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聚酰胺酰亚胺是热固性或热塑性无定形聚合物,具有优异的机械、耐热和耐化学性能。聚酰胺酰亚胺在制造漆包线时被广泛用作线材涂层。它们由异氰酸酯和 TMA(偏苯三酸酐)在 N-甲基-2-吡咯烷酮 (NMP) 中制备。聚酰胺酰亚胺的主要分销商是索尔维特种聚合物公司,该公司使用Torlon商标。

聚酰胺酰亚胺具有聚酰胺和聚酰亚胺的多种特性,例如高强度、熔融加工性、[需要澄清]出色的高耐热性和广泛的耐化学性。[需要引证]聚酰胺-酰亚胺聚合物可以加工成多种形式,从注塑或压缩成型部件和铸锭,到涂料、薄膜、纤维和粘合剂。通常,这些制品在随后的热固化过程中达到其最大性能。

同一领域的其他高性能聚合物是聚醚醚酮和聚酰亚胺。

化学
目前流行的合成聚酰胺酰亚胺的商业化方法是酰氯路线和异氰酸酯路线。

酰氯路线
聚酰胺-酰亚胺的最早途径是芳香族二胺的缩合,例如亚甲基二苯胺 (MDA) 和偏苯三酰氯 (TMAC)。酸酐与二胺反应生成中间氨基酸。酰氯官能团与芳香胺反应生成酰胺键和盐酸 (HCl) 作为副产物。在聚酰胺酰亚胺的商业制备中,聚合在偶极性非质子溶剂中进行,例如 N-甲基吡咯烷酮 (NMP)、二甲基乙酰胺 (DMAC)、二甲基甲酰胺 (DMF) 或二甲基亚砜 (DMSO),温度在 20–60 °C 之间。 副产物HCl必须原位中和,或通过从沉淀的聚合物中洗涤除去。聚酰胺酰亚胺聚合物的进一步热处理增加了分子量,并导致酰胺酸基团随着水的逸出而形成酰亚胺。

二异氰酸酯路线
这是通往聚酰胺酰亚胺的主要途径,聚酰胺酰亚胺被用作漆包线漆。二异氰酸酯,通常是 4,4'-亚甲基二苯基二异氰酸酯 (MDI),与偏苯三酸酐 (TMA) 反应。在该过程结束时获得的产品是一种高分子量、完全亚胺化的聚合物溶液,没有冷凝副产物,因为二氧化碳气体副产物很容易去除。这种形式便于制造漆包线漆或涂层。溶液粘度由化学计量、单官能试剂和聚合物固体控制。典型的聚合物固体含量为35-45%,供应商或用户可以用稀释剂进一步稀释。

制造
聚酰胺酰亚胺在商业上用于涂料和模塑制品。

涂料
主要用于涂料的产品以粉末形式出售,大约有50%的亚胺化。主要用途之一是作为漆包线漆包。漆包线漆是通过将PAI粉末溶解在强非质子溶剂(如N-甲基吡咯烷酮)中制成的。可以添加稀释剂和其他添加剂,以提供正确的粘度,以应用于铜或铝导体。应用通常是通过将导体拉过搪瓷浴,然后通过模具来控制涂层厚度来完成的。然后将焊丝通过烘箱以驱除溶剂并固化涂层。线材通常要经过几次工艺,以达到所需的涂层厚度。

PAI搪瓷具有很强的热稳定性、耐磨性和耐化学性。PAI通常用于聚酯漆包线漆,以获得更高的耐热等级。

PAI还用于工业用途的装饰性耐腐蚀涂料,通常与含氟聚合物结合使用。PAI有助于将含氟聚合物粘附在金属基材上。它们还可用于不粘炊具涂层。虽然可以使用溶剂,但也使用一些水性体系。这些是可能的,因为酰胺酰亚胺含有酸官能团。

模制或机加工制品
用于模塑制品的聚酰胺酰亚胺也基于芳香族二胺和偏苯三酸氯,但二胺与涂料产品中使用的二胺不同,聚合物在复合和造粒之前被更充分地亚胺化。注塑成型用树脂包括非增强树脂、玻璃纤维增强树脂、碳纤维增强树脂和耐磨等级。这些树脂以相对较低的分子量出售,因此可以通过挤出或注塑成型进行熔融加工。然后,在高达 260 °C (500 °F) 的温度下对模制制品进行数天的热处理。在这种处理过程中,通常称为后固化,分子量通过链延伸而增加,聚合物变得更坚固,更耐化学腐蚀。在后固化之前,零件可以重新研磨和再加工。后固化后,再处理是不切实际的。


注塑成型
聚酰胺酰亚胺树脂具有吸湿性,可吸收环境水分。在加工树脂之前,需要干燥以避免易碎的零件、起泡和其他成型问题。树脂必须干燥至500ppm或更低的水分含量。建议使用能够保持露点为 -40 °F (-40 °C) 的吸附式干燥机。如果在平底锅或托盘中干燥,请将树脂分层放入干燥托盘中,深度不超过 2 至 3 英寸(5 至 8 厘米)。在 250 °F 下干燥 24 小时,在 300 °F 下干燥 16 小时,或在 350 °F 下干燥 8 小时。 如果在 350 °F (177 °C) 下干燥,请将干燥时间限制为 16 小时。对于注塑机,建议使用干燥剂料斗干燥机。循环吸气管应位于料斗底部,尽可能靠近进料喉。

一般而言,建议使用具有闭环控制的微处理器控制装置的现代往复式螺杆注塑机来成型PAI。压力机应配备低压缩比、恒定锥度螺杆。压缩比应在 1.1 到 1.5 比 1 之间,不应使用检查装置。

其他应用
聚酰胺酰亚胺的耐高温性和耐化学性使其原则上适用于基于膜的气体分离。从天然气井中分离出CO2、H2S等污染物和其他杂质是一项重要的工业过程。超过 1000 psia 的压力要求材料具有良好的机械稳定性。由于杂质含量高,高极性的H 2 S和可极化的CO2分子可以与聚合物膜强烈相互作用,导致溶胀和塑化[1]。聚酰胺酰亚胺可以抵抗塑化,因为聚酰亚胺功能会产生强烈的分子间相互作用,并且聚合物链由于酰胺键而相互氢键的能力。虽然目前尚未用于任何主要的工业分离,但聚酰胺酰亚胺可用于需要化学和机械稳定性的这些类型的工艺。"





Polyamide-imides are either thermosetting or thermoplastic, amorphous polymers that have exceptional mechanical, thermal and chemical resistant properties. Polyamide-imides are used extensively as wire coatings in making magnet wire. They are prepared from isocyanates and TMA (trimellic acid-anhydride) in N-methyl-2-pyrrolidone (NMP). A prominent distributor of polyamide-imides is Solvay Specialty Polymers, which uses the trademark Torlon.

Polyamide-imides display a combination of properties from both polyamides and polyimides, such as high strength, melt processibility,[clarification needed] exceptional high heat capability, and broad chemical resistance.[citation needed] Polyamide-imide polymers can be processed into a wide variety of forms, from injection or compression molded parts and ingots, to coatings, films, fibers and adhesives. Generally these articles reach their maximum properties with a subsequent thermal cure process.

Other high-performance polymers in this same realm are polyetheretherketones and polyimides.

Chemistry
The currently popular commercial methods to synthesize polyamide-imides are the acid chloride route and the isocyanate route.

Acid chloride route

Trimellitic acid chloride

Methylene dianiline
The earliest route to polyamide-imides is the condensation of an aromatic diamine, such as methylene dianiline (MDA) and trimellitic acid chloride (TMAC). Reaction of the anhydride with the diamine produces an intermediate amic acid. The acid chloride functionality reacts with the aromatic amine to give the amide bond and hydrochloric acid (HCl) as a by-product. In the commercial preparation of polyamideimides, the polymerization is carried out in a dipolar, aprotic solvent such as N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), dimethylformamide (DMF), or dimethylsulfoxide (DMSO) at temperatures between 20–60 °C. The byproduct HCl must be neutralized in situ or removed by washing it from the precipitated polymer. Further thermal treatment of the polyamideimide polymer increases molecular weight and causes the amic acid groups to form imides with the evolution of water.

Diisocyanate route
This is the primary route to polyamide-imides which are used as wire enamels. A diisocyanate, often 4,4’-methylenediphenyldiisocyanate (MDI), is reacted with trimellitic anhydride (TMA). The product achieved at the end of this process is a high molecular weight, fully imidized polymer solution with no condensation byproducts, since the carbon dioxide gas byproduct is easily removed. This form is convenient for the manufacture of wire enamel or coatings. The solution viscosity is controlled by stoichiometry, monofunctional reagents, and polymer solids. The typical polymer solids level is 35-45% and it may be diluted further by the supplier or user with diluents.

Fabrication
Polyamide-imides are commercially used for coatings and molded articles.

Coatings
The product used mainly for coatings is sold in a powdered form and is roughly 50% imidized. One of the major uses is as a magnet wire enamel. The magnet wire enamel is made by dissolving the PAI powder in a strong, aprotic solvent such as N-methyl pyrrolidone. Diluents and other additives can be added to provide the correct viscosity for application to the copper or aluminum conductor. Application is typically done by drawing the conductor through a bath of enamel and then through a die to control coating thickness. The wire is then passed through an oven to drive off the solvent and cure the coating. The wire usually is passed through the process several times to achieve the desired coating thickness.

The PAI enamel is very thermally stable as well as abrasion and chemical resistant. PAI is often used over polyester wire enamels to achieve higher thermal ratings.

PAI is also used in decorative, corrosion resistant coatings for industrial uses, often in conjunction with fluoropolymers. The PAI aids in adhering the fluoropolymer to the metal substrate. They also find usage in non-stick cookware coatings. While solvents can be used, some water-borne systems are used. These are possible because the amide-imide contains acid functionality.

Molded or machined articles
The polyamide-imides used for molded articles are also based on aromatic diamines and trimellitic acid chloride, but the diamines are different from those used in the products used for coatings and the polymer is more fully imidized prior to compounding and pelletizing. Resins for injection molding include unreinforced, glass-fiber reinforced, carbon fiber reinforced, and wear resistant grades. These resins are sold at a relatively low molecular weight so they can be melt processed by extrusion or injection-molding. The molded articles are then thermally treated for several days at temperatures up to 260 °C (500 °F). During this treatment, commonly referred to a postcure, the molecular weight increases through chain extension and the polymer gets much stronger and more chemically resistant. Prior to postcure, parts can be reground and reprocessed. After postcure, reprocessing is not practical.



Injection molding
Polyamide-imide resin is hygroscopic, and picks up ambient moisture. Before processing the resin, drying is required to avoid brittle parts, foaming, and other molding problems. The resin must be dried to a moisture content of 500 ppm or less. A desiccant dryer capable of maintaining a dew point of ?40 °F (?40 °C) is recommended. If drying is done in pans or trays, put the resin in layers no more than 2 to 3 inches (5 to 8 cm) deep in drying trays. Dry for 24 hours at 250 °F, or 16 hours at 300 °F, or 8 hours at 350 °F. If drying at 350 °F (177 °C), limit drying time to 16 hours. For the injection molding press, a desiccant hopper dryer is recommended. The circulating air suction pipe should be at the base of the hopper, as near the feed throat as possible.

In general, modern reciprocating-screw injection molding presses with microprocessor controls capable of closed-loop control are recommended for molding PAI. The press should be fitted with a low compression ratio, constant taper screw. The compression ratio should be between 1.1 and 1.5 to 1, and no check device should be used. The starting mold temperatures are specified as follows:[citation needed]

Other applications
The high temperature and chemical resistance of polyamide-imides make them in principle suitable for membrane based gas separations. The separation of contaminants such as CO2, H2S, and other impurities from natural gas wells is an important industrial process. Pressures exceeding 1000 psia demand materials with good mechanical stability. The highly polar H2S and polarizable CO2 molecules can strongly interact with the polymer membranes causing swelling and plasticization[37] due to high levels of impurities. Polyamide-imides can resist plasticization because of the strong intermolecular interactions arising from the polyimide functions as well as the ability of the polymer chains to hydrogen bond with one another as a result of the amide bond. Although not currently used in any major industrial separation, polyamide-imides could be used for these types of processes where chemical and mechanical stability are required.