Diverse metastable diarylacetonitrile radicals generated by polymer mechanochemistry

Yamamoto, Takumi; Aoki, Daisuke; Mikami, Koichiro; Otsuka, Hideyuki

doi:10.1039/d3mr00031a

“…The mechanochromic probe material, DAAN− triOMe/triOMe, was synthesized according to a previously reported method. 14 All materials were used without additional purification.…”

Section: Methodsmentioning

confidence: 99%

“…Commercial-grade PS, designated grade 679 ( M w ∼ 255,123, M n ∼ 107,653, and MWD ∼ 2.37), was procured from PSJ Japan Co., Ltd. The mechanochromic probe material, DAAN–triOMe/triOMe, was synthesized according to a previously reported method . All materials were used without additional purification.…”

Section: Methodsmentioning

confidence: 99%

“…For each kneading condition, the torque and temperature of the melt polymer were simultaneously recorded (Figure 4). DAAN−triOMe/triOMe exhibits mechanochromic behavior when polymeric mechanoradicals abstract hydrogen radical from DAAN−triOMe/triOMe 14,20 and generate the corre- sponding DAAN−triOMe/triOMe radical that emits orange fluorescence with a band around 580 nm. As shown in Figure 2a, b, the fluorescence intensity sequentially increases as the temperature decreases from 180 to 150 °C.…”

Section: Mechanochromic Behavior At Different Screw Speeds and Kneadi...mentioning

confidence: 99%

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Visualization of Polymer Chain Scission during Melt Processing Using a Mechanochromic Probe

Khawdas,

Kubota,

Yamamoto

et al. 2024

Macromolecules

0

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We thoroughly investigated polymer chain scission occurring through thermal and mechanical degradation during kneading via complex viscosity, torque, shear stress, and feeding rate measurements. We visualized polystyrene chain scission using a diarylacetonitrile derivative (DAAN− triOMe/triOMe) that can react with mechanoradicals to generate the corresponding fluorescent DAAN−triOMe/triOMe radicals. We kneaded polystyrene containing 5 wt % DAAN−triOMe/triOMe at various screw speeds and kneading temperatures using a twin-screw kneader. The results reveal that changes in complex viscosity and fluorescence intensity are correlated, indicating polystyrene chain scission and free radical generation. Mechanochromic behavior was also associated with heat-induced polymer deformation. Furthermore, the complex viscosity decreased with increasing speed and temperature. The analyses of torque, shear stress, and feeding rate revealed intricate relationships between speed, temperature, and polymer chain scission. This study highlights the effectiveness of DAAN−triOMe/triOMe in visualizing polymer chain scission using color change during both at-line and offline observations.

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“…[1][2][3][4][5] Much of the research into the fundamentals of mechanochemistry has focused on how electronic, steric, and stereochemical factors influence the reactivity of mechanophores as these parameters are the main drivers of reactivity in thermal or photo-chemical reactions. [6][7][8][9][10][11][12][13] Many studied mechanochemical reactions involve the homolytic cleavage of a CÀ C bond to generate diradical species in the first step of mechanoactivation. The extent of electronic stabilization of the formed diradical intermediates can impact the mechanochemical reactivity.…”

Section: Introductionmentioning

confidence: 99%

Force Transduction Through Distant Force‐Bearing Regioisomeric Linkages Affects the Mechanochemical Reactivity of Cyclobutane

Flear,

Horst,

Yang

et al. 2024

Angewandte Chemie

1

0

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Fundamental understanding of mechanochemical reactivity is important for designing new mechanophores. Besides the core structure of mechanophores, substituents on a mechanophore can affect its mechanochemical reactivity through electronic stabilization of the intermediate or effectiveness of force transduction from the polymer backbone to the mechanophore. The latter factor represents a unique mechanical effect in considering polymer mechanochemistry. Here, we show that regioisomeric linkage that is not directly adjacent to the first cleaving bond in cyclobutane can still significantly affect the mechanochemical reactivity of the mechanophore. We synthesized three non‐scissile 1,2‐diphenyl cyclobutanes, varying their linkage to the polymer backbone via the o, m, or p‐position of the diphenyl substituents. Even though the regioisomers share the same substituted cyclobutane core structure and similar electronic stabilization of the diradical intermediate from cleaving the first C‐C bond, the p isomer exhibited significantly higher mechanochemical reactivity than the o and m isomers. The observed difference in reactivity can be rationalized as the much more effective force transduction to the scissile bond through the p‐position than the other two substitution positions. These findings point to the importance of considering force‐bearing linkages that are more distant from the bond to be cleaved when incorporating mechanophores into polymer backbones.

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Force Transduction Through Distant Force‐Bearing Regioisomeric Linkages Affects the Mechanochemical Reactivity of Cyclobutane

Flear,

Horst,

Yang

et al. 2024

Angew Chem Int Ed

2

0

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Fundamental understanding of mechanochemical reactivity is important for designing new mechanophores. Besides the core structure of mechanophores, substituents on a mechanophore can affect its mechanochemical reactivity through electronic stabilization of the intermediate or effectiveness of force transduction from the polymer backbone to the mechanophore. The latter factor represents a unique mechanical effect in considering polymer mechanochemistry. Here, we show that regioisomeric linkage that is not directly adjacent to the first cleaving bond in cyclobutane can still significantly affect the mechanochemical reactivity of the mechanophore. We synthesized three non‐scissile 1,2‐diphenyl cyclobutanes, varying their linkage to the polymer backbone via the o, m, or p‐position of the diphenyl substituents. Even though the regioisomers share the same substituted cyclobutane core structure and similar electronic stabilization of the diradical intermediate from cleaving the first C‐C bond, the p isomer exhibited significantly higher mechanochemical reactivity than the o and m isomers. The observed difference in reactivity can be rationalized as the much more effective force transduction to the scissile bond through the p‐position than the other two substitution positions. These findings point to the importance of considering force‐bearing linkages that are more distant from the bond to be cleaved when incorporating mechanophores into polymer backbones.

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Diverse metastable diarylacetonitrile radicals generated by polymer mechanochemistry

Abstract: Diverse diarylacetonitrile radicals were generated by polymeric mechanochemical reactions. Fluorescence wavelengths could be tuned by changing the substituents on the aromatic rings of the generated radicals.

Cited by 4 publications

References 53 publications

Visualization of Polymer Chain Scission during Melt Processing Using a Mechanochromic Probe

Visualization of Polymer Chain Scission during Melt Processing Using a Mechanochromic Probe

Force Transduction Through Distant Force‐Bearing Regioisomeric Linkages Affects the Mechanochemical Reactivity of Cyclobutane

Force Transduction Through Distant Force‐Bearing Regioisomeric Linkages Affects the Mechanochemical Reactivity of Cyclobutane

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