Ion Confinement in Self-Assembled Precisely Segmented Polyolefin Ionomers*

Confining ions within self-assembled nanoscale structures is demonstrated in a series of single-ion conducting segmented polyolefins, nominally multiblock copolymers. We report a series of precisely-segmented polyethylene-like ionomers containing sulfonate groups (PES) with Li+, Na+, Cs+, or NBu4+ counterions synthesized from step-growth polymerization. At room temperature, the PES ionomers with long methylene units are semicrystalline with well-defined nanoscale ionic layers with spacings influenced by the spacer length and cation type. In situ X-ray scattering measurements reveal that the layered ionic aggregates in some of these polymers transform, upon melting the PE segments, into gyroid morphologies. The gyroid structure can further evolve into hexagonal symmetry as T increases. The ion transport behavior of these polymers is strongly dependent on the ionic aggregate morphologies. Specifically, a 3D interconnected gyroid morphology exhibits higher ionic conductivity than the isotropic layered or hexagonal morphologies. 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.