Alternative solvent blends for use in forming and applying thermosetting polyamide-imide

Abstract

Solvent blends useful for the formulation and application of polyamide-imide resins are described. A solvent blend may include a primary solvent and a co-solvent, wherein the primary solvent is provided at a higher concentration than the co-solvent. The primary solvent may include one or more first materials, wherein the first materials include at least one of 1,3- Dimethyl-2-imidazolidinone, N-Cyclohexyl-2-pyrrolidone, or N,N'-Dimethyl propyleneurea. The co-solvent may include one or more second materials different than the one or more first materials, wherein the second materials include at least one of N,N-Diethylacetamide, N,NDimethylpropionamide, gamma-butyrolactone, N-butylpyrrolidinone, N-Methylmorpholine, 2,5,7,10-Tetraoxaundecane, 3-Methoxy-N,N-dimethyl propenamide, Anisole, Cyrene, 1,1,3,3- Tetramethylurea, Diethylene Glycol Diethyl Ether, 1,3-Dimethyl-2-imidazolidinone, NCyclohexyl- 2-pyrrolidone, or N,N'-Dimethyl propyleneurea.

Description

ALTERNATIVE SOLVENT BLENDS FOR USE IN FORMING AND APPLYINGTHERMOSETTING POLYAMIDE-IMIDECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application No. 63 / 644,416, filed May 8, 2024 and entitled “Low Toxicity Solvent Blends for Use in Forming and Applying Thermosetting Resins’' and U.S. Provisional Application No. 63 / 679,212, filed August 5, 2024 and entitled “Low Toxicity Solvent Blends for Use in Forming and Applying Thermosetting Polyamide-imide” the contents of which are incorporated by reference herein in their entirety.TECHNICAL FIELD

[0002] Embodiments of the disclosure relate generally to solvents used in conj unction with thermosetting polyamide-imide resins and, more particularly, to relatively low toxicity solvent blends for use in the formation and application of thermosetting polyamide-imide resins.BACKGROUND

[0003] Thermosetting polyamide-imide (“PAI”) is utilized in a wide variety of applications including, but not limited to, insulations, coatings, and adhesives. For example. PAI is often used to form insulation on magnet wire or winding wire intended for use in motors, generators, transformers, or other electrical devices. Thermosetting PAI may provide enhanced heat resistance, adhesion, and structural integrity relative to many thermoplastic resins. A thermosetting resin strengthens when cured by forming chemical bonds that make it impossible to remold. In other words, a thermosetting resin irreversibly cures when subjected to heat or another suitable curing technique. As such, thermosetting resins are typically suspended within solvents prior to application. The solvent, or a substantial portion of the solvent, is then evaporated as a thermosetting resin is cured following application.

[0004] Additionally, thermosetting resins are typically manufactured or synthesized within the presence of solvents. For example, a polyamide-imide (“PAI”) or its precursor (i.e., a polyamide amic acid) may be formed by reacting a suitable acid chloride (e.g., trimellitic anhydride chloride or “TAC”) or anhydride (e.g.. trimellitic anhydride or “TMA”) with a suitable diamine (e.g., 4,4’ -methylenedianiline or “MDA”) or diisocyanate (e.g., 4, d’methylene diisocyanate or “MDI”) within solvent to form a solution or dispersion. The PAI precursor solution or dispersion may subsequently be cured to form a PAI film coating. Another option involves adding PAI solids into solvent to form a suitable dispersion.

[0005] The most commonly utilized solvents for the synthesis and application of PAI are N-methyl pyrrolidone (“NMP”, CAS no [872-50-4]) and N,N-Dimethylacetamide (“DMAc”, CAS no [127-19-5]). However, NMP and DMAc are found to be materials s that could lead to a certain health risks. In particular, NMP is known as a teratogenic material - a material that can cause birth defects - making is a substance of high concern. Further, bans or prohibitions of NMP are currently being considered by the United States Environmental Protection Agency and other global governmental bodies and agencies. Accordingly, there is an opportunity for the utilization of relatively low toxicity solvents or solvents with potentially lower adverse health effects at typical exposure limits. In particular, there is an opportunity to utilize alternative solvent blends in the synthesis and application of PAI thermosetting resins.DETAILED DESCRIPTION

[0006] Various embodiments of the present disclosure are directed to relatively low toxicity solvent blends that may be utilized in the manufacture or synthesis and / or in the application of thermosetting polyamide-imide (“PAI”). According to an aspect of the disclosure, a solvent blend may include a primary solvent and a co-solvent or secondary solvent. Additionally, the primary solvent may be provided in a higher concentration (e.g., a higher weight percentage) than the co-solvent. The primary solvent may include one or more of l,3-Dimethyl-2-imidazolidinone (“DMI”, CAS no [80-73-9]), N-Cyclohexyl-2-pyrrolidone (“CHP”, CAS no [6837-24-7]), or N.N’-Dimethyl propyleneurea (“DMPU”, CAS no [7226- 23-5]). The co-solvent may be different from the primary solvent and may include one or moreof N,N-Diethylacetamide (“DEAc”, CAS no [685-91-6]), N,N-Dimethylpropionamide (‘ DMPA”, CAS no [758-96-3]), gamma-butyrolactone (“GBL”, CAS no [96-48-0]), N- butylpyrrolidinone (“NBP”, CAS no [3470-98-2]), A-Methylmorpholine (“NMM”, CAS no [109-02-4]), 2,5,7,10-Tetraoxaundecane (TOU; Bis(2-methoxyethoxy)methane) (“TOU”, CAS no [4431-83-3]), 3-Methoxy-N,N-dimethyl propenamide ('‘MO-MPA”, CAS no [53185- 52-7]), Anisole (CAS no [100-66-3]), Cyrene (CAS no [53716-82-8]), 1,1,3,3-Tetramethylurea (“TMU”, CAS no [632-22-4]), Diethylene Gly col Diethyl Ether (“DEGDE”, CAS no [112-36- 7]). DMI, CHP, or DMPU.

[0007] As desired in various embodiments, any suitable blend ratio between a primary solvent and a co-solvent can be utilized as long as the primary solvent is provided in a higher concentration. For example, the primary solvent may constitute greater than 50% and up to 99% by weight of a blend. In other embodiments, the primary solvent may constitute approximately 51 , 55, 60, 65, 70, 75, 80, 85, 90, 95, 98, or 99% by weight of a blend, a concentration percentage included in a range between any two of the above values (e.g., between 55 and 70%, etc.), or a concentration percentage included in a range bounded on a minimum end by one of the above values (e.g., at least 55%, etc.). For certain solvent blends, increasing the concentration of primary solvent may result in improved solubility properties. Increasing the concentration of co-solvent may result in lower cost for a solvent blend. Additionally, certain co-solvents (e.g., GBL) have been found to improve the solubility of anhydrides in some cases, resulting in more efficient overall synthesis.

[0008] In certain embodiments, an inventive solvent blend as described herein may be utilized during the synthesis or formulation of a thermosetting PAI resin. For example, a PAI precursor may be synthesized within a solvent blend. In one example embodiment, a PAI precursor (i.e., a polyamide amic acid) may be formed by reacting a suitable acid chloride (e.g., trimellitic anhydride chloride or “TAC”) or anhydride (e.g., trimellitic anhydride or “TMA”) with a suitable diamine (e.g., 4,4’-methylenedianiline or “MDA”) or diisocyanate (e.g., 4, d’methylene diisocyanate or “MDI”) within a solvent blend to form a solution or dispersion. The PAI precursor solution or dispersion may subsequently be cured to form PAI solid or a PAI film layer.

[0009] In other embodiments, an inventive solvent blend as described herein may be utilized during the application of a thermosetting resin. For example, PAI or its precursor may be dissolved or suspended within a solvent blend. The resulting mixture or varnish may beapplied within a desired application (e.g., as a wire insulation layer, as a protective coating, etc.) via any number of suitable devices (e.g., application dies, etc.) and subsequently cured to form a polymeric layer. A wide variety of suitable devices may be utilized to cure an applied thermosetting varnish, such as heat curing (e.g., curing in an oven, etc.), ultraviolet curing, etc. During the curing process, at least a portion of the solvent may be evaporated or otherwise removed.

[0010] As a result of utilizing one or more of the solvent blends described herein, the use of NMP, DMAc and other toxic solvents may be reduced and / or eliminated while still permitting desired synthesis and application of thermosetting resins. In other words, the solvent blends are designed to be less hazardous than NMP and DMAc. The solvent blends discussed herein are referred to as low toxicity solvent blends. For purposes of this disclosure, the term ‘"low toxicity” means less toxic or relatively less toxic than conventional solvents used in the magnet wire industry, particularly NMP and N,N-dimethyl acetamide (“DMAc”). Referring to a solvent blend as a low toxicity blend does not mean that the blend is nontoxic. Further, use of solvent blends that incorporate both a primary solvent and a secondary solvent allow the overall solution to provide or improve the desired properties (e.g., material solubility, shelf life of varnishes or enamels, curing rate for forming PAI solid, film forming performance, varnish or enamel rheological properties, PAI-insulated wire properties, etc.) while lowering the overall cost relative to certain single material solvents.

[0011] Embodiments of the disclosure now will be described more fully hereinafter in the following description. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0012] Various embodiments of the present disclosure are directed to relatively low7toxicity solvent blends that may be utilized in the manufacture or synthesis and / or in the application of thermosetting PAI resins. According to an aspect of the disclosure, a solvent blend may include a primary solvent and a co-solvent or secondary solvent. Additionally, the primary' solvent may be provided in a higher concentration than the co-solvent.

[0013] A wide variety of primary solvents may be utilized in various embodiments of the disclosure. According to an aspect of the disclosure, the primary solvent may include at leastone of L3-Dimethyl-2-imidazolidinone ( ‘DMI”), N-Cyclohexyl-2-pyrrolidone ("CHP"). or N,N’ -Dimethyl propyleneurea (“DMPU”). In other words, the primary solvent may include one or more first materials, and the first materials may include at least one of DMI, CHP, or DMPU. In certain embodiments, a primary solvent for inclusion in a solvent blend may be formed from a single material. For example, the primary solvent may include all DMI, CHP, or DMPU. In other embodiments, the primary solvent may include a combination of materials. For example, a primary solvent may include a combination of two or more of DMI, CHP, or DMPU. As another example, a primary solvent may include at least one of DMI, CHP, or DMPU and another material other than those materials listed herein for use as co-solvents.

[0014] In the event that the primary7solvent is formed from a combination of materials, any suitable blend ratio of the constituent component materials may be utilized as desired in various embodiments. For example, in certain embodiments, each constituent component of a primary solvent may constitute approximately 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 99% by weight of the combination of materials, or a percentage amount included in a range between any two of the above values. In preferred embodiments, a combination of two components as a primary solvent will include a greater amount of a first component relative to a second component. For example, two primary solvent components may be blended at a ratio of 60:40, 70:30, 80:20, or 90: 10 by7weight of the components.

[0015] In certain embodiments, a solvent blend may include one of the example primary solvents listed above as a primary solvent and another of the example primary solvents listed above as a co-solvent. In other words, one or more of the primary7solvents listed above may be utilized as co-solvents in certain blends. A few examples of solvent blends that incorporate a combination of DMI, CHP. and / or DMPU are discussed in greater detail below. These examples include various blends of DMI and CHP; DMI and DMPU; and CHP and DMPU.

[0016] In other embodiments, a primary7solvent may include a combination of two or more of DMI, CHP, or DMPU, and the multi-component primary7solvent may be combined with a co-solvent. These same blends may be characterized as having a single primary solvent and multiple co-solvents where one of the co-solvents constitutes one of DMI, CHP, or DMPU. As one non-limiting example, a solvent blend may include DMI, CHP, and gamma-buty rolactone (“GBL”). Further, the DMI may constitute greater than 50% by weight of the overall blend. For instance the blend may include 50-80% by weight DMI, 10-25% by weight CHP, and 10- 25% by weight GBL, such as approximately 60% DMI, approximately 20% CHP, andapproximately 20% GBL by weight. Such a blend may be characterized as including a primary solvent of DMI and CHP with the primary solvent constituting approximately 80% by weight of the blend; and a co-sol vent of GBL constituting approximately 20% by weight of the blend. Alternatively, the blend may be characterized as including DMI as a primary’ solvent constituting approximately 60% by weight of the blend, CHP as a first co-solvent constituting approximately 20% by weight of the blend, and GBL as a second co-solvent constituting approximately 20% by weight of the blend.

[0017] Additionally, a wide variety of suitable co-solvents may be utilized as desired in various embodiments of the disclosure. According to an aspect of the disclosure, the co-solvent may include one or more components or materials that are different than those used for the primary- solvent. In other yvords. the co-solvent may include one or more second materials and each of the second materials may be different from each of the first material(s). Further, the co-solvent or secondary solvent may include at least one of N,N-Diethylacetamide (“DEAc”), N,N-Dimethylpropionamide (“DMPA”), gamma-butyrolactone (“GBL”), N- butylpyrrolidinone (“NBP”), / V-Methylmorpholine (“NMM”), 2,5,7, 10-Tetraoxaundecane (TOU; Bis(2-methoxyethoxy)methane) (“TOU”), 3-Methoxy-N,N-dimethyl propenamide (“MO-MPA”), Anisole, Cyrene, 1,1,3,3-Tetramethylurea (“TMU”), Diethylene Glycol Diethyl Ether (“DEGDE”), DMI, CHP, or DMPU. In certain embodiments, a co-solvent may be formed from a single material, such as all DEAc, DMPA, GBL, NBP, NMM, TOU, MO-MPA, Anisole, Cyrene, TMU, DEGDE, DMI, CHP, or DMPU. In other embodiments, a co-solvent for use in a solvent blend may include a combination of two or more of DEAc. DMPA, GBL. NBP, NMM, TOU, MO-MPA, Anisole, Cyrene, TMU, DEGDE, DMI, CHP, or DMPU. In the event that a co-solvent is formed from a combination of materials, any suitable blend ratio of the constituent component materials may be utilized as desired in various embodiments. For example, in certain embodiments, each constituent component of a co-solvent may constitute approximately 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 99% of the combination of materials, or a percentage amount included in a range betyveen any two of the above values. In certain preferred embodiments, multi-component co-solvents may be blended in approximately equal parts by weight. Alternatively, if a solvent blend includes a plurality of co-solvents, each of the co-solvents may constitute an approximately equal weight percentage of the overall blend, such as approximately 20% each, etc.

[0018] According to an aspect of the disclosure, a solvent blend may include a primary solvent provided in a higher concentration (e.g., a higher weight percentage, etc.) than a cosolvent. As desired in various embodiments, any suitable blend ratio between primary solvent and co-solvent may be utilized provided that the primary solvent is provided in a higher concentration. For the purposes of this disclosure, the term '‘higher concentration” means that the primary solvent is provided at a weight percentage of a solvent blend that is higher than the respective weight percentages of any individual co-solvents. In certain embodiments, the weight percentage of the primary solvent may exceed 50% of the total weight of a solvent blend. For example, the primary solvent may constitute greater than 50% and up to 99% by weight of a blend. In other embodiments, the primary solvent may constitute approximately 51, 55, 60, 65, 70, 75, 80, 85, 90, 95, 98, or 99% by weight of a blend, a concentration percentage included in a range between any two of the above values (e.g., between 55 and 70%, etc.), or a concentration percentage included in a range bounded on a minimum end by one of the above values (e.g., at least 55%, etc.). In various embodiments, a weight percentage ratio between primary solvent and co-solvent may be between approximately 95:5 and 55:45, such as a ratio of approximately 95:5, 90: 10, 85: 15, 80:20, 75:25, 70:30, 65:35, 60:40, 55:45, or a ratio included in a range between any two of the above values.

[0019] In other embodiments, a primary solvent may constitute less than 50% by weight of a blend provided that the primary solvent is provided in a higher concentration than any individual co-solvent incorporated into the blend. For example, a primary solvent may be combined with two co-solvents and the primary solvent may constitute a higher weight percentage of the blend than either of the co-solvents while still constituting less than 50% by weight of the overall blend. One example is a blend that includes 40% by weight of a primary solvent, 30% by weight of a first co-solvent, and 30% by weight of a second co-solvent.

[0020] In certain embodiments, a solvent blend may be formed from a combination of DMI, CHP, and or DMPU. In other words, as previously mentioned, a solvent blend may include a combination of chemicals listed above as suitable primary solvents. A first chemical in the blend may constitute a primary solvent while a second chemical constitutes a co-solvent. Blends of DMI, CHP, and DMPU may include any suitable weight ratio of the constituent components.

[0021] One example blend may include DMI as a primary solvent and CHP as a co-solvent. A ratio of primary solvent to co-solvent may be between 55:45 and 85: 15 by weight percentage.preferably between 75:25 and 85: 15 by weight percentage, such as approximately 80:20 by weight percentage. A PAI solid was produced from a PAI precursor or PAI solution using a blend of approximately 80% by weight of DMI and approximately 20% by weight of CHP. When applied as heavy build PAI insulation on magnet wire, the magnet wire passed applicable specifications and requirements established by the National Electrical Manufacturers Association (“NEMA”). Another example blend may include DMI as a primary solvent and DMPU as a co-solvent. A ratio of primary solvent to co-solvent may be between 55:45 and 85: 15 by weight percentage, preferably between 75:25 and 85: 15 by weight percentage, such as approximately 80:20 by weight percentage.

[0022] Another example blend may include CHP as a primary' solvent and DMI as a cosolvent. A ratio of primary solvent to co-solvent may be between 55:45 and 75:25 by weight percentage, preferably between 55:45 and 65:35 by weight percentage, such as approximately 60:40 by weight percentage. Yet another example blend may include CHP as a primary solvent and DMPU as a co-solvent. A ratio of primary solvent to co-solvent may be between 55:45 and 75:25 by weight percentage, preferably between 55:45 and 65:35 by weight percentage, such as approximately 60:40 by weight percentage.

[0023] Another example blend may include DMPU as a primary solvent and DMI as a cosolvent. A ratio of primary' solvent to co-solvent may be between 55:45 and 85:15 by weight percentage, preferably between 60:40 and 80:20 by weight percentage, such as approximately 70:30 by weight percentage. Yet another example blend may include DMPU as a primary solvent and CHP as a co-solvent. A ratio of primary solvent to co-solvent may be between 55:45 and 85:15 by weight percentage, preferably between 60:40 and 80:20 by weight percentage, such as approximately 70:30 by weight percentage.

[0024] In various embodiments, suitable blends may include DMI as a primary solvent with CHP or DMPU as a co-solvent; CHP as a primary solvent with DMI or DMPU as a cosolvent; or DMPU as a primary solvent with DMI or CHP as a co-solvent.

[0025] In other embodiments, a solvent blend may include a primary solvent and a cosolvent with relatively lower solubility' than the primary' solvent, such as a co-solvent of GBL, NBP. DMPA, TOU, DEAc, NMM, MO-MPA, Anisole. Cyrene, TMU, or DEGDE.

[0026] Certain blends may include DMI as a primary solvent and one of GBL, NBP, DMPA, TOU, DEAc, NMM, MO-MPA, Anisole, Cyrene, TMU, or DEGDE as a co-solvent. One example solvent blend may include DMI as the primary' solvent and GBL as the cosolvent. Another example solvent blend may include DMI as the primary’ solvent and NBP as the co-solvent. Another example solvent blend may include DMI as the primary solvent and DMPA as the co-solvent. Another example solvent blend may include DMI as the primary solvent and TOU as the co-solvent. Another example solvent blend may include DMI as the primary’ solvent and DEAc as the co-solvent. Another example solvent blend may include DMI as the primary solvent and NMM as the co-solvent. Another example solvent blend may include DMI as the primary solvent and MO-MPA as the co-solvent. Another example solvent blend may include DMI as the primary’ solvent and Anisole as the co-solvent. Another example solvent blend may include DMI as the primary' solvent and Cyrene as the co-solvent. Another example solvent blend may include DMI as the primary solvent and TMU as the co-solvent. Yet another example solvent blend may include DMI as the primary solvent and DEGDE as the co-solvent. For each of the above example blends, a ratio of the primary solvent to the cosolvent may be between 55:45 and 85:15 by weight percentage, preferably between 75:25 and 85: 15 by weight percentage, such as approximately 80:20 by weight percentage.

[0027] Other blends may include CHP as a primary’ solvent and one of GBL, NBP, or DMPA as a co-solvent. One example solvent blend may include CHP as the primary’ solvent and GBL as the co-solvent. Another example solvent blend may include CHP as the primary solvent and NBP as the co-solvent. Yet another example solvent blend may include CHP as the primary' solvent and DMPA as the co-solvent. For each of the above example blends, a ratio of the primary’ solvent to the co-solvent may be between 55:45 and 75:25 by weight percentage, preferably between 55:45 and 65:35 by weight percentage, such as approximately 60:40 by weight percentage.

[0028] Other blends may include DMPU as a primary' solvent and one of GBL, NBP, DMPA, TOU, DEAc, NMM, MO-MPA, Anisole, Cyrene, TMU. or DEGDE as a co-solvent. One example solvent blend may include DMPU as the primary solvent and GBL as the cosolvent. Another example solvent blend may include DMPU as the primary solvent and NBP as the co-solvent. Another example solvent blend may include DMPU as the primary solvent and DMPU as the co-solvent. Another example solvent blend may include DMPU as the primary’ solvent and TOU as the co-solvent. Another example solvent blend may includeDMPU as the primary solvent and DEAc as the co-solvent. Another example solvent blend may include DMPU as the primary solvent and NMM as the co-solvent. Another example solvent blend may include DMPU as the primary solvent and MO-MPA as the co-solvent. Another example solvent blend may include DMPU as the primary solvent and Anisole as the co-solvent. Another example solvent blend may include DMPU as the primary solvent and Cyrene as the co-solvent. Another example solvent blend may include DMPU as the primary solvent and TMU as the co-solvent. Yet another example solvent blend may include DMPU as the primary solvent and DEGDE as the co-solvent. For each of the above example blends, a ratio of the primary solvent to the co-solvent may be between 55:45 and 85: 15 by weight percentage, preferably between 60:40 and 80:20 by weight percentage, such as approximately 70:30 by weight percentage.

[0029] In other embodiments, a solvent blend may include a primary solvent and two cosolvents with relatively lower solubility than the primary solvent, such as GBL, NBP, DMPA, TOU, DEAc, NMM, MO-MPA, Anisole, Cyrene, TMU, and / or DEGDE. Certain solvent blends may include DMI as the primary solvent with two co-solvents selected from the group of GBL, NBP, DMPA. TOU, DEAc, NMM. MO-MPA. Anisole, Cyrene. TMU, and DEGDE. For example, DMI may be utilized as the primary solvent with a combination of GBL and NBP as the two co-solvents. As another example, DMI may be utilized as the primary solvent with a combination of GBL and DMPA as the two co-solvents. As another example, DMI may be utilized as the primary solvent with a combination of GBL and TOU as the two co-solvents. As another example. DMI may be utilized as the primary solvent with a combination of DMPA and NBP as the two co-solvents. As another example, DMI may be utilized as the primary solvent with a combination of DMPA and TOU as the two co-solvents. As another example, DMI may be utilized as the primary solvent with a combination of NBP and TOU as the two co-solvents. For each of the above blends combining DMI with two co-solvents, a ratio of the primary solvent to the co-solvents may be between 40:30:30 and 90:5:5 by weight percentage, preferably between 50:25:25 and 70: 15: 15 by weight percentage, such as approximately 60:20:20 by weight percentage. Alternatively, a preferred ratio may be between 70: 15: 15 and 90:5:5 by weight percentage, such as approximately 80: 10: 10 by weight percentage.

[0030] Other solvent blends may include CHP as the primary solvent with two solvents selected from the group of GBL, NBP, DMPA, TOU, DEAc, NMM, MO-MPA, Anisole, Cyrene, TMU, and DEGDE. Preferred blends may include CHP as the primary solvent withtwo co-sol vents selected from the group of GBL, NBP, and DMPA. For example, CHP may be utilized as the primary solvent with a combination of GBL and NBP as the two co-solvents. As another example, CHP may be utilized as the primary solvent with a combination of GBL and DMPA as the two co-solvents. As another example, CHP may be utilized as the primary solvent with a combination of NBP and DMPA as the two co-solvents. For each of the above blends combining DMI with two co-solvents, a ratio of the primary solvent to the co-solvents may be between 40:30:30 and 90:5:5 by weight percentage, preferably between 50:25:25 and 70: 15: 15 by weight percentage, such as approximately 60:20:20 by weight percentage. Alternatively, a preferred ratio may be between 70: 15: 15 and 90:5:5 by weight percentage, such as approximately 80: 10: 10 by weight percentage.

[0031] Other solvent blends may include DMPU as the primary solvent with two cosolvents selected from the group of GBL. NBP, DMPA. TOU, DEAc, NMM, MO-MPA, Anisole, Cyrene, TMU, and DEGDE. For example, DMPU may be utilized as the primary solvent with a combination of GBL and NBP as the two co-solvents. As another example, DMPU may be utilized as the primary solvent with a combination of GBL and DMPA as the two co-solvents. As another example, DMPU may be utilized as the primary solvent with a combination of GBL and TOU as the two co-solvents. As another example, DMPU may be utilized as the primary solvent with a combination of DMPA and NBP as the two co-solvents. As another example, DMPU may be utilized as the primary solvent with a combination of DMPA and TOU as the two co-solvents. As another example, DMPU may be utilized as the primary solvent with a combination of NBP and TOU as the two co-solvents. For each of the above blends combining DMPU with two co-solvents, a ratio of the primary solvent to the cosolvents may be between 40:30:30 and 90:5:5 by weight percentage, preferably between 50:25:25 and 70: 15: 15 by weight percentage, such as approximately 60:20:20 by weight percentage. Alternatively, a preferred ratio may be between 70: 15: 15 and 90:5:5 by weight percentage, such as approximately 80: 10: 10 by weight percentage.

[0032] As previously stated, a solvent blend may include co-solvents that are included in the list of suitable primary solvents. For example, DMI, CHP, and / or DMPU may be utilized as either primary solvents or co-solvents. Further, a ternary or three-part solvent blend including at least one of DMI, CHP, or DMPU as co-solvents may include any suitable ratio of the three combined solvents. In certain embodiments, one of DMI, CHP, or DMPU may be utilized as a primary solvent, another one of DMI, CHP, or CHP may be utilized as a first co-solvent, and one of GBL, NBP, DMPA, TOU, DEAc, NMM, MO-MPA, Anisole, Cyrene, TMU, and DEGDE may be utilized as a second co-solvent. In other embodiments, one of DMI, CHP, or DMPU may be utilized as a primary' solvent, another one of DMI, CHP, or CHP may be utilized as a first co-solvent, and one of GBL, NBP, DMPA. and TOU may be utilized as a second co-solvent.

[0033] Certain solvent blends may include DMI as a primary' solvent, CHP as a first cosolvent, and one of GBL, NBP, DMPA, and TOU as a second co-solvent. For example, DMI, CHP, and GBL may be utilized in a blend. As another example, DMI, CHP, and NBP may be utilized in a blend. As another example, DMI, CHP, and DMPA may7be utilized in a blend. As another example, DMI, CHP, and TOU may be utilized in a blend. Other solvent blends may include DMI as a primary solvent, DMPU as a first co-solvent, and one of GBL, NBP, DMPA, and TOU as a second co-solvent. For example, DMI, DMPU, and GBL may be utilized in a blend. As another example, DMI, DMPU, and NBP may be utilized in a blend. As another example, DMI, DMPU, and DMPA may be utilized in a blend. As another example, DMI, DMPU, and TOU may be utilized in a blend. For each of these blends including DMI as a primary’ solvent, a ratio of the primary solvent to the co-solvents may be between 40:30:30 and 90:5:5 by weight percentage, preferably between 50:25:25 and 70: 15: 15 by weight percentage, such as approximately 60:20:20 by weight percentage. Alternatively, a preferred ratio may be between 70: 15:15 and 90:5:5 by weight percentage, such as approximately 80: 10:10 by weight percentage.

[0034] Other solvent blends may include CHP as a primary' solvent, DMI as a first cosolvent, and one of GBL, NBP, DMPA, and TOU as a second co-solvent. For example, CHP, DMI. and GBL may be utilized in a blend. As another example, CHP, DMI, and NBP may be utilized in a blend. As another example, CHP. DMI. and DMPA may be utilized in a blend. As another example, CHP, DMI, and TOU may be utilized in a blend. Other solvent blends may include CHP as a primary7solvent, DMPU as a first co-solvent, and one of GBL, NBP, DMPA, and TOU as a second co-solvent. For example, CHP, DMPU, and GBL may be utilized in a blend. As another example, CHP, DMPU. and NBP may be utilized in a blend. As another example, CHP, DMPU, and DMPA may be utilized in a blend. As another example, CHP, DMPU, and TOU may be utilized in a blend. For each of these blends including CHP as a primary' solvent, a ratio of the primary solvent to the co-solvents may be between 40:30:30 and 90:5:5 by weight percentage, preferably between 50:25:25 and 70: 15: 15 by weight percentage,such as approximately 60:20:20 by weight percentage. Alternatively, a preferred ratio may be between 70: 15:15 and 90:5:5 by weight percentage, such as approximately 80: 10:10 by weight percentage.

[0035] Other solvent blends may include DMPU as a primary solvent, DMI as a first cosolvent, and one of GBL, NBP, DMPA, and TOU as a second co-solvent. For example, DMPU, DMI, and GBL may be utilized in a blend. As another example, DMPU, DMI, and NBP may be utilized in a blend. As another example, DMPU. DMI, and DMPA may be utilized in a blend. As another example, DMPU, DMI, and TOU may be utilized in a blend. Other solvent blends may include DMPU as a primary solvent, CHP as a first co-solvent, and one of GBL, NBP, DMPA, and TOU as a second co-solvent. For example, DMPU, CHP, and GBL may be utilized in a blend. As another example, DMPU, CHP, and NBP may be utilized in a blend. As another example, DMPU. CHP. and DMPA may be utilized in a blend. As another example, DMPU, CHP, and TOU may be utilized in a blend. For each of these blends including DMPU as a primary solvent, a ratio of the primary solvent to the co-solvents may be between 40:30:30 and 90:5:5 by weight percentage, preferably between 50:25:25 and 70: 15: 15 by weight percentage, such as approximately 60:20:20 by weight percentage. Alternatively, a preferred ratio may be between 70: 15: 15 and 90:5:5 by weight percentage, such as approximately 80: 10: 10 by weight percentage.

[0036] In yet other embodiments, a solvent blend may include more than three components. For example, one of DML CHP, or DMPU may be utilized as a primary solvent, another one of DMI, CHP, or DMPU may be utilized as a first co-solvent, one of GBL, NBP, DMPA, TOU, DEAc, NMM, MO-MPA, Anisole, Cyrene, TMU, and DEGDE may be utilized as a second co-solvent, and another one of GBL, NBP, DMPA, TOU, DEAc, NMM. MO-MPA. Anisole, Cyrene, TMU, and DEGDE may be utilized as a third co-solvent. In certain embodiments, one of DMI, CHP, or DMPU may be utilized as a primary solvent, another one of DMI, CHP, or DMPU may be utilized as a first co-solvent, one of GBL, NBP, DMPA, and TOU may be utilized as a second co-solvent, and another one of GBL, NBP, DMPA, and TOU may be utilized as a third co-solvent. Indeed, a wide variety of suitable solvent blends may combine at least two materials from a first set of DMI, CHP, and DMPU (e.g., first and second materials, etc.) with at least two materials from a second set of GBL, NBP, DMPA, TOU, DEAc, NMM, MO-MPA, Anisole, Cyrene, TMU, and DEGDE (e.g., third and fourth materials).Notwithstanding the foregoing, certain solvent blends may include small amountsof other materials as additives or co-solvents. For example, relatively small weight percentage amounts of toluene, xylene, naphtha, or other suitable aromatic hydrocarbon liquid chemicals, may be utilized as co-solvents. In certain embodiments, the aromatic hydrocarbon may constitute between one (1) and twenty’ (20) percent by weight of a solvent blend, more preferably between one (1) and ten (10) percent by weight of a solvent blend, such as approximately 5 percent by weight of a solvent blend. For example, a blend of DMI, NBP, and xylene may have a blend ratio of the primary solvent to the co-solvents between 50:45:5 and 80: 10: 10 by weight percentage, preferably betyveen 50:45:5 and 70:20: 10 by weight percentage, such as approximately 60:35:5 by weight percentage. As another example, a blend of DMI, CHP, and xylene may have a blend ratio of the primary solvent to the co-solvents betyveen 50:45:5 and 80: 10: 10 by yveight percentage, preferably betyveen 50:45:5 and 70:20: 10 by weight percentage, such as approximately 60:35:5 by yveight percentage. As another example, a blend of DMI, NBP, and naphtha may have a blend ratio of the primary solvent to the co-solvents betyveen 50:45:5 and 80: 10: 10 by weight percentage, preferably between 50:45:5 and 70:20: 10 by yveight percentage, such as approximately 60:35:5 by yveight percentage. As another example, a blend of DMI, CHP, and naphtha may have a blend ratio of the primary solvent to the co-solvents between 50:45:5 and 80: 10: 10 by weight percentage, preferably between 50:45:5 and 70:20: 10 by weight percentage, such as approximately 60:35:5 by weight percentage.

[0037] For certain solvent blends described herein, it has been found that providing a higher concentration of the primary solvent may result in improved solubility properties. In other words, it may be easier for the PAI resins to form a solution and / or be dissolved yvithin the solvent blend. Conversely, it has been found that providing higher amounts of certain cosolvents may result in loyvering the overall cost of a solvent blend. Notwithstanding cost considerations, certain co-solvents have been found to be relatively good diluents. For example, GBL has been found to improve the solubility of certain resin components during synthesis. In certain embodiments, a blend ratio of primary solvent to co-solvent may be selected in order to strike a desirable or optimal balance betyveen sol ability properties and cost, or to achieve a desired curing rate from liquid to solid under desired processing conditions.

[0038] According to an aspect of the disclosure, a solvent blend may have a relatively low toxicity yvhen compared to conventional solvents utilized in conjunction with thermosetting PAI resins, particularly N-methyl pyrrolidone ( ‘NMP’ ) and N,N-Dimethylacetamide("DAI Ac"). Indeed, NMP and DMAc may be found to be toxic materials that could lead to a wide variety of health risks based on exposure to humans. Further, bans or prohibitions of NMP are currently being considered by the United States Environmental Protection Agency and other global governmental bodies and agencies. By contrast, the inventive solvent blends described herein may have relatively lower toxicities while still providing desirable solubility properties for synthesis and application of thermosetting materials. In certain embodiments, the inventive solvent blends may be free of or include no NMP and / or DMAc. Accordingly, the solvent blends discussed herein have the technical effect of being suitable for use in the formulation and / or application of PAI resins as magnet wire insulation while also being relatively less toxic than conventional solvents, particularly NMP and DMAc. Further, the solvent blends have been found to allow the formulation and application of PAI insulation layers on magnet wire that satisfy applicable standards established by NEMA.

[0039] As desired, the solvent blends described herein may be used for a wide variety of suitable purposes, such as the synthesis of thermosetting PAI resins and / or the application of thermosetting PAI resins. In certain embodiments, a solvent blend may be utilized in the synthesis or formulation of PAI. For example, a PAI or its precursor (i.e., poly(amide-amic acid), etc.) may be formed by reacting a suitable acid chloride or anhydride component with a suitable diamine component or diisocyanate component within a solvent blend. The PAI precursor may subsequently be cured to form PAI. A wide variety of suitable acid chloride or anhydride components may be utilized as desired in various embodiments including, but not limited to, trimellitic anhydride f‘TMA”). and / or other suitable anhydride components as will be understood by those of ordinary skill in the art. Similarly, a wide variety of suitable diamine and / or diisocyanate components may be utilized as desired including, but not limited to 4,4’- methylene diphenyldiisocyanate (“MDI”) and / or other suitable diamines and / or diisocyanates as will be understood by those of ordinary skill in the art. Indeed, a wide variety of different components and / or combinations of components may be utilized to synthesize a PAI or its precursor within one of the solvent blends described herein. Alternatively, PAI solids material may be fully or partially dissolved in a suitable solvent blend to form a PAI solution or dispersion.

[0040] As desired, any suitable amount of solvent blend can be used in the synthesis of a PAI resin. For example, any suitable ratio between total solvent (i.e., total amount of a solvent blend) to polymeric material may be utilized. In certain embodiments, a ratio of total solventto polymeric material may be in a range between approximately 35:65 to approximately 85: 15 although other suitable ranges may be utilized. For example, a ratio may be approximately 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85: 15, or any ratio included in a range between any two of the preceding values. In certain embodiments, an amount or ratio of total solvent to polymeric material may be selected in order to achieve one or more desired properties for the synthesized polymeric resin. For example, an amount of total solvent may be selected such that the synthesized resin has a desirable color and / or is substantially free of precipitates.

[0041] In various embodiments, a wide variety of other components may be included in the synthesis of a PAI or other polymeric resin. In other words, one or more additional components and / or modifiers may be added to a reaction or synthesis performed within a solvent blend. As an example, one or more suitable end capping agents, crosslinkers, fillers, and / or other modifiers or additives may be added as additional components during the synthesis of a polymeric resin.

[0042] In addition to and / or as an alternative to the synthesis of a PAI resin, the inventive solvent blends described herein may be utilized during the application of PAI resins. In certain embodiments, a suitable polymeric material, such as a PAI precursor, may be dissolved or suspended within a solvent blend. The resulting mixture or varnish may then be applied within a desired application (e.g., as a wire insulation layer, as a coating, etc.) via any number of suitable devices (e.g., application dies, etc.) and subsequently cured to form a stable polymeric layer. A wide variety of suitable devices may be utilized to cure an applied thermosetting varnish, such as heat curing (e.g., curing in an oven, etc.), ultraviolet curing, etc. During the curing process, at least a portion of the solvent may be evaporated or otherwise removed.

[0043] As desired, any suitable amount of solvent blend can be used in the application of aPAI resin. For example, any suitable ratio between total solvent (i.e., total amount of a solvent blend) to polymeric solids material may be utilized. In certain embodiments, a ratio of total solvent to polymeric solids material may be in a range between approximately 35:65 to approximately 85: 15 although other suitable ranges may be utilized. For example, a ratio may be approximately 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85: 15, or any ratio included in a range betw een any two of the preceding values.

[0044] In yet other embodiments, a solvent blend may be utilized in the synthesis, formulation, and / or application of a wide variety of other thermosetting resins. Examples of other suitable thermosetting resins that may be synthesized and / or applied within one of the inventive solvent blends include, but are not limited to polyimide, polyurethane, polyester, THEIC (e.g., tris(hydroxyethylisocyanurate) or l,3,5-tris(2-hydroxyethyl)cyanunc acid) polyester, polyester imide, a phenolics polymer, an epoxide polymer, a silicone polymer, etc.

[0045] As a result of utilizing one or more of the solvent blends described herein, the use of NMP, DMAc, and / or other relatively toxic solvents may be reduced and / or eliminated while still permitting desired synthesis and application of thermosetting and / or other polymeric resins. In other words, the solvent blends are less hazardous than conventional solvents. Further, use of solvent blends that incorporate both a primary solvent and a secondary solvent allow the overall solution to provide desired properties (e.g., desired solubility, etc.) while lowering the overall cost relative to certain single material solvents.

[0046] Examples

[0047] As set forth above, thermosetting PAI resins may be used in a wide variety’ of suitable applications, such as magnet wire insulation applications, insulation coatings in motor parts (e.g., stator cores, slot liner applications, etc ), circuit board coatings, coatings for electronic parts, cookware coatings, etc. One particular application in which the inventive solvent blends may be utilized is in the formation and application of thermosetting PAI resins as magnet wire insulation.

[0048] A few non-limiting examples of the use of the inventive solvent blends are described in greater detail below with reference to Tables 1 and 2. Table 1 sets forth example PAI varnishes or enamels that may be synthesized within various solvent blends in accordance with example embodiments of the disclosure. Any number of the synthesized PAI varnishes may then be applied within a solvent blend around a conductor and cured to form thermosetting PAI magnet wire insulation. Table 2 provides example mechanical and electrical test results for magnet wire insulation utilizing certain solvent blends set forth in Table 1. The Co-Solvent “D59” is an Exxon Mobil Aromatic 100 including approximately 100% light aromatic naphtha (CAS no [64742-95-6]).Table 1 : Example Solvent Blends Used to Synthesize and / or Apply PAI

[0049] Turning first to Table 1, a few example solvent blends that may be utilized in the synthesis or formulation of PAI resins are illustrated. As desired, the solvent blends may additionally or alternatively be used to apply a formulated PAI resin. For example, a particular solvent blend may be utilized both to formulate and apply a PAI resin. As another example, a first solvent blend may be utilized to formulate a PAI resin while a second solvent blend is utilized to apply the formulated PAI resin.

[0050] A wide variety of suitable methods or techniques may be utilized as desired to synthesize or formulate a PAI resin within a solvent blend. For each of the example PAI resins included in Table 1, a respective solvent blend was loaded at room temperature into a suitable reactor, such as a 5-gallon lab pilot reactor with 200 rpm stirring and nitrogen purging. The solvent blend was then heated to approximately 50 °C. An end-capping agent or end blocker was introduced into the reactor and dissolved. Trimetallic anhydride (“TMA’’) was added as flakes and heated to approximately 85 °C over a desired time period. 4,4'-methylene diisocyanate (“MDI”) was then added to the solution to react with the TMA. The mixture was heated to a relatively high temperature above approximately 1 10 °C to form a viscous solution,and then cooled to a lower temperature (i.e., a temperature below about 85 °C). A methanol containing solution within the solvent blend was added to stop the polymerization reaction. The mixture was stirred overnight to cool down to approximately 50 °C and then filtered to obtain a brow n, clear, medium viscous solution without bubbles. While the samples discussed herein were all made utilizing a similar process, it will be appreciated that the reaction time and / or various temperatures may be modified or controlled in order to modify certain characteristics of the resulting PAI resins. For example, the viscosity of a PAI resin may be modified by controlling the reaction time and / or reaction temperature. Further, formulating a PAI resin with a higher viscosity may generally permit a higher solids content to be incorporated into the PAI solution.

[0051] Table 1 provides data associated with example PAI enamels or varnishes synthesized or reacted within various solvent blends according to illustrative embodiments of the disclosure. For example, the different PAI varnishes may be reacted utilizing the example method or technique set forth above. Table 1 further includes reference data for conventional solvents, such as NMP and unblended DMI. The viscosity data in Table 1 was measured at approximately 30 °C. The solids percentage data (i.e.. an amount of PAI solids material suspended within the solvent) was measured at 150 °C for 1 hour, and then at 250 °C for another one hour in air. The curing temperature onset was measured using a viscometer at a temperature rate of +10 °C per minute from 25 °C to 160 °C. As shown in Table 1, similar viscosity and solids percentage may be achieved utilizing the inventive solvent blends relative to conventional solvents. Accordingly, the inventive solvent blends may be utilized as alternatives to certain conventional solvents, particularly NMP and DMAc. Further, the inventive solvent blends may be used as cost-effective materials to certain single material solvents, such as DMI.

[0052] In addition to utilizing solvent blends to synthesize or formulate PAI resins, the inventive solvent blends may be utilized to apply the PAI resins. Table 2 depicts information associated with magnet wire on which certain inventive solvent blends have been utilized to form PAI enamel insulation layers.Table 2: Selected Testing for Heavy Build Magnet Wire

[0053] Each of the example magnet wires set forth in Table 2 includes polyamide-imide insulation formed with a "heavy’7enamel build on a copper conductor. A "heavy” enamel build denotes a nominal insulation thickness of approximately 3.0 mils (0.0762 mm). Table 2 includes example mechanical and electrical test results for magnet wire insulation formed using certain solvent blends of Table 1. In particular. Table 2 includes concentricity, flexibility, elongation, dielectric breakdown, and thermoplastic flow data for PAI enamel insulation layers. The tests utilized to evaluate the magnet wire insulation are standard NEMA tests as set forth by the National Electrical Manufacturers Association and are readily understood by those of ordinary skill in the art. Concentricity generally refers to a ratio of a thickest portion of the insulation relative to a thinnest portion of the insulation at a given cross-sectional point along a longitudinal length of a magnet wire. Under a NEMA flexibility test, a magnet wire sample is elongated by 20%, wrapped three times around a mandrel of a specified diameter or size for the wire gauge, and evaluated for cracks in the insulation. Under a wire elongation test, the wire is elongated until cracks or faults are identified in the insulation. Under dielectric breakdown tests, twisted pair specimens are formed from the wire and subjected to ramped up voltages at different temperatures until the insulation fails. A thermoplastic flow test is utilized to determine and confirm the cut through temperature of magnet wire insulation. As show n in Table 2, magnet wire insulation formed with the inventive solvent blends has comparable performance to magnet wire insulation formed with conventional solvents. Accordingly, the inventive solvent blends may be utilized as alternatives to conventional NMP-based solvents and / or as cost-effective alternatives to certain single material conventional solvents.

[0054] Conditional language, such as, among others, “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments could include, while other embodiments do not include, certain features, elements, and / or operations. Thus, such conditional language is not generally intended to imply that features, elements, and / or operations are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements, and / or operations are included or are to be performed in any particular embodiment.

[0055] Many modifications and other embodiments of the disclosure set forth herein will be apparent having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosure is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

CLAIMSThat which is claimed:

1. A solvent blend for forming and applying thermosetting polyamide-imide, the solvent blend comprising: a primary solvent comprising one or more first materials, the first materials comprising at least one of l,3-Dimethyl-2-imidazolidinone, N-Cyclohexyl-2-pyrrolidone, or N,N’ -Dimethyl propyleneurea; and a co-solvent comprising one or more second materials different than the one or more first materials, the second materials comprising at least one of N,N-Diethylacetamide, N,N- Dimethylpropionamide, gamma-butyrolactone, N-butylpyrrolidinone, A-Methylmorpholine, 2,5,7,10-Tetraoxaundecane, 3-Methoxy-N,N-dimethyl propenamide, Anisole, Cyrene,1.1.3.3-Tetramethylurea, Diethylene Glycol Diethyl Ether, l,3-Dimethyl-2-imidazolidinone, N-Cyclohexyl-2-pyrrolidone, or N,N’ -Dimethyl propyleneurea; wherein the primary solvent is provided at a higher weight percentage than the cosolvent.

2. The solvent blend of Claim 1, wherein the primary solvent comprises between 55 percent and 95 percent by weight of the solvent blend.

3. The solvent blend of Claim 1 or 2, wherein the primary solvent comprises between 60 percent and 80 percent by weight of the solvent blend.

4. The solvent blend of Claim 1, wherein the primary solvent comprises a first one of1.3-Dimethyl-2-imidazolidinone, N-Cyclohexyl-2-pyrrolidone, or N,N’-Dimethyl propyleneurea and the co-solvent comprises a second one of l,3-Dimethyl-2- imidazolidinone, N-Cyclohexyl-2-pyrrolidone, or N,N’ -Dimethyl propyleneurea.

5. The solvent blend of Claim 1 or 4, wherein the primary solvent comprises Dimethyl- 2-imidazolidinone and the co-solvent comprises N-Cyclohexyl-2-pyrrolidone.

6. The solvent blend of Claim 1 or 4, wherein the primary solvent comprises Dimethyl- 2-imidazolidinone and the co-solvent comprises N,N’-Dimethyl propyleneurea.

7. The solvent blend of Claim 1 or 4, wherein the primary solvent comprises N- Cyclohexyl-2-pyrrolidone and the co-solvent comprises Dimethyl-2-imidazolidinone.

8. The solvent blend of Claim 1 or 4, wherein the primary solvent comprises N- Cyclohexyl-2-pyrrolidone and the co-solvent comprises N,N’-Dimethyl propyleneurea.

9. The solvent blend of Claim 1 or 4, wherein the primary solvent comprises N,N’- Dimethyl propyleneurea and the co-solvent comprises N.N’ -Dimethyl propyleneurea.

10. The solvent blend of Claim 1 or 4, wherein the primary solvent comprises N,N’- Dimethyl propyleneurea and the co-solvent comprises N-Cyclohexyl-2-pyrrolidone.1 1. The solvent blend of any of Claims 1, 4, or 5-10, wherein the primary solvent comprises between 55 percent and 85 percent by weight of the solvent blend and the cosolvent comprises between 15 percent and 45 percent by weight of the solvent blend.

12. The solvent blend of any of Claims 1, 4. or 5-10, wherein the primary solvent comprises between 75 percent and 85 percent by weight of the solvent blend and the cosolvent comprises between 15 percent and 25 percent by weight of the solvent blend.

13. The solvent blend of Claim 1, wherein the primary solvent comprises one of 1,3- Dimethyl-2-imidazolidinone, N-Cyclohexyl-2-pyrrolidone, or N,N’-Dimethyl propyleneurea and the co-solvent comprises one of gamma-butyrolactone, N-butylpyrrolidinone, or N,N’- Dimethyl propyleneurea.

14. The solvent blend of Claim 1 or 13, wherein the primary solvent comprises Dimethyl- 2-imidazolidinone and the co-solvent comprises gamma-butyrolactone.

15. The solvent blend of Claim 1 or 13, wherein the primary solvent comprises Dimethyl- 2-imidazolidinone and the co-solvent comprises N-butylpyrrolidinone.

16. The solvent blend of Claim 1 or 13, wherein the primary solvent comprises Dimethyl- 2-imidazolidinone and the co-solvent comprises N,N’-Dimethyl propyleneurea.

17. The solvent blend of Claim 1 or 13, wherein the primary’ solvent comprises N- Cyclohexyl-2-pyrrolidone and the co-solvent comprises gamma-butyrolactone.

18. The solvent blend of Claim 1 or 13, wherein the primary' solvent comprises N- Cyclohexyl-2-pyrrolidone and the co-solvent comprises N-butylpyrrolidinone.

19. The solvent blend of Claim 1 or 13, wherein the primary solvent comprises N- Cyclohexyl-2-pyrrolidone and the co-solvent comprises N,N’-Dimethyl propyleneurea.

20. The solvent blend of Claim 1 or 13, wherein the primary solvent comprises N,N’- Dimethyl propyleneurea and the co-solvent comprises gamma-butyrolactone.

21. The solvent blend of Claim 1 or 13, wherein the primary' solvent comprises N,N’- Dimethyl propyleneurea and the co-solvent comprises N-butylpyrrolidinone.

22. The solvent blend of Claim 1 or 13, wherein the primary solvent comprises N,N’- Dimethyl propyleneurea and the co-solvent comprises N,N’-Dimethyl propyleneurea.

23. The solvent blend of any of Claims 1 or 13-22, wherein the primary solvent comprises between 55 percent and 85 percent by weight of the solvent blend and the co-solvent comprises between 15 percent and 45 percent by weight of the solvent blend.

24. The solvent blend of any of Claims 1 or 13-22, wherein the primary solvent comprises between 75 percent and 85 percent by weight of the solvent blend and the co-solvent comprises between 15 percent and 25 percent by weight of the solvent blend.

25. The solvent blend of Claim 1, wherein the primary’ solvent comprises l,3-Dimethyl-2- imidazolidinone and the co-solvent comprises one of one of N,N-Diethylacetamide, N.N- Dimethylpropionamide, gamma-butyrolactone, N-butylpyrrolidinone, JV-Methylmorpholine, 2,5,7,10-Tetraoxaundecane, 3-Methoxy-N,N-dimethyl propenamide, Anisole, Cyrene,1,1,3,3-Tetramethylurea, Diethylene Glycol Diethyl Ether, N-Cyclohexyl-2-pyrrolidone, or N,N’ -Dimethyl propyleneurea.

26. The solvent blend of Claim 25, wherein the primary solvent comprises between 55 percent and 85 percent by weight of the solvent blend and the co-solvent comprises between 15 percent and 45 percent by weight of the solvent blend.

27. The solvent blend of Claim 25, wherein the primary solvent comprises between 75 percent and 85 percent by weight of the solvent blend and the co-solvent comprises between 15 percent and 25 percent by weight of the solvent blend.

28. The solvent blend of Claim 1, wherein the primary solvent comprises N-Cyclohexyl- 2-pyrrolidone and the co-solvent comprises one of one of N,N-Dimethylpropionamide, gamma-butyrolactone, N-butylpyrrolidinone, l,3-Dimethyl-2-imidazolidinone, or N,N’- Dimethyl propyleneurea.

29. The solvent blend of Claim 28, wherein the primary solvent comprises between 55 percent and 75 percent by weight of the solvent blend and the co-solvent comprises between 25 percent and 45 percent by weight of the solvent blend.

30. The solvent blend of Claim 1, wherein the primary solvent comprises N,N’-Dimethyl propyleneurea and the co-solvent comprises one of one of N,N-Diethylacetamide, N.N- Dimethylpropionamide, gamma-butyrolactone, N-butylpyrrolidinone, A-Methylmorpholine, 2,5,7,10-Tetraoxaundecane, 3 -Methoxy -N,N-dimethyl propenamide, Anisole, Cyrene, 1,1,3,3-Tetramethylurea, Diethylene Glycol Diethyl Ether, l,3-Dimethyl-2-imidazolidinone, or N-Cyclohexyl-2-pyrrolidone.

31. The solvent blend of Claim 30, wherein the primary solvent comprises between 55 percent and 85 percent by weight of the solvent blend and the co-solvent comprises between 15 percent and 45 percent by weight of the solvent blend.

32. The solvent blend of Claim 30, wherein the primary solvent comprises between 60 percent and 80 percent by weight of the solvent blend and the co-solvent comprises between 20 percent and 40 percent by weight of the solvent blend.

33. The solvent blend of Claim 1, wherein the co-solvent comprises two of N,N-Di ethylacetamide, N,N-Dimethylpropionamide, gamma-butyrolactone, N-butylpyrrolidinone. A-Methylmorpholine. 2,5,7, 10-Tetraoxaundecane, 3-Methoxy-N,N-dimethyl propenamide, Anisole, Cyrene, 1,1,3,3-Tetramethylurea. Diethylene Glycol Diethyl Ether, l,3-Dimethyl-2- imidazolidinone. N-Cyclohexyl-2-pyrrolidone, or N,N’ -Dimethyl propyleneurea.

34. The solvent blend of Claim 1, wherein the co-solvent comprises two of Dimethyl-2- imidazolidinone, N-Cyclohexyl-2-pyrrolidone, N,N’ -Dimethyl propyleneurea, gammabutyrolactone, N-butylpyrrolidinone, or N,N’ -Dimethyl propyleneurea.

35. The solvent blend of Claims 33 or 34, wherein the primary solvent comprises between between 40 percent and 90 percent by weight of the solvent blend and each of the co-solvent components respectively comprise between 5 percent and 30 percent by weight of the solvent blend.

36. The solvent blend of Claim 33 or 34, wherein the primary solvent comprises between 50 percent and 70 percent by weight of the solvent blend and each of the co-sol vent components respectively comprise between 15 percent and 25 percent by weight of the solvent blend.

37. A method of synthesizing a polyamide-imide precursor utilizing any of the solvent blends of Claims 1-36. the method comprising: providing the solvent blend; and reacting a plurality of components for a polyamide-imide thermosetting resin within the solvent blend.

38. The method of Claim 37. wherein reacting a plurality of components within the solvent blend comprises reacting a dianhydride component with a diamine component.

39. The method of Claims 37 or 38, wherein reacting a plurality of components within the solvent blend comprises reacting trimetallic anhydride with 4,4 ’-methylene diisocyanate.

40. The method of Claim 4, wherein a weight ratio of the solvent blend to the plurality of components for the polyamide-imide thermosetting resin is between 35:65 and 85: 15.

41. A method of applying a thermosetting polyamide-imide resin utilizing any of the solvent blends of Claims 1-36. the method comprising: suspending a polyamide-imide resin material within the solvent blend to form a varnish; applying the varnish; and curing the applied varnish to form a thermosetting polymeric layer.

42. The method of Claim 41 , wherein a weight ratio of the solvent blend to the polyamide-imide thermosetting resin material is between 35:65 and 85:15.

43. The method of Claim 41 or 42. wherein applying the varnish comprises applying the varnish on a magnet wire.

44. The method of Claim 41 or 42, wherein curing the applied varnish comprises heat curing the applied varnish in an enamelling oven.

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