CN115260056A - Cross-linking agent and preparation method thereof, polyimide 3D printing ink and preparation method of recyclable thermosetting polyimide product - Google Patents

Cross-linking agent and preparation method thereof, polyimide 3D printing ink and preparation method of recyclable thermosetting polyimide product Download PDF

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CN115260056A
CN115260056A CN202210947440.2A CN202210947440A CN115260056A CN 115260056 A CN115260056 A CN 115260056A CN 202210947440 A CN202210947440 A CN 202210947440A CN 115260056 A CN115260056 A CN 115260056A
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王齐华
张晶
陶立明
王廷梅
张耀明
徐明坤
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Lanzhou Institute of Chemical Physics LICP of CAS
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Abstract

The invention provides a cross-linking agent and a preparation method thereof, polyimide 3D printing ink and a preparation method of a recyclable thermosetting polyimide product, and relates to the technical field of thermosetting polyimide preparation. The crosslinking agent containing dynamic covalent bonds is prepared, the crosslinking agent and amino-terminated polyimide are mixed to obtain the ink, the crosslinking of linear polyimide under 365nm light is realized without the existence of a photoinitiator, the ink has rheological property suitable for 3D printing, and the printing of three-dimensional latticed polyimide is realized. Due to the fact that the dynamic covalent bond-imine bond is introduced into the cross-linked network of the 3D printed thermosetting polyimide, the 3D printed thermosetting polyimide can be recycled, remolded and reprocessed for the first time by means of the bond breaking property of the imine bond under the acidic condition.

Description

Cross-linking agent and preparation method thereof, polyimide 3D printing ink and preparation method of recyclable thermosetting polyimide product
Technical Field
The invention relates to the technical field of thermosetting polyimide preparation, in particular to a cross-linking agent and a preparation method thereof, and a preparation method of polyimide 3D printing ink and a recyclable thermosetting polyimide product.
Background
Polyimide (PI) is a high-performance special engineering plastic, and a rigid benzene ring structure in a molecular chain of the Polyimide (PI) endows the Polyimide with high heat resistance and excellent mechanical properties, but the Polyimide (PI) also has the problems of poor solubility and high melting point, so that the 3D printing preparation of the Polyimide is limited. Current methods for making PI three-dimensional structures are hot pressing, injection molding, etc., and structures produced using such methods offer limited resolution and complexity and cannot be processed in specific on-demand shapes. Recently, emerging 3D printing technology provides an opportunity for preparing polyimide with a three-dimensional complex shape, and many researches and reports about a method for preparing polyimide ink. For example, researchers at home and abroad prepare thermosetting polyimide by using a 3D printing technology, and although the purpose of customizing the three-dimensional shape of the polyimide is achieved, the thermosetting polyimide cannot be recycled, remolded or reprocessed like thermoplastic polymer.
Disclosure of Invention
The invention aims to provide a cross-linking agent and a preparation method thereof, polyimide 3D printing ink and a preparation method of a recyclable thermosetting polyimide product, and the thermosetting polyimide prepared by the 3D printing technology can be recycled, remolded and reprocessed.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a crosslinking agent containing dynamic covalent bonds, which has a structure shown in a formula 1:
Figure BDA0003787870070000021
the invention provides a preparation method of the crosslinking agent containing the dynamic covalent bond, which comprises the following steps:
mixing vanillin, methyl 4-bromobutyrate, N-dimethylformamide and potassium carbonate, and carrying out etherification reaction to obtain a compound with a structure shown in a formula 2;
mixing the compound with the structure shown in the formula 2 with a nitric acid solution, and carrying out nitration reaction to obtain a compound with the structure shown in the formula 3;
mixing the compound with the structure shown in the formula 3, sodium borohydride and an ethanol-tetrahydrofuran mixed solvent, and carrying out reduction reaction to obtain a compound with the structure shown in the formula 4;
mixing the compound with the structure shown in the formula 4, ethylenediamine and methanol, and carrying out substitution reaction to obtain a compound with the structure shown in the formula 5;
mixing the compound with the structure shown in the formula 5, N-methyl pyrrolidone and mesitylene, and carrying out Schiff base reaction to obtain a solution containing a cross-linking agent with the structure shown in the formula 1;
Figure BDA0003787870070000022
preferably, the mass ratio of the vanillin to the methyl 4-bromobutyrate is (8-9): (9-10), wherein the mass ratio of the vanillin to the potassium carbonate is (8-9): (10 to 11).
Preferably, the temperature of the etherification reaction is 25 ℃ and the time is 10 to 24 hours.
Preferably, the mass concentration of the nitric acid solution is 50-80%; the dosage ratio of the compound with the structure shown in the formula 2 to the nitric acid solution is (90-100) g: (1000-1500) mL; the temperature of the nitration reaction is-10 to 10 ℃ and the time is 1 to 3 hours.
Preferably, the mass ratio of the compound having the structure shown in formula 3 to sodium borohydride is (7-9): (1-3); the temperature of the reduction reaction is 0 ℃ and the time is 1-3 hours.
The invention provides polyimide 3D printing ink which comprises a cross-linking agent, amino-terminated polyimide and N-methylpyrrolidone; the cross-linking agent is the cross-linking agent containing the dynamic covalent bond described in the above scheme or the cross-linking agent containing the dynamic covalent bond prepared by the preparation method described in the above scheme.
The invention provides a preparation method of a recyclable thermosetting polyimide product, which comprises the following steps: 3D printing is carried out by using the polyimide 3D printing ink in the scheme, and in-situ ultraviolet light curing is carried out while printing to obtain a prefabricated member; and performing heat curing treatment on the prefabricated member to obtain the recyclable thermosetting polyimide product.
Preferably, the wavelength adopted by the in-situ ultraviolet curing is 365nm; the time of in-situ ultraviolet curing is more than 1 min.
Preferably, the heat curing treatment comprises a first heat curing treatment and a second heat curing treatment which are sequentially carried out, wherein the temperature of the first heat curing treatment is 80 ℃, and the time is 12h; the temperature of the second heat curing treatment is 150 ℃, and the time is 1h.
The invention provides a crosslinking agent containing dynamic covalent bonds, which has a structure shown in a formula 1:
Figure BDA0003787870070000031
the cross-linking agent provided by the invention contains dynamic covalent bond-imine bond (-N =), which can be broken under an acidic condition and rearrange cross-linked network topology under a high-temperature condition, so that the cross-linked polymer has functions of remodeling, reprocessing and recycling, and the integrity of cross-linked networks such as thermosetting resin is maintained.
According to the invention, a cross-linking agent and amino-terminated polyimide form 3D printing ink, and then the 3D printing ink is used for 3D printing of thermosetting polyimide products, the cross-linking agent of the invention contains imine bonds, the cross-linking agent is subjected to photoproduction aldehyde group reaction under ultraviolet irradiation, and then the generated aldehyde group and amino-terminated polyimide complete cross-linking reaction, so that a large number of dynamic covalent bond-imine bonds are introduced into the 3D printing thermosetting polyimide products, the imine bonds can be broken under an acidic condition, and cross-linking network topology can be rearranged under a high-temperature condition, so that the 3D printing thermosetting polyimide products have the functions of recovery, remodeling and reprocessing.
Drawings
FIG. 1 is a nuclear magnetic representation of a compound having the structure shown in formula 4;
FIG. 2 is a nuclear magnetic representation of a compound having the structure shown in formula 5;
FIG. 3 is a graph of the infrared characterization of a compound having the structure shown in formula 4 before and after illumination;
FIG. 4 is an IR spectrum of an amino terminated polyimide prepared in example 1;
FIG. 5 is a pictorial representation of a thermoset polyimide article prepared in example 1.
Detailed Description
The invention provides a crosslinking agent containing dynamic covalent bonds, which has a structure shown in a formula 1:
Figure BDA0003787870070000041
the cross-linking agent provided by the invention contains dynamic covalent bond-imine bond (-N =), which can be broken under an acidic condition and rearrange cross-linked network topology under a high-temperature condition, so that the cross-linked polymer has functions of remodeling, reprocessing and recycling, and meanwhile, the integrity of cross-linked networks such as thermosetting resin and the like is maintained.
The invention provides a preparation method of the crosslinking agent containing the dynamic covalent bond, which comprises the following steps:
mixing vanillin, methyl 4-bromobutyrate, N-dimethylformamide and potassium carbonate, and carrying out etherification reaction to obtain a compound with a structure shown in a formula 2;
mixing the compound with the structure shown in the formula 2 with a nitric acid solution, and carrying out nitration reaction to obtain a compound with the structure shown in the formula 3;
mixing the compound with the structure shown in the formula 3, sodium borohydride and an ethanol-tetrahydrofuran mixed solvent, and carrying out reduction reaction to obtain a compound with the structure shown in the formula 4;
mixing the compound with the structure shown in the formula 4, ethylenediamine and methanol, and carrying out substitution reaction to obtain a compound with the structure shown in the formula 5;
mixing the compound with the structure shown in the formula 5, N-methyl pyrrolidone and mesitylene, and carrying out Schiff base reaction to obtain a solution containing a cross-linking agent with the structure shown in the formula 1;
Figure BDA0003787870070000051
in the present invention, the starting materials used are all commercially available products well known in the art, unless otherwise specified.
The method comprises the steps of mixing vanillin, methyl 4-bromobutyrate, N-dimethylformamide and potassium carbonate, and carrying out etherification reaction to obtain a compound with a structure shown in a formula 2.
In the present invention, the mass ratio of vanillin to methyl 4-bromobutyrate is preferably (8 to 9): (9-10); the mass ratio of the vanillin to the potassium carbonate is preferably (8-9): (10-11); the dosage ratio of the vanillin to the N, N-dimethylformamide is preferably (80-90) g: (400-500) mL. In the invention, the N, N-dimethylformamide is used as a solvent, and the potassium carbonate is used as a catalyst.
The invention has no special requirement on the mixing, and can completely dissolve the vanillin, the methyl 4-bromobutyrate and the potassium carbonate into the N, N-dimethylformamide.
In the present invention, the temperature of the etherification reaction is preferably 25 ℃, and the time of the etherification reaction is preferably 10 to 24 hours, more preferably 15 to 20 hours, and still more preferably 16 hours.
After the etherification reaction is completed, the reaction product obtained is preferably filtered, the liquid obtained by filtering is poured into ice water for precipitation, the obtained precipitate is dissolved into dichloromethane, magnesium sulfate is used for drying and water removal, and finally the solvent is removed by rotary evaporation to obtain the compound with the structure shown in formula 2. In the present invention, the precipitation time is preferably 10 to 20 minutes, and the temperature of the rotary evaporation is preferably 40 ℃.
After the compound with the structure shown in the formula 2 is obtained, the compound with the structure shown in the formula 2 is mixed with a nitric acid solution, and a nitration reaction is carried out to obtain the compound with the structure shown in the formula 3.
In the present invention, the mass concentration of the nitric acid solution is preferably 50 to 80%, more preferably 60 to 70%; the use amount ratio of the compound having the structure represented by formula 2 to the nitric acid solution is preferably (90 to 100) g: (1000-1500) mL; the temperature of the nitration reaction is preferably-10 ℃, and more preferably-5 ℃; the time is preferably 1 to 3 hours, more preferably 1.5 to 2.5 hours. In the present invention, the nitration reaction is preferably carried out in an ice-water bath with stirring.
After the nitration reaction is finished, the reaction solution is preferably slowly added into ice water for precipitation for 10-20 minutes, the solution is dissolved in dichloromethane again after being filtered, the solution is dried by magnesium sulfate, and finally the solvent is removed by rotary evaporation to obtain the compound with the structure shown in the formula 3. In the present invention, the temperature of the rotary evaporation is preferably 60 ℃.
After the compound with the structure shown in the formula 3 is obtained, the compound with the structure shown in the formula 3, sodium borohydride and an ethanol-tetrahydrofuran mixed solvent are mixed for reduction reaction, and the compound with the structure shown in the formula 4 is obtained.
In the present invention, the mass ratio of the compound having the structure represented by formula 3 to sodium borohydride is preferably (7 to 9): (1 to 3), more preferably 8: (1-3). In the present invention, the volume ratio of ethanol to tetrahydrofuran in the mixed solvent is preferably 1; the use amount ratio of the compound having the structure represented by formula 3 to the mixed solvent is preferably (70 to 90) mg:1mL.
In the present invention, mixing the compound having the structure represented by formula 3, sodium borohydride, and ethanol-tetrahydrofuran mixed solvent preferably includes: dissolving a compound having a structure shown in formula 3 in an ethanol-tetrahydrofuran mixed solvent, and then adding sodium borohydride slowly at 0 ℃.
In the present invention, the temperature of the reduction reaction is preferably 0 ℃ and the time is preferably 1 to 3 hours.
After the reduction reaction is completed, the present invention preferably performs a first rotary evaporation on the obtained reaction solution to remove the solvent, dissolves the first crude product obtained by the rotary evaporation in a mixed solution of water and dichloromethane, dries the organic layer with magnesium sulfate, removes the solvent by a second rotary evaporation to obtain a second crude product, adds methanol and p-toluenesulfonic acid to the second crude product to perform stirring dissolution, removes the solvent by a third rotary evaporation, dissolves the residue in water and dichloromethane, dries the organic layer with magnesium sulfate, removes the solvent in the organic layer by a fourth rotary evaporation to obtain yellow powder, and purifies the yellow powder in a silica gel column to obtain the compound having the structure represented by formula 4.
In the present invention, the temperature of the first rotary evaporation, the second rotary evaporation, the third rotary evaporation and the fourth rotary evaporation is preferably 50 ℃. In the present invention, the silica gel column preferably has a diameter of 10cm, a height of 13cm when packed, and a height of 5cm when packed. In the present invention, the washing solution used for purification is preferably a mixed solution of petroleum ether and ethyl acetate, and the volume ratio of petroleum ether to ethyl acetate is preferably 2.
After the compound with the structure shown in the formula 4 is obtained, the compound with the structure shown in the formula 4, ethylenediamine and methanol are mixed for substitution reaction, and the compound with the structure shown in the formula 5 is obtained.
In the present invention, the ratio of the compound having the structure represented by formula 4 to ethylenediamine is preferably (0.3 to 1) g: (1-5) mL. The invention has no special requirement on the using amount of the methanol, and the compound with the structure shown in the formula 4 can be completely dissolved. In the present invention, the methanol serves as a solvent.
In the present invention, mixing the compound having the structure represented by formula 4, ethylenediamine, and methanol preferably includes: the compound having the structure represented by formula 4 was dissolved in ethylenediamine, and then methanol was added. In the present invention, the temperature of the substitution reaction is preferably 50 to 100 ℃, more preferably 70 to 90 ℃; the time is preferably 12 hours. In the present invention, the substitution reaction is preferably carried out under reflux conditions.
After the substitution reaction is finished, the obtained substitution reaction system is subjected to rotary evaporation to remove the solvent, then the solvent is dissolved in methanol, ethyl acetate is used for reprecipitation, and the filtered product is dried at 60 ℃ for 12 hours to obtain the compound with the structure shown in the formula 5.
After the compound with the structure shown in the formula 5 is obtained, the compound with the structure shown in the formula 5, N-methylpyrrolidone and mesitylene are mixed for Schiff base reaction, and a solution containing the cross-linking agent with the structure shown in the formula 1 is obtained.
In the present invention, the N-methylpyrrolidone is used as a solvent. In the present invention, the molar ratio of the compound having the structure represented by formula 5 to trimesic aldehyde is preferably (1 to 3): 1. in the present invention, the mass ratio of N-methylpyrrolidone to trimesic aldehyde is preferably (4 to 8): 1.
in the present invention, mixing the compound having the structure represented by formula 5, N-methylpyrrolidone, and trimesic aldehyde preferably includes: dissolving the compound with the structure shown in the formula 5 into N-methylpyrrolidone, slowly adding trimesic aldehyde, and stirring. Before the mixing, the present invention preferably purifies the N-methylpyrrolidone to remove moisture and impurities as much as possible.
In the present invention, the temperature of the schiff base reaction is preferably normal temperature, and the time of the schiff base reaction is preferably 6 to 10 hours, and more preferably 7 to 8 hours. The solution obtained after the Schiff base reaction is finished is directly used for preparing the polyimide 3D printing ink without post-treatment.
In the present invention, the preparation process of the cross-linking agent having the structure shown in formula 1 is as follows:
Figure BDA0003787870070000081
wherein a is etherification reaction, b is nitration reaction, c is reduction reaction, d is substitution reaction, and e is Schiff base reaction.
The invention provides polyimide 3D printing ink which comprises a cross-linking agent, amino-terminated polyimide and N-methylpyrrolidone; the cross-linking agent is the cross-linking agent containing the dynamic covalent bond described in the above scheme or the cross-linking agent containing the dynamic covalent bond prepared by the preparation method described in the above scheme.
In the present invention, the crosslinking agent is used in the form of a crosslinking agent solution, that is, a solution containing the crosslinking agent having the structure represented by formula 1. In the present invention, the mass ratio of the crosslinking agent solution to the amino-terminated polyimide is preferably 1: (5 to 50), more preferably 1: (10 to 40), more preferably 1: (20 to 30).
In the invention, the structural general formula of the amino-terminated polyimide is shown as formula 6:
Figure BDA0003787870070000091
note:the imide ring is omitted from the main chain of formula 6.
The amino-terminated polyimide has no special requirement on the source of the amino-terminated polyimide and can be prepared by adopting a preparation method well known in the field. In the present invention, the method for preparing the amino terminated polyimide preferably comprises the steps of:
dissolving a diamine monomer into N-methyl pyrrolidone, adding a dianhydride monomer after the diamine monomer is completely dissolved, and carrying out condensation reaction under the conditions of ice water bath and nitrogen to obtain a polyimide precursor;
and removing the ice water bath, adding toluene into the polyimide precursor, and performing dehydration reaction to obtain the amino-terminated polyimide.
In the present invention, the diamine monomer is preferably one or two of diaminodiphenyl ether (ODA), 2 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl (TFDB), and m-phenylenediamine (mPD); the dianhydride monomer is preferably one or two of hexafluoro dianhydride (6 FDA), pyromellitic dianhydride (PMDA), and bisphenol a type diether dianhydride (BPADA). In the present invention, the molar ratio of the diamine monomer to the dianhydride monomer is preferably (1 to 4): 1, more preferably (1 to 2): 1. the invention has no special requirements on the dosage of the N-methylpyrrolidone, and the diamine monomer and the dianhydride monomer can be completely dissolved. In the present invention, the time of the polycondensation reaction is preferably 12 to 24 hours.
In the present invention, the amount of toluene added is preferably 1/10 of the total volume of toluene and polyimide precursor. In the present invention, the dehydration reaction is preferably performed under reflux conditions, the reflux temperature is preferably 200 ℃, and the reflux time is preferably 2 to 8 hours, and more preferably 5 hours. In the present invention, the toluene functions to form an azeotrope with the generated water and promote the reaction in the dehydration direction, i.e., the direction in which the polyimide on the amino end is generated.
After the dehydration reaction is finished, the obtained reaction solution is slowly dripped into a mixed solvent of ethanol and water for precipitation, the solid obtained after filtration is dried in a vacuum oven, and the dried solid is ground into powder to obtain the amino-terminated polyimide. The volume ratio of the ethanol to the water in the mixed solvent of the ethanol and the water is not particularly required. In the present invention, the drying preferably comprises drying at 80 ℃ for 12 hours and drying at 100 ℃ for 2 hours in this order.
In the present invention, the mass ratio of the crosslinking agent to the amino terminated polyimide is preferably 1: (5 to 50), more preferably 1: (10 to 45), more preferably 1: (20 to 35). In the present invention, the crosslinking agent is preferably used in the form of an N-methylpyrrolidone solution.
The preparation method has no special requirements on the preparation process of the polyimide 3D printing ink, and can be realized by directly mixing the components into a uniform solution and then removing bubbles. The invention has no special requirement on the bubble removing process, and the bubble removing mode known in the field can be adopted, such as vacuum degassing and ultrasound. The 3D printing ink of polyimide provided by the invention has rheological property suitable for 3D printing and good printability.
The invention provides a preparation method of a recyclable thermosetting polyimide product, which comprises the following steps: 3D printing is carried out by using the polyimide 3D printing ink in the scheme, and in-situ ultraviolet light curing is carried out while printing, so that a prefabricated member is obtained; and performing heat curing treatment on the prefabricated member to obtain the recyclable thermosetting polyimide product.
The invention has no special requirement on the equipment adopted by the 3D printing, and in the embodiment of the invention, a DIW printer is specifically adopted. In the invention, the wavelength adopted by the in-situ ultraviolet curing is preferably 365nm; the time of the in-situ ultraviolet curing is preferably more than 1min, and more preferably 1-3 min. In the in-situ ultraviolet curing process, the cross-linking agent generates aldehyde group reaction under the ultraviolet illumination condition, and then the generated aldehyde group and amino group generate Schiff base reaction to generate thermosetting polyimide, so that a cross-linking network is generated in the extruded ink, and a prefabricated member with certain self-supporting property is formed.
After the prefabricated member is obtained, the prefabricated member is subjected to thermosetting treatment to obtain the recyclable thermosetting polyimide product. In the present invention, the heat curing treatment preferably includes sequentially performing a first heat curing treatment and a second heat curing treatment, wherein the temperature of the first heat curing treatment is preferably 80 ℃, and the time is preferably 12h; the temperature of the second heat curing treatment is preferably 150 ℃ and the time is preferably 1h. According to the invention, the first thermosetting treatment is utilized to remove the solvent and promote the complete reaction of amino and aldehyde groups, so that a denser macromolecular network structure is generated, and the mechanical property and the thermal property of the thermosetting polyimide are improved; the second stage completes further crosslinking. In the present invention, the heat curing treatment is preferably performed in a dry box.
According to the polyimide ink prepared by synthesis, under the condition that any photoinitiator is completely not needed, the aldehyde group generated by the cross-linking agent prepared by the method under ultraviolet light reacts with Schiff base of amino in polyimide to establish a macromolecular cross-linked network structure, and simultaneously contains dynamic covalent bond-imine bond, so that 3D printing of a recyclable thermosetting polyimide product is realized for the first time.
In the present invention, the reaction equation of the crosslinking agent and amino-terminated polyimide is as follows:
Figure BDA0003787870070000111
the cross-linking agent of the invention has imine bonds (site 2) in addition, the cross-linking agent generates photoproduction aldehyde group reaction under the ultraviolet irradiation, then the generated aldehyde group and the polyimide with the end capping of amino group complete the cross-linking reaction, and further generates imine bonds (site 1), thereby introducing a large amount of dynamic covalent bond-imine bonds into the 3D printing thermosetting polyimide product, the imine bonds can be broken under the acid condition, the cross-linking network topology can be rearranged under the high temperature condition, and the 3D printing thermosetting polyimide product has the functions of recycling, reshaping and reprocessing.
The following examples are provided to illustrate the crosslinking agent and the preparation method thereof, the polyimide 3D printing ink, and the preparation method of the recyclable thermosetting polyimide product, but they should not be construed as limiting the scope of the present invention.
Example 1
(1) Preparation of a crosslinking agent containing dynamic covalent bonds: dissolving 89g of vanillin, 100g of methyl 4-bromobutyrate and 100g of potassium carbonate in DMF (N, N-dimethylformamide) and stirring for 16 hours to carry out etherification reaction, filtering the obtained reaction solution, pouring the obtained reaction solution into an ice-water bath for precipitation, dissolving the obtained precipitate in dichloromethane, drying with magnesium sulfate, and finally removing the solvent by rotary evaporation to obtain the compound with the structure shown in the formula 2; mixing 90g of the compound with the structure shown in the formula 2 with 1300mL of nitric acid solution (the mass concentration is 65-68%), stirring for 3 hours in ice water bath for nitration reaction, slowly adding the obtained reaction solution into ice water for precipitation, wherein the precipitation time is 10 minutes, filtering, dissolving in dichloromethane again, drying with magnesium sulfate, and finally performing rotary evaporation at 60 ℃ to remove the solvent to obtain the compound with the structure shown in the formula 3; dissolving 70g of a compound having a structure shown in formula 3 and 15g of sodium borohydride in 1000mL of a mixed solvent of ethanol and tetrahydrofuran (volume ratio 1; carrying out substitution reaction on 5g of the compound with the structure shown in the formula 4 and 20mL of ethylenediamine in methanol at the temperature of 100 ℃ for 12 hours to obtain a reaction solution, removing the solvent by rotary evaporation, dissolving the reaction solution in methanol, carrying out reprecipitation by using ethyl acetate, and drying the filtered product at the temperature of 60 ℃ for 12 hours to obtain the compound with the structure shown in the formula 5; 5g of the compound having the structure represented by formula 5 and 0.9g of trimesic aldehyde were dissolved in 5ml of NMP (N-methylpyrrolidone), and stirred for 10 hours to obtain a solution containing the crosslinking agent having the structure represented by formula 1.
(2) Preparation of amino-terminated polyimide: dissolving 16g of ODA and 18g of 6FDA in NMP for mixing, stirring in an ice-water bath for 12 hours for condensation polymerization to obtain a polyimide precursor, then adding toluene with the content of 1/10 of the volume of NMP into a reaction container, heating the solution to 200 ℃ for reflux for 5 hours, slowly dropwise adding the reaction solution into a mixed solvent of ethanol and water for precipitation after the reaction is finished, drying the filtered yellow solid in a vacuum oven at 80 ℃ for 12 hours and 100 ℃ for 2 hours in sequence to obtain a yellowish solid, and grinding the yellowish solid into powder by using a mortar for later use.
(3) Preparation of 3D printing ink: 1.9g of amino-terminated polyimide prepared by the method and 1.5mL of cross-linking agent solution prepared by the method are mixed and stirred until the solid is completely dissolved, so that polyimide 3D printing ink is obtained.
(4) 3D printing of recyclable thermoset polyimide articles: carrying out DIW printing on the prepared polyimide 3D printing ink and carrying out in-situ photocuring; wherein the wavelength of the used UV light is 365nm, and the irradiation time is 1min, so as to obtain a prefabricated part; carrying out heat curing treatment on the prefabricated member, wherein the temperature and the time of the first stage of the heat curing treatment are 90 ℃/12h; the temperature and time of the second stage are 150 ℃/1h, and the recyclable thermosetting polyimide product is obtained.
Nuclear magnetic testing: the nuclear magnetic resonance spectra of the third step product (compound having the structure shown in formula 4) and the fourth step product (compound having the structure shown in formula 5) in the synthesis process of the crosslinking agent containing dynamic covalent bonds are respectively shown in fig. 1 and fig. 2; as can be seen from the figure 1 of the drawings, 1 HNMR(CDCl 3 400MHz, delta (ppm)): 2.15-2.24 (m, 2H), 2.60 (t, 3H), 3.70 (s, 3H), 3.97 (s, 3H), 4.15 (t, 2H), 4.97 (s, 2H) 7.17 (s, 1H), 7.72 (s, 1H) ppm, consistent with the H atom in the chemical formula of the compound having the structure shown in formula 4, indicating that the product of the third step was successfully prepared. As can be seen from the view of figure 2, 1 H NMR(CDCl 3 ,400MHz,δ(ppm)):7.75(s,1H),7.22(s,3H),6.06(t,1H)4.96(s,2h) 4.13 (t, 2H), 3.99 (s, 3H), 3.32 (dd, 2H), 2.82 (t, 2H), 2.44 (t, 2H), 2.26 to 2.17 (m, 2H) ppm, which corresponds to the H atom in the chemical structure of the compound having the structure shown in formula 5, indicate that the product of the fourth step is successfully prepared.
And (3) infrared testing: the infrared spectra of the product (compound having the structure shown in formula 4) obtained in the third step of the synthesis process of the crosslinking agent containing dynamic covalent bonds before and after illumination are shown in fig. 3: as can be seen from FIG. 3, the compound having the structure represented by formula 4 was irradiated at 1685cm -1 The oscillation peak of aldehyde carbonyl appears, which indicates that hydroxyl can be successfully converted into aldehyde group under 365nm light.
The infrared spectrum of the amino-terminated polyimide is shown in FIG. 4, and in FIG. 4, at 3484cm -1 And 3369cm -1 A stretching vibration peak of the amino group appears, which indicates the successful preparation of the amino-terminated polyimide.
A physical diagram of the recyclable thermosetting polyimide product printed in this example is shown in fig. 4. The ink printed grid structure prepared by the above preparation method is shown in fig. 4, further demonstrating the support performance of the prepared ink under in-situ illumination.
Example 2
(1) The preparation conditions for the crosslinker containing dynamic covalent bonds were the same as in example 1.
(2) Preparation of amino-terminated polyimide: 10g of ODA and 13g of BPADA are dissolved in NMP and mixed, and then stirred in an ice water bath for 12 hours to carry out polycondensation reaction to obtain a polyimide precursor, then toluene with the content of 1/10 of the volume of the NMP is added into a reaction container, and the solution is heated to 200 ℃ and refluxed for 5 hours. After the reaction is finished, slowly dropwise adding the reaction solution into a mixed solvent of ethanol and water for precipitation, drying the filtered yellow solid in a vacuum oven at 80 ℃ for 12 hours and 100 ℃ for 2 hours in sequence to obtain a yellowish solid, and grinding the yellowish solid into powder by using a mortar for later use.
(3) Preparation of 3D printing ink: 1.3g of amino-terminated polyimide prepared by the method and 1mL of cross-linking agent solution prepared by the method are mixed and stirred until the solid is completely dissolved, so that polyimide 3D printing ink is obtained.
(4) 3D printing of recyclable thermoset polyimide articles: carrying out DIW printing on the prepared polyimide 3D printing ink and carrying out in-situ photocuring; wherein the wavelength of the used UV light is 365nm, and the irradiation time is 1min, so as to obtain a prefabricated member; carrying out heat curing treatment on the prefabricated member, wherein the temperature and the time of the first stage of the heat curing treatment are 90 ℃/12h; the temperature and time of the second stage are 150 ℃/1h, and the recyclable thermosetting polyimide product is obtained.
Example 3
(1) The preparation conditions for the crosslinker containing dynamic covalent bonds were the same as in example 1.
(2) Preparation of amino-terminated polyimide: 32g of TFDB and 23g 6FDA are dissolved in NMP and mixed, and then stirred in an ice water bath for 12 hours to carry out polycondensation reaction, so as to obtain a polyimide precursor, then toluene with the content of 1/10 of the volume of the NMP is added into a reaction container, and the solution is heated to 200 ℃ and refluxed for 5 hours. After the reaction is finished, slowly dropwise adding the reaction solution into a mixed solvent of ethanol and water for precipitation, drying the white solid obtained after filtration in a vacuum oven at 80 ℃ for 12 hours and 100 ℃ for 2 hours in sequence to obtain yellowish solid, and grinding the yellowish solid into powder by using a mortar for later use.
(3) Preparation of 3D printing ink: 2.3g of amino-terminated polyimide prepared by the method and 1.5ml of crosslinking agent containing dynamic covalent bonds prepared by the method are mixed and stirred until the solid is completely dissolved, so that polyimide 3D printing ink is obtained.
(4) 3D printing of recyclable thermoset polyimide articles: carrying out DIW printing on the prepared polyimide 3D printing ink and carrying out in-situ photocuring; wherein the wavelength of the UV light is 365nm, and the irradiation time is about 1min to obtain a prefabricated member; carrying out heat curing treatment on the prefabricated member, wherein the temperature and the time of the first stage of the heat curing treatment are 90 ℃/12h; the temperature and time of the second stage are 150 ℃/1h, and the recyclable thermosetting polyimide product is obtained.
Example 4
(1) The preparation conditions for the crosslinker containing dynamic covalent bonds were the same as in example 1.
(2) Preparation of amino-terminated polyimide: 13gTFDB and 9g 6FDA dissolved in NMP for mixing, in ice water bath stirring for 12 hours to condensation polymerization, to obtain polyimide precursor, then to the reaction vessel adding toluene, the content of NMP volume 1/10, the solution is heated to 200 degrees C and reflux for 5 hours. After the reaction is finished, slowly dropwise adding the reaction solution into a mixed solvent of ethanol and water for precipitation, drying the filtered white solid in a vacuum oven at 80 ℃ for 12 hours and 100 ℃ for 2 hours in sequence to obtain a yellowish solid, and grinding the yellowish solid into powder by using a mortar for later use.
(3) Preparation of 3D printing ink: 1.5g of amino-terminated polyimide prepared by the method and 1ml of cross-linking agent solution prepared by the method are mixed and stirred until the solid is completely dissolved, so that polyimide 3D printing ink is obtained.
(4) 3D printing of recyclable thermoset polyimide articles: carrying out DIW printing on the prepared polyimide 3D printing ink and carrying out in-situ photocuring; wherein the wavelength of the used UV light is 365nm, and the irradiation time is 1min, so as to obtain a prefabricated member; performing heat curing treatment on the prefabricated member, wherein the temperature and the time of the first stage of the heat curing treatment are 90 ℃/12h; the temperature and time of the second stage are 150 ℃/1h, and the recyclable thermosetting polyimide product is obtained.
From the above examples, it can be seen that the ink prepared by mixing the cross-linking agent containing the dynamic covalent bond with the amino-terminated polyimide realizes the cross-linking of the linear polyimide under 365nm light without the existence of the photoinitiator, and the ink has rheological property suitable for 3D printing and realizes the printing of the three-dimensional latticed polyimide. Due to the fact that dynamic covalent bond-imine bond is introduced into a cross-linked network of the 3D printed thermosetting polyimide, the method realizes recycling of the 3D printed thermosetting polyimide for the first time by utilizing the bond breaking property of the imine bond under the acidic condition.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and amendments can be made without departing from the principle of the present invention, and these modifications and amendments should also be considered as the protection scope of the present invention.

Claims (10)

1. A crosslinking agent containing a dynamic covalent bond, having the structure shown in formula 1:
Figure FDA0003787870060000011
2. a method of preparing a crosslinking agent containing a dynamic covalent bond as defined in claim 1, comprising the steps of:
mixing vanillin, methyl 4-bromobutyrate, N-dimethylformamide and potassium carbonate, and carrying out etherification reaction to obtain a compound with a structure shown in a formula 2;
mixing the compound with the structure shown in the formula 2 with a nitric acid solution, and carrying out nitration reaction to obtain a compound with the structure shown in the formula 3;
mixing the compound with the structure shown in the formula 3, sodium borohydride and an ethanol-tetrahydrofuran mixed solvent, and carrying out reduction reaction to obtain a compound with the structure shown in the formula 4;
mixing the compound with the structure shown in the formula 4, ethylenediamine and methanol, and carrying out substitution reaction to obtain a compound with the structure shown in the formula 5;
mixing the compound with the structure shown in the formula 5, N-methyl pyrrolidone and mesitylene, and carrying out Schiff base reaction to obtain a solution containing a cross-linking agent with the structure shown in the formula 1;
Figure FDA0003787870060000012
3. the method according to claim 2, wherein the mass ratio of vanillin to methyl 4-bromobutyrate is (8-9): (9-10), wherein the mass ratio of the vanillin to the potassium carbonate is (8-9): (10 to 11).
4. The process according to claim 2, wherein the etherification reaction is carried out at 25 ℃ for 10 to 24 hours.
5. The preparation method according to claim 2, wherein the mass concentration of the nitric acid solution is 50-80%; the dosage ratio of the compound with the structure shown in the formula 2 to the nitric acid solution is (90-100) g: (1000-1500) mL; the temperature of the nitration reaction is-10 to 10 ℃ and the time is 1 to 3 hours.
6. The production method according to claim 2, wherein the mass ratio of the compound having the structure represented by formula 3 to sodium borohydride is (7 to 9): (1-3); the temperature of the reduction reaction is 0 ℃, and the time is 1-3 hours.
7. The polyimide 3D printing ink is characterized by comprising a cross-linking agent, amino-terminated polyimide and N-methylpyrrolidone; the cross-linking agent is the cross-linking agent containing the dynamic covalent bond disclosed in claim 1 or the cross-linking agent containing the dynamic covalent bond prepared by the preparation method disclosed in any one of claims 2 to 6.
8. A preparation method of a recyclable thermosetting polyimide product is characterized by comprising the following steps: 3D printing is carried out by using the polyimide 3D printing ink of claim 7, and in-situ ultraviolet light curing is carried out while printing is carried out, so as to obtain a prefabricated member; and carrying out heat curing treatment on the prefabricated member to obtain the recyclable thermosetting polyimide product.
9. The preparation method of claim 8, wherein the in-situ UV curing is carried out at a wavelength of 365nm; the time of in-situ ultraviolet curing is more than 1 min.
10. The method according to claim 8, wherein the heat curing treatment comprises a first heat curing treatment and a second heat curing treatment which are sequentially performed, and the temperature of the first heat curing treatment is 80 ℃ and the time is 12 hours; the temperature of the second heat curing treatment is 150 ℃, and the time is 1h.
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