Polyolefin-organoclay nanocomposites containing a synthetic tetrasilisic fluoromica were prepared from metallocene-catalyzed and conventional Ziegler-Natta-catalyzed linear low-density polyethylenes (LLDPE) by means of melt-compounding. The effects of maleic-anhydride grafted compatibilizer (PE-g-MA) level, clay concentration, and blending procedure were investigated and compared. Morphology and structural analysis using transmission electron microscopy (TEM) and X-ray diffraction (XRD) suggested the clay exfoliation was more intense in the metallocene LLDPE matrix, conceivably because of the controlled short-chain branching and viscosity effects. When exfoliated, these silicate sheets were shown to restrict the lamellar crystallization, as seen by the decrease in crystallinity using differential scanning calorimetry analysis (DSC). The dynamic mechanical thermal analysis DMTA) study suggested that the three alpha, beta, and gamma-relaxations of the LLDPE were affected by polymer chain branching and clay exfoliation level. (C) 2004 society of Plastics Engineers.