(521c) Controlled Self-Assembly and Ionic Conductivity Via Interfacial Modification of Lithium-Doped Block Polymers

Ion-conducting block polymers have drawn attention as electrolytes in lithium batteries due to their ability to self-assemble into ordered nanostructures.  Such nanostructured block polymers permit the simultaneous control over ionic transport and mechanical strength, thus providing an enticing opportunity toward fabricating designer materials for polymer electrolytes.  From the standpoint of increasing processability in polymer electrolytes, tapered block polymers provide an efficient way to decouple the processing temperatures from the polymer molecular weight by reducing interfacial interactions between pure blocks; in other words, the order–disorder transition temperatures (T_ODT) can be tuned independent of molecular weight using tapered interfaces.  Recently, we successfully synthesized poly(styrene-b-oligo(oxyethylene) methacrylate) (P(S-OEM)), normal tapered P(S-SOEM-OEM), and inverse tapered P(S-OEMS-OEM) block copolymers with comparable molecular weights and compositions via atom transfer radical polymerization (ATRP) (note: the POEM is potentially superior to poly(ethylene oxide) due to its improved room temperature conductivity as a result of the lack of crystallization in POEM.).  We found that the block copolymer nanostructures can be tuned by adjusting the taper volume fraction and the taper composition.  Additionally, the effective interaction parameters (χ_eff) for the salt-doped copolymers were estimated to determine the overall influence of tapering on copolymer assembly.  Moreover, the ion mobility in salt-doped materials was examined through Vogel-Fulcher-Tammann temperature dependence to explore the effects of interfacial modification on transport properties of salt-doped block polymer membranes.  By developing better controls over interfacial interactions using tapered materials, we are able to design nanostructured membrane systems with increased conductivity, improved mechanical properties, and enhanced processability (reduced T_ODT) in ion transport devices.