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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.