The properties of two new ethylene-a-olefin copolymers, namely, ethylene-l-hexene copolymer (EHC) and ethylene-l-octadecene copolymers (EOC), synthesized via metallocene catalysts were evaluated. The copolymerization was carried out in an autoclave reactor with Et(Indenyl)(2)ZrCl2/methylaluminoxane as a catalyst system. These single-site catalysts (metallocene type) allow one to obtain very homogeneous copolymers with excellent control of the molecular weight distribution and proportion of comonomer incorporation. So, copolymers with 18 mol % comonomer in the case of EHC and 12 mol % for EOC were shaped, and activities around 100,000 kg of polymer mol(-1) of Zr bar(-1) h(-1) were reached. The properties of these co-polymers were compared with other commercial elastomers, such as ethylene-propylene copolymers synthesized by Ziegler-Natta catalysts and an ethylene-octene copolymer obtained via metallocene catalysts. The results show that these new copolymers, in particular, EOC, had excellent elastomeric properties. Furthermore, they had a relatively low viscosity, which implied a good response during processing. Moreover, the effectiveness of these copolymers as impact modifiers for polyolefins was also studied. (C) 2004 Wiley Periodicals, Inc.