Crystallization behavior of regioregular poly(3-dodecylthiophene)

Non-isothermal and isothermal crystallization 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 melt. During heating, the side chains melted from 27 to 80 degrees C, while the main chains exhibited up to three overlapped melting peaks. Avrami analysis for the non-isothermal crystallization revealed a sharp transition in the log(-In(1-theta)) vs. logt curves at the relative crystallinity of 63% for all cooling rates studied. The average Avrami exponent, n, was around 4.9 when the relative crystallinity was lower than 63%, while the n is around 1.5 when the relative crystallinity was higher than 63%. The non-isothermal crystallization activation energy was estimated to be 222kJ/mol by Kissinger method. Isothermal crystallization was also investigated at different temperatures. The formation of ordered structure and subsequent melting behavior 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.