Ionic Conductivity in Telechelic Polyethylenes Oligomers from Fatty Acids*

Telechelic polyethylenes (PEs) containing metal cation (e.g. Na⁺, Cs⁺ or Zn²⁺) coordinated carboxylate end groups with 21 or 46 CH₂ units (C21 or C46) in between have been synthesized from chain doubling of erucic acid. These linear and monodisperse telechelic PEs crystallize into well-defined lamellar structures with acid or ion-rich layers embedded in the orthorhombic or monoclinic crystallites at room temperature. Interestingly, C₄₆(COOCs)₂, C₄₆(COONa)₂, and C₂₁(COONa)₂ exhibit a crystal phase transition from orthorhombic to hexagonal or monoclinic structure prior to the melt state, according to DSC and X-ray scattering. The crystal phase transition are mainly due to increased chain rotation at elevated temperature, but the strong ionic interaction in the layered structure prevents the crystal from directly melting. The ionic conductivity of C₄₆(COONa)₂, C₄₆(COO)₂Zn and C₄₆(COOCs)₂ exhibit an Arrhenius-like ion conduction behavior suggesting that the ion transport in the layers are decoupled from the PE segmental movements. This work offers important insights for designing telechelic molecules with well-defined morphologies and tunable ion transport properties through the two-dimensional ionic channels.