Polyimide (PI) nanocomposites prepared by the in situ generation of crosslinked organosilicon nanophase (ON) through the sol‐gel process were characterized by densities, thermally stimulated depolarization currents and dielectric relaxation spectroscopy. Both a looser molecular packing of PI chain fragments adjacent to the ON and a loose inner structure of the spatial aggregates of ON were assumed to be responsible for a non‐additive decrease of the experimental values of dielectric permittivity for the nanocomposites. The pattern of composition dependence of the apparent dielectric permittivity of the ON suggested a probability of a morphological change around the composition PAAS/MTS = 100/16 (presumably, a sort of percolation transition from small‐size, individual clusters into large‐size, infinite clusters). Thus, PI reinforced with the sol‐gel derived nanophase may have a reasonably good potential as low dielectric permittivity materials. Copyright © 2004 John Wiley & Sons, Ltd.

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Polyimide-based nanocomposites prepared by the in situ generation of inorganic nanoparticles (silica) through the sol-gel process were characterized by kinetics of water uptake, thermogravimetry and dynamic mechanical analysis.Silica particles turned out to possess a rather loose inner structure characterized by enhanced water diffusivities and by dynamic elasticity moduli comparable to that of the pristine, glassy PI. Thermal stability and thermomechanical properties of nanocomposites in the glassy state remained nearly the same as those of the pristine PI, while a significant reinforcement effect was observed for the rubbery PI matrix. q