Ethylene and Ethylene/α-Olefin (Co)Polymerization Behavior of Bis(phenoxy−imine)Ti Catalysts: Significant Substituent Effects on Activity and Comonomer Incorporation

DFT insight into metals and ligands substitution effects on reactivity of phenoxy-imine catalysts for ethylene polymerization

The reaction mechanism of ethylene (ET) polymerization catalyzed by the phenoxy-imine (FI) ligands using DFT calculations was studied. Among five possible isomers, isomer A which has an octahedral geometry and a (cis-N/trans-O/cis-Cl) arrangement is the most stable pre-reaction Ti-FI dichloride complex. The isomer A can be activated by MAO to form the active catalyst and the active form was used for the study of the mechanism for Ti-FI. The second ethylene insertion was found to be the rate-determining step of the catalyzed ethylene polymerization. To examine the effect of group IVB transition metals (M = Ti, Zr, Hf) substitutions, calculated activation energies at the rate-determining step (EaRDS) were compared, where values of EaRDS of Zr < Hf < Ti agree with experiments. Moreover, we examined the effect of substitution on (O, X) ligands of the Ti-phenoxy-imine (Ti-1) based catalyst. The results revealed that EaRDS of (O, N) > (O, O) > (O, P) > O, S). Hence, the (O, S) ligand has the highest potential to improve the catalytic activity of the Ti-FI catalyst. We also found the activation energy to be related to the Ti-X distance. In addition, a novel Ni-based FI catalyst was investigated. The results indicated that the nickel (II) complex based on the phenoxy-imine (O, N) ligand in the square-planar geometry is more active than in the octahedral geometry. This work provides fundamental insights into the reaction mechanism of M - FI catalysts which can be used for the design and development of M - FI catalysts for ET polymerization.

Enhancement of Ethylene and Ethylene/1-Hexene (Co)polymerization Activities by Titanium(IV) and Zirconium(IV) Complexes Bearing Constrained Hydroxyindanone-Imine Ligands

A new series of catalysts for ethylene and ethylene/1-hexene (co)polymerizations bearing constrained hydroxyindanone-imine ligands was developed for titanium(IV) and zirconium(IV) metals with variations of steric and electronic contributions on the ligands. X-ray crystal structures revealed significantly higher open space for the constrained titanium and zirconium complexes, compared to the conventional FI counterparts. Upon activation with MAO, significantly higher ethylene polymerization activities (up to 379.4 kg-PE/mmol-M h for Zr) and notably almost doubled 1-hexene content in the ethylene/1-hexene copolymerizations were observed as a result of the constrained five-membered ring backbone.

Solution copolymerization of ethylene and propylene by salicylaldiminato-derived [O-NS]TiCl3/MAO catalysts: synthesis, characterization and reactivity ratio estimation

Salicylaldiminato-derived [O-NS]TiCl₃ is used in the copolymerization of ethylene and propylene in toluene solution with methylaluminoxane as the co-catalyst.

Synthesis of Ti, Zr, and Hf complexes with a new tetra-azane ligand by one-pot HCl-elimination and their properties as catalysts for production of UHMWPE

The first example for the HCl-elimination reaction being applied in the attachment of an amido-containing ligand to Zr and Hf.