Palladium-catalyzed direct arylation polycondensation afforded a bithiazole-based homopolymer and donor-acceptor (D-A)-type copolymers where the bithiazole unit served as an acceptor unit. The results of polymerization strongly depended on the solubility of the polymers; long alkyl chain substituents were required for the formation of high-molecular-weight polymers in high yields owing to low solubility of the bithiazole-based polymers. X-ray diffraction studies revealed that the obtained polymers were highly crystalline. In particular, a well-ordered lamellar structure was observed in the D-A-type copolymer with flexible alkyl chains after thermal annealing, presumably owing to the combination of interchain interactions between the bithiazole units and the electrostatic D-A interactions. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1396-1402