Multi-modal mechanophores based on cinnamate dimers

Abstract

Mechanochemistry offers exciting opportunities for molecular-level engineering of stress-responsive properties of polymers. Reactive sites, sometimes called mechanophores, have been reported to increase the material toughness, to make the material mechanochromic or optically healable. Here we show that macrocyclic cinnamate dimers combine these productive stress-responsive modes. The highly thermally stable dimers dissociate on the sub-second timescale when subject to a stretching force of 1–2 nN (depending on isomer). Stretching a polymer of the dimers above this force more than doubles its contour length and increases the strain energy that the chain absorbs before fragmenting by at least 600 kcal per mole of monomer. The dissociation produces a chromophore and dimers are reformed upon irradiation, thus allowing optical healing of mechanically degraded parts of the material. The mechanochemical kinetics, single-chain extensibility, toughness and potentially optical properties of the dissociation products are tunable by synthetic modifications.

Polymer Mechanochemistry: Manufacturing Is Now a Force to Be Reckoned With

“…Further resolved saw-tooth patterns were discerned in the plateau of macrocyclic cinnamate dimers. 37 The measured peak to peak separations of individual mechanochemical transitions were distributed approximately around 2.5 nm, matching the corresponding computational calculations, which provided elongation of 2.46 and 2.49 nM for the syn-and anti-cinnamate dimer species, respectively ( Figures 8B and 8C). Using increasingly strained stilbene-containing macrocycles, the Boulatov group has demonstrated that the micromechanical behavior of polymers can be predicted by examining the distortion of the mechanophore as a function of restoring force applied to appropriate molecular coordinates.…”

“…A similar finding has also been reported by Zhang et al when examining cinnamate dimers using SFMS. 37 This work showed that by choice of stereoisomer, the force at which the dimer dissociates at useful rates is tunable over >1 nN. These studies highlight the concept that changes in geometry, beyond those associated with bond making/breaking, can be used to independently manipulate the mechanical and thermal stability of reagents.…”

“…Mechanochemical coupling is dictated by the overall change in length, explaining the relative lack of mechanochemical activity in the benzyl ether compared with its thermodynamic bond strength. A similar link between geometry Adapted with permission from Zhang et al 37 Copyright 2017 Springer Nature.…”

Design and Applications of Photoresponsive Hydrogels

“…Due to their orthogonality with many functional groups, electrocyclic reactions, such as [47] coumarins, [48,49] Adv. Mater.…”

Force‐induced melting of a single polyethylene oxide chain from single crystal: Molecular behavior and influencing factors

“…The combination of subnanometer spatial resolution and piconewton force sensitivity enables not only the measurement of the single‐molecule mechanics but also the extraction of kinetic parameters . The single‐molecule mechanics can also provide the structural information while measuring the length of the unfolded chain . Much has been learned about the working mechanism of molecular motor and the adsorption behavior at solid‐liquid interfaces, as well as the force‐induced conformation transition of individual polymer chain .…”