example 4 It is basically the same as Example 1, except that hexamethylene diisocyanate in step (34) is replaced with toluene diisocyanate (TDI).

[0053] Example 5 The results were essentially the same as in Example 1, except that the amount of sodium 4-styrenesulfonate was changed to 822 mg to obtain PCL. 62 -b-PSSNa 15 High molecular weight polymers.

[0054] Example 6 The results were essentially the same as in Example 1, except that the amount of sodium 4-styrenesulfonate was changed to 1176 mg to obtain PCL. 62 -b-PSSNa 20 High molecular weight polymers.

[0055] Example 7 The results were essentially the same as in Example 1, except that the amount of sodium 4-styrenesulfonate was changed to 1470 mg to obtain PCL. 62 -b-PSSNa 25 High molecular weight polymers.

[0056] Example 8 Preparation of polymer electrolyte membrane: 200 mg of the polymer prepared in Example 5 was taken, 200 mg of the ionic liquid HMIMTFSI was added, 20 mg of cellulose powder was added, DMF was used as solvent, and the mixture was stirred and mixed at 75 °C for 6 h. Then, it was dried in a vacuum oven at 100 °C for 6 h to obtain PCL. 62 -b-PSSNa 15 -HMIMTFSI-50% polymer electrolyte membrane.

[0057] Example 9 It is basically the same as Example 8, except that the ionic liquid HMIMTFSI is replaced with EMIMTFO.

[0058] Example 10 It is basically the same as Example 8, except that the ionic liquid HMIMTFSI is replaced with EMIMBF4.

[0059] Example 11 This is essentially the same as Example 8, except that the amount of ionic liquid HMIMTFSI was changed to 300 mg to obtain PCL. 62 -b-PSSNa 15 -HMIMTFSI-60%.

[0060] Example 12 This is essentially the same as Example 8, except that the amount of ionic liquid EMIMTFO was changed to 467 mg to obtain PCL. 62 -b-PSSNa 15 -HMIMTFSI-70%.

[0061] Example 13 This is essentially the same as Example 8, except that the amount of ionic liquid EMIMTFO was changed to 800 mg to obtain PCL. 62 -b-PSSNa 15 -HMIMTFSI-80%.

[0062] Example 14 Preparation of polymer electrolyte membrane: 200 mg of the polymer prepared in Example 6 was taken, 200 mg of the ionic liquid HMIMTFSI was added, 20 mg of cellulose powder was added, DMF was used as solvent, and the mixture was stirred and mixed at 75 °C for 6 h. Then, it was dried in a vacuum oven at 100 °C for 6 h to obtain PCL. 62 -b-PSSNa 20 -HMIMTFSI-50% polymer electrolyte membrane.

[0063] Example 15 This is essentially the same as Example 14, except that the amount of ionic liquid HMIMTFSI was changed to 300 mg to obtain PCL. 62 -b-PSSNa 20 -HMIMTFSI-60%.

[0064] Example 16 This is essentially the same as Example 14, except that the amount of ionic liquid EMIMTFO was changed to 467 mg to obtain PCL. 62 -b-PSSNa 20 -HMIMTFSI-70%.

[0065] Example 17 This is essentially the same as Example 14, except that the amount of ionic liquid EMIMTFO was changed to 800 mg to obtain PCL. 62 -b-PSSNa 20 -HMIMTFSI-80%.

[0066] In Examples 1-4 of this invention, different isocyanates were selected for chain extension, and the optimal chain extender type was chosen by comparing the colors of the synthesized materials. The colors of the polymers obtained in Examples 1-4 are shown in Table 1. It can be seen that different isocyanates used as chain extenders resulted in polymers of different colors. For aesthetic purposes in later use, this invention preferentially uses white polymers. Furthermore, since 4,4-diisocyanate dicyclohexylmethane contains a benzene ring, which may cause interaction effects, hexamethylene diisocyanate was selected as the optimal chain extender for subsequent experiments.

[0067] Table 1

[0068] Figure 1 The NMR data for the PCL-b-PSSNa block copolymers prepared in Examples 1, 5-7 are from... Figure 1 It can be seen that the PCL homopolymer and PSSNa successfully reacted to obtain the PCL-b-PSSNa block copolymer. Furthermore, this invention allows for the preparation of PCL-b-PSSNa block copolymers with different degrees of polymerization by adjusting the amount of PSSNa used.

[0069] Appearance comparison of three different products prepared in Example 1 Figure 2 As shown, the PCL homopolymer exhibits typical morphological characteristics of a crystalline polymer. The presence of the RAFT reagent, trithiocarbonate, gives the PCL homopolymer a bright yellow color. When the PCL homopolymer copolymerizes with PSSNa, its color undergoes a slight change; the resulting PCL-b-PSSNa block copolymer is slightly lighter in color than the PCL homopolymer. Further chain extension of the PCL-b-PSSNa block copolymer yields the desired polymer. During this process, the material's color changes significantly. The initially slightly yellow PCL-b-PSSNa block copolymer becomes even lighter after chain extension, almost approaching white. This significant color change is likely due to the introduction of polyurethane groups during chain extension. The unique molecular structure of the polyurethane groups may influence the material's color, resulting in a lighter, almost white hue. The color differences of the three products indicate that the PCL homopolymer and PSSNa reacted successfully, and further chain extension was achieved.

[0070] The present invention analyzed the crystallization behavior of each product prepared in Example 1 to determine whether it exhibits rapid crystallization behavior. Figure 3The DSC images of the PCL homopolymer show the curves for the first cooling and the second heating, respectively, with heating and cooling rates of 10℃ / min and a heating / cooling window from -50℃ to 100℃. Analysis reveals that the prepared PCL homopolymer has a crystallization initiation temperature of 35.3℃, a crystallization peak temperature of 31.4℃, and a crystallization enthalpy of 35.4 J / g. Simultaneously, the PCL homopolymer has a melting initiation temperature of 51.9℃, a melting peak temperature of 54.1℃, and a melting enthalpy of 37.2 J / g. This indicates that the PCL homopolymer possesses good crystallization ability.

[0071] Figure 4 The image shows a DSC image of the PCL-b-PSSNa block copolymer obtained in Example 1. Analysis revealed that the crystallization onset temperature of the prepared PCL-b-PSSNa block copolymer was 34.5℃, the crystallization peak temperature was 28.7℃, and the enthalpy of crystallization was 63.1 J / g. Simultaneously, the melting onset temperature of this PCL-b-PSSNa block copolymer was 48.5℃, the melting peak temperature was 53.9℃, and the enthalpy of melting was 76.0 J / g. The crystallization peak temperature of this PCL-b-PSSNa block copolymer was 2.7℃ lower than that of the PCL homopolymer, and the melting peak temperature was correspondingly 0.2℃ lower. This indicates that the added PSSNa block has a certain limiting effect on the crystallization kinetics of the PCL-b-PSSNa block copolymer, resulting in a slight decrease in crystallinity compared to the PCL homopolymer.

[0072] Figure 5 The image shows a DSC image of the polymer obtained after isocyanate chain extension in Example 1. Analysis revealed a crystallization initiation temperature of 37.7°C, a crystallization peak temperature of 33.8°C, and a crystallization enthalpy of 42.9 J / g. Simultaneously, the sample exhibited a melting initiation temperature of 50.8°C, a melting peak temperature of 55.0°C, and a melting enthalpy of 45.5 J / g. Compared to the unextended PCL-b-PSSNa block copolymer, the crystallization enthalpy and melting enthalpy of the extended product decreased by 20.2 J / g and 30.5 J / g, respectively. This indicates that the crystallization ability of the PCL homopolymer significantly decreased due to the increase in the overall molecular weight of the polymer. This may be because PSSNa acts as a physical crosslinking point, restricting the movement of the entire polymer chain.

[0073] This invention investigates the thermodynamic behavior of the polymer obtained after chain extension in Example 5.

[0074] First, the polymer was placed in a mold, heated to melt, and then cooled to obtain a polymer film. The dimensions of the polymer film were: length 1.8 cm, width 0.5 cm, and thickness 0.1 cm. To measure the thermodynamic properties of the polymer, the polymer film was first bent to a certain extent. Due to the crystallization and solidification characteristics of the polymer, the polymer film could easily maintain its bent state. The bent polymer film was then placed on a preheated hot plate (temperature controlled at 70°C). The increase in temperature caused the polymer film to deform. The deformation process was recorded by a camera. In this invention, several moments of deformation were captured, such as... Figure 6 As shown. Combined with Figure 7 It can be observed that when the time reaches 30 seconds, the polymer film undergoes significant deformation, with the distance between its two ends rapidly increasing from 1.2 cm at 0 seconds to 1.5 cm. After waiting another 30 seconds, the distance reaches 1.7 cm. After waiting for 90 seconds, the film deformation returns to its initial planar state. This result demonstrates that the polymer of the present invention possesses thermal actuation capability and a fast response speed.

[0075] Subsequently, the synthesized polymer is melt-extruded, a relatively mature process for polymer materials. However, research on processing and molding methods for ionomers is not yet in-depth. This invention employs the following two methods to process the polymer: Method (1): The polymer is heated above its melting point. Due to the high glass transition temperature of the PSSNa block and the difficulty in molding high molecular weight substances after chain extension, different temperatures need to be tried to determine the optimal molding temperature. The final molding temperature is 120℃. Next, the polymer is placed in a metal syringe, heated to the molding temperature, and a rod-shaped structure is injected. Then, it is rapidly cooled to form the desired shape. Subsequently, it is stretched and oriented at high temperature. After cooling, the polymer chains are frozen. Heating can achieve a thermal actuation effect.

[0076] Method (2): Design a polytetrafluoroethylene mold to form a rod-shaped structure; place a polymer dissolved in DMF solution into the mold. The mold consists of two semi-cylindrical polytetrafluoroethylene plates connected together. After drying in a vacuum oven at 120°C, it is demolded and stretched and oriented at high temperature. After cooling, the polymer chains are frozen, and after heating, a thermo-actuated effect can be achieved.

[0077] This invention investigates the thermal actuation effect of polymers. First, different stretching ratios obtained by method (1) were compared, for example, stretching ratios of 10%, 50%, and 100%, to explore their actuation effect at different stretching ratios. Under a stretching ratio of 10%, the actuation rate was 2% at 10s and 5% at 30s, and remained unchanged over time. Under a stretching ratio of 50%, the actuation rate was 20% at 10s and 35% at 30s, and remained unchanged over time. Under a stretching ratio of 100%, the actuation rate was 40% at 10s and 50% at 30s, and remained unchanged over time. These results indicate that the polymer of this invention possesses thermal actuation capability and a fast response speed.

[0078] The electro-actuation of the polymer of this invention was studied. The conductivity of the polymer electrolyte membranes prepared in Examples 8, 11-13 was tested, and the results are as follows: Figure 8 As shown, it can be seen that the conductivity of the polymer electrolyte membrane gradually increases with the increase of the ionic liquid addition. When the ionic liquid addition reaches 80%, the conductivity basically stabilizes and no longer shows significant changes. It can also be seen that at room temperature (25°C), the polymer electrolyte membrane of this invention can achieve a maximum ionic conductivity of 1.1 mS / cm. Similarly, the conductivity of the polymer electrolyte membranes prepared in Examples 14-17 was tested, and the results are as follows... Figure 9 As shown, the conductivity of the polymer electrolyte membrane gradually increases with the increase of the amount of ionic liquid added.

[0079] A soft actuator structure was formed by combining a polymer electrolyte membrane with electrodes, and the effect of electro-actuation was tested.

[0080] Electrode preparation: 33 mg of CNT and 50 mg of polyvinylidene fluoride (PVDF) powder were ground in a mortar. The ground material was then mixed with 82 mg of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) and 6 mL of dimethylacetamide (DMAc) solvent until homogeneous. Three large ceramic particles (5 mm in diameter) and six small ceramic particles (1 mm in diameter) were added and mixed thoroughly using a vortex mixer, followed by ultrasonication. The mixture was then placed in a PTFE mold and dried at 75°C for 24 hours to obtain the electrode.

[0081] Fabrication of the soft actuator: An electrode is sandwiched between two sides of the polymer electrolyte membrane to form a composite three-layer actuator. The thickness of the three-layer actuator is 0.3 mm, and it is cut into a rectangle of 20 mm × 3 mm.

[0082] The actuation effect of the soft actuator: The actuation effect of the soft actuator was tested at different voltages and frequencies (e.g., 10 and 10). Figure 11 Test results at voltages of 0.5V, 1.0V, 2.0V, and 3.0V show that its actuation effect increases with increasing voltage.

[0083] The above research results show that the polymer of the present invention, after being doped with ionic liquid, can achieve an ionic conductivity of up to 1.1 mS / cm, and the soft actuator formed therefrom has good potential for electro-actuation.

[0084] In summary, this invention improves upon existing thermally responsive soft actuators for polymer materials. Crystalline polymers suffer from drawbacks such as instability and low modulus. Block polymers, however, possess excellent structural and functional design capabilities. From a structural design perspective, careful design of the types and compositions of block copolymers can yield various microphase separation structures, including spherical, columnar, layered, and bicontinuous phases, enabling the control of material mechanical properties. From a functional design perspective, the chemical structures and compositions of each segment within the block copolymer can be partitioned, separating functional responsive units from mechanical structural units, thereby contributing to a dual improvement in both material responsiveness and mechanical properties.

[0085] The elastic modulus of homopolymers often decreases significantly after entering the melt. Therefore, to prevent a significant decrease in modulus after heating, this invention introduces polymer electrolyte (PSSNa) blocks with a high glass transition temperature. These polymer electrolyte blocks act as physical crosslinking points, significantly improving the elastic modulus of the material. However, it should be noted that the high glass transition temperature of the polymer electrolyte also significantly increases the brittleness of the material, potentially leading to structural instability during shape changes. To address this, this invention performs a chain extension reaction on PCL-b-PSSNa to further increase its molecular weight, thereby improving the polymer's toughness. This ensures that the resulting polymer will not suffer defects or damage due to excessive brittleness during future processing, molding, and actuation.

[0086] In the molten state without external force, the polymer chains of this invention are microscopically random coils, and the mean square end-to-end distance is proportional to the product of the degree of polymerization of the polymer and the square of the chain segment length (R0). 2 =Nb 2 High molecular polymers exhibit typical isotropy on a macroscopic scale.

[0087] Subsequently, the polymer chains are stretched and oriented, causing them to break away from their original random coil conformation on a microscopic level. After stretching, the polymer chain segments become oriented, and macroscopically, the polymer (fiber) is stretched axially and contracted laterally. Due to the loss of conformational entropy, a certain amount of tensile elastic potential energy is generated within the polymer chains. Therefore, if the external force is removed at this point, the fiber will revert to its shape without external force.

[0088] Next, the temperature needs to be lowered under the stretched state to induce crystallization of the polymer. Along with crystal orientation, the movement of the polymer chain segments is frozen. At this point, due to the solidification effect of crystallization, the macroscopic morphology of the fiber material is fixed. Even if the external force is removed, the shape of the fiber will not change. The axial elastic modulus of the fiber will further increase due to the effect of crystallization, exhibiting typical anisotropy macroscopically. When a thermal response is required, the fiber only needs to be heated above the melting point of the crystalline polymer. At this point, the molten polymer chains can re-move, allowing the fiber to return to its original unstretched state. This melting phase transition caused by heating generally requires a very short time (on the order of seconds or minutes), so this type of polymer has a short response time.

[0089] When this polymer is doped with ionic liquid, its ionic conductivity can reach up to 1.1 mS / cm. Under low voltage, the polymer electrolyte membrane has good actuation capability. Therefore, actuators made of this polymer electrolyte membrane have good electro-actuation potential.

Claims

1. A method for preparing a polymer, characterized in that, include: S1, polycaprolactone and sodium 4-styrenesulfonate were subjected to RAFT polymerization to obtain PCL-b-PSSNa block copolymer; S2, PCL-b-PSSNa block copolymer undergoes chain extension reaction with chain extender to obtain high molecular weight polymer.

2. The method for preparing the polymer according to claim 1, characterized in that, In S1, the preparation method of polycaprolactone is as follows: caprolactone, RAFT reagent and stannous octoate solution are mixed, toluene is added, and the reaction is carried out under heating conditions. After the reaction is completed, the resulting reaction solution is dissolved in a mixed solution of dichloromethane and n-hexane, methanol is added to precipitate, the precipitate is collected, dried, and polycaprolactone is obtained.

3. The method for preparing the polymer according to claim 1, characterized in that, In S1, the mass ratio of polycaprolactone to sodium 4-styrenesulfonate is 1:(0.5~1.5).

4. The method for preparing the polymer according to claim 1, characterized in that, S1 specifically includes: dissolving polycaprolactone, azodicyanovalerate, and sodium 4-styrenesulfonate in a mixed solution of ethanol and water, reacting under inert gas protection by heating, and washing with a poor solvent after the reaction is completed to obtain PCL-b-PSSNa block copolymer.

5. The method for preparing the polymer according to claim 1, characterized in that, In S2, the chain extender is hexamethylene diisocyanate, 4,4-diisocyanate dicyclohexylmethane, isoflurone diisocyanate, or toluene diisocyanate.

6. The polymer obtained by the preparation method according to any one of claims 1 to 5.

7. A polymer electrolyte membrane, characterized in that, Includes the polymer and ionic liquid described in claim 6.

8. The polymer electrolyte membrane according to claim 7, characterized in that, The mass ratio of the polymer to the ionic liquid is 1:(1~4).

9. The method for preparing the polymer electrolyte membrane according to claim 7, characterized in that, The polymer, ionic liquid, and cellulose powder are dispersed in a solvent, heated and stirred, and dried to obtain a polymer electrolyte membrane.

10. A soft actuator, characterized in that, It includes the polymer of claim 6 or the polymer electrolyte membrane of claim 7.

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