CN112048062B

CN112048062B - Preparation of polyimide by catalyzing dehydration of polyamic acid with choline chloride-urea eutectic solvent

Info

Publication number: CN112048062B
Application number: CN201910487811.1A
Authority: CN
Inventors: 冯树波; 武金亮; 翟倩楠
Original assignee: Hebei Huanene Technology Co ltd
Current assignee: Hebei Huanene Technology Co ltd
Priority date: 2019-06-05
Filing date: 2019-06-05
Publication date: 2022-05-06
Anticipated expiration: 2039-06-05
Also published as: CN112048062A

Abstract

The invention adopts choline chloride-urea eutectic solvent and acetic anhydride to synergistically catalyze polyamic acid to dehydrate and cyclize to prepare powdery polyimide. The method overcomes the problems of environmental pollution, difficult separation and the like caused by the fact that the prior chemical dehydration method for preparing the polyimide has to adopt the expensive and toxic strong alkaline dehydration catalyst such as pyridine, picoline, imidazole and the like. The choline chloride-urea eutectic solvent catalytic dehydrating agent adopted by the invention has the advantages of rich source, low price, easy preparation, no toxicity and recycling, and can be used at low temperature in the imidization process of polyamic acid by matching with an acetic anhydride dehydrating agent, thereby realizing the high-efficiency, controllable and clean preparation of the powdery polyimide PI product.

Description

Preparation of polyimide by catalyzing dehydration of polyamic acid with choline chloride-urea eutectic solvent

Technical Field

The invention belongs to the field of chemical manufacturing industry, and particularly relates to a dehydration cyclization reaction catalyst for preparing powdery polyimide by catalyzing dehydration of polyamic acid and a catalytic dehydration imidization process.

Background

Polyimide, abbreviated as PI, is a polymer having an imide ring (-CO-NH-CO-) in its main chain. The PI is one of the materials with the best comprehensive performance in organic polymer materials, has excellent mechanical, dielectric, radiation resistance, corrosion resistance, ablation resistance and other performances within the temperature range of-269-300 ℃, and has the advantages of continuously expanding the application of the PI in the aspects of insulating materials and structural materials. At present, PI is manufactured into films, resin matrix composite materials, high-temperature-resistant foam plastics, engineering plastics, heat-resistant and high-strength fibers and the like, and is widely applied to a plurality of fields. The polyimide composite material is divided into a thermosetting polyimide fiber reinforced composite material and a polyimide inorganic hybrid material. The material does not deform under the severe external conditions and also has certain plasticity and composite performance. Most are made from diamines and dianhydrides. The polyamic acid is prepared by reacting 4, 4-diaminodiphenyl ether and pyromellitic dianhydride in N, N-dimethyl formamide DMF solvent under the protection of nitrogen. The most common preparation method of polyimide is usually a two-step process, i.e. diamine and dianhydride are polymerized in an aprotic polar solvent to obtain a precursor polyamide acid PAA, and the PAA is subjected to high-temperature thermal dehydration cyclization or chemical catalytic dehydration cyclization to obtain PI. The chemical imidization process of PAA has mild conditions and needs the synergistic action of a dehydrating agent and a catalyst. In the 60's of the 20 th century, researchers in the soviet union conducted more intensive and systematic studies on the chemical imidization of polyamic acids. The polyamic acid may be imidized in a reaction bath containing a dehydrating agent in the form of a film, fiber or powder, or cyclized by directly adding a dehydrating agent to the solution, and the polyimide formed at this time may be dissolved, kept in a solution state or precipitated. Compared with high-temperature thermal imidization, chemical imidization has the advantages of low reaction temperature (generally 25-100 ℃), cyclization under the catalysis of aliphatic carboxylic anhydride dehydration and tertiary amine, high conversion speed, reduction of decomposition of polyamide acid, maintenance of mechanical strength of products and the like. With the progress of research, the understanding and understanding of the chemical imidization of polyamic acid is increasing.

The polyamic acid chemical cyclodehydration system generally consists of a dehydrating agent and a dehydrating catalyst. The commonly used dehydrating agent is acid anhydride, such as acetic anhydride, propionic anhydride, etc., or a mixture of the above acid anhydride and aromatic monocarboxylic acid anhydride; the catalyst is a tertiary amine, such as triethylamine, imidazole, pyridine, etc., with acetic anhydride/pyridine or picoline being the most commonly used. The method has the advantages that the degradation of the polyamic acid can not be caused even at 140-150 ℃, and the imidization reaction can be rapidly carried out at a lower temperature. As the dehydrating agent, acetyl chloride, Dicyclohexylcarbodiimide (DCC), trifluoroacetic anhydride, thionyl chloride and the like are mentioned. When acetic anhydride/pyridine (substituted pyridine) is used as a cyclodehydration system, PAA is simultaneously converted into imide and isoimide in the initial stage of reaction. (imide formation is faster than isoimide), as the reaction proceeds, the isoimide is slowly converted to imide, and the conversion is irreversible.

The polyimide PI has a phthalimide structure. Having imide repeating units. Polyimides are classified into three types. 1. Semi-aromatic; 2. aromatic; 3. an aliphatic polyimide. The typical structure of PI is as follows:

the PAA film is soaked in a dehydrating agent and a catalyst, and the PI film with higher imidization degree can be obtained under the condition of room temperature or heating at lower temperature. The method changes the mode of generating the polyimide film by the prior physical method, has higher imidization degree, and the prepared PI film has more excellent performance. The following diagram is the process mechanism of preparing PI film by two-step method:

it has been reported that the catalytic effect of 26 kinds of hydroxy acid compounds (such as hydroxybenzoic acid, hydroxybenzyl alcohol, methyl benzoic acid, etc.) was investigated under the condition of treating at 100 ℃ for 1 hour, and 9 kinds of catalysts having excellent catalytic effect were found, among which 5 kinds of hydroxy acids: m-hydroxybenzoic acid, p-hydroxybenzoic acid, 2, 4-dihydroxybenzoic acid, p-hydroxyphenylacetic acid, 3- (4-hydroxyphenyl) propionic acid; 2 hydroxy compounds: p-hydroxybenzene sulfonic acid, p-aminophenol; 2 carboxylic acids: m-aminobenzoic acid and p-aminobenzoic acid. And taking p-hydroxyphenylacetic acid as an example, the PMDA/ODA type polyamic acid is catalyzed, the molar ratio of the used amount to the polyamic acid is 2:1, the minimum imidization temperature is 140 ℃, and the treatment time is 60 min. The method greatly reduces the prior reaction temperature. These compounds are all aromatic and each contain 2 or more polar groups, such as; -NH₂-COOH, -OH and-SO₃H, etc., wherein at least 1 group is directly bonded to the benzene ring. Although hydroxycarboxylic acids have good catalytic effect, the amount of the catalyst is large, and the process of removing the catalyst brings many limitations to the application. Therefore, the search for suitable methods for catalyst removal will be a focus of research in such systems.

Benzimidazole also has catalytic dehydrative ring closure and is used in the best catalytic effect at a molar ratio of 1:1 to polyamic acid PAA. It is also found that in the process of raising the temperature from 50 to 300 ℃ for 1 hour, the imidization degree of the polyamic acid to which benzimidazole has been added reaches 65% when the temperature is raised to 80 ℃, while the imidization reaction of the polyamic acid to which no catalyst has been added starts when the temperature is raised to 100 ℃ or higher. After 1:1 equivalent of benzimidazole was added and treated at 80 ℃/24 hours, the IR spectrum was substantially identical to that of pure PI, and it was confirmed that the polyamic acid was imidized. And it was found that the effect of benzimidazole on imidization was the highest at 100 ℃. The discovery of benzimidazole as a catalyst reduces the reaction temperature to another extent, and also improves the performance of reactants, so that the performance of the generated polyimide film is better, the stability is better, and impurities are less, so that the method has a further breakthrough in the field of catalytic dehydration by a chemical method. Imidazole compounds, indole compounds, indazole compounds, indene compounds and the like have weak catalytic effects on imidization of PAA. The research result of the cyclized dehydration system adopting acetic anhydride and pyridine shows that the imidization degree of PAA is increased along with the increase of the addition amount of acetic anhydride, the crystallinity of the polyimide film is gradually increased, and the PI mechanical property also shows an increasing trend. When the molar ratio of pyridine to acetic anhydride was increased from 1.5:2.5 to 4: 2.5, the gel time decreased from 29h to 18h, indicating that the base catalyst significantly accelerated the imidization reaction.

Disclosure of Invention

The chemical imidization method for preparing polyimide has the advantages that the reaction temperature can be effectively reduced, the reaction is carried out in a homogeneous phase, the reaction is more sufficient, the product performance is more excellent, and byproducts are less. The invention provides a green and nontoxic dehydration catalyst, which is a method for dehydrating and imidizing carboxyl and amino in polyamide acid (PAA) molecules by utilizing a urea-choline chloride eutectic solvent and acetic anhydride to cooperatively catalyze the carboxyl and the amino in the PAA molecules, in order to overcome the technical problems that in the existing polyamide acid (PAA) dehydration and cyclization technology, pyridine and other dehydration catalysts have high toxicity, the dehydration catalysts are difficult to separate from reaction materials, products are not suitable to be purified, and the like.

The invention is realized by adopting the following technical scheme:

polycondensing a mixture of pyromellitic dianhydride PMDA and 4, 4-diaminodiphenyl ether ODA in a molar ratio of 1:1.05 in a dimethylformamide DMF solution at 40-60 ℃ under the protection of nitrogen to obtain a polyamic acid PAA solution, and removing part of DMF at 60-80 ℃ under the vacuum degree of-0.08 MPa to obtain a concentrated polyamic acid PAA-DMF mixed solution; uniformly stirring and mixing a certain amount of acetic anhydride and a certain amount of choline chloride CC-urea U eutectic solvent CC-U DES, adding the mixture into the polyamic acid PAA-DMF mixed solution, stirring and heating the mixed material to a certain temperature, stirring under the protection of nitrogen, carrying out dehydration cyclization reaction for a period of time until yellowish white powdery solid crystals are generated, and carrying out vacuum filtration to obtain a polyimide PI crude product; the filtrate containing the choline chloride CC-urea U eutectic solvent CC-U DES is recycled; washing the crude product of PI with a certain amount of DMF to remove unreacted PAA, washing with a certain amount of ethanol to remove other impurities, washing with a certain amount of water to remove a choline chloride CC-urea U eutectic solvent CC-U DES, and drying to obtain a fine product of powdery polyimide PI.

Compared with the prior art, the invention has the following beneficial effects:

the dehydration catalyst of the urea-choline chloride eutectic solvent CC-U DES is low in cost, non-toxic, biodegradable and recyclable, and realizes green preparation of polyimide prepared by dehydration cyclization of the polyamic acid PAA. The method has the advantages of simple process operation, mild dehydration condition, low-temperature normal-pressure operation and high production safety, and avoids the possible damage caused by catalysts such as pyridine or imidazole.

According to the method, the imidization degree of the polyamic acid can be effectively regulated and controlled by changing the addition amounts of the dehydrating agent acetic anhydride and the dehydrating catalyst urea-choline chloride CC-U DES and the proportion of the dehydrating agent acetic anhydride and the dehydrating catalyst urea-choline chloride CC-U DES, so that the requirements of different purposes on the imidization degree of the PI are met.

Imidization is extremely temperature sensitive. The thermal imidization method may cause an excessively high imidization ratio or an insufficient imidization ratio due to a slightly high or low temperature exceeding 140 ℃, and the imidization ratio may not be within an appropriate range. According to the invention, by controlling the proportion of acetic anhydride and CC-U DES, the imidization temperature and the imidization time, the imidization degree of the product PI can be flexibly regulated and controlled at a lower imidization temperature, and the solvent can be dried at a low temperature, so that the problem that the imidization proportion is difficult to control in high-temperature thermal imidization is solved, and the stability of the batch of products is effectively ensured.

Drawings

FIG. 1 is a schematic diagram of a process flow for realizing the dehydration and cyclization of polyamide acid PAA by using a urea-choline chloride eutectic solvent catalysis method.

The polyimide PI preparation scheme is described below: adding pyromellitic dianhydride PMDA, 4-diaminodiphenyl ether ODA and N, N-dimethylformamide DMF (dimethyl formamide) into a polycondensation kettle 1 according to a certain proportion, and carrying out a polycondensation reaction for a certain time under stirring at a certain temperature; then pumping into a PAA concentration kettle 2, and removing partial DMF under reduced pressure at a certain vacuum degree and temperature; pumping the PAA concentrated solution into a dehydration cyclization kettle 3, adding a certain amount of acetic anhydride and urea-choline chloride eutectic solvent mixed solution in batches, stirring and heating to a certain temperature, and filtering in a filter 4 after yellow white solid particles are separated out by reaction; the filtrate is pumped into a dehydration cyclization kettle 3 for recycling after decompression dehydration and acetic acid removal, a filter cake is sent into a DMF washing kettle 5, a certain amount of DMF is added, the mixture is stirred for a certain time, and the mixture is filtered in a filter 6; sending the filter cake into a washing kettle 7, adding a certain amount of deionized water, stirring for a certain time, and filtering in a filter 8; sending the filter cake into a washing kettle 9, adding a certain amount of 95% ethanol, stirring for a certain time, and filtering in a filter 10; and (3) feeding the filter cake into a dryer 11 for drying to obtain a powdery polyimide PI product.

FIG. 1 is a schematic diagram of a process for preparing polyimide PI

Description of the symbols in figure 1:

1. a condensation polymerization kettle for the pyromellitic anhydride and the 1, 4-diaminodiphenyl ether; 2. polyamide acid PAA concentration kettle; PAA dehydration cyclization kettle; 4. 6, 8 and 10, a filter; 5. 7, 9, washing the kettle; 11. and (3) a polyimide PI drier product.

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings.

Example 1

Adding 100 kg of dimethylformamide DMF, 11 kg of pyromellitic dianhydride PMDA and 10 kg of 1, 4-diaminodiphenyl ether ODA into a polycondensation kettle, polycondensing for 90 minutes at 45 ℃ under the protection of nitrogen to obtain a polyamic acid PAA solution, and removing part of DMF at 80 ℃ under the vacuum degree of-0.08 MPa to obtain a concentrated polyamic acid PAA-DMF mixed solution; stirring and mixing 20 kg of acetic anhydride and 30 kg of choline chloride CC-urea U eutectic solvent CC-U DES with the molar ratio of choline chloride to urea being 1:1.8 uniformly, adding the mixture into the polyamic acid PAA-DMF mixed solution, stirring and heating the mixed material to 80 ℃, stirring and heating the mixed material under the protection of nitrogen to perform dehydration cyclization reaction for 120 minutes until yellowish white powdery solid crystals are generated, and performing vacuum filtration to obtain a polyimide PI crude product; the filtrate containing the choline chloride CC-urea U eutectic solvent CC-U DES is recycled; washing the crude product of PI with 25 kg of DMF to remove unreacted PAA, filtering to obtain 10 kg of filter cake, washing with 95% ethanol to remove other impurities, and recycling the filtrate; and washing the obtained filter cake with 15 kg of water to remove a choline chloride CC-urea U eutectic solvent CC-U DES, and drying the filtered product to obtain a powdery fine polyimide PI product. And dehydrating the filtrate in vacuum to obtain regenerated CC-U DES for recycling.

The quality yield of the refined polyimide PI product reaches 89%; thermogravimetric analysis data show that the heat resistance is obviously improved compared with polyamide acid PAA; the characteristic absorption peak of imine in infrared spectrum is obvious; C. the analysis of N and O elements accords with the molecular structure characteristics of polyimide.

Example 2

Adding 100 kg of dimethylformamide DMF, 11 kg of pyromellitic dianhydride PMDA and 10 kg of 1, 4-diaminodiphenyl ether ODA into a polycondensation kettle, polycondensing at 55 ℃ for 60 minutes under the protection of nitrogen to obtain a polyamic acid PAA solution, and removing part of DMF at 80 ℃ and under the vacuum degree of-0.08 MPa to obtain a concentrated polyamic acid PAA-DMF mixed solution; uniformly stirring and mixing 30 kg of acetic anhydride and 20 kg of choline chloride CC-urea U eutectic solvent CC-U DES with the molar ratio of choline chloride to urea being 1:1.6, adding the mixture into the polyamic acid PAA-DMF mixed solution, stirring and heating the mixed material to 80 ℃, stirring and carrying out dehydration cyclization reaction for 180 minutes under the protection of nitrogen until yellowish white powdery solid crystals are generated, and carrying out vacuum filtration to obtain a polyimide PI crude product; the filtrate containing the choline chloride CC-urea U eutectic solvent CC-U DES is recycled; washing the crude product of PI with 25 kg of DMF to remove unreacted PAA, filtering to obtain 10 kg of filter cake, washing with 95% ethanol to remove other impurities, and recycling the filtrate; and washing the obtained filter cake with 15 kg of water to remove a choline chloride CC-urea U eutectic solvent CC-U DES, and drying the filtered product to obtain a powdery fine polyimide PI product. And dehydrating the filtrate in vacuum to obtain regenerated CC-U DES for recycling.

The quality yield of the refined polyimide PI product reaches 93 percent; thermogravimetric analysis data show that the heat resistance is obviously improved compared with polyamide acid PAA; the characteristic absorption peak of imine in infrared spectrum is obvious; C. the analysis of N and O elements accords with the molecular structure characteristics of polyimide.

Example 3

Adding 100 kg of dimethylformamide DMF, 11 kg of pyromellitic dianhydride PMDA and 10 kg of 1, 4-diaminodiphenyl ether ODA into a polycondensation kettle, polycondensing for 120 minutes at 40 ℃ under the protection of nitrogen to obtain a polyamic acid PAA solution, and removing part of DMF at 80 ℃ and under the vacuum degree of-0.08 MPa to obtain a concentrated polyamic acid PAA-DMF mixed solution; uniformly stirring and mixing 30 kg of acetic anhydride and 30 kg of choline chloride CC-urea U eutectic solvent CC-U DES with the molar ratio of choline chloride to urea being 1:2, adding the mixture into the polyamic acid PAA-DMF mixed solution, stirring and heating the mixed material to 70 ℃, stirring and cyclizing for 180 minutes under the protection of nitrogen until yellowish white powdery solid crystals are generated, and carrying out vacuum filtration to obtain a polyimide PI crude product; the filtrate containing the choline chloride CC-urea U eutectic solvent CC-U DES is recycled; washing the crude product of PI with 25 kg of DMF to remove unreacted PAA, filtering to obtain 10 kg of filter cake, washing with 95% ethanol to remove other impurities, and recycling the filtrate; and washing the obtained filter cake with 15 kg of water to remove a choline chloride CC-urea U eutectic solvent CC-U DES, and drying the filtered product to obtain a powdery fine polyimide PI product. And dehydrating the filtrate in vacuum to obtain regenerated CC-U DES for recycling.

The quality yield of the refined polyimide PI product reaches 96 percent; thermogravimetric analysis data show that the heat resistance is obviously improved compared with polyamide acid PAA; the characteristic absorption peak of imine in infrared spectrum is obvious; C. the analysis of N and O elements accords with the molecular structure characteristics of polyimide.

Example 4

Adding 100 kg of dimethylformamide DMF, 11 kg of pyromellitic dianhydride PMDA and 10 kg of 1, 4-diaminodiphenyl ether ODA into a polycondensation kettle, polycondensing at 45 ℃ for 60 minutes under the protection of nitrogen to obtain a polyamic acid PAA solution, and removing part of DMF at 80 ℃ and under the vacuum degree of-0.08 MPa to obtain a concentrated polyamic acid PAA-DMF mixed solution; stirring and mixing 20 kg of acetic anhydride and 40 kg of choline chloride CC-urea U eutectic solvent CC-U DES with the mol ratio of 1:2 to urea uniformly, adding the mixture into the polyamic acid PAA-DMF mixed solution, stirring and heating the mixed material to 75 ℃, stirring and carrying out dehydration cyclization reaction for 160 minutes under the protection of nitrogen until yellowish white powdery solid crystals are generated, and carrying out vacuum filtration to obtain a polyimide PI crude product; the filtrate containing the choline chloride CC-urea U eutectic solvent CC-U DES is recycled; washing the PI crude product with 25 kg of DMF to remove unreacted PAA, filtering to obtain 10 kg of filter cake, washing with 95% ethanol to remove other impurities, and recycling the filtrate; and washing the obtained filter cake with 15 kg of water to remove the choline chloride-urea eutectic solvent CC-U DES, and drying the filtered product to obtain a powdery fine polyimide PI product. And dehydrating the filtrate in vacuum to obtain regenerated CC-U DES for recycling.

The quality yield of the refined polyimide PI product reaches 90 percent; thermogravimetric analysis data show that the heat resistance is obviously improved compared with polyamide acid PAA; the characteristic absorption peak of the imide can be obviously observed in the infrared spectrum: 1779cm^-1,1719cm^-1,1370cm^-1,742cm^-1And the characteristic absorption peak of polyamic acid (3200 cm)^-1、2900cm^-1，1660cm^-1) Very weak, indicating that the imidization transition is substantially complete; C. the analysis of N and O elements accords with the molecular structure characteristics of polyimide.

Claims

1. The preparation method of the polyimide by catalyzing the dehydration of the polyamic acid by the choline chloride-urea eutectic solvent is characterized in that the catalytic dehydration process comprises the following steps:

a. polycondensing a mixture of pyromellitic dianhydride PMDA and 1, 4-diaminodiphenyl ether ODA in a molar ratio of 1:1.05 in a dimethylformamide DMF solution at 40-60 ℃ under the protection of nitrogen to obtain a polyamic acid PAA solution, and removing part of DMF at 60-80 ℃ and under the vacuum degree of-0.08 MPa to obtain a concentrated polyamic acid PAA-DMF mixed solution, wherein the PAA concentration is 6-12%;

b. uniformly stirring and mixing acetic anhydride with the amount of 3-5 times of PAA and a choline chloride CC-urea U eutectic solvent CC-U DES with the amount of 2-3 times of PAA, adding the mixture into the polyamic acid PAA-DMF mixed solution, stirring and heating the mixed material to 70-80 ℃, stirring and carrying out dehydration cyclization reaction for 2-6 hours under the protection of nitrogen until yellowish white powdery solid crystals are generated, and carrying out vacuum filtration to obtain a polyimide PI crude product; the filtrate containing the choline chloride CC-urea U eutectic solvent CC-U DES is recycled; the molar ratio of choline chloride to urea in the choline chloride CC-urea U eutectic solvent CC-U DES is 1: 1.5-1: 2.5;

c. washing the crude product of PI with a certain amount of DMF to remove unreacted PAA, washing with a certain amount of ethanol to remove other impurities, washing with a certain amount of water to remove a choline chloride CC-urea U eutectic solvent CC-U DES, and drying to obtain a fine product of powdery polyimide PI.

2. The method for preparing polyimide by dehydrating polyamic acid catalyzed by choline chloride-urea eutectic solvent according to claim 1, wherein the PAA concentration of the de-concentrated polyamic acid PAA-DMF mixed solution is preferably 8-10%.

3. The method for preparing polyimide by dehydrating polyamic acid through the choline chloride-urea eutectic solvent as claimed in claim 1, wherein the molar ratio of choline chloride to urea in the choline chloride CC-urea U eutectic solvent CC-U DES is preferably 1: 1.8-1: 2.0.