Polymer–Inorganic Composites with Dynamic Covalent Mechanochromophore

Abstract

Polymer–inorganic composites with diaryl­bibenzo­furanone (DABBF) moieties, dynamic covalent mechanochromophores, were prepared, and their mechanochromic behavior was systematically investigated. The central C–C bonds in DABBF moieties can be cleaved by mechanical force to form the corresponding stable blue radicals, which can be quantitatively evaluated by electron paramagnetic resonance (EPR) spectroscopy. One controversial issue but attractive property in the DABBF system is the equilibrium between the activated and deactivated states. Although the deactivation process decreases the sensitivity of some equilibrium mechanophores, the equilibrium has rarely been considered when establishing molecular and/or material design of these systems. Herein, a rational macromolecular design to suppress the deactivation of activated dynamic mechanophores and improve sensitivity by limiting their molecular motion is proposed. Polymer–inorganic composite materials with rigid networks prepared from DABBF alkoxysilane derivatives exhibited significant activation of the incorporated DABBF linkages by grinding, with sensitivities more than 50 times as high as that of DABBF monomers. The increased sensitivity is due to the effective transmission of mechanical force to the DABBF moieties in the network structures and suppression of the recombination of the generated radicals by the rigid frameworks. Furthermore, when the rigid frameworks were incorporated into elastomers as inorganic hard domains, the DABBF mechanophores at the interface between the organic and inorganic domains were preferentially activated by elongation.

Mechanochromic Polymers That Turn Green Upon the Dissociation of Diarylbibenzothiophenonyl: The Missing Piece toward Rainbow Mechanochromism

“…The ultimate advantage of radical‐type mechanochromic polymers is not only the qualitative visualization of the mechanical stress, but also its quantitative evaluation by electron paramagnetic resonance (EPR) spectroscopy, both in solution and the solid state. We have already reported two radical‐type mechanochromic polymers that bear diarylbibenzofuranone (DABBF) or tetraarylsuccinonitrile (TASN) moieties (Figure a and b) . Homolytic cleavage of the central carbon‐carbon bond in the DABBF and TASN units in response to mechanical stress affords arylbenzofuranone (blue) and diarylacetonitrile radicals (pink), respectively.…”

High-intensity focused ultrasound-induced mechanochemical transduction in synthetic elastomers

“…The advantage of the proposed method over existing triggering methods is the capability to achieve spatiotemporal control of mechanophore activation. In particular, while previous studies have demonstrated mechanochemical activation in bulk polymers using compression and tension (3,4,8,45), the HIFU-based triggering system demonstrated here is a remote energy source capable of localizing the region of activation and triggering polymer mechanochemistry noninvasively. These advances enable mechanoactivation of two different mechanophore systems.…”

Self‐Reporting Fiber‐Reinforced Composites That Mimic the Ability of Biological Materials to Sense and Report Damage

“…Good mechanical activation of the mechanophore diarylbibenzofuranone at the interface between silica particles and a rubbery poly(butyl acrylate) matrix was recently reported . The composite rubbers changed from colorless to blue when stretched because stable blue radicals formed.…”