Metathesis of Alkylnorbornenes as a New Route to Synthetic Oils: The Synthesis and Rheo-Tribological Behavior of 5-n-Butylnorbornene Oligomers

We propose a new route to liquid branched hydrocarbon oligomers that can be of interest as potential synthetic oil base stocks. The core of the approach is the ring-opening metathesis polymerization of a norbornene derivative. Oligomerization of 5-n-butyl-2-norbornene in the presence of low loadings of the second-generation Grubbs catalyst and 1-hexene used as a chain transfer agent afforded oligomeric products with a degree of oligomerization in the range of 1 to 7. The metathesis oligomers were hydrogenated using a one-pot technique over the residual ring-opening metathesis polymerization (ROMP) catalyst. After oligomerization and modification, the product yields exceeded 99% and 94%, respectively. Both series of synthesized oligomers are characterized by low glass transition temperatures, which lie in the range from −45 to −125 °C, and depend primarily on the degree of polymerization and on the nature of the main chains. Detailed studies of the rheological properties showed the glass-forming behavior of the synthesized oligomers, allowing for tuning their viscosity in a wide range at any desired temperature, e.g., from 1.4·10⁵ to 4.1·10^–2 Pa·s at −40 °C. The viscosity characteristics of the systems in question are governed by the degree of oligomerization and by the structure of the main chains. Tribological tests revealed a low friction coefficient of steel surfaces when using norbornene oligomers as lubricating oils and a significant wear reduction in comparison with commercial mineral and polyalphaolefin base oils. These results offer prospects for the targeted synthesis of norbornene oligomers with desired low-temperature parameters and remarkable antiwear performance.