Stabilizing the Double Gyroid at Room Temperature in Neat Ion-Containing Multiblock Copolymers for Enhanced Ionic Conductivity

In previous work, the double gyroid morphology was reported in multiblock copolymers with strictly alternating linear alkyl blocks of 12 to 23 carbons and sodium sulfonated blocks (PESxNa). The bicontinuous morphology showed enhanced ionic conductivity compared to layers or hexagonally packed cylinders, but it was not accessible below ~100 °C due to the crystallization of the alkyl block. In this work, the sulfonated block is modified by adding an additional carbon (PESxNa-C5) to increase its flexibility and disrupt crystallization. This modification successfully inhibits polymer recrystallization upon cooling which, for some values of x, results in the double gyroid morphology at room temperature. This morphology remains stable at room temperature after several months, and the bicontinuous morphology affords enhanced ionic conductivities of up to ~1 order of magnitude below 100 °C relative to the previously reported materials. The additional atom in the polar block increases the rotational freedom which increases the entropic penalty for crystallization, and the increased size of the polar block promotes the double gyroid morphology. This highlights the importance of considering packing frustration in both blocks when designing ion-containing multiblock copolymers for network morphologies.