Molecular Design of Base Oils with High Viscosity Index

Abstract

This article describes a novel molecular design of synthetic base oils, aimed at developing a new class of base oils with a viscosity index (VI) greater than 200, and the viscosity properties of oligosiloxane-based oils with a VI of 170‒226. The proposed molecular design is derived from the molecular design of liquid crystalline molecules, in which oil molecules consist of a flexible unit and flexible chains, and contain two phenyl rings or less. Based on the molecular design, diphenylbis(alkyldimethylsiloxy)silanes and phenyltris(alkyldimethylsiloxy)silanes have been synthesized, and their structure‒property relationships investigated. The results show that the oligosiloxane oils are a new family of high VI base oils, and that the length of the alkyl chains and the number of the siloxy groups are structural factors that affect the viscosity properties. The kinematic viscosity increases significantly with increasing alkyl chain length, and the VI value increases greatly with increasing siloxy substitution.