Mechanochromic Dynamic Covalent Elastomers: Quantitative Stress Evaluation and Autonomous Recovery

Abstract

Stress evaluation in polymeric materials is important in order to not only spot danger in them before serious failure, but also precisely interpret the destructive mechanism, which can improve the lifetime and durability of polymeric materials. Here, we are able to visualize stress by color changes, as well as quantitatively estimate the stress in situ, in segmented polyurethane elastomers with diarylbibenzofuranone-based dynamic covalent mechanophores. We prepared films of the segmented polyurethanes, in which the mechanophores were incorporated in the soft segments, and efficiently activated them by mechanical force. Cleavage of the mechanophores during uniaxial elongation and their recovery after the removal of the stress were quantitatively evaluated by in situ electron paramagnetic resonance measurements, accompanied by drastic color changes.

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

“…Mechanoresponsive materials have recently received increasing interest . In particular, mechanochromic polymers, which exhibit color changes upon exposure to mechanical stress, have attracted much attention in the field of materials science, because they are able to detect damage in materials, thus potentially preventing serious accidents by providing the chance to easily identify damaged parts and replace or repair them . The main strategy for the design of mechanochromic polymers involves the incorporation of mechanochromophores, that is, optically mechanoresponsive moieties, into polymer chains.…”

Stress-induced colouration and crosslinking of polymeric materials by mechanochemical formation of triphenylimidazolyl radicals

“…36 For this purpose PU-1 as well as polyurethane containing solution-blended HABI were first swollen in DMF and then immersed into liquid N 2 . Despite the fast radical recombination of TPI radicals to form HABI in systems with limited translational diffusion, we could achieve stress-sensing with a weightfraction of only 4% 1 which is a considerable improvement compared to the radical systems reported in the literature 15,16 (a movie of the fading coloration of compressed PU-1 in mpg format is available in the ESI †). 2a and c it becomes clear that the reference polyurethane with HABI not covalently attached to the polymer backbone does not change its colour upon freezing and thus does not cleave the HABI-moiety through the application of mechanical stress.…”

“…[1][2][3][4][5] Commonly, this is achieved by incorporating mechanically activatable molecular moieties (mechanophores) into polymer architectures. The former was recently demonstrated by Otsuka and co-workers relying on the reversibly induced cleavage of the diarylbibenzofuranone moiety [15][16][17] while the latter is reported exploiting unspecific, ultrasound-induced polymer scission to unstabilized radicals in solution yielding end-capped, chainextended or grafted polymers. Amongst the motifs for stress-report, functional moieties changing their optical properties upon the application of stress are highly desirable as they allow the visualization of areas under heavy loading.…”

Dynamic covalent bond from first principles: Diarylbibenzofuranone structural, electronic, and oxidation studies

“…Imato et al achieved a unique set of conditions. Using as cross‐linker diarylbibenzofuranone (DABBF), the dimer of arylbenzofuranone (ABF, analog to widely used commercial product HP‐136), the polymer gel synthesized was able to undergo self‐healing under mild conditions at room temperature, due to the dynamic covalent bond in its structure.…”