Octaepoxysilsesquioxane (POSS-Ep) was first synthesized by the hydrolysis and condensation of ?-[(2,3)-epoxypropoxy]propyltrimethoxysilicane (KH-560) with the presence of ethanol and HCl at 55 degrees C for 72 h. Then, it was cured with 4,4'-diaminodiphenylsulfone (DDS) and methylnadic anhydride (MNA), respectively. The curing reactions between POSS-Ep and DDS or MNA were investigated by FTIR. Thermal stability of the cured nanocomposites was studied by TGA. The micromophologies of the obtained hybrids were observed by SEM. FTIR results show that POSS-Ep can be cured completely with DDS or MNA to obtain the final organicinorganic (OI) hybrids after the same experimental curing cycle: 120 degrees C/2 h + 140 degrees C/2 h + 160 degrees C/2 h + 180 degrees degrees C/2 h + 200 degrees C/2 h. TGA results show that POSS-Ep/DDS hybrid displays better thermal stability than that of POSS-Ep/MNA hybrid. Initial thermal degradation temperature (Tdi) of POSS-Ep/DDS hybrid is 420 degrees C, 195 degrees C higher than that of POSS-Ep/MNA (225 degrees C). SEM images of the fracture surfaces of the hybrids suggest the cured POSS-Ep possesses good mechanical properties. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012