The influence of silylene-bridged bis(indenyl) ligand substitution, especially benzannelation and a-methyl substitution, on methylaluminoxane-activated metallocene-catalyzed ethene/1-octene copolymerization in toluene at 40 degrees C was investigated. 2-Methyl substitution gave significantly higher molecular masses at the expense of catalyst activity, whereas benzannelation promoted 1-octene incorporation and randomness of the resulting poly(ethene-co-1-octene) copolymers. Force field calculations based on steric arguments were used to explain experimental copolymerization results. Activation energy differences between ethene and 1-octene insertion accounted for improved 1-octene incorporation in the case of benzannelated metallocenes. According to C-13-NMR microstructure analysis, copolymerization followed first-order Markov statistics.