Tuning hard phase towards synergistic improvement of toughness and self-healing ability of poly(urethane urea) by dual chain extenders and coordinative bonds

It is challenging to simultaneously improve the toughness and self-healing ability of thermoplastic polyurethane (TPU) due to mutually exclusive dependence on chain motion and hard phase. In this work, a novel poly(urethane urea) (PUU) was synthesized by using 2, 6-diamimopyridine (Py) and cystamine (Cy) as chain extenders and subsequently complexed with Zn2+ ions. It is revealed that the pyridine moieties together with formation of coordinative bonds significantly influences microphase separation by interfering with hydrogen bonding. A Py/Cy molar ratio of 1:2 is optimal to remarkably improve the toughness and self-healing ability. Specifically, its tensile strength, toughness and self-healing efficiency simultaneously improve to 9.40 +/- 0.10 MPa, 64.49 +/- 1.75 MJ/m(3), and 96.64 +/- 1.52% with 92%, 139% and 29% increment compared to PUU-Cy, respectively. The synergistic enhancing effect is the consequence of compromised hard phase and coordinative bonds. Firstly, decrease of hard domain content leads to loosely packed hard segments dispersing in soft phase, facilitating disulfide exchange. Secondly, the coordinative bonds serving as dynamic crosslinking joints not only restrict chain dislocation but also contribute to better self-healing ability than hydrogen bonds. An electrode film derived from embedding silver nanowires (AgNWs) into this material exhibits self-repairable and robust sensing properties due to reconstructing conducting network by self-healable matrix. This unique feature endows it with a great potential in the field of flexible electronics and wearable devices.