Preparation and Characterization of Single-Component Poly-α-olefin Oil Base Stocks

In this paper, a single-component poly-α-olefin (PAO) oil base stock of an α-olefin tetramer was prepared via two-step oligomerization using a metallocene catalyst and a Ziegler–Natta catalyst in sequence. The structure was characterized, the performance was investigated, and the effects of the molecular structure and composition on performance were evaluated. First, the α-olefins were dimerized with different metallocenes as the catalyst, and the effects of the oligomerization conditions (amount of catalyst, temperature, and ratio of Al/Zr) on the molecular weight distribution of the obtained polymers were investigated. The dimerization selectivity reached 83.1%, and the content of branched α-olefin was 91.7%. In the second step, the obtained α-olefin dimer was polymerized by a Ziegler–Natta catalyst, and the dimerization reaction was dominant. A PAO with a tetramer content of 89.6% was obtained, and at 100 °C, the kinematic viscosity was 6.4 cSt and the viscosity index was 148. Further results suggested that both molecular structure parameters (the length of the main chain and the length of the branches) affect the PAO properties when the number of branches and the branch position on the molecular skeleton are the same. It was also found that, as the length of the main chain and the length of the branches increased, the kinematic viscosity and viscosity index increased, while the pour point decreased; however, when the length of the main chain, the number of branches, and the length of the branches were the same, the presence of quaternary carbons in the main chain lowered the viscosity index and increased the pour point.