Abstract
Ethylene-propylene copolymers and hydrogenated styrene-diene copolymers were used for a comparative study aiming at their application as viscosity index improvers in multigrade engine oils. The variation of viscosity with temperature has been evaluated as a function of the polymer concentrations. The thickening effect of different viscosity index improvers and the dependence of reduced viscosities on temperature were determined. At concentrations lower than 3% (w/w) the viscosity/temperature characteristic suggested the occurrence of polymer coil expansion with temperature for hydrogenated styrene-diene copolymer. The direct dependence of mechanical stability on the copolymer molecular weight was observed.
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