Polyamide-imide

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.The currently popular commercial methods to synthesize polyamide-imides are the acid chloride route and the isocyanate route.Polyamide-imides are commercially used for coatings and molded articles.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.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 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.