Homogeneous {Ti2Ni} Heterotrinuclear Catalyst for Ethylene Polymerization and Copolymerization

Abstract

We synthesized and spectroscopically characterized a new heterotrimetallic {Ti2Ni} ethylene (co)polymerization precatalyst containing one (α-diimine)NiBr2 and two (phenoxy-imine)TiCl4 scaffolds. Its calculated structure was investigated at the DFT B3LYP/LACVP** level. Our calculations showed that the titanium(IV) centers were in a slightly distorted trigonal bipyramidal environment, and the average Ti···Ni distance was 8.76 Å. The precatalyst was used for synthesizing polyethylene and ethylene copolymers. The results of GPC analyses showed that the obtained polyethylenes had the desired bimodal molecular weight distributions. The FTIR spectra revealed that polydispersity decreased as the vinyl end-group content increased. These results suggested that high mechanical resistance can increase the mechanical energy needed for processing the material. All 13C NMR signals were assigned to short-chain branches with specific spatial arrangements along the polymer backbone. The chain walking mechanism of branch formation controls the spacing and conformational arrangements between these short chains.