To provide a modified polyolefin which is useful as an intermediate to the clearing dispersant for a lubricating oil; a method for producing the same; a method for producing a polyolefin-substituted dicarboxylic acid derivative in a high yield which is essentially free from a halogen atom such as chlorine bringing about a harmful substance by burning to discharge; and a dispersant for a lubricating oil obtained through producing a polyolefin- substituted succinimide using the polyolefin-substituted dicarboxylic acid derivative, wherein the dispersant has a low halogen content and is excellent in dispersion performance.

The method comprises reacting (A) a polyolefin with (C) a radical polymerization initiator in the presence of the carboxylic acid salt of a specific transition metal (B) to produce the modified polyolefin which is abundantly reactive with an unsaturated dicarboxylic acid derivative.