Dielectric studies of molecular mobility in hybrid polyimide–poly(dimethylsiloxane) networks

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 γ relaxation of PI, the primary α relaxation, associated to the glass transition of PDMS, and the interfacial Maxwell–Wagner–Sillars relaxation, 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 γ and the α relaxations, whereas the time scale of the relaxations remains practically unchanged.