Abstract: The structures and properties of six lube base oils produced by Fischer-Tropsch synthesis and fourteen hydroisomeric lube base oils were studied and analyzed by nuclear magnetic resonance(NMR) technology. The correlations of viscosity index(VI) and contents of 8 kinds of isomers were established. The influences of hydrocarbon composition and structure of lube base oils on their VI were investigated. The specific structures played an important role in controlling the viscosity-temperature performance of lube base oils. The presence of the molecules with methyl-substituted at position 2, 3 and 4 in lube base oils reduced the VI of lube base oils, while normal paraffins and the methyl substituted at position 6 or 7 structures contribute positively to the VI. For lube base oils produced by Fischer-Tropsch synthesis, the larger the branched degree and branched number of lube base oils were, the higher the branching degree of lube base oils were. For lube base oils with different average carbon numbers of molecules, the branching degree decreased with the reduction of relative branched number. VI corresponded linearly to the relative branched number with correlation coefficient of 0.95.

Key words: lube base oil, NMR, structural composition, viscosity index