Collaborative phase separation induced by double noncovalent dynamic crosslinkers in polyurethane for supertoughness and triboelectric generator electrodes

Abstract

It is a huge challenge to overcome the trade-off among the mechanical properties, solvent resistance and recyclability by regulating the phase separation, size and spatial distribution of polymeric materials. Herein, a strategy involving two noncovalent dynamic crosslinkers is employed to address this issue. By simultaneously introducing adipic dihydrazide (AD) as a hydrogen-bonding crosslinker and 4,4′-bis(hydroxymethyl)-2,2′-bipyridine (BPY) as a complexation crosslinker, a collaborative phase-separation topology of polycaprolactone-based polyurethanes is obtained with similar composition. Differing from the large and sparse phase-separation topology of PU with a single crosslinker, the collaborative phase-separation topology is characterized by a smaller size and spacing. This microstructure, together with proper crosslinking and nanodomain reinforcement, not only augments its tensile strength but also significantly increases its energy dissipation. Consequently, the optimal elastomer (A₅B₅-Zn) achieves a high tensile strength of 37.77 MPa, an exceptional toughness of 504.5 MJ m⁻³, and an ultrahigh fracture energy of 248 kJ m⁻², nearly 6 times that of its counterpart. The strong AD hydrogen bonding combined with PCL crystallization also improves the solvent resistance of this PU, which is otherwise deteriorated by BPY coordination bonding. Additionally, its ionic conductivity of 22.6 mS m⁻¹ makes it an elastic electrode. The assembled single-electrode triboelectric nanogenerators demonstrate rapid response (∼5 ms) and a high power density of 76.56 mW m⁻², capable of driving wearable electronics. This work elucidates the mechanism of collaborative phase separation induced by two noncovalent dynamic crosslinkers, providing a flexible pathway for designing super-tough functional elastomers.