ADDITIVI MIGLIORATORI DELL'INDICE DI VISCOSITA' DI OLI LUBRIFICANTI E PROCEDIMENTO PER LA LORO PREPARAZIONE

Viscosity index improver (V.I.I.) additive for lubricating oils comprising an ethylene-propylene copolymer, said additive having the following features: a shear stability index (SSI) comprised between 18% and 30%, preferably comprised between 20% and 28%, measured according to ASTM D7109-12 standard (30 cycles of shearing) in Group I base oil; a thickening power (TP) comprised between 3 cSt and 8 cSt, preferably comprised between 4 cSt and 7.5 cSt, measured according to ASTM D7042-04 standard in Group I base oil; a gelation index defined by the ratio: (η0°C/η40°C)/(η60°C/η40°C) where r| represents the steady state dynamic viscosity measured in Group III base oil, said gelation index being lower than or equal to 7000, preferably comprised between 30 and 6000, more preferably comprised between 50 and 5000; an incipient gelation temperature, measured in Group III base oil, at a temperature lower than or equal to 10 C, preferably comprised between 0 C and 10°C; a shape stability defined according to the following formula: ΔL% = [(L/L0)-1)]*100 wherein L is the length after 24 hours and L0 is the initial length equal to 10 cm, lower than or equal to 5%, preferably lower than or equal to 4%, more preferably lower than or equal to 3%. The aforesaid viscosity index improver (V.I.I.) additive for lubricating oils is advantageously usable in base oils of mineral origin, or of synthetic origin, or mixtures thereof. Preferably, said base oils of mineral origin or of synthetic origin are selected from the base oils belonging to Group I, or Group II or Group III.