In this manuscript, the Kumada catalyst transfer polymerization (KCTP) of cyclopenta[2,1-b;3,4-b']dithiophene (CPDT), a monomer consisting of two fused thiophene entities, is investigated. It is shown that this polymerization follows a controlled chain-growth mechanism. Furthermore, the formation of block copolymers with poly(3-alkylthiophene)s is investigated, and it is shown that these block copolymers can be formed if 3-alkylthiophene is used as the first block and CPDT as the second. The resulting all-conjugated block copolymers consist of two blocks with substantially different electronic and physical properties and it is shown that the blocks influence each other, resulting in a unique material with different properties compared to a blend.