Preparation of polyurethane nanocomposites via covalent incorporation of functionalized graphene and its shape memory effect

High-performance polyurethane nanocomposites with surface-functionalized, nano-layered graphene sheets were fabricated by covalent incorporation. Partially reduced graphene nanosheets or surface-functionalized graphene with diazonium salts carrying phenethyl alcohol groups were physically-blended or covalently-bonded with amorphous polyurethane. FTIR-ATR, XPS, WAXD, and AFM characterization of the graphene demonstrated the surface functional groups and the enlarged interlayer space of the single or few-layered graphene. Functionalized graphene/PU composites with a crosslinked structure, which was introduced by the urethane linkages between the multifunctional graphene and the NCO-terminated PU, showed greater shape memory properties, as well as greater mechanical, thermal, and dynamic mechanical properties, than the reduced graphene/PU composites with good shape memory properties, due to fine dispersion–induced hydrogen interactions. The functionalized graphene/PU showed up to 98% shape fixity and a 94% shape recovery ratio after four cycles, and the hysteresis loss was as low as 2% at an extremely low loading of 0.5%.