Mechanical properties of ethylene/1-hexene copolymers with tailored short chain branching distributions

Recently, we have investigated a metallocene catalyst system that can produ ce polyethylene and ethylene/alpha -olefin copolymers with tailored molecul ar weight and short chain branching distributions (SCBD). Ethylene/alpha -o lefin copolymers produced with this system have narrow molecular weight dis tributions as expected from metallocene catalysts. However, these copolymer s are quite unique in that their SCBDs are broad and sometimes bimodal, sim ilar to Ziegler-Natta LLDPE. To examine the effect of these broad SCBDs on the polymer properties, a ser ies of poly(ethylene-co-1-hexene) resins with very distinct, and in some ca ses bimodal crystalline distributions, were synthesized. The attractive fea ture of the resins in this study is that their molecular weight distributio ns are similar but each possesses a different SCBD, thus effectively minimi zing the effect of molecular weight on the properties investigated. It was found that the tensile properties of a copolymer could be controlled by the ratio of the crystalline species present in the sample. In this stu dy, a balance of stiffness and toughness was exhibited by a copolymer conta ining a large proportion of crystalline material and a small fraction of ma terial of lower crystallinity. (C) 2001 Elsevier Science Ltd. All rights re served.