A new class of mesomorphic polymer electrolytes (side group liquid crystalline polyethers) is described whose members exhibit significant ionic conductivity in both liquid crystalline and glassy states. It is suggested that the pendent side groups effectively “jacket” the ethylene oxide backbones, and prevent the ethylene oxide units from adopting a close-packed structure during cooling. The resulting open structure and multiplicity of ion sites is probably the origin of the decoupling process which permits ion migration even below T g. This could be a widespread phenomenon in polymer electrolytes.