This paper reports the synthesis of a novel soluble poly(thienylene methylene) by a straightforward process based on the methanesulfonic acid-catalyzed self-condensation of 2-acetoxymethyl-3,4-dimethylthiophene. These macromolecules were found to generate in situ conjugated sequences consisting of thiophene and exo-unsaturated 2,5-dihydrothiophene moieties. The kinetics of these polycondensations, in which both the temperature and the monomer-to-catalyst molar ratio were varied, were followed by HPLC, as regards the rate of monomer consumption, and by GPC, as regards the evolution of the molecular weight of the growing chains. The ensuing polymers were characterized by FTIR, H-1 NMR, UV-vis spectroscopy, DSC, and TGA.