Ethylene and optional comonomers are polymerized in the presence of an organozinc compound and a catalyst system to produce an ethylene polymer. The catalyst system comprises a bridged indenoindolyl Group 3-10 transition metal complex and an activator. The organozinc compound is used in an amount effective to increase the polymer bulk density compared with that observed in the absence of the organozinc compound. The organozinc compound can also narrow the particle size distribution of the polymer and the wt. % of polyolefin chunks produced. The operability of processes utilizing bridged indenoindolyl metal complexes is enhanced while maintaining desirably high polyolefin molecular weights.