Two types of electrically active polymers, namely poly(thiophene-3-acetic acid-co-3-hexylthiophene) or Received 5 March 2008 poly(TAA-co-HT), and poly(thiophene-3-acetic acid) or PTAA were synthesized by oxidizing polymerization, and compared in terms of structure, surface resistivity and doping rate. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy data revealed that there is a smaller content of acetic acid functional groups in poly(TAA-co-HT) than in PTAA. Importantly, poly(TAA-co-HT) showed lower surface resistivity and higher doping rate when doped with iodine vapor in comparison with PTAA. The different surface resistivities and doping rates of the two polymers are related with the differences in their relative abundance of polar side groups and packing density of the polymer chains. (C) 2008 Elsevier B.V. All rights reserved.