Thermal and mechanical properties of ethylene/alpha-olefin copolymers (LLDPE) produced over bis(2-methyl indenyl)zirconium dichloride((2-MeInd)(2)ZrCl2) were compared with those of LLDPEs synthesized with a conventional heterogeneous Ziegler-Natta (Z-N) catalyst, titanium tetrachloride supported on magnesium diethoxide with diisobutyl phthalate as an internal donor(Mg(OEt)(2)/DIBP/TiCl4). DSC thermogram of LLDPE by the Z-N catalyst showed that the melting peak moved to a lower temperature region and the peak became broader as the density of LLDPE decreased. On the other hand, in case of LLDPE produced over (2-MeInd)(2)ZrCl2, the melting peak shifted to a lower temperature zone with the decreasing copolymer density without a significant loss in the peak sharpness. The density of LLDPE was a decreasing function of mole fraction of alpha-olefin, and the decrease was more pronounced as the molecular weight of the incorporated alpha-olefin increased. However, when the density was plotted against weight fraction of alpha-olefin, a similar declining curve was observed irrespective of the type of alpha-olefins except the LLDPE made by the Z-N catalyst in which more a-olefin units were required to reach the same density as that of LLDPEs by (2-MeInd)(2)ZrCl2. LLDPE made by the Z-N catalyst had lower tensile strength but similar elongation and elastic modulus compared to those of poly(ethylene-co-1-dodecene) and poly(ethylene-co-1-octadecene) synthesized by (2-MeInd)(2)ZrCl2. Poly(ethylene-co-1-hexene) by (2-MeInd)(2)ZrCl2, however, exhibited lower elastic modulus and higher elongation compared with the other LLDPEs. Measurement of dynamic mechanical properties of LLDPEs revealed that beta-transition peak appeared at a lower temperature and became more intense, as the density decreased, until the crystallinity of LLDPEs disappeared completely when the beta-transition peak became fixed around -45 degrees C. gamma-transition was monitored at around -125 degrees C and was thought to be induced by the limited motion of the main backbone chain. (C) 2000 Elsevier Science Ltd. All rights reserved.