The temperature dependence of DC conductivity in some hydrogen-bonded polymers

The conductivity of four polyurethane elastomers is reported in the temperature range 27 to 110 degrees C. The charging and discharging currents are also studied as a function of both time and applied field. The conductivity is mainly found to be electronic above the hard-segment glass transition temperature (T_gh) and the corresponding charging currents show linear field dependence. At temperatures about fifty to sixty degrees above T_gh the conductivity shows considerable ionic contribution. In this region the charging currents show a time dependence. The mechanism of conduction is discussed. A power-law slowing down of conductivity of the form sigma varies as (T-T'_g)^r on lowering the temperature towards the major glass transition temperature is found in the above polymers and this empirical equation is extended to a number of other polymers including some nylons. The plasticising action of humidity in nylon 66 and nylon 610 is studied. The power-law constant r is found to vary with humidity as r=r₀-Cm^k, where f₀ and C are constants and m is the weight percentage of the water absorbed. A similar law is found to hold for T'_g also. The role of plasticisers and hydrogen bonding in conduction are discussed.