The Tris‐Urea Motif and Its Incorporation into Polydimethylsiloxane‐Based Supramolecular Materials Presenting Self‐Healing Features

Abstract

Materials of supramolecular nature have attracted much attention owing to their interesting features, such as self-reparability and material robustness, that are imparted by noncovalent interactions to synthetic materials. Among the various structures and synthetic methodologies that may be considered for this purpose, the introduction of extensive arrays of multiple hydrogen bonds allows for the formation of supramolecular materials that may, in principle, present self-healing behavior. Hydrogen bonded networks implement dynamic noncovalent interactions. Suitable selection of structural units gives access to novel dynamic self-repairing materials by incrementing the number of hydrogen-bonding sites present within a molecular framework. Herein, we describe the formation of a tris-urea based motif giving access to six hydrogen-bonding sites, easily accessible through reaction of carbohydrazide with an isocyanate derivative. Extension towards the synthesis of multiply hydrogen-bonded supramolecular materials has been achieved by polycondensation of carbohydrazide with a bis-isocyanate component derived from poly-dimethylsiloxane chains. Such materials underwent self-repair at a mechanically cut surface. This approach gives access to a broad spectrum of materials of varying flexibility by appropriate selection of the bis-isocyanate component that forms the polymer backbone.

Intrinsic Self-Healing Polymers Based on Supramolecular Interactions: State of the Art and Future Directions

“…Single-or double-stranded structures were also observed for self-healing supramolecular silicones prepared by crosslinking of tris(urea)-modified PDMS with hydrazine units [93] via sextuple hydrogen bonding interactions. These materials revealed a self-healing ability when cut films were reassembled immediately, whereas no self-healing behavior was observed after keeping cut surfaces apart for more than 10 min as a result of equilibrating and reassembling of hydrogen bonding moieties [93].…”

NMR spectroscopy and DFT calculations of a self-assembled arene ruthenium rectangle obtained from a combination of coordination and hydrogen bonds

“…6(a). The full assignment of 1 H and 13 C resonances has been carried out using HSQC and HMBC spectra ( Fig. ESI3 and ESI4, † respectively) and is reported in Table 2.…”

“…The final structures produced were used for the measurements of internuclear distances to be compared with those measured experimentally with ROE spectra. In the cases of UPy monomeric and dimeric structures, also calculations of 1 H and 13 C chemical shifts to be compared with those observed experimentally were performed. In order to reduce the computational time, the aliphatic chains of UPy were truncated to ethyls and triflate anions replaced with chlorides.…”

“…The latter approach results in parallel arrays of contiguous donor/acceptor pairs on heterocyclic scaffolds capable of establishing a H-bonding network that drives the selfassembly process. [6][7][8][9][10][11] Examples of up to six consecutive H-bonds have been reported, 12,13 but those involving three and four H-bond arrays are the most studied in molecular recognition and self-assembly of supramolecules. [14][15][16][17][18] Among the most popular scaffolds used to design quadruple H-bonding self-assembled systems is 2-ureido-4-[1H]-pyrimidinone (UPy).…”

Healable supramolecular polymer solids

“…A disc-shaped sample of the 27 kDa polymer (T g ~ -70 °C) was cut into two pieces that were then brought together. Complete disappearance of the cut was observed after 48 h. Lehn and coworkers recently introduced a sextuple H-bonding tris-urea motif as a novel supramolecular building block, which was used to synthesize PDMS-based supramolecular polymers [79]. A simple synthesis involving the condensation of carbohydrazide with isocyanate-terminated PDMS yielded materials that could be solvent-casted into inelastic polymeric films.…”