AbstractPoly(methyl acrylate)‐b‐polystyrene with controlled molecular weight distribution of each block was synthesized via activators regenerated by electron transfer atom transfer radical polymerization. Polymers with tunable dispersity, in the range of Mw/Mn 1.32 to 2.0, were achieved by adjusting the concentration of the copper catalyst and reaction temperature, thereby controlling the rate of reversible deactivation reaction as well as the number of monomer units added during each activation cycle. Regardless of the increased dispersity, high chain‐end functionality was retained and the livingness of the macroinitiators was confirmed by chain extension, resulting in diblock copolymers with controlled dispersity in each block. Liquid chromatography under critical conditions was employed to determine if any macroinitiator remained in the final product.