Conductivity of some semiconducting polyazophenylenes

The electrical conductivity of a series of semiconducting polyazophenylenes was studied as a function of temperature and molecular weight in the temperature range 293–493°K and for molecular weights between 9500 and 62800. The compounds studied included poly-2,4-diminotoluene and poly-2,5-diaminotoluene. The temperature dependence of conductivity obeys the exponential law σ = σ₀ exp {–E_a/kT}. All of the compounds studied show a break in the conductivity curve at a temperature of about 380°K with the slope of the curve greater at temperatures above 380°K. The activation energies E_a determined from the higher slopes are in the range 0.63–0.89 eV, and the corresponding σ₀ values are in the range 10^?4-10° (ohm-cm)^?1. Both E_a and σ₀ show a tendency to increase with increasing molecular weight such that the compensation law was valid. Activation energies and σ₀ values determined from the (smaller) slope below the temperature of the break point showed a tendency to decrease with successive measurements on new samples. This indicates some kind of orientation effect, and conclusions concerning the properties of the material on basis of results below the break point are therefore difficult.