Patent Description:
For a structure of a flexible device, there are needs for a stack of various multi-layered films. For example, a transparent flexible display device needs a stack of multi-layers of an outmost hard coating layer, a transparent window substrate material, an adhesive, a polarization film, an adhesive, a light emission driver, and the like. The multi-layers are currently stacked and bonded by using an adhesive film, and adherence of this adhesive film to a substrate material is an important factor for realizing reliability of a product in a flexibility evaluation and the like. Accordingly, an attempt to improve the reliability has been made by improving adherence characteristics of an adhesive, but since various substrate materials have their own different surface characteristics, there is a limit in developing an adhesive to realize excellent adherence to the substrate materials.

On the other hand, a transparent plastic film capable of replacing a window cover glass is required to satisfy high hardness and optical properties in order to be applied to a flexible display. The hardness may be complemented by coating a hard coating layer thereon, but herein, a base film having a high tensile modulus (hereinafter, referred to be a 'modulus') may contribute to increasing the hardness of a final film. The optical properties may include high light transmittance, a low haze, a low yellowness index (YI), UV coloring resistance characteristics, and the like.

<CIT> discloses a composition including a plurality of oligomers including at least two repeating units, wherein at least a part of the plurality of oligomers includes at least one terminal end having an amino group.

<CIT> discloses a composition for preparing a polyimide-inorganic particle composite, including a tetracarboxylic acid dianhydride, a diamine, and an inorganic particle having an amino group on its surface.

<CIT> discloses a polyimide precursor composition, a manufacturing method of a polyimide, a polyimide manufactured by the method, and a film including the polyimide.

<CIT> discloses a poly(amide-imide) block copolymer that includes a first segment and a second segment, an article including the same, and a display device including the article.

A poly(imide-amide) copolymer having high mechanical strength and optical properties after a curing process, while enforcing adherence with an adhesive is provided.

An aspect of the invention provides a composition for preparing a poly(imide-amide) copolymer according to claim <NUM>.

An article including the poly(imide-amide) copolymer is provided.

An electronic device including the article is provided.

A poly(imide-amide) copolymer includes an imide structural unit being a reaction product of a first diamine and dianhydride, and an amide structural unit being a reaction product of a second diamine and diacyl halide, each of the first and the second diamines includes <NUM>,<NUM>'-bis-trifluoromethyl-<NUM>,<NUM>'-biphenyldiamine (TFDB), and at least one of the first and the second diamines further includes a compound represented by Chemical Formula <NUM>, the dianhydride includes <NUM>,<NUM>',<NUM>,<NUM>'-biphenyltetracarboxylic dianhydride (BPDA) and <NUM>,<NUM>'-hexafluoroisopropylidene diphthalicanhydride (6FDA), and the diacyl halide includes terephthaloylchloride (TPCI), and the compound represented by Chemical Formula <NUM> is included in an amount of less than or equal to about <NUM> mol% based on the total moles of the diamine:.

(Chemical Formula <NUM>)     NH<NUM>-A-NH<NUM>.

In Chemical Formula <NUM>,
A includes a substituted or unsubstituted C6 to C30 aromatic ring, the aromatic ring is substituted with at least one hydroxyl group, the aromatic ring is a single ring, or a condensed ring including two or more single rings fused, or a ring including two or more aromatic rings where two or more single rings or two or more condensed rings are linked to each other by a single bond or a linking group selected from -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)<NUM>-, -Si(CH<NUM>)<NUM>-, -(CH<NUM>)p-(wherein, <NUM>≤p≤<NUM>), -(CF<NUM>)q- (wherein, <NUM>≤q≤<NUM>), -CRR'- (wherein, R and R' are the same or different, and are independently hydrogen, a substituted or unsubstituted C1 to C10 aliphatic hydrocarbon group, a substituted or unsubstituted C6 to C20 aromatic hydrocarbon group, a substituted or unsubstituted C3 to C20 alicyclic hydrocarbon group, a substituted or unsubstituted C7 to C20 arylalkyl group, a substituted or unsubstituted C7 to C20 alkylaryl group, or a C1 to C4 alkyl group substituted with at least one halogen atom, provided that R and R' are not simultaneously hydrogen), - C(=O)NH-, and a fluorenylene group.

The A may be selected from chemical formulae of Group <NUM>:
<CHM>
<CHM>.

In the chemical formulae,
L is a single bond or a linking group selected from -O-, -S-, -C(=O)-, - CH(OH)-, -S(=O)<NUM>-, -Si(CH<NUM>)<NUM>-, -(CH<NUM>)p- (wherein, <NUM>≤p≤<NUM>), -(CF<NUM>)q- (wherein, <NUM>≤q≤<NUM>), -CRR'- (wherein, R and R' are the same or different, and are independently hydrogen, a C1 to C4 alkyl group, a phenyl group, a phenyl group substituted with a C1 to C4 alkyl group, a C1 to C4 alkyl group substituted with a phenyl group, or a C1 to C4 alkyl group substituted with at least one fluorine atom, provided that R and R' are not simultaneously hydrogen), -C(=O)NH- and a fluorenylene group, and * indicates a point of attachment to a nitrogen atom.

The A may be represented by Chemical Formula <NUM> or Chemical Formula <NUM>:
<CHM>
<CHM>.

In Chemical Formulae <NUM> and <NUM>, * indicates a point of attachment to a nitrogen atom.

The diamine represented by Chemical Formula <NUM> may be included in an amount of about <NUM> mol% to about <NUM> mol% based on the total amount of the diamine of the poly(imide-amide) copolymer.

In the poly(imide-amide) copolymer, the imide structural unit and the amide structural unit may be included in a mole ratio of about <NUM> to <NUM> : about <NUM> to <NUM>.

The poly(imide-amide) copolymer may include (i) a structural unit represented by Chemical Formula <NUM>, (ii) a structural unit represented by Chemical Formula <NUM>, (iii) a structural unit represented by Chemical Formula <NUM> and (iv) at least one of a structural unit represented by Chemical Formula <NUM>, a structural unit represented by Chemical Formula <NUM> and a structural unit represented by Chemical Formula <NUM>, wherein the total amount of the (iv) at least one of the structural unit represented by Chemical Formula <NUM>, the structural unit represented by Chemical Formula <NUM> and the structural unit represented by Chemical Formula <NUM> may be less than or equal to about <NUM> mol% based on the total moles of the structural units of the (i) to (iv):
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>.

In Chemical Formulae <NUM> to <NUM>, * indicates a point of attachment to a nitrogen atom or a carbon atom.

The poly(imide-amide) copolymer includes (i) the structural unit represented by Chemical Formula <NUM>, (ii) the structural unit represented by Chemical Formula <NUM>, (iii) the structural unit represented by Chemical Formula <NUM>, and (iv) at least one of the structural unit represented by Chemical Formula <NUM> and the structural unit represented by Chemical Formula <NUM>, wherein the total amount of the (iv) at least one of the structural unit represented by Chemical Formula <NUM> and the structural unit represented by Chemical Formula <NUM> may be about <NUM> mol% to about <NUM> mol% based on the total moles of the structural units of the (i) to (iv).

A method of preparing the poly(imide-amide) copolymer may further include imidizing the reaction product after reacting the compound of Chemical Formula <NUM> with the diamine represented by Chemical Formula <NUM>, BPDA and 6FDA.

The imidizing may include chemical imidizing or thermal imidizing.

An article may include the poly(imide-amide) copolymer.

The article may be a film, and the film may have a yellowness index (YI) of less than or equal to <NUM> and tensile modulus of greater than or equal to <NUM> GPa at a thickness of about <NUM> to about <NUM>.

An electronic device may include the article.

This disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments are shown. This disclosure may, however, be embodied in many different forms and is not to be construed as limited to the exemplary embodiments set forth herein.

As used herein, when a specific definition is not otherwise provided, the term "substituted" refers to a functional group substituted with at least one substituent selected from a halogen atom (F, Br, Cl or I), a hydroxy group, a nitro group, a cyano group, an amino group (-NH<NUM>, -NH(R<NUM>) or -N(R<NUM>)(R<NUM>), wherein R<NUM>, R<NUM>, and R<NUM> are the same or different, and are independently a C1 to C10 alkyl group), an amidino group, a hydrazine group, a hydrazone group, a carboxyl group, an ester group, a ketone group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alicyclic organic group, a substituted or unsubstituted aryl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted heteroaryl group, and a substituted or unsubstituted heterocyclic group, in place of at least one hydrogen of a functional group, or the substituents may be linked to each other to provide a ring.

As used herein, when specific definition is not otherwise provided, the term "alkyl group" refers to a C1 to C30 alkyl group, and specifically a C1 to C15 alkyl group, the term "cycloalkyl group" refers to a C3 to C30 cycloalkyl group, and specifically a C3 to C18 cycloalkyl group, the term "alkoxy group" refers to a C1 to C30 alkoxy group, and specifically a C1 to C18 alkoxy group, the term "ester group" refers to a C2 to C30 ester group, and specifically a C2 to C18 ester group, the term "ketone group" refers to a C2 to C30 ketone group, and specifically C2 to C18 ketone group, the term "aryl group" refers to a C6 to C30 aryl group, and specifically C6 to C18 aryl group, the term "alkenyl group" refers to a C2 to C30 alkenyl group, and specifically a C2 to C18 alkenyl group, the term "alkynyl group" refers to a C2 to C30 alkynyl group, and specifically a C2 to C18 alkynyl group, the term "alkylene group" refers to a C1 to C30 alkylene group, and specifically a C1 to C18 alkylene group, and the term "arylene group" refers to a C6 to C30 arylene group, and specifically a C6 to C16 arylene group.

As used herein, when specific definition is not otherwise provided, the term "aliphatic organic group" refers to a C1 to C30 alkyl group, a C2 to C30 alkenyl group, a C2 to C30 alkynyl group, a C1 to C30 alkylene group, a C2 to C30 alkenylene group, or a C2 to C30 alkynylene group, and specifically a C1 to C15 alkyl group, a C2 to C15 alkenyl group, a C2 to C15 alkynyl group, a C1 to C15 alkylene group, a C2 to C15 alkenylene group, or a C2 to C15 alkynylene group, the term "alicyclic organic group" refers to a C3 to C30 cycloalkyl group, a C3 to C30 cycloalkenyl group, a C3 to C30 cycloalkynyl group, a C3 to C30 cycloalkylene group, a C3 to C30 cycloalkenylene group, or a C3 to C30 cycloalkynylene group, and specifically a C3 to C15 cycloalkyl group, a C3 to C15 cycloalkenyl group, a C3 to C15 cycloalkynyl group, a C3 to C15 cycloalkylene group, a C3 to C15 cycloalkenylene group, or a C3 to C15 cycloalkynylene group, the term "aromatic organic group" refers to a C6 to C30 group, for example, a C6 to C30 aryl group, or a C6 to C30 arylene group, and specifically a C6 to C16 aryl group, or a C6 to C16 arylene group such as a phenylene group including a single aromatic ring, a condensed ring including two or more aromatic rings, or two or more aromatic rings linked by a single bond, or a fluorenylene group, a functional group selected from -O-, -S-, C-(=O)-, -CH(OH)-, -S(=O)<NUM>-, -Si(CH<NUM>)<NUM>-, - (CH<NUM>)p- (wherein, <NUM>≤p≤<NUM>), -(CF<NUM>)q- (wherein, <NUM>≤q≤<NUM>), -C(CH<NUM>)<NUM>-, -C(CF<NUM>)<NUM>-, and -C(=O)NH-, particularly -S(=O)<NUM>-, and the term "hetero cyclic group" refers to a C2 to C30 cycloalkyl group, a C2 to C30 cycloalkylene group, a C2 to C30 cycloalkenyl group, a C2 to C30 cycloalkenylene group, a C2 to C30 cycloalkynyl group, a C2 to C30 cycloalkynylene group, a C2 to C30 heteroaryl group, or a C2 to C30 heteroarylene group including <NUM> to <NUM> heteroatoms selected from O, S, N, P, Si, and a combination thereof in one ring, and specifically a C2 to C15 cycloalkyl group, a C2 to C15 cycloalkylene group, a C2 to C15 cycloalkenyl group, C2 to C15 cycloalkenylene group, a C2 to C15 cycloalkynyl group, C2 to C15 cycloalkynylene group, a C2 to C15 heteroaryl group, or a C2 to C15 heteroarylene group including <NUM> to <NUM> heteroatoms selected from O, S, N, P, Si, and a combination thereof in one ring.

As used herein, when a definition is not otherwise provided, "combination" commonly refers to mixing or copolymerization.

In addition, in the specification, " * " may refer to a point of attachment to nitrogen or another atom.

The same material or the same elements in the drawings are provided with the same reference number. For better understanding and ease of description, sizes of each element of the drawings may be exaggerated in the drawings, so may be larger or smaller than actual sizes.

A poly(imide-amide) copolymer includes an imide structural unit being a reaction product of a first diamine and dianhydride, and an amide structural unit being a reaction product of a second diamine and diacyl halide, each of the first and the second diamines includes <NUM>,<NUM>'-bis-trifluoromethyl-<NUM>,<NUM>'-biphenyldiamine (TFDB), and at least one of the first and the second diamines further include a compound represented by Chemical Formula <NUM>, the dianhydride includes <NUM>,<NUM>',<NUM>,<NUM>'-biphenyltetracarboxylic dianhydride (BPDA) and <NUM>,<NUM>'-hexafluoroisopropylidene diphthalicanhydride (6FDA), and the diacyl halide includes terephthaloylchloride (TPCI), and the compound represented by Chemical Formula <NUM> is included in an amount of less than or equal to about <NUM> mol% based on the total moles of the diamine:.

For a substrate material of a flexible device, various polymer films such as polyethylene terephthalate, polycarbonate, polyimide, or polydimethylsiloxane have been used. Of these, polyimide having improved stability in mechanical and chemical properties according to a use temperature has been actively researched. In addition, in order to improve mechanical properties of a substrate, a poly(imide-amide) film including an amide structure unit has drawn attention as a substrate material of a flexible device. A development of a flexible device, particularly a flexible display device using such a film having high hardness and high strength instead of a conventional glass substrate of electronic materials has been actively made.

As described above, a flexible device needs a stack of various films including a plurality of layers. Currently, such stack and bonding thereof have been implemented using an adhesive film, and there are needs for improvement of adherence between films in order to decrease defects in a flexible device, particularly, a bent portion during use of a device. In order to improve the adherence, improvements of adhesion characteristics of an adhesive has been mainly studied, but there are limits for implementing adhesives having excellent adherence with all substrate materials, as surface characteristics of various substrate materials are different.

The inventors have developed a poly(imide-amide) copolymer that is used as a substrate material, particularly, a transparent window substrate material having improved adherence with an adhesive, and thereby adherence and adhesion reliability may be improved even if a general adhesive is used, and optical properties and mechanical characteristics of the poly(imide-amide) copolymer as a novel substrate material is not deteriorated.

As described above, a poly(imide-amide) copolymer includes an imide structural unit obtained from a first diamine and dianhydride and an amide structural unit obtained from a second diamine and diacyl halide, wherein each of the first and the second diamines providing the imide structural unit and the amide structural unit includes TFDB, that is, <NUM>,<NUM>'-bis-trifluoromethyl-<NUM>,<NUM>'-biphenyldiamine, and at least one of the first and the second diamines further include the diamine represented by Chemical Formula <NUM>, the dianhydride includes <NUM>,<NUM>',<NUM>,<NUM>'-biphenyltetracarboxylic dianhydride (BPDA) and <NUM>,<NUM>'-hexafluoroisopropylidene diphthalicanhydride (6FDA), and the diacyl halide includes terephthaloylchloride (TPCI), and the compound represented by Chemical Formula <NUM> is included in an amount of less than or equal to about <NUM> mol%, for example, about <NUM> mol% to about <NUM> mol%, based on the total moles of the diamine.

That is, both the first and the second diamines include TFDB, and one or both of them further include the diamine represented by Chemical Formula <NUM>, where the diamine represented by Chemical Formula <NUM> is included in an amount of less than or equal to about <NUM> mol% based on the total moles of the diamines included in the first and the second diamines.

The first diamine may include TFDB and the second diamine may include TFDB and the diamine represented by Chemical Formula <NUM>. The first diamine may include TFDB and the diamine represented by Chemical Formula <NUM> and the second diamine may include TFDB.

The first diamine may include TFDB and the diamine represented by Chemical Formula <NUM> and the second diamine may include TFDB and the diamine represented by Chemical Formula <NUM>.

The compound represented by Chemical Formula <NUM> includes a substituted or unsubstituted C6 to C30 aromatic ring, the aromatic ring is substituted with at least one hydroxyl group, and the aromatic ring includes a single ring, a condensed ring including two or more single rings fused, or a ring including two or more aromatic rings where two or more single rings or two or more condensed rings are linked to each other by a single bond or the specific linking groups that are described above.

The compound represented by Chemical Formula <NUM> includes at least one aromatic ring substituted with at least one hydroxyl group, and reacts with a dianhydride to provide the imide structural unit of the poly(imide-amide) copolymer or with a diacyl halide compound to provide the amide structural unit of the copolymer and thus is included in the imide structural unit or the amide structural unit. Thereby, the poly(imide-amide) copolymer including the imide structural unit and the amide structural unit includes a polymer chain substituted with at least one hydroxyl group. When the poly(imide-amide) copolymer substituted with the at least one hydroxyl group is used as a high hardness window film, the at least one hydroxyl group forms a hydrogen bond with a hydrogen of an amino group, a carboxyl group, or a hydroxyl group of a conventional adhesive, or of a hard coating layer, applied to or coated on the window film. Therefore, additional hydrogen bonds between the at least one hydroxyl group derived from the compound represented by Chemical Formula <NUM> and hydrogens of the functional groups of the adhesion layer or the hard coating layer may be formed in addition to the hydrogen bonds between the amino groups that are basically included in the poly(imide-amide) copolymer chain and the hydrogens of the functional groups of the adhesion layer or the hard coating layer. Accordingly, the poly(imide-amide) copolymer film may have further improved adherence with an adhesive or a hard coating layer thereon.

Therefore, the diamine represented by Chemical Formula <NUM> may include any diamine that has the moiety represented by A of Chemical Formula <NUM>, which includes a C6 to C30 aromatic ring substituted with at least one hydroxyl group, without particular limitation. For example, the C6 to C30 aromatic ring may have two or more hydroxyl groups, and particularly, when the A includes two or more aromatic rings, hydroxyl groups may substitute each aromatic ring positioned at both terminal ends among the two or more aromatic rings.

In the chemical formulae, each hydroxyl group may be positioned at an ortho position with respect to the position linked to the nitrogen atom.

The diamine represented by Chemical Formula <NUM> may be included in an amount of about <NUM> mol% to about <NUM> mol% based on the total moles of the diamines comprised of the poly(imide-amide) copolymer. When the diamine represented by Chemical Formula <NUM> is included within the range, adherence with the poly(imide-amide) copolymer may be improved compared with a poly(imide-amide) copolymer film that does not include a structural unit derived from the diamine represented by Chemical Formula <NUM>, while maintaining excellent mechanical characteristics and optical properties of the poly(imide-amide) copolymer that does not include a structural unit derived from the diamine represented by Chemical Formula <NUM>.

The diamine represented by Chemical Formula <NUM> may be included in an amount of about <NUM> mol% to about <NUM> mol%, for example, about <NUM> mol% to about <NUM> mol%, based on the total moles of the diamine comprised of the poly(imide-amide) copolymer. When the diamine represented by Chemical Formula <NUM> is included within the range, adherence of the poly(imide-amide) copolymer is improved, as well as mechanical characteristic and optical properties may be maintained to be an improved level.

In the poly(imide-amide) copolymer, the imide structural unit and the amide structural unit may be included in a mole ratio of about <NUM> to <NUM> : about <NUM> to <NUM>. For example, the imide structural unit and the amide structural unit may be included in a mole ratio of about <NUM> to <NUM> : about <NUM> to <NUM>. When the imide structural unit and the amide structural unit are included within the range, optical properties and mechanical properties of the poly(imide-amide) copolymer may be maintained to be an improved level without deterioration.

The poly(imide-amide) copolymer includes (i) a structural unit represented by Chemical Formula <NUM>, (ii) a structural unit represented by Chemical Formula <NUM>, (iii) a structural unit represented by Chemical Formula <NUM> and (iv) at least one of a structural unit represented by Chemical Formula <NUM>, a structural unit represented by Chemical Formula, and a structural unit represented by Chemical Formula <NUM>, wherein the total amount of the (iv) at least one of the structural unit represented by Chemical Formula <NUM>, the structural unit represented by Chemical Formula <NUM>, and the structural unit represented by Chemical Formula <NUM> may be less than or equal to about <NUM> mol% based on the total moles of the structural units of the (i) to (iv):
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>
<CHM>.

A poly(imide-amide) copolymer is a reaction product of a compound represented by Chemical Formula <NUM>, diamine represented by Chemical Formula <NUM>, and dianhydride including BPDA and 6FDA, wherein the diamine represented by Chemical Formula <NUM> is included in an amount of less than or equal to about <NUM> mol% based on the total moles of a structural unit derived from TFDB in the compound represented by Chemical Formula <NUM> and the diamine represented by Chemical Formula <NUM>:
<CHM>.

In Chemical Formula <NUM>, n0 is an integer of <NUM> or more.

In Chemical Formula <NUM>,
A may include a substituted or unsubstituted C6 to C30 aromatic ring, the aromatic ring is substituted with at least one hydroxyl group, the aromatic ring is a single ring, or a condensed ring including two or more single rings fused, or a ring including two or more aromatic rings where two or more single rings or two or more condensed rings are linked to each other by a single bond or a linking group selected from -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)<NUM>-, -Si(CH<NUM>)<NUM>-, -(CH<NUM>)p-(wherein, <NUM>≤p≤<NUM>), -(CF<NUM>)q- (wherein, <NUM>≤q≤<NUM>), -CRR'- (wherein, R and R' are the same or different, and are independently hydrogen, a substituted or unsubstituted C1 to C10 aliphatic hydrocarbon group, a substituted or unsubstituted C6 to C20 aromatic hydrocarbon group, a substituted or unsubstituted C3 to C20 alicyclic hydrocarbon group, a substituted or unsubstituted C7 to C20 arylalkyl group, a substituted or unsubstituted C7 to C20 alkylaryl group, or a C1 to C4 alkyl group substituted with at least one halogen atom, provided that R and R' are not simultaneously hydrogen), - C(=O)NH-, and a fluorenylene group.

A conventional poly(imide-amide) copolymer is prepared by adding monomers providing an imide structural unit, that is, diamine (TFDB) and dianhydride (BPDA and/or 6FDA) and monomers providing an amide structural unit, that is, diamine (TFDB) and diacyl dichloride (TPCI) in one reactor followed by polymerization in a reaction solvent. Meanwhile, the poly(imide-amide) copolymer may be prepared by first reacting monomers providing an amide structural unit, that is, for example, TFDB and TPCI to prepare an amide oligomer including amino groups at both terminal ends, adding the diamine represented by Chemical Formula <NUM> and dianhydride, BPDA and 6FDA, to the prepared amide oligomer, followed by an additional reaction, and preparing a precursor of the poly(imide-amide) copolymer, a poly(amic acid-amide) copolymer.

Accordingly, a composition according to the invention for preparing a poly(imide-amide) copolymer comprises a compound of Chemical Formula <NUM>, a diamine represented by Chemical Formula <NUM>, and the dianhydrides BPDA and 6FDA; wherein the compound of Chemical Formula <NUM> is a reaction product of TFDB with TPCl; and wherein an amount of the diamine represented by Chemical Formula <NUM> is <NUM> mol% to <NUM> mol% based on the total moles of TFDB and the diamine represented by Chemical Formula <NUM>:
<CHM>.

In Chemical Formula <NUM>,
A is selected from chemical formulae of Group <NUM>:
<CHM>
wherein, in the chemical formulae,.

The compound represented by Chemical Formula <NUM> may be prepared through a general polyamide preparation method, for example, polymerization of TFDB and TPCI in aprotic polar solvent.

The aprotic polar solvent may include a sulfoxide-based solvent such as dimethylsulfoxide and diethylsulfoxide, a formamide-based solvent such as N,N-dimethyl formamide and N,N-diethylformamide, an acetamide-based solvent such as N,N-dimethylacetamide and N,N-diethylacetamide, a pyrrolidone-based solvent such as N-methyl-<NUM>-pyrrolidone and N-vinyl-<NUM>-pyrrolidone, a phenol-based solvent such as phenol, o-, m-, or p-cresol, xylenol, halogenated phenol, and catechol, hexamethylphosphoramide, γ-butyrolactone, or a mixture thereof. However, this disclosure is not limited to them, and an aromatic hydrocarbon such as xylene and toluene may be used. Also, to promote the dissolution of a polymer, an alkali metal salt or an alkaline earth metal salt may be further added to the solvent in an amount of about <NUM> wt% or less based on the total amount of the solvent.

The prepared compound represented by Chemical Formula <NUM> may have a number average molecular weight of about <NUM> to about <NUM>,<NUM>, without limitation. The number average molecular weight of the compound may be easily controlled by adjusting the amount of the reactants, TFDB and TPCI. By controlling the molecular weight of the compound within the range, it is easy to control the polymerization equivalent ratio or the polymerization viscosity during subsequent reactions with the dianhydride compound.

When n0 of Chemical Formula <NUM> is <NUM>, the compound represented by Chemical Formula <NUM> refers to unreacted TFDB that does not reacted with TPCI. Accordingly, after completion of the reaction for preparing the amide group-containing oligomer, the reaction product may include amide group-containing oligomers including amino groups at both terminal ends, as well as unreacted TFDB. To the reaction product, the diamine represented by Chemical Formula <NUM> and dianhydrides, BPDA and 6FDA, are added and reacted to prepare a precursor of the poly(imide-amide) copolymer, a poly(amic acid-amide) copolymer. The preparation of the poly(amic acid-amide) copolymer may be performed by polymerization of the reactants in an aprotic polar solvent using a known imide preparation process.

Meanwhile, although only the compound represented by Chemical Formula <NUM>, which is a reaction product of TFDB and TPCI, is described, persons skilled in the art could readily understand that the diamine represented by Chemical Formula <NUM> may also be added and reacted with TPCI, along with TFDB, to prepare an amide group-containing oligomer having a chemical formula that is similar to Chemical Formula <NUM>.

The prepared poly(amic acid-amide) copolymer may be partially or completely imidized by chemical or thermal imidization to prepare a partially or completely imidized poly(imide-amide) copolymer.

The chemical imidization may include adding an imidization catalyst to the poly(amic acid-amide) copolymer, followed by agitating the resultant. In addition, the thermal imidization may include heating the prepared poly(amic acid-amide) copolymer at a predetermined temperature for a predetermined time.

The imidization catalyst may include any known catalyst in the related art without limitation, and may be, for example, acid anhydride such as acetic anhydride, isoquinoline, β-picoline, pyridine, azole, phosphine, malononitrile, <NUM>,<NUM>-dimethylpiperidine, triethylamine, N,N,N',N'-tetramethylethyleneamine, triphenylphosphine, <NUM>-dimethylaminopyridine, tripropylamine, tributylamine, N,N-dimethylbenzylamine, <NUM>,<NUM>,<NUM>-triazole and triisobutylamine, and the like.

The imidization may be performed by combining chemical imidization with thermal imidization. For example, a dehydration agent and an imidization catalyst are added to a solution including poly(amic acid-amide) copolymer and heated to activate the dehydration agent and the imidization catalyst to perform partial imidization. The imidization may be performed at about <NUM> to about <NUM>, for example, about <NUM> to about <NUM>, for about <NUM> minutes or more, to achieve <NUM> % or more of imidization.

The imidization catalyst may be added in a mole ratio of <NUM>:<NUM> or greater, for example, <NUM>:<NUM> or greater with respect to polyamic acid. When the imidization catalyst is added in a more excessive amount than the amount of the polyamic acid, dehydration reaction may be effectively derived and imidization may be smoothly performed, at a lower temperature, which prevents color changes and thermal stability deterioration of the copolymer by a long-tern reaction at a high temperature.

The partially or completely imidized poly(imide-amide) copolymer may be added in a solvent of water, methanol, or ethylether, and the like, having lower polarity than the polymerization solvent, and then is precipitated in a solid form. The obtained solid poly(imide-amide) copolymer is dissolved in a solvent again, casted on a support, and imidized to be manufactured to an article of a film and the like.

The article may be formed of the poly(imide-amide) copolymer through a dry-wet method, a dry method, or a wet method, but is not limited thereto.

When the article is a film of the article, the film may be manufactured using a solution including the poly(imide-amide) copolymer through the dry-wet method, where a layer is formed by extruding the solution of the poly(amideimide) copolymer from a mouth piece on a supporter, such as drum or an endless belt, drying the layer, and evaporating the solvent from the layer until the layer has a self-maintenance property. The drying may be performed, for example, at about <NUM> to about <NUM>, for about <NUM> hour or less. When the surface of the drum and/or the endless belt used for the drying process becomes flat, a layer with a flat surface is formed. The layer obtained after the drying process is delaminated from the supporter, and inputted to a wet process, desalted, and/or desolventized. The manufacturing of the film is completed as the layer is elongated, dried, and/or heat treated.

The elongating may be performed at an elongation ratio in terms of surface ratio, which may range from about <NUM> to about <NUM>, and about <NUM> to about <NUM>. As used herein, the term "surface ratio" refers to a value obtained by dividing the area of a layer after the elongating, by an area of the layer before the elongating. A value of <NUM> or less denotes a relaxed state. On the other hand, the elongating may be performed not only in a surface direction but also in a thickness direction.

The heat treatment may be performed at a temperature of about <NUM> to about <NUM>, particularly at about <NUM> to about <NUM>, for several seconds to about several minutes.

Also, the layer after elongating and heat treatment may be cooled slowly, for example, at a speed of about <NUM>/second or lower.

The layer may be formed as a single layer or as multiple layers.

The article may be a film, and the film may have a yellowness index (YI) of less than or equal to <NUM> at a thickness of about <NUM> to about <NUM>, for example, at about <NUM>, according to ASTM D1926.

The article may be a film, and the film may have a tensile modulus of greater than or equal to <NUM> GPa at a thickness of about <NUM> to about <NUM>, for example, at about <NUM>, according to ASTM D882.

That is, the article may maintain excellent optical properties of the poly(imide-amide) copolymer, particularly a low yellowness index (YI) and high tensile modulus, and may improve adherence with a conventional adhesive, which will be evidenced by the Examples.

Accordingly, the article may be advantageously applied to a flexible device, for example, a flexible display device that may be manufactured by stacking multi-layered films.

In the flexible display device, the poly(imide-amide) copolymer may be used as a window film due to high mechanical characteristics and optical properties, but this disclosure is not limited thereto, and may be applied as various substrate materials in a flexible device. When the poly(imide-amide) copolymer film according to the embodiment is used as a window substrate, adherence between a hard coating layer coated on the window substrate upper, or a transparent adhesive film under a window film, and the window substrate may be further improved.

An adhesive that may be used with the poly(imide-amide) copolymer film may improve adherence in a device including these may be known various adhesive used during manufacture of a flexible device, or a flexible display device, and useable adhesives may be a photocurable polyacrylate-based adhesive film, such as optically clear adhesive <NUM> of <NUM>, but are not particularly limited thereto.

Hereinafter, this disclosure is described in detail with reference to examples. The following examples and comparative examples are not restrictive but are illustrative.

<NUM> mol (<NUM>) of <NUM>,<NUM>'-bis(trifluoromethyl)benzidine (TFDB) and <NUM> mol (<NUM>) of pyridine are dissolved in <NUM> of N,N-dimethyl acetamide (DMAc) as a solvent in a round-bottomed flask, and <NUM> of DMAc was further added to the flask to dissolve the remaining TFDB. <NUM> mol (<NUM>) of TPCI is divided into <NUM> portions and individually added in ten times to be mixed with the TFDB solution at room temperature, and then the mixture is vigorously stirred and reacted for <NUM> hours.

The resultant solution is stirred under a nitrogen atmosphere for <NUM> hours, and then added to <NUM> of water containing <NUM> of NaCl. Then, the mixture is stirred for <NUM> minutes. Subsequently, a solid produced therein is collected by filtration, re-suspended twice, and then re-filtered with <NUM> of deionized water. Then, water remaining in the solid is removed as much as possible by appropriately pressing the solid in a filter, and then the solid obtained is dried at <NUM> under vacuum, obtaining a compound (an amide group-containing oligomer and TFDB) represented by Chemical Formula <NUM> as a product.

In Chemical Formula <NUM>, n<NUM> is an integer of <NUM> or more.

<NUM> of N,N-dimethyl acetamide (DMAc) is put in a reactor under a nitrogen atmosphere, and <NUM> mol (<NUM>) of the amide group-containing oligomer represented by Chemical Formula <NUM> according to Synthesis Example is added thereto and completely dissolved therein at <NUM>. Then, <NUM> mol (<NUM>) of <NUM>,<NUM>',<NUM>,<NUM>'-biphenyltetracarboxylic dianhydride (BPDA) and <NUM> mol (<NUM>) of <NUM>,<NUM>' hexafluoroisopropylidene diphthalicanhydride (6FDA) are added to the solution and dissolved therein. Subsequently, N,N-dimethyl acetamide (DMAc) is additionally added to the solution, such that the total solid content becomes <NUM> wt%, to manufacture a poly(amic acid-amide) copolymer.

When the reaction is complete, <NUM> mole of acetic anhydride is added thereto, and the mixture is stirred for <NUM> minutes. Then, the same moles of pyridine are added thereto, and the obtained mixture is further stirred at <NUM> for <NUM> hours for a chemical imidization. After the chemical imidization, the resultant is purified into powder through precipitation. The powder is vacuum-dried at <NUM> for <NUM> hours and redissolved in N,N-dimethyl acetamide, preparing a poly(imide-amide) copolymer solution.

The poly(imide-amide) copolymer solution is used to from a film on a glass plate by using a doctor blade. The film is pre-baked on an <NUM> hot plate for <NUM> hour, heated up to <NUM> at <NUM>/min in a furnace, dried, and thermally imidized.

A poly(imide-amide) copolymer including <NUM> mol% of bis-APAF and a film formed thereof are manufactured by using <NUM> mol% of the compound represented by Chemical Formula <NUM> according to Synthesis Example and <NUM> mol% of the bis-APAF ((<NUM>,<NUM>'-bis(<NUM>-amino-<NUM>-hydroxyphenyl)-hexafluoropropane) as a diamine moiety based on the total moles of the diamines.

Specifically, <NUM> of N,N-dimethyl acetamide (DMAc) is put in a reactor under a nitrogen atmosphere, and <NUM> mol (<NUM>) of the amide group-containing oligomer represented by Chemical Formula <NUM> prepared in Synthesis Example is added thereto and dissolved therein at <NUM>. Subsequently, <NUM> mol (<NUM>) of bis-APAF is added to the solution and completely dissolved therein. Then, <NUM> mol (<NUM>) of <NUM>,<NUM>',<NUM>,<NUM>'-biphenyltetracarboxylic dianhydride (BPDA) and <NUM> mol (<NUM>) of <NUM>,<NUM>' hexafluoroisopropylidene diphthalicanhydride (6FDA) are added thereto and dissolved therein. Subsequently, N,N-dimethyl acetamide (DMAc) is added thereto, such that the total solid content becomes <NUM> wt%, and reacted therewith, preparing a poly(amic acid-amide) copolymer.

When the reaction is complete, <NUM> mol of acetic anhydride is added thereto, the mixture is stirred for <NUM> minutes, the same moles of pyridine are added thereto, and the obtained mixture is further stirred at <NUM> for <NUM> hours for a chemical imidization. After the chemical imidization, the resulting solution is purified into powder through a precipitation process. The powder is vacuum-dried at <NUM> for <NUM> hours and redissolved in N,N-dimethyl acetamide, preparing a poly(imide-amide) copolymer solution.

The prepared poly(imide-amide) copolymer solution is used to form a film on a glass plate by using a doctor blade. The film is pre-baked on an <NUM> hot plate for one hour, heated up to <NUM> at <NUM>/min in a furnace, and then, dried and thermally imidized.

Each poly(imide-amide) copolymer film according to Examples <NUM> to <NUM> is manufactured by using the same material and method as Example <NUM>, except for using the compound represented by Chemical Formula <NUM> prepared in Synthesis Example and bis-APAF as a diamine moiety, and herein, the bis-APAF respectively in an amount of <NUM> mol%, <NUM> mol%, <NUM> mol%, and <NUM> mol%, based on the total amount of the amide group-containing oligomer and the bis-APAF.

Adherence of the films according to Comparative Example <NUM> and Examples <NUM> to <NUM> is tested. The adherence test is performed as follows.

First of all, the film according to each Example is cut into two pieces having a size of <NUM> X <NUM>, and a PSA adhesive, 3M8126, made by <NUM>, is applied to be <NUM> thick over the length of <NUM> out of the entire length of <NUM> except for the end of <NUM> on one of the films. Then, the other film is overlapped on the film applied with the adhesive and bonded, while the end of <NUM> is left. The bonded film is maintained at room temperature for <NUM> hours and completely dried, and Instron3365 made by Instron in a <NUM>° peel test mode is used.

Specifically, the front parts of the films not applied with the adhesive <NUM> in two sheets of the films <NUM> bonded by the adhesive are vertically separated at the front end of the tester and elongated in two opposite directions (refer to <FIG>). In other words, the front part of the bottom film in which the adhesive is not applied is vertically down fixed, and the front part of the top film in which the adhesive is not applied is vertically pulled up to perform an adherence test. The adherence test measures adherence between the films and the adhesive in a method of measuring strength consumed per a tensile length. The films according to the Examples and Comparative Example are respectively tested four times in total, and their average values are shown depending on a film peeling length (a tensile length) in Table <NUM>.

Referring to the result of Table <NUM>, the films including <NUM> mol% to <NUM> mol% of the bis-APAF according to Examples <NUM> to <NUM> require much more strength compared with the film including no bis-APAF according to Comparative Example <NUM>, when the film is peeled off up to <NUM>, <NUM>, and <NUM> long. In other words, the film including the bis-APAF shows increased adherence compared with the film including no bis-APAF.

In addition, the film according to Comparative Example <NUM> shows sharply deteriorated adherence when peeled off up to <NUM> and <NUM> long compared with when peeled off up to <NUM> long. The reason is that adherence on the interface between the adhesive <NUM> and the film <NUM> is weak and destroyed even by pulling and peeling the end of the film when the pulling and peeling continues for a predetermined time. <FIG> is a view schematically showing the adhesive and the film.

On the contrary, as shown in Table <NUM>, the films according to Examples <NUM> to <NUM> maintain uniform adherence to a degree when respectively peeled off <NUM>, <NUM>, and <NUM> long, and in particular, the films including the bis-APAF respectively in an amount of <NUM> mol% and <NUM> mol% according to Examples <NUM> and <NUM> maintain almost equivalent adherence even when their tensile lengths are increased. The reason is that two sheets of films maintain a uniform bond when bonded through an adhesive, and accordingly, the adherence between the film <NUM> and the adhesive <NUM> is not destroyed on the interface of the film with the adhesive, but the film is delaminated by internal fracture of the adhesive during the peeling. <FIG> is a view schematically showing the adhesive and the film.

<FIG> is a graph showing adherence changes of four pairs of the films according to Comparative Example <NUM> depending on a peeling length.

Referring to <FIG>, when a film including no bis-APAF is greater than or equal to <NUM> peeled off, adherence is sharply deteriorated. In other words, when greater than or equal to <NUM> peeled off, the film may be easily delaminated on the interface with the adhesive.

<FIG> is a graph showing adherence changes of four pairs of the films including <NUM> mol% of the bis-APAF according to Example <NUM> depending on a peeling length.

When the bis-APAF is included in an amount of <NUM> mol%, adherence of Example <NUM> is a little decreased compared with Example <NUM> or <NUM> but uniformly maintained to a degree when the film is peeled off up to at least <NUM> long and has a higher absolute value than that of Comparative Example <NUM>.

When the bis-APAF is included in an amount of <NUM> mol%, the highest adherence and the most uniform adherence are shown. Evan when the film is extensively peeled off up to <NUM> long, the film maintains almost the same adherence, and all four pairs of the films have almost the same absolute value of adherence one another. In other words, when the bis-APAF is included in an amount of <NUM> mol% based on the total amount of the diamine, the most excellent adherence is shown.

When the bis-APAF is included in an amount of <NUM> mol%, the film of Example <NUM> shows a little decreased adherence compared with the film of Example <NUM> but maintains remarkably high adherence compared with that of Example <NUM> or Comparative Example, and when the film is peeled off up to about <NUM>, adherence is uniformly maintained. In addition, four pairs of the films show uniformly high adherence to a degree.

The optical properties and mechanical characteristics of the films including <NUM> mol% to <NUM> mol% of the bis-APAF as a diamine component according to Examples <NUM> to <NUM> and the film without bis-APAF according to Comparative Example <NUM> are evaluated, and the results are shown in Table <NUM>.

In Table <NUM>, each measurement value is measured as follows:.

The thickness is measured using a micrometer (manufactured by Mitutoyo).

With an Instron <NUM> device, a film sample having a width of <NUM> and a length of <NUM> is drawn at a speed of <NUM>/min at room temperature, and each sample is measured <NUM> times according to an ASTM D882 method and averaged.

The yellowness index is measured by using UV Spectrophotometer (KONICA MINOLTA, cm-3600d) according to ASTM E313.

The haze is measured according to ASTM E313.

Pencil scratch hardness is measured using a pencil hardness measurer and a Mitsubishi pencil according to the ASTM D3363 standard. Specifically, a film is held on a glass plate having a thickness of <NUM> and measured <NUM> times in each <NUM> with a vertical load of <NUM> at a pencil speed of <NUM>/min, and then the highest hardness when it is not scratched is determined.

As shown in Table <NUM>, the films including <NUM> mol% to <NUM> mol% of the bis-APAF according to Examples <NUM> to <NUM> have high mechanical strength (modulus of <NUM> or greater) and high optical properties (YI of less than or equal to <NUM>). The results show that the optical properties and mechanical strength of films including a small amount of bis-APAF is not largely deteriorated compared with the film without bis-APAF according to Comparative Example <NUM>.

That is, the poly(imide-amide) copolymer including <NUM> mol% or less of bis-APAF may improve adherence with adhesives, without decrease of optical properties and mechanical characteristics, and thus may be advantageously used for manufacture a flexible device and the like.

Hygroscopicity change of the film including <NUM> mol% of bis-APAF is examined comparing the film without bis-APAF.

Claim 1:
A composition for preparing a poly(imide-amide) copolymer, comprising:
a compound of Chemical Formula <NUM>,
a diamine represented by Chemical Formula <NUM>, and
the dianhydrides BPDA and 6FDA;
wherein the compound of Chemical Formula <NUM> is a reaction product of TFDB with TPCl; and
wherein an amount of the diamine represented by Chemical Formula <NUM> is <NUM> mol% to <NUM> mol% based on the total moles of TFDB and the diamine represented by Chemical Formula <NUM>:
<CHM>
wherein, in Chemical Formula <NUM>, n0 is an integer of more than <NUM>,

        (Chemical Formula <NUM>)     NH<NUM>-A-NH<NUM>

wherein, in Chemical Formula <NUM>,
A is selected from chemical formulae of Group <NUM>:
<CHM>
<CHM>
wherein, in the chemical formulae,
L is a single bond or a linking group selected from -O-, -S-, -C(=O)-, - CH(OH)-, -S(=O)<NUM>-, -Si(CH<NUM>)<NUM>-, -(CH<NUM>)p- (wherein, <NUM>≤p≤<NUM>), -(CF<NUM>)q- (wherein, <NUM>≤q≤<NUM>), -CRR'- (wherein, R and R' are the same or different, and are independently hydrogen, a C1 to C4 alkyl group, a phenyl group, a phenyl group substituted with a C1 to C4 alkyl group, a C1 to C4 alkyl group substituted with a phenyl group, or a C1 to C4 alkyl group substituted with at least one fluorine atom, provided that R and R' are not simultaneously hydrogen), -C(=O)NH- and a fluorenylene group, and * indicates a point of attachment to a nitrogen atom, and
* indicates a point of attachment to a nitrogen atom.