Mechanically Adaptive Polymers Constructed from Dynamic Coordination Equilibria.

Designing materials capable of adapting their mechanical properties in response to external stimuli is the key to preventing failure and extending their service life. However, existing mechanically adaptive polymers are hindered by limitations such as inadequate load-bearing capacity, difficulty in achieving reversible changes, high cost, and a lack of multiple responsiveness. Herein, we address these challenges using dynamic coordination bonds. A new type of mechanically adaptive material with both rate- and temperature-responsiveness was developed. Owing to the stimuli-responsiveness of the coordination equilibria, the prepared polymers, PBMBD-Fe and PBMBD-Co, exhibit mechanically adaptive properties, including temperature-sensitive strength modulation and rate-dependent impact hardening. Benefitting from the dynamic nature of the coordination bonds, the polymers exhibited impressive energy dissipation, damping capacity (loss factors of 1.15 and 2.09 at 1.0 Hz), self-healing, and 3D printing abilities, offering durable and customizable impact resistance and protective performance. The development of impact-resistant materials with comprehensive properties has potential applications in the sustainable and intelligent protection fields.

Tough, Reprocessable, and Recyclable Dynamic Covalent Polymers with Ultrastable Long-Lived Room-Temperature Phosphorescence.

Room-temperature phosphorescence (RTP) polymers, whose emission can persist for a long period after photoexcitation, are of great importance for practical applications. Herein, dynamic covalent boronic ester linkages with internal B-N coordination are incorporated into a commercial epoxy matrix. The reversible dissociation of B-N bonds upon loading provides an efficient energy dissipation pathway for the epoxy network, while the rigid epoxy matrix can inhibit the quenching of triplet excitons in boronic esters. The obtained polymers exhibit enhanced mechanical toughness (12.26 MJ m-3 ), ultralong RTP (τ=540.4 ms), and shape memory behavior. Notably, there is no apparent decrease in the RTP property upon prolonged immersion in various solvents because the networks are robust. Moreover, the dynamic bonds endow the polymers with superior reprocessablity and recyclability. These novel properties have led to their potential application for information encryption and anti-counterfeiting.

Transmetalation and Demetallization for Open-Oyster-like Non-Ionic Cd(II) Macrocycles.

This work designed a nonionic extended dialdehyde 6,6'-(phenylazanediyl)dipicolinaldehyde (PDPA) for constructing Schiff-base macrocyclic complexes with weaker metal-ligand interactions, so as to solve the long-standing challenges of transmetalation and demetallization in macrocyclic complexes. An enantiomeric pair of open-oyster-like 26-membered [2 + 2] Schiff-base macrocyclic dinuclear Cd(II) complexes (S,S-1a, R,R-1b) could be obtained, having S,S/R,R-1,2-diaminocyclohexane (S,S/R,R-DACH) precursors, while Cu(II) ion template only resulted in a mononuclear Schiff-base Cu(II) acyclic complex (S,S-2) accompanied by the half-oxidation of PDPA instead of expected [2 + 2] Cu(II) macrocyclic complexes. It is suggested that the weak oxidization capability of Cu(II) ion is responsible for the formation of S,S-2 because X-ray photoelectron spectroscopy (XPS) for the solid powder of reaction mixture of direct Cu(II) ion template synthesis implies that both Cu(I) and Cu(II) species are present. In fact, corresponding [2 + 2] dinuclear Cu(II) macrocycles and even metal-free macrocycles unsuitable for direct synthesis can be obtained via Cd(II) → Cu(II) transmetalation and Na2S demetalation verified by ESI-MS and UV-vis spectra. In addition, control experiments indicate that the synthesis of metal-free macrocycles via the direct nontemplate method merely results in the mixture of multiple components of [1 + 1], [2 + 2], and [3 + 3] Schiff-base macrocycles, and they are difficult to isolate.

A Self-Healing Polymer with Fast Elastic Recovery upon Stretching.

The design of polymers that exhibit both good elasticity and self-healing properties is a highly challenging task. In spite of this, the literature reports highly stretchable self-healing polymers, but most of them exhibit slow elastic recovery behavior, i.e., they can only recover to their original length upon relaxation for a long time after stretching. Herein, a self-healing polymer with a fast elastic recovery property is demonstrated. We used 4-[tris(4-formylphenyl)methyl]benzaldehyde (TFPM) as a tetratopic linker to crosslink a poly(dimethylsiloxane) backbone, and obtained a self-healing polymer with high stretchability and fast elastic recovery upon stretching. The strain at break of the as-prepared polymer is observed at about 1400%. The polymer can immediately recover to its original length after being stretched. The damaged sample can be healed at room temperature with a healing efficiency up to 93% within 1 h. Such a polymer can be used for various applications, such as functioning as substrates or matrixes in soft actuators, electronic skins, biochips, and biosensors with prolonged lifetimes.

Transmetalation for Flexible Pendant-Armed Schiff-Base Macrocyclic Complexes Influenced by Halide Effects.

Three 46-membered [2 + 2] pendant-armed Schiff-base macrocyclic dinuclear CdII and CuII complexes (2a, 2b, and 3b) and one 23-membered [1 + 1] CuII macrocycle 4a were prepared from the template-directed condensation reactions between 1,2-bis(2-aminoethoxy)-ethane and extended Cl-dialdehyde in the presence of CdX2 and CuX2 (X = Cl and Br), in which halide effects play important roles in the organization of final macrocyclic complexes in addition to the dominant influence of metal cations. Transmetalation was intensively studied among these CdII and CuII complexes with large and flexible macrocyclic ligands, including two previously synthesized dinuclear ZnII macrocycles (1a and 1b). Our results indicate that ZnII → CuII and CdII → CuII transmetalation proceeds more quickly than that from CdII to ZnII, and all the processes are found to be irreversible. It is noted that a [2 + 2] heterodinuclear CdIIZnII macrocyclic intermediate could be detected by ESI-MS together with [2 + 2] homodinuclear CdII and ZnII macrocyclic complexes. Furthermore, distinct halide behavior was observed in the in situ CdII → CuII and ZnII → CuII metal-ion exchange. That is to say, [2 + 2] macrocycles (1a and 2a) could be converted to [1 + 1] macrocycles 4a and 4b under the reflux condition in the case of CuCl2, accompanied by the configurational transformation from half-folded dinuclear ZnII and CdII to unfolded CuII macrocyclic skeleton. In contrast, CuBr2 leads to a highly efficient transmetalation to corresponding [2 + 2] dinuclear CuII complex 3b from both 1b and 2b no matter the experimental condition used.

Construction of Chiral [4 + 4] and [2 + 2] Schiff-Base Macrocyclic Zinc(II) Complexes Influenced by Counterions and Pendant Arms.

Chiral and racemic 68-membered [4 + 4] tetranuclear and 34-membered [2 + 2] dinuclear Schiff-base macrocyclic zinc(II) complexes 1-10 can be selectively synthesized based on the secondary template effects of counterions and pendant arms, when [(S,S), (R,R), (±)]-1,2-diaminocyclohexane precursors are first used to react with a pair of extended dialdehydes with different pendant arms via zinc(II) ion template-assisted imine condensation.