PhS- and PhNH-functionalized dienes are copolymerized efficiently with butadiene to stereoregular copolymers by [(mesitylene)Ni(allyl)] [BAr4F] (Ni-1). Overall polymerization rates and comonomer incorporations depend strongly on the linker length between the diene moiety and functional group, in, e.g., PhS-(CH2)(x)C(=CH2)-CH=CH2 (PhS-x-BD, x = 3-7), in particular for certain linker lengths high comonomer reactivity ratios stand out. This effect is related to a favorable binding of the comonomer to the active site comprising coordination of its functional group, which significantly enhances comonomer incorporation in the growing polymer chain.