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Abstract Synthetic plastics sourced from petroleum have gained widespread use since the 1950s. Polystyrene (PS) is one of the most extensively used plastics, as it is colorless, has high mechanical strength, and exhibits excellent chemical and thermal stability; however, it is also one of the least recycled plastics because of the high cost and low profit in recycling. Herein, we demonstrate a mechanochemical recycling approach that allows PS to be efficiently degraded into benzene when it is ground in a ball mill with AlCl₃. For example, when 165 kDa PS pellets are milled with AlCl₃, the extent of degradation reaches 90% at 15 min. Isotope labeling experiments indicate that both ambient water and the polymer backbone can be proton sources for the formation of benzene. The benzene generated in the mechanochemical degradation can be used to synthesize styrene, which can be repolymerized to produce polystyrene, allowing for the closed‐loop recycling of PS. In addition, a mechanochemical Friedel–Crafts acylation between the generated benzene and the subsequently added benzoic anhydride produces benzophenone in 40%–50% yield. The mechanochemical degradation process demonstrated here is solvent‐free, cost‐effective, and energy‐efficient, providing a promising route for the chemical recycling and upcycling of PS. 

Abstract The field of polymer mechanochemistry has been revolutionized by implementing force-responsive functional groups—mechanophores. The rational design of mechanophores enables the controlled use of force to achieve constructive molecular reactivity and material responses. While a variety of mechanophores have been developed, this Mini Review focuses on cyclobutane, which has brought valuable insights into molecular reactivity and dynamics as well as innovations in materials. We discuss its reactivity and mechanism, dynamics and stereoselectivity, as well as impacts on material properties. 

Abstract The accumulation of plastic waste, due to lack of recycling, has led to serious environmental pollution. Although mechanical recycling can alleviate this issue, it inevitably reduces the molecular weight and weakens the mechanical properties of materials and is not suitable for mixed materials. Chemical recycling, on the other hand, breaks the polymer into monomers or small‐molecule constituents, allowing for the preparation of materials of quality comparable to that of the virgin polymers and can be applied to mixed materials. Mechanochemical degradation and recycling leverages the advantages of mechanical techniques, such as scalability and efficient energy use, to achieve chemical recycling. We summarize recent progress in mechanochemical degradation and recycling of synthetic polymers, including both commercial polymers and those designed for more efficient mechanochemical degradation. We also point out the limitations of mechanochemical degradation and present our perspectives on how the challenges can be mitigated for a circular polymer economy. 

Abstract Polymers with low ceiling temperatures (T_c) are highly desirable as they can depolymerize under mild conditions, but they typically suffer from demanding synthetic conditions and poor stability. We envision that this challenge can be addressed by developing high-T_cpolymers that can be converted into low-T_cpolymers on demand. Here, we demonstrate the mechanochemical generation of a low-T_cpolymer, poly(2,5-dihydrofuran) (PDHF), from an unsaturated polyether that contains cyclobutane-fused THF in each repeat unit. Upon mechanically induced cycloreversion of cyclobutane, each repeat unit generates three repeat units of PDHF. The resulting PDHF completely depolymerizes into 2,5-dihydrofuran in the presence of a ruthenium catalyst. The mechanochemical generation of the otherwise difficult-to-synthesize PDHF highlights the power of polymer mechanochemistry in accessing elusive structures. The concept of mechanochemically regulating theT_cof polymers can be applied to develop next-generation sustainable plastics. 

Abstract Helices are unique structures that play important roles in biomacromolecules and chiral catalysis. The mechanochemical unfolding of helical structures has attracted the attention of chemists in the past few years. However, it is limited to a few cases which investigated how the mechanochemical reactivity is impacted by helical configurations. No synthetic helical mechanophore is reported. Herein, a Zn (II) bidipyrrin (BDPR‐Zn) double helix is designed as a potential mechanophore. A cyclic olefin containing a doubly strapped BDPR‐Zn is prepared and used for ring‐opening metathesis polymerization. The corresponding polymer is subjected to pulsed ultrasonication for mechanochemical testing. The sonication results reveal the mechanochemical inertness of BDPR‐Zn unit, which is further supported by force‐coupled simulation. Although no obvious activation is observed, our preliminary results on BDPR‐Zn unit could inspire further rational designs on force‐induced helix unfolding. 

Integrating mechanophores into multiple-network elastomers enables 20-fold toughness enhancement and 37% activation and provides insights into the toughening mechanismviabond scission visualization. 

A polymer coating autonomously reports damageviafluorescence from a force-induced retro-Diels–Alder reaction. The optical signal correlates with impact energy, enabling real-time, equipment-free damage detection, even in pigmented coatings. 

In this study, we investigate three different polymeric networks in terms of their tensile strength as a function of stretching rate, or temperature, or medium viscosity.