(410g) Multiblock Copolymers Swollen with Selective Solvents and Their Lithium Conductivity

While periodic structures in diblock and triblock copolymers are well-established, ordered microdomains are less common in multiblock copolymers. We have recently found a variety of self-assembled periodic morphologies in multiblock polymers have blocks of precise length, flexible backbones, and large chi parameters. These precise multiblock copolymers have alkyl blocks of a fixed length strictly alternating with polar blocks having one lithium sulfonate group. As a function of alkyl block length and temperature we observed layered, double gyroid, and hexagonally-packed cylindrical morphologies. In the dry state, these ionic domains exhibit low ion conductivity, because the lithium ions are tightly bound. This talk explores the effects of various solvents, which are selective for the ionic microdomains, using both experiments and all-atom molecular dynamics simulations. When the dry multiblock copolymer forms semi-crystalline layers, the selective solvents can eliminate the crystallinity and change the areal density of sulfonate groups on the layers. The simulations identify a variety of local environments around the Li cations, as well as the lifetime and mobility of these various configurations. Swelling with propylene carbonate proves to be more effective at increasing lithium conductivity than swelling with ethylene carbonate or diglyme. Insights from these techniques are guiding the rational solvent selection for enhanced conductivity in polymer electrolytes.