The copolymerization of zirconium oxo-clusters (Zr12) with 3-methacryloxypropyl (trimethoxy)silane (MPTMS), using a Si/Zr molar ratio of 4, was investigated. The hybrid samples were prepared both with and without organosilane prehydrolysis. Differential scanning calorimetry (DSC), multinuclear liquid, and solid state NMR analyses and Fourier transform infrared (FTIR) spectroscopy were used to characterize the hybrid materials and study the influence of synthesis conditions on condensation and polymerization. The degree of condensation (DOC) of the silsesquioxane network and the polymerization yield are generally high. However, the organosilane prehydrolysis step leads to the reduction of the extent of phase interaction, thus favoring the phase separation between silica-zirconia-based domains. Dynamic mechanical spectroscopy (DMS) analyses were performed on the hybrid polymers obtained by means of the two synthetic pathways. The sample prepared without the organosilane prehydrolysis step presents a higher glass transition temperature (Tg) than the one with silane prehydrolysis. By heating above the Tg, the samples retain shape and size, due to the lack of viscous flow. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012