Hydrophobic-oleophobic polyurethane with mechanical reinforcement: Synthesized by thiol-ene click chemistry

Polyurethane (PU) is a universal polymer material with excellent performance, widely used as foam materials, adhesives, coatings, rubber, etc. Nevertheless, the considerable presence of ester and ether bonds in the polyurethane backbone, combined with the hydrophilic -OH group located at the end of molecular chain, renders it intrinsically hydrophilic. This inherent hydrophilicity presents substantial constraints on its potential utilization in flexible electronic displays, wearable electronic devices, and various other fields. It is a great challenge for hydrophobic polyurethane to simultaneously achieve mechanical reinforcement. Herein, the fluorinated chain extenders were introduced into PU, which not only resulted in low surface energy but also improved the surface roughness through the microphase separation due to the difference in the solubility parameters between the fluorine-containing side chain and the main chain. The long-chain perfluorinated extender was achieved via thiol-ene click chemistry, thus regulating the fluorine content by adjusting the amount of chain extender. The low surface energy and high roughness, developed by microphase separation, make the DFX-PU films exhibit excellent hydrophobicity (120 degrees) and oleophobicity (121 degrees). Additionally, the fluorine-containing side chains aggregate to form physical cross-linking points, reinforcing the mechanical properties of the film. When the fluorine-containing chain extender accounted for 10% (DF0.5-PU), the PU film showed the best mechanical properties. Compared with the control group, tensile strength is enhanced by 165%, the toughness is increased by 287%, and the elongation-at-break was improved by 156%.