Glass transition and ionic conduction in plasticized and doped ionomers

The relationship between ionic conduction and matrix glass transition was investigated in selected plasticized and doped poly((ethylene glycol)n-co-5-sulfoisophthalate lithium) ionomers. Plasticization with a poly(ethylene glycol) oligomer significantly increases the ionic conductivity, despite a decrease in lithium concentration. Doping with LiClO4 leads to much lower conductivity, despite the increase in Li+ content. These observations were reconciled by considering the corresponding change in ionomer glass transition temperature (Tg), and it was found that ionomers with different plasticizer/dopant levels exhibit similar conductivity at constant T − Tg. The fact that Tg plays such a strong role suggests that Li+ ion mobility is controlled by segmental motion of PEO.