A benzoxazine monomer (VB-a) containing an allyl groups was synthesized through the Mannich condensation of bisphenol A, formaldehyde, and allylarnine (bisphenol-A and allylamine as VB-a). This monomer was then reacted with polyhedral oligomeric silsesquioxane (POSS) through hydrosilylation, followed by thermal curing to form poly(VB-a)/POSS hybrid nanocomposites. The curing behavior of the nanocomposites was monitored using Fourier transform infrared spectroscopy (FTIR), and their thermal and morphological properties were investigated through thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and scanning electron microscopy. DMA revealed that the glass transition temperatures of the poly(VB-a)/POSS nanocomposites were higher than that of the pristine poly(VB-a), presumably because the POSS cages effectively hindered the motion of the polyrner chains. TGA confirmed that the thermal degradation temperatures and char yields of the polybenzoxazines increased after incorporation of the POSS moieties. 0 2008 wiley Periodicals, Inc. J Appl Polym Sci 111: 628-634, 2009