We reported a novel method of producing the cross-linked polybutadiene elastomer which could be thermally recycled like the plastic materials without the sacrifice of functional utility. The commercial polybutadiene was first attached with furan via thiol−ene reaction, and the cross-linked network was then built via Diels−Alder click reaction between the bismaleimide and attached furan groups from polybutadiene. The obtained polymer had good solvent resistance from ambient temperature to 100 °C. The mechanical properties of modified polybutadiene could be tailored by the amount of attached furan and the ratio of furan to bismaleimide. Furthermore, the dynamic cross-linked polybutadiene had good thermally remolded and self-healing behaviors. By this method, the dynamic cross-linked polybutadiene could be recycled to use in a sustainable way. Concerning all the raw materials were available in large quantities without tedious and multistep synthetic routes, this work demonstrated the high performance recycling solution to the commercial cross-linked polybutadiene, which might be applied in industry in relatively short time.

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Covalent adaptable networks (CANs) have various potential applications for their dynamic features benefiting from the existence of dynamic covalent bonds (DCBs). Here we exploit acetoacetyl chemistry to design CANs in which acetoacetyl formed amides (AFAs) act as a type of DCBs. We first illuminate that the transamidation of AFAs is ascribed to a "proton-switch" mechanism via model study and DFT calculations. When such AFA linkages are incorporated into cross-linked polymer networks, the malleability and recyclability are demonstrated. After recycling the polymer networks for three times, there are no significant mechanical changes or degradations observed. The study reveals that the transamidation is an economic and efficient exchange reaction in the preparation of CANs.

Pristine carbon nanotubes (CNTs) were activated to exhibit Diels-Alder (DA) reactivity in a polymer matrix, which was modified with monomers containing furan groups. The DA-active polymer matrix was transferred into a dynamic reversible cross-linked inorganic-organic network via a Diels-Alder reaction with CNTs, where pristine CNTs were used as dienophile chemicals and furan-modified SBS acted as the macromolecular diene. In this system, the mechanical properties as well as resilience and solvent resistance were greatly improved even with the presence of only 1 wt % CNTs. Meanwhile, the hybrids retained recyclability and exhibited some smart behaviors, including self-healing and reprogrammable shape memory properties. Furthermore, due to the photothermal effect of CNTs, a retro-Diels-Alder (rDA) reaction was activated under laser irradiation, and healing of a crack on the hybrid surface was demonstrated in approximately 10 s with almost complete recovery of the mechanical properties. Such fast and efficient self-healing performance provides a new concept in designing self-healing nanocomposites with tunable structures and mechanical properties. Furthermore, the DA and rDA reactions could be combined to reprogram the shape memory behavior under laser irradiation or thermal treatment, wherein the temporary shape of the sample could be transferred to a permanent shape via the rDA reaction at high temperature.

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