Characterization of poly(3‐octylthiophene). II: Melt rheological characterization

The poly(3‐alkythiophenes) are electrically conducting polymers which are of particular interest due to their melt‐processibility. We have studied the melt properties of poly(3‐octylthiophene) (P3OT) by dynamic rheological measurements at temperatures between 180 and 250°C. The samples investigated have molecular weights in the range Mw = 30,000 to 400,000 and have been carefully characterized by dilute solution techniques, Residual iron chloride, a reagent used in the polymerization of these materials, was found to cause a high degree of crosslinking in the polymer melt. By contrast, samples which had been carefully purified demonstrated a negligible rate of crosslinking in a nitrogen atmosphere; however, the presence of air and higher temperatures were found to increase the rate of crosslinking substantially. The temperature dependence of the viscoelastic properties was characterized according to the principles of time‐temperature superposition, and the influence of molecular weight was also evaluated. Overall, the rheological behavior was determined to be similar to that commonly observed for linear flexible polymers, which is in agreement with the results of our solution characterization of these materials.