Novel thermoplastic hyperbranched polyurethane (HBP) elastomer hybrids containing polyhedral oligomeric silsesquioxane (PUSS) have been synthesized using an A(2) + B-3 approach. Different compositions of these hybrid nanomaterials were obtained from reactions of POSS-diol, triethanolamine, poly(epsilon-caprolactone)diol, and 4,4'-methylenebis(phenyl isocyanate) with a chain extender. The covalent attachment of POSS molecules to the backbone of the polyurethane chain was characterized with FT-IR and NMR spectroscopies. The non-agglomerated homogeneous dispersion obtained through the covalent attachment of POSS molecules and the HBP matrix was observed by SEM imaging. The mechanical properties, including the tensile and yield strengths, Young's modulus, and toughness, significantly increased after the introduction of POSS molecules into the hybrids; this increase can be ascribed to the nano-reinforcement effect of the POSS cages and the long-range branched structure of the polymer. Thermogravimetric analyses indicated that the thermal stability of the polymer matrix was improved by the introduction of a small amount of POSS. (c) 2012 Elsevier Ltd. All rights reserved.