We
investigated the nanoscale morphologies and ionic conductivities
of polyethylene-based multiblock copolymers as single-ion conducting
polymer electrolytes. These polymers contain short polar blocks with
a single sodium sulfonate group separated by polyethylene blocks of
fixed length (PESxNa, x = 10, 12,
and 18). At room temperature, these multiblock copolymers exhibit
layered ionic aggregates with semicrystalline polyethylene backbones.
For PES12Na and PES18Na, the layered ionic aggregate morphologies
transition into Ia3̅d gyroid
morphologies upon melting the polyethylene blocks and further transition
into hexagonal morphologies at higher temperatures. With a shorter
polyethylene block, PES10Na exhibits a layered to hexagonal transition
at the melting temperature, without an intermediate gyroid morphology.
The phase diagram of these PESxNa polymers is reminiscent
of conventional diblock copolymers and identifies the presence of
gyroid morphologies at a polar block volume fraction of ∼0.27
to 0.41, which is broad compared to typical diblock copolymers. Temperature-dependent
ionic conductivities reveal faster ion transport through bicontinuous
gyroids than hexagonal ionic aggregate morphologies and a relationship
between conductivity and the characteristic distance between ionic
aggregates. This study presents material design strategies for single-ion
conducting polymers with a bicontinuous ionic aggregate and toward
efficient ion transport.