Non-isothermal and isothermal crystallization and melting behavior of regioregular poly(3-dodecylthiophene) (P3DT) was investigated by differential scanning calorimetry (DSC) with an emphasis on the main chain crystallization. P3DT showed a sharp exothermic peak at 114 degrees C which was attributed to the main chain crystallization and a broad one peaked at 59 degrees C which was due to the side chain crystallization during cooling at 2.5 degrees C/min from the isotropic melt. During heating, the side chains melting took place from 27 to 80 degrees C, while the main chains melting consisted up to three overlapped melting peaks. Avrami analysis for the non-isothermal crystallization revealed two linear regions with a sharp transition in the log(-ln (1 - theta)) vs. log t plots at the relative crystallinity of 63% for all cooling rates studied. The average Avrami exponent, n, was around 3.9 when the relative crystallinity was lower than 63%, while the n was around 1.5 when the relative crystallinity was higher than 63%. The Ozawa method failed to describe the non-isothermal crystallization process. The non-isothermal crystallization activation energy was estimated to be 222 kJ/mol by the Kissinger method, which was in good agreement with that of isothermal crystallization. Isothermal crystallization and subsequent melting were also investigated at different temperatures. The formations of ordered structures were highly dependent on the crystallization temperatures and time. At lower crystallization temperatures, three melting peaks could be discerned. However, only one melting peak could be observed when the crystallization temperature was high. (C) 2000 Elsevier Science Ltd, All rights reserved.