In this study, the copolymerization of ethylene with nonconjugated diene (5-ethylidene-2-norbornene) was carried out with a bis(2-PhInd) ZrCl2 metallocene catalyst. Some polymerization factors that were considered affective on the catalyst activity, including comonomer content in the feed, ethylene pressure, and polymerization temperature, were investigated via response surface methodology to determine the optimum polymerization conditions. We found that the comonomer content in the feedstock had no enormous effect on the catalyst activity depression. Also, the polymerization temperature increment through the scrutinized range decreased the copolymerization activity. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013