Although mechanically robust polymer materials had not been thought to self-heal, we recently found that poly­(ether thiourea) PTUEG3, which is a glassy polymer with high mechanical strength, self-heals even at ambient temperatures. This finding updated the above preconception. Nevertheless, it should also be noted that PTUEG3, under high humidity, absorbs water and is plasticized to lose its mechanical strength. Humidity-induced plasticization is a general problem for polymers with polar groups. Herein, we report that PTUEG3, if designed by copolymerization to contain only 10 mol % of a dicyclohexylmethane (Cy2M) thiourea unit (TUCy2M), serves as a humidity-tolerant, mechanically robust polymer material that can self-heal at ambient temperatures. This copolymer contained, in its ether thiourea (TUEG3)-rich domain, a humidity-tolerant, noncovalently cross-linked 3D network with mechanical robustness formed by stacking of the Cy2M group. The present work provides a promising design strategy for mechanically robust, self-healable polymers usable under high humidity.

Can commodity polymers are made to be healable just by blending with self‐healable polymers? Here we report the first study on the fundamental aspect of this practically challenging issue. Poly(ether thiourea) (PTUEG3; Tg=27 °C) reported in 2018 is extraordinary in that it is mechanically robust but can self‐heal even at 12 °C. In contrast, poly(octamethylene thiourea) (PTUC8; Tg=50 °C), an analogue of PTUEG3, cannot heal below 92 °C. We found that their polymer blend self‐healed in a temperature range above 32 °C even when its PTUEG3 content was only 20 mol %. Unlike PTUEG3 alone, this polymer blend, upon exposure to high humidity, barely plasticized, keeping its excellent mechanical properties due to the non‐hygroscopic nature of the PTUC8 component. CP/MAS 13C NMR analysis revealed that the polymer blend was nanophase‐separated, which possibly accounts for why such a small amount of PTUEG3 provided the polymer blend with humidity‐tolerant self‐healable properties.

Can commodity polymers are made to be healable just by blending with self-healable polymers? Here we report the first study on the fundamental aspect of this practically challenging issue. Poly(ether thiourea) (PTUEG 3 ; T g = 27 °C) reported in 2018 is extraordinary in that it is mechanically robust but can self-heal even at 12 °C. In contrast, poly(octamethylene thiourea) (PTUC 8 ; T g = 50 °C), an analogue of PTUEG 3 , cannot heal below 92 °C. We found that their polymer blend self-healed in a temperature range above 32 °C even when its PTUEG 3 content was only 20 mol %. Unlike PTUEG 3 alone, this polymer blend, upon exposure to high humidity, barely plasticized, keeping its excellent mechanical properties due to the non-hygroscopic nature of the PTUC 8 component. CP/MAS 13 C NMR analysis revealed that the polymer blend was nanophase-separated, which possibly accounts for why such a small amount of PTUEG 3 provided the polymer blend with humidity-tolerant self-healable properties.