Efforts to copolymerize polar comonomers led to catalysts based upon nickel and palladium, inspired by the success of the Shell Higher Olefin Process. Typical post-metallocene catalysts feature bulky, neutral, alpha-diimine ligands. DuPont commercialized the Versipol olefin polymerization system. Eastman commercialized the related Gavilan technology. These complexes catalyze the homopolymerize ethylene to a variety of structures that range from high density polyethylene through hydrocarbon plastomers and elastomers by a mechanism referred to as “chain-walking”. By modifying the bulk of the alpha-diimine, the product distribution of these systems can be 'tuned' to consist of hydrocarbon oils (alpha-olefins), similar to those produced by more tradition nickel(II) oligo/polymerization catalysts. As opposed to metallocenes, they can also randomly copolymerize ethylene with polar comonomers such as methyl acrylate.