POLYMERS USED AS VISCOSITY INDEX IMPROVERS - A COMPARATIVE-STUDY

Ethylene-propylene copolymers and hydrogenated styrene-diene copolymer s were used for a comparative study aiming at their application as vis cosity index improvers in multigrade engine oils. The variation of vis cosity with temperature has been evaluated as a function of the polyme r concentrations. The thickening effect of different viscosity index i mprovers and the dependence of reduced viscosities on temperature were determined. At concentrations lower than 3% (w/w) the viscosity/tempe rature characteristic suggested the occurrence of polymer coil expansi on with temperature for hydrogenated styrene-diene copolymer. The dire ct dependence of mechanical stability on the copolymer molecular weigh t was observed.