We have investigated a new means to control the morphology and conductivity of block copolymer electrolytes by the inclusion of ionic units at the chain ends. A set of poly(styrene-b-ethylene oxide) (PS-b-PEO) block copolymers having dissimilar PEO end groups were synthesized. Thiol-ene click chemistry particularly provided orthogonal control over the type and number of end groups in PS-b-PEO. This approach permitted the synthesis of PEO chains with reduced crystallinity, reminiscent of PEO oligomers. Intriguingly, the incorporation of diol or dicarboxylic acid end groups in PS-b-PEO produced a well-defined gyroid structure, leading to order of magnitude improvements in the storage modulus. Strikingly, the addition of Li salts to PS-b-PEO with sulfonate terminal groups afforded enriched nanostructures with significant differences in their conductivities depending on the salt concentration. Out of the various samples examined, the electrolytes bearing terminal diol displayed the highest ionic conductivity and a twofold increase in lithium transference number. The improvements in performance are attributed to the reduced inter-chain aggregation and the anion-stabilization mediated by the terminal diol group. This work presents fascinating experimental insights on the enhancement of ion transport efficiencies by modulating the self-assembly nature of polymer electrolytes by substituting with a single end-functional group.

Self-assembly of end-functionalized block copolymers

255th National Meeting (2018)

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