The influence of the main chain stereoregularity on the properties of poly(3-decylthiophene-2,5-diyl) as anticorrosive additive of conventional organic coatings have been examined. For this purpose a small concentration (0.3% w/w) of regiorandom and regioregular conducting polymers were added to alkyd, epoxy, and polyurethane paints typically used in marine environments. The Young's modulus and the elongation at break of the alkyd and epoxy coatings modified with the regiorandom conducting polymer were significantly better than those of the films generated with the original paints, evidencing a very favorable interaction between the additive and the resins. On the other hand, the anticorrosive properties imparted by the modified paints are better when the conducting polymer is regiorandom than when it is regioregular, although even the degree of protection provided by all the modified coatings was higher than that of the original ones. (C) 2008 Wiley Periodicals, Inc.