Castor-oil-based, Robust, Self-Healing, Shape Memory, and Reprocessable Polymers Enabled by Dynamic Hindered Urea Bonds and Hydrogen Bonds

Developing biobased polyurethanes with repairability, reprocessability as well as robust mechanical properties remains a great challenge. Herein, novel, robust biobased polyurethane materials bearing hindered urea bonds (HUBs) derived from renewable castor oil are reported. The dynamic HUBs and hydrogen bonds that existed in HUBs provided these materials extremely low relaxation times (12.3 to 221 s at 100 degrees C) as well as excellent scratch healing efficiency (88.9-100% at 100 degrees C for 10 min) and recyclability (without obviously sacrificing the tensile properties at least 4 times). The selected sample also exhibited good shape memory behavior, with a shape fixity ratio above 88.4% and a shape recovery ratio above 81.3%. Remarkably, the polymers could undergo a rapid and reversible solid/liquid transformation under cooling and heating treatment. Besides, these HUBs materials demonstrated high adhesion strength (up to 2.53 MPa) when bonding stainless steel, and can be reused for at least 5 times without significant deterioration in adhesion strength. Finally, by mixing a certain amount of carbon nanotubes (CNTs) and adjusting the compositions of HUBs, recyclable and malleable conductive composites were achieved. In general, this work presents a green, simple, and universal approach to fabricate robust, sustainable polyurethanes with multiple functions like repairability, shape memory, malleability, and recyclability.