Organic-inorganic composite polyurethane vitrimers with high toughness, self-healing ability and recyclability

Abstract

Polyurethanes (PUs) have become a class of promising and popular materials in households and industries due to its versatility in chemistry. The combination of self-healing ability, reprocessability with high strength and great toughness for PUs is highly desired in the practical applications, which remains a challenge as the mechanisms for the above properties are normally conflictive. Herein, we proposed a novel concept of PU vitrimers with superb mechanical properties, improved solvent resistance and excellent recyclability. Specifically, linear PUs with maleimide pendant groups was covalently crosslinked with the dithiol-bearing boronic ester cross-linker through thiol-ene “click” chemistry reaction, forming a self-healable and recyclable PU vitrimer network. Furthermore, 2-ureido-4-[1H]-pyrimidione (UPy) motifs capable of forming quadruple hydrogen bonds as the physical cross-linkages were successfully introduced into the vitrimer network, significantly enhancing the mechanical properties. Finally, 2.5 wt% of SiO2 nanofillers functionalized with UPy motifs (SiO2-UPy) were added into the polymer matrices to further improve the mechanical properties of PU vitrimers. Due to the strong interfacial interactions via H-bonds between SiO2-UPy nanofillers and UPy motifs in the PU chains, the PU vitrimer composites exhibited excellent comprehensive performance, including high strength (∼60 MPa) and great toughness (520 MJ m−3) without sacrificing the elongation at break (∼2500 %), excellent self-healing ability and recyclability. Overall, this study offers a strategy to achieve comprehensive enhancement of mechanical properties as well as self-healing/recycling ability with the incorporation of dynamic covalent and non-covalent bonds, which would forward the broad applications of PUs in various industrial scenarios.