Nanocomposite films were prepared through the blending of polyimide (PI) with octaphenyl silsesquioxane (OPS) and an amino-functionalized analogue, octaaminophenyl silsesquioxane (OAPS), with a solution-casting method. Although the PI-OPS composites showed visible phase separation at 5 wt%, the PI-OAPS composites were transparent with visible phase separation occurring only at 50 wt% OAPS. The interfacial interactions and homogeneity of the composites were characterized with scanning electron microscopy (SEM) and dynamic mechanical analysis. SEM analysis showed a uniform fracture surface for OAPS composites at concentrations up to 20 wt%. Interestingly, OAPS-rich particles with sizes of less than 1 mu m were formed within the PI matrix for the 50 wt% composite. The PI-OAPS composites showed higher glass-transition temperatures (Tg's) than the pure PI. The PI-OPS composites showed a T, lower than that of the pure PI, and this suggested poor interfacial interactions. The slightly enhanced thermal stability of PI-OAPS composites (up to 20 wt%) was attributed to the inherent thermal stability of OAPS at higher temperatures. There were small increases in the modulus and strength for the composites with respect to the base polymer. (c) 2008 Wiley Periodicals, Inc.