One-Pot Thermo-Remendable Shape Memory Polyurethanes

Furan-based thermoset polyurethanes have been prepared in a one-pot fashion with the ability to self-mend under mild temperature conditions, by making use of a Diels-Alder shape-memory assisted self-healing (DASMASH) approach. For this, thermoreversible covalent bonds, obtained by Diels-Alder chemistry, are introduced as cross-linkers into a polycaprolactone (PCL) containing polyurethane material. It is demonstrated that, after introduction of a crack into the PU-thermoset, Diels-Alder bonds preferentially break, regenerating free furan/maleimide functional groups, while the shape memory effect favors the crack closure at temperatures above the melting point of PCL, simultaneously resulting in a reformation of the reversible cross-links. The reversibility and shape memory ability of the materials were optimized and studied by FTIR, H-1 NMR and tensile measurements. Different compositions were used to properly understand the role and influence of each component. The polyurethane materials healed at 50 degrees C after mechanical damage induced by either the application of a large tensile deformation or by performing controlled macro/micro scratches with a depth sensing indenter. Online FT-IR monitoring provided a kinetic description of the system reversibility for numerous cycles. Furthermore, mechanical recovery with complete disappearance of the microscratches was accomplished after multiple cycles of large tensile deformation. The results were not only confirmed by an optical inspection and scanning electron microscopy, but also with confocal microscopic mapping, by comparison of the cross-section profiles of the microscratches before and after healing.