High ionic conductivity in PEO. PPO block polymer + salt solutions

The conductivity of LiI dissolved in a block copolymer of polypropylene and polyethylene oxide sections of comparable length has been measured and found greater than for either of the pure polymer solutions. The composition of maximum conductivity occurs at low concentration as predicted from entropy theories in which the salt mainly serves to raise the glass transition temperature. A VTF equation gives a good description of the temperature dependence at high salt concentrations. At low concentrations, however, complications due to redistribution of salt between the distinct microregions of the microscopically segregated block units, causes a complex temperature dependence. At intermediate compositions two distinct glass transitions are observed. These blend into a single transition as the microregions blend at high salt concentrations.