Controlling the self-assembled nanoscale ionic aggregates in single-ion conducting polymers is a crucial step toward exceptional transport properties. We report a series of precisely-segmented polyethylene-like ionomers containing sulfonate groups (PES) with Na+ or Li+ counterions synthesized from step-growth polymerization. At room temperature, the PESxNa ionomers with 10, 12, 18, 23 or 48 methylene units are semicrystalline with well-defined nanoscale ionic layers with spacings influenced by the spacer length and cation. In situ X-ray scattering measurements reveal that some of these layered ionic aggregates, upon melting the PE segments, transform into the gyroid morphology. These gyroidal ionic aggregates further evolve into hexagonal symmetry as the temperature increases. These phase transitions are nicely summarized in phase diagram that is strikingly similar to that of diblock copolymers expect that the gyroid morphology exists over a wider composition range (~ 0.27 – 0.41). The order-to-order transitions in ionic aggregate morphologies were also confirmed by oscillatory shear rheology. This innovative and versatile molecular design of ionomers leads to unprecedented percolated gyroidal ionic aggregate morphologies that provide a continuous pathway for improved ion transport. In addition, the PES12Li polymer enters the disordered state and the random phase approximation for multiblock copolymers was used to extract an effective interaction parameter.

Self-assembly of segmented polyolefin Ionomers: New morphologies and ion conductivity

ACS Spring Meeting 2021

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