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

Recently, we have investigated a metallocene catalyst system that can produce polyethylene and ethylene/alpha -olefin copolymers with tailored molecular weight and short chain branching distributions (SCBD). Ethylene/alpha -olefin copolymers produced with this system have narrow molecular weight distributions as expected from metallocene catalysts. However, these copolymers are quite unique in that their SCBDs are broad and sometimes bimodal, similar to Ziegler-Natta LLDPE. To examine the effect of these broad SCBDs on the polymer properties, a series of poly(ethylene-co-1-hexene) resins with very distinct, and in some cases bimodal crystalline distributions, were synthesized. The attractive feature of the resins in this study is that their molecular weight distributions are similar but each possesses a different SCBD, thus effectively minimizing 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 study, a balance of stiffness and toughness was exhibited by a copolymer containing a large proportion of crystalline material and a small fraction of material of lower crystallinity. (C) 2001 Elsevier Science Ltd. All rights reserved.