Recyclable Solid-Solid Phase Change Materials with Superior Latent Heat via Reversible Anhydride-Alcohol Crosslinking for Efficient Thermal Storage.

Solid-solid phase change materials (SSPCMs) with crosslinked polymer structures have received sustained interest due to their remarkable shape stability, enabling their application independently without the need for encapsulation or supporting materials. However, the crosslinking structure also compromises their latent heat and poses challenges to their recyclability. Herein, a novel strategy harnessing the internal-catalyzed reversible anhydride-alcohol crosslinking reaction to fabricate SSPCMs with superior latent heat and exceptional dual recyclability is presented. Easily accessible anhydride copolymers (e.g., propylene-maleic anhydride alternating copolymers), provide abundant reactive anhydride sites within the polymer matrix; polyethylene glycol serves as both the grafted phase change component and the crosslinker. The resulting SSPCMs attain a peak latent heat value of 156.8 J g-1 which surpasses all other reported recyclable crosslinked SSPCMs. The materials also exhibit certain flexibility and a tunable tensile strength ranging from 6.6 to 11.0 MPa. Beyond that, leveraging the reversible anhydride-alcohol crosslinks, the SSPCMs demonstrate dual recyclability through bond-exchange remolding and reversible-dissociation-enabled dissolving-recrosslinking without any reactive chemicals. Furthermore, by integrating solar-thermal conversion fillers like polydopamine nanoparticles, the potential of the system in efficient conversion, storage, and release of solar energy is highlighted.

Reconfigurable and Recyclable Photoactuators Based on Azobenzene-Containing Polymers.

Photoactuators are promising smart materials that can adapt their shapes upon light illumination. Smart materials with recycling, reusable, and reconfigurable properties are crucial for a sustainable society, and it is important to expand their function. Recently, much effort was made to address the issue of reprocessability and recyclability of photoactuators. Based on the development of polymer chemistry, supramolecular chemistry, and dynamic covalent chemistry, it is now possible to prepare reconfigurable and recyclable photoactuators using azobenzene-containing polymers (azopolymers). Herein, the recent advances on reconfigurable and reprocessable photoactuators, including dynamic crosslinked networks systems and non-covalently crosslinked azobenzene-containing polymers, were reviewed. We discuss the challenges in the field as well as the directions for the development of such photoactuators.

Light-Switchable Polymer Adhesive Based on Photoinduced Reversible Solid-to-Liquid Transitions.

The development of switchable adhesives for reversible bonding and debonding can overcome the problems associated with conventional adhesives in separating, recycling, and repairing glued surfaces. Here, a photoresponsive azobenzene-containing polymer (azopolymer) is developed for photocontrolled adhesion. The azopolymer P1 (poly(6-(4-(p-tolyldiazenyl)phenoxy)hexyl acrylate)) exhibits photoinduced reversible solid-to-liquid transitions due to trans-cis photoisomerization. Trans P1 is a solid that glues two substrates with a stiffness comparable to that of conventional adhesives. UV light induces trans-to-cis isomerization, liquefies P1, weakens the adhesion, and facilitates the separation of glued substrates. Conversely, visible light induces cis-to-trans isomerization, solidifies P1, and enhances the adhesion. P1 enables photocontrolled reversible adhesion for various substrates with different wettability, chemical compositions, and surface roughness. P1 can also be implemented in both dry and wet environments. Light can control the adhesion process with high spatiotemporal resolution when using P1 as a switchable adhesive. Photoinduced reversible solid-to-liquid transitions represent a strategy for materials recycling and automated production processes that require reversible bonding and debonding.

Stimuli-Responsive Ruthenium-Containing Polymers.

Ruthenium-containing polymers (RCPs) are a type of functional metallopolymer. Stimuli-responsive RCPs in which the responsive behaviors derive from the structure variation of Ru complexes are reviewed in this Feature Article, with particular focus on redox responsive RCPs and photoresponsive RCPs. On the basis of the recent progress, the response principle, syntheses, structures, properties, applications, and remaining challenges of such stimuli-responsive RCPs are discussed.