Nanometer-scale structure, molecular dynamics (at 100-580 K) and membrane properties were studied in two series of poly(imide-amide) (PIA)-poly(ethylene glycol) (PEG) hybrid networks with regularly varied composition and different lengths of PEG crosslinks (Mn= 1000 or 3400). Combined WAXD/SAXS/polarized microscopy/DSC/DRS/TSDC/creep rate spectroscopy (CRS) analysis of these hybrids was performed. Depending on their composition, semicrystalline or mesomorphous, or amorphous state, and nanostructural heterogeneity were observed for these networks. They could be subdivided into (a) the PIA-rich hybrids with spatially isolated PEG domains, “suppressed” dynamics in the PEG glass transition, and PIA domains with Tg=520–570 K (group 1), and (b) the other hybrids with a continuous PEG phase and low-temperature glass transition only (group 2). Heterogeneity in segmental dynamics was revealed by CRS over the temperature range from TgPEG to TgPIA. In the second group of hybrids, the permeability coefficients were higher, by two or three orders of magnitude, for organic vapors than those for air gases.