Self-Healable and Ultrahydrophobic Polyurethane-POSS Hybrids by Diels–Alder “Click” Reaction: A New Class of Coating Material

Polyurethane functionalized with pendant furan moiety (FPU) was prepared using a novel chain extender (FA-FGE) which was obtained from the reaction between furfurylamine (FA) and furfuryl glycidyl ether (FGE). This furan containing PU (FPU) was grafted with maleimide functionalized polyhedral oligomeric silsesquioxanes (POSS maleimide isobutyl, POSS-M) via Diels–Alder (DA) “click” reaction. The resultant DA adducts of FPU-POSS-M hybrid material showed a remarkable increase in water contact angle (WCA) from 84° to 141.3°. This remarkable increase in the WCA is due to the combined effect of the grafting of hydrophobic POSS-M units as well as the increased micro- and nanoscale surface roughness, as evidenced by AFM and FESEM analyses. The self-healing characteristic of this organic–inorganic hybrid was evaluated by the tensile test as well as by monitoring the disappearance of the crack using optical microscopy. The formation of FPU-POSS-M hybrid material was confirmed by GPC, FT-IR, and ¹H NMR analyses, and their thermoreversible nature was confirmed by DSC analysis. The tensile strength and tensile modulus of the FPU-POSS-M hybrid film were much higher than those of pristine FPU. The surface hardness and the penetration depth of the nanoindent in FPU and FPU-POSS-M hybrid coating were evaluated using the nanoindentation experiment. The adhesion property of the hybrid material with the metal surface was studied by lap shear test. TGA analysis showed a significant improvement in thermal stability of the FPU-POSS-M hybrid material. This self-healable and ultrahydrophobic FPU-POSS-M hybrid material can be used in specialty coating application.