Proton-Coupled Mechanochemical Transduction: A Mechanogenerated Acid

Diesendruck, Charles E.; Steinberg, Brian D.; Sugai, Naoto; Silberstein, Meredith N.; Sottos, Nancy R.; White, Scott R.; Braun, Paul V.; Moore, Jeffrey S.

doi:10.1021/ja305645x

Cited by 204 publications

(178 citation statements)

References 38 publications

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“…In the context of mechanoresponsive polymers, these systems represent a first generation of mechanochemical devices, in which localized covalent chemical changes (here, the conversion of spiropyran to merocyanine) and their association function can be turned on and off repeatedly in response to an external signal remotely controlled. Numerous mechanophores with chemical functionality including catalysis 56,57 and small molecule release 33,35 have been reported, and mechanochemical coupling offers the potential to add chemical response to existing soft device functionality. To that end, the development of material platforms that can trigger covalent mechanochemistry while recovering their initial shape 33,35 motivates the need for new mechanophores that, like the materials, are reversibly and repeatably activated.…”

Section: Discussionmentioning

confidence: 99%

Cephalopod-inspired design of electro-mechano-chemically responsive elastomers for on-demand fluorescent patterning

et al. 2014

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Cephalopods can display dazzling patterns of colours by selectively contracting muscles to reversibly activate chromatophores -pigment-containing cells under their skins. Inspired by this novel colouring strategy found in nature, we design an electro-mechano-chemically responsive elastomer system that can exhibit a wide variety of fluorescent patterns under the control of electric fields. We covalently couple a stretchable elastomer with mechanochromic molecules, which emit strong fluorescent signals if sufficiently deformed. We then use electric fields to induce various patterns of large deformation on the elastomer surface, which displays versatile fluorescent patterns including lines, circles and letters on demand. Theoretical models are further constructed to predict the electrically induced fluorescent patterns and to guide the design of this class of elastomers and devices. The material and method open promising avenues for creating flexible devices in soft/wet environments that combine deformation, colorimetric and fluorescent response with topological and chemical changes in response to a single remote signal.

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Section: Discussionmentioning

confidence: 99%

Cephalopod-inspired design of electro-mechano-chemically responsive elastomers for on-demand fluorescent patterning

et al. 2014

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“…31 Our exploration of productive mechanochemistry continued with the development of a gem-dichlorocyclopropanated indene mechanoacid generator, which undergoes a force-induced rearrangement and subsequent elimination driven by aromatization to produce acid (Figure 2). 27 The mechanoacid design was conceived based on a report by Craig et al that describes the mechanically activated rearrangement of gem-dihalocyclopropane to 2,3-dihaloalkenes. 59 This example is the only known mechanoacid reported to date.…”

Section: Etymology Of "Mechanophore": From Destructive To Productivementioning

confidence: 99%

Polymer Mechanochemistry: From Destructive to Productive

Nagamani

Moore³

2015

Acc. Chem. Res.

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When one brings "polymeric materials" and "mechanical action" into the same conversation, the topic of this discussion might naturally focus on everyday circumstances such as failure of fibers, fatigue of composites, abrasion of coatings, etc. This intuitive viewpoint reflects the historic consensus in both academia and industry that mechanically induced chemical changes are destructive, leading to polymer degradation that limits materials lifetime on both macroscopic and molecular levels. In the 1930s, Staudinger observed mechanical degradation of polymers, and Melville later discovered that polymer chain scission caused the degradation. Inspired by these historical observations, we sought to redirect the destructive mechanical energy to a productive form that enables mechanoresponsive functions. In this Account, we provide a personal perspective on the origin, barriers, developments, and key advancements of polymer mechanochemistry. We revisit the seminal events that offered molecular-level insights into the mechanochemical behavior of polymers and influenced our thinking. We also highlight the milestones achieved by our group along with the contributions from key comrades at the frontier of this field. We present a workflow for the design, evaluation, and development of new "mechanophores", a term that has come to mean a molecular unit that chemically responds in a selective manner to a mechanical perturbation. We discuss the significance of computation in identifying pairs of points on the mechanophore that promote stretch-induced activation. Attaching polymer chains to the mechanophore at the most sensitive pair and locating the mechanophore near the center of a linear polymer are thought to maximize the efficiency of mechanical-to-chemical energy transduction. We also emphasize the importance of control experiments to validate mechanochemical transformations, both in solution and in the solid state, to differentiate "mechanical" from "thermal" activation. This Account offers our first-hand perspective of the change-in-thinking in polymer mechanochemistry from "destructive" to "productive" and looks at future advances that will stimulate this growing field.

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“…,13,33−35 catalysis,12,36,37 small molecule and acid release,16,34,38 and soft devices. 39 ■ ASSOCIATED CONTENT * S Supporting Information Sonication experiments; IR and GPC-MALS characterization; rheology (PDF).…”

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confidence: 99%

Mechanochemical Strengthening of a Multi-mechanophore Benzocyclobutene Polymer

2015

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The mechanical stresses that materials experience during use can lead to aging and failure. Recent developments in covalent mechanochemistry have provided a mechanism by which those stresses can be channeled into constructive, rather than destructive, responses, including strengthening in materials. Here, the synthesis and mechanical response of a polymer containing multiple benzocyclobutene (BCB) mechanophores along its backbone are reported. When solutions of the BCB polymer were exposed to the normally destructive elongational flow forces generated by pulsed ultrasonication, the number of intermolecular bond-forming reactions was greater than the number of bondbreaking reactions, leading to a net increase in polymer molecular weight. The molecular weight increase could be turned into gelation by introducing a bismaleimide cross-linker that reacts with the ortho-quinodimethide intermediate generated by mechanically assisted ring opening of the BCB mechanophores and using polymer concentrations in excess of the critical overlap concentration. Unlike a previous mechanically induced gelation of a mechanophore-based polymer, the BCB cross-linking requires no ionic components and represents an attractive, second platform for stress-strengthening materials.T he inevitable stress that almost all materials experience during use leads in many cases to bond breakage, materials aging, and failure, as is reflected in both polymer solutions 1 and solid state polymers. 2 To solve this problem, biological materials have evolved to have the ability to remodel and become stronger in response to otherwise destructive forces. 3,4 This form of mechanical adaptation has provided significant inspiration to current synthetic polymer chemistry efforts. Our group has recently demonstrated that the activation of multiple gem-dibromocyclopropane (gDBC) mechanophores 5 embedded along a polybutadiene backbone turns otherwise destructive chemical responses into constructive responses. 6 When the polymer was exposed to large forces, through either pulsed ultrasonication of polymer solutions or the extrusion of bulk materials, the gDBCs undergo electrocyclic ring-opening reactions to form 2,3-dibromoalkenes that react intermolecularly with carboxylate nucleophiles. The number of intermolecular bond-forming reactions exceeds the number of bond-breaking reactions and leads to a cross-linked polymer network. 6 While the gDBC system represents an important first example of mechanophore-based self-strengthening, the ultimate utility of the approach will depend on the ability to create mechanophore-based systems that match the demands of a particular application. To that end, we sought to develop multi-mechanophore polymers that might overcome the relatively low reactivity of the 2,3-dibromoalkene, 6 the irreversibility of gDBC ring opening in the absence of crosslinking, and the presence of ionic reactants.Because of the substantial recent activity in the realm of covalent polymer mechanochemistry, 7−9 and especially the exploration of mechanophor...

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Proton-Coupled Mechanochemical Transduction: A Mechanogenerated Acid

Cited by 204 publications

References 38 publications

Cephalopod-inspired design of electro-mechano-chemically responsive elastomers for on-demand fluorescent patterning

Cephalopod-inspired design of electro-mechano-chemically responsive elastomers for on-demand fluorescent patterning

Polymer Mechanochemistry: From Destructive to Productive

Mechanochemical Strengthening of a Multi-mechanophore Benzocyclobutene Polymer

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