DSC was used to follow the degree of conversion (DC) for the methacrylic groups in the case of some hybrid systems based on urethane dimethacrylate (UDMA) monomer and various polyhedral oligomeric silsesquioxane (POSS) structures (HISO-POSS, CPENTYL-POSS, and MA-POSS). The chemical structure of the POSS compound directly influences the DC value. The conversion of the methacrylic groups from the hybrid composites after thermal curing was determined by measuring the residual heat of reaction. Both SEM and AFM techniques were additionally used to performed an advanced morphological characterization for the obtained POSS-nanocomposites. The DSC data have been corroborated with those resulted from the NIR spectroscopy. The introduction of POSS compound within the UDMA matrix leads to a decrease of the hybrid material transparency due to the formation of agglomerates also pointed out by SEM analysis. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121:2919-2926, 2011