Advanced Functional Materials
Advanced Functional Materials
5 years ago

Tuning the Viscosity Profile of Ionic Vitrimers Incorporating 1,2,3-Triazolium Cross-Links

Tuning the Viscosity Profile of Ionic Vitrimers Incorporating 1,2,3-Triazolium Cross-Links
Antoine Jourdain, Mona M. Obadia, Eric Drockenmuller, Philippe Cassagnau, Damien Montarnal
Vitrimers are dynamic polymer networks with unique viscoelastic behavior combining the best attributes of thermosets and thermoplastics. Ionic vitrimers are a recent class of dynamic materials, where 1,2,3-triazolium cross-links are reshuffled by trans-N-alkylation exchange reactions. Comparison of dynamic properties with a selection of vitrimers relying on different exchange reactions highlights the particularly high viscous flow activation energies of trans-N-alkylation reactions, thus providing an enhanced compromise between fast reprocessing at moderately high temperatures and low creep at service temperature. Varying the [monomer]/[cross-linker] ratio in the initial formulation of these 1,2,3-triazolium-based networks affords a fine tuning of their viscosity profiles. Confrontation of rheometry and X-ray photoelectron spectroscopy data allows the correlation of variations in chemical composition with changes in the covalent exchange dynamics. This unprecedented approach enables the proposition of a dissociative two-step mechanism for the trans-N-alkylation of 1,2,3-triazoliums initiated by a nucleophilic attack of the 1,2,3-triazolium cross-links by the iodide counteranion, yielding uncrosslinking by de-N-alkylation. Subsequent rapid re-N-alkylation of the formed 1,2,3-triazole by surrounding iodide-functionalized dangling chains affords exchange of the cross-link position. This study highlights that strictly associative exchange reactions are not compulsory to induce vitrimer behavior, and may pave the way to a much wider variety of vitrimers relying on conventional reversible covalent reactions. 1,2,3-Triazolium-based ionic vitrimers show particularly high viscous flow activation energies up to 162 kJ mol−1, which affords enhanced compromises between fast reprocessing at high temperatures and long-term stability at service temperature. Confrontation of rheometry and X-ray photoelectron spectroscopy characterization on networks having drastically different chemical composition and cross-linking density corroborates a dissociative two-step mechanism for the trans-N-alkylation dynamic covalent exchanges.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adfm.201703258

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