Ethylene/Polar Monomer Copolymerization by [N, P] Ti Complexes: Polar Copolymers with Ultrahigh-Molecular Weight

A series of novel titanium complexes (2a-2e) bearing [N, P] aniline-chlorodiphenylphosphine ligands (1a-1e) featuring CH₃ and F substituents have been synthesized and characterized. Surprisingly, in the presence of polar additive, the complexes (2a-2e) all displayed high catalytic activities (up to 1.04 × 10⁶ gPolymer (mol·Ti)^-1·h^-1 and produced copolymer with the ultrahigh molecular weight up to 1.37 × 10⁶ g/mol. The catalytic activities are significantly enhanced by introducing electron-withdrawing group (F) into the aniline aromatic ring. Especially, the increase in activity based on different complexes followed the order of 2e > 2d > 2c > 2b > 2a. Simultaneously, density functional theory (DFT) calculations have been performed to probe the polymerization mechanism as well as the electronic and steric effects of various substituents on the catalyst backbone. DFT computation revealed that the polymerization behaviors could be adjusted by the electronic effect of ligand substituents; however, it has little to do with the steric hindrance of the substituents. Furthermore, theoretical calculation results keep well in accordance with experimental measurement results. The article provided an appealing design method that the employment of fluorine atom as electron-withdrawing to be studied is the promotive effect of transition-metal coordination polymerization.