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.

The development of photochemical self-healing polymers faces the the following bottlenecks: i) only the surface cracks can be restored and ii) materials' mechanical properties are lower. To break these bottlenecks, cross-linked poly(urethane-dithiocarbamate)s carrying photo-reversible dithiocarbamate bonds covalently linked to indole chromophores and benzyl groups are designed. 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 cross-linked networks via dynamic exchange between the activated dithiocarbamates is enabled in both surface layer and the interior upon exposure to the low-intensity ultraviolet (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 cross-linking 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.

Tailored modular assembly derived self-healing polythioureas with largely tunable properties covering plastics, elastomers and fibers.

To impart self-healing polymers largely adjustable dynamicity and mechanical performance, here we develop libraries of catalyst-free reversible polythioureas directly from commodity 1,4-phenylene diisothiocyanate and amines via facile click chemistry based modular assembly. By using the amine modules with various steric hindrances and flexibilities, the reversible thiourea units acquire triggering temperatures from room temperature to 120 °C. Accordingly, the derived self-healable, recyclable and controlled degradable dynamically crosslinked polythioureas can take effect within wide temperature range. Moreover, mechanical properties of the materials can be tuned covering plastics, elastomers and fibers using (i) different assemble modules or (ii) solid-state stretching. Particularly, unidirectional stretching leads to the record-high tensile strength of 266 MPa, while bidirectional stretching provides the materials with biaxial strengths up to over 120 MPa. The molecular mechanism and technological innovations discussed in this work may benefit promotion and application of self-healing polymers towards greatly diverse demands and scenarios.

Reversibly Interlocked Macromolecule Networks with Enhanced Mechanical Properties and Wide pH Range of Underwater Self-Healability.

A novel strategy for developing homogeneous reversibly interlocking polymer networks (RILNs) with enhanced mechanical properties and underwater self-healing ability is proposed. The RILNs are prepared by the topological reorganization of two preformed cross-linked polymers containing reversible catechol-Fe3+ coordinate bonds and imine bonds and exhibit enhanced mechanical properties, superior underwater self-healing effect within a wide pH range, and water-assisted recycling ability through synergetic action between the reversible catechol-Fe3+ and imine bonds. At higher pH values, the catechol-Fe3+ coordinate bonds are responsible for self-healing, while the imine bonds maintain the stability of the materials. In neutral water, the imine bonds mainly account for self-healing, and hydrogen bonds and entanglements between the two networks prevent the material from collapsing. Under a lower pH value, intermolecular hydrogen bonds and entanglements contribute to self-healing. The outcomes of this work provide a new idea for developing robust multifunctional underwater self-healing materials.

Performance improvement of N-doped carbon ORR catalyst via large through-hole structure.

N-doped carbon-based materials are crucial electrically conductive additives and non-metal electrocatalysts for the oxygen reduction reaction. At present, many pieces of research are focused on the effects of micropore, mesopore and hierarchical pore structure on the catalytic activity, however, there are few works concerning the role of large-dimension through-hole structure. Hence, in this work, we prepare two kinds of carbon materials with large through-hole structure, i.e. N-doped carbon hollow-spheres and hollow-tubes, as the oxygen reduction catalysts. The synthesis follows template-free morphology-controlled pyrolysis, which is more convenient than the preparation of conventional N-doped nanotubes and graphene. The resultant N-doped carbon hollow-spheres and hollow-tubes evidently enhanced their ORR catalytic activity, remarkable long-term stability and methanol resistance. The large-dimension through-hole structure is found to account for the increase in mass transfer.