A series of phthalonitrile nanocomposites, obtained from bisphenol A based bisphthalonitrile (BAPhN) with 0.5 wt.% of different reactive amino- or epoxy-functionalized polyhedral oligomeric silsesquioxane (POSS) nanoparticles or montmorillonite (MMT) nanolayers, were synthesized and studied in detail. Their structure, dynamics and properties were characterized by TEM, mid-IR, far-IR and EDX spectroscopies, DSC, and by DMA and TGA measurements performed in air and N-2 atmosphere at temperatures from 20 degrees to 600-700 degrees C. Predominance of phthalocyanine macrocycles in the nodes of the matrix network is suggested; a satisfactory dispersion and a quasi-regular distribution of POSS nanoparticles have been revealed. For post-cured nanocomposites, DMA demonstrated an anomalous ("quasi-phase") glass transition, dynamic heterogeneity in this transition, and "constrained dynamics" effects. T-g (DMA) was found to vary from 460 degrees to 560 degrees C. After a high-temperature treatment in N-2 atmosphere, disappearance of relaxation spectrum and glass transition as well as the constancy of the nanocomposite modulus E' approximate to 3.2 GPa at 20-600 degrees C were observed. A relatively satisfactory thermal stability of the nanocomposites was registered at temperatures up to similar to 500 degrees C in air and 700 degrees C in N-2.( )