The Effect of Electron Deficiency of the N-aryl Fragment on the Catalytic Properties of Titanium Phenoxy-Imine Complexes in the Ethylene Polymerization

A series of novel post-metallocene titanium complexes bearing polyfluorinated phenoxy-imines with para-substituents of varying electron-withdrawing (–NO₂, –F) or electron-donating (–OMe, –OEt, ‒OⁱPr, –OPh) properties in N-phenyl fragments were synthesized and used as ethylene polymerization catalysts. Upon activation with modified methylaluminoxane these complexes produce highly crystalline ultra-high molecular weight polyethylene. The resulting catalysts were investigated in terms of the impact of the mesomeric effect of the introduced substituent and the electron unsaturation of the N-aryl fragment on the catalytic activity and molecular weight of the polyethylene produced. A nonmonotonic character of the dependences of the activity of the catalyst and the molecular weight of the synthesized polymers on the electrophilicity of the titanium atom was found. An unexpected increase in polymerization activity was also found in the OAlk series upon the transition from OMe to larger groups. To explain these effects, possible reasons were considered clarifying the details of the studied process. The obtained results demonstrate that fine tuning of electronic features of the phenoxy-imine ligand by altering the para-substituents of N-aryl fragments is a powerful tool for control the activity of titanium catalysts as well as properties of the resulting polymers.