Organic/inorganic hybrid composites from cubic silsesquioxanes

A new class of epoxy nanocomposites with completely defined organic/inorgan ic phases was prepared by reacting octakis(glycidyldimethylsiloxy)octasilse squioxane [(glydicylMe(2)SiOSiO(1.5))(8)] (OG) with diamino-diphenylmethane (DDM) at various compositional ratios. The effects of reaction curing cond itions on nanostructural organization and mechanical properties were explor ed. A commercial epoxy resin based on the diglycidyl ether of bisphenol A ( DGEBA) was used as a reference material throughout these studies. FTIR was used to follow the curing process and to demonstrate that the silsesquioxan e structure is preserved during processing. OG/DDM composites possess compa rable tensile moduli (E) and fracture toughness (KIC) to, and better therma l stabilities than, DGEBA/DDM cured under similar conditions. Dynamic mecha nical analysis and model reaction studies suggest that the maximum cross-li nk density is obtained at N = 0.5 (NH2:epoxy groups = 0.5) whereas the mech anical properties are maximized at N = 1.0. Digestion of the inorganic core with HF followed by GPC analysis of the resulting organic tether fragments when combined with the model reaction studies confirms that, at N = 0.5, e ach organic tether connects four cubes, while, at N = 1.0, linear tethers c onnecting two cubes dominate the network structure. Thus, well-defined nano composites with controlled variation of the organic tether architecture can be made and their properties assessed.