Bisbenzimidazole copper dichloride complexes (CuBBIMs), when activated with methylaluminoxane, catalyze the random copolymerization of ethylene with acrylates to produce highly linear functional copolymers. To probe the sensitivity of the copolymerization to the catalyst structure, a series of CuBBIM catalysts with various steric, electronic, and geometric ligand characteristics was prepared, including CuBBIMs having benzimidazole ring substituents and ligand backbones of various lengths. Four different acrylates were also evaluated as comonomers (t-butyl acrylate, methyl acrylate, t-butyl methacrylate, and methyl methacrylate). Although no obvious ligand-based influences on copolymerization were identified, the structure of the acrylate comonomer was found to exert significant effects. Copolymers prepared with t-butyl methacrylate comonomer exhibited the highest ethylene contents (31-63%), whereas those prepared with methyl acrylate contained only minor amounts of ethylene (< 15%). Copolymerizations carried out at lowered acrylate feed levels generally had increased ethylene contents but showed smaller yields, lowered molecular weights, and increased branching. Unusual ketoester structures were also observed in the methyl acrylate and methyl methacrylate containing copolymers, suggesting that the acrylate ester group size may be an important controlling factor for copolymerization. (c) 2006 Wiley Periodicals, lnc.