Crystalline segments in a photo-detachable adhesive

Designed to Degrade: Tailoring Polyesters for Circularity

A powerful toolbox is needed to turn the linear plastic economy into circular. Development of materials designed for mechanical recycling, chemical recycling, and/or biodegradation in targeted end-of-life environment are all necessary puzzle pieces in this process. Polyesters, with reversible ester bonds, are already forerunners in plastic circularity: poly(ethylene terephthalate) (PET) is the most recycled plastic material suitable for mechanical and chemical recycling, while common aliphatic polyesters are biodegradable under favorable conditions, such as industrial compost. However, this circular design needs to be further tailored for different end-of-life options to enable chemical recycling under greener conditions and/or rapid enough biodegradation even under less favorable environmental conditions. Here, we discuss molecular design of the polyester chain targeting enhancement of circularity by incorporation of more easily hydrolyzable ester bonds, additional dynamic bonds, or degradation catalyzing functional groups as part of the polyester chain. The utilization of polyester circularity to design replacement materials for current volume plastics is also reviewed as well as embedment of green catalysts, such as enzymes in biodegradable polyester matrices to facilitate the degradation process.

Phase Change Energy Storage Material with Photocuring, Photothermal Conversion, and Self-Cleaning Performance via a Two-Layer Structure

Compared with the thermal curing process, the photocuring process has advantages such as high efficiency and less energy consumption. However, the preparation of photocurable phase change materials (PCMs) with photothermal conversion and self-cleaning properties is challenging due to the conflict between the transparency required by the photocurable resin system and the opacity deduced by the large number of fillers required by photothermal conversion and the negative effect of filler steric hindrance on the reaction rate and crystallinity. In this work, a "thiol-ene" click chemical reaction induced using UV was used to prepare photocurable PCMs, followed by spraying a carboxylated multiwalled carbon nanotube (CCNT) suspension (with ethyl acetate) onto the surface to achieve an effective two-layer composite of the PCM and CCNTs, by which the rough surface of the PCM and the interaction offered by the hydrogen bonds on the interface of the PCM and the CCNTs provide sufficient adhesion for the two phases. The "thiol-ene" cross-linked polymer network provided shape stability as a support material. 1-Octadectanethiol (ODT) and beeswax (BW) were encapsulated in the cross-linked polymer network as phase change components, providing phase change latent heat. The CCNT layer provided excellent photothermal conversion and self-cleaning properties. The experimental results show that the latent heat of the PCM can reach 124.2 J/g, the water contact angle is 144°, the photothermal conversion efficiency reaches 75%, and it has significant self-cleaning performance. To the best of our knowledge, this is the first report on a photocurable PCM with photothermal conversion and self-cleaning properties.

Photo-Controlled [4+4] Cycloaddition of Anthryl-Polymer Systems: A Versatile Approach to Fabricate Functional Materials

The reversible photo-induced [4+4] cycloaddition reaction of anthracene enables multiple cycles of dimerization and scission, allowing phototunable linkage of molecular fragments for the synthesis of polymer scaffolds. New functional materials ranging from hydrogels to shape-memory polymers were designed from anthryl-polymer systems because of their diverse photochemical reactivity and responsiveness. Light as an external stimulus allows for the remote and precise spatiotemporal control of materials without the need for additional reagents. Depending on how the photoreactive anthracene moieties were introduced, the interaction of anthryl-polymer systems with light results in various processes such as polymerization, cyclization, and cross-linking. Structural modifications of anthracene derivatives could shift their absorption from the ultraviolet to the visible light region, widening their range of applications including biologically relevant studies. These applications are further diversified and enhanced by the reversibility of the dimerization reaction using light and heat as stimuli. In this review, current developments in the synthesis and photodimerization of anthracene-containing polymers and their emerging applications in the fabrication of new materials are discussed.