Phenylboronic acid-terminated polyimide, preparation method and application thereof, and recoverable 3D printing PI ink

Abstract

The invention provides phenylboronic acid-terminated polyimide, a preparation method and application thereof, and recyclable 3D printing PI ink, and belongs to the technical field of 3D printing ink. The phenylboronic acid-terminated low-molecular-weight polyimide PI is firstly designed and synthesized, and the completely recyclable 3D printing PI ink is prepared for the first time by utilizing a trimerization cyclization mechanism of phenylboronic acid at a high temperature and dynamic reversibility of a boron-oxygen bond (B-O); the ink shows rheological characteristics of quick response and instantaneous recovery, personalized manufacturing of high-resolution and high-performance PI components is realized, and the personalized PI components can be recovered to an original ink state for reprinting of other shapes.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D printing inks, and in particular to a phenylboronic acid-terminated polyimide, a preparation method and application thereof, and a recyclable 3D printing PI ink. Background Art

[0002] High-performance engineering polymer polyimide (PI) has strong mechanical properties, excellent high and low temperature resistance and dielectric properties, and has been widely used in aerospace, 5G communications, flexible electronics and other fields. However, polyimide has poor solubility and melting properties, making it difficult to manufacture complex and delicate high-resolution PI geometries through 3D printing without sacrificing performance, which limits the expanded application of polyimide 3D printed parts in various fields.

[0003] At the same time, 3D printing, as an emerging material processing and molding technology, has set off a widespread research boom in many disciplines. This is accompanied by the waste of resources and environmental pollution caused by the large-scale use of disposable printing materials. There is an urgent need to develop recyclable 3D printing materials to repeatedly construct customized geometric shapes, thereby alleviating the energy crisis.

[0004] In the currently known research, there is no preparation method for recyclable 3D printing polyimide ink. It is very meaningful to use 3D printing technology to develop new recyclable polyimide ink, realize customized PI high-resolution geometry and recycle it to print other customized PI geometry. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a phenylboronic acid-terminated polyimide and a preparation method and application thereof, and a recyclable 3D printing PI ink. When the phenylboronic acid-terminated polyimide provided by the present invention is used as a 3D printing ink, high-resolution PI parts can be printed without sacrificing inherent performance, and the 3D-printed PI parts can be restored to the original ink state for reprinting in various other shapes.

[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 phenylboronic acid-terminated polyimide having a structure shown in Formula I:

[0008]

[0009] In formula I, n=1-30.

[0010] The present invention provides a method for preparing the above-mentioned phenylboronic acid-terminated polyimide, comprising the following steps:

[0011] Mixing bisphenol A dianhydride, 4,4'-diaminodiphenyl ether and an organic solvent, adding aminophenylboronic acid in an ice-water bath to carry out a polycondensation reaction to obtain a polycondensation reaction liquid;

[0012] The polycondensation reaction liquid is mixed with pyridine and acetic anhydride to carry out an imidization reaction to obtain a phenylboronic acid-terminated polyimide having a structure shown in Formula I.

[0013] Preferably, the mass ratio of bisphenol A dianhydride to 4,4'-diaminodiphenyl ether is 5-15:2-5;

[0014] The mass ratio of the bisphenol A dianhydride to aminophenylboric acid is 5-15:0.1-1.

[0015] Preferably, the mass ratio of bisphenol A dianhydride to pyridine is 5-15:5-15;

[0016] The mass ratio of the bisphenol A dianhydride to acetic anhydride is 5-15:15-25.

[0017] Preferably, the polycondensation reaction temperature is 0 to 25°C and the time is 12 to 24 hours;

[0018] The temperature of the imidization reaction is 0 to 50° C., and the time is 10 to 24 hours.

[0019] The present invention provides the use of the phenylboronic acid-terminated polyimide in 3D printing ink.

[0020] The present invention provides a recyclable 3D printing PI ink, comprising the above-mentioned phenylboronic acid-terminated polyimide and a good solvent.

[0021] The present invention provides a printing method for the above-mentioned recyclable 3D printing PI ink, comprising the following steps:

[0022] Performing 3D printing on the recyclable 3D printing PI ink to obtain a 3D printing part precursor;

[0023] The 3D printed part precursor is subjected to a gradient temperature rise thermal curing treatment to obtain a 3D printed PI molded part.

[0024] Preferably, the temperature increase procedure of the gradient temperature increase thermal curing process includes:

[0025] Raising the temperature to a first temperature, and keeping the temperature at the first temperature for 12 to 36 hours, wherein the first temperature is 60 to 100° C.;

[0026] Raising the temperature from the first temperature to the second temperature, and keeping the temperature at the second temperature for 1 to 24 hours, wherein the second temperature is 150 to 200° C.;

[0027] The temperature is raised from the second temperature to the third temperature, and kept at the third temperature for 0.1 to 6 hours, wherein the third temperature is 240°C.

[0028] The present invention provides a method for recycling the above-mentioned recyclable 3D printing PI ink, comprising the following steps:

[0029] The 3D printed PI molded part prepared by the recyclable 3D printing PI ink is placed in a mixed solvent and subjected to ultrasonic treatment to obtain a regenerated 3D printing PI ink;

[0030] The mixed solvent is a mixture of an organic solvent and alcohol, or a mixture of an organic solvent and water.

[0031] The present invention provides a phenylboronic acid-terminated polyimide having a structure shown in Formula I. The present invention uses bisphenol A dianhydride (BPADA) and 4,4'-diaminodiphenyl ether (ODA) as monomers and aminophenylboronic acid (BN) as a capping agent. The obtained phenylboronic acid-terminated polyimide is a low molecular weight polyimide. When used as a 3D printing ink, it exhibits rheological characteristics of rapid response and instantaneous recovery, and can print high-resolution PI components; specifically, during the 3D printing process, the ink is extruded through the nozzle of the 3D printer and accumulated layer by layer to produce a 3D printed part precursor with a customized geometric shape, and then the 3D printed part precursor undergoes a gradient temperature rise thermal curing treatment to obtain a final 3D printed PI molded part, and the mechanical and thermal properties of the obtained 3D printed PI molded part are comparable to those of traditional PI. In the present invention, the purpose of the gradient temperature rise heat curing treatment is to remove the solvent and to cause the trimerization ring reaction of phenylboronic acid. During the high temperature treatment process, the solvent is continuously removed, and the phenylboronic acid at the end of the low molecular weight PI chain is trimerized under heating to form a dynamic borane six-membered ring, resulting in the formation of the final cross-linked PI structure; in the present invention, since the end-capping group-phenylboronic acid will be trimerized into a borane six-membered ring, and the chemical structure of this six-membered ring is similar to that of a benzene ring, the inherent properties of polyimide will not be lost. In addition, the boron oxygen bond (BO) in the borane six-membered ring is dynamic and can be reversibly broken and reorganized in the presence of alcohol or water, which enables the 3D printed PI molded parts to be completely restored to the original ink state for reprinting of other shapes, and the recycled ink still exhibits rheological characteristics suitable for DIW extrusion printing, and has excellent printability.

[0032] The present invention realizes the preparation of recyclable 3D printing PI ink for the first time without sacrificing the inherent properties of PI. The results of the embodiment show that the mechanical properties of the recycled and reprinted 3D printed PI molded parts remain unchanged even after ten recycling cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1This is the nuclear magnetic resonance spectrum of the phenylboronic acid-terminated low molecular weight PI obtained in Example 1;

[0034] Figure 2 This is the infrared spectrum of the 3D printed PI molded part obtained in Example 1 before and after heat treatment;

[0035] Figure 3 The mechanical and thermal properties of the 3D printed PI molded parts obtained in Examples 1 to 4 after heat treatment;

[0036] Figure 4 The mechanical properties test results of the recycled 3D printed PI molded parts;

[0037] Figure 5 This is a physical picture of the 3D printed PI molded part of Example 1 and a physical picture of the recycled and reprinted molded part. DETAILED DESCRIPTION

[0038] The present invention provides a phenylboronic acid-terminated polyimide having a structure shown in Formula I:

[0039]

[0040] In formula I, n=1 to 30, preferably 5 to 20. As a specific embodiment of the present invention, n=6, 9, 13 or 20.

[0041] The present invention provides a method for preparing the above-mentioned phenylboronic acid-terminated polyimide, comprising the following steps:

[0042] Mixing bisphenol A dianhydride, 4,4'-diaminodiphenyl ether and an organic solvent, adding aminophenylboronic acid in an ice-water bath to carry out a polycondensation reaction to obtain a polycondensation reaction liquid;

[0043] The polycondensation reaction liquid is mixed with pyridine and acetic anhydride to carry out an imidization reaction to obtain a phenylboronic acid-terminated polyimide having a structure shown in Formula I.

[0044] Unless otherwise specified, the raw materials used in the present invention are all commercially available.

[0045] The present invention mixes bisphenol A dianhydride, 4,4'-diaminodiphenyl ether and an organic solvent, adds aminophenylboronic acid under ice-water bath conditions, and performs polycondensation reaction to obtain a polycondensation reaction liquid. In the present invention, the mass ratio of bisphenol A dianhydride to 4,4'-diaminodiphenyl ether is preferably 5-15:2-5, and more preferably 8-12:2-5. In the present invention, the organic solvent is preferably one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF) and N-methylpyrrolidone. In the present invention, the mass ratio of bisphenol A dianhydride to the organic solvent is preferably 5-15:50-70, and more preferably 8-12:55-60.

[0046] In the present invention, the mixing is preferably carried out under the conditions of nitrogen and mechanical stirring; in the present invention, the mixing is preferably carried out by stirring bisphenol A dianhydride and an organic solvent first, then adding 4,4'-diaminodiphenyl ether and continuing stirring, and the stirring time is preferably 1 hour.

[0047] In the present invention, the mass ratio of bisphenol A dianhydride to aminophenylboronic acid is 5-15:0.1-1, preferably 8-12:0.1-1.

[0048] In the present invention, the temperature of the polycondensation reaction is preferably 0 to 25°C, more preferably 15 to 25°C; the time is preferably 12 to 24 hours. As a specific embodiment of the present invention, the time of the polycondensation reaction is 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours. In the present invention, the polycondensation reaction is preferably carried out under stirring.

[0049] After obtaining the polycondensation reaction liquid, the present invention mixes the polycondensation reaction liquid with pyridine and acetic anhydride to carry out an imidization reaction to obtain a phenylboronic acid-terminated polyimide having a structure shown in Formula I. In the present invention, the mass ratio of the bisphenol A dianhydride to pyridine is preferably 5-15:5-15, more preferably 8-12:8-12; the mass ratio of the bisphenol A dianhydride to acetic anhydride is preferably 5-15:15-25, more preferably 8-12:18-20.

[0050] In the present invention, the mixing is preferably: slowly adding acetic anhydride and pyridine to the polycondensation reaction liquid. In the present invention, the acetic anhydride acts as a dehydrating agent, and the pyridine acts as a catalyst.

[0051] In the present invention, the temperature of the imidization reaction is preferably 0 to 50°C, more preferably 20 to 40°C, and further preferably 25°C, and the time is preferably 10 to 24 hours, and more preferably 12 to 18 hours; as a specific embodiment of the present invention, the time of the imidization reaction is 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours. In the present invention, the imidization reaction is preferably carried out under stirring conditions.

[0052] In the present invention, the synthesis route of the phenylboronic acid-terminated polyimide is shown in Formula II:

[0053]

[0054] After the imidization reaction, the present invention preferably performs post-treatment on the obtained imidization reaction solution, and the post-treatment preferably comprises the following steps:

[0055] The obtained imidization reaction liquid was diluted with tetrahydrofuran, and the obtained diluted liquid was poured into distilled water to precipitate a solid, and the obtained solid was dried to obtain a phenylboronic acid-terminated polyimide powder.

[0056] In the present invention, the volume ratio of tetrahydrofuran to imidization reaction liquid is preferably 5 to 20: 1, more preferably 10 to 15: 1. In the present invention, the drying is preferably vacuum drying.

[0057] The present invention provides the use of the above-mentioned phenylboronic acid-terminated polyimide in 3D printing ink. In the present invention, the 3D printing ink is preferably DIW-3D printing ink.

[0058] The present invention provides a recyclable 3D printing PI ink, comprising the above-mentioned phenylboronic acid-terminated polyimide and a good solvent.

[0059] In the present invention, the good solvent is preferably one or two of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), tetrahydrofuran and N,N-dimethylformamide. When the good solvent is selected from two of the above solvents, the present invention has no special requirements for the mass ratio of the two.

[0060] In the present invention, the solid content of the recyclable 3D printing PI ink is preferably 40-60%; as a specific embodiment of the present invention, the solid content of the recyclable 3D printing PI ink is 40%, 45%, 50%, 55% or 60%.

[0061] In the present invention, the method for preparing the recyclable 3D printing PI ink preferably comprises the following steps:

[0062] Phenylboronic acid-terminated polyimide was mixed with a good solvent to obtain a recyclable 3D printing PI ink.

[0063] The present invention has no special requirements for the mixing method, and any mixing method well known to those skilled in the art may be used, such as stirring and mixing.

[0064] After obtaining the recyclable 3D printing PI ink, the present invention preferably performs a defoaming treatment. In the present invention, the defoaming treatment is preferably ultrasound or high-speed centrifugation. In the present invention, the power of the ultrasound is preferably 80 to 200 W, and the time is preferably 12 to 24 hours; the speed of the high-speed centrifugation is preferably 5000 to 20000 r / min, and the time is preferably 15 to 50 minutes.

[0065] In the present invention, the recyclable 3D printing PI ink is preferably stored in a refrigerator for use.

[0066] The present invention provides a printing method for the above-mentioned recyclable 3D printing PI ink, comprising the following steps:

[0067] Performing 3D printing on the recyclable 3D printing PI ink to obtain a 3D printing part precursor;

[0068] The 3D printed part precursor is subjected to a gradient temperature rise thermal curing treatment to obtain a 3D printed PI molded part.

[0069] The present invention performs 3D printing on recyclable 3D printing PI ink to obtain a 3D printed part precursor. In the present invention, the printer used for the 3D printing is preferably a DIW extrusion printer. The present invention loads the recyclable 3D printing PI ink into the low-temperature barrel of the printer, sets the printing parameters, and the ink is extruded through the pneumatic nozzle of the printer and accumulated layer by layer to obtain a 3D printed part precursor. In the present invention, the printing parameters of the 3D printing preferably include: a printing speed of 0.01 to 0.11 mm / s, more preferably 0.05 to 0.08 mm / s; the printing layer height is preferably 0.1 to 1.2 mm, more preferably 0.4 to 0.8 mm.

[0070] After obtaining the 3D printed part precursor, the present invention performs a gradient temperature rise thermal curing treatment on the 3D printed part precursor to obtain a 3D printed PI molded part. In the present invention, the temperature rise procedure of the gradient temperature rise thermal curing treatment includes:

[0071] Raising the temperature to a first temperature, and keeping the temperature at the first temperature for 12 to 36 hours, wherein the first temperature is 60 to 100° C.;

[0072] Raising the temperature from the first temperature to the second temperature, and keeping the temperature at the second temperature for 1 to 24 hours, wherein the second temperature is 150 to 200° C.;

[0073] The temperature is raised from the second temperature to the third temperature, and kept at the third temperature for 0.1 to 6 hours, wherein the third temperature is 240°C.

[0074] The present invention preferably heats up from room temperature to the first temperature. In the present invention, the heating rate of heating up to the first temperature is preferably 5 to 10°C / min. As a specific embodiment of the present invention, the first temperature can be 60, 80 or 100°C, and the holding time can be 12h, 18h, 24h or 36h.

[0075] The present invention heats the temperature from the first temperature to the second temperature. In the present invention, the heating rate to the second temperature is preferably 2 to 8°C / min. As a specific embodiment of the present invention, the second temperature can be 150°C, 160°C, 180°C or 200°C, and the holding time can be 1h, 5h, 10h, 15h, 20h or 24h.

[0076] The present invention heats the temperature from the second temperature to the third temperature. In the present invention, the heating rate to the third temperature is preferably 2 to 5°C / min. As a specific embodiment of the present invention, the holding time after heating to the third temperature can be 0.1h, 0.2h, 0.5h, 1h, 3h or 6h.

[0077] As a specific embodiment of the present invention, the temperature rise program of the gradient temperature rise thermal curing process is:

[0078] First, heat to 80°C and keep at 80°C for 24h;

[0079] Raise the temperature from 80°C to 160°C and keep at 160°C for 1 hour;

[0080] Raise the temperature from 160°C to 240°C and keep at 240°C for 0.2h.

[0081] In the present invention, the purpose of the gradient temperature heat curing treatment is to remove the solvent and cause the trimerization ring reaction of phenylboronic acid. During the high-temperature treatment process, the solvent is continuously removed, and the phenylboronic acid at the end of the low molecular weight PI chain is trimerized under heating to form a dynamic boron oxygen six-membered ring, resulting in the formation of the final cross-linked PI structure.

[0082] The present invention provides a method for recycling the above-mentioned recyclable 3D printing PI ink, comprising the following steps:

[0083] The 3D printed PI molded part prepared by the recyclable 3D printing PI ink is placed in a mixed solvent and subjected to ultrasonic treatment to obtain the regenerated 3D printing PI ink.

[0084] In the present invention, the mixed solvent is a mixture of an organic solvent and an alcohol, or a mixture of an organic solvent and water. In the present invention, the organic solvent is preferably one or more of N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide, and the alcohol is preferably ethanol and / or methanol. In the present invention, when the mixed solvent is a mixture of an organic solvent and an alcohol, the volume ratio of the organic solvent to the alcohol is preferably 5 to 15:1, and may be 5:1, 8:1, 10:1, 12:1 or 15:1. In the present invention, when the mixed solvent is a mixture of an organic solvent and water, the volume ratio of the organic solvent to water is preferably 8 to 16:1, and may be 8:1, 10:1, 12:1, 14:1 or 16:1. As a specific embodiment of the present invention, the mixed solvent is a mixture of N-methylpyrrolidone and ethanol, and the volume ratio of N-methylpyrrolidone to ethanol is preferably 5 to 15:1, more preferably 9:1.

[0085] In the present invention, the mass ratio of the 3D printed PI molded part to the mixed solvent is preferably 0.5 to 1:1, more preferably 0.6 to 0.8:1.

[0086] In the present invention, the power of the ultrasonic treatment is preferably 80 to 200 W, more preferably 100 to 150 W, and the time is preferably 12 to 24 h, more preferably 16 to 20 h. In the present invention, the boron-oxygen bond (BO) in the boron-oxygen six-membered ring is dynamic and can undergo reversible fracture and recombination in the above-mentioned mixed solvent, so that the 3D printed PI molded part can be completely restored to the original ink state for reprinting in other shapes.

[0087] The present invention firstly designs and synthesizes a low molecular weight polyimide PI terminated with phenylboronic acid, and utilizes the trimerization ring-forming mechanism of phenylboronic acid at high temperature and the dynamic reversibility of the boron-oxygen bond (BO) to prepare a completely recyclable 3D printing PI ink for the first time; the ink exhibits rheological characteristics of rapid response and instantaneous recovery, realizing the personalized manufacturing of high-resolution and high-performance PI components, and the personalized PI components can be restored to the original ink state for reprinting of other shapes.

[0088] The following is a detailed description of a phenylboronic acid-terminated polyimide, a preparation method and application thereof, and a recyclable 3D printing PI ink provided by the present invention in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0089] Example 1

[0090] 1) Preparation of low molecular weight PI (n=6) terminated with phenylboronic acid: 8.3 g BPADA was dissolved in 50 g DMAc in a three-necked flask equipped with a nitrogen inlet and mechanical stirring, followed by slow addition of 2.8 g ODA and stirring for 1 hour. Then, 0.6 g BN was added as a capping agent under ice-water bath conditions and continued to stir for 12 hours to obtain a polycondensation reaction solution. The ice-water bath was removed, and 16 g acetic anhydride and 10 g pyridine were added to the polycondensation reaction solution, and stirred at room temperature overnight. After the reaction was completed, the reaction solution was diluted with tetrahydrofuran solution, and then slowly poured into distilled water to precipitate a yellow solid, which was vacuum dried to obtain a low molecular weight PI (n=6) powder terminated with phenylboronic acid.

[0091] 2) Preparation of recyclable 3D printing PI ink: The prepared phenylboronic acid-terminated low molecular weight PI (n=6) powder was dissolved in NMP, and after ultrasonic treatment, a uniform solution with a solid content of 50% was obtained, which was the recyclable 3D printing PI ink.

[0092] 3) Printing of 3D printed PI molded parts: The above ink is centrifuged at high speed to remove bubbles, and placed in the low-temperature barrel of the DIW printer. The printing parameters are set to a printing speed of 0.04 mm / s and a printing layer height of 0.6 mm. The ink is extruded through the pneumatic nozzle of the printer and accumulated layer by layer to obtain a 3D printed part precursor. Finally, the 3D printed part precursor is placed in an oven for gradient heating to remove the solvent and to cause a trimerization reaction of phenylboronic acid to obtain a 3D printed PI molded part. The gradient heating program is set to 80℃ / 24h, 160℃ / 5h and 240℃ / 0.2h.

[0093] 4) Recycling and reprinting of 3D printed PI molded parts: The dynamic reversibility of the hexacyclic boron oxide allows 3D printed PI molded parts to be recycled into the original ink state for reprinting in other shapes. Specifically, the 3D printed PI molded parts are placed in a mixed solvent of NMP / ethanol, where the volume ratio of NMP to ethanol is 9:1, and then ultrasonically treated at 150W for 15 hours to recover the 3D printed PI ink. The recycled ink still has excellent printability and can be remanufactured in various other shapes.

[0094] Performance Testing

[0095] NMR test: The NMR spectrum of the phenylboronic acid-terminated low molecular weight PI obtained in Example 1 is as follows: Figure 1 shown; from Figure 1 It can be seen that 1H NMR (CDCl3, 400 MHz, δ (ppm)): δ = 1.76 ppm represents the hydrogen atom in the methyl group (-CH3), δ = 6.9-7.5 ppm and δ = 7.8-8.0 ppm represent the proton hydrogen on the benzene ring, and δ = 7.57-7.68 ppm represents the proton hydrogen of -OH in phenylboronic acid. The above results indicate the successful synthesis of low molecular weight PI terminated with phenylboronic acid.

[0096] Infrared test: The infrared spectra of the 3D printed PI molded part of Example 1 before and after heat treatment are as follows: Figure 2 As shown. Figure 2 It can be seen that after the gradient heating treatment, the -1 The vibration signal of -OH of phenylboronic acid disappears, while the vibration peak of the dynamic borane oxygen six-membered ring (B3O3) is at 691cm -1 Appears everywhere.

[0097] Mechanical and thermal properties test: The mechanical and thermal properties of the 3D printed PI molded part of Example 1 after heat treatment are as follows: Figure 3 As shown in the figure, it can be seen that the tensile strength of the 3D printed PI molded part obtained by capping the low molecular weight PI with phenylboronic acid of n=6 is 50.54MPa, the Young's modulus is 2.73GPa, and the T g is 208℃ and T d It is 521℃.

[0098] Recycling performance test: The mechanical properties of the recycled 3D printed PI molded parts are tested, such as Figure 4 It can be seen that even after ten recycling cycles, the mechanical properties of the 3D printed PI molded parts remain unchanged, which shows that the product provided by the present invention has excellent recycling stability, and the solvent recovery method provided by the present invention will not damage the original performance of the high-performance PI.

[0099] The actual picture of the 3D printed PI molded part of Example 1 and the actual picture of the recycled and reprinted molded part are as follows: Figure 5 As shown, Figure 5 The left picture shows the initial 3D printed PI molded part, and the right picture shows the molded part printed after recycling. The initial 3D printed PI molded part shows a complex and exquisite high-resolution PI geometry, and the molded part printed after recycling also has a complex and exquisite structure, which shows that the recyclable 3D printing PI ink provided by the present invention has excellent printability, and even after recycling, it maintains the original rheological characteristics and can print high-resolution PI shapes.

[0100] Example 2

[0101] 1) Preparation of low molecular weight PI (n=9) terminated with phenylboronic acid: 9.5 g BPADA was dissolved in 55 g DMAc in a three-necked flask equipped with a nitrogen inlet and mechanical stirring, followed by slow addition of 3.3 g ODA and stirring for 1 hour. Then, 0.5 g BN was added as a capping agent under ice-water bath conditions and continued stirring for 12 hours, at which time a polycondensation reaction liquid was obtained. The ice-water bath was removed, and 19 g acetic anhydride and 11 g pyridine were added to the polycondensation reaction liquid, and stirred at room temperature overnight. After the reaction was completed, the reaction solution was diluted with tetrahydrofuran solution, and then slowly poured into distilled water to precipitate a yellow solid, which was vacuum dried to obtain a low molecular weight PI (n=9) powder terminated with phenylboronic acid.

[0102] 2) Preparation of recyclable 3D printing PI ink: The prepared phenylboronic acid-terminated low molecular weight PI (n=9) powder was dissolved in NMP, and after ultrasonic treatment, a uniform solution with a solid content of 51% was obtained, which was the recyclable 3D printing PI ink.

[0103] 3) Printing of 3D printed PI molded parts: The above ink is centrifuged at high speed to remove bubbles, and placed in the low-temperature barrel of the DIW printer. The printing parameters are set to a printing speed of 0.03mm / s and a printing layer height of 0.6mm. The ink is extruded through the pneumatic nozzle of the printer and accumulated layer by layer to obtain a 3D printed part precursor. Finally, the 3D printed part precursor is placed in an oven for gradient heating to remove the solvent and to cause a trimerization reaction of phenylboronic acid to obtain a 3D printed PI molded part. The gradient heating program is set to 80℃ / 24h, 160℃ / 5h and 240℃ / 0.2h.

[0104] like Figure 3 As shown in Figure 2, the tensile strength of the 3D printed PI molded part obtained by capping the low molecular weight PI with phenylboronic acid of n=9 is 70.95 MPa, the Young's modulus is 2.58 GPa, and the T g is 218℃ and T d It is 538℃.

[0105] 4) Recycling and reprinting of 3D printed PI molded parts: The dynamic reversibility of the hexacyclic borane enables 3D printed PI molded parts to be recycled into the original ink state for reprinting in other shapes. Specifically, the 3D printed PI molded parts are placed in a mixed solvent of NMP / ethanol, wherein the volume ratio of NMP to ethanol is 10:1, and then ultrasonically treated at 20W for 20 hours to recover the 3D printed PI ink. The recycled ink still has excellent printability and can be remanufactured in various other shapes. In addition, this solvent recovery method will not damage the mechanical properties of the 3D printed PI molded parts. Even after ten recycling processes, the 3D printed PI molded parts still maintain their original mechanical properties.

[0106] Example 3

[0107] 1) Preparation of low molecular weight PI (n=13) terminated with phenylboronic acid: 9.8 g BPADA was dissolved in 55 g DMAc in a three-necked flask equipped with a nitrogen inlet and mechanical stirring, followed by slow addition of 3.5 g ODA and stirring for 1 hour. Then, 0.4 g BN was added as a capping agent under ice-water bath conditions and continued stirring for 12 hours, at which time a polycondensation reaction liquid was obtained. The ice-water bath was removed, and 19 g acetic anhydride and 12 g pyridine were added to the polycondensation reaction liquid, and stirred at room temperature overnight. After the reaction was completed, the reaction solution was diluted with tetrahydrofuran solution, and then slowly poured into distilled water to precipitate a yellow solid, which was vacuum dried to obtain a low molecular weight PI (n=13) powder terminated with phenylboronic acid.

[0108] 2) Preparation of recyclable 3D printing PI ink: The prepared phenylboronic acid-terminated low molecular weight PI (n=13) powder was dissolved in NMP, and after ultrasonic treatment, a uniform solution with a solid content of 52% was obtained, which was the recyclable 3D printing PI ink.

[0109] 3) Printing of 3D printed PI molded parts: The above ink is centrifuged at high speed to remove bubbles, and placed in the low-temperature barrel of the DIW printer. The printing parameters are set to a printing speed of 0.02 mm / s and a printing layer height of 0.5 mm. The ink is extruded through the pneumatic nozzle of the printer and accumulated layer by layer to obtain a 3D printed part precursor. Finally, the 3D printed part precursor is placed in an oven for gradient heating to remove the solvent and to cause a trimerization reaction of phenylboronic acid to obtain a 3D printed PI molded part. The gradient heating program is set to 80℃ / 24h, 160℃ / 5h and 240℃ / 0.2h.

[0110] like Figure 3 As shown, the 3D printed PI molded part obtained by end-capping low molecular weight PI with phenylboronic acid having n=13 has a tensile strength of 105.01 MPa, a Young's modulus of 2.44 GPa, a Tg of 223°C and a Td of 539°C.

[0111] 4) Recycling and reprinting of 3D printed PI molded parts: The dynamic reversibility of the hexacyclic borane enables PI molded parts to be recycled into the original ink state for reprinting in other shapes. Specifically, the 3D printed PI molded parts are placed in a mixed solvent of NMP / ethanol, where the volume ratio of NMP to ethanol is 10:1, and then ultrasonically treated at 150W for 24 hours to recover the 3D printed PI ink. The recycled ink still has excellent printability and can be remanufactured in various other shapes. In addition, this solvent recovery method will not damage the mechanical properties of the 3D printed PI molded parts. Even after ten recycling processes, the 3D printed PI molded parts still maintain their original mechanical properties.

[0112] Example 4

[0113] 1) Preparation of low molecular weight PI (n=20) terminated with phenylboronic acid: 11.5 g BPADA was dissolved in 65 g DMAc in a three-necked flask equipped with a nitrogen inlet and mechanical stirring, followed by slow addition of 4.2 g ODA and stirring for 1 hour. Then, 0.3 g BN was added as a capping agent under ice-water bath conditions and continued stirring for 12 hours to obtain a polycondensation reaction solution. The ice-water bath was removed, and 22 g acetic anhydride and 14 g pyridine were added to the polycondensation reaction solution, and stirred at room temperature overnight. After the reaction was completed, the reaction solution was diluted with tetrahydrofuran solution, and then slowly poured into distilled water to precipitate a yellow solid, which was vacuum dried to obtain a low molecular weight PI (n=20) powder terminated with phenylboronic acid.

[0114] 2) Preparation of recyclable 3D printing PI ink: The prepared phenylboronic acid-terminated low molecular weight PI (n=20) powder was dissolved in NMP, and after ultrasonic treatment, a uniform solution with a solid content of 49% was obtained, which was the recyclable 3D printing PI ink.

[0115] 3) Printing of 3D printed PI molded parts: The above ink is centrifuged at high speed to remove bubbles, and placed in the low-temperature barrel of the DIW printer. The printing parameters are set to a printing speed of 0.01mm / s and a printing layer height of 0.4mm. The ink is extruded through the pneumatic nozzle of the printer and accumulated layer by layer to obtain a 3D printed part precursor. Finally, the 3D printed part precursor is placed in an oven for gradient heating to remove the solvent and to cause a trimerization reaction of phenylboronic acid to obtain a 3D printed PI molded part. The gradient heating program is set to 80℃ / 24h, 160℃ / 5h and 240℃ / 0.2h.

[0116] like Figure 3 As shown in Figure 2, the tensile strength of the 3D printed PI molded part obtained by capping the low molecular weight PI with phenylboronic acid of n=20 is 98.31 MPa, the Young's modulus is 2.09 GPa, and the T g is 221℃ and T d It is 538℃.

[0117] 4) Recycling and reprinting of 3D printed PI molded parts: The dynamic reversibility of the hexacyclic borane enables PI molded parts to be recycled to the original ink state for reprinting in other shapes. Specifically, the 3D printed PI molded parts are placed in a mixed solvent of NMP / ethanol, where the volume ratio of NMP to ethanol is 12, and then ultrasonically treated for 24 hours to recover the 3D printed PI ink. The recycled ink still has excellent printability and can be remanufactured in various other shapes. In addition, this solvent recovery method will not damage the mechanical properties of the 3D printed PI molded parts. Even after ten recycling processes, the 3D printed PI molded parts still maintain their original mechanical properties.

[0118] As can be seen from the above examples, the present invention designs and synthesizes a low molecular weight PI functionalized with phenylboronic acid, uses this as a basic building block, and uses the thermally induced trimerization mechanism of phenylboronic acid to the borane hexacyclic ring and the solvent reversibility of the dynamic borane hexacyclic ring to prepare a completely recyclable 3D printing PI ink. The ink is printed by a DIW extrusion printer, which not only realizes the customized manufacturing of high-resolution, high-performance PI geometries, but also realizes the recycling and reprinting of customized PI geometries to manufacture other complex and delicate PI geometries. The present invention realizes the recycling of 3D printing PI ink for the first time, and retains the original performance of high-performance PI.

[0119] 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 principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A phenylboronic acid terminated polyimide, characterized in that: It has the structure shown in formula I: In formula I, n=1-30.

2. The method for preparing the phenylboronic acid-terminated polyimide according to claim 1, characterized in that: The following steps are involved: Mixing bisphenol A dianhydride, 4,4'-diaminodiphenyl ether and an organic solvent, adding aminophenylboronic acid in an ice-water bath to carry out a polycondensation reaction to obtain a polycondensation reaction liquid; The polycondensation reaction liquid is mixed with pyridine and acetic anhydride to carry out an imidization reaction to obtain a phenylboronic acid-terminated polyimide having a structure shown in Formula I.

3. The preparation method according to claim 2, characterized in that: The mass ratio of bisphenol A dianhydride to 4,4'-diaminodiphenyl ether is 5-15:2-5; The mass ratio of the bisphenol A dianhydride to aminophenylboric acid is 5-15:0.1-1.

4. The preparation method according to claim 2, characterized in that: The mass ratio of bisphenol A dianhydride to pyridine is 5-15:5-15; The mass ratio of the bisphenol A dianhydride to acetic anhydride is 5-15:15-25.

5. The preparation method according to claim 2 or 4, characterized in that: The polycondensation reaction temperature is 0 to 25°C and the time is 12 to 24 hours; The temperature of the imidization reaction is 0 to 50° C., and the time is 10 to 24 hours.

6. Use of the phenylboronic acid-terminated polyimide according to claim 1 or the phenylboronic acid-terminated polyimide prepared by the preparation method according to any one of claims 2 to 5 in 3D printing ink.

7. A recyclable 3D printing PI ink, characterized in that: The invention comprises the phenylboronic acid-terminated polyimide according to claim 1 or the phenylboronic acid-terminated polyimide prepared by the preparation method according to any one of claims 2 to 5 and a good solvent.

8. The printing method of recyclable 3D printing PI ink according to claim 7, characterized in that: The following steps are involved: Performing 3D printing on the recyclable 3D printing PI ink to obtain a 3D printing part precursor; The 3D printed part precursor is subjected to a gradient temperature rise thermal curing treatment to obtain a 3D printed PI molded part.

9. The printing method according to claim 8, characterized in that: The temperature rise procedure of the gradient temperature rise thermal curing process includes: Raising the temperature to a first temperature, and keeping the temperature at the first temperature for 12 to 36 hours, wherein the first temperature is 60 to 100° C.; Raising the temperature from the first temperature to the second temperature, and keeping the temperature at the second temperature for 1 to 24 hours, wherein the second temperature is 150 to 200° C.; The temperature is raised from the second temperature to the third temperature, and kept at the third temperature for 0.1 to 6 hours, wherein the third temperature is 240°C.

10. The method for recycling recyclable 3D printing PI ink according to claim 7, characterized in that: The following steps are involved: The 3D printed PI molded part prepared by the recyclable 3D printing PI ink is placed in a mixed solvent and subjected to ultrasonic treatment to obtain a regenerated 3D printing PI ink; The mixed solvent is a mixture of an organic solvent and alcohol, or a mixture of an organic solvent and water.

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