Novel rod-coil-rod ABA triblock copolymers, poly(3-hexylthiophene)-block-poly(ethylene)-block-poly(3-hexylthiophene) (P3HT-b-PE-b-P3HT) were synthesized by using a combination of a Ru-catalyzed ring-opening metathesis polymerization of 1,4-cyclooctadiene in the presence of a suitable chain transfer agent (CTA) and a Ni-catalyzed Grignard metathesis polymerization of 5-chloromagnesio-2-bromo-3hexylthiophene followed by hydrogenation. Using this methodology, the molecular weights of the poly(butadiene) (PBD) or the P3HT blocks were controlled by adjusting the initial monomer/ CTA or the initial monomer/ macroinitiator ratio, respectively. In addition, the triblock structure was confirmed by selective oxidative degradation of the PBD block found in the intermediate P3HT-b-PBD-b-P3HT copolymer produced in the aforementioned method, followed by analysis of the degradation products. Thermal analysis and atomic force microscopy of P3HT-b-PE-b-P3HT revealed that the material underwent phase separation in the solid state, a feature which may prove useful for improving charge mobilities within electronic devices. (C) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3810-3817