Phase Behavior and Flory-Huggins Interaction Parameter of Polyethylene-based Multiblock Copolymers with Tethered Lithium Sulfonates

We investigated the temperature-dependent phase behavior and Flory-Huggins interaction parameter of polyethylene-based multiblock copolymer with tethered lithium sulfonates, which are single-ion conducting polymers. The polymer contains short polar blocks with a single lithium sulfonate group precisely separated by polyethylene blocks of 12 carbons (PES12Li). At room temperature, PES12Li exhibits layered morphologies with semicrystalline polyethylene backbones. Upon heating, X-ray scattering observes a transition into hexagonally perforated lamella morphology ~70°C. Above the melting temperature of the PES12Li (~110°C), PES12Li exhibits an order-to-disorder transition (ODT) as indicated by the maximum scattering intensity (I_m) at first-order peak (q*). With increasing temperatures, disordered PES12Li melts exhibits increasing I_m^-1 and q*, consistent with typical polymer melt. The random phase approximation is applied at 150 - 170°C to obtain a Flory-Huggins interaction parameter for PES12Li. Understanding phase behavior and measuring the interaction parameter of polyethylene-based multiblock copolymers will facilitate the design of single-ion conducting polymers with controlled morphology and enhanced ionic conductivities.