A comprehensive study on highly active pentiptycenyl-substituted bis(imino)pyridyl iron(II) mediated ethylene polymerization

Investigations on the Ethylene Polymerization with Bisarylimine Pyridine Iron (BIP) Catalysts

The kinetics and terminations of ethylene polymerization, mediated by five bisarylimine pyridine (BIP) iron dichloride precatalysts, and activated by large amounts of methyl aluminoxane (MAO) was studied. Narrow distributed paraffins from initially formed aluminum polymeryls and broader distributed 1-polyolefins and (bimodal) mixtures, thereof, were obtained after acidic workup. The main pathway of olefin formation is beta-hydrogen transfer to ethylene. The rate of polymerization in the initial phase is inversely proportional to the co-catalyst concentration for all pre-catalysts; a first-order dependence was found on ethylene and catalyst concentrations. The inhibition by aluminum alkyls is released to some extent in a second phase, which arises after the original methyl groups are transformed into n-alkyl entities and the aluminum polymeryls partly precipitate in the toluene medium. The catalysis is interpretable in a mechanism, wherein, the relative rate of chain shuttling, beta-hydrogen transfer and insertion of ethylene are determining the outcome. Beta-hydrogen transfer enables catalyst mobility, which leads to a (degenerate) chain growth of already precipitated aluminum alkyls. Stronger Lewis acidic centers of the single site catalysts, and those with smaller ligands, are more prone to yield 1-olefins and to undergo a faster reversible alkyl exchange between aluminum and iron.

Systematic studies on dibenzhydryl and pentiptycenyl substituted pyridine-imine nickel(ii) mediated ethylene polymerization

Pyridine-imine nickel catalysts bearing different N-aryl/imine substituents were systematically studied for ethylene polymerization to produce low-molecular-weight and branched polyethylenes.

Comprehensive studies of the ligand electronic effect on unsymmetrical α-diimine nickel(ii) promoted ethylene (co)polymerizations

The ligand electronic effects on the horizontal axis and vertical axis are systematically disclosed in unsymmetrical α-diimine Ni(ii)-promoted ethylene polymerization and copolymerization reactions.