A POLYMER USEFUL AS VISCOSITY INDEX IMPROVER

The present invention describes a polymer useful as viscosity index improver comprising units derived from one or more ethylenically unsaturated ester compounds of formula (I), where R is hydrogen or methyl, R1 means a linear, branched or cyclic alkyl residue with 1-6 carbon atoms, R2 and R3 independently represent hydrogen or a group of the formula -COOR', where R' means hydrogen or a alkyl group with 1-6 carbon atoms, units of one or more ethylenically unsaturated ester compounds of formula (II), where R is hydrogen or methyl, R4 means a 2-alkyl branched alkyl residue with 12-18 carbon atoms, R5 and R6 independently are hydrogen or a group of the formula - COOR' ', where R' ' means hydrogen or an alkyl group with 12- 18 carbon atoms, and units of one or more ethylenically unsaturated ester compounds of formula (III), where R is hydrogen or methyl, R7 means a linear alkyl residue with 12-24 carbon atoms, R8 and R9 independently are hydrogen or a group of the formula -COOR' ', where R' ' means hydrogen or an alkyl group with 12-24 carbon atoms wherein said polymer comprises at least 10 % by weight units derived from one or more ethylenically unsaturated ester compounds of formula (I), based on the total weight of the polymer, said polymer comprises at least 10 % by weight units derived from one or more ethylenically unsaturated ester compounds of formula (II), based on the total weight of the polymer, and said polymer comprises at least 10 % by weight units derived from one or more ethylenically unsaturated ester compounds of formula (III), based on the total weight of the polymer. La présente invention concerne un polymère utile comme agent améliorant l'indice de viscosité, comprenant des motifs dérivés d'un ou de plusieurs composés ester éthyléniquement insaturé de formule (I), dans laquelle R représente un atome d'hydrogène ou un groupe méthyle, R1 représente un résidu alkyle linéaire, ramifié ou cyclique contenant 1-6 atomes de carbone, R2 et R3 représentent indépendamment un atome d'hydrogène ou un groupe de formule -COOR', R' représentant un atome d'hydrogène ou un groupe alkyle contenant 1-6 atomes de carbone, des motifs d'un ou de plusieurs composés ester éthyléniquement insaturé de formule (II), dans laquelle R représente un atome d'hydrogène ou un groupe méthyle, R4 représente un résidu alkyle à 2 ramifications alkyle contenant 12-18 atomes de carbone, R5 et R6 représentent indépendamment un atome d'hydrogène ou un groupe de formule -COOR'', R''