New dithienothiophene-containing conjugated polymers, such as poly(2,6-bis(2-thiopheny1-3-dodecylthiophene-2-yl)dithieno[3,2-b;2',3'-d ]thiophene, 4 and poly(2,6-bis (2-thiophenyl-4-dodecylthiophene-2-yl)dithieno[3,2-b;2',3'-d]thiophene, 8 have been successfully synthesized via Stille coupling reactions using dodecyl-substituted thiophene-based monomers, bistributyltin dithienothiophene, and bistributyltin bithiophene; these polymers have been fully characterized. The main difference between the two polymers is the substitution position of the dodecyl side chains in the repeating group. Grazing-incidence X-ray diffraction (GI-XRD) gave clear evidence of edge-on orientation of polycrystallites to the substrate. The semiconducting properties of the two polymers have been evaluated in organic thin film transistors (OTFTs). The two conjugated polymers 4 and 8 exhibit fairly high hole carrier mobilities as high as mu(ave) = 0.05 cm(2)Ns (I-ON/OFF = 3.42 x 10(4)) and mu(ave) = 0.01 cm(2)/Vs, (I-ON/OFF = 1.3 x 10(5)), respectively, after thermal annealing process. The solvent annealed films underwent reorganization of the molecules to induce higher crystallinity. Well-defined atomic force microscopy (AFM) topography supported a significant improvement in TFT device performance. The hole carrier mobilities of the solvent annealed films are comparable to those obtained for a thermally annealed sample, and were one-order higher than those obtained with a pristine sample. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 55-64, 2011