This article describes the preparation and characterization of hybrid materials obtained from the polymerization of vinyl-substituted zirconium oxo-clusters [Zr6O4(OH)4(OOCCH2CHCH2)12(n-PrOH)]2·4(CH2CHCH2COOH) (Zr12) and 2-hydroxyethyl methacrylate (HEMA). The zirconium oxo-clusters serve as cross-linking agents, forming a 3D network by means of the copolymerization of their vinylic ligands with HEMA. To optimize the conditions for cross-linking, the polymerization was monitored with a differential scanning calorimeter. The resulting hybrid materials were also characterized using thermo-mechanical techniques. There was evidence not only of a greater rigidity above Tg, but also of a better thermal stability for several hybrid formulations than for simple poly-2-hydroxyethyl methacrylate. After immersion in water, the hybrids containing 20 or 60% w/w zirconium oxo-clusters also showed a stable behavior with an equilibrium swelling at about 27 and 18% w/w of water, respectively. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41568.