Synthesis and molecular characterization of well-defined polyanion miktoarm star copolymers

Abstract

Over the last year, the synthesis of polyanion copolymers has attracted considerable attention for their utilization in single-ion electrolytes in lithium battery applications. Morphology has a significant impact on the properties of such materials thus, reliable synthetic protocols are needed for different macromolecular architectures. In this work, we report the synthesis and molecular characterization of a number of novel miktoarm star copolymers consisting of poly(ethylene oxide), PEO, and poly(lithium 4-styrenesulfonyl trifluoromethylsulfonyl imide), PSTFSILi, arms and a poly(divinylbenzene), PDVB, core. Initially, a PEO–NMP macroinitiator was synthesized. The “arm-first” method, was employed to produce a PEO star with approximately 22 arms, (PEO)₂₂, with a spacious PDVB core, bearing active NMP initiation sites. Subsequent polymerization of the STFSIK monomer (“in–out” method), followed by ion exchange using LiCl, produced well-defined PEO/PSTFSILi miktoarm stars. By varying the polymerization conditions, a series of miktoarm stars with various PSTFSILi molecular weights and Li⁺ molar ratios, r = [Li⁺]/[EO], were synthesized. A kinetic study on the polymerization of STFSIK on the PEO star core, was completed, to reveal well-controlled and “living” features. We show that the macromolecular architecture and the ratio r have a huge impact on the crystallization, the segmental dynamics, and ion-conductivity of the miktoarm star copolymers.