Shape memory polyimide molding powder, preparation method and application thereof, and shape memory polyimide three-dimensional block material

Abstract

The present invention provides a shape-memory polyimide molding powder, a preparation method and application thereof, and a shape-memory polyimide three-dimensional bulk material, relating to the technical field of shape-memory polymers. The method for preparing the shape-memory polyimide molding powder provided by the present invention comprises the following steps: mixing an aromatic diamine, an aromatic dianhydride, a reactive end-capping group donor, and a polar aprotic solvent, and performing a condensation reaction to obtain polyamic acid; and mixing the polyamic acid and a dehydrating agent, and performing an imidization dehydration reaction to obtain the shape-memory polyimide molding powder. The shape-memory polyimide molding powder prepared by the present invention can be formed into a three-dimensional bulk material by hot compression molding, and has simple preparation and convenient molding, making it suitable for large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of shape memory polymers, and in particular to shape memory polyimide molding powder, a preparation method and application thereof, and a shape memory polyimide three-dimensional block material. Background Art

[0002] Shape memory polyimide (SMPI) is a type of shape memory polymer with the highest temperature resistance currently available. It has enormous application potential in high-tech fields such as deployable space mechanisms, high-temperature sensors, and intelligent actuators. All of these applications are based on its "deformation" (shape fixation) and "rebound" (shape recovery) behaviors in response to external stimuli (light, heat, electricity, magnetism, etc.).

[0003] Existing shape-memory polyimides have certain limitations. First, in terms of material form, the vast majority are in thin film form, with a thickness generally not exceeding 150 microns. This material form is suitable for coatings or thin films, but it is difficult to meet the molding and performance requirements for the application of three-dimensional bulk or bulk materials in practical applications. This is because the molding of polyimide in film or coating form is relatively simple, while the molding of three-dimensional bulk materials requires molding, injection molding (extrusion), etc. It is well known that these molding methods place high demands on both the chemical structure of polyimide (PI) and the raw material form (molding powder). Secondly, from the design concept point of view, most of the existing shape memory polyimides use monomers with three or more functional groups (such as tertiary aromatic amine, tetraarylamine or octaarylamine, etc.) as cross-linking agents to introduce a certain proportion of chemical cross-linking points as the fixed phase. Due to the ultra-high reactivity between acid anhydride and amino group, gelation must be strictly prevented during the synthesis of polyamic acid precursors. Therefore, whether chemical imidization (addition of acetic anhydride / tertiary amine dehydrating agent) or thermal imidization (toluene azeotropic dehydration) is used, gelation will occur. Once gelation occurs in the polymerization system, it means that the polymerization reaction has failed. Therefore, from the perspective of synthesis and molding methods, the vast majority of existing shape-memory polyimides enter the molding stage from the polyamic acid precursor stage (film laying on a flat surface followed by thermal imidization molding), i.e., "imidization while molding." This synthesis and molding method is destined to fail in obtaining materials with three-dimensional bulk structures and is only suitable for thin films or coatings. The large amount of pores in the polyamic acid precursor, caused by necessary steps such as solvent volatilization and dehydration, makes it incompatible with three-dimensional bulk molding methods such as molding and injection molding (extrusion). Many parts and components in the engineering field, such as sealing structures and secondary load-bearing support structures, require three-dimensional bulk material form.

[0004] Despite the increasing research on shape-memory polyimide materials, these materials are primarily in the form of thin films or coatings, which cannot meet the demand for three-dimensional bulk materials in practical applications (such as sealing and load-bearing). In practical applications, these materials mostly exist in three-dimensional structures such as rings, loops, and components. Given the existing design concepts and preparation methods of shape-memory polyimides, developing new shape-memory polyimide materials with shape-memory properties compatible with hot compression molding processes remains a major technical challenge in the design and synthesis of intelligent polyimides. Summary of the Invention

[0005] The purpose of the present invention is to provide a shape memory polyimide molding powder, a preparation method and application thereof, and a shape memory polyimide three-dimensional block material. The shape memory polyimide molding powder prepared by the present invention can be used to obtain a three-dimensional block material by hot molding, and the preparation is simple, the molding is convenient, and it is suitable for large-scale production.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing shape memory polyimide molding powder, comprising the following steps:

[0008] An aromatic diamine, an aromatic dibasic anhydride, a reactive end-capping group donor and a polar aprotic solvent are mixed and subjected to a condensation reaction to obtain a polyamic acid;

[0009] The polyamic acid and the dehydrating agent are mixed and subjected to imidization and dehydration reaction to obtain shape memory polyimide molding powder.

[0010] Preferably, the aromatic diamine includes one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, m-phenylenediamine and p-phenylenediamine.

[0011] Preferably, the aromatic dianhydride includes one or more of bisphenol A diether dianhydride, triphenyl diether dianhydride, 3,3',4,4'-diphenyl ether dianhydride and 2,3,3',4'-diphenyl ether dianhydride.

[0012] Preferably, the polar aprotic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

[0013] Preferably, the temperature of the condensation reaction is room temperature; and the time of the condensation reaction is 12 to 24 hours.

[0014] Preferably, the dehydrating agent is a mixture of pyridine and acetic anhydride; the molar ratio of the pyridine to acetic anhydride is 0.5 to 1:1; and the molar ratio of the acetic anhydride to the aromatic diamine is 2 to 10:1.

[0015] Preferably, the temperature of the imidization dehydration reaction is room temperature; and the time of the imidization dehydration reaction is 12 to 24 hours.

[0016] The present invention provides shape memory polyimide molding powder prepared by the preparation method described in the above technical solution.

[0017] The present invention provides the use of the shape memory polyimide molding powder described in the above technical solution in the preparation of a shape memory polyimide film, a shape memory polyimide coating or a shape memory polyimide three-dimensional block material.

[0018] The present invention provides a shape memory polyimide three-dimensional block material, which is obtained by hot-molding the shape memory polyimide molding powder described in the above technical solution.

[0019] The present invention provides a method for preparing shape-memory polyimide molding powder, comprising the following steps: mixing an aromatic diamine, an aromatic dianhydride, a reactive end-capping group donor, and a polar aprotic solvent, and performing a condensation reaction to obtain polyamic acid; and mixing the polyamic acid with a dehydrating agent, and performing an imidization dehydration reaction to obtain the shape-memory polyimide molding powder. The present invention utilizes a reactive end-capping group post-crosslinking method to achieve chemical crosslinking of linear polyimide oligomers, thereby increasing the molecular weight and introducing chemical crosslinking points, thereby meeting the requirements of shape-memory performance for chemical crosslinking points and high molecular weight. Traditional methods generally utilize multifunctional monomers such as aromatic triamines, tetraamines, and even octaamines for copolymerization. During the preparation of polyamic acid, chemical crosslinking is performed by the multifunctional monomers. This method easily leads to irreversible gelation during synthesis due to the high reactivity between the anhydride and the amine. The present invention, however, produces linear polyimide molecules without the use of multifunctional crosslinkers, lacks branched structures, and eliminates the possibility of chemical crosslinking during the synthesis process. This radically differs from the inherent design principles of existing shape-memory polyimides. Given the well-established industrial processes for synthesizing polyimide molding powders, whether through thermal or chemical dehydration, the technical solution employed in the present invention can be directly produced using existing industrial methods. It requires no special reactants and operates under mild reaction conditions, making it suitable for industrial scale-up.

[0020] The polyimide prepared by the present invention is obtained in the form of molding powder, and this molding powder can be used to prepare and mold three-dimensional profiles through conventional hot molding processes, which is significantly different from existing shape memory polyimides. Most existing shape memory polyimides appear in the form of films or coatings. After synthesizing polyamic acid, a film is applied and then gradually thermal imidization and dehydration are performed to obtain polyimide. The limitation of this traditional method is that it is only applicable to macroscopically "thin" material forms such as films or coatings, because the conversion of polyamic acid to polyimide involves the volatilization of a large amount of high-boiling point organic solvents and the removal of small molecules of water. If it is not "thin" enough, the solvent and water are difficult to completely remove from the system, and a large number of pore defects are formed at high temperatures. The present invention directly adds a dehydrating agent to the system after obtaining polyamic acid. After dehydration is completed to obtain polyimide, it is precipitated from the poor solvent system in the form of molding powder. This molding powder already has a polyimide structure and will no longer release water molecules and solvents in the subsequent molding process. Therefore, the shape memory polyimide obtained by the present invention is compatible with the conventional hot compression molding process for preparing three-dimensional profiles, unlike the conventional technology which is only applicable to thinner film or coating molding processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the shape memory curve of the test specimen prepared in Application Example 1;

[0022] Figure 2 The shape memory curve of the test specimen prepared for comparative application example 1;

[0023] Figure 3 This is the shape memory curve of the test specimen prepared in Application Example 2;

[0024] Figure 4 The shape memory curve of the test specimen prepared for comparative application example 2;

[0025] Figure 5 This is the shape memory curve of the test specimen prepared in Application Example 3;

[0026] Figure 6 The shape memory curve of the test specimen prepared for comparative application example 3;

[0027] Figure 7 This is the shape memory curve of the test specimen prepared in Application Example 4;

[0028] Figure 8 The shape memory curve of the test specimen prepared for comparative application example 4;

[0029] Figure 9 This is the shape memory curve of the test specimen prepared in Application Example 5;

[0030] Figure 10The shape memory curve of the test specimen prepared for comparative application example 5;

[0031] Figure 11 A comparison chart of tensile strength between application examples 1 to 5 and comparative application examples 1 to 5;

[0032] Figure 12 A comparison chart of elongation at break between application examples 1 to 5 and comparative application examples 1 to 5;

[0033] Figure 13 Thermogravimetric curves of application examples 1 to 5;

[0034] Figure 14 The thermogravimetric curves of comparative application examples 1 to 5 are shown. DETAILED DESCRIPTION

[0035] The present invention provides a method for preparing shape memory polyimide molding powder, comprising the following steps:

[0036] An aromatic diamine, an aromatic dibasic anhydride, a reactive end-capping group donor and a polar aprotic solvent are mixed and subjected to a condensation reaction to obtain a polyamic acid;

[0037] The polyamic acid and the dehydrating agent are mixed and subjected to imidization and dehydration reaction to obtain shape memory polyimide molding powder.

[0038] The present invention comprises mixing an aromatic diamine, an aromatic dianhydride, a reactive end-capping group donor, and a polar aprotic solvent to carry out a condensation reaction to obtain a polyamic acid. In the present invention, the molar ratio of the aromatic dianhydride to the aromatic diamine is preferably 0.900 to 0.978:1, more preferably 0.933 to 0.973:1, and even more preferably 0.957 to 0.967:1; and the molar ratio of the aromatic dianhydride to the reactive end-capping group donor is preferably 4.50 to 22.30:1, more preferably 7 to 22.23:1, and even more preferably 11 to 14:1.

[0039] In the present invention, the aromatic diamine preferably includes one or more of 4,4'-diaminodiphenyl ether (4,4'-ODA), 3,4'-diaminodiphenyl ether (3,4'-ODA), 1,3-bis(3-aminophenoxy)benzene (1,3,3-APB), 1,3-bis(4-aminophenoxy)benzene (1,3,4-APB), 1,4-bis(4-aminophenoxy)benzene (1,4,4-APB), m-phenylenediamine and p-phenylenediamine.

[0040] In the present invention, the aromatic dianhydride preferably includes one or more of bisphenol A diether dianhydride (BPADA), triphenyl diether dianhydride (HQDA), 3,3',4,4'-diphenyl ether dianhydride (ODPA) and 2,3,3',4'-diphenyl ether dianhydride (aODPA).

[0041] In the present invention, the reactive end-capping group donor preferably includes nadic anhydride (NA), 4-phenylethynylphthalic anhydride (PEPA), 4-phenylethynylaniline (PEA), maleic anhydride (MA) or 4-aminobenzocyclobutene (NBCB).

[0042] In the present invention, the polar aprotic solvent preferably includes one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP). In the present invention, the mass ratio of the polar aprotic solvent to the aromatic dianhydride is preferably 3.9 to 8:1, more preferably 5.8 to 6.2:1.

[0043] In the present invention, the condensation reaction temperature is preferably room temperature, specifically preferably 20-30°C; the condensation reaction time is preferably 12-24 hours, more preferably 15-21 hours, and even more preferably 15-18 hours. In the present invention, the condensation reaction is preferably carried out under stirring conditions; the stirring rate is preferably 200-300 rpm.

[0044] After obtaining the polyamic acid, the present invention mixes the polyamic acid with a dehydrating agent to carry out imidization and dehydration reaction to obtain shape memory polyimide molding powder.

[0045] In the present invention, the dehydrating agent is preferably a mixture of pyridine and acetic anhydride; the molar ratio of pyridine to acetic anhydride is preferably 0.5 to 1:1, more preferably 0.6 to 0.8:1, and further preferably 0.6 to 0.7:1; the molar ratio of acetic anhydride to aromatic diamine is preferably 2 to 10:1, more preferably 4:1.

[0046] In the present invention, the temperature of the imidization dehydration reaction is preferably room temperature; the time of the imidization dehydration reaction is preferably 12 to 24 hours, more preferably 15 to 21 hours, and even more preferably 18 to 21 hours. In the present invention, the imidization dehydration reaction is preferably carried out under stirring conditions; the stirring rate is preferably 200 to 300 rpm.

[0047] In the present invention, after the imidization-dehydration reaction, the resulting reaction system is preferably poured into a poor solvent to precipitate a powder; the resulting powder is then washed and dried to obtain a shape-memory polyimide molding powder. In the present invention, the poor solvent preferably includes water and / or ethanol. In the present invention, the water is preferably deionized water; the ethanol is preferably anhydrous ethanol. The present invention does not have any particular requirements for the specific washing and drying procedures; washing and drying processes familiar to those skilled in the art can be employed.

[0048] The present invention provides shape memory polyimide molding powder prepared by the preparation method described in the above technical solution.

[0049] The present invention provides the use of the shape-memory polyimide molding powder described in the above-mentioned technical solution in the preparation of shape-memory polyimide films, shape-memory polyimide coatings, or shape-memory polyimide three-dimensional bulk materials. In the present invention, the method for preparing a shape-memory polyimide film using the shape-memory polyimide molding powder preferably comprises: mixing the shape-memory polyimide molding powder with an organic solvent to obtain a coating liquid; applying the coating liquid to a glass plate and curing the liquid to obtain a shape-memory polyimide film. In the present invention, the organic solvent preferably comprises N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone. In the present invention, the concentration of the coating liquid is preferably 5-25wt%, more preferably 15-20wt%. In the present invention, the coating method preferably utilizes a glass rod for blade coating; the curing temperature is preferably 300-380°C, more preferably 350°C; and the curing time is preferably 1-5 hours, more preferably 2-3 hours. During the curing process, the organic solvent is removed, and curing and crosslinking are performed. In the present invention, the thickness of the shape memory polyimide film is preferably 10 to 100 micrometers, more preferably 25 to 50 micrometers.

[0050] In the present invention, the method for preparing a shape-memory polyimide coating using the shape-memory polyimide molding powder preferably includes: mixing the shape-memory polyimide molding powder with an organic solvent to obtain a coating liquid; spraying the coating liquid onto a glass plate using a high-pressure spray gun and curing the coating to obtain a shape-memory polyimide coating. In the present invention, the organic solvent preferably includes N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone. In the present invention, the concentration of the coating liquid is preferably 1 to 15 wt%, more preferably 3 to 5 wt%. In the present invention, the curing temperature is preferably 300 to 380°C, more preferably 350°C; and the curing time is preferably 1 to 5 hours, more preferably 1 to 2 hours. During the curing process, the organic solvent is removed, and curing and cross-linking are performed. In the present invention, the thickness of the shape-memory polyimide coating is preferably 100 nm to 1 micron, more preferably 300 to 500 nm.

[0051] The present invention provides a shape memory polyimide three-dimensional block material, which is obtained by hot compression molding the shape memory polyimide molding powder described in the above technical solution. In the present invention, the hot compression molding is preferably performed in a metal mold.

[0052] In the present invention, the pressure of the hot compression molding is preferably 2 to 20 MPa, more preferably 7 to 17 MPa, and further preferably 7 to 12 MPa; the temperature of the hot compression molding is preferably 250 to 350°C, more preferably 280 to 330°C, and further preferably 300°C; the heat preservation and pressure holding time is preferably 1 to 3 hours, more preferably 1.5 to 2 hours.

[0053] In the present invention, the shape memory polyimide three-dimensional block material can be machined to prepare seals or other parts in desired shapes for use in sealing at high and low temperatures.

[0054] In the present invention, the glass transition temperature T of the shape memory polyimide three-dimensional block material is g Preferably ≥210℃, more preferably 214~219℃; shape fixation rate (R f ) preferably ≥97%; shape recovery rate (R r ) is preferably ≥98%.

[0055] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0056] In the present invention, a dynamic mechanical analyzer (DMA) is used to quantitatively characterize the shape memory performance. The shape memory curve is tested as follows: a rectangular test specimen of a certain length is clamped on a fixture, the test specimen is stretched by 20% at 230°C, the stretched state is maintained and the temperature is lowered to 110°C to fix the shape; the temperature of the test specimen is raised to 230°C again;

[0057] Shape fixation rate (R f ) and shape recovery rate (R r ) are calculated from the DMA curve according to the following formulas (1) and (2), respectively:

[0058]

[0059] In formula (1) and formula (2), ε unload is the strain after unloading the tensile force at 110℃, ε load is the strain before unloading the tensile force at 110°C, ε rec is the strain after recovery at 230 °C, and N is the number of shape memory test cycles.

[0060] Example 1

[0061] 0.10 mol of aromatic diamine 4,4'-ODA, 0.0933 mol of aromatic dibasic anhydride BPADA and 0.0133 mol of nadic anhydride NA were added to 283 g of polar aprotic solvent DMF, and stirred at room temperature for 12 hours to obtain polyamic acid; then, dehydrating agents 0.20 mol of acetic anhydride and 0.10 mol of pyridine were added thereto, and the stirring reaction was continued for 24 hours to complete the imidization dehydration reaction; the reaction system was poured into a mixed solution of 1 L of water and 1 L of ethanol, and powder was precipitated, collected by filtration, washed, and fully dried to obtain shape memory polyimide molding powder.

[0062] Application Example 1

[0063] The shape memory polyimide molding powder prepared in Example 1 was loaded into a metal mold using a hot compression molding process and kept warm at 250°C and a contact pressure of 2 MPa for 3 hours to form a three-dimensional profile. The three-dimensional profile was machined into a test specimen of 20 mm × 3 mm × 1 mm and other three-dimensional parts.

[0064] Comparative Example 1

[0065] 0.10 mol of aromatic diamine 4,4'-ODA and 0.10 mol of aromatic dianhydride BPADA were added to 288 g of polar aprotic solvent DMF, and the mixture was stirred and reacted at room temperature for 12 hours to obtain polyamic acid; then, 0.20 mol of acetic anhydride and 0.10 mol of pyridine as dehydrating agents were added thereto, and the mixture was stirred and reacted for 24 hours to complete the imidization dehydration reaction; the reaction system was poured into a mixed solution of 1 L of water and 1 L of ethanol, and powder was precipitated, collected by filtration, washed, and fully dried to obtain shape memory polyimide molding powder.

[0066] Comparative Application Example 1

[0067] Using a hot compression molding process, the shape memory polyimide molding powder prepared in Comparative Example 1 was loaded into a metal mold and kept warm for 3 hours at 250°C and a contact pressure of 2 MPa to form a three-dimensional profile; the three-dimensional profile was machined into a test specimen of 20 mm × 3 mm × 1 mm and other three-dimensional parts.

[0068] Figure 1 This is the shape memory curve of the test specimen prepared in Application Example 1; Figure 2 This is the shape memory curve of the test specimen prepared for comparative application example 1. Figure 1 and Figure 2 From the shape memory curve, it can be clearly seen that the material prepared in Example 1 (R r =99.18%) is significantly higher than that of the comparative application example 1 (R r =49.13%), which shows that compared with linear polyimide that relies solely on physical crosslinking points such as molecular entanglement, the design method of the present invention, under the condition that other conditions are the same, the introduction of reactive end-capping groups (nadic anhydride) undergoes thermal crosslinking at high temperature to produce chemical crosslinking points, which greatly improves the shape memory performance.

[0069] Example 2

[0070] 0.10 mol of aromatic diamine 3,4'-ODA, 0.0957 mol of aromatic dianhydride HQDA and 0.0087 mol of nadic anhydride NA were added to 240 g of polar aprotic solvent DMAc, and the mixture was stirred and reacted at room temperature for 15 hours to obtain polyamic acid; then, 0.40 mol of acetic anhydride and 0.24 mol of pyridine as dehydrating agents were added thereto, and the mixture was stirred and reacted for 21 hours to complete the imidization dehydration reaction; the reaction system was poured into a mixed solution of 0.5 L of water and 1.5 L of ethanol, and powder was precipitated, collected by filtration, washed, and fully dried to obtain shape memory polyimide molding powder.

[0071] Application Example 2

[0072] The shape memory polyimide molding powder prepared in Example 2 was loaded into a metal mold using a hot compression molding process and kept warm for 2 hours at 280°C and a contact pressure of 7 MPa to form a three-dimensional profile. The three-dimensional profile was machined into a test specimen of 20 mm × 3 mm × 1 mm and other three-dimensional parts.

[0073] Comparative Example 2

[0074] 0.10 mol of aromatic diamine 3,4'-ODA and 0.10 mol of aromatic dianhydride HQDA were added to 241 g of polar aprotic solvent DMAc, and the mixture was stirred and reacted at room temperature for 15 hours to obtain polyamic acid; then, 0.40 mol of acetic anhydride and 0.24 mol of pyridine as dehydrating agents were added thereto, and the mixture was stirred and reacted for 21 hours to complete the imidization dehydration reaction; the reaction system was poured into a mixed solution of 0.5 L of water and 1.5 L of ethanol, and powder was precipitated, collected by filtration, washed, and fully dried to obtain shape memory polyimide molding powder.

[0075] Comparative Application Example 2

[0076] Using a hot compression molding process, the shape memory polyimide molding powder prepared in Comparative Example 2 was loaded into a metal mold and kept warm for 2 hours at 280°C and a contact pressure of 7 MPa to form a three-dimensional profile; the three-dimensional profile was machined into a test specimen of 20 mm × 3 mm × 1 mm and other three-dimensional parts.

[0077] Figure 3 This is the shape memory curve of the test specimen prepared in Application Example 2; Figure 4 This is the shape memory curve of the test specimen prepared for comparative application example 2. Figure 3 and Figure 4 From the shape memory curve, it can be clearly seen that the material prepared in Example 2 (R r =97.96%) is significantly higher than that of the comparative application example 2 (R r =66.78%), which shows that compared with linear polyimide that relies solely on physical crosslinking points such as molecular entanglement, the design method of the present invention, under the same conditions, the introduction of reactive end-capping groups (nadic anhydride) undergoes thermal crosslinking at high temperature to produce chemical crosslinking points, which greatly improves the shape memory performance.

[0078] Example 3

[0079] 0.10 mol of aromatic diamine 1,3,4-APB, 0.0967 mol of aromatic dianhydride ODPA and 0.0067 mol of nadic anhydride NA were added to 241 g of polar aprotic solvent NMP, and the mixture was stirred and reacted at room temperature for 18 hours to obtain polyamic acid; then, dehydrating agents 0.60 mol of acetic anhydride and 0.42 mol of pyridine were added thereto, and the stirring reaction was continued for 18 hours to complete the imidization dehydration reaction; the reaction system was poured into a mixed solution of 1.5 L of water and 0.5 L of ethanol, and powder was precipitated, collected by filtration, washed, and fully dried to obtain shape memory polyimide molding powder.

[0080] Application Example 3

[0081] The shape memory polyimide molding powder prepared in Example 3 was loaded into a metal mold using a hot compression molding process and kept warm at 300°C and a contact pressure of 12 MPa for 1.5 hours to form a three-dimensional profile. The three-dimensional profile was machined into a test specimen of 20 mm × 3 mm × 1 mm and other three-dimensional parts.

[0082] Comparative Example 3

[0083] 0.10 mol of aromatic diamine 1,3,4-APB and 0.10 mol of aromatic dianhydride ODPA were added to 241 g of polar aprotic solvent NMP, and the mixture was stirred and reacted at room temperature for 18 hours to obtain polyamic acid; then, 0.60 mol of acetic anhydride and 0.42 mol of pyridine as dehydrating agents were added thereto, and the mixture was stirred and reacted for 18 hours to complete the imidization dehydration reaction; the reaction system was poured into a mixed solution of 1.5 L of water and 0.5 L of ethanol, and powder was precipitated, collected by filtration, washed, and fully dried to obtain shape memory polyimide molding powder.

[0084] Comparative Application Example 3

[0085] Using a hot compression molding process, the shape memory polyimide molding powder prepared in Comparative Example 3 was loaded into a metal mold and kept warm at 300°C and a contact pressure of 12 MPa for 1.5 hours to form a three-dimensional profile; the three-dimensional profile was machined into a test specimen of 20 mm × 3 mm × 1 mm and other three-dimensional parts.

[0086] Figure 5 This is the shape memory curve of the test specimen prepared in Application Example 3; Figure 6 This is the shape memory curve of the test specimen prepared for comparative application example 3. Figure 5 and Figure 6 From the shape memory curve, it can be clearly seen that the material prepared in Example 3 (R r =98.94%) is significantly higher than that of the comparative application example 3 (R r=69.21%), which shows that compared with linear polyimide that relies solely on physical crosslinking points such as molecular entanglement, the design method of the present invention, under the condition that other conditions are the same, the introduction of reactive end-capping groups (nadic anhydride) undergoes thermal crosslinking at high temperature to produce chemical crosslinking points, which greatly improves the shape memory performance.

[0087] Example 4

[0088] 0.10 mol of aromatic diamine 1,4,4-APB, 0.0973 mol of aromatic dianhydride aODPA and 0.0054 mol of nadic anhydride NA were added to 120 g of DMF and 120 g of NMP as polar aprotic solvents, and the mixture was stirred and reacted at room temperature for 21 hours to obtain polyamic acid; then, 0.80 mol of acetic anhydride and 0.64 mol of pyridine as dehydrating agents were added thereto, and the stirring reaction was continued for 15 hours to complete the imidization dehydration reaction; the reaction system was poured into a mixed solution of 1 L of water and 1 L of ethanol, and powder was precipitated, collected by filtration, washed, and fully dried to obtain shape memory polyimide molding powder.

[0089] Application Example 4

[0090] The shape memory polyimide molding powder prepared in Example 4 was loaded into a metal mold using a hot compression molding process and kept at 330°C and a contact pressure of 17 MPa for 1.5 hours to form a three-dimensional profile; the three-dimensional profile was machined into a test specimen of 20 mm × 3 mm × 1 mm and other three-dimensional parts.

[0091] Comparative Example 4

[0092] 0.10 mol of aromatic diamine 1,4,4-APB and 0.10 mol of aromatic dibasic anhydride aODPA were added to 120 g of DMF and 120 g of NMP (polar aprotic solvents), and the mixture was stirred and reacted at room temperature for 21 hours to obtain polyamic acid; then, 0.80 mol of acetic anhydride and 0.64 mol of pyridine as dehydrating agents were added thereto, and the stirring reaction was continued for 15 hours to complete the imidization dehydration reaction; the reaction system was poured into a mixed solution of 1 L of water and 1 L of ethanol, and powder was precipitated, collected by filtration, washed, and fully dried to obtain shape memory polyimide molding powder.

[0093] Comparative Application Example 4

[0094] Using a hot compression molding process, the shape memory polyimide molding powder prepared in Comparative Example 4 was loaded into a metal mold and kept warm at 330°C and a contact pressure of 17 MPa for 1.5 hours to form a three-dimensional profile; the three-dimensional profile was machined into a test specimen of 20 mm × 3 mm × 1 mm and other three-dimensional parts.

[0095] Figure 7This is the shape memory curve of the test specimen prepared in Application Example 4; Figure 8 This is the shape memory curve of the test specimen prepared for comparative application example 4. Figure 7 and Figure 8 From the shape memory curve, it can be clearly seen that the material prepared in Example 4 (R r =99.10%) is significantly higher than that of the comparative application example 4 (R r =51.37%), which shows that compared with linear polyimide that relies solely on physical crosslinking points such as molecular entanglement, the design method of the present invention, under the condition that other conditions are the same, the introduction of reactive end-capping groups (nadic anhydride) undergoes thermal crosslinking at high temperature to produce chemical crosslinking points, which greatly improves the shape memory performance.

[0096] Example 5

[0097] 0.10 mol of aromatic diamine 1,3,3-APB, 0.0489 mol of aromatic dibasic anhydrides BPADA and 0.0489 mol of ODPA, and 0.0044 mol of nadic anhydride NA were added to 94 g of DMAc and 188 g of NMP as polar aprotic solvents, and the mixture was stirred and reacted at room temperature for 24 hours to obtain polyamic acid; then, 1.0 mol of acetic anhydride and 1.0 mol of pyridine as dehydrating agents were added thereto, and the stirring reaction was continued for 12 hours to complete the imidization dehydration reaction; the reaction system was poured into a mixed solution of 1 L of water and 1 L of ethanol, and powder was precipitated, collected by filtration, washed, and fully dried to obtain shape memory polyimide molding powder.

[0098] Application Example 5

[0099] The shape memory polyimide molding powder prepared in Example 5 was loaded into a metal mold using a hot compression molding process and kept at 350°C and a contact pressure of 20 MPa for 1 hour to form a three-dimensional profile; the three-dimensional profile was machined into a test specimen of 20 mm × 3 mm × 1 mm and other three-dimensional parts.

[0100] Comparative Example 5

[0101] 0.10 mol of aromatic diamine 1,3,3-APB, 0.05 mol of aromatic dibasic anhydride BPADA and 0.05 mol of ODPA were added to 94 g of DMAc and 188 g of NMP as polar aprotic solvents, and the mixture was stirred and reacted at room temperature for 24 hours to obtain polyamic acid; then, 1.0 mol of acetic anhydride and 1.0 mol of pyridine as dehydrating agents were added thereto, and the stirring reaction was continued for 12 hours to complete the imidization dehydration reaction; the reaction system was poured into a mixed solution of 1 L of water and 1 L of ethanol, and powder was precipitated, collected by filtration, washed, and fully dried to obtain shape memory polyimide molding powder.

[0102] Comparative Application Example 5

[0103] Using a hot compression molding process, the shape memory polyimide molding powder prepared in Comparative Example 5 was loaded into a metal mold and kept warm at 350°C and a contact pressure of 20 MPa for 1 hour to form a three-dimensional profile; the three-dimensional profile was machined into a test specimen of 20 mm × 3 mm × 1 mm and other three-dimensional parts.

[0104] Figure 9 This is the shape memory curve of the test specimen prepared in Application Example 5; Figure 10 This is the shape memory curve of the test specimen prepared for comparative application example 5. Figure 9 and Figure 10 From the shape memory curve, it can be clearly seen that the material prepared in Example 5 (R r =98.85%) is significantly higher than that of comparative application example 5 (R r =72.84%), which shows that compared with linear polyimide that relies solely on physical crosslinking points such as molecular entanglement, the design method of the present invention, under the condition that other conditions are the same, the introduction of reactive end-capping groups (nadic anhydride) undergoes thermal crosslinking at high temperature to produce chemical crosslinking points, which greatly improves the shape memory performance.

[0105] Figure 11 A comparison chart of tensile strength between application examples 1 to 5 and comparative application examples 1 to 5; Figure 12 A comparison chart of elongation at break between application examples 1 to 5 and comparative application examples 1 to 5; Figure 13 Thermogravimetric curves of application examples 1 to 5; Figure 14 The thermogravimetric curves of comparative application examples 1 to 5 are shown.

[0106] Tensile strength and elongation at break were measured in accordance with the following national standard: GB / T 1040.1-2018 Plastics—Determination of Tensile Properties—Part 1—General Principles. Thermal stability was characterized using thermogravimetric analysis in accordance with the following standard: JYT 014-1996 Thermal Analysis Methods—General Rules. Table 1 shows a comparison of the mechanical properties and thermal stability of Application Examples 1-5 and Comparative Application Examples 1-5.

[0107] Table 1 Comparison of mechanical properties and thermal stability of application examples 1 to 5 and comparative application examples 1 to 5

[0108]

[0109] Table 1 T 5wt％ Refers to the 5% weight loss temperature of the thermogravimetric curve (generally represents the thermal stability of polymer materials); R 800 Refers to the residual weight ratio at 800°C.

[0110] Since the shape memory polyimide of the present invention is obtained by crosslinking with reactive end-capping groups, its tensile strength and elongation at break are lower than those of the linear polyimide without crosslinking with reactive end-capping groups (i.e., the corresponding comparative example). However, as the designed molecular weight increases, the gap between the tensile strength and elongation at break of the embodiment and the corresponding comparative example gradually narrows. Figure 11 and Figure 12 This trend of change can be seen in .

[0111] The thermal stability of the examples and the comparative examples is similar, which can be seen from the Figure 13 and Figure 14 From the comparison, it can be seen that since they are all high molecular weight polymers, the difference in chemical structure (whether cross-linking reaction occurs) does not cause significant difference in the thermal stability of the material.

[0112] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A shape memory polyimide three-dimensional block material, obtained by hot compression molding a shape memory polyimide molding powder, wherein the preparation method of the shape memory polyimide molding powder comprises the following steps: An aromatic diamine, an aromatic dibasic anhydride, a reactive end-capping group donor and a polar aprotic solvent are mixed and subjected to a condensation reaction to obtain a polyamic acid; the aromatic diamine is one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, m-phenylenediamine and p-phenylenediamine; the The aromatic dianhydride is one or more of bisphenol A diether dianhydride, triphenyl diether dianhydride, 3,3',4,4'-diphenyl ether dianhydride and 2,3,3',4'-diphenyl ether dianhydride; the reactive end-capping group donor is nadic anhydride; the molar ratio of the aromatic dianhydride to the aromatic diamine is 0.900-0.978:1; the molar ratio of the aromatic dianhydride to the reactive end-capping group donor is 4.50-22.30:1; The polyamic acid and the dehydrating agent are mixed and subjected to imidization and dehydration reaction to obtain shape memory polyimide molding powder.

2. The shape memory polyimide three-dimensional block material according to claim 1, characterized in that: The polar aprotic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

3. The shape memory polyimide three-dimensional block material according to claim 1, characterized in that: The condensation reaction temperature is room temperature; the condensation reaction time is 12 to 24 hours.

4. The shape memory polyimide three-dimensional block material according to claim 1, characterized in that: The dehydrating agent is a mixture of pyridine and acetic anhydride; the molar ratio of the pyridine to the acetic anhydride is 0.5-1:1; the molar ratio of the acetic anhydride to the aromatic diamine is 2-10:

1.

5. The shape memory polyimide three-dimensional block material according to claim 1, characterized in that: The temperature of the imidization dehydration reaction is room temperature; the time of the imidization dehydration reaction is 12 to 24 hours.

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