CN109880096B

CN109880096B - Polyimide foam and its preparation method and application

Info

Publication number: CN109880096B
Application number: CN201910169797.0A
Authority: CN
Inventors: 王旭; 欧安平
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2019-03-06
Filing date: 2019-03-06
Publication date: 2020-04-21
Anticipated expiration: 2039-03-06
Also published as: CN109880096A

Abstract

The invention provides a polyimide foam, a preparation method and application thereof, and belongs to the technical field of polymer materials. The invention provides a preparation method of polyimide foam, which comprises the following steps: mixing a glue solution containing polyester ammonium salt oligomer and aromatic bismaleimide, and removing the solvent to obtain a foaming precursor body; foaming, curing and heat treatment to obtain polyimide foam. In this method, the cross-linking curing reaction of aromatic bismaleimide is carried out simultaneously with the imidization process of polyimide, which realizes the hybridization enhancement at the molecular scale and forms an interwoven thermoplastic-thermosetting polymer chain network. , endows the foam with strength and toughness; the aromatic bismaleimide makes the obtained polyimide foam smaller and uniform, improves the mechanical properties of the polyimide foam, and maintains heat resistance; The obtained polyimide foam has both good mechanical properties and heat resistance.

Description

Polyimide foam and preparation method and application thereof

Technical Field

The invention belongs to the technical field of high polymer materials, and particularly relates to polyimide foam and a preparation method and application thereof.

Background

The polymer foam material is widely applied to the industries of construction, transportation, home furnishing, vehicles, insulating materials, packaging materials, electric appliances, sports facilities, electronic products, chemistry, textile and the like due to the characteristics of light weight, good damping property, high specific strength, heat insulation, sound absorption, easy processing and the like, but the biggest problems of the traditional polymer foam, such as polyethylene foam, polystyrene foam and polyurethane foam, are very low heat resistance and poor flame retardant property, and the defects limit the application of the traditional polymer foam in extreme environments.

Polyimide foam, as a high-performance foam, has excellent high and low temperature resistance (can resist-200 ℃ to 300 ℃), high-temperature heat insulation, dimensional stability, wave-transmitting performance and flame retardant performance compared with the traditional polymer foam material, and therefore, the polyimide foam is applied to many extreme environments, such as heat insulation materials of marine ships and protective covers of space radars.

There are currently two main methods for preparing Polyimide (PI) foams: a method is that dianhydride and diamine form polyamic acid in polar aprotic solvent, get polyamic acid solid after removing most solvent, then pulverize into homogeneous powder, place in oven and foam, the polyimide foam that the pellet adheres together and forms the block at higher temperature that get, the foam density that this method prepares is too high, and the adhesion among the pellet of foaming is relatively bad, the actual use of the foam is not high; the other method is that dianhydride and diamine form polyester ammonium salt, desolventization is carried out to prepare powder, and then the powder is foamed by microwave or thermal foaming to prepare polyimide foam. In contrast, the second method is more beneficial to large-scale industrial production and is also the main production process method of PI foam adopted at present.

At present, aiming at the defect of poor mechanical property of the polyimide foam obtained by the second method, the common modification method comprises the following steps: one measure is to add nano-fillers, such as graphene oxide (CN20131293520.1), organoclay (CN201010569307.5) or carbon fiber powder (CN201510398367.8), because of the foaming of powder, the viscosity of the matrix rapidly increases after the polyimide reaction, and excessive addition of fillers will cause failure of foaming, while the addition of a smaller amount of fillers does not significantly improve the mechanical and thermal properties of the foam, and is not conducive to industrial production. Another approach is to use blocking agent to block, such as polyisocyanate as blocking agent (CN201710661250.3), and improve the mechanical properties of polyimide foam by chemical crosslinking method. However, the method often introduces too many aliphatic structures, which greatly damages the heat resistance of the foam, and meanwhile, the polyimide foam after chemical crosslinking needs to be carried out under high temperature (more than 310 ℃) in the whole foaming process, the post-curing temperature is higher, a special mold is needed, the preparation efficiency is very low, and the method is not beneficial to industrial production.

In view of this, the invention is particularly proposed.

Disclosure of Invention

A first object of the present invention is to provide a method for preparing polyimide foam, which overcomes or at least partially solves the above-mentioned problems.

The second object of the present invention is to provide a polyimide foam obtained by the above preparation method, which has smaller cells and uniform blastholes.

The third purpose of the invention is to provide the application of the polyimide foam obtained by the preparation method in electronic products, carrier rockets, aviation, ships or railway locomotives, and the obtained polyimide foam can be continuously used in high-temperature (more than 250 ℃) environment and meets the use requirement of the foam material in extreme environment.

According to a first aspect of the present invention, there is provided a method for preparing a polyimide foam, comprising the steps of:

(A) providing glue solution containing a polyester ammonium salt oligomer, uniformly mixing the glue solution containing the polyester ammonium salt oligomer with aromatic bismaleimide, and removing a solvent to obtain foaming precursor powder;

(B) and (B) foaming the foaming precursor powder obtained in the step (A), then curing, and then carrying out heat treatment to obtain the polyimide foam.

Preferably, the aromatic dianhydride is added into a mixed solvent of alcohol and ether, the aromatic dianhydride and the alcohol are subjected to esterification reaction, and then the aromatic diamine is added to obtain a glue solution containing the polyester ammonium salt oligomer.

Preferably, the aromatic dianhydride is at least one of pyromellitic dianhydride, bisphenol a type diether dianhydride, 2,3,3',4' -biphenyl tetracarboxylic dianhydride, 3,3',4,4' -benzophenone tetracarboxylic dianhydride, 3,3',4,4' -triphenyldiether tetracarboxylic dianhydride, or hexafluoro dianhydride;

and/or the aromatic diamine is at least one of p-phenylenediamine, m-phenylenediamine, diaminodiphenyl methyl ether or diaminodiphenyl methane;

and/or, the alcohol is C₁-C₈Monohydric alcohol of (2), preferably C₁-C₄Further preferably at least one of methanol, ethanol or propanol;

and/or the ether is C₂-C₈Preferably tetrahydrofuran and/or dioxane.

Preferably, the molar ratio of the aromatic dianhydride to the aromatic diamine is 0.9-1.1: 1, preferably 1: 1.

preferably, in the step (a), the aromatic bismaleimide is at least one of N, N ' -m-phenylene bismaleimide, N ' - (1, 4-phenylene) bismaleimide, 4' -methylenebis (N-phenylmaleimide), 1, 2-phenylene-bis-maleimide or N, N- (4-methyl-1, 3-phenylene) bismaleimide.

Preferably, in the step (a), the content of the aromatic bismaleimide in the foaming precursor powder is 10% to 50% by mass, and preferably 20% to 40% by mass.

Preferably, in the step (B), the foaming temperature is 120-160 ℃, preferably 130-150 ℃;

and/or in the step (B), the foaming time is 10-60min, preferably 20-40 min.

Preferably, in step (B), the temperature of the heat treatment is 300-360 ℃, preferably 320-340 ℃;

and/or, in the step (B), the time of the heat treatment is 30-60min, preferably 40 min.

According to a second aspect of the present invention, there is provided a polyimide foam obtained by the above-mentioned production method.

According to a third aspect of the present invention, there is provided a use of the polyimide foam obtained by the above-mentioned production method in an electronic product, a carrier rocket, aviation, a ship or a railway locomotive.

The invention provides a preparation method of polyimide foam, which comprises the steps of uniformly mixing polyester ammonium salt oligomer and aromatic bismaleimide, removing a solvent to obtain foaming precursor powder, and then carrying out foaming and heat treatment to obtain the polyimide foam with light weight and high strength. In the method, the cross-linking curing reaction of the aromatic bismaleimide and the imidization process of the polyimide are synchronously carried out, so that the aromatic bismaleimide and the polyimide realize the hybridization enhancement of molecular scale; the bismaleimide resin is crosslinked while the imidization degree is increased in the heat treatment process, so that a mutually interlaced thermoplastic-thermosetting polymer chain network is formed, and the foam strength and toughness are endowed; the reactive cross-linked aromatic bismaleimide introduced in the foaming stage greatly improves the viscosity of a polymer matrix in the foaming stage, so that the obtained polyimide foam has smaller and uniform pores, and the mechanical property of the polyimide foam is greatly improved; the aromatic bismaleimide contains a large number of aromatic heterocyclic rings, so that the polyimide foam can keep the heat resistance; the polyimide foam obtained by the method of the invention can have good mechanical property and heat resistance. The whole foam preparation process has simple process and low cost and is beneficial to industrial production.

If the compression strain is 10%, the compression strength can be improved to 1MPa, and the polyimide foam is subjected to compression cycle test, and the result shows that when the maximum compression deformation is 40%, the resilience of more than 90% can be maintained after 30 cycles; the long-term use temperature is more than 250 ℃; the foam was subjected to high temperature insulation tests and found to have no significant increase in thermal diffusivity relative to that at 25 ℃ after the temperature was raised to 30 ℃.

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, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a scanning electron micrograph of a bismaleimide-containing polyimide foam obtained in example 1;

FIG. 2 is a scanning electron micrograph of a polyimide foam obtained in comparative example 1 without bismaleimide added thereto.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to examples and drawings, but those skilled in the art will understand that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

It should be noted that:

in the present invention, all the embodiments and preferred methods mentioned herein can be combined with each other to form a new technical solution, if not specifically stated.

In the present invention, all the technical features mentioned herein and preferred features may be combined with each other to form a new technical solution, if not specifically stated.

In the present invention, the percentage (%) or parts means the weight percentage or parts by weight with respect to the composition, if not otherwise specified.

In the present invention, the components referred to or the preferred components thereof may be combined with each other to form a novel embodiment, if not specifically stated.

In the present invention, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0.9 to 1.1" indicates that all real numbers between "0.9 to 1.1" have been listed herein and "0.9 to 1.1" is only a shorthand representation of the combination of these values.

The "ranges" disclosed herein may have one or more lower limits and one or more upper limits, respectively, in the form of lower limits and upper limits.

In the present invention, unless otherwise specified, the individual reactions or operation steps may be performed sequentially or may be performed in sequence. Preferably, the reaction processes herein are carried out sequentially.

Unless otherwise defined, technical and scientific terms used herein have the same meaning as is familiar to those skilled in the art. In addition, any methods or materials similar or equivalent to those described herein can also be used in the present invention.

The source of the glue solution containing the polyester ammonium salt oligomer is not limited and can be prepared by a method commonly used by a person skilled in the art. For example, the aromatic dianhydride is added into a mixed solvent of alcohol and ether, the aromatic dianhydride and the alcohol are subjected to esterification reaction, and then the aromatic diamine is added to obtain a glue solution containing the polyester ammonium salt oligomer.

The kind of the aromatic dianhydride is not limited, and aromatic dianhydrides commonly used by those skilled in the art can be used; for example, pyromellitic anhydride, bisphenol a type diether dianhydride, 2,3,3',4' -biphenyltetracarboxylic dianhydride, 3,3',4,4' -benzophenonetetracarboxylic dianhydride, 3,3',4,4' -triphenyldiether tetracarboxylic dianhydride, or hexafluoro dianhydride.

The kind of the aromatic diamine is not limited, and aromatic diamines commonly used by those skilled in the art may be used; for example, p-phenylenediamine, m-phenylenediamine, diaminoanisole or diaminodiphenylmethane.

The alcohol is not limited in kind, and C which is commonly used by those skilled in the art is used₁-C₈The monohydric alcohol solvent is used; can be selected as C₁-C₄For example, methanol, ethanol or propanol.

C₁-C₈The minimum and maximum carbon atom contents of the monoalcohols of (a) are indicated by a prefix, e.g. C₁-C₈The monohydric alcohol of (a) is an alcohol containing 1 to 8 carbon atoms and having one hydroxyl group, and may be linear or cyclic.

The ether is not limited in kind, and C which is commonly used by those skilled in the art is used₂-C₈An ether solvent of (a); for example tetrahydrofuran or dioxane.

C₂-C₈The minimum and maximum carbon atom contents of the ethers of (A) are indicated by a prefix, e.g. C₂-C₈The ether of (b) is an ether having 2 to 8 carbon atoms, and may be a linear ether or a cyclic ether.

It can be understood that the aromatic dianhydride is added into the mixed solvent of alcohol and ether, the aromatic dianhydride and alcohol are subjected to esterification reaction to obtain diacid diester, then the aromatic diamine is added, and the aromatic diamine and diacid diester are reacted to obtain glue solution containing polyester ammonium salt oligomer. The temperature of the esterification reaction is 50-80 ℃, and the time is 100-300 min; optionally, the temperature of the esterification reaction is 60-70 ℃, and the time is 150-. The reaction temperature of the aromatic diamine and the diacid diester is 20-50 ℃, and the reaction time is 1-6 h; optionally, the aromatic diamine is reacted with the diacid diester at a temperature of 30-40 ℃ for 2-4 hours.

It will be appreciated that the molar ratio of aromatic dianhydride to aromatic diamine may be any molar ratio commonly used by those skilled in the art, for example, the molar ratio of aromatic dianhydride to aromatic diamine is from 0.9 to 1.1: 1, optionally 1: 1.

the kind of the aromatic bismaleimide is not limited, and aromatic bismaleimide commonly used by those skilled in the art can be used; for example, N, N ' -m-phenylenebismaleimide, N, N ' - (1, 4-phenylene) bismaleimide, 4' -methylenebis (N-phenylmaleimide), 1, 2-phenylene-bis-maleimide or N, N- (4-methyl-1, 3-phenylene) bismaleimide.

The aromatic bismaleimide contains benzene rings, imide heterocyclic rings and has high crosslinking density, so that a cured product of the aromatic bismaleimide has excellent heat resistance, the Tg of the aromatic bismaleimide is generally higher than 250 ℃, meanwhile, the aromatic bismaleimide is endowed with high strength by high crosslinking degree, and the mechanical property of the foam can be effectively improved by adding the aromatic bismaleimide into polyimide foam.

The manner of removing the solvent is not limited, and may be performed in a manner well known to those skilled in the art; the method can be a mode of removing the solvent by rotary evaporation or a mode of removing the solvent by a vacuum oven, or a mode of drying under normal pressure, evaporating and drying or drying under reduced pressure. The temperature for removing the solvent can be in the range of 60-90 ℃, and can be selected in the range of 70-80 ℃; the time for removing the solvent can be within the range of 100-180min, and can be within the range of 120-150 min.

It is understood that the solvent is removed and then pulverized to obtain a foaming precursor powder. The particle size of the foaming precursor powder is not limited, and may be one known to those skilled in the art.

The foaming method is not limited, and a resistance heating oven can be used, wherein the foaming temperature is 120-160 ℃, and the foaming time is 10-60 min. Or a microwave oven can be used, wherein the power during foaming is 1000-; optionally, the power during foaming is 1500-.

The curing temperature and time are not limited, and those commonly used by those skilled in the art can be used; the curing temperature can be 180-220 ℃, and the curing time can be 100-150 min.

The gas atmosphere for the heat treatment is not limited, and may be a vacuum state, an air atmosphere, or a nitrogen atmosphere.

The temperature and time of the heat treatment are not limited, and the temperature and time of the heat treatment which are commonly used by those skilled in the art can be adopted; the temperature of the heat treatment can be 300-360 ℃, and the time of the heat treatment can be 30-60 min.

As a preferred embodiment, in the step (a), the content of the aromatic bismaleimide in the foaming precursor powder is 10% to 50% by mass.

Typically, but not by way of limitation, the aromatic bismaleimide may be present in the foaming precursor powder in an amount of 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% by weight.

If the mass percentage of the aromatic bismaleimide in the foaming precursor powder is less than 10 percent, too little bismaleimide resin is dispersed in a large amount of polyimide, a cross-linked network cannot be effectively formed, and the reinforcing effect on polyimide foam is not obvious; if the aromatic bismaleimide is contained in the foaming precursor powder in an amount of more than 50% by mass, a large amount of cross-linked structure is formed, and the entire foam becomes brittle due to too much cross-linking.

As a preferred embodiment, in the step (a), the content of the aromatic bismaleimide in the foaming precursor powder is 20% to 40% by mass.

The mass percentage of the aromatic bismaleimide in the foaming precursor powder is reasonably adjusted and optimized, so that the obtained polyimide foam can have good heat resistance and mechanical properties.

As a preferred embodiment, in the step (B), the foaming temperature is 130-150 ℃, and the foaming time is 20-40 min.

The polyimide foam with excellent comprehensive performance is obtained by reasonably adjusting and optimizing the foaming temperature and time.

As a preferred embodiment, in step (B), the temperature of the heat treatment is 320-340 ℃, and the time of the heat treatment is 40 min.

The polyimide foam with excellent comprehensive performance is obtained by reasonably adjusting and optimizing the temperature and time of heat treatment. The obtained brittle block foam can be subjected to heat treatment to obtain polyimide foam, and the polyimide foam is mainly characterized in that an imide degree is increased in the heat treatment process, and bismaleimide resin is crosslinked to form a mutually interlaced thermoplastic-thermosetting polymer chain network, so that the foam is endowed with strength and toughness.

The polyimide foam prepared by the preparation method has small and uniform pores, light weight and good mechanical property and heat resistance

The obtained polyimide foam can be continuously used in a high-temperature (more than 250 ℃) environment, meets the use requirement of the foam material in an extreme environment, and can be applied to electronic products, carrier rockets, aviation, ships or railway locomotives.

The technical solution of the present invention will be further described with reference to examples and comparative examples.

Example 1

A preparation method of polyimide foam comprises the following steps:

(1) providing glue solution containing polyester ammonium salt oligomer

Adding 32.22g of 3,3',4,4' -benzophenone tetracarboxylic dianhydride (0.1mol) into a mixed solvent of 15g of methanol and 30g of tetrahydrofuran, heating to 60 ℃ under the protection of nitrogen, refluxing for 150min to obtain a clear and transparent solution, reducing the temperature of the solution to 30 ℃, adding 19.83g of diaminodiphenylmethane (0.1mol), and continuously reacting for 30min to obtain a glue solution containing the polyester ammonium salt oligomer.

(2) Preparation of foaming precursor powder

Adding 5.7g of 4,4' -methylene bis (N-phenyl maleimide) into the glue solution containing the polyester ammonium salt oligomer obtained in the step (1), and continuously and violently stirring for 30min to obtain a uniform light brown transparent solution; and concentrating the solution, and removing the solvent to obtain foaming precursor powder.

(3) Foaming and heat treatment to obtain polyimide foam

Placing the foaming precursor powder obtained in the step (2) into a blowing oven at 150 ℃, and foaming for 30min at constant temperature to obtain block foam; and then, transferring the block foam into a 200 ℃ oven to be cured for 120min, and then transferring the block foam into a 320 ℃ high-temperature oven to be subjected to imidization treatment for 60min to obtain the light-weight high-strength polyimide foam.

Examples 2 to 7

Examples 2 to 7 differ from example 1 in the amount of 4,4' -methylenebis (N-phenylmaleimide) used in step (2), as shown in Table 1.

TABLE 1

Examples 8 to 16

Examples 8 to 16 are different from example 1 in the kind and amount of the aromatic bismaleimide different from example 1, and examples 8 to 16 each contain 10g of the aromatic bismaleimide, as shown in Table 2.

TABLE 2

Example 17

Example 17 is different from example 5 in the kind of aromatic dianhydride and 32.22g of 3,3',4,4' -benzophenone tetracarboxylic dianhydride (0.1mol) was replaced with 29.42g of 2,3,3',4' -biphenyl tetracarboxylic dianhydride (0.1 mol).

Example 18

A preparation method of polyimide foam comprises the following steps:

(1) providing glue solution containing polyester ammonium salt oligomer

29.42g of 2,3,3',4' -biphenyltetracarboxylic dianhydride (0.1mol) is added into a mixed solvent of 15g of methanol and 30g of tetrahydrofuran, the temperature is raised to 60 ℃ under the protection of nitrogen, the mixture is refluxed for 150min to obtain a clear and transparent solution, 19.83g of diaminodiphenylmethane (0.1mol) is added after the temperature of the solution is reduced to 30 ℃, and the reaction is continued for 30min to obtain a glue solution containing the polyester ammonium salt oligomer.

(2) Preparation of foaming precursor powder

Adding 15g of N, N' - (1, 4-phenylene) bismaleimide into the glue solution containing the polyester ammonium salt oligomer obtained in the step (1), and continuously and violently stirring for 30min to obtain a uniform light brown transparent solution; and concentrating the solution, and removing the solvent to obtain foaming precursor powder.

(3) Foaming and heat treatment to obtain polyimide foam

Example 19

A preparation method of polyimide foam comprises the following steps:

(1) providing glue solution containing polyester ammonium salt oligomer

(2) Preparation of foaming precursor powder

Adding 12g of N, N- (4-methyl-1, 3-phenylene) bismaleimide into the glue solution containing the polyester ammonium salt oligomer obtained in the step (1), and continuously and violently stirring for 30min to obtain a uniform light brown transparent solution; and concentrating the solution, and removing the solvent to obtain foaming precursor powder.

(3) Foaming and heat treatment to obtain polyimide foam

Comparative example 1

The difference between the comparative example 1 and the example 1 is that no aromatic bismaleimide is added into the glue solution containing the polyester ammonium salt oligomer, and the specific steps are as follows:

(1) providing glue solution containing polyester ammonium salt oligomer

(2) Preparation of foaming precursor powder

And (2) concentrating the glue solution containing the polyester ammonium salt oligomer obtained in the step (1), and removing the solvent to obtain foaming precursor powder.

(3) Foaming and heat treatment to obtain polyimide foam

Test example 1

The foams obtained in examples 1 to 19 and comparative example 1 were subjected to compression test and heat resistance test, and the results are shown in Table 3.

The density test method comprises the following steps: according to the national standard GB-T-6343-2009, a drainage method is used for testing.

The test method of the compressive strength at the compressive strain of 60 percent comprises the following steps: the foam samples were made to a size of 20mm by 20mm using an instron 5960 dual post bench tester with a compression rate of 5 mm/min.

The test method of the permanent deformation generated after 30 times of circulation comprises the following steps: according to the result obtained by the testing machine, the absolute value of the original height is subtracted from the height of the foam when the pressure is zero every time, and then the absolute value is divided by the original height, so that the permanent deformation of every time can be obtained.

The glass transition temperature test method comprises the following steps: the DSC curve of the foam is made by using a Perkinelmer DSC8000 differential scanning calorimeter, and the glass transition temperature of the material is obtained by the DSC curve.

The test method for the 5 wt% weight loss temperature is as follows: the thermal weight loss of the foam was measured using a relaxation-resistant TG209F1 thermogravimetric analyzer, and the 5 wt% weight loss temperature of the foam was calculated from the residual amount.

TABLE 3

The test results show that, as shown in examples 1 to 5, the content of bismaleimide has a great influence on the performance of polyimide foam, and the increase of the content can cause the increase of the foam density, the decrease of 5 wt% weight loss temperature, when the content is intermediate, the strength of the foam is higher and the permanent deformation generated after 30 times of cyclic compression is reduced, and when the content is 30 wt%, the comprehensive performance is best.

From examples 8 to 16, it is understood that, under the same addition amount, the kind of maleimide resin does not largely affect the foam, and the 5 wt% weight loss temperature in the system having a relatively rigid molecular chain is slightly increased.

From example 17, it is understood that the kind of dianhydride in the polyimide foam does not greatly affect the overall properties of the foam, but the 5 wt% weight loss temperature of the foam can be slightly raised, mainly the density and number of benzene rings in the molecular chain are increased, resulting in an increase in heat resistance.

The comparative example 1 shows that the introduction of bismaleimide resin can greatly improve the comprehensive performance of polyimide foam, firstly, the density of the foam is increased, the compression strength is greatly increased, the permanent deformation after 30 times of cyclic compression is greatly reduced, the elasticity of the foam is increased, and meanwhile, due to the cross-linking effect of the bismaleimide resin, a mutually penetrating and interweaving network structure is formed with linear polyimide molecular chains, so that the movement of the molecular chains of the material under a high-temperature condition is limited, the glass transition temperature of the foam can be effectively improved, and the service temperature of the foam is improved.

Test example 2

The foams obtained in example 1 and comparative example 1 were characterized separately and the electron micrographs obtained are shown in fig. 1 and 2.

FIG. 1 is a scanning electron micrograph of a bismaleimide-containing polyimide foam obtained in example 1.

As can be seen from FIGS. 1 and 2, after bismaleimide is added, the viscosity of the system at the foaming stage is greatly improved due to the formation of a cross-linking structure, the pore size of the cells is greatly reduced, the distribution is more uniform, and the pores on the cell walls are also significantly reduced, as shown in FIG. 1. The foam without bismaleimide resin had larger cells, uneven distribution and many holes in the cell walls, as shown in FIG. 2.

It should be understood that the contents not described in detail in the description of the above preparation method are common parameters that can be easily conceived by those skilled in the art, and thus the detailed description thereof may be omitted.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of polyimide foam is characterized by comprising the following steps:

(A) providing a glue solution containing a polyester ammonium salt oligomer, uniformly mixing the glue solution containing the polyester ammonium salt oligomer with aromatic bismaleimide, and removing a solvent to obtain a foaming precursor;

(B) and (B) foaming the foaming precursor obtained in the step (A), and then carrying out heat treatment to obtain the polyimide foam.

2. The preparation method according to claim 1, wherein the aromatic dianhydride is added to a mixed solvent of alcohol and ether, the aromatic dianhydride and the alcohol are subjected to esterification reaction, and then the aromatic diamine is added to obtain a glue solution containing the polyester ammonium salt oligomer.

3. The production method according to claim 2, wherein the aromatic dianhydride is at least one of pyromellitic dianhydride, bisphenol a type diether dianhydride, 2,3,3',4' -biphenyl tetracarboxylic dianhydride, 3,3',4,4' -benzophenone tetracarboxylic dianhydride, 3,3',4,4' -triphenylbisether tetracarboxylic dianhydride, or hexafluoro dianhydride;

and/or, the alcohol is C₁-C₈A monohydric alcohol of (a);

and/or the ether is C₂-C₈An ether of (a).

4. The method according to claim 3, wherein the alcohol is C₁-C₄A monohydric alcohol of (1).

5. The method according to claim 4, wherein the alcohol is at least one of methanol, ethanol, or propanol.

6. The process according to claim 3, wherein the ether is tetrahydrofuran and/or dioxane.

7. The method according to claim 2, wherein the molar ratio of the aromatic dianhydride to the aromatic diamine is 0.9-1.1: 1.

8. the method according to claim 7, wherein the molar ratio of the aromatic dianhydride to the aromatic diamine is 1: 1.

9. the production method according to any one of claims 1 to 8, wherein in the step (A), the aromatic bismaleimide is at least one of N, N ' -m-phenylenebismaleimide, N ' - (1, 4-phenylene) bismaleimide, 4' -methylenebis (N-phenylmaleimide), 1, 2-phenylene-bis-maleimide, or N, N- (4-methyl-1, 3-phenylene) bismaleimide.

10. The production method according to any one of claims 1 to 8, wherein in the step (A), the aromatic bismaleimide is contained in an amount of 10% to 50% by mass in the foam precursor.

11. The method according to claim 10, wherein in the step (a), the aromatic bismaleimide is present in the foam precursor in an amount of 20 to 40% by mass.

12. The process according to any one of claims 1 to 8, wherein the foaming temperature in step (B) is 120-160 ℃, and/or the foaming time in step (B) is 10-60min, and/or the heat treatment time in step (B) is 30-60 min.

13. The method as claimed in claim 12, wherein the foaming temperature in step (B) is 130-150 ℃.

14. The method of claim 12, wherein the foaming time is 20-40 min.

15. The method of claim 12, wherein the heat treatment time is 40 min.

16. The method according to any one of claims 1 to 8, wherein the temperature of the heat treatment in step (B) is 300-360 ℃.

17. The method according to claim 16, wherein the temperature of the heat treatment in the step (B) is 320 ℃ to 340 ℃.

18. Polyimide foam obtained by the production method according to any one of claims 1 to 17.

19. Use of a polyimide foam obtained by the production process according to any one of claims 1 to 17 in electronic products, aviation, marine or railroad locomotives.

20. A polyimide foam article comprising the polyimide foam of claim 18.