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1. Material properties and applications of mechanically interlocked polymers

   https://doi.org/10.1038/s41578-021-00278-z  

   Hart, Laura F.; Hertzog, Jerald E.; Rauscher, Phillip M.; Rawe, Benjamin W.; Tranquilli, Marissa M.; Rowan, Stuart J. (January 2021, Nature Reviews Materials)

   null (Ed.)

   Mechanically interlocked polymers (MIPs), polymer architectures that incorporate the mechanical bond, have seen a dramatic growth in interest over the last decade or so. Of particular interest in these architectures are the high mobility and conformational freedom of the interlocked components, which can give rise to unique property profiles. Over the years the research advances, from the chemistry, physics, material science and engineering fields, has started to build an understanding of how incorporating mechanical bonds into a polymer structure impacts its properties. This review focuses on summarizing the state-of-the-art understanding of the structure-property relationships in these materials and an outlook toward their applications, specifically focusing on four main classes of MIPs, polyrotaxanes, slide-ring gels, daisy-chain polymers and polycatenanes. 

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2. Exploring the Impact of Ring Mobility on the Macroscopic Properties of Doubly Threaded Slide‐Ring Gel Networks

   https://doi.org/10.1002/anie.202411172  

   Oh, Jongwon; Liu, Guancen; Kim, Hojin; Hertzog, Jerald E; Nitta, Natsumi; Rowan, Stuart J (September 2024, Angewandte Chemie International Edition)

   Abstract The integration of mechanically interlocked molecules (MIMs) into polymeric materials has led to the development of mechanically interlocked polymers (MIPs). One class of MIPs that have gained attention in recent years are slide‐ring gels (SRGs), which are generally accessed by crosslinking rings on a main‐chain polyrotaxane. The mobility of the interlocked crosslinking moieties along the polymer backbone imparts enhanced properties onto these networks. An alternative synthetic approach to SRGs is to use a doubly threaded ring as the crosslinking moiety, yielding doubly threaded slide‐ring gel networks (dt‐SRGs). In this study, a photo‐curable ligand‐containing thread was used to assemble a series of metal‐templated pseudo[3]rotaxane crosslinkers that allow access to polymer networks that contain doubly threaded interlocked rings. The physicochemical and mechanical properties of these dt‐SRGs with varying size of the ring crosslinking moieties were investigated and compared to an entangled gel (EG) prepared by polymerizing the metal complex of the photo‐curable ligand‐containing thread, and a corresponding covalent gel (CG). Relative to the EG and CG, the dt‐SRGs exhibit enhanced swelling behavior, viscoelastic properties, and stress relaxation characteristics. In addition, the macroscopic properties of dt‐SRGs could be altered by “locking” ring mobility in the structure through remetalation, highlighting the impact of the mobility of the crosslinks. 

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3. Covalent Mechanochemistry and Contemporary Polymer Network Chemistry: A Marriage in the Making

   https://doi.org/10.1021/jacs.2c09623  

   Lloyd, Evan M.; Vakil, Jafer R.; Yao, Yunxin; Sottos, Nancy R.; Craig, Stephen L. (January 2023, Journal of the American Chemical Society)

   Over the past 20 years, the field of polymer mechanochemistry has amassed a toolbox of mechanophores that translate mechanical energy into a variety of functional responses ranging from color change to small-molecule release. These productive chemical changes typically occur at the length scale of a few covalent bonds (Å) but require large energy inputs and strains on the micro-to-macro scale in order to achieve even low levels of mechanophore activation. The minimal activation hinders the translation of the available chemical responses into materials and device applications. The mechanophore activation challenge inspires core questions at yet another length scale of chemical control, namely: What are the molecular-scale features of a polymeric material that determine the extent of mechanophore activation? Further, how do we marry advances in the chemistry of polymer networks with the chemistry of mechanophores to create stress-responsive materials that are well suited for an intended application? In this Perspective, we speculate as to the potential match between covalent polymer mechanochemistry and recent advances in polymer network chemistry, specifically, topologically controlled networks and the hierarchical material responses enabled by multi-network architectures and mechanically interlocked polymers. Both fundamental and applied opportunities unique to the union of these two fields are discussed. 

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4. Syntheses of three-dimensional catenanes under kinetic control

   https://doi.org/10.1073/pnas.2118573119  

   Wu, Yong; Guo, Qing-Hui; Qiu, Yunyan; Weber, Jacob A.; Young, Ryan M.; Bancroft, Laura; Jiao, Yang; Chen, Hongliang; Song, Bo; Liu, Wenqi; et al (March 2022, Proceedings of the National Academy of Sciences)

   Although catenanes comprising two ring-shaped components can be made in large quantities by templation, the preparation of three-dimensional (3D) catenanes with cage-shaped components is still in its infancy. Here, we report the design and syntheses of two 3D catenanes by a sequence of S N 2 reactions in one pot. The resulting triply mechanically interlocked molecules were fully characterized in both the solution and solid states. Mechanistic studies have revealed that a suit[3]ane, which contains a threefold symmetric cage component as the suit and a tribromide component as the body, is formed at elevated temperatures. This suit[3]ane was identified as the key reactive intermediate for the selective formation of the two 3D catenanes which do not represent thermodynamic minima. We foresee a future in which this particular synthetic strategy guides the rational design and production of mechanically interlocked molecules under kinetic control. 

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5. Polymer‐Grafted Nanoparticles as Single‐Component, High Filler Content Composites via Simple Transformative Aging

   https://doi.org/10.1002/adfm.202107139  

   Kubiak, Joshua_M; Macfarlane, Robert_J (October 2021, Advanced Functional Materials)

   Abstract Polymer‐grafted nanoparticles (PGNPs) are ideal additives to enhance the mechanical properties and functionality of a polymer matrix and can even potentially serve as single‐component building blocks for highly filled composites if the polymer content is kept low. The major challenge facing such syntheses is that PGNP‐based solids with short polymer brushes often have low mechanical strength and limited processability. It therefore remains difficult to form robust architectures with a variety of 3D macroscopic shapes from single‐component PGNP composites. Forming covalent bonds between cross‐linkable PGNPs is a promising route for overcoming this limitation in processability and functionality, but cross‐linking strategies often require careful blending of components or slow assembly methods. Here, a transformative aging strategy is presented that uses anhydride cross‐linking to enable facile processing of single‐component PGNP solids via thermoforming into arbitrary shapes. The use of lowT_gpolymer brushes enables the production of macroscopic composites with>30 vol% homogeneously distributed filler, and aging increases stiffness by 1–2 orders of magnitude. This strategy can be adapted to a variety of polymer and nanofiller compositions and is therefore a potentially versatile approach to synthesize nanocomposites that are functional, mechanically robust, and easily processable. 

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