Low-Temperature Stability of the Double Gyroid Morphology in Ultrahigh-χ Low-N Multiblock Copolymers

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 or lithium sulfonated blocks which contain 4 carbons (PES4Mx). 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 (PES5Nax) 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 for over 1 year when x = 18. Recrystallization on cooling is only seen for polymers where x ≥ 18. Fitting of disordered X-ray scattering data indicates an ultrahigh-χ for this class of materials, similar to what was previously observed in PES4Li12.  This highlights the importance of considering packing frustration in both blocks when designing ion-containing multiblock copolymers with network morphologies.