A process for preparing polymeric amides is disclosed. The process comprises sequentially reacting a hydrocarbon polymer functionalized (e.g., via the Koch reaction) to contain acid, ester, thioacid and/or thioester groups with a heavy polyamine to form a partially derivatized product in which at least about 85% of the functional groups are converted to heavy (thio)amide groups, and then reacting the partially derivatized product with an excess of light amine to complete the derivatization by converting substantially all of the remaining functional groups to light (thio)amide groups. Products of the foregoing process are also disclosed, which products are useful as additives in fuels and in lubricants.