PURPOSE: To obtain a polymeric dispersant useful as lubricating oil and fuel by reacting a mixture (or reaction product) of a polyolefin (derivative) and a polyamine with CO, H2 and a diene.

CONSTITUTION: (A) Mixture of A1: a polyolefin (preferably that comprising a 2-6C olefin monomer) or a succinic anhydride derivative of polyolefin, and A2: a polyamine having NH2 at a terminal that is a compound of the formula ((x), and (y) are 1-3; A is O, S; (m) is 0-2; (n) is 1-10) or (B) a reaction product of A1 and A2 is reacted with Co, H2 and a diene (preferably a 4-20C diene) in the presence of a catalyst system containing a cationic rhodium source (oxide or salt, for example), an aromatic N-heterocyclic ligand (pyridine, for example), an anion source other than halides (nitric acid anion, for example) and optionally a cationic ruthenium source and a solvent (cyclohexane, for example) to obtain the objective polymeric dispersant to be favorably used for producing lubricating oil and fuel.