Poly[(3-hexyliminomethyl)thiophene]s (P3HITs) were synthesized from the polymerizations of 2,5-dibromo-(hexyliminomethyl)thiophene and 5-bromo-2-iodo-3-(hexyliminomethyl)thiophene by Grignard metathesis method. The corresponding P3HITs with low regioregularity (70%) and high regioregularity (95%) were obtained, respectively. UV-vis and photoluminescence spectra of P3HIT were dependent on the regioregularity and solvent polarity. By hydrolysis of the imino groups in the side chains under acidic conditions, P3HIT was successfully converted into the polythiophene (P3TCHO) having aldehyde groups. This transformation was also performed facilely by exposing the P3HIT film to HCl gas to give the polythiophene having aldehyde moiety. The reverse way from aldehyde to imine was also successfully demonstrated by treating the film with triethylamine vapor. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1190-1194, 2011