Skeletal Network Enabling New-Generation Thermoplastic Vulcanizates.

Upcycling of cross-linked rubbers is pressing. The introduction of dynamic covalent bonds into the networks is a popular tactic for recycling thermosetting polymers, but it is very challenging to integrate engineering performance and continuous yet stable reprocessability. Based on traditional rubber formulations, herein, a straightforward strategy is presented for constructing a skeletal network (SN) through interfacial crosslinking and percolation of rubbery granules in a rubber matrix. Rapid exchange reactions involving dynamic interfacial sulfides realize repeated "fragmentation and healing" in the solid-state and consequent reconfiguration of the SN topology of the elastomer, thus endowing the resultant SN elastomer with continuous yet stable re-extrudability. These SN elastomers with hierarchical structures exhibit high gel contents, high resilience, low creep, and reinforcibility competitive to traditional vulcanizates. Specifically, SN elastomers exhibit better overall performance than commercial thermoplastic vulcanizates (TPVs) materials. Overall, a new concept of thermoplastic vulcanizates is proposed, which will promote the sustainable development of rubbers.

Catalyst-Free Metathesis of Cyclic Acetals and Spirocyclic Acetal Covalent Adaptable Networks.

Due to the exchangeability of dynamic covalent bonds in the covalent adaptable networks (CANs) at elevated temperature, they possess recyclability while still maintaining many of the superior properties of thermosets. The exploration of dynamic covalent chemistry is of great significance to the expansion of CANs library and hence the sustainable development of thermosets. In this work, we discovered that, in absence of catalyst, the direct metathesis of the cyclic acetals proceeds while the acyclic acetals cannot. The metathesis kinetics of the cyclic acetals were fully revealed with model compounds. For the CANs demonstration, a series of cross-linked spirocyclic acetal polymers with excellent reprocessability, high thermal stability, and high refractivity were prepared via thiol-ene click polymerization. We envisage that the uncovering of the catalyst-free metathesis of cyclic acetals will enrich the dynamic chemistry of acetals and greatly promote the development of acetal-based CANs and their potential applications in optical devices.

Elastomer Reinforced with Innate Sulfur-Based Cross-Links as Ligands.

Although the incorporation of sacrificial bonds into an elastomer is an effective way to provide a combination of high strength and high fracture toughness, this method normally involves complicated chemical processes. The coordination between metal ions and polysulfides has been documented. However, the potential of polysulfide structures in vulcanizates as ligands has long been neglected. Using innate sulfur-based cross-links, we show how weak and nonpolar elastomers achieve significant reinforcement without modification of the backbone. By simply soaking vulcanizates into solutions containing metal ions, dual ions are simultaneously introduced into the vulcanizate to generate coordinations with different bond strengths, resulting in an unprecedented high modulus. Overall, this work presents a universal yet high-efficiency reinforcing strategy to prepare high-performance elastomers without additional chemical modifications, which should promote comprehensive research and industrial application of sacrificial bond strategies for elastomers.