Effect of metal type on the metallocene-catalyzed oligomerization of 1-hexene and 1-octene to produce polyα-olefin-based synthetic lubricants

1-Hexene and 1-octene oligomerization reactions were performed with Cp2ZrCl2 and Cp2HfCl2 in the presence of methylaluminoxane as cocatalyst at 25 and 80 degrees C to produce poly alpha-olefin-type oils. By examining the molecular weight results, obtained from gel permeation chromatography, the oligomeric structure of the products was confirmed. Hafnocene produced oligomers with higher molecular weights in comparison with zirconocene under the same reaction condition. In addition, with increasing temperature, the molecular weight decreased. Differential scanning calorimetry analysis of the poly1-hexene- and poly1-octene-type oligomers confirmed their amorphous nature. H-1-nuclear magnetic resonance (NMR) analysis was performed to study the mechanism of termination reactions. The results obtained from the H-1-NMR analysis confirmed the vinylidine form (vd) as the only unsaturated structure in all synthesized oligomers. Therefore, in the 1-hexene and 1-octene oligomerization reactions with these two catalytic systems, the chain termination is totally accomplished by beta-hydride elimination at both reaction temperatures.