Organic–inorganic nanocomposites from cubic silsesquioxane epoxides: direct characterization of interphase, and thermomechanical properties

Novel organic–inorganic nanocomposites were prepared by in situ curing of poly(amic acid) macromolecules with POSS epoxide, octa(ethylcyclohexylepoxidedimethylsiloxy) silsesquioxane (OC). Solid-state 29Si NMR data show that properties of the interphase can be varied systemically by adjusting the nano-tether structure of the POSS molecules. DMA studies conclude that the cross-linking densities of the nanocomposites increase significantly so that some of these nancomposites are found to lose glass transition temperature; the nanocomposite networks were predominantly formed by the linkage between the terminal amine groups of the polyimide molecules and the epoxide groups of the POSS molecules. Furthermore, in the nanocomposites two factors, the soft interphase around OC molecules and the increasing cross-linking density, compete with each other, and their influences on morphologies, coefficient of thermal expansion, mechanical strength and hardness of these nanocomposites were also investigated.