Polyhedral oligomeric silsequioxane (POSS), having eight hydroxyl groups for the preparation of nanocomposites with polyimide (PI) was synthesized by the direct hydrosilylation of allyl alcohol with octasilsesquioxane (Q(8)M(8)(H)) with platinum divinyltetramethyl disiloxane Pt(dvs) as a catalyst. The structure of ally] alcohol terminated-POSS (POSS-OH) was confirmed by FTIR, NMR, and XRD. A high performance, low-k PI nanocomposite from pyromellitic dianhydride (PMDA)-4,4'-oxydianiline (ODA) polyamic acid cured with POSS-OH was also successfully synthesized. The incorporation of POSS-OH into PI matrix reduced dielectric constant of PI without loosing mechanical properties. Furthermore, the effects of POSS-OH on. the morphology and properties of the PI/POSS-OH nanocomposites were investigated using UV-vis, FTIR, XRD, SEM, AFM, transmission electron microscope (TEM), TGA, and contact angle. The homogeneous dispersion of POSS particles was confirmed by SEM, AFM, and TEM. The nanoindentation showed that the modulus increased upon increasing the concentration of POSS-OH in PI, whereas the hardness did not increase very much with respect to loading of POSS, due to soft-interphase around POSS molecules in the resulting nanocomposites. Overall results demonstrated the nanometer-level integration of the polymer and POSS-OH. (c) 2008 Wiley Periodicals, Inc.