Dielectric techniques, including broadband dielectric relaxation spectroscopy and thermally stimulated depolarization currents, and to a lesser extent differential scanning calorimetry and equilibrium water sorption :isotherm measurements, were employed to investigate molecular mobility in relation to morphology in polyimide-poly(dimethylsiloxane) hybrid networks (PI-PDMS). NMR measurements on the same samples had indicated that short PDMS chains with both ends chemically bound to the PI phase, form spherical domains of nanometer size. The local, secondary gamma relaxation of PI, the primary ot relaxation, associated to the glass transition of PDMS, and the interfacial Maxwell-Wagner-Sillars elaxation, related to the microphase-separated morphology, were studied in detail. The results are discussed in terms of nanoscale confinement of both components and of fixed chain ends of the PDMS component. These factors were found to affect considerably the magnitude of gamma and the alpha relaxations, whereas the time scale of the relaxations remains practically unchanged. (C) 2003 Elsevier Science Ltd. All rights reserved.