CN116693927A

CN116693927A - Porous polyimide composition and polyamic acid composition

Info

Publication number: CN116693927A
Application number: CN202310173678.9A
Authority: CN
Inventors: 森裕贵
Original assignee: Asahi Kasei Corp
Current assignee: Asahi Kasei Corp
Priority date: 2022-03-03
Filing date: 2023-02-28
Publication date: 2023-09-05

Abstract

The present invention relates to a porous polyimide composition and a polyamic acid composition. The present invention aims to provide a porous polyimide composition having low coloring and high light transmittance. The present invention provides a porous polyimide composition, which has an average pore diameter (L) of 5nm to 500nm based on a pore volume (V) and a BET specific surface area (A) as determined by a gas adsorption method, wherein the average pore diameter (L) is represented by the following formula: l=4v/a, a light transmittance at a film thickness of 1mm is 10% to 100% at 450nm, and a degree of polymerization (n) is 5 to less than 40.

Description

Porous polyimide composition and polyamic acid composition

Technical Field

The present invention relates to a porous polyimide composition and a polyamic acid composition for obtaining the porous polyimide composition.

Background

Aerogel has been conventionally defined as a porous substance in which a solvent contained in the gel is replaced with a gas by supercritical drying, but in recent years, it has been more widely recognized as a porous substance in which a solvent is removed from a colloid or polymer network containing a solvent while suppressing shrinkage, volume reduction, and the like. Aerogels have various properties such as low density, high porosity, porosity (mesopores), high specific surface area, high specific strength, high heat insulation, high electrical insulation, and high sound insulation due to their fine pore structure. As the type of aerogel, for example, silica aerogel, polymer aerogel, polyimide aerogel, carbon aerogel, and the like are known.

Patent documents 1 and 2 describe a crosslinked polyimide aerogel and a method for producing the same. The aerogel has polyamide crosslinks formed using a triacyl chloride crosslinker. The aerogel comprises a polyimide oligomer component and a polyamide crosslink, the polyamide crosslink being associated with the polyimide oligomer component, the polyimide oligomer component comprising the reaction product of a diamine and a dianhydride in a ratio of (n+1): n (n is the number of repeating units of the oligomer).

Patent document 3 describes a method for producing polyimide aerogel. By properly adjusting the ratio of pyromellitic anhydride and 4,4' -hexafluoroisopropylidenedi (phthalic anhydride) (6 FDA) as aromatic dicarboxylic anhydrides to diamines such as 2,2' -dimethyl-4, 4' -benzidine, the transparency of the polyimide aerogel can be improved.

Non-patent document 1 describes a method for producing polyimide aerogel from an amine-terminated oligomer crosslinked with 1,3, 5-benzenetricarboxylic acid chloride (BTC). The aerogel prepared by the method has the same elastic modulus and high surface area compared with substances with the same crosslinking density such as 1,3, 5-tri (4-aminophenoxy) benzene (TAPB) and octa (aminophenoxy) silsesquioxane (OAPS) reported so far.

Non-patent document 2 describes a polyimide aerogel having improved transparency and a method for producing the same. The transparency of the polyimide aerogel can be improved by properly adjusting the ratio of pyromellitic anhydride and 4,4' -hexafluoroisopropylidenedi (phthalic anhydride) (6 FDA) to 2,2' -dimethyl-4, 4' -benzidine.

Non-patent document 3 describes a polyimide aerogel using an alicyclic acid anhydride and a method for producing the same. Polyimide aerogels obtained by crosslinking polyimides composed of 1,2,3, 4-cyclobutanetetracarboxylic anhydride (CBDA) and 2,2 '-bis (trifluoromethyl) -4,4' -benzidine (TFMB) with octa (aminophenyl) silsesquioxane (OAPS) exhibit high hydrophobicity and low dielectric properties.

Non-patent document 4 describes a method for producing a nanoporous polyimide aerogel. The method comprises the following steps: an acid anhydride-terminated polyamine acid oligomer is crosslinked in a solution with an aromatic triamine, imidized chemically, thereby obtaining a polyimide gel, and the gel is subjected to supercritical drying, thereby obtaining a nanoporous polyimide aerogel.

Prior art literature

Patent literature

Patent document 1: U.S. Pat. No. 9434832 Specification

Patent document 2: U.S. Pat. No. 10358539 Specification

Patent document 3: U.S. Pat. No. 10800883 Specification

Non-patent literature

Non-patent document 1: mary Ann B.meador, et al, "" Polyimide Aerogels with Amide Cross-Links: a Low Cost Alternative for Mechanically Strong Polymer Aerogels ", ACS appl. Mater. Interfaces, (2015), 7 (2), 1240-1249

Non-patent document 2: stephanie l.vivod, et al, "Toward Improved Optical Transparency of Polyimide Aerogels", ACS appl. Mater. Interfaces, (2020), 12,8622-8633

Non-patent document 3: dengxiong Shen, et al, "Intrinsically Highly Hydrophobic Semi-alicyclic Fluorinated Polyimide Aerogel", chem. Lett., (2013), 42,1230-1232

Non-patent document 4: mary Ann B Meador, et al, "Mechanically strong, flexible polyimide aerogels cross-linked with aromatic triamine", ACS appl. Mater. Interfaces, (2012), 4 (2), pp.536-544

Disclosure of Invention

Problems to be solved by the invention

The polyimide aerogels described in patent documents 1 and 2 and non-patent document 1 are significantly colored from yellow to orange in the aromatic polyimide structure. Further, it is considered that the light-transmitting material has a fine pore structure (fine pores) for diffusely reflecting light and has low light transmittance.

The polyimide aerogel described in non-patent document 2 is also clear in yellow to orange coloring derived from an aromatic polyimide structure, as in non-patent document 1.

The polyimide aerogel described in non-patent document 3 uses alicyclic dianhydride, and therefore has a low coloring property of the polyimide skeleton itself. On the other hand, as in non-patent documents 1 and 2, it is considered that the aerogel has a pore structure (micropores) for diffusely reflecting light and is white and opaque.

In the methods described in patent document 3 and non-patent document 4, it is difficult to obtain polyimide aerogels having low colorability and high light transmittance.

An object of the present invention is to provide a porous polyimide composition having low coloring and high light transmittance, and a polyamic acid composition for obtaining the porous polyimide composition.

Means for solving the problems

Examples of embodiments of the present invention are listed below.

[1]

A porous polyimide composition having an average pore diameter (L) as determined by a gas adsorption method of 5nm to 500nm, wherein the average pore diameter (L) is obtained by the following formula based on a pore volume (V) and a BET specific surface area (A), and L=4V/A

A light transmittance at a film thickness of 1mm of 10% to 100% at 450nm, and

the degree of polymerization (n) is 5 or more and less than 40.

[2]

The porous polyimide composition according to item 1, wherein in the desorption curve in the nitrogen adsorption/desorption isotherm of 77K,

the ratio of the adsorption amount under the conditions of the relative pressures of 0.90, 0.85, 0.80 and 0.75 to the adsorption amount under the conditions of the relative pressure of 0.98 is respectively 0.50 to 1.0, 0.30 to 1.0, 0.25 to 0.90, and 0.20 to 0.85.

[3]

The porous polyimide composition according to item 1 or 2, which has a crosslinked polyimide structure obtained by crosslinking a polyamic acid obtained by polymerizing tetracarboxylic dianhydride and diamine at a ratio of n+1:n.

[4]

The porous polyimide composition according to any one of items 1 to 3, wherein a minimum value of light transmittance at a film thickness of 1mm of between 400nm and 700nm is 5% or more.

[5]

The porous polyimide composition according to any one of items 1 to 4, wherein a difference between a maximum value and a minimum value of light transmittance at a film thickness of 1mm of 400nm to 700nm is 1% to 80%.

[6]

The porous polyimide composition according to any one of items 1 to 5, wherein an average value of light transmittance at a film thickness of 1mm between 400nm and 700nm is 30% to 100%.

[7]

The porous polyimide composition according to any one of items 1 to 6, which has a bulk density of 0.05g/cm ³ Above 0.50g/cm ³ The following is given.

[8]

The porous polyimide composition according to any one of items 1 to 7, which has a breaking point strain of 5% or more in a three-point bending test.

[9]

The porous polyimide composition according to any one of items 1 to 8, which has a flexural strength of 5MPa or more in a three-point flexural test.

[10]

The porous polyimide composition according to any one of items 1 to 9, which has a flexural modulus of 50MPa or more in a three-point flexural test.

[11]

The porous polyimide composition according to any one of items 1 to 10, which has a BET specific surface area of 10m after heat treatment at 200℃and 1 hour ² Per gram of above 2,000m ² And/g or less.

[12]

The porous polyimide composition according to any one of items 1 to 11, which has a sheet shape.

[13]

The porous polyimide composition according to item 12, which has an average thickness of 10mm or less.

[14]

The porous polyimide composition according to any one of items 1 to 13, wherein when the light transmittance at 450nm is LT [% ] and the thickness is T [ mm ], the following formula is satisfied:

0<(100－LT)/T≤70

the relationship represented.

[15]

The porous polyimide composition according to any one of items 1 to 14, wherein the polyimide constituting the porous polyimide composition has a polyimide main skeleton and a crosslinked structure that crosslinks the polyimide main skeleton.

[16]

The porous polyimide composition according to item 15, wherein the crosslinked structure is based on:

a group having 3 or more valencies derived from a monocyclic or polycyclic aromatic ring having or not having a substituent, or

A group of 3 or more valencies derived from a plurality of aromatic rings having or not having a substituent, which are bonded to each other by direct bonding or bonding via a hetero atom

Is a structure of (a).

[17]

The porous polyimide composition according to item 15, wherein the polyimide main skeleton has a molecular chain represented by the following general formula (1):

[ chemical formula 1 ]

In the general formula (1), X and/or Y have an alicyclic structure, and n is the degree of polymerization of the polyimide.

[18]

The porous polyimide composition according to any one of items 1 to 17, wherein the polyimide constituting the porous polyimide composition contains a polymerization product of a polymerization component comprising tetracarboxylic dianhydride, diamine and an amine having 3 or more functions,

the proportion of the amine having 3 or more functions is 1 to 40 mass% based on 100 mass% of the total of the tetracarboxylic dianhydride, the diamine and the amine having 3 or more functions.

[19]

The porous polyimide composition according to any one of items 1 to 18, which contains a polymerization product of a polymerization component comprising tetracarboxylic dianhydride, diamine and an amine having 3 or more functions among polyimides constituting the porous polyimide composition,

The ratio of the tetracarboxylic dianhydride containing an aromatic ring is less than 50% by mass relative to 100% by mass of the total of the tetracarboxylic dianhydrides, and/or

The proportion of the diamine containing an aromatic ring is less than 50% by mass relative to 100% by mass of the total of the diamines.

[20]

The porous polyimide composition according to any one of items 1 to 17, which is used as a heat-resistant material having low coloration and high light transmittance.

[21]

A polyamic acid composition comprising a resin precursor and a solvent for obtaining a heat-resistant material having low coloration and high light transmittance, wherein,

the porous polyimide composition obtained by adding a crosslinking agent to the polyamic acid composition and then immersing the composition in a solution to chemically imidize the composition satisfies the following conditions (1) to (2):

(1) An average pore diameter (L) obtained by a gas adsorption method is 5nm to 500nm, and the average pore diameter (L) is obtained from the following formula based on a pore volume (V) and a BET specific surface area (A);

L＝4V/A

(2) The transmittance at a film thickness of 1mm is 10% or more at 450nm, and,

the polyimide has a polymerization degree (n) of 5 or more and less than 40.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a porous polyimide composition having low colorability and high light transmittance, and a polyamic acid composition for obtaining the porous polyimide composition can be provided.

Detailed Description

Hereinafter, an embodiment of the present invention (hereinafter, simply referred to as "embodiment") will be described in detail. The present invention is not limited to the following embodiments, and may be implemented by various modifications within the scope of the gist thereof.

In the following description, an upper limit or a lower limit in a numerical range described in stages may be replaced with an upper limit or a lower limit in a numerical range described in other stages. In the following description, the upper limit value or the lower limit value in a certain numerical range may be replaced with the value described in the examples. The term "step" in the following description includes, of course, a separate step, and even if the step cannot be clearly distinguished from other steps, the term may be included in the term as long as the function of the "step" is achieved.

Porous polyimide composition

One embodiment of the present invention provides a porous polyimide composition composed of polyimide (hereinafter, sometimes simply referred to as "porous polyimide"). The porous polyimide is typically made of polyimide, but may contain components other than polyimide within a range that does not impair the effects of the present invention. The porous polyimide according to one embodiment has an average pore diameter (L) of 5nm to 500nm based on the pore volume (V) and BET specific surface area (A) as determined by a gas adsorption method,

L＝4V/A

The light transmittance at a film thickness of 1mm is 10% to 100% at 450nm, and the degree of polymerization (n) is 5 to less than 40.

In one embodiment, the porous polyimide is in the form of a sheet. The thickness of the sheet is not limited, and in one embodiment, the average thickness is 10mm or less, or 8mm or less, or 5mm or less, or 3mm or less, or 1mm or less, or 500 μm or less, or 400 μm or less, or 300 μm or less, or in one embodiment, 0.1 μm or more. Porous polyimide having a sheet shape, particularly a sheet shape having an average thickness of 10mm or less, is useful as a aerogel sheet for various applications, such as a heat insulating material, a low dielectric material, a filter material, and the like. Alternatively, the average thickness of the sheet may be more than 10mm, and the porous polyimide may be in a block shape.

In one embodiment, the porous polyimide is used as a heat-resistant material having low coloration and high light transmittance. The porous polyimide is suitable for fields requiring heat resistance, such as optical materials (window glass and the like), coating materials, interlayer materials, covering materials and the like in the aviation field, the vehicle field and the like, because it transmits visible light (light having a wavelength of 400nm to 700nm in one embodiment) effectively. Alternatively, the porous polyimide according to one embodiment may be a material having low coloration and high light transmittance, and at least one material selected from the group consisting of a high electric insulating material, a high sound insulating material, and a high heat insulating material. Alternatively, the porous polyimide according to one embodiment may be a low-coloring and high-light-transmitting material or a high-strength material.

"colorability" and "transparency" are not strictly the same concept. The colorability, for example, relates to charge transfer or interaction between the aromatic diamine moiety and the aromatic anhydride moiety. The "transparency" relates to, for example, scattering of visible light (light having a wavelength of 400nm to 700nm in one embodiment) of the porous polyimide. Here, as confirmed in the examples, the porous polyimide of one embodiment has low colorability and high light transmittance. The "colorability" and "light transmittance" of the degree that can be confirmed in the examples correspond to "low colorability" and "high light transmittance" that are particularly suitable for the above-mentioned applications.

In one embodiment, the porous polyimide has a light transmittance of 10% to 100% at 450nm at a film thickness of 1 mm. The light transmittance falling within the above range means that the low coloring property and the high light transmittance are more suitably exhibited. In one embodiment, the light transmittance is preferably 15% or more, 17.5% or more, or 20% or more. In one embodiment, the light transmittance may be 50% or more, or 60% or more. The term "light transmittance at a film thickness of 1 mm" as used herein refers to light transmittance at an average thickness of 1mm or light transmittance at an average thickness of 1 mm.

In one embodiment, the minimum value of the light transmittance between 400nm and 700nm at a film thickness of 1mm of the porous polyimide is 5% or more. The minimum value being within the above range means that the porous polyimide has a certain degree of low coloring and light transmittance in the visible light (in one embodiment, light having a wavelength of 400nm to 700 nm) regardless of the shape and/or film thickness. In one embodiment, the minimum value is preferably 7% or more, 10% or more, or 15% or more.

In one embodiment, the difference between the maximum value and the minimum value of light transmittance between 400nm and 700nm at a film thickness of 1mm of the porous polyimide is 1% or more. The difference falling within the above range means that the fluctuation of low coloring property and the fluctuation of light transmittance in the porous polyimide are small in the region of visible light (in one embodiment, light having a wavelength of 400nm to 700 nm). In one embodiment, the difference is preferably 1% or more, 5% or more, or 10% or more, and preferably 90% or less, 85% or less, or 80% or less. The difference may be 70% or less.

In one embodiment, the average value of light transmittance between 400nm and 700nm at a film thickness of 1mm of the porous polyimide is 30% to 100%. The average value falling within the above range means that the porous polyimide has low coloring and light transmittance over the entire visible light (in one embodiment, light having a wavelength of 400nm to 700 nm). In one embodiment, the average value is preferably 35% or more, 40% or more, or 45% or more. The average light transmittance can be obtained by setting the wavelength range to 400nm to 700nm as the average light transmittance at each wavelength.

In one embodiment, the porous polyimide has a degree of polymerization (n) of 5 or more and less than 40. The above-mentioned degree of polymerization (n) is also related to "low coloring" and "high light transmittance". The polymerization degree (n) is preferably 30 or less, 25 or less, or 20 or less from the viewpoint of low coloring property and high light transmittance.

In addition, if the polymerization degree (n) is too small, that is, if the crosslinking degree is too large, the time required for the polyamic acid solution to gel is too short, and thus it is often difficult to mold the gel into a desired shape. On the other hand, if the polymerization degree (n) is too high, that is, the crosslinking degree is too low, the obtained polyamic acid wet gel tends to have insufficient physical strength, and therefore, the obtained gel tends not to gel or tends to be brittle and difficult to handle. Therefore, when the degree of polymerization (n) is within the above range, it is easy to achieve both the gelation time and sufficient physical strength for processing the obtained wet gel when the polyamic acid is crosslinked to obtain the polyamic acid wet gel.

In one embodiment, the porous polyimide has a ratio of the adsorption amount at the relative pressures of 0.90, 0.85, 0.80, and 0.75 to the adsorption amount at the relative pressure of 0.98 in the desorption curve in the 77K nitrogen adsorption/desorption isotherm of 0.50 to 1.0, 0.30 to 1.0, 0.25 to 0.90, and 0.20 to 0.85, respectively. Satisfying these means that it is easy to realize a structure that makes the contribution of visible light diffuse reflection or voids small, that is, a structure that contributes to high transparency of the porous polyimide. From the viewpoints of low coloring property and high light transmittance, the ratio of the adsorption amount under the conditions of relative pressures 0.90, 0.85, 0.80 and 0.75 to the adsorption amount under the conditions of relative pressures 0.98 is more preferably 0.55 to 1.0, 0.35 to 1.0, 0.30 to 0.90 and 0.20 to 0.80, respectively, and the ratio of the adsorption amount under the conditions of relative pressures 0.90, 0.85, 0.80 and 0.75 to the adsorption amount under the conditions of relative pressures 0.98 is more preferably 0.60 to 1.0, 0.40 to 1.0, 0.35 to 0.90 and 0.25 to 0.80, respectively.

Regarding the shape of the pore diameter, the following is examined.

In the prior art in which a crosslinking agent having an electrophilic functional group such as acid chloride or acid anhydride is added to ungelled polyamic acid, there is a possibility that side chains of the polyamic acid react with the electrophilic functional group of the crosslinking agent, and a side chain crosslinked gel may be generated. The gel causes an uneven pore structure. On the other hand, in the present embodiment in which such a non-uniform pore structure is avoided, the pore structure as described above is easily realized.

In one embodiment, when the light transmittance at 450nm is LT [% ] and the thickness is T [ mm ], the porous polyimide satisfies the following formula:

0<(100－LT)/T≤70

the relationship represented. The porous polyimide satisfying the above relation is, needless to say, particularly suitable for the above application, in which it is easy to efficiently transmit visible light (in one embodiment, light having a wavelength of 450 nm) even when it is a thick film to some extent. In one embodiment, the above relationship is preferably 0 or more, 1 or more, or 2 or more, and preferably 80 or less, 75 or less, or 70 or less.

The porous polyimide according to one embodiment has an average pore diameter (L) of 5nm to 500nm based on the pore volume (V) and BET specific surface area (A) as determined by a gas adsorption method, and is obtained by the following formula.

L＝4V/A

The average pore diameter (L) in this range is an index indicating the submicron pore size. The present inventors focused on controlling the average pore diameter (L) to be the submicron pore size, and the porous polyimide according to one embodiment of the present invention was less in diffuse reflectance of light in the visible light region (in one embodiment, light having a wavelength of 400nm to 700 nm) than in the case of the polyimide having other pore sizes. In one embodiment, the average pore diameter (L) is 5nm or more, or 6nm or more, or 7nm or more, or 8nm or more, or 9nm or more, or 10nm or more, and in one embodiment, 500nm or less, or 300nm or less, or 200nm or less, or 100nm or less, or 50nm or less, or 30nm or less, or 20nm or less.

In one embodiment, the porous polyimide has a BET specific surface area of 10m ² Per gram of above 2,000m ² And/g or less. The BET specific surface area within the above range is also an index indicating the submicron pore size. In one embodiment, the BET specific surface area is 10m ² Per gram or more, or 50m ² Per gram or more, or 100m ² /g or more, or 200m ² Per gram or more, or 300m ² In one embodiment, the ratio of the total weight of the catalyst to the total weight of the catalyst is 2,000m ² Per gram or less, or 1,500m ² /g or less, or 1,000m ² Per gram or less, or 800m ² And/g or less.

In one embodiment, the porous polyimide has a BET specific surface area of 10m after heat treatment at 200 ℃ for 1 hour ² Per gram of above 2,000m ² And/g or less. The BET specific surface area falling within the above range means that the porous polyimide maintains a pore structure after the heat treatment. In one embodiment, the BET specific surface area is 10m ² Per gram or more, or 50m ² Per gram or more, or 100m ² /g or more, or 200m ² Per gram or more, or 300m ² In one embodiment, the ratio of the total weight of the catalyst to the total weight of the catalyst is 2,000m ² Per gram or less, or 1,500m ² /g or less, or 1,000m ² Per gram or less, or 800m ² And/g or less.

In one embodiment, the porous polyimide has a flexural modulus of 50MPa or more in a three-point bending test. When the flexural modulus is within the above range, the porous polyimide can exhibit excellent toughness useful for various uses of the aerogel, which is advantageous from the viewpoint of being advantageous. In one embodiment, the flexural modulus is 100MPa or more, 150MPa or more, or 200MPa or more, or 300MPa or more, or 400MPa or more. The upper limit of the flexural modulus is not limited, and may be 1,000mpa or less in one embodiment, in view of the ease of producing the porous polyimide.

In one embodiment, the flexural strength (flexural strength) of the porous polyimide in the three-point bending test is 5MPa or more. When the flexural strength is within the above range, the porous polyimide can exhibit excellent bending resistance useful for various uses of the aerogel, which is advantageous from the viewpoint of being advantageous. In one embodiment, the bending strength is 7MPa or more, 10MPa or more, 12MPa or more, 13MPa or more, 14MPa or more, or 15MPa or more. The upper limit of the flexural strength is not limited, and may be 30MPa or less in one embodiment from the viewpoint of easiness of producing the porous polyimide.

In one embodiment, the porous polyimide has a fracture point of 5% or more in the three-point bending test. When the breaking point strain is within the above range, the porous polyimide can exhibit excellent flexibility useful for various uses of the aerogel, which is advantageous from the viewpoint of being advantageous. In one embodiment, the breaking point strain is 6% or more, 8% or more, 10% or more, 11% or more, 12% or more, 13% or more, 14% or more, or 15% or more. The upper limit of the breaking point strain is not limited, and may be 50% or less in one embodiment from the viewpoint of easiness of producing the porous polyimide. The breaking point strain can be measured by a three-point bending test, and for example, can be measured by the method described in examples.

In one embodiment, the porous polyimide has a bulk density of 0.05g/cm ³ Above 0.80g/cm ³ The following is given. The bulk density within the above range is also an index indicating the submicron pore size. In one embodiment, the bulk density is 0.05g/cm ³ Above, or 0.06g/cm ³ Above, or 0.07g/cm ³ Above, or 0.08g/cm ³ Above, or 0.09g/cm ³ Above, or 0.10g/cm ³ In one embodiment, the concentration is 0.50g/cm ³ Below, or 0.45g/cm ³ Below, or 0.40g/cm ³ The following is given.

The bulk density of the porous polyimide after heat treatment at 200 ℃ and 1 hour is preferably in the same numerical range as the bulk density, in terms of maintaining the pore structure satisfactorily even after heat treatment. That is, in one embodiment, the bulk density after heat treatment at 300℃and 1 hour0.05g/cm ³ Above, or 0.06g/cm ³ Above, or 0.07g/cm ³ Above, or 0.08g/cm ³ Above, or 0.09g/cm ³ Above, or 0.10g/cm ³ In one embodiment, the concentration is 0.50g/cm ³ Below, or 0.45g/cm ³ Below, or 0.40g/cm ³ The following is given.

As a method for controlling the above-described constitution and characteristics of the porous polyimide within the range of the present embodiment, there can be exemplified, but not limited to

(1) Controlling the molecular structure of polyimide, and/or

(2) In the production of polyimide, gelation is performed before imidization.

Polyimide molecular structure

In one embodiment, the polyimide constituting the porous polyimide is a crosslinked polyimide having a polyimide main skeleton and a crosslinked structure that crosslinks the polyimide main skeleton.

In one embodiment, the polyimide is a polymerization product of a polymeric component comprising tetracarboxylic dianhydride, diamine, and an amine of 3 or more functions. The proportion of the amine having 3 or more functions is preferably 1% by mass or more, or 1.5% by mass or more, and from the same point of view, it is preferably 40% by mass or less, or 35% by mass or less, or 30% by mass or less, relative to 100% by mass of the total of the tetracarboxylic dianhydride, the diamine, and the amine having 3 or more functions, in order to obtain a desired pore structure of the porous polyimide by making the crosslinking density of the polyimide within a suitable range.

In one embodiment, the polyimide has a crosslinked polyimide structure obtained by crosslinking a polyamic acid obtained by polymerizing a tetracarboxylic dianhydride and a diamine at a ratio of n+1:n. Thus, the method described in "production of porous polyimide" described later can be easily used, and thus porous polyimide having low coloring and high light transmittance can be easily realized.

The polyimide backbone and the crosslinked structure may each have an aliphatic structure (including an alicyclic structure) or an aromatic structure or a combination thereof.

The main skeleton of polyimide constituting the porous polyimide preferably has a molecular chain represented by the following general formula (1):

[ chemical formula 2 ]

{ in the general formula (1), X and Y are divalent organic groups, and n is the degree of polymerization of polyimide }. In one embodiment, X is a tetravalent organic radical from a tetracarboxylic dianhydride, Y is a divalent organic radical from a diamine, and n is a positive integer.

(Structure comprising alicyclic ring)

In one embodiment, X and/or Y have a structure including an alicyclic ring (i.e., a cycloalkane structure, an alicyclic structure, etc.). The above structure has small intermolecular interactions compared to aromatic rings, for example, and therefore can suppress coloration due to large intermolecular interactions. Further, although a polyimide obtained from a dianhydride having an aromatic ring (dianhydride not including an alicyclic structure) and a diamine having an aromatic ring (diamine not including an alicyclic structure) is easily colored as a yellow system due to its structure having an aromatic ring, the porous polyimide in one embodiment has a structure including an alicyclic ring, and accordingly the proportion of the structure having an aromatic ring can be reduced, whereby coloring of such a yellow system can be suppressed.

In one embodiment, X and Y may have a structure including an alicyclic ring only, or may both have a structure including an alicyclic ring. In the case where both X and Y have an alicyclic structure, the "alicyclic structure" may be the same or different from each other. The "alicyclic structure", "diamine having an alicyclic structure (alicyclic diamine)" and "dianhydride having an alicyclic structure (alicyclic dianhydride)" may each have an aromatic ring within the scope of the gist of the present invention. The "aromatic ring" which may be optionally provided may have a substituent, and the "alicyclic ring" in the "alicyclic structure" may have a substituent.

In order to introduce the alicyclic structure into X, a polyimide precursor (polyamide acid) is obtained using a dianhydride having the above structure, and the polyimide precursor is crosslinked and imidized. Specifically, the dianhydride having the above-mentioned structure may be exemplified by

1,2,3, 4-cyclobutane tetracarboxylic dianhydride (CBDA),

1, 3-dimethyl-1, 2,3, 4-cyclobutane tetracarboxylic dianhydride,

1,2,3, 4-tetramethyl-1, 2,3, 4-cyclobutane tetracarboxylic dianhydride,

4- (2, 5-Dioxotetrahydrofuran-3-yl) -1,2,3, 4-tetrahydronaphthalene-1, 2-dicarboxylic anhydride,

Norbornane-2-spiro-2 ' -cyclopentanone-5 ' -spiro-2 ' -norbornane-5, 5', 6 ' -tetracarboxylic dianhydride (CpODA),

5- (2, 5-Dioxotetrahydrofuranyl) -3-methyl-3-cyclohexene-1, 2-dicarboxylic anhydride,

3- (carboxymethyl) -1,2, 4-cyclopentanetrimoic acid 1,4:2, 3-dianhydride (TCA),

Bicyclo [2.2.2] oct-7-ene-2, 3,5, 6-tetracarboxylic dianhydride,

Bicyclo [2.2.2] octane-2, 3,5, 6-tetracarboxylic acid 2,3:5, 6-dianhydride,

Cyclopentane tetracarboxylic dianhydride,

Cyclohexane tetracarboxylic dianhydride,

Meso-butane-1, 2,3, 4-tetracarboxylic dianhydride

1,1' -bicyclohexane-3, 3',4' -tetracarboxylic acid-3, 4:3',4' -dianhydride, and the like.

Preferably 1,2,3, 4-cyclobutane tetracarboxylic dianhydride (CBDA),

3- (carboxymethyl) -1,2, 4-cyclopentane tricarboxylic acid 1,4:2, 3-dianhydride (TCA),

from the viewpoint of polymerization reactivity and the physical strength of the obtained gel, 1,2,3, 4-cyclobutane tetracarboxylic dianhydride (CBDA) is particularly preferred.

In order to introduce an alicyclic structure into Y, a polyimide precursor (polyamide acid) is obtained by using a diamine having the above structure, and the polyimide precursor is crosslinked and imidized. The diamine having the above structure is specifically exemplified by

1, 4-Cyclohexanediamine (CHDA),

1, 3-cyclohexanediamine,

1, 2-cyclohexanediamine,

1, 4-bis (aminomethyl) cyclohexane,

1, 3-bis (aminomethyl) cyclohexane,

Bis (4-aminocyclohexyl) methane,

4,4' -methylenebis (2-methylcyclohexylamine),

3,3 '-dimethyl-4, 4' -diaminodicyclohexylmethane,

Isophoronediamine,

2, 5-bis (aminomethyl) bicyclo [2.2.1] heptane and the like.

In one embodiment, in the polyimide constituting the porous polyimide, the proportion of the tetracarboxylic dianhydride containing an alicyclic is 50 mass% or more and 100 mass% or less relative to 100 mass% of the total of the tetracarboxylic dianhydrides, and/or the proportion of the diamine containing an alicyclic is 50 mass% or more and 100 mass% or less relative to 100 mass% of the total of the diamines. Thus, the increase in the interaction between molecules is easily suppressed, and thus a porous polyimide having low colorability and high light transmittance can be suitably obtained.

In one embodiment, in the polyimide constituting the porous polyimide, the proportion of the tetracarboxylic dianhydride containing an aromatic ring is 0 or more and less than 50 mass%, or more than 0 and less than 50 mass%, and/or the proportion of the diamine containing an aromatic ring is 0 or more and less than 50 mass%, or more than 0 and less than 50 mass%, relative to the total 100 mass% of the diamines. Thus, the coloring of the yellow system which is colored by the skeleton having an aromatic ring is easily suppressed in the obtained polyimide, and thus a porous polyimide having low coloring and high light transmittance can be suitably obtained.

X may have a structure that imparts linearity to the molecular chain of the obtained polyimide, or may have a structure that imparts flexibility. X preferably has a structure that imparts linearity to the molecular chain of the obtained polyimide. In the present application, the term "imparting linearity" to a molecular chain of polyimide means a structure in which two single bonds connecting a monomer unit to be subjected to the alignment and two other monomer units adjacent thereto are aligned in a straight line. In the present application, the term "imparting flexibility" to a molecular chain of polyimide means a structure in which two single bonds connecting a monomer unit to be subjected to bending and two other monomer units adjacent thereto are not aligned in a straight line. By providing X with a structure that imparts linearity to the molecular chain of the obtained polyimide, the heat resistance of the porous polyimide sheet can be controlled to be high. Therefore, by providing X and/or Y with a "structure including an alicyclic ring" and a "structure imparting linearity" and/or a "structure imparting bendability", the obtained polyimide can obtain a contribution from the "structure including an alicyclic ring" and a contribution from the "structure imparting linearity" and/or the "structure imparting bendability".

(Structure for imparting linearity or bendability)

The X having a structure imparting linearity to the molecular chain of polyimide is, for example, a substituted or unsubstituted tetravalent aromatic ring or polycyclic aromatic ring, and an aromatic ring or polycyclic aromatic ring having 2 acid anhydride groups at positions where single bonds of 2 acid imide bonds are aligned in a straight line when 2 acid anhydride groups form an imide bond with amino groups of diamine. Examples of the aromatic ring or polycyclic aromatic ring of X include benzene, naphthalene, anthracene, phenanthrene, naphthacene, triphenylene, and the like,And aromatic rings such as pyrene and condensed aromatic rings.

Examples of the tetracarboxylic dianhydride in which X is an aromatic ring or a polycyclic aromatic ring and has a structure imparting linearity to the molecular chain of polyimide include the following general formula:

[ chemical 3 ]

The compound represented. In the above general formula, R may each independently be at least one organic group selected from the group consisting of hydrogen, halogen, hydroxy, aryl, and aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be a branched or unbranched, saturated or unsaturated aliphatic hydrocarbon group.

Specific examples of the tetracarboxylic dianhydride having a structure imparting linearity to the molecular chain of polyimide include pyromellitic dianhydride (PMDA), 1,4,5, 8-naphthalene tetracarboxylic dianhydride (NTCDA), and 2,3,6, 7-naphthalene tetracarboxylic dianhydride, and pyromellitic dianhydride (PMDA) is particularly preferred.

Specific examples of the tetracarboxylic dianhydride having a structure imparting flexibility to the molecular chain of polyimide include 3,3',4' -biphenyltetracarboxylic dianhydride (BPDA), 2, 3',4' -biphenyltetracarboxylic dianhydride (α -BPDA), 3',4,4' -Benzophenone Tetracarboxylic Dianhydride (BTDA), 4 '-Oxydiphthalic Dianhydride (ODPA), 3',4 '-biphenyl ether tetracarboxylic dianhydride, 2, 3',4 '-biphenyl ether tetracarboxylic dianhydride, 3',4,4 '-biphenylsulfone tetracarboxylic dianhydride (DSDA), 2' -bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride, 2 '-bis (3, 4-dicarboxyphenyl) propane dianhydride, 1,2,4, 5-cyclohexane tetracarboxylic dianhydride (HPMDA), 1,2,3, 4-cyclopentane tetracarboxylic dianhydride (CPDA), 1,2,3, 4-cyclobutane tetracarboxylic dianhydride (CBDA), 1-carboxymethyl-2, 3, 5-cyclopentane tricarboxylic acid-2, 6:3, 5-dianhydride (TCA-AH), 4' - (hexafluoroisopropylidene) diphthalic anhydride (6 FDA), bicyclo [2.2.2] oct-7-ene-2, 3,5, 6-tetracarboxylic dianhydride (BTA), bicyclo [2, 1] heptane-2, 3,5, 6-tetracarboxylic dianhydride (NBn), 1,3, 4,5,9 b-hexahydro-2- (2-TDa-5-dioxa) 2, 3-naphthyridine-1-TDC, etc.

The tetracarboxylic dianhydride having a structure imparting flexibility to the molecular chain of polyimide is more preferably aromatic, and examples thereof include 3,3',4' -biphenyltetracarboxylic dianhydride (BPDA), 2, 3',4' -biphenyltetracarboxylic dianhydride (α -BPDA), 3',4,4' -Benzophenone Tetracarboxylic Dianhydride (BTDA), 4' -Oxydiphthalic Dianhydride (ODPA), 3',4' -biphenyl ether tetracarboxylic dianhydride, 2, 3',4' -biphenyl ether tetracarboxylic dianhydride, and 3,3',4' -biphenyl sulfone tetracarboxylic dianhydride (DSDA). More preferably 3,3',4' -biphenyltetracarboxylic dianhydride (BPDA).

Y may have a structure that imparts linearity to the molecular chain of the obtained polyimide, or may have a structure that imparts flexibility. Y preferably has a structure that imparts linearity to the molecular chain of the obtained polyimide. By providing Y with a structure that imparts linearity to the molecular chain of the obtained polyimide, the heat resistance of the porous polyimide sheet can be controlled to be high.

As Y having a structure imparting linearity to the molecular chain of polyimide, for example, an aromatic ring or a polycyclic aromatic ring which is a substituted or unsubstituted divalent aromatic ring and has 2 amino groups at positions aligned on a straight line by single bonds of 2 imide bonds when 2 amino groups form imide bonds with the acid anhydride group of tetracarboxylic dianhydride is preferable. Typically, there may be a position in which one amino group is para to another amino group. Examples of the aromatic ring or polycyclic aromatic ring of Y include benzene, naphthalene, anthracene, phenanthrene, naphthacene, triphenylene, and the like,And aromatic rings such as pyrene and condensed aromatic rings, and aromatic rings bonded by a single bond such as biphenyl and terphenyl.

Examples of the diamine in which Y is an aromatic ring or a polycyclic aromatic ring and has a structure imparting linearity to the molecular chain of polyimide include the following general formula:

[ chemical formula 4 ]

Specific examples of diamines having a structure imparting linearity to the molecular chain of polyimide include p-phenylenediamine (PPDA), 2, 5-dimethyl-p-phenylenediamine (DMPDA), 2,3,5, 6-tetramethyl-p-phenylenediamine (TMPDA), 4 '-diaminobiphenyl, 2' -Dimethylbenzidine (DMBZ), 3 '-dimethylbenzidine, 2' -bis (trifluoromethyl) benzidine (TFMB), 2, 5-diaminotoluene, 2, 5-dihydroxy-1, 4-phenylenediamine, o-tolidine, 3 '-dihydroxy-4, 4' -diaminobiphenyl, and 3,3 '-dimethoxy-4, 4' -diaminobiphenyl. The diamine having a structure imparting linearity to the molecular chain of the polyimide is preferably at least one selected from the group consisting of p-phenylenediamine (PPDA), 2, 5-dimethyl-p-phenylenediamine (DMPDA), 2,3,5, 6-tetramethyl-p-phenylenediamine (TMPDA), 4 '-diaminobiphenyl, 2' -Dimethylbenzidine (DMBZ), 3 '-dimethylbenzidine, and 2,2' -bis (trifluoromethyl) benzidine (TFMB).

Examples of the diamine having a structure imparting flexibility to the molecular chain of polyimide include the following general formula:

[ chemical 5 ]

/>

As the diamine having a structure imparting flexibility to the molecular chain of polyimide, examples thereof include m-phenylenediamine (MPDA), 2, 4-diaminotoluene, 2, 4-diaminoxylene, 3 '-diaminodiphenyl sulfone (3 DAS), 4' -diaminodiphenyl sulfone (4 DAS), 4 '-diaminobenzophenone (4, 4' -DABP), 3 '-diaminobenzophenone (3, 3' -DABP), 1, 5-diaminonaphthalene (1, 5-DAN), m-tolidine, and aromatic diamines such as 5-amino-2- (4-aminophenyl) -benzimidazole (ABI), 4 '-Diaminobenzidine (DABA), 9-bis (4-aminophenyl) fluorene, 9-bis (4-aminophenoxyphenyl) fluorene, 2,4, 6-trimethyl-1, 3-phenylenediamine (TMPDA), 2-bis (4-aminophenyl) hexafluoropropane (6 FDAm), and 4,4' -Oxydiphenylamine (ODA); and aliphatic diamines such as N, N-dimethyl-1, 3-propanediamine (DMPDA), 1, 4-cyclohexanediamine (trans-form, cis-form, or cis-trans-form mixture) (CHDA), 1, 4-diaminomethylcyclohexane (trans-form, cis-form, or cis-trans-form mixture) (14 BAC), hexamethylenediamine, 1, 3-cyclohexanediamine, 4 '-diaminodicyclohexyl, and 3,3' -diaminodicyclohexyl.

Among diamines having a structure imparting flexibility, preferred examples of aromatic diamines include 1, 5-diaminonaphthalene (1, 5-DAN).

(crosslinked structure)

The crosslinked structure is a 3-functional or more structure, and in one embodiment, is derived from a 3-functional or more crosslinking agent. The functional group of the crosslinking agent is a group reactive with an acid anhydride group or an amino group as a terminal group of the polyamic acid. Thus, the crosslinking agent has an effect of crosslinking the polyamic acids with each other to form a polyamic acid gel. The crosslinker is typically a carboxylic acid or amine of 3 or more functionalities, more typically an amine of 3 or more functionalities.

In one embodiment, the crosslinking agent is a compound represented by the following general formula (4).

Z-(R) _a (4)

(wherein Z is an a-valent organic group, R is each independently an amino group or a carboxyl group, and a is an integer of 3 or more.)

In one embodiment, Z in formula (4) comprises a substituted or unsubstituted aliphatic or aromatic group or a combination thereof. The aliphatic groups may be chain or cyclic, branched or unbranched, saturated or unsaturated. The aromatic groups may be formed from carbocycles and/or fused rings (heterocycles).

The number of carbon atoms of Z is preferably 6 to 24, more preferably 6 to 18, and still more preferably 6 to 12.

In one embodiment, R is all amino groups or all carboxyl groups, preferably all amino groups.

In one embodiment, a is 3 or 4, preferably 3.

In one embodiment, Z is a group having 3 or more valencies derived from a single-ring or multi-ring aromatic ring with or without a substituent (that is, a ring obtained by removing 3 or more hydrogen atoms from the ring), or a group having 3 or more valencies derived from a bonded aromatic ring in which a plurality of aromatic rings with or without a substituent are bonded to each other by direct bonding or bonding via a heteroatom (that is, a ring obtained by removing 3 or more hydrogen atoms from the ring). More specifically, examples of Z include a group having 3 or more valences obtained by removing 3 or more hydrogen atoms from a single-ring or multi-ring aromatic ring with or without a substituent, or a plurality of aromatic rings with or without a substituent (for example, biphenyl) which are directly bonded (also referred to as a wholly aromatic group in the present invention), a group having 3 or more valences obtained by removing 3 or more hydrogen atoms from a plurality of aromatic rings with or without a substituent bonded to each other via a hetero atom (for example, benzophenone, diphenyl ether, diphenyl sulfone, benzanilide, etc.), a group having 3 or more valences of an aliphatic carbon atom in a molecular skeleton (also referred to as a group having an aliphatic skeleton in the present invention), and a group having 3 or more valences (also referred to as a group having an aliphatic skeleton in the present invention). The molecular skeleton of the crosslinking agent means a site involved in the mutual bonding of 3 or more functional groups present in the crosslinking agent. Examples of the substituent include an aliphatic group, an aromatic group, and a combination thereof. The number of carbon atoms of the substituent is preferably 4 or less.

Examples of the crosslinking agent in which Z is a wholly aromatic group include 1,3, 5-tris (4-aminophenyl) benzene (TAB), 2,4, 6-tris (4-aminophenyl) pyridine (TAPP), and 1,3, 5-benzenetricarboxylic acid chloride (BTC).

Examples of the crosslinking agent in which Z is a heteroskeleton-containing group include 1,3, 5-tris (4-aminophenoxy) benzene and the like.

Examples of the crosslinking agent in which Z is an aliphatic skeleton-containing group include 4,4', 4' -Triaminotrityl methane, 4', 4' -methane tetrayl-tetraaniline, etc.

From the viewpoint of obtaining a porous polyimide excellent in heat resistance, Z is preferably a wholly aromatic group or a group containing a heteroskeleton, and more preferably a wholly aromatic group.

In one embodiment, the polyimide has a structure represented by the following general formula (5).

[ 6 ] A method for producing a polypeptide

(wherein X, Y and Z are the same as X in the general formula (2), Y in the general formula (3) and Z in the general formula (4), respectively, and n is a positive integer.)

n is the polymerization degree of polyimide, and may be preferably 3 or more and 5 or more, and may be preferably 40 or less, 30 or less, or 20 or less.

From the aspect of heat resistance of the porous polyimide, a preferable combination of structures of X, Y and Z may be: x is a pure aromatic group and Y and Z are respectively a combination of a wholly aromatic group or a heteroskeleton group, X is a pure aromatic group or a group containing a bendable skeleton, and Y and Z are respectively a combination of wholly aromatic groups.

Superiority of this embodiment

The following describes advantages of the present embodiment over the prior art.

For example, in the method described in patent document 3, it is difficult to obtain polyimide aerogel having low colorability and high light transmittance as in the present embodiment.

In addition, in the method described in patent document 3, it is known that chemical imidization of polyamic acid using alicyclic dianhydride is very slow as compared with chemical imidization of polyamic acid using aromatic dianhydride monomer described in patent documents 1 and 2 and non-patent documents 1 and 2 (literature "scheme of polyimide enhancement and functionalization by enterprise technicians", release of print 1 st edition, 25 th month 2020, authors: post-vine is calm, release station: the signal is the signal of the bus the company "ii). Therefore, it is difficult to obtain an alicyclic polyimide aerogel having a uniform structure by the method described in patent document 3.

Production of porous polyimide

In one embodiment, the porous polyimide of the present invention can be produced by a method comprising the steps of:

A polymerization step of polymerizing the dianhydride of the present invention and the diamine of the present invention to obtain a polyamic acid;

a gelation step of crosslinking the polyamic acid with the crosslinking agent of the present invention to obtain a polyamic acid wet gel;

an imidization step of imidizing the polyamic acid wet gel to obtain a polyimide wet gel; and

and a drying step of drying the polyimide wet gel to obtain a porous polyimide as a polyimide aerogel.

Conventionally, polyimide gels are generally produced by imidizing a polyamic acid to obtain a polyimide, and then gelling the polyimide. In this method, polyimide is easily aggregated during gelation, and therefore, there is a limit in material selection such as selection of polyimide having a molecular structure which is difficult to aggregate in order to stably obtain polyimide aerogel having a desired pore structure. In particular, when the rigidity of the molecular skeleton of polyimide is high, polyimide tends to aggregate during gelation after imidization, and it is difficult to produce polyimide having a desired pore structure. Further, polyimide gels obtained by gelation after imidization are often unsuitable for the production of porous carbon because they lack shape retention properties upon heating, and in particular tend to deform significantly under severe heating conditions such as carbonization.

On the other hand, in the method of imidizing a polyamic acid after gelation, the following advantages can be obtained: by properly adjusting the gelation conditions, a desired pore structure can be stably formed without being limited by the molecular structure of polyimide. In particular, according to this method, even when the rigidity of the molecular skeleton of polyimide is high, polyimide aerogel having a desired pore structure can be stably produced, and therefore, the advantage of this method is particularly remarkable when the rigidity of the molecular skeleton of polyimide is high. In the case where X and/or Y in the general formula (2) of the present invention have an alicyclic structure, the method of imidizing a polyamic acid after gelation is particularly advantageous in that a porous polyimide having low coloring and high light transmittance is obtained.

In one embodiment, the polyamic acid composition of the present invention is a polyamic acid composition comprising a resin precursor and a solvent for obtaining a heat-resistant material having low coloration and high light transmittance,

the porous polyimide obtained by adding a crosslinking agent and chemical imidization by dipping in a solution satisfies the following conditions (1) to (2) in the above polyamide acid composition:

(1) An average pore diameter (L) obtained by a gas adsorption method is 5nm to 500nm, the average pore diameter (L) is obtained by the following formula based on a pore volume (V) and a BET specific surface area (A),

L＝4V/A

(2) A light transmittance of 10% or more at 450nm at a film thickness of 1mm, and

the polyimide has a degree of polymerization (n) of 5 or more and less than 40.

The polyamide acid composition of the present invention can suitably provide the polyimide composition of the present invention satisfying the above (1) and (2). The polyamic acid composition according to one embodiment is particularly suitable for applications requiring low colorability, high light transmittance, and heat resistance, such as optical materials (window glass, etc.), coating materials, and covering materials in the fields of aviation, vehicles, and the like, for example. Alternatively, the polyamic acid composition according to one embodiment is particularly suitable for applications requiring low coloring property, high light transmittance, and at least one property selected from the group consisting of high electrical insulation property, high sound insulation property, high heat insulation property, and high strength.

In one embodiment, the polyamic acid composition of the present invention contains a polyamic acid having a structure derived from a dianhydride and a structure derived from a diamine, and a solvent. The polyamic acid composition may comprise a polymer other than polyamic acid, for example, may comprise polyimide. As used herein, "polyamic acid" refers to a polymer having an imidization rate of less than 20%, i.e., a polymer having a majority of repeating units of the formula. The Polyamic acid is also referred to as a "polyimide precursor" or "polyamide acid".

[ chemical 7 ]

(wherein X and Y are the same as defined above and n is a positive integer)

In the polyamic acid composition according to one embodiment, the polyamic acid further has a structure derived from a crosslinking agent. The structure from the cross-linking agent, i.e. the cross-linked structure, is based on: a 3-valent or higher group derived from a monocyclic or polycyclic aromatic ring with or without a substituent, or a 3-valent or higher group derived from a bonded aromatic ring in which a plurality of aromatic rings with or without substituents are bonded to each other by direct bonding or bonding via a heteroatom.

In the polyamide acid composition of one embodiment, the composition, properties, and the like that are preferable in the case of porous polyimide are substantially the same.

Thus, in the polyamic acid composition according to one embodiment,

in the desorption curve in the 77K nitrogen adsorption/desorption isotherm, the ratio of the adsorption amount under the conditions of the relative pressures of 0.90, 0.85, 0.80 and 0.75 to the adsorption amount under the conditions of the relative pressure of 0.98 may be 0.50 to 1.0, 0.30 to 1.0, 0.25 to 0.90 and 0.20 to 0.85, respectively,

the polyamide acid may be obtained by polymerizing tetracarboxylic dianhydride and diamine in a ratio of n+1:n.

Polymerization procedure

In this step, the dianhydride and the diamine are polymerized in a polymerization solvent, and crosslinked with a crosslinking agent to obtain a polyamic acid. As the polymerization solvent, a solvent having an ability to dissolve polyamic acid may be used, and examples thereof include an amide-based solvent, an ether-based solvent, an ester-based solvent, a ketone-based solvent, a phenol-based solvent, a sulfone-based solvent, and a sulfoxide-based solvent.

Examples of the amide-based solvent include N-methyl-2-pyrrolidone (NMP), N-Dimethylformamide (DMF), and N, N-dimethylacetamide (DMAc).

Examples of the ester-based solvent include cyclic esters (e.g., lactones such as gamma-butyrolactone (GBL), delta-valerolactone, epsilon-caprolactone, gamma-crotonlactone, gamma-caprolactone, alpha-methyl-gamma-butyrolactone, gamma-valerolactone, alpha-acetyl-gamma-butyrolactone, and delta-caprolactone), methyl acetate, ethyl acetate, butyl acetate, and dimethyl carbonate.

Examples of the ketone solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and cyclopentanone.

Examples of the phenol solvent include m-cresol.

Examples of the sulfone-based solvent include methylsulfone, ethylphenyl sulfone, diethyl sulfone, diphenyl sulfone, sulfolane, bisphenol S, phenylpropyl sulfone, dapsone, bisphenol A polysulfone, and sulfolane.

Examples of the sulfoxide solvent include dimethyl sulfoxide (DMSO).

The boiling point of the solvent may be preferably 80℃or higher, or 100℃or higher, or 120℃or higher. According to such a high boiling point solvent, the polymerization rate of polyamic acid and the gelation rate of polyamic acid or polyimide can be reduced as compared with the volatilization rate of the solvent, and thus, for example, polymerization and/or gelation can be performed at around room temperature, which is preferable in terms of process control. The high boiling point solvent is preferably an amide solvent, more preferably at least one selected from the group consisting of N-methyl-2-pyrrolidone (NMP, boiling point 202 ℃), N-dimethylformamide (DMF, boiling point 153 ℃) and N, N-dimethylacetamide (DMAc, boiling point 165 ℃), and particularly preferably N-methyl-2-pyrrolidone (NMP).

In one embodiment, the polymerization temperature may be 10℃or higher, and may be 80℃or lower, or 60℃or lower, or 40℃or lower. In a preferred manner, the entire polymerization process can maintain the polymerization solvent without cooling or heating (i.e., in the ambient environment).

Gelation Process

In this step, the crosslinking agent of the present invention is added to the polyamic acid solution obtained in the polymerization step to obtain a polyamic acid wet gel. The crosslinking agent may be added to the polyamic acid solution alone or in a solvent (also referred to as a crosslinking agent solvent in the present invention) in the form of a solution. The preferable examples of the crosslinking agent solvent are the same as those exemplified for the above-mentioned polymerization solvent, and the above-mentioned high boiling point solvent is particularly preferable. The high boiling point solvent is capable of stably gelling because the volatilization rate is slower than the gelation rate, without requiring, for example, a gelation temperature of 10 ℃ or higher and/or a cooling operation of the system. The polymerization solvent and the crosslinking agent solvent may be the same kind or different kinds from each other, and are preferably the same kind.

In one embodiment, the above mixture may be cast onto a substrate and allowed to stand, thereby allowing gelation to proceed. The thickness of the mixture may be selected according to the thickness of the target porous polyimide, and in one embodiment, may be 0.1 μm to 10mm. The gelation atmosphere is not limited, and may be air, an inert gas (for example, nitrogen), or the like.

The gelation temperature is preferably 10 ℃ or higher from the viewpoint of shortening the gelation time and improving the process efficiency, and is preferably 80 ℃ or lower, or 60 ℃ or lower, or 40 ℃ or lower from the viewpoint of stably forming a desired pore structure. In a preferred manner, the entire gelation process may maintain the polymerization solvent without cooling or heating (i.e., under ambient conditions).

The gelation time is preferably 1 minute or more, or 2 minutes or more, from the viewpoint of stably forming a desired pore structure, and is preferably 60 minutes or less, or 30 minutes or less, or 10 minutes or less, from the viewpoint of process efficiency.

Imidization step

In this step, the polyamic acid wet gel obtained in the gelation step is imidized to obtain a polyimide gel. In one embodiment, a dehydrated imidizing agent is used for imidization. The dehydrated imidizing agent is not particularly limited as long as it can dehydrate and cyclize the amide bond of the polyamic acid wet gel and the carboxyl group adjacent thereto to form an imide bond. The dehydrated imidizing agent is typically carboxylic anhydride, and may be used in the form of a mixture with an imidizing accelerator (amine, etc.). Examples of the carboxylic anhydride include acetic anhydride, and examples of the amine include tertiary amines such as triethylamine and condensed ring aromatic amines such as pyridine. Among them, a combination of acetic anhydride and triethylamine or a combination of acetic anhydride and pyridine is preferable.

In one embodiment, the dehydrated imidizing agent and the imidizing accelerator are dissolved in a solvent (also referred to as an impregnating solvent in the present invention), and the obtained imidizing liquid is impregnated with the polyamic acid wet gel to effect imidization. The total concentration of the dehydrated imidizing agent and the imidizing accelerator in 100 mass% of the imidizing liquid is preferably 1 mass% or more, or 3 mass% or more, from the viewpoint of rapidly advancing imidization, and from the viewpoint of suppressing deformation of the polyamic acid wet gel and obtaining a polyimide gel that favorably maintains the pore structure of the polyamic acid wet gel, it is preferably 50 mass% or less, or 40 mass% or less, or 30 mass% or less, or 20 mass% or less.

The preferable examples of the impregnating solvent are the same as those exemplified for the above-mentioned polymerization solvent. The polymerization solvent and the crosslinking agent solvent may be the same kind or different kinds from each other, and are preferably the same kind. The impregnating solvent is preferably an amide-based solvent, more preferably at least one selected from the group consisting of NMP, DMF and DMAc, and still more preferably NMP.

The imidization temperature may be, for example, 10℃or higher, or 80℃or lower, or 60℃or lower, or 40℃or lower. In a preferred manner, the entire imidization process can maintain the impregnating solvent without cooling or heating (i.e., in the ambient environment).

As described above, a polyimide wet gel can be obtained. According to one embodiment, as described above, by gelation prior to imidization, a polyimide wet gel having submicron-sized dense pores, which is chemically crosslinked by a properly dispersed polyamic acid composition, is obtained. The above method of one embodiment is preferable because polyimide wet gel can be suitably obtained even when alicyclic diamine and/or alicyclic dianhydride are used.

Drying process

In this step, the polyimide wet gel obtained in the imidization step is dried to obtain a polyimide aerogel. As a drying method, supercritical drying is preferable in terms of maintaining a polymer network structure of the polyimide wet gel well and stably obtaining a polyimide aerogel having a desired pore structure. As a method of supercritical drying, a method of replacing a solvent contained in the polyimide wet gel with a ketone-based solvent such as acetone or a replacement solvent such as a lower alcohol (e.g., ethanol), and replacing the replacement solvent with an inert gas such as carbon dioxide, is exemplified. The supercritical drying may be carried out using a commercially available supercritical drying apparatus.

Superiority of this embodiment

In one embodiment, the porous polyimide of the present invention can be produced according to the following process (1) in one embodiment.

In this flow, attention can be paid to the state of the polymer and the composition of the solvent at the time of gelation. In this procedure, the polyamic acid is crosslinked substantially in a good solvent. Therefore, phase separation is difficult to perform. As a result, the obtained porous structure becomes dense and is difficult to suspend, whereby low colorability and high light transmittance are easily achieved.

In the above-described flow (1), flows (2) and (3) are shown in comparison. An example of comparison of the respective flows is as follows.

[ Table 1 ]

Examples

The following examples are given to further illustrate the present invention, but the present invention is not limited to these examples.

Method of measurement and evaluation

Polymerization degree (n)

The polymerization degree (n) is adjusted based on the molar ratio of diamine to dianhydride in the polymerization step. In the case of the present invention, in examples 1 to 4 and comparative examples 3 to 6, the diamine/dianhydride (molar ratio) in the polymerization step was set to n+1. In comparative examples 1 and 2, the diamine/dianhydride (molar ratio) in the polymerization step was set to n+1:n.

Determination of weight average molecular weight

The weight average molecular weight (Mw) was measured by Gel Permeation Chromatography (GPC) under the following conditions. As the solvent, N-dimethylformamide (manufactured by Wako pure chemical industries, ltd., for high performance liquid chromatography) was used, and 24.8mmol/L of lithium bromide monohydrate (manufactured by Wako pure chemical industries, ltd., purity: 99.5%) and 63.2mmol/L of phosphoric acid (manufactured by Wako pure chemical industries, ltd., for high performance liquid chromatography) were added before the measurement. The calibration curve for calculating the weight average molecular weight was prepared using standard polystyrene (manufactured by Tosoh corporation).

Column: shodex KD-806M (manufactured by Zhaohe electric company)

Flow rate: 1.0 mL/min

Column temperature: 40 DEG C

And (3) a pump: PU-2080Plus (manufactured by JASCO Co., ltd.)

A detector: RI-2031Plus (RI: differential refractometer, manufactured by JASCO Co., ltd.)

UV-2075Plus (UV-VIS: ultraviolet visible absorptometer, manufactured by JASCO Co.)

Determination of average pore diameter and BET specific surface area of porous polyimide

About 0.2g of the sample was placed in a glass test tube, and heated and vacuum deaerated at 50℃and 0.001mmHg or less for 18 hours by a sample pretreatment apparatus. The sample weight was measured after heating and vacuum degassing and used as the sample weight in the calculation of the specific surface area. The specific surface area was calculated from the adsorption isotherm of nitrogen gas at the liquid nitrogen temperature (77K) using a multi-sample high performance specific surface area/pore distribution measuring apparatus (manufactured by 3Flex, micrometrics Co.) from the intercept and slope of a straight line (BET plot) having a relative pressure (P/P0) of 0.05 to 0.30 inclusive. The pore volume was derived from the adsorption amount at 760mmHg, and the average pore diameter (L) was calculated from the relation l=4v/a using the pore volume (V) and the specific surface area (S). The pore distribution was calculated by the BJH method.

Pore diameter distribution of porous polyimide

77K of nitrogen (N) obtained in the measurement of the average pore diameter and BET specific surface area of the porous polyimide ₂ ) In the desorption curve in the adsorption/desorption isotherm, the evaluation was performed according to the following evaluation.

A: all of the following 1) to 4) are satisfied.

B: 3 or 2 of the following 1) to 4) are satisfied.

C: 1 or 1 of the following 1) to 4) is not satisfied.

1) The ratio of the adsorption amount under the condition of the relative pressure of 0.90 to the adsorption amount under the condition of the relative pressure of 0.98 is 0.50 to 1.0

2) The ratio of the adsorption amount under the condition of the relative pressure of 0.85 to the adsorption amount under the condition of the relative pressure of 0.98 is 0.30 to 1.0

3) The ratio of the adsorption amount under the condition of the relative pressure of 0.80 to the adsorption amount under the condition of the relative pressure of 0.98 is 0.25 to 0.90

4) The ratio of the adsorption amount under the condition of the relative pressure of 0.75 to the adsorption amount under the condition of the relative pressure of 0.98 is 0.25 to 0.80

Three-point flexural modulus and three-point flexural Strength of porous polyimide

Samples of 30mm wide by 14mm deep by about 2mm thick (more specifically, 2mm thick) cut from the dried disc-shaped porous polyimide were subjected to a three-point bending test. The measurement conditions were as follows.

Testing machine: INSTRON corporation manufactures materials tester 5982 type

Temperature: 23 DEG C

Test speed: 1 mm/min

Support span: 20mm of

Fracture point strain of porous polyimide

The three-point bending test was performed under the same conditions as described above, and the porous polyimide was stretched until the porous polyimide was broken. The strain at the time of breaking (rapid decrease in stress) of the test piece was defined as the breaking point strain. The maximum strain was measured to 15%, and when the specimen was not broken, the breaking point strain was recorded as ">15% (more than 15%)".

Determination of bulk Density of porous polyimide

The bulk density d (g/cm) was calculated from the following formula, assuming that the weight of the dried disk-shaped porous polyimide sample was m (g), the radius was r (cm), the average thickness was h (cm) ³ )。

d＝m/πhr ²

In the formula, the diameter 2r at the position 10 is measured by a vernier caliper so that the measurement interval is substantially equal to the radius r, and calculated as 1/2 of the average value. The average thickness h was measured as the average value of the circular surface at 20 points so that the measurement intervals were substantially uniform. In addition, the average thickness h is given by:

0<(100－LT)/T≤70

the film thickness T (mm) is used.

Determination of transmittance of porous polyimide

Samples of 30mm wide by 30mm deep by 1mm thick cut from the dried disc-shaped porous polyimide were subjected to light transmittance measurement. The measurement conditions were as follows. The measurement itself was carried out at 300nm to 800nm in the wavelength range, and the interval of 400nm to 750nm was used for evaluation.

Testing machine: UV-2450 manufactured by Shimadzu corporation

Wavelength range: 300nm to 800nm

Scanning speed: low speed

Sampling interval: 0.5nm

Measurement mode: single unit

S/R switching: standard of

Transmittance slit width: 5.0nm

Light source switching wavelength: 320nm

The transmittance was measured to obtain

1) Light transmittance at 450nm,

2) A minimum light transmittance between 400nm and 700nm,

3) The difference between the maximum value and the minimum value of the light transmittance between 400nm and 700nm, and

4) An average value of light transmittance between 400nm and 700 nm.

Among them, for examples that do not satisfy the criteria of 1) and 2) below, the evaluations of 3) and 4) are not performed.

Evaluation of transparency of porous polyimide

The transparency of the porous polyimide was evaluated by the following method. That is, a sample was placed on a paper surface on which any one of the marks (letters or signs) of 10mm square was recorded so as to cover one of the letters. Then, observation of the marker was attempted from a position about 30cm away from the sample, and evaluation was performed according to the following evaluation. The evaluation was performed under normal room light.

(evaluation criterion)

A: the presence of the mark can be confirmed and what mark is can be judged.

B: the presence of the mark can be confirmed, but it cannot be determined what mark is.

C: the presence of the marker cannot be confirmed.

Production example of Block porous polyimide

Example 1

To p-phenylenediamine (PPDA: 1.08g;10.0 mmol) was added N-methyl-2-pyrrolidone (NMP: 35.1 g) in a 100mL glass bottle, and the mixture was dissolved while being stirred by a magnetic stirrer, and then 1,2,3, 4-cyclobutane tetracarboxylic anhydride (CBDA: 2.09g;10.67 mmol) was added under stirring. The solution was stirred at room temperature (25 ℃) until the molecular weight was saturated, giving a polyamic acid (PAA) solution.

To the above polyamic acid (PAA) solution was added a solution of 1,3, 5-tris (4-aminophenyl) benzene (TAB: 0.156g;0.444 mmol) dissolved in 3.1g of NMP in another 10mL glass bottle, and stirred for 1 minute. The resulting solution was transferred to a PFA mold (. Phi.100 mm, depth: 30 mm) so as to have a thickness of about 1mm, and allowed to stand at room temperature (25 ℃) for about 30 minutes, whereby a polyamide acid wet gel (PAA-WG) having no fluidity was obtained.

The PAA-WG was allowed to stand at room temperature (25 ℃) for 24 hours in a SUS-made closed vessel in a NMP saturated atmosphere, then taken out of the mold, and immersed in a mixed solution of acetic anhydride (26.1 g;256 mmol), triethylamine (TEA: 3.2g;32 mmol) and NMP 264g for 24 hours at room temperature (25 ℃) to give a polyimide wet gel (PI-WG).

The PI-WG was taken out of the above solution, immersed in a solution of acetone: nmp=1:1 by weight for 24 hours, then washed with acetone, immersed in acetone for 24 hours, and then dried by a supercritical drying apparatus (manufactured by Rexxam, inc., SCRD 4) 3 times, thereby obtaining porous polyimide (ppri).

Examples 2 to 4

In the same manner as in example 1, the same procedure as in example 1 was carried out except that the types and amounts of diamine, tetracarboxylic anhydride, crosslinking agent, imidizing agent (dehydrated imidizing agent and imidizing accelerator) and solvent were changed to the types and amounts described in the table, respectively, to obtain porous polyimide (pPI).

Comparative example 1

Referring to non-patent document 1, porous polyimide ppri was produced in the following procedure. To 4,4' -oxydiphenylamine (ODA: 2.10g;10.5 mmol) was added N-methyl-2-pyrrolidone (NMP: 44.4 g) in a 100mL glass bottle, and the mixture was dissolved while stirring with a magnetic stirrer, and then 3,3'4,4' -biphenyltetracarboxylic dianhydride (BPDA: 2.94g;10.0 mmol) was added as a powder, and the mixture was stirred at room temperature (25 ℃ C.) until the molecular weight was saturated, to obtain a polyamic acid (PAA) solution.

Then, acetic anhydride (8.2 g;80 mmol) was added while stirring the polyamic acid (PAA) solution, and stirred until uniform. Further, triethylamine (1.0 g;10 mmol) was added thereto and after stirring to homogeneity, the mixture was stirred at room temperature (25 ℃ C.) for 15 minutes, whereby a Polyimide (PI) solution was obtained.

To the Polyimide (PI) solution was added a solution of 1,3, 5-benzenetricarboxylic acid chloride (BTC: 88mg;0.333 mmol) dissolved in 1.8g of NMP in another 10mL glass vial, and stirred at room temperature until uniform. After stirring, the obtained solution was transferred to a PFA mold (Φ100mm, depth 30 mm) so as to have a thickness of about 1mm, and left standing at room temperature for 30 minutes, whereby a polyimide wet gel (PI-WG) having no fluidity was obtained.

The resulting PI-WG was allowed to stand at room temperature (25 ℃) for 24 hours in a SUS-made closed vessel in an NMP saturated atmosphere, then immersed in a solution of acetone: NMP (mass ratio) =25:75 for 24 hours, immersed in a solution of acetone: NMP (mass ratio) =50:50 for 24 hours, immersed in a solution of acetone: NMP (mass ratio) =75:25 for 24 hours, and then washed with acetone and immersed in acetone for 24 hours, followed by repeating the operation of displacing the solvent 3 times. The acetone-impregnated polyimide wet gel was dried using a supercritical drying apparatus (manufactured by Rexxam, inc., ltd., "SCRD 4"), to thereby obtain a porous polyimide (ppri).

Comparative example 2

Referring to non-patent document 2, porous polyimide ppri was produced in the following procedure. To 2,2 '-dimethylbenzidine (m-tolidine, DMBZ:2.17g;10.2 mmol) was added N-methyl-2-pyrrolidone (NMP: 43.9 g) in a 100mL glass bottle, and after dissolution with stirring by a magnetic stirrer, 4' -hexafluoroisopropylidenedi (phthalic anhydride) (6 FDA:1.11g;2.5 mmol) was added in small portions at room temperature for 10 minutes while stirring, and stirred until the powder was completely dissolved. Thereafter, a powder of pyromellitic anhydride (PMDA: 1.64g;7.5 mmol) was added to the solution, and stirred at room temperature (25 ℃ C.) for about 10 minutes until uniform, to obtain a polyamic acid (PAA) solution.

Then, acetic anhydride (8.2 g;80 mmol) was added while stirring the polyamic acid (PAA) solution, and stirred until uniform. Further, triethylamine (1.0 g;10 mmol) was added thereto and after stirring to homogeneity, the mixture was stirred at room temperature (25 ℃ C.) for 10 minutes, whereby a Polyimide (PI) solution was obtained.

To the Polyimide (PI) solution was added a solution of 1,3, 5-benzenetricarboxylic acid chloride (BTC: 35mg;0.133 mmol) dissolved in NMP 0.7g in another 10mL glass vial, and stirred at room temperature until uniform. After stirring, the obtained solution was transferred to a PFA mold (Φ100mm, depth 30 mm) so as to have a thickness of about 1mm, and left standing at room temperature for about 120 minutes, whereby a polyimide wet gel (PI-WG) having no fluidity was obtained.

Thereafter, the same solvent substitution and supercritical drying as in comparative example 1 were performed, thereby obtaining porous polyimide (ppri).

Comparative example 3

Referring to non-patent document 3, porous polyimide ppri was produced in the following procedure. To 2,2 '-bis (trifluoromethyl) -4,4' -benzidine (TFMB: 1.975;6.16 mmol) was added N-methyl-2-pyrrolidone (NMP: 25.0 g) in a 100mL glass bottle, and the mixture was dissolved while stirring with a magnetic stirrer, and then 1,2,3, 4-cyclobutane tetracarboxylic anhydride (CBDA: 1.248g;6.36 mmol) was added as a powder, and then N-methyl-2-pyrrolidone (NMP: 25.0 g) was added and the mixture was stirred at room temperature (25 ℃ C.) for about 12 hours until the molecular weight was saturated, to obtain a polyamic acid (PAA) solution.

Thereafter, while stirring the polyamic acid (PAA) solution, a powder of octa (aminophenoxy) silsesquioxane (OAPS: 58mg;0.050 mmol) was added. After stirring at room temperature for about 12 hours, acetic anhydride (3.2 g;31.6 mmol) was added and stirred to homogeneity, followed by pyridine (2.5 g;31.6 mmol) and stirred to homogeneity, and then stirred at room temperature for 30 minutes.

The solution was transferred to a PFA mold (Φ100mm, depth 30 mm) so as to have a thickness of about 1mm, and left standing at room temperature for about 120 minutes, whereby a polyimide wet gel (PI-WG) having no fluidity was obtained. The resulting polyimide wet gel (PI-WG) was suspended in white.

Comparative example 4

Referring to patent document 3, porous polyimide ppri was produced in the following procedure. To 2,2' -dimethylbenzidine (m-tolidine, DMBZ:2.17g;10.2 mmol) was added N-methyl-2-pyrrolidone (NMP: 47.2 g) in a 100mL glass bottle, and the mixture was dissolved while being stirred by a magnetic stirrer. While stirring at room temperature, a powder of 1,2,3, 4-cyclobutane tetracarboxylic anhydride (CBDA: 1.96g;10.0 mmol) was added thereto, and the mixture was stirred at room temperature (25 ℃ C.) for 4 hours to obtain a polyamic acid (PAA) solution.

Then, acetic anhydride (8.2 g;80 mmol) was added while stirring the polyamic acid (PAA) solution, and stirred until uniform. Further, triethylamine (1.0 g;10 mmol) was added thereto, and after stirring to homogeneity, the mixture was stirred at room temperature (25 ℃ C.) for 15 minutes.

To this solution was then slowly added a solution of 1,3, 5-benzenetricarboxylic acid chloride (BTC: 35mg;0.133 mmol) dissolved in NMP 0.7g in another 10mL glass vial. As a result, gelation proceeds rapidly in the vicinity of the NMP solution of BTC, and a heterogeneous system in which a gel in the form of droplets and a solution are mixed in the solution is formed, so that a uniform gel cannot be obtained.

Comparative example 4A

The result of comparative example 4 is considered to be because the chemical imidization rate of the polyamic acid using the alicyclic dianhydride is significantly slower than that of the polyamic acid using the aromatic dianhydride.

That is, in the case of using the method of the example of reference patent document 3 (comparative example 4A), it is considered that the crosslinking agent is mixed in a state where the conversion from the polyamic acid to the polyimide is insufficient. In this case, the carboxylic acid site of the polyamic acid reacts with the crosslinking agent rapidly, and as a result, gelation is thought to occur rapidly around the droplet of the solution containing the crosslinking agent.

Comparative example 5

Referring to non-patent document 4, a porous polyimide pPIr4 in a block form was produced in the following order. Porous polyimide pPI was prepared in the following manner. To 2,2' -dimethylbenzidine (m-tolidine, DMBZ:2.12g;10.0 mmol) was added N-methyl-2-pyrrolidone (NMP: 45.4 g) in a 100mL glass bottle, and the mixture was dissolved by stirring with a magnetic stirrer. A powder of 3,3', 4' -biphenyltetracarboxylic dianhydride (BPDA: 3.09g;10.5 mmol) was added while stirring the solution, and stirred at room temperature for 2 hours.

Thereafter, while stirring the above solution, a solution of 1,3, 5-tris (4-aminophenoxy) benzene (TAPB: 0.133g;0.33 mmol) dissolved in 2.7g of NMP in another 20mL glass flask was added, and the mixture was stirred at room temperature for 10 minutes. Acetic anhydride (8.6 g;84 mmol) and pyridine (6.6 g;84 mmol) were then added and stirred until homogeneous.

The solution was transferred to a PFA mold (Φ100mm, depth 30 mm) so as to have a thickness of about 1mm, and left standing at room temperature for about 30 minutes, whereby a polyimide wet gel (PI-WG) having no fluidity was obtained. The resulting polyimide wet gel (PI-WG) was suspended in yellow.

Comparative example 6

Referring to patent document 3 and non-patent document 4, porous polyimide ppri was produced in the following order. To 2,2' -dimethylbenzidine (m-tolidine, DMBZ:2.12g;10.0 mmol) was added N-methyl-2-pyrrolidone (NMP: 46.9 g) in a 100mL glass bottle, and the mixture was dissolved while stirring with a magnetic stirrer. A powder of 1,2,3, 4-cyclobutane tetracarboxylic anhydride (CBDA: 2.06g;10.5 mmol) was added while stirring at room temperature, and stirred at room temperature (25 ℃ C.) for 4 hours to give a polyamic acid (PAA) solution.

Then, while stirring the above polyamic acid (PAA) solution, a solution of 1,3, 5-tris (4-aminophenoxy) benzene (TAPB: 0.133g;0.333 mmol) dissolved in 2.7g of NMP in another 20mL glass bottle was added, and after stirring at room temperature for 10 minutes, acetic anhydride (8.6 g;84 mmol) and pyridine (6.6 g;84 mmol) were added and stirred for 5 minutes to homogeneity.

The solution was transferred to a PFA mold (Φ100mm, depth 30 mm) so as to have a thickness of about 1mm, and left standing at room temperature for about 300 minutes, whereby a polyimide wet gel (PI-WG) having no fluidity was obtained. The resulting polyimide wet gel (PI-WG) was suspended in white.

[ Table 2 ]

		Example 1	Example 2	Example 3	Example 4
						Diamines		PPDA	DMBZ	PPDA	DMBZ
MW	(g/mol)	108.14	212.3	108.14	212.3
						Acid anhydrides		CBDA	CBDA	CBDA	CBDA
MW	(g/mol)	196.11	196.11	196.11	196.11
						Crosslinking agent		TAB	TAB	TAB	TAB
MW	(g/mol)	351.45	351.45	351.45	351.45
						Degree of polymerization n		15	15	10	10
Solid content ratio NV	(wt％)	8	8	7	7
						Solvent(s)		NMP	NMP	NMP	NMP
Dehydrated imidizing agent		Acetic anhydride	Acetic anhydride	Acetic anhydride	Acetic anhydride
						Imidization accelerator		TEA	TEA	TEA	TEA
Diamines	(g)	1.08	2.12	1.08	2.12
							(mmol)	10.0	10.0	10.0	10.0
Acid anhydrides	(g)	2.09	2.09	2.16	2.16
							(mmol)	10.67	10.67	11	11
Crosslinking agent	(g)	0.156	0.156	0.234	0.234
							(mmol)	0.444	0.444	0.667	0.667
Polymerization solvent	(g)	35.1	47.1	41.5	55.3
						Cross-linker solvent	(g)	3.1	3.1	4.7	4.7
Dehydrated imidizing agent	(g)	26.1	26.1	27	27
							(mmol)	256	256	264	264
Imidization accelerator	(g)	3.2	3.2	3.3	3.3
							(mmol)	32	32	33	33
Impregnating solvent	(g)	264	264	273	273
						Gelation time	(minutes)	45	30	50	40
Average pore diameter	(nm)	7.8	8	7.3	7.5
						BET specific surface area	(m ² /g)	439	450	408	421
Bulk density of	(g/cm ³ )	0.24	0.22	0.23	0.22
						Flexural modulus	(MPa)	558	426	521	404
Flexural Strength	(MPa)	18.2	16.3	16.6	15.4
						Fracture point strain	(％)	＞15	＞15	＞15	＞15
Pore size distribution	－	A	A	A	A
						Transparency of	－	A	A	A	A
Light transmittance at 450nm	(％)	65	70	66	68
						Minimum light transmittance of 400-700nm	(％)	53	58	54	56
The light transmittance difference is between 400 and 700nm	(％)	30	28	31	30
						The light transmittance is average between 400 and 700nm	(％)	68	78	70	77
(100-transmittance at 450 nm)/film thickness	(％/nm)	35	30	34	32

[ Table 3 ]

		Comparative example 1	Comparative example 2	Comparative example 3	Comparative example 4	Comparative example 5	Comparative example 6
								Diamines		ODA	DMBZ	TFMB	DMBZ	DMBZ	DMBZ
MW	(g/mol)	200.24	212.3	320.23	212.3	212.3	212.3
								Acid anhydrides		BPDA	PMDA/6FDA	CBDA	CBDA	BPDA	CBDA
MW	(g/mol)	294.22	218.12/444.24	196.11	196.11	294.22	196.11
								Crosslinking agent		BTC	BTC	OAPS	BTC	TAPB	TAPB
MW	(g/mol)	265.47	265.47	1153.63	265.47	399.45	399.45
								Degree of polymerization n		20	50	30	50	20	20
Solid content ratio NV	(wt％)	10	10	7	8	10	8
								Polymerization solvent		NMP	NMP	NMP	NMP	NMP	NMP
Dehydrated imidizing agent		Acetic anhydride	Acetic anhydride	Acetic anhydride	Acetic anhydride	Acetic anhydride	Acetic anhydride
								Imidization accelerator		TEA	TEA	Pyridine compound	TEA	Pyridine compound	Pyridine compound
Impregnating solvent		－	－	－	－	－	－
								Diamines	(g)	2.10	2.17	1.975	2.17	2.12	2.12
	(mmol)	10.5	10.2	6.16	10.2	10.0	10.0
								Acid anhydrides	(g)	2.94	1.64/1.11	1.248	1.96	3.09	2.06
	(mmol)	10.0	7.5/2.5	6.36	10.0	10.5	10.5
								Crosslinking agent	(g)	0.088	0.035	0.058	0.035	0.133	0.133
	(mmol)	0.333	0.133	0.050	0.133	0.333	0.333
								Polymerization solvent	(g)	44.4	43.9	50	47.2	45.4	46.9
Cross-linker solvent	(g)	1.8	0.7	0	0.7	2.7	2.7
								Dehydrated imidizing agent	(g)	8.2	8.2	3.2	8.2	8.6	8.6
	(mmol)	80	80	31.6	80	84	84
								Imidization accelerator	(g)	1.0	1.0	2.5	1.0	6.6	6.6
	(mmol)	10	10	31.6	10	84	84
								Impregnating solvent	(g)	0	0	0	0	0	0
Gelation time	(minutes)	20	120	120	－	30	180
								Average pore diameter	(nm)	13.2	13.5	33	－	13.1	15.4
BET specific surface area	(m ² /g)	390	770	410	－	340	380
								Bulk density of	(g/cm ³ )	0.15	0.17	0.23	－	0.18	0.25
Flexural modulus	(MPa)	45	99	23	－	55	43
								Flexural Strength	(MPa)	0.9	2.9	0.5	－	1.5	3.3
Fracture point strain	(％)	1.9	3.5	1.2	－	2.6	2.6
								Wet gel appearance	－	Colored opaque	Colored transparent	Colorless and opaque	－	Colored opaque	Colorless and opaque
Aerogel appearance	－	Colored opaque	Colored transparent	Colorless and opaque	－	Colored opaque	Colorless and opaque
								Pore size distribution	－	B	C	B	－	B	C
Transparency of	－	C	A	C	－	C	C
								Light transmittance at 450nm	(％)	＜1	＜1	＜1	－	＜1	＜1
Minimum light transmittance of 400-700nm	(％)	＜1	＜1	＜1	－	＜1	＜1
								The light transmittance difference is between 400 and 700nm	(％)	－	－	－	－	－	－
The light transmittance is average between 400 and 700nm	(％·nm)	－	－	－	－	－	－
								(100-transmittance at 450 nm)/film thickness	(％/nm)	－	－	－	－	－	－

Industrial applicability

The porous polyimide of the present invention can be suitably used for various applications such as a material for producing a porous carbon sheet, including applications of a heat-resistant material, particularly a heat-resistant material in a field where low colorability and high light transmittance are required.

Claims

1. A porous polyimide composition having an average pore diameter L of 5nm to 500nm based on a pore volume V and a BET specific surface area A, which is obtained by a gas adsorption method,

L＝4V/A

a light transmittance at a film thickness of 1mm of 10% to 100% at 450nm, and

the polymerization degree n is 5 or more and less than 40.

2. The porous polyimide composition according to claim 1, wherein in the desorption curve in the nitrogen adsorption/desorption isotherm of 77K,

3. The porous polyimide composition according to claim 1 or 2, which has a crosslinked polyimide structure obtained by crosslinking a polyamic acid obtained by polymerizing a tetracarboxylic dianhydride/diamine in a ratio of n+1:n.

4. The porous polyimide composition according to claim 1 or 2, wherein the minimum value of light transmittance at a film thickness of 1mm of between 400nm and 700nm is 5% or more.

5. The porous polyimide composition according to claim 1 or 2, wherein a difference between a maximum value and a minimum value of light transmittance at a film thickness of 1mm of 400nm to 700nm is 1% to 80%.

6. The porous polyimide composition according to claim 1 or 2, wherein an average value of light transmittance at a film thickness of 1mm between 400nm and 700nm is 30% to 100%.

7. The porous polyimide composition according to claim 1 or 2, which has a bulk density of 0.05g/cm ³ Above 0.50g/cm ³ The following is given.

8. The porous polyimide composition according to claim 1 or 2, wherein the breaking point in the three-point bending test is 5% or more.

9. The porous polyimide composition according to claim 1 or 2, which has a flexural strength of 5MPa or more in a three-point flexural test.

10. The porous polyimide composition according to claim 1 or 2, which has a flexural modulus of 50MPa or more in a three-point bending test.

11. The porous polyimide composition according to claim 1 or 2, which has a BET specific surface area of 10m after heat treatment at 200℃for 1 hour ² Per gram of above 2,000m ² And/g or less.

12. The porous polyimide composition according to claim 1 or 2, which has a sheet shape.

13. The porous polyimide composition according to claim 12, which has an average thickness of 10mm or less.

14. The porous polyimide composition according to claim 1 or 2, wherein when the light transmittance at 450nm is LT in mm and the thickness is T in mm, the following formula is satisfied:

0<(100－LT)/T≤70

the relationship represented.

15. The porous polyimide composition according to claim 1 or 2, wherein a polyimide constituting the porous polyimide composition has a polyimide main skeleton and a crosslinked structure that crosslinks the polyimide main skeleton.

16. The porous polyimide composition of claim 15, wherein the crosslinked structure is based on:

A structure in which a plurality of aromatic rings having a substituent or not are bonded to each other by direct bonding or by hetero atom bonding, and a group having 3 or more valencies is bonded to the aromatic rings.

17. The porous polyimide composition according to claim 15, wherein the polyimide main skeleton has a molecular chain represented by the following general formula (1):

[ chemical formula 1 ]

In the general formula (1), X and/or Y have a structure containing an alicyclic ring, and n is the degree of polymerization of the polyimide.

18. The porous polyimide composition according to claim 1 or 2, wherein the polyimide constituting the porous polyimide composition comprises a polymerization product of a polymerization component comprising tetracarboxylic dianhydride, diamine and an amine having 3 or more functions,

the proportion of the amine having 3 or more functions is 1 to 40 mass% based on 100 mass% of the total of the tetracarboxylic dianhydride, the diamine, and the amine having 3 or more functions.

19. The porous polyimide composition according to claim 1 or 2, which comprises a polymerization product of a polymerization component comprising tetracarboxylic dianhydride, diamine and 3-functional or more amine among polyimides constituting the porous polyimide composition,

The proportion of the tetracarboxylic dianhydride including an aromatic ring is less than 50 mass% relative to 100 mass% of the total of the tetracarboxylic dianhydrides, and/or

20. The porous polyimide composition according to claim 1 or 2, which is used as a heat-resistant material having low coloration and high light transmittance.

21. A polyamic acid composition comprising a resin precursor and a solvent for obtaining a heat-resistant material having low coloration and high light transmittance, wherein,

the porous polyimide composition obtained by adding a crosslinking agent to the polyamic acid composition and then subjecting the composition to chemical imidization by immersing the composition in a solution satisfies the following conditions (1) to (2):

(1) The average pore diameter L obtained by the gas adsorption method is 5nm to 500nm, and is obtained by the following formula based on the pore volume V and BET specific surface area A,

L＝4V/A

the polyimide has a polymerization degree n of 5 or more and less than 40.