TWI890777B - Imide-amic acid copolymer and method for producing same, varnish, and polyimide film - Google Patents

Abstract

An imide-amic acid copolymer, containing a repeating unit represented by formula (1) below, formed from an imide component (IM), an amic acid component (AM1), and an amic acid component (AM2). (In formula (1), X¹ represents a tetravalent aromatic group of 4 to 39 carbon atoms, X² represents a tetravalent aromatic group of 4 to 39 carbon atoms different from that represented by X¹ , Y¹ represents a group derived from diaminodiphenylsulfone or the like, Y² represents a group derived from 4-aminophenyl 4-aminobenzoate or the like, and s, t, and u represent positive integers.)

Description

Acetylimide-acetamide copolymer and its production method, varnish, and polyimide film

The present invention relates to an amide-amide copolymer as a precursor of a polyimide resin, a method for producing the same, a varnish containing the copolymer, and a polyimide film.

Polyimide resins are being explored for various applications in fields such as electrical and electronic components. For example, there is a desire to replace the glass substrates used in image display devices such as liquid crystal displays (LCDs) and organic light-emitting diode (OLED) displays with plastic substrates to achieve lighter and more flexible devices. Research is underway on polyimide films suitable for these plastic substrates. Polyimide films for such applications require transparency and low yellowing. Furthermore, when a varnish applied to a glass substrate or silicon wafer is heated and cured to form the polyimide film, residual stress is generated in the film. High residual stress in the polyimide film can cause warping of the glass substrate or silicon wafer, leading to the need for reduced residual stress in polyimide films.

To address these issues, Patent Document 1, for example, discloses a polyimide precursor characterized by containing two specific amide structural units at a specific ratio, in order to achieve a polyimide film with low residual stress, minimal warping, low yellowness, and high elongation. [Prior Art Document] [Patent Document]

[Patent Document 1] International Publication No. 2017/051827

[The problem that the invention aims to solve]

As mentioned above, polyimide films for certain applications require transparency and low yellowing. However, LTPS (low-temperature polysilicon TFT) devices have processing temperatures exceeding 400°C. The polyimide substrate must be heat-resistant, capable of withstanding temperatures exceeding 400°C, and must maintain transparency and low yellowing even under such thermal history. Furthermore, as mentioned above, due to the issue of support warping, there is a need to reduce residual stress. Furthermore, considering the difference in linear thermal expansion coefficient with the inorganic layers that constitute the device, which can lead to concerns about delamination at the bonding interface and product deformation, a reduction in the linear thermal expansion coefficient is also necessary. Patent Document 1 discloses a technique for reducing residual stress and yellowing, but it still has shortcomings, particularly in achieving a polyimide film that maintains transparency and low yellowing while also exhibiting excellent heat resistance. The present invention was developed in response to this situation. The present invention aims to provide an imide-amidite copolymer as a precursor for a polyimide resin, a method for producing the copolymer, a varnish containing the copolymer, and a polyimide film that can produce a polyimide film having low residual stress and linear thermal expansion coefficient, excellent transparency and heat resistance, and low yellowing. [Means for Solving the Problem]

The inventors have discovered that copolymers containing a specific combination of constituent units can solve the above-mentioned problems, and thus have completed the invention.

That is, the present invention relates to the following [1] to [18]. [1] An imide-amide copolymer comprising repeating units represented by the following formula (1) consisting of an imide portion (IM), an amide portion (AM1), and an amide portion (AM2). [Chemical 1] In formula (1), ^X1 is a tetravalent aromatic group having 4 to 39 carbon atoms, and may have at least one selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _2- , _-C2H4O- , and -S- as a bonding group; ^X2 is a tetravalent aromatic group having 4 to ₃₉ carbon atoms different from ^X1 , and may have at least one selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _2- , _{-C2H4O- ,} and -S- as a bonding group; ^Y1 is a group represented by at least one selected from the group consisting of the following formula (2), the following general formula (3), and the following general formula (4); ^Y2 is a group represented by the following general formula (5); s, t, and u are positive integers. [2] In formula (3), ^Z1 represents a single bond or a group represented by -O-. In formula (4), R1 independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms. [Chemistry 3] In formula (5), Z ² and Z ³ each independently represent a group represented by -COO- or a group represented by -OCO-. R ¹ , R ² , and R ³ each independently represent a monovalent organic group having 1 to 20 carbon atoms. h, i, j, and k are integers from 0 to 4. [2] The amide-amide copolymer described in [1] above, wherein s is 1 to 50 and t is 1 to 50. [3] The amide-amide copolymer described in [1] or [2] above, wherein u is 5 to 200. [4] The amide-amide copolymer described in any one of [1] to [3] above, wherein X ¹ is a group represented by the following formula (6). [Chemical 4] [5] The amide-amide copolymer according to any one of [1] to [4], wherein ^X2 is a group represented by the following formula (7). [6] The imide-amide copolymer according to any one of [1] to [5], wherein the imide portion (IM) comprises a constituent unit X1A derived from tetracarboxylic dianhydride and a constituent unit Y1B derived from a diamine, the amide portion (AM1) comprises a constituent unit X2A derived from tetracarboxylic dianhydride and a constituent unit Y1B derived from a diamine, the amide portion (AM2) comprises a constituent unit X2A derived from tetracarboxylic dianhydride and a constituent unit Y2B derived from a diamine, the constituent unit X1A comprises a constituent unit derived from an aromatic tetracarboxylic dianhydride, the constituent unit X2A comprises a constituent unit derived from an aromatic tetracarboxylic dianhydride different from the constituent unit X1A, Constituent unit Y1B contains a constituent unit (B1) derived from a diamine (b1), and constituent unit (B1) contains at least one selected from the group consisting of a constituent unit (B11) derived from a compound represented by the following formula (b11), a constituent unit (B12) derived from a compound represented by the following general formula (b12), and a constituent unit (B13) derived from a compound represented by the following general formula (b13). Constituent unit Y2B contains a constituent unit (B2) derived from a compound represented by the following general formula (b2). [Chemistry 6] In formula (b12), ^Z1 represents a single bond or a group represented by -O-. In formula (b13), R1 represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms. In formula (b2), ^Z2 and ^Z3 each independently represent a group represented by -COO- or a group represented by -OCO-. ^R1 , ^R2 , and ^R3 each independently represent a monovalent organic group having 1 to 20 carbon atoms. h, i, j, and k are integers from 0 to 4. [7] The amide-amide copolymer described in [6] above, wherein the constituent unit X2A contains a constituent unit (A2) derived from an aromatic tetracarboxylic dianhydride (a2), and the constituent unit (A2) contains at least one selected from the group consisting of a constituent unit (A21) derived from a compound represented by the following formula (a21), a constituent unit (A22) derived from a compound represented by the following formula (a22), a constituent unit (A23) derived from a compound represented by the following formula (a23), a constituent unit (A24) derived from a compound represented by the following formula (a24), and a constituent unit (A25) derived from a compound represented by the following formula (a25). [Chemistry 7] [8] The imide-amide copolymer described in [6] or [7] further contains a constituent unit (B3) derived from a compound represented by the following general formula (b3). [Chemical 8] In formula (b3), ^Z4 and ^Z5 each independently represent a divalent aliphatic group or a divalent aromatic group, ^R4 and ^R5 each independently represent a monovalent aromatic group or a monovalent aliphatic group, ^R6 and ^R7 each independently represent a monovalent aliphatic group, ^R8 and ^R9 each independently represent a monovalent aliphatic group or a monovalent aromatic group, m and n each independently represent an integer greater than 1, and the sum of m and n represents an integer from 2 to 1000. However, at least one of ^R4 and ^R5 represents a monovalent aromatic group. [9] The amide-amide copolymer described in [8] above, wherein ^R4 and ^R5 are phenyl groups, and ^R6 and ^R7 are methyl groups. [10] The amide-amide copolymer described in [8] or [9] above, wherein the content of the polyorganosiloxane unit in the amide-amide copolymer is 1 to 20% by mass. [11] The amide-amide copolymer described in any one of [6] to [10] above, wherein the constituent unit X1A contains a constituent unit (A1) derived from a compound represented by the following formula (a1). [Chemical 9] [12] A varnish obtained by dissolving a copolymer as described in any one of the above [1] to [11] in an organic solvent. [13] A polyimide film comprising a polyimide resin obtained by imidizing the amide moiety in the copolymer as described in any one of the above [1] to [11]. [14] The polyimide film as described in the above [13], wherein the weight average molecular weight (Mw) of the polyimide resin is 100,000 to 300,000. [15] A method for producing an imide-amide copolymer comprising the following steps 1 and 2. Step 1: reacting a tetracarboxylic acid component constituting an imide portion (IM) with a diamine component to obtain an imide oligomer. Step 2: reacting the imide oligomer obtained in step 1 with a tetracarboxylic acid component and a diamine component constituting an amide portion (AM2) to obtain an imide-amide copolymer comprising repeating units consisting of an imide portion (IM), an amide portion (AM1), and an amide portion (AM2) represented by the following formula (1): In formula (1), ^X1 is a tetravalent aromatic group having 4 to 39 carbon atoms, and may have at least one selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _2- , _-C2H4O- , and -S- as a bonding group; ^X2 is a tetravalent aromatic group having 4 to ₃₉ carbon atoms different from ^X1 , and may have at least one selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _2- , _{-C2H4O- ,} and -S- as a bonding group; ^Y1 is a group represented by at least one selected from the group consisting of the following formula (2), the following general formula (3), and the following general formula (4); ^Y2 is a group represented by the following general formula (5); s, t, and u are positive integers. [11] In formula (3), ^Z1 represents a single bond or a group represented by -O-. In formula (4), R1 independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms. [Chemistry 12] In formula (5), Z ² and Z ³ each independently represent a group represented by -COO- or a group represented by -OCO-. R ¹ , R ² , and R ³ each independently represent a monovalent organic group having 1 to 20 carbon atoms. h, i, j, and k are integers from 0 to 4. [16] The method for producing an imide-amide copolymer as described in [15] above, wherein the imide oligomer obtained in step 1 has amino groups at both ends of the main chain of the molecular chain. [17] The method for producing an imide-amide copolymer as described in [15] or [16] above, wherein, in step 1, the molar ratio of the diamine component to the tetracarboxylic acid component (diamine/tetracarboxylic acid) is 1.01 to 2. [18] A method for producing an imide-amide copolymer as described in any one of [15] to [17], wherein after step 2, a diamine containing a polyorganosiloxane unit is reacted. [Effects of the Invention]

The present invention provides an amide-amide copolymer as a precursor of a polyimide resin, which can produce a polyimide film having low residual stress and linear thermal expansion coefficient, excellent transparency and heat resistance, and low yellowness, and a method for producing the same, a varnish containing the copolymer, and a polyimide film.

[Imide-Amide Copolymer] The imide-amide copolymer of the present invention comprises repeating units composed of an imide portion (IM), an amide portion (AM1), and an amide portion (AM2) represented by the following formula (1). [Chemical 13] In formula (1), ^X1 is a tetravalent aromatic group having 4 to 39 carbon atoms, and may have at least one selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _2- , _-C2H4O- , and -S- as a bonding group; ^X2 is a tetravalent aromatic group having 4 to ₃₉ carbon atoms different from ^X1 , and may have at least one selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _2- , _{-C2H4O- ,} and -S- as a bonding group; ^Y1 is a group represented by at least one selected from the group consisting of the following formula (2), the following general formula (3), and the following general formula (4); ^Y2 is a group represented by the following general formula (5); s, t, and u are positive integers. [14] In formula (3), ^Z1 represents a single bond or a group represented by -O-. In formula (4), R1 independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms. [Chemistry 15] In formula (5), Z ² and Z ³ each independently represent a group represented by -COO- or a group represented by -OCO-. R ¹ , R ² , and R ³ each independently represent a monovalent organic group having 1 to 20 carbon atoms. h, i, j, and k are integers from 0 to 4.

The imide-amic acid copolymer of the present invention is an excellent raw material for polyimide films. The resulting polyimide film exhibits low residual stress and linear thermal expansion coefficient, excellent transparency, and maintains low yellowness while also possessing excellent heat resistance. The reasons for this are not yet understood, but are believed to be as follows. The copolymer, composed of a component derived from a tetracarboxylic acid containing an aromatic group and the aforementioned specific diamine component, is believed to possess a bulky backbone with a trifluoromethyl, sulfonyl, or cardo structure, a rigid biphenyl backbone, and an ester backbone in appropriate ratios. This allows it to achieve the low residual stress, low linear thermal expansion coefficient, transparency, low yellowness, and high heat resistance required for TFT substrates and the like. On the other hand, it is believed that even in the case of an appropriate ratio, the polyamide component containing a cardole structure is not easily thermally imidized during film formation, and polymers containing polyamide components containing a cardole structure generally do not exhibit good physical properties when formed into thin films. However, in the imide-amide copolymer of the present invention, a portion of the component containing a cardole structure is imidized beforehand during polymer polymerization, resulting in excellent physical properties after film formation.

<Imide moiety (IM)> The imide moiety (IM) constituting the imide-amidic acid copolymer of the present invention is the moiety represented by (IM) in the aforementioned formula (1). In the aforementioned formula (1), ^X1 is a tetravalent aromatic group having 4 to 39 carbon atoms, and may also have at least one type selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _2- , _-C2H4O- , and -S- _as a bonding group. Here, the tetravalent aromatic group means that all four carbon atoms bonding to the imide group are aromatic carbon atoms. Furthermore, the aforementioned bonding group refers to a bonding group bonding to each aromatic ring when ^X1 contains two or more aromatic rings. In addition, the bonding group is not limited thereto. ^X1 is preferably an aromatic group because the heat resistance of the polyimide is good.

^X1 is preferably a group obtained by excluding two dicarboxylic anhydride moieties (four carboxyl groups) from tetracarboxylic dianhydride, which is a raw material for the constituent unit X1A derived from tetracarboxylic dianhydride described later. Among these, ^X1 is more preferably a group represented by the following formula (6). [Chemical 16]

In the aforementioned formula (1), Y ¹ is a group represented by at least one selected from the group consisting of the following formula (2), the following general formula (3), and the following general formula (4). [Chemical 17] In formula (3), ^Z1 represents a single bond or a group represented by -O-. In formula (4), R1 independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms.

^Y1 is preferably a diamine which is a raw material of the diamine-derived structural unit Y1B described later, excluding two amino groups.

<Amine moiety (AM2)> The amidine moiety (AM2) constituting the amidine-amidine copolymer of the present invention is the moiety represented by (AM2) in the aforementioned formula (1). In the aforementioned formula (1), ^X2 is a tetravalent aromatic group having 4 to 39 carbon atoms, which is different from ^X1 , and may also have at least one type selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _{2- , -C2H4O-} , and -S- as a bonding group. Here, the tetravalent aromatic group means that the four carbon atoms bonding to the amidine group and the carboxyl group are all aromatic carbon atoms. Furthermore, the aforementioned bonding group refers to a bonding group bonding to each aromatic ring when ^X2 contains two or more aromatic rings. In addition, the bonding group is not limited thereto.

^X2 is preferably a group obtained by excluding two dicarboxylic anhydride moieties (four carboxyl groups) from tetracarboxylic dianhydride, which is a raw material for the constituent unit X2A derived from tetracarboxylic dianhydride described later. Among these, ^X2 is more preferably a group represented by the following formula (7). [Chemical 18]

In the above formula (1), Y ² is a group represented by the following general formula (5). In formula (5), Z ² and Z ³ each independently represent a group represented by -COO- or a group represented by -OCO-. R ¹ , R ² , and R ³ each independently represent a monovalent organic group having 1 to 20 carbon atoms. h, i, j, and k are integers from 0 to 4.

^Y2 is preferably a diamine which is a raw material of the diamine-derived structural unit Y2B described later, excluding two amino groups.

<Acetamine Moiety (AM1)> The acetamine moiety (AM1) constituting the acetamine copolymer of the present invention is the moiety represented by (AM1) in the aforementioned formula (1). The acetamine moiety (AM1) serves as the linking moiety between the acetamine moiety (IM) and the acetamine moiety (AM2). ^X₂ in the acetamine moiety (AM1) is the same as that in the acetamine moiety (AM2), and ^Y₁ in the acetamine moiety (AM1) is the same as that in the acetamine moiety (IM).

<Structure of Imido-Amide Copolymer> In the aforementioned formula (1), s represents the number of repeating units of the imide moiety (IM) and is a positive integer. From the perspectives of transparency, low yellowness, and high heat resistance, s is preferably 1 to 50, more preferably 1 to 15, even more preferably 1 to 10, and even more preferably 1 to 5. The average number of repeating units of the imide moiety (IM), i.e., the average value of s, is preferably 1 to 10, more preferably 1.5 to 9, even more preferably 1.5 to 8, and even more preferably 1.7 to 5. The average number of repetitions of the imide moiety (IM) mentioned above refers to the average number of repetitions of the imide moiety (IM) in all the imide-amic acid copolymers contained in the polyimide varnish and polyimide film described below, and the average number of s refers to the average number of s in all the imide-amic acid copolymers contained in the polyimide varnish and polyimide film described below.

In the aforementioned formula (1), t represents the number of repeating units of the amide moiety (AM2) and is a positive integer. From the perspective of high heat resistance, low residual stress, and low linear thermal expansion coefficient, t is preferably 1 to 50, more preferably 1 to 15, even more preferably 1 to 10, and even more preferably 1 to 5. The average number of repeating units of the amide moiety (AM2), i.e., the average value of t, is preferably 1 to 10, more preferably 1.5 to 9, even more preferably 1.5 to 8, and even more preferably 1.7 to 5. The average repetition number of the amide portion (AM2) mentioned above refers to the average repetition number of the amide portion (AM2) of all the amide imide-amide copolymers contained in the polyimide varnish and polyimide film described later, and the average value of t refers to the average value of t of all the amide imide-amide copolymers contained in the polyimide varnish and polyimide film described later.

In the aforementioned formula (1), u represents the number of repeating units consisting of an imide moiety (IM), an amide moiety (AM1), and an amide moiety (AM2), and is a positive integer. From the perspectives of heat resistance, low residual stress, and low linear thermal expansion coefficient, u is preferably 5 to 200, more preferably 6 to 150, and even more preferably 10 to 120. The average number of repeating units consisting of an imide moiety (IM), an amide moiety (AM1), and an amide moiety (AM2), i.e., the average value of u, is preferably 5 to 200. The aforementioned average repetition number of repeating units consisting of an imide portion (IM), an amide portion (AM1), and an amide portion (AM2) refers to the average repetition number of repeating units consisting of an imide portion (IM), an amide portion (AM1), and an amide portion (AM2) in all the imide-amide copolymers contained in the polyimide varnish and the polyimide film described later. The average value of u refers to the average value of u in all the imide-amide copolymers contained in the polyimide varnish and the polyimide film described later.

The total ratio of the imide portion (IM), the amide portion (AM1), and the amide portion (AM2) relative to the imide-amide copolymer is preferably 80% by mass or more, more preferably 82% by mass or more, and even more preferably 85% by mass or more. The upper limit is not limited and is 100% by mass or less.

Compared to conventional imide-amide copolymers, in which imide and amide moieties are randomly present, the imide-amide copolymers of the present invention are believed to have a specific structure of imide moieties (IM), amide moieties (AM1), and amide moieties (AM2), resulting in low residual stress and linear thermal expansion coefficient, transparency, low yellowness, and excellent heat resistance.

<Constituent Units of the Imido-Amino Acid Copolymer> The imide-amino acid copolymer of the present invention comprises repeating units composed of an imide portion (IM), an amino acid portion (AM1), and an amino acid portion (AM2), represented by the aforementioned formula (1). The constituent units constituting the copolymer are described below.

The imide-amide copolymer of the present invention preferably comprises: the imide portion (IM) comprising a constituent unit X1A derived from tetracarboxylic dianhydride and a constituent unit Y1B derived from a diamine; the amide portion (AM1) comprising a constituent unit X2A derived from tetracarboxylic dianhydride and a constituent unit Y1B derived from a diamine; the amide portion (AM2) comprising a constituent unit X2A derived from tetracarboxylic dianhydride and a constituent unit Y2B derived from a diamine; the constituent unit X1A comprises a constituent unit derived from an aromatic tetracarboxylic dianhydride; the constituent unit X2A comprises a constituent unit derived from an aromatic tetracarboxylic dianhydride different from the constituent unit X1A; Constituent unit Y1B contains a constituent unit (B1) derived from a diamine (b1), and constituent unit (B1) contains at least one selected from the group consisting of a constituent unit (B11) derived from a compound represented by the following formula (b11), a constituent unit (B12) derived from a compound represented by the following general formula (b12), and a constituent unit (B13) derived from a compound represented by the following general formula (b13). Constituent unit Y2B contains a constituent unit (B2) derived from a compound represented by the following general formula (b2). [Chemistry 20] In formula (b12), ^Z1 represents a single bond or a group represented by -O-. In formula (b13), R1 represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms. In formula (b2), ^Z2 and ^Z3 each independently represent a group represented by -COO- or a group represented by -OCO-. ^R1 , ^R2 , and ^R3 each independently represent a monovalent organic group having 1 to 20 carbon atoms. h, i, k, and n are integers from 0 to 4.

(Constituent Unit X1A) Constituent Unit X1A is the tetracarboxylic dianhydride-derived unit present in the imide portion (IM) of the copolymer of the present invention, and also contains units derived from aromatic tetracarboxylic dianhydride.

There is no limitation on the constituent unit X1A as long as it contains a constituent unit derived from an aromatic tetracarboxylic dianhydride, but it is preferable that the constituent unit X1A contains a constituent unit (A1) derived from a compound represented by the following formula (a1). [Chemical 21]

The compound represented by formula (a1) is 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF). The inclusion of the constituent unit (A1) derived from the compound represented by formula (a1) results in transparency, low yellowness, and high heat resistance, making it ideal.

When the constituent unit X1A includes the constituent unit (A1), the content of the constituent unit (A1) in the constituent unit X1A is preferably 50 mol% or more, more preferably 55 mol% or more, even more preferably 60 mol% or more, even more preferably 80 mol% or more, even more preferably 90 mol% or more, and even more preferably 95 mol% or more. The upper limit of the content of the constituent unit (A1) is not particularly limited and is 100 mol% or less. The constituent unit A may also be composed solely of the constituent unit (A1).

Constituent unit X1A may also contain constituent units other than constituent unit (A1). Tetracarboxylic dianhydrides providing such constituent units are not particularly limited, and examples thereof include alicyclic tetracarboxylic dianhydrides such as 1,2,4,5-cyclohexanetetracarboxylic dianhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclopentanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, and dicyclohexyltetracarboxylic dianhydride; and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride. In this specification, "alicyclic tetracarboxylic dianhydride" refers to a tetracarboxylic dianhydride in which, among the four alpha carbon atoms of two anhydrides (four carboxyl groups), the two alpha carbon atoms of at least one anhydride (two adjacent carboxyl groups) constitute an aliphatic ring. "Aromatic tetracarboxylic dianhydride" refers to a tetracarboxylic dianhydride in which the four alpha carbon atoms of two anhydrides (four carboxyl groups) constitute an aromatic ring. "Aliphatic tetracarboxylic dianhydride" refers to a tetracarboxylic dianhydride that is neither alicyclic nor aromatic. The constituent units optionally contained in constituent unit X1A may be one or two or more.

(Constituent Unit X2A) Constituent Unit X2A is the tetracarboxylic dianhydride-derived unit present in the amide portion (AM2) and the amide portion (AM1) of the copolymer of the present invention. It also contains units derived from an aromatic tetracarboxylic dianhydride different from Unit X1A.

There are no restrictions on the constituent unit X2A as long as it contains a constituent unit derived from an aromatic tetracarboxylic dianhydride different from the constituent unit X1A, but the constituent unit X2A preferably contains a constituent unit (A2) derived from an aromatic tetracarboxylic dianhydride (a2). Here, the constituent unit (A2) contains at least one selected from the group consisting of a constituent unit (A21) derived from a compound represented by the following formula (a21), a constituent unit (A22) derived from a compound represented by the following formula (a22), a constituent unit (A23) derived from a compound represented by the following formula (a23), a constituent unit (A24) derived from a compound represented by the following formula (a24), and a constituent unit (A25) derived from a compound represented by the following formula (a25). [Chemistry 22]

The compound represented by formula (a21) is biphenyltetracarboxylic dianhydride (BPDA). Specific examples thereof include 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) represented by the following formula (a21s), 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA) represented by the following formula (a21a), and 2,2',3,3'-biphenyltetracarboxylic dianhydride (i-BPDA) represented by the following formula (a21i). Among them, 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) represented by the following formula (a21s) is preferred.

[Chemistry 23]

The compound represented by formula (a22) is p-phenylenebis(trimellitate)dianhydride (TAHQ).

The compound represented by formula (a23) is oxydiphthalic anhydride (ODPA), and specific examples thereof include 4,4'-oxydiphthalic anhydride (s-ODPA) represented by formula (a23s), 3,4'-oxydiphthalic anhydride (a-ODPA) represented by formula (a23a), and 3,3'-oxydiphthalic anhydride (i-ODPA) represented by formula (a23i). Among them, 4,4'-oxydiphthalic anhydride (s-ODPA) represented by formula (a23s) is preferred.

[Chemistry 24]

The compound represented by formula (a24) is pyromellitic dianhydride (PMDA).

The compound represented by formula (a25) is 2,3,6,7-naphthalenetetracarboxylic dianhydride.

From the perspectives of high heat resistance and low residual stress, component (A2) preferably includes at least one member selected from the group consisting of component (A21) and component (A22), with component (A21) being more preferred. Component (A21) is particularly preferred from the perspective of improving the film's heat resistance and thermal stability while further reducing residual stress. Component (A22) is particularly preferred from the perspective of reducing residual stress and the coefficient of linear thermal expansion.

Constituent unit X2A may also contain constituent units other than constituent unit (A2). Tetracarboxylic dianhydrides providing such constituent units are not particularly limited, and examples thereof include alicyclic tetracarboxylic dianhydrides such as 1,2,4,5-cyclohexanetetracarboxylic dianhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclopentanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, and dicyclohexyltetracarboxylic dianhydride; and aliphatic tetracarboxylic dianhydrides such as 1,2,3,4-butanetetracarboxylic dianhydride. The constituent units optionally contained in the constituent unit X2A may be one type or two or more types.

The total ratio of constituent units (A21) to (A25) in constituent units (A2) is preferably 45 mol% or greater, more preferably 70 mol% or greater, even more preferably 90 mol% or greater, and particularly preferably 99 mol% or greater. The upper limit of this ratio is not particularly limited and is 100 mol% or less. Constituent units (A2) may comprise at least one type selected from constituent units (A21) to (A25), or may comprise only one type selected from constituent units (A21) to (A25). When constituent units (A2) comprise two or more types of constituent units selected from constituent units (A21) to (A25), the ratio of each constituent unit in constituent units (A2) is not particularly limited and may be set to any ratio.

The ratio of the constituent unit (A2) in the constituent unit X2A is preferably 45 mol% or more, more preferably 60 mol% or more, and even more preferably 85 mol% or more. The upper limit of the content ratio is not particularly limited and is 100 mol% or less.

When the constituent unit X1A contains the constituent unit (A1) and the constituent unit X2A contains the constituent unit (A2), the molar ratio [(A1)/(A2)] of the constituent unit (A1) to the constituent unit (A2) in the tetracarboxylic dianhydride-derived constituent unit of the imide-amide copolymer is preferably 10/90 to 55/45, more preferably 15/85 to 50/50, and even more preferably 20/80 to 45/55.

(Constituent unit Y1B) Constituent unit Y1B is a constituent unit derived from diamine which accounts for the imide portion (IM) and the amido portion (AM1) of the copolymer of the present invention, and contains a constituent unit (B1) derived from diamine (b1), and constituent unit (B1) contains at least any one selected from the group consisting of a constituent unit (B11) derived from a compound represented by the following formula (b11), a constituent unit (B12) derived from a compound represented by the following general formula (b12), and a constituent unit (B13) derived from a compound represented by the following general formula (b13). From the perspective of heat resistance, it is preferable to include a constituent unit (B13) derived from a compound represented by formula (b13) having a carbole structure. From the perspective of transparency, it is preferable to include a constituent unit (B11) derived from a compound represented by formula (b11) having an electron-withdrawing group and a constituent unit (B12) derived from a compound represented by formula (b12). The total ratio of constituent units (B11) to (B13) in constituent unit (B1) is preferably 45 mol% or more, more preferably 70 mol% or more, even more preferably 90 mol% or more, and particularly preferably 99 mol% or more. The upper limit of this ratio is not particularly limited and is 100 mol% or less. [Chemistry 25] In formula (b12), ^Z1 represents a single bond or a group represented by -O-. In formula (b13), R1 independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms.

The constituent unit (B11) is preferably at least one selected from the group consisting of a constituent unit (B111) derived from a compound represented by the following formula (b111) and a constituent unit (B112) derived from a compound represented by the following formula (b112). The constituent unit (B11) may be only the constituent unit (B111), only the constituent unit (B112), or a combination of the constituent unit (B111) and the constituent unit (B112). [Chemistry 26]

The compound represented by formula (b111) is 4,4'-diaminodiphenylsulfone (4,4'-DDS), and the compound represented by formula (b112) is 3,3'-diaminodiphenylsulfone (3,3'-DDS).

The constituent unit (B12) preferably comprises at least one constituent unit selected from the group consisting of a constituent unit (B121) derived from a compound represented by the following formula (b121) and a constituent unit (B122) derived from a compound represented by the following formula (b122). More preferably, it comprises a constituent unit (B122) derived from a compound represented by the following formula (b122). [Chemistry 27]

The compound represented by formula (b121) is 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether (6FODA). The compound represented by formula (b122) is 2,2'-bis(trifluoromethyl)benzidine (TFMB).

The constitutional unit (B13) is a constitutional unit derived from the compound represented by the aforementioned formula (b13).

In the aforementioned formula (b13), R each independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms, preferably a hydrogen atom, a fluorine atom, or a methyl group, with a hydrogen atom being more preferred. Compounds represented by the aforementioned formula (b13) include 9,9-bis(4-aminophenyl)fluorene (BAFL), 9,9-bis(3-fluoro-4-aminophenyl)fluorene, and 9,9-bis(3-methyl-4-aminophenyl)fluorene. Preferably, the compound is at least one selected from the group consisting of these three compounds. From the perspective of heat resistance, 9,9-bis(4-aminophenyl)fluorene is more preferred.

Constituent unit Y1B may also contain constituent units other than constituent unit (B1). The diamines providing such constituent units are not particularly limited, and examples thereof include: 1,4-phenylenediamine, p-phenylenediamine, 3,5-diaminobenzoic acid, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenylmethane, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)-2,3-dihydro- Aromatic diamines such as 1,3,3-trimethyl-1H-indene-5-amine, α,α’-bis(4-aminophenyl)-1,4-diisopropylbenzene, N,N’-bis(4-aminophenyl)-p-terylene diamine, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, and 1,4-bis(4-aminophenoxy)benzene; alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine. In this specification, an aromatic diamine refers to a diamine containing one or more aromatic rings, an alicyclic diamine refers to a diamine containing one or more alicyclic rings and no aromatic rings, and an aliphatic diamine refers to a diamine containing neither aromatic nor alicyclic rings. The constituent units optionally contained in the constituent unit Y1B may be one or more.

(Constituent Unit Y2B) Constituent Unit Y2B is a diamine-derived constituent unit that occupies the amide portion (AM2) of the copolymer of the present invention. Furthermore, from the perspectives of low residual stress, low linear thermal expansion coefficient, and heat resistance, Constituent Unit Y2B contains a constituent unit (B2) derived from a compound represented by the following general formula (b2). [Chemistry 28] In formula (b2), Z ² and Z ³ each independently represent a group represented by -COO- or a group represented by -OCO-. R ¹ , R ² , and R ³ each independently represent a monovalent organic group having 1 to 20 carbon atoms. h, i, j, and k are integers of 0 to 4.

The constituent unit (B2) preferably includes a constituent unit (B21) derived from a compound represented by the following formula (b21) from the viewpoint of heat resistance, low residual stress, and low linear thermal expansion coefficient. [Chemical 29]

The compound represented by formula (b21) is 4-aminophenyl 4-aminobenzoate (4-BAAB).

Constituent unit Y2B may also include constituent units other than constituent unit (B2). The diamines providing such constituent units are not particularly limited, and examples thereof include: 1,4-phenylenediamine, p-phenylenediamine, 3,5-diaminobenzoic acid, 1,5-diaminonaphthalene, 2,2'-dimethylbiphenyl-4,4'-diamine, 2,2'-dimethylbiphenyl-4,4'-diamine, 4,4'-diaminodiphenylmethane, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 2,2-bis(4-aminophenyl)hexafluoropropane, 4,4'-diaminobenzanilide, 1-(4-aminophenyl)- Aromatic diamines such as bis(amino)-2,3-dihydro-1,3,3-trimethyl-1H-inden-5-amine, α,α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, N,N'-bis(4-aminophenyl)-p-terylene diamine, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, and 1,4-bis(4-aminophenoxy)benzene; alicyclic diamines such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane; and aliphatic diamines such as ethylenediamine and hexamethylenediamine. The constituent units optionally contained in the constituent unit Y2B may be one or two or more.

When the total of the constituent units Y1B and Y2B is taken as 100 mol%, the ratio of the constituent units (B1) among the diamine-derived units in the copolymer is preferably 10 to 55 mol%, more preferably 20 to 50 mol%, and even more preferably 25 to 45 mol%. When the total of the constituent units Y1B and Y2B is taken as 100 mol%, the ratio of the constituent units (B2) among the diamine-derived units in the copolymer is preferably 45 to 90 mol%, more preferably 50 to 80 mol%, and even more preferably 55 to 75 mol%. When the constituent unit Y1B contains the constituent unit (B1) and the constituent unit Y2B contains the constituent unit (B2), the molar ratio [(B1)/(B2)] of the constituent unit (B1) to the constituent unit (B2) in the diamine-derived constituent unit in the amide-amide copolymer is preferably 10/90 to 55/45, more preferably 20/80 to 50/50, and even more preferably 25/75 to 45/55. When the total of the constituent units Y1B and Y2B is 100 mol%, the total ratio of the constituent units (B1) and the constituent units (B2) among the constituent units derived from diamine in the copolymer is preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more. The upper limit is not particularly limited and is 100 mol% or less.

The total ratio of the constituent units X1A, X2A, Y1B and Y2B to the total ratio of the constituent units constituting the imide-amide copolymer is preferably 80% by mass or more, more preferably 82% by mass or more, and even more preferably 85% by mass or more. The upper limit is not limited and is 100% by mass or less.

(Other Constituent Units) The imide-amide copolymer of the present invention may contain constituent units other than the aforementioned constituent units X1A, X2A, Y1B, and Y2B. The imide-amide copolymer of the present invention may further contain a constituent unit (B3) derived from a compound represented by the following general formula (b3). By containing the constituent unit (B3), the residual stress is reduced. [Chemistry 30]

In formula (b3), ^Z4 and ^Z5 each independently represent a divalent aliphatic group or a divalent aromatic group, ^R4 and ^R5 each independently represent a monovalent aromatic group or a monovalent aliphatic group, ^R6 and ^R7 each independently represent a monovalent aliphatic group, ^R8 and ^R9 each independently represent a monovalent aliphatic group or a monovalent aromatic group, m and n each independently represent an integer greater than 1, and the sum of m and n represents an integer from 2 to 1000. However, at least one of ^R4 and ^R5 represents a monovalent aromatic group. In formula (b3), two or more different repeating units described in parallel using [ ] may be repeated in any form and order, including random, alternating, or block repeating units.

In formula (b3), the divalent aliphatic group or divalent aromatic group in ^Z4 and ^Z5 may be substituted with a fluorine atom and may contain an oxygen atom. When an oxygen atom is contained in the form of an ether bond, the carbon number shown below refers to the total number of carbon atoms contained in the aliphatic group or aromatic group. Examples of divalent aliphatic groups include divalent saturated or unsaturated aliphatic groups having 1 to 20 carbon atoms. The carbon number of the divalent aliphatic group is preferably 3 to 20. Examples of divalent saturated aliphatic groups include alkylene groups and alkyleneoxy groups having 1 to 20 carbon atoms. Examples of alkylene groups include methylene, ethylene, propylene, trimethylene, tetramethylene, hexamethylene, octamethylene, decamethylene, and dodecamethylene. Examples of alkyleneoxy groups include propyleneoxy and trimethyleneoxy. Examples of divalent unsaturated aliphatic groups include alkenylene groups having 2 to 20 carbon atoms, such as ethenylene, propenylene, and alkylene groups having an unsaturated double bond at the terminal. Examples of divalent aromatic groups include arylene groups having 6 to 20 carbon atoms and arylalkylene groups having 7 to 20 carbon atoms. Specific examples of arylene groups having 6 to 20 carbon atoms in ^Z4 and ^Z5 include o-phenylene, m-phenylene, p-phenylene, 4,4'-biphenylene, and 2,6-naphthylene. ^Z4 and ^Z5 are particularly preferably trimethylene or p-phenylene, with trimethylene being more preferred.

In formula (b3), the monovalent aliphatic groups in R ⁴ to R ⁹ include monovalent saturated or unsaturated aliphatic groups. Examples of monovalent saturated aliphatic groups include alkyl groups having 1 to 22 carbon atoms, such as methyl, ethyl, and propyl. Examples of monovalent unsaturated aliphatic groups include alkenyl groups having 2 to 22 carbon atoms, such as ethenyl and propenyl. These groups may be substituted with fluorine atoms. Examples of monovalent aromatic groups in R ⁴ , R ⁵ , R ⁸ , and R ⁹ in formula (b3) include aryl groups having 6 to 20 carbon atoms, aryl groups having 7 to 30 carbon atoms substituted with an alkyl group, and aralkyl groups having 7 to 30 carbon atoms. The monovalent aromatic group is preferably an aryl group, more preferably a phenyl group. At least one of ^R4 and ^R5 represents a monovalent aromatic group. ^Z4 and ^Z5 are both preferably monovalent aromatic groups, and ^R4 and ^R5 are both more preferably phenyl groups. ^R6 and ^R7 are preferably alkyl groups having 1 to 6 carbon atoms, and are more preferably methyl groups. ^R8 and ^R9 are preferably monovalent aliphatic groups, and are more preferably methyl groups.

As described above, among the compounds represented by the general formula (b3), the compounds represented by the following formula (b31) are preferred.

[Chemistry 31] In formula (b31), m and n have the same meanings as m and n in formula (b3), and their ideal ranges are also the same.

In formula (b3) and formula (b31), m represents the number of repetitions of siloxane units bonded to at least one monovalent aromatic group, and n represents the number of repetitions of siloxane units bonded to a monovalent aliphatic group. In formula (b3) and formula (b31), m and n each independently represent an integer greater than 1, and the sum of m and n (m+n) represents an integer between 2 and 1000. The sum of m and n is preferably an integer between 3 and 500, more preferably between 3 and 100, and even more preferably between 3 and 50. In formula (b3) and formula (b31), the ratio of m/n is preferably between 5/95 and 50/50, more preferably between 10/90 and 40/60, and even more preferably between 20/80 and 30/70.

The functional group equivalent weight (amine equivalent weight) of the compound represented by formula (b3) is preferably 150-5,000 g/mol, more preferably 400-4,000 g/mol, and even more preferably 500-3,000 g/mol. Functional group equivalent weight refers to the mass of the compound represented by formula (b3) per 1 mol of functional groups (amine groups).

Among the compounds represented by the general formula (b3), commercially available products include "X-22-9409", "X-22-1660B", "X-22-161A", and "X-22-161B" manufactured by Shin-Etsu Chemical Co., Ltd.

When the constituent unit (B3) is contained, the ratio of the constituent unit (B3) to the total amount of the constituent unit (B3), the constituent unit Y1B and the constituent unit Y2B is preferably 0.01~15.0 mol %, more preferably 0.5~12.0 mol %, and even more preferably 1.0~8.0 mol %.

When the constituent units (B3) are present, the content of the polyorganosiloxane units relative to the total content of the constituent units constituting the imide-amide copolymer is preferably 1-20 mass%, more preferably 2-18 mass%, and even more preferably 5-15 mass%. When the content of the polyorganosiloxane units falls within the aforementioned range, both low phase retardation and low residual stress can be achieved to a greater degree.

Commercially available products of the compound represented by formula (b3) include "X-22-9409" and "X-22-1660B-3" manufactured by Shin-Etsu Chemical Co., Ltd.

[Method for Preparing Imido-Amino Acid Copolymers] The imido-amido copolymers described above can be prepared by any method, but are preferably obtained by the following method. The method for preparing the imido-amido copolymers of the present invention comprises the following steps 1 and 2. Step 1: reacting a tetracarboxylic acid component constituting an imide portion (IM) with a diamine component to obtain an imide oligomer; Step 2: reacting the imide oligomer obtained in Step 1 with a tetracarboxylic acid component and a diamine component constituting an amide portion (AM2) to obtain an imide-amide copolymer comprising repeating units composed of an imide portion (IM), an amide portion (AM1), and an amide portion (AM2) represented by the following formula (1); [Chemical 32] In formula (1), ^X1 is a tetravalent aromatic group having 4 to 39 carbon atoms, and may have at least one selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _2- , _-C2H4O- , and -S- as a bonding group; ^X2 is a tetravalent aromatic group having 4 to ₃₉ carbon atoms different from ^X1 , and may have at least one selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _2- , _{-C2H4O- ,} and -S- as a bonding group; ^Y1 is a group represented by at least one selected from the group consisting of the following formula (2), the following general formula (3), and the following general formula (4); ^Y2 is a group represented by the following general formula (5); s, t, and u are positive integers. [33] In formula (3), ^Z1 represents a single bond or a group represented by -O-. In formula (4), R1 independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms. [Chemical 34] In formula (5), Z ² and Z ³ each independently represent a group represented by -COO- or a group represented by -OCO-. R ¹ , R ² , and R ³ each independently represent a monovalent organic group having 1 to 20 carbon atoms. h, i, j, and k are integers from 0 to 4.

It is believed that the method for producing an imide-amic acid copolymer of the present invention allows the imide and amic acid moieties to be controlled into a specific structure. Therefore, unlike conventional imide-amic acid copolymers in which imide and amic acid moieties are randomly present, the imide-amic acid copolymer has both polyimide and polyamic acid moieties in response to the thermal imidization reactivity of each component. This results in an imide-amic acid copolymer that is expected to have improved heat resistance, low residual stress, and low linear thermal expansion coefficient.

The method for producing the ideal copolymer of the present invention comprises the following steps 1 and 2. Step 1: reacting a compound providing constituent units X1A derived from tetracarboxylic dianhydride with a compound providing constituent units Y1B derived from a diamine to obtain an imide oligomer; Step 2: reacting the imide oligomer obtained in Step 1 with a compound providing constituent units X2A derived from tetracarboxylic dianhydride and a compound providing constituent units Y2B derived from a diamine to obtain an imide-amic acid copolymer comprising repeating units represented by the aforementioned formula (1) consisting of an imide portion (IM), an amic acid portion (AM1), and an amic acid portion (AM2); However, the compound providing constituent units X1A comprises an aromatic tetracarboxylic dianhydride, and the compound providing constituent units X2A comprises an aromatic tetracarboxylic dianhydride different from the constituent units X1A. The compound constituting unit Y1B includes the compound constituting unit (B1), and the compound constituting unit (B1) includes at least one selected from the group consisting of a compound represented by the following formula (b11), a compound represented by the following general formula (b12), and a compound represented by the following general formula (b13). The compound constituting unit Y2B includes the compound represented by the following general formula (b2). In formula (b12), ^Z1 represents a single bond or a group represented by -O-. In formula (b13), R1 represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms. In formula (b2), ^Z2 and ^Z3 each independently represent a group represented by -COO- or a group represented by -OCO-. ^R1 , ^R2 , and ^R3 each independently represent a monovalent organic group having 1 to 20 carbon atoms. h, i, j, and k are integers from 0 to 4.

The production method comprising steps 1 and 2 described above can produce a copolymer capable of forming a film exhibiting excellent transparency and heat resistance, low yellowness, and low residual stress. The following describes the production method of the copolymer of the present invention.

<Step 1> Step 1 involves reacting the tetracarboxylic acid component constituting the imide portion (IM) with a diamine component to obtain an imide oligomer. The tetracarboxylic acid component constituting the imide portion (IM) is preferably an aromatic tetracarboxylic dianhydride.

Step 1 is preferably a step of reacting a compound providing constituent units X1A derived from tetracarboxylic dianhydride with a compound providing constituent units Y1B derived from a diamine to obtain an imide oligomer. The compound providing constituent units X1A comprises aromatic tetracarboxylic dianhydride. The compound providing constituent units Y1B comprises a compound providing constituent units (B1), and the compound providing constituent units (B1) comprises at least one selected from the group consisting of compounds represented by formula (b11), compounds represented by general formula (b12), and compounds represented by general formula (b13).

The tetracarboxylic acid component used in Step 1 preferably includes the compound that provides the constituent units (A1), and the entire amount thereof is preferably used in Step 1. Tetracarboxylic acid components other than the compound that provides the constituent units (A1) may also be included, as long as the effects of the present invention are not impaired. The diamine component used in Step 1 preferably includes the compound that provides the constituent units (B1). Diamine components other than the compound that provides the constituent units (B1) may also be included, as long as the effects of the present invention are not impaired. In Step 1, the diamine component is preferably present in an amount of 1.01 to 2 moles relative to the tetracarboxylic acid component, preferably 1.05 to 1.9 moles, and even more preferably 1.1 to 1.7 moles.

The method for reacting the tetracarboxylic acid component and the diamine component to obtain the imide oligomer in step 1 is not particularly limited, and a known method can be used. Specific reaction methods include: (1) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor, stirred at 10-110°C for 0.5-30 hours, and then the temperature is raised to carry out an imidization reaction; (2) a method in which a diamine component and a reaction solvent are charged into a reactor and dissolved, and then a tetracarboxylic acid component is charged into the reactor, stirred at 10-110°C for 0.5-30 hours as needed, and then the temperature is raised to carry out an imidization reaction; (3) a method in which a tetracarboxylic acid component, a diamine component, and a reaction solvent are charged into a reactor and the temperature is immediately raised to carry out an imidization reaction, etc.

The imidization reaction is preferably carried out using a Dean-Stark apparatus, etc., while removing the water generated during the production. By carrying out such an operation, the degree of polymerization and the imidization rate can be further increased.

A known imidization catalyst can be used in the above-mentioned imidization reaction. Examples of the imidization catalyst include base catalysts and acid catalysts. Base catalysts include organic base catalysts such as pyridine, quinoline, isoquinoline, α-picoline, β-picoline, 2,4-lutidine, 2,6-lutidine, trimethylamine, triethylamine, tripropylamine, tributylamine, triethylenediamine, imidazole, N,N-dimethylaniline, and N,N-diethylaniline; and inorganic base catalysts such as potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, potassium bicarbonate, and sodium bicarbonate. Examples of acid catalysts include crotonic acid, acrylic acid, trans-3-hexenoic acid, cinnamic acid, benzoic acid, methylbenzoic acid, hydroxybenzoic acid, terephthalic acid, benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid. These imidized catalysts may be used alone or in combination. Among these, from the perspective of operability, alkaline catalysts are preferred, with organic alkaline catalysts being more preferred, and at least one selected from triethylamine and triethylenediamine being even more preferred, with triethylamine being even more preferred.

The temperature of the imidization reaction is preferably 120-250°C, more preferably 160-200°C, from the viewpoint of reaction rate and inhibition of gelation. Furthermore, the reaction time is preferably 0.5-10 hours after the start of distillation of the generated water.

The imide oligomer obtained in step 1 preferably has an imide repeating structural unit formed from a compound providing constitutional unit (A1) and a compound providing constitutional unit (B1). Furthermore, the oligomer obtained in step 1 preferably has amino groups at both ends of the main molecular chain. The above method can produce a solution containing the imide oligomer dissolved in a solvent. The solution containing the imide oligomer obtained in step 1 may contain at least a portion of the components used as the tetracarboxylic acid component or diamine component in step 1 as unreacted monomers, to the extent that the effects of the present invention are not impaired.

<Step 2> Step 2 of the production method of the present invention involves reacting the imide oligomer obtained in Step 1 with a tetracarboxylic acid component and a diamine component constituting the amide portion (AM2) to obtain an imide-amide copolymer comprising repeating units of the imide portion (IM), the amide portion (AM1), and the amide portion (AM2) represented by the aforementioned formula (1). The tetracarboxylic acid component constituting the amide portion (AM2) used in Step 2 is preferably an aromatic tetracarboxylic dianhydride.

Step 2 is preferably a step of reacting a compound providing constituent units X2A derived from a tetracarboxylic dianhydride with a compound providing constituent units Y2B derived from a diamine to obtain an imide-amide copolymer. The compound providing constituent units X2A comprises an aromatic tetracarboxylic dianhydride. The compound providing constituent units Y2B comprises a compound providing constituent units (B2), and the compound providing constituent units (B2) comprises a compound represented by the aforementioned general formula (b2), preferably a compound represented by the aforementioned formula (b21).

The tetracarboxylic acid component used in Step 2 preferably includes a compound that provides units (A2). It may also include a tetracarboxylic acid component other than the compound that provides units (A2) to the extent that the effects of the present invention are not impaired. Tetracarboxylic acid components other than the compound that provides units (A2) can include compounds that provide units (A1). However, the tetracarboxylic acid component used in Step 2 preferably does not include a compound that provides units (A1). Furthermore, the entire amount of the compound that provides units (A2) is preferably used in Step 2. The diamine component used in Step 2 preferably includes a compound that provides units (B2). It may also include a diamine component other than the compound that provides units (B2) to the extent that the effects of the present invention are not impaired. After step 2, when introducing the polyorganosiloxane unit into the amide-amide copolymer, a diamine or tetracarboxylic dianhydride containing the polyorganosiloxane unit may be reacted. Preferably, the diamine containing the polyorganosiloxane unit is reacted, and more preferably, the compound that provides the constituent unit (B3) is reacted.

The method for reacting the tetracarboxylic acid component with the imide oligomer obtained in step 1 to obtain the imide-amide copolymer in step 2 is not particularly limited, and a known method can be used. Specific reaction methods include: (1) a method in which the imide oligomer obtained in step 1, a tetracarboxylic acid component, a diamine component, and a solvent are charged into a reactor and stirred at a temperature in the range of 0 to 120°C, preferably 5 to 80°C, for 1 to 72 hours; (2) a method in which the imide oligomer obtained in step 1 and a solvent are charged into a reactor and dissolved, and then a tetracarboxylic acid component and a diamine component are charged and stirred at a temperature in the range of 0 to 120°C, preferably 5 to 80°C, for 1 to 72 hours. When the reaction is carried out at a temperature below 80°C, the molecular weight of the copolymer obtained in step 2 does not change depending on the temperature history during polymerization, and the progress of thermal imidization can also be suppressed, so the copolymer can be produced stably.

The above method yields a copolymer solution containing an imide-amidite copolymer dissolved in a solvent. The copolymer concentration in the resulting copolymer solution is typically 1-50% by mass, preferably 3-35% by mass, and more preferably 5-30% by mass.

The number average molecular weight of the imide-amidite copolymer obtained by the production method of the present invention is preferably 5,000 to 500,000, considering the mechanical strength of the resulting polyimide film. Furthermore, the weight average molecular weight (Mw), also considering the same considerations, is preferably 10,000 to 800,000, more preferably 100,000 to 300,000. The number average molecular weight of the copolymer can be determined, for example, by using a standard polymethyl methacrylate (PMMA) conversion value determined by gel filtration analysis. Next, the raw materials used in this production method will be described.

<Tetracarboxylic Acid Component> The tetracarboxylic acid component used as a raw material for the imide-amide copolymer in this production method is preferably a compound providing the respective constituent units described in (Constituent Unit XIA) and (Constituent Unit X2A) of the <Constituent Units of the Imine-Amide Copolymer>. For example, the compound providing constituent unit (A1) may be a compound represented by formula (a1), but is not limited thereto and may be a derivative thereof within the scope of providing the same constituent units. Examples of such derivatives include tetracarboxylic acids corresponding to the compound represented by formula (a1) and alkyl esters of such tetracarboxylic acids. The compound providing constituent unit (A1) is preferably a compound represented by formula (a1). Similarly, compounds that provide constituent unit (A2) include compounds represented by formula (a21), compounds represented by formula (a22), compounds represented by formula (a23), compounds represented by formula (a24), and compounds represented by formula (a25), but are not limited thereto. Derivatives thereof may also be provided within the scope of providing the same constituent unit. Examples of such derivatives include tetracarboxylic acids corresponding to compounds represented by any one of formulas (a21) to (a25) and alkyl esters of such tetracarboxylic acids. The compound that provides constituent unit (A2) is preferably a compound represented by any one of formulas (a21) to (a25).

The molar ratio [(A1)/(A2)] of the compound providing the constituent units (A1) to the compound providing the constituent units (A2) in the tetracarboxylic acid component used as a raw material for the imide-amide copolymer in the present production method is preferably 10/90 to 55/45, more preferably 15/85 to 50/50, and even more preferably 20/80 to 45/55.

The total ratio of compounds providing constituent units (A21) to (A25) in the compounds providing constituent units (A2) is preferably 45 mol% or greater, more preferably 70 mol% or greater, even more preferably 90 mol% or greater, and particularly preferably 99 mol% or greater. The upper limit of this ratio is not particularly limited and is 100 mol% or less. The tetracarboxylic acid component used as a raw material for the imide-amide copolymer may also contain compounds other than the compounds providing constituent units (A1), (A21), (A22), (A23), (A24), and (A25). These compounds may be one or two or more.

<Diamine Component> The molar ratio [(B1)/(B2)] of the compound providing units (B1) and the compound providing units (B2) in the diamine component used as a raw material for the imide-amide copolymer in this production method is preferably 10/90 to 55/45, more preferably 20/80 to 50/50, and even more preferably 25/75 to 45/55. The compound providing units (B1) is preferably one or more selected from the group consisting of compounds providing units (B11), compounds providing units (B12), and compounds providing units (B13). The total ratio of compounds providing units (B11) to (B13) in the compounds providing units (B1) is preferably 45 mol% or greater, more preferably 70 mol% or greater, even more preferably 90 mol% or greater, and particularly preferably 99 mol% or greater. The upper limit of this ratio is not particularly limited and is 100 mol% or less. The compound providing units (B2) is preferably one or more compounds providing units (B2). The diamine component used as a raw material for the imide-amide copolymer may also contain compounds other than the compound providing units (B11), the compound providing units (B12), the compound providing units (B13), and the compound providing units (B2). These compounds may be one or more. The compound providing the constituent unit (B1) and the compound providing the constituent unit (B2) can be, but is not limited to, a diamine. Within the scope of providing the same constituent unit, a derivative thereof can also be used. Such a derivative can be, for example, a diisocyanate corresponding to the diamine. The compound providing the constituent unit (B1) and the compound providing the constituent unit (B2) are preferably diamines.

When the copolymer contains a compound providing the constituent unit (B3), the compound providing the constituent unit (B3) is preferably present in an amount of 0.01 to 15.0 mol%, more preferably 0.5 to 12.0 mol%, and even more preferably 1.0 to 8.0 mol%, relative to the total amount of the compound providing the constituent unit (B3) and the diamine component.

In the present invention, the feed ratio of the tetracarboxylic acid component to the diamine component used in all steps of the copolymer production, including step 1, step 2, and the step of reacting other components such as the compound constituting unit (B3) after step 2, is preferably 0.9 to 1.1 mol of the diamine component per 1 mol of the tetracarboxylic acid component.

<End-Capping Agent> In addition, in the present invention, in the production of the imide-amide copolymer, in addition to the aforementioned tetracarboxylic acid component and diamine component, an end-capping agent may also be used. The end-capping agent is preferably used in step 2 or after step 2, during the reaction with other components such as the compound constituting unit (B3). The end-capping agent is preferably a monoamine or a dicarboxylic acid. The amount of the end-capping agent introduced is preferably 0.0001 to 0.1 mol, and particularly preferably 0.001 to 0.06 mol, per 1 mol of the tetracarboxylic acid component. Recommended monoamine end-capping agents include methylamine, ethylamine, propylamine, butylamine, benzylamine, 4-methylbenzylamine, 4-ethylbenzylamine, 4-dodecylbenzylamine, 3-methylbenzylamine, 3-ethylbenzylamine, aniline, 3-methylaniline, and 4-methylaniline. Benzylamine and aniline are particularly preferred. Dicarboxylic acid end-capping agents are preferably dicarboxylic acids, some of which may be ring-closed. Recommended examples include phthalic acid, phthalic anhydride, 4-chlorophthalic acid, tetrafluorophthalic acid, 2,3-benzophenonedicarboxylic acid, 3,4-benzophenonedicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, and 4-cyclohexene-1,2-dicarboxylic acid. Phthalic acid and phthalic anhydride are particularly preferred.

<Solvent> The solvent used in the copolymer production method of the present invention can be any solvent capable of dissolving the resulting imide-amide copolymer. Examples include aprotic solvents, phenolic solvents, ether solvents, and carbonate solvents.

Specific examples of aprotic solvents include: amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 1,3-dimethylimidazolidinone, and tetramethylurea; lactone solvents such as γ-butyrolactone and γ-valerolactone; phosphorus-containing amide solvents such as hexamethylphosphatamide and hexamethylphosphinetriamide; sulfur-containing solvents such as dimethyl sulfone, dimethylsulfoxide, and cyclobutanesulfonate; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, and methylcyclohexanone; and ester solvents such as (2-methoxy-1-methylethyl) acetate.

Specific examples of phenolic solvents include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, and 3,5-xylenol. Specific examples of etheric solvents include 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether, tetrahydrofuran, and 1,4-dioxane. Specific examples of carbonate-based solvents include diethyl carbonate, ethyl methyl carbonate, ethyl carbonate, and propyl carbonate. Among the above reaction solvents, amide solvents or lactone solvents are preferred, amide solvents are more preferred, and N-methyl-2-pyrrolidone is even more preferred. The above reaction solvents may be used alone or in combination of two or more.

[Varnish] The varnish of the present invention is prepared by dissolving the polyimide resin precursor, namely the imide-amide copolymer of the present invention, in an organic solvent. Specifically, the varnish of the present invention contains the copolymer of the present invention and an organic solvent, wherein the copolymer is dissolved in the organic solvent. The organic solvent is not particularly limited as long as it dissolves the copolymer of the present invention. It is preferably a single compound or a mixture of two or more compounds used as solvents in the production of the copolymer of the present invention. The varnish of the present invention may be the copolymer solution itself or a solution obtained by adding a diluting solvent to the copolymer solution.

To facilitate more efficient imidization of the amide moieties in the copolymer of the present invention, the varnish of the present invention may further contain an imidization catalyst and a dehydration catalyst. The imidization catalyst can be one with a boiling point of 40°C or higher and 180°C or lower, with amine compounds having a boiling point of 180°C or lower being preferred. An imidization catalyst with a boiling point of 180°C or lower eliminates the risk of discoloration during high-temperature drying after film formation, which could degrade the film's appearance. Furthermore, an imidization catalyst with a boiling point of 40°C or higher avoids the possibility of volatilization before imidization has fully progressed. Examples of amine compounds that can be preferably used as imidization catalysts include pyridine and picoline. These imidization catalysts can be used alone or in combination of two or more. Dehydration catalysts include acid anhydrides such as acetic anhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride, and trifluoroacetic anhydride; and carbodiimide compounds such as dicyclohexylcarbodiimide. These can be used alone or in combination of two or more.

The copolymer contained in the varnish of the present invention is solvent-soluble, allowing for the production of high-concentration varnishes. The varnish of the present invention preferably contains 3-40% by mass of the copolymer of the present invention, more preferably 5-40% by mass, and even more preferably 10-30% by mass. The viscosity of the varnish is preferably 0.1-100 Pa·s, more preferably 0.1-20 Pa·s. The viscosity of the varnish is measured at 25°C using an E-type viscometer. Furthermore, the varnish of the present invention may contain various additives, such as inorganic fillers, adhesion promoters, release agents, flame retardants, UV stabilizers, surfactants, leveling agents, defoaming agents, fluorescent brighteners, crosslinking agents, polymerization initiators, and photosensitizers, as long as the required properties of the polyimide film are not impaired. The production method of the varnish of the present invention is not particularly limited, and known methods may be used.

[Polyimide Film] The polyimide film of the present invention comprises a polyimide resin obtained by imidizing the amide moieties of the amide-amide copolymer of the present invention. Consequently, the polyimide film of the present invention exhibits excellent transparency and heat resistance, low yellowness, and low residual stress. The ideal physical properties of the polyimide film of the present invention are as described above. The polyimide film of the present invention can be produced using a varnish prepared by dissolving the copolymer in an organic solvent.

The method for producing a polyimide film using the varnish of the present invention is not particularly limited, and known methods can be used. For example, the varnish of the present invention can be applied to a smooth support such as a glass plate, metal plate, or plastic, or formed into a film. The varnish is then heated to remove organic solvents such as reaction solvents and dilution solvents contained in the varnish to obtain a copolymer film. The amide sites of the copolymer in the copolymer film are then subjected to imidization (dehydration and ring closure) by heating, and then the film is peeled off from the support to produce a polyimide film. The weight average molecular weight (Mw) of the polyimide resin contained in the polyimide film of the present invention is preferably 10,000-800,000, more preferably 30,000-500,000, even more preferably 50,000-400,000, and even more preferably 100,000-300,000, from the perspective of the film's mechanical strength. The number average molecular weight of the copolymer can be determined, for example, by using a standard polymethyl methacrylate (PMMA) conversion value determined by gel filtration analysis.

The heating temperature for drying the varnish of the present invention to obtain a copolymer film is preferably 50-150°C. The heating temperature for imidization of the copolymer of the present invention is preferably 200-500°C, preferably 250-450°C, and even more preferably 300-400°C. The heating time is generally 1 minute to 6 hours, preferably 5 minutes to 2 hours, and more preferably 15 minutes to 1 hour. The heating environment may include air, nitrogen, oxygen, hydrogen, and nitrogen/hydrogen mixed gases. To suppress coloration of the resulting polyimide resin, nitrogen with an oxygen concentration of 100 ppm or less and nitrogen/hydrogen mixed gases with a hydrogen concentration of 0.5% or less are preferred. In addition, the imidization method is not limited to thermal imidization, and chemical imidization can also be used.

The thickness of the polyimide film of the present invention can be appropriately selected depending on the intended application, preferably ranging from 1 to 250 μm, more preferably from 5 to 100 μm, and even more preferably from 5 to 50 μm. A thickness of 1 to 250 μm allows for practical use as a self-supporting film. The thickness of the polyimide film can be easily controlled by adjusting the solids concentration and viscosity of the varnish.

<Polyimide Film Properties> The use of the imide-amidite copolymer of the present invention enables the formation of polyimide films exhibiting excellent transparency and heat resistance, low yellowness, and low residual stress. The desired properties of such films are as follows: The total light transmittance, when formed into a film with a thickness of 10 μm, is preferably 85% or higher, preferably 86% or higher, and even more preferably 87% or higher. The yellowness index (YI), when formed into a film with a thickness of 10 ± 3 μm, is preferably 15.0 or lower, preferably 13.0 or lower, even more preferably 12.0 or lower, and even more preferably 11.0 or lower. The glass transition temperature (Tg) is preferably 400°C or higher, preferably 420°C or higher, and even more preferably 430°C or higher. The residual stress is preferably 35 MPa or less, more preferably 30 MPa or less, and even more preferably 24 MPa or less. The coefficient of linear thermal expansion (100°C to 400°C range) is preferably 40 ppm/°C or less, more preferably 30 ppm/°C or less, and even more preferably 20 ppm/°C or less. The above-mentioned physical properties of the present invention can be measured using the methods described in the Examples.

The polyimide film of the present invention is ideally suited for use as a film for various components, such as color filters, flexible displays, semiconductor components, and optical components. The polyimide film of the present invention is particularly ideal for use as a substrate for image display devices, such as liquid crystal displays and OLED displays. [Examples]

The present invention is further described below using examples. However, the present invention is not limited in any way by these examples. The physical properties of the films obtained in the examples and comparative examples were measured using the methods described below.

(1) Film thickness The film thickness was measured using a micrometer manufactured by Mitutoyo Corporation.

(2) Total light transmittance and yellowness index (YI) Total light transmittance and YI were measured in accordance with JIS K7105:1981 using the COH7700 color and turbidity simultaneous tester manufactured by Nippon Denshoku Industries Co., Ltd.

(3) Haze The measurement was carried out in accordance with JIS K7361-1:1997 using the COH7700 color and turbidity simultaneous tester manufactured by Nippon Denshoku Industries Co., Ltd.

(4) Glass transition temperature (Tg) Using a thermomechanical analyzer "TMA/SS6100" manufactured by Hitachi High-Tech Science Co., Ltd., the residual stress was removed by heating the specimen to a temperature sufficient to remove the residual stress in the tensile mode with a sample size of 3 mm × 20 mm, a load of 0.1 N, a nitrogen flow (flow rate of 200 mL/min), and a heating rate of 10°C/min. The specimen was then cooled to room temperature. The elongation of the specimen was then measured under the same conditions as those for the aforementioned treatment to remove the residual stress, and the temperature at which the inflection point of the elongation was observed was determined as the glass transition temperature.

(5) Coefficient of Linear Thermal Expansion (CTE) Thermomechanical analyzer "TMA/SS6100" manufactured by Hitachi High-Tech Science Co., Ltd. was used in the tensile mode with a sample size of 3 mm × 20 mm, a load of 0.1 N, a nitrogen flow rate of 200 mL/min, and a heating rate of 10°C/min. The sample was heated to a temperature sufficient to remove the residual stress and then cooled to room temperature. The elongation of the test piece was then measured under the same conditions as the aforementioned treatment for removing the residual stress, and the CTE from 100°C to 400°C was determined.

(6) 1% weight loss temperature (Td1%) A differential thermal and thermogravimetric simultaneous measurement device "TG/DTA6200" manufactured by Hitachi High-Tech Science Co., Ltd. was used. The sample was heated from 40°C to 550°C at a heating rate of 10°C/min and the weight at 300°C was compared. The temperature at which the weight loss was 1% was defined as the 1% weight loss temperature. The larger the value of the weight loss temperature, the better.

(7) Tensile strength and tensile modulus Tensile strength and tensile modulus were measured in accordance with JIS K7127:1999 using a tensile testing machine "STROGRAPH VG-1E" manufactured by Toyo Seiki Co., Ltd. The clamp spacing was set to 50 mm, the specimen size was set to 10 mm × 70 mm, and the test speed was set to 20 mm/min.

(8) Residual Stress Using the residual stress measuring device "FLX-2320" manufactured by KLA-Tencor, the varnish obtained in the examples and comparative examples was applied to a 4-inch silicon wafer with a thickness of 525μm±25μm and a previously measured "warp amount" using a spin coater and pre-baked. Subsequently, a heat curing treatment was applied at 400°C for 60 minutes (heating rate 5°C/minute) in a nitrogen environment using a hot air dryer to obtain a silicon wafer with a polyimide film having a thickness of 6~15μm after curing. The warp amount of this wafer was measured using the aforementioned residual stress measuring device to evaluate the residual stress generated between the silicon wafer and the polyimide film.

The tetracarboxylic acid components and diamine components used in the Examples and Comparative Examples, as well as their abbreviations, are as follows. <Tetracarboxylic acid component> BPAF: 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (manufactured by JFE Chemical Co., Ltd.; compound represented by formula (a1)) s-BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride (manufactured by Mitsubishi Chemical Co., Ltd.; compound represented by formula (a21s)) <Diamine component> 4,4'-DDS: 4,4'-diaminodiphenylsulfonium (manufactured by SEIKA Co., Ltd.; compound represented by formula (b111)) TFMB: 2,2'-bis(trifluoromethyl)benzidine (manufactured by SEIKA Co., Ltd.; compound represented by formula (b122)) 4-BAAB: 4-aminophenyl 4-aminobenzoate (manufactured by Japan Junryo Pharmaceutical Co., Ltd.; compound represented by formula (b21))

The abbreviations for solvents and catalysts used in the Examples and Comparative Examples are as follows. NMP: N-methyl-2-pyrrolidone (manufactured by Tokyo Junyaku Industries, Ltd.) TEA: triethylamine (manufactured by Kanto Chemical Co., Ltd.)

<Example 1> Into a 500 mL, five-necked round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet, a Dean-Stark apparatus with a cooling tube, a thermometer, and glass end caps, 9.932 g (0.040 mol) of 4,4'-DDS and 46.380 g of NMP were added. The flask was stirred at 200 rpm under a nitrogen atmosphere at a temperature of 70°C to obtain a solution. To this solution, 13.753 g (0.030 mol) of BPAF and 11.595 g of NMP were added all at once. Then, 0.152 g of TEA, an imidization catalyst, was added. The reaction system was heated using a mantle heater, raising the temperature to 190°C over approximately 20 minutes. The distilled components were collected, and the rotational speed was adjusted according to the viscosity increase while maintaining the reaction system at 190°C under reflux for one hour. Subsequently, 95.849 g of NMP was added, and the reaction system was cooled to 50°C to obtain a solution containing an oligomer with repeating imide units. To the resulting solution, 20.595 g (0.070 mol) of s-BPDA, 13.695 g (0.060 mol) of 4-BAAB, and 16.858 g of NMP were added all at once and stirred at 50°C for 5 hours. NMP was then added to a solids concentration of approximately 15% by mass and homogenized to obtain a varnish containing a copolymer having repeating imide units and amide units. The resulting varnish was then spin-coated onto a glass plate and maintained at 80°C on a hot plate for 20 minutes. The solution was then heated at 430°C in a hot air dryer under a nitrogen atmosphere for 60 minutes to evaporate the solvent, yielding a polyimide film. The results are shown in Table 1.

<Example 2> A varnish having a solids concentration of approximately 15% by mass was obtained using the same method as in Example 1, except that the amount of BPAF was changed from 13.753 g (0.030 mol) to 9.169 g (0.020 mol) and the amount of s-BPDA was changed from 20.595 g (0.070 mol) to 23.538 g (0.080 mol). The resulting varnish was used to obtain a film using the same method as in Example 1.

<Example 3> A varnish having a solids concentration of approximately 15% by mass was obtained using the same method as in Example 1, except that the amount of BPAF was changed from 13.753 g (0.030 mol) to 9.169 g (0.020 mol), the amount of s-BPDA was changed from 20.595 g (0.070 mol) to 23.538 g (0.080 mol), the amount of 4,4'-DDS was changed from 9.932 g (0.040 mol) to 7.449 g (0.030 mol), and the amount of 4-BAAB was changed from 13.695 g (0.060 mol) to 15.978 g (0.070 mol). The resulting varnish was used to obtain a film using the same method as in Example 1.

<Example 4> A polyimide varnish having a solids concentration of approximately 15% by mass was obtained using the same method as in Example 1, except that 9.932 g (0.040 mol) of 4,4'-DDS was replaced with 12.810 g (0.040 mol) of TFMB. The resulting varnish was used to obtain a film using the same method as in Example 1.

<Example 5> A varnish having a solids concentration of approximately 15% by mass was obtained using the same method as in Example 4, except that the amount of BPAF was changed from 13.753 g (0.030 mol) to 9.169 g (0.020 mol), the amount of s-BPDA was changed from 20.595 g (0.070 mol) to 23.538 g (0.080 mol), the amount of TFMB was changed from 12.810 g (0.040 mol) to 9.607 g (0.030 mol), and the amount of 4-BAAB was changed from 13.695 g (0.060 mol) to 15.978 g (0.070 mol). The resulting varnish was used to obtain a film using the same method as in Example 1.

Comparative Example 1 Into a 500 mL, five-necked round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet, a Dean-Stark apparatus with a cooling tube, a thermometer, and glass end caps, 22.825 g (0.100 mol) of 4-BAAB and 167.190 g of NMP were placed. The mixture was stirred at 200 rpm under a nitrogen atmosphere at 50°C to obtain a solution. To this solution, 29.422 g (0.100 mol) of s-BPDA and 41.798 g of NMP were added in one portion and stirred at room temperature for 5 hours. Subsequently, 87.078 g of NMP was added to achieve a solids concentration of approximately 15% by mass, and the mixture was stirred for approximately 1 hour for homogenization to obtain a polyamide (PAA) varnish. The resulting varnish was used to obtain a thin film using the same method as in Example 1. The polyamide contained in the varnish obtained in Comparative Example 1 contained only repeating amide units formed from s-BPDA and 4-BAAB.

<Comparative Example 2> A polyamide (PAA) varnish having a solids concentration of approximately 15% by mass was obtained using the same method as in Comparative Example 1, except that 29.422 g (0.100 mol) of s-BPDA was replaced with 45.843 g (0.100 mol) of BPAF. The resulting varnish was used to obtain a film using the same method as in Example 1. The polyamide contained in the varnish obtained in Comparative Example 2 consisted solely of repeating amide units formed from BPAF and 4-BAAB.

Comparative Example 3 Into a 500 mL, five-necked round-bottom flask equipped with a stainless steel half-moon stirring blade, a nitrogen inlet, a Dean-Stark apparatus with a cooling tube, a thermometer, and glass end caps, 9.932 g (0.040 mol) of 4,4'-DDS, 13.695 g (0.060 mol) of 4-BAAB, and 139.141 g of NMP were added. The mixture was stirred at 200 rpm under a nitrogen atmosphere at a temperature of 50°C to obtain a solution. To this solution, 13.753 g (0.030 mol) of BPAF, 20.595 g (0.070 mol) of s-BPDA, and 34.785 g of NMP were added all at once and stirred at room temperature for 5 hours. NMP was then added to a solids concentration of approximately 15% by mass and the mixture was homogenized to obtain a polyamide (PAA) varnish. The resulting varnish was used to obtain a thin film using the same method as in Example 1. The polyamide contained in the varnish obtained in Comparative Example 3 consists solely of repeating amide units formed from BPAF, s-BPDA, 4,4'-DDS, and 4-BAAB.

[Table 1] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative example 1 Comparative example 2 Comparative example 3 Imine-amidite copolymer (numbers represent molar ratio) Imine moiety Tetracarboxylic acid component (X1A) BPAF (a1) 30 20 20 30 20 - - - Diamine component (Y1B) 4,4'-DDS (b111) 40 40 30 - - - - - TFMB (b122) - - - 40 30 - - - Acylamidin moiety Tetracarboxylic acid component (X2A) s-BPDA (a21s) 70 80 80 70 80 100 - 70 BPAF (a1) - - - - - - 100 30 Diamine component (Y2B) 4-BAAB (b21) 60 60 70 60 70 100 100 60 4,4'-DDS (b111) - - - - - - - 40 Film evaluation Film thickness [μm] 8 7 7 8 8 7 7.7 8.0 Total light transmittance [%] 86.0 86.3 85.9 86.5 85.4 75.6 87.4 86.9 Haze[%] 0.5 0.5 0.6 0.4 1.0 1.7 0.40 0.33 YI 12.1 10.4 11.2 12.1 13.6 32.0 9.40 10.30 Tg[℃] 430 425 425 441 425 564 383 403 CTE 100-400℃[ppm/℃] 29 26 20 30 19 4 - 72 Td1%[℃] 521 502 527 524 525 523 489 490 Tensile strength [MPa] 105 160 159 153 219 296 140 110 Tensile modulus [GPa] 4.9 5.1 5.9 5.6 6.6 9.9 4.1 3.8 Residual stress [MPa] 29 26 19 27 19 2 47 43

As shown in Table 1, the polyimide film obtained from the imide-amic acid copolymer of the Example, which has specific imide repeating structural units and amic acid structural units, exhibits low residual stress and linear thermal expansion coefficient, excellent transparency and heat resistance, and low yellowness. Although Example 1 and Comparative Example 3 use the same raw material composition to form the polyimide film, the polyimide film of Example 1 maintains transparency and low yellowness, while also exhibiting exceptionally good heat resistance, and lower residual stress and linear thermal expansion coefficient than the polyimide film of Comparative Example 3 derived from polyamic acid.

Claims (16)

An imide-amide copolymer comprising repeating units represented by the following formula (1) consisting of an imide portion (IM), an amide portion (AM1), and an amide portion (AM2); In formula (1), ^X1 is a tetravalent aromatic group having 4 to 39 carbon atoms, and may have at least one selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _2- , _-C2H4O- , and -S- as a bonding group; ^X2 is a tetravalent aromatic group having 4 to ₃₉ carbon atoms different from ^X1 , and may have at least one selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _2- , _{-C2H4O- ,} and -S- as a bonding group; ^Y1 is a group represented by at least one selected from the group consisting of the following formula (2), the following general formula (3), and the following general formula (4); ^Y2 is a group represented by the following general formula (5); s, t and u are positive integers; In formula (3), ^Z1 represents a single bond or a group represented by -O-; In formula (4), R1 independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms; In formula (5), Z ² and Z ³ each independently represent a group represented by -COO- or a group represented by -OCO-; R ¹ , R ² , and R ³ each independently represent a monovalent organic group having 1 to 20 carbon atoms; h, i, j, and k are integers from 0 to 4; the imide portion (IM) comprises a constituent unit X1A derived from tetracarboxylic dianhydride and a constituent unit Y1B derived from a diamine; the amide portion (AM1) comprises a constituent unit X2A derived from tetracarboxylic dianhydride and a constituent unit Y1B derived from a diamine; the amide portion (AM2) comprises a constituent unit X2A derived from tetracarboxylic dianhydride and a constituent unit Y2B derived from a diamine; the constituent unit X1A comprises a constituent unit (A1) derived from a compound represented by the following formula (a1); The constituent unit X2A contains a constituent unit (A2) derived from an aromatic tetracarboxylic dianhydride (a2), and the constituent unit (A2) contains at least one selected from the group consisting of a constituent unit (A21) derived from a compound represented by the following formula (a21), a constituent unit (A22) derived from a compound represented by the following formula (a22), a constituent unit (A23) derived from a compound represented by the following formula (a23), a constituent unit (A24) derived from a compound represented by the following formula (a24), and a constituent unit (A25) derived from a compound represented by the following formula (a25); . The imide-amide copolymer of claim 1, wherein s is 1-50, and t is 1-50. The imide-amide copolymer of claim 1 or 2, wherein u is 5-200. The imide-amide copolymer of claim 1 or 2, wherein X ¹ is a group represented by the following formula (6); . The imide-amide copolymer of claim 1 or 2, wherein X ² is a group represented by the following formula (7); . The imide-amide copolymer of claim 1 or 2, wherein the constituent unit Y1B comprises a constituent unit (B1) derived from a diamine (b1), and the constituent unit (B1) comprises at least one selected from the group consisting of a constituent unit (B11) derived from a compound represented by the following formula (b11), a constituent unit (B12) derived from a compound represented by the following general formula (b12), and a constituent unit (B13) derived from a compound represented by the following general formula (b13); and the constituent unit Y2B comprises a constituent unit (B2) derived from a compound represented by the following general formula (b2); In formula (b12), Z ¹ represents a single bond or a group represented by -O-; in formula (b13), R 1 each independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms; in formula (b2), Z ² and Z ³ each independently represent a group represented by -COO- or a group represented by -OCO-; R ¹ , R ² , and R ³ each independently represent a monovalent organic group having 1 to 20 carbon atoms; and h, i, j, and k are integers from 0 to 4. The imide-amide copolymer of claim 6 further comprises a constituent unit (B3) derived from a compound represented by the following general formula (b3); In formula (b3), ^Z4 and ^Z5 each independently represent a divalent aliphatic group or a divalent aromatic group, ^R4 and ^R5 each independently represent a monovalent aromatic group or a monovalent aliphatic group, ^R6 and ^R7 each independently represent a monovalent aliphatic group, ^R8 and ^R9 each independently represent a monovalent aliphatic group or a monovalent aromatic group, m and n each independently represent an integer greater than 1, and the sum of m and n represents an integer from 2 to 1000; provided that at least one of ^R4 and ^R5 represents a monovalent aromatic group. The amide-amide copolymer of claim 7, wherein R ⁴ and R ⁵ are phenyl groups, and R ⁶ and R ⁷ are methyl groups. The imide-amide copolymer of claim 7 or 8, wherein the content of the polyorganosiloxane unit in the imide-amide copolymer is 1-20% by mass. A varnish is prepared by dissolving the imide-amide copolymer according to any one of claims 1 to 9 in an organic solvent. A polyimide film comprises a polyimide resin obtained by imidizing the amide moiety of the amide-amide copolymer according to any one of claims 1 to 9. The polyimide film of claim 11, wherein the weight average molecular weight (Mw) of the polyimide resin is 100,000-300,000. A method for producing an imide-amide copolymer comprises the following steps 1 and 2: Step 1: reacting a tetracarboxylic acid component constituting an imide portion (IM) with a diamine component to obtain an imide oligomer; Step 2: reacting the imide oligomer obtained in Step 1 with a tetracarboxylic acid component and a diamine component constituting an amide portion (AM2) to obtain an imide-amide copolymer comprising repeating units composed of an imide portion (IM), an amide portion (AM1), and an amide portion (AM2) represented by the following formula (1); In formula (1), ^X1 is a tetravalent aromatic group having 4 to 39 carbon atoms, and may have at least one selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _2- , _-C2H4O- , and -S- as a bonding group; ^X2 is a tetravalent aromatic group having 4 to ₃₉ carbon atoms different from ^X1 , and may have at least one selected from the group consisting of -O-, _-SO2- , -CO-, _-CH2- , -C( _CH3 ) _2- , _{-C2H4O- ,} and -S- as a bonding group; ^Y1 is a group represented by at least one selected from the group consisting of the following formula (2), the following general formula (3), and the following general formula (4); ^Y2 is a group represented by the following general formula (5); s, t and u are positive integers; In formula (3), ^Z1 represents a single bond or a group represented by -O-; In formula (4), R1 independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms; In formula (5), Z ² and Z ³ each independently represent a group represented by -COO- or a group represented by -OCO-; R ¹ , R ² , and R ³ each independently represent a monovalent organic group having 1 to 20 carbon atoms; h, i, j, and k are integers from 0 to 4; the imide portion (IM) comprises a constituent unit X1A derived from tetracarboxylic dianhydride and a constituent unit Y1B derived from a diamine; the amide portion (AM1) comprises a constituent unit X2A derived from tetracarboxylic dianhydride and a constituent unit Y1B derived from a diamine; the amide portion (AM2) comprises a constituent unit X2A derived from tetracarboxylic dianhydride and a constituent unit Y2B derived from a diamine; the constituent unit X1A comprises a constituent unit (A1) derived from a compound represented by the following formula (a1); The constituent unit X2A contains a constituent unit (A2) derived from an aromatic tetracarboxylic dianhydride (a2), and the constituent unit (A2) contains at least one selected from the group consisting of a constituent unit (A21) derived from a compound represented by the following formula (a21), a constituent unit (A22) derived from a compound represented by the following formula (a22), a constituent unit (A23) derived from a compound represented by the following formula (a23), a constituent unit (A24) derived from a compound represented by the following formula (a24), and a constituent unit (A25) derived from a compound represented by the following formula (a25); . The method for producing an imide-amide copolymer according to claim 13, wherein the imide oligomer obtained in step 1 has amino groups at both ends of the main chain of the molecular chain. The method for producing an imide-amide copolymer according to claim 13 or 14, wherein: In step 1, the molar ratio of the diamine component to the tetracarboxylic acid component (diamine/tetracarboxylic acid) is 1.01 to 2. The method for producing an imide-amide copolymer according to claim 13 or 14 comprises reacting a diamine containing a polyorganosiloxane unit after step 2.