A series of poly(3-hexylthiophene)-b-poly(hexadecyloxylallene) copolymers has been synthesized in one pot via sequential monomer addition by using Ni(dppp)Cl2 as a single catalyst. The copolymerization has been revealed to proceed by a controlled chain extension mechanism and the block copolymer can self-assemble into a well-defined supramolecular structure in solution and exhibit microphase separation in the solid state.