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Effect of Added Salt on Disordered Poly(ethylene oxide)-Block-Poly(methyl methacrylate) Copolymer Electrolytes

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journal contribution
posted on 21.01.2021, 19:33 by Neel J. Shah, Sajjad Dadashi-Silab, Michael D. Galluzzo, Saheli Chakraborty, Whitney S. Loo, Krzysztof Matyjaszewski, Nitash P. Balsara
We studied the effect of salt addition on a diblock copolymer system with a negative Flory–Huggins interaction parameter, χ, indicative of attractive interactions between the two blocks. The system studied is poly­(ethylene oxide)-block-poly­(methyl methacrylate) (PEO-PMMA) with added lithium bis­(trifluoromethanesulfonyl)­imide (LiTFSI) salt. We studied two asymmetric block copolymers, PEO-PMMA(10–33) and PEO-PMMA(10–64), where the numbers refer to the molar masses of the blocks in kg mol–1. The small-angle X-ray scattering (SAXS) profiles for PEO-PMMA(10–33) were featureless at all salt concentrations. In contrast, PEO-PMMA(10–64) exhibited SAXS peaks when the salt concentration was between 0.22 ≤ m (mol Li/kg polymer) ≤ 0.44. The appearance of SAXS peaks only in PEO-PMMA(10–64) is consistent with the predictions of ionic self-consistent field theory developed by de la Cruz and co-workers, which predicts that in systems with negative χ, ordered phases are only found when the volume fraction of the ionic block is about 10%.