Copolythiophenes (Co-PTs), poly(3-hexylthiophene-co-3-thiophene carboxylic acid) (P3HT-TCa), poly(3-hexyloxylthiophene-co-3-thiophene carboxylic acid) (P3HOT-TCa), and poly(3-phenylthiophene-co-3-thiophene carboxylic acid) (P3PhT-TCa), were synthesized by chemical oxidized polymerization to investigate the effect of copolymerization on the properties of polythiophenes (PTs). Gel permeation chromatography showed that the molecular weight (MW) of Co-PT was lower than that of homopolythiophene. Fourier transform infrared (FTIR) spectra indicated that the copolymerization was successful between the monomers. The lambda(max) of Co-PTs gave a "blue shift" in ultraviolet-visible (UV-VIS) spectra. Photoluminescence (PL) spectra showed that the PL intensity of Co-PT became weaker than that of homopolythiophene and the disappearance of PL had been observed in P3HOT-TCa. The thermal stability of Co-PT was influenced by the carboxyl for its low decomposition temperature. Furthermore, the copolymerization between multiwall carbon nanotube containing thiophene ring (MWNT-Th) and 3-hexyloxylthiphene could also take place successfully. (C) 2007 Wiley Periodicals, Inc.