A healable poly(urethane-urea) elastomer with ultra-high mechanical strength enabled by tailoring multiple relaxation dynamics of hierarchical hard domains

Abstract

It is still a challenge to develop strong and tough polymers with efficient healing capability. In this work, we develop a nonstoichiometric–stoichiometric sequential feeding approach, which combines a one-pot method and a step method to fabricate mechanically robust and healable poly(urethane-urea) (PUU). Such an approach can construct polydisperse hard segments, which aggregate into hierarchical hard domains. Moreover, the morphology and hydrogen bonds of the hierarchical hard domains can be facilely tailored by adjusting the feeding ratio of isophorone diisocyanate (IPDI), 4-amino phenyl disulfide (APS), polytetramethylene ether glycol (PTMEG) and 2,6-pyridinedimethanol (PDM). As a result, the optimized sample shows high molecular mobility of soft domains and multiple relaxation of hierarchical hard domains. The synergistic effects of the soft and hierarchical hard domains enable the highest tensile strength ever recorded for healable PUU elastomers (75.8 MPa), outstanding fracture energy (155.7 kJ m⁻²) and healing capacity with a recovered strength of 64.7 MPa at 85 °C for 12 h.