POLYAMIDE-IMIDE POLYMER SOLUTION AND METHOD FOR THE PRODUCTION THEREOF

Abstract

This publication refers to a polyamide-imide solution comprising: a polymer containing the 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.% i) of at least one compound according to formula (IA) ROOC-A 2 -COOR (IA) where: A 2 a C3-C8 alkylene or a C6 arylene; and each R is independently a C1-C2 alkyl group; and 0 to 99.9 wt.% ii) at least one aprotic compound which does not correspond to formula (IA) and which has a boiling point of at least 150 °C, measured at 1 bar pressure.

Description

TECHNICAL AREA

[0001] This publication relates to a polyamide-imide solution and a process for preparing such a solution. In particular, this publication relates to a polyamide-imide solution containing a dibasic ester solvent and to the usefulness of such a solution in the manufacture of a conductive wire provided with an insulating coating containing the polyamide-imide. BACKGROUND

[0002] Electrically conductive wires are provided with an insulating covering to prevent, among other things, electrical leakage, to prevent the wires from coming into contact with other conductors, and to preserve the material integrity of the wire by protecting it from the effects of abrasion, heat, and the ingress of liquids.

[0003] Polyamide-imide polymers have become established in the field of conductive wire insulation due to their processability, insulating properties, and high temperature stability. Such polymers are typically used in a two-layer design as a coating on conductive wires coated with cross-linked polyester materials. The polyamide-imide imparts thermal stability and solvent resistance to the conductive wire that polyester alone does not offer.

[0004] Exemplary synthesis methods for polyamide-imide resins include the direct polymerization of an aromatic diamine with an aromatic tricarboxylic acid under dehydrogenation catalysis, as described in U.S. Patent No. 3,860,559 and Japanese Patent Laid-Open No. Sho 58-180532, the acid chloride method, and the isocyanate method.

[0005] The acid chloride method involves the condensation of an aromatic tricarboxylic acid chloride with an aromatic diamine. The condensation reaction can be carried out by homogeneous solution polymerization at low temperature, typically at room temperature in a non-aqueous polar solvent, or by precipitation polymerization (or interfacial polymerization) at low temperature in an organic solvent that is sparingly soluble in water or in an aqueous solvent with an acid acceptor. Because these polymerization processes require expensive acid chloride as raw material and often yield polyamide-imide resins with unfavorable molecular weight distributions, the acid chloride method is no longer considered economically viable.

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

[0007] Amide-based solvents have proven useful for the isocyanate method because they not only offer good solubility for the polyamide-imide resin but are also manageable as solvents. Examples of amide solvents include N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), N,N-dimethylacetamide, and N,N-dimethylformamide. Furthermore, DE102014104223A1 publishes the use of 3-methoxy-N,N-dimethylpropanamide as a solvent. However, concerns about the reprotoxicity of amide-based solvents exist. This has led to their use being regulated and the search for alternative solvents that can at least partially replace them.

[0008] The exclusive use of γ-butyrolactone (GBL) as solvent was proposed in JP2008-285660A: Although this solvent is non-hygroscopic and dissolves polyamide-imide resins with a narrow molar ratio of diisocyanate to anhydride, drying of the resulting solutions was not easy due to the high boiling point (204 °C) of γ-butyrolactone, and poor leveling behavior was observed in certain coating applications. Perhaps as a result, JP2012-62355A described the use of γ-butyrolactone in combination with cyclopentanone in polyamide-imide synthesis, US20060240255A1 described the use of butyrolactone in combination with cyclohexanone and methylcyclohexanone, and JP2011-210645A proposed the use of γ-butyrolactone in combination with the dipolar aprotic solvent 1,3-dimethylimidazolidinone. However, cyclohexanone is (foul) smelling as a co-solvent.Furthermore, precipitation of polyamide-imides has been observed when the ratio of co-solvent to γ-butyrolactone is not maintained within strictly controlled ranges. Furthermore, maintaining the stability of such mixed solutions when additives such as nanoparticles are included can be difficult: Particle aggregation and inhibiting viscosity increases in the solution have been observed, necessitating the use of stabilizing diluents such as the problematic amide solvents mentioned above.

[0009] It is considered necessary in the art to provide alternative solvents that can at least partially replace the use of γ-butyrolactone and amide solvents either as the solvent phase for the isocyanate method by which the polyamide-imide is synthesized or as diluents for stabilizing the polyamide-imide polymer solution obtained in this synthesis. SHORT SUMMARY

[0010] According to a first aspect of the present publication, a polyamide-imide polymer solution is presented, comprising: a polymer containing the structural unit of formula (II) where: 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.% i) of at least one compound according to formula (IA) ROOC-A 2 -COOR (IA) where: A 2a C3-C8 alkylene or a C6 arylene; and, each R is independently a C1-C2 alkyl; and, 0 to 99.9 wt.% ii) at least one aprotic compound which does not correspond to formula (IA) and which has a boiling point of at least 150 °C, measured at 1 bar pressure.

[0011] The present publication further provides a process for preparing a polyamide-imide solution, the process comprising: a) Reaction at a temperature of 60 to 180 °C and in the presence of a first solvent (S 1 ) and a catalyst: a1) a diisocyanate component comprising at least one diisocyanate selected from: monomeric methylenediphenyl diisocyanate (MDI); polymeric methylenediphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI); isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (H-MDI), xylene diisocyanate (XDI), hydrogenated xylene diisocyanate; tolylene diisocyanate (TDI), diphenylsulfone diisocyanate (SDI), m-xylylene diisocyanate, and mixtures thereof; and a2) an anhydride component comprising trimellitic anhydride (TMA) to prepare a first solution of a polyamide-imide polymer, wherein the first solvent (S 1 ) comprises at least one aprotic compound having a boiling point of at least 150 °C, measured at 1 bar pressure; and b) Diluting the first polymer solution with a second solvent (S 2) for preparing a second solution of the polyamide-imide polymer, wherein the second solvent is different from the first solvent; wherein at least one of the first solvent (S 1 ) and the second solvent (S 2 ) includes: at least one compound according to formula (I) ROOC-A 1 -COOR (I) where: A is a C1-C8 alkylene or a C6 arylene; and each R is independently a C1-C2 alkyl group; with the proviso that when A is a C2 alkylene group, each R is a C2 alkyl group.

[0012] The present publication further provides a process for preparing a polyamide-imide solution, the process comprising: a) Reaction at a temperature of 60 to 180 °C and in the presence of a first solvent (S 1 ) and a catalyst: a1) a diisocyanate component comprising at least one diisocyanate selected from: monomeric methylenediphenyl diisocyanate (MDI), polymeric methylenediphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (H-MDI), xylene diisocyanate (XDI), hydrogenated xylene diisocyanate, tolylene diisocyanate (TDI), diphenylsulfone diisocyanate (SDI), m-xylylene diisocyanate, and mixtures thereof; and, a2) an anhydride component comprising trimellitic anhydride (TMA) to prepare a first solution of a polyamide-imide polymer, wherein the first solvent (S 1 ) comprises at least one aprotic compound having a boiling point of at least 150 °C, measured at 1 bar pressure; and, b) Diluting the first polymer solution with a second solvent (S 2) to prepare a second solution of the polyamide-imide polymer, wherein the second solvent is different from the first solvent; and, wherein at least one of the first solvent (S 1 ) and the second solvent (S 2 ) includes: at least one compound according to formula (IA) ROOC-A 2 -COOR (IA) where: A 2 a C3-C8 alkylene or a C6 arylene; and each R is independently a C1-C2 alkyl group.

[0013] In embodiments of the latter process, the first solvent (S1) comprises: i) at least one compound according to formula (IA) ROOC-A 2 -COOR (IA) where: A 2 is a C3-C8 alkylene or C6 arylene; and each R is independently a C1-C2 alkyl group; and / or, (ii) at least one aprotic compound not corresponding to formula (IA) and having a boiling point of at least 150 °C, measured at a pressure of 1 bar.

[0014] The first solvent (S1) may, for example, comprise, based on the total weight of the first solvent (S1): 0.1 to 100 wt.% i) of the at least one compound according to formula (IA); and 0 to 99.9 wt.% ii) of at least one aprotic compound which does not correspond to formula (IA) and which has a boiling point of at least 150 °C, measured at 1 bar pressure.

[0015] In further exemplary embodiments, the first solvent (S1) comprises, based on the total weight of the first solvent (S1): 0.5 to 70 wt.% or 10 to 70 wt.% i) of the at least one compound according to formula (IA); and, 30 to 99.5% by weight or 30 to 90% by weight of ii) at least one aprotic compound which does not correspond to formula (IA) and which has a boiling point of at least 150 °C, measured at a pressure of 1 bar.

[0016] In exemplary compounds according to formula (IA): A2 is C3-C6 alkylene or C6 arylene; and each R is independently a C1-C2 alkyl group. In other exemplary compounds according to formula (IA): A2 is -(CH2)m- or C6 arylene; m is an integer from 3 to 6; and each R is independently a C1-C2 alkyl group.

[0017] In certain embodiments, each R substituent is the same. In other embodiments, each R is methyl. For example, the at least one compound according to formula (IA) can typically be selected from: dimethyl phthalate, diethyl phthalate, dimethyl glutarate, diethyl glutarate, dimethyl adipate, diethyl adipate, and mixtures thereof. The use of dimethyl phthalate, dimethyl glutarate, dimethyl adipate, or mixtures thereof may be advantageous under certain circumstances. As an example, the use of dimethyl phthalate, either alone or in combination with one or more other compounds according to formula (IA), may be mentioned.

[0018] In embodiments, 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: 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'-dimethylpropanamide (MDP), and mixtures thereof. As an example, the use of γ-butyrolactone in or as part ii) of the first solvent (S1) may be mentioned.

[0019] In embodiments of the above processes, the diisocyanate component comprises at least one diisocyanate selected from: monomeric methylenediphenyl diisocyanate (MDI), polymeric methylenediphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), tolylene diisocyanate (TDI), and mixtures thereof.

[0020] Under certain circumstances, monomeric methylenediphenyl diisocyanate (MDI) can be used either as the reactive diisocyanate or as one of the reactive diisocyanates in reaction step a). In a first exemplary embodiment, the diisocyanate component comprises, based on the total moles of diisocyanate, 10 to 90 mol% of monomeric methylenediphenyl diisocyanate (MDI) and 90 to 10 mol% of at least one diisocyanate selected from: polymeric methylenediphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (H-MDI), xylene diisocyanate (XDI), hydrogenated xylene diisocyanate, tolylene diisocyanate (TDI), diphenylsulfone diisocyanate (SDI), m-xylylene diisocyanate, and mixtures thereof.

[0021] In another exemplary embodiment, the diisocyanate component comprises, based on the total moles of diisocyanate, 30 to 70 mol% of monomeric methylenediphenyl diisocyanate (MDI) and 70 to 30 mol% of at least one diisocyanate selected from: polymeric methylenediphenyl diisocyanate (pMDI), tolylene diisocyanate (TDI), and mixtures thereof.

[0022] In another exemplary embodiment, the diisocyanate component comprises, based on the total moles of diisocyanate, 55 to 65 mol% monomeric methylenediphenyl diisocyanate (MDI) and 45 to 35 mol% tolylene diisocyanate (TDI).

[0023] Also typical is the use of tolylene diisocyanate (TDI) either as the reactive diisocyanate or as one of the reactive diisocyanates in reaction step a). In an exemplary embodiment, the diisocyanate component comprises, based on the total moles of diisocyanate, 10 to 100 mol% of tolylene diisocyanate (TDI) and 0 to 90 mol% of at least one diisocyanate selected from: monomeric methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), and mixtures thereof.

[0024] Also typical is the use of hexamethylene diisocyanate (HDI) either as the reactive diisocyanate or as one of the reactive diisocyanates in reaction step a). In an exemplary embodiment, the diisocyanate component comprises, based on the total moles of diisocyanate, 10 to 100 mol% of hexamethylene diisocyanate (HDI) and 0 to 90 mol% of at least one diisocyanate selected from: monomeric methylene diphenyl diisocyanate (MDI); polymeric methylene diphenyl diisocyanate (pMDI), tolylene diisocyanate (TDI), and mixtures thereof.

[0025] In the aforementioned reaction step a), the anhydride component may, in certain embodiments, comprise, based on the total number of moles of anhydride, 80 to 100 mol% of trimellitic anhydride (TMA) and 0 to 20 mol% of at least one tetracarboxylic dianhydride.

[0026] 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: 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride (DSDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic dianhydride (ODPA), butanetetracarboxylic dianhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, and mixtures thereof.

[0027] In certain embodiments, the second solvent (S2) comprises at least one compound according to formula (IA): ROOC-A 2 -COOR (IA) where: A 2 a C3-C8 alkylene or a C6 arylene; and, each R is independently a C1-C2 alkyl group.

[0028] In other embodiments, the second solvent (S2) comprises at least one nonpolar compound with a boiling point of less than 225°C. Compounds that satisfy this boiling point requirement can typically be selected from: linear C1-C8 alkanes, cyclic alkanes, branched C1-C8 alkanes, C1-C8 alkyl halides, aromatics, and mixtures thereof. Other exemplary compounds that satisfy this boiling point requirement and that can be used alone or in combination are: n-pentane, n-hexane, cyclohexane, n-heptane, isooctane, trimethylpentane, toluene, xylene, benzene, and naphthenes. In one embodiment, the second solvent (S2) comprises xylene.

[0029] The present publication also provides a polyamide-imide solution obtained by the process defined above and in the appended claims. In certain embodiments, the polyamide-imide solution may have a solids content of 20 to 50 wt.%, determined according to DIN 53216.

[0030] Another aspect of the present disclosure provides a method for producing an insulated wire, comprising: providing a conductive wire; coating the conductive wire with a polymer solution as defined above and in the appended claims; and subjecting the coated conductive wire to a heat treatment to remove solvents therefrom.

[0031] According to a further aspect of the present disclosure, there is provided a process for preparing a polyamide-imide solution, the process comprising: a) Reaction at a temperature of 60 to 180 °C and in the presence of a solvent (S) and a catalyst: a1) a diisocyanate component comprising at least one diisocyanate selected from: monomeric methylenediphenyl diisocyanate (MDI), polymeric methylenediphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (H-MDI), xylene diisocyanate (XDI), hydrogenated xylene diisocyanate, tolylene diisocyanate (TDI), diphenylsulfone diisocyanate (SDI), m-xylylene diisocyanate, and mixtures thereof; and, a2) an anhydride component comprising trimellitic anhydride (TMA) for preparing a solution of a polyamide-imide polymer, wherein, based on the weight of the solvent (S), the solvent comprises: from 0.1 to 100 wt.% i) of the at least one compound according to formula (I) ROOC-A 1 -COOR (I) where: A 1a C1-C8 alkylene or a C6 arylene; and, each R is independently a C1-C2 alkyl group; and, 0 to 99.9 wt.% ii) at least one aprotic compound which does not correspond to formula (I) and which has a boiling point of at least 150 °C, measured at 1 bar pressure.

[0032] Where aspects of the disclosure are described herein with specific embodiments, unless otherwise stated, any of these embodiments may be implemented in or combined with any other embodiment, even if such combination is not expressly described. In other words, the described embodiments are not mutually exclusive unless specifically identified, and permutations thereof remain within the scope of this disclosure. DETAILED DESCRIPTION

[0033] The following detailed description is merely exemplary and is not intended to limit this publication or its application and uses. Furthermore, there is no intention to be bound by the theory presented in the preceding background or the following detailed description.

[0034] The singular forms “ein” and “der / die / das” used here include the plural, unless the context clearly indicates otherwise.

[0035] As used herein, the terms "comprising," "comprises," and "consisting of" are synonymous with "including," "includes," "contains," or "includes" and are inclusive or open-ended, not excluding additional, unlisted members, elements, or process steps. The phrase "consisting of" is closed, in this case, and excludes all further elements. The phrase "consists essentially of" can describe various non-limited embodiments that are free of one or more optional compounds described herein.

[0036] Where quantities, concentrations, dimensions and other parameters are expressed in terms of one or more ranges, one or more upper limits or one or more lower limits, it shall be assumed that all ranges that can be obtained by combining an upper limit with a lower limit are also expressly stated, regardless of whether the ranges obtained are clearly mentioned in the context.

[0037] The terms "approximately" or "approximately" refer to all numerical values, whether expressly stated or not, except for specific examples. The term "about" can describe values ​​of ± 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10% in various embodiments.

[0038] Furthermore, a weight range represented as “0 to x” is generally understood to explicitly include 0 wt%: the constituent defined by this range may be absent from the material or may be present in the material in an amount of up to x wt%.

[0039] The words "exemplary" and "illustrative" are used herein to serve as an example, instance, or illustration. Any aspect or design described herein as "exemplary" or "illustrative" should not necessarily be construed as preferential or advantageous over other aspects or designs. Rather, the use of the terms "exemplary" and "illustrative" is intended to concretely demonstrate concepts.

[0040] In this motion, the word ‘can’ is used in the sense of ‘may’ and not in the sense of ‘must’, ie there is a possibility of doing so.

[0041] All percentages, ratios and proportions used herein are by weight unless otherwise stated.

[0042] The room temperature used here is 23 °C plus or minus 2 °C.

[0043] The molecular weights mentioned in this specification can be measured by gel permeation chromatography (GPC) using polystyrene calibration standards as per ASTM 3536.

[0044] As used herein, the term "drying" of the coating composition refers to the evaporation of the solvents present in the composition (drying). Evaporation of the solvent may be accompanied by the coalescence of the particulate, dispersed, or solvated phase of the composition. This drying may occur under ambient conditions or by targeted heat and / or irradiation. The degree of drying may be partial or complete.

[0045] Unless otherwise stated, the term "particle size" refers to the particle's largest axis. For a generally spherical particle, the largest axis is the diameter.

[0046] "D50 particle size" means that the particle size distribution is such that at least 50 percent by volume of the particles have a particle diameter smaller than the specified value. Unless otherwise stated, particle size is determined by dynamic light scattering (DLS) in conjunction with a particle size analyzer.

[0047] As used herein, "solids content" refers to the weight percentage of non-volatile components in the composition. Solids content can be determined as the inverse of the volatile content, which is determined according to ASTM D2369 Standard Test Method for Volatile Content of Coatings.

[0048] “Solvents” are substances that are capable of dissolving another substance to form a uniform solution; during the dissolution process, neither the solvent nor the dissolved substance undergoes any chemical change.

[0049] The term "aprotic solvents" used here refers to solvents that do not donate or accept a proton. Conversely, "protic solvents" are those that can donate or accept a proton.

[0050] Solvents can be either polar or nonpolar. The term "polar solvent" as used herein refers to a solvent with 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 skill of the skilled person. The use of measured voltages across parallel-plate capacitors in such determinations may be mentioned.

[0051] The term “Mannich base” is used herein in accordance with its standard definition as a ketonic amine obtainable from the condensation of a ketone with formaldehyde and ammonia or a primary or secondary amine.

[0052] The term "diisocyanate" refers to a compound with two functional N=C=O groups. The term "aromatic diisocyanate" is used here to describe organic isocyanates in which the isocyanate groups are directly bonded to the ring(s) of a mono- or polynuclear aromatic hydrocarbon group.

[0053] The term "metallic" refers to any type of metal, metal alloy, or mixture thereof. As used here, the term "alloy" refers to a substance consisting of two or more metals, or of a metal and a non-metal, that are intimately bonded together, usually by fusion and dissolution in a melt.

[0054] As used herein, the term "C1-Cn alkyl group" refers to a monovalent group containing 1 to n carbon atoms, which is a residue of an alkane and includes straight-chain and branched organic groups. A "C1-C4 alkyl" group is a monovalent group containing 1 to 4 carbon atoms, which is a 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 this publication, such alkyl groups may be unsubstituted or substituted with one or more halogens. Where appropriate, a tolerance for one or more non-halogen substituents within an alkyl group will be stated in the specification when applicable to a particular group (R).

[0055] The term “CI-Cn-alkylene” as used herein refers to a divalent radical counterpart of a C1-Cn-alkyl group.

[0056] As used herein, a "C6-C18 aryl" group, used alone or as part of a larger moiety—as in "aralkyl group"—refers to monocyclic, bicyclic, and tricyclic ring systems where the monocyclic ring system is aromatic, or at least one of the rings in a bicyclic or tricyclic ring system is aromatic. The bicyclic and tricyclic ring systems include benzofused 2-3 membered carbocyclic rings. In the present publication, such aryl groups may be unsubstituted or substituted with one or more halogens. Where appropriate, a tolerance for one or more non-halogen substituents within an aryl group is indicated in the specification when applicable for a particular group (R). Examples of aryl groups include: phenyl, (C1-C4)alkylphenyl, such as tolyl and ethylphenyl, indenyl, naphthalenyl, tetrahydronaphthyl, tetrahydroindenyl; Tetrahydroanthracenyl and anthracenyl.

[0057] As used herein, "alkylaryl" refers to alkyl-substituted aryl groups, and "substituted alkylaryl" refers to alkylaryl groups additionally bearing one or more substituents as described above. Furthermore, "aralkyl" herein means an alkyl group substituted with an aryl radical as defined above.

[0058] The term “Cn-arylene” used here refers to a divalent radical counterpart to a Cn-aryl group.

[0059] A mono- or polynuclear aromatic hydrocarbon group is an essentially planar cyclic hydrocarbon unit with conjugated double bonds, which may consist of a single ring or comprise multiple fused (fused) or covalently linked rings. The term aromatic also includes alkylaryl. Typically, the hydrocarbon (backbone) chain comprises 5, 6, 7, or 8 main chain atoms in a cycle. Examples of such planar cyclic hydrocarbon units include cyclopentadienyl, phenyl, naphthalenyl,

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

[12] annulenyl, [8]annulenyl, phenaline (perinaphthene), 1,9-dihydropyrene, and chrysene (1,2-benzophenanthrene). Examples of alkylaryl units are benzyl, phenethyl, 1-phenylpropyl, 2-phenylpropyl, 3-phenylpropyl, 1-naphthylpropyl, 2-naphthylpropyl, 3-naphthylpropyl and 3-naphthylbutyl.

[0060] The term "substituted" refers to substitution with at least one suitable substituent. For completeness, the substituents may be attached to the indicated group or moiety at one or more positions, and multiple degrees of substitution are permitted unless otherwise stated. Furthermore, the terms "substitution" or "substituted with" carry the implicit condition that such substitution is consistent with the permitted valence of the substituted atom and the substituent, and that the substitution results in a stable compound that is not subject to spontaneous transformation, e.g., by rearrangement, cyclization, or elimination.

[0061] The term "essentially free" is intended to mean that the constituent, component, compound, moiety, functional group, element, ion, or the like is not intentionally added to the subject material and is present at most in trace amounts that will have no (adverse) effect on the desired properties of the material. For compositions, an exemplary trace amount is less than 1000 ppm, based on the weight of the composition. The term "essentially free" encompasses those embodiments in which the specified compound, moiety, functional group, element, ion, or other similar constituent is completely absent from the subject material or is not present in an amount measurable by methods generally customary in the art.

[0062] The term "anhydrous" as used here is synonymous with the term "essentially free of water." Water is not intentionally added to a particular composition and is present at most in trace amounts that have no (adverse) impact on the desired properties of the composition.

[0063] The processes of the present publication require the reaction at a temperature of 60 to 180 °C and in the presence of a solvent and a catalyst of: a1) a diisocyanate component; and, a2) an anhydride component comprising trimellitic anhydride (TMA) to prepare a solution of a polyamide-imide polymer, wherein the solvent comprises at least one aprotic compound having a boiling point of at least 150 °C, measured at 1 bar pressure.

[0064] The reaction can, for example, be carried out with a molar ratio of isocyanate groups to anhydride groups of 2:3 to 6:1. The molar ratio of isocyanate groups to anhydride groups can, for example, be 2:1 to 4:1 or 2:1 to 3:1. For the sake of completeness, it should be noted that the term "molar ratio" also includes the contribution of monofunctional reactive compounds, such as the monoisocyanates mentioned below.

[0065] Depending on the type of reactive diisocyanate, the amount of catalyst used in the reaction typically ranges from 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 salts of tertiary amines; 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.

[0066] In certain embodiments, the catalyst comprises a tertiary amine or a salt thereof. Exemplary tertiary amines include: 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, morpholines such as N-methylmorpholine, N-ethylmorpholine, and N-cocomorpholine, imidazolines, and imidazoles such as N-methylimidazole, N-vinylimidazole, and 1,2-dimethylimidazole.

[0067] The diisocyanate component of the reactants comprises at least one diisocyanate selected from: monomeric methylenediphenyl diisocyanate (MDI), polymeric methylenediphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (H-MDI), xylene diisocyanate (XDI), hydrogenated xylene diisocyanate, tolylene diisocyanate (TDI), diphenylsulfone diisocyanate (SDI), m-xylylene diisocyanate, and mixtures thereof. In certain embodiments, the diisocyanate component comprises at least one diisocyanate selected from: monomeric methylenediphenyl diisocyanate (MDI), polymeric methylenediphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), tolylene diisocyanate (TDI), and mixtures thereof.

[0068] The reaction can, under certain circumstances, be illustrated by the presence of monomeric methylenediphenyl diisocyanate (MDI) as the reacting diisocyanate or diisocyanates. The diisocyanate component can, for example, comprise, based on the total moles of diisocyanate: 10 to 90 mol% of monomeric methylenediphenyl diisocyanate (MDI), and 90 to 10 mol% of at least one diisocyanate selected from: polymeric methylenediphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (H-MDI), xylene diisocyanate (XDI), hydrogenated xylene diisocyanate, tolylene diisocyanate (TDI), diphenylsulfone diisocyanate (SDI), m-xylylene diisocyanate, and mixtures thereof.In another example, the diisocyanate component may comprise, based on the total moles of diisocyanate, 30 to 70 mol% of monomeric methylenediphenyl diisocyanate (MDI), and 70 to 30 mol% of at least one diisocyanate selected from polymeric methylenediphenyl diisocyanate (pMDI) and tolylene diisocyanate (TDI). In another example, the diisocyanate component may comprise, based on the total moles of diisocyanate, 35 to 65 mol% of monomeric methylenediphenyl diisocyanate (MDI) and 65 to 35 mol% of tolylene diisocyanate (TDI).

[0069] Under other circumstances, the reaction may be exemplified by the presence of tolylene diisocyanate (TDI) as the diisocyanate reactant or diisocyanates. For example, the diisocyanate component may comprise, based on the total moles of diisocyanate, from 10 to 100 mol% of tolylene diisocyanate (TDI), and from 0 to 90 mol% of at least one diisocyanate selected from: monomeric methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), and mixtures thereof.

[0070] In further cases, the reaction may be characterized by the presence of hexamethylene diisocyanate (HDI) as the diisocyanate reactant or as a diisocyanate reactant. For example, the diisocyanate component may comprise, based on the total moles of diisocyanate, from 10 to 100 mol% of hexamethylene diisocyanate (HDI), and from 0 to 90 mol% of at least one diisocyanate selected from: monomeric methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyl diisocyanate (pMDI), tolylene diisocyanate (TDI), and mixtures thereof.

[0071] It is not strictly excluded that the diisocyanate component contains further diisocyanates in addition to the diisocyanates mentioned, whereby these additional diisocyanates can be aliphatic, cycloaliphatic, or aromatic. Such an additional diisocyanate can typically make up 0 to 20 mol%, e.g., 0 to 10 mol%, of the total moles of diisocyanate. Examples of aliphatic isocyanates include: ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, octamethylene diisocyanate, nonamethylene diisocyanate, decamethylene diisocyanate, 1,6,11-undecane triisocyanate, bis(isocyanatoethyl) carbonate, and bis(isocyanatoethyl) ether.Examples of cycloaliphatic polyisocyanates include dicyclohexylmethane 4,4'-diisocyanate (H12MDI); 1-isocyanatomethyl-3-isocyanato-1,5,5-trimethylcyclohexane (isophorone diisocyanate, IPDI); cyclohexane 1,4-diisocyanate, hydrogenated xylylene diisocyanate (H6XDI), 1-methyl-2,4-diisocyanatocyclohexane, m- or p-tetramethylxylene diisocyanate (m-TMXDI, p-TMXDI); and dimer fatty acid diisocyanate. Examples of aromatic diisocyanates include naphthalene 1,5-diisocyanate, xylylene diisocyanate (XDI); Diphenyldimethylmethane-4,4'-diisocyanate, di- and tetraalkyldiphenylmethane diisocyanates, dibenzyl-4,4'-diisocyanate, phenylene-1,3-diisocyanate and phenylene-1,4-diisocyanate.

[0072] The anhydride-reactive component comprises trimellitic anhydride (TMA). However, the presence of other anhydride-functional compounds is not excluded. Thus, in certain embodiments, the anhydride component comprises, based on the total moles of anhydride: 80 to 100 mol% of trimellitic anhydride (TMA); and 0 to 20 mol% of at least one tetracarboxylic dianhydride. For example, the anhydride component can 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: 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride (DSDA); 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA); 4,4'-oxydiphthalic dianhydride (ODPA); butanetetracarboxylic acid dianhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride and mixtures thereof.

[0073] In certain embodiments, the reacting components may also comprise a3) at least one polycarboxylic acid. The reaction mixture may contain, for example, 0 to 10 mol% or alternatively 0 to 5 mol% of a3) of the at least one polycarboxylic acid, based on the total number of moles of the anhydride.

[0074] The polycarboxylic acid can be aliphatic, cycloaliphatic, or aromatic and typically contains 2 to 4 carboxyl groups. Examples of suitable dicarboxylic acids include: adipic acid, glutaric acid, pimelic acid, suberic acid, nonanedicarboxylic acid, decanedicarboxylic acid, succinic acid, maleic acid, sebacic acid, azelaic acid, terephthalic acid, isophthalic acid, o-phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, trimellitic acid, and 1,4-cyclohexanedicarboxylic acid. Examples of higher carboxylic acids include: 3,3',4,4'-benzophenonetetracarboxylic acid, 2,3,3',4'-benzophenonetetracarboxylic acid, pyromellitic acid, 3,3',4,4'-biphenyltetracarboxylic acid, and 2,3,3',4'-biphenyltetracarboxylic acid.

[0075] The reaction step can be carried out at subatmospheric, atmospheric, or superatmospheric pressure, but pressures at or slightly above atmospheric pressure are typical. Pressures of 50 to 150 kPa, e.g., 75 to 125 kPa, are particularly suitable in this context.

[0076] Typically, the reaction described above is carried out over a total period of 2 to 10 hours. The reaction temperature maintained throughout this period is typically between 80 and 180 °C, for example, between 80 and 160 °C.

[0077] It should be noted that the reaction can be carried out at more than one temperature within the specified ranges. For example, the reaction can be carried out in sub-steps comprising a first period of time during which the reaction mixture is maintained at a first temperature and a second period of time during which the reaction mixture is maintained at a second temperature. Typically, the second temperature is higher than the first and serves to complete the reaction.

[0078] The duration of these sub-steps can each have a fixed length. Alternatively, a specific time period can also be determined by monitorable points in the reaction. A first time period can, for example, be determined by the cessation of carbon dioxide evolution. After this cessation, the temperature of the reaction mixture is increased either for a specific time or to a second, monitored point, for example, until a certain dynamic viscosity of the polymer solution is reached. In addition to measuring the viscosity and flow rate of gaseous CO2 evolution, the course of the reaction can be monitored using known techniques such as 1H NMR, Fourier transform infrared spectroscopy, ultra-performance liquid chromatography (UPLC), or thin-layer chromatography (TLC).

[0079] Regardless of the temperature regime of the reaction, it is assumed that the entire reaction or an initial sub-stage of the reaction can be carried out either in batch or semi-batch mode. In a batch reaction, it is assumed that all reactants are added to the reaction vessel at the beginning of the reaction. In a semi-batch reaction, it is assumed that a portion of the reactants is added to the reaction vessel at the beginning of the reaction, and the remaining portion is added either periodically or continuously, either throughout the entire reaction or in an initial sub-stage.

[0080] The reaction can be selectively terminated by cooling the reaction mixture, by adding the diluent discussed below, and / or by adding a mono-ol—e.g., a C1-C6 alkanol—to scavenge any residual isocyanate functionalities. It is also contemplated that the reaction can be terminated by adding a mono-isocyanate, such as a mono-isocyanate of the formula Rx-NCO, where: Rx is C1-C18 alkyl or C6-C18 aryl. Exemplary monoisocyanates according to this formula include: methyl isocyanate, isopropyl isocyanate, n-butyl isocyanate, tert-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.

[0081] The reaction described above is carried out in the presence of a solvent. This solvent can serve as a reaction medium, and the amount of solvent present during the reaction can be at least sufficient for the reaction to proceed and the polymer products to dissolve at the reaction temperature.

[0082] The present publication provides, in an exemplary embodiment, a process for preparing a polyamide-imide solution, the process comprising: a) Reaction at a temperature of 60 to 180 °C and in the presence of a first solvent (S 1 ) and a catalyst: a1) the diisocyanate component described above; and, a2) the anhydride component comprising trimellitic anhydride (TMA) as described above, to prepare a first solution of a polyamide-imide polymer, wherein the first solvent (S 1) comprises at least one aprotic compound having a boiling point of at least 150 °C, measured at 1 bar pressure; and, b) Diluting the first polymer solution with a second solvent (S 2 ) to prepare a second solution of the polyamide-imide polymer, wherein the second solvent (S 2 ) from the first solvent (S 1 ) is different; and, wherein at least one of the first solvent (S 1 ) and the second solvent (S 2 ) includes: at least one compound according to formula (I) ROOC-A-COOR (I) where: A is a C1-C8 alkylene or a C6 arylene; and, each R is independently a C1-C2 alkyl group with the proviso that when A is a C2 alkylene group, each R is a C2 alkyl group.

[0083] In certain cases, the second solvent is substantially free of dimethyl succinate. In other embodiments, both the first and second solvents are substantially free of dimethyl succinate.

[0084] According to a second exemplary embodiment of this process, at least one compound of formula (I) is present in reaction step a). To ensure safety, the present publication is intended to cover only the implementation of step a) in this case and thus the polymer solution that is the product of this reaction step.

[0085] A process for preparing a polyamide-imide solution is provided, the process comprising: a) Reacting at a temperature of 60 to 180 °C and in the presence of a first solvent (S 1 ) and a catalyst: a1) a diisocyanate component comprising at least one diisocyanate selected from: monomeric methylenediphenyl diisocyanate (MDI), polymeric methylenediphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (H-MDI), xylene diisocyanate (XDI), hydrogenated xylene diisocyanate, tolylene diisocyanate (TDI), diphenylsulfone diisocyanate (SDI), m-xylylene diisocyanate, and mixtures thereof; and, a2) an anhydride component comprising trimellitic anhydride (TMA) for preparing a first solution of a polyamide-imide polymer, b) Diluting the first polymer solution with a second solvent (S 2 ) to prepare a second solution of the polyamide-imide polymer, wherein the second solvent (S 2 ) from the first solvent (S 1 ) is different; and, where, based on the total weight of the first solvent (S 1 ), the first solvent (S1 ) includes: from 0.1 to 100 wt.% i) of the at least one compound according to formula (I) ROOC-A 1 -COOR (I) where: A 1 a C1-C8 alkylene or a C6 arylene; and, each R is independently a C1-C2 alkyl group; and from 0 to 99.9% by weight of ii) at least one aprotic compound which does not correspond to formula (I) and which has a boiling point of at least 150 °C, measured at 1 bar pressure.

[0086] In one embodiment, the first solvent (S1), based on the total weight of the first solvent (S1), may comprise: 0.5 to 70 wt.% of i) the at least one compound according to formula (I); and 30 to 99.5 wt.% of ii) at least one aprotic compound which does not correspond to formula (I) and which has a boiling point of at least 150°C, measured at a pressure of 1 bar. In an alternative embodiment, the first solvent (S1), based on the total weight of the first solvent (S1), may comprise: 10 to 70 wt.% of i) the at least one compound according to formula (I); and 30 to 90 wt.% of ii) at least one aprotic compound which does not correspond to formula (I) and which has a boiling point of at least 150°C, measured at a pressure of 1 bar.

[0087] In exemplary compound(s) according to formula (I) of the first solvent (S1): A1 is C1-C6 alkylene or C6 arylene; and each R is independently a C1-C2 alkyl group. In other exemplary compounds: A1 is -(CH2)m- or C6 arylene, wherein m is an integer from 1 to 6; and each R is independently a C1-C2 alkyl group.

[0088] In certain embodiments of formula (I), each R substituent is the same. 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) either individually or in combination are: dimethyl phthalate, diethyl phthalate, dimethyl malonate, diethyl malonate, dimethyl succinate, diethyl succinate, dimethyl glutarate, diethyl glutarate, dimethyl adipate, and diethyl adipate. The at least one compound according to formula (I) can, for example, be selected from: dimethyl phthalate, dimethyl malonate, dimethyl succinate, dimethyl glutarate, dimethyl adipate, and mixtures thereof. In one exemplary embodiment, the at least one compound according to formula (I) present in the first solvent (S1) comprises dimethyl phthalate.

[0089] The first solvent (S1) may ii) contain at least one aprotic compound which does not correspond to 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 part ii) of the solvent (S1), which 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'-dimethylpropanamide (NMP), N-formylmorpholine, N-acetylmorpholine, phenylmethanol, 2,6-xylenol; 4-methylphenol, hexamethylphosphoramide and dimethyl sulfoxide (DMSO).

[0090] Exemplary compounds that may be included in part ii), which may be used alone or in combination, include: γ-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'-dimethylpropanamide (MDP). In certain embodiments, part ii) of the solvent (S1) comprises γ-butyrolactone (GBL).

[0091] The process of this embodiment may comprise step (b)) of diluting the first polymer solution with a second solvent (S2) to produce a second solution of the polyamide-imide polymer. The second solvent (S2) differs from the first solvent (S1), meaning that the compositions of the first and second solvents are not identical. As such, the first (S1) and second (S2) solvents may consist of different compounds. It is also contemplated that the second solvent (S2) may contain the same components as the first solvent (S1), but differ from it in the weight ratio of these components.

[0092] The second solvent (S2) may contain at least one compound according to formula (I): ROOC-A 1 -COOR (I) where: A 1 a C1-C8 alkylene or a C6 arylene; and, each R is independently a C1-C2 alkyl group.

[0093] The aforementioned considerations for the substituents A and R of formula (I) apply when a compound according to this formula is present in the second solvent (S2). Compounds that can be used individually or in combination as diluents 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) comprises dimethyl phthalate.

[0094] Regardless of the presence of a compound of formula (I) in the second solvent (S2), the second solvent (S2) may contain at least one non-polar compound having a boiling point of less than 225°C. Compounds that satisfy this boiling point requirement can typically be selected from: linear C1-C8 alkanes, cyclic alkanes, branched C1-C8 alkanes, C1-C8 alkyl halides, aromatics, and mixtures thereof. Further exemplary compounds that satisfy this boiling point requirement and that can be used alone or in combination are: n-pentane, n-hexane, cyclohexane, n-heptane, isooctane, trimethylpentane, toluene, xylene, benzene, and naphthenes. In one embodiment, the second solvent (S2) comprises xylene.

[0095] The present publication provides a process for preparing a polyamide-imide solution, the process comprising: a) Reacting at a temperature of 60 to 180 °C and in the presence of a first solvent (S 1 ) and a catalyst: a1) a diisocyanate component comprising at least one diisocyanate selected from: monomeric methylenediphenyl diisocyanate (MDI), polymeric methylenediphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (H-MDI), xylene diisocyanate (XDI), hydrogenated xylene diisocyanate, tolylene diisocyanate (TDI), diphenylsulfone diisocyanate (SDI), m-xylylene diisocyanate, and mixtures thereof; and, a2) an anhydride component comprising trimellitic anhydride (TMA) to prepare a first solution of a polyamide-imide polymer, wherein the first solvent (S 1 ) comprises at least one aprotic compound having a boiling point of at least 150 °C, measured at 1 bar pressure; and, b) Diluting the first polymer solution with a second solvent (S 2 ) to prepare a second solution of the polyamide-imide polymer, wherein the second solvent (S 2 ) from the first solvent (S 1 ) is different; and, wherein at least one of the first solvent (S 1 ) and the second solvent comprises: at least one compound according to formula (IA) ROOC-A 2 -COOR (IA) where: A 2 a C3-C8 alkylene or a C6 arylene; and, each R is independently a C1-C2 alkyl group.

[0096] In embodiments of this process, the first solvent (S1) comprises: i) at least one compound according to formula (IA) ROOC-A 2 -COOR (IA) where: A 2 a C3-C8 alkylene or a C6 arylene; and, each R is independently a C1-C2 alkyl group; and / or, (ii) at least one aprotic compound not corresponding to formula (IA) and having a boiling point of at least 150 °C, measured at a pressure of 1 bar.

[0097] For safety reasons, it is noted that at least one compound according to formula (I) may be present in: the reaction step (a)) which produces a first polyamide-imide polymer solution, the step in which this first polymer solution is stabilized by dilution (b)) or in both of these steps.

[0098] In certain embodiments, the skilled person may choose to include the compound(s) of formula (I) in or as the first solvent (S1). The compound(s) of formula (I) may therefore constitute the entire first solvent or be present therein as a trace additive. The first solvent (S1) may, for example, comprise, based on the total weight of the first solvent (S1): 0.1 to 100 wt.% of i) the at least one compound of formula (I); and 0 to 99.9 wt.% of ii) at least one aprotic compound which does not correspond to formula (I) and which has a boiling point of at least 150°C, measured at a pressure of 1 bar.

[0099] In one embodiment, the first solvent (S1) comprises, based on the total weight of the first solvent (S1): from 0.5 to 70 wt.% of i) the at least one compound according to formula (I), and from 30 to 99.5 wt.% of ii) at least one aprotic compound which does not correspond to formula (I) and which has a boiling point of at least 150°C, measured at a pressure of 1 bar. In another embodiment, the first solvent (S1) comprises, based on the total weight of the first solvent (S1): from 10 to 70 wt.% of i) the at least one compound according to formula (I); and from 30 to 90 wt.% of ii) at least one aprotic compound which does not correspond to formula (I) and which has a boiling point of at least 150°C, measured at a pressure of 1 bar.

[0100] In exemplary compounds according to formula (IA): A2 is C3-C6 alkylene or C6 arylene; and each R is independently a C1-C2 alkyl group. In other exemplary compounds according to formula (IA): A2 is -(CH2)m- or C6 arylene, where m is an integer from 3 to 6; and each R is independently a C1-C2 alkyl group.

[0101] In certain embodiments of formula (IA), each R substituent is the same. In other embodiments of formula (IA), each R is methyl. Exemplary compounds according to formula (IA), which can be used individually or in combination, are: dimethyl phthalate, diethyl phthalate, dimethyl glutarate, diethyl glutarate, dimethyl adipate, and diethyl adipate. The at least one compound according to formula (IA) can be selected, for example, from: dimethyl phthalate, dimethyl glutarate, and dimethyl adipate. In a further illustrative embodiment, the at least one compound according to formula (IA) comprises dimethyl phthalate.

[0102] The first solvent (S1) may comprise ii) at least one aprotic compound which does not correspond to formula (IA) and which has a boiling point of at least 150 °C, measured at a pressure of 1 bar. In one embodiment, the compounds that can form part ii) of the first solvent (S1) and that can be used alone or in combination include the following: 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'-dimethylpropanamide (MDP), N-formylmorpholine, N-acetylmorpholine, phenylmethanol, 2,6-xylenol, 4-methylphenol, hexamethylphosphoramide and dimethyl sulfoxide (DMSO).

[0103] In another embodiment, the compounds that can form part ii) of the first solvent (S1), which can be used alone or in combination, include: γ-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'-dimethylpropanamide (MDP). In a further embodiment, part ii) of the first solvent (S1) comprises γ-butyrolactone (GBL).

[0104] The process of this embodiment comprises step (b)) of diluting the first polymer solution with a second solvent (S2) to produce a second solution of the polyamide-imide polymer. The second solvent (S2) differs from the first solvent (S1), meaning that the compositions of the first and second solvents are not identical. The first (S1) and second (S2) solvents may, as such, consist of different compounds. It is also contemplated that the second solvent (S2) may contain the same components as the first solvent (S1), but differ from it in the weight ratio of these components.

[0105] The second solvent (S2) contains at least one compound of formula (IA): ROOC-A 2 -COOR (IA) where: A 2 a C3-C8 alkylene or a C6 arylene; and, each R is independently a C1-C2 alkyl group.

[0106] If no compound of formula (IA) is present in the first solvent (S1), the second solvent (S2) must contain such a compound. The presence of a compound of formula (IA) in this first solvent (S1) does not preclude the presence of such a compound in the diluting second solvent (S2).

[0107] The above considerations for the substituents A2 and R of formula (IA) apply when a compound according to this formula is present in the second solvent (S2). Compounds that can be used individually or in combination with the second solvent (S2) 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) comprises dimethyl phthalate.

[0108] Regardless of the presence of a compound of formula (IA) in the second solvent (S2), the second solvent (S2) may contain at least one non-polar compound having a boiling point of less than 225°C. Compounds that satisfy this boiling point requirement can typically be selected from: linear C1-C8 alkanes, cyclic alkanes, branched C1-C8 alkanes, C1-C8 alkyl halides, aromatics, and mixtures thereof. Further exemplary compounds that satisfy this boiling point requirement and that can be used alone or in combination are: n-pentane, n-hexane, cyclohexane, n-heptane, isooctane, trimethylpentane, toluene, xylene, benzene, and naphthenes. In one embodiment, the second solvent (S2) comprises xylene.

[0109] In the processes described above, the aim is not to limit the amount of the second solvent (S2) added in the dilution step; rather, dilution generally allows a stable solution with a processable viscosity to be achieved. However, it can be disadvantageous to dilute the first polymer solution to such an extent that the subsequent recovery of the solid polyamide-imide from the polymer solution requires considerable energy expenditure for the evaporation of the solvents. Thus, it is typical for dilution step b) to yield a polyamide-imide solution having a solids content of 20 to 50 wt. %, for example, 25 to 45 wt. % or 25 to 40 wt. %, determined according to DIN 53216.

[0110] The polymer solutions defined herein are suitable for coating conductive wires to provide them with an insulating layer. While the following discussion focuses on this use of polyamide-imides, this does not preclude the use of the polyamide-imide solution as a varnish for other substrates or the use of the polyamide-imide in the form of a free-standing film, suitable, for example, for phase insulation and coil wrapping.

[0111] The resulting polymer solutions can be used as such to form one or more insulating coating layers on a conductive wire. However, in certain embodiments, a coating composition is applied to the conductive wire, comprising the polymer solution along with adjuvants and additives that can impart improved properties to the compositions and the coatings obtained therefrom. The adjuvants and additives can, for example, impart one or more of the following properties to the insulating coating: improved tensile strength, improved elastic properties, improved elastic recovery, longer activated working time, faster drying time, improved thermal conductivity, and reduced thermal expansion coefficient.These auxiliaries and additives include: tougheners, plasticizers, stabilizers, including UV stabilizers, adhesion promoters, flame retardants, lubricants, including polytetrafluoroethylene (PTFE) and graphite, rheological aids and colorants such as pigments or dyes.

[0112] A "plasticizer" as defined in this publication is a substance that reduces the viscosity of the composition and thus facilitates its processability. The plasticizer may constitute up to 10% or up to 5% by weight, based on the total weight of the composition, and is typically selected from: diurethanes; Ethers of monofunctional, linear or branched C4-C16 alcohols, such as Cetiol OE (available from BASF), esters of abietic acid, butyric acid, thiobutyric acid, acetic acid, propionic acid esters and citric acid, esters based on nitrocellulose and polyvinyl acetate, fatty acid esters, dicarboxylic acid esters, esters of OH group-bearing or epoxidized fatty acids, glycolic acid esters, benzoic acid esters, phosphoric acid esters, sulfonic acid esters, trimellitic acid esters, polyether plasticizers, such as end-capped polyethylene or polypropylene glycols, polystyrene, hydrocarbon plasticizers, chlorinated paraffin and mixtures thereof.

[0113] For the purposes of this publication, "stabilizers" are understood to mean antioxidants, heat stabilizers, or hydrolysis stabilizers. The stabilizers may total up to 10 wt.% or up to 5 wt.%, based on the total weight of the composition. Commercially available examples of stabilizers that may be used include: hindered phenols, thioethers, benzotriazoles, benzophenones, hydroquinones, benzoates, cyanoacrylates, acrylates, hindered amine light stabilizers (HALS), phosphorus, sulfur, and mixtures thereof.

[0114] The coating compositions may contain a rheology control agent, with electrically non-conductive fillers being one example. There is no intention to limit the shape of the particles used as non-conductive fillers: particles that are acicular, spherical, ellipsoidal, cylindrical, bead-shaped, cubic, or platelet-shaped may be used individually or in combination. Furthermore, it is envisaged that agglomerates of more than one particle type may be used. Nor is there any intention to limit the size of the particles used as non-conductive fillers. However, such non-conductive fillers typically have a volume-average particle size (Dv50) of 0.01 to 1500 µm, e.g., from 0.01 to 50 µm, as measured by laser diffraction / scattering methods.

[0115] Examples of non-conductive fillers include calcium carbonate, calcium oxide, calcium hydroxide (lime powder), precipitated and / or fumed silica, zeolites, bentonites, 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.

[0116] The inclusion of particulate inorganic oxides such as silicon dioxide and titanium dioxide can have benefits beyond simply controlling the rheology of the compositions. The oxides can also help improve thermal conductivity, reduce thermal expansion, and increase coating strength. Furthermore, they can prevent partial discharge erosion caused by the concentration of electric fields in the gaps between the insulating coating and the conducting wire.

[0117] To produce a coating composition, the polymer solution and the auxiliaries and additives are combined and mixed. Under certain circumstances, a multi-stage mixing process may be appropriate to ensure the homogeneity of the coating compositions. For example, silicon dioxide and titanium dioxide can be provided in colloidal form rather than in solid, particulate form for admixture into the coating compositions.

[0118] These auxiliaries and additives may be used in any combination and in any proportions, provided they do not impair the nature and essential properties of the coating composition. Although there may be exceptions in some cases, these auxiliaries and additives generally do not exceed 40% by weight of the total composition and generally do not constitute more than 30% by weight of the composition. In an alternative formulation, which is not intended to be mutually exclusive, the coating compositions may be formulated to have 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 so that it does not form bubbles (foam) during formation, mixing with any additives, and subsequent application and heat treatment.

[0119] As mentioned above, one aspect of the present disclosure is a method for producing an insulated wire, the method comprising: providing a conductive wire; coating the conductive wire with a polymer solution as defined hereinabove; and subjecting the coated conductive wire to a thermal treatment to remove solvents therefrom.

[0120] An example of conductive wires is, but is not limited to, magnet wires. The proposed wires can be formed from a variety of conductive materials, including: metallic material, e.g., metals, silver, gold, copper, platinum, palladium, molybdenum, aluminum, nickel, and tin; graphite; graphene; electrically conductive ceramics; and electrically conductive polymeric materials. The proposed wire can be made in one piece or assembled from multiple parts. The latter design includes wires composed of a multitude of microwires or nanowires, as well as wires composed of conductive particles that are sintered, welded, or agglomerated together.

[0121] The intended wire can have a variety of cross-sectional shapes depending on the intended use of the wire: for example, the wire can have a circular, elliptical, or rectangular cross-section. Regardless of this cross-sectional shape, the conductive wire can have a diameter of, for example, 0.01 to 5 mm, for example, 0.01 to 2 mm, or 0.01 to 1 mm.

[0122] According to the broadest process aspects of the present publication, the polymer solutions described above are applied to a substrate, e.g., the substrate of the conductive wire(s), and then thermally treated in situ. Before applying the solutions, it is often advisable to pretreat the surfaces in question to remove any foreign matter. This step may facilitate the subsequent adhesion of the solutions to them. Such treatments are known in the art and can be performed in one or more steps.For conductive metal substrates, the treatments may, for example, consist of one or more of the following processes: etching treatment with an acid suitable for the substrate and, optionally, an oxidizing agent; sonication; 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 or demineralized water. In cases where an aqueous alkaline degreasing bath is used, the degreaser remaining on the surface can be removed by rinsing the substrate surface with deionized or demineralized water.

[0123] In some embodiments, the adhesion of the solutions of the present publication to the optionally pretreated substrate can be facilitated by applying a primer. Primer compositions can be used to ensure effective fixation of the compositions to inactive substrates.

[0124] The solutions are then applied to the optionally pretreated, optionally primed surfaces of the substrate by conventional application methods such as: dipping, coating tools, roller coating, felt application and spraying methods including but not limited to air atomized spraying, air assisted spraying, airless spraying and high volume low pressure spraying.

[0125] It is recommended to apply the compositions to a surface with a wet film thickness of 10 to 500 µm. Applying thinner layers within this range is more economical and reduces the likelihood of damaging thick cured areas. However, great care must be taken when applying thinner layers to avoid the formation of discontinuous cured films.

[0126] Conventional curing ovens can be used to heat the coated wire. For effective drying and curing, such ovens can be maintained at a temperature of 300 to 700 °C, e.g., 400 to 600 °C. The appropriate temperature depends on the specific compounds present and the desired curing rate and can be determined in each individual case by a specialist, possibly through simple preliminary tests.

[0127] It should be noted that more than one layer of polyamide-imide may be applied to the substrate. For example, the polyamide-imide may be applied in 2 to 8 layers. If multiple layers are applied, each individual layer may be at least partially dried before the application of a subsequent layer such that the at least partially dried previous layer substantially retains its shape when exposed to the ambient conditions. By "substantially dimensionally stable" is meant that at least 50 volume percent, and typically at least 80 or 90 volume percent, of the at least partially dried layer retains its shape and does not flow or deform when exposed to the ambient conditions for 5 minutes.Under these circumstances, gravity generally has no significant influence on the shape of the at least partially cured or partially dried layer when exposed to ambient conditions.

[0128] It is further noted that the polyamide-imide coating may form one or more layers of a multilayer system in which the substrate is also provided with one or more coating layers comprising other polymers: in this context, polyesters, polyurethanes, polyimides and polyvinyl formal may be mentioned.

[0129] The following examples serve to illustrate this publication and are not intended to limit the scope of the publication in any way. EXAMPLES

[0130] The following commercial product was used in the following examples: DBE: Mixture of the dibasic esters dimethyl glutarate, dimethyl succinate and dimethyl adipate, available as Rhodiasolv® RPDE from Solvay.

[0131] In the examples below, the following test methods were used: Viscosity (η): Viscosity measurements were performed using a Brookfield DV-IIT LV cone and plate viscometer. The viscometer was equipped with a CP-35 cone and operated at a shear rate of 100 s-1 and a temperature of 23 °C. The formulation was filled into the viscometer with a volume of 0.5 ml and incubated at the specified shear rate before data acquisition. Solids content: The solids content is the weight of the residue obtained after baking 1 g of wire enamel at a temperature of 180 °C for 1 hour according to DIN 53 216. The solids content is expressed as a percentage by weight of the total weight of the wire enamel. Example 1:

[0132] 100 g of γ-buryrolactone (GBL), 236 g of dimethyl phthalate (DMP), 1 g of triethylenediamine, and 6 g of benzyl alcohol were added to a dry glass reactor. 128 g of trimellitic anhydride (TMA), 68 g of methylenediphenyl diisocyanate (MDI), and 71 g of toluene diisocyanate (TDI) were added while stirring at 40 °C. The mixture was then heated to 90 °C over a period of two hours and held at 90 °C for four hours until CO2 evolution ceased. The reaction temperature was increased to 150 °C, and the reaction was held at 150 °C for another two hours. Subsequently, 195 g of dimethyl phthalate (DMP) and 195 g of xylene were added, and the mixture was cooled to room temperature.

[0133] The resulting wire enamel had a solids content of 35.0 wt.% and a viscosity of 7100 mPas. Dimethyl phthalate (DMP) accounted for 59.3 wt.% of the total weight of the solvents. The diisocyanate component consisted of 40 mol.% MDI and 60 mol.% TDI. Example 2:

[0134] 380 g of γ-buryrolactone (GBL), 1 g of triethylenediamine, and 15 g of benzyl alcohol were added to 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 with stirring at 40 °C. The mixture was then heated to 90 °C over a period of two hours and held at 90 °C for four hours until CO2 evolution ceased. The reaction temperature was increased to 150 °C, and the reaction was held at 150 °C for another two hours. 300 g of dimethyl phthalate (DMP) was added, and the mixture was cooled to room temperature.

[0135] The resulting wire enamel had a solids content of 37.0 wt.% and a viscosity of 2800 mPas. Dimethyl phthalate (DMP) accounted for 44.1 wt.% of the total weight of the solvents. The diisocyanate component consisted of 60 mol.% MDI and 40 mol.% TDI. Example 3:

[0136] 470 g of γ-buryrolactone (GBL), 150 g of dimethyl phthalate (DMP), 1 g of triethylenediamine, and 14 g of benzyl alcohol were added to a dry glass reactor. 136 g of trimellitic anhydride (TMA), 109 g of methylenediphenyl diisocyanate (MDI), and 50 g of toluene diisocyanate (TDI) were added with stirring at 40 °C. The mixture was then heated to 90 °C over a period of two hours and held at 90 °C for four hours until CO2 evolution ceased. The reaction temperature was increased to 150 °C, and the reaction was held at 150 °C for another two hours. 70 g of xylene was added, and the mixture was cooled to room temperature.

[0137] The resulting wire enamel had a solids content of 35.0 wt.% and a viscosity of 1150 mPas. Dimethyl phthalate (DMP) accounted for 21.7 wt.% of the total weight of the solvents. The diisocyanate component consisted of 60 mol.% MDI and 40 mol.% TDI. Example 4:

[0138] 390 g of γ-buryrolactone (GBL), 1 g of triethylenediamine, and 15 g of benzyl alcohol were added to 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 with stirring at 40 °C. The mixture was then heated to 90 °C over a period of two hours and held at 90 °C for four hours until CO2 evolution ceased. The reaction temperature was increased to 150 °C, and the reaction was held at 150 °C for another two hours. 20 g of dimethyl phthalate (DMP), 180 g of γ-buryrolactone (GBL), and 90 g of xylene were added, and the mixture was cooled to room temperature.

[0139] The resulting wire enamel had a solids content of 31.0 wt.% and a viscosity of 700 mPas. Dimethyl phthalate (DMP) accounted for 2.9% of the total weight of the solvents. The diisocyanate component consisted of 60 mol.% MDI and 40 mol.% TDI. Example 5

[0140] 380 g of γ-buryrolactone (GBL), 1 g of triethylenediamine, and 15 g of benzyl alcohol were added to 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 with stirring at 40 °C. The mixture was then heated to 90 °C over a period of two hours and held at 90 °C for four hours until CO2 evolution ceased. The reaction temperature was increased to 150 °C, and the reaction was held at 150 °C for another two hours. 200 g of dimethyl phthalate (DMP) and 100 g of dibasic ester (DBE) were added, and the mixture was cooled to room temperature.

[0141] The resulting wire enamel had a solids content of 35.3 wt.% and a viscosity of 1930 mPas. Dimethyl phthalate (DMP) accounted for 29.4% of the total solvent weight. Dibasic ester (DBE) accounted for 14.7% of the total solvent weight. The diisocyanate component consisted of 60 mol.% MDI and 40 mol.% TDI. Example 6

[0142] 380 g of γ-buryrolactone (GBL), 1 g of triethylenediamine, and 15 g of benzyl alcohol were added to a dry glass reactor. 138 g of trimellitic anhydride (TMA), 126 g of methylenediphenyl diisocyanate (MDI), and 40 g of toluene diisocyanate (TDI) were added with stirring at 40 °C. The mixture was then heated to 90 °C over a period of two hours and held at 90 °C for four hours until CO2 evolution ceased. The reaction temperature was increased to 150 °C, and the reaction was held at 150 °C for another two hours. 200 g of dimethyl phthalate (DMP) and 100 g of dibasic ester (DBE) were added, and the mixture was cooled to room temperature.

[0143] The resulting wire enamel had a solids content of 34.8 wt.% and a viscosity of 1770 mPas. Dimethyl phthalate (DMP) accounted for 29.4% of the total solvent weight. Dibasic ester (DBE) accounted for 14.7% of the total solvent weight. The diisocyanate component consisted of 68 mol.% MDI and 32 mol.% TDI. Example 7

[0144] 280 g of γ-buryrolactone (GBL), 100 g of dimethyl phthalate (DMP), 1 g of triethylenediamine, and 15 g of benzyl alcohol were added to 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 with stirring at 40 °C. The mixture was then heated to 90 °C over a period of two hours and held at 90 °C for four hours until CO2 evolution ceased. The reaction temperature was increased to 150 °C, and the reaction was held at 150 °C for another two hours. 130 g of dimethyl phthalate (DMP) and 170 g of dibasic ester (DBE) were added, and the mixture was cooled to room temperature.

[0145] The resulting wire enamel had a solids content of 35.1 wt.% and a viscosity of 2250 mPas. Dimethyl phthalate (DMP) accounted for 33.8% of the total solvent weight. Dibasic ester (DBE) accounted for 25.0% of the total solvent weight. The diisocyanate component consisted of 60 mol% MDI and 40 mol% TDI.

[0146] Although at least one exemplary embodiment has been presented in the foregoing detailed description, it should be understood that numerous variations exist. It should also be understood that the exemplary embodiment or embodiments are only examples and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing detailed description is intended to provide one skilled in the art with a convenient guide for implementing an exemplary embodiment. It should be understood that various changes in the function and arrangement of the elements described in an exemplary embodiment may be made without departing from the scope of the appended claims.Furthermore, all combinations of the above-mentioned ingredients, compositions, process steps, formulation steps, etc. are hereby expressly contemplated for use in various non-limited embodiments, even if such combinations are not expressly described in the same or similar sections.

[0147] With respect to all Markush groups used herein to describe particular features or aspects of various embodiments, different, unique, and / or unexpected results may be achieved by each member of the respective Markush group independently of all other Markush members. Each member of a Markush group may be used individually or in combination and provides reasonable support for particular embodiments within the scope of the appended claims.

[0148] Furthermore, all ranges and subranges referred to in describing various embodiments of the present invention independently and jointly fall within the scope of the appended claims and are to be understood as describing and encompassing all ranges, including whole and / or fractional values ​​therein, even if such values ​​are not expressly stated herein. One skilled in the art will readily recognize that the ranges and subranges enumerated herein sufficiently describe and enable various embodiments of the present invention, and that these ranges and subranges may be further subdivided into respective halves, thirds, quarters, fifths, etc. As just one example, a range "from 0.1 to 0.9" may be further subdivided 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, which individually and collectively fall within the scope of the appended claims and which may be relied upon individually and / or collectively and which provide reasonable support for particular embodiments within the scope of the appended claims. With regard to language defining or modifying a range, such as "at least," "greater than," "less than," "not more than," and the like, it is to be understood that these language include sub-ranges and / or an upper or lower limit. As a further example, a range of "at least 10" naturally includes a sub-range of at least 10 to 35, a sub-range of at least 10 to 25, a sub-range of 25 to 35, etc.and each subrange may be relied upon individually and / or collectively and will provide reasonable support for particular embodiments within the scope of the appended claims. A single number within a disclosed range may be relied upon as a basis for particular embodiments within the scope of the appended claims. For example, a range "from 1 to 9" includes various single integers, such as 3, as well as single numbers with a decimal point (or fraction), such as 4.1, that may be relied upon and will provide reasonable support for particular embodiments within the scope of the appended claims. Finally, it is understood that the term "about," with respect to the numbers and ranges described herein, is used to denote values ​​within the standard error, equivalence function, efficacy, final loading, etc.used as understood by those skilled in the art having the relevant conventional techniques and methods for formulating and / or using compounds and compositions as described herein. Thus, the term "about" may refer to a value within 10, alternatively within 5, alternatively within 1, alternatively within 0.5, alternatively within 0.1% of the enumerated value or range.

[0149] While the present disclosure has been described with reference to specific embodiments, it is evident that numerous other forms and modifications will be apparent to those skilled in the art. The appended claims and this disclosure should be broadly construed to cover all obvious forms and modifications falling within the true scope of the present disclosure. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 3,860,559

[0004] JP 58-180532

[0004] DE 102014104223A1

[0007] JP 2008-285660A

[0008] JP 2012-62355A

[0008] US 20060240255A1

[0008] JP 2011-210645A

[0008] Cited non-patent literature

[0000] DIN 53216

[0029]

Claims

[1] A polyamide-imide solution comprising: a polymer containing the 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, from 0.1 to 100 wt.% i) at least one compound according to formula (IA) ROOC-A 2 -COOR (IA) where: A 2 a C3-C8 alkylene or a C6 arylene; and, each R is independently a C1-C2 alkyl group; and, from 0 to 99.9 wt.% ii) at least one aprotic compound which does not correspond to formula (IA) and which has a boiling point of at least 150 °C, measured at 1 bar pressure. [2] A process for preparing a polyamide-imide solution, the process comprising: a) Preparation of a first solution of a polyamide-imide polymer by reaction 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: monomeric methylenediphenyl diisocyanate (MDI), polymeric methylenediphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (H-MDI), xylene diisocyanate (XDI), hydrogenated xylene diisocyanate, tolylene diisocyanate (TDI), diphenylsulfone diisocyanate (SDI), m-xylylene diisocyanate, and mixtures thereof; and, 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 solution of the polyamide-imide polymer, 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) where: A 2 a C3-C8 alkylene or a C6 arylene; and, each R is independently a C1-C2 alkyl group. [3] The method of claim 2, wherein the first solvent comprises: i) at least one compound according to formula (IA); and (ii) at least one aprotic compound not corresponding to formula (IA) and having a boiling point of at least 150 °C, measured at a pressure of 1 bar. [4] A process according to claim 2 or 3, wherein the first solvent comprises, based on the total weight of the first solvent: from 0.1 to 100 wt.% i) of the at least one compound according to formula (IA); and from 0 to 99.9 wt.% ii) of the at least one aprotic compound. [5] A process according to any one of claims 2 to 4, wherein the first solvent comprises, based on the total weight of the solvent: from 0.5 to 70 wt.% i) of the at least one compound according to formula (IA); and from 30 to 99.5 wt.% ii) of the at least one aprotic compound. [6] A process according to any one of claims 2 to 5, wherein, based on the total weight of the solvent, the first solvent consists of: from 10 to 70 wt.% i) of the at least one compound according to formula (IA); and from 30 to 90 wt.% of ii) the at least one aprotic compound. [7] Process according to any one of claims 2 to 6, wherein in formula (IA): A 2 a C3-C6 alkylene group or a C6 arylene group; and each R is independently a C1-C2 alkyl group. [8] A process according to any one of claims 2 to 7, wherein in formula (IA): A 2 either -(CH2) m - where m is an integer from 3 to 6, or a C6-arylene, and each R is independently a C1-C2 alkyl group. [9] Process according to any one of claims 2 to 8, 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. [10] Process according to any one of claims 2 to 9, wherein the at least one compound according to formula (IA) is selected from: dimethyl phthalate, dimethyl glutarate, dimethyl adipate and mixtures thereof. [11] A process according to any one of claims 2 to 10, wherein the at least one compound according to formula (IA) comprises dimethyl phthalate. [12] A process according to any one of claims 2 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 1 bar pressure. [13] A process according to any one of claims 2 to 12, wherein ii) the at least one aprotic compound is selected from: 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'-dimethylpropanamide (MDP) and mixtures thereof. [14] A process according to any one of claims 2 to 13, wherein the first solvent comprises γ-butyrolactone. [15] A process according to any one of claims 2 to 14, wherein the diisocyanate component comprises at least one diisocyanate selected from: monomeric methylenediphenyl diisocyanate (MDI), polymeric methylenediphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), tolylene diisocyanate (TDI) and mixtures thereof. [16] A process according to any one of claims 2 to 15, wherein the diisocyanate component comprises, based on the total moles of diisocyanate: from 10 to 90 mol% monomeric methylenediphenyl diisocyanate (MDI); and, from 90 to 10 mol% of at least one diisocyanate selected from: polymeric methylene diphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (H-MDI), xylene diisocyanate (XDI), hydrogenated xylene diisocyanate, tolylene diisocyanate (TDI), diphenylsulfone diisocyanate (SDI), m-xylylene diisocyanate and mixtures thereof. [17] A process according to any one of claims 2 to 16, wherein the diisocyanate component comprises, based on the total moles of diisocyanate: from 30 to 70 mol% monomeric methylenediphenyl diisocyanate (MDI); and, from 70 to 30 mol% of at least one diisocyanate selected from: polymeric methylenediphenyl diisocyanate (pMDI), toluene diisocyanate (TDI) and mixtures thereof. [18] A process according to any one of claims 2 to 17, wherein the diisocyanate component comprises, based on the total moles of diisocyanate: from 35 to 65 mol% monomeric methylenediphenyl diisocyanate (MDI); and from 65 to 35 mol% toluene diisocyanate (TDI). [19] A process according to any one of claims 2 to 18, wherein, based on the total number of moles of diisocyanate, the diisocyanate component consists of: from 10 to 100 mol% tolylene diisocyanate (TDI); and from 0 to 90 mol% of at least one diisocyanate selected from: monomeric methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI) and mixtures thereof. [20] A process according to any one of claims 2 to 19, wherein, based on the total number of moles of diisocyanate, the diisocyanate component consists of: from 10 to 100 mol% hexamethylene diisocyanate (HDI); and from 0 to 90 mol% of at least one diisocyanate selected from: monomeric methylenediphenyl diisocyanate (MDI), polymeric methylenediphenyl diisocyanate (pMDI), tolylene diisocyanate (TDI) and mixtures thereof. [21] A process according to any one of claims 2 to 20, wherein the anhydride component comprises, based on the total moles of anhydride: from 80 to 100 mol% trimellitic anhydride (TMA); and from 0 to 20 mol% of at least one tetracarboxylic acid dianhydride. [22] A process according to any one of claims 2 to 21, wherein, based on the total number of moles of anhydride, the anhydride component consists of: from 80 to 100 mol% trimellitic anhydride (TMA); and from 0 to 20 mol% of at least one anhydride selected from: 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride (DSDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic dianhydride (ODPA), butanetetracarboxylic dianhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride and mixtures thereof. [23] A method according to any one of claims 2 to 22, wherein the reacting components further comprise: a3) at least one polycarboxylic acid. [24] A process according to any one of claims 2 to 23, wherein the catalyst is a tertiary amine. [25] Process according to any one of claims 2 to 24, wherein the second solvent comprises at least one compound according to formula (IA): ROOC-A2-COOR (IA) where: A 2 a C3-C8 alkylene or a C6 arylene; and, each R is independently a C1-C2 alkyl group. [26] A process according to any one of claims 2 to 25, wherein the second solvent comprises at least one non-polar compound having a boiling point of less than 225°C. [27] The method of claim 26, wherein the second solvent comprises at least one compound selected from: Linear C 1- C8 alkanes, cyclic alkanes, branched C1-C8 alkanes, C1-C8 alkyl halides, aromatics and mixtures thereof. [28] A process according to claim 26 or 27, wherein the second solvent comprises at least one compound selected from: n-pentane, n-hexane, cyclohexane, n-heptane, isooctane, trimethylpentane, toluene, xylene, benzene, naphthenes and mixtures thereof. [29] A process according to any one of claims 26 to 29, wherein the second solvent comprises xylene. [30] Polyamide-imide solution obtained by the process according to any one of claims 2 to 29. [31] Polyamide-imide solution according to claim 30 having a solids content of 20 to 50 wt.%, determined according to DIN 53216. [32] A method of manufacturing an insulated wire, comprising: Providing a conductive wire; Coating the conductive wire with a polyamide-imide solution according to claim 30 or 31; and thermal treatment of the coated wire to remove the solvent. [33] A process for preparing a polyamide-imide solution, the process comprising: a) Reaction at a temperature of 60 to 180 °C and in the presence of a solvent and a catalyst: a1) a diisocyanate component comprising at least one diisocyanate selected from: monomeric methylenediphenyl diisocyanate (MDI), polymeric methylenediphenyl diisocyanate (pMDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (H-MDI), xylene diisocyanate (XDI), hydrogenated xylene diisocyanate, tolylene diisocyanate (TDI), diphenylsulfone diisocyanate (SDI), m-xylylene diisocyanate, and mixtures thereof; and a2) an anhydride component comprising trimellitic anhydride (TMA) for preparing a solution of a polyamide-imide polymer, wherein the solvent comprises: from 0.1 to 100 wt.% i) of the at least one compound according to formula (I) ROOC-A 1 -COOR (I) where: A 1 a C1-C8 alkylene or a C6 arylene; and each R is independently a C1-C2 alkyl group; and from 0 to 99.9% by weight of ii) at least one aprotic compound which does not correspond to formula (I) and which has a boiling point of at least 150 °C, measured at 1 bar pressure.