A Curtin-Hammett mechanism for the copolymerization of ethylene and methyl acrylate monomer using a PymNox nickel catalyst as revealed by DFT computational studies

Abstract

In this work, the copolymerization of ethylene and methyl acrylate (MA) as catalyzed by a new Ni-based PymNox organometallic compound was studied computationally. We recently tested the behavior of this type of catalyst in ethylene homopolymerization. Experimental results show that the unsubstituted catalyst Ni2 (aldimino PymNox catalyst) is unable to incorporate the MA monomer, whereas methyl-substituted Ni1 (acetaldimino PymNox catalyst) is able to achieve copolymerization. The reactivities of both catalysts were examined using density functional theory (DFT) models. Based on energy profiles calculated at the BP86 level, a Curtin-Hammett mechanism was proposed to explain the different reactivities of the catalysts in ethylene/MA copolymerization. Our results indicate that the methyl substituent Ni1 introduces additional steric hindrance that results in a catalyst conformation that is better suited to polar monomer incorporation. This model provides insights into the design of new catalysts to produce polar functionalized copolymers based on ethylene. © Springer-Verlag 2011.