The solid state packing of neutral chains of the conjugated polymers is studied by theoretical simulations. The conjugated systems considered here are the pol(3,4-ethylenedioxythiophene (PEDOT) and their substituted PEDOT derivatives PEDOT-C10H21. The molecular mechanics calculations indicate that the polymers tend to form stable pi stacks and indicate that the alkyl side groups freeze the conjugated segments and allow a good organization of PEDOT-C10H21 chains. This explains the increase of conductivity in these systems compared to un-substituted PEDOT. Finally, the introduction of one defect in region-regularity causes a steric hindrance, resulting in less order and less compact pi-stacking. (c) 2006 Elsevier B.V. All rights reserved.