Polyurethane-poly(2-hydroxyethyl methacrylate)-3-D nanodiamond (PU-PHEMA-ND) composites were studied using combined CRS/DSC/AFM approach. The peculiar behavior and the pronounced heterogeneity of their glass transition dynamics were revealed. Two opposite tendencies for changing dynamics by 3-D NDs, with prevailing sharp suppression of motions, and three-fold increasing elastic properties were shown. Maximal effects were found at minimal ND content of 0.25 wt%. This was associated, besides the improved dispersion/spatial distribution of NDs, with formation of thoroughly cross-linked nanocomposite network, due to the double hybridization resulting in a low theological percolation threshold and the synergistic effect in dynamics. (C) 2008 Elsevier Ltd. All rights reserved.