▎ 摘　　要

Strength and toughness are commonly two contradictory properties in polymer materials. For polymer elastomers, the addition of stiff filler frequently results in enhanced stiffness but reduced toughness and ductility. Inspired by biomimetic studies, here we demonstrate a new method that can simultaneously improve strength and toughness while maintaining the good ductility of polyurethane elastomers. This method constructs sacrificial bonds and hidden lengths at the interface of graphene nanosheet/polyurethane (GN/PU) composites by exploiting covalently and non-covalently functionalized GNs (HO-GNs). GNs are prepared by reduction of graphene oxide with hydrazine. The residual functional groups such as hydroxyl and epoxide groups on GNs enable PU oligomer chains to be covalently bonded to GNs by sequentially reacting with diisocyanate and polyethylene glycol oligomer. Non-covalently bonded PU oligomer chains are formed by the pi-pi interaction between GNs and pyrene derivatives. Both Fourier transform infrared spectra and thermogravimetric results provide direct evidence for the covalent bonding in HO-GNs while fluorescence spectra and decay curves confirm the existence of non-covalent bonding. The resulting HO-GNs exhibit a good dispersion capacity in organic solvents and the PU matrix, improving the load transfer and the particle mobility in GN/PU composites. Upon loading, both rupture of the pi-pi interaction (sacrificial bonds) and release of the hidden length (dissociation of H-bonds between the PU oligomer and polymer chains) enable the composite to exhibit high toughness and ductility nearly identical to the neat polyurethane (strain at break >900%). This approach is expected to be helpful for developing novel strong, tough and highly ductile polymer elastomers.