CN113307972A - Polyimide and preparation method thereof, and polyimide sealing ring and preparation method thereof - Google Patents

Polyimide and preparation method thereof, and polyimide sealing ring and preparation method thereof Download PDF

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CN113307972A
CN113307972A CN202110661691.XA CN202110661691A CN113307972A CN 113307972 A CN113307972 A CN 113307972A CN 202110661691 A CN202110661691 A CN 202110661691A CN 113307972 A CN113307972 A CN 113307972A
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polyimide
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graphene oxide
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CN113307972B (en
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邓鹏飏
魏巍
史彦东
赵阳
潘利江
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Changchun Institute of Applied Chemistry of CAS
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    • C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
    • C08G73/10—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
    • C08G73/1067—Wholly aromatic polyimides, i.e. having both tetracarboxylic and diamino moieties aromatically bound
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Abstract

The invention provides polyimide and a preparation method thereof, and a polyimide sealing ring and a preparation method thereof. The preparation method of the polyimide comprises the following steps: a) mixing and reacting a compound shown in the formula (1), graphene oxide and a solvent to form amino modified graphene oxide; b) mixing and reacting the amino modified graphene oxide with a dianhydride monomer of formula (2) and a diamine monomer of formula (3) to form polyamic acid; c) and carrying out imidization reaction on the polyamic acid to obtain polyimide. The compound of formula (1) is adopted to react with graphene oxide to form amino modified graphene oxide; and then reacting the modified graphene oxide with a dianhydride monomer of a formula (2) and a diamine monomer of a formula (3) to finally prepare the polyimide. The polyimide prepared by the method can generate good self-lubrication and wear resistance while maintaining good heat resistance, lower thermal expansion coefficient and higher toughness.

Description

Polyimide and preparation method thereof, and polyimide sealing ring and preparation method thereof
Technical Field
The invention relates to the field of organic materials, in particular to polyimide and a preparation method thereof, and a polyimide sealing ring and a preparation method thereof.
Background
The sealing ring is an annular sealing element with a notch, the sealing ring is placed in an annular groove of the sleeve, the sleeve and the shaft rotate together, and the sealing ring is tightly abutted against the inner hole wall of the static element by the elasticity of the pressed notch, so that the sealing effect can be achieved. The seal ring is a general term for a dynamic ring and a static ring, and is the most important element constituting a mechanical seal. The service performance and the service life of the mechanical seal are determined to a great extent by the sealing ring.
The seal ring is generally made of metal, such as alloy steel, alloy cast iron, and the like. However, the metal seal ring is worn obviously, even worn out, and simultaneously can cause the abrasion of the sleeve and the ring groove, and the metal seal ring has no self-lubricating property and needs to be assisted by lubricating oil and the like.
In recent years, polymer type seal rings such as polytetrafluoroethylene, polyimide, and the like have appeared. The polytetrafluoroethylene sealing ring changes along with high and low temperature in the use process, the dimensional stability of the polytetrafluoroethylene sealing ring can be changed to a large extent, and therefore sealing failure is caused. The polyimide has excellent mechanical property, high and low temperature resistance and good dimensional stability, and has wide application in the fields of microelectronics, aerospace and the like. However, the direct use of the self-lubricating wear-resistant material as a high-performance self-lubricating wear-resistant material still has the problem of higher friction coefficient, and the wear resistance is to be further improved. Moreover, various properties of polyimide are mutually influenced, for example, when the wear resistance is improved by adding a wear-resistant agent, other properties such as stability, toughness, heat resistance and the like are easily influenced, and how to balance and give consideration to various properties is also a difficult problem in solving the problem of wear resistance.
Disclosure of Invention
In view of the above, the present invention provides a polyimide and a method for preparing the same, and a polyimide sealing ring and a method for preparing the same. The polyimide provided by the invention can effectively improve the wear resistance of the sealing ring, and keeps good heat resistance, lower thermal expansion coefficient and higher toughness.
The invention provides a preparation method of polyimide, which comprises the following steps:
a) mixing and reacting a compound shown in the formula (1), graphene oxide and a solvent to form amino modified graphene oxide;
b) mixing and reacting the amino modified graphene oxide with a dianhydride monomer of formula (2) and a diamine monomer of formula (3) to form polyamic acid;
c) carrying out imidization reaction on the polyamic acid to obtain polyimide;
Figure BDA0003115320870000021
preferably, in the step a), the mass ratio of the graphene oxide to the compound of the formula (1) is 1.00 to (0.85-1.00).
Preferably, in the step a), the reaction temperature is 50-70 ℃ and the reaction time is 12-24 h.
Preferably, in the step b), the molar ratio of the diamine monomer of the formula (3) to the dianhydride monomer of the formula (2) is 1.00 to (0.99-1.01);
the mass ratio of the graphene oxide in the polyimide is 0.3% -2.5%.
Preferably, in the step c), the imidization reaction is a chemical imidization reaction;
the imidization reaction is carried out under the action of an imidization catalyst and a dehydrating agent;
the imidization catalyst is selected from one or more of methylamine, ethylamine, trimethylamine, triethylamine, propylamine, tripropylamine, butylamine, tributylamine, tert-butylamine, hexylamine, triethanolamine, N-dimethylethanolamine, N-diethylethanolamine, triethylenediamine, N-methylpyrrolidine, N-ethylpyrrolidine, aniline, benzylamine, toluidine, trichloroaniline, pyridine, collidine, lutidine, picoline, quinoline, isoquinoline and valerolactone;
the dehydrating agent is selected from one or more of acetic anhydride, propionic anhydride, butyric anhydride and benzoic anhydride.
Preferably, in the step c), the temperature of the imidization reaction is 10-50 ℃ and the time is 2-8 h.
The invention also provides polyimide prepared by the preparation method in the technical scheme.
The invention also provides a polyimide sealing ring, which is prepared by processing polyimide; the polyimide is the polyimide in the technical scheme.
The invention also provides a preparation method of the polyimide sealing ring in the technical scheme, which comprises the following steps:
s1, carrying out mould pressing, curing and forming on the polyimide molding powder to obtain a polyimide pipe;
s2, machining the polyimide pipe to obtain a polyimide sealing ring;
the polyimide molding powder is formed from the polyimide according to claim 7.
Preferably, in step S1, the conditions for mold pressing, curing and forming are as follows: the pressure is 20-100 MPa, the temperature is 370-450 ℃, and the pressure maintaining time is 100-150 min.
The compound of formula (1) is adopted to react with graphene oxide to form compound modified graphene oxide of formula (1); and then reacting the modified graphene oxide with a dianhydride monomer of a formula (2) and a diamine monomer of a formula (3) to finally prepare the polyimide. Wherein the surface of the graphene oxide contains C-O-C group, and-NH at one end of the compound of the formula (1)2C-O is subjected to ring opening to form C-OH and C-N bonds, so that the compound (1) modified graphene oxide is prepared; the dianhydride monomer of the formula (2) reacts with the diamine monomer of the formula (3) to form polyimide, meanwhile, the compound (1) modified graphene oxide is uniformly dispersed in a polyimide system and is combined with the polyimide through covalent bonds and intermolecular forces, so that the polyimide can generate good self-lubrication and wear resistance while maintaining good heat resistance and low thermal expansion coefficient, and the dianhydride monomer of the formula (2) and the diamine monomer of the formula (3) both contain trifluoromethyl and ether bonds and have certain structural distribution, so that the toughness of the polyimide can be improved.
The experimental result shows that the friction coefficient of the polyimide prepared by the invention is below 0.44,the wear rate is 11.5mm3Less than N.m, 5% thermal weight loss temperature of 520 deg.C or higher, and linear expansion coefficient of 4.1 × 10-5Hereinafter, the elongation at break is 5.9% or more, and the steel sheet exhibits good wear resistance, good heat resistance, a low thermal expansion coefficient, and high toughness.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a TGA profile of the product obtained in example 3;
FIG. 2 is a graph showing the linear thermal expansion test of the product obtained in example 3;
FIG. 3 is a graph showing a frictional wear test of the product obtained in example 3.
Detailed Description
The invention provides a preparation method of polyimide, which comprises the following steps:
a) mixing and reacting a compound shown in the formula (1), graphene oxide and a solvent to form amino modified graphene oxide;
b) mixing and reacting the amino modified graphene oxide with a dianhydride monomer of formula (2) and a diamine monomer of formula (3) to form polyamic acid;
c) carrying out imidization reaction on the polyamic acid to obtain polyimide;
Figure BDA0003115320870000041
the compound of formula (1) is adopted to react with graphene oxide to form amino modified graphene oxide; and then reacting the modified graphene oxide with a dianhydride monomer of a formula (2) and a diamine monomer of a formula (3) to finally prepare the polyimide. The polyimide prepared by the method can generate good self-lubrication and wear resistance while maintaining good heat resistance, lower thermal expansion coefficient and higher toughness.
With respect to step a): and (2) mixing and reacting the compound of the formula (1), graphene oxide and a solvent to form amino modified graphene oxide.
In the present invention, the sources of the compound of formula (1) and Graphene Oxide (GO) are not particularly limited, and may be generally commercially available or prepared according to a conventional preparation method well known to those skilled in the art. In the invention, the mass ratio of the graphene oxide to the compound of the formula (1) is preferably 1.00 to (0.85-1.00); in some embodiments of the invention, the mass ratio is 1.00: 0.85.
In the present invention, the solvent is preferably an organic solvent. The organic solvent is preferably one or more of N, N-dimethylacetamide (i.e., DMAC), N-dimethylformamide (i.e., DMF), and N-methylpyrrolidone (i.e., NMP). In the invention, the preferable dosage ratio of the graphene oxide to the solvent is (0.1-0.6) g: 60 mL; in some embodiments of the invention, the ratio is 0.1 g: 60mL, 0.2 g: 60mL, 0.3 g: 60mL, 0.5 g: 60mL, or 0.6 g: 60 mL.
In the present invention, the reaction is preferably carried out under a protective gas atmosphere. The type of the protective gas is not particularly limited in the present invention, and may be a conventional protective gas known to those skilled in the art, such as nitrogen or argon.
In the invention, the reaction temperature is preferably 50-70 ℃, and more preferably 60 ℃. The reaction time is preferably 12-24 h, and more preferably 24 h. The surface of the graphene oxide contains C-O-C groups, and after the compound of the formula (1) is added, one end of the compound is provided with-NH2C-O is subjected to ring opening to form C-OH and C-N bonds, and then the compound (1) modified graphene oxide is prepared.
In the present invention, the step of the above-mentioned material mixing reaction is preferably:
a1) firstly, dispersing graphene oxide in a solvent to obtain a GO suspension;
a2) and (3) mixing the GO suspension with a compound of the formula (1) for reaction to form amino modified graphene oxide.
In step a1), the dispersion is preferably ultrasonic dispersion. In step a2), the mixing reaction is preferably carried out under stirring.
According to the invention, after the compound of formula (1), graphene oxide and a solvent are mixed and reacted, amino modified graphene oxide is formed in a solution system, namely, an amino modified graphene oxide solution is obtained. According to the invention, the amino-modified graphene oxide solution is preferably not treated to extract the amino-modified graphene oxide, but rather, the subsequent reaction is directly carried out in the form of the amino-modified graphene oxide solution.
With respect to step b): and (3) mixing and reacting the amino modified graphene oxide with a dianhydride monomer of formula (2) and a diamine monomer of formula (3) to form polyamic acid.
In the present invention, the molar ratio of the diamine monomer of formula (3) to the dianhydride monomer of formula (2) is preferably 1.00: (0.99 to 1.01). The diamine monomer of formula (3) and the dianhydride monomer of formula (2) are not particularly limited in the present invention, and may be prepared by general commercial products or preparation methods known to those skilled in the art.
In the present invention, in the mixing process, it is preferable to further add a solvent, that is, a dianhydride monomer of formula (2), a diamine monomer of formula (3), and a solvent are mixed and reacted with the amino-modified graphene oxide solution obtained in step a) to obtain a polyamic acid. Wherein, the solvent is preferably an organic solvent, and the organic solvent is preferably one or more of N, N-dimethylacetamide (i.e. DMAC), N-dimethylformamide (i.e. DMF) and N-methylpyrrolidone (i.e. NMP). In the invention, the preferable dosage ratio of the dianhydride monomer of the formula (2) to the solvent is (15-35) mmol: 60 mL.
In the invention, the reaction temperature is not particularly limited, and the reaction can be carried out at room temperature, specifically 15-35 ℃. The reaction time is preferably 12-24 h. After the reaction, polyamic acid is formed in the system to obtain polyamic acid solution.
With respect to step c): and carrying out imidization reaction on the polyamic acid to obtain polyimide.
In the present invention, the imidization reaction is preferably a chemical imidization reaction. The imidization reaction is carried out under the action of an imidization catalyst and a dehydrating agent.
Wherein:
the imidization catalyst is preferably one or more of methylamine, ethylamine, trimethylamine, triethylamine, propylamine, tripropylamine, butylamine, tributylamine, tert-butylamine, hexylamine, triethanolamine, N-dimethylethanolamine, N-diethylethanolamine, triethylenediamine, N-methylpyrrolidine, N-ethylpyrrolidine, aniline, benzylamine, toluidine, trichloroaniline, pyridine, collidine, lutidine, picoline, quinoline, isoquinoline and valerolactone. The molar ratio of the imidization catalyst to the dianhydride monomer of formula (2) is preferably (0.5-1.5) to 1.
The dehydrating agent is preferably one or more of acetic anhydride, propionic anhydride, butyric anhydride and benzoic anhydride. The molar ratio of the dehydrating agent to the dianhydride monomer of the formula (2) is preferably (0.6-1.5) to 1.
In the invention, the temperature of the imidization reaction is preferably 10-50 ℃, and more preferably 40 ℃. The time of the imidization reaction is preferably 2-8 h, and more preferably 4 h. After the imidization reaction, polyimide is formed in the system.
The reaction route for the reaction of dianhydride monomer with diamine monomer to form polyimide is shown in the following formula:
Figure BDA0003115320870000061
in the present invention, after the imidization reaction, the following post-treatment is preferably further performed: alcohol solvent is adopted for alcohol precipitation, and precipitated precipitate is washed and dried to obtain the polyimide. Among them, the drying is preferably vacuum drying. The drying temperature is preferably 80-120 ℃; the drying time is preferably 2-6 h. In the present invention, after the above-mentioned drying, cooling and pulverization treatment may be further carried out to obtain a polyimide molding powder.
In the present invention, the obtained polyimide is actually a polyimide composite, specifically, in the process of forming polyimide by imidization, the compound (1) modified graphene oxide obtained in step a) is uniformly dispersed in a polyimide system, and the compound (1) modified graphene oxide and polyimide are bonded by covalent bonds and intermolecular forces, so as to obtain the polyimide composite.
In the invention, the mass ratio of the graphene oxide to the whole polyimide product in the obtained polyimide product is preferably 0.3 wt% -2.5 wt%, and the amount of the graphene oxide added in actual feeding can be reversely deduced according to the ratio. The polyimide can have better wear resistance and maintain good heat resistance, stability and toughness only at the above proportion, and if the proportion is too low or too high, the product performance is deteriorated. In some embodiments of the invention, the mass ratio is 0.3 wt%, 0.5 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%. In the present invention, the mass ratio is more preferably 0.5 to 2.5 wt%, and most preferably 1.0 to 2.0 wt%.
The invention also provides polyimide prepared by the preparation method in the technical scheme.
The invention also provides a polyimide sealing ring, which is prepared by processing polyimide; the polyimide is the polyimide in the technical scheme.
The invention also provides a preparation method of the polyimide sealing ring in the technical scheme, which comprises the following steps:
s1, carrying out mould pressing, curing and forming on the polyimide molding powder to obtain a polyimide pipe;
s2, machining the polyimide pipe to obtain a polyimide sealing ring;
the polyimide molding powder is formed by the polyimide in the technical scheme.
In step S1, the conditions for the mold pressing, curing and molding are preferably as follows: the pressure is 20-100 MPa, the temperature is 370-450 ℃, and the pressure maintaining time is 100-150 min. In some embodiments of the present invention, the conditions for the press curing molding are: the pressure is 50MPa, the temperature is 400 ℃, and the pressure maintaining time is 120 min. In the step S2, the machining method is not particularly limited, and may be any conventional machining method known to those skilled in the art, and various shapes and sizes of the sealing ring may be obtained by machining.
The compound of formula (1) is adopted to react with graphene oxide to form compound modified graphene oxide of formula (1); and then reacting the modified graphene oxide with a dianhydride monomer of a formula (2) and a diamine monomer of a formula (3) to finally prepare the polyimide. Wherein the surface of the graphene oxide contains C-O-C group, and-NH at one end of the compound of the formula (1)2C-O is subjected to ring opening to form C-OH and C-N bonds, so that the compound (1) modified graphene oxide is prepared; the dianhydride monomer of the formula (2) reacts with the diamine monomer of the formula (3) to form polyimide, meanwhile, the compound (1) modified graphene oxide is uniformly dispersed in a polyimide system and is combined with the polyimide through covalent bonds and intermolecular forces, so that the polyimide can generate good self-lubrication and wear resistance while maintaining good heat resistance and low thermal expansion coefficient, and the dianhydride monomer of the formula (2) and the diamine monomer of the formula (3) both contain trifluoromethyl and ether bonds and have certain structural distribution, so that the toughness of the polyimide can be improved.
The experimental result shows that the friction coefficient of the polyimide prepared by the invention is below 0.44, and the wear rate is 11.5mm3Less than N.m, 5% thermal weight loss temperature of 520 deg.C or higher, and linear expansion coefficient of 4.1 × 10-5Hereinafter, the elongation at break is 5.9% or more, and the steel sheet exhibits good wear resistance, good heat resistance, a low thermal expansion coefficient, and high toughness.
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims. In the following examples, room temperature means 25 ℃.
Example 1
1. Preparation of polyimide
S1, adding 0.3g of GO into 60mL of DMAC solvent, and carrying out ultrasonic treatment for 1 hour to obtain GO suspension. Then, the dispersed GO suspension was poured into a reaction apparatus equipped with a magnetic stirrer under nitrogen atmosphere, 0.255g of the compound of formula (1) was added, and stirring was continued at 60 ℃ for 24 hours to obtain an amino-modified graphene oxide solution.
S2, adding 16.36mmol of diamine monomer (3), 16.36mmol of dianhydride monomer (2) and 60mL of DMAC solvent into the reaction device in the step S1, mixing, stirring, performing microwave radiation for 2min, and reacting at room temperature for 24h to obtain a polyamic acid solution.
S3, 13.57mmol of acetic anhydride and 13.57mmol of triethylamine are added to the polyamic acid solution, and the mixture is reacted at 40 ℃ for 4 hours to obtain a polyimide solution. Precipitating by adopting 120mL of ethanol, separating out yellow precipitate, washing by using the ethanol for 2 times, drying for 3 hours at 100 ℃ under the vacuum condition, and cooling to obtain the polyimide with the GO content of 1.5 wt%.
2. Preparation of polyimide seal ring
The obtained polyimide was pulverized to obtain a polyimide molding powder. Molding and curing the polyimide molding powder under the following conditions: and keeping the pressure at 50MPa and 400 ℃ for 120min to obtain the polyimide pipe. And (4) machining the obtained polyimide pipe to obtain the sealing ring meeting the size requirement.
Example 2
1. Preparation of polyimide
S1, adding 0.3g of GO into 60mL of DMAC solvent, and carrying out ultrasonic treatment for 1 hour to obtain GO suspension. Then, the dispersed GO suspension was poured into a reaction apparatus equipped with a magnetic stirrer under nitrogen atmosphere, 0.255g of the compound of formula (1) was added, and stirring was continued at 60 ℃ for 24 hours to obtain an amino-modified graphene oxide solution.
S2, adding 25.69mmol of diamine monomer (3), 25.69mmol of dianhydride monomer (2) and 60mL of DMAC solvent into the reaction device in the step S1, mixing, stirring and carrying out microwave radiation for 2min, and then carrying out reaction for 24h at room temperature to obtain a polyamic acid solution.
S3, adding 15.41mmol acetic anhydride and 15.41mmol triethylamine to the polyamic acid solution, and reacting at 40 ℃ for 4h to obtain a polyimide solution. Precipitating by adopting 120mL of ethanol, separating out yellow precipitate, washing by using the ethanol for 2 times, drying for 3 hours at 100 ℃ under the vacuum condition, and cooling to obtain the polyimide with the GO content of 1.0 wt%.
2. Preparation of polyimide seal ring
The obtained polyimide was pulverized to obtain a polyimide molding powder. Molding and curing the polyimide molding powder under the following conditions: and keeping the pressure at 50MPa and 400 ℃ for 120min to obtain the polyimide pipe. And (4) machining the obtained polyimide pipe to obtain the sealing ring meeting the size requirement.
Example 3
1. Preparation of polyimide
S1, adding 0.1g of GO into 60mL of DMAC solvent, and carrying out ultrasonic treatment for 1 hour to obtain GO suspension. Then, the dispersed GO suspension was poured into a reaction apparatus equipped with a magnetic stirrer under nitrogen atmosphere, 0.085g of the compound of formula (1) was added, and stirring was continued at 60 ℃ for 24 hours to obtain an amino-modified graphene oxide solution.
S2, adding 28.32mmol of diamine monomer (3), 28.32mmol of dianhydride monomer (2) and 60mL of DMAC solvent into the reaction device in the step S1, mixing, stirring and carrying out microwave radiation for 2min, and then carrying out reaction for 24h at room temperature to obtain a polyamic acid solution.
S3, adding 17.35mmol acetic anhydride and 17.35mmol triethylamine to the polyamic acid solution, and reacting at 40 ℃ for 4h to obtain a polyimide solution. Precipitating by adopting 120mL of ethanol, separating out yellow precipitate, washing by using the ethanol for 2 times, drying for 3 hours at 100 ℃ under the vacuum condition, and cooling to obtain the polyimide with the GO content of 0.3 wt%.
2. Preparation of polyimide seal ring
The obtained polyimide was pulverized to obtain a polyimide molding powder. Molding and curing the polyimide molding powder under the following conditions: and keeping the pressure at 50MPa and 400 ℃ for 120min to obtain the polyimide pipe. And (4) machining the obtained polyimide pipe to obtain the sealing ring meeting the size requirement.
Example 4
1. Preparation of polyimide
S1, adding 0.2g of GO into 60mL of DMAC solvent, and carrying out ultrasonic treatment for 1 hour to obtain GO suspension. Then, the dispersed GO suspension was poured into a reaction apparatus equipped with a magnetic stirrer under nitrogen atmosphere, 0.17g of the compound of formula (1) was added, and stirring was continued at 60 ℃ for 24 hours to obtain an amino-modified graphene oxide solution.
S2, adding 34.73mmol of diamine monomer (3), 34.57mmol of dianhydride monomer (2) and 60mL of DMAC solvent into the reaction device in the step S1, mixing, stirring, performing microwave radiation for 2min, and reacting at room temperature for 24h to obtain a polyamic acid solution.
S3, 20.84mmol of acetic anhydride and 20.84mmol of triethylamine are added to the polyamic acid solution, and the mixture is reacted at 40 ℃ for 4 hours to obtain a polyimide solution. Precipitating by adopting 120mL of ethanol, separating out yellow precipitate, washing by using the ethanol for 2 times, drying for 3 hours at 100 ℃ under the vacuum condition, and cooling to obtain the polyimide with the GO content of 0.5 wt%.
2. Preparation of polyimide seal ring
The obtained polyimide was pulverized to obtain a polyimide molding powder. Molding and curing the polyimide molding powder under the following conditions: and keeping the pressure at 50MPa and 400 ℃ for 120min to obtain the polyimide pipe. And (4) machining the obtained polyimide pipe to obtain the sealing ring meeting the size requirement.
Example 5
1. Preparation of polyimide
S1, adding 0.5g of GO into 60mL of DMAC solvent, and carrying out ultrasonic treatment for 1 hour to obtain GO suspension. Then, the dispersed GO suspension was poured into a reaction apparatus equipped with a magnetic stirrer under nitrogen atmosphere, 0.425g of the compound of formula (1) was added, and stirring was continued at 60 ℃ for 24 hours to obtain an amino-modified graphene oxide solution.
S2, adding 21.00mmol of diamine monomer (3), 21.00mmol of dianhydride monomer (2) and 60mL of DMAC solvent into the reaction device in the step S1, mixing, stirring and carrying out microwave radiation for 2min, and then carrying out reaction for 24h at room temperature to obtain a polyamic acid solution.
S3, adding 12.6mmol acetic anhydride and 12.6mmol triethylamine to the polyamic acid solution, and reacting at 40 ℃ for 4h to obtain the polyimide solution. Precipitating by adopting 120mL of ethanol, separating out yellow precipitate, washing by using the ethanol for 2 times, drying for 3 hours at 100 ℃ under the vacuum condition, and cooling to obtain the polyimide with the GO content of 2.0 wt%.
2. Preparation of polyimide seal ring
The obtained polyimide was pulverized to obtain a polyimide molding powder. Molding and curing the polyimide molding powder under the following conditions: and keeping the pressure at 50MPa and 400 ℃ for 120min to obtain the polyimide pipe. And (4) machining the obtained polyimide pipe to obtain the sealing ring meeting the size requirement.
Example 6
1. Preparation of polyimide
S1, adding 0.6g of GO into 60mL of DMAC solvent, and carrying out ultrasonic treatment for 1 hour to obtain GO suspension. Then, the dispersed GO suspension was poured into a reaction apparatus equipped with a magnetic stirrer under nitrogen atmosphere, 0.51g of the compound of formula (1) was added, and stirring was continued at 60 ℃ for 24 hours to obtain an amino-modified graphene oxide solution.
S2, adding 19.37mmol of diamine monomer (3), 19.37mmol of dianhydride monomer (2) and 60mL of DMAC solvent into the reaction device in the step S1, mixing, stirring and carrying out microwave radiation for 2min, and then carrying out reaction for 24h at room temperature to obtain a polyamic acid solution.
S3, adding 15.49mmol acetic anhydride and 15.49mmol triethylamine to the polyamic acid solution, and reacting at 40 ℃ for 4h to obtain the polyimide solution. Precipitating by adopting 120mL of ethanol, separating out yellow precipitate, washing by using the ethanol for 2 times, drying for 3 hours at 100 ℃ under the vacuum condition, and cooling to obtain the polyimide with the GO content of 2.5 wt%.
2. Preparation of polyimide seal ring
The obtained polyimide was pulverized to obtain a polyimide molding powder. Molding and curing the polyimide molding powder under the following conditions: and keeping the pressure at 50MPa and 400 ℃ for 120min to obtain the polyimide pipe. And (4) machining the obtained polyimide pipe to obtain the sealing ring meeting the size requirement.
Example 7
The polyimide seal rings obtained in examples 1 to 6 were subjected to performance tests, and the results are shown in Table 1.
TABLE 1 Properties of polyimide seal rings obtained in examples 1 to 6
Figure BDA0003115320870000111
The performance test graphs of the product obtained in example 3 are shown in fig. 1-3, fig. 1 is a TGA graph of the product obtained in example 3, fig. 2 is a linear thermal expansion test graph of the product obtained in example 3, and fig. 3 is a friction wear test graph of the product obtained in example 3.
As can be seen from the test results in Table 1, the friction coefficient of the polyimide prepared by the present invention is below 0.44, and the wear rate is 11.5mm3Less than N.m, 5% thermal weight loss temperature of 520 deg.C or higher, and linear expansion coefficient of 4.1 × 10-5Hereinafter, the elongation at break is 5.9% or more, and the steel sheet exhibits good wear resistance, good heat resistance, a low thermal expansion coefficient, and high toughness. Wherein, when the proportion of the graphene oxide in the polyimide product is 0.5 wt% to 2.5 wt% (corresponding to examples 1-2,4-6), the comprehensive performance of the product can be further improved, the friction coefficient of the product is reduced to be below 0.38, and the wear rate is 10.8mm3Less than N.m, 5% thermal weight loss temperature over 524 deg.C, and linear expansion coefficient of 4.0 × 10-5The elongation at break is 6.1% or more. When the proportion of the graphene oxide in the polyimide product is 1.0 wt% to 2.0 wt% (corresponding to examples 1-2 and 5), the wear resistance of the product can be further remarkably improved, the friction coefficient of the product is reduced to be below 0.27, and the wear rate is 6.5mm3V (N.m) or less; simultaneously maintains good heat resistance, stability and toughness, the 5 percent thermal weight loss temperature is above 528 ℃, and the linear expansion coefficient is 4.0 multiplied by 10-5The elongation at break is 6.1% or more.
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A preparation method of polyimide is characterized by comprising the following steps:
a) mixing and reacting a compound shown in the formula (1), graphene oxide and a solvent to form amino modified graphene oxide;
b) mixing and reacting the amino modified graphene oxide with a dianhydride monomer of formula (2) and a diamine monomer of formula (3) to form polyamic acid;
c) carrying out imidization reaction on the polyamic acid to obtain polyimide;
Figure FDA0003115320860000011
2. the preparation method of claim 1, wherein in the step a), the mass ratio of the graphene oxide to the compound of formula (1) is 1.00: 0.85-1.00.
3. The preparation method according to claim 1, wherein in the step a), the reaction temperature is 50-70 ℃ and the reaction time is 12-24 h.
4. The preparation method according to claim 1, wherein in the step b), the molar ratio of the diamine monomer of the formula (3) to the dianhydride monomer of the formula (2) is 1.00 to (0.99-1.01);
the mass ratio of the graphene oxide in the polyimide is 0.3% -2.5%.
5. The method according to claim 1, wherein in step c), the imidization reaction is a chemical imidization reaction;
the imidization reaction is carried out under the action of an imidization catalyst and a dehydrating agent;
the imidization catalyst is selected from one or more of methylamine, ethylamine, trimethylamine, triethylamine, propylamine, tripropylamine, butylamine, tributylamine, tert-butylamine, hexylamine, triethanolamine, N-dimethylethanolamine, N-diethylethanolamine, triethylenediamine, N-methylpyrrolidine, N-ethylpyrrolidine, aniline, benzylamine, toluidine, trichloroaniline, pyridine, collidine, lutidine, picoline, quinoline, isoquinoline and valerolactone;
the dehydrating agent is selected from one or more of acetic anhydride, propionic anhydride, butyric anhydride and benzoic anhydride.
6. The method according to claim 1 or 5, wherein the imidization reaction is carried out at a temperature of 10 to 50 ℃ for 2 to 8 hours in step c).
7. A polyimide produced by the production method according to any one of claims 1 to 6.
8. A polyimide sealing ring is prepared by processing polyimide; wherein the polyimide is the polyimide according to claim 7.
9. A method for preparing the polyimide seal ring according to claim 8, comprising:
s1, carrying out mould pressing, curing and forming on the polyimide molding powder to obtain a polyimide pipe;
s2, machining the polyimide pipe to obtain a polyimide sealing ring;
the polyimide molding powder is formed from the polyimide according to claim 7.
10. The method according to claim 9, wherein in step S1, the conditions for mold pressing, curing and forming are as follows: the pressure is 20-100 MPa, the temperature is 370-450 ℃, and the pressure maintaining time is 100-150 min.
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