KR101692137B1 - Preparation method for polyimide powder and polyimide product from water soluble polyamic acid - Google Patents

Abstract

The present invention provides a method for producing polyamic acid, comprising: a) preparing a polyamic acid aqueous solution by adding a water-soluble polyamic acid to water; And b) adding a dehydrating agent to the polyamic acid solution and heating the polyimide powder to prepare a polyimide powder. According to the method, unlike conventional polyimide production methods, Since a solvent is not used, it is economical, environmentally friendly, and polyimide can be produced at a relatively low temperature, so that a colorless transparent polyimide can be produced. Moreover, since the polyimide to be produced has a powdery form, The process is simplified.

Description

[0001] The present invention relates to a method for producing a polyimide powder and a polyimide molding product using a water-soluble polyamic acid,

The present invention relates to a method for producing a polyimide powder and a polyimide molded product using a water-soluble polyamic acid.

Polyimide is one of polymeric materials showing better properties than other polymers and is widely used in high-tech industries due to its excellent mechanical properties, high glass transition temperature and high thermal stability.

The general synthesis method of polyimide is composed of two steps of synthesizing the precursor polyamic acid by the reaction of dianhydride and diamine and then imidizing the polyamic acid in the next step. The synthesis of the polyamic acid is a process in which a diamine and a dianhydride dissolved in a solvent are opened to produce a polyamic acid by the action of a middle part, and the reaction solvent used is N, N -dimethylacetamide, N, Polar organic solvents such as methyl formamide, N -methyl-2-pyrrolidone, and meta-cresol are predominant. On the other hand, the synthesized polyamic acid is imidized by a dehydration and ring-closing reaction through a chemical method or a thermal method to produce a polyimide.

The chemical imidization method is a method in which a chemical dehydrating agent represented by an acid anhydride such as acetic anhydride and an imidation catalyst represented by a tertiary amine such as pyridine are added to a polyamic acid solution as a precursor and heated at 160 ° C or higher. On the other hand, the thermal imidization method is a method of applying a solution of polyamic acid as a precursor to a substrate, evaporating the solvent, and then thermally imidizing by heating at 250 to 350 캜 without a chemical dehydrating agent and a catalyst.

Korean Registered Patent No. 1,004,096

As described above, the conventional imidization method requires a high temperature condition of 160 to 350 DEG C, requires a separate reprecipitation step in the production of a molded article, and requires the use of an organic solvent which is harmful to the environment and the human body. In addition, the polyimide synthesized by the conventional imidization method has a problem of low transparency because the reaction solvent is colored under high temperature conditions of 160 to 350 ° C.

According to an embodiment of the present invention, there is provided a method of manufacturing a polyamic acid solution, comprising: a) preparing a polyamic acid solution by adding a water-soluble polyamic acid to water; And b) adding a dehydrating agent to the aqueous solution of polyamic acid and heating the polyimide powder to prepare a polyimide powder.

In another embodiment of the present invention, there is provided a wholly aromatic polyimide, a partially aliphatic polyimide or a wholly aliphatic polyimide powder produced by the above method.

According to another embodiment of the present invention, there is provided a method of manufacturing a polyimide molded article, further comprising the step of putting the polyimide powder into a molding apparatus to produce a polyimide molded article.

According to another embodiment of the present invention, there is provided a polyimide molded article produced by the above method, wherein the polyimide film is a polyimide film, a high heat resistant engineering plastic, an adhesive, a tape, a fiber, a liquid crystal alignment film, an interlayer insulator, And a flexible display substrate, wherein the polyimide molded article is at least one selected from the group consisting of polyimide resin, polyimide resin, polyimide resin, and flexible display substrate.

In the present invention, polyimide powder is prepared by dissolving a water-soluble polyamic acid in water, followed by adding a dehydrating agent and conducting an imidation reaction, thereby producing polyimide in an economical and environmentally friendly manner compared to a conventional polyimide- .

In addition, since the imidization reaction of the present invention can proceed at a relatively low temperature, it is possible to produce a colorless transparent polyimide.

On the other hand, the polyimide powder produced according to the present invention can be directly formed into a molded product after filtration and drying without a separate re-precipitation process, so that it is advantageous in that the process of manufacturing a polyimide molded article is simplified.

1 shows FT-IR spectra of 3,3 ', 4,4'-benzopyrone tetracarboxylic dianhydride and 4,4'-oxydianiline polyimide according to Example 1 of the present invention.
2 shows FT-IR spectra of 4,4 '- (hexafluoroisopropylidene) diphthalic anhydride and 1,4-phenylene diamine polyimide according to Example 2 of the present invention.
3 and 9 are FT-IR spectra of 1,2,4,5-cyclohexanetetracarboxylic dianhydride and 4,4'-diaminodiphenylmethane polyimide according to Example 3 of the present invention Uv-vis absorption spectrum.
FIGS. 4 and 10 are graphs showing FT-IR spectra of 3,3'4,4'-biphenyltetracarboxylic dianhydride and 4,4'-methylenebis (cyclohexylamine) polyimide according to Example 4 of the present invention Spectrum and Uv-vis absorption spectrum.
5 and 11 are graphs showing FT-IR spectra of 1,2,3,4-cyclopentane dianhydride and 1,4-bis (aminomethyl) cyclohexane polyimide according to Example 5 of the present invention and Uv- vis absorption spectrum.
FIGS. 6 and 12 are schematic cross-sectional views of bicyclo [2.2.2] ox-7-ene-2,3,5,6-tetracarboxylic dianhydride and 1,4-diaminocyclohexane FT-IR spectrum and Uv-vis absorption spectrum of polyimide are shown.
7 and 13 are FT-IR spectra and absorption spectra of 1,2,3,4-cyclopentane dianhydride and 1,4-bis (aminomethyl) cyclohexane polyimide according to Comparative Example 1 of the present invention. -vis spectra.
FIGS. 8 and 14 are graphs showing FT-IR spectra of 1,2,3,4-cyclopentane dianhydride and 1,4-bis (aminomethyl) cyclohexane polyimide according to Comparative Example 2 of the present invention and Uv- vis absorption spectrum.

The present invention provides a method for producing polyamic acid, comprising: a) preparing a polyamic acid aqueous solution by adding a water-soluble polyamic acid to water; And b) adding a dehydrating agent to the polyamic acid solution and heating the polyimide powder to prepare a polyimide powder.

The method may further include filtering and drying the polyimide powder produced in the step b) in the production of the polyimide powder.

Unlike conventional polyimide manufacturing methods, the polyimide powder manufacturing method uses water-soluble polyamic acid, so water is used instead of an organic solvent as a solvent, which is economical and environmentally friendly. Further, the imidization reaction proceeds at a relatively low temperature, so that coloration of the polyimide to be produced is prevented, and a colorless transparent polyimide can be produced. Further, since a dehydrating agent is added to a polyamic acid aqueous solution and then imidized, a step of repulse is not required in the production of the polyimide molded article since the polyimide powder form is produced, which simplifies the process.

Hereinafter, the present invention will be described in more detail.

First, a water-soluble polyamic acid is added to water to prepare an aqueous solution of polyamic acid (step a).

In one embodiment of the present invention, the water-soluble polyamic acid may be in powder form, but the form thereof is not particularly limited.

For example, the water-soluble polyamic acid in powder form according to an embodiment of the present invention may be one prepared by preparing polyamic acid as a water-soluble polyamic acid in an organic solvent, re-precipitating it, filtering and drying.

Meanwhile, in one embodiment of the present invention, the water-soluble polyamic acid used in the above step may be prepared by reacting a polyamic acid represented by the following formula (1) prepared by the reaction between a dianhydride compound and a diamine compound, with an amine compound, a metal hydroxide compound, And a metal carbonate compound in the presence of a catalyst.

≪ Formula 1 >

(R ₁ in the formula 1 is the chemical structure:

≪ / RTI >

In the above formula (1), R < ₂ >

≪ / RTI > X is an integer satisfying 1? X? 50, n is a natural number in the range of 1 to 20, W, X and Y are each an alkyl or aryl group having 1 to 30 carbon atoms, and Z is an ester group , An amide group, an imide group and an ether group.

Meanwhile, in one embodiment of the present invention, the amine compound is selected from the group consisting of trimethylamine, triethylamine, methylpyrrolidine, N, N -dimethylhexylamine, imidazole, 1,2-dimethylimidazole, N -methylimidazole, N-benzyl-2-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 5-methyl benzimidazole, N-benzyl-2-methylimidazole Is selected from the group consisting of pyrrolidine, pyridine, imidazole, imidazole, imidazole, imidazole, imidazole, imidazole, imidazole, And may be one kind or two or more kinds.

Meanwhile, in one embodiment of the present invention, the metal hydroxide compound may be a compound of the following formula (2).

M _x (OH) _y

(2)

Wherein M is selected from the group consisting of Li, Na, K, Mg and Ca and 0 < x <

Meanwhile, in one embodiment of the present invention, the metal carbonate compound may be a compound of the following formula (3).

M _a (CO ₃ ) _b

(3)

(Wherein M is selected from the group consisting of Li, Na, K, Mg and Ca and 0 < a < 2 and 0 &

In one embodiment of the present invention, the concentration of the water-soluble polyamic acid in the polyamic acid solution is, for example, 1 to 10% by weight, specifically 1 to 8% by weight, more specifically 2 to 7% If the concentration of the water-soluble polyamic acid in the aqueous solution of polyamic acid is less than 1% by weight, the imidization rate becomes low. If the concentration of the water-soluble polyamic acid is more than 10% by weight, gelation may occur.

Next, a dehydrating agent is added to the prepared aqueous solution of polyamic acid, which is then heated to produce a polyimide powder (step b). On the other hand, the polyimide powder to be produced may be prepared by further performing additional steps of filtration and drying.

In one embodiment of the present invention, the dehydrating agent may be a chemical dehydrating agent, for example, acetic anhydride, anhydrous propionic acid, anhydrous butyric acid, anhydrous benzoic acid, anhydrous adipic acid, anhydrous isophthalic acid, phthalic anhydride and trimellitic anhydride And at least one substance selected from the group consisting of

On the other hand, the dehydrating agent may be added in a molar number of 2 to 40 times, specifically 2 to 20 times, more specifically 5 to 15 times, the number of moles of the water-soluble polyamic acid repeating unit, When the amount is less than 2 times, the imidization rate is lowered, and when the amount is more than 40 times, the manufacturing cost is high and economical efficiency may be a problem.

Meanwhile, the method of adding the dehydrating agent in the step b) may be added at one time, or may be sequentially adding the dehydrating agent at a predetermined amount. More specifically, in the case where gelation occurs in the imidization step of step b), the method of sequentially adding may be effective, and when the gelation is not occurring, the method of adding the gelation may be effective.

On the other hand, after the dehydrating agent is added in the step b), the thermal imidization reaction in which the imidization is carried out by heating.

The step b) may be carried out, for example, within a temperature range of 40 to 250 ° C, specifically 60 to 160 ° C. If the temperature is lower than 40 ° C, the imidization reaction may not proceed. If the temperature is higher than 250 ° C, hydrolysis of the polyimide to be produced may occur, which is not economically feasible. In particular, when the imidization reaction proceeds according to the present invention, the imidization proceeds well in a temperature range of 160 ° C or lower. The temperature range corresponds to a low temperature condition relative to the conventional technique, It is possible to prevent the polyimide finally produced from being colored, thereby making it possible to manufacture a colorless transparent polyimide.

On the other hand, the step b) may be performed within a pressure range of, for example, 1 to 40 bar. Specifically, the imidization rate is lowered when the pressure is less than 1 bar, and the molecular weight may decrease when the pressure exceeds 40 bar.

Meanwhile, the step b) may be performed for, for example, 10 minutes to 72 hours. If the step b) is carried out for less than 10 minutes, the imidization may not be sufficiently performed. If the step b) is performed for more than 72 hours, the polyimide itself is hydrolyzed or is not economically feasible.

The polyimide powder obtained after the step b) may be further subjected to further filtration and drying.

In this case, the drying temperature in the drying process may be room temperature, for example, 25 to 200 ° C.

The polyimide prepared according to the above series of methods may be a fully aromatic polyimide, a partially aliphatic polyimide or a fully aliphatic polyimide.

Meanwhile, in one embodiment of the present invention, the polyimide powder may be dissolved in an organic solvent to prepare a film, and the polyimide film produced by the method may be used in a display field.

Meanwhile, in another embodiment of the present invention, the polyimide powder may be put into a molding apparatus by itself to produce a polyimide molded article. The polyimide molded product produced according to the above method may be at least one product selected from the group consisting of a polyimide film, a high heat resistant engineering plastic, an adhesive, a tape, a fiber, a liquid crystal alignment film, an interlayer insulator, a coating film resin, a printed circuit board and a flexible display substrate Lt; / RTI &gt;

According to the method for producing polyimide powder of the present invention described above, unlike the conventional method, water is used instead of an organic solvent in the production of polyimide from polyamic acid, which is environmentally friendly and economical. Further, the imidization reaction proceeds at a relatively low temperature, so that coloration of the polyimide to be produced is prevented, and a colorless transparent polyimide can be produced.

In addition, since the dehydrating agent is added to the polyamic acid aqueous solution prior to the imidization reaction, the final polyimide is in the form of powder, so that it can be directly prepared into a molded article without any re-precipitation process. It becomes simple.

Accordingly, the polyimide powder prepared according to the present invention can be applied to a wide variety of fields such as space, aviation, electric / electronic, semiconductor, transparent / flexible display, liquid crystal alignment film, automobile, precision instrument, packaging, medical material, It is highly valued for use in industry.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. It should be understood, however, that the following examples and comparative examples are intended to assist the understanding of the present invention and are not intended to limit the scope of the present invention thereto.

Example

Example 1: Synthesis of wholly aromatic polyimide

N -methyl-2-pyrrolidone (NMP) (282 mL) was added to a 500-mL two-necked round bottom flask substituted with nitrogen gas, and 19.33 g of 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride (0.060 mol) and 12.01 g (0.060 mol) of 4,4'-oxydianiline were placed in a reaction vessel and reacted at room temperature for 24 hours to prepare a polyamic acid solution. 6.60 g (0.096 mol) of imidazole was added to the prepared polyamic acid solution, reacted for 45 minutes, and reprecipitated in acetone. After filtration and drying, a water-soluble polyamic acid powder was prepared.

Next, 1 g of the above water-soluble polyamic acid powder was added to 100 mL of distilled water, and 1.22 g (0.012 mol) of acetic anhydride was added to a 250-mL pressure vessel which had been substituted with nitrogen gas. The mixture was refluxed at 160 ° C. and 20 bar for 6 hours, Followed by filtration. Washed with 100 mL of water and 100 mL of methanol, and vacuum dried to synthesize a wholly aromatic polyimide.

In the infrared absorption spectrum (FIG. 1) of the synthesized polymer, the C═O absorption band of the imide group and the CNC absorption band of the imide group at 1379 cm ^-1 were observed at 1778 cm ^-1 and 1723 cm ^-1 , respectively. The imidization rate was measured to be 94% based on the absorbance of the CNC absorption bands based on the absorption band of the aromatic ring in the infrared absorption spectrum of the polymer.

Example 2 Synthesis of wholly aromatic polyimide

282 mL of N -methyl-2-pyrrolidone (NMP) was added to a 500-mL 2-necked round bottom flask substituted with nitrogen gas and 4,4 '- (hexafluoroisopropylidene) diphthalic anhydride 26.65 g (0.060 mol) and 6.49 g (0.060 mol) of 1,4-phenylenediamine were placed in a reaction vessel and reacted at room temperature for 24 hours to prepare a polyamic acid solution. To the prepared polyamic acid solution, 9.81 g (0.096 mol) of triethylamine was added, reacted for 45 minutes, and reprecipitated in acetone. After filtration and drying, a water-soluble polyamic acid powder was prepared.

Next, 1 g of the above-mentioned water-soluble polyamic acid powder was added to 100 mL of distilled water, and 27.15 g (0.12 mol) of anhydrous benzoic acid was added to a 250 mL pressure vessel which had been substituted with nitrogen gas. The mixture was refluxed at 80 ° C and 1 bar for 12 hours, The temperature was lowered and then filtered. Washed with 100 mL of water and 100 mL of methanol, and vacuum dried to synthesize a wholly aromatic polyimide.

In the infrared absorption spectrum (FIG. 2) of the synthesized polymer, the C═O absorption band of the imide group and the CNC absorption band of the imide group at 1384 cm ^-1 were observed at 1785 cm ^-1 and 1726 cm ^-1 , respectively. In the infrared absorption spectrum of the polymer, the imidization rate was measured to be 95% based on the absorbance of the CNC absorption band on the basis of the absorption band of the aromatic ring.

Example 3 Synthesis of Partial Aliphatic Polyimide

304 mL of N -methyl-2-pyrrolidone (NMP) was added to a 500-mL 2-necked round bottom flask substituted with nitrogen gas, and 17.93 g (0.080 mmol) of 1,2,4,5-cyclohexanetetracarboxylic dianhydride mol) and 15.86 g (0.080 mol) of 4,4'-diaminodiphenylmethane were added thereto, and the mixture was reacted at room temperature for 24 hours to prepare a polyamic acid solution. 12.43 g (0.13 mol) of 1,2-diimidazole was added to the prepared polyamic acid solution, reacted for 45 minutes, and reprecipitated in acetone. After filtration and drying, a water-soluble polyamic acid powder was prepared.

Next, 1 g of the above-mentioned water-soluble polyamic acid powder was added to 100 mL of distilled water in a 250 mL pressure vessel which had been substituted with nitrogen gas, and 8.16 g (0.080 mol) of acetic anhydride was added thereto. The mixture was refluxed at 100 ° C. and 1 bar for 1 hour, Followed by filtration. Washed with 100 mL of water and 100 mL of methanol, and vacuum dried to synthesize a partially aliphatic polyimide.

In the infrared absorption spectrum (FIG. 3) of the synthesized polymer, the C═O absorption band of the imide was observed at 1780 cm ^-1 and 1728 cm ^-1 , and the CNC absorption band of the imide was observed at 1392 cm ^-1 . In the infrared absorption spectrum of the polymer, the imidization rate was measured to be 96% based on the absorbance of the CNC absorption band based on the absorption band of the aromatic ring. The synthesized polyimide was dissolved in NMP to obtain a polyimide film having a thickness of 21 탆 and a light transmittance of 93% or more at 400 nm (FIG. 9).

Example 4 Synthesis of Partial Aliphatic Polyimide

317 mL of N -methyl-2-pyrrolidone (NMP) was added to a 500-mL two-necked round bottom flask substituted with nitrogen gas, and 20.59 g of 3,3'4,4'-biphenyltetracarboxylic dianhydride 0.070 mol) and 14.72 g (0.070 mol) of 4,4'-methylenebis (cyclohexylamine) were placed and reacted at room temperature for 24 hours to prepare a polyamic acid solution. 12.43 g (0.11 mol) of methylpyrrolidine was added to the prepared polyamic acid solution, reacted for 45 minutes, and reprecipitated in acetone. After filtration and drying, a water-soluble polyamic acid powder was prepared.

Next, 1 g of the above-mentioned water-soluble polyamic acid powder was added to 100 mL of distilled water, and 18.22 g (0.14 mol) of anhydrous propionic acid was added to the 250-mL pressure vessel which had been substituted with nitrogen gas. The mixture was refluxed at 60 DEG C and 1 bar for 24 hours, Followed by filtration. Washed with 100 mL of water and 100 mL of methanol, and vacuum dried to synthesize a partially aliphatic polyimide.

In the infrared absorption spectrum (FIG. 4) of the synthesized polymer, the C═O absorption band of the imide group and the CNC absorption band of the imide group at 1388 cm ^-1 were observed at 1789 cm ^-1 and 1723 cm ^-1 , respectively. In the infrared absorption spectrum of the polymer, the imidization rate was measured to be 95% based on the absorbance of the CNC absorption band on the basis of the absorption band of the aromatic ring. The synthesized polyimide was dissolved in NMP to obtain a polyimide film having a thickness of 29 탆 and a light transmittance of 91% or more at 400 nm (FIG. 10).

Example 5: Synthesis of all aliphatic polyimide

285 mL of N -methyl-2-pyrrolidone (NMP) was added to a 500-mL two-necked round bottom flask substituted with nitrogen gas, and 18.91 g (0.090 mol) of 1,2,3,4-cyclopentane dianhydride And 12.80 g (0.090 mol) of 1,4-bis (aminomethyl) cyclohexane were placed in the flask and reacted at room temperature for 24 hours to prepare a polyamic acid solution. To the prepared polyamic acid solution, 11.94 g (0.14 mol) of N - methylimidazole was added and reacted for 45 minutes and then reprecipitated in acetone. After filtration and drying, a water-soluble polyamic acid powder was prepared.

Next, 1 g of the above-mentioned water-soluble polyamic acid powder was added to 100 mL of distilled water, and 9.19 g (0.090 mol) of acetic anhydride was added to a 250 mL pressure vessel which had been substituted with nitrogen gas. The mixture was refluxed at 80 ° C and 1 bar for 12 hours, The temperature was lowered and then filtered. Washed with 100 mL of water and 100 mL of methanol, and vacuum dried to synthesize all aliphatic polyimide.

In the infrared absorption spectrum of the synthesized polymer (FIG. 5), the C═O absorption band of the imide group and the CNC absorption band of the imide group at 1381 cm ^-1 were observed at 1784 cm ^-1 and 1717 cm ^-1 , respectively. In the infrared absorption spectrum of the polymer, the imidization rate was measured to be 95% based on the absorbance of the CNC absorption band relative to the C = O absorption band of the dianhydride. The synthesized polyimide was dissolved in NMP to obtain a polyimide film having a thickness of 26 탆 and a light transmission of 96% or more at 400 nm (FIG. 11).

Example 6 Synthesis of Prealiphatic Polyimide

293 mL of N -methyl-2-pyrrolidone (NMP) was added to a 500-mL 2-necked round bottom flask substituted with nitrogen gas, and bicyclo [2.2.2] 22.34 g (0.090 mol) of tetracarboxylic dianhydride and 10.28 g (0.090 mol) of 1,4-diaminocyclohexane were placed and reacted at room temperature for 24 hours to prepare a polyamic acid solution. N, N - Dimethylethylamine (10.64 g, 0.14 mol) was added to the prepared polyamic acid solution, reacted for 45 minutes, and reprecipitated in acetone. After filtration and drying, a water-soluble polyamic acid powder was prepared.

Next, 1 g of the above-mentioned water-soluble polyamic acid powder was placed in 100 mL of distilled water, and 30.54 g (0.13 mol) of anhydrous benzoic acid was added to a 250 mL pressure vessel which had been substituted with nitrogen gas. The mixture was refluxed at 40 DEG C and 1 bar for 18 hours, Followed by filtration. Washed with 100 mL of water and 100 mL of methanol, and vacuum dried to synthesize all aliphatic polyimide.

In the infrared absorption spectrum of the synthesized polymer (FIG. 6), the C═O absorption band of the imide group and the CNC absorption band of the imide group at 1382 cm ^-1 were observed at 1786 cm ^-1 and 1710 cm ^-1 , respectively. In the infrared absorption spectrum of the cohesion, the imidization rate was measured to be 94% based on the absorbance of the CNC absorption band based on the C = O absorption band of dianhydride. The synthesized polyimide was dissolved in NMP to obtain a polyimide film having a thickness of 28 탆 and exhibiting a light transmittance of 98% or more at 400 nm (FIG. 12).

Comparative Example 1: Polyimide synthesis by chemical imidization method using an organic solvent

285 mL of N -methyl-2-pyrrolidone (NMP) was added to a 500-mL two-necked round bottom flask substituted with nitrogen gas, and 18.91 g (0.090 mol) of 1,2,3,4-cyclopentane dianhydride And 12.80 g (0.090 mol) of 1,4-bis (aminomethyl) cyclohexane were placed in the flask and reacted at room temperature for 24 hours to prepare a polyamic acid solution.

Next, 9.19 g (0.090 mol) of acetic anhydride and 7.19 g (0.090 mol) of pyridine were added to the solution, refluxed at 160 ° C for 6 hours, and reprecipitated using ice water. After filtration, the filtrate was washed with 100 mL of water and 100 mL of methanol, followed by vacuum drying to synthesize a wholly aromatic polyimide.

In the infrared absorption spectrum of the synthesized polymer (Fig. 7), C = O absorption band of imide group and CNC absorption band of imide group at 1382 cm ^-1 were observed at 1781 cm ^-1 and 1728 cm ^-1 . In the infrared absorption spectrum of the polymer, the imidization rate was measured to be 92% based on the absorbance of the CNC absorption band based on the absorption band of the aromatic ring. The synthesized polyimide was dissolved in NMP to obtain a polyimide film having a thickness of 30 탆 and a light transmittance of 88% or more at 400 nm (FIG. 13).

Comparative Example 2: Thermal imidation method

285 mL of N -methyl-2-pyrrolidone (NMP) was added to a 500-mL two-necked round bottom flask substituted with nitrogen gas, and 18.91 g (0.090 mol) of 1,2,3,4-cyclopentane dianhydride And 12.80 g (0.090 mol) of 1,4-bis (aminomethyl) cyclohexane were added thereto. The reaction mixture was reacted at room temperature for 24 hours to prepare a polyamic acid solution and then reprecipitated in water. After filtration, the filtrate was washed with 100 mL of water and 100 mL of methanol, followed by vacuum drying to obtain a wholly aromatic polyamic acid powder.

Next, the polyamic acid powder was heated at 250 to 350 ° C in an oven or hot plate stepwise and heated for 12 hours to synthesize a wholly aromatic polyimide.

In the infrared absorption spectrum (FIG. 8) of the synthesized polymer, the C═O absorption band of the imide group and the CNC absorption band of the imide group at 1385 cm ^-1 were observed at 1785 cm ^-1 and 1728 cm ^-1 , respectively. In the infrared absorption spectrum of the polymer, the imidization rate was measured to be 99% based on the absorbance of the CNC absorption band based on the absorption band of the aromatic ring. The synthesized polyimide was dissolved in NMP to obtain a polyimide film having a thickness of 29 탆 and exhibiting a light transmittance of 84% or more at 400 nm (Fig. 14).

The results of Table 1 are compared with those of Examples 1 to 6 according to the present invention and the polyimide prepared according to the comparative example according to the prior art.

Referring to Table 1, polyimides prepared according to the present invention (Examples 1 to 6) can be produced at relative low temperatures, and are environmentally friendly and economical because no organic solvent is used. In addition, the polyimide films (Examples 3 to 6) produced using the polyimide powder produced according to the present invention are colorless and transparent to the polyimide films (Comparative Examples 1 and 2) produced by the conventional method.

Claims (15)

a) preparing a polyamic acid aqueous solution by adding a water-soluble polyamic acid made of a polyamic acid and an amine compound to water; And
b) adding a dehydrating agent to the polyamic acid solution, and heating the polyimide powder to prepare a polyimide powder. The method according to claim 1,
Further comprising filtering and drying the polyimide powder prepared in the step b). The method according to claim 1,
The water-soluble polyamic acid may be prepared by reacting a polyamic acid represented by the following formula (1), which is prepared by a reaction between a dianhydride compound and a diamine compound,
Wherein the polyimide powder is prepared by reacting a polyimide compound with an amine compound.

&Lt; Formula 1 >
(In the general formula 1 R ₁ is

, &Lt; / RTI &gt;
In the above formula (1), R ₂ is

&Lt; / RTI &gt; X is an integer satisfying 1? X? 50, n is a natural number in the range of 1 to 20, W, X and Y are each an alkyl or aryl group having 1 to 30 carbon atoms, and Z is an ester An amide group, an imide group and an ether group. The method according to claim 1,
The amine compound is trimethyl amine, triethyl amine, methyl-pyrrolidine, N, N - dimethyl-hexylamine, N, N - dimethyl-amine, imidazole, 1,2-dimethyl-imidazole, N - methylimidazole, N - benzyl-2-methylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 5-methyl benzimidazole, N - benzyl-2-methylimidazole 1 &gt; is selected from the group consisting of a halogen atom, a hydroxyl group, a hydroxyl group, a hydroxyl group, a hydroxyl group, a hydroxyl group, a hydroxyl group, Or two or more kinds of amine compounds. delete delete The method according to claim 1,
Wherein the concentration of the water-soluble polyamic acid in the aqueous polyamic acid solution prepared in the step a) is 1 to 10% by weight. The method according to claim 1,
The dehydrating agent in step b) may be a chemical dehydrating agent, and may be at least one selected from the group consisting of acetic anhydride, anhydrous propionic acid, anhydrous butyric acid, anhydrous benzoic acid, anhydrous adipic acid, anhydrous isophthalic acid, phthalic anhydride and trimellitic anhydride &Lt; / RTI &gt; The method according to claim 1,
Wherein the dehydrating agent in step b) is added in a molar ratio of 2 to 40 times the number of moles of the water-soluble polyamic acid repeating unit. The method according to claim 1,
Wherein the step (b) is carried out at a temperature in the range of 40 to 250 占 폚. The method according to claim 1,
Wherein the step b) is carried out in a pressure range of 1 to 40 bar. The method according to claim 1,
And the step b) is performed for 10 minutes to 72 hours. delete delete delete

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