Main content area

Monodisperse and Telechelic Polyethylenes Form Extended Chain Crystals with Ionic Layers

Yan, Lu, Häußler, Manuel, Bauer, Julia, Mecking, Stefan, Winey, Karen I.
Macromolecules 2019 v.52 no.13 pp. 4949-4956
X-ray scattering, ambient temperature, cesium, crystal structure, crystallites, crystallization, differential scanning calorimetry, electrolytes, melting, microwave treatment, plant fats and oils, polyethylenes, protons, saponification, sodium, zinc
We report the synthesis of ionic telechelic low-molecular-weight polyethylenes (PEs) with precise chain lengths that are derived from plant oils along with their morphologies and temperature-dependent ionic conductivities. Starting from the C₄₈ telechelic dimethyl ester, or the C₂₃ analogue for comparison, different ionic carboxylate end groups (H⁺, Na⁺, Cs⁺, Zn²⁺) were introduced by microwave-assisted saponification chemistry. Because of the precise length of the polymethylene sequence, these difunctional telechelic PEs crystallize into exceptionally well-ordered nanoscale-layered structures at room temperature. As a consequence of their extended chain crystal nature, the layer thickness is directly encoded by the telechelic molecules methylene chain length. Notably, C₂₁(COONa)₂, C₄₆(COONa)₂, and C₄₆(COOCs)₂ exhibit transitions in the crystalline structure prior to the fully disordered melt state, as evidenced by differential scanning calorimetry and in situ X-ray scattering. The melting transition is typically accompanied by a transition from layered ionic nanoaggregates between the crystallites to disordered ionic aggregates, with an interesting exception wherein the ionic layers transform to hexagonal symmetry. The temperature-dependent ionic conductivities of layered crystalline morphologies in the C₄₈ materials exhibit an Arrhenius-like behavior, indicating a decoupling from the slower polymer segmental motions at T < Tₘ. These new precise ionic telechelic PEs produce well-defined nanoscale-layered morphologies with tunable ion transport properties that could be further developed as solid-state electrolytes.