PU/ZnO nanocomposites are provided wherein the addition of less than 1 vol % 33 nm ZnO nanoparticles into a PU matrix effect a decrease in the Young's Modulus and storage modulus of the polymer, while simultaneously effecting an increase glass transition temperature of the polymer. Detailed experiments are described (e.g., FTIR, DMTA, FESEM and AFM) that suggest that the reaction between hydroxyl groups of the ZnO nanoparticles and isocyanate groups of the polyurethane prepolymer disrupts the self-assembly of the phase separation in PU. Phase separation is responsible for the good mechanical properties of PU. Further, detailed experiments suggest that the increase of the glass transition temperature results from the crosslinking effect of the ZnO nanoparticles.