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Biobased furan polymers (BFPs) derived from 5‐hydroxymethylfurfural (HMF) are eco‐friendly polymers obtained from inedible biomass resources. Modification of such polymers is expected to expand their practical uses. BFPs have furan moieties that can react as dienophiles with maleimide, facilitating well‐designed polymer reactions. Herein, we report the preparation of various maleimides using p‐maleimidophenylisocyanate (PMPI), which has a highly reactive isocyanate group and a maleimide group, to modify BFP through the Diels–Alder reaction of the maleimide group. Two reactive sites in PMPI exhibit orthogonal reactivity, enabling us to achieve tailor‐made modification agents. The Tg values and rheological properties of modified polymers can be tuned according to the structure of maleimide and their reaction conversion, which demonstrates the practical usability of BFP derived from furfural. The strategy proposed herein can be applied to obtain biobased materials with desirable functions and physical properties. [ABSTRACT FROM AUTHOR]

We report a novel and versatile approach to achieving swelling‐induced mechanochemistry using a multinetwork (MN) strategy that enables polymer networks to repeatedly swell with monomers and solvents. The isotropic expansion of the first network (FN) provides sufficient force to drive the mechanochemical scission of a radical‐based mechanophore, difluorenylsuccinonitrile (DFSN). Although prompt recombination generally occurs in such highly mobile environments, the resulting pink radicals are kinetically stabilized in the gels, probably due to limited diffusion in the extended polymer chains. Moreover, the DFSN embedded in the isotropically strained chain exhibits increased thermal reactivity, which can be reasonably explained by an entropic contribution of the FN to the dissociation. The utility of the MN polymers is demonstrated not only in terms of swelling‐force‐induced network modification, but also in the context of tunable reactivity of the dissociative unit through proper design of the hierarchical network architecture. [ABSTRACT FROM AUTHOR]

Radical‐type mechanophores (RMs) can undergo homolytic cleavage of their central C−C bonds upon exposure to mechanical forces, which affords radical species. Understanding the characteristics of these radical species allows bespoke mechanoresponsive materials to be designed and developed. The thermal stability of the central C−C bonds and the oxygen tolerance of the generated radical species are crucial characteristics that determine the functions and applicability of such RM‐containing mechanoresponsive materials. In this paper, we report the synthesis and characterization of two series of arylfluorene‐based RM derivatives, that is, 9,9'‐bis(5‐methyl‐2‐pyridyl)‐9,9'‐bifluorene (BPyF) and 9,9'‐bis(4,6‐diphenyl‐2‐triazyl)‐9,9'‐bifluorene (BTAF). BPyF and BTAF derivatives were synthesized without generating any peroxides initially, albeit that BPyF slowly converted to the corresponding peroxide in solution. DFT calculations revealed the importance of the thermodynamic stability and the values of the α‐SOMO levels of the corresponding radical species for their thermal stability and oxygen tolerance. Furthermore, the mechanochromism of BTAF was demonstrated by ball‐milling a BTAF‐centered polymer, which was synthesized by atom‐transfer radical polymerization (ATRP). [ABSTRACT FROM AUTHOR]

Mechanochromic elastomers that exhibit force‐induced cross‐linking reactions in the bulk state are introduced. The synthesis of segmented polyurethanes (SPUs) that contain difluorenylsuccinonitrile (DFSN) moieties in the main chain and methacryloyl groups in the side chains was carried out. DFSN was selected as the mechanophore because it dissociates under mechanical stimuli to form pink cyanofluorene (CF) radicals, which can also initiate the radical polymerization of methacrylate monomers. The obtained elastomers generated CF radicals and changed color by compression or extension; they also became insoluble due to the mechanically induced cross‐linking reactions. Additionally, an SPU containing diphenylmethane units also exhibited highly sensitive mechanofluorescence. To the best of our knowledge, this is the first report to demonstrate damage detection ability and changes in the mechanical properties of bulk elastomers induced by simple compression or extension. [ABSTRACT FROM AUTHOR]

Since the beginning of polymer science, understanding the influence of mechanical stress on polymer chains has been a fundamental and important research topic. The detection of mechanoradicals generated by homolytic cleavage of the polymer chains in solution has been studied in many cases. However, the detection of mechanoradicals in the bulk is still limited owing to their high reactivity. Herein, we propose an innovative strategy to detect mechanoradicals visually and quantitatively using a chain‐transfer agent that generates relatively stable fluorescent radicals as a molecular probe. Mechanoradicals generated by ball milling of polystyrene samples were successfully detected by using a diarylacetonitrile compound as a fluorescent molecular probe through this radical chain‐transfer mechanism. This probe enables the visualization and quantitative evaluation of mechanoradicals generated by polymer‐chain scission. [ABSTRACT FROM AUTHOR]

Mechanochromic polymers can be used as stress‐ and damage‐detecting sensors in polymeric materials, given that mechanical stimuli can be visualized by color changes. Although many types of mechanochromic polymers have been reported so far, there are only few examples on their further functionalization based on multiple color changes (multicolor mechanochromism). Herein, preliminary results are reported on the use of multicolor mechanochromism to detect the duration of the mechanical stimulation by simply mixing white powders of two mechanochromic polystyrene samples that contain a different radical‐type mechanochromophore at the midpoint of each polymer chain and thus exhibit different colors in response to mechanical stimuli. The mechanosensitivity can be tuned via the polymer length and shape, and a combination of these two types of mechanochromic polymers allows detecting the duration with multicolor mechanochromism, i.e., a color change from white to blue upon short exposure to grinding and a color change from white to gray upon longer exposure to grinding. Electron paramagnetic resonance and solid‐state UV–vis measurements support the mechanism proposed for this multiple mechanochromism. [ABSTRACT FROM AUTHOR]

Crosslinked polymers (CLPs) exhibit exceptional mechanical properties as well as good chemical and solvent resistance. However, their reprocessing, recycling, and modification remain difficult. One promising approach to overcome this limitation is to introduce dynamic covalent bonds that enable chain‐exchange reactions and network‐structure rearrangements in identical polymer networks (A–A fusion), resulting in self‐healing and reprocessing properties. Reported here is the fusion of two distinct polymer networks (A–B fusion) by the dynamic behavior of bis(2,2,6,6‐tetramethylpiperidin‐1‐yl)disulfide (BiTEMPS) at the interface between different CLPs. The appearance, swelling behavior, and mechanical properties of the fused samples indicate exchange reactions of the BiTEMPS units and the formation of topological bonds at the interface, commensurate with the generation of a CLP that exhibits tunable properties. [ABSTRACT FROM AUTHOR]

A simple and efficient method to generate macrocyclic structures has been developed based on the dynamic behavior of the linker bis(2,2,6,6‐tetramethylpiperidin‐1‐yl)disulfide (BiTEMPS). The prime linear structure was transformed into a (macro)cycle using the following sequence: 1) thiol–ene reaction with a BiTEMPS derivative to afford the linear precursor, then 2) an entropy‐driven transformation induced by diluting and heating. The radicals generated from BiTEMPS upon heating are highly tolerant toward a variety of chemical species, including oxygen and olefins, but they exhibit high reactivity in exchange reactions, which can be applied to the topology transformation of various skeletons. The advantages of the present method, namely, its procedural simplicity and substrate versatility, are demonstrated by the gram‐scale synthesis of cyclic compounds with low and relatively high molecular weight. [ABSTRACT FROM AUTHOR]

The maleimide structure is highly reactive, exemplified by thiol–ene click reactions with thiols and Diels–Alder reactions with furans. Although postpolymerization modifications and macromolecular conjugations involving maleimide units have been widely studied, mostly due to their selectivity and high reactivity, little has been reported on the one‐pot postpolymerization introduction of maleimides in polymer chains. Herein, we report p‐maleimidophenyl isocyanate and its derivatives as modification agents to introduce maleimide moieties by reaction with hydroxy groups into polymer chains. The high reactivity of the resulting modification agents and of the corresponding maleimide structures once inserted in the polymer chains was examined by studying their reaction kinetics. Furthermore, these modification agents were successfully applied to the synthesis of macromonomers for graft polymerization and various block copolymers, with, for example, AB‐type, star‐shaped, and H‐shaped architectures. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2396–2406 [ABSTRACT FROM AUTHOR]

Three component mobility controlling vinylic rotaxane crosslinkers with two radically polymerizable vinyl groups (RC_Rs) were synthesized to prove that the mobility of the components of the RC_Rs plays a crucial role in determining the properties of rotaxane‐crosslinked polymers (RCPs). RC_Rs (R=H, Me, or Et) were obtained from living ring‐opening polymerization. RCP_Et was prepared using RC_Et, which exhibits the lowest component mobility. The low component mobility is reflected in inferior mechanical strength and stretching ability in tensile stress tests compared to components with good (R=Me) and high (R=H) mobility. However, RCP_Et exhibited significantly higher stress and strain values than the corresponding covalently crosslinked polymers (CCP_Rs). These results indicate that a suitable component mobility substantially enhances the mechanical strength of RCPs. This behavior could serve as a guiding principle for the molecular design of advanced RCs. Stretching out: Rotaxane crosslinkers (RC_Rs) with two radically polymerizable vinyl groups were synthesized to evaluate the mobility of the components in determining the properties of rotaxane‐crosslinked polymers (RCP Rs). RCP_Et exhibits the lowest component mobility, as reflected in inferior mechanical strength and stretching ability of the RCP compared to those with components with good (R=Me) and high (R=H) mobility. [ABSTRACT FROM AUTHOR]

Abstract: Mechanochromic polymers, that is, polymers sensitive to mechanical impact, promise great potential for applications in damage sensors. In particular, radical‐type mechanochromic polymers, which produce colored radical species in response to mechanical stress, may enable not only the visualization of mechanical stress, but also its quantitative evaluation by electron paramagnetic resonance analysis. Herein, a radical‐type mechanochromic polymer that exhibits a color change from white to green upon dissociation of a diarylbibenzothiophenonyl moiety at the mid‐point of a polystyrene chain is presented, and its mechanochromic behavior is examined. Mechanochromic materials that show a variety of colors (“rainbow colors”) in response to mechanical stress were prepared by simply mixing radical‐type mechanochromic polymers of primary colors. [ABSTRACT FROM AUTHOR]

Intrinsically exchangeable dynamic covalent bonds that can be triggered by readily usable stimuli offer easy incorporation of their dynamic properties in various molecular systems, but the library of such bonds is still being developed. Herein, we report the dynamic covalent chemistry of 2,2,6,6-tetramethylpiperidine-1-sulfanyl (TEMPS) dimers derived from thermally reversible homolytic dissociation of disulfide linkages. High air stability of TEMPS was observed even at 100 °C, affording facile employment of thermal dissociation-association equilibria and adjustable bond exchange properties under atmospheric conditions. We also established an efficient synthetic route for a modifiable derivative of the dimer that enabled incorporation of dynamic properties into linear and network polymer structures. The obtained polymers showed controllable molecular weights, temperature-dependent swelling properties, healing ability, and recyclability, reflecting the thermally tunable dynamics of the dimer. [ABSTRACT FROM AUTHOR]

Keywords: Chromophores; Gels; Mechanochemistry; Polymers; Radicals EN Chromophores Gels Mechanochemistry Polymers Radicals 1 1 1 02/21/23 20230220 NES 230220 B The swelling force b exerted by solvents in polymer gels is revealed to trigger mechanochemical reactions, as reported by Takuma Watabe and Hideyuki Otsuka in their Research Article (e202216469). Chromophores, Gels, Mechanochemistry, Polymers, Radicals A multinetwork strategy based on sequential monomer swelling and polymerization processes makes the original network sensitive to mechanical stimuli. [Extracted from the article]

Chromophores, Gels, Mechanochemistry, Polymers, Radicals A multinetwork strategy based on sequential monomer swelling and polymerization processes makes the original network sensitive to mechanical stimuli. Keywords: Chromophores; Gels; Mechanochemistry; Polymers; Radicals EN Chromophores Gels Mechanochemistry Polymers Radicals 1 1 1 02/21/23 20230220 NES 230220 B The swelling force b exerted by solvents in polymer gels is revealed to trigger mechanochemical reactions, as reported by Takuma Watabe and Hideyuki Otsuka in their Research Article (e202216469). [Extracted from the article]

Keywords: mechanochemistry; mechanochromism; mechanophores; polymers; radicals EN mechanochemistry mechanochromism mechanophores polymers radicals 1 1 1 02/28/23 20230224 NES 230224 B A human dive into the ocean of -SOMO levels b : Exhaled oxygen bubbles cause peroxidation of radical-type mechanophores (RMs), which generate shallow -SOMO level radical species; however, RMs that generate deep -SOMO level radical species did not afford peroxide compounds. Front Cover: Theoretical and Experimental Investigations of Stable Arylfluorene-Based Radical-Type Mechanophores (Chem. Eur. J. 12/2023) Mechanochemistry, mechanochromism, mechanophores, polymers, radicals. [Extracted from the article]

Visualization and quantitative evaluation of covalent bond scission in polymeric materials are highly important for understanding failure, fatigue, and deterioration mechanisms and improving the lifetime, durability, toughness, and reliability of the materials. The diarylbibenzofuranone-based mechanophore radical system enabled, through electron paramagnetic resonance spectroscopy, in situ quantitative evaluation of scission of the mechanophores and estimation of mechanical energy induced along polymer chains by external forces. The coagulation of polymer solutions by freezing probably generated force but did not cleave the mechanophores. On the other hand, cross-linking led to efficient propagation of the force of more than 80 kJ mol−1 to some mechanophores, resulting their cleavage and generation of colored stable radicals. This mechanoprobe concept has the potential to elucidate other debated issues in the polymer field as well. [ABSTRACT FROM AUTHOR]

Visualization and quantitative evaluation of covalent bond scission in polymeric materials are highly important for understanding failure, fatigue, and deterioration mechanisms and improving the lifetime, durability, toughness, and reliability of the materials. The diarylbibenzofuranone-based mechanophore radical system enabled, through electron paramagnetic resonance spectroscopy, in situ quantitative evaluation of scission of the mechanophores and estimation of mechanical energy induced along polymer chains by external forces. The coagulation of polymer solutions by freezing probably generated force but did not cleave the mechanophores. On the other hand, cross-linking led to efficient propagation of the force of more than 80 kJ mol−1 to some mechanophores, resulting their cleavage and generation of colored stable radicals. This mechanoprobe concept has the potential to elucidate other debated issues in the polymer field as well. [ABSTRACT FROM AUTHOR]

Direct measurement of the chemical force between chiral molecules was investigated by chemical force microscopy (CFM). 2,2,2-Trifluoro-1-(9-anthryl)ethanol (TFAE) and N-(3,5-dinitrobenzoyl)phenylglycine (DNBP), a well-known pair of enantiomers, were strongly immobilized on the surface of the cantilever tip and the substrate surface, respectively, by the use of aminosilane, to propose a chiral stationary phase model system of a silica-based chiral column. The modification of TFAE on a cantilever tip and DNBP on the substrate surface was confirmed by x-ray photoelectron spectroscopic and time-of-flight secondary ion mass spectrometric measurements. The force curve between (R or S)-TFAE and (R or S)-DNBP enantiomers were measured using the force measurement mode scanning force microscopy to determine the magnitude of the interaction. The histograms of the adhesion force for a different chirality pair [(R)-ATEA vs (S)-DNBP and (S)-ATEA vs (R)-DNBP] showed a broader distribution than those for the identical chirality pair [(R)-ATEA vs (R)-DNBP and (S)-ATEA vs (S)-DNBP]. Since CFM measurement cans recognize the difference of in nanonewton forces, the results can be regarded as a rational design for chiral recognition in a silica-based chiral column. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Keywords: electron paramagnetic resonance; mechanochromism; polymer mechanochemistry; polyurethanes; self-strengthening EN electron paramagnetic resonance mechanochromism polymer mechanochemistry polyurethanes self-strengthening 8555 8555 1 04/01/21 20210406 NES 210406 B Mechanofunctional polymers b that exhibit color change, fluorescence, and self-strengthening ability were developed by Hideyuki Otsuka et al. in their Communication on page 8406. Electron paramagnetic resonance, mechanochromism, polymer mechanochemistry, polyurethanes, self-strengthening Inside Back Cover: Segmented Polyurethane Elastomers with Mechanochromic and Self-Strengthening Functions (Angew. [Extracted from the article]

Electron paramagnetic resonance, mechanochromism, polymer mechanochemistry, polyurethanes, self-strengthening Innenrücktitelbild: Segmented Polyurethane Elastomers with Mechanochromic and Self-Strengthening Functions (Angew. Keywords: electron paramagnetic resonance; mechanochromism; polymer mechanochemistry; polyurethanes; self-strengthening EN electron paramagnetic resonance mechanochromism polymer mechanochemistry polyurethanes self-strengthening 8639 8639 1 04/01/21 20210406 NES 210406 B Mechanofunktionelle Polymere b , die einen Farbwechsel, Fluoreszenz und die Fähigkeit zur Selbstverfestigung aufweisen, werden von Hideyuki Otsuka et al. in ihrer Zuschrift auf S. 8487 vorgestellt. [Extracted from the article]

Rücktitelbild: Fusion of Different Crosslinked Polymers Based on Dynamic Disulfide Exchange (Angew. Chem. 11/2020) In ihrer Zuschrift auf S. 4324 erläutern H. Otsuka et al., wie die Fusion der mit BiTEMPS-Einheiten versehenen CLPs durch einfaches Mischen und Heißpressen der pulverisierten Proben gelingt. [Extracted from the article]

The synthesis and characterization of a series of diarylbiindolinone derivatives as substituent‐tunable mechanochromophores that generate pink carbon‐centered radicals in response to mechanical stimuli are reported. The changes in mechano‐responsiveness, which result from the introduction of various substituents on the diarylbiindolinone skeleton, are systematically studied and mechanochromic polymers that contain such diarylbiindolinone units are developed. [ABSTRACT FROM AUTHOR]

The cover page of the journal "Angewandte Chemie International Edition" is presented.