We have demonstrated the formation of segregated enantiomeric dynamic rods in water, from the self-sorting of chiral trans-1,2-bisureido cyclohexane-based bolaamphiphiles. Fluorescence probes have ...been used to investigate the self-sorting through forming exciplex and FRET.
The ultrasound-induced scission of silver carbene coordination complexes with polytetrahydrofuran-functionalized N-heterocyclic carbene ligands is reported. In solution, scission is very efficient, ...with complete conversion within 10 min when the polymers have a molecular weight of 6.7 kDa. The mechanochemical origin of the scission is supported by the molecular weight dependence of the scission rate and by the low reactivity of the silver complex with low molecular weight ligands. The mechanochemical process at room temperature is much faster than thermal scission at 60 °C, which has a conversion of 30% in 18 h.
A latent olefin metathesis catalyst, bearing two polymeric NHC ligands, was embedded in a semicrystalline polymer matrix containing cyclic olefins. The catalyst was activated by straining the solid ...material under compression, resulting in polymerization and cross-linking reactions of the monomers in situ. Catalyst activation in the solid state may be employed in new self-healing materials.
Mechanophores capable of releasing N‐heterocyclic carbene (NHC), a strong base, are combined with triggerable chemiluminescent substrates to give a novel system for mechanically induced ...chemiluminescence. The mechanophores are palladium bis‐NHC complexes, centrally incorporated in poly(tetrahydrofuran) (pTHF). Chemiluminescence is induced from two substrates, adamantyl phenol dioxetane (APD) and a coumaranone derivative, upon sonication of dilute solutions of the polymer complex and either APD or the coumaranone. Control experiments with a low molecular weight Pd complex showed no significant activation and the molecular weight dependence of the coumaranone emission supports the mechanical origin of the activation. The development of this system is a first step towards mechanoluminescence at lower force thresholds and catalytic mechanoluminescence.
Mechanophores capable of releasing N‐heterocyclic carbene are combined with triggerable chemiluminescent substrates to give a novel system for mechanically induced chemiluminescence. The mechanophores are palladium bis‐NHC complexes centrally incorporated in poly(tetrahydrofuran). Chemiluminescence is induced upon sonication of dilute solutions of the polymer complex and either APD or a coumaranone derivative.
Dioxetane-based force-induced light emission from polymers, or mechanoluminescence, is a powerful new way of characterizing the behavior of polymeric materials under stress. Here, we reveal that ...breaking the dioxetane mechanically gives strikingly similar products to those formed on thermal activation, with a singlet/triplet ratio of 1:9.9 and a total quantum yield of 9.8%. A sensitized relay scheme ensured high reproducibility in the detection of the short-lived triplet products. In addition to guiding the design of more sensitive mechanoluminescent probes, the similarity in the scission products indicates that once mechanical force releases the steric lock between the adamantyl groups, the dioxetane undergoes scission in a pathway that resembles the thermal process. Excited states are formed only after the main transition state in a region in which the excited- and ground-state surfaces are nearly degenerate, which, thus, accounts for the remarkable similarity in the scission products.
The diamide–imide equilibrium was successfully exploited for the synthesis of dynamic covalent polymer networks in which a dissociative bond exchange mechanism leads to high processibility at ...temperatures above ≈110 °C. Dynamic covalent networks bridge the gap between thermosets and thermoplastic polymers. At the operating temperature, when the network is fixed, dynamic covalent networks are elastic solids, while at high temperatures, chemical exchange reactions turn the network into a processible viscoelastic material. Upon heating a dissociative network, the viscosity may also decrease due to a shift of the chemical equilibrium; in such materials, the balance between processibility and excessive flow is important. In this study, a network is prepared that upon heating to above ≈110 °C dissociates to a significant extent due to a shift in the amide–imide equilibrium of a bisimide, pyromellitic diimide, in combination with poly(tetrahydrofuran) diamines. At room temperature, the resulting materials are elastic rubbers with a tensile modulus of 2–10 MPa, and they become predominantly viscous above a temperature of approximately 110 °C, which is dependent on the stoichiometry of the components. The diamide–imide equilibrium was studied in model reactions with NMR, and variable temperature infrared (IR) spectroscopy was used to investigate the temperature dependence of the equilibrium in the network. The temperature-dependent mechanical properties of the networks were found to be fully reversible, and the material could be reprocessed several times without loss of properties such as modulus or strain at break. The high processibility of these networks at elevated temperatures creates opportunities in additive manufacturing applications such as selective laser sintering.
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