Nanocomposites of fluorinated polyimides (FPI) with covalently grafted polymethacrylate side chains containing polyhedral digomerie silsesquioxane (R7R'Si8O12 or POSS) units were prepared by thermally-initiated free-radical grit polymerization of methacrylcyclopentyl-POSS(MA-POSS) with the ozone-pretreated FPI．The chemical composition and structure of the FPI with grafted methaeryleyclopentyl-POSS side chains were characterized by nuclear magnetic resonance(1H-NMR) and X-ray diffraction (XRD)．The morphology of the POSS/FPI nanocomposite films was observed by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM)．A layer-by-layer structure was revealed

which supports the formation of an ordered architecture by POSS crystallites in the FPI matrix

as the result of self-assembled POSS units of MA-POSS side chins The POSS/FPI nanocomposite films had both lower and tunable dielectric constants

in comparison with that of the pristine FPI films．Dielectric constants(k’s) of about 2.5 to 2.1 were obtained．The reduction of dielectric constant was most likely due to a combined contribution of the nanoporosity of the POSS units and the extemal porosity introduced by the grafting of MA-POSS to the FPI chains．