An acylated hydrocarbon polymer is aminated by reacting a primary or secondary aromatic amine which is solid at room temperature with an acyl group of the polymer, by: supplying a melt of the acylated polymer; supplying a solution of the aromatic amine in a polar aprotic solvent which has a boiling point of at least about 15° C., a melting point below about 40° C., and a dielectric constant of at least about 5° at 25° C.; mixing the solution at 140° C. to 185° C.; and cooling the resulting amine-reacted polymer with a liquid while retaining the polar aprotic solvent in the polymer.