Unsymmetrical α-diimine palladium catalysts and their properties in olefin (co)polymerization†
Previously, it was demonstrated that nickel complexes bearing unsymmetrical α-diimine ligands generated polymers with a broad molecular weight distribution in ethylene polymerization. In this contribution, the influence of some unsymmetrical α-diimine ligands on the catalytic properties of their palladium complexes was investigated in ethylene polymerization, ethylene–methyl acrylate copolymerization and 1-hexene polymerization. Quite interestingly, the unsymmetrical α-diimine ligand structures did not lead to a broad molecular weight distribution in these polymerization and copolymerization reactions. In addition, the influence of different substituents (OMe, Me, Cl and NO2) and different backbone structures was studied. The palladium complexes bearing electron-donating groups showed higher thermal stability and afforded polymers with a much higher molecular weight. The palladium complex bearing naphthalene backbone showed a much lower catalytic activity, generating polymers or copolymers with a much lower molecular weight. The mechanical and surface properties of the resulting polymer and copolymer were also investigated.