Polyimide molecular composites containing a stiff‐chain polymer derived from 1,5‐diaminonaphathalene and pyromellitic dianhydride

Abstract Polyimide molecular composite (MC) films were prepared by embedding a stiff‐chain polyimide (PI_S) in the ductile matrix of a flexible‐chain polyimide (PI_F) by blending their respective poly(amic acid) precursor solutions, followed by casting, drying, and thermal imidization upto 300°C. The PI_S was prepared from pyromellitic dianhydride (PMDA) and 1,5‐diaminonaphathalene (DAN), whereas the PI_F was prepared from the same dianhydride and 4,4′‐oxydianiline (ODA). Transparent, tough, and creasable MC films were obtained with 2.5–40 wt% of PI_S content. The disruption of crystalline order of PI_S in the MC films evidenced its fine dispersion in the matrix. Visco‐elastic measurements showed a single and enhanced value of the glass transition temperature for MC films indicating miscibility of this polyimide pair. Furthermore, the variation of charge transfer (CT) fluorescence intensity with the PI_S content in the blends verified complete miscibility upto 30 wt% of PI_S loading. These MCs showed a notable enhancement in the mechanical properties. Among all, the blend containing 30 wt% of stiff‐chain molecules gave the best combination of properties when compared with the matrix polyimide: a 50% higher value of tensile modulus, a 17°C rise in the glass transition temperature, and better thermal stability. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers