A double-layer gradient polyimide composite material capable of realizing three-stage shape memory and a preparation method and application thereof

Abstract

This invention provides a bilayer gradient polyimide composite material capable of achieving three-segment shape memory, its preparation method, and its applications, belonging to the field of photoelectrode material technology. This invention utilizes nucleophilic substitution to form a three-dimensional cyclic thermosetting crosslinked network, followed by thermal imidization, to give low-molecular-weight amino-terminated polyimide mechanical strength and toughness comparable to high-molecular-weight polyimide. By combining low-molecular-weight thermoplastic polyimide with paraformaldehyde and then cyclizing it, high mechanical properties can be obtained. Through stacking a pure matrix layer and a composite layer containing GO, the bilayer composite material achieves two loss factor peaks and a wide transition temperature range, thus enabling three-segment shape memory deformation. This allows the bilayer gradient composite material prepared by this invention to achieve three-segment shape memory deformation while possessing excellent mechanical properties and a high glass transition temperature, which is beneficial for its application under complex working conditions.

Description

Technical Field

[0001] This invention relates to the field of photoelectrode materials technology, and in particular to a bilayer gradient polyimide composite material capable of achieving three-segment shape memory, its preparation method, and its application. Background Technology

[0002] As is well known, the synthetic monomer, molecular weight, and degree of crosslinking all play a decisive role in the various properties of polymer materials. By regulating these influencing factors, it is possible to achieve enhancement of one or even multiple properties as required. Taking polyimide as an example, the glass transition temperature and shape memory properties of synthesized polyimide vary greatly depending on the diamine and dianhydride monomers. The degree of crosslinking usually affects the comparison between thermosetting and thermoplastic polyimide. Thermosetting polyimide with a high degree of chemical crosslinking often has higher mechanical properties and better shape recovery. Molecular weight also has a significant impact on the mechanical properties and reprocessing properties of polyimide. The higher the molecular weight, the greater the tensile strength of the material tends to be until it stabilizes after reaching a critical value. However, if the molecular weight is too low, its strength and toughness will be extremely poor and it may even be difficult to form a film. Currently, the molecular weight of common polyimide is generally in the tens of thousands or even hundreds of thousands. However, the defects of high molecular weight materials, such as difficulty in dissolving and reprocessing, may cause resource waste or environmental pollution to a certain extent. This is contrary to the requirements of green science in today's world development. Therefore, the problem of how to design shape memory materials with high mechanical properties at a relatively low molecular weight urgently needs to be solved.

[0003] Chinese patent CN108794752A discloses a thermosetting polyimide and its application in realizing complex 3D structures. The material has good repair properties, weldability and recyclability, but it does not have multi-segment shape memory behavior and cannot be applied to complex working conditions. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a bilayer gradient polyimide composite material capable of achieving three-segment shape memory, its preparation method, and its application. The bilayer gradient polyimide composite material obtained by this invention has three-segment shape memory function.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a bilayer gradient polyimide composite material capable of achieving three-segment shape memory, comprising the following steps:

[0007] A nucleophilic substitution reaction was carried out by mixing 4,4'-diaminodiphenyl ether, bisphenol A dianhydride and an organic aprotic solvent to obtain a polyamic acid solution;

[0008] The polyamic acid solution was mixed with toluene and subjected to thermal imidization to obtain polyimide;

[0009] The polyimide, paraformaldehyde, and organic aprotic solvent are mixed and subjected to a first hyperbranching reaction to obtain the hyperbranched product.

[0010] The hyperbranched product was first cured to obtain a PI-HDCN film.

[0011] The polyimide, paraformaldehyde, graphene oxide dispersion and organic aprotic solvent are mixed to carry out a second hyperbranching reaction to obtain a hyperbranched polyimide composite material containing GO.

[0012] After coating the hyperbranched polyimide composite material containing GO onto the surface of the PI-HDCN film, a second curing and cyclization process is performed sequentially to obtain the bilayer gradient polyimide composite material capable of achieving three-segment shape memory.

[0013] Preferably, the mass percentage of GO in the hyperbranched polyimide containing GO is 1-5%.

[0014] Preferably, the temperature of the first hyperbranching reaction and the second hyperbranching reaction are independently 50-60°C, and the time is independently 0.5-1h.

[0015] Preferably, the temperature of the first curing and the second curing are independently 80-90°C, and the time is independently 0.5-5h.

[0016] Preferably, the cyclization includes the following process: heating to 100-120°C and holding for 1-2 hours, then heating to 140-160°C and holding for 1-2 hours, continuing to heat to 200-220°C and holding for 1-2 hours, then heating to 240-260°C and holding for 1-2 hours, and finally heating to 280-300°C and holding for 1-2 hours.

[0017] Preferably, the cyclization includes the following process: heating to 120°C and holding for 1 hour, then heating to 150°C and holding for 1 hour, continuing to heat to 200°C and holding for 1 hour, then heating to 250°C and holding for 1 hour, and finally heating to 280°C and holding for 1 hour.

[0018] Preferably, the thermal imidization temperature is 210–240°C and the time is 5–6 hours.

[0019] Preferably, the molar ratio of 4,4'-diaminodiphenyl ether to bisphenol A dianhydride is 1:0.92 to 1.02:0.91.

[0020] The present invention also provides a bilayer gradient polyimide composite material capable of achieving three-segment shape memory, prepared by the preparation method described in the above technical solution.

[0021] The present invention also provides the application of the bilayer gradient polyimide composite material with three-segment shape memory as described in the above technical solution in shape memory deformation.

[0022] This invention provides a method for preparing a bilayer gradient polyimide composite material capable of achieving three-segment shape memory, comprising the following steps: mixing 4,4'-diaminodiphenyl ether, bisphenol A dianhydride, and an organic aprotic solvent to perform a nucleophilic substitution reaction to obtain a polyamic acid solution; mixing the polyamic acid solution with toluene to perform thermal imidization to obtain a polyimide; mixing the polyimide, paraformaldehyde, and an organic aprotic solvent to perform a first hyperbranching reaction to obtain a hyperbranched product; subjecting the hyperbranched product to a first curing to obtain a PI-HDCN film (PI-PHT precursor); mixing the polyimide, paraformaldehyde, graphene oxide dispersion, and an organic aprotic solvent to perform a second hyperbranching reaction to obtain a hyperbranched polyimide composite material containing GO; coating the hyperbranched polyimide composite material containing GO onto the surface of the PI-HDCN film, followed by a second curing and cyclization to obtain the bilayer gradient polyimide composite material (PI-PHT) capable of achieving three-segment shape memory.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This invention forms a three-dimensional cyclic thermosetting crosslinked network through nucleophilic substitution, followed by thermal imidization, enabling low-molecular-weight amino-terminated polyimide to possess mechanical strength and toughness comparable to high-molecular-weight polyimide. The combination of low-molecular-weight thermoplastic polyimide and paraformaldehyde, after cyclization, achieves high mechanical properties. By stacking a pure matrix layer with a GO-containing composite layer, the bilayer composite material obtains two loss factor peaks and a wide transition temperature range, thus enabling three-stage shape memory deformation. This allows the bilayer gradient composite material obtained by this invention to achieve three-stage shape memory deformation while possessing excellent mechanical properties and a high glass transition temperature, which is beneficial for its application under complex working conditions. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the reaction principle for preparing polyimide according to the present invention.

[0026] Figure 2 This is a schematic diagram illustrating the reaction principle of the first stage of curing and cyclization.

[0027] Figure 3 The thermomechanical properties of the bilayer gradient polyimide composites prepared in the examples and comparative examples are shown in the graphs, where (a) is the storage modulus and (b) is the loss factor.

[0028] Figure 4The two-segment shape memory properties of the bilayer gradient polyimide composites prepared in the examples and comparative examples are shown, wherein (a) is PI-PHT-01, (b) is PI-PHT-03, (c) is PI-PHT-05, (d) is PI-PHT-13, (e) is PI-PHT-15, and (f) is PI-PHT-35;

[0029] Figure 5 This describes the three-segment shape memory fixation and recovery process of the bilayer gradient polyimide composite material prepared in Example 3;

[0030] Figure 6 The figures show the three-segment shape memory performance test results of the bilayer gradient polyimide composite materials prepared in Examples 1-3. Detailed Implementation

[0031] This invention provides a method for preparing a bilayer gradient polyimide composite material capable of achieving three-segment shape memory, comprising the following steps:

[0032] A nucleophilic substitution reaction was carried out by mixing 4,4'-diaminodiphenyl ether, bisphenol A dianhydride and an organic aprotic solvent to obtain a polyamic acid solution;

[0033] The polyamic acid solution was mixed with toluene and subjected to thermal imidization to obtain polyimide;

[0034] The polyimide, paraformaldehyde, and organic aprotic solvent are mixed and subjected to a first hyperbranching reaction to obtain the hyperbranched product.

[0035] The hyperbranched product was first cured to obtain a PI-HDCN film.

[0036] The polyimide, paraformaldehyde, graphene oxide dispersion and organic aprotic solvent are mixed to carry out a second hyperbranching reaction to obtain a hyperbranched polyimide composite material containing GO.

[0037] After coating the hyperbranched polyimide composite material containing GO onto the surface of the PI-HDCN film, a second curing and cyclization process is performed sequentially to obtain the bilayer gradient polyimide composite material capable of achieving three-segment shape memory.

[0038] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field.

[0039] In this invention, 4,4'-diaminodiphenyl ether, bisphenol A dianhydride and an organic aprotic solvent are mixed and subjected to a nucleophilic substitution reaction to obtain a polyamic acid solution (PAA).

[0040] In this invention, the molar ratio of 4,4'-diaminodiphenyl ether (ODA) to bisphenol A dianhydride (BPADA) is preferably 1:0.92 to 1.02:0.91.

[0041] In this invention, the organic aprotic solvent is preferably N-methyl-2-pyrrolidone (NMP).

[0042] In this invention, the preferred ratio of the amount of 4,4'-diaminodiphenyl ether to the organic aprotic solvent is 1.0 g: 25-30 mL.

[0043] In this invention, the nucleophilic substitution reaction is preferably carried out under nitrogen and ice-water bath conditions. There is no special limitation on the time of the nucleophilic substitution reaction in this invention, as long as the nucleophilic substitution reaction can be carried out completely.

[0044] In this invention, the 4,4'-diaminodiphenyl ether is first poured into a three-necked flask equipped with a top stirrer. The three-necked flask contains N-methyl-2-pyrrolidone. After the ODA is completely dissolved, the bisphenol A dianhydride is added in three equal batches under a nitrogen atmosphere and an ice-water bath. Mechanical stirring is used to ensure that the nucleophilic substitution reaction is complete, thereby obtaining the polyamic acid solution.

[0045] After obtaining the polyamic acid solution, the present invention mixes the polyamic acid solution with toluene and performs thermal imidization to obtain polyimide.

[0046] In this invention, the temperature of the thermal imidization is preferably 210-240°C, and the time is preferably 5-6 hours.

[0047] The present invention preferably involves adding toluene to the polyamic acid solution, heating the resulting mixture using an electric heating mantle, and simultaneously removing the moisture in the PAA through azeotropic reflux and condensation in a combination of a Dean-Stark device and a spherical condenser to carry out the thermal imidization.

[0048] In this invention, after the thermal imidization is completed, it is preferable to wait for the temperature to drop naturally to room temperature, pour the mixture after the water has been removed into stirred industrial alcohol to precipitate the precipitate, and then wash and filter the precipitate, and then dry it in an oven. The final powder obtained is the polyimide, which is an amino-terminated low molecular weight polyimide (denoted as PI-NH2 or NH2-PI-NH2).

[0049] In this invention, the reaction principle for preparing the polyimide is shown in the diagram below. Figure 1 As shown.

[0050] After obtaining the polyimide, the present invention mixes the polyimide, paraformaldehyde and organic aprotic solvent to carry out a first hyperbranching reaction to obtain the hyperbranched product.

[0051] In this invention, the molar ratio of polyimide to paraformaldehyde is preferably 1:3.5 to 1:4.

[0052] In this invention, the organic aprotic solvent is preferably N-methyl-2-pyrrolidone (NMP).

[0053] In this invention, the polyimide is preferably dissolved in NMP to obtain a polyimide solution for later use. The paraformaldehyde is dissolved in a single-necked flask containing NMP, then distilled water is added, and the flask is placed in an oil bath and continuously magnetically stirred until the solution becomes transparent to obtain a paraformaldehyde solution. When the temperature of the paraformaldehyde solution drops to 50-60°C, the polyimide solution is added to the single-necked flask and magnetic stirring is continued to carry out the first hyperbranching reaction.

[0054] In this invention, the temperature of the first hyperbranching reaction is preferably 50-60°C, and the time is preferably 0.5-1h.

[0055] After obtaining the hyperbranched product, the present invention performs a first curing on the hyperbranched product to obtain a PI-HDCN film (PI-HDCN film, i.e., pure polyimide layer, without GO).

[0056] In this invention, the temperature of the first curing is preferably 80-90°C, and the time is preferably 0.5-5 hours. The purpose of the first curing is to remove the solvent.

[0057] In this invention, the first curing is preferably carried out in an oven.

[0058] The present invention preferably involves casting the hyperbranched product naturally onto a pre-cleaned horizontal glass plate for the first curing.

[0059] After obtaining the polyimide, the present invention mixes the polyimide, paraformaldehyde, graphene oxide dispersion and organic aprotic solvent to carry out a second hyperbranching reaction to obtain a hyperbranched polyimide composite material containing GO.

[0060] In this invention, the graphene oxide dispersion is used to uniformly disperse graphene oxide (GO) in the polyimide matrix.

[0061] In this invention, the mass percentage of GO in the hyperbranched polyimide containing GO is preferably 1-5%, more preferably 3%.

[0062] In this invention, the molar ratio of polyimide to paraformaldehyde is preferably 1:3.5 to 1:4.

[0063] In this invention, the temperature of the second hyperbranching reaction is preferably 50-60°C, and the time is preferably 0.5-1h.

[0064] In this invention, the organic aprotic solvent is preferably consistent with the above scheme, and will not be repeated here.

[0065] Preferably, the polyimide is dissolved in NMP to obtain a polyimide solution for later use. The paraformaldehyde is dissolved in a single-necked flask containing NMP, then distilled water is added, and the flask is placed in an oil bath and continuously magnetically stirred until the solution becomes transparent to obtain a paraformaldehyde solution. When the temperature of the paraformaldehyde solution drops to 50-60°C, the graphene oxide dispersion and the polyimide solution are added to the single-necked flask and magnetic stirring is continued to carry out the second hyperbranching reaction.

[0066] The present invention obtains a PI-HDCN film and a hyperbranched polyimide composite material containing GO. After coating the hyperbranched polyimide composite material containing GO onto the surface of the PI-HDCN film, the present invention performs a second curing and cyclization sequentially to obtain the bilayer gradient polyimide composite material capable of achieving three-segment shape memory (denoted as PI-PHT or PI-PHT-XY, where XY represents the mass percentage of different GO in the two layers, X is 0, that is, the first layer does not contain GO, and PHT represents the highly cross-linked network structure obtained by the reaction of amino and aldehyde groups).

[0067] In this invention, the preferred temperature for the second curing is 80-90°C, and the preferred time is 0.5-5 hours. The purpose of the second curing is to remove the solvent.

[0068] In this invention, the cyclization preferably includes the following process: heating to 100-120°C and holding for 1-2 hours, then heating to 140-160°C and holding for 1-2 hours, continuing to heat to 200-220°C and holding for 1-2 hours, then heating to 240-260°C and holding for 1-2 hours, and finally heating to 280-300°C and holding for 1-2 hours. More preferably, it includes the following process: heating to 120°C and holding for 1 hour, then heating to 150°C and holding for 1 hour, continuing to heat to 200°C and holding for 1 hour, then heating to 250°C and holding for 1 hour, and finally heating to 280°C and holding for 1 hour.

[0069] In this invention, the hyperbranched polyimide containing GO is naturally cast onto the surface of the PI-HDCN film for the second curing and cyclization.

[0070] In this invention, the second curing is preferably carried out in an oven.

[0071] In this invention, the cyclization is preferably carried out in a blower drying oven.

[0072] In this invention, the reaction principle diagram of the second curing and cyclization is as follows: Figure 2 As shown.

[0073] The present invention also provides a bilayer gradient polyimide composite material capable of achieving three-segment shape memory, prepared by the preparation method described in the above technical solution.

[0074] The present invention also provides the application of the bilayer gradient polyimide composite material with three-segment shape memory as described in the above technical solution in shape memory deformation.

[0075] The present invention does not impose any special limitation on the specific method of application, and any method known to those skilled in the art can be used.

[0076] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0077] Example 1

[0078] Preparation of PI-PHT-01

[0079] First, ODA (10 mmol, 2.0 g) was poured into a 100 mL three-necked flask equipped with a top stirrer, containing NMP solution (the total amount of NMP required is 60 g based on a 10% solids content). After the ODA was completely dissolved, BPADA (9.2 mmol, 4.3 g) was weighed and added in three equal batches over 1 hour under a nitrogen atmosphere and an ice-water bath. The mixture was mechanically stirred for 12 hours to ensure complete reaction and obtain a polyamic acid solution (PAA). Subsequently, 6 g of toluene (one-tenth the mass of NMP) was added to the PAA. The mixture was heated to 230°C using an electric heating mantle, and simultaneously subjected to thermal imidization in a Dean-Stark apparatus and a spherical condenser combination device, using high-temperature azeotropic reflux to remove moisture from the PAA. This process was to be continued for 5 hours. After the temperature cooled to room temperature, the mixture after moisture removal was poured into rapidly stirred industrial alcohol to precipitate the precipitate. The precipitate was washed and filtered multiple times, then dried in an oven for 2 hours to obtain an amino-terminated low molecular weight polyimide powder. This powder was dissolved in NMP to obtain a polyimide solution for later use. Subsequently, 0.875 mmol of paraformaldehyde was dissolved in a single-necked flask containing 5 mL of NMP, and then 0.1 mL of distilled water was added. The flask was placed in an oil bath at 80°C and continuously magnetically stirred for 0.5 hours until the solution became transparent. When the temperature dropped to 50°C, the polyimide solution was added to the single-necked flask, and magnetic stirring was continued for another 0.5 hours. The mixed solution was then naturally cast onto a pre-cleaned horizontal glass plate and cured in an oven at 80°C for 1 hour to remove the solvent, resulting in a pure polyimide layer. The above steps were then repeated. When the temperature dropped to 50°C, a polyimide solution and a mixed solution containing GO dispersion were added to a single-necked flask. The fully reacted mixed solution was then directly spread onto the already cured film. The solvent was removed for another 5 hours, and after complete curing, a polyimide-GO composite layer (excluding the pure polyimide layer) was obtained. The amount of GO added was such that the mass fraction of GO in the polyimide-GO composite layer was 1%. The layer was then transferred to a forced-air drying oven for cyclization. A segmented programmed heating strategy was adopted to prevent the formation of bubbles: 120°C for 1 hour, 150°C for 1 hour, 200°C for 1 hour, 250°C for 1 hour, and 280°C for 1 hour. This resulted in a double-layer PI-PHT-01 composite material with two glass transition temperatures: 162.3°C and 190.3°C; a shape memory fixation rate of 99.57% and a shape recovery rate of 45.4%; and the ability to achieve three-segment shape memory.

[0080] Example 2

[0081] Preparation of PI-PHT-03

[0082] Same as Example 1, except that the amount of GO added during the preparation of the polyimide-GO composite layer was 3% by mass.

[0083] A bilayer PI-PHT-03 composite material was obtained, which has two glass transition temperatures: 164.7℃ and 192.6℃; the shape memory fixation rate is 99.42%, the shape recovery rate is 61.1%, and it can achieve three-segment shape memory.

[0084] Example 3

[0085] Preparation of PI-PHT-05

[0086] Same as Example 1, except that the amount of GO added during the preparation of the polyimide-GO composite layer was 5% by mass.

[0087] A bilayer PI-PHT-05 composite material was obtained, which has two glass transition temperatures: 163.8℃ and 193.3℃; the shape memory fixation rate is 99.22%, the shape recovery rate is 72.8%; and it can achieve three-segment shape memory.

[0088] Comparative Example 1

[0089] Preparation of PI-PHT-13

[0090] First, ODA (10 mmol, 2.0 g) was poured into a 100 mL three-necked flask equipped with a top stirrer, containing NMP solution (the total amount of NMP required is 60 g based on a 10% solids content). After the ODA was completely dissolved, BPADA (9.2 mmol, 4.3 g) was weighed and added in two equal batches over 1 hour under a nitrogen atmosphere and an ice-water bath. The mixture was mechanically stirred for 12 hours to ensure complete reaction and obtain a polyamic acid solution (PAA). Subsequently, 6 g of toluene (one-tenth the mass of NMP) was added to the PAA. The mixture was heated to 230 °C using an electric heating mantle, and simultaneously subjected to thermal imidization in a Dean-Stark apparatus and a spherical condenser combination device, using high-temperature azeotropic reflux to remove moisture from the PAA. This process was to be continued for 5 hours. After the temperature cooled to room temperature, the mixture, after the moisture was removed, was poured into rapidly stirred industrial alcohol to precipitate the precipitate. The precipitate was washed and filtered multiple times, then dried in an oven for 2 hours to obtain an amino-terminated low molecular weight polyimide powder. This powder was dissolved in NMP to obtain a polyimide solution for later use. Subsequently, 0.875 mmol of paraformaldehyde was dissolved in a single-necked flask containing 5 mL of NMP, followed by the addition of 0.1 mL of distilled water. The flask was then placed in an oil bath at 80°C and continuously magnetically stirred for 0.5 hours until the solution became transparent. When the temperature dropped to 50°C, the polyimide solution and the first GO dispersion were added to the single-necked flask, and magnetic stirring was continued for another 0.5 hours. The mixed solution was then naturally cast onto a pre-cleaned horizontal glass plate and cured in an oven at 80°C to remove the solvent, resulting in the first polyimide-GO composite layer. The amount of GO added to the first GO dispersion was such that the mass fraction of GO in the first polyimide-GO composite layer was 1%. The above steps were then repeated. When the temperature dropped to 50°C, a mixture of polyimide solution and second GO dispersion was added to a single-necked flask. The fully reacted mixture was then directly spread onto the already cured film. The solvent was removed for another 5 hours, and after complete curing, a second polyimide-GO composite layer (excluding the first polyimide-GO composite layer) was obtained. The amount of GO added in the second GO dispersion was such that the mass fraction of GO in the second polyimide-GO composite layer was 3%. The mixture was then transferred to a forced-air drying oven for cyclization. A segmented programmed heating strategy was adopted to prevent the formation of bubbles: 120°C for 1 hour, 150°C for 1 hour, 200°C for 1 hour, 250°C for 1 hour, and 280°C for 1 hour. This yielded a bilayer PI-PHT-13 composite material with a glass transition temperature of 202.5°C, a shape memory fixation rate of 99.09%, and a shape recovery rate of 91.3%. However, it could not achieve three-segment shape memory.

[0091] Comparative Example 2

[0092] Preparation of PI-PHT-15

[0093] Similar to Comparative Example 1, except that the amount of GO added to the second GO dispersion was such that the mass fraction of GO in the second polyimide-GO composite layer was 5%.

[0094] A bilayer PI-PHT-15 composite material was obtained, which has a glass transition temperature of 202.5℃; a shape memory fixation rate of 98.78% and a shape recovery rate of 93.2%; but cannot achieve three-segment shape memory.

[0095] Comparative Example 3

[0096] Preparation of PI-PHT-35

[0097] Similar to Comparative Example 1, except that the amount of GO added in the first GO dispersion makes the mass fraction of GO in the first polyimide-GO composite layer 3%, and the amount of GO added in the second GO dispersion makes the mass fraction of GO in the second polyimide-GO composite layer 5%.

[0098] A bilayer PI-PHT-35 composite material was obtained, which has a glass transition temperature of 201.8℃; a shape memory fixation rate of 98.38% and a shape recovery rate of 93.9%; but cannot achieve three-segment shape memory.

[0099] Figure 3 The graphs show the thermomechanical properties of the bilayer gradient polyimide composites prepared in the examples and comparative examples. Figure 3 In the figure, (a) represents the energy storage modulus and (b) represents the loss factor. It can be seen that the bilayer composite material consisting of a pure polyimide film and a GO composite film exhibits the conditions for achieving three-segment shape memory: a wide glass transition temperature range and two loss factor peaks; while the bilayer composite material consisting of two GO composite films does not exhibit this phenomenon in terms of energy storage modulus and loss factor.

[0100] Figure 4 The two-stage shape memory properties of the bilayer gradient polyimide composite materials prepared in the examples and comparative examples are shown. (a) is PI-PHT-01, (b) is PI-PHT-03, (c) is PI-PHT-05, (d) is PI-PHT-13, (e) is PI-PHT-15, and (f) is PI-PHT-35. It can be seen that the composite material prepared by the present invention has two-stage shape memory properties.

[0101] Figure 5 This describes the three-stage shape memory fixation and recovery process of the bilayer gradient polyimide composite material prepared in Example 3, where S0 is the initial material; S1 is the first fixation programming at 210℃; and S2 is the second fixation programming at 180℃. 1R The first stage of recovery occurs automatically after reheating to 180℃, which is compared with S1; S 0RThis is the second stage of recovery that occurs after heating to 210℃. Compared with S0, this shows that the bilayer gradient polyimide composite material prepared by this invention has a three-stage shape memory function.

[0102] Figure 6 The figures shown are test images of the three-segment shape memory properties of the bilayer gradient polyimide composite materials prepared in Examples 1-3, where (a) is PI-PHT-01, (b) is PI-PHT-03, and (c) is PI-PHT-05. It can be seen that the bilayer composite material composed of a layer of pure polyimide and a layer of composite film containing GO can achieve three-segment shape memory properties, which is consistent with... Figure 5 The conclusions were consistent. Among them, the PI-PHT-05 prepared in Example 3 showed the best performance.

[0103] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a bilayer gradient polyimide composite material capable of achieving three-segment shape memory, characterized in that, Includes the following steps: A nucleophilic substitution reaction was carried out by mixing 4,4'-diaminodiphenyl ether, bisphenol A dianhydride and an organic aprotic solvent to obtain a polyamic acid solution; The polyamic acid solution was mixed with toluene and subjected to thermal imidization to obtain polyimide; The polyimide, paraformaldehyde, and organic aprotic solvent are mixed and subjected to a first hyperbranching reaction to obtain the hyperbranched product. The hyperbranched product was first cured to obtain a PI-HDCN film. The polyimide, paraformaldehyde, graphene oxide dispersion and organic aprotic solvent are mixed to carry out a second hyperbranching reaction to obtain a hyperbranched polyimide composite material containing GO. After coating the hyperbranched polyimide composite material containing GO onto the surface of the PI-HDCN film, a second curing and cyclization were performed sequentially to obtain the bilayer gradient polyimide composite material capable of achieving three-segment shape memory. The mass percentage of GO in the hyperbranched polyimide containing GO is 1-5%; The molar ratio of polyimide to paraformaldehyde is 1:3.5 to 1:

4.

2. The preparation method according to claim 1, characterized in that, The temperature of the first hyperbranching reaction and the temperature of the second hyperbranching reaction are independently 50~60℃, and the time is independently 0.5~1h.

3. The preparation method according to claim 1, characterized in that, The first curing and the second curing are independently cured at temperatures of 80~90℃ and independently cured for times of 0.5~5h.

4. The preparation method according to claim 1, characterized in that, The cyclization process includes the following steps: heating to 100-120℃ and holding for 1-2 hours, then heating to 140-160℃ and holding for 1-2 hours, then heating to 200-220℃ and holding for 1-2 hours, then heating to 240-260℃ and holding for 1-2 hours, and finally heating to 280-300℃ and holding for 1-2 hours.

5. The preparation method according to claim 1 or 4, characterized in that, The cyclization process includes the following steps: heating to 120°C and holding for 1 hour, then heating to 150°C and holding for 1 hour, continuing to heat to 200°C and holding for 1 hour, then heating to 250°C and holding for 1 hour, and finally heating to 280°C and holding for 1 hour.

6. The preparation method according to claim 1, characterized in that, The thermal imidization temperature is 210~240℃, and the time is 5~6h.

7. The preparation method according to claim 1, characterized in that, The molar ratio of the 4,4'-diaminodiphenyl ether to bisphenol A dianhydride is 1:0.92 to 1.02:0.

91.

8. A bilayer gradient polyimide composite material capable of achieving three-segment shape memory, prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the bilayer gradient polyimide composite material capable of achieving three-segment shape memory as described in claim 8 in shape memory deformation.

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