Preparation method of recyclable polymer with shape memory function based on dynamic acylhydrazone bond

Abstract

The application discloses a recyclable polymer with shape memory function based on dynamic acylhydrazone bond, which is prepared by copolymerization of p-methyl acryloylhydrazone methyl phenyl ester (monomer 3) as a reversible crosslinking agent and butyl methacrylate as a base monomer to construct a covalent adaptive network, and by selectively introducing a permanent crosslinking agent to form a double crosslinking structure. The preparation method comprises the following steps: 1, preparation of acylhydrazone functional monomer; 2, preparation of single crosslinking or double crosslinking polymer; 3, purification and molding of the polymer. The added mole amount of the monomer 3 accounts for 1% to 5% of the total mole amount of monomers; the molding hot-pressing temperature is 100-150 DEG C. The obtained polymer utilizes the associated dynamic exchange mechanism of the internal acylhydrazone bond under heating, and the strain fixation rate and recovery rate are both above 97%; and after physical crushing and closed-loop hot-pressing recycling, the shape memory characteristics are not obviously attenuated, lossless cyclic reshaping is realized, and the service life is prolonged.

Description

Technical Field

[0002] This invention belongs to the field of intelligent polymer materials technology, specifically relating to a recyclable polymer with shape memory function based on dynamic acylhydrazone bonds and its preparation method. Background Technology

[0004] Shape memory polymers (SMPs) are a class of smart responsive materials that can spontaneously recover from a temporary shape to an initial permanent shape in response to external stimuli. Traditional SMPs are typically based on an irreversible covalent network structure. This thermosetting network endows the material with excellent mechanical strength and creep resistance. However, because its internal three-dimensional covalent network is permanently fixed after molding, once the material suffers macroscopic physical damage or reaches its service life, it cannot be reshaped or physically recycled by heating and melting, unlike thermoplastics. This limits the material's lifespan and leads to resource waste.

[0005] To address this issue, the concept of glass-like polymers was proposed, the core of which lies in introducing dynamic covalent bonds into the polymer network to form covalent adaptive networks (CANs). CANs can undergo reversible breakage and recombination under specific external conditions, endowing the material with the ability to rearrange its topological network. Acylhydrazone bonds, as a typical type of dynamic covalent bond, have advantages such as mild synthesis conditions, high dynamic exchange activity, and strong controllability. For example, existing literature 1 (Kuhl N, Bode S, Bose RK, et al. Polymeric Healing Based on Dynamic Covalent Acylhydrazone Bonds [J]. Advanced Functional Materials, 2015, 25 (22): 3295-3301.) reported the spontaneous healing behavior of polymer interfaces using dynamic covalent acylhydrazone bonds. For example, existing literature 2 (Roig A, Petrauskaitė A, Ramis X, et al. Synthesis and Characterization of New Bio-Based Poly(acylhydrazone) Vanillin Vitrimers [J]. Polymer Chemistry, 2022, 13 (10):1510-1519.) explores the synthesis, characterization and stress relaxation properties of bio-based polyacylhydrazone glass polymers.

[0006] However, in existing research, how to rationally design the monomer structure and network crosslinking density so that the polymer based on acylhydrazone bonds can maintain sufficient rigidity at room temperature to lock temporary deformation, release stress at high temperature to restore shape, and still be able to heal through hot pressing after physical crushing and maintain various properties without degradation remains a technical challenge that urgently needs to be overcome in the field of smart materials. Summary of the Invention

[0008] To overcome the shortcomings of existing thermosetting SMPs (Solid Polymer Materials) which cannot be recycled and reshaped, and the poor recovery performance of traditional thermoplastic SMPs, the present invention aims to provide a recyclable polymer with shape memory function based on dynamic acylhydrazone bonds and its preparation method. This polymer utilizes the unique associative dynamic exchange mechanism of internal acylhydrazone bonds when heated, achieving closed-loop crushing and physical reshaping of the material without sacrificing macroscopic mechanical strength and shape memory accuracy, thus extending the material's service life.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing a recyclable polymer with shape memory function based on dynamic acylhydrazone bonds includes the following steps:

[0011] Step 1, Preparation of acylhydrazone functional monomers. First, methacrylic anhydride and hydrazine hydrate were reacted dropwise in an ice-water bath. After extraction and recrystallization purification, methacryloyl hydrazine (monomer 1) was obtained. Then, 4-hydroxybenzaldehyde and methacryloyl chloride were reacted under the protection of an acid-binding agent. After washing and separation by silica gel column chromatography, 4-formylphenyl methacrylate (monomer 2) was obtained. Finally, monomer 1 and monomer 2 were subjected to a closed condensation reaction at room temperature in the presence of a dehydrating agent. After the reaction, the mixture was purified by vacuum filtration, silica gel column chromatography, and vacuum drying to obtain para-methacryloylhydrazone methylphenyl methacrylate containing a dynamically reversible bond (monomer 3).

[0012] Step 2, Preparation of the monocrosslinked polymer. The matrix monomers, butyl methacrylate or 2-ethylhexyl methacrylate, are weighed and added sequentially to a microwave-safe reaction flask. Then, monomer 3 and azobisisobutyronitrile (initiator) are added. The mixture is dissolved in N,N-dimethylformamide solvent to form a homogeneous solution. High-purity nitrogen gas is continuously bubbled into the bottom of the solution to remove oxygen. Finally, the reaction flask is sealed, and a isothermal free radical polymerization reaction is carried out under closed heating on a heated magnetic stirrer to obtain an N,N-dimethylformamide solution containing the monocrosslinked polymer.

[0013] Step 3: Purification and molding of the monocrosslinked polymer. The N,N-dimethylformamide solution containing the monocrosslinked polymer was transferred to a dialysis bag and purified by continuous dialysis using tetrahydrofuran as a solvent to remove impurities. The purified monocrosslinked polymer was then placed in a vacuum drying oven and dried under vacuum until constant weight. Finally, the dried monocrosslinked polymer was physically pulverized and evenly spread in a mold, then hot-pressed under pressure. After natural cooling and demolding, a recyclable polymer sample with shape memory function based on dynamic acylhydrazone bonds was obtained.

[0014] As a further preferred embodiment of the present invention, in step 2, the molar amount of monomer 3 accounts for 5% of the total molar amount of monomer, and the molar ratio of the total amount of monomer to the initiator is controlled at 100:1.

[0015] As a further extension of the present invention, in step 2, when preparing the reaction solution, an appropriate amount of triethylene glycol dimethacrylate (permanent crosslinking agent) may be added to prepare a double crosslinked polymer containing reversible acylhydrazone bonds and irreversible covalent bonds.

[0016] Compared with the prior art, the present invention has the following significant advantages:

[0017] 1. Excellent shape memory and recovery properties. This invention, through the rational control of the proportion of monomer 3, enables the polymer network to possess sufficient rigidity and locked deformation at room temperature, and to activate the dynamic exchange of acylhydrazone bonds when heated to the switching temperature. Thermomechanical analysis (TMA) tests show that the strain fixation rate of the monocrosslinked polymer reaches 98.4%, and the strain recovery rate reaches 97.7%, demonstrating precise response. This is because the uniformly distributed acylhydrazone bonds in the covalent network are activated when heated to the switching temperature, endowing the macromolecular backbone network with the ability to rearrange its topology and release internally accumulated stress.

[0018] 2. Excellent closed-loop recycling and hot-press remodeling capabilities. This invention utilizes the reversible chain exchange reaction of the polymer fracture network at high temperatures to heal damaged physical interfaces and rebuild the covalent cross-linked network. After physical pulverization and closed-loop hot-press recycling, the strain fixation rate of the obtained sample is 98.1%, and the strain recovery rate is 96.0%, achieving non-destructive cyclic remodeling. This is because, under high-temperature hot-pressing conditions, the polymer fracture network can undergo a reversible chain exchange reaction through internal dynamic acylhydrazone bonds, healing damaged physical interfaces at the molecular scale.

[0019] 3. Adjustability of Structure and Heat Resistance. The preparation strategy provided by this invention has universality. By replacing the matrix monomer with a monomer containing flexible long-branched side groups, or by introducing a permanent crosslinking agent into the system in proportion to construct a double crosslinking network, the lower limit of the glass transition temperature of the polymer and the rigidity of the material can be effectively fine-tuned to meet the specific requirements of different engineering applications for the material's heat resistance and driving temperature. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the synthetic route of para-methacryloylhydrazone methylphenyl methacrylate in Example 1 of the present invention.

[0022] Figure 2 The images show the temperature-varying Raman spectra of the single crosslinked polymer in Example 1 of this invention at different temperatures.

[0023] Figure 3 The graphs show the high-temperature stress relaxation test curves of the various polymer examples and comparative examples of the present invention.

[0024] Figure 4 This is a comparison chart of the shape memory cycle test curves of the various polymer examples and comparative examples of the present invention. Detailed Implementation

[0026] The present invention will be further described in detail through embodiments and data tables, but this is not intended to limit the scope of the invention.

[0027] Example 1

[0028] A method for preparing a recyclable polymer with shape memory function based on dynamic acylhydrazone bonds includes the following steps:

[0029] Step 1, Preparation of the acylhydrazone functional monomer. First, 18.50 g of methacrylic anhydride was dissolved in 90 mL of chloroform. The reaction vessel was placed in an ice-water bath to lower the system temperature to 0 °C, and a magnetic stirrer was turned on at a speed of 400 rpm. Under these conditions, the solution was added dropwise through a constant-pressure dropping funnel to a reaction flask containing 25 mL of hydrazine hydrate. After the addition was complete, the temperature was raised to 25 °C, and the reaction was stirred for another 10 min. The reaction solution was transferred to a separatory funnel and allowed to stand for separation. The lower chloroform solution was collected, and the upper aqueous phase was extracted three times by adding an appropriate amount of fresh chloroform each time. The chloroform solutions obtained from separation and extraction were combined and transferred to a rotary evaporator flask. The chloroform was removed by vacuum distillation at 40 °C and 0.08 MPa. The resulting solid was heated and dissolved in a 10:1 (v / v) mixture of toluene and dichloromethane, and then allowed to cool naturally for recrystallization purification. After crystallization, the product was filtered under reduced pressure using a Buchner funnel. The filter cake was dried to constant weight at 40 °C in a vacuum drying oven to obtain 8.5 g of white needle-like crystals of methacrylhydrazine (monomer 1). Under nitrogen protection, 10.00 g of 4-hydroxybenzaldehyde was dissolved in 100 mL of dehydrated chloroform, and 12.5 mL of triethylamine was added as an acid-binding agent. The reaction system was placed in an ice-water bath at 0 °C, and the magnetic stirring speed was set to 450 rpm. A 30 mL chloroform solution containing 9.40 g of methacrylyl chloride was added dropwise through a dropping funnel. After the addition was complete, the temperature was raised to 25 °C, and the reaction was stirred for 18 h. After the reaction, most of the chloroform was removed by vacuum evaporation using a rotary evaporator. The intermediate was dissolved in dichloromethane and transferred to a separatory funnel. The solution was washed and extracted three times each with 5% sodium hydroxide aqueous solution and deionized water, and allowed to stand for separation. The lower dichloromethane solution was collected, and anhydrous sodium sulfate was added and allowed to stand for drying. After removing sodium sulfate by filter paper filtration, the sample was purified by silica gel column chromatography. A glass column was dry-packed with silica gel, the sample was loaded onto the top of the column, and pure chloroform was added dropwise as the mobile phase for elution. The eluent was collected in fractions. The chloroform was removed by rotary evaporation under reduced pressure, yielding 10.9 g of a yellow oily 4-formylphenyl methacrylate (monomer 2). Finally, 8.5 g of monomer 1 and 10.9 g of monomer 2 were dissolved in 100 mL of chloroform, and 10 g of anhydrous magnesium sulfate solid was added. The reaction flask was placed at 25 ℃ at room temperature, and the mixture was stirred at 500 rpm under sealed conditions for 24 h. After the reaction, magnesium sulfate was removed by vacuum filtration through a Buchner funnel lined with filter paper, and the filtrate was collected. After removing most of the chloroform by distillation under reduced pressure, the filtrate was purified by silica gel column chromatography. A silica gel column was packed with a 1:1 volume ratio of ethyl acetate to chloroform as the mobile phase, the sample was loaded onto the column head, and the eluent was added for separation. The eluents containing the target compound were combined and the solvent was removed by rotary evaporation. The eluents were then placed in a vacuum drying oven at 40 °C for 24 h to obtain 12.9 g of pale yellow solid para-methacryloylhydrazone methyl phenyl methacrylate (monomer 3).

[0030] Step 2, Preparation of the monocrosslinked polymer. In a 20 mL microwave-safe reaction flask, 1000 mg of butyl methacrylate (matrix monomer) was added, followed by 96 mg of monomer 3 and 12.14 mg of azobisisobutyronitrile (initiator). The molar amount of monomer 3 accounted for 5% of the total monomer molar amount, and the molar ratio of total monomer to initiator was controlled at 100:1. 10 mL of dried and dehydrated N,N-dimethylformamide was added to the reaction flask, and the mixture was stirred with a magnetic stir bar to dissolve. High-purity nitrogen gas was bubbled through the bottom of the solution for 45 min to remove oxygen. The reaction flask was sealed with a rubber cap and placed on a heated magnetic stirrer for a isothermal free radical polymerization reaction at 70 °C and 400 rpm for 12 h. After the reaction, the mixture was naturally cooled to 25 °C to obtain an N,N-dimethylformamide solution containing the monocrosslinked polymer (polymer P1).

[0031] Step 3: Purification and molding of the single crosslinked polymer. The solution containing polymer P1 was transferred to a semi-permeable dialysis bag with a molecular weight cutoff of 3500 Da and sealed with a snap-fit. The dialysis bag was immersed in tetrahydrofuran for dialysis purification, with fresh tetrahydrofuran replaced morning and evening for 3 consecutive days. The purified polymer P1 was transferred to a petri dish and placed in a vacuum drying oven at 40 ℃ and a vacuum degree of 0.08 MPa for 24 h until constant weight was achieved. The dried polymer P1 was physically pulverized and evenly spread into the cavity of a standard-sized rectangular stainless steel mold. It was placed between the upper and lower heating plates of a hot press and hot-pressed at 130 ℃ with a total vertical pressure of 2 t for 15 min. Heating was stopped, and the mold was allowed to cool naturally to room temperature. The mold was then demolded, and the edges were polished to obtain the standard test strip of polymer P1.

[0032] To demonstrate the thermal properties of polymer P1, DSC and TGA tests were performed. The test results are shown in Table 1. The glass transition temperature (Tg) of polymer P1 is 40 °C, and the thermal decomposition temperature is 260 °C.

[0033] To demonstrate the molecular structure and dynamic crosslinking mechanism of polymer P1, variable-temperature Raman spectroscopy was performed. The test conditions were as follows: a Nd:YAG laser with an output wavelength of 1064 nm was used as the excitation source, and the actual laser power reaching the polymer P1 sample plane was set to 345 mW. The test results are as follows: Figure 2As shown, the spectrum of polymer P1 exhibits a characteristic peak of carbon-nitrogen double bond stretching vibration at a wavenumber of 1604 cm⁻¹. When the ambient temperature increases from 25 ℃ to above 60 ℃, this characteristic peak red-shifts and stabilizes at 1602 cm⁻¹. Furthermore, throughout the entire heating test, neither the 1632 cm⁻¹ characteristic peak corresponding to free hydrazide nor the 1699 cm⁻¹ bond-breaking characteristic peak corresponding to free aldehyde group was detected in the spectrum. The test results indicate that the increase in ambient temperature triggers dynamic chemical exchange between hydrazone bonds within the polymer covalent network, and the microscopic exchange mechanism follows an associative exchange mechanism. This is because, under thermal response conditions, the breaking of chemical bonds in the original covalent crosslinked network and the formation of new crosslinked bonds occur simultaneously, maintaining a constant macroscopic crosslinking density in the overall polymer network. This prevents polymer P1 from experiencing a decrease in macroscopic viscosity or loss of structural mechanical properties during the high-temperature thermal response phase.

[0034] To demonstrate the dynamic topological rearrangement properties of polymer P1, high-temperature stress relaxation tests were conducted. The test results are as follows: Figure 3 As shown, linear fitting calculations based on the Arrhenius equation indicate that the activation energy of this covalently cross-linked network constructed based on dynamic acylhydrazone bonds is between 132 and 150 kJ / mol. Test results show that polymer P1 exhibits rheological characteristics similar to glass polymers, possessing stress relaxation and network topology recombination capabilities at high temperatures.

[0035] To demonstrate the shape memory properties of polymer P1, a TMA test was conducted. The test conditions were as follows: using a rotational rheometer fixture, a constant shear stress was applied to a polymer P1 sample at a set shape memory switching temperature of 90 °C, causing it to undergo torsional deformation and form a temporary shape. Subsequently, while maintaining the shear-torsional stress constant, the test environment was cooled to 30 °C to fix the temporary shape. Then, the shear stress was unloaded to 0 Pa, and the sample was kept in a stress-free state. Finally, the ambient temperature was heated back to 90 °C to restore it to its initial permanent shape.

[0036] The test results are shown in Table 2 and Figure 4 As shown, polymer P1 exhibits a strain fixation rate of 98.4% and a strain recovery rate of 97.7%. The test results demonstrate that polymer P1 possesses excellent shape memory and recovery properties. This is because the uniformly distributed acylhydrazone bonds in the covalent network are activated when heated to a switching temperature of 90 °C. Their dynamic association and reversible exchange properties endow the polymer backbone network with the ability to rearrange its topology, release internal accumulated stress, and drive the chain segments to recover their shape. Simultaneously, the 5% reversible monomer ratio prevents the generation of excessive steric stress that would hinder the thermal rebound motion of the polymer chain segments.

[0037] To demonstrate the recyclable, closed-loop recovery and remodeling performance of polymer P1, a TMA (Tracking and Remodeling Analysis) test was conducted. The test conditions were as follows: Polymer P1 samples that had undergone shape memory cycling were shredded into irregular physical fragments with a particle size of approximately 2-5 mm. These polymer fragments were then uniformly spread back into a hot-pressing mold and physically remodeled for 15 min at a hot-pressing temperature of 130 ℃ and a total pressure of 2 t. The test results showed that after physical destruction and closed-loop hot-pressing recovery, polymer P1 maintained a strain rate of 98.1% and a strain recovery rate of 96.0%. The results indicate that the shape memory properties of polymer P1 did not significantly decrease after shredding and closed-loop recovery. This is because, under the high-temperature hot-pressing environment of 130 ℃, the polymer fracture network can undergo a reversible chain exchange reaction through its rich internal dynamic acylhydrazone bonds, healing the damaged physical interface and reconstructing the three-dimensional covalent cross-linked network.

[0038] Table 1 Summary of Thermal Properties Tests for Various Polymers

[0039] Polymer Name Glass transition temperature Tg (°C) Thermal decomposition temperature Td (°C) P1 40 260 P2 49 230 P3 37 252 CP1 45 228 CP2 60 220

[0040] Table 2 Summary of Shape Memory Performance Tests for Various Polymers

[0041] Polymer Name Strain fixation rate / % Strain recovery rate / % P1 98.4 97.7 P2 98.9 90.2 P3 91.9 97.9 CP1 98.9 93.3 CP2 99.5 78.2

[0042] Example 2

[0043] A method for preparing a double crosslinked polymer comprising a reversible crosslinked network and a permanent crosslinked network is disclosed. Unless otherwise specified, the preparation steps are the same as in Example 1, except that in step 2, the reaction feed formulation for preparing the double crosslinked polymer is changed. 1000 mg of matrix monomer, 101 mg of monomer 3, and an additional 96 mg of triethylene glycol dimethacrylate (permanent crosslinking agent) are dissolved together with 13.00 mg of initiator in 10 mL of dried N,N-dimethylformamide. Subsequently, deoxygenation, polymerization, dialysis, and hot pressing are performed according to the same process steps to obtain a double crosslinked polymer (polymer CP1) comprising reversible acylhydrazone bonds and irreversible covalent bonds.

[0044] To demonstrate the thermal and shape memory properties of polymer CP1, DSC and TMA tests were conducted. The test results are shown in Tables 1 and 2. The Tg of polymer CP1 increased to 45 °C, with a strain fixation rate of 98.9% and a strain recovery rate of 93.3%. The results indicate that by introducing an appropriate proportion of permanent crosslinking agent into the reversible network to construct a double crosslinking network, excellent shape memory thermal response behavior can be maintained, and the lower limit of the heat transition temperature of the polymer material can be effectively controlled. Furthermore, polymer CP1 also successfully completed recycling and remodeling tests, and the retention rate of various mechanical properties remained stable after recycling.

[0045] To demonstrate the effects of crosslinking density, comonomer side chain structure, and permanent crosslinking agent content on the final properties of the polymer, Comparative Examples 1, 2, and 3 are provided for comparison.

[0046] Comparative Example 1

[0047] A method for preparing a monocrosslinked polymer with high reversible crosslinking density is disclosed. Unless otherwise specified, the preparation steps are the same as in Example 1, except that in step 2, the amount of monomer 3 is increased from 96 mg to 192 mg, so that its molar amount accounts for 10% of the total monomer molar amount, and the amount of initiator is correspondingly adjusted to 12.80 mg. The resulting monocrosslinked polymer (polymer P2) has a high crosslinking network density.

[0048] To demonstrate the performance changes of polymer P2, TMA testing was conducted. The test results are shown in Tables 1 and 2. The strain recovery rate of polymer P2 decreased from 97.7% to 90.2%. The results indicate that the shape recovery ability of the polymer decreases as the proportion of the reversible crosslinking agent in the system increases. This is because the increased density of the dynamic acylhydrazone network leads to a denser network of chemical crosslinking points within the polymer during the initial thermal response triggering, making it difficult to effectively release microscopic internal stress and thus reducing the ability of the molecular chain segments to recover after deformation. Furthermore, in the subsequent closed-loop recycling and remodeling test, polymer P2 experienced macroscopic embrittlement and fracture after hot-press remodeling, making it impossible to continue the testing on the rheometer fixture. This phenomenon further demonstrates that an increase in reversible crosslinking density leads to a decrease in the overall toughness of the polymer material, which is detrimental to closed-loop recycling.

[0049] Comparative Example 2

[0050] A method for preparing a single crosslinked polymer containing flexible long-branched side groups is disclosed. Unless otherwise specified, the preparation steps are the same as in Example 1, except that in step 2, 1000 mg of the matrix monomer is replaced with 1000 mg of 2-ethylhexyl methacrylate (flexible monomer) with long flexible alkyl branches. Simultaneously, the amount of monomer 3 is adjusted to 69 mg, and the amount of initiator is adjusted to 8.60 mg. Furthermore, the hot-pressing temperature in step 3 is lowered from 130 °C to 110 °C. The resulting single crosslinked polymer containing flexible long-branched side groups (polymer P3) is obtained.

[0051] To demonstrate the performance changes of polymer P3, TMA testing was conducted. Due to the decrease in its Tg, the shape memory switching temperature used in the test was correspondingly lowered to 70 °C. The test results are shown in Tables 1 and 2. The Tg of polymer P3 decreased to 37 °C, and its strain fixation rate decreased to 91.9%. The test results indicate that changing the alkyl branched chemical structure of the copolymer matrix monomer weakens the polymer network's ability to fix temporary deformations. This is because the flexible monomer has a spatially flexible long alkyl branched structure, which increases the free volume within the polymer network. This leads to increased flexibility of the molecular chain segments at room temperature, making it unable to provide sufficient rigid network support to resist deformation rebound stress when the temperature is lowered to 30 °C for shape fixation, resulting in a decrease in the strain fixation rate.

[0052] Comparative Example 3

[0053] A method for preparing a double-crosslinked polymer with ultra-high crosslinking density is provided. Unless otherwise specified, the preparation steps are the same as in Example 2, except that in step 2, the amount of monomer 3 is increased to 202 mg, and the amount of permanent crosslinking agent is increased to 192 mg. The resulting double-network polymer (polymer CP2) has ultra-high crosslinking density.

[0054] To demonstrate the performance changes of polymer CP2, TMA testing was conducted. The test results are shown in Tables 1 and 2. When the Tg of polymer CP2 increased to 60 °C, the strain recovery rate decreased to 78.2%. The test results indicate that an excessively high total crosslinking density in the double crosslinked network system leads to the polymer losing its shape memory thermal recovery response capability. This is because an excessive amount of irreversible permanent covalent bonds are introduced into the crosslinking system, which physically hinders and spatially restricts the sliding motion and dynamic topological recombination processes of macromolecular chain segments within the polymer network when heated. This results in the residual stress generated by deformation being locked within the network and unable to be effectively released.

Claims

1. A method for preparing a recyclable polymer with shape memory function based on dynamic acylhydrazone bonds, characterized in that, Includes the following steps: Step 1, Preparation of acylhydrazone functional monomers. Methacrylhydrazide (monomer 1) and 4-formylphenyl methacrylate (monomer 2) were subjected to a closed condensation reaction at room temperature in the presence of a dehydrating agent. After the reaction was completed, the monomers were separated and purified to obtain para-methacryloylhydrazone methylphenyl methacrylate (monomer 3) containing a dynamically reversible bond. Step 2, Preparation of the monocrosslinked polymer. The matrix monomer, monomer 3, and azobisisobutyronitrile (initiator) are added sequentially to the reaction vessel. The above mixed raw materials are dissolved in an organic solvent to form a homogeneous solution. Inert gas is continuously passed through the solution to purge oxygen. Finally, the reaction vessel is sealed and heated to carry out a isothermal free radical polymerization reaction to obtain a solution containing the monocrosslinked polymer. Step 3: Purification and molding of the monocrosslinked polymer. The solution containing the monocrosslinked polymer was transferred to a dialysis bag and purified by continuous dialysis with dialysis solvent to remove impurities. The purified monocrosslinked polymer was then placed in a vacuum drying oven and dried under vacuum until constant weight. Finally, the dried monocrosslinked polymer was physically pulverized and evenly spread in a mold. It was then hot-pressed and molded under pressure. After natural cooling and demolding, a recyclable polymer strip with shape memory function based on dynamic acylhydrazone bonds was obtained.

2. The method for preparing a recyclable polymer with shape memory function based on dynamic acylhydrazone bonds according to claim 1, characterized in that, In step 1, monomer 1 is prepared by reacting methacrylic anhydride with hydrazine hydrate at a low temperature of 0-10℃, followed by extraction and recrystallization purification. The preparation process of monomer 2 involves reacting 4-hydroxybenzaldehyde with methacryloyl chloride under the protection of an acid-binding agent, followed by washing and purification.

3. The method for preparing a recyclable polymer with shape memory function based on dynamic acylhydrazone bonds according to claim 1, characterized in that, In step 2, the matrix monomer is an alkyl methacrylate monomer, preferably butyl methacrylate; the organic solvent is preferably N,N-dimethylformamide.

4. The method for preparing a recyclable polymer with shape memory function based on dynamic acylhydrazone bonds according to claim 1, characterized in that, In step 2, the molar amount of monomer 3 accounts for 1%-5% of the total molar amount of monomer, and the molar ratio of the total amount of monomer to the initiator is controlled at 50:1-200:1; the reaction temperature of the isothermal free radical polymerization reaction is set at 60-80 ℃, and the reaction time is 8-24 h.

5. The method for preparing a recyclable polymer with shape memory function based on dynamic acylhydrazone bonds according to claim 1, characterized in that, In step 2, triethylene glycol dimethacrylate (a permanent crosslinking agent) may be added to the reaction solution to prepare a double crosslinked polymer containing reversible acylhydrazone bonds and irreversible covalent bonds.

6. The method for preparing a recyclable polymer with shape memory function based on dynamic acylhydrazone bonds according to claim 1, characterized in that, In step 3, the dialysis solvent used for continuous dialysis purification is tetrahydrofuran, and the dialysis time is 1-5 days; the conditions for holding pressure and hot pressing are: hot pressing temperature 100-150 ℃, applied vertical total pressure 1-5 t, and hot pressing time 10-30 min.

7. A recyclable polymer with shape memory function based on dynamic acylhydrazone bonds, characterized in that, The polymer is prepared by the preparation method according to any one of claims 1-6.

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