Recent progress in preparation of branched polyethylene with nickel, titanium, vanadium and chromium catalytic systems and EPR study of related catalytic systems

Catalysts play a pivotal role in the olefin polymerization process. After decades of development, a growing number of transition metal catalysts have been widely used in the field of olefin polymerization. Among them, the performance of catalysts such as nickel, titanium, vanadium and chromium are the most attractive. During catalysis process, the chemical valence of the metal in the catalysts usually changed and formed active center with unpaired electron at their outmost electron orbital. Electron Paramagnetic Resonance (EPR) is a good means to detect unpaired electron and free radicals and avoid distraction of other species such as co-catalyst, solvent, monomer etc. This paper reviews the recent progress in the preparation of branched polyethylene with nickel, titanium, vanadium and chromium catalytic systems and EPR analysis of related catalytic systems.