Properties can be tailored through choice of proportions of dianhydrides and APB.
Imide copolymers that contain 1,3-bis (3- aminophenoxy) benzene (APB) and other diamines and dianhydrides and that are terminated with appropriate amounts of reactive end caps have been invented. The reactive end caps investigated thus far include 4-phenylethynyl phthalic anhydride (PEPA), 3-amino- phenoxy-4'- phenylethynyl benzophenone (3-APEB), maleic anhydride (MA), and 5-norbornene-2,3-dicarboxylic anhydride [also known as nadic anhydride (NA)]. The advantage of these copolyimides terminated with reactive groups, relative to other polyimides terminated with reactive groups, is a combination of (1) higher values of desired mechanical-property parameters and (2) greater ease of processing into useful parts.
Homopolymers that contain only other diamines and dianhydrides and that are not processable under conditions reported previously can be made processable by incorporating various amounts of APB according to this invention, depending on the chemical structures of the diamines and dianhydrides used. These copolyimides exhibit high degrees of resistance to solvents, high glass-transition temperatures, and high moduli of elasticity, but are processable at low pressures [≤ 200 psi (≤1.38 MPa)], when the appropriate amounts of APB are utilized. In addition, when these copolymers are terminated with phenylethynyl groups, they exhibit long-term melt stability (several hours at temperatures approaching 300 °C).
The dianhydride incorporated into a polymer of this type has a rigid molecular structure that tends to degrade processability. The addition of the highly flexible APB diamine improves processability, while the imide structure provides stiffness to the polymer backbone, increases resistance to solvents, and improves mechanical properties. The resulting combination of properties is important for the use of the copolymer as a matrix in a composite material or as an adhesive or a film, coating, or molding material: If too little APB is incorporated into the polymer backbone, the resulting material is not processable under desired processing limitations. If too much APB is incorporated into the polymer backbone, the resulting material becomes highly flexible with a lower glass-transition temperature than desired.
Hence, by choosing the ratio between the amount of APB and the amount of the other diamine in the polyimide backbone, one can obtain a material that has a unique combination of solubility, glass-transition temperature, melting temperature, melt viscosity, toughness, and high-temperature mechanical properties. The exact amount of APB needed to optimize this combination of properties is not predictable and must be determined for the intended application and for the proposed method of processing the copolymer for use in the application.
This work was done by Brian J. Jensen of Langley Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Materials category.