Optical properties and dual electrical and ionic conductivity in poly(3-methylhexa(oxyethylene)oxy-4-methylthiophene)

A new regioregular polythiophene derivative bearing side chains with exactl y six oxyethylene units has been synthesized. From the thermochromic and io nochromic behavior of this polymer, it is concluded that the hexa(oxyethyle ne) side chains induce a more planar conformation of the polythiophene back bone than random-length oxyethylene side chains with on average seven oxyet hylene units. It is further observed that the ionochromic transition from t he planar to the nonplanar conformation is [K+](2) dependent, suggesting th at solvation of Kions by adjacent side chains is required. The polymer is i onically as well as electronically conductive. The ionic conductivity is on ly measurable at 80 degrees C, i.e., above T-g and the order-disorder tempe rature of the polymer.