Linear, one-binding-site or two-binding-site (N+) organifiers with two hydroxyl end groups were synthesized, and novel organoclays were prepared through a cation-exchange reaction between pristine sodium montmorillonite and the synthesized organifiers. After sonication of the as-prepared organoclay in N,N'-dimethylformamide for 10 min, the average size of the clay decreased to about 1 mu m. The X-ray diffraction patterns confirmed that the d-spacirtg of the silicate layers of the organoclay expanded from 1.1 to about 1.9 nm and the peak intensity decreased with the molecular weight of the organifier increasing. Polyurethane/clay nanocomposites were synthesized by a one-shot polymerization method. Both intercalated and exfoliated structures of the layered silicates in the polyurethane matrix were observed from transmission electron microscopy micrographs, and the d-spacing ranged from 4 to 10 nm. The thermal and mechanical properties of the nanocomposite were enhanced by the introduction of the organoclay into the polyurethane matrix. An approximately 40-46 degrees C increase in the onset decomposition temperature, a 200% increase in the tensile strength with a 0.5 wt % clay loading, and a 49% increase in Young's modulus with a 3 wt % clay loading were achieved. The effects of the molecular weight and the number of binding sites of the organifier on the properties of the nanocomposites were also evaluated. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 2090-2100, 2010