Epoxy resins containing polyhedral oligomeric silsesquioxane (POSS) N-phenylaminopropyl nanocomposites were prepared. Modulated differential scanning calorimetry (MDSC) was performed to evaluate the thermodynamic glass transition (T-g) of these materials. The transmission electron microscopy (TEM) images reveal that the dispersion of the POSS in the resin was effective when concentrations greater than 5 wt% were added. The microstructure and the morphology of the epoxy, which were observed using atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively, became more homogenous for the nanocomposites. The addition of POSS promotes a decrease in the rate of variation of the heat capacity (C-p). This C-p reduction was supported by the increase in the average size, Z(T), of the cooperative rearrangements regions (CRR) and the approach between the experimental and theoretical T-g determined using the Adam-Gibbs and Kauzmann theories. The increase in the Z(T) occurs because a more homogenous structure formed and caused the reduction of the fragility index, which was determined using Angel's theory. (C) 2013 Elsevier Ltd. All rights reserved.