Polyamide-imide polymer solution and preparation method thereof

Abstract

The present invention relates to a polyamide-imide solution comprising: a polymer comprising a structural unit of formula (II) wherein: n is an integer from 2 to 400; and a solvent comprising, based on the total weight of the solvent: 0.1 to 100 wt% of i) at least one compound according to formula (IA) ROOC-A2-COOR wherein: A2 is a C3-C8 alkylene group or a C6 arylene group; and each R is independently a C1-C2 alkyl group; ii) 0 to 99.9 wt% of at least one aprotic compound which does not satisfy formula (IA) and has a boiling point of at least 150 DEG C measured at a pressure of 1 bar.

Description

Technical Field

[0001] The present disclosure relates to a polyamide-imide solution and a method for preparing the solution. More specifically, the present disclosure relates to a polyamide-imide solution comprising a dibasic ester solvent and to the use of the solution in forming a wire provided with an insulating coating comprising the polyamide-imide. Background Art

[0002] The conductive wires are provided with an insulating coating to, among other things: prevent electrical leakage; prevent the wires from coming into contact with other conductors; and maintain the material integrity of the wires by protecting them from abrasion, heat, and liquid intrusion.

[0003] Polyamide-imide polymers are widely used in wire insulation due to their processability, insulating properties, and high-temperature stability. These polymers are often used in a two-coat construction as a cover coat over a wire already coated with a cross-linked polyester. Polyamide-imide provides thermal stability and solvent resistance to the wire, properties not inherent in polyester.

[0004] Exemplary synthesis methods of polyamide-imide resins include: direct polymerization of aromatic diamines and aromatic tricarboxylic acids under dehydrogenation catalysis, as described in US Pat. No. 3,860,559 and Japanese Patent Application Laid-Open No. Sho 58-180532; an acid chloride method; and an isocyanate method.

[0005] The acyl chloride process involves the condensation of an aromatic tricarboxylic acid chloride with an aromatic diamine. The condensation reaction can be carried out typically at room temperature in a non-aqueous polar solvent by low-temperature homogeneous solution polymerization, or in an aqueous solvent that is slightly soluble in water and provided with an acid acceptor by low-temperature precipitation (or interfacial) polymerization. Since these polymerization methods require expensive acyl chlorides as raw materials and generally provide polyamide-imide resins with unfavorable molecular weight distributions, the acyl chloride process is no longer considered economically viable.

[0006] The isocyanate process, which is the subject of this disclosure, involves the decarboxylation reaction of an aromatic diisocyanate with an aromatic tricarboxylic anhydride. This reaction is carried out in a solvent medium to produce a polyamide-imide polymer solution. Because diisocyanates are water-sensitive, the decarboxylation reaction must be carried out under anhydrous conditions. Furthermore, the solvent medium must be carefully selected to avoid gelation during the decarboxylation reaction.

[0007] Amide-based solvents have been found to be useful in the isocyanate process because, in addition to being a solvent that facilitates processing, these solvents also provide effective solubility for polyamide-imide resins. Exemplary amide solvents include: N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), N,N-dimethylacetamide, and N,N-dimethylformamide. In addition, DE 10 2014 104 223 A1 discloses the use of 3-methoxy-N,N-dimethylpropionamide as a solvent. However, there are concerns about the reproductive toxicity of amide-based solvents: this has led to regulations on their use and has prompted the search for alternative solvents to at least partially replace them.

[0008] JP2008-285660A proposes using only γ-butyrolactone (GBL) as a solvent. While this solvent is non-hygroscopic and has been found to dissolve polyamide-imide resins with a narrow range of diisocyanate to anhydride molar ratios, the resulting solution is difficult to dry due to γ-butyrolactone's high boiling point (204°C) and has been found to exhibit poor leveling in certain coating applications. Perhaps related to this, JP2012-62355A describes the use of γ-butyrolactone in combination with cyclopentanone in polyamide-imide synthesis, US20060240255A1 describes the use of GBL in combination with cyclohexanone and methylcyclohexanone, and JP2011-210645A proposes the use of γ-butyrolactone in combination with the dipolar aprotic solvent 1,3-dimethylimidazolidinone. However, the cyclohexanone cosolvent has an unpleasant odor. Furthermore, when the ratio of cosolvent to gamma-butyrolactone is not maintained within a tightly controlled range, precipitation of the polyamide-imide has been observed. Furthermore, when adjuvant materials such as nanoparticles are included, the stability of such mixed solutions can be difficult to maintain: particle aggregation and inhibitory viscosity increases in the solution have been observed, and stabilizing diluents such as the aforementioned (and problematic) amide solvents must be used.

[0009] It is believed that there is a need in the art to provide alternative solvents that can at least partially replace the use of gamma-butyrolactone and amide solvents as the solvent phase of the isocyanate process for the synthesis of polyamide-imides or as diluents for stabilizing the polyamide-imide polymer solutions obtained in such synthesis. Summary of the Invention

[0010] According to a first aspect of the present disclosure, there is provided a polyamide-imide solution comprising:

[0011] Polymers comprising structural units of formula (II)

[0012]

[0013] wherein: n is an integer from 2 to 400; and,

[0014] The solvent, based on the total weight of the solvent, comprises:

[0015] 0.1 to 100% by weight of i) at least one compound according to formula (IA)

[0016] ROOC-A 2 -COOR(IA)

[0017] Among them: A 2 is a C3-C8 alkylene group or a C6 arylene group; and

[0018] Each R is independently C1-C2 alkyl; and,

[0019] 0 to 99.9% by weight of ii) at least one aprotic compound which does not satisfy formula (IA) and has a boiling point of at least 150° C., measured at a pressure of 1 bar.

[0020] The present disclosure also provides a method for producing a polyamide-imide solution, the method comprising:

[0021] a) producing a first polyamide-imide polymer solution by reacting a1) and a2) at a temperature of 60 to 180° C. and in the presence of a first solvent (S1) and a catalyst:

[0022] a1) a diisocyanate component comprising at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); isophorone diisocyanate (IPDI); dicyclohexylmethane diisocyanate (H-MDI); xylene diisocyanate (XDI); hydrogenated xylene diisocyanate; toluene diisocyanate (TDI); diphenyl sulfone diisocyanate (SDI); meta-xylene;

[0023] Diisocyanates; and mixtures thereof;

[0024] a2) an anhydride component comprising trimellitic anhydride (TMA);

[0025] wherein the first solvent (S1) comprises at least one aprotic compound having a boiling point of at least 150° C. measured at a pressure of 1 bar, and

[0026] b) diluting the first polymer solution with a second solvent (S2) to produce a second polyamide-imide polymer solution, wherein the second solvent is different from the first solvent;

[0027] wherein at least one of the first solvent (S1) and the second solvent (S2) comprises:

[0028] At least one compound according to formula (I)

[0029] ROOC-A 1 -COOR(I)

[0030] Among them: A 1 is a C1-C8 alkylene group or a C6 arylene group; and each R is independently a C1-C2 alkyl group;

[0031] The condition is that when A 1 When it is a C2 alkylene group, each R is a C2 alkyl group.

[0032] The present disclosure also provides a method for producing a polyamide-imide solution, the method comprising:

[0033] a) producing a first polyamide-imide polymer solution by reacting a1) and a2) at a temperature of 60 to 180° C. and in the presence of a first solvent (S1) and a catalyst:

[0034] a1) a diisocyanate component comprising at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); isophorone diisocyanate (IPDI); dicyclohexylmethane diisocyanate (H-MDI); xylene diisocyanate (XDI); hydrogenated xylene diisocyanate; toluene diisocyanate (TDI); diphenyl sulfone diisocyanate (SDI); meta-xylene diisocyanate; and mixtures thereof; and

[0035] a2) an anhydride component comprising trimellitic anhydride (TMA)

[0036] wherein the first solvent (S1) comprises at least one aprotic compound having a boiling point of at least 150° C. measured at a pressure of 1 bar; and

[0037] b) diluting the first polymer solution with a second solvent (S2) to produce a second polyamide-imide polymer solution, wherein the second solvent is different from the first solvent; and,

[0038] wherein at least one of the first solvent (S1) and the second solvent (S2) comprises:

[0039] At least one compound according to formula (IA)

[0040] ROOC-A 2 -COOR(IA)

[0041] Among them: A 2 is a C3-C8 alkylene group or a C6 arylene group; and each R is independently a C1-C2 alkyl group.

[0042] In an embodiment according to the latter method, the first solvent (S1) comprises:

[0043] i) at least one compound according to formula (IA)

[0044] ROOC-A 2 -COOR(IA)

[0045] Among them: A 2 is a C3-C8 alkylene group or a C6 arylene group; and each R is independently a C1-C2 alkyl group; and / or,

[0046] ii) at least one aprotic compound which does not satisfy formula (IA) and has a boiling point of at least 150° C., measured at a pressure of 1 bar.

[0047] For example, the first solvent (S1) may comprise, based on the total weight of the first solvent (S1), 0.1 to 100 wt% of i) the at least one compound according to formula (IA); and 0 to 99.9 wt% of ii) at least one aprotic compound that does not satisfy formula (IA) and has a boiling point of at least 150° C. measured at a pressure of 1 bar.

[0048] In another exemplary embodiment, based on the total weight of the first solvent (S1), the first solvent (S1) comprises:

[0049] 0.5 to 70 wt. % or 10 to 70 wt. % of i) the at least one compound according to formula (IA); and,

[0050] 30 to 99.5% by weight or 30 to 90% by weight of ii) at least one aprotic compound which does not satisfy formula (IA) and has a boiling point of at least 150° C. measured at a pressure of 1 bar.

[0051] In exemplary compounds according to formula (IA): A 2 is a C3-C6 alkylene or C6 arylene group; and each R is independently a C1-C2 alkyl group. In other exemplary compounds according to formula (IA): A 2 -(CH2) m - or C6 arylene; m is an integer from 3 to 6; and each R is independently a C1-C2 alkyl.

[0052] In certain embodiments, each substituent R is the same. In other embodiments, each R is methyl. For example, the at least one compound according to formula (IA) can generally be selected from: dimethyl phthalate; diethyl phthalate; dimethyl glutarate; diethyl glutarate; dimethyl adipate; diethyl adipate; and mixtures thereof. In some cases, it may be advantageous to use dimethyl phthalate, dimethyl glutarate, dimethyl adipate, or mixtures thereof. For example, it may be mentioned that dimethyl phthalate is used alone or in combination with one or more other compounds according to formula (IA).

[0053] In an embodiment, part ii) of the first solvent (S1) comprises at least one nitrogen-containing polar aprotic compound having a boiling point of at least 150° C., measured at a pressure of 1 bar. For example, part ii) of the first solvent may comprise at least one compound selected from the group consisting of: γ-butyrolactone; cyclohexanone; methylcyclohexanone; N-methyl-2-pyrrolidone (NMP); N-ethyl-2-pyrrolidone (NEP); N-butyl-2-pyrrolidone (NBP); N,N-dimethylacetamide; N-formylmorpholine; N-acetylmorpholine; 3-methoxy-N,N′-dimethylpropionamide (MDP); and mixtures thereof. For example, it may be mentioned that γ-butyrolactone is used in the first solvent (S1) or as part ii) of the first solvent (S1).

[0054] In an embodiment of the above method, the diisocyanate component includes at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); toluene diisocyanate (TDI); and mixtures thereof.

[0055] In some cases, monomeric methylene diphenyl diisocyanate (MDI) can be used as the reactant diisocyanate or one of the reactant diisocyanates in reaction step a). In a first exemplary embodiment, the diisocyanate component comprises: 10 to 90 mol% of monomeric methylene diphenyl diisocyanate (MDI); and 90 to 10 mol% of at least one diisocyanate selected from the group consisting of polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); isophorone diisocyanate (IPDI); dicyclohexylmethane diisocyanate (H-MDI); xylene diisocyanate (XDI); hydrogenated xylene diisocyanate; toluene diisocyanate (TDI); diphenyl sulfone diisocyanate (SDI); meta-xylene diisocyanate; and mixtures thereof, based on the total moles of diisocyanates.

[0056] In another exemplary embodiment, the diisocyanate component comprises, based on the total moles of diisocyanates: 30 to 70 mole percent of monomeric methylene diphenyl diisocyanate (MDI); and 70 to 30 mole percent of at least one diisocyanate selected from the group consisting of polymeric methylene diphenyl diisocyanate (pMDI); toluene diisocyanate (TDI); and mixtures thereof.

[0057] In yet another exemplary embodiment, the diisocyanate component comprises: 55 to 65 mole % of monomeric methylene diphenyl diisocyanate (MDI); and 45 to 35 mole % of toluene diisocyanate (TDI), based on the total moles of diisocyanates.

[0058] It is also typical to use toluene diisocyanate (TDI) as the reactant diisocyanate or one of the reactant diisocyanates in reaction step a). In an exemplary embodiment thereof, the diisocyanate component comprises: 10 to 100 mol% of toluene diisocyanate (TDI); and 0 to 90 mol% of at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); and mixtures thereof, based on the total moles of diisocyanates.

[0059] It is also typical to use hexamethylene diisocyanate (HDI) as the reactant diisocyanate or one of the reactant diisocyanates in reaction step a). In an exemplary embodiment thereof, the diisocyanate component comprises: 10 to 100 mol% of hexamethylene diisocyanate (HDI); and 0 to 90 mol% of at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); toluene diisocyanate (TDI); and mixtures thereof, based on the total moles of diisocyanates.

[0060] In the aforementioned reaction step a), in certain embodiments, based on the total moles of the anhydride, the anhydride component may be: 80 to 100 mol % of trimellitic anhydride (TMA); and 0 to 20 mol % of at least one tetracarboxylic dianhydride.

[0061] For example, the anhydride component may comprise, based on the total moles of anhydride, 80 to 100 mol % of trimellitic anhydride (TMA); and 0 to 20 mol % of at least one anhydride selected from the group consisting of 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA); 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA); 4,4'-oxydiphthalic dianhydride (ODPA); butanetetracarboxylic dianhydride; 5-(2,5-dioxotetrahydro-3-furyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride; and mixtures thereof.

[0062] In certain embodiments, the second solvent (S2) comprises at least one compound according to formula (IA):

[0063] ROOC-A 2 -COOR(IA)

[0064] Among them: A 2 is a C3-C8 alkylene group or a C6 arylene group; and

[0065] Each R is independently a C1-C2 alkyl group.

[0066] In other embodiments, the second solvent (S2) comprises at least one non-polar compound having a boiling point of less than 225° C. The compound meeting this boiling point condition can generally be selected from: C1-C8 linear alkanes; cyclic alkanes; C1-C8 branched alkanes; C1-C8 alkyl halides; aromatic compounds; and mixtures thereof. In addition, exemplary compounds that meet this boiling point condition and can be used alone or in combination include: n-pentane; n-hexane; cyclohexane; n-heptane; isooctane; trimethylpentane; toluene; xylene; benzene; and naphthalene (naphthenics). In one embodiment, the second solvent (S2) comprises xylene.

[0067] The present disclosure also provides a polyamide-imide solution obtained according to the method defined above and in the appended claims.In certain embodiments, the solids content of the polyamide-imide solution may be 20 to 50 wt %, as determined according to DIN 53216.

[0068] Another aspect of the present disclosure provides a method of forming an insulated wire comprising: providing a conductor; coating the conductor with a polymer solution as defined above and in the appended claims; and heat treating the coated conductor to remove solvent therefrom.

[0069] According to another aspect of the present disclosure, there is provided a method for producing a polyamide-imide solution, the method comprising:

[0070] a) producing a polyamide-imide polymer solution by reacting a1) and a2) at a temperature of 60 to 180° C. in the presence of a solvent (S) and a catalyst:

[0071] a1) a diisocyanate component comprising at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); isophorone diisocyanate (IPDI); dicyclohexylmethane diisocyanate (H-MDI); xylene diisocyanate (XDI); hydrogenated xylene diisocyanate; toluene diisocyanate (TDI); diphenyl sulfone diisocyanate (SDI); meta-xylene;

[0072] Diisocyanates; and mixtures thereof;

[0073] a2) an anhydride component comprising trimellitic anhydride (TMA)

[0074] Wherein, based on the weight of the solvent (S), the solvent comprises:

[0075] 0.1 to 100% by weight of i) at least one compound according to formula (I)

[0076] ROOC-A 1 -COOR(I)

[0077] Among them: A 1 is a C1-C8 alkylene group or a C6 arylene group; and

[0078] Each R is independently C1-C2 alkyl; and,

[0079] 0 to 99.9% by weight of ii) at least one aprotic compound which does not satisfy formula (I) and has a boiling point of at least 150° C., measured at a pressure of 1 bar.

[0080] When aspects of the present disclosure are described herein as having certain embodiments, unless otherwise stated, any one or more of these embodiments may be implemented in or combined with any of the further embodiments, even if the combination is not explicitly described. In other words, unless otherwise stated, the described embodiments are not mutually exclusive and their permutations remain within the scope of the present disclosure. DETAILED DESCRIPTION

[0081] The following detailed description is merely illustrative and is not intended to limit the present disclosure or its application and uses. In addition, there is no intention to be bound by any theory presented in the foregoing background or the following detailed description.

[0082] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0083] As used herein, the terms "comprising," "comprises," and "comprised of" are synonymous with "including," "includes," "containing," or "contains," and are inclusive or open-ended, not excluding additional, unrecited members, elements, or method steps. If used, the phrase "consisting of is closed, excluding all additional elements. The term "consisting essentially of can describe various non-limiting embodiments that do not include one or more optional compounds described herein.

[0084] When amounts, concentrations, sizes, and other parameters are expressed in terms of one or more ranges, one or more upper limits, or one or more lower limits, it is to be understood that any range obtained by combining any upper limit with any lower limit is also specifically disclosed, regardless of whether the resulting range is explicitly mentioned in the context.

[0085] As used herein, the term "about" or "approximately" applies to all numerical values, whether or not explicitly stated, except in actual examples. In various embodiments, the term "about" can describe a value of ±0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10%.

[0086] Furthermore, according to standard understanding, weight ranges expressed as "0 to x" specifically include 0 wt %: the component defined by the range may be absent from the material, or may be present in the material in an amount up to x wt %.

[0087] The words "exemplary" and "illustrative" are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "exemplary" or "illustrative" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, the use of the words "exemplary" and "illustrative" is intended to present concepts in a concrete manner.

[0088] As used throughout this application, the words "may" and "may" are used in a permissive sense, that is, meaning having the potential, rather than the mandatory sense.

[0089] All percentages, ratios and proportions used herein are given on a weight basis unless otherwise specified.

[0090] As used herein, room temperature is 23°C ± 2°C.

[0091] Molecular weights referred to in this specification can be determined by gel permeation chromatography (GPC), such as according to ASTM 3536, using polystyrene calibration standards.

[0092] As used herein, "drying" of a coating composition refers to the evaporation (drying) of any solvent present in the composition; evaporation of the solvent may be accompanied by coalescence of the particulate, dispersed, or solvated phase of the composition. Such drying may be carried out under ambient conditions or by intentional exposure to heat and / or radiation. The degree of drying may be partial or complete.

[0093] Unless otherwise indicated, the term "particle size" refers to the largest axis of the particle. For approximately spherical particles, the largest axis is the diameter.

[0094] As used herein, "D50 particle size" refers to a particle size distribution such that at least 50% by volume of the particles have a particle diameter less than the specified value. Unless otherwise stated, particle size is determined by dynamic light scattering (DLS) in conjunction with a particle size analyzer.

[0095] As used herein, the term "solids content" refers to the weight percent of non-volatile components in a composition. Solids content can be determined as the inverse value of the volatile content obtained according to ASTM D2369 Standard Test Method for Volatile Content of Coatings.

[0096] As used herein, a "solvent" is a substance that is capable of dissolving another substance to form a homogeneous solution; during dissolution, neither the solvent nor the dissolved substance undergoes chemical changes.

[0097] As used herein, the term "aprotic solvent" refers to a solvent that does not generate or accept protons. In contrast, a "protic solvent" refers to a solvent that can generate or accept protons.

[0098] The solvent may be polar or non-polar. The term "polar solvent" as used herein refers to a solvent having a dielectric constant (ε) greater than 5, measured at 25°C: this term encompasses both aprotic and protic solvents. The determination of the dielectric constant (ε) is well known in the art and is within the knowledge of those skilled in the art: it may be mentioned that the voltage measured across a parallel plate capacitor is used in such determinations.

[0099] The term "Mannich Base" as used herein is defined according to standard practice in the art as a ketoamine derived from the condensation of a ketone with formaldehyde and ammonia or a primary or secondary amine.

[0100] As used herein, "diisocyanate" refers to a compound containing two -N=C=O functional groups. The term "aromatic diisocyanate" is used herein to describe an organic isocyanate in which the isocyanate groups are directly attached to the ring(s) of a mononuclear or polynuclear aromatic hydrocarbon group.

[0101] As used herein, "metal" refers to any type of metal, metal alloy, or mixture thereof. As used herein, the term "alloy" refers to a substance composed of two or more metals or a metal and a non-metal, the components being intimately bound together, usually by being fused together, and mutually soluble in each other when melted.

[0102] The “C1-C n "Alkyl" refers to a monovalent group containing 1 to n carbon atoms, which is the residue of an alkane and includes straight-chain and branched organic groups. Thus, "C1-C4 alkyl" refers to a monovalent group containing 1 to 4 carbon atoms, which is the residue of an alkane and includes straight-chain and branched organic groups. Examples of alkyl groups include, but are not limited to: methyl; ethyl; propyl; isopropyl; n-butyl; isobutyl; sec-butyl; and tert-butyl. In the present disclosure, such alkyl groups may be unsubstituted or substituted with one or more halogens. Where applicable to a given moiety (R), the specification will indicate the tolerance for one or more non-halogen substituents within the alkyl group.

[0103] The “C1-C n "Alkylene" refers to C1-C n The divalent residue counterpart of an alkyl group.

[0104] The “C6-C 18 "Aryl" (used alone or as part of a larger moiety as in "aralkyl") refers to monocyclic, bicyclic, and tricyclic ring systems, wherein the monocyclic ring system is aromatic or at least one ring of the bicyclic or tricyclic ring system is aromatic. Bicyclic and tricyclic ring systems include benzofused 2-3 membered carbocyclic rings. In the present disclosure, such aryl groups may be unsubstituted or substituted with one or more halogens. Where applicable to a given moiety (R), the specification will note the tolerance for one or more non-halogen substituents within the aryl group. Exemplary aryl groups include: phenyl; (C1-C4)alkylphenyls such as tolyl and ethylphenyl; indenyl; naphthyl, tetrahydronaphthyl, tetrahydroindenyl; tetrahydroanthracenyl; and anthracenyl.

[0105] As used herein, "alkylaryl" refers to an aryl group substituted with an alkyl group, and "substituted alkylaryl" refers to an alkylaryl group further bearing one or more substituents as listed above. In addition, "aralkyl" as used herein refers to an alkyl group substituted with an aryl group as defined above.

[0106] The term "C n "Arylene" refers to C n The divalent residue counterpart of an aryl group.

[0107] As used herein, mononuclear or polynuclear aromatic hydrocarbon groups refer to substantially planar cyclic hydrocarbon moieties of conjugated double bonds, which may be monocyclic or may include multiple condensed (fused) or covalently linked rings. The term "aromatic" also includes alkylaryl groups. Typically, the hydrocarbon (main) chain includes 5, 6, 7 or 8 main chain atoms in one ring. Examples of such planar cyclic hydrocarbon moieties include, but are not limited to, cyclopentadienyl, phenyl, naphthyl-,

[10] annulenyl-(1,3,5,7,9-cyclodecene pentaenyl-),

[12] annulenyl-, [8] annulenyl-, phenalene (perinaphthene), 1,9-dihydropyrene and (1,2-Triphenylene). Examples of alkylaryl moieties are benzyl, phenethyl, 1-phenylpropyl, 2-phenylpropyl, 3-phenylpropyl, 1-naphthylpropyl, 2-naphthylpropyl, 3-naphthylpropyl and 3-naphthylbutyl.

[0108] The term "substituted" refers to substitution with at least one suitable substituent. For completeness: a substituent may be attached to a specified group or moiety at one or more positions; and, unless otherwise indicated, multiple degrees of substitution are permitted. Furthermore, the term "substituted" or "substituted with" includes the implicit proviso that such substitution complies with the permitted valencies of the substituted atom and the substituent, and that the substitution results in a stable compound that is not spontaneously transformed by, for example, rearrangement, cyclization, or elimination.

[0109] The term "substantially free" is intended to mean that the ingredient, component, compound, moiety, functional group, element, ion, etc. is not intentionally added to the host material and is present only in trace amounts that do not (adversely) affect the desired properties of the material. For a composition, an exemplary trace amount is less than 1000 ppm by weight of the composition. The term "substantially free" encompasses embodiments in which the specified compound, moiety, functional group, element, ion, or other similar component is completely absent from the host material or is not present in any amount measurable using techniques commonly used in the art.

[0110] As used herein, the term "anhydrous" is synonymous with the term "substantially free of water." Water is not intentionally added to a given composition and is present only in trace amounts at most that do not (adversely) affect the desired properties of the composition.

[0111] The method of the present disclosure requires producing a polyamide-imide polymer solution by reacting a1) and a2) at a temperature of 60 to 180° C. in the presence of a solvent and a catalyst:

[0112] a1) diisocyanate component;

[0113] a2) an anhydride component comprising trimellitic anhydride (TMA);

[0114] The solvent comprises at least one aprotic compound having a boiling point of at least 150° C., measured at a pressure of 1 bar.

[0115] The reaction can be exemplified by a molar ratio of isocyanate groups to anhydride groups of 2:3 to 6:1. For example, the molar ratio of isocyanate groups to anhydride groups can be 2:1 to 4:1 or 2:1 to 3:1. For the sake of completeness, the term "molar ratio" includes any contribution from the presence of monofunctional reactive compounds (such as the monoisocyanates mentioned below).

[0116] Depending on the nature of the reactant diisocyanate, the amount of catalyst used in the reaction is generally in the range of 0.005 to 10 wt % based on the total weight of the reactants. Exemplary catalysts that can be used alone or in combination include: i) tertiary amines and tertiary amine salts; ii) quaternary ammonium salts such as benzyltrimethylammonium chloride; iii) amidines such as triazabicyclodecene (TBD), triazabicyclodecene (TBD), diazabicyclononane (DBN) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU); iv) guanidines such as 1,1,3,3-tetramethylguanidine (TMG) and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene; and v) Mannich bases.

[0117] In certain embodiments, the catalyst comprises a tertiary amine or a salt thereof. Exemplary tertiary amines include, but are not limited to, triethylenediamine (TED, 1,4-diazabicyclo[2.2.2]octane); triethylamine; tributylamine; N,N,N',N'-tetramethyl-1,3-butanediamine; N,N-dimethylcyclohexylamine; N,N-dimethylbenzylamine; α-methylbenzyldimethylamine; N,N-diethylbenzylamine; triethanolamine, dimethylaminopropylamine; morpholine, such as N-methylmorpholine, N-ethylmorpholine, and N-cocoylmorpholine; imidazoline; and imidazoles, such as N-methylimidazole, N-vinylimidazole, and 1,2-dimethylimidazole.

[0118] The diisocyanate component of the reactants includes at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (H-MDI), xylene diisocyanate (XDI), hydrogenated xylene diisocyanate, toluene diisocyanate (TDI), diphenyl sulfone diisocyanate (SDI), meta-toluene diisocyanate, and mixtures thereof. In certain embodiments, the diisocyanate component includes at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), and mixtures thereof.

[0119] In some cases, the reaction can be exemplified by the presence of monomeric methylene diphenyl diisocyanate (MDI) as the one or more reactant diisocyanates. For example, the diisocyanate component can comprise, based on the total moles of diisocyanates, 10 to 90 mole percent of monomeric methylene diphenyl diisocyanate (MDI); and 90 to 10 mole percent of at least one diisocyanate selected from the group consisting of polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); isophorone diisocyanate (IPDI); dicyclohexylmethane diisocyanate (H-MDI); xylene diisocyanate (XDI); hydrogenated xylene diisocyanate; toluene diisocyanate (TDI); diphenyl sulfone diisocyanate (SDI); meta-xylene diisocyanate; and mixtures thereof. In another embodiment, the diisocyanate component may comprise, based on the total moles of diisocyanates, 30 to 70 mole % of monomeric methylene diphenyl diisocyanate (MDI); and 70 to 30 mole % of at least one diisocyanate selected from the group consisting of polymeric methylene diphenyl diisocyanate (pMDI) and toluene diisocyanate (TDI). In another embodiment, the diisocyanate component may comprise, based on the total moles of diisocyanates, 35 to 65 mole % of monomeric methylene diphenyl diisocyanate (MDI); and 65 to 35 mole % of toluene diisocyanate (TDI).

[0120] In other cases, the reaction may be exemplified by the presence of toluene diisocyanate (TDI) as the one or more diisocyanate reactants. For example, the diisocyanate component may comprise, based on the total moles of diisocyanates, 10 to 100 mol% of toluene diisocyanate (TDI); and 0 to 90 mol% of at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); and mixtures thereof.

[0121] In other cases, the reaction may be carried out using hexamethylene diisocyanate (HDI) as one or more diisocyanate reactants. For example, the diisocyanate component may comprise, based on the total moles of diisocyanates, 10 to 100 mol% of hexamethylene diisocyanate (HDI); and 0 to 90 mol% of at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); toluene diisocyanate (TDI); and mixtures thereof.

[0122] In addition to the above-mentioned diisocyanates, the diisocyanate component is not strictly excluded from further comprising other diisocyanates, and these supplementary diisocyanates may be aliphatic, cycloaliphatic or aromatic. Such other diisocyanates may generally be 0 to 20 mol %, such as 0 to 10 mol %, of the total moles of diisocyanates. Exemplary aliphatic isocyanates include, but are not limited to: ethylene diisocyanate; trimethylene diisocyanate; tetramethylene diisocyanate; octamethylene diisocyanate; nonamethylene diisocyanate; decamethylene diisocyanate; 1,6,11-undecane triisocyanate; bis(isocyanatoethyl)carbonate; and bis(isocyanatoethyl) ether. Exemplary alicyclic polyisocyanates include, but are not limited to, dicyclohexylmethane 4,4'-diisocyanate (H12MDI); 1-isocyanatomethyl-3-isocyanato-1,5,5-trimethyl-cyclohexane (isophorone diisocyanate, IPDI); cyclohexane 1,4-diisocyanate; hydrogenated xylene diisocyanate (H6XDI); 1-methyl-2,4-diisocyanatocyclohexane; meta- or para-tetramethylxylene diisocyanate (m-TMXDI, p-TMXDI); and dimerized fatty acid diisocyanates. Exemplary aromatic diisocyanates include, but are not limited to: naphthalene 1,5-diisocyanate; xylene diisocyanate (XDI); diphenyldimethylmethane 4,4'-diisocyanate; di- and tetra-alkyldiphenylmethane diisocyanates; dibenzyl 4,4'-diisocyanate; phenylene-1,3-diisocyanate; and phenylene-1,4-diisocyanate.

[0123] The anhydride reactive component includes trimellitic anhydride (TMA). However, the presence of other anhydride functional compounds is not excluded. Therefore, in certain embodiments, based on the total moles of anhydride, the anhydride component includes: 80 to 100 mol% of trimellitic anhydride (TMA); and 0 to 20 mol% of at least one tetracarboxylic dianhydride. For example, based on the total moles of anhydride, the anhydride component may include: 80 to 100 mol% of trimellitic anhydride (TMA); and 0 to 20 mol% of at least one anhydride selected from the following: 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride (DSDA); 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA); 4,4'-oxydiphthalic dianhydride (ODPA); butane tetracarboxylic dianhydride; 5-(2,5-dioxotetrahydro-3-furyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride; and mixtures thereof.

[0124] In certain embodiments, the reaction components may further comprise a3) at least one polycarboxylic acid. For example, based on the total moles of anhydride, the reaction mixture may comprise 0 to 10 mol % or 0 to 5 mol % of a3) at least one polycarboxylic acid.

[0125] The polycarboxylic acid may be aliphatic, cycloaliphatic, or aromatic and typically contains 2 to 4 carboxyl groups. Examples of suitable dicarboxylic acids include, but are not limited to, adipic acid; glutaric acid; pimelic acid; suberic acid; nonanedicarboxylic acid; decanedicarboxylic acid; succinic acid; maleic acid; sebacic acid; azelaic acid; terephthalic acid; isophthalic acid; phthalic acid; tetrahydrophthalic acid; hexahydrophthalic acid; trimellitic acid; and 1,4-cyclohexanedicarboxylic acid. Exemplary higher carboxylic acids include: 3,3',4,4'-benzophenonetetracarboxylic acid; 2,3,3',4'-benzophenonetetracarboxylic acid; pyromellitic acid; 3,3',4,4'-biphenyltetracarboxylic acid; 2,3,3',4'-biphenyltetracarboxylic acid.

[0126] The reaction step can be carried out at a pressure below atmospheric pressure, atmospheric pressure or above atmospheric pressure, but typically the pressure is atmospheric pressure or slightly above atmospheric pressure. In this regard, pressures of 50 to 150 kPa, for example 75 to 125 kPa, may be mentioned.

[0127] Typically, the reaction is carried out for a total of 2 to 10 hours, during which time the reaction temperature is typically maintained at 80 to 180°C, such as 80 to 160°C.

[0128] It is noteworthy that the reaction can be carried out at a plurality of temperatures within the ranges provided. For example, the reaction can be carried out in stages, including a first time span in which the reaction mixture is maintained at a first temperature, and a second time span in which the reaction mixture is maintained at a second temperature. Typically, the second temperature will be higher than the first temperature and will serve to complete the reaction.

[0129] The time span of any such sub-stages may each have a fixed length. Alternatively, a given time span may be determined by a monitorable point in the reaction. For example, a first time span may be determined by stopping the release of carbon dioxide, after which the temperature of the reaction mixture is raised for a fixed time or to a second monitoring point, such as to a specific dynamic viscosity of the polymer solution. In addition to viscosity measurements and flow measurements of gaseous CO2 release, the progress of the reaction may be monitored by known techniques, among which may be mentioned 1 HNMR, Fourier transform infrared spectroscopy, ultra performance liquid chromatography (UPLC) or thin layer chromatography (TLC).

[0130] Regardless of the temperature regime of the reaction, it is contemplated that the entire reaction or the first sub-phase of a reaction step can be conducted in batch or semi-batch mode. Batch reaction mode assumes that all reactants are added to the reaction vessel at the start of the reaction. Semi-batch reaction mode assumes that a portion of the reactants are added to the reaction vessel at the start of the reaction and the remainder are added periodically or continuously throughout the duration of the reaction or its first sub-phase.

[0131] The reaction may be intentionally terminated by cooling the reaction mixture, by adding a diluent solvent as discussed below, and / or by adding a monohydric alcohol such as a C1-C6 alkanol to trap any residual isocyanate functionality. It is also contemplated that the reaction may be terminated by adding a monoisocyanate, for example, of formula R x -NCO monoisocyanate, wherein: R x It is C1-C 18 Alkyl or C6-C 18 Aryl. Exemplary monoisocyanates according to this formula include: methyl isocyanate; isopropyl isocyanate; n-butyl isocyanate; t-butyl isocyanate; n-hexyl isocyanate; cyclohexyl isocyanate; stearyl isocyanate; phenyl isocyanate; m-, p-, or -tolyl isocyanate; p-isopropylphenyl isocyanate; 2,6-diisopropylphenyl isocyanate; and 1-naphthyl isocyanate.

[0132] The above reaction is carried out in the presence of a solvent. The solvent can provide a reaction medium, and the amount of the solvent present during the reaction can be at least sufficient to allow the reaction to proceed and to dissolve the polymer product at the reaction temperature.

[0133] In an exemplary embodiment, the present disclosure provides a method for producing a polyamide-imide solution, the method comprising:

[0134] a) producing a first polyamide-imide polymer solution by reacting a1) and a2) at a temperature of 60 to 180° C. and in the presence of a first solvent (S1) and a catalyst:

[0135] a1) a diisocyanate component as described above;

[0136] a2) an anhydride component as described above, comprising trimellitic anhydride (TMA)

[0137] wherein the first solvent (S1) comprises at least one aprotic compound having a boiling point of at least 150° C. measured at a pressure of 1 bar; and

[0138] b) diluting the first polymer solution with a second solvent (S2) to produce a second polyamide-imide polymer solution, wherein the second solvent is different from the first solvent; and,

[0139] wherein at least one of the first solvent (S1) and the second solvent (S2) comprises:

[0140] At least one compound according to formula (I)

[0141] ROOC-A-COOR(I)

[0142] Wherein: A is C1-C8 alkylene or C6 arylene; and

[0143] Each R is independently a C1-C2 alkyl group;

[0144] Provided that, when A is C2 alkylene, each R is C2 alkyl.

[0145] In embodiments, the second solvent is substantially free of dimethyl succinate. In other embodiments, the first and second solvents are substantially free of dimethyl succinate.

[0146] According to a second exemplary embodiment of the process, at least one compound according to formula (I) is present in reaction step a). For the sake of certainty, only in this case is the present disclosure intended to cover the performance of step a) and thus the polymer solution that is the product of this reaction step.

[0147] A method for preparing a polyamide-imide solution is provided, the method comprising:

[0148] a) producing a first polyamide-imide polymer solution by reacting a1) and a2) at a temperature of 60 to 180° C. and in the presence of a first solvent (S1) and a catalyst:

[0149] a1) a diisocyanate component comprising at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); isophorone diisocyanate (IPDI); dicyclohexylmethane diisocyanate (H-MDI); xylene diisocyanate (XDI); hydrogenated xylene diisocyanate; toluene diisocyanate (TDI); diphenyl sulfone diisocyanate (SDI); meta-xylene;

[0150] Diisocyanates; and mixtures thereof;

[0151] a2) an anhydride component comprising trimellitic anhydride (TMA);

[0152] b) diluting the first polymer solution with a second solvent (S2) to produce a second polyamide-imide polymer solution, wherein the second solvent (S2) is different from the first solvent (S1); and,

[0153] Wherein, based on the total weight of the first solvent (S1), the first solvent (S1) comprises:

[0154] 0.1 to 100% by weight of i) at least one compound according to formula (I)

[0155] ROOC-A 1 -COOR(I)

[0156] Among them: A 1 is a C1-C8 alkylene group or a C6 arylene group; and

[0157] Each R is independently C1-C2 alkyl; and,

[0158] 0 to 99.9% by weight of ii) at least one aprotic compound which does not satisfy formula (I) and has a boiling point of at least 150° C., measured at a pressure of 1 bar.

[0159] In one embodiment, the first solvent (S1) may comprise: 0.5 to 70 wt. % of i) at least one compound according to formula (I); and 30 to 99.5 wt. % of ii) at least one aprotic compound that does not satisfy formula (I) and has a boiling point of at least 150° C., measured at a pressure of 1 bar, based on the total weight of the first solvent (S1). In an alternative embodiment, the first solvent (S1) may comprise: 10 to 70 wt. % of i) at least one compound according to formula (I); and 30 to 90 wt. % of ii) at least one aprotic compound that does not satisfy formula (I) and has a boiling point of at least 150° C., measured at a pressure of 1 bar, based on the total weight of the first solvent (S1).

[0160] In the exemplary compounds of formula (I) according to the first solvent (S1): A 1 is a C1-C6 alkylene group or a C6 arylene group; and each R is independently a C1-C2 alkyl group. In other exemplary compounds: A 1 -(CH2) m - or a C6 arylene group, wherein m is an integer from 1 to 6; and each R is independently a C1-C2 alkyl group.

[0161] In other embodiments of formula (I), each substituent R is identical. In other embodiments of formula (I), each R is methyl. Exemplary compounds according to formula (I) that can be used in the first solvent (S1) alone or in combination include: dimethyl phthalate; diethyl phthalate; dimethyl malonate; diethyl malonate; dimethyl succinate; diethyl succinate; dimethyl glutarate; diethyl glutarate; dimethyl adipate; and diethyl adipate. For example, the at least one compound according to formula (I) can be selected from: dimethyl phthalate; dimethyl malonate; dimethyl succinate; dimethyl glutarate; dimethyl adipate; and mixtures thereof. In an exemplary embodiment, the at least one compound according to formula (I) present in the first solvent (S1) includes dimethyl phthalate.

[0162] The first solvent (S1) may comprise ii) at least one aprotic compound that does not satisfy formula (I) and has a boiling point of at least 150°C measured at a pressure of 1 bar. Exemplary compounds that may be present in the portion ii) of the solvent (S1) and that may be used alone or in combination include: γ-butyrolactone (GBL); cyclohexanone; methylcyclohexanone; 1,3-dimethyl-2-imidazolidinone; N-methyl-2-pyrrolidone (NMP); N-ethyl-2-pyrrolidone (NMP); N-butyl-2-pyrrolidone (NBP); N,N-dimethylformamide (DMF); N,N-diethylformamide (DEF); N,N-dimethylacetamide (DMAc); N,N-diethylacetamide; 3-methoxy-N,N'-dimethylpropionamide (MDP); N-formylmorpholine; N-acetylmorpholine; phenylmethanol; 2,6-dimethylphenol; 4-methylphenol; hexamethylphosphoramide; and dimethyl sulfoxide (DMSO).

[0163] Exemplary compounds that may be present in part ii) and that may be used alone or in combination include: gamma-butyrolactone (GBL); cyclohexanone; methylcyclohexanone; N-methyl-2-pyrrolidone (NMP); N-ethyl-2-pyrrolidone (NMP); N-butyl-2-pyrrolidone (NBP); N,N-dimethylacetamide (DMAc); N-formylmorpholine; N-acetylmorpholine; and 3-methoxy N,N'-dimethylpropionamide (MDP). In certain embodiments, part ii) of the solvent (S1) includes gamma-butyrolactone (GBL).

[0164] The method of this embodiment may include step (b)) of diluting the first polymer solution with a second solvent (S2) to produce a second polyamide-imide polymer solution. The second solvent (S2) is different from the first solvent (S1), which means that the composition of the first and second solvents is different. The first solvent (S1) and the second solvent (S2) themselves may include different compounds. It is also considered that the second solvent (S2) may include the same constituent compounds as the first solvent (S1), but the weight ratio of these constituent compounds is different from that of the first solvent (S1).

[0165] The second solvent (S2) may comprise at least one compound according to formula (I):

[0166] ROOC-A 1 -COOR(I)

[0167] Among them: A 1 is a C1-C8 alkylene group or a C6 arylene group; and

[0168] Each R is independently a C1-C2 alkyl group.

[0169] When a compound according to formula (I) is present in the second solvent (S2), the substituent A of the formula 1 The above description of R and R is applicable. In addition, exemplary compounds that can be used as diluents alone or in combination include: dimethyl phthalate; diethyl phthalate; dimethyl malonate; diethyl malonate; dimethyl succinate; diethyl succinate; dimethyl glutarate; diethyl glutarate; dimethyl adipate; and diethyl adipate. For example, the at least one diluent compound according to formula (I) in the second solvent (S2) can be selected from: dimethyl phthalate; dimethyl glutarate; dimethyl adipate; and mixtures thereof. In another exemplary embodiment, the second solvent (S2) includes dimethyl phthalate.

[0170] Regardless of whether there is a compound of formula (I) in the second solvent (S2), the second solvent (S2) may include at least one non-polar compound having a boiling point lower than 225° C. The compound meeting the boiling point condition may generally be selected from: C1-C8 linear alkanes; cyclic alkanes; C1-C8 branched alkanes; C1-C8 alkyl halides; aromatic compounds; and mixtures thereof. In addition, exemplary compounds that meet the boiling point condition and can be used alone or in combination include: n-pentane; n-hexane; cyclohexane; n-heptane; isooctane; trimethylpentane; toluene; xylene; benzene; and naphthalene. In one embodiment, the second solvent (S2) comprises xylene.

[0171] The present disclosure provides a method for producing a polyamide-imide solution, the method comprising:

[0172] a) reacting a1) and a2) at a temperature of 60 to 180° C. and in the presence of a first solvent (S1) and a catalyst to produce a first polyamide-imide polymer solution:

[0173] a1) a diisocyanate component comprising at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); isophorone diisocyanate (IPDI); dicyclohexylmethane diisocyanate (H-MDI); xylene diisocyanate (XDI); hydrogenated xylene diisocyanate; toluene diisocyanate (TDI); diphenyl sulfone diisocyanate (SDI); meta-xylene;

[0174] Diisocyanates; and mixtures thereof;

[0175] a2) an anhydride component comprising trimellitic anhydride (TMA)

[0176] wherein the first solvent (S1) comprises at least one aprotic compound having a boiling point of at least 150° C. measured at a pressure of 1 bar; and

[0177] b) diluting the first polymer solution with a second solvent (S2) to produce a second polyamide-imide polymer solution, wherein the second solvent (S2) is different from the first solvent (S1); and

[0178] wherein at least one of the first solvent (S1) and the second solvent comprises:

[0179] At least one compound according to formula (IA)

[0180] ROOC-A 2 -COOR(IA)

[0181] Among them: A 2is a C3-C8 alkylene group or a C6 arylene group; and

[0182] Each R is independently a C1-C2 alkyl group.

[0183] In an embodiment of the method, the first solvent (S1) comprises:

[0184] i) at least one compound according to formula (IA)

[0185] ROOC-A 2 -COOR(IA)

[0186] Among them: A 2 is a C3-C8 alkylene group or a C6 arylene group; and

[0187] Each R is independently C1-C2 alkyl; and / or,

[0188] ii) at least one aprotic compound which does not satisfy formula (IA) and has a boiling point of at least 150° C., measured at a pressure of 1 bar.

[0189] For the sake of certainty, it is noted that at least one compound according to formula (I) may be present in: the reaction step (a)) of producing the first polyamide-imide polymer solution; the step (b)) of stabilizing the first polymer solution by dilution; or in both steps.

[0190] In certain embodiments, the skilled person may choose to include a compound according to formula (I) in the first solvent (S1) or as the first solvent (S1). Thus, the compound of formula (I) may constitute the entirety of the first solvent or may be included in the first solvent as a trace additive. For example, based on the total weight of the first solvent (S1), the first solvent (S1) may comprise: 0.1 to 100 wt % of i) at least one compound according to formula (I); and 0 to 99.9 wt % of ii) at least one aprotic compound that does not satisfy formula (I) and has a boiling point of at least 150° C. measured at a pressure of 1 bar.

[0191] In one embodiment, the first solvent (S1) comprises: 0.5 to 70 wt.-% of i) at least one compound according to formula (I); and 30 to 99.5 wt.-% of ii) at least one aprotic compound that does not satisfy formula (I) and has a boiling point of at least 150° C., measured at a pressure of 1 bar, based on the total weight of the first solvent (S1). In another embodiment, the first solvent (S1) comprises: 10 to 70 wt.-% of i) at least one compound according to formula (I); and 30 to 90 wt.-% of ii) at least one aprotic compound that does not satisfy formula (I) and has a boiling point of at least 150° C., measured at a pressure of 1 bar, based on the total weight of the first solvent (S1).

[0192] In exemplary compounds according to formula (IA): A 2 is a C3-C6 alkylene or C6 arylene group; and each R is independently a C1-C2 alkyl group. In other exemplary compounds according to formula (IA): A 2 -(CH2) m - or a C6 arylene group, wherein m is an integer from 3 to 6; and each R is independently a C1-C2 alkyl group.

[0193] In certain embodiments of formula (IA), each substituent R is the same. In other embodiments of formula (IA), each R is methyl. Exemplary compounds according to formula (IA) that can be used alone or in combination include: dimethyl phthalate; diethyl phthalate; dimethyl glutarate; diethyl glutarate; dimethyl adipate; and diethyl adipate. For example, the at least one compound according to formula (IA) can be selected from: dimethyl phthalate; dimethyl glutarate; and dimethyl adipate. In further exemplary embodiments, the at least one compound according to formula (IA) includes dimethyl phthalate.

[0194] The first solvent (S1) may comprise ii) at least one aprotic compound which does not satisfy formula (IA) and has a boiling point of at least 150°C measured at a pressure of 1 bar. In one embodiment, the compounds that can constitute the ii) part of the first solvent (S1) and can be used alone or in combination include: γ-butyrolactone (GBL); cyclohexanone; methylcyclohexanone; 1,3-dimethyl-2-imidazolidinone; N-methyl-2-pyrrolidone (NMP); N-ethyl-2-pyrrolidone (NMP); N-butyl-2-pyrrolidone (NBP); N,N-dimethylformamide (DMF); N,N-diethylformamide (DEF); N,N-dimethylacetamide (DMAc); N,N-diethylacetamide; 3-methoxy N,N'-dimethylpropionamide (MDP); N-formylmorpholine; N-acetylmorpholine; phenylmethanol; 2,6-dimethylphenol; 4-methylphenol; hexamethylphosphoramide; and dimethyl sulfoxide (DMSO).

[0195] In another embodiment, the compounds that can constitute the part ii) of the first solvent (S1) and can be used alone or in combination include: gamma-butyrolactone (GBL); cyclohexanone; methylcyclohexanone; N-methyl-2-pyrrolidone (NMP); N-ethyl-2-pyrrolidone (NMP); N-butyl-2-pyrrolidone (NBP); N,N-dimethylacetamide (DMAc); N-formylmorpholine; N-acetylmorpholine; and 3-methoxy N,N'-dimethylpropionamide (MDP). In yet another embodiment, the part ii) of the first solvent (S1) includes gamma-butyrolactone (GBL).

[0196] The method of this embodiment includes step (b)), i.e. diluting the first polymer solution with a second solvent (S2) to produce a second polyamide-imide polymer solution. The second solvent (S2) is different from the first solvent (S1), which means that the composition of the first and second solvents is different. The first solvent (S1) and the second solvent (S2) themselves may include different compounds. It is also considered that the second solvent (S2) may include the same constituent compounds as the first solvent (S1), but the weight ratio of these constituent compounds is different from that of the first solvent (S1).

[0197] The second solvent (S2) comprises at least one compound according to formula (IA):

[0198] ROOC-A 2 -COOR(IA)

[0199] Among them: A 2 is a C3-C8 alkylene group or a C6 arylene group; and

[0200] Each R is independently a C1-C2 alkyl group.

[0201] When no compound according to formula (IA) is present in the first solvent (S1), the second solvent (S2) must contain such a compound. When a compound according to formula (IA) is present in the first solvent (S1), this does not exclude the presence of such a compound in the diluted second solvent (S2).

[0202] When a compound according to formula (IA) is present in the second solvent (S2), the substituent A described above with respect to the formula 2 The description of R and R is applicable. Therefore, exemplary compounds that can be used for the second solvent (S2) alone or in combination include: dimethyl phthalate; diethyl phthalate; dimethyl glutarate; diethyl glutarate; dimethyl adipate; and diethyl adipate. For example, the at least one compound according to formula (IA) used in the second solvent (S2) can be selected from: dimethyl phthalate; dimethyl glutarate; dimethyl adipate; and mixtures thereof. In one embodiment, the second solvent (S2) includes dimethyl phthalate.

[0203] Regardless of whether the compound of formula (IA) is present in the second solvent (S2), the second solvent (S2) may comprise at least one non-polar compound having a boiling point below 225° C. The compound satisfying this boiling point condition may generally be selected from: C1-C8 linear alkanes; cyclic alkanes; C1-C8 branched alkanes; C1-C8 alkyl halides; aromatic compounds; and mixtures thereof. In addition, exemplary compounds that satisfy this boiling point condition and can be used alone or in combination include: n-pentane; n-hexane; cyclohexane; n-heptane; isooctane; trimethylpentane; toluene; xylene; benzene; and naphthalene. In one embodiment, the second solvent (S2) comprises xylene.

[0204] In the above-described method, the amount of the second solvent (S2) added during the dilution step is not particularly limited, but dilution generally results in a stable solution with a workable viscosity. However, diluting the first polymer solution to such an extent that subsequent evaporation of the solvent to obtain a solid polyamide-imide from the polymer solution can be disadvantageous. Therefore, the dilution step b) generally results in a polyamide-imide solution having a solids content of 20 to 50% by weight, e.g., 25 to 45% by weight, or 25 to 40% by weight, as determined according to DIN 53216.

[0205] The polymer solution as defined above is used to coat the conductor to provide an insulating layer thereon. Although the discussion below focuses on the use of polyamide-imide, this does not exclude the use of polyamide-imide solutions as varnishes for other substrates or the use of polyamide-imide in the form of self-supporting films, for example, for phase insulation and coil winding.

[0206] The obtained polymer solution can be used as is to form one or more insulating coatings on the conductor. However, in certain embodiments, a coating composition is applied to the conductor, the composition comprising the polymer solution and adjuvants and additives that can impart improved properties to the composition and the coating obtained therefrom. For example, the adjuvants and additives can impart one or more of the following properties to the insulating coating: improved tensile strength; improved elastic properties; improved elastic recovery; longer guaranteed processing time; faster drying time; improved thermal conductivity; and reduced thermal expansion coefficient. These adjuvants and additives include: toughening agents; plasticizers; stabilizers (including UV stabilizers); adhesion promoters; flame retardants; lubricants (including polytetrafluoroethylene (PTFE) and graphite); rheological adjuvants; and colorants (such as pigments or dyes).

[0207] For the purposes of this disclosure, a "plasticizer" is a substance that reduces the viscosity of the composition and thus facilitates its processability. The plasticizer may comprise up to 10% or 5% by weight of the total weight of the composition and is typically selected from: diurethanes; monofunctional, linear or branched C4-C 16Ethers of alcohols, such as Cetiol OE (available from BASF); esters of abietic acid, butyric acid, thiobutyric acid, acetic acid, propionic acid and citric acid; esters based on nitrocellulose and polyvinyl acetate; fatty acid esters; dicarboxylic acid esters; esters with OH groups or epoxidized fatty acids; glycolates; benzoates; phosphates; sulfonates; trimellitates; polyether plasticizers, such as blocked polyethylene glycol or polypropylene glycol; polystyrene; hydrocarbon plasticizers; chlorinated paraffins; and mixtures thereof.

[0208] For the purposes of this disclosure, "stabilizer" is understood to mean an antioxidant, a thermal stabilizer, or a hydrolysis stabilizer. Here, the stabilizer may comprise up to 10% or 5% by weight of the total weight of the composition. Standard commercial examples of stabilizers suitable for use herein include: hindered phenols; thioethers; benzotriazoles; benzophenones; hydroquinones; benzoates; cyanoacrylates; acrylates; amines of the hindered amine light stabilizer (HALS) type; phosphorus; sulfur; and mixtures thereof.

[0209] The coating composition may include a rheology control agent, with non-conductive fillers providing an example of a rheology control agent. Broadly speaking, there is no specific limitation on the shape of the particles used as non-conductive fillers: particles having needle-shaped, spherical, elliptical, cylindrical, beaded, cubic, or platelet-shaped shapes may be used alone or in combination. In addition, it is contemplated that agglomerates of more than one type of particle may be used. Likewise, there is no specific limitation on the size of the particles used as non-conductive fillers. However, such non-conductive fillers typically have an average volume particle size (Dv50) of 0.01 to 1500 μm, for example, 0.01 to 50 μm, as measured by laser diffraction / scattering methods.

[0210] Exemplary non-conductive fillers include, but are not limited to, calcium carbonate, calcium oxide, calcium hydroxide (lime powder), precipitated and / or fumed silica, zeolites, bentonite, wollastonite, magnesium carbonate, diatomaceous earth, barium sulfate, aluminum oxide, clay, talc, titanium oxide, iron oxide, zinc oxide, sand, quartz, flint, mica, glass beads, glass powder, boron nitride, silicon carbide; and ground oxides of transition metals, lanthanides, and actinides.

[0211] The addition of particulate inorganic oxides such as silica and titania may have more uses than simply controlling the rheological properties of the composition. These oxides may further contribute to increasing thermal conductivity, reducing thermal expansion, and improving coating strength. In addition, they may inhibit partial discharge corrosion caused by electric field concentration in the gap between the insulating coating and the conductor.

[0212] To form the coating composition, the polymer solution and adjuvants and additives are brought together and mixed. In some cases, a multi-stage mixing process may be appropriate to ensure uniformity of the coating composition. For example, silicon dioxide and titanium dioxide can be provided in colloidal form rather than in solid particulate form for mixing into the coating composition.

[0213] Such adjuvants and additives may be used in desired combinations and proportions, as long as they do not adversely affect the properties and essential performance of the coating composition. Although there may be exceptions in certain circumstances, these adjuvants and additives generally do not exceed 40% by weight of the total composition, and generally do not exceed 30% by weight of the composition. In an alternative embodiment (which is not intended to be mutually exclusive with the embodiments given above), the coating composition may be formulated to exhibit a dynamic viscosity of less than 10,000 mPa·s, for example less than 8,000 mPa·s, at 25°C. Independently of or in addition to these properties, the coating composition may be formulated to be free of bubbles (foam) when formed, when mixed with any adjuvants, and when subsequently applied and heat treated.

[0214] As described above, one aspect of the present disclosure is a method of forming an insulated wire, the method comprising: providing a conductive wire; coating the conductive wire with a polymer solution as defined above; and heat-treating the coated conductive wire to remove a solvent therein.

[0215] Exemplary conductive wires include, but are not limited to, magnet wire. The provided wires can be formed from a variety of conductive materials, including: metallic materials, such as metals, silver, gold, copper, platinum, palladium, molybdenum, aluminum, nickel, and tin; graphite; graphene; conductive ceramics; and conductive polymeric materials. The provided wires can be a single structure or can be composed of multiple components. The latter embodiment contemplates wires composed of multiple microwires or nanowires and wires composed of conductive particles sintered, welded, or agglomerated together.

[0216] The provided wires can have various cross-sectional shapes, depending on their intended use. For example, the wires can have circular, oval, or rectangular cross-sections. Regardless of the cross-sectional shape, the wire diameter can be, for example, 0.01 to 5 mm, such as 0.01 to 2 mm or 0.01 to 1 mm.

[0217] According to the broadest process aspects of the present disclosure, the above-mentioned polymer solution is applied to a substrate (such as a substrate of a conductor) and then subjected to an in-situ heat treatment. Before applying the solution, it is generally recommended to pre-treat the relevant surface to remove foreign matter thereon: if applicable, this step can promote the subsequent adhesion of the solution thereto. Such treatments are known in the art and can be carried out in a single-stage or multi-stage manner. For conductive metal substrates, the treatment can, for example, consist of one or more of the following: etching treatment with an acid suitable for the substrate and an optional oxidizing agent; ultrasonic treatment; plasma treatment, including chemical plasma treatment, corona treatment, atmospheric plasma treatment and flame plasma treatment; immersion in an aqueous alkaline degreasing bath; treatment with an aqueous cleaning emulsion; treatment with a cleaning solvent such as carbon tetrachloride or trichloroethylene; and water rinsing, typically with deionized water or demineralized water. In the case of using an aqueous alkaline degreasing bath, any degreasing agent remaining on the surface can be removed by rinsing the substrate surface with deionized water or demineralized water.

[0218] In some embodiments, the adhesion of the disclosed solution to the substrate can be promoted by applying a primer to the optionally pretreated substrate. In fact, the primer composition can be used to ensure an effective fixation time of the composition on the inactive substrate.

[0219] The solution is then applied to the optionally pretreated, optionally primed substrate surface by conventional application methods such as: immersion; die coating; roller coating; felt application; and spray methods including, but not limited to, air atomized spray, air-assisted spray, airless spray, and high volume, low pressure spray.

[0220] It is recommended that the composition be applied to the surface at a wet film thickness of 10 to 500 μm. Applying thinner coats within this range is more economical and reduces the likelihood of unwanted thick cured areas. However, strict control must be exercised when applying thinner coats or layers to avoid the formation of discontinuous cured films.

[0221] Conventional curing ovens can be used to heat the coated wire. For efficient drying and curing, such ovens can be maintained at temperatures between 300 and 700° C., for example, between 400 and 600° C. The appropriate temperature depends on the specific compounds present and the desired cure rate, and can be determined on a case-by-case basis by a skilled artisan using simple preliminary tests, if necessary.

[0222] It is worth noting that more than one layer of polyamide-imide can be applied to the substrate. For example, the polyamide-imide can be applied in 2 to 8 layers. When multiple layers are applied, each individual layer can be at least partially dried prior to application of the subsequent layer, such that the at least partially dried previous layer is capable of substantially retaining its shape after exposure to ambient conditions. "Substantially retaining its shape" means that at least 50% by volume, and more typically at least 80% or 90% by volume, of the at least partially dried layer retains its shape and does not flow or deform when exposed to ambient conditions for 5 minutes. In this case, gravity generally may not have a significant effect on the shape of the at least partially cured or partially dried layer when exposed to ambient conditions.

[0223] It should also be noted that the polyamide-imide coating may constitute one or more layers of a multicoat system, in which the substrate is further provided with a coating comprising other polymers: coatings made of polyesters, polyurethanes, polyimides and polyvinyl formals may be mentioned in this regard.

[0224] The following examples serve to illustrate the present disclosure and are not intended to limit the scope of the disclosure in any way.

[0225] Example

[0226] The following commercially available products were used in the following examples:

[0227] DBE: A blend of the following dibasic esters: dimethyl glutarate, dimethyl succinate, and dimethyl adipate, available from Solvay as RPDE obtained.

[0228] The following test methods were used in the following examples:

[0229] Viscosity (η): Viscosity measurements were performed using a Brookfield DV-IIT LV cone and plate viscometer equipped with a CP-35 cone and a 100s -1 The viscometer was operated at a shear rate of 1000 nm and a temperature of 23° C. A volume of 0.5 mL of the formulation was loaded into the viscometer and incubated at a given shear rate, and the measurements were then collected.

[0230] Solids content: The solids content is the weight of the residue obtained after baking 1 g of enamel at 180° C. for 1 hour in accordance with DIN 53 216. The solids content is expressed as a percentage by weight based on the total weight of the enamel.

[0231] Example 1:

[0232] 100 g of gamma-butyrolactone (GBL), 236 g of dimethyl phthalate (DMP), 1 g of triethylenediamine, and 6 g of benzyl alcohol were placed in a dry glass reactor. 128 g of trimellitic anhydride (TMA), 68 g of methylene diphenyl diisocyanate (MDI), and 71 g of toluene diisocyanate (TDI) were added at 40°C with stirring. The mixture was then heated to 90°C over two hours and held at 90°C for four hours, until CO2 formation ceased. The reaction temperature was raised to 150°C, and the batch was held at 150°C for an additional two hours. 195 g of dimethyl phthalate (DMP) and 195 g of xylene were then added, and the mixture was allowed to cool to room temperature.

[0233] The resulting paint had a solids content of 35.0% by weight and a viscosity of 7100 mPa·s. Dimethyl phthalate (DMP) accounted for 59.3% by weight of the total solvent weight. The diisocyanate component consisted of: 40 mol % MDI; and 60 mol % TDI.

[0234] Example 2:

[0235] 380 g of gamma-butyrolactone (GBL), 1 g of triethylenediamine, and 15 g of benzyl alcohol were placed in a dry glass reactor. 140 g of trimellitic anhydride (TMA), 112 g of methylenediphenyl diisocyanate (MDI), and 52 g of toluene diisocyanate (TDI) were added at 40°C with stirring. The mixture was then heated to 90°C over two hours and held at 90°C for four hours, until CO2 formation ceased. The reaction temperature was raised to 150°C and the batch was held at 150°C for an additional two hours. 300 g of dimethyl phthalate (DMP) was added, and the mixture was allowed to cool to room temperature.

[0236] The resulting paint had a solids content of 37.0% by weight and a viscosity of 2800 mPa·s. Dimethyl phthalate (DMP) accounted for 44.1% by weight of the total solvent weight. The diisocyanate component consisted of: 60 mol % MDI; and 40 mol % TDI.

[0237] Example 3:

[0238] 470 g of gamma-butyrolactone (GBL), 150 g of dimethyl phthalate (DMP), 1 g of triethylenediamine, and 14 g of benzyl alcohol were placed in a dry glass reactor. 136 g of trimellitic anhydride (TMA), 109 g of methylene diphenyl diisocyanate (MDI), and 50 g of toluene diisocyanate (TDI) were added at 40°C with stirring. The mixture was then heated to 90°C over two hours and held at 90°C for four hours, until CO2 formation ceased. The reaction temperature was raised to 150°C and the batch was held at 150°C for an additional two hours. 70 g of xylene was added, and the mixture was allowed to cool to room temperature.

[0239] The resulting paint had a solids content of 35.0% by weight and a viscosity of 1150 mPa·s. Dimethyl phthalate (DMP) accounted for 21.7% by weight of the total solvent weight. The diisocyanate component consisted of: 60 mol % MDI; and 40 mol % TDI.

[0240] Example 4:

[0241] 390 g of gamma-butyrolactone (GBL), 1 g of triethylenediamine, and 15 g of benzyl alcohol were placed in a dry glass reactor. 140 g of trimellitic anhydride (TMA), 112 g of methylene diphenyl diisocyanate (MDI), and 52 g of toluene diisocyanate (TDI) were added at 40°C with stirring. The mixture was then heated to 90°C over two hours and held at 90°C for four hours, until CO2 formation ceased. The reaction temperature was raised to 150°C, and the batch was held at 150°C for an additional two hours. 20 g of dimethyl phthalate (DMP), 180 g of gamma-butyrolactone (GBL), and 90 g of xylene were added, and the mixture was allowed to cool to room temperature.

[0242] The resulting paint had a solids content of 31.0% by weight and a viscosity of 700 mPa·s. Dimethyl phthalate (DMP) accounted for 2.9% of the total weight of the solvent. The diisocyanate component consisted of: 60 mol % MDI; and 40 mol % TDI.

[0243] Example 5

[0244] 380 g of gamma-butyrolactone (GBL), 1 g of triethylenediamine, and 15 g of benzyl alcohol were placed in a dry glass reactor. 140 g of trimellitic anhydride (TMA), 112 g of methylene diphenyl diisocyanate (MDI), and 52 g of toluene diisocyanate (TDI) were added at 40°C with stirring. The mixture was then heated to 90°C over two hours and held at 90°C for four hours, until CO2 formation ceased. The reaction temperature was raised to 150°C, and the batch was held at 150°C for an additional two hours. 200 g of dimethyl phthalate (DMP) and 100 g of dibasic ester (DBE) were added, and the mixture was allowed to cool to room temperature.

[0245] The resulting paint had a solids content of 35.3% by weight and a viscosity of 1930 mPa·s. Dimethyl phthalate (DMP) accounted for 29.4% of the total solvent weight. The dibasic ester (DBE) accounted for 14.7% of the total solvent weight. The diisocyanate component consisted of: 60 mol % MDI; and 40 mol % TDI.

[0246] Example 6

[0247] 380 g of gamma-butyrolactone (GBL), 1 g of triethylenediamine, and 15 g of benzyl alcohol were placed in a dry glass reactor. 138 g of trimellitic anhydride (TMA), 126 g of methylene diphenyl diisocyanate (MDI), and 40 g of toluene diisocyanate (TDI) were added at 40°C with stirring. The mixture was then heated to 90°C over two hours and held at 90°C for four hours, until CO2 formation ceased. The reaction temperature was raised to 150°C, and the batch was held at 150°C for an additional two hours. 200 g of dimethyl phthalate (DMP) and 100 g of dibasic ester (DBE) were added, and the mixture was allowed to cool to room temperature.

[0248] The resulting paint had a solids content of 34.8% by weight and a viscosity of 1770 mPa·s. Dimethyl phthalate (DMP) accounted for 29.4% of the total solvent weight. The dibasic ester (DBE) accounted for 14.7% of the total solvent weight. The diisocyanate component consisted of: 68 mol% MDI; and 32 mol% TDI.

[0249] Example 7

[0250] 280 g of gamma-butyrolactone (GBL), 100 g of dimethyl phthalate (DMP), 1 g of triethylenediamine, and 15 g of benzyl alcohol were placed in a dry glass reactor. 140 g of trimellitic anhydride (TMA), 112 g of methylene diphenyl diisocyanate (MDI), and 52 g of toluene diisocyanate (TDI) were added at 40°C with stirring. The mixture was then heated to 90°C over two hours and held at 90°C for four hours, until CO2 formation ceased. The reaction temperature was raised to 150°C, and the batch was held at 150°C for an additional two hours. 130 g of dimethyl phthalate (DMP) and 170 g of dibasic ester (DBE) were added, and the mixture was allowed to cool to room temperature.

[0251] The resulting paint had a solids content of 35.1% by weight and a viscosity of 2250 mPa·s. Dimethyl phthalate (DMP) accounted for 33.8% of the total solvent weight. The dibasic ester (DBE) accounted for 25.0% of the total solvent weight. The diisocyanate component consisted of: 60 mol% MDI; and 40 mol% TDI.

[0252] The present disclosure includes the following aspects:

[0253] 1. A polyamide-imide solution comprising:

[0254] Polymers comprising structural units of formula (II)

[0255]

[0256] wherein: n is an integer from 2 to 400; and,

[0257] The solvent, based on the total weight of the solvent, comprises:

[0258] 0.1 to 100% by weight of i) at least one compound according to formula (IA)

[0259] ROOC-A 2 -COOR(IA)

[0260] Among them: A 2 is a C3-C8 alkylene group or a C6 arylene group; and

[0261] Each R is independently C1-C2 alkyl; and,

[0262] 0 to 99.9% by weight of ii) at least one aprotic compound which does not satisfy formula (IA) and has a boiling point of at least 150° C., measured at a pressure of 1 bar.

[0263] 2. A method for producing a polyamide-imide solution, the method comprising:

[0264] a) preparing a first polyamide-imide polymer solution by reacting a1) and a2) at a temperature of 60 to 180° C. and in the presence of a first solvent and a catalyst:

[0265] a1) a diisocyanate component comprising at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); isophorone diisocyanate (IPDI); dicyclohexylmethane diisocyanate (H-MDI); xylene diisocyanate (XDI); hydrogenated xylene diisocyanate; toluene diisocyanate (TDI); diphenyl sulfone diisocyanate (SDI); meta-xylene;

[0266] Diisocyanates; and mixtures thereof;

[0267] a2) an anhydride component comprising trimellitic anhydride (TMA);

[0268] wherein the first solvent comprises at least one aprotic compound having a boiling point of at least 150° C. measured at a pressure of 1 bar; and

[0269] b) diluting the first polymer solution with a second solvent to produce a second polyamide-imide polymer solution, wherein the second solvent is different from the first solvent,

[0270] wherein at least one of the first solvent and the second solvent comprises:

[0271] i) at least one compound according to formula (IA)

[0272] ROOC-A 2 -COOR(IA)

[0273] Among them: A 2 is a C3-C8 alkylene group or a C6 arylene group; and

[0274] Each R is independently a C1-C2 alkyl group.

[0275] 3. The method according to 2, wherein the first solvent comprises:

[0276] i) said at least one compound according to formula (IA); and

[0277] ii) at least one aprotic compound which does not satisfy formula (IA) and has a boiling point of at least 150° C., measured at a pressure of 1 bar.

[0278] 4. The method according to claim 3, wherein the first solvent comprises, based on the total weight of the first solvent:

[0279] 0.1 to 100 wt. % of i) the at least one compound according to formula (IA); and

[0280] 0 to 99.9% by weight of ii) the at least one aprotic compound.

[0281] 5. The method according to claim 3, wherein the first solvent comprises, based on the total weight of the solvent:

[0282] 0.5 to 70 wt. % of i) the at least one compound according to formula (IA); and

[0283] 30 to 99.5% by weight of ii) the at least one aprotic compound.

[0284] 6. The method according to claim 3, wherein the first solvent is composed of the following based on the total weight of the solvent:

[0285] 10 to 70 wt. % of i) the at least one compound according to formula (IA); and

[0286] 30 to 90% by weight of ii) the at least one aprotic compound.

[0287] 7. The method according to any one of aspects 2 to 6, wherein in formula (IA):

[0288] A 2 is a C3-C6 alkylene group or a C6 arylene group; and

[0289] Each R is independently a C1-C2 alkyl group.

[0290] 8. The method according to any one of aspects 2 to 6, wherein in formula (IA):

[0291] A 2 -(CH2) m -, wherein m is an integer from 3 to 6, or a C6 arylene group; and

[0292] Each R is independently a C1-C2 alkyl group.

[0293] 9. The method according to any one of aspects 2 to 6, wherein the at least one compound according to formula (IA) is selected from: dimethyl phthalate; diethyl phthalate; dimethyl glutarate; diethyl glutarate; dimethyl adipate; diethyl adipate; and mixtures thereof.

[0294] 10. The method according to any one of aspects 2 to 6, wherein the at least one compound according to formula (IA) is selected from: dimethyl phthalate; dimethyl glutarate; dimethyl adipate; and mixtures thereof.

[0295] 11. The method according to any one of aspects 2 to 6, wherein the at least one compound according to formula (IA) comprises dimethyl phthalate.

[0296] 12. The method according to any one of aspects 3 to 11, wherein the at least one aprotic compound is further defined as a nitrogen-containing polar aprotic compound having a boiling point of at least 150°C measured at a pressure of 1 bar.

[0297] 13. The method according to any one of aspects 3 to 11, wherein ii) the at least one aprotic compound is selected from the group consisting of: γ-butyrolactone; cyclohexanone; methylcyclohexanone; N-methyl-2-pyrrolidone (NMP); N-ethyl-2-pyrrolidone (NMP); N-butyl-2-pyrrolidone (NBP); N,N-dimethylacetamide; N-formylmorpholine; N-acetylmorpholine; 3-methoxy N,N'-dimethylpropionamide (MDP); and mixtures thereof.

[0298] 14. The method according to 13, wherein the first solvent comprises γ-butyrolactone.

[0299] 15. The method of any one of aspects 2 to 14, wherein the diisocyanate component comprises at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); toluene diisocyanate (TDI); and mixtures thereof.

[0300] 16. The method according to any one of aspects 2 to 14, wherein the diisocyanate component comprises, based on the total moles of diisocyanate:

[0301] 10 to 90 mole percent of monomeric methylene diphenyl diisocyanate (MDI); and

[0302] 90 to 10 mole percent of at least one diisocyanate selected from the group consisting of polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); isophorone diisocyanate (IPDI); dicyclohexylmethane diisocyanate (H-MDI); xylene diisocyanate (XDI); hydrogenated xylene diisocyanate; toluene diisocyanate (TDI); diphenyl sulfone diisocyanate (SDI); meta-xylene diisocyanate; and mixtures thereof.

[0303] 17. The method according to any one of aspects 2 to 14, wherein the diisocyanate component comprises, based on the total moles of diisocyanate:

[0304] 30 to 70 mole percent of monomeric methylene diphenyl diisocyanate (MDI); and

[0305] 70 to 30 mole percent of at least one diisocyanate selected from the group consisting of polymeric methylene diphenyl diisocyanate (pMDI); toluene diisocyanate (TDI); and mixtures thereof.

[0306] 18. The method according to any one of aspects 2 to 14, wherein the diisocyanate component comprises, based on the total moles of diisocyanate:

[0307] 35 to 65 mole percent of monomeric methylene diphenyl diisocyanate (MDI); and

[0308] 65 to 35 mole percent toluene diisocyanate (TDI).

[0309] 19. The method according to any one of aspects 2 to 14, wherein the diisocyanate component consists of the following, based on the total moles of diisocyanate:

[0310] 10 to 100 mole percent of toluene diisocyanate (TDI); and

[0311] 0 to 90 mole percent of at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); and mixtures thereof.

[0312] 20. The method according to any one of aspects 2 to 14, wherein the diisocyanate component consists of:

[0313] 10 to 100 mole percent hexamethylene diisocyanate (HDI); and

[0314] 0 to 90 mole percent of at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); toluene diisocyanate (TDI); and mixtures thereof.

[0315] 21. The method according to any one of aspects 2 to 20, wherein the anhydride component comprises, based on the total moles of anhydride:

[0316] 80 to 100 mole percent trimellitic anhydride (TMA); and

[0317] 0 to 20 mol % of at least one tetracarboxylic dianhydride.

[0318] 22. The method according to any one of aspects 2 to 20, wherein the anhydride component consists of the following, based on the total moles of anhydride:

[0319] 80 to 100 mole percent trimellitic anhydride (TMA); and

[0320] 0 to 20 mole percent of at least one anhydride selected from the group consisting of: 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (DSDA); 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA); 4,4'-oxydiphthalic dianhydride (ODPA); butanetetracarboxylic dianhydride; 5-(2,5-dioxotetrahydro-3-furyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride; and mixtures thereof.

[0321] 23. The method according to any one of aspects 2 to 22, wherein the reaction components further comprise:

[0322] a3) at least one polycarboxylic acid.

[0323] 24. The method according to any one of aspects 2 to 22, wherein the catalyst is a tertiary amine.

[0324] 25. The method according to any one of aspects 2 to 24, wherein the second solvent comprises at least one compound according to formula (IA):

[0325] ROOC-A 2 -COOR(IA)

[0326] Among them: A 2 is a C3-C8 alkylene group or a C6 arylene group; and each R is independently a C1-C2 alkyl group.

[0327] 26. The method according to any one of aspects 2 to 24, wherein the second solvent comprises at least one non-polar compound having a boiling point below 225°C.

[0328] 27. The method according to 26, wherein the second solvent comprises at least one compound selected from the group consisting of: C1-C8 linear alkanes; cyclic alkanes; C1-C8 branched alkanes; C1-C8 alkyl halides; aromatic compounds; and mixtures thereof.

[0329] 28. The method according to 26, wherein the second solvent comprises at least one compound selected from the group consisting of: n-pentane; n-hexane; cyclohexane; n-heptane; isooctane; trimethylpentane; toluene; xylene; benzene; naphthalene; and mixtures thereof.

[0330] 29. The method according to 26, wherein the second solvent comprises xylene.

[0331] 30. A polyamide-imide solution obtained according to the method as defined in any one of aspects 2 to 29.

[0332] 31. The polyamide-imide solution according to 30, having a solids content of 20 to 50% by weight, measured according to DIN 53216.

[0333] 32. A method of forming an insulated wire, comprising:

[0334] Provide wires;

[0335] coating the wire with a polyamide-imide solution as defined in 30; and

[0336] The coated wire is heat treated to remove the solvent.

[0337] 33. A method for producing a polyamide-imide solution, the method comprising:

[0338] a) producing a polyamide-imide polymer solution by reacting a1) and a2) at a temperature of 60 to 180° C. in the presence of a solvent and a catalyst:

[0339] a1) a diisocyanate component comprising at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); isophorone diisocyanate (IPDI); dicyclohexylmethane diisocyanate (H-MDI); xylene diisocyanate (XDI); hydrogenated xylene diisocyanate; toluene diisocyanate (TDI); diphenyl sulfone diisocyanate (SDI); meta-xylene diisocyanate; and mixtures thereof; and

[0340] a2) an anhydride component comprising trimellitic anhydride (TMA);

[0341] wherein the solvent comprises:

[0342] 0.1 to 100% by weight of i) at least one compound according to formula (I)

[0343] ROOC-A 1 -COOR(I)

[0344] Among them: A 1 is a C1-C8 alkylene group or a C6 arylene group; and each R is independently a C1-C2 alkyl group; and

[0345] 0 to 99.9% by weight of ii) at least one aprotic compound which does not satisfy formula (IA) and has a boiling point of at least 150° C., measured at a pressure of 1 bar.

[0346] Although at least one exemplary embodiment has been proposed in the foregoing detailed description, it will be appreciated that there are a large number of variations. It will also be appreciated that the one or more exemplary embodiments are merely examples and are not intended to limit the scope, applicability, or configuration in any way. On the contrary, the foregoing detailed description will provide a convenient roadmap for those skilled in the art to implement the exemplary embodiments. It will be understood that various changes may be made to the functions and arrangements of the elements described in the exemplary embodiments without departing from the scope defined in the appended claims. In addition, all combinations of the above-mentioned components, compositions, method steps, formulation steps, etc. are expressly contemplated for use in various non-limiting embodiments, even if such combinations are not explicitly described in the same or similar paragraphs.

[0347] With respect to the Markush groups relied upon herein to describe specific features or aspects of various embodiments, different, special, and / or unexpected results may be obtained from each member of the respective Markush group, independent of all other Markush members. Each member of the Markush group can be used alone or in combination and provides adequate support for specific embodiments within the scope of the appended claims.

[0348] In addition, any ranges and subranges relied upon in describing various embodiments of the present invention are independently and collectively within the scope of the appended claims and are understood to describe and contemplate all ranges including integer and / or fractional values ​​therein, even if such values ​​are not explicitly set forth herein. Those skilled in the art will readily recognize that the ranges and subranges listed herein are sufficient to describe and implement various embodiments of the present invention, and that these ranges and subranges can be further divided into related halves, thirds, quarters, fifths, etc. As just one example, the range "from 0.1 to 0.9" can be further divided into a lower third, i.e., from 0.1 to 0.3, a middle third, i.e., from 0.4 to 0.6, and an upper third, i.e., from 0.7 to 0.9, each of which falls within the scope of the appended claims individually and collectively and can be relied upon individually and / or collectively and provide sufficient support for specific embodiments within the scope of the appended claims. In addition, for phrases defining or modifying a range, such as "at least," "greater than," "less than," "not greater than," etc., it should be understood that such phrases include subranges and / or upper or lower limits. As another example, the range "at least 10" inherently includes the sub-range from at least 10 to 35, the sub-range from at least 10 to 25, the sub-range from 25 to 35, and so on, and each sub-range can be relied upon individually and / or collectively and provide sufficient support for specific embodiments within the scope of the appended claims. Individual numerical values ​​within the disclosed ranges can be relied upon and provide sufficient support for specific embodiments within the scope of the appended claims. For example, the range "from 1 to 9" includes various individual integers, such as 3, and individual numerical values ​​including decimal points (or fractions), such as 4.1, which can be relied upon and provide sufficient support for specific embodiments within the scope of the appended claims. Finally, it should be understood that

[0349] The term "about" with respect to any particular numerical value and range described herein is used to indicate a value that is within a standard deviation, equivalent function, efficacy, end load, etc., as understood by one skilled in the art using relevant conventional techniques and formulation methods and / or utilizing compounds and compositions such as those described herein. Thus, the term "about" can indicate a value that is within 10%, or within 5%, or within 1%, or within 0.5%, or within 0.1% of the recited value or range.

[0350] While the disclosure has been described with reference to particular embodiments thereof, numerous other forms and modifications will be apparent to those skilled in the art. The appended claims and this disclosure should generally be construed to cover all such obvious forms and modifications, which fall within the true scope of the disclosure.

Claims

1. A polyamide-imide solution comprising: Polymers comprising structural units of formula (II) in: n is an integer from 2 to 400; and, The solvent, based on the total weight of the solvent, comprises: 0.1 to 100% by weight of i) at least one compound according to formula (IA) ROOC-A 2 -COOR(IA) Among them: A 2 is a C3-C8 alkylene group or a C6 arylene group; and Each R is independently C1-C2 alkyl; and, 0 to 99.9% by weight of ii) at least one aprotic compound which does not satisfy formula (IA) and has a boiling point of at least 150° C., measured at a pressure of 1 bar.

2. A method for producing a polyamide-imide solution, the method comprising: a) preparing a first polyamide-imide polymer solution by reacting a1) and a2) at a temperature of 60 to 180° C. and in the presence of a first solvent and a catalyst: a1) a diisocyanate component comprising at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); isophorone diisocyanate (IPDI); dicyclohexylmethane diisocyanate (H-MDI); xylene diisocyanate (XDI); hydrogenated xylene diisocyanate; toluene diisocyanate (TDI); diphenyl sulfone diisocyanate (SDI); meta-xylene diisocyanate; and mixtures thereof; a2) an anhydride component comprising trimellitic anhydride (TMA); wherein the first solvent comprises at least one aprotic compound having a boiling point of at least 150° C. measured at a pressure of 1 bar; and b) diluting the first polymer solution with a second solvent to produce a second polyamide-imide polymer solution, wherein the second solvent is different from the first solvent, wherein at least one of the first solvent and the second solvent comprises: i) at least one compound according to formula (IA) ROOC-A 2 -COOR(IA) Among them: A 2 is a C3-C8 alkylene group or a C6 arylene group; and Each R is independently a C1-C2 alkyl group.

3. The method of claim 2, wherein the first solvent comprises: i) said at least one compound according to formula (IA); and ii) at least one aprotic compound which does not satisfy formula (IA) and has a boiling point of at least 150° C., measured at a pressure of 1 bar.

4. The method according to any one of claims 2 to 3, wherein the at least one compound according to formula (IA) is selected from the group consisting of: dimethyl phthalate; diethyl phthalate; dimethyl glutarate; diethyl glutarate; dimethyl adipate; diethyl adipate; and mixtures thereof.

5. The process according to any one of claims 2 to 3, wherein the at least one compound according to formula (IA) is selected from: dimethyl phthalate; dimethyl glutarate; dimethyl adipate; and mixtures thereof.

6. The process according to any one of claims 2 to 5, wherein ii) the at least one aprotic compound is selected from the group consisting of: γ-butyrolactone; cyclohexanone; methylcyclohexanone; N-methyl-2-pyrrolidone (NMP); N-ethyl-2-pyrrolidone (NMP); N-butyl-2-pyrrolidone (NBP); N,N-dimethylacetamide; N-formylmorpholine; N-acetylmorpholine; 3-methoxy N,N'-dimethylpropionamide (MDP); and mixtures thereof.

7. The method according to any one of claims 2 to 6, wherein the diisocyanate component comprises at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); toluene diisocyanate (TDI); and mixtures thereof.

8. Polyamide-imide solution obtainable according to the process as defined in any one of claims 2 to 7.

9. A method of forming an insulated wire, comprising: Provide wires; Coating the conductor with a polyamide-imide solution as defined in claim 8; and The coated wire is heat treated to remove the solvent.

10. A method for producing a polyamide-imide solution, the method comprising: a) producing a polyamide-imide polymer solution by reacting a1) and a2) at a temperature of 60 to 180° C. in the presence of a solvent and a catalyst: a1) a diisocyanate component comprising at least one diisocyanate selected from the group consisting of monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI); hexamethylene diisocyanate (HDI); isophorone diisocyanate (IPDI); dicyclohexylmethane diisocyanate (H-MDI); xylene diisocyanate (XDI); hydrogenated xylene diisocyanate; toluene diisocyanate (TDI); diphenyl sulfone diisocyanate (SDI); meta-xylene diisocyanate; and mixtures thereof; and a2) an anhydride component comprising trimellitic anhydride (TMA); wherein the solvent comprises: 0.1 to 100% by weight of i) at least one compound according to formula (I) ROOC-A 1 -COOR(I) Among them: A 1 is a C1-C8 alkylene group or a C6 arylene group; and Each R is independently C1-C2 alkyl; and 0 to 99.9% by weight of ii) at least one aprotic compound which does not satisfy formula (IA) and has a boiling point of at least 150° C., measured at a pressure of 1 bar.

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