6. Phthalonitrile Composites with POSS Nanoparticles

The results of the physical study of a series of phthalonitrile nanocomposites with 0.5 wt.% of functionalized POSS nanoparticles are of four types. Their nanostructure, dynamics, relaxation, elastic and thermal properties were examined by TEM, mid-IR, far-IR, EDXS, DMA, DSC, and TGA techniques. Polymerization at temperatures not exceeding 300 °C resulted in the completion of the process by ~70–80% only, and post-curing at higher temperatures increased the degree of polymerization to 90–95%. Far-IR spectra confirmed the main contribution of phthalocyanine cycles to the matrix structure. TEM images and histograms of Si content in the nanovolumes of the composites (EDXS data) indicated a quasi-regular, at the first approximation, distribution of POSS nanoparticles in the amorphous matrix. The introduction of POSS nanoparticles and post-curing led to some suppression of the matrix dynamics and increasing T_g from 380–410 °C to 446 °C for neat matrix and to 520–560 °C for the nanocomposites, with the manifestation of dynamic heterogeneity in the glass transition. A complete suppression of the glass transition as well as the constancy of the dynamic modulus E′ ≈ 3.2 GPa over the range from 20° to 560 °C was observed after heating nanocomposites in an inert atmosphere. The total thermal stability of the nanocomposite up to ~ 400 °C and the “switching on” of thermo-oxidation processes in an air medium from 550 °C were registered by TGA.