CN115850703B - Preparation method of biological basic characteristic photosensitive shape memory polyimide and three-dimensional intelligent polyimide - Google Patents

Abstract

The invention provides a preparation method of bio-based intrinsic photosensitive shape memory polyimide and three-dimensional intelligent polyimide. The invention takes lignin derivatives as raw materials to synthesize bio-diamine and dianhydride, and then prepares SMPI which contains a photosensitive structure capable of undergoing cross-linking reaction under ultraviolet light and has a shape memory function in a main chain structure of a PI macromolecular chain; can realize SMPI application in the field of photo-curing 4D printing additive manufacturing. The lignin derivative is used as a raw material, so that the biomass resource is recycled, and the problems of energy shortage, environmental pollution and the like can be solved; the method can not only avoid the damage of monomers synthesized by petroleum-based compounds as raw materials to human bodies, but also endow the prepared PI with more functional characteristics. The invention solves the problems of reduced resolution, performance degradation and the like of a three-dimensional PI intelligent structure caused by the fact that photosensitive groups grafted on a precursor of PI or a side chain of a macromolecular chain of PI are easy to lose in a high-temperature treatment process.

Description

A preparation method of a biological basic characteristic photosensitive shape memory polyimide and a three-dimensional intelligent polyimide

Technical Field

The invention relates to a preparation method of a biological basic characteristic photosensitive shape memory polyimide and a three-dimensional intelligent polyimide, belonging to the technical field of intelligent materials and additive manufacturing.

Background technique

Polyimide (PI for short) is a class of polymers containing an imide ring on the main chain, which has been widely used in the fields of thermal insulation film, fuel cell, heater, liquid crystal, separation membrane, laser, etc. The PI with excellent mechanical properties, thermal stability, solvent resistance, radiation resistance and dielectric properties studied at present usually has a benzene ring structure. This type of aromatic PI usually has strong intermolecular/intramolecular forces in the molecular chain structure, but this strong force makes it difficult to reprocess it, and the price is relatively expensive, which limits its further application. In addition, when synthesizing aromatic PI, diamine and dianhydride monomers synthesized from petrochemicals are mostly used. When synthesizing functional PI, the existing diamine and dianhydride monomers in the market also limit the ability to give PI more characteristics, such as bio-based characteristics, to a certain extent. Moreover, some diamine and dianhydride monomers synthesized from petrochemicals are toxic and pose a potential threat to human health, so it is necessary to seek green, safe and effective solutions in the future.

In the face of increasingly depleted non-renewable petroleum resources, it is an effective method to use renewable resources to synthesize safe, green and effective new diamine and dianhydride monomers to prepare PI with excellent mechanical properties, reprocessing performance and thermal stability. In recent years, scientific researchers have also achieved certain results in the research on the preparation of bio-based PI using renewable resources. However, the current research hotspots of scientific researchers are mainly focused on giving PI bio-based characteristics, while research on the use of bio-based monomers to synthesize multifunctional PIs, such as shape memory function, photosensitivity and its three-dimensional intelligent structure, is less studied and needs further advancement.

When converting a two-dimensional PI into a three-dimensional PI structure, 3D or 4D printing additive manufacturing technology is currently usually used. In order to meet the requirements of PI for application in photocuring 3D or 4D printing additive manufacturing technology, it is necessary to graft photosensitive groups on the precursor of PI or the side chain of the macromolecular chain of PI to increase the photosensitivity of PI, but the grafted photosensitive substances will be lost during the high-temperature treatment process, resulting in a decrease in the structural resolution and performance degradation of the three-dimensional smart polyimide (Shape memory polyimide, referred to as SMPI). Although "Li Xiao. Preparation and Performance Research of 4D Printing Shape Memory Polyimide [D]. Beijing. University of Chinese Academy of Sciences, 2019.", SMPI is prepared by a one-step chemical imide method to solve the above problems, but it still grafts photosensitive functional groups on the SMPI molecular chain to increase the photosensitivity of SMPI. However, this method still does not introduce a photosensitive structure that can undergo cross-linking reaction under ultraviolet light on the main chain structure of the macromolecular chain of PI. Therefore, there is an urgent need for a new type of photosensitive SMPI that has a photosensitive structure in the main chain structure of the PI macromolecular chain that can undergo a cross-linking reaction under ultraviolet light and will not cause material loss during high-temperature treatment to be compatible with photocuring 4D printing additive manufacturing technology.

Summary of the invention

In view of the deficiencies in the prior art, the present invention provides a method for preparing a bio-basic characteristic photosensitive shape memory polyimide and a three-dimensional smart polyimide. The present invention uses lignin derivatives as raw materials to synthesize bio-based diamines and dianhydride monomers, and then prepares a bio-basic characteristic photosensitive shape memory polyimide (SMPI) having a shape memory function and a photosensitive structure that can undergo a cross-linking reaction under ultraviolet light in the main chain structure of the PI macromolecular chain; the application of SMPI in the field of photocuring 4D printing additive manufacturing can be realized to prepare a three-dimensional PI smart structure with high precision and excellent mechanical properties, solve the problem of the transformation of two-dimensional shape PI to three-dimensional PI smart structure, solve the problem that the photosensitive group grafted on the side chain of the PI precursor or the macromolecular chain of PI is easily lost during high-temperature treatment, resulting in reduced resolution and performance degradation of the three-dimensional PI smart structure, and further enrich the photocuring 4D printing material system. The present invention uses lignin derivatives as raw materials, realizes the recycling of biomass resources, can solve the problems of energy shortage and environmental pollution, and can also reduce energy consumption; it can not only avoid the damage to the human body caused by aromatic diamines and dianhydride monomers synthesized with petroleum-based compounds as raw materials, but also can give the prepared PI more functional properties.

The technical solution of the present invention is as follows:

A method for preparing a biological basic characteristic photosensitive shape memory polyimide comprises the steps of:

(1) Preparation of diamine:

i. Dissolve the lignin derivative in ethyl acetate, add tributyl borate and _{acetylacetone} - _B2O3 complex, and mix well; add n-butylamine dropwise at 70-80°C, stir and react at 70-80°C for 4-5h, and stand and react at 70-80°C for 10-16h; then add an aqueous solution of an acid with a temperature of 40-70°C and a mass concentration of 1-10wt%, and stir and react at 70-80°C for 1-6h; cool to room temperature, filter, wash, recrystallize with acetic acid, and dry to obtain an intermediate product I; the lignin derivative is vanillin, syringaldehyde or 4-hydroxybenzaldehyde;

ii. The intermediate product I, p-fluoronitrobenzene, DMF and potassium carbonate are mixed evenly, and reacted at 70-80° C. for 4-8 hours under nitrogen protection; the obtained reaction solution is poured into a sodium hydroxide aqueous solution with a mass concentration of 3-10% to precipitate a solid, and the obtained solid is washed with water until neutral, recrystallized with DMF/water, filtered, and dried to obtain the intermediate product II;

iii. Under nitrogen protection, the intermediate product II, dioxane and palladium carbon are fully mixed, hydrazine hydrate is added dropwise at room temperature, and after the addition is completed, reflux reaction is carried out under nitrogen protection for 4-8 hours; filter while hot, pour the filtrate into deionized water to obtain a white product, and then dry it to diamine;

Diamine

Wherein, the substituent R' is a phenyl group; the substituent R is:

(2) Preparation of dianhydride:

i. Mix the lignin derivative, p-hydroxyacetophenone and piperidine evenly, and react under nitrogen protection at 60-100° C. with stirring for 20-30 hours; pour the resulting reaction solution into water, add 0.5-3 mol/L dilute hydrochloric acid to adjust the pH to less than 1, and place at room temperature for 10-15 hours; then filter, recrystallize and dry to obtain the intermediate product III; the lignin derivative is vanillin, syringaldehyde or 4-hydroxybenzaldehyde;

ii. The intermediate product III, anhydrous potassium carbonate, DMF and toluene are fully mixed, and water is separated at 130-150° C. for 4-6 hours under nitrogen protection. After the system is cooled to room temperature, N-methyl-3-nitrophthalimide is added, and the reaction is carried out at 120-140° C. for 15-25 hours under nitrogen protection. After cooling to room temperature, the reaction solution is slowly poured into dilute hydrochloric acid with a pH of 2-3 to precipitate. The precipitate is washed with water, recrystallized with acetic acid, and dried to obtain the intermediate product IV.

iii. The intermediate product IV, deionized water and sodium hydroxide are fully mixed, refluxed at 120-160° C. for 30-40 hours under nitrogen protection, cooled to room temperature and filtered; 5-6 mol/L hydrochloric acid is added to acidify the system to pH = 1-3, and then filtered, recrystallized from acetic acid and recrystallized from acetic anhydride to obtain dianhydride.

Wherein, the substituent R is:

(3) dissolving the diamine and the dianhydride in a low-boiling point organic solvent, stirring and reacting for 12-24 hours at 10-20° C. under nitrogen protection to obtain a polyimide precursor solution - polyamic acid; then standing at 30-50° C. for 2-4 hours to remove bubbles; and finally performing a high-temperature imidization reaction to obtain a biological basic characteristic photosensitive shape memory polyimide;

Biological basic characteristic photosensitive shape memory polyimide

Wherein, n = 10-200;

The substituent R" is:

The substituent R' and the substituent R have the same meanings as the substituent R' and the substituent R in the diamine, respectively.

Preferably, according to the present invention, in step (1)i, the volume ratio of the mass of the lignin derivative to ethyl acetate is (8-12):(15-30) g/mL; the volume ratio of the mass of the lignin derivative to tributyl borate is (8-12):(10-20) g/mL.

Preferably according to the present invention, in step (1) i, the preparation method of the acetylacetone- _{B2O3 complex} comprises the steps of: refluxing acetylacetone and boric anhydride in a molar ratio of 1:1 in ethyl acetate at a temperature of 76°C for 40 minutes; the mass ratio of acetylacetone to ethyl acetate is (0.1-0.5):1 g/mL; the molar ratio of the lignin derivative to acetylacetone is (1-5):(1-3), preferably 2:1.

Preferably according to the present invention, in step (1)i, the mass of n-butylamine is 5-15% of the mass of the lignin derivative.

Preferably according to the present invention, in step (1)i, the acid is hydrochloric acid, sulfuric acid, acetic acid or phosphoric acid; and the volume ratio of the aqueous solution of the acid to ethyl acetate is (10-20):(1-3).

Preferably according to the present invention, in step (1) ii, the molar ratio of the intermediate product I, p-fluoronitrobenzene and potassium carbonate is (0.05-2): (0.1-4); (0.1-1); the volume ratio of the mass of the intermediate product I and DMF is: (1-5): (10-300).

Preferably, according to the present invention, in step (1) ii, the volume ratio of the reaction solution to the sodium hydroxide aqueous solution is (2-5): (3-10).

Preferably, according to the present invention, in step (1) iii, the mass ratio of the intermediate product II to the volume of dioxane is 1: (1-10) g/mL; the mass of palladium carbon is (25-30)% of the mass of the intermediate product II; and the mass ratio of the intermediate product II to hydrazine hydrate is (2-3):1.

Preferably according to the present invention, in step (1) iii, the dripping rate of hydrazine hydrate is 3-7 mL/h.

Preferably, in step (2)i, the molar ratio of the lignin derivative to p-hydroxyacetophenone is 1:1; the volume ratio of the molar amount of the lignin derivative to piperidine is 1:(1-10) mol/L; and the volume ratio of the reaction solution to water is 1:(40-60).

Preferably, according to the present invention, in step (2) ii, the molar ratio of the intermediate product III to anhydrous potassium carbonate is 1:(1-2); the volume ratio of the molar amount of the intermediate product III to DMF is 1:(1-5) mol/L; the volume ratio of DMF to toluene is (10-20):(4-10); the molar ratio of N-methyl-3-nitrophthalimide to the intermediate product III is 2:1.

Preferably according to the present invention, in step (2) iii, the mass ratio of the intermediate product IV, deionized water and sodium hydroxide is (3-10):(100-200):(10-20).

Preferably according to the present invention, in step (2) iii, the method for recrystallizing acetic anhydride comprises the steps of: refluxing the crude product and acetic anhydride at 140° C. for 12 hours, wherein the mass ratio of the crude product to acetic anhydride is: (3-10):(10-20).

Preferably, in step (3), the low boiling point organic solvent is one or a combination of two or more of N-methylpyrrolidone, N,N-dimethylformamide or N,N-dimethylacetamide; and the volume ratio of the molar amount of the diamine to the low boiling point organic solvent is 0.1-0.5 mol/L.

Preferably according to the present invention, in step (3), the molar ratio of diamine to dianhydride is 1:(0.94-1.02).

According to the preferred embodiment of the present invention, in step (3), the high temperature imidization reaction method comprises the steps of: heating the reaction solution from room temperature to 70-90°C at a heating rate of 0.5-2°C/min, and keeping the temperature at 70-90°C for 1-3h; then heating the reaction solution to 110-130°C at a heating rate of 0.5-2°C/min, and keeping the temperature at 110-130°C for 1-3h; then heating the reaction solution to 160-180°C at a heating rate of 0.5-2°C/min, and keeping the temperature at 160-180°C for 1h. The method comprises the steps of: heating the mixture to 220-240°C at a heating rate of 0.5-2°C/min, and keeping the mixture at 220-240°C for 1-3h; heating the mixture to 290-310°C at a heating rate of 0.5-2°C/min, and keeping the mixture at 290-310°C for 1-3h; finally, heating the mixture to 350-370°C at a heating rate of 0.5-2°C/min, and keeping the mixture at 350-370°C for 1-3h to obtain a photosensitive shape memory polyimide having a basic biological characteristic.

According to the present invention, the preparation method of the lignin derivative can be based on existing methods, such as extracting from lignin using an alkaline oxidation method.

A biological basic characteristic photosensitive shape memory polyimide is prepared by the above method.

A method for preparing a three-dimensional intelligent polyimide comprises the following steps:

(1) preparing a biological basic characteristic photosensitive shape memory polyimide according to the above method;

(2) Three-dimensional polyimide was prepared by photocuring 4D printing.

According to the present invention, the photocuring 4D printing method can be carried out according to the existing method. Preferably, in step (2), the photocuring 4D printing method is used to prepare the three-dimensional polyimide, which comprises the following steps:

(1) dissolving a biological basic characteristic photosensitive shape memory polyimide in a low boiling point solvent to obtain a printing ink having a viscosity of 100-300 mPa·s at 25° C.; the low boiling point solvent is N-methylpyrrolidone, N,N-dimethylformamide or N,N-dimethylacetamide;

(2) using a photocuring printer with a UV light wavelength of 300-410 nm, and performing layer-by-layer photocuring 4D printing at room temperature according to the established 3D model and the equivalent thickness of the 3D model slices; setting the exposure time and thickness of each layer of 4D printing to 20-40 s and 20-60 μm respectively;

(3) After the photocuring printing is completed, continue to photocuring at room temperature under ultraviolet light with a wavelength of 300-410 nm for 0.5-1 h, and finally vacuum dry at 150-250° C. for 6-12 h to obtain a three-dimensional smart polyimide.

A three-dimensional intelligent polyimide is prepared by the method.

The reaction scheme of the present invention is as follows:

The synthetic route of diamine is as follows:

The synthetic route of dianhydride is as follows:

The synthesis route of biological basic characteristic photosensitive shape memory polyimide is as follows:

Wherein, the substituent R is:

The substituent R" is:

The substituent R' is a phenyl group.

n＝10～200.

The technical features and beneficial effects of the present invention are as follows:

1. The present invention uses bio-based units such as vanillin extracted from lignin as reaction monomers, introduces bio-based units and cinnamic acid and chalcone photosensitive groups into diamine and dianhydride monomers through chemical reactions such as nucleophilic addition, nucleophilic substitution, reduction, and acidification, and then synthesizes a photosensitive structure in the molecular chain structure that can undergo a cross-linking reaction under ultraviolet light irradiation and has a biological basic characteristic photosensitive SMPI with shape memory function by low-temperature polycondensation-high-temperature imide method. By studying the relationship between the photosensitive structure and the performance of PI, its regulatory mechanism is found to optimize the molecular chain structure of SMPI so that it has the best photosensitivity and shape memory function. Finally, the optimal light-curing 4D printing method is explored to prepare a three-dimensional intelligent SMPI with high precision, small dimensional shrinkage, and excellent mechanical properties.

2. The present invention uses vanillin extracted from lignin as a bio-based monomer, thereby realizing the recycling of biomass resources, solving problems such as energy shortage and environmental pollution, and reducing energy consumption. It can not only avoid the damage to the human body caused by aromatic diamines and dianhydride monomers synthesized from petroleum-based compounds, but also be green, environmentally friendly and safe, and can also give the prepared PI more functional properties.

3. The method of the present invention solves the problem that the photosensitive groups grafted on the side chains of the precursor of PI or the macromolecular chain of PI are easily lost during high-temperature treatment, resulting in reduced resolution, performance degradation, and large volume shrinkage of the three-dimensional intelligent SMPI structure. The main chain of the macromolecular chain of PI obtained by the method of the present invention contains photosensitive groups, has high-temperature stability, can undergo photocrosslinking reaction under ultraviolet light, and uses a photocuring 4D printing method to prepare a three-dimensional intelligent SMPI structure, and the prepared SMPI and its three-dimensional intelligent SMPI structure have excellent performance.

4. The polyimide prepared by the method of the present invention has excellent photosensitivity and shape memory function. The photosensitivity of the biological basic characteristic photosensitive polyimide prepared by the present invention enables it to be used as a photoresist to reduce the photocuring time and photocuring intensity of the photoresist, slow down the processing steps, and improve production efficiency. The shape memory property of the biological basic characteristic photosensitive polyimide enables it to be used as a packaging material, and its shape deformation property will increase the fun and convenience of people's lives. At the same time, the three-dimensional intelligent SMPI prepared by the present invention has low thermal conductivity, excellent mechanical strength, and non-toxicity, etc., especially in the fields of building thermal insulation, biomedical stents, aerospace deployable structures, and automotive filters. It has broad application prospects.

5. The preparation process of the present invention is sophisticated, low in cost, and has good repeatability, and can be used for large-scale preparation of bio-based shape memory polyimide and its three-dimensional intelligent structure.

6. In the process of preparing polyimide from diamine and dianhydride of the present invention, the temperature program of high-temperature imidization reaction is more important. If the temperature program conditions are not appropriate, a large number of bubbles will be generated, which will have an adverse effect on the performance of the obtained polyimide; if the temperature is too high or too low, the obtained polyimide material will be very brittle and not conducive to application. At the same time, if the molar ratio of diamine to dianhydride is too high or too low, the obtained polyimide material will also be broken, and the mechanical strength, shape memory performance, etc. will be reduced. The preparation method of the present invention as a whole requires the joint action of various conditions and steps to achieve the effect of the present invention. Any change in any condition will affect the yield of the polyimide material, and the performance of the obtained polyimide material will also be affected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a UV absorption spectrum curve of the biological basic characteristic photosensitive SMPI prepared in Example 1;

FIG2 is an infrared spectrum of the biological basic characteristic photosensitive SMPI prepared in Example 1 before (a) and after (b) ultraviolet light irradiation;

FIG3 is a thermogravimetric curve of the biological basic characteristic photosensitive SMPI prepared in Example 1 after ultraviolet irradiation;

FIG4 is a diagram showing the shape memory state (a) and recovery state (b) of the biological basic characteristic photosensitive SMPI prepared in Example 1 after ultraviolet irradiation;

FIG5 is a picture of the three-dimensional smart SMPI structure prepared in Example 4.

Detailed ways

The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

Meanwhile, the experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

Example 1

A method for preparing a biological basic characteristic photosensitive shape memory polyimide comprises the steps of:

(1) Preparation of diamine:

i. Dissolve 100g of vanillin in 200mL of anhydrous ethyl acetate, then add 180mL of tributyl borate and 65g of acetylacetone-B ₂ O ₃ complex and mix well; add 15mL of n-butylamine at 75°C, drip it for 1h, stir it for 4.5h at 75°C, and let it stand for 12h at 75°C; then add 1500mL of 60°C hydrochloric acid with a mass concentration of 2% and continue stirring at 75°C for 1h to complete the reaction. Cool to room temperature and filter, wash with water 3-4 times, filter out the product, wash with ethyl acetate 2-3 times to obtain a crude product, and finally recrystallize it with acetic acid and dry it to obtain intermediate product I, with a product yield of 91%.

The preparation method of acetylacetone- _{B2O3 complex} comprises the following steps: reflux acetylacetone (50 g) and boric anhydride in a molar ratio of 1:1 in 200 mL of ethyl acetate at 76°C for 40 minutes; the molar ratio of lignin derivative to acetylacetone is 2:1.

ii. Add 18.4g of intermediate product I, 14.11g of p-fluoronitrobenzene, 200mL of DMF, and 13.8g of potassium carbonate into a 300mL three-necked flask equipped with a mechanical stirring paddle, a nitrogen inlet (nitrogen protection), a condenser and a thermometer, mix well, react at 75°C for 6h, and after the reaction, pour the system into 500mL of a 5wt% sodium hydroxide aqueous solution to precipitate the product. After filtering, the product was repeatedly washed with water until neutral, and recrystallized and filtered with DMF/water (volume ratio of 1:20) to obtain a light yellow product, which was vacuum dried at 80°C for 10 hours to obtain intermediate product II, with a product yield of 97%.

iii. Under nitrogen protection, 30 mL of dioxane, 24.45 g of intermediate product II, and 7 g of palladium carbon were added to a 100 mL three-necked flask equipped with a mechanical stirrer, a condenser, and a dropping funnel, and mixed thoroughly. 10 mL of hydrazine hydrate (mass concentration of 80%) was added dropwise at room temperature within two hours. After reflux reaction for 6 hours under nitrogen protection, the product was hot filtered, and the filtrate was poured into 500 mL of deionized water to obtain a white product, which was vacuum dried at 80° C. for 10 hours to obtain diamine. The product yield was 90%.

(2) Preparation of dianhydride:

i. Add 0.01 mol vanillin and 0.01 mol p-hydroxyacetophenone into a three-necked flask containing 20 ml piperidine, mix well, heat to 80 degrees Celsius, and react for 24 hours under magnetic stirring under nitrogen protection. After the reaction, pour the dark red viscous solution in the flask into 1000 ml water, add enough 1 mol/L dilute hydrochloric acid, adjust the pH to below 1, and leave at room temperature for 12 hours; collect the product by filtration and recrystallize it with a mixed solution of ethanol and water (volume ratio = 1:10), and dry it to obtain intermediate product III, with a product yield of 92%.

ii. Add 0.09mol of intermediate III, 15g of anhydrous potassium carbonate, 200mL of DMF, and 50mL of toluene to a branched flask equipped with a magnetic stirrer, a water separator, and a condenser tube, and separate water at 140 degrees Celsius for 5 hours under nitrogen protection. After the system is cooled to room temperature, add 0.045mol of N-methyl-3-nitrophthalimide. Heat to 130 degrees Celsius under nitrogen protection and react at this reaction temperature for 20 hours. After cooling to room temperature, slowly pour the solution into dilute hydrochloric acid (pH=2-3) to precipitate, wash with water, and then vacuum dry at 100 degrees Celsius to obtain an off-white solid, which is recrystallized from acetic acid and dried to obtain intermediate IV, with a product yield of 93%.

iii. Add 10g of intermediate product IV, 200mL of deionized water and 15g of sodium hydroxide to a branched flask equipped with a magnetic stirrer, a water separator and a condenser tube, heat and reflux at 140°C for 36 hours under nitrogen protection, cool to room temperature and filter to obtain a red solution. Acidify with 6mol/L hydrochloric acid to a pH of 2-3, filter to obtain a white solid, recrystallize the crude product with acetic acid to obtain a white solid, and recrystallize with acetic anhydride (reflux the crude product and acetic anhydride at 140°C for 12h, wherein the mass ratio of the crude product to acetic anhydride is: 5:15) to obtain dianhydride, with a product yield of 96%.

(3) 5 mmol of diamine and 5 mmol of dianhydride were added to a three-necked flask containing 20 ml of a low-boiling point organic solvent (DMF), and magnetically stirred for 24 hours at a low temperature (15°C) under nitrogen protection to obtain a polyimide precursor solution - polyamic acid. The precursor solution was then placed in a vacuum oven at 40°C for 3 hours to remove bubbles, and then a high-temperature imidization process was performed in a gradually heated and heat-insulated manner to obtain a biological basic characteristic photosensitive shape memory polyimide film with a product yield of 92%.

The method of performing thermal amidation in a gradual heating and heat preservation manner is as follows: heating the low-temperature prepolymer solution from room temperature to 80°C at a heating rate of 1°C/min, keeping it at 80°C for 2 hours, then heating it to 120°C at a heating rate of 1°C/min, keeping it at 120°C for 2 hours, then heating it to 170°C at a heating rate of 1°C/min, keeping it at 170°C for 2 hours, then heating it to 230°C at a heating rate of 1°C/min, keeping it at 230°C for 2 hours, then heating it to 300°C at a heating rate of 1°C/min, keeping it at 300°C for 2 hours, and finally heating it to 360°C at a heating rate of 1°C/min, keeping it at 360°C for 2 hours, thus completing the high-temperature thermal amidation process in a gradual heating and heat preservation manner.

The ultraviolet absorption spectrum curve of the biological basic characteristic photosensitive shape memory polyimide prepared in this embodiment is shown in FIG1 . The obtained material has the characteristic of being sensitive to ultraviolet light in the ultraviolet light region of 300-400nm, and has the maximum absorption at 350nm.

The bio-based photosensitive polyimide prepared in this embodiment was irradiated under ultraviolet light of 365nm wavelength for 10min; the infrared spectra before (a) and after (b) ultraviolet irradiation are shown in Figure 2. The association absorption peak in the range of 3500-3100cm ^-1 in the infrared spectrum is caused by the stretching vibration of -NH and -OH functional groups on the PI macromolecular chain; but the stretching vibration absorption peak of C=O of the keto carbonyl functional group in the diamine and dianhydride monomers at 1680-1630cm ^-1 on the PI macromolecular chain becomes very weak, which to a certain extent indicates that the content of the photosensitive carbonyl functional group is greatly reduced, and a new absorption peak of the CO functional group appears at 1076cm ^-1 . The above results verify that the PI macromolecular chain undergoes a cross-linking reaction under ultraviolet irradiation.

The thermogravimetric curve of the biological basic characteristic photosensitive shape memory polyimide prepared in this embodiment after the above-mentioned ultraviolet light irradiation is shown in Figure 3. It can be seen from the figure that the obtained material has excellent thermal stability, and no loss of small molecular substances is detected in the low temperature stage. The thermal decomposition temperature at the maximum mass loss is ~480°C, which means that the biological basic characteristic photosensitive SMPI prepared in this embodiment not only has excellent thermal stability itself, but also when used for photocuring 4D printing of three-dimensional intelligent PI structure, the process of removing solvent will not affect the molecular chain structure of PI, that is, it will not cause performance loss, thereby effectively solving the current problems of volume shrinkage, reduced precision and degradation of mechanical properties of three-dimensional intelligent PI structure.

The shape memory state (a) and recovery state (b) of the biological basic characteristic photosensitive shape memory polyimide prepared in this embodiment after the above-mentioned ultraviolet light irradiation are shown in Figure 4. It can recover 98% of its shape to the initial shape, indicating that the material prepared by the present invention has excellent shape memory function.

Example 2

A method for preparing a biologically basic characteristic photosensitive shape memory polyimide is as described in Example 1, except that the lignin derivative used in the preparation of diamine and dianhydride is syringaldehyde; the other steps and conditions are consistent with those in Example 1.

Example 3

A method for preparing a biological basic characteristic photosensitive shape memory polyimide is as described in Example 1, except that the lignin derivative used in the preparation of diamine and dianhydride is 4-hydroxybenzaldehyde; the other steps and conditions are consistent with Example 1.

Example 4

A method for preparing a three-dimensional intelligent polyimide comprises the following steps:

(1) preparing a biological basic characteristic photosensitive shape memory polyimide according to the method of Example 1;

(2) Preparing three-dimensional smart polyimide by using a photocuring 4D printing method, comprising the steps of:

i. Dissolving the biological basic characteristic photosensitive shape memory polyimide in a low boiling point solvent (DMF) to obtain a printing ink with a viscosity of 200 mPa·s at 25° C.;

ii. Use a photocuring printer with a UV light wavelength of 355-410nm to perform photocuring 4D printing layer by layer at room temperature according to the established 3D model and the equivalent thickness of the 3D model slices; set the exposure time and thickness of each layer of 4D printing to 30s and 20μm respectively;

iii. After the photocuring printing is completed, continue to photocuring at room temperature for 1 hour under ultraviolet light with a wavelength of 361nm, and finally vacuum dry at 200°C for 6 hours to obtain a three-dimensional smart polyimide.

The picture of the three-dimensional smart polyimide prepared by 4D printing in this embodiment is shown in FIG5 , which is a hollow cylindrical shape.

Claims (10)

1. A preparation method of bio-based intrinsic photosensitive shape memory polyimide comprises the following steps:

(1) Preparation of diamine:

i. Dissolving lignin derivative in ethyl acetate, adding tributyl borate and acetylacetone-B ₂O₃ complex, and mixing uniformly; dripping n-butylamine at 70-80 ℃, stirring at 70-80 ℃ for 4-5h, and standing at 70-80 ℃ for 10-16h after dripping; then adding an aqueous solution of acid with the mass concentration of 1-10wt% and the temperature of 40-70 ℃ to stir and react for 1-6h at 70-80 ℃; cooling to room temperature, filtering, washing, recrystallizing with acetic acid, and drying to obtain intermediate I; the lignin derivative is vanillin, syringaldehyde or 4-hydroxybenzaldehyde;

ii. Uniformly mixing the intermediate product I, p-fluoronitrobenzene, DMF and potassium carbonate, and reacting for 4-8 hours at 70-80 ℃ under the protection of nitrogen; pouring the obtained reaction solution into a sodium hydroxide aqueous solution with the mass concentration of 3-10%, separating out solid, washing the obtained solid to be neutral, recrystallizing with DMF/water, filtering, and drying to obtain an intermediate product II;

iii, fully and uniformly mixing the intermediate product II, dioxane and palladium-carbon under the protection of nitrogen, dropwise adding hydrazine hydrate at room temperature, and carrying out reflux reaction for 4-8h under the protection of nitrogen after the dropwise adding; filtering while the mixture is hot, pouring the filtrate into deionized water to obtain a white product, and drying the white product to diamine;

Wherein the substituent R' is phenyl; the substituent R is:

(2) Preparation of dianhydride:

i. Uniformly mixing lignin derivatives, p-hydroxyacetophenone and piperidine, and stirring and reacting for 20-30h at 60-100 ℃ under the protection of nitrogen; pouring the obtained reaction solution into water, adding 0.5-3mol/L dilute hydrochloric acid to adjust the pH value to be less than 1, and standing at room temperature for 10-15h; then filtering, recrystallizing and drying to obtain an intermediate product III; the lignin derivative is vanillin, syringaldehyde or 4-hydroxybenzaldehyde;

ii. Fully and uniformly mixing an intermediate product III, anhydrous potassium carbonate, DMF and toluene, carrying out nitrogen protection, and carrying out water diversion at 130-150 ℃ for 4-6 hours, adding N-methyl-3-nitrophthalimide after the system is cooled to room temperature, and carrying out reaction for 15-25 hours at 120-140 ℃ under the nitrogen protection; cooling to room temperature, slowly pouring the reaction solution into dilute hydrochloric acid with pH=2-3 to separate out precipitate, washing the obtained precipitate with water, recrystallizing with acetic acid, and drying to obtain an intermediate product IV;

iii, fully and uniformly mixing the intermediate product IV, deionized water and sodium hydroxide, carrying out reflux reaction for 30-40h at 120-160 ℃ under the protection of nitrogen, cooling to room temperature, and filtering; adding 5-6mol/L hydrochloric acid to acidify until the pH value of the system is 1-3, and then filtering, recrystallizing with acetic acid, and recrystallizing with acetic anhydride to obtain dianhydride;

Wherein, substituent R is:

(3) Dissolving diamine and dianhydride in a low boiling point organic solvent, and stirring and reacting for 12-24 hours at the temperature of 10-20 ℃ under the protection of nitrogen to obtain polyimide precursor solution-polyamide acid; then standing for 2-4h at 30-50deg.C to remove bubbles; finally, the bio-based intrinsic photosensitive shape memory polyimide with the following structure is obtained through high-temperature imidization reaction;

Wherein n=10-200;

The substituent R' is:

the meaning of the substituent R 'and the substituent R are the same as the meaning of the substituent R' and the substituent R in diamine in sequence.

2. The method of preparing a bio-based intrinsic type photosensitive shape memory polyimide according to claim 1, wherein in step (1) i, one or more of the following conditions are included:

i. The volume ratio of lignin derivative mass and ethyl acetate is (8-12): (15-30) g/mL; the mass ratio of lignin derivative and tributyl borate is (8-12): 10-20 g/mL;

ii. The preparation method of the acetylacetone-B ₂O₃ complex comprises the following steps: refluxing acetylacetone and boric anhydride with a molar ratio of 1:1 in ethyl acetate at 76 ℃ for 40min; the volume ratio of the mass of the acetylacetone to the ethyl acetate is (0.1-0.5): 1g/mL; the molar ratio of lignin derivative to acetylacetone is (1-5): (1-3);

iii, the mass of the n-butylamine is 5-15% of the mass of the lignin derivative;

iv, the acid is hydrochloric acid, sulfuric acid, acetic acid or phosphoric acid; the volume ratio of the aqueous acid solution to the ethyl acetate is (10-20): (1-3).

3. The method of preparing a bio-based intrinsic type photosensitive shape memory polyimide according to claim 1, wherein in step (1) ii), one or more of the following conditions are included:

i. the molar ratio of the intermediate product I to the p-fluoronitrobenzene to the potassium carbonate is (0.05-2): (0.1-4); (0.1-1); the mass and DMF volume ratio of the intermediate product I is: (1-5): (10-300);

ii. The volume ratio of the reaction solution to the sodium hydroxide aqueous solution is (2-5): (3-10).

4. The method of preparing a bio-based intrinsic type photosensitive shape memory polyimide according to claim 1, wherein in step (1) iii, one or more of the following conditions are included:

i. The volume ratio of the mass of the intermediate product II to the dioxane is 1 (1-10) g/mL; the mass of palladium-carbon is (25-30)% of the mass of the intermediate product II; the mass ratio of the intermediate product II to the hydrazine hydrate is (2-3) 1;

ii. The dripping rate of the hydrazine hydrate is 3-7mL/h.

5. The method of preparing a bio-based intrinsic type photosensitive shape memory polyimide according to claim 1, wherein in step (2), one or more of the following conditions are included:

i. In the step (2) i, the molar ratio of the lignin derivative to the p-hydroxyacetophenone is 1:1; the molar amount of lignin derivative and the volume ratio of piperidine are 1: (1-10) mol/L; the volume ratio of the reaction liquid to the water is 1: (40-60);

ii. In step (2) ii, the molar ratio of intermediate III to anhydrous potassium carbonate is 1 (1-2): the molar amount of intermediate III and the volume ratio of DMF was 1: (1-5) mol/L; the volume ratio of DMF to toluene is (10-20): (4-10); the molar ratio of N-methyl-3-nitrophthalimide to intermediate III is 2:1;

iii, in the step (2) iii, the mass ratio of the intermediate product IV to deionized water to sodium hydroxide is (3-10): 100-200): 10-20;

in step iv, step (2) iii, the method for recrystallizing acetic anhydride comprises the steps of: refluxing the crude product and acetic anhydride for 12 hours at 140 ℃, wherein the mass ratio of the crude product to the acetic anhydride is as follows: (3-10): (10-20).

6. The method of preparing a bio-based intrinsic type photosensitive shape memory polyimide according to claim 1, wherein in step (3), one or more of the following conditions are included:

i. The low-boiling point organic solvent is one or the combination of more than two of N-methyl pyrrolidone, N, N-dimethylformamide or N, N-dimethylacetamide; the volume ratio of the molar quantity of diamine to the low-boiling point organic solvent is 0.1-0.5mol/L;

ii. The molar ratio of diamine to dianhydride is 1 (0.94-1.02);

The high-temperature imidization reaction method comprises the following steps: heating the reaction solution from room temperature to 70-90 ℃ at a heating rate of 0.5-2 ℃/min, and preserving heat for 1-3h under the condition that the temperature is 70-90 ℃; then heating to 110-130 ℃ at a heating rate of 0.5-2 ℃/min, and preserving heat for 1-3h under the condition of 110-130 ℃; then heating to 160-180 ℃ at a heating rate of 0.5-2 ℃/min, and preserving heat for 1-3h under the condition of 160-180 ℃; continuously heating to 220-240 ℃ at a heating rate of 0.5-2 ℃/min, and preserving heat for 1-3h under the condition that the temperature is 220-240 ℃; then heating to 290-310 ℃ at a heating rate of 0.5-2 ℃/min, and preserving heat for 1-3h under the condition of 290-310 ℃; finally, the temperature is increased to 350-370 ℃ at the heating rate of 0.5-2 ℃/min, and the temperature is kept for 1-3 hours under the condition of 350-370 ℃ to obtain the bio-based intrinsic photosensitive shape memory polyimide.

7. The bio-based intrinsic photosensitive shape memory polyimide prepared by the method of any one of claims 1 to 6.

8. A preparation method of three-dimensional intelligent polyimide comprises the following steps:

(1) Preparing a bio-based intrinsic photosensitive shape memory polyimide according to the method of any one of claims 1 to 6;

(2) The photo-curing 4D printing method is adopted to prepare the three-dimensional polyimide.

9. The method for preparing three-dimensional intelligent polyimide according to claim 8, wherein in the step (2), the method for preparing three-dimensional polyimide by using the photo-curing 4D printing method comprises the steps of:

(1) Dissolving the bio-based intrinsic photosensitive shape memory polyimide in a low boiling point solvent to obtain printing ink with the viscosity of 100-300 mPa.s at 25 ℃; the low boiling point solvent is N-methyl pyrrolidone, N-dimethylformamide or N, N-dimethylacetamide;

(2) Adopting a light curing printer with the illumination wavelength of 300-410nm, and performing light curing 4D printing layer by layer at room temperature according to the established 3D model and the equivalent thickness of the 3D model slice; setting the exposure time and thickness of each layer of 4D printing to be 20-40s and 20-60 mu m respectively;

(3) And after the photo-curing printing is finished, continuing to photo-cure for 0.5-1h at room temperature under the illumination wavelength of 300-410nm, and finally drying in vacuum for 6-12h at the temperature of 150-250 ℃ to obtain the three-dimensional intelligent polyimide.

10. A three-dimensional intelligent polyimide prepared by the method of claim 8 or 9.