Organic/inorganic epoxy nanocomposites containing diglycidyl ether of bisphenol A (DGEBA), 4-methylhexahydrophthalic anhydride (MHHPA) and poly(aminopropyl/phenyl) silsesquioxanes (PAPPS) were prepared and characterized. PAPPS were synthesized via fluoride-catalyzed cage formation from random-structured poly(phenyl)silsesquioxane (PPS) and 3-aminopropyltriethoxysilane (APTES) in tetrahydrofuran (THF) using tetrabutylammonium fluoride (TBAF) catalyst containing substantial water. The PPS/APTES stoichiometric ratios were varied. The FTIR, 1H, solid-state 29Si-NMR studies show that PAPPS probably consists of cages, partial cages, and some linear structures containing phenyl and aminopropyl functional groups. The amine content was determined by back titration and elemental analysis. In comparison with neat epoxy, incorporation of these materials can improve the resultant thermal stabilities, raise glass transition temperatures (Tgs), and reduce coefficients of thermal expansion (CTEs) of epoxy nanocomposites as confirmed by TG/DTA, DMA and TMA tests, respectively. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013