Photo-induced topological self-reorganization and self-growth of polymer based on dynamic reversible aromatic pinacol units

Self-Growing Organic Materials

The growth of living systems is ubiquitous. Living organisms can continually update their sizes, shapes, and properties to meet various environmental challenges. Such a capability is also demonstrated by emerging self-growing materials that can incorporate externally provided compounds to grow as living organisms. In this Minireview, we summarize these materials in terms of six aspects. First, we discuss their essential characteristics, then describe the strategies for enabling crosslinked organic materials to self-grow from nutrient solutions containing polymerizable compounds. The developed examples are grouped into five categories based on their molecular mechanisms. We then explain the mechanism of mass transport within polymer networks during growth, which is critical for controlling the shape and morphology of the grown products. Afterwards, simulation models built to explain the interesting phenomena observed in self-growing materials are discussed. The development of self-growing materials is accompanied by various applications, including tuning bulk properties, creating textured surfaces, growth-induced self-healing, 4D printing, self-growing implants, actuation, self-growing structural coloration, and others. These examples are then summed up. Finally, we discuss the opportunities brought by self-growing materials and their facing challenges.

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.

Photocatalytic Homocoupling Transformations

Homocoupling reactions promoted by photocatalysts are not very abundant in the literature. However, the products generated from such processes are very interesting. In this review, we highlight the most relevant reports concerning photocatalyzed dimerizations covering the literature until the middle of 2020. Reactions will be classified according to the type of starting material employed, with an emphasis being placed on the corresponding mechanism.

1 Introduction

2 Arenes and Heteroarenes

3 Alkenes

4 Alkanes

5 Alkynes

6 Aldehydes, Ketones, Alcohols, Amines and Imines

7 Carboxylic Acids

8 Nitro Compounds

9 Conclusions

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.