Microphase Separation of Linear-Comb Block Copolymer Electrolyte: Electrostatic Effect and Conformational Asymmetry

Abstract

In this work, we synthesize a series of linear-comb block copolymers, polystyrene-b-poly(polyethylene glycol methyl ether acrylate) (PS–PPEGMEA), and study the microphase separation mechanism by LiTFSI-doping. The increasing salt concentration promotes the microphase separation of PS–PPEGMEA and also deflects the phase transition boundaries to the lower PPEGMEA volume fraction. We reveal that the effective interaction parameter exhibits a linear to nonlinear dependence on increasing salt concentration and is eventually weakened by the formation of ion clusters at high salt concentration. We further quantify the conformational asymmetry of PS–PPEGMEA by theoretical analysis and point out that the limit of the order–order transition boundaries is defined by strong segregation theory. Therefore, electrostatic interaction and conformational asymmetry jointly determine the microphase separation of PS–PPEGMEA block copolymer electrolytes. This study provides a fundamental understanding of the phase behaviors of salt-doped linear-comb block copolymers and suggests experimental strategies to modulate their nanostructures, which could be very useful for developing novel solid polymer electrolytes.