Transition behavior and ionic conductivity of lithium perchlorate-doped polystyrene-b-poly(2-vinylpyridine)

We report the transition behavior and the ionic conductivity of ion-doped amorphous block copolymer, based on two compositionally different polystyrene-block-poly(2-vinylpyridine) copolymers (PS-b-P2VPs) that can self-assemble into nanostructures, where P2VP block is ionophilic to lithium perchlorate (LiClO₄). The transition temperatures of LiClO₄-doped PS-b-P2VP, like the order-to-disorder transition (T_ODT), were measured by small-angle X-ray scattering (SAXS) and depolarized light scattering (DPLS). The selective ionic coordination to the nitrogen units of P2VP block leads to the increase of the repulsive interactions between two block components from weak- to strong-segregation regime with increasing amount of LiClO₄, which results subsequently in the increased T_ODT. However, for a compositionally asymmetric PS-b-P2VP under lamellar morphology, the ionic conductivity by the addition of LiClO₄ was remarkably increased at higher temperatures, representing that the effective ionic coordination at the greater volume fraction of P2VP block component improves the ionic conductivity as the temperature approaches to a rubbery phase.