Blending to Make Nonhealable Polymers Healable: Nanophase Separation Observed by CP/MAS 13C NMR Analysis

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. Blending with only 20 mol % of PTUEG3 resulted in making PTUC8 to be self‐healable at ambient temperatures without spoiling its non‐hygroscopic properties. A nanophase‐separated structure as observed by CP/MAS 13C NMR spectroscopy is responsible: PTUEG3‐rich domains certainly contribute to the self‐healing properties, while PTUC8‐rich non‐hygroscopic domains likely prevent the polymer blend from humidity‐induced plasticization.