Oil-soluble dispersant additives are disclosed. The additives comprise the reaction product of a functionalized 1-butene copolymer and at least one nucleophilic reactant selected from amines, amino alcohols, alcohols, and reactive metal compounds. The functionalized copolymer has within its structure at least one acyl functional group selected from the group consisting of C4 to C10 dicarboxylic acids and derivatives thereof and C3 to C10 monocarboxylic acids and derivatives thereof. The 1-butene copolymer is derived from 1-butene and at least one other alpha -olefin of the formula CH2=CHR', wherein R' is methyl or a C3 to C12 linear or branched alkyl group. The copolymer has a number average molecular weight of at least about 700, a molecular weight distribution of less than 5, and ethenylidene groups terminating at least about 30 % of all polymer chains. The dispersant additives are useful in oleaginous compositions including lubricating oil compositions and concentrates and fuel compositions.