CN114044903B

CN114044903B - Hard polyimide foam and preparation method and application thereof

Info

Publication number: CN114044903B
Application number: CN202111634450.2A
Authority: CN
Inventors: 邹华维; 罗银富; 周生态; 倪龙
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2021-12-29
Filing date: 2021-12-29
Publication date: 2022-12-16
Anticipated expiration: 2041-12-29
Also published as: CN114044903A

Abstract

The invention provides a hard polyimideFoam, a preparation method and application thereof, belonging to the field of high polymer materials. The rigid polyimide foam has a structure shown in formula I. The polyimide foam prepared by the invention has high compression strength, excellent comprehensive mechanical property, low apparent density, small self weight, convenient transportation and construction and can be used as a light material. Meanwhile, the polyimide foam has excellent thermal stability and thermal insulation performance and can be used at high temperature. The polyimide foam disclosed by the invention has the characteristics of good thermal stability, high compression strength, low density and small self weight, can be used as a structural material in various high-tech fields such as aerospace, military ships, energy sources and high-speed rail automobiles, and has a wide application prospect.

Description

Hard polyimide foam and preparation method and application thereof

Technical Field

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

Background

The Polyimide (PI) foam material is a porous material which takes PI resin as a main component and contains open-closed pore structures with different sizes inside. The chain segment of the PI contains a large number of benzene rings and imide rings, so that the PI foam has excellent characteristics of thermal stability, high and low temperature resistance, self-extinguishing flame retardance, chemical resistance, irradiation resistance and the like, and can be widely applied to various high-tech fields such as aerospace, military ships, energy sources, high-speed rail automobiles and the like.

With the rapid development of the science and technology industries such as aerospace and the like, the PI foam with higher mechanical strength and rigidity is urgently needed to be used as a structural material, such as a radome liner, a spherical frame, a wing and an airtight partition plate of an airtight cabin of an airplane, a composite material blade of a wind driven generator, a submarine shell, a frame component and the like. Currently, rigid polymer foams used in this field are typically Polymethacrylimide (PMI) foams. However, PMI foams cannot be used in an environment of 200 ℃ or higher because their segments start to decompose at 200 ℃ due to their weaker polyolefin polymer chains, and the structure is destroyed. In addition, the isocyanate-based PI foam is not suitable for use as a structural material in view of poor mechanical properties and limited high-temperature properties. Therefore, the preparation of rigid PI foams with excellent mechanical properties and lower density is of great significance for the development of high-tech fields.

The production of PI foams has been a process which has been developed for decades and the production of PI foams is efficient by thermal foaming using polyesterammonium salts (PEAS) as precursor powder. On the basis, methods for improving the strength of the PI foam mainly comprise a method for adding a reinforcing filler and a method for modifying PI chain segments. The method of adding reinforcing filler is to add fiber, graphene, inorganic clay, honeycomb, etc. to PEAS to improve the mechanical property of the foam. The problem of poor compatibility between the filler and the matrix exists in the reinforced filler method, so that the strength of the prepared PI foam is improved to a limited extent. The chain segment modification method is to introduce a cross-linked network structure or a rigid structure into a PI chain segment structure to strengthen a PI main chain and endow foam with excellent pressure resistance. However, the addition of fillers and the construction of crosslinked networks or rigid structures can increase the viscosity during foaming and make forming difficult, while the high viscosity can weaken the interaction between cells, resulting in a decrease in the mechanical strength of the PI foam. Patent CN102964834A discloses a high temperature resistant and high compression resistant cross-linked polyimide foam material, which is prepared from organic tetracarboxylic dianhydride or diacid diester of organic tetracarboxylic acid, norbornene monoacid monoester and aromatic diamine as raw materials. Although the polyimide foam has the advantages of high temperature resistance, good toughness and small compression deformation at high temperature, the polyimide foam has the problems of high cost, low closed cell rate, low compression strength and complex forming process.

At present, development of a PI foam with good comprehensive performance, low density, high strength and good thermal stability is urgently needed.

Disclosure of Invention

The invention aims to provide a rigid polyimide foam, a preparation method and application thereof.

The invention provides a rigid polyimide foam, which has a structure shown in formula I:

wherein the content of the first and second substances,

a ring is selected from

R ₁ Is selected from

R ₂ Is selected from

n is an integer of 1 or more.

Further, the air conditioner is characterized in that,

n is an integer of 1 to 7;

preferably, n is 3.

Further, the rigid polyimide foam is prepared by taking bifunctional acid anhydride, diamine and monofunctional acid anhydride as raw materials;

the mole ratio of the difunctional anhydride, the diamine and the monofunctional anhydride is 1: (1-5): (0.1-1).

Further, the mole ratio of the difunctional anhydride, the diamine and the monofunctional anhydride is 1: (1.1-1.5): (0.25-1);

preferably, the molar ratio of difunctional anhydride, diamine and monofunctional anhydride is 1.

Further, the air conditioner is characterized in that,

the difunctional anhydride is selected from one or more of 3,3',4,4' -diphenyl ether tetracid anhydride, 3,3',4,4' -biphenyl tetracid dianhydride, pyromellitic dianhydride, 3,3',4,4' -benzophenone tetracarboxylic acid dianhydride, 3,3',4,4' -biphenyl sulfone tetracid dianhydride, 2,3,3',4' -biphenyl tetracid dianhydride;

and/or the diamine is selected from one or more of 3,4 '-diaminodiphenyl ether, 4,4' -diaminodiphenyl ether, m-phenylenediamine, p-phenylenediamine, 3,3 '-diaminodiphenyl sulfone, 4,4' -diaminodiphenyl sulfone, 4,4 '-diaminodiphenyl methane, 2,2' -dimethyldiaminobiphenyl, 2,6-diaminopyridine;

and/or the monofunctional anhydride is selected from one or more of nadic anhydride, 4-phenylethynyl phthalic anhydride, 4-ethynyl phthalic anhydride and maleic anhydride;

preferably, the first and second electrodes are formed of a metal,

the difunctional anhydride is selected from 3,3',4,4' -benzophenone tetracarboxylic dianhydride;

and/or the diamine is selected from 4,4' -diaminodiphenylmethane;

and/or, the monofunctional anhydride is selected from nadic anhydride.

The present invention also provides a method for preparing the rigid polyimide foam, which comprises the following steps:

(1) Adding a ring-opening catalyst, an alcohol solvent and an ether solvent into bifunctional acid anhydride, and reacting to obtain bifunctional polyamic acid precursor solution;

(2) Adding a ring-opening catalyst, an alcohol solvent and an ether solvent into monofunctional anhydride, and reacting to obtain monofunctional polyamic acid precursor solution;

(3) Mixing and stirring the solution obtained in the step (1) and the solution obtained in the step (2) to obtain a clear system;

(4) Adding diamine, a surfactant and an imidization catalyst into the clarified system obtained in the step (3) to react, and purifying to obtain PEAS salt;

(5) Foaming PEAS salt to obtain expanded microspheres, and then imidizing to obtain the hard polyimide foam.

Further, the air conditioner is provided with a fan,

in the step (1), the molar ratio of the bifunctional anhydride to the ring-opening catalyst to the alcohol solvent to the ether solvent is 1: (0.001-0.1): (1-10): (1-10);

and/or in the step (2), the mole ratio of the monofunctional anhydride to the ring-opening catalyst to the alcohol solvent to the ether solvent is 1: (0.001-0.1): (1-10): (1-10);

and/or, in the step (4), the molar ratio of the diamine to the imidization catalyst is 1: (0.01 to 0.1);

and/or in the step (4), the dosage of the surfactant is 0.1-0.5wt% of the total mass of the bifunctional acid anhydride, the monofunctional acid anhydride and the diamine;

preferably, the first and second liquid crystal display panels are,

in the step (1), the molar ratio of the bifunctional anhydride to the ring-opening catalyst to the alcohol solvent to the ether solvent is 1:0.01:7:8;

and/or, in the step (2), the mole ratio of the monofunctional anhydride to the ring-opening catalyst to the alcohol solvent to the ether solvent is 1:0.01:3.5:4;

and/or, in step (4), the molar ratio of diamine to imidization catalyst is 1:0.04;

and/or, in the step (4), the amount of the surfactant is 0.5wt% of the total mass of the bifunctional acid anhydride, the monofunctional acid anhydride and the diamine.

Further, the air conditioner is provided with a fan,

in the step (1), the ring-opening catalyst is dimethyl imidazole;

and/or, in the step (1), the alcohol solvent is one or more of methanol, ethanol, propanol and isopropanol;

and/or, in the step (1), the ether solvent is tetrahydrofuran;

and/or, in the step (2), the ring-opening catalyst is dimethyl imidazole;

and/or, in the step (2), the alcohol solvent is one or more of methanol, ethanol, propanol and isopropanol;

and/or, in the step (2), the ether solvent is tetrahydrofuran;

and/or, in the step (4), the surfactant is silicone oil;

and/or, in the step (4), the imidization catalyst is isoquinoline.

Further, the air conditioner is provided with a fan,

in the step (1), the reaction is an oil bath reflux reaction under the nitrogen atmosphere;

and/or in the step (2), the reaction is stirred under the nitrogen atmosphere;

and/or in the step (4), the reaction is carried out for 1-5 h at 70-80 ℃;

and/or, in the step (4), the purification is to remove the solvent, so that the solvent content in the obtained PEAS salt is 14-17%;

and/or, in the step (5), the PAES salt is crushed into the particle size of 0.1mm-0.3mm;

and/or, in the step (5), the foaming condition is that the temperature is kept between 150 and 200 ℃ for 30 to 60min;

and/or in the step (5), the imidization condition is kept for 1 to 3 hours at the temperature of between 250 and 300 ℃.

Preferably, the first and second electrodes are formed of a metal,

in the step (1), the reaction is an oil bath reflux reaction at 60-65 ℃ for 0.1-5 h under the nitrogen atmosphere;

and/or in the step (2), stirring for 0.1-5 h at the temperature of 60-65 ℃ under the nitrogen atmosphere;

and/or in the step (4), the reaction is carried out for 3h at 70 ℃;

and/or, in the step (4), the solvent removing condition is that the temperature is 60-65 ℃, and the pressure is-0.6 to-0.1 MPa;

and/or, in the step (5), the foaming condition is that the temperature is kept at 180 ℃ for 30min;

and/or, in the step (5), the imidization condition is that the temperature is kept for 2 hours at 300 ℃.

The invention also provides application of the hard polyimide foam in preparing devices used as structural materials in the fields of aerospace, military ships, energy sources, high-speed rails and automobiles.

The polyimide foam prepared by the invention has high compression strength, excellent comprehensive mechanical property, low apparent density, small self weight, convenient transportation and construction and can be used as a light material. Meanwhile, the polyimide foam has excellent thermal stability and thermal insulation performance and can be used at high temperature. The polyimide foam disclosed by the invention has the characteristics of good thermal stability, high compression strength, low density and small self weight, can be used as a structural material in various high-tech fields such as aerospace, military ships, energy sources and high-speed rail automobiles, and has a wide application prospect.

It will be apparent that various other modifications, substitutions and alterations can be made in the present invention without departing from the basic technical concept of the invention as described above, according to the common technical knowledge and common practice in the field.

The present invention will be described in further detail with reference to the following examples. This should not be understood as limiting the scope of the above-described subject matter of the present invention to the following examples. All the technologies realized based on the above contents of the present invention belong to the scope of the present invention.

Drawings

FIG. 1 shows the apparent density and closed cell content of each rigid polyimide foam.

Fig. 2 shows the compressive strength (10% strain) and the compressive modulus of each rigid polyimide foam under normal temperature conditions.

FIG. 3 shows the compressive strength (10% strain) and the compressive modulus at 200 ℃ for each of the rigid polyimide foams.

FIG. 4 is a thermal degradation curve of each rigid polyimide foam in a nitrogen and air atmosphere: a is in nitrogen and b is in air.

Fig. 5 is a plot of storage modulus and tan delta for each rigid polyimide foam: a is the storage modulus and b is the tan delta curve.

Fig. 6 is a thermal conductivity of each rigid polyimide foam.

FIG. 7 is a graph of the viscosity of PEAS salts with different numbers of repeating links as a function of temperature.

FIG. 8 is an internal cell structure of each rigid polyimide foam; a is PIF-2,b, PIF-4,c, PIF-6,d, PIF-8,e and PIF- ∞.

Detailed Description

The raw materials and equipment used in the embodiment of the present invention are known products and obtained by purchasing commercially available products.

EXAMPLE 1 preparation of rigid polyimide foam of the present invention

1. Preparation of polyester ammonium salt precursor

(1) 0.1mol of 3,3',4,4' -benzophenonetetracarboxylic dianhydride (BTDA) was accurately weighed into a 500ml three-necked flask, 1mmol of dimethylimidazole (2-MI) and 0.7mol of anhydrous methanol (CH) were weighed ₃ OH), 0.8mol Tetrahydrofuran (THF) were added to the three-necked flask. And introducing nitrogen into the system to remove air in the flask, and carrying out reflux reaction for 1h at 62 ℃ in an oil bath kettle under the nitrogen atmosphere to gradually change the color of the system solution from milky liquid to a light yellow clear solution to obtain the BTDA diacid diester solution.

(2) At the same time, 0.1mol of Nadic Anhydride (NA) and 0.35mol of CH were weighed ₃ OH, 0.4mol of THF and 1mmol of 2-MI are stirred for 1h at 62 ℃ under a nitrogen atmosphere, and the solution becomes clear to obtain a norbornene diacid diester solution. And transferring the norbornene diacid diester solution into a BTDA diacid diester solution, mixing and stirring for 15min, and converting the solution from turbid to clear to obtain a clear system.

(3) 0.15mol of 4,4' -diaminodiphenylmethane (MDA), 0.39g of surfactant (silicone oil) and 5mmol of isoquinoline were weighed into the above clarified system, the temperature of the system was raised to 70 ℃ and reacted for 3 hours to obtain a reddish brown liquid with a certain viscosity. Part of the solvent was removed at 65 ℃ and-0.6 MPa to give the PEAS salt. In the system, the content of the solvent in the PEAS salt is controlled to be 16-17%.

2. Preparation of polyimide foams

Mechanically pulverizing the PEAS salt with 16-17% solvent content to obtain particles with particle diameter of 0.1-0.3mm, heating the particles from room temperature to 180 deg.C, and maintaining at 180 deg.C for 30min to obtain micro-foamed PEAS microspheres. And filling the micro-foamed PEAS microspheres into a mold, heating to 300 ℃, and keeping for 2 hours to complete foaming and imidization to obtain the hard polyimide foam. The rigid polyimide foam had a number of links of 2 (n = 2) and was designated PIF-2.

Polyimide foams of different number of links (n =4, 6, 8 or ∞) were prepared according to the preparation method described in example 1, and the resulting polyimide foams were named PIF-4, PIF-6, PIF-8 and PIF- ∞, respectively. Infinity indicates that the number of links in the polyimide foam is infinite. The raw material formulation of each polyimide foam is shown in table 1. CH (CH) ₃ OH, THF and 2-MI were added in two portions, and in Table 1, "/" was preceded by the amount added to BTDA for the first time and was followed by the amount added to norbornene for the second time. When the number of chain links is ∞, the norbornene diacid diester solution is not added into the BTDA diacid diester solution.

TABLE 1 raw material formulation of each polyimide foam

The advantageous effects of the present invention are demonstrated by specific test examples below.

Test example 1 characterization of properties of rigid polyimide foam of the present invention

1. Test method

(1) Apparent density

The method is characterized in that the test is carried out according to the standard of GB/T6343-2009 'determination of apparent density of foam and rubber', not less than 5 samples are selected, the size of the PUF sample is 30mm multiplied by 20mm, the mass of each foam sample is weighed, and the sample is utilized

And calculating the apparent density, wherein the apparent density is an average value of multiple test results.

(2) Closed porosity

The closed cell content test is performed by placing a known mass of PI foam in water until its mass remains constant, the open cell content being calculated as the ratio of displaced water volume to sample volume, closed cell content =100% -open cell content.

(3) Mechanical properties

The compression performance test refers to GB/T8813-2008 'test method for compression strength of rigid foam', the size of a PI foam sample is 30mm multiplied by 20mm, the test number is not less than 5, the test compression direction is vertical to the cell growth direction, the compression rate is 2mm/min, and the test result is an average value obtained by multiple measurements.

(4) Thermal performance

Analyzing the thermal stability of the PI foam by using a thermal weight loss analyzer, wherein the testing atmosphere is nitrogen and air, the testing temperature of a PI foam sample is 30-800 ℃, and the heating rate is 10 ℃/min; testing the storage modulus and the glass transition temperature of the PI foam by adopting dynamic mechanical thermal analysis, wherein the test mode is a compression mode, the test frequency is 1HZ, and the heating rate is 5 ℃/min; the thermal conductivity of the PI foam was measured using hot disk testing. The hot plate sensor was placed between two prepared samples. The thermal conductivity of the two samples was collected simultaneously and the reported value was the average of the two samples.

(5) Rheological Properties

PEAS rheological characteristics are analyzed by a torque rheometer, the strain is set to be 0.5 percent, and the angular velocity is 10rad s ^-1 . The temperature scanning range is 50-300 ℃, and the heating rate is 10 ℃ min ^-1 。

(6) Cell morphology

The cell structure was observed using a scanning electron microscope. All PI foam samples were treated with gold blasting before observation.

2. Test results

The results of the property characterization of the polyimide foams having different numbers of links are shown in tables 2 and 3 and FIGS. 1 to 8.

TABLE 2 physical Property characterization results of the respective polyimide foams

TABLE 3 thermal Property characterization results of the respective polyimide foams

For porous materials, high apparent density is beneficial to improving mechanical strength, but high apparent density increases the dead weight of the material, is inconvenient to transport and construct, and cannot be used as a light material. Therefore, it is important to develop a polyimide foam having a low density and a high strength for its application. The research of the invention finds that (table 2 and figures 1-3), the polyimide foam prepared by the invention has the beneficial effects of low density and high strength, particularly PIF-4, which obviously improves the compressive strength and the compressive modulus at lower apparent density. Namely, the polyimide foam has the advantages of obviously improved comprehensive mechanical properties, excellent toughness and strength, better effect and contribution to the application of the polyimide foam under low apparent density. Meanwhile, the polyimide foam prepared by the invention still has certain strength at high temperature, and can be used in a high-temperature environment. In addition, the thermal performance results (Table 3 and FIGS. 4 to 6) also show that the polyimide foam prepared according to the present invention has good thermal stability and excellent thermal insulation properties, which can be used at high temperatures.

FIG. 7 is a graph showing the relationship between the viscosity of the PEAS salt having different numbers of repeating links and the temperature. The viscosity results, taken in conjunction with fig. 8, show that: as the number of links decreased, the viscosity of the system showed a downward trend, which helped to improve the cell-cell interaction (fig. 8 b); when the number of the links is ∞ it has a higher viscosity and a wider temperature range, which causes a state of separation between cells to appear (fig. 8 e). When the number of the chain links is 2, the viscosity of the system is low, so that the strength of the cell wall is insufficient to maintain the expansion process, and a combined cell structure is formed (fig. 8 a). The proper viscosity is shown to be beneficial for the formation of cells inside the polyimide foam, so that the polyimide foam has good mechanical properties; the PIF-4 has uniform and tight connection of internal foam pores, good mechanical properties and obviously improved compressive strength.

In conclusion, the polyimide foam prepared by the invention has high compression strength, excellent comprehensive mechanical property, low apparent density, small self weight, convenient transportation and construction and can be used as a light material. Meanwhile, the polyimide foam has excellent thermal stability and thermal insulation performance and can be used at high temperature. The polyimide foam disclosed by the invention has the characteristics of good thermal stability, high compression strength, low density and small self weight, can be used as a structural material in various high-tech fields such as aerospace, military ships, energy sources and high-speed rail automobiles, and has a wide application prospect.

Claims

1. A method of preparing a rigid polyimide foam, characterized by: it comprises the following steps:

(5) Foaming PEAS salt to obtain expanded microspheres, and then imidizing to obtain rigid polyimide foam;

in the step (4), the purification is to remove the solvent, so that the solvent content in the obtained PEAS salt is 14-17%;

in the step (5), the PEAS salt is crushed to a particle size of 0.1mm-0.3mm;

in the step (5), the foaming condition is kept at 150 to 200 ℃ for 30 to 60min;

the rigid polyimide foam has a structure represented by formula I:

formula I

Wherein, the first and the second end of the pipe are connected with each other,

a ring selected from

、

、

、

、

；

R ₁ Is selected from

、

、

、

、

、

；

R ₂ Is selected from

、

、

；

n is an integer of 1 or more.

2. The method of claim 1, wherein: n is an integer of 1~7.

3. The method of claim 2, wherein: and n is 3.

4. The method of claim 1, wherein: the mole ratio of the difunctional anhydride, the diamine and the monofunctional anhydride is 1: (1~5): (0.1 to 1).

5. The method of claim 4, wherein: the mole ratio of the difunctional anhydride, the diamine and the monofunctional anhydride is 1: (1.1 to 1.5): (0.25 to 1).

6. The method of claim 5, wherein: the molar ratio of difunctional anhydride, diamine and monofunctional anhydride is 1.

7. The method of any of claims 1~6, wherein:

the difunctional anhydride is selected from one or more of 3,3',4,4' -diphenyl ether tetra-anhydride, 3,3',4,4' -biphenyl tetra-carboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4' -benzophenone tetracarboxylic dianhydride, 3,3',4,4' -biphenyl sulfone tetra-carboxylic dianhydride, 2,3,3',4' -biphenyl tetra-carboxylic dianhydride;

the diamine is selected from one or more of 3,4 '-diaminodiphenyl ether, 4,4' -diaminodiphenyl ether, m-phenylenediamine, p-phenylenediamine, 3,3 '-diaminodiphenyl sulfone, 4,4' -diaminodiphenyl sulfone, 4,4 '-diaminodiphenyl methane, 2,2' -dimethyldiaminobiphenyl, 2,6-diaminopyridine;

the monofunctional anhydride is selected from nadic anhydride.

8. The method of claim 7, wherein:

the diamine is selected from 4,4' -diaminodiphenylmethane.

9. The method of claim 1, wherein:

in the step (1), the molar ratio of the bifunctional anhydride to the ring-opening catalyst to the alcohol solvent to the ether solvent is 1: (0.001 to 0.1): (1 to 10): (1 to 10);

in the step (2), the mole ratio of the monofunctional anhydride to the ring-opening catalyst to the alcohol solvent to the ether solvent is 1: (0.001 to 0.1): (1 to 10): (1 to 10);

in the step (4), the molar ratio of the diamine to the imidization catalyst is 1: (0.01 to 0.1);

in the step (4), the dosage of the surfactant is 0.1-0.5wt% of the total mass of the bifunctional acid anhydride, the monofunctional acid anhydride and the diamine.

10. The method of claim 9, wherein:

in the step (2), the mole ratio of the monofunctional anhydride to the ring-opening catalyst to the alcohol solvent to the ether solvent is 1:0.01:3.5:4;

in the step (4), the molar ratio of the diamine to the imidization catalyst is 1:0.04;

in the step (4), the amount of the surfactant is 0.5wt% of the total mass of the bifunctional acid anhydride, the monofunctional acid anhydride and the diamine.

11. The method of claim 1, wherein:

in the step (1), the ring-opening catalyst is dimethyl imidazole;

in the step (1), the alcohol solvent is one or more of methanol, ethanol, propanol and isopropanol;

in the step (1), the ether solvent is tetrahydrofuran;

in the step (2), the ring-opening catalyst is dimethyl imidazole;

in the step (2), the alcohol solvent is one or more of methanol, ethanol, propanol and isopropanol;

in the step (2), the ether solvent is tetrahydrofuran;

in the step (4), the surfactant is silicone oil;

in the step (4), the imidization catalyst is isoquinoline.

12. The method of claim 1, wherein:

in the step (2), the reaction is stirred under the nitrogen atmosphere;

in the step (4), the reaction is carried out for 1 to 5 hours at the temperature of 70 to 80 ℃;

in the step (5), the imidization condition is that the temperature is kept at 250-300 ℃ for 1-3h.

13. Use of the rigid polyimide foam prepared by the method according to any one of claims 1 to 12 in the preparation of devices used as structural materials in the fields of aerospace, military ships, energy sources, high-speed rails and automobiles.