Thermoplastic character of polyimide blends

Polyimide blends consisting of pyromellitic dianhydride/4,4′‐oxydianiline (PMDA/ODA) and biphenyl‐tetracarboxylic dianhydride/p‐phenylene diamine (BPDA/PDA) show a distinct glass transition behavior at temperatures lower than each component does. Disruption of molecular packing by blending of polymers having dissimilar interaction sites leads to a significant increase in molecular mobility at much lower temperatures. This is examined by laminating two pieces of film cast from the blend and measuring the adhesive strength at the interface. A strong adhesion, 11.5 N/cm (6.6 lbf/in) by 180° peel test, was achieved indicating interpenetration of polyimide molecules. It was also found that the polyimide blends can be converted into highly ordered states by mechanical deformation of the blends above their glass transition temperatures (Tgs). Copyright © 1993 Society of Plastics Engineers