Polyurethanes (PUs) have many applications resulting from their preeminent properties, but being commonly used toxic catalysts, and the lack of processability for PU thermosets cause limitations. Herein, we report a new class of the PU-like dynamic covalent polymers, poly(oxime-urethanes) (POUs), which are prepared from the uncatalyzed polyaddition of multifunctional oximes and hexamethylene diisocyanate (HDI) at ambient temperature. Kinetics studies reveal that almost complete polymerization (∼99% conversion) can be achieved in 3 h at 30 °C in dichloromethane (DCM), the most effective among the solvents evaluated, producing linear POUs with comparable molecular weights to the catalyzed PUs. We find that the oxime-carbamate structures are reversible at about 100 °C through oxime-enabled transcarbamoylation via a thermally dissociative mechanism. The cross-linked POUs based on oxime-carbamate bonds show efficient catalyst-free healable/recyclable properties. Density functional theory (DFT) calculations suggest that the fast oxime-urethanation and the mild thermoreversible nature are mediated by the characteristic nitrone tautomer of the oxime. Given widespread urethane-containing materials, POUs are of promising potential in applications because of the excellent mechanical performances, facile preparation, and dynamic property without using catalysts.

Constructing responsive and adaptive materials by dynamic covalent bonds is an attractive strategy in material design. Here, we present a kind of dynamic covalent polyureas which can be prepared from the highly efficient polyaddition reaction of pyrazoles and diisocyanates at ambient temperature in the absence of a catalyst. Owing to multiphase structural design, poly(pyrazole-ureas) (PPzUs) show excellent mechanical properties and unique crystallization behavior. Besides, the crosslinked PPzUs can be successfully recycled upon heating (~130 °C) and the molecular-level blending of polyurea and polyurethane is realized. Theoretical studies prove that the reversibility of pyrazole-urea bonds (PzUBs) arises from the unique aromatic nature of pyrazole and the N-assisting intramolecular hydrogen transfer process. The PzUBs could further broaden the scope of dynamic covalent bonds and are very promising in the fields of dynamic materials.

This article reports preparation of a crosslinked polydimethylsiloxane (PDMS) network via dynamic transesterification reaction between PDMS-diglycidyl ether and pripol 1017 with Zn(OAc)2 as the catalyst. The thermal dynamic nature of the network was investigated by the creep-recovery and stress-relaxation tests. The synthesized PDMS elastomer showed excellent solvent resistance even under high temperature, and could be reprocessed by hot pressing at 180 °C with the mechanical properties maintained after 10 cycles. Application of the PDMS elastomer in constructing micro-patterned stamps repeatedly has been demonstrated. The high plastic temperature and good solvent resistance distinguish the research from other reported thermoplastic PDMS elastomers and broaden the practical application areas.

A facile cross-linking strategy of using small molecules as physcial crosslinkers to facilitate recyclable polybutadiene (PB) elastomer with excellent toughness and stretchability is demonstrated. Carboxylic acid groups were incorporated along the PB backbone via thiol-ene reaction, and then the polymer can be cross-linked by ionic hydrogen bonds between the carboxylic acid groups from PB and the amine groups of the cross-linkers. The ionic hydrogen bonds can dynamiclly break and reconstruct upon deformation, thus endowing the resultant polymer with not only high toughness and stretchability (1800%), but also good selfrecovery and enhanced damping properties. Remarkably, the dynamically cross-linked PB elastomer can be thermally recycled owing to the thermal reversibility of the ionic hydrogen bonds and the mechanical properties can be largely recovered after reprocessing.

Natural products are a vital source of lead compounds in drug discovery. Development of efficient tandem reactions to build useful compounds and apply them to the synthesis of natural products is not only a significant challenge but also an important goal for chemists. Here we describe a tandem C–H oxidation/cyclization/rearrangement of isochroman-derived allylic silylethers, promoted by DDQ and InCl3. This method allows the efficient construction of tricyclic benzoxa[3.2.1]octanes with a wide substrate scope. We employ this tandem reaction to achieve the asymmetric total syntheses of (−)-brussonol and (−)-przewalskine E.

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The design of responsive materials by introducing dynamic covalent bonds (DCBs), that can undergo reversible association and dissociation under certain conditions, is an appealing research field in recent years. The...

Three new compounds, atriplicone A (I), B (II), and C (III) are isolated together with five known compounds.