Sunlight Stimulated Photochemical Self-Healing Polymers Capable of Re-bonding Damages up to a Centimeter Below the Surface Even Out of the Reach of the Illumination.

TO BREAK THE BOTTLENECKS IN DEVELOPING PHOTOCHEMICAL SELF-HEALING POLYMERS: : (i) only the surface cracks can be restored and (ii) materials' mechanical properties are lower, we design crosslinked poly(urethane-dithiocarbamate)s carrying photo-reversible dithiocarbamate bonds covalently linked to indole chromophores and benzyl groups. The conjugated structure of the chromophore and benzyl enhances the addition reactivity of thiocarbonyl moiety and facilitates photo-cleavage of C-S bond, so that transfer of the created radicals among dithiocarbamate linkages is promoted. Accordingly, reshuffling of the reversibly crosslinked networks via dynamic exchange between the activated dithiocarbamates is enabled in both surface layer and the interior upon exposure to the low-intensity UV light from the sun. It is found that the damages up to a centimeter below the surface can be effectively recovered in the sunshine, which greatly exceeds the maximum penetration distance of UV light (hundreds of microns). Besides, tensile strength and failure strain of the poly(urethane-dithiocarbamate) are superior to the reported photo-reversible polymers, achieving the record-high 33.8 MPa and 782.0% owing to the wide selectivity of soft/hard blocks, multiple interactions and appropriate crosslinking architecture. The present work provides a novel paradigm of photo self-healing polymers capable of re-bonding cracks even out of the reach of the illumination. This article is protected by copyright. All rights reserved.