Abstract A HYDROCARBON-OIL SOLUBLE POLYMERIC ADDITIVE HAVING MULTIFUNCTION QUALITIES INCLUDING VISCOSITY-INDEX-IMPROVING PROPERTIES AND SLUDGE-DISPERRSING PROPERTIES IS PREPARED BY REACTING AN OIL-SOLUBLE POLYMERIC MATERIAL WHICH CONTAINS ACID OR ACID ANHYDRIDE GROUPS DISTRIBUTED ALONG THE POLYMER CHAIN WITH A HETEROCYCLIC AMINO COMPOUND UNDER CONDITIONS WHICH CAUSE THE FORMATION OF AN AMIDE OR IMIDE LINKAGE BETWEEN CARBOXYL OR CARBOXYL ANHYDRIDE GROUPS OF THE POLYMER AND THE AMINO GROUPS OF THE HETEROCYCLIC AMINO COMPOUND. THE LATTER IS CHARACTERIZED AS A HETEROCYCLIC AMINO COMPOUND OF THE PSEUDO-AROMATIC TYPE THAT HAS EITHER OXYGEN OR NITROGEN IN THE RING, HAS ONLY ONE GROUP WITH AN ACTIVE AMINO HYDROGEN, CONTAINS NO OTHER ACTIVE HYDROGEN GROUPS, AND HAS THE AMINO GROUP SEPARATED FROM THE RING BY FROM ONE TO FIVE CARBON ATOMS.