Synthesis of self-healable waterborne isocyanate-free poly(hydroxyurethane)-based supramolecular networks by ionic interactions†
A novel synthetic strategy to isocyanate-free supramolecular polyhydroxyurethanes based on ionic interactions is described. Water-dispersible non-isocyanate polyhydroxyurethanes (WPHUs) dispersions were first prepared from aminoalkyl-terminated poly(dimethylsiloxane), diglycerol dicarbonate and a 8-membered cyclic carbonate (bis-N-8-C) via phase inversion polymerization. Taking advantage of the tertiary amino-groups present in bis-N-8-C, which acted as an internal emulsifier in presence of acetic acid, WPHUs dispersions could thus be achieved. After optimizing the internal surfactant concentration, namely at 30 mol% of bis-N-8-C, stable waterborne PHU dispersions with particle size around 200 nm were obtained. Supramolecular PHU assemblies based on ionic interactions were generated by mixing carboxylic acids of different functionalities, including adipic acid or citric acid, with the optimal dispersion, in absence of any organic solvents. This simple post-chemical modification step enabled to improve the film properties. Formation of the supramolecular network was evidenced by FTIR and 1H NMR spectroscopies. Use of citric acid was found to greatly improve the mechanical properties of the resulting films, as characterized by a transition solid/liquid, which varied from <−10 °C to >60 °C. Supramolecular interactions impart healing abilities to the films, as determined by optical microscopy. Altogether, this study demonstrates for the first time the potential of combining water-dispersible non-isocyanate polyhydroxyurethanes with simple carboxylic acid-containing reagents, providing a straightforward and sustainable approach to novel reprocessable PHU-type materials.