The influence of ligand structure on copolymerization properties of metallocene catalysts was elucidated with three C-1-symmetric methylalumoxane (MAO) activated zirconocene dichlorides, ethylene(1-(7, 9)-diphenylcyclopenta-[alpha]-acenaphthadienyl-2-phenyl-2-cyclopentadien yl)ZrCl2 (1), ethylene(1-(7, 9)-diphenylcyclopenta[alpha]-acenaphthadienyl-2-phenyl-2-fluorenyl)ZrCl2 (2), and ethylene(1-(9)-fluorenyl-(R)1-phenyl-2-(1-indenyl)ZrCl2 (3). Polyethenes produced with 1/MAO had considerable, ca. 10% amount of trans-vinylene end groups, resulting from the chain end isomerization prior to the chain termination. When ethene was copolymerized with 1-hexene or 1-hexadecene using 1/MAO, molar mass of the copolymers varied from high to moderate (531-116 kg/mol) depending on the comonomer feed. At 50% comonomer feed, ethene/1-olefin copolymers with high hexene or hexadecene content (around 10%) were achievable. In the series of catalysts, polyethenes with highest molar mass, up to 985 kg/mol, were obtained with sterically most crowded 2/MAO, but the catalyst was only moderately active to copolymerize higher olefins. Catalyst 3/MAO produced polyethenes with extremely small amounts of trans-vinylene end groups and relatively low molar mass 1-hexene copolymers (from 157 to 38 kg/mol) with similar comonomer content as 1. These results indicate that the catalyst structure, which favors chain end isomerization, is also capable to produce high molar mass 1-olefin copolymers with high comonomer content. In addition, an exceptionally strong synergetic effect of the comonomer on the polymerization activity was observed with catalyst 3/MAO. (C) 2007 Wiley Periodicals, Inc.