This investigation presents the synthesis of simultaneous interpenetrating polymer networks based on dimethacrylic/epoxy resins with or without polyhedral oligomeric silsesquioxane (POSS) via in situ polymerization. The curing behavior was studied using differential scanning calorimetry (DSC). The influence of the organic groups from the POSS cages on the curing kinetics of the IPNs was also studied by FT-IR spectrometry. The homogeneous phase structure of the cured IPN was proved by DMA tests. Additionally the integrity of the IPN was also demonstrated by thermal decomposition which occurs in one single step. (C) 2011 Elsevier Ltd. All rights reserved.