The preparation and properties of poly(1-butene) (PB)/clay nanocomposites are described for the first time. Nanocomposites were prepared with the melt-intercalation technique, using organically modified clay. The X-ray diffraction patterns portrayed well-defined diffraction peaks at higher d-spacing than pristine clay, confirming the intercalation of polymer in silicate layers. Because PB exhibits time-dependent polymorphism, the effect of clay on the phase transformation of PB was examined with thermal analysis. The phase transformation from a metastable tetragonal form to a stable hexagonal form was enhanced because of incorporation of layered silicates in the polymer matrix. The nanocomposites exhibited about a 40-140% increase in storage modulus depending on the clay content and significantly lower coefficient of thermal expansion. (C) 2003 Wiley Periodicals, Inc.