Thermomechanical properties of polyimide-epoxy nanocomposites from cubic silsesquioxane epoxides

Novel polyimide-epoxy organic - inorganic nanocomposites are prepared by in situ curing of polyamic acid macromolecules with two POSS epoxides, octa[(epoxycyclohexylethyl) dimethylsilyloxy] silsesquioxane (OC) and octa[(epoxyhexyl) dimethylsilyloxy] silsesquioxane ( OH). Comparison between two series of nanocomposites from OC and OH provides a typical example of controlling the macro-scale properties by adjusting the nano-tether structure of the POSS molecules. DMA studies conclude that the crosslink densities of the polyimide-epoxy nanocomposites increase significantly; the nanocomposite networks are predominantly formed by the linkage between the terminal amine groups of the polyimide molecules and the epoxide groups of the POSS molecules. Furthermore, it is interesting to observe that although the crosslink densities of nanocomposites increase significantly, the compressive moduli, hardness and coefficients of thermal expansion change only slightly.