Dynamically Cross-Linked Polyolefins via Hydrogen Bonds: Tough yet Soft Thermoplastic Elastomers with High Elastic Recovery

The fabrication of polyolefin thermoplastic elastomers (PTPEs) with superior robustness (high strength and high toughness) is challenging. Integrating dynamic (reversible) noncovalent cross-links into PTPEs may solve the trade-off between strength and toughness and permanent (irreversible) cross-linking and elasticity. Here, we report a two-step synthesis of P-TPEs that contain flexible polymer chains and different thiol branches (less than 2.0 mol %) that cross-link the polymer chains through dynamic hydrogen bonding. The cross-linked polymers exhibit negligible hysteresis after being circularly stretched 10 times at low strain, that is, few dynamic H-bonds break per cycle and delocalize the stress concentration to withstand load and delay premature fracture. At large deformation, the polymers dissipate vast stress energy by the sacrificial H-bond scission: the H-bonds break and reform to prevent failure and to dictate simultaneously high fracture strength (sigma up to 10.2 MPa) and high toughness (U-T up to 22.6 MJ/m(3)). Meanwhile, the resultant materials present low stiffness (E approximate to 2.5 MPa), good extensibility (epsilon > 600%), and elastic recovery of 90% even at 680% strain. The cross-linked polyolefins are readily (re)processable, and tensile and elastic properties are largely recovered after being remolded at least twice.