Room temperature self-healable and recyclable polyurethanes with tunable mechanical properties by integrating dual dynamic units of hydrogen bonding and metal−lysine coordination bonds

Abstract

It is challenging to achieve the room-temperature self-healing polymers with high healing efficiency and excellent integrated mechanical properties, which are highly desirable in various fields. Herein, we propose a new design strategy to prepare room temperature self-healable and recyclable polyurethanes (PUs), in which both dynamic metal–lysine coordination bonds and dual H-bonds were simultaneously embedded. At first, three metal–lysine coordination complexes, i.e. Zn(Lys)₂, Cu(Lys)₂ and Mg(Lys)₂, were synthesized and characterized, which were used as chain-extenders for the subsequent preparation of PUs. These complexes of Zn(Lys)₂, Cu(Lys)₂ and Mg(Lys)₂ exhibited a distinct behavior after incorporation into PUs. The mechanical and self-healing properties of these metal-lysine containing PUs (PU-M−x, M = Zn²⁺, Cu²⁺ and Mg²⁺, x represents molar percentage of M(Lys)₂ in chain extenders) can be easily tuned by simply adjusting the type and the amount of metal–lysine coordination complexes added. The PU films displayed excellent mechanical properties with the tensile strength at break varying from 17.2 to 43.0 MPa, the ultimate elongation above 657.0 % and toughness above 45.0 MJ m⁻³. Among these elastomers, both PU-Zn-20 and PU-Mg-10 shows outstanding self-healing efficiency over 92.0 % based on toughness at 25 °C for 24 h due to the the multiple dynamic interactions including dynamic metal–lysine coordination bonds and hydrogen bonds within their networks. In particular, PU-Zn-20 exhibits the best comprehensive properties, of which tensile strength, breaking strain, and toughness are as high as 25.4 MPa, 832.3 %, and 59.8 MJ m⁻³, respectively. Furthermore, these PUs could also be reprocessed with excellent recovered mechanical properties. We demonstrate that the self-healing elastomers have a potential application as a flexible substrate for the easy fabrication of healable electrodes.