In this study, polyhedral oligomeric silsesquioxane glycidylisobutyl‐POSS was dispersed in epoxy resin by ultrasound, and the parameters of a phantom model, the Williams–Landel–Ferry (WLF) and Vogel–Fulcher–Tammann (VFT) equations were modeled using dynamic mechanical analysis (DMA) to evaluate their influence on the glass transition state. The relaxation and retardation time distributions were estimated using a nonlinear regularization method, and the estimated physical parameters were discussed based on the results obtained from transmission electron microscopy (TEM). The TEM analysis indicated higher POSS dispersion with a spherical shape. The POSS dispersion was associated with the formation of micelles due to their hybrid character. The micelles favored the interconnections of the nodular microstructure of the epoxy thermosetting, which led to an increase in their Tg values. These interconnections increased the structure's percolation, promoted a reduction in the thermal expansion coefficient and resulted in a more homogeneous glass transition, in terms of a cooperative distribution in the relaxation times at the time scale measured. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41453.

In this study, polyhedral oligomeric silsesquioxane glycidylisobutyl-POSS was dispersed in an epoxy resin (DGEBA) using ultrasound, and the thermal degradation was investigated by the Flynn-Wall-Ozawa and Criado methods using thermogravimetric analysis. The TEM analysis indicated higher polyhedral oligomeric silsesquioxane (POSS) dispersion in spherical shape. The POSS dispersion was associated with the formation of micelles as a result of their hybrid character. The addition of POSS did not change the degradation of the resin until *380°C, and above this temperature, increase in the thermal stability was observed. The kinetic results revealed that the addition of POSS decreased E a values primarily to 10 % POSS and did not affect the mechanism of degradation for all contents. The reduction in E a was associated with the easier breaking of bonds at the interface of the DGEBA/POSS nanocomposite. The thermodynamic parameters suggested an increased ''degree of arrangement'' for the formation of an active complex during the degradation process and corroborate the lower E a values. The results suggest that the addition of POSS is able to cause an effect of thermal barrier at higher temperatures without affecting the homogeneity of the microstructure of the cured resin.