American Chemical Society
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Ion–Dipole-Interaction-Driven Complexation of Polyethers with Polyviologen-Based Single-Ion Conductors

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journal contribution
posted on 2019-05-29, 14:08 authored by Minjae Lee, Harry W. Gibson, Taehoon Kim, Ralph H. Colby, U Hyeok Choi
The role of solvating polyethers on single-ion conduction and segmental dynamics is investigated for an amorphous main-chain polycation, polyviologen (PV), with two different [−(CH2)6– and −(CH2)10−] spacers and bis­(trifluoromethylsulfonyl)­imide (Tf2N) counteranions and its blends with three polyethers: 18-crown-6 (18C6), 30-crown-10 (30C10), or poly­(ethylene glycol) dimethyl ether 1000. Compared to the neat PV, the addition of polyethers steps up the ion rearrangement (α2) and segmental motion (α), both processes following the Vogel temperature dependence, consistent with a reduction in the glass-transition temperature (Tg) and fragility due to the plasticization by the polyether. An electrode polarization model is used to determine the number density of simultaneously conducting ions and their mobilities. Incorporating polyethers lowers the activation energy of simultaneously conducting Tf2N ions so that the counteranion’s participation in the blends in the ion conduction is more than 4 times higher than that of the unplasticized PV. This is consistent with an increase in the static dielectric constant (εs). The maximum enhancement in εs is observed in the 30C10 blend with εs = 54, whereas the blend with 18C6 having a relatively smaller cavity size shows a value εs = 24, similar to that of the neat PV (εs = 21). This suggests that 30C10 may be large enough to wrap both pyridiniums in the viologen repeat unit, promoting the dissociation of viologen–Tf2N ion pairs, thereby creating separated ion pairs with a larger dipole. The plasticization and complexation play a significant role in directly boosting ionic conductivity (σDC) of the single-ion conducting PV blends by ∼10 times over the whole temperature range measured.